Professor S. Ravi P. Silva CBE FREng

Director, Advanced Technology Institute (ATI) and Head of NanoElectronics Centre
+44 (0)1483 689825
20 ATI 01
Lynn Tumilty
+44 (0)1483 686080


Free Energy, Cheap Solar, The Smart Grid Revolution with Professor Ravi Silva of Surrey University


How big data can play a big role in society
Expert Speaker
International Business Times, India
Chairing Day 2 Sessions on 'Net Zero World for 2050' in the Key Technologies for the Future joint conference for the Royal Academy of Engineers and CESAER 1-2 July 2021
MC for the evening at “The path to net zero emissions in the UK”; given by Professor Dame Julia King, Baroness Brown of Cambridge, an internationally renowned engineer and climate change expert.
Press interview after keynote at Nanotexnology 2019, Thessaloniki, Greece, July 2019. Free Energy, Cheap Solar and the Smart Grid.
National Trust of Sri Lanka - 118th Lecture - Clean, Green and Free: Solar Electricity for 2035
Nano-Biotechnology for Health and Wellbeing |2015|
Innovation in materials - Professor Ravi Silva on the green energy challenge
Carbon electronics
Public Lecture: Nanotechnology for Green Energy (part 1 of 7)
2009 Materials/Chemistry Award finalist: Surrey Nanosystems
Nanotechnology [ENGLISH]


Research interests

Research collaborations


Bowei Li, Jun Deng, K. D. G. Imalka Jayawardena, Xueping Liu, Yuren Xiang, Aobo Ren, Abayomi Titilope Oluwabi, Steven Hinder, Benjamin Putland, John F Watts, Hui Li, Shixuan Du, S Ravi P Silva, Wei Zhang (2023)Unraveling the Degradation Pathway of Inverted Perovskite Solar Cells Based on ISOS-D-1 Protocol, In: Small methods8(2)2300223pp. e2300223-e2300223 Wiley

Perovskite solar cells (PSCs) have shown rapid development recently, whereas nonideal stability remains the chief obstacle toward commercialization. Thus, it is of utmost importance to probe the degradation pathway for the entire device. Here, the extrinsic stability of inverted PSCs (IPSCs) is investigated by using standard shelf-life testing based on the International Summit on Organic Photovoltaic Stability protocols (ISOS-D-1). During the long-term assessment of 1700 h, the degraded power conversion efficiency is mainly caused by the fill factor (53% retention) and short-circuit current density (71% retention), while the open-circuit voltage still maintains 97% of the initial values. Further absorbance evolution and density functional theory calculations disclose that the perovskite rear-contact side, in particular for the perovskite/fullerene interface, is the predominant degradation pathway. This study contributes to understanding the aging mechanism and enhancing the durability of IPSCs for future applications.

Steven Clowes, S Silva, I Yahya, F Bonaccorso, AC Ferrari (2015)Temperature dependent separation of metallic and semiconducting carbon nanotubes using gel agarose chromatography, In: Carbon93pp. 574-594 Elsevier

Post-synthesis separation of metallic (m-SWNTs) and semiconducting (s-SWNTs) single-wall carbon nanotubes (SWNTs) remains a challenging process. Gel agarose chromatography is emerging as an efficient and large scale separation technique. However, the full (100%) separation has not been achieved yet, mainly due to the lack of understanding of the underlying mechanism. Here, we study the temperature effect on the SWNTs separation via gel agarose chromatography, for four different SWNT sources. Exploiting a gel agarose micro-beads filtration technique we achieve up to 70% m-SWNTs and over 90% s-SWNTs, independent of the source material. The process is temperature dependent, with yields up to 95% for s-SWNT (HiPco) at 6 °C. Temperature affects the sodium dodecyl sulfate surfactant-micelle distribution along the SWNT sidewalls, thus determining the effectiveness of the SWNTs sorting by electronic type. The sorted SWNTs are then used to fabricate transistors with very low OFF-currents (∼10−13 A), high ON/OFF current ratio (>106) and charge carriers mobility ∼ 40 cm2 V−1 s−1.

Michal Delkowski, Christopher T.G. Smith, Jose V. Anguita, S. Ravi P Silva (2023)Radiation and electrostatic resistance for ultra-stable polymer composites reinforced with carbon fibers, In: Science advances9(11)eadd6947 American Association for the Advancement of Science

Future space travel needs ultra-lightweight and robust structural materials that can 10 withstand extreme conditions with multiple entry points to orbit to ensure mission reliability. This is unattainable with current inorganic materials, while ultra-highly stable carbon fibre reinforced polymers (CFRP´s) have shown susceptibility to environmental instabilities and electrostatic discharge, thereby limiting the full lightweight potential of CFRP. To improve space travel and structural engineering further, a robust CFRP is required. Here, we address these 15 challenges and present a superlattice nano-barrier enhanced CFRP (SNBE-CFRP) with a density of ~3.18 [g/cm 3 ] that blends within the mechanical properties of the CFRP, thus becoming part of the composite itself. We demonstrate composites with enhanced radiation resistance coupled with electrical conductivity (3.2x10-8 Ωm), while ensuring ultra-dimensionally stable physical properties even after temperature cycles from 77 to 573 K. 20

BHASKAR DUDEM, RANDUNU DEVAGE ISHARA GIHAN DHARMASENA, Raheel Riaz, VIVEKANANTHAN VENKATESWARAN, K.G.U. Wijayantha, Paolo Lugli, Luisa Petti, S RAVI PRADIP SILVA (2022)Wearable Triboelectric Nanogenerator from Waste Materials for Autonomous Information Transmission via Morse Code, In: ACS applied materials & interfaces14(4)pp. 5328-5337 American Chemical Society

Electronic waste produced by plastic, toxic, and semiconducting components of existing electronic devices is dramatically increasing environmental pollution. To overcome these issues the use of eco-friendly materials for designing such devices are attaining great concern. This current work presents a recycled materials-based triboelectric nanogenerator (TENG) made of plastic waste and carbon-coated paper wipes (C@PWs), in which the PWs also collected from a waste bin. The resultant C@PWs-based TENG is then used for powering low-power electronic devices, and later, to generate a Morse code from a wearable for autonomous communication. Other end-users in a customized LabVIEW programme decode the Morse code signals and read the transmitted message. With further redesigning, a 9-segment keyboard is developed using nine-TENGs, connected to an Arduino controller to display the 9-segment actuation on a computer screen. Based on the above analysis, our C@PW-TENG device is expected to have an impact on future self-powered sensors and IoT systems.

Manman Wang, Kai Yang, Yuchen Ji, Xiaobin Liao, Guangpeng Zhang, Mateus G. Masteghin, Nianhua Peng, Filipe Richheimer, Huanxin Li, Jianan Wang, Xinhua Liu, Shichun Yang, Enrico Petrucco, Paul Shearing, Fernando A. Castro, S. Ravi P. Silva, Yan Zhao, Feng Pan, Yunlong Zhao (2023)Developing highly reversible Li-CO2 batteries: from on-chip exploration to practical application, In: Energy & environmental science

Li–CO 2 batteries (LCBs) hold significant potential for meeting the energy transition requirements and mitigating global CO 2 emissions. However, the development of efficient LCBs is still in its early stages, necessitating the search for highly effective electrocatalysts and a deeper understanding of their mechanisms. To address these challenges, we have designed a versatile on-chip electrochemical testing platform, which enables simultaneous catalyst screening and in-situ analysis of the chemical composition and morphological evolution of reaction products. Six different metal nanoparticle catalysts were evaluated and it was found that Pt-based LCBs demonstrated a low overpotential (∼0.55 V). The reaction pathways and reversible nature of the LCBs were studied using in situ electrochemical Raman spectroscopy and atomic force microscopy, and were supported by ab initio calculations. As a result of the platform studies, LCB coin cells and pouch cells were fabricated which demonstrated high capacity, stability, and an energy efficiency of up to 90%. A multimodal lab-on-a-chip platform has a wide range of applications in other systems, such as metal–air batteries, electrocatalysts, fuel cells, and photoelectrochemical systems, thereby opening up new opportunities for rapid catalyst screening, mechanism investigation, and the development of practical applications.

Apostolos Panagiotopoulos, Temur Maksudov, George Kakavelakis, George Perrakis, Essa A. Alharbi, Dimitar Kutsarov, Furkan H. Isikgor, Salman Alfihed, Konstantinos Petridis, Maria Kafesaki, S. Ravi P. Silva, Thomas D. Anthopoulos, Michael Graetzel (2023)A critical perspective for emerging ultra-thin solar cells with ultra-high power-per-weight outputs, In: Applied Physics Reviews10(4)

Ultrathin, solution-processed emerging solar cells with high power-per-weight (PPW) outputs demonstrate unique potential for applications where low weight, high power output, and flexibility are indispensable. The following perspective explores the literature of emerging PVs and highlights the maximum reported PPW values of perovskite solar cells (PSCs) 29.4 W/g, organic solar cells (OSCs) 32.07 W/g, and quantum dot solar cells 15.02 W/g, respectively. The record PPW values of OSCs and PSCs are approximately one order of magnitude higher compared to their inorganic ultrathin solar cells counterparts (approximately 3.2 W/g for CIGS and a-Si). This consists emerging PVs, very attractive for a variety of applications where the PPW is the key parameter. In particular, both OSCs and PSCs can be implemented in different scenarios of applications (indoor and biocompatible applications for OSCs and outdoor and high-energy radiation conversion conditions for the PSCs) due to their unique optoelectronic and physiochemical properties. Finally, our theoretical optical and electrical simulation and optimization study for the most promising and well-suited PV technologies showed an impressive maximum realistic theoretical PPW limit of 74.3 and 93.7 W/g for PSCs and OSCs, respectively. Our finding in the theoretical section shows that the experimental results achieved in the literature of PSCs and OSCs toward high PPW outputs is not quite close to the theoretical maximum (35% and 40% of the theoretical maximum for OSCs and PSCs, respectively), and thus, more work needs to be done to further increase the experimental PPW output of these promising PV technologies.

Apostolos Panagiotopoulos, Temur Maksudov, George Kakavelakis, George Perrakis, Essa Alharbi, Dimitar Kutsarov, Furkan Isikgor, Salman Alfihed, Konstantinos Petridis, Maria Kafesaki, S Silva, Thomas Anthopoulos, Michael Graetzel A critical perspective for emerging ultra-thin solar cells with ultra-high power-per-weight outputs, In:

Ultrathin, solution-processed emerging solar cells with high power-per-weight (PPW) outputs demonstrate unique potential for applications where low weight, high power output, and flexibility are indispensable. The following perspective explores the literature of emerging PVs and highlights the maximum reported PPW values of Perovskite Solar Cells (PSCs) 29.4 W/g, Organic Solar Cells (OSCs) 32.07 W/g and Quantum Dot Solar Cells (QDSC) 15.02 W/g, respectively. The record PPW values of OSCs and PSCs are approximately one order of magnitude higher compared to their inorganic ultrathin solar cells counterparts (approx. 3.2 W/g for CIGS and a-Si). This consists emerging PVs, very attractive for a variety of applications where the PPW is the key parameter. In particular, both OSCs and PSCs can be implemented in different scenarios of applications (indoor and biocompatible applications for OSCs and outdoor and high-energy radiation conversion conditions for the PSCs) due to their unique optoelectronic and physiochemical properties. Finally, our theoretical optical and electrical simulation and optimization study for the most promising and well-suited PV technologies, showed an impressive maximum realistic theoretical PPW limit of 74.3 and 93.7 W/g for PSCs and OSCs, respectively. Our finding shows that the literature PSCs and OSCs towards high PPW outputs, is not quite close to the theoretical maximum and thus more work needs to be done to further increase the PPW output of these promising PV technologies.

Xuhui Yao, Xuekun Lu, Yundong Zhou, Tomas Samoril, Jinxin Bi, Mateus G. Masteghin, Huixing Zhang, Leslie Askew, JeongWon Kim, Fangyu Xiong, Jianan Wang, David C. Cox, Tan Sui, Ian Gilmore, S. Ravi P. Silva, Liqiang Mai, Gareth Hinds, Paul R. Shearing, Juyeon Park, Yunlong Zhao (2023)Rectifying interphases for preventing Li dendrite propagation in solid-state electrolytes, In: Energy & environmental science16(5)pp. 2167-2176 Royal Soc Chemistry

Solid-state electrolytes have emerged as the grail for safe and energy-dense Li metal batteries but still face significant challenges of Li dendrite propagation and interfacial incompatibility. In this work, an interface engineering approach is applied to introduce an electronic rectifying interphase between the solid-state electrolyte and Li metal anode. The rectifying behaviour restrains electron infiltration into the electrolyte, resulting in effective dendrite reduction. This interphase consists of a p-Si/n-TiO2 junction and an external Al layer, created using a multi-step sputter deposition technique on the surface of garnet pellets. The electronic rectifying behaviour is investigated via the asymmetric I-V responses of on-chip devices and further confirmed via the one-order of magnitude lower current response by electronic conductivity measurements on the pellets. The Al layer contributes to interface compatibility, which is verified from the lithiophilic surface and reduced interfacial impedance. Electrochemical measurements via Li symmetric cells show a significantly improved lifetime from dozens of hours to over two months. The reduction of the Li dendrite propagation behaviour is observed through 3D reconstructed morphologies of the solid-state electrolyte by X-ray computed tomography.

C. Preddy, R. Singh, P. Aaen, S. R. P. Silva (2023)Integrated Carbon Fiber Microwave Circuits for Lightweight Antenna Applications, In: 2023 17TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION, EUCAP IEEE

The implementation of a slotted substrate integrated waveguide (SIW) antenna within a fiber reinforced composite is presented as a lightweight method of integrating microwave functionality into composite components. The SIW circuit is fabricated within a foam core composite using copper-coated carbon veils. The use of a coated veil as the conductor reduces the attenuation effects normally experienced with carbon based microwave circuits, while minimizing the introduction of additional materials that could mechanically weaken the composite. The application of an integrated composite SIW as an antenna is demonstrated through the design, fabrication and gain characterization of two slotted waveguide antennas, with measured gains of -3 dBi at 3.66 GHz and 0.2 dBi at 6.75 GHz respectively.

Khushboo Borah Slater, Muhammad Ahmad, Aurore Poirier, Ash Stott, Bianca S. Siedler, Matthew Brownsword, Jai Mehat, Joanna Urbaniec, Nicolas Locker, Yunlong Zhao, Roberto La Ragione, S. Ravi P. Silva, Johnjoe McFadden (2023)Development of a loop-mediated isothermal amplification (LAMP)-based electrochemical test for rapid detection of SARS-CoV-2, In: iScience

Rapid, reliable, sensitive, portable, and accurate diagnostics are required to control disease outbreaks such as COVID-19 that pose an immense burden on human health and the global economy. Here we developed a loop-mediated isothermal amplification (LAMP)-based electrochemical test for the detection of SARS-CoV-2 that causes COVID-19. The test is based on the oxidation-reduction reaction between pyrophosphates (generated from positive LAMP reaction) and molybdate that is detected by cyclic voltammetry using inexpensive and disposable carbon screen printed electrodes. Our test showed higher sensitivity (detecting as low as 5.29 RNA copies/μL) compared to the conventional fluorescent reverse transcriptase (RT)-LAMP. We validated our tests using human serum and saliva spiked with SARS-CoV-2 RNA and clinical (saliva and nasal-pharyngeal) swab samples demonstrating 100% specificity and 93.33% sensitivity. Our assay provides a rapid, specific, and sensitive test with an electrochemical readout in less than 45 min that could be adapted for point-of-care settings.

Vincenzo Pecunia, S Ravi P Silva, Jamie Dean Phillips, Elisa Artegiani, Alessandro Romeo, Hongjae Shim, Jongsung Park, Jin-Hyeok Kim, Jae Sung Yun, Gregory Charles Welch, Bryon W Larson, Myles Creran, Audrey Laventure, Kezia Sasitharan, Natalie Flores-Diaz, Marina Freitag, Jie Xu, Thomas M Brown, Benxuan Li, Yiwen Wang, Zhe Li, Bo Hou, Behrang H Hamadani, Emmanuel Defay, Veronika Kovacova, Sebastjan Glinsek, Sohini Kar-Narayan, Yang Bai, Da Bin Kim, Yong Soo Cho, Agnė Žukauskaitė, Stephan Barth, Feng Ru Fan, Wenzhuo Wu, Pedro Costa, Javier del Campo, Senentxu Lanceros-Mendez, Hamideh Khanbareh, Zhong Lin Wang, Xiong Pu, Caofeng Pan, Renyun Zhang, Jing Xu, Xun Zhao, Yihao Zhou, Guorui Chen, Trinny Tat, Il Woo Ock, Jun Chen, Sontyana Adonijah Graham, Jae Su Yu, Ling-Zhi Huang, Dan-Dan Li, Ming-Guo Ma, JiKui Luo, Feng Jiang, Pool See Lee, Bhaskar Dudem, Venkateswaran Vivekananthan, Hongyao Xie, Mercouri G Kanatzidis, Xiao-Lei Shi, Zhi-Gang Chen, Alexander Riss, Michael Parzer, Fabian Garmroudi, Ernst Bauer, Duncan Zavanelli, Madison K Brod, Muath Al Malki, G. Jeffrey Snyder, Kirill Kovnir, Susan M Kauzlarich, Ctirad Uher, Jinle Lan, Yuan-Hua Lin, Luis Fonseca, Alex Morata, Marisol Martin-Gonzalez, Giovanni Pennelli, David Berthebaud, Takao Mori, Robert J Quinn, Jan-Willem G Bos, Christophe Candolfi, Patrick Gougeon, Philippe Gall, Bertrand Lenoir, Deepak Venkateshvaran, Bernd Kaestner, Yunshan Zhao, Gang Zhang, Yoshiyuki Nonoguchi, Bob C Schroeder, Emiliano Bilotti, Akanksha K Menon, Jeffrey J Urban, Oliver Fenwick, Ceyla Asker, A. Alec Talin, Thomas D Anthopoulos, Tommaso Losi, Fabrizio Viola, Mario Caironi, Dimitra G Georgiadou, Li Ding, Lian-Mao Peng, Zhenxing Wang, Muh-Dey Wei, Renato Negra, Max C Lemme, Mahmoud Wagih, Steve Beeby, Taofeeq Ibn-Mohammed, K.B Mustapha, A.P Joshi (2023)Roadmap on energy harvesting materials IOP Publishing

Ambient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g., combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g., smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and electromagnetic power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyzes the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere.

Daniel Sebastia-Saez, Tomas Ramirez Reina, Ravi Silva, Harvey Arellano-Garcia (2020)Synthesis and characterisation of n‐octacosane@silica nanocapsules for thermal storage applications, In: International journal of energy research44(3)pp. 2306-2315

Summary This work reports the synthesis and characterisation of a core‐shell n‐octacosane@silica nanoencapsulated phase‐change material obtained via interfacial hydrolysis and polycondensation of tetraethyl orthosilicate in miniemulsion. Silica has been used as the encapsulating material because of its thermal advantages relative to synthesised polymers. The material presents excellent heat storage potential, with a measured melting latent heat varying between 57.1 and 89.0 kJ kg−1 (melting point between 58.2°C and 59.9°C) and a small particle size (between 565 and 227 nm). Degradation of the n‐octacosane core starts between 150°C and 180°C. Also, the use of silica as shell material gives way to a heat conductivity of 0.796 W m−1 K−1 (greater than that of nanoencapsulated materials with polymeric shell). Charge/discharge cycles have been successfully simulated at low pressure to prove the suitability of the nanopowder as phase‐change material. Further research will be carried out in the future regarding the use of the synthesised material in thermal applications involving nanofluids.

Qing Sun, Xiangxin Meng, Jianguo Deng, Bo Shen, Die Hu, Bonan Kang, S. Ravi P. Silva (2023)Buried interface defects passivation of perovskite film by choline halide for high performance inverted perovskite solar cells with efficiency exceeding 22%, In: Journal of alloys and compounds959 Elsevier B.V

Defect-induced charge carrier recombination between charge transport layers and perovskite layer limits the further improvement of the performance of perovskite solar cells (PSCs). Defect passivation is a promising path for further development improves in the open-circuit voltage (VOC) and the short-circuit current density (JSC) of PSCs. Here, we report a simple method via spin-coating choline halide to passivate buried interface defects of perovskite applied to inverted PSCs. The introduction of choline chloride (CHCl) can remarkably improve the crystalline quality of perovskite films, speed up the transport of carriers and reduce the trap density in perovskite, which universally enhance the performance of PSCs. Finally, the champion CHCl modified device got a high PCE of 22.61% with negligible hysteresis, which is one of the highest efficiencies of inverted PSCs fabricated with a two-step method. This optimization can also improve the stability of PSCs, the CHCl modified device without encapsulation maintained 89% of its initial PCE in air with a relative humidity of 40 ± 5% after near 800 h ageing. This work reveals an effective way of using choline halide for buried interface defects passivation of perovskite film to further improve both the stability and efficiency of solar cells. [Display omitted] •The introduction of choline halide can passivate buried interface defects of perovskite.•Choline halide is demonstrated to improve stability of the inverted perovskite solar cells.•PCE exceeding 22.6% is achieved for inverted perovskite solar cells via a two-step sequential deposition.

Ehsan Rezaee, Dimitar I. Kutsarov, Jing Zhang, George Koutsourakis, Bowei Li, Fernando A. Castro, S. Ravi P. Silva (2023)Green Solvent Ethanol-Based Inks for Industrially Applicable Deposition of High-Quality Perovskite Films for Optoelectronic Device Applications, In: Small methodspp. e2300564-e2300564
H. Altuntas, K. Snashall, F. Oke-Altuntas, I. Jayawerdane, M. O. Tas, S. Ravi P. Silva (2023)Effect of Pyrene-1 Boronic Acid Functionalization on the Electrical Characteristics of Carbon Nanotube Field-Effect Transistor, In: Electronic materials letters Korean Inst Metals Materials

Carbon nanotube field-effect transistor (CNT-FET) based sensor devices are widely used in sensing applications of biomolecules in high sensitivity. In addition, covalent functionalization process can increase the interaction between the CNTs and biological molecules. In this article, we present the effect of boronic acid functionalization on the electrical properties of the CNT-FET due to boronic acid and its derivatives have been widely used for the glucose recognition. For this purpose, CNT-FET transistors were fabricated on SiO2/Si substrates utilising high purity semiconducting nanotubes as the channel layer and functionalized with pyrene-1-boronic acid. It was found that boronic acid functionalization causes a variation in electrical parameters of CNT-FET transistors such as conductance, transconductance, threshold voltage, field effect mobility, resistance, hysteresis gap, and charge transfer of carriers per unit length. The results show that pyrene-1-boronic acid treatment was observed to have a significant beneficial effect on the electrical properties of the CNT-FET and pyrene-1-boronic acid functionalized CNT-FET sensor devices may have great potential for glucose sensing applications. [GRAPHICS] .

Xiangxin Meng, Bo Shen, Qing Sun, Jianguo Deng, Die Hu, Bonan Kang, S. Ravi P. Silva, Xu Wang, Lijun Wang (2023)Multifunctional Molecule Assists Passivate Method to Simultaneously Improve the Efficiency and Stability of Perovskite Solar Cells, In: ChemSusChem16(7)pp. e202202092-n/a Wiley

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has been greatly improved recently. However, in organic-inorganic polycrystalline perovskite films many defects inevitably exist, which limits the PCE and stability of PSCs. Herein, a small organic molecule 2-chlorothiazole-4-carboxylic acid (SN) is spin coated on a perovskite film to enhance the performance of PSCs. We find that the multifunctional molecule SN reacts with under-coordinated Pb2+ ions and I- vacancies because of the presence of the sulfur and nitrogen donor atoms, and the -COOH groups, which are conducive to suppressing charge recombination and passivating defects. Even more, the introduction of the SN layer can effectively adjust the energy level alignment, which is conducive to the separation and extraction of charge carriers in PSCs. Therefore, devices with SN modification show a champion PCE of 22.55 %. Besides, PSCs with SN show impressive stability, retaining 96 % of its initial PCE after storage in ambient air for 500 h.

Pengpeng Zhang, Yige Zhao, Yukun Li, Neng Li, S. Ravi P. Silva, Guosheng Shao, Peng Zhang (2023)Revealing the Selective Bifunctional Electrocatalytic Sites via In Situ Irradiated X-Ray Photoelectron Spectroscopy for Lithium–Sulfur Battery, In: Advanced science10(8)pp. e2206786-n/a Wiley

The electrocatalysts are widely applied in lithium-sulfur (Li-S) batteries to selectively accelerate the redox kinetics behavior of Li2S, in which bifunctional active sites are established, thereby improving the electrochemical performance of the battery. Considering that the Li-S battery is a complex closed "black box" system, the internal redox reaction routes and active sites cannot be directly observed and monitored especially due to the distribution of potential active-site structures and their dynamic reconstruction. Empirical evidence demonstrates that traditional electrochemical test methods and theoretical calculations only probe the net result of multi-factors on an average and whole scale. Herein, based on the amorphous TiO2-x@Ni selective bifunctional model catalyst, these limitations are overcome by developing a system that couples the light field and in situ irradiated X-ray photoelectron spectroscopy to synergistically convert the "black box" battery into a "see-through" battery for direct observation of the charge transportation, thus revealing that amorphous TiO2-x and Ni nanoparticle as the oxidation and reduction sites selectively promote the decomposition and nucleation of Li2S, respectively. This work provides a universal method to achieve a deeper mechanistic understanding of bidirectional sulfur electrochemistry.

Xiaoyi Hu, S. Ravi P. Silva, Peng Zhang, Kangli Liu, Shijie Zhang, Guosheng Shao (2023)A multifunctional fire-retardant gel electrolyte to enable Li-S batteries with higher Li-ion conductivity and effectively inhibited shuttling of polysulfides, In: Chemical engineering journal (Lausanne, Switzerland : 1996)467 Elsevier B.V

[Display omitted] •A gel electrolyte with asymmetric structure was prepared.•The gel electrolyte possesses thermal stability and flame retardant.•The gel electrolyte utilizes an electro-spun network as structural scaffolds.•The SiO2-polyvinyl alcohol was loaded at one surface of an electro-spun network.•The gel electrolyte simultaneously solves problems of the S cathode and Li anode. A main huddle against the practical application of lithium-sulfur battery lies in serious safety concerns due to liquid organic electrolyte, shuttling of polysulfides and formation of lithium dendrites. Herein, we have devised an asymmetric and structurally stable gel electrolyte system to enable high ionic conductivity, flame-retardancy, and effective blockage of shuttling. Such a multi-functional gel electrolyte utilizes an electro-spun network of interwoven nano-fibers of poly vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) as structural scaffolds, with SiO2-polyvinyl alcohol (SiO2@PVA) suspension being loaded at one surface by blade coating. Such asymmetrically coated PVDF-HFP membranes are highly wettable that is essential to thorough gelling, with its well-connected porous channels to enable outstanding ionic conductivity above the limit by conventional Celgard separator, to accommodate huge volumetric changes over redox reactions, to shield polysulfides and fend off lithium dendrites. Ultimately, application of the gel electrolyte to a model Li-S cell with cathode containing 90% S delivered high initial capacity of 1439 mA h g−1 at 0.1C and a remarkable cycling stability over 300 cycles at 1C. The current gel electrolyte is expected to provide a valuable means for developing safe low-cost and durable Li–S batteries of practical importance.

Ehsan Rezaee, Danish Khan, Siyuan Cai, Lei Dong, Hui Xiao, S. Ravi P. Silva, Xiaoyuan Liu, Zong-Xiang Xu (2023)Phthalocyanine in perovskite solar cells: a review, In: Materials chemistry frontiers7(9)pp. 1704-1736

Presently, due to the rapid development of perovskite solar cells (PSCs), their commercialization is not only attractive but perhaps the only choice to replace both thin film photovoltaics (PV) and conventional silicon PV. However, although the power conversion efficiency (PCE) of PSCs is has reached above 25%, which is suitable for their commercialization, their poor long-term stability with scalability remains a challenge due to the sensitivity of perovskites under ambient conditions. Therefore, the top and bottom layers sandwiching the perovskite layer are critical. In this case, the charge transport layers (CTLs) not only enable charge extraction but also play the role of encrusting, passivating, and supporting the perovskite layer. Therefore, the perovskite interface has a dominant influence on the performances of PSCs. In this case, phthalocyanines (Pcs) have a large π-conjugated framework, outstanding thermal stability, excellent physical/chemical stability, low cost, and can be endowed with a tunable energy band, good carrier mobility, solubility in common solvents, and facile synthesis through their appropriate design, making them a robust charge selective layer, passivation layer or both in PSCs. In this review, we summarize the studies on the application of Pc compounds in PSCs, including dopant-free macrocycle molecules, from the perspectives of molecular engineering, doped hole transporting material (HTM), and employment of Pcs as additives in the perovskite layer or HTMs. This review provides helpful insight for further enhancing the efficiency of PSC devices, while improving their long-term operational life by utilizing Pc materials.

Swati Panda, Sugato Hajra, Hang Gyeom Kim, Haejin Jeong, P. G. R. Achary, Seonki Hong, Bhaskar Dudem, S. Ravi P. Silva, Venkateswaran Vivekananthan, Hoe Joon Kim (2023)Carbohydrate–protein interaction-based detection of pathogenic bacteria using a biodegradable self-powered biosensor, In: Journal of materials chemistry. B, Materials for biology and medicine

Battery-free and biodegradable sensors can detect biological elements in remote areas. The triboelectric nanogenerator (TENG) can potentially eliminate the need for a battery by simply converting the abundant vibrations from nature or human motion into electricity. A biodegradable sensor system integrated with TENG to detect commonly found disease-causing bacteria ( E. coli ) in the environment is showcased herein. In this system, d -mannose functionalized 3D printed polylactic acid (PLA) with the brush-painted silver electrode was used to detect E. coli by a simple carbohydrate–protein interaction mechanism. The adsorption capacity of d -mannose is generally altered by varying the concentration of E. coli resulting in changes in resistance. Thus, the presented biosensor can detect bacterial concentrations by monitoring the output current. The PLA TENG generates an output of 70 V, 800 nA, and 22 nC, respectively. In addition, tap water and unpasteurized milk samples are tested for detecting bacteria, and the output is measured at 6 μA and 5 μA, respectively. Further, the biosensor was tested for biodegradability in soil compost by maintaining constant temperature and humidity. This study not only proposes an efficient and fast method for screening E. coli but also gives important insights into the ability to degrade and long-term reliability of TENG-based sensor platforms.

Venkateswaran Vivekananthan, Arunkumar Chandrasekhar, Bhaskar Dudem, Gaurav Khandelwal, S Ravi P Silva, Sang-Jae Kim (2023)Contact-electrification enabled water-resistant triboelectric nanogenerators as demonstrator educational appliances, In: JPhys Energy IOP Publishing Ltd

Abstract Triboelectric nanogenerators (TENG) work on the principle of tribo and contact electrification, which is a common effect observed in daily life. TENGs are moving closer to commercialization, particularly for small scale energy harvesting and self-powered sensing. The toys and games industry has attracted a huge audience recently with the introduction of digital toys. In this paper we embedded TENGs to power up a toy and operate during its specific application. We have modified two potential electronic demonstrator applications using TENG for lobster toy (LT-TENG) and stress ball (SB-TENG) device. The LT-TENG device generates a maximum electrical response of 60 V/ 2 µA, with a power of 55 µW and power density of 0.065 µW/m2 at a load resistance value of 10 MΩ. Similarly, the SB-TENG device made of aluminum and PDMS as the triboelectric layers generates a maximum electrical output response of 800 V and 4 µA peak to peak current with an instantaneous power of 6 mW and a power density of 3.5 mW/m2 respectively at a load resistance of 10 MΩ. In addition, the layers of the TENGs are packed with polyethylene to maintain the performance of the nanogenerator under harsh environmental conditions, especially with humid environments. The water resistance studies proved that the packed SB-TENG is impervious to water. The LT-TENG device is accompanied by four LEDs, and the device lights up upon actuating the handle. The stress ball is connected with the measuring instrument to record the quantity of force at which the stress ball is pressed. The adopted approach paves the way to convert these traditional toys into battery-free electronic designs and its commercialization.

Raheel Riaz, Bhaskar Dudem, Martina Aurora Costa Angeli, Ali Douaki, Mukhtar Ahmad, Abraham Mejia-Aguilar, Roberto Monsorno, Paolo Lugli, S. Ravi P Silva, Luisa Petti (2023)Surface Textured Double Layer Triboelectric Nanogenerator for Autonomous and Ultra‐Sensitive Biomedical Sensing, In: Advanced materials technologies
CAMERON CHRISTOPHER UNDERWOOD, Zhuo Wang, David Carey, Guosheng Shao, S. Ravi P. Silva (2022)The electronic stability of tin-halide perovskite charged regions, In: Materials Advances Royal Society of Chemistry

We report on the evolution of the electronic structure with partial oxidation state of tin and iodine from ASnI¬3 to model a space charged region¬, where A = CH3NH3(MA), CH(NH2)2 (FA) or Cs, with a view to develop stable long-term non-toxic halide-perovskite solar cells. Although charge cannot be directly removed from specific elements, we show reduction of the charge primarily of SnI3 in a hypothetical [ASnI3]2+ unit cell is calculated due to the valence band edge being dominated by Sn 5s and I 5p anti-bonding states, accompanied by a reduction in unit cell volume in [ASnI3]2+ compared to ASnI3. Band structure calculations show semiconducting behaviour in ASnI3, with metallic behaviour in [ASnII3]2+; a similar behaviour is also found for APbI3 and [APbI3]2+, where the Pb atoms partial charge than Sn. This research al-lows for the analysis of localised charged regions, directing the ultimate long-term electronic stability in perovskite solar absorbers, such as interface recombination and deep trap states.

James Crawshaw, S. Ravi P. Silva (2022)CO2 Emissions Post-COP26: Who is Responsible to Curb the Flow? Does it Matter if We Can Make it a Win-Win?, In: Energy & environmental materials (Hoboken, N.J.)5(3)pp. 683-685 Wiley

The Earth is moving toward a tipping point in terms of global warming, with atmospheric CO2 trapping heat which reduces light-reflective snow cover and GHG release from the arctic tundra. The effects on our planet include rising sea levels, increased precipitation, and, most obviously, rising temperatures. In this editorial we argue that it is now time the world comes together to solve the energy problem by collectively embracing the lowest cost energy solutions which, fortuitously, also happen to be green. Vested interests can no longer hide behind economic arguments as, after years of technological improvements, wind and solar are now found to be cheaper than fossil fuels in most cases for energy generation.

Victoria Ferguson, Bowei Li, Mehmet O Tas, Thomas Webb, Muhammad T Sajjad, Stuart A. J Thomson, Zhiheng Wu, Yonglong Shen, Guosheng Shao, José V Anguita, S. Ravi P Silva, Wei Zhang (2020)Direct Growth of Vertically Aligned Carbon Nanotubes onto Transparent Conductive Oxide Glass for Enhanced Charge Extraction in Perovskite Solar Cells, In: Advanced materials interfaces7(21)2001121

Vertically aligned carbon nanotubes (VACNTs) present an exciting avenue for nanoelectronics due to their predetermined orientation and exceptional transport capabilities along the tube length, with the potential to be employed in a variety of optoelectronic applications. However, growth of VACNTs using conventional chemical vapor deposition (CVD) methods requires elevated temperatures (>720 °C) and therefore, the suitability of commonly used transparent conductive oxide (TCO) glasses, such as fluorine‐doped tin oxide (FTO) and indium‐tin oxide (ITO), as the substrates for nanotube growth are limited by their temperature‐sensitive nature. Here, the successful growth of multi‐walled VACNTs directly onto commonly used TCO glasses, FTO and ITO, using the photo‐thermal chemical vapor deposition (PTCVD) growth method is reported. The benefit of reflection, within the infrared region, of the TCO substrate and the effect of surface roughness on the growth of VACNTs is investigated. The application of VACNTs on ITO in inverted planar perovskite solar cells is investigated, which shows superior charge transfer, larger grain sizes in the perovskite film, and a champion device efficiency approaching 16%. Vertically aligned carbon nanotubes are grown directly onto temperature‐sensitive transparent conductive oxide glass; the morphology, quality and electrical properties are analyzed and used to fabricate optimized patterned carbon nanotube forest films which are used in perovskite solar cells to improve charge extraction resulting in a champion efficiency approaching 16%.

DINESHA PRIYADARSHANI WATTE VIDANELAGE, ANGELA FATIMA DANIL DE NAMOR, S. Ravi P. Silva (2022)Rising of a global silent killer: critical analysis of chronic kidney disease of uncertain aetiology (CKDu) worldwide and mitigation steps, In: Environmental geochemistry and health Springer Nature
Michal Delkowski, Christopher T.G. Smith, José V. Anguita, S. Ravi P. Silva (2021)Increasing the robustness and crack resistivity of high-performance carbon fiber composites for space applications, In: iScience24(6)pp. 102692-102692 Elsevier

The endeavors to develop manufacturing methods that can enhance polymer and composite structures in spacecraft have led to much research and innovation over many decades. However, the thermal stability, intrinsic material stress, and anisotropic substrate properties pose significant challenges and inhibit the use of previously proposed solutions under extreme space environment. Here, we overcome these issues by developing a custom-designed, plasma-enhanced cross-linked poly(p-xylylene):diamond-like carbon superlattice material that enables enhanced mechanical coupling with the soft polymeric and composite materials, which in turn can be applied to large 3D engineering structures. The superlattice structure developed forms an integral part with the substrate and results in a space qualifiable carbon-fiber-reinforced polymer featuring 10–20 times greater resistance to cracking without affecting the stiffness of dimensionally stable structures. This innovation paves the way for the next generation of advanced ultra-stable composites for upcoming optical and radar instrument space programs and advanced engineering applications. • Plasma-enhanced cross-linked poly(p-xylylene) (PECLP):DLC superlattice is deposited • PECLP exhibits ∼10 times higher elastic modulus compared to classic poly(p-xylylene) • PECLP:DLC barrier provides near-zero stress conditions for use on composites • Enhanced composites exhibit mechanical integrity and improved crack resistivity Aerospace Engineering; Engineering materials; Materials physics

Yongshang Zhang, Peng Zhang, Shijie Zhang, Zheng Wang, Neng Li, S. Ravi P. Silva, Guosheng Shao (2021)A flexible metallic TiC nanofiber/vertical graphene 1D/2D heterostructured as active electrocatalyst for advanced Li–S batteries, In: InfoMat3(7)pp. 790-803
Filip Mandys, Mona Chitnis, S. Ravi P. Silva (2023)Response to “Low cost, uncertain value: Why cheap PV may still not become UK's main power source”, In: Patterns (New York, N.Y.)4(5) Elsevier

We endorse the ideas presented by the authors Klöckl et al. on the need of a mixed bag of energy supplies, with this likely being a combination of solar, wind, hydro, and nuclear in the future. Nevertheless, based on our analysis, we believe that the increased deployment capacity of solar photovoltaic (PV) systems will decrease their cost more than wind, making solar PV important in meeting the Intergovernmental Panel on Climate Change (IPCC) requirements for greater sustainability.

Xuhui Yao, Tomáš Šamořil, Jiří Dluhoš, John F Watts, Zhijia Du, Bohang Song, S. Ravi P Silva, Tan Sui, Yunlong Zhao (2021)Degradation Diagnostics from the Subsurface of Lithium-Ion Battery Electrodes, In: Energy & Environmental Materials Wiley

Despite the long-established rocking-chair theory of lithium-ion batteries (LIBs), developing novel characterization methodology with higher spatiotemporal resolution facilitates a better understanding of the solid electrolyte interphase studies to shape the reaction mechanisms. In this work, we develop a Xenon ion plasma focused ion beam (Xe+ PFIB)-based characterization technique to probe the cross-sectional interface of both ternary cathode and graphite anode electrodes, with the focus on revealing the chemical composition and distribution underneath the electrode surface by in-depth analysis of secondary ions. Particularly, the lithium fluoride is detected in the pristine cathode prior to contact with the electrolyte, reflecting that the electrode degradation is in the form of the loss of lithium inventory during electrode preparation. This degradation is related to the hydrolysis of the cathode material and the decomposition of the PVDF binder. Through the quantitative analysis of the transition-metal degradation products, manganese is found to be the dominant element in the newly formed inactive fluoride deposition on the cathode, while no transition metal signal can be found inside the anode electrode. These insights at high resolution implemented via a PFIB-based characterization technique not only enrich the understanding of the degradation mechanism in the LIBs but also identify and enable a high-sensitivity methodology to obtain the chemical survey at the subsurface, which will help remove the capacity-fade observed in most LIBs.

EHSAN REZAEE, DIMITAR IVANOV KUTSAROV, BOWEI LI, JINXIN BI, S. Ravi P. Silva (2022)A route towards the fabrication of large-scale and high-quality perovskite films for optoelectronic devices, In: Scientific reports Nature Research
JING ZHANG, Xiangang Hu, HUI LI, Kangyu Ji, BOWEI LI, XUEPING LIU, YUREN XIANG, Pengxiang Hou, Chang Liu, Zhiheng Wu, Yonglong Shen, Samuel D. Stranks, S RAVI PRADIP SILVA, HUIMING CHENG, WEI ZHANG (2021)High-Performance ITO-Free Perovskite Solar Cells Enabled by Single-Walled Carbon Nanotube Films, In: Advanced Functional Materials2104396 Wiley

The unprecedented advancement in power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) has rendered them a promising game-changer in photovoltaics. However, unsatisfactory environmental stability and high manufacturing cost of window electrodes are bottlenecks impeding their commercialization. Here, a strategy is introduced to address these bottlenecks by replacing the costly indium tin oxide (ITO) window electrodes via a simple transfer technique with single-walled carbon nanotubes (SWCNTs) films, which are made of earth-abundant elements with superior chemical and environmental stability. The resultant devices exhibit PCEs of ≈19% on rigid substrates, which is the highest value reported to date for ITO-free PSCs. The facile approach for SWCNTs also enables application in flexible PSCs (f-PSCs), delivering a PCE of ≈18% with superior mechanical robustness over their ITO-based counterparts due to the excellent mechanical properties of SWCNTs. The SWCNT-based PSCs also deliver satisfactory performances on large-area (1 cm2 active area in this work). Furthermore, these SWCNT-based PSCs can retain over 80% of original PCEs after exposure to air over 700 h while ITO-based devices only sustain ≈60% of initial PCEs. This work paves a promising way to accelerate the commercialization of ITO-free PSCs with reduced material cost and prolonged lifetimes.

Mozhgan Yavari, Xueping Liu, Thomas Webb, K D G Imalka Jayawardena, Yuren Xiang, Stefanie Kern, Steven Hinder, Thomas J Macdonald, S Ravi P Silva, Stephen J Sweeney, Wei Zhang (2021)A synergistic Cs2CO3ETL treatment to incorporate Cs cation into perovskite solar cells: Via two-step scalable fabrication, In: Journal of Materials Chemistry C Materials for optical and electronic devices9(12)pp. 4367-4377 Royal Society of Chemistry

Triple cation CsFAMA perovskite films fabricated via a one-step method have recently gained attention as an outstanding light-harvesting layer for photovoltaic devices. However, questions remain over the suitability of one-step processes for the production of large-area films, owing to difficulties in controlling the crystallinity, in particular, scaling of the frequently used anti-solvent washing step. This can be mitigated through the use of the two-step method which has recently been used to produce large-area films via techniques such as slot dye coating, spray coating or printing techniques. Nevertheless, the poor solubility of Cs containing salts in IPA solutions has posed a challenge for forming triple cation perovskite films using the two-step method. In this study, we tackle this challenge through fabricating perovskite films on a caesium carbonate (Cs2CO3) precursor layer, enabling Cs incorporation within the film. Synergistically, we find that Cs2CO3 passivates the SnO2 electron transport layer (ETL) through interactions with Sn 3d orbitals, thereby promoting a reduction in trap states. Devices prepared with Cs2CO3 treatment also exhibited an improvement in the power conversion efficiency (PCE) from 19.73% in a control device to 20.96% (AM 1.5G, 100 mW cm−2) in the champion device. The Cs2CO3 treated devices (CsFAMA) showed improved stability, with un-encapsulated devices retaining nearly 80% efficiency after 20 days in ambient air.

Bhaskar Dudem, R.D. Ishara G Dharmasena, Sontyana Adonijah Graham, Jung Woo Leem, Harishkumarreddy Patnam, Anki Reddy Mule, S. Ravi P Silva, Jae Su Yu (2020)Exploring the theoretical and experimental optimization of high-performance triboelectric nanogenerators using microarchitectured silk cocoon films, In: Nano energy74 Elsevier Ltd

Triboelectric nanogenerators (TENGs) developed using eco-friendly natural materials instead of traditional electronic materials are more favorable for biocompatible applications, as well as from a sustainable life-cycle analysis perspective. Microarchitectured silkworm fibroin films with high surface roughness and an outstanding ability to lose electrons are used to design TENGs. An alcohol-annealing treatment is utilized to strengthen the resistance of the silk film (SF) against humidity and aqueous solubility. Herein, for the first time, the distance-dependent electric field theoretical model is employed to optimize the TENG parameters to achieve high output, which shows excellent agreement with the experimental outputs of SF-based TENG. The alcohol-treated microarchitectured SF (AT-MASF) with a polytetrafluoroethylene positive contact exhibits a stable and high electrical output even in harsh environments. These studies can lead us closer to the attractive future vision of realizing biodegradable TENG systems for harness/sensing various biomechanical activities even under real/humid environments. The potential and real-time application of the proposed AT-MASF-based TENG is demonstrated by directly employing its electric power to drive a number of low-power portable electronics and for sensing in human-body centric activities.

Bowei Li, Yuren Xiang, K.D.G. Imalka Jayawardena, Deying Luo, Zhuo Wang, Xiaoyu Yang, John F. Watts, Steven Hinder, Muhammad T. Sajjad, Thomas Webb, Haitian Luo, Igor Marko, Hui Li, Stuart A.J. Thomson, Rui Zhu, Guosheng Shao, Stephen J. Sweeney, S. Ravi P. Silva, Wei Zhang (2020)Reduced bilateral recombination by functional molecular interface engineering for efficient inverted perovskite solar cells, In: Nano Energy105249 Elsevier

Interface-mediated recombination losses between perovskite and charge transport layers are one of the main reasons that limit the device performance, in particular for the open-circuit voltage (VOC) of perovskite solar cells (PSCs). Here, functional molecular interface engineering (FMIE) is employed to retard the interfacial recombination losses. The FMIE is a facile solution-processed means that introducing functional molecules, the fluorene-based conjugated polyelectrolyte (CPE) and organic halide salt (OHS) on both contacts of the perovskite absorber layer. Through the FMIE, the champion PSCs with an inverted planar heterojunction structure show a remarkable high VOC of 1.18 V whilst maintaining a fill factor (FF) of 0.83, both of which result in improved power conversion efficiencies (PCEs) of 21.33% (with stabilized PCEs of 21.01%). In addition to achieving one of the highest PCEs in the inverted PSCs, the results also highlight the synergistic effect of these two molecules in improving device performance. Therefore, the study provides a straightforward avenue to fabricate highly efficient inverted PSCs.

Michael George Spencer, Marco Sacchi, Jeremy Allam, S. R. P. Silva (2022)Porphyrin-Nanocarbon Complexes to Control the Photodegradation of Rhodamine, In: ACS omega7(45)pp. 41304-41313 American Chemical Society

Porphyrin–nanocarbon systems were used to generate a photocatalyst for the control of rhodamine B and rhodamine 6G photodegradation. Carboxylic functionalized multi-walled carbon nanotubes (o-MWCNTs) were decorated by two different porphyrin moieties: 5-(4-aminophenyl)-10,15,20-(triphenyl)­porphyrin (a-TPP) with an amine linker and 5-(4-carboxyphenyl)-10,15,20-(triphenyl)­porphyrin (c-TPP) with a carboxyl linker to the o-MWCNT, respectively, with their photocatalyst performances investigated. The optical properties of the mixed nanocomposite materials were investigated to reveal the intrinsic energy levels and mechanisms of degradation. The charge-transfer states of the o-MWCNTs were directly correlated with the performance of the complexes as well as the affinity of the porphyrin moiety to the o-MWCNT anchor, thus extending our understanding of energy-transfer kinetics in porphyrin–CNT systems. Both a-TPP and c-TPP o-MWCNT complexes offered improved photocatalytic performance for both RhB and Rh6G compared to the reference o-MWCNTs and both porphyrins in isolated form. The photocatalytic performance improved with higher concentration of o-MWCNTs in the complexed sample, indicating the presence of greater numbers of −H/–OH groups necessary to more efficient photodegradation. The large presence of the −H/–OH group in the complexes was expected and was related to the functionalization of the o-MWCNTs needed for high porphyrin attachment. However, the photocatalytic efficiency was affected at higher o-MWCNT concentrations due to the decomposition of the porphyrins and changes to the size of the CNT agglomerates, thus reducing the surface area of the reactant. These findings demonstrate a system that displays solar-based degradation of rhodamine moieties that are on par, or an improvement to, state-of-the-art organic systems.

Rajapakshe Mudiyanselage Indrachapa Bandara, Shashini M. Silva, Cameron C. L. Underwood, K. D. G. Imalka Jayawardena, Radu A. Sporea, S. Ravi P. Silva (2022)Progress of Pb-Sn Mixed Perovskites for Photovoltaics: A Review, In: Energy & environmental materials (Hoboken, N.J.)5(2)pp. 370-400 Wiley

Pb-Sn mixed perovskites are becoming increasingly popular as narrow-bandgap (1.2-1.3 eV) light absorbers in single-junction perovskite solar cells (PSCs) and as bottom cells for all-perovskite tandem solar cells, for high-efficiency, low-cost, lightweight, roll-to-roll printable photovoltaic (PV) applications. From the first report of planar Pb:Sn mixed PSCs in 2014, the power conversion efficiencies (PCE) have increased from 10% to 21% by the end of 2020 with an exponential growth in research conducted in this field. Despite much effort, the performance and stability of Pb-Sn mixed PSCs are still limited, which constrains their long-term use in all-perovskite tandem devices. This review highlights the avenues explored in improving different aspects of Pb-Sn mixed PSCs and provides a comprehensive discussion of the interdependent factors affecting the device performance. This includes compositional engineering of the perovskite crystal, absorber layer fabrication and crystallization methods, bandgap tuning, Sn4+ reduction, and surface passivation of the absorber layer, as well as the selection of interlayers and electrodes of the final PSC.

Yongshang Zhang, Peng Zhang, Bin Li, Shijie Zhang, Kangli Liu, Ruohan Hou, Xilai Zhang, S. Ravi P. Silva, Guosheng Shao (2020)Vertically aligned graphene nanosheets on multi-yolk/shell structured TiC@C nanofibers for stable Li–S batteries, In: Energy Storage Materials27pp. 159-168 Elsevier B.V

Maintaining structural stability and alleviating the intrinsic poor conductivity of cathode materials are of great importance for practical application of Li–S batteries. Introducing void space and a highly conductive host to accommodate the volume changes and enhance the conductivity would be a smart design to achieve robust construction; effective electron and ion transportation, thus, lead to prolonged cycling life and excellent rate performance. In this regard, we report the design of carbonaceous hybrid with vertically aligned graphene assembled on multi-yolk/shell structured TiC@C nanofibers to afford synergistic properties of enough space, strong chemisorption and active electrocatalysis, high electrical conductivity as a sulfur host. Thus, the as-prepared sulfur cathode delivers an excellent cyclability over 800 cycles, a high areal capacity of 6.81 ​mA ​h ​cm2 at a high sulfur loading (10.5 ​mg). More importantly, soft package battery was also prepared with a capacity of 530 ​mAh g−1 and 46.5 ​mAh in the first cycle at a sulfur loading of 4.5 ​mg ​cm−2, which reveals its potential in promoting the practical application of Li–S batteries. [Display omitted] •A carbonaceous hybrid with vertically aligned graphene assembled on multi-yolk/shell structured TiC@C nanofibers.•The porous carbon nanofibers skeleton was obtained by the transformation of TiO2 to TiC.•A self-standing and long-range electron conduction network provide more surface area for the deposition of Li2S.•In-situ XRD and EIS were performed to investigate the mechanism during the cycling of Li–S batteries.•The cathode with high S content could deliver remarkable specific capacity, and great cycling durability.

CAMERON CHRISTOPHER UNDERWOOD, JAMES DAVID CAREY, S RAVI PRADIP SILVA (2021)Influence of A site cation on nonlinear band gap dependence of 2D Ruddlesden-Popper A2Pb1-: X Snx I4perovskites, In: Materials Advances Royal Society of Chemistry

Ruddlesden-Popper phase (RPP) perovskites of the form A1n−1A22BnX3n+1 show great promise in stable photovoltaic (PV) devices or as light emitting diodes (LEDs). In particular, n= 1, mono-layer RPPs of the form ABX4 have also shown great progress as the passivating layer for 3D perovskite PVs. We study the electronic behaviour of mixed B site An−1Pb1-xSnxX3n+1 where A = PEA or MA to investigate if the size of the A site cation indirectly affects the nonlinear band gap dependence of a 2D monolayer RPP layer. Both perovskites show a nonlinear behaviour primarily due to the relative energy difference between the Sn 5s - I 5p antibonding states and the Pb 6s - I 5p antibonding states, though the extent of the nonlinearity is reduced relative to 3D bulk perovskites due to the reduced dimensionality of these 2D structures. We also discuss the influence on bandgap nonlinearity due to the structural distortions induced by the differences between the A site cation. This research presents a strategy to the design of mixed solid state 2D perovskites by tuning the structural parameters as well as metal and halide composition.

Hao Tian, Huajun Tian, Wu Yang, Fan Zhang, Wang Yang, Qiaobao Zhang, Yong Wang, Jian Liu, S. Ravi P. Silva, Hao Liu, Guoxiu Wang (2021)Stable Hollow-Structured Silicon Suboxide-Based Anodes toward High-Performance Lithium-Ion Batteries, In: Advanced functional materials31(25)pp. 1-14 Wiley

Silicon has been regarded as an attractive high-capacity anode material for next-generation lithium-ion batteries (LIBs). However, Si anodes suffer from huge volume variation during cycling, which poses a critical challenge for stable battery operation. Compared with Si, Si suboxide (SiOx) is one of the most promising candidates for high-energy-density LIBs because of its alleviated swelling and highly stable cycling performance. Whereas, the poor electronic conductivity and low (initial) Coulombic efficiency of SiOx anodes severely hinder practical applications for LIBs. Herein, for the first time, these issues are successfully solved through rationally designing hollow-structured SiOx@carbon nanotubes (CNTs)/C architectures with graphitic carbon coatings and in situ growth of CNTs. When applied as anodes in LIBs, the SiOx@CNTs/C anodes exhibit high reversible capacity, high initial Coulombic efficiency (88%), outstanding cycling performance, and extraordinary mechanical strength during the calendaring process (200 MPa). This work paves the way for developing SiOx-based anode materials for high-energy-density LIBs.

Beibei Zong, Die Hu, Qing Sun, Jianguo Deng, Zizhao Zhang, Xiangxin Meng, Bo Shen, Bonan Kang, S. Ravi P. Silva, Geyu Lu (2023)2, 3, 4, 5, 6-Pentafluorophenylammonium bromide-based double-sided interface engineering for efficient planar heterojunction perovskite solar cells, In: Chemical engineering journal (Lausanne, Switzerland : 1996)452 Elsevier B.V

[Display omitted] •The 5PFP-Br is used as a double-interface passivator for PSCs.•The ETL with 5PFP-Br passivation has higher conductivity and electron mobility.•The perovskite with 5PFP-Br passivation has lower interfacial carrier defect state.•The PCE of the treated device increased from 18.09% to 21.15%.•The device based 5PFP-Br double-interface passivator have good stability. In order to obtain high power conversion efficiency and high stability perovskite solar cells, many innovative optimization schemes have been proposed. Thereinto, the interface modification become an effective way to improve the performance of device. Here, A dual-interface passivation by 2, 3, 4, 5, 6-pentafluorophenylammonium bromide-based (5PFP-Br) is used to optimize the performance of device with the structure of ITO/SnO2/perovskite/PTAA/Ag. We design the 5PFP-Br layer at SnO2/perovskite and perovskite/PTAA interface respectively. The results show that the interface contact between perovskite and charge transport layer is improved obviously. At the same time, the density of carrier transport defect states in the device is reduced, thus reducing the non-radiative recombination of carriers. Meanwhile, the 5PFP-Br layer at perovskite/PTAA interface can effectively passivate Pb defects and reduce the number of grain boundaries in perovskite film, and increase the carrier transfer and collection efficiency. Finally, 5PFP-Br double-interface passivation can further optimize and improve the performance of device. The device based 5PFP-Br double-interface passivation presents an increased efficiency from 18.09% to 21.15%, where FF is raised from 73.30% to 80.04%. At the same time, unpackaged device can still be maintained to more than 90% efficiency after about 1200 h at 25 °C and 25%RH.

Bowei Li, Yuren Xiang, Imalka Jayawardena, Deying Luo, John Watts, Steven Hinder, Hui Li, Victoria Ferguson, Haitian Luo, Rui Zhu, S. Ravi P. Silva, Wei Zhang (2020)Tailoring Perovskite Adjacent Interfaces by Conjugated Polyelectrolyte for Stable and Efficient Solar Cells, In: Solar RRL4(5)2000060 Wiley

Interface engineering is an effective means to enhance the performance of thin‐film devices, such as perovskite solar cells (PSCs). Herein, a conjugated polyelectrolyte, poly[(9,9‐bis(3′‐((N,N‐dimethyl)‐N‐ethyl‐ammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]di‐iodide (PFN‐I), is used at the interfaces between the hole transport layer (HTL)/perovskite and perovskite/electron transport layer simultaneously, to enhance the device power conversion efficiency (PCE) and stability. The fabricated PSCs with an inverted planar heterojunction structure show improved open‐circuit voltage (Voc), short‐circuit current density (Jsc), and fill factor, resulting in PCEs up to 20.56%. The devices maintain over 80% of their initial PCEs after 800 h of exposure to a relative humidity 35–55% at room temperature. All of these improvements are attributed to the functional PFN‐I layers as they provide favorable interface contact and defect reduction.

Ciara O'Flynn, Valentine Seymour, James Crawshaw, Thomas Parrott, Catriona Reeby, S. Ravi P. Silva (2021)The road to net zero: A case study of innovative technologies and policy changes used at a medium-sized university to achieve Czero by 2030, In: Sustainability (Basel, Switzerland)13(17) Mdpi

The need for the world to follow a more carbon-neutral path is clear, with growing evidence highlighting the existential threat posed by unregulated GHG emissions. Responsibility for achieving this does not only lie with policy makers but is shared with all stakeholders including governments, private sectors, charities and civil society as a whole. Several methodological approaches have been developed to set emission reduction targets, including the Science-Based Targets Initiative (SBTi). However, it is yet to be widely adopted, and as thought leaders in the field, universities must take a lead in its interpretation and application. This study is reported from the perspective of a UK university, which is adopting climate change considerations to facilitate achieving Czero by 2030 and will act as an exemplar case. We calculate baseline emissions, science-based reduction targets for different carbon emission reduction methods and options in terms of financing emission reduction pathways at present and in the future. The study outcomes show that incorporating a SBTi methodology can serve as insight into other medium-sized organisations and universities wishing to develop a net-zero pathway. These results have been summarised into a series of recommendations.

Beibei Zong, Jianguo Deng, Qing Sun, Zizhao Zhang, Xiangxin Meng, Bo Shen, Bonan Kang, S. Ravi P. Silva, Geyu Lu (2022)Facile Surface Engineering of Composite Electron Transport Layer for Highly Efficient Perovskite Solar Cells with a Fill Factor Exceeding 81%, In: Advanced materials interfaces9(6)pp. 2102331-n/a Wiley

After perovskite became a star material, research on perovskite solar cells (PSCs) became a hot topic and developed rapidly. Electron transport layers (ETLs) with high mobility, low-defect state, and suitable energy level arrangement dominate the development of planar heterojunction PSCs. In this work, the K+ and Cs+ doped composite SnO2 ETL (x mg KC-SnO2) by a continuous spin-coating of the x mg Cs+@KOH and SnO2 aqueous solution shows a substantial improvement in carries extraction, transport and collection properties, leading to the increased fill factor (FF) from 72.48% to 81.00% of the planar heterojunction PSCs, and finally the champion device average efficiency is 21.62%. Moreover, this work improves the interface contacts between ETL/Perovskite, as it reduces energy disorder and simultaneously promotes electron transport, charge extraction at the interface, improve energy level alignment and quasi-Fermi level splitting, and decreased resistance for charge transfer in the device. In conclusion, this simple and effective method of improving the FF value provides a certain shortcut to the performance of plane heterogeneous perovskite devices.

Beibei Zong, Zizhao Zhang, Qing Shun, Bonan Kang, S. Ravi P. Silva, Ge yu Lu (2021)High-Performance Planar Heterojunction Perovskite Solar Cells Based on BaCl2 Additive and Power Conversion Efficiency of Over 21%, In: Advanced electronic materials7(6)pp. 1-n/a

The photoelectric conversion efficiency of perovskite solar cells (PSCs) has rapidly developed in the past decade. However, the development of PSCs still has many limitations: for instance, the accumulation of harmful defects on their surfaces and grain boundaries limit their performance. Here, PSCs with ITO/SnO2/FAxMA1−xPb(IyBr1−y)3/Spiro‐OMeTAD/Ag structure are fabricated under air conditions, meanwhile, the effect the different masses of BaCl2 (0, 10, 15, 20, and 25 mg) added to FAxMA1−xPb(IyBr1−y)3 perovskite precursor solution on the performance of PSCs is investigated. The results show that the best performance is obtained when 20 mg BaCl2 is added, and the performance parameters Jsc, Voc, FF of the PSCs (those with 20 mg BaCl2) are 24.43 mA cm−2, 1137 mV, and 75.82, respectively, and their power conversion efficiency is up to 21.06%, which is ≈25% higher than that of the reference devices (those without BaCl2). Test results, such as XRD, SEM, TRPL, SCLC, UV–Vis, show that right amount of BaCl2 additive can significantly improve the crystallinity, absorbance, and interface defect state of perovskite films. It can also increase the separation and mobility of charge carriers, thus greatly improving the performance of PSCs. PSCs with different masses of BaCl2 additive in the perovskite precursor solution are fabricated under air conditions. The results show that the champion PSC can be obtained when BaCl2 is 20 mg, because it significantly improves the crystallinity, absorbance, and interface defect state of perovskite films. Additionally, the PCE of the device increases from 16.85 to 21.06%.

Shigeyuki Umezawa, Takashi Douura, Koji Yoshikawa, Yohei Takashima, Mika Yoneda, Kazuma Gotoh, Vlad Stolojan, S. Ravi P. Silva, Yasuhiko Hayashi, Daisuke Tanaka (2021)Supercapacitor electrode with high charge density based on boron-doped porous carbon derived from covalent organic frameworks, In: Carbon (New York)184pp. 418-425 Elsevier Ltd

We developed a facile and unique process for preparing boron-doped porous carbon by direct carbonization of a boron-based covalent organic framework (COF-5). Boron oxides, which are formed during the carbonization of COF-5, were readily removed through water treatment of the resulting carbon to obtain boron-doped porous carbon. Thus, boron atoms were successfully incorporated into the carbon matrix. Supercapacitor electrodes made of the fabricated boron-doped carbon exhibited a specific capacitance of 15.3 μF cm−2 at 40 mA g−1, which is twice that of the conventional activated carbon electrode (∼6.9 μF cm−2) at the same current density, owing to the presence of boron atoms in the carbon material. The supercapacitors based on boron-doped carbon demonstrated 72% capacitance retention after 10000 charge/discharge cycles. The boron-doped COF-derived carbon materials can serve as a new class of multifunctional carbon materials for energy storage devices. [Display omitted] •Porous B-doped carbon is produced from a B-based covalent organic framework (COF).•Water treatment eliminated B oxides by COF calcination.•B atoms are atomically distributed in the porous carbon.•B-doped porous carbon can serve as supercapacitor electrode material.•Achieved 15 μF cm−2 specific capacitance at 40 mA g−1 in organic electrolyte.

Yongshang Zhang, Xilai Zhang, S. Ravi P. Silva, Bin Ding, Peng Zhang, Guosheng Shao (2022)Lithium–Sulfur Batteries Meet Electrospinning: Recent Advances and the Key Parameters for High Gravimetric and Volume Energy Density, In: Advanced science9(4)pp. e2103879-n/a John Wiley and Sons Inc

Lithium–sulfur (Li–S) batteries have been regarded as a promising next‐generation energy storage technology for their ultrahigh theoretical energy density compared with those of the traditional lithium‐ion batteries. However, the practical applications of Li–S batteries are still blocked by notorious problems such as the shuttle effect and the uncontrollable growth of lithium dendrites. Recently, the rapid development of electrospinning technology provides reliable methods in preparing flexible nanofibers materials and is widely applied to Li–S batteries serving as hosts, interlayers, and separators, which are considered as a promising strategy to achieve high energy density flexible Li–S batteries. In this review, a fundamental introduction of electrospinning technology and multifarious electrospinning‐based nanofibers used in flexible Li–S batteries are presented. More importantly, crucial parameters of specific capacity, electrolyte/sulfur (E/S) ratio, sulfur loading, and cathode tap density are emphasized based on the proposed mathematic model, in which the electrospinning‐based nanofibers are used as important components in Li–S batteries to achieve high gravimetric ( W G ) and volume ( W V ) energy density of 500 Wh kg −1 and 700 Wh L −1 , respectively. These systematic summaries not only provide the principles in nanofiber‐based electrode design but also propose enlightening directions for the commercialized Li–S batteries with high W G and W V . A mathematic model is proposed using the electrospinning‐based nanofibers serve as a cathode and anode host, and separator to achieve high gravimetric ( W G ) and volume ( W V ) energy density of 500 Wh kg −1 and 700 Wh L −1 in Li–S batteries, respectively, by emphasizing the crucial parameters of specific capacity, electrolyte/sulfur (E/S) ratio, sulfur loading, and cathode tap density in the cell.

Filip Mandys, Mona Chitnis, S. Ravi P. Silva (2023)Levelized cost estimates of solar photovoltaic electricity in the United Kingdom until 2035, In: Patterns (New York, N.Y.) Elsevier Inc

Solar photovoltaic (PV) electricity represents one of the most promising sources of clean and affordable energy; however, the share of solar power in electricity production remains low, primarily because of the high installation costs. By conducting a large-scale analysis of electricity pricing, we show that solar PV systems are quickly becoming one of the most competitive sources of electricity. Collecting a contemporary UK dataset of 2010–2021, we analyze the historical levelized cost of electricity for several PV system sizes, project until 2035, and conduct a sensitivity analysis. The cost of PV electricity is currently at about 149 ₤/MWh for the smallest-scale and 51 ₤/MWh for large-scale PV systems, already lower than the wholesale price of electricity, with PV systems predicted to get cheaper by 40%–50% until 2035. The government should focus on supporting solar PV system developers with benefits such as simpler land purchases for PV farms or preferential loans with low interest rates. [Display omitted] •The cost of PV systems has been steadily falling in the last decade, regardless of system size•The 2021 cost of electricity was 149 ₤/MWh for small and 51 ₤/MWh for large-scale PV systems•Large PV systems in 2021 were cheaper than wholesale electricity; small PV systems will break even by 2027•PV systems are predicted to get cheaper by 40%–50% by 2035 A growing number of countries worldwide are concerned about the adverse effects of anthropogenic climate change and the gradual depletion of fossil fuels. Many countries are therefore committed to finding ways of reducing their carbon emissions and ultimately reaching carbon neutrality. Solar photovoltaic (PV) electricity represents one of the most promising sources of clean and renewable energy, but it has suffered in the past from steep costs. Our research uses the latest available data to estimate past UK solar PV system costs while accounting for several key assumptions, and it projects the costs until 2035. This analysis can provide a better understanding of the expansion potential of solar PV systems, even in high-latitude countries. Lower PV system costs and the related potential for increased diffusion of this technology could make a huge difference in the overall carbon emissions of a society. Cost estimates of this kind may help governments and others make better decisions in the short and long term regarding PV system policies and investment. This research evaluates the past UK levelized cost of electricity for several PV system sizes and makes projections of the costs until 2035 using current data from 2010–2021. The findings confirm that the cost of solar PV systems has decreased substantially in the last decade, with solar PV electricity production getting cheaper with system size. Large-scale PV system cost is already lower than the wholesale electricity price and is predicted to get cheaper by 40%–50% by 2035, making solar PV systems very attractive.

Yiyan Wang, ZHONG LI, P Zhang, Yuan Pan, Ying Zhang, QIONG CAI, S. Ravi P. Silva, JIAN LIU, G.X. Zhang, X Sun, Z Yan (2021)Flexible carbon nanofiber film with diatomic Fe-Co sites for efficient oxygen reduction and evolution reactions in wearable zinc-air batteries, In: Nano energy87106147 Elsevier Ltd

Carbon nanofiber (CNF) papers have been widely used in many renewable energy systems, and the development of its catalytic function is of great significance and a major challenge. In this work, we pioneer a time- and cost-efficient strategy for the preparation of large-area flexible CNF films with uniformly distributed diatomic FeN3-CoN3 sites (Fe1Co1-CNF). Due to the excellent compatibility and similar functionality of the pre-designed ZnFeCo-NC precursors (ZnFeCo-pre) with the electrospun polymer polyacrylonitrile (PAN), the mixture of ZnFeCo-pre and PAN can be co-electrospun and subject to a standard CNF fabrication process. The resulting Fe1Co1-CNF exhibits excellent bifunctional catalytic performance for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), attributing to the abundant dual catalytic FeN3-CoN3 sites which are mutually beneficial for attaining optimal electronic properties for the adsorption/desorption of reaction intermediates. The assembled liquid-electrolyte ZAB provides a high specific power of 201.7 mW cm−2 and excellent cycling stability. More importantly, due to the good mechanical strength and flexibility of Fe1Co1-CNF, portable ZAB with exceptional shape deformability and stability can be demonstrated, in which Fe1Co1-CNF utility as an integrated free-standing membrane electrode. These findings provide a facile strategy for manufacturing flexible multi-functional catalytic electrodes with high production. [Display omitted] •Large-area self-standing flexible CNF film with diatomic Fe-Co sites was developed.•The diatomic Fe-Co sites render optimized adsorption of O-containing intermediates.•The Fe1Co1-CNF exhibits superior bifunctional ORR/OER performance.•The Fe1Co1-CNF shows great potential in liquid/flexible Zn-air battery.

Jing Zhang, Wei Zhang, Huiming Cheng, Ravi Silva (2020)Critical review of recent progress of flexible perovskite solar cells, In: Materials Today Elsevier

Perovskite solar cells (PSCs) have emerged as a ‘rising star’ in recent years due to their high-power conversion efficiency (PCE), extremely low cost and facile fabrication techniques. To date, PSCs have achieved a certified PCE of 25.2% on rigid conductive substrates, and 19.5% on flexible substrates. The significant advancement of PSCs has been realized through various routes, including perovskite composition engineering, interface modification, surface passivation, fabrication process optimization, and exploitation of new charge transport materials. However, compared with rigid counterparts, the efficiency record of flexible perovskite solar cells (FPSCs) is advancing slowly, and therefore it is of great significance to scrutinize recent work and expedite the innovation in this field. In this article, we comprehensively review the recent progress of FPSCs. After a brief introduction, the major features of FPSCs are compared with other types of flexible solar cells in a broad context including silicon, CdTe, dye-sensitized, organic, quantum dot and hybrid solar cells. In particular, we highlight the major breakthroughs of FPSCs made in 2019/2020 for both laboratory and large-scale devices. The constituents of making a FPSC including flexible substrates, perovskite absorbers, charge transport materials, as well as device fabrication and encapsulation methods have been critically assessed. The existing challenges of making high performance and long-term stable FPSCs are discussed. Finally, we offer our perspectives on the future opportunities of FPSCs in the field of photovoltaics.

Yuting Tang, Yu Pang, Xu Li, Beibei Zong, Bonan Kang, S. Ravi P. Silva, Geyu Lu (2020)Interface passivation and electron transport improvement via employing calcium fluoride for polymer solar cells, In: Journal of colloid and interface science562(C)pp. 142-148 Elsevier Inc

[Display omitted] To enhance the performance of inverted structure polymer solar cells (PSCs), interfacial engineering considered as an effective and straightforward method was employed. In this study, to overcome the surface traps and energy level mismatches of the electron transport layer, a means of interface passivation by evaporating an ultrathin CaF2 layer above ZnO thin film as the electron transport layer was successfully adopted. We display that CaF2 layer could passivate the surface traps of ZnO thin film and decrease the interfacial barrier between PC61BM and ZnO, so that electron transfer efficiency is facilitated, the recombination of electrons and holes is inhibited at the contact interface, and the series resistance is reduced. After the introduction of the CaF2 layer, the short-circuit current and the fill factor was greatly improved, also the power conversion efficiency (PCE) was increased from 3.21% of the reference device without the CaF2 layer to 4.22% in the inverted PSCs based on P3HT:PC61BM bulk heterojunction photoactive layer. These results could have special guiding significance for high-efficiency PSCs and also great potential for applications of photovoltaic devices in the future.

Eva Bestelink, Kham M. Niang, George Bairaktaris, Luca Maiolo, Francesco Maita, Kalil Ali, Andrew J. Flewitt, Ravi Silva, Radu Sporea (2020)Compact Source-Gated Transistor Analog Circuits for Ubiquitous Sensors, In: IEEE Sensors Institute of Electrical and Electronics Engineers

Silicon-based digital electronics have evolved over decades through an aggressive scaling process following Moore’s law with increasingly complex device structures. Simultaneously, large-area electronics have continued to rely on the same field-effect transistor structure with minimal evolution. This limitation has resulted in less than ideal circuit designs, with increased complexity to account for shortcomings in material properties and process control. At present, this situation is holding back the development of novel systems required for printed and flexible electronic applications beyond the Internet of Things. In this work we demonstrate the opportunity offered by the source-gated transistor’s unique properties for low-cost, highly functional large-area applications in two extremely compact circuit blocks. Polysilicon common-source amplifiers show 49 dB gain, the highest reported for a twotransistor unipolar circuit. Current mirrors fabricated in polysilicon and InGaZnO have, in addition to excellent current copying performance, the ability to control the temperature dependence (degrees of positive, neutral or negative) of output current solely by choice of relative transistor geometry, giving further flexibility to the design engineer. Application examples are proposed, including local amplification of sensor output for improved signal integrity, as well as temperature-regulated delay stages and timing circuits for homeostatic operation in future wearables. Numerous applications will benefit from these highly competitive compact circuit designs with robust performance, improved energy efficiency and tolerance to geometrical variations: sensor front-ends, temperature sensors, pixel drivers, bias analog blocks and high-gain amplifiers.

Qing Sun, Shaocong Duan, Gang Liu, Xiangxin Meng, Die Hu, Jianguo Deng, Bo Shen, Bonan Kang, S. Ravi P. Silva (2023)Porous Lead Iodide Layer Promotes Organic Amine Salt Diffusion to Achieve High Performance p-i-n Flexible Perovskite Solar Cells, In: Advanced energy materials13(36)2301259

Abstract Flexible perovskite solar cells (FPSCs) are attracting widespread research and attention for their benefits as the next‐generation wearable electronic products. However, there are still many challenges in the quest to achieve dense, pinhole‐free, high crystal quality, low defect, and stable perovskite films, which limit further improvement in the efficiency and stability of FPSCs. Herein, a novel technique for the incorporation of quaternary ammonium halide (QAH) additives to prepare fluffy porous lead iodide layers by using a two‐step sequential deposition method, is reported. Benefiting from the good diffusion of organic amine salts on porous PbI 2 layers, flat and dense perovskite films are produced with large particle sizes, few defects, and high crystal quality. Finally, the champion rigid and flexible p‐i‐n PSCs with the 2‐(acetyloxy)‐N,N,N‐trimethylethanium chloride (AtaCl) additive achieves exciting power conversion efficiencies (PCE) of 23.40% and 21.10%, respectively. The device with the AtaCl additive retains over 90% of its original PCE under ambient conditions (40 ± 5% relative humidity (RH)) over 1000 h of aging without encapsulation. In addition, the flexible device with the AtaCl additive shows excellent stability under mechanical bending conditions, retaining ≈85% of its original PCE after 10 000 cycles (bending radius = 5 mm).

Yongshang Zhang, Zhiheng Wu, Shaobin Wang, Neng Li, S. Ravi P. Silva, Guosheng Shao, Peng Zhang (2022)Complex permittivity-dependent plasma confinement-assisted growth of asymmetric vertical graphene nanofiber membrane for high-performance Li-S full cells, In: InfoMat4(7) Wiley

Vertical graphene (VG), possessing superior chemical, physical, and structural peculiarities, holds great promise as a building block for constructing a high-energy density lithium-sulfur (Li-S) battery. Therefore, it is desirable to develop a new VG growth technique with a novel structure to enable wide applications. Herein, we devise a novel complex permittivity-dependent plasma confinement-assisted VG growth technique, via asymmetric growing a VG layer on one side of N-doped carbon nanofibers for the first time, using a unique lab-built high flux plasma-enhanced chemical vapor deposition system, as a bifunctional nanofiber membrane to construct Li-S batteries with low negative/positive (N/P) and electrolyte/sulfur (E/S) ratios. The unique nanofiber membrane could simultaneously protect the cathode and anode, enabling an excellent electrochemical performance with low N/P and E/S ratios in Li-S batteries. Such a full cell delivers high gravimetric energy density and volumetric energy density of 340 Wh kg(-1) and 547 Wh L-1, respectively, at low N/P (2:1) and E/S (4:1) ratios. Furthermore, a pouch cell achieves a high areal capacity of 7.1 mAh cm(-2) at a sulfur loading of 6 mg cm(-2). This work put forward a novel pathway for the design of high-energy density Li-S batteries.

Christopher Preddy, Rajinder Singh, Peter Aaen, Ravi Silva (2020)Integrated Carbon-Fiber-Reinforced Plastic Microstrip Patch Antennas, In: IEEE antennas and wireless propagation letters19(4)pp. 1-1 IEEE

A carbon fiber microstrip patch antenna is presented, constructed entirely from fiber reinforced plastic materials, and fabricated directly into CFRP composites as part of the composite manufacturing process. Fabrication of antennas as part of the composite manufacturing process provides numerous benefits, such as conformation to complex curvatures, reduced weight and reduced aerodynamic impact. Modification of the localized conductivity of the carbon fiber using materials such as copper meshes is shown to improve the gain of the antenna by as much as 5 dB, while also improving the interlaminar shear strength of the composite by 22%.

Dannielle Cox-Pridmore, Fernando A. Castro, S Ravi Pradip Silva, Patrizia Camelliti, Yunlong Zhao (2022)Emerging Bioelectronic Strategies for Cardiovascular Tissue Engineering and Implantation, In: Small (Weinheim an der Bergstrasse, Germany)18(17)e2105281

Heart diseases are currently the leading cause of death worldwide. The ability to create cardiovascular tissue has numerous applications in understanding tissue development, disease progression, pharmacological testing, bio‐actuators, and transplantation; yet current cardiovascular tissue engineering (CTE) methods are limited. However, there have been emerging developments in the bioelectronics field, with the creation of biomimetic devices that can intimately interact with cardiac cells, provide monitoring capabilities, and regulate tissue formation. Combining bioelectronics with cardiac tissue engineering can overcome current limitations and produce physiologically relevant tissue that can be used in various areas of cardiovascular research and medicine. This review highlights the recent advances in cardiovascular‐based bioelectronics. First, cardiac tissue engineering and the potential of bioelectronic therapies for cardiovascular diseases are discussed. Second, advantageous bioelectronic materials for CTE and implantation and their properties are reviewed. Third, several representative cardiovascular tissue‐bioelectronic interface models and the beneficial functions that bioelectronics can demonstrate in in vitro and in vivo applications are explored. Finally, the prospects and remaining challenges for clinical application are discussed. This review highlights recent advances in cardiovascular‐based bioelectronics. Cardiac tissue engineering and the potential of bioelectronic therapies for cardiovascular diseases are discussed, followed by advantageous bioelectronic materials for cardiovascular tissue engineering/implantation and their properties. Representative cardiovascular tissue‐bioelectronic interface models and their beneficial functions are also explored. Finally, prospects and remaining challenges are discussed for clinical applications.

Ehsan Rezaee, Wei Zhang, S. Ravi P Silva (2021)Solvent Engineering as a Vehicle for High Quality Thin Films of Perovskites and Their Device Fabrication, In: Small (Weinheim an der Bergstrasse, Germany)2008145 Wiley

Organic–inorganic halide perovskite solar cells (PSCs) have shown a significant growth in power conversion efficiencies (PCEs) during last decade. Progress in device architecture and high-quality perovskite film fabrication has led to an incredible efficiency over 25% in close to a decade. Developments in solution-based thin film deposition techniques for perovskite layer preparation in PSCs provide low cost and ease of process for their manufacturing, making them a potential contender in future solar energy harvesting technologies. From small area single solar cells to large area perovskite solar modules, solvents play crucial roles in thin film quality and therefore, the device performance and stability. A comprehensive overview of solvent engineering toward achieving the highest qualities for perovskite light absorbing layers with various compositions and based on different fabrication processes is provided in this review. The mechanisms indicating the essential roles a solvent, or a solvent mixture can play to improve the crystallinity, uniformity, coverage and surface roughness of the perovskite films, are discussed. Finally, the role of solvent engineering in transferring from small area laboratory scale PSC fabrication to large area perovskite film deposition processes is explored.

Wenting Li, Huan Zhang, Shengwei Shi, Jinxin Xu, Xin Qin, Qiqi He, Kecong Yang, Wubin Dai, Gang Liu, Quanguo Zhou, Huangzhong Yu, S. Ravi P. Silva, Mats Fahlman (2020)Recent progress in silver nanowire networks for flexible organic electronics, In: Journal of materials chemistry. C, Materials for optical and electronic devices8(14)pp. 4636-4674

Recently, flexible transparent electrodes (FTEs) have attracted extensive attention as an essential element for future organic electronics (OEs), i.e. solution-processable, scalable and flexible organic electronics (FOEs). Although the traditional transparent electrode indium tin oxide (ITO) has been widely used in OEs, its brittleness and high cost significantly limit its application in the next generation of devices, typically flexible electronics. Thus, many alternatives, such as graphene, carbon nanotubes, conductive polymers, metal nanowires, metal grids and electrospun metallic nanofibers, have arisen at the forefront of FTEs. Among them, silver nanowire (AgNW) networks have attracted particular attention due to their excellent electrical conductivity and high transmittance, as well as facile availability and low cost. Since many studies on AgNWs have been published, a comprehensive review highlighting the advantages of AgNWs in FOEs is highly required. In this review, the synthesis and film fabrication of AgNWs have been firstly summarized, focusing especially on the properties of conductivity and light transmittance. Next, post treatments with different approaches to improve the conductivity of AgNWs have been included. And then, characterization of FTEs has been introduced with details on key parameters for FOEs. Furthermore, AgNW-based FOEs have been summarized to demonstrate the recent progress, such as organic light-emitting diodes (OLEDs), organic solar cells (OSCs), light-emitting electrochemical cells (LECs), organic field effect transistors (OFETs), organic memory devices (OMDs), etc. Finally, perspectives for AgNWs in FOEs have been discussed and concluded as well. It is expected that AgNWs could be the focus of future FOEs compared with other alternatives in terms of their advantages of optoelectronic properties, film-formation, solution-processability and flexibility.

Bowei Li, Jun Deng, Joel A. Smith, Pietro Caprioglio, Kangyu Ji, Deying Luo, James D. McGettrick, K. D. G. Imalka Jayawardena, Rachel Kilbride, AOBO REN, Stephen Sweeney, Steven John Hinder, Jinxin Bi, S Ravi Pradip Silva, Wei Zhang, THOMAS WEBB, Igor Marko, Xueping Liu, YUREN XIANG, Joshua Dean Reding, HUI LI, Shixuan Du, D. G. Lidzey, Samuel D. Stranks, Trystan M. Watson, H. J. Snaith (2022)Suppressing Interfacial Recombination with a Strong-Interaction Surface Modulator for Efficient Inverted Perovskite Solar Cells, In: Advanced energy materials Wiley

Successful manipulation of halide perovskite surfaces is typically achieved via the interactions between modulators and perovskites. Herein, it is demonstrated that a strong-interaction surface modulator is beneficial to reduce interfacial recombination losses in inverted (p-i-n) perovskite solar cells (IPSCs). Two organic ammonium salts are investigated, consisting of 4-hydroxyphenethylammonium iodide and 2-thiopheneethylammonium iodide (2-TEAI). Without thermal annealing, these two modulators can recover the photoluminescence quantum yield of the neat perovskite film in contact with fullerene electron transport layer (ETL). Compared to the hydroxyl-functionalized phenethylammonium moiety, the thienylammonium facilitates the formation of a quasi-2D structure onto the perovskite. Density functional theory and quasi-Fermi level splitting calculations reveal that the 2-TEAI has a stronger interaction with the perovskite surface, contributing to more suppressed non-radiative recombination at the perovskite/ETL interface and improved open-circuit voltage (V-OC) of the fabricated IPSCs. As a result, the V-OC increases from 1.11 to 1.20 V (based on a perovskite bandgap of 1.63 eV), yielding a power conversion efficiency (PCE) from approximate to 20% to 21.9% (stabilized PCE of 21.3%, the highest reported PCEs for IPSCs employing poly[N,N ''-bis(4-butylphenyl)-N,N ''-bis(phenyl)benzidine] as the hole transport layer, alongside the enhanced operational and shelf-life stability for unencapsulated devices.

Qing Sun, Beibei Zong, Xiangxin Meng, Bo Shen, Xu Li, Bonan Kang, S. Ravi P. Silva (2022)Interface Regulation by an Ultrathin Wide-Bandgap Halide for Stable and Efficient Inverted Perovskite Solar Cells, In: ACS applied materials & interfaces14(5)pp. 6702-6713 Amer Chemical Soc

The nonradiative recombination between hole transport layers (HTLs) and perovskites generally leads to obvious energy losses. The trap states at the HTL/perovskite interface directly influence the improvement of the power conversion efficiency (PCE) and stability. Interface regulation is a simple and commonly used method to decrease nonradiative recombination in inverted perovskite solar cells (PSCs). Here, a wide-bandgap halide was used to regulate the PTAA/MAPbI(3) interface, in which n-hexyltrimethylammonium bromide (HTAB) was used to modify the upper surface of poly[bis(4-phenyl)-(2,4,6-trimethylphenyl)amine] (PTAA). Upon introduction of the HTAB layer, the contact between PTAA and MAPbI(3) is strengthened, the defect state density in PSCs is reduced, the MAPbI(3) crystallinity is improved, and the nonradiative recombination loss is suppressed. The device with HTAB delivers the highest PCE of 21.01% with negligible hysteresis, which is significantly higher than that of the control device (17.71%), and it maintains approximately 87% of its initial PCE for 1000 h without encapsulation in air with a relative humidity of 25 +/- 5%. This work reveals an effective way of using a widebandgap halide to regulate the PTAA/MAPbI(3) interface to simultaneously promote the PCE and stability of PSCs.

W. Hashini K. Perera, Mateus G. Masteghin, Hongjae Shim, Joshua L. Ryan, Steven J. Hinder, Jae S. Yun, Wei Zhang, K. D. G. Imalka Jayawardena, S Ravi Pradip Silva (2023)Modification of Hydrophobic Self-Assembled Monolayers with Nanoparticles for Improved Wettability and Enhanced Carrier Lifetimes Over Large Areas in Perovskite Solar Cells, In: Solar RRL Wiley

The development of perovskite solar cells (PSCs) with low recombination losses, at low processing temperatures is an area of growing research interest as it enables compatibility with roll-to-roll processing on flexible substrates as well as with tandem solar cells. The inverted or p-i-n device architecture has emerged as the most promising PSC configuration due to the possibility of using low temperature processable organic hole transport layers and more recently, self-assembled monolayers such as, [4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl]phosphonic Acid (Me-4PACz). However, devices incorporating these interlayers suffer from poor wettability of the precursor leading to pin hole formation and poor device yield. Here, we demonstrate the use of alumina nanoparticles (Al2O3 NPs) for pinning the perovskite precursor on Me-4PACz, thereby improving the device yield. While similar wettability enhancements can also be achieved by using poly[(9,9-bis(3’-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]dibromide (PFN-Br), a widely employed surface modifier, the incorporation of Al2O3 NPs results in significantly enhanced Shockley-Read-Hall recombination lifetimes exceeding 3 μs, which is higher than those on films coated directly on Me-4PACz and on PFN-Br modified Me-4PACz. This translates to a champion power conversion efficiency of 19.9% for PSCs fabricated on Me-4PACz modified with Al2O3, which is a ∽20% improvement compared to the champion device fabricated on PFN-Br modified Me-4PACz.

R.C. Smith, L.D. Filip, J.D. Carey, S.R.P. Silva (2007)Calculation of field enhancement factor and screening effects in carbon nanotube arrays, In: 2007 IEEE 20th International Vacuum Nanoelectronics Conferencepp. 171-172 IEEE

Computational 3D simulations of individual carbon nanotubes (CNTs) and vertically aligned arrays of CNTs were conducted in order to gain insight into their field emission characteristics. We find that the widely used approximation that the enhancement factor is equal to the aspect ratio of the emitter to be an over-estimation, and that the enhancement factor is only loosely related to the aspect ratio, among other parameters.

Raphael D.C. Balboni, Guilherme K. Maron, MATEUS GALLUCCI MASTEGHIN, MEHMET ORHAN TAS, Lucas S. Rodrigues, Veridiana Gehrke, José H. Alano, Robson Andreazza, Neftali L.V. Carreño, S RAVI PRADIP SILVA (2022)Easy to assemble PDMS/CNTs/PANI flexible supercapacitor with high energy-to-power density, In: Nanoscale [e-journal] Royal Society of Chemistry

The fabrication of a flexible supercapacitor with state-of-the-art performance is described, based on a facile and low-cost fabrication method that encompass aligned carbon nanotube arrays (ACNTA) – polyaniline/polydimethylsiloxane electrodes (ACNTA-PANI/PDMS). The ACNTA was partially embedded in PDMS to ensure excellent adhesion and integration whilst PANI was electrodeposited on its surface to improve energy storage properties. The supercapacitor structure and morphology were investigated by Raman spectroscopy and scanning electron microscope (SEM), respectively. The energy storage properties of the electrodes were evaluated in two and three-electrode configurations. The maximum value of specific capacitance was 408 (265 F.g-1) at 1 , and a high energy density of 20 µ (25.5 was achieved at power density of 100 µ (126.6 W.Kg-1) for a symmetric two-electrode device. The device showed a good capacitance retention of 76% after 5000 cycles and was able to maintain 80% of its electrochemical properties while measured at different bending angles, demonstrating excellent mechanical agility performance under extreme conditions and some of the highest carbon-based energy storage.

Christopher M. Preddy, Rajinder Singh, Haris Votsi, Peter H. Aaen, S. Ravi P. Silva (2019)Characterization of Carbon Fiber Reinforced Plastic for Microwave Circuit Design, In: 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP)pp. 121-123 IEEE

This paper presents the extraction of the complex propagation constant from carbon fiber reinforced plastic (CFRP) transmission lines up to 5 GHz. A test-fixture is designed and fabricated to obtain the propagation constant using a line-line extraction method. Use of this method reduces the required number of fabricated transmission lines compared to calibration algorithms such as TRL. Comparison of the extracted propagation constant with simulation data indicates CFRP conductivity of 1.0 -1.5x10 4 S/m.

Iskandar Yahya, Muhamad Azuddin Hassan, Seri Mastura Mustaza, Huda Abdullah, S. K. Clowes, S. Ravi P. Silva (2021)The Influence of Growth Method Towards Carbon Nanotube Field Effect Transistor Performance, In: 2021 IEEE Regional Symposium on Micro and Nanoelectronics (RSM)pp. 149-152 IEEE

Due to its exceptional electronic properties, single walled carbon nanotubes (SWCNTs) can be applied as the active channel of high-performance carbon nanotube field effect transistors (CNTFETs). The electronic properties of SWCNTs are known to be affected by its intrinsic properties, including electronic type, diameter and structural defects. Since tube defect is dependent of the growth method, it is shown that the latter can also influence the CNTFET device performance. Four SWCNT samples from different growth methods were sourced to fabricate CNTFETs. Raman analysis was carried out to quantify the tube defect level of SWCNTs by determining the G-peak to D-peak height ratio. Electrical measurement was carried out to assess the key device performance parameters that include on-off current ratio, \boldsymbol{I}_{\mathbf{ON}}/\boldsymbol{I}_{\mathbf{OFF}} transconductance, \boldsymbol{g}_{\mathbf{m}} , subthreshold slope, \boldsymbol{S}_{\mathbf{p}} and field effect mobility, \mu_{\mathbf{FE}} . Correlation between the optical analysis and electrical measurement concludes that the SWCNT growth method does influence the CNTFET performance significantly.

Iskandar Yahya, S. Ravi P. Silva, Steven Clowes, Arulampalam Kunaraj, Seri Mastura Mustaza (2022)Methods for Estimating Composition of Single Walled Carbon Nanotubes Based on Electronic Type, In: Materials science forum1055pp. 77-86 Trans Tech Publications Ltd

— Synthesized single-walled carbon nanotubes (SWCNTs) consist of a mixture of chiralities and therefore a post-synthesis separation is essential to separate them based on electronic type i.e., metallic (m-SWCNT) or semiconducting (s-SWCNT) for device applications. A key parameter to measure the effectiveness of separation process is the enrichment composition percentage between m-SWCNT and s-SWCNT, which can be estimated via several methods based on optical characterizations. In this paper, we compare the composition percentage estimations from 3 different methods based on Raman spectroscopy and UV-Vis optical absorption spectroscopy. The estimation methods are radial breathing mode (RBM) peak analysis, optical absorption area under curve (OUA) and first derivative amplitude of the optical absorption curve (FDA). Four different SWCNT sources were used in this study, which were subjected to post-synthesis separation process via agarose gel chromatography. Raman and UV-Vis spectroscopy measurements were carried out on all samples, before and after separation. From the estimations, we observed firstly that there are some variations on the estimated enrichment compositions between different methods, although the values are comparable. Secondly, for some SWCNTs samples, only a certain estimation method showed reliable composition percentage. The results presented in this work may provide viable options for characterizations of SWCNTs as there is no direct method to quantify the absolute composition percentage of SWCNTs based on electronic type. Keywords— single-walled carbon nanotube, separation, electronic type, optical characterization, purity percentage.

Xueping Liu, THOMAS WEBB, Linjie Dai, Kangyu Ji, Joel A. Smith, Rachel Kilbride, MOZHGAN YAVARI, Jinxin Bi, AOBO REN, Yuanyuan Huang, Zhuo Wang, Yonglong Shen, Guosheng Shao, Stephen Sweeney, Steven John Hinder, HUI LI, D. G. Lidzey, Samuel D. Stranks, Neil C Greenham, Wei Zhang, S Ravi Pradip Silva (2022)Influence of halide choice on formation of low‐dimensional perovskite interlayer in efficient perovskite solar cells Wiley

Recent advances in heterojunction and interfacial engineering of perovskite solar cells (PSCs) have enabled great progress in developing highly efficient and stable devices. Nevertheless, the effect of halide choice on the formation mechanism, crystallography and photoelectric properties of the low-dimensional phase still requires further detailed study. In this work, we present key insights into the significance of halide choice when designing passivation strategies comprising large organic spacer salts, clarifying the effect of anions on the formation of quasi2D/3D heterojunctions. To demonstrate the importance of halide influences, we employ novel neo-pentylammonium halide salts with different halide anions (neoPAX, X = I, Br or Cl). We find that regardless of halide selection, iodide-based (neoPA)2(FA)(n-1)PbnI(3n+1) phases are formed above the perovskite substrate, while the added halide anions diffuse and passivate the perovskite bulk. In addition, we also find the halide choice has an influence on the degree of dimensionality (n). Comparing the three halides, we find that chloride-based salts exhibit superior crystallographic, enhanced carrier transport and extraction compared to the iodide and bromide analogs. As a result, we report high power conversion efficiency in quasi-2D/3D PSCs, which are optimal when using chloride salts, reaching up to 23.35% and improving long-term stability.

R. M. I. Bandara, K. D. G. I. Jayawardena, S. O. Adeyemo, S. J. Hinder, J. A. Smith, H. M. Thirimanne, N. C. Wong, F. M. Amin, B. G. Freestone, A. J. Parnell, D. G. Lidzey, H. J. Joyce, R. A. Sporea, S. R. P. Silva (2019)Tin(iv) dopant removal through anti-solvent engineering enabling tin based perovskite solar cells with high charge carrier mobilities, In: Journal of Materials Chemistry C Royal Society of Chemistry

We report the need for careful selection of anti-solvents for Sn-based perovskite solar cells fabricated through the commonly used anti-solvent method, compared to their Pb-based counterparts. This, in combination with the film processing conditions used, enables the complete removal of unwanted Sn4+ dopants, through engineering the anti-solvent method for Sn-based perovskites. Using a Cs0.05(FA0.83MA0.17)0.95Pb0.5Sn0.5I3 perovskite, charge carrier mobilities of 32 ± 3 cm2 V−1 s−1 (the highest reported for such systems through the optical-pump terahertz probe technique) together with ∼28 mA cm−2 short circuit current densities are achieved. A champion efficiency of 11.6% was obtained for solvent extraction using toluene (an 80% enhancement in efficiency compared to the other anti-solvents) which is further improved to 12.04% following optimised anti-solvent wash and thermal treatment. Our work highlights the importance of anti-solvents in managing defects for high efficiency low bandgap perovskite materials and develops the potential for all-perovskite tandem solar cells.

LD Filip, Rhodri Smith, JD Carev, S Silva, D Nicolaescu (2007)Modelling of electron transfer from a carbon nanotube cap into the vacuum under high extraction fields, In: Technical Digest of the 20th International Vacuum Nanoelectronics Conference, IVNC 07pp. 48-49
Elizabeth J. Legge, Muhammad Ahmad, Christopher T. G. Smith, Barry Brennan, Christopher A. Mills, Vlad Stolojan, Andrew J. Pollard, S. Ravi P. Silva (2018)Physicochemical characterisation of reduced graphene oxide for conductive thin films, In: RSC Advances8(65)pp. 37540-37549 Royal Society of Chemistry

Graphene is a desirable material for next generation technology. However, producing high yields of single-layer flakes with industrially applicable methods is currently limited. We introduce a combined process for the reduction of graphene oxide (GO) via vitamin C (ascorbic acid) and thermal annealing at temperatures of

Wei Zhang, Xudong Zuo, Ying Niu, Chengwei Wu, Shuping Wang, Shui Guan, S Silva (2017)Novel nanoparticles with Cr3+ substituted ferrite for self-regulating temperature hyperthermia, In: Nanoscale9(37)pp. 13929-13937 Royal Society of Chemistry

For hyperthermia to be used under clinical conditions for cancer therapeutics the temperature regulation needs to be precise and accurately controllable. In the case of the metal nanoparticles used for such activities, a high coercivity is a prerequisite in order to couple more energy in a single heating cycle for efficient and faster differential heating. The chemically stable Co–Zn ferrite nanoparticles have typically not been used in such self-regulating hyperthermia temperature applications to date due to their low Curie temperature usually accompanied by a poor coercivity. The latter physical property limitation under clinically applied magnetic field conditions (frequency: 100 kHz, intensity: 200 Oe) restricts the transfer of a reasonable heat energy, and thus limits the hyperthermia efficiency. Here, we report a novel Cr3+ substituted Co–Zn ferrite (Zn0.54Co0.46Cr0.6Fe1.4O4), whose Curie temperature and coercivity values are 45.7 °C and 174 Oe, respectively. Under clinically acceptable magnetic field conditions, the temperature of these nanoparticle suspensions can be self-regulated to 44.0 °C and, most importantly with a specific absorption rate (SAR) of 774 W kg−1, which is two-fold higher than the SAR standard for magnetic nanoparticles used in hyperthermia (300 W kg−1). The evaluation of the in vitro cytotoxicity of the nanoparticles reports a low toxicity, which points to a novel set of magnetic nanoparticles for use in self-regulating hyperthermia.

MRR Prabhath, J Romanova, Richard Curry, S Silva, PD Jarowski (2015)The Role of Substituent Effects in Tuning Metallophilic Interactions and Emission Energy of Bis-4-(2-pyridyl)-1,2,3-triazolatoplatinum(II) Complexes, In: Angewandte Chemie - International Edition54(27)pp. 7949-7953 Wiley

The photoluminescence spectra of a series of 5-substituted pyridyl-1,2,3-triazolato PtII homoleptic complexes show weak emission tunability (ranging from λ=397-408 nm) in dilute (10-6 M) ethanolic solutions at the monomer level and strong tunability in concentrated solutions (10-4 M) and thin films (ranging from λ=487-625 nm) from dimeric excited states (excimers). The results of density functional calculations (PBE0) attribute this "turn-on" sensitivity and intensity in the excimer to strong Pt-Pt metallophilic interactions and a change in the excited-state character from singlet metal-to-ligand charge transfer (1MLCT) to singlet metal-metal-to-ligand charge transfer (1MMLCT) emissions in agreement with lifetime measurements. Turn-on tunability: A series of bis-4-(2-pyridyl)-1,2,3-triazolatoplatinum(II) complexes display variable emission tunability. At low concentration, the emission can be tuned only slightly by changing the nature of the substituent but at higher concentrations tunability is enhanced. This "turn-on" sensitivity in the excimeric emission is attributed to strong Pt-Pt metallophilic interactions and a change in the excited-state character.

SM Lyth, F Oyeleye, Richard Curry, S Silva, J Davis (2005)Field emission from multiwall carbon nanotubes prepared by electrodeposition without the use of a dispersant, In: Technical Digest of the 18th International Vacuum Nanoelectronics Conference, IVNC 20052005pp. 304-305

Carbon nanotubes (CNTs) are ideal candidates to be used as field emission sources. Electrodeposition could provide a viable method to deposit CNTs over large areas as part of an industrialized process. It has been shown that CNTs can be co-deposited with nickel onto various substrates, using a suitable CNT dispersant. In the present study, a multiwall carbon nanotube (MWNT): nickel (Ni) composite has been electrodeposited without the use of a dispersant. The field emission properties of the resulting electrodeposits were studied. Unpurified MWNTs grown by CVD were added to a Ni plating bath comprising of IM NiSO·6HO, 0.2M NiCl and 0.5M HBO. Due to their hydrophobic nature, MWNTs did not disperse naturally, so the plating solution was placed in a sonic bath for 15 minutes before electrodeposition. Electrochemical measurements were conducted using a μAutolab computer controlled potentiostat with a three-electrode configuration and typical cell volume of 10 cm. A spiral wound platinum wire served as the counter electrode with a Ag:AgCl wire reference electrode. Cu plates were used as cathodes, with an exposed surface area of 2 cm. After deposition, samples were thoroughly rinsed in deionised water to remove Ni salts. The resulting electrodeposits were imaged using a scanning electron microscope (FIG.1) Importantly, these deposits were observed after the samples were thoroughly rinsed in deionised water, suggesting that there is a strong adhesion between the nickel coated nanotubes and the substrate surface. FIG.1 (a) shows MWNTs (0.013 mg/ml) electrodeposited directly after sonication. Note that a thick Ni coating is not observed (see inset), and that uniform MWNT deposition is observed over a relatively large area. FIG.1(b) shows MWNTs deposited with the same solution after five minutes. A much thicker Ni coating indicates that a relatively higher concentration of Ni to MWNT was present. This was probably due to a rebundling of MWNTs over time, after the sonication process. FIG.1(c) and (d) show MWNTs deposited with a much lower concentration (0.005 mg/ml), and therefore relatively higher concentration of Ni, resulting in thicker Ni coating. Beads of Ni (visible in FIG.1(d)), approximately one micron in diameter completely encased the MWNTs, previously observed by Aria et al., using a poly(acrylic acid) dispersant. Subsequently, the substrates were subjected to field emission characterisation using a 5 mm spherical stainless steel anode. The emission current was recorded as a function of macroscopic electric field at a vacuum of around 10 mbar. The threshold field was taken to be the field at which an emission current of 1 nA was detected and the macroscopic field was calculated by dividing the applied voltage by the electrode gap, which was typically 25 μm. Threshold fields of the order 20 V/μm were observed (FIG.2), after conditioning. It is expected that by altering the deposition conditions, the much lower threshold fields would be observed. © 2005 IEEE.

KDG Imalka Jayawardena, S Li, LF Sam, Christopher Smith, MJ Beliatis, KK Gandhi, MR Ranga Prabhath, TR Pozegic, S Chen, X Xu, DMR Dabera, LJ Rozanski, RA Sporea, Chris Mills, X Guo, S Silva (2015)High efficiency air stable organic photovoltaics with an aqueous inorganic contact, In: Nanoscale(34)pp. 14241-14247 The Royal Society of Chemistry

We report a ZnO interfacial layer based on an environmentally friendly aqueous precursor for organic photovoltaics. Inverted PCDTBT devices based on this precursor show power conversion efficiencies of 6.8–7%. Unencapsulated devices stored in air display prolonged lifetimes extending over 200 hours with less than 20% drop in efficiency compared to devices based on the standard architecture.

Randunu Devage Ishara Gihan Dharmasena, Imalka Jayawardena, Christopher Mills, Jonathan Deane, Jose Anguita, Robert Dorey, S Silva (2017)Triboelectric Nanogenerators: Providing a Fundamental Framework, In: Energy & Environmental Science10(8)pp. 1801-1811 Royal Society of Chemistry

A new model which comprehensively explains the working principles of contact-mode Triboelectric Nanogenerators (TENGs) based on Maxwell’s equations is presented. Unlike previous models which are restricted to known simple geometries and derived using the parallel plate capacitor model, this model is generic and can be modified to a wide range of geometries and surface topographies. We introduce the concept of a distance-dependent electric field, a factor not taken in to account in previous models, to calculate the current, voltage, charge, and power output under different experimental conditions. The versatality of the model is demonstrated for non-planar geometry consisting of a covex-conave surface. The theoretical results show excellent agreement with experimental TENGs. Our model provides a complete understanding of the working principles of TENGs, and accurately predicts the output trends, which enables the design of more efficient TENG structures.

Christopher Smith, Christopher A. Mills, Silvia Pani, Rhys Rhodes, Josh J. Bailey, Samuel J. Cooper, Tanveerkhan S. Pathan, Vlad Stolojan, Daniel J. L. Brett, Paul R. Shearing, S. Ravi P. Silva (2019)X-ray micro-computed tomography as a non-destructive tool for imaging the uptake of metal nanoparticles by graphene-based 3D carbon structures, In: Nanoscale11pp. 14734-14741 Royal Society of Chemistry

Graphene-based carbon sponges can be used in different applications in a large number of fields including microelectronics, energy harvesting and storage, antimicrobial activity and environmental remediation. The functionality and scope of their applications can be broadened considerably by the introduction of metallic nanoparticles into the carbon matrix during preparation or post-synthesis. Here, we report on the use of X-ray micro-computed tomography (CT) as a method of imaging graphene sponges after the uptake of metal (silver and iron) nanoparticles. The technique can be used to visualize the inner structure of the graphene sponge in 3D in a non-destructive fashion by providing information on the nanoparticles deposited on the sponge surfaces, both internal and external. Other deposited materials can be imaged in a similar manner providing they return a high enough contrast to the carbon microstructure, which is facilitated by the low atomic mass of carbon.

We report on high luminance organic light-emitting diodes using acid functionalized multi-walled carbon nanotube (o-MWCNTs) as efficient hole injector electrodes, using a simple, solution processable device structure. At only 10 V, the luminance approaches 50,000 cd/m with an external quantum efficiency over 2% and a current efficiency greater than 21 cd/A. The investigation of hole-only devices shows that the mechanism for hole injection changes from injection limited to bulk limited because of the higher effective work function of the anode modified by the o-MWCNTs. We expect the enhancement of the local electric field, brought about by both the dielectric inhomogeneities within the o-MWCNT containing anode and the high aspect ratio carbon nanotubes, improves hole injection from the anode to the organic active layer at much lower applied voltage. © 2012 Elsevier Ltd. All rights reserved.

EVA BESTELINK, Olivier de Sagazan, Lea Motte, Max Bateson, Benedikt Schultes, S RAVI PRADIP SILVA, RADU A SPOREA (2020)Versatile Thin‐Film Transistor with Independent Control of Charge Injection and Transport for Mixed Signal and Analog Computation, In: Advanced Intelligent Systems

New materials and optimized fabrication techniques have led to steady evolution in large area electronics, yet significant advances come only with new approaches to fundamental device design. The multimodal thin‐film transistor introduced here offers broad functionality resulting from separate control of charge injection and transport, essentially using distinct regions of the active material layer for two complementary device functions, and is material agnostic. The initial implementation uses mature processes to focus on the device's fundamental benefits. A tenfold increase in switching speed, linear input–output dependence, and tolerance to process variations enable low‐distortion amplifiers and signal converters with reduced complexity. Floating gate designs eliminate deleterious drain voltage coupling for superior analog memory or computing. This versatile device introduces major new opportunities for thin‐film technologies, including compact circuits for integrated processing at the edge and energy‐efficient analog computation.

Eva Bestelink, S. Ravi P. Silva, Radu A. Sporea, Luca Maiolo, Francesco Maita (2019)49dB depletion-load amplifiers with polysilicon source-gated transistors, In: ESSDERC 2019 - 49th European Solid-State Device Research Conference (ESSDERC)2019-pp. 114-117 IEEE

Two-transistor zero-VGS amplifiers made with polysilicon source-gated transistors achieve voltage gain approaching 300 (49dB). TCAD simulations reveal the effect of load and driver transistor geometry on gain and operating frequency. The SGT circuits have simultaneously superior gain and reduced layout area (two-transistor, channel length L = 3μm and width W = 10 and 30μm), relative to conventional TFT implementations. These results recommend low-complexity, compact SGT designs for flexible and printed amplifiers, such as bio- and chemical sensors.

Salman Alfarisyi, Patryk Golec, EVA BESTELINK, Kham M. Niang, Andrew J. Flewitt, S Ravi Pradip Silva, Radu A Sporea (2023)Evidence of improved thermal stability via nanoscale contact engineering in IGZO source-gated thin-film transistors, In: IEEE transactions on electron devices IEEE

Despite rapidly expanding interest in thin-film source-gated transistors (SGTs), the high temperature dependence of drain current (TDDC) in devices comprising Schottky source barriers is delaying wide adoption. To reduce this effect, alternative source designs have been theorized. Specifically, introducing additional nanoscale layers at the source contact should facilitate tunneling of charge carriers at the Fermi energy level with negligible TDDC. Here, we fabricate amorphous In₂Ga₂ZnO₇ tunnel-contact SGTs (TCSGTs) with three times lower TDDC than polysilicon transistors with Schottky contacts. Numerical simulations help elucidate the control mechanisms. We show that the potential profile across the semiconductor in the bulk of the source-gate overlap region determines injection current, and the introduction of a thin interfacial layer at the contact reduces the role of the contact metal work function in current control and associated temperature effects. This device architecture adds improved thermal stability to the long list of SGT benefits, including low voltage saturation, power-efficient operation, high intrinsic gain, device-to-device uniformity, and robustness to mechanical and electrical stress.

Philippe Basset, Stephen Paul Beeby, Chris Bowen, Zheng Jun Chew, Ahmad Delbani, R. Dharmasena, Bhaskar Dudem, Feng Ru Fan, Dimitri Galayko, Hengyu Guo, Jianhua Hao, Yuchen Hou, Chenguo Hu, Qingshen Jing, Young Hoon Jung, Sumanta Kumar Karan, Sohini Kar-Narayan, Miso Kim, Sang-Woo Kim, Yang Kuang, Keon Jae Lee, Jialu Li, Zhaoling Li, Yin Long, Shashank Priya, Xianjie Pu, Tingwen Ruan, S. Ravi P. Silva, Hee Seung Wang, Kai Wang, Xudong Wang, Zhong Lin Wang, Wenzhuo Wu, Wei Xu, Hemin Zhang, Yan Zhang, Meiling Zhu (2022)Roadmap on nanogenerators and piezotronics, In: APL materials10(10)109201 AIP Publishing
Guilherme K. Maron, Mateus G. Masteghin, Veridiana Gehrke, Lucas S. Rodrigues, José H. Alano, Jéssica H.H. Rossato, Valmor Roberto Mastelaro, Jairton Dupont, Marcia Tsuyama Escote, S. Ravi P. Silva, Mateus Gallucci Masteghin, Neftali Lenin Villarreal Carreno (2023)Enhanced pseudocapacitive behaviour in laser-written graphene micro-supercapacitors decorated with nickel cobalt sulphide nanoparticles, In: Materials Research Bulletin168112490 Elsevier

The next generation of energy storage technologies requires enhanced fabrication techniques such as the use of CO2 infrared lasers to pattern micro-supercapacitor (MSC) electrodoes. This study reports direct-writen laser-induced graphene (LIG) micro-supercapacitors with electrodepositated NiCo2S4-nanoparticles on commercial polyimide sheets. X-ray photoelectron spectroscopy (XPS) combined with transmission electron microscopy (TEM) showed NiCo2S4 nanoparticles decorating the graphene, within a highly porous carbon-based electrode. The LIG/NiCo2S4 exhibited outstanding properties with a specific capacitance of 30.4 mF cm-2 at 0.75 mA cm-2 and an energy density of 16.9 µWh cm-2 at a power density of 367.5 µW cm-2. High capacitance retention of 1.22-fold was measured after 5000 cycles of charge/discharge, and of ~90% when bent to 120ångle. Here, it is demonstrated that surface decoration is an effective route in improving LIG MSC storage properties, and that the LIG/NiCo2S4 MSC is suitable for use in next generation of flexible and miniaturized portable devices.

Ash Stott, Décio B de Freitas Neto, JM Rosolen, Radu A. Sporea, S. Ravi P. Silva (2021)Exploring the underlying kinetics of electrodeposited PANI-CNT composite using distribution of relaxation times, In: Electrochimica Acta139501

The Distribution of Relaxation Times (DRT) was successfully demonstrated in the analysis of the impedance spectra of a parametric series of composite polyaniline (PANI) coated carbon nanotubes (CNT) electrodes. DRT was then applied to the measured spectra and polarization processes were separated based on their typical time constants. The main processes were identified, and their contribution quantified by analysing a set of electrodes with PANI deposited under various conditions, forming a parametric set. For the first time we have shown that DRT can be used to identify individual internal processes of complex composite electrodes without a priori knowledge of the system. This method offers a model-free approach for the study of EIS spectra and the characterization of resistive-capacitive systems. This was demonstrated by the optimisation of our PANI coated CNT electrodes which have exhibited a PANI specific capacitance of 772 F g − 1 and rate capability of 76% from 1 to 100 mV s − 1.

TR Pozegic, K. D. G. I. Jayawardena, J-S Chen, Jose Virgilio Anguita, P Ballocchi, Vlad Stolojan, S Ravi Pradip Silva, I. Hamerton (2016)Development of sizing-free multi-functional carbon fibre nanocomposites, In: Composites. Part A, Applied science and manufacturing90pp. 306-319 Elsevier

High quality multi-walled carbon nanotubes (CNTs) grown at high density using a low temperature growth method are used as an alternative material to polymer sizing and is utilised in a series of epoxy composites reinforced with carbon fibres to provide improved physical and electrical properties. We report improvements for sizing-sensitive mechanical and physical properties, such as the interfacial adhesion, shear properties and handling of the fibres, whilst retaining resin-infusion capability. Following fibre volume fraction normalisation, the carbon nanotube-modified carbon fibre composite offers improvements of 146% increase in Young's modulus; 20% increase in ultimate shear stress; 74% increase in shear chord modulus and an 83% improvement in the initial fracture toughness. The addition of CNTs imparts electrical functionalisation to the composite, enhancements in the surface direction are 400%, demonstrating a suitable route to sizing-free composites with enhanced mechanical and electrical functionality. (C) 2016 Elsevier Ltd. All rights reserved.

Muhammad Ahmad, Jose Anguita, Vlad Stolojan, T Corless, J Chen, James Carey, S Silva (2015)High Quality Carbon Nanotubes on Conductive Substrates Grown at Low Temperatures, In: Advanced Functional Materials25(28)pp. 4419-4429 Wiley

For carbon nanotubes (CNTs) to be exploited in electronic applications, the growth of high quality material on conductive substrates at low temperatures (

Jose Anguita, Muhammad Ahmad, S Haq, Jeremy Allam, S Silva (2016)Ultra-broadband light trapping using nanotextured decoupled graphene multilayers, In: Science Advances2(2)e1501238 American Association for the Advancement of Science

The ability to engineer a thin two-dimensional surface for light trapping across an ultra-broad spectral range is central for an increasing number of applications including energy, optoelectronics, and spectroscopy. Although broadband light trapping has been obtained in tall structures of carbon nanotubes with millimeter-tall dimensions, obtaining such broadband light–trapping behavior from nanometer-scale absorbers remains elusive. We report a method for trapping the optical field coincident with few-layer decoupled graphene using field localization within a disordered distribution of subwavelength-sized nanotexturing metal particles. We show that the combination of the broadband light–coupling effect from the disordered nanotexture combined with the natural thinness and remarkably high and wavelength-independent absorption of graphene results in an ultrathin (15 nm thin) yet ultra-broadband blackbody absorber, featuring 99% absorption spanning from the mid-infrared to the ultraviolet. We demonstrate the utility of our approach to produce the blackbody absorber on delicate opto-microelectromechanical infrared emitters, using a low-temperature, noncontact fabrication method, which is also large-area compatible. This development may pave a way to new fabrication methodologies for optical devices requiring light management at the nanoscale.

W Zhang, MK Lei, S Silva, L Johnson (2012)The effect of plasma modification on the sheet resistance of nylon fabrics coated with carbon nanotubes, In: Applied Surface Science258(20)pp. 8209-8213 Elsevier

Low-pressure oxygen and argon plasmas were used to pre-treat nylon fabrics, and the modified fabrics, together with the raw fabrics, were subsequently coated with single walled carbon nanotubes (SWCNTs) by a dip-drying process. Scanning electron microscopy (SEM) and Raman spectroscopy analyses indicated the attachment of SWCNTs onto nylon fabrics. After the coating with SWCNTs, the plasma modified fabrics exhibited sheet resistance of as low as 2.0 kΩ/sq. with respect to 4.9 kΩ/sq. of the raw fabrics, presumably owing to the increase of fibre surface roughness incurred by the plasma modification, which is evidenced by SEM analyses. Fourier transform infrared spectroscopy (FTIR) analysis indicates the incorporation of oxygen functionalities on fibre surfaces in the plasma modification. This is responsible for the variation of the electrical conductance of SWCNT-coated fabrics with the type of plasma and the duration of plasma ablation. © 2012 Elsevier B.V. All rights reserved.

GDMR Dabera, MRR Prabhath, KT Lai, KDGI Jayawardena, FLM Sam, LJ Rozanski, AADT Adikaari, S Silva (2015)Does Electronic Type Matter when Single-Walled Carbon Nanotubes are Used for Electrode Applications?, In: Advanced Functional Materials25(28)pp. 4520-4530 Wiley

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Single-walled carbon nanotube (SWNT) electrodes that are chemically and mechanically robust are fabricated using a simple drop cast method with thermal annealing and acid treatment. An electronic-type selective decrease in sheet resistance of SWNT electrodes with HNO3 treatment is shown. Semiconducting SWNTs show a significantly higher affinity toward hole doping in comparison to metallic SWNTs; a ≈12-fold and a ≈fivefold drop in sheet resistance, respectively. The results suggest the insignificance of the electronic type of the SWNTs for the film conductivity after hole doping. The SWNT films have been employed as transparent hole extracting electrodes in bulk heterojunction (BHJ) organic photovoltaics. Performances of the devices enlighten the fact that the electrode film morphology dominates over the electronic type of the doped SWNTs with similar sheet resistance and optical transmission. The power conversion efficiency (PCE) of 4.4% for the best performing device is the best carbon nanotube transparent electrode incorporated large area BHJ solar cell reported to date. This PCE is 90% in terms of PCEs achieved using indium tin oxide (ITO) based reference devices with identical film fabrication parameters indicating the potential of the SWNT electrodes as an ITO replacement toward realization of all carbon solar cells. Fabrication of electronic-type separated single-walled carbon nanotube (SWNT) electrodes for organic solar cells, using a simple drop cast method followed by thermal and acid treatment. The thermal and acid treatment processes significantly enhance the conductivity of the SWNT films, enabling the use of the conductivity-enhanced SWNT layers as hole extracting, transparent electrodes in organic bulk heterojunction solar cells.

JD Carey, S R Silva (2004)Disorder, Clustering, and Localization Effects in Amorphous Carbon, In: Physical Review B70(23)

The nanostructure of amorphous carbon thin films is described in terms of a disordered nanometer-sized conductive sp(2) phase embedded in an electrically insulating sp(3) matrix. It is shown that the degree of clustering and disorder within the sp(2) phase plays a determining role in the electronic properties of these films. Clustering of the sp(2) phase is shown to be important in explaining several experimental results including the reduction of the electron spin resonance linewidth with increasing spin density and the dispersion associated with the width of the Raman active G band. The influence of structural disorder, associated with sp(2) clusters of similar size, and topological disorder, due to undistorted clusters of different sizes, on both spin density and Raman measurements, is discussed. An extension of this description to intercluster interactions to explain some of the electrical transport and electron field emission behavior is also presented.

Vlad Stolojan, L McCafferty, Simon King, Wei Zhang, S Haq, Ravi Silva (2015)Decoration of multiwalled carbon nanotubes with protected iron nanoparticles, In: Carbon84pp. 47-55 Elsevier

A method to simultaneously synthesize carbon-encapsulated magnetic iron nanoparticles (Fe-NPs) and attach these particles to multi-walled carbon nanotubes (MWCNT) is presented. Thermal decomposition of cyclopentadienyliron dicarbonyl dimer [(C5H5)(2)Fe-2(CO)(4)], over a range of temperatures from 250 degrees C to 1200 degrees C, results in the formation of Fe-NPs attached to MWCNT. At the same time, a protective carbon shell is produced and surrounds the Fe-NPs, covalently attaching the particles to the MWCNT and leading to resistance to acid dissolution. The carbon coating varies in degree of graphitisation, with higher synthesis temperatures leading to a higher degree of graphitisation. The growth model of the nanoparticles and subsequent mechanism of MWCNT attachment is discussed. Adsorption potential of the hybrid material towards organic dyes (Rhodamine B) has been displayed, an indication of potential uses as a material for water treatment. The material has also been electrospun into aligned nanocomposite fibres to produce a soft magnetic composite (SMC) with future applications in sensors and fast switching solenoids.

A. Tagliaferro, W.I. Milne, J. Robertson, S.R.P. Silva, G.A.J. Amaratunga (2001)Preface, In: Diamond and related materials10(2)
X Guo, T Ishii, S Silva (2008)Improving switching performance of thin-film transistors in disordered silicon, In: IEEE ELECTRON DEVICE LETTERS29(6)pp. 588-591 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

The silicon integrated electronics on glass or plastic substrates attracts wide interests. The design, however, depends critically on the switching performance of transistors, which is limited by the quality of silicon films due to the materials and substrate process constraints. Here, the ultrathin channel device structure is proposed to address this problem. In a previous work, the ultrathin channel transistor was demonstrated as an excellent candidate for ultralow power memory design. In this letter, theoretical analysis shows that, for an ultrathin channel transistor, as the channel becomes thinner, stronger quantum confinement can induce a marked reduction of OFF-state leakage current (I-OFF), and the subthreshold swing (S) is also decreased due to stronger control of channel from the gate. Experimental results based on the fabricated nanocrystalline silicon thin-film transistors prove the theoretical analysis. For the 2.0-nm-thick channel devices, I-ON/I-OFF ratio of more than 10(11) can be achieved, which can never be obtained for normal thick channel transistors in disordered silicon.

J.L. Andujar, G.A.J. Amaratunga, W.I. Milne, J. Robertson, S.R.P. Silva, A. Tagliaferro (2003)Preface, In: Diamond and related materials12(2)pp. v-vi
SIMON GEORGE KING, WESLEY GUY BUXTON, KASPAR MARTIN SNASHALL, B Mirkhaydarov, MAXIM SHKUNOV, S. Ravi P. Silva, VLAD STOLOJAN (2022)A route towards metal-free electrical cables via carbon nanotube wires, In: Carbon trends7100159 Elsevier Ltd

Carbon nanotubes (CNTs) have unique properties with promise to outperform the electrical characteristics of bulk copper, giving rise to its primary driver for use in electronic devices. The challenge still hindering their full exploitation stems from an inability to manufacture them to long lengths, resulting in a requirement to align and entwine them into a yarn or wire. There have been several methods presented in achieving this, however, the common disadvantage has been that they are only applicable to specific types and morphologies of CNTs. In the work reported here, using electrospinning as a universally applicable route for any CNT type, we re-engineer and optimise the various formulation, fabrication and processing steps required to manufacture CNT wires. Through a series of investigations using a materials agnostic approach, we experimentally probe the choice of solvent, surfactant and thermal treatment temperature of the CNT inks, demonstrating the CNT-type optimum using a range of commercially available single- double- and multiwalled CNTs. Finally, this allowed us to develop and probe an electrical conditioning process to further enhance the electrical performance, achieving the highest reported un-doped electrical conductivity of 36,000 S⋅m− 1 for electrospun CNT wires, or a specific conductivity of 0.2×106S·m−1/g·cm−3. [Display omitted]

KDGI Jayawardena, J Fryar, S Ravi, P Silva, SJ Henley (2010)Morphology Control of Zinc Oxide Nanocrystals via Hybrid Laser/Hydrothermal Synthesis, In: JOURNAL OF PHYSICAL CHEMISTRY C114(30)pp. 12931-12937 AMER CHEMICAL SOC
K. D. G. Imalka Jayawardena, Hashini M. Thirimanne, Sandro Francesco Tedde, Judith E. Huerdler, Andrew J. Parnell, R. M. Indrachapa Bandara, Christopher A. Mills, S. Ravi P. Silva (2019)Millimeter-Scale Unipolar Transport in High Sensitivity Organic–Inorganic Semiconductor X-ray Detectors, In: ACS Nano American Chemical Society

Hybrid inorganic-in-organic semiconductors are an attractive class of materials for optoelectronic applications. Traditionally, the thicknesses of organic semiconductors are kept below 1 μm due to poor charge transport in such systems. However, recent work suggests that charge carriers in such organic semiconductors can be transported over centimeter length scales opposing this view. In this work, a unipolar X-ray photoconductor based on a bulk heterojunction architecture, consisting of poly(3-hexylthiophene), a C70 derivative, and high atomic number bismuth oxide nanoparticles operating in the 0.1–1 mm thickness regime is demonstrated, having a high sensitivity of ∼160 μC mGy–1 cm–3. The high performance enabled by hole drift lengths approaching a millimeter facilitates a device architecture allowing a high fraction of the incident X-rays to be attenuated. An X-ray imager is demonstrated with sufficient resolution for security applications such as portable baggage screening at border crossings and public events and scalable medical applications.

JB Emah, Richard Curry, Ravi Silva (2008)Low cost patterning of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) films to increase organic photovoltaic device efficiency, In: Applied Physics Letters93103301 American Institute of Physics

A low-cost lithographic technique to pattern poly (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) films with 10 nm deep features of 700 nm periodicity is demonstrated. The use of these patterned films in poly (3-hexylthiophene) : [6,6]-phenylC(61)-butyric acid methyl ester organic photovoltaic devices leads to an increase in short circuit current (J(sc)), fill factor, and power conversion efficiency (PCE) with only a slight reduction in open circuit voltage. Patterning the PEDOT: PSS at 150 degrees C increases Jsc from 2.44 to 3.03 mA/cm(2) improving the PCE from 0.63% to 0.81% with similar increases due to patterning also being obtained at other temperatures.

S Ravi P Silva, Shi Xu, B X Tay, H S Tan, W I Milne (1996)Nanocrystallites in Tetrahedral Amorphous Carbon Films, In: Applied Physics Letters69(4)pp. 491-493 American Institute of Physics

The microstructure of filtered cathodic vacuum arc deposited tetrahedral amorphous carbon films is studied as a function of ion energy. An optimum energy window in the density and C–C sp3 content at an ion energy of ;90 eV observed in this study. It is shown that the density of the amorphous carbon films are closely related to the sp3 content. The observation of nanocrystals embedded in the amorphous carbon matrix is reported. Most of the crystals observed by transmission electron microscopy can be indexed to graphite, but some of the crystals can be indexed to cubic diamond. The chemical composition of the crystals is analyzed using electron energy loss spectroscopy ~EELS!. The only discernible EELS edge is that of C at an energy of 285 eV.

R. C. Barklie, M Collins, S R P Silva (2000)EPR Linewidth Variation, Spin Relaxation Times, and Exchange in Amorphous Hydrogenated Carbon, In: Physical Review B (PRB)61(5)pp. 3546-3554 American Physical Society

Electron paramagnetic resonance ~EPR! measurements have been made of amorphous hydrogenated carbon ~a-C:H! films grown by plasma enhanced chemical vapor deposition ~PECVD! with negative self-bias voltages Vb in the approximate range 10–540 V. For Vb,100 V, as the film changes from polymerlike to diamondlike, the changes in linewidth and shape are interpreted in terms of changes to two contributions—one due to dipolar interactions between the unpaired spins and one due to unresolved lines arising from hyperfine interactions with H1. The former yields a Lorentzian line, the latter a Gaussian, and the resultant spectrum has the Voigt shape. The empirical relation DBpp G ~in Gauss!5~0.1860.05!3~at.%H) between the peak-to-peak Gaussian contribution ~in Gauss! DBpp G and the hydrogen content in atomic percentage is obtained. For Vb.100 V the linewidth is shown to be dominated by the dipolar interactions and exchange and it decreases as Vb increases; the change is shown to arise primarily from a change in the exchange interaction. Evidence for this comes from measurements which show that the spin-lattice relaxation time appreciably shortens and the spin-spin relaxation time lengthens as the bias voltage is increased. The magnitude and variation with bias of the linewidth are consistent with the EPR signal originating from the p-type radicals.

Hashini Thirimanne, K Jayawardena, A Parnell, R Bandara, A Karalasingam, Silvia Pani, J Huerdler, D Lidzey, S Tedde, Andrew Nisbet, Chris Mills, Ravi Silva (2018)High sensitivity organic inorganic hybrid X ray detectors with direct transduction and broadband response, In: Nature Communications92926 Nature Publishing Group

X-ray detectors are critical to healthcare diagnostics, cancer therapy and homeland security, with many potential uses limited by system cost and/or detector dimensions. Current X-ray detector sensitivities are limited by the bulk X-ray attenuation of the materials and consequently necessitate thick crystals (~ 1 mm – 1 cm), resulting in rigid structure, high operational voltages and high cost. Here we present a disruptive, flexible, low cost, broad-band, and high sensitivity direct X-ray transduction technology produced by embedding high atomic number bismuth oxide nanoparticles in an organic bulk heterojunction. These hybrid detectors demonstrate sensitivities of 1712 µC mGy-1 cm-3 for “soft” X-rays and ~30 and 58 µC mGy-1 cm-3 under 6 and 15 MV “hard” X-rays generated from a medical linear accelerator; strongly competing with the current solid state detectors, all achieved at low bias voltages (-10 V) and low power, enabling detector operation powered by coin cell batteries.

J Fryar, KDGI Jayawardena, S Silva, Simon Henley (2012)The origin of the metal enrichment of carbon nanostructures produced by laser ablation of a carbon-nickel target, In: Carbon50(15)pp. 5505-5520 Elsevier

Compositional analysis of metal-containing carbon thin films and nanostructures produced by pulsed laser ablation of a carbon-nickel target revealed significantly higher fractions of nickel in the materials than in the target used to produce them. Ablation of mixed targets is used routinely in the synthesis of carbon nanotubes and to enhance the conductivity of amorphous carbon films by metal incorporation. In this extensive study we investigate the physical mechanisms underlying this metal-enrichment and relate changes in the dynamics of the ablation plumes with increasing background gas pressure to the composition of deposited materials. The failure to preserve the target atom ratios cannot, in this case, be attributed to conventional mechanisms for non-stoichiometric transfer. Instead, nickel-enrichment of the target surface by back-deposition, combined with significantly different propagation dynamics for C atoms, Ni atoms and alloy clusters through the background gas, appears to be the main cause of the high nickel fractions. © 2012 Elsevier Ltd. All rights reserved.

SJ Henley, MJ Beliatis, V Stolojan, SR Silva (2012)Laser implantation of plasmonic nanostructures into glass., In: Nanoscale

A laser direct-writing method producing high-resolution patterns of gold, silver and alloy plasmonic nanoparticles implanted into the surface of glass substrates is demonstrated, by scanning a pulsed UV laser beam across selected areas of ultra-thin metal films. The nanoparticles are incorporated beneath the surface of the glass and hence the patterns are scratch-resistant. The physical mechanisms controlling the process are investigated and we demonstrate that this technique can be used to fabricate a wide range of plasmonic optical structures such as wavelength selected diffraction gratings and high-density substrates for lab-on-chip surface-enhanced Raman spectroscopy.

Simon King, L McCafferty, Vlad Stolojan, Ravi Silva (2015)Highly aligned arrays of super resilient carbon nanotubes by steam purification, In: Carbon84(1)pp. 130-137

Steam treatment has been applied to our prefabricated highly aligned areas of electrospun carbon nanotube composite nano-fibres, leading to controlled and targeted removal of polymeric and amorphous carbon materials, resulting in areas of highly aligned, highly crystalline, pure nanotubes. Raman analysis shows how the ID to IG intensity ratio was reduced to 0.03, and the radial breathing mode peak intensity, used for nanotube diameter calculation, changes. Therefore, suggesting that some carbon nanotubes are more resistant to steam assisted oxidation, meaning that specific carbon nanotube diameters are preferentially oxidised. The remaining carbon nanotubes have displayed a significant improvement in both quality, with respect to defect density, and in crystallinity, resulting in an increased resistance to oxidation. These steam treated super resilient carbon nanotubes are shown to withstand temperatures of above 900 °C under ambient conditions. Applying this purification method to electrospun nano-fibres leads the way for the next generation of composite materials which can be used in high temperature extreme environments.

R.D.I.G. Dharmasena, K.D.G.I. Jayawardena, C.A. Mills, R.A. Dorey, Ravi Silva (2018)A unified theoretical model for Triboelectric Nanogenerators, In: Nano Energy48pp. 391-400 Elsevier

A unified theoretical model applicable to different types of Triboelectric Nanogenerators (TENGs) is presented based on Maxwell’s equations, which fully explains the working principles of a majority of TENG types. This new model utilizes the distance-dependent electric field (DDEF) concept to derive a universal theoretical platform for all vertical charge polarization TENG types which overcomes the inaccuracies of the classical theoretical models as well as the limitations of the existing electric field-based model. The theoretical results show excellent agreement with experimental TENGs for all working modes, providing an improved capability of predicting the influence of different device parameters on the output behaviour. Finally, the output performances of different TENG types are compared. This work, for the first time, presents a unified framework of analytical equations for different TENG working modes, leading to an in-depth understanding of their working principles, which in turn enables more precise design and construction of efficient energy harvesters.

Simon King, Evandro Castaldelli, Liam McCaffterty, S Ravi P Silva, Vlad Stolojan (2018)A Micro-Centrifugal Technique for Improved Assessment and Optimization of Nanomaterial Dispersions: The Case for Carbon Nanotubes, In: ACS Applied Nano Materials1(11)pp. 6217-6225 American Chemical Society

Large-scale incorporation of nanomaterials into manufactured materials can only take place if they are suitably dispersed and mobile within the constituent components, typically within a solution/ink formulation so that the additive process can commence. Natural hydrophobicity of many nanomaterials must be overcome for their successful incorporation into any solution-based manufacturing process. To date, this has been typically achieved using polymers or surfactants, rather than chemical functionalization, to preserve the remarkable properties of the nanomaterials. Quantifying surfactant or dispersion technique efficacy has been challenging. Here we introduce a new methodology to quantify dispersions applicable to high-weight fraction suspensions of most nanomaterials. It’s based on centrifuging and weighing residue of undispersed material. This enables the determination of the efficacy of surfactants to disperse nanomaterials (e.g. ultrasonication power and duration) and leads to increased nanomaterial solution loading. To demonstrate this technique, we assessed carbon nanotube dispersions using popular surfactants: Benzalkonium chloride (ADBAC), Brij®52, Brij®58, Pluronic®F127, sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), Triton™ X-100, Triton™X-405 and Tween®80, evaluating the dispersion outcome when varying sonicator power and horn depth, as well as imaging sono-intensity within the solution with luminol. The methodology is shown to be applicable for high-weight fraction nanomaterial suspensions, enabling greater deployment.

Radu A. Sporea, Luke J. Wheeler, Vlad Stolojan, S. Ravi P. Silva (2018)Towards manufacturing high uniformity polysilicon circuits through TFT contact barrier engineering, In: Scientific Reports Nature Research

Abstract The predicted 50 billion devices connected to the Internet of Things by 2020 has renewed interest in polysilicon technology for high performance new sensing and control circuits, in addition to traditional display usage. Yet, the polycrystalline nature of the material presents significant challenges when used in transistors with strongly scaled channel lengths due to non-uniformity in device performance. For these new applications to materialize as viable products, uniform electrical characteristics on large areas will be essential. Here, we report on the effect of deliberately engineered potential barrier at the source of polysilicon thin-film transistors, yielding highly-uniform on-current (

Simon King, Vlad Stolojan, Ravi Silva (2017)Large area uniform electrospun polymer nanofibres by balancing of the electrostatic field, In: Reactive and Functional Polymers129pp. 89-94 Elsevier

As a technique, electrospinning has been increasingly utilised for polymer nanofibre production, which has a growing list of advanced applications to which they are being applied. However, commercially scaling the process is challenging, especially when the uniformity of the nanofibres across the bulk of the material is important for the required application. At present, most commercially-scalable systems tend to rely on a drum or cylindrical-style electrode, where a multitude of electrospinning jets are formed with no specific controlled distribution or uniformity over its surface. These electrospinning systems also have the drawback of possessing a varying electrostatic field across the length of the electrode, resulting in a range of spinning conditions which result in an inconsistency in the produced nanofibres. Due to the high centrifugal stresses exerted on the polymer during electrospinning, controlling the electrostatic field is crucial for consistent nanofibre production, which forms the basis for applications such as cellular scaffolds and smart materials. In the work reported here, we utilise computational simulation to explore a range of electrode designs to achieve a large area electrospinning system with a balanced electrostatic field across its entire active surface. We demonstrate the output by producing a high-throughput of nanofibres with comparable properties to that of a traditional single spinneret system, but at a processing rate two orders of magnitude faster.

Harry M. Cronin, Zlatka Stoeva, Martin Brown, Maxim Shkunov, S. Ravi P. Silva (2018)Photonic Curing of Low-Cost Aqueous Silver Flake Inks for Printed Conductors with Increased Yield, In: ACS Applied Materials & Interfaces10(25)pp. 21398-21410 American Chemical Society

Printing of highly conductive tracks at low cost is of primary importance for the emerging field of flexible, plastic, and large-area electronics. Commonly, this is achieved by printing of metallic conductive inks, often based on Ag or Cu nanoparticles dispersed in organic solvents. The solvents, which must be safely removed, have particular storage and handling requirements, thus increasing the process costs. By using water-based inks containing micron-sized silver flakes, both material and process costs can be reduced, making these inks attractive for industrial applications. However, the sintering of flake inks requires higher temperatures than nano-sized inks owing to the particles’ smaller surface area-to-volume ratio, meaning that when cured thermally the conductivity of many flake inks is lower than nanoparticle alternatives. This problem can be addressed by the application of visible light photonic curing; however, the substrate must be protected and so process parameters must be defined for each material/substrate combination. Here, we report results of a large-scale trial of photonic curing of aqueous flake silver inks on poly(ethylene terephthalate) substrates in an industrial setting. The resistivity of printed patterns after an optimized photocuring regime matched those reported for typical nanoparticle inks; on the order of 100 μΩ cm depending on substrate and geometry. Scanning electron microscopy revealed evidence for structural changes within the printed films consistent with localized melting and necking between adjacent particles, leading to an improved percolation network. Furthermore, in the large-scale industrial trial employing screen-printed silver lines, the manufacturing yield of conductive lines was increased from 44% untreated to 80% after photocuring and reached 100% when photocuring was combined with thermal curing. We believe this to be the first reported observation of an increase in the yield of printed electronic structures following photocuring. We propose a crack-healing mechanism to explain these increases in yield and conductivity. We further report on the effects of the photonic curing on the mechanical bending stability of the printed conductors and discuss their suitability for wearable applications.

Victoria Ferguson, S. Ravi P. Silva, Wei Zhang (2019)Carbon Materials in Perovskite Solar Cells: Prospects and Future Challenges, In: Energy and Environmental Materials2(2)pp. 107-118 Wiley

Metal halide perovskite solar cells are emerging candidates for next‐generation thin‐film photovoltaic devices with the potential for extremely low fabrication cost and high power conversion efficiency. Perovskite solar cells have demonstrated a rapid development in device performance over the last decade, from an initial 3.81% to a most recently certified 24.2%, though the challenges of long‐term stability and lead toxicity still remain. Carbon materials, ranging from zero‐dimensional carbon quantum dots to three‐dimensional carbon black materials, are promising candidates for the enhancement of both efficiency and stability of perovskite solar cells, offering unique advantages for incorporation into various device architectures. In this review article, we present a concise overview of important and exciting advancements of perovskite solar cells that incorporate different dimensions of carbon material in their device architectures in an effort to simultaneously improve device performance and long‐term stability. We also discuss the major advantages and potential challenges of each technique that has been developed in the most recent work. Finally, we outline the future opportunities toward more efficient and stable perovskite solar cells utilizing carbon materials.

Muhammad Ahmad, S. Ravi P. Silva (2020)Low Temperature Growth of Carbon Nanotubes – A Review, In: Carbon158pp. 24-44 Elsevier

Carbon nanotubes (CNTs) have gained much interest from academia and industry due to their unique properties that include high electrical and thermal conductivity, high mechanical strength, high aspect ratio, high surface area and chemical resistance. Although composite structures containing CNTs are probably the most commercially advanced applications in the market, the area that holds most promise is in electronic applications. Low temperature CVD growth of high quality CNTs can be utilized in many applications particularly next generation IoTs, wearable electronic devices, TSVs, interconnects, and sensors. CNT growth temperature generally reported in literature ranges from 600 – 1000oC, which is not suitable for temperature sensitive substrates. However, there is ongoing research to achieve CNT growth at low temperatures, with a number reporting the growth below 550oC. In this review, we examine and discuss various techniques and approaches adopted to achieve growth of carbon nanotubes at low temperatures and its effect on various parameters of CNTs.

W Zhang, X Zuo, D Zhang, C Wu, SRP Silva, S Ravi Pradip Silva (2016)Cr3+ substituted spinel ferrite nanoparticles with high coercivity, In: NANOTECHNOLOGY27(24)ARTN 24570 IOP PUBLISHING LTD
H Liang, Christopher Smith, Chris Mills, S Silva (2015)The band structure of graphene oxide examined using photoluminescence spectroscopy, In: Journal of Materials Chemistry C3(48)pp. 12484-12491 The Royal Society of Chemistry

Photoluminescence (PL) spectra have been used to elucidate the band structure of graphene oxide (GO) reduced in aqueous solution. The GO reduction is measured in situ via the identification of four PL peaks produced from GO solutions with different concentrations. Using corresponding UV-visible and photoluminescence excitation (PLE) spectroscopy, and on progressing from high energy to low energy transitions, the four PL peaks are identified as σ–σ* and π–π* transitions, a π band tail due to oxygen localized states, and a π band tail due to trapped water, respectively. The labeling of the band structure has been used to challenge the prevailing assignation of the low energy transitions, reported in the literature, to molecular σ–σ* and π–π* transitions alone.

Christopher A. Mills, Erdni Batyrev, Maurice J. R. Jansen, Muhammad Ahmad, Tanveerkhan S. Pathan, Elizabeth J. Legge, Digvijay B. Thakur, Samson N. Patole, Dan J. L. Brett, Paul R. Shearing, Hans van der Weijde, S. Ravi P. Silva (2019)Improvement in the Electrical Properties of Nickel Plated Steel using Graphitic Carbon Coatings, In: Advanced Engineering Materials21(10)1900408pp. 1-9 Wiley

Thin layers of highly conductive graphitic carbon have been deposited onto nickel plated steel substrates using a direct photothermal chemical vapour deposition (PTCVD) technique. The coated nickel plated steel substrates have improved electrical properties (sheet resistance and interfacial contact resistance) compared to the pristine nickel plated steel, which makes it a cost effective alternative to stainless steel for steel producers to use in high-end electrical applications such as energy storage and microelectronics. The coated nickel plated steel has been found to have an approximately 10% reduction in sheet resistance, and a 200 times reduction in interfacial contact resistance (under compression at 140 N cm-2), compared to the pristine nickel plated steel. The interfacial contact resistance is also three times lower than that of a benchmark gold coated stainless steel equivalent at the same pressure.

S J Henley, C H Poa, A A Adikaari, C E Giusca, JD Carey, S R Silva (2004)Excimer Laser Nanostructuring of Nickel Thin Films for the Catalytic Growth of Carbon Nanotubes, In: Applied Physics Letters84(20)

Pulse laser ablation and subsequent laser nanostructuring at room temperature has been employed to produce nanostructured Ni on SiO2/Si substrates for catalytic growth of carbon nanotubes. The resultant nanostructured surface is seen to consist of nanometer sized hemispherical droplets whose mean diameter is controlled by the initial metal thickness, which in turn is readily controlled by the number of laser pulses. Vertically aligned multiwall carbon nanotube mats were then grown using conventional plasma enhanced chemical vapor deposition. We show that within a single processing technique it is possible to produce the initial metal-on-oxide thin film to a chosen thickness but also to be able to alter the morphology of the film to desired specifications at low macroscopic temperatures using the laser parameters. The influence of the underlying oxide is also explored to explain the mechanism of nanostructuring of the Ni catalyst. (C) 2004 American Institute of Physics.

NLV Carreno, MT Escote, A Valentini, L McCafferty, V Stolojan, M Beliatis, Chris Mills, R Rhodes, Christopher Smith, S Silva (2015)Adsorbent 2D and 3D carbon matrices with protected magnetic iron nanoparticles, In: NANOSCALE7(41)pp. 17441-17449 ROYAL SOC CHEMISTRY
R C Smith, JD Carey, C H Poa, D C Cox, S R Silva (2004)Electron Field Emission From Room Temperature Grown Carbon Nanofibers, In: Journal of Applied Physics95(6)

The observation of field induced electron emission from room temperature grown carbon nanofibers at low (5 V/mum) macroscopic electric fields is reported. The nanofibers were deposited using methane as a source gas in a conventional rf plasma enhanced chemical vapor deposition reactor using a Ni metal catalyst previously subjected to an Ar plasma treatment. Analysis of the scanning electron microscopy images of the nanofibers show them to possess an average diameter of 300 nm and that the nanofibers are observed to be radially dispersed over an area of 50 mum in diameter. No evidence of hysteresis in the current-voltage characteristic or conditioning of the emitters is observed. The mechanism for emission at low fields is attributed to field enhancement at the tips rather than from the surrounding amorphous carbon film which is shown to have a higher threshold field (20 V/mum) for emission.

H Shiozawa, Anne Skeldon, David Lloyd, V Stolojan, DC Cox, SR Silva (2011)Spontaneous emergence of long-range shape symmetry, In: Nano Letters11(1)pp. 160-163

Self-organization of matter is essential for natural pattern formation, chemical synthesis, as well as modern material science. Here we show that isovolumetric reactions of a single organometallic precursor allow symmetry breaking events from iron nuclei to the creation of different symmetric carbon structures: microspheres, nanotubes, and mirrored spiraling microcones. A mathematical model, based on mass conservation and chemical composition, quantitatively explains the shape growth. The genesis of such could have significant implications for material design.

Mateus G. Masteghin, Muhammad Ahmad, Mehmet Tas, Christopher Smith, Vlad Stolojan, David Cox, Ravi Silva (2020)Field electron emission measurements as a complementary technique to assess carbon nanotube quality, In: Applied physics letters116103101 American Institute of Physics

Carbon nanotubes (CNTs) can be used in many different applications. Field emission (FE) measurements were used together with Raman spectroscopy to show a correlation between the microstructure and field emission parameters. However, field emission characterization does not suffer from fluorescence noise present in Raman spectroscopy. In this study, Raman spectroscopy is used to characterize vertically aligned CNT forest samples based on their D/G band intensity ratio (ID/IG), and FE properties such as the threshold electric field, enhancement coefficient, and anode to CNT tip separation (ATS) at the outset of emission have been obtained. A relationship between ATS at first emission and the enhancement factor, and, subsequently, a relationship between ATS and the ID/IG are shown. Based on the findings, it is shown that a higher enhancement factor (3070) results when a lower ID/IG is present (0.45), with initial emissions at larger distances (47 lm). For the samples studied, the morphology of the CNT tips did not play an important role; therefore, the field enhancement factor (b) could be directly related to the carbon nanotube structural properties such as breaks in the lattice or amorphous carbon content. Thus, this work presents FE as a complementary tool to evaluate the quality of CNT samples, with the advantages of alarger probe size and an averaging over the whole nanotube length. Correspondingly, one can find the best field emitter CNT according to its ID/IG.

Simon G. King, Nicholas J. Terrill, Andrew J. Goodwin, Robert Stevens, Vlad Stolojan, Ravi P. Silva (2018)Probing of Polymer to Carbon Nanotube Surface Interactions within Highly Aligned Electrospun Nanofibers for Advanced Composites, In: Carbon138pp. 207-214 Elsevier

By electrospinning poly(ethylene oxide) (PEO)-blended sodium dodecyl sulfate (SDS) functionalized carbon nanotube (CNT) solutions, we engineered single- and double-walled nanotubes into highly aligned arrays. CNT alignment was measured using electron microscopy and polarised Raman spectroscopy. Mechanical tensile testing demonstrates that a CNT loading of 3.9wt% increases the ultimate tensile strength and ductility of our composites by over a factor of 3, and the Young's modulus by over a factor of 4, to ∼260MPa. Transmission electron microscopy (TEM) reveals how the aligned nanotubes provide a solid structure, preventing polymer chains from slipping, as well as polymer crystallisation structures such as ‘shish-kebabs’ forming, which are responsible for the improved mechanical properties of the composite. Differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) reveals micellar and hexagonal columnar structures along the axis of the fibers, some of which are associated with the presence of the CNT, where these hexagonal structures are associated with the SDS functionalization on the CNT surfaces. This work demonstrates the benefits of CNT alignment within composites, revealing the effectiveness of the electrospinning technique, which enables significantly improved functionality, increasing the utility of the composites for use in many different technological areas.

RC Smith, Ravi Silva (2009)Maximizing the electron field emission performance of carbon nanotube arrays, In: APPLIED PHYSICS LETTERS94(13)ARTN 1pp. ?-? AMER INST PHYSICS

The field emission screening effect is one of great importance when aiming to design efficient and powerful cathodes. It has long been assumed that the degrading effect is at a minimum when neighboring emitters are at least twice their height from each other. In this work, we show that the screening effect is underestimated and diminishes at far greater separations of five times the height of the emitter. We further observe that to achieve maximum emission efficiency in an array, one requires a trade off between screening and emitter number, resulting in a separation of three times their height.

Christopher Smith, R Rhodes, M Beliatis, K Jayawardena, L Rozanski, Chris Mills, S Silva (2014)Graphene oxide hole transport layers for large area, high efficiency organic solar cells, In: Applied Physics Letters105(7)073304 American Institute of Physics

Graphene oxide (GO) is becoming increasingly popular for organic electronic applications. We present large active area (0.64 cm^2), solution processable, poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]:[6,6]-Phenyl C71 butyric acid methyl ester (PCDTBT:PC70BM) organic photovoltaic (OPV) solar cells, incorporating GO hole transport layers (HTL). The power conversion efficiency (PCE) of ~5% is the highest reported for OPV using this architecture. A comparative study of solution-processable devices has been undertaken to benchmark GO OPV performance with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) HTL devices, confirming the viability of GO devices, with comparable PCEs, suitable as high chemical and thermal stability replacements for PEDOT:PSS in OPV.

Wei Zhang, Chengwei Wu, S. Ravi P. Silva (2018)Proposed use of self-regulating temperature nanoparticles for cancer therapy, In: Expert Review of Anticancer Therapy18(8)pp. 723-725 Taylor & Francis

The concept of magnetic induction of hyperthermia was first proposed by Gilchrist et al. in 1957. The physics is based on the simple principle that when exposed to an alternating magnetic field, the magnetic media can transform the electromagnetic energy to thermal energy, causing the temperature increase of any surrounding media or tissue. In biological tissue, normal cells usually possess higher heat resistance and resilience to temperature than tumor cells. As such, cancerous cells can be selectively destroyed by increasing the local temperature of the tissue to a desired temperature range (42–46°C), while ensuring healthy cells are unharmed.

E Castaldelli, KDGI Jayawardena, David Cox, GJ Clarkson, RI Walton, L Le-Quang, J Chauvin, S Silva, GJ-F Demets (2017)Electrical semiconduction modulated by light in a cobalt and naphthalene diimide metal-organic framework, In: Nature Communications82139 Nature Publishing Group

Metal-organic frameworks (MOFs) have emerged as an exciting class of porous materials that can be structurally designed by choosing particular components according to desired applications. De- spite the wide interest in and many potential applications of MOFs, such as in gas storage, catal- ysis, sensing and drug delivery, electrical semiconductivity and its control is still rare. The use and fabrication of electronic devices with MOF-based components has not been widely explored, despite the significant progress of these components made in recent years. Here we report the syn- thesis and properties of a new highly crystalline, electrochemically active, cobalt and naphthalene diimide-based MOF that is an efficient electrical semiconductor and has a broad absorption spec- trum, from 300 nm to 2500 nm. Its semiconductivity was determined by direct voltage bias using a four-point device, and it features a wavelength dependant photoconductive-photoresistive dual behaviour, with a very high responsivity of 2.5×105 A W−1.

S J Henley, JD Carey, S R Silva (2004)Room Temperature Photoluminescence From Nanostructured Amorphous Carbon, In: Applied Physics Letters85(25)

Visible room-temperature photoluminescence (PL) was observed from hydrogen-free nanostructured amorphous carbon films deposited by pulsed laser ablation in different background pressures of argon (P-Ar). By varying P-Ar from 5 to 340 mTorr, the film morphology changed from smooth to rough and at the highest pressures, low-density filamentary growth was observed. Over the same pressure regime an increase in the ordering of sp(2) bonded C content was observed using visible Raman spectroscopy. The origin of the PL is discussed in terms of improved carrier localization within an increased sp(2) rich phase.

GD Dabera, KD Jayawardena, MR Prabhath, I Yahya, YY Tan, NA Nismy, H Shiozawa, M Sauer, G Ruiz-Soria, P Ayala, V Stolojan, AA Adikaari, PD Jarowski, T Pichler, SR Silva (2013)Hybrid carbon nanotube networks as efficient hole extraction layers for organic photovoltaics., In: ACS Nano7(1)pp. 556-565

Transparent, highly percolated networks of regioregular poly(3-hexylthiophene) (rr-P3HT)-wrapped semiconducting single-walled carbon nanotubes (s-SWNTs) are deposited, and the charge transfer processes of these nanohybrids are studied using spectroscopic and electrical measurements. The data disclose hole doping of s-SWNTs by the polymer, challenging the prevalent electron-doping hypothesis. Through controlled fabrication, high- to low-density nanohybrid networks are achieved, with low-density hybrid carbon nanotube networks tested as hole transport layers (HTLs) for bulk heterojunction (BHJ) organic photovoltaics (OPV). OPVs incorporating these rr-P3HT/s-SWNT networks as the HTL demonstrate the best large area (70 mm(2)) carbon nanotube incorporated organic solar cells to date with a power conversion efficiency of 7.6%. This signifies the strong capability of nanohybrids as an efficient hole extraction layer, and we believe that dense nanohybrid networks have the potential to replace expensive and material scarce inorganic transparent electrodes in large area electronics toward the realization of low-cost flexible electronics.

J.V. Anguita, C.T.G. Smith, T. Stute, M. Funke, M. Delkowski, S.R.P. Silva (2019)Dimensionally and environmentally ultra-stable polymer composites reinforced with carbon fibres, In: Nature Materials Nature Research

The quest to develop materials that enables the manufacture of dimensionally ultra-stable structures for critical-dimension components in spacecraft, has led to much research and evolution of carbon-fibre reinforced polymer materials (CFRP) over many decades. This has resulted in structural designs that feature a near-zero coefficient of thermal expansion. However, the dimensional instabilities that result from moisture ingression and release remains the fundamental vulnerability of the matrix, which restricts many such applications. Here, we address this challenge by developing a space-qualifiable physical surface barrier that blends within the mechanical properties of the composite, thus becoming part of the composite itself. The resulting enhanced composite features mechanical integrity and strength that is superior to the underlying composite, whilst remaining impervious to moisture and outgassing. We demonstrate production capability on a model-sized component for Sentinel-5 mission and demonstrate such capability for future European Space Agency (ESA) and National Aeronautics and Space Administration (NASA) programs such as Copernicus Extension, Earth Explorer and Science Cosmic Visions.

CE Giusca, V Stolojan, J Sloan, F Börrnert, H Shiozawa, K Sader, MH Rümmeli, B Büchner, SR Silva (2013)Confined crystals of the smallest phase-change material., In: Nano Lett13(9)pp. 4020-4027

The demand for high-density memory in tandem with limitations imposed by the minimum feature size of current storage devices has created a need for new materials that can store information in smaller volumes than currently possible. Successfully employed in commercial optical data storage products, phase-change materials, that can reversibly and rapidly change from an amorphous phase to a crystalline phase when subject to heating or cooling have been identified for the development of the next generation electronic memories. There are limitations to the miniaturization of these devices due to current synthesis and theoretical considerations that place a lower limit of 2 nm on the minimum bit size, below which the material does not transform in the structural phase. We show here that by using carbon nanotubes of less than 2 nm diameter as templates phase-change nanowires confined to their smallest conceivable scale are obtained. Contrary to previous experimental evidence and theoretical expectations, the nanowires are found to crystallize at this scale and display amorphous-to-crystalline phase changes, fulfilling an important prerequisite of a memory element. We show evidence for the smallest phase-change material, extending thus the size limit to explore phase-change memory devices at extreme scales.

C Nagavolu, K Susmitha, M Raghavender, L Giribabu, KBS Rao, Christopher Smith, CA Mills, VVSS Srikanth, S Ravi Pradip Silva (2016)Pt-free spray coated reduced graphene oxide counter electrodes for dye sensitized solar cells, In: SOLAR ENERGY137pp. 143-147 PERGAMON-ELSEVIER SCIENCE LTD
V Sanz, E Borowiak, P Lukanov, AM Galibert, E Flahaut, HM Coley, SRP Silva, J McFadden (2011)Optimising DNA binding to carbon nanotubes by non-covalent methods, In: Carbon49(5)pp. 1775-1781 Elsevier

The use of carbon nanotubes as a gene delivery system has been extensively studied in recent years owing to its potential advantages over viral vectors. To achieve this goal, carbon nanotubes have to be functionalized to become compatible with aqueous media and to bind the genetic material. To establish the best conditions for plasmid DNA binding, we compare the dispersion properties of single-, double- and multi-walled carbon nanotubes (SWCNTs, DWCNTs and MWCNTs, respectively) functionalized with a variety of surfactants by non-covalent attachment. The DNA binding properties of the functionalized carbon nanotubes were studied and compared by electrophoresis. Furthermore, a bilayer functionalization method for DNA binding on SWCNTs was developed that utilized RNA-wrapping to solubilize the nanotubes and cationic polymers as a bridge between nanotubes and DNA.

P OBrien, JR Walsh, IM Watson, L Hart, SRP Silva (1996)Properties of cadmium sulphide films grown by single-source metalorganic chemical vapour deposition with dithiocarbamate precursors, In: JOURNAL OF CRYSTAL GROWTH167(1-2)pp. 133-142 ELSEVIER SCIENCE BV
RC Smith, David Cox, S Silva (2005)Electron field emission from a single carbon nanotube: Effects of anode location, In: APPLIED PHYSICS LETTERS87(10)103112 AMER INST PHYSICS

Electron field emission from an isolated carbon nanotube (CNT) was performed in situ in a modified scanning electron microscope, over a range of anode to CNT tip separations, D, of 1-60 mu m. The threshold field required for an emission current of 100 nA was seen to decrease from a value of 42 V mu m(-1) at an anode to CNT tip separation of 1 mu m, asymptotically, to approach 4 V mu m(-1) at a separation of 60 mu m. It is proposed that at low D, the electric field enhancement factor (beta) reduces as the anode electrode approaches the CNT mimicking a parallel plate configuration. Under "far field" conditions, where D > 3 h, where h is the CNT height, the CNT enhancement factor is no longer dependant on D, as shown by the asymptotic behavior of the threshold field, and is purely a factor of the CNT height and radius. For each CNT to tip separation, measured emission current data together with the threshold field and enhancement, are consistent with a Fowler-Nordheim analysis for the far field conditions, and dispels the need for a novel emission mechanism to explain the results as has been proposed recently. (c) 2005 American Institute of Physics.

Y Miyajima, AADT Adikaari, Simon Henley, John Shannon, S Silva (2008)Electrical properties of pulsed UV laser irradiated amorphous carbon, In: APPLIED PHYSICS LETTERS92(15)ARTN 1 AMER INST PHYSICS

Amorphous carbon films containing no hydrogen were irradiated with a pulsed UV laser in vacuum. Raman spectroscopy indicates an increase in the quantity of sp(2) clustering with the highest laser energy density and a commensurate reduction in resistivity. The reduction of resistivity is explained to be associated with thermally induced graphitization of amorphous carbon films. The high field transport is consistent with a Poole-Frenkel type transport mechanism via neutral trapping centers related to sp(2) sites which are activated under high fields. Decreasing the resistivity is an important feature for use of carbon as an electronic material. (C) 2008 American Institute of Physics.

Harry M Cronin, K D G Imalka Jayawardena, Zlatka Stoeva, Maxim Shkunov, S Ravi P Silva (2017)Effects of ambient humidity on the optimum annealing time of mixed-halide Perovskite solar cells, In: Nanotechnology28(11) IOP Publishing

Mixed halide Perovskite solar cells (PSCs) are commonly produced by depositing PbCl2 and CH3NH3I from a common solvent followed by thermal annealing, which in an up-scaled manufacturing process is likely to take place under ambient conditions. However, it has been reported that, similar to the effects of thermal annealing, ambient humidity also affects the crystallisation behaviour and subsequent growth of the Perovskite films. This implies that both of these factors must be accounted for in solar cell production. In this work, we report for the first time the correlation between the annealing time, relative humidity (RH) and device performance for inverted, mixed halide CH3NH3PbI(3−x)Cl x PSCs with active area ≈1 cm2. We find a trade-off between ambient humidity and the required annealing time to produce efficient solar cells, with low humidities needing longer annealing times and vice-versa. At around 20% RH, device performance weakly depends on annealing time, but at higher (30%–40% RH) or lower (0%–15% RH) humidities it is very sensitive. Processing in humid environments is shown to lead to the growth of both larger Perovskite grains and larger voids; similar to the effect of thermal annealing, which also leads to grain growth. Therefore, samples which are annealed for too long under high humidity show loss of performance due to low open circuit voltage caused by an increased number of shunt paths. Based on these results it is clear that humidity and annealing time are closely interrelated and both are important factors affecting the performance of PSCs. The findings of this work open a route for reduced annealing times to be employed by control of humidity; critical in roll-to-roll manufacture where low manufacturing time is preferred for cost reductions.

PCP Watts, SJ Henley, E Mendoza, SRP Silva, JK Irvine, ET McAdams (2007)Core-shell silver/silver chloride nanoparticles on carbon nanofibre arrays for bio-potential monitoring, In: NANOTECHNOLOGY18(20)ARTN 20550 IOP PUBLISHING LTD
MJ Beliatis, NA Martin, EJ Leming, SR Silva, SJ Henley (2011)Laser ablation direct writing of metal nanoparticles for hydrogen and humidity sensors., In: Langmuir27(3)pp. 1241-1244 American Chemical Society

A UV pulsed laser writing technique to fabricate metal nanoparticle patterns on low-cost substrates is demonstrated. We use this process to directly write nanoparticle gas sensors, which operate via quantum tunnelling of electrons at room temperature across the device. The advantages of this method are no lithography requirements, high precision nanoparticle placement, and room temperature processing in atmospheric conditions. Palladium-based nanoparticle sensors are tested for the detection of water vapor and hydrogen within controlled environmental chambers. The electrical conduction mechanism responsible for the very high sensitivity of the devices is discussed with regard to the interparticle capacitance and the tunnelling resistance.

Muhammad Ahmad, José V. Anguita, C. Ducati, J. David Carey, S. Ravi P. Silva (2019)Protected catalyst growth of graphene and carbon nanotubes, In: Carbon149pp. 71-85 Elsevier

Some of the key challenges in the applications of graphene and carbon nanotubes are associated with their poor attachment to the substrate and poisoning of the catalyst by environmental contamination prior to the growth phase. Here we report a ‘protected catalyst’ technique which not only overcomes these challenges but also provides a new material production route compatible with many applications of carbon nanomaterials. The breakthrough technique involves capping the catalyst with a protective layer of a suitable material (examples include TiN, Cr, Ta) which protects the catalyst from environmental contaminants such as oxidation, etchant attack, etc., whilst maintaining carbon supply to the catalyst for the CVD growth of desired nanomaterial. A thin Fe catalyst layer remained protected due to the capping layer in the CF4 based reactive-ion-etching of SiO2. We show that the carbon nanostructures grown using this technique exhibit significantly improved adhesion to the substrate in sonication bath tests. We demonstrate the fabrication of 3D structures and CNT based vias in a buried catalyst arrangement using the protected catalyst technique. The technique also allows better control over various growth parameters such as number of graphene layers, growth rate, morphology, and structural quality.

Bruno Marchon, Jing Gui, Kevin Grannen, Gary C Rauch, Joel W Ager III, S R P Silva, John Robertson (2010)Photoluminescence and Raman Spectroscopy in Hydrogenated Carbon Films, In: IEEE Transactions on Magnetics33(5)pp. 3148-3150 Institute of Electrical and Electronics Engineers

a-C:H films prepared by DC-magnetron sputtering in an H2:Ar mixture exhibit strong photoluminescence (PL) peaks superimposed upon the Raman scattering spectrum. PL becomes observable at a hydrogen content of ca. 34%, and increases exponentially thereafter, driven by the progressive saturation of carbon dangling bonds. In this %H range, hardness and elastic modulus decrease and CSS durability reaches an optimum. The Raman G peak position is very sensitive to deposition temperature (shift of 0.1 cm-1/°C) and was found to correlate with the sp3 /sp2 bonding ratio as measured by EELS, and therefore can also be used as a predictor of carbon tribological performance

We report prediction of selected physical properties (e.g. glass transition temperature, moduli and thermal degradation temperature) using molecular dynamics simulations for a difunctional epoxy monomer (the diglycidyl ether of bisphenol A) when cured with p-3,30 -dimethylcyclohexylamine to form a dielectric polymer suitable for microelectronic applications. Plots of density versus temperature show decreases in density within the same temperature range as experimental values for the thermal degradation and other thermal events determined using e.g. dynamic mechanical thermal analysis. Empirical characterisation data for a commercial example of the same polymer are presented to validate the network constructed. Extremely close agreement with empirical data is obtained: the simulated value for the glass transition temperature for the 60 C cured epoxy resin (simulated conversion a = 0.70; experimentally determined a = 0.67 using Raman spectroscopy) is ca. 70–85 C, in line with the experimental temperature range of 60–105 C (peak maximum 85 C). The simulation is also able to mimic the change in processing temperature: the simulated value for the glass transition temperature for the 130 C cured epoxy resin (simulated a = 0.81; experimentally determined a = 0.73 using Raman and a = 0.85 using DSC) is ca. 105–130 C, in line with the experimental temperature range of 110–155 C (peak maximum 128 C). This offers the possibility of optimising the processing parameters in silico to achieve the best final properties, reducing labour- and material-intensive empirical testing.

R. U. A. Khan, JD Carey, S. R. P. Silva, B. J. Jones, R. C. Barklie (2001)Electron delocalization in amorphous carbon by ion implantation, In: Physical Review B63(121201)

The electrical properties of amorphous carbon are governed by the high localization of the sp2 π states, and conventional methods of altering the sp2 content result in macroscopic graphitization. By using ion beams we have achieved a delocalization of the π states by introducing nanoclustering and hence improving the connectivity between existing clusters, as demonstrated by the increase in the conductivity by two orders of magnitude without modification of the band gap. At higher doses, paramagnetic relaxation-time measurements indicate that exchange effects are present. This unveils the possibility of amorphous carbon-based electronics by tailoring the ion-beam conditions, which we demonstrate in the form of a rectifying device.

LJ Rozanski, Christopher Smith, KK Gandhi, MJ Beliatis, GDMR Dabera, KDGI Jayawardena, AADT Adikaari, MJ Kearney, S Silva (2014)A critical look at organic photovoltaic fabrication methodology: Defining performance enhancement parameters relative to active area, In: SOLAR ENERGY MATERIALS AND SOLAR CELLS130pp. 513-520 ELSEVIER SCIENCE BV
V Stolojan, Y Tison, GY Chen, R Silva (2006)Controlled growth-reversal of catalytic carbon nanotubes under electron-beam irradiation., In: Nano Lett6(9)pp. 1837-1841

The growth of carbon nanotubes from Ni catalysts is reversed and observed in real time in a transmission electron microscope, at room temperature. The Ni catalyst is found to be Ni3C and remains attached to the nanotube throughout the irradiation sequence, indicating that C most likely diffuses on the surface of the catalyst to form nanotubes. We calculate the energy barrier for saturating the Ni3C (2-13) surface with C to be 0.14 eV, thus providing a low-energy surface for the formation of graphene planes.

SRP Silva, S Xu, BX Tay, HS Tan, WI Milne, S Ravi (1996)Nanocrystallites in tetrahedral amorphous carbon films (vol 69, pg 491, 1996), In: APPLIED PHYSICS LETTERS69(4)pp. 491-493 AMER INST PHYSICS

The microstructure of filtered cathodic vacuum arc deposited tetrahedral amorphous carbon films is studied as a function of ion energy. An optimum energy window in the density and C–C  sp 3 content at an ion energy of ∼90 eV observed in this study. It is shown that the density of the amorphous carbon films are closely related to the sp 3 content. The observation of nanocrystals embedded in the amorphous carbon matrix is reported. Most of the crystals observed by transmission electron microscopy can be indexed to graphite, but some of the crystals can be indexed to cubic diamond. The chemical composition of the crystals is analyzed using electron energy loss spectroscopy (EELS). The only discernible EELS edge is that of C at an energy of 285 eV.

Radu A. Sporea, Kham M. Niang, Andrew J. Flewitt, S. Ravi P. Silva Silva (2019)Novel Tunnel-Contact-Controlled IGZO Thin-Film Transistors with High Tolerance to Geometrical Variability, In: Advanced Materials Wiley

For the first time, thin insulating layers are used to modulate a depletion region at the source of a thin-film transistor. Bottom contact, staggered electrode transistors fabricated using RFsputtered IGZO as the channel layer, with a 3 nm ALD Al2O3 layer between the semiconductor and Ni source-drain contacts show behaviours typical of source-gated transistors (SGTs): low saturation voltage (VD_SAT ~ 3V), change in VD_SAT with gate voltage of only 0.12 V/V and flat saturated output characteristics (small dependence of drain current on drain voltage). The transistors show high tolerance to geometry variations: saturated current changes only 0.15x for channel lengths between 2 - 50 μm, and only 2x for sourcegate overlaps between 9 - 45 μm. A higher than expected (5x) increase in drain current for a 30K change in temperature, similar to Schottky-contact SGTs, underlines a more complex device operation than previously theorised. Optimizations for increasing intrinsic gain and reducing temperature effects are discussed. These devices complete the portfolio of contactcontrolled transistors, comprising devices with: Schottky contacts, bulk barrier or heterojunctions, and now, tunnelling insulating layers. The findings should also apply to nanowire transistors, leading to new low-power, robust design approaches as large-scale fabrication techniques with sub-nanometre control mature.

R C Smith, R D Forrest, JD Carey, W K Hsu, S R Silva (2005)Interpretation of Enhancement Factor in Nonplanar Field Emitters, In: Applied Physics Letters87(1) American Institute of Physics

A comparison of the field emission properties of exposed nanotubes lying on a tipped carbon nanorope, with the emission properties from a sharpened iron tip of similar dimensions is performed. By varying the electrode separation it is observed that the threshold field for emission for both structures decreases as the electrode separation initially increases; however, for sufficiently large electrode separations, the threshold field is observed to reach an asymptotic value. Our results show that the field enhancement factor is fundamentally associated with the electrode separation, and depending on the experimental conditions in order to obtain a true value for electric field a set of alternative definitions for enhancement factors is required. We further confirm our experimental synopsis by simulation of the local electrostatic field which gives results similar to those obtained experimentally.

RA Hatton, NP Blanchard, V Stolojan, AJ Miller, SRP Silva (2007)Nanostructured copper phthalocyanine-sensitized multiwall carbon nanotube films, In: LANGMUIR23(11)pp. 6424-6430 AMER CHEMICAL SOC
V Neves, E Heister, S Costa, C Tîlmaciu, E Flahaut, B Soula, HM Coley, J McFadden, SR Silva (2012)Design of double-walled carbon nanotubes for biomedical applications., In: Nanotechnology23(36)pp. 365102-? Institute of Physics

Double-walled carbon nanotubes (DWNTs) prepared by catalytic chemical vapour deposition were functionalized in such a way that they were optimally designed as a nano-vector for the delivery of small interfering RNA (siRNA), which is of great interest for biomedical research and drug development. DWNTs were initially oxidized and coated with a polypeptide (Poly(Lys:Phe)), which was then conjugated to thiol-modified siRNA using a heterobifunctional cross-linker. The obtained oxDWNT-siRNA was characterized by Raman spectroscopy inside and outside a biological environment (mammalian cells). Uptake of the custom-designed nanotubes was not associated with detectable biochemical perturbations in cultured cells, but transfection of cells with DWNTs loaded with siRNA targeting the green fluorescent protein (GFP) gene, serving as a model system, as well as with therapeutic siRNA targeting the survivin gene, led to a significant gene silencing effect, and in the latter case a resulting apoptotic effect in cancer cells.

N Mureau, E Mendoza, SRP Silva (2007)Dielectrophoretic manipulation of fluorescing single-walled carbon nanotubes, In: ELECTROPHORESIS28(10)pp. 1495-1498 WILEY-BLACKWELL
SRP Silva, J Robertson, GAJ Rusli, J Amaratunga, Schwan (1996)Structure and luminescence properties of an amorphous hydrogenated carbon, In: PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES74(4)pp. 369-386 TAYLOR & FRANCIS LTD
SA Almeida, SRP Silva (1997)Stoichiometric limitations of RF plasma deposited amorphous silicon-nitrogen alloys, In: THIN SOLID FILMS311(1-2)pp. 133-137 ELSEVIER SCIENCE SA
Jose Anguita, David Cox, Muhammad Ahmad, YY Tan, Jeremy Allam, S Silva (2013)Highly transmissive carbon nanotube forests grown at low substrate temperature, In: Advanced Functional Materials23(44)pp. 5502-5509 Wiley

Despite the "darker than black" association attributed to carbon nanotube forests, here is shown that it is also possible to grow these structures, over heat-sensitive substrates, featuring highly transmissive characteristics from the UV to infrared wavelengths, for forest heights as high as 20 μm. The optical transmission is interpreted in terms of light propagation along channels that are self-generated by localized bundling of tubes, acting as waveguides. A good correlation is shown between the distribution of diameter sizes of these sub-wavelength voids and the transmission spectrum of the forests. For the shorter visible and near-UV wavelengths, this model shows that light propagates by channeling along individual vertical voids in the forests, which elucidates the origin for the widely-reported near-zero reflectance values observed in forests. For the longer infrared wavelengths, the mode spreads over many nanotubes and voids, and propagates along a "homogeneous effective medium". The strong absorption of the forest at the shorter wavelengths is correlated in terms of the stronger attenuation inside a waveguide cavity, according to the λ attenuation dependency of standard waveguide theory. The realization of this material can lead to novel avenues in new optoelectronic device design, where the carbon nanotube forests can be used as highly conducting "scaffolds" for optically active materials, whilst also allowing light to penetrate to significant depths into the structure, in excess of 20 μm, enabling optical functionality. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

S Xu, D Flynn, BK Tay, S Prawer, KW Nugent, SRP Silva, Y Lifshitz, WI Milne (1997)Mechanical properties and Raman spectra of tetrahedral amorphous carbon films with high sp(3) fraction deposited using a filtered cathodic arc, In: PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES76(3)pp. 351-361 TAYLOR & FRANCIS LTD
JD Carey, S. R. P. Silva (2004)Disorder, clustering, and localization effects in amorphous carbon, In: Physical Review B70(235417)

The nanostructure of amorphous carbon thin films is described in terms of a disordered nanometer-sized conductive sp2 phase embedded in an electrically insulating sp3 matrix. It is shown that the degree of clustering and disorder within the sp2 phase plays a determining role in the electronic properties of these films. Clustering of the sp2 phase is shown to be important in explaining several experimental results including the reduction of the electron spin resonance linewidth with increasing spin density and the dispersion associated with the width of the Raman active G band. The influence of structural disorder, associated with sp2 clusters of similar size, and topological disorder, due to undistorted clusters of different sizes, on both spin density and Raman measurements, is discussed. An extension of this description to intercluster interactions to explain some of the electrical transport and electron field emission behavior is also presented.

SRP Silva, J Robertson, GAJ Amaratunga, B Rafferty, LM Brown, J Schwan, DF Franceschini, G Mariotto (1997)Nitrogen modification of hydrogenated amorphous carbon films, In: JOURNAL OF APPLIED PHYSICS81(6)pp. 2626-2634 AMER INST PHYSICS
M Alenezi, Simon Henley, Neil Emerson, Ravi Silva (2013)From 1D and 2D ZnO nanostructures to 3D hierarchical structures with enhanced gas sensing properties., In: Nanoscale6(1)pp. 235-247

Facile and low cost hydrothermal routes are developed to fabricate three-dimensional (3D) hierarchical ZnO structures with high surface-to-volume ratios and an increased fraction of (0001) polar surfaces. Hierarchical ZnO nanowires (ZNWs) and nanodisks (ZNDs) assembled from initial ZnO nanostructures are prepared from sequential nucleation and growth following a hydrothermal process. These hierarchical ZnO structures display an enhancement of gas sensing performance and exhibit significantly improved sensitivity and fast response to acetone in comparison to other mono-morphological ZnO, such as nanoparticles, NWs, or NDs. In addition to the high surface-to-volume ratio due to its small size, the nanowire building blocks show the enhanced gas sensing properties mainly ascribed to the increased proportion of exposed active (0001) planes, and the formation of many nanojunctions at the interface between the initial ZnO nanostructure and secondary NWs. This work provides the route for structure induced enhancement of gas sensing performance by designing a desirable nanostructure, which could also be extended to synthesize other metal oxide nanostructures with superior gas sensing performance.

Ehsan Rezaee, Dimitar Ivanov Kutsarov, Jing Zhang, George Koutsourakis, Bowei Li, Fernando A. Castro, S. Ravi P. Silva (2023)Ethanol-based inks for industrially applicable deposition of high-quality perovskite films for optoelectronic device applications, In: small methods Wiley

Incontrovertibly there is an increasing demand for the development of benign inks suitable for the fabrication of high performing perovskite-based thin film functional layers. Nevertheless, most reported perovskite precursors rely on the use of highly toxic solvents such as acetonitrile (ACN), 2-mercaptoethanol (2-ME), dimethylformamide (DMF) and many others. Hence, there is a strong imperative for the development of novel and greener inks, which will facilitate a smoother commercialisation of technologies based on functional perovskites films. Therefore, we studied four perovskite precursors, some of which consist of up to 90% ethanol (EtOH). All inks were developed to fulfil the requirements of a high-throughput deposition compatible with roll-to-roll techniques at room temperature, assisted by an air knife for instant solvent removal. Two of the inks are particularly suitable for the fabrication of high-quality and densely packed multi-crystalline (CH3NH3)PbI3 (MAPbI3) layers, as confirmed by numerous nanoscale spectroscopic and material characterisation techniques. Additionally, large-area luminescence imaging is applied to improve the quality of the deposited perovskite films and to enhance the deposition uniformity towards upscaling to larger areas appropriate for manufacture. The genuine potential of the developed greener perovskite inks was demonstrated with the fabrication of solar cells with power conversion efficiencies above 19.5%.

M. Anderle, G.A.J. Amaratunga, W.I. Milne, J. Robertson, S.R.P. Silva, A. Tagliaferro (2005)Preface, In: Diamond and related materials14(8)
S. L. James, M. Illsley, S. E. James, E. Mendoza, S. R. P. Silva, P. Vadgama, P. Tomlins, S. V. Mikhalovsky (2006)The interaction of nanostructured biomaterials with human cell cultures - The choice of cell cultures for use as biocompatability probes, In: J P Blitz, V M GunKo (eds.), SURFACE CHEMISTRY IN BIOMEDICAL AND ENVIRONMENTAL SCIENCE228pp. 205-214 Springer Nature

The study of the interaction of cells with nanoparticles or nanosurfaces is increasingly being performed using in vitro methods, largely with immortal cell lines. Immortal cell lines may behave differently from cells initially isolated from living tissue in these assays. Thus we have established a cell bank of primary human cell cultures stored at different stages from initial isolation through to senescence. We have examined the effects of culture age oil proliferation upon carbon nanotube arrays, and adhesion to polystyrene surfaces. These data have been compared with an equivalent telomerase transformed line, and a commercially available line. Initial results suggest very large errors can be introduced into nanotoxicity and adhesion assays by inappropriate use of cell strains and lines.

Bojan O Boskovic, Vlad Stolojan, Rizwan U. A Khan, Sajad Haq, S. Ravi P Silva (2003)Large-area synthesis of carbon nanofibres at room temperature, In: Nature materials2(2)pp. 126-126
Christos Melios, Michael Winters, Wlodek Strupinski, Vishal Panchal, Cristina E Giusca, K. D. G. Imalka Jayawardena, Niklas Rorsman, S. Ravi P Silva, Olga Kazakova Tuning epitaxial graphene sensitivity to water by hydrogen intercalation, In: Nanoscale9(10)pp. 3440-3448

C. Melios et al. Nanoscale, 2017,9, 3440-3448 The effects of humidity on the electronic properties of quasi-free standing one layer graphene (QFS 1LG) are investigated via simultaneous magneto-transport in the van der Pauw geometry and local work function measurements in a controlled environment. QFS 1LG on 4H-SiC(0001) is obtained by hydrogen intercalation of the interfacial layer. In this system, the carrier concentration experiences a two-fold increase in sensitivity to changes in relative humidity as compared to the as-grown epitaxial graphene. This enhanced sensitivity to water is attributed to the lowering of the hydrophobicity of QFS 1LG, which results from spontaneous polarization of 4H-SiC(0001) strongly influencing the graphene. Moreover, the superior carrier mobility of the QFS 1LG system is retained even at the highest humidity. The work function maps constructed from Kelvin probe force microscopy also revealed higher sensitivity to water for 1LG compared to 2LG in both QFS 1LG and as-grown systems. These results point to a new field of applications for QFS 1LG, i.e., as humidity sensors, and the corresponding need for metrology in calibration of graphene-based sensors and devices.

E Borowiak-Palen, M H Ruemmeli, E Mendoza, S J Henley, D C Cox, CHP Poa, Stolojan, T Gemming, T Pichler, SRP Silva (2005)Silver intercalated carbon nanotubes, In: H Kuzmany, J Fink, M Mehring, S Roth (eds.), Electronic Properties of Novel Nanostructures786pp. 236-239 Amer Inst Physics

The intercalation of metals within carbon nanotube structures has extended the potential applications of these materials to possible quantum memory elements as well as high density magnetic storage media. In our study we use methodologies based on wet chemistry and solid state physical (excimer laser) processes to incorporate silver nanoparticles in single and multiwall carbon nanotubes. We show high resolution TEM as evidence for the formation of very long (similar to 100-150 nm) silver quantum wires within SWCNT, and their properties are probed using various analytical techniques. The variation of the silver intercalated nanotube percentage and yield are compared for the SW- and MW-CNTs, when using wet chemistry versus physical processes.

Stephen M. Lyth, R. A. Hatton, S. R. P. Silva (2007)Li-salt functionalised carbon nanotubes as low work function field emitters, In: EIGHTH IEEE INTERNATIONAL VACUUM ELECTRONICS CONFERENCEpp. 195-2 IEEE
R Sporea, A Alshammari, S Georgakopoulos, J Underwood, M Shkunov, SRP Silva, S Ravi Pradip Silva (2013)Micron-scale inkjet-assisted digital lithography for large-area flexible electronics, In: IEEE Conferencespp. 280-283

Large-area electronics require cost-effective yet precise patterning of electrodes. We demonstrate a simple electrode patterning technique capable of micron-scale gap formation, that allows the patterning of a larger variety of metals than the current portfolio of jettable metallic ink comprises and does not require a high-temperature sintering step. However, this method can produce large variations in gap size resulting in inconsistent and irreproducible transistor drain current. We propose that source-gated transistors (SGTs) are well suited to this technique, as they have a saturated drain current independent of source-drain separation, thus leading to improved current uniformity despite inconsistencies in gap size.

SRP Silva, S Xu, B X Tay, H S Tan, W I Milne (1996)Nanocrystallites in tetrahedral amorphous carbon films (vol 69, pg 491, 1996), In: Applied physics letters69(13)pp. 1980-1980 Amer Inst Physics
V. Neves, H. M. Coley, J. McFadden, S. R. P. Silva (2011)Uptake, Intracellular Localization and Biodistribution of Carbon Nanotubes, In: R Klingeler, R B Sim (eds.), Carbon Nanostructurespp. 169-182 Springer Nature

Carbon nanotubes (CNTs) exhibit unique size, shape and physical properties, which make them promising candidates for biomedical applications. In particular, carbon nanotubes have been intensively studied for conjugation with pre-existing therapeutic agents for more effective targeting, as a result of their ability to cross cell membranes. However, to utilise them effectively in biological systems it is extremely important to understand how they behave at the cellular level and their distribution in vivo. Additionally, in order to consider carbon nanotubes as candidate delivery systems of therapeutic agents it is important to ascertain their fate in vivo, but also take into account many factors, such as solubility, stability and clearance. Issues surrounding their short term and long term safety are currently the subject of toxicology testing. Herein, we propose to summarize the main findings on the uptake, trafficking and biodistribution of carbon nanotubes, with special focus on functionalized carbon nanotubes for delivery of therapeutic agents.

James Clark, Jose V. Anguita, Ying Chen, S. Ravi P. Silva (2016)Optical nanostructures in 2D for wide-diameter and broadband beam collimation, In: Scientific reports6(1)pp. 18767-18767 Springer Nature

Eliminating curved refracting lensing components used in conventional projection, imaging and sensing optical assemblies, is critical to enable compactness and miniaturisation of optical devices. A suitable means is replacing refracting lenses with two-dimensional optical media in flat-slab form, to achieve an equivalent optical result. One approach, which has been the focus of intense research, uses a Veselago lens which features a negative-index metamaterial. However, practical implementations rely on resonance techniques, thus broadband operation at optical frequencies imposes significant technical challenges that have been difficult to overcome. Here, we demonstrate a highly-collimated, broadband, wide-diameter beam from a compact source in flat-slab form, based on light collimation using nanomaterials ordered in patterns and embedded into flexible polymers. These provide a highly anisotropic absorption coefficient due to patterns created by vertical carbon nanotube structures grown on glass, and the anisotropic electrical conductivity of the nanotubes. We show this nanostructure strongly absorbs unwanted off-axis light rays, whilst transmitting the desired on-axis rays, to achieve the required optical effect over broadband, from visible to short-infrared, thus circumventing some technical limitations of negative-index metamaterials. We further show a low substrate-temperature system for nanotube growth, allowing direct implementation into heat-sensitive large-area devices.

Naigui Shang, Pagona Papakonstantinou, Peng Wang, S. Ravi P. Silva (2012)Platinum Integrated Graphene for Methanol Fuel Cells (vol 114, pg 15837, 2010), In: Journal of physical chemistry. C116(22)pp. 12376-12376 Amer Chemical Soc
Stephen M. Lyth, S. R. P. Silva (2007)A study of field emission from glass spheres, coated with carbon nanotubes, In: EIGHTH IEEE INTERNATIONAL VACUUM ELECTRONICS CONFERENCEpp. 327-2 IEEE
V.P. Mammana, S. Silva, R.D. Mansano, P. Verdonck, A. Pavani Filho, M.C. Salvadori, I.G. Brown, S Ravi Pradip Silva (1999)Porous freestanding diamond membranes with reduced pore diameter, In: Thin solid films353(1)pp. 239-243 Elsevier B.V

We have shown previously that porous diamond membranes can be fabricated using a method based on growing diamond on a patterned silicon substrate. The technique used to pattern the silicon is conventional lithography. In this work we present a method for reducing the pore size using diamond post-deposition over the membrane. An important concern in this work was to determine the pore-shutting rate, considering the time post-deposition and the pore morphology.

S Silva, M. C Salvadori, K Kawakita, M. T Pereira, R. M Galvao, M Cattani, S Ravi Pradip Silva (2002)Diamond flow controller microtubes, In: Journal of micromechanics and microengineering12(2)pp. 108-110 Institute of Physics
S. Silva, M.C. Salvadori, K. Kawakita, M.T. Pereira, W. Rossi, M. Cattani, S Ravi Pradip Silva (2002)Fabrication of diamond flow controller micronozzles, In: Diamond and related materials11(2)pp. 237-241 Elsevier B.V

In this work we show how to manufacture diamond sonic micronozzles. The advantage in using diamond to fabricate the micronozzles, compared with other materials, is that it is the hardest material known, has low thermal expansion, thermal conductivity is very high and it is chemically inert. In our process, tungsten wires, used as molds, have been fabricated by using an electrochemical etching process. These molds have been coated with diamond films by Chemical Vapor Deposition. By a wet etching, the tungsten mold was removed, obtaining the micronozzle. Flow measurements have shown that the diamond micronozzles work as passive flow controllers and flowmeters under choking conditions.

Elena Heister, Vera Neves, S. Ravi P. Silva, Johnjoe McFadden, Helen M. Coley (2011)Carbon Nanotubes Loaded with Anticancer Drugs: A Platform for Multimodal Cancer Treatment, In: R Klingeler, R B Sim (eds.), Carbon Nanostructurespp. 223-245 Springer Nature

Approximately every fourth person in the world currently dies of cancer. Although many efficient anticancer drugs have been developed over the last 60 years or more, most therapeutic approaches still lack specificity for their intended site of action in the body, resulting in reduced effectiveness and severe side effects. The emerging field of nanomedicine provides a whole range of materials and techniques to develop customizable drug delivery vehicles that assist the targeting of therapeutic agents to the desired site of action. Amongst these, carbon nanotubes have emerged as promising candidates, being capable of penetrating mammalian cell membranes and allowing for the attachment of high loads of drugs and targeting agents on their surface or the inner cavity. This chapter will discuss the principles of targeted, anticancer chemotherapies and introduce carbon nanotubes as novel tools for vector-based, targeted drug delivery.

Christopher T. G Smith, Michal Delkowski, José V Anguita, David C Cox, Catherine Haas, S. Ravi P Silva (2021)Correction to “Complete Atomic Oxygen and UV Protection for Polymer and Composite Materials in Low Earth Orbit”, In: ACS applied materials & interfaces13(11)pp. 13907-13907 American Chemical Society
Shuai Huang, Yunhe Wang, Si Shen, Yuting Tang, Ancan Yu, Bonan Kang, S. Ravi P. Silva, Geyu Lu (2019)Enhancing the performance of polymer solar cells using solution-processed copper doped nickel oxide nanoparticles as hole transport layer, In: Journal of colloid and interface science535(C)pp. 308-317 Elsevier

Polymer solar cells (PSCs) are considered promising energy power suppliers due to their light weight, printability, low-energy fabrication and roll-to-roll processability. Recently, the solution-processed NiOx nanoparticles have been a desirable interfacial material for hole transport in the PSCs, instead of organic semiconductors. However, pure NiOx films restrain the high performance of PSCs due to their poor electrical characteristics caused by the localized orbital distribution at the top of valence band. Therefore, metal ion doping has been explored as a method to endow NiOx nanoparticles with the appropriate electrical characteristics. Herein, we applied solution-processed Cu-doped NiOx (Cu:NiOx) nanoparticles as an efficient hole transport layer (HTL) in PSCs. The Cu-doped NiOx enhanced the electrical conductivity of the material and improved the interface contact with the active layer, which remarkably facilitated the hole extraction and effectively suppressed the carrier recombination at the interface. Thus, a higher power conversion efficiency of 7.05%, corresponding to an approximately 30% efficiency improvement compared with that of a pristine NiOx interlayer (5.44%) in poly[N- 9 ''-hepta-d ecanyl-2,7-carbazolealt-5,5-(4',7'-di-2-thieny1-2',1',3'-ben-zothiadiazole)]:[6,6]-phenyl-C-71-butyric acid methyl ester (PCDTBT:PC71BM)-based PSCs, was achieved by the proposed device. The developed solution-processed Cu:NiOx nanoparticles may be an excellent alternative for interfacial materials in PSCs or other optoelectronic devices requiring HTLs. (C) 2018 Elsevier Inc. All rights reserved.

Shuai Huang, Yuting Tang, Ancan Yu, Yunhe Wang, Si Shen, Bonan Kang, S. Ravi P. Silva, Geyu Lu (2018)Solution-processed SnO(2 )nanoparticle interfacial layers for efficient electron transport in ZnO-based polymer solar cells, In: Organic electronics62pp. 373-381 Elsevier

Polymer solar cells (PSCs) suffer energy loss due to a number of reasons including high thermalisation, large exciton binding energy and electron-hole recombination within the active layer of the device. Although much effort has gone into addressing the above, interface recombination between a FTO cathode and ZnO electron transport layer (ETL) has remained relatively unnoticed. In this paper, an efficient inverted PSC is demonstrated by introducing a solution-processed SnO2 film between the ZnO ETL and FTO cathode. The use of the SnO2 layer, improves significantly all the device performance parameters of PSCs based on P3HT:PC61BM and PCDTBT:PC71BM system, achieving higher power conversion efficiency (PCE) up to 4.25% and 7.16%, compared to that without the SnO2 film (PCE 3.10% and 5.52%). The improved performance is attributed to the enhanced optical transmission, the reduced energy barrier and suppression of carrier recombination at the interface between the ZnO layer and cathode. Furthermore, the SnO2 film is shown to facilitate electron injection as well as effective hole blocking from the active layer. This study provides an efficient approach to optimize the device performance of PSCs by interfacial modification at bottom conducive electrode.

Shuai Huang, Yu Pang, Xu Li, Yunhe Wang, Ancan Yu, Yuting Tang, Bonan Kang, S. Ravi P Silva, Geyu Lu (2019)Strontium Fluoride and Zinc Oxide Stacked Structure as an Interlayer in High-Performance Inverted Polymer Solar Cells, In: ACS applied materials & interfaces11(2)pp. 2149-2158 American Chemical Society

Enhanced power conversion efficiency is reported in inverted polymer solar cells when an ultrathin layer of strontium fluoride (SrF2) is evaporated on the surface of the solution-processed zinc oxide (ZnO) electron transport layer. The photoactive layer is made up of bulk heterojunction composites of poly­[4,8-bis­(5­(2-ethylhexyl)­thiophen-2-yl)­benzo­[1,2-b:4,5-b′]­dithiopheneco-3-fluorothieno­[3,4-b]-thiophene-2-carboxylate] and [6,6]-phenyl-C71-butyric acid methyl ester. The ZnO film acts as an effective electron transport layer, whereas the ultrathin SrF2 layer improves the energy level alignment and enhances the built-in potential via the formation of an interfacial dipole layer at the interfaces between the ZnO film and the photoactive layer, resulting in an enhanced electron extraction efficiency and a decreased carrier recombination loss. Furthermore, the SrF2 layer reduces the inherent incompatibility between the hydrophilic ZnO film and the hydrophobic photoactive layer. As a result, all the photovoltaic performance parameters are remarkably improved, leading to a high efficiency of up to 10.46% (with a fill factor of 71.38%), corresponding to a ca. 21% improvement over the reference device performance (8.64%). The use of a ZnO/SrF2 stacked interlayer provides a simple, but effective, approach to obtain high-efficiency inverted PSCs.

Shuai Huang, Ancan Yu, Yunhe Wang, Yuting Tang, Si Shen, Bonan Kang, S. Ravi P. Silva, Geyu Lu (2019)Nickel oxide and polytetrafluoroethylene stacked structure as an interfacial layer for efficient polymer solar cells, In: Electrochimica acta299pp. 366-371 Elsevier Ltd

An efficient polymer solar cell (PSC) has been demonstrated by incorporating an ultrathin interfacial insulating organic layer of polytetrafluoroethylene (PTFE) between a photoactive layer and hole-collecting buffer layer (NiOx). The photoactive layer is made with bulk heterojunction composites of poly[N-9’’-hepta-decanyl-2,7-carbazolealt-5,5-(4′,7′-di-2-thienyl- 2′,1′,3′-ben-zothiadiazole)]:[6,6]-phenyl-C71-butyric acid methyl ester (PCDTBT:PC71BM). The PTFE layer not only improves the energy level alignment by forming an interfacial dipole at the interface but also reduces the inherent incompatibility between the hydrophobic active layer and hydrophilic NiOx layer, thereby benefiting to the charge extraction and transport in the solar cells. As a result, with the NiOx/PTFE stacked structure, all the photovoltaic performance parameters are significantly improved, leading to a higher power conversion efficiency (PCE) of up to 7.11% compared to the control device without PTFE layer (PCE 5.50%). The PTFE layer provides a superior alternative to interfacial engineering of the metal oxide/organic semiconductor interface in polymer solar cells and other organic electronic devices.

Zizhao Zhang, Jianguo Deng, Qing Sun, Hongyu Zhao, Die Hu, Bo Shen, Xiangxin Meng, Beibei Zong, Bonan Kang, S. Ravi P. Silva (2022)High-performance red phosphorescent light-emitting diodes built on bipolar host materials obtained from dibenzo[F,H]quinoxaline and dibenzothiophene, In: Organic electronics104 Elsevier B.V

DTBDQ, a bipolar host material with an acceptor unit dibenzo[F,H]quinoxaline and a donor unit dibenzothiophene connected by two interstitial benzenes, was employed. DTBDQ exhibits deep LUMO and HOMO energy levels, along with a triplet energy of 2.75 eV, owing to rational molecular design. Red phosphorescent organic light-emitting diodes (PhOLEDs) devices with DTBDQ here as the host and Ir(piq)2acac as the guest layer have an external quantum efficiency(EQE) of 19.79% with a limited roll-off and an EQE of 18.08% at 1000 cd/m2, with CIE coordinates of (0.68,0.32), which is quite comparable to the National Television Systems Committee (NTSC) CIE coordinates of (0.67,0.33). The device performance is significantly better than that of devices using hole-type host CBP, electron-type host TPBI, and electron and hole-type hosts together, indicating that the performance of bipolar host materials transferring both electrons and holes is superior to that of simply two hosts as a double light-emitting layer separately, which is beneficial to carrier transport balancing and avoiding carrier buildup. DTBDQ demonstrates that it is an excellent bipolar host candidate. [Display omitted] •First synthesis of bipolar host material using dibenzo[F,H]quinoxaline and dibenzothiophene.•The deeper LUMO and HOMO energy levels are −2.94 eV and −6.20 eV respectively.•High triplet state energy level of 2.75 eV ensures good energy transfer.•Devices with DTBDQ achieved a high EQE of 19.79% and had a low efficiency roll-off.

Maurizio Monti, K. D. G. Imalka Jayawardena, Edward Butler-Caddle, Rajapakshe M. Bandara, Jack M. Woolley, Michael Staniforth, S. Ravi P. Silva, James Lloyd-Hughes (2020)Hot carriers in mixed Pb-Sn halide perovskite semiconductors cool slowly while retaining their electrical mobility, In: Physical review. B102(24) Amer Physical Soc

The electron-phonon interaction controls the intrinsic mobility of charges in metal halide perovskites, and determines the rate at which carriers lose energy. Here, the carrier mobility and cooling dynamics were directly examined using a combination of ultrafast transient absorption spectroscopy and optical pump, THz probe spectroscopy, in perovskites with different lead and tin content, and for a range of carrier densities. Significantly, the carrier mobility in the "hot phonon bottleneck" regime, where the LO phonon bath keeps carriers warm, was found to be similar to the mobility of cold carriers. A model was developed that provides a quantitative description of the experimental carrier cooling dynamics, including electron-phonon coupling, phonon-phonon coupling and the Auger mechanism. In the Pb and Sn alloy the duration of the hot carrier regime was extended as a result of the slower decay of optical phonons. The findings offer an intuitive link between macroscopic properties and the underlying microscopic energy transfer processes, and suggest new routes to control the carrier cooling process in metal halide perovskites to optimize optoelectronic devices.

M. Monti, J. M. Woolley, M. Staniforth, A. Wijesekara, S. X. Tao, R. M. I. Bandara, I. Jayawardena, A. Crocker, E. Griffin, S. R. P. Silva, R. A. Hatton, J. Lloyd-Hughes (2019)Efficient Intraband Hot Carrier Relaxation in Sn and Pb Perovskite Semiconductors Mediated by Strong Electron-phonon Coupling, In: M Betz, A Y Elezzabi (eds.), ULTRAFAST PHENOMENA AND NANOPHOTONICS XXIII10916pp. 109160M-109160M-8 Spie-Int Soc Optical Engineering

The dynamic increase in terahertz photoconductivity resulting from energetic intraband relaxation was used to track the formation of highly mobile charges in thin films of the tin iodide perovskite Cs1-xRbxSnI3 and compared to the lead based Cs-0(.)05(FA(0.)(83)MA(0.)(17))(0.95)Pb(I0.83Br0.17)(3). Energy relaxation times were found to be around 500 fs, comparable to those in GaAs and longer than the ones of the lead-based perovskite (around 300 fs). At low excess energies the efficient intraband relaxation can be understood within the context of the Frohlich electron-phonon interaction. For higher excess energies the photoconductivity rise time lengthens in accordance with carrier injection higher in the bands, or into multiple bands. The findings contribute to the development of design rules for photovoltaic devices capable of extracting hot carriers from perovskite semiconductors.

Mateus G. Masteghin, Ranilson A. Silva, David C. Cox, Denis R. M. Godoi, S. Ravi P. Silva, Marcelo O. Orlandi (2021)The role of surface stoichiometry in NO2 gas sensing using single and multiple nanobelts of tin oxide, In: Physical chemistry chemical physics : PCCP23(16)pp. 9733-9742 Royal Soc Chemistry

Typically used semiconducting metal oxides (SMOs) consist of several varying factors that affect gas sensor response, including film thickness, grain size, and notably the grain-grain junctions within the active device volume, which complicates the analysis and optimisation of sensor response. In comparison, devices containing a single nanostructured element do not present grain-grain junctions, and therefore present an excellent platform to comprehend the correlation between nanostructure surface stoichiometry and sensor response to the depletion layer (Debye length, L-D) variation after the analyte gas adsorption/chemisorption. In this work, nanofabricated devices containing SnO2 and Sn3O4 individual nanobelts of different thicknesses were used to estimate their L-D after NO2 exposure. In the presence of 40 ppm of NO2 at 150 degrees C, L-D of 12 nm and 8 nm were obtained for SnO2 and Sn3O4, respectively. These values were associated to the sensor signals measured using multiple nanobelts onto interdigitated electrodes, outlining that the higher sensor signal of the Sn4+ surface (up to 708 for 100 ppm NO2 at 150 degrees) in comparison with the Sn2+ (up to 185) can be explained based on a less depleted initial state and a lower surface electron affinity caused by the Lewis acid/base interactions with oxygen species from the baseline gas. To support the proposed mechanisms, we investigated the gas sensor response of SnO2 nanobelts with a higher quantity of oxygen vacancies and correlated the results to the SnO system.

Qinglong Liu, Haodong Shi, Tianyu Yang, Yan Yang, Zhong-Shuai Wu, Jianqiang Yu, S. Ravi P. Silva, Jian Liu (2019)Sequential growth of hierarchical N-doped carbon-MoS2 nanocomposites with variable nanostructures, In: Journal of materials chemistry. A, Materials for energy and sustainability7(11)pp. 6197-6204 Royal Soc Chemistry

To develop high performance nanocomposites with potential commercialization value, general synthesis strategies that could provide nanocomposites with finely tunable nanostructures and physicochemical properties are desirable. In this work, a universal approach was developed that fulfilled these requirements for the sequential growth of nitrogen-doped carbon-molybdenum disulfide (denoted as NC-MoS2) nanocomposites with versatile nanostructures, namely, dual-shell, yolk-shell, core-shell, hollow spheres and nanorods. The formation mechanism of the different nanostructures is proposed to arise from the synergistic effect of dual surfactants, the complexing effect between amine groups and Mo species, hydrogen bonding interactions among aminophenol resols, cysteine and sodium molybdate dihydrate (Na2MoO4 center dot 2H(2)O), and the sequential formation of Mo-resol clusters. The NC-MoS2 hollow spheres displayed higher lithium-ion storage capacity than the N-free hollow sample, NC-MoS2 dual-shell and yolk-shell spheres, and may benefit from the strengthened charge transfer rate originating from the N-doping, higher N-content and hollow nanostructures.

Federico Bertagna, Rebecca Lewis, S. Ravi P. Silva, Johnjoe McFadden, Kamalan Jeevaratnam (2021)Effects of electromagnetic fields on neuronal ion channels: a systematic review, In: Annals of the New York Academy of Sciences1499(1)pp. 82-103 Wiley

Many aspects of chemistry and biology are mediated by electromagnetic field (EMF) interactions. The central nervous system (CNS) is particularly sensitive to EMF stimuli. Studies have explored the direct effect of different EMFs on the electrical properties of neurons in the last two decades, particularly focusing on the role of voltage-gated ion channels (VGCs). This work aims to systematically review published evidence in the last two decades detailing the effects of EMFs on neuronal ion channels as per the PRISM guidelines. Following a predetermined exclusion and inclusion criteria, 22 papers were included after searches on three online databases. Changes in calcium homeostasis, attributable to the voltage-gated calcium channels, were found to be the most commonly reported result of EMF exposure. EMF effects on the neuronal landscape appear to be diverse and greatly dependent on parameters, such as the field's frequency, exposure time, and intrinsic properties of the irradiated tissue, such as the expression of VGCs. Here, we systematically clarify how neuronal ion channels are particularly affected and differentially modulated by EMFs at multiple levels, such as gating dynamics, ion conductance, concentration in the membrane, and gene and protein expression. Ion channels represent a major transducer for EMF-related effects on the CNS.

R. D. Ishara G. Dharmasena, Jonathan H. B. Deane, S. Ravi P. Silva (2018)Nature of Power Generation and Output Optimization Criteria for Triboelectric Nanogenerators, In: Advanced energy materials8(31)pp. 1802190-n/a

Triboelectric nanogenerators (TENGs) are in the forefront of next‐generation energy harvesting technologies, having been demonstrated as a leading candidate for numerous applications in energy harvesting and self‐powered sensing. However, critical parameters affecting TENG output behavior and their optimization are not well understood. Herein, for the first time, the power output characteristics of TENGs are fully unveiled by vigorously analyzing their impedance behavior as a function of excitation source and device parameters. In this paper, Norton's theorem, first presented in 1926 for two terminal linear electrical networks, is extended to represent TENGs, allowing accurate visualization of their dynamic power output behavior via small signal analysis. TENG impedance plots are introduced to accurately determine the peak power point of a given design, which holds paramount importance in understanding and improving TENGs. The knowledge with empirical understanding for these variations results in the design and construction of more efficient TENG devices for future applications. Triboelectric nanogenerators are emerging as a leading energy harvesting and self‐powered sensing technology; however, their power generation characteristics are not fully understood. This work reveals the power generation and transmission characteristics of triboelectric nanogenerators, establishing optimization strategies that are critical in enhancing their output power and designing end applications.

Zakaria Saadi, Simon G. King, Jose Anguita, Vlad Stolojan, S. Ravi P. Silva (2023)Effect of Surfactants on the Thermoelectric Performance of Double-Walled Carbon Nanotubes, In: Energy & environmental materials (Hoboken, N.J.)6(1) Wiley

Thermoelectrics are a promising solution to the recovery of some of the 60% of the worldwide energy wasted as heat. However, their conversion efficiency is low and the best performing materials are brittle, toxic, and made of expensive ceramics. The challenge in developing better performing materials is in disrupting the electrical vs thermal conductivity correlation, to achieve low thermal conductivity simultaneously with a high electrical conductivity. Carbon nanotubes allow for the decoupling of the electronic density of states from the phonon density of states and this paper shows that flexible, thin films of double-walled carbon nanotube (DWCNT) can form effective n- and p-doped semiconductors that can achieve a combined Seebeck coefficient of 157.6 mu V K-1, the highest reported for a single DWCNT device to date. This is achieved through selected surfactant doping, whose role is correlated with the length of the hydrocarbon chain of the hydrophobic tail group of the surfactant's molecules. CNTs functionalized with Triton X-405 show the highest output power consisting of a single junction of p- and n-type thermoelectric elements, reaching as high as 67 nW for a 45 K temperature gradient. Thus enabling flexible, cheaper, and more efficient thermoelectric generators through the use of functionalized CNTs.

Yang Dang, Yunhe Wang, Si Shen, Shuai Huang, Xiangwei Qu, Yu Pang, S. Ravi P. Silva, Bonan Kang, Geyu Lu (2019)Solution processed hybrid Graphene-MoO3 hole transport layers for improved performance of organic solar cells, In: Organic electronics67pp. 95-100 Elsevier B.V

A facile hydrothermal process is used to prepare hybrid graphene-MoO3 particles to be used as hole transport layers (HTLs) in organic solar cells (OSCs). The OSCs with active layer donor/acceptor combinations of Poly[N-9″-hepta-decanyl-2,7-carbazolealt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and fullerene derivative [6,6]-phenyl-C71-butyric acid methylester (PC71BM) exhibit an enhanced power conversion efficiency (PCE) of 7.07%, an increase by 19% with the hybrid HTL compared to those devices with only MoO3 HTLs. Through investigating the optical and electrical properties of the devices, we found that the superior PCE originates from an enhanced hole transport property resulting from the extraction capabilities of G-MoO3. Comparing with thermal evaporated MoO3, the G-MoO3 exhibits a higher optical transmittance, improved electrical conductivity and enhanced hole mobility. Moreover, the work function of the hybrid G-MoO3 was close to the highest occupied molecular orbital (HOMO) level of PCDTBT, which reduced the energy barrier for the carriers and was suited for hole transport. [Display omitted] •Hybrid graphene-MoO3 (G-MoO3) particles were synthesized via a simple hydrothermal method.•The G-MoO3 was introduced into organic solar cells as hole transportion layers.•The organic solar cells with G-MoO3 hole transportion layers exhibited higher conductivity and hole mobility.

Elizabeth J. Legge, Keith R. Paton, Magdalena Wywijas, Greg McMahon, Rory Pemberton, Naresh Kumar, Arun Prakash Aranga Raju, Craig P. Dawson, Andrew J. Strudwick, James W. Bradley, Vlad Stolojan, S. Ravi P. Silva, Stephen A. Hodge, Barry Brennan, Andrew J. Pollard (2020)Determining the Level and Location of Functional Groups on Few-Layer Graphene and Their Effect on the Mechanical Properties of Nanocomposites, In: ACS applied materials & interfaces12(11)pp. 13481-13493 Amer Chemical Soc

Graphene is a highly desirable material for a variety of applications; in the case of nanocomposites, it can be functionalized and added as a nanofiller to alter the ultimate product properties, such as tensile strength. However, often the material properties of the functionalized graphene and the location of any chemical species, attached via different functionalization processes, are not known. Thus, it is not necessarily understood why improvements in product performance are achieved, which hinders the rate of product development. Here, a commercially available powder containing few-layer graphene (FLG) flakes is characterized before and after plasma or chemical functionalization with either nitrogen or oxygen species. A range of measurement techniques, including tip-enhanced Raman spectroscopy (TERS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and NanoSIMS, were used to examine the physical and chemical changes in the FLG material at both the micro- and nanoscale. This is the first reported TERS imaging of commercially available FLG flakes of submicron lateral size, revealing the location of the defects (edge versus basal plane) and variations in the level of functionalization. Graphene-polymer composites were then produced, and the dispersion of the graphitic material in the matrix was visualized using ToF-SIMS. Finally, mechanical testing of the composites demonstrated that the final product performance could be enhanced but differed depending on the properties of the original graphitic material.

K. N. Prajapati, Anoop A. Nair, Jervis Fernandes, S. Ravi P. Silva, J. Mitra (2022)Imaging with Raman photons: a novel use of mixed-mode spectroscopy, In: Nano express3(3) IOP Publishing Ltd

Surface enhanced Raman spectroscopy is today an established technique used for chemical fingerprinting. Here, we showcase an engineered hierarchical substrate, in which the plasmonically active regions, restricted to a micron scale, two dimensional hexagonal pattern are examined. Spatial variation of the enhanced Raman signal from any analyte, uniformly coating the substrate, consequently bears a high registry with the underlying pattern. This spatially contrasted enhancement allows optical imaging of the 2D pattern solely using the Raman scattered photons from the analyte. While the pattern brightness and contrast determine analyte identification and detection sensitivity, hyperspectral imaging can be exploited for increasing specificity. Proof of concept demonstration of the technique is carried out via the acquisition of Raman images with rhodamine and fluorescein dyes and then applied to detect glucose in 40 mM concentration. The large area optical imaging and the requirement of long-range uniformity in the detected patterns for positive analyte detection, is implemented using a machine learning based pattern recognition protocol which also increases the statistical confidence of detection. This simultaneous, large area signal detection sacrifices continuous spectral information at the cost of speed, reproducibility and minimising human error via automation of detection in the hyperspectral imaging technique presented here.

Shigeyuki Umezawa, Takashi Douura, Koji Yoshikawa, Daisuke Tanaka, Vlad Stolojan, S. Ravi P. Silva, Mika Yoneda, Kazuma Gotoh, Yasuhiko Hayashi (2023)Zinc-Based Metal-Organic Frameworks for High-Performance Supercapacitor Electrodes: Mechanism Underlying Pore Generation, In: Energy & environmental materials (Hoboken, N.J.)6(2) Wiley

Heat treatment of metal-organic frameworks (MOFs) has provided a wide variety of functional carbons coordinated with metal compounds. In this study, two kinds of zinc-based MOF (ZMOF), C16H10O4Zn (ZMOF1) and C8H4O4Zn (ZMOF2), were prepared. ZMOF1 and ZMOF2 were carbonized at 1000 degrees C, forming CZMOF1 and CZMOF2, respectively. The specific surface area (S-BET) of CZMOF2 was similar to 2700 m(2) g(-1), much higher than that of CZMOF1 (similar to 1300 m(2) g(-1)). A supercapacitor electrode based on CZMOF2 achieved specific capacitances of 360, 278, and 221 F g(-1) at 50, 250, and 1000 mA g(-1) in an aqueous electrolyte (H2SO4), respectively, the highest values reported to date for ZMOF-derived electrodes under identical conditions. The practical applicability of the CZMOF-based supercapacitor was verified in non-aqueous electrolytes. The initial capacitance retention was 78% after 100 000 charge/discharge cycles at 10 A g(-1). Crucially, the high capacitance of CZMOF2 arises from pore generation during carbonization. Below 1000 degrees C, pore generation is dominated by the Zn/C ratio of ZMOFs, as carbon atoms reduce the zinc oxides formed during carbonization. Above 1000 degrees C, a high O/C ratio becomes essential for pore generation because the oxygen functional groups are pyrolyzed. These findings will provide insightful information for other metal-based MOF-derived multifunctional carbons.

Jianguo Deng, Die Hu, Zizhao Zhang, Beibei Zong, Xiangxin Meng, Qing Sun, Bo Shen, Bonan Kang, S. Ravi P. Silva (2022)3-Aminobenzeneboronic acid self-assembled monolayer-modified ITO for efficient and stable OLED devices, In: Journal of alloys and compounds911 Elsevier B.V

Interface modification of indium tin oxide (ITO) is a hot research topic to obtain highly efficient and stable organic light-emitting diodes (OLEDs), and the key point is to improve the hole injection efficiency between the electrode and organic layer. In this study, we demonstrate an optimization strategy based on the use of 3-aminobenzeneboronic acid (3ABBA) for modifying ITO at the anode interface. The protonation reaction of boronic acid groups with oxides and hydroxyl groups forms a self-assembled monolayer (SAM). Since the ionization potential (IP) of 3ABBA-SAM is 5.44 eV, the hole injection barrier at the interface is minimized. Compared with a control device using PEDOT:PSS, the synergistic effects of the optimized 3ABBA-SAM significantly improves the maximum power efficiency (PEmax of 8.52 lm W−1) and maximum current efficiency (CEmax of 10.45 cd A−1) of the device, and the turn-on voltage is reduced by 0.2 V. In addition, effective interface modification reduces the hydrophilicity of the device and provides support for the stability of the OLED in the ambient environment. Therefore, we believe that a simple 3ABBA-SAM interface modification project can promote the development of high-performance and low-cost OLEDs. •The ITO interface modified by 3-Aminobenzeneboronic acid is reported for the first time.•The self-assembled monolayer reduces the hole injection barrier and promotes.•Compared with PEDOT:PSS as hole injection layer, the device shows better performance and lower cost.

Raheel Riaz, Bhaskar Dudem, Martina Costa Angeli, Ali Douaki, Mukhtar Ahmed, Mattia Petrelli, Abraham Mejia-Aguilar, Roberto Monsorno, S. Ravi P. Silva, Paolo Lugli, Luisa Petti (2021)Flexible, biocompatible, and ridged silicone elastomers based robust sandwich-type triboelectric nanogenerator, In: 2021 IEEE International Flexible Electronics Technology Conference (IFETC)pp. 0020-0022 IEEE

Energy harvesters for smart wearables are gaining increasing attention world-wide. Among the various type of options availabel, triboelectric nanogenerators harvesting mechanical energy from human body movements are especially attractive. In this work, a flexible sandwich-type triboelectric nanogenerator (FS-TENG) based on ridged and biocompatible silicone elastomers and thermoplastic polyurethane is proposed. The proposed FS- TENG exhibits the open-circuit voltages and maximum power density of ~80 volts and 0.35 mW/cm 2 , respectively. This preliminary performance already makes the device extremely promising to power low energy smart wearable devices, as well as monitor pressure in bespoke biomedical applications.

Thomas Pozegic, Simon King, Mohamad Fotouhi, Vlad Stolojan, S. Ravi P. Silva, Ian Hamerton (2019)Delivering Interlaminar Reinforcement in Composites through Electrospun Nanofibres, In: Advanced Manufacturing: Polymer & Composites Science5(4)pp. 155-171

Electrospun nonwoven veils comprising thermoplastic fibres (average diameter 400–600 nm) based on polysulfone (PSU), polyamide (PA-6,6), and polyetherimide (PEI) have been fabricated and used as interlaminar reinforcements in carbon fibre composites containing a commercial epoxy resin (8552/IM7). Samples were tested for their interlaminar properties and improvements were observed in the initial mode I interlaminar toughness of 30% (PA-6,6), 36% (PEI), and 44% (PSU), while improvements of 7% (PSU) and 8% (PEI) were observed in the propagation of the mode I interlaminar toughness. A reduction of 11% was observed for the propagation of the mode I interlaminar toughness for PA-6,6. Post-testing analysis of the cross-section and the fracture surface revealed that the crack front avoids the reinforcement significantly for PA-6,6. For mode II, however, this failure mechanism leads to improvements of 30% in interlaminar toughness for the PA-6,6, whereas the other reinforcements display negligible (PEI) and 31% reduction (PSU) interlaminar toughness.

Guilherme Kurz Maron, Jose Henrique Alano, Bruno da Silveira Noremberg, Lucas da Silva Rodrigues, Vlad Stolojan, S. Ravi P. Silva, Neftali Lenin Villarreal Carreno (2020)Electrochemical supercapacitors based on 3D nanocomposites of reduced graphene oxide/carbon nanotube and ZnS, In: Journal of alloys and compounds836 Elsevier

Carbon-based hybrid structures have attracted much attention due to their superior chemical, thermal, mechanical and electrical properties. A 3D sponge-like structure based on reduced graphene oxide/carbon nanotubes decorated with zinc sul fide synthetized by a hydrothermal micro-wave assisted synthesis (MHS) was produced and its chemical, structural, morphological and electrochemical properties evaluated as electrodes for supercapacitor devices. XRD con firmed the structure of the nano-composite, XPS was performed to examine the chemical state of the compounds. The morphology analysis realized by FESEM con firmed the success of the proposed methodology to produce the rGO/MWCNTf-ZnS nanocomposites revealing good homogeneity. The electrochemical properties were studied by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge. It was observed that the increase of MWCNTf-ZnS content increased the specific capacitance and reduced the resistivity of the 3D hybrid structure, reaching 95 F g(-1) , thus, approaching the ideal electric double layer storage capacitor behavior in samples containing MWCNTf-ZnS. (C) 2020 Elsevier B.V. All rights reserved.

M. Monti, J. Lloyd-Hughes, J. M. Woolley, E. Butler-Caddle, M. Staniforth, A. Wijesekara, R. M. I. Bandara, I. Jayawardena, S. R. P. Silva, R. A. Hatton (2019)Rapid Hot Carrier Relaxation and Mobility Increase in Sn- and Pb-Containing Halide Perovskite Semiconductors, In: 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)pp. 1-1 IEEE

The remarkable optoelectronic performance of metal halide perovskites has instigated fundamental research into their photophysics and photochemistry, including the fundamentals of light absorption and emission, and electrical transport. Recent studies have revealed unexpected hot carrier phenomena in metal halide perovskites, whereby at energies high above the band gap, and at high excitation intensities, long-lived hot carriers have been observed 1 which can undergo long-range transport. 2 This has opened the possibility of harvesting and exploiting hot carriers in semiconductor devices, for instance to overcome the Schockley-Queisser limit in photovoltaic cells.

M. Monti, J. Lloyd-Hughes, J. M. Woolley, E. Butler-Caddle, M. Staniforth, A. Wijesekara, R. M. I. Bandara, I. Jayawardena, S. R. P. Silva, R. A. Hatton (2019)Rapid Hot Carrier Relaxation and Mobility Increase in Sn- and Pb-Containing Halide Perovskite Semiconductors, In: 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)pp. 1-1 IEEE

The remarkable optoelectronic performance of metal halide perovskites has instigated fundamental research into their photophysics and photochemistry, including the fundamentals of light absorption and emission, and electrical transport. Recent studies have revealed unexpected hot carrier phenomena in metal halide perovskites, whereby at energies high above the band gap, and at high excitation intensities, long-lived hot carriers have been observed 1 which can undergo long-range transport. 2 This has opened the possibility of harvesting and exploiting hot carriers in semiconductor devices, for instance to overcome the Schockley-Queisser limit in photovoltaic cells.

Masaki Hada, Kotaro Makino, Hirotaka Inoue, Taisuke Hasegawa, Hideki Masuda, Hiroo Suzuki, Keiichi Shirasu, Tomohiro Nakagawa, Toshio Seki, Jiro Matsuo, Takeshi Nishikawa, Yoshifumi Yamashita, Shin-ya Koshihara, Vlad Stolojan, S. Ravi P. Silva, Jun-ichi Fujita, Yasuhiko Hayashi, Satoshi Maeda, Muneaki Hase (2020)Phonon transport probed at carbon nanotube yarn/sheet boundaries by ultrafast structural dynamics, In: Carbon (New York)170pp. 165-173 Elsevier

Modern integrated devices and electrical circuits have often been designed with carbon nanostructures, such as carbon nanotubes (CNTs) and graphene due to their high thermal and electrical transport properties. These transport properties are strongly correlated to their acoustic phonon and carrier dynamics. Thus, understanding the phonon and carrier dynamics of carbon nanostructures in extremely small regions will lead to their further practical applications. Here, we demonstrate ultrafast time-resolved electron diffraction and ultrafast transient spectroscopy to characterize the phonon and carrier dynamics at the boundary of quasi-one-dimensional CNTs before and after Joule annealing. The results from ultrafast time-resolved electron diffraction show that the CNTs after Joule annealing reach the phonon equilibrium state extremely fast with a timescale of 10 ps, which indicates that thermal transport in CNTs improves following Joule annealing. The methodology described in this study connects conventional macroscopic thermo- and electrodynamics to those at the nanometer scale. Realistic timescale kinetic simulations were performed to further elaborate on the phenomena that occur in CNTs during Joule annealing. The insights obtained in this study are expected to pave the way to parameterize the unexplored thermal and electrical properties of carbon materials at the nanometer scale. (C) 2020 Elsevier Ltd. All rights reserved.

Federico Bertagna, Rebecca Lewis, S. Ravi P. Silva, Johnjoe McFadden, Kamalan Jeevaratnam (2022)Thapsigargin blocks electromagnetic field-elicited intracellular Ca2+ increase in HEK 293 cells, In: Physiological reports10(9)pp. e15189-n/a Wiley

Biological effects of electromagnetic fields (EMFs) have previously been identified for cellular proliferation and changes in expression and conduction of diverse types of ion channels. The major effect elicited by EMFs seems to be directed toward Ca2+ homeostasis. This is particularly remarkable since Ca2+ acts as a central modulator in various signaling pathways, including, but not limited to, cell differentiation and survival. Despite this, the mechanisms underlying this modulation have yet to be unraveled. Here, we assessed the effect of EMFs on intracellular [Ca2+], by exposing HEK 293 cells to both radio-frequency electromagnetic fields (RF-EMFs) and static magnetic fields (SMFs). We detected a constant and significant increase in [Ca2+] subsequent to exposure to both types of fields. Strikingly, the increase was nulled by administration of 10 mu M Thapsigargin, a blocker of sarco/endoplasmic reticulum Ca2+-ATPases (SERCAs), indicating the involvement of the endoplasmic reticulum (ER) in EMF-related modulation of Ca2+ homeostasis.

Elizabeth J Legge, Muhammad M Ali, Hina Y Abbasi, Benjamen P Reed, Barry Brennan, Lidija Matjačić, Zari Tehrani, Vlad Stolojan, S Ravi P Silva, Owen J Guy, Andrew J Pollard (2021)Understanding the bonding mechanisms of organic molecules deposited on graphene for biosensing applications, In: The Journal of chemical physics155(17)pp. 174703-174703

Graphene is an ideal material for biosensors due to the large surface area for multiple bonding sites, the high electrical conductivity allowing for high sensitivity, and the high tensile strength providing durability in fabricated sensor devices. For graphene to be successful as a biosensing platform, selectivity must be achieved through functionalization with specific chemical groups. However, the device performance and sensor sensitivity must still be maintained after functionalization, which can be challenging. We compare phenyl amine and 1,5-diaminonaphthalene functionalization methods for chemical vapor deposition grown graphene, both used to obtain graphene modified with amine groups-which is required for surface attachment of highly selective antibody bio-receptors. Through atomic force microscopy (AFM), Raman spectroscopy, and time-of-flight secondary ion mass spectrometry imaging of co-located areas, the chemistry, thickness, and coverage of the functional groups bound to the graphene surface have been comprehensively analyzed. We demonstrate the modification of functionalized graphene using AFM, which unexpectedly suggests the removal of covalently bonded functional groups, resulting in a "recovered" graphene structure with reduced disorder, confirmed with Raman spectroscopy. This removal explains the decrease in the I /I ratio observed in Raman spectra from other studies on functionalized graphene after mechanical strain or a chemical reaction and reveals the possibility of reverting to the non-functionalized graphene structure. Through this study, preferred functionalization processes are recommended to maintain the performance properties of graphene as a biosensor.

Arijit Kayal, Harikrishnan G, K Bandopadhyay, Amit Kumar, S Ravi P Silva, J Mitra (2021)Controlling the macroscopic electrical properties of reduced graphene oxide by nanoscale writing of electronic channels, In: Nanotechnology32(17)pp. 175202-175202 IOP Publishing

The allure of all-carbon electronics stems from the spread of its physical properties across all its allotropes. The scheme also harbours unique challenges, such as tunability of band gap, variability of doping and defect control. Here, we explore the technique of scanning probe tip-induced nanoscale reduction of graphene oxide (GO), which nucleates conducting, sp 2 rich graphitic regions on the insulating GO background. The flexibility of direct writing is supplemented with control over the degree of reduction and tunability of band gap through macroscopic control parameters. The fabricated reduced GO channels and ensuing devices are investigated via spectroscopy and temperature and bias-dependent electrical transport and correlated with spatially resolved electronic properties, using surface potentiometry. The presence of carrier localization effects, induced by the phase-separated sp 2 sp 3 domains, and large local electric field fluctuations are reflected in the non-linear transport across the channels. Together, the results indicate a complex transport phenomenon, which may be variously dominated by tunnelling or variable range hopping or activated depending on the electronic state of the material.

J. V. Anguita, C. T. G. Smith, T. Stute, M. Funke, M. Delkowski, S. R. P. Silva (2020)Dimensionally and environmentally ultra-stable polymer composites reinforced with carbon fibres (vol 5, pg 531, 2019), In: Nature materials19(4)pp. 474-474 Springer Nature
Tianyu Yang, Ji Liang, Irin Sultana, Md Mokhlesur Rahman, Michael J. Monteiro, Ying (Ian) Chen, Zongping Shao, S. Ravi P. Silva, Jian Liu (2018)Formation of hollow MoS2/carbon microspheres for high capacity and high rate reversible alkali-ion storage, In: Journal of materials chemistry. A, Materials for energy and sustainability6(18)pp. 8280-8288 Royal Soc Chemistry

Nanocomposites of carbon and molybdenum disulfide have attracted much attention due to their significant potential in energy conversion and storage applications. However, the preparation of these 0-D MoS2/carbon composites with controllable structures and desirable properties remains a major manufacturing challenge, particularly at low cost suitable for scaling-up. Here, we report a facile solution-based method to prepare porous hierarchical 0-D MoS2/carbon nanocomposites with vertical MoS2 growth on a hollow carbon support, suitable for the electrochemical storage of lithium and sodium ions. The vertically aligned MoS2/hollow carbon material shows excellent performance in the storage of a series of alkali-metal ions (e.g. Li+, Na+, and K+) with high capacity, excellent rate capacity, and stable cyclability. When used for the storage of Li+ ions, it possesses a high capacity of over 800 mA h g(-1) at a rate of 100 mA g(-1), with a negligibly small capacity decay as low as 0.019% per cycle. At a substantially higher rate of 5 A g(-1), this MoS2/carbon nanocomposite still delivers a capacity of over 540 mA h g(-1), showing its excellent performance at high rates. Remarkably, this material uniquely delivers high capacities of over 450 mA h g(-1) and 300 mA h g(-1) for Na+ and K+ ion storage, respectively, which are among the highest values reported to date in the literature. These excellent characteristics confirm the hollow MoS2/carbon nanocomposites to be a primary contender for next generation secondary batteries.

Ash Stott, Mehmet O. Tas, Elaine Y. Matsubara, Mateus G. Masteghin, Jose M. Rosolen, Radu A. Sporea, S. Ravi P. Silva (2020)Exceptional rate capability from carbon‐encapsulated polyaniline supercapacitor electrodes, In: Energy & environmental materials (Hoboken, N.J.)3(3)pp. 389-397

A high‐rate capability carbon‐encapsulated polyaniline (PANI) composite is fabricated by a novel electrodeposition method of polyaniline on a carbon nanotube (CNT) forest, grown on carbon paper. This is followed by coating of an amorphous carbon layer via hydrothermal carbonization (HTC) of glucose, forming a three‐layer structure. We demonstrate that a slow scan rate, voltage‐restricted electrodeposition process can be used to produce a uniform PANI coating on individual CNTs throughout the network. The CNT forest structure offers excellent electronic and structural connection for the PANI nanofiber network, while the coating of amorphous carbon reduces electrode resistance, promoting enhanced electrochemical performance and reinforced structural stability during charging and discharging. The as‐prepared CNT/PANI/HTC composite exhibited a high specific capacitance of 571 F g−1 at 1 A g−1, and 557 F g−1 at 100 A g−1,whilst demonstrating a record rate capability of 98% capacitance retention, when the current density is increased 100‐fold. This advanced rate performance indicates that a slow electrodeposition process produces an electrochemically stable three‐layer composite with enhanced diffusion kinetics. Hence, the method developed in this work establishes further control on the electrochemical deposition of energy storage materials, for high‐rate capability. Carbon‐encapsulated PANI structures show an exceptional high‐rate capability of 98% for current density of 1 A g−1 to 100 A g−1. Low scan rate electrodeposition of PANI is used to synthesize conformal coatings on CNT forests, followed by a coating of an amorphous carbon layer, to enhance energy storage performance.

Iskandar Yahya, Muhammad Azuddin Hassan, Seri Mastura Mustaza, Huda Abdullah, Steven K. Clowes, S. Ravi P. Silva (2022)Performance Evaluation of CNTFETs Fabricated with Carbon Nanotubes of Different Synthesis Methods, In: INTERNATIONAL JOURNAL OF INTEGRATED ENGINEERING14(3)pp. 202-208 Univ Tun Hussein Onn Malaysia

Single walled carbon nanotubes (SWCNTs) exhibit extraordinary electronic properties that render it as an exciting candidate to be applied as the active channel of high-performance carbon nanotube field effect transistors (CNTFETs). The electronic properties of SWCNTs have been demonstrated to be dependent on the tube intrinsic properties that includes structural defects, chirality and diameter. Structural tube defects can be affected by the synthesis method and therefore the latter should also affect the device performance. Hence, this paper aims to present the influence of SWCNTs source synthesis method towards the resulting CNTFET device characteristics. A total of four SWCNT samples were sourced from different synthesis methods in fabricating CNTFETs. The synthesis methods are arc-discharge and three different variation of chemical vapor deposition (CVD) processes, which are DIPS, HiPco and CoMoCAT, respectively. Prior to fabrication, the SWCNT samples were characterized via Raman spectroscopy to quantify the tube defect levels of each sample, which are directly proportional to the G-peak to D-peak height ratio, G/D. Electrical characterization was carried out via 3-terminal field effect I-V measurement to evaluate key device performance parameters such as on-off current ratio, I-ON/T-OFF, transconductance, g(m), subthreshold slope, S-p and field effect mobility, mu(FE). Analysis shows that G/D affects the I-OFF more significantly relative to I-ON, resulting in increasing I-O(N)/I-OFF, and hence switching performance, when G/D increases. It is shown an increase of similar to 50% to the G/D of the SWCNT source resulted in similar to 860% increase in mu(FE). Based on the correlation between the optical analysis and electrical measurement, we conclude that the SWCNT growth method can significantly affect the CNTFET device performance.

Hashini M. Thirimanne, K. D. G. Imalka Jayawardena, Andrew Nisbet, Yonglong Shen, R. M. Indrachapa Bandara, Christopher A. Mills, Guosheng Shao, S. Ravi P. Silva (2020)Hybrid Multipixel Array X-Ray Detectors for Real-Time Direct Detection of Hard X-Rays, In: IEEE transactions on nuclear science67(10)pp. 2238-2245 IEEE

X-ray detectors currently employed in dosimetry suffer from a number of drawbacks including the inability to conform to curved surfaces and being limited to smaller dimensions due to available crystal sizes. In this study, a hybrid X-ray detector (HXD) has been developed which offers real-time response with added advantages of being highly sensitive over a broad energy range, mechanically flexible, relatively inexpensive, and able to be fabricated over large areas on the desired surface. The detector comprises an organic matrix embedded with high-atomic-number inorganic nanoparticles which increase the radiation attenuation and within the device allows for simultaneous transfer of electrons and holes. The HXD delivers a peak response of 14 nA cm(-2), which corresponds to a sensitivity of 30.8 mu C Gy(-1) cm(-2), under the exposure of 6-MV hard X-rays generated by a medical linear accelerator. The angular dependence of the HXD has been studied, which offers a maximum variation of 26% in the posterior versus lateral beam directions. The flexible HXD can be conformed to the human body shape and is expected to eliminate variations due to source-to-skin distance with reduced physical evaluation complexities.

Abdullah S. Alshammari, Mohammad R. Alenezi, S.R.P. Silva (2019)Excimer laser sintereing of silver nanoparticles electrodes for fully solution processed organic thin film transistors, In: Optics and laser technology120 Elsevier Ltd

•Excimer laser sintering of printed Ag nanoparticles electrodes was investigated.•Sintering process parameters were optimized to produce highly conductive electrodes.•The laser sintered Ag electrodes were utilized to fabricate high performance OTFTs.•Excimer laser is a promising alternative tool for metallic nanoparticles sintering. Printing and related processing technologies of electronic materials have become an essential part in the production of many components of today's electronics. Laser processing of metal based inks in particular has received a great attention and can eliminate the need of the conventional high temperature sintering methods. Here, silver nanoparticles ink was printed using a drop on demand (DOD) printer and cured to produce highly conductive silver patterns. The printed silver nanoparticles were sintered using excimer laser and thermal treatment. The effects of curing parameters such as energy density, scan speed and annealing temperature on the surface morphology and electrical performance of the inkjet printed structures were investigated. The results revealed strong dependence of the morphology and electrical performance of the printed samples on the process parameters namely the laser fluence and the scanning speed. The production of discontinuous samples and laser ablation of silver sintered patterns at some treatment stages were also noticed. Moreover, using optimized sintering conditions, highly conductive patterns similar to those thermally treated were produced. The printed conductive patterns were then successfully utilized as S/D electrodes for organic thin film transistors. The fully solution processed transistors with printed silver electrodes exhibited excellent ohmic contact characteristics with mobility and on/off ratio in the range of 10−2 cm2/V·s and 103, respectively. The results indicate that, in addition to the various material processing uses, excimer laser can also be used as a sintering tool for printed metallic nanoparticles in the roll-to-roll manufacturing processes.

S. Ravi P. Silva (2021)EDITORIAL: Now is the Time for Energy Materials Research to Save the Planet, In: Energy & environmental materials (Hoboken, N.J.)4(4)pp. 497-499 Wiley
Anna A. Iurchenkova, Egor V. Lobiak, Anna A. Kobets, Alexey N. Kolodin, Ash Stott, S. Ravi P. Silva, Ekaterina O. Fedorovskaya (2021)A complex study of the dependence of the re duce d graphite oxide electrochemical behavior on the annealing temperature and the type of electrolyte, In: Electrochimica acta370 Elsevier

In this work we investigate the influence of thermal treatment of reduced graphite oxide (RGO) on its functional composition and electrochemical performance. It is found that carboxyl, carbonyl, hydroxyl and epoxy groups are present on the RGO surface, witch when subject to thermal annealing in the temperature range 230-250 degrees C can be controllably modified. In the process of thermal annealing, we show the formation of quinoid groups due to an increase in the number of defects. Decrease of the number of layers in RGO material and the quantity of oxygen-containing functional groups (OCFG) also occurs. With increase in annealing temperature, sequential removal of OCFG occurs as follows: carboxyl (250 degrees C-600 degrees C), hydroxyl (600 degrees C-800 degrees C), carbonyl and quinoid (700 degrees C-1000 degrees C). Electrochemical measurements over a wide range of pH values of the buffer electrolytes is possible to correlate the peaks in the cyclic voltammogram curves with the redox reactions of oxygen-containing functional groups as a function of applied potential. Peaks correlated with specific redox reactions which are identified as two-electron. The dependence of the specific capacities of materials on the electrolyte type has been studied. Highest capacitance was detected in 1M NaOH at a scan rate 2 mVs(-1) and is equal to 210 Fg(-1). (C) 2021 Elsevier Ltd. All rights reserved.

K. N. Prajapati, Ben Johns, K. Bandopadhyay, S. Ravi P. Silva, J. Mitra (2020)Interaction of ZnO nanorods with plasmonic metal nanoparticles and semiconductor quantum dots, In: The Journal of chemical physics152(6)pp. 064704-064704 Amer Inst Physics

We model the enhancement of near band edge emission from ZnO nanorods using plasmonic metal nanoparticles and compare it with emission enhancement from ZnO with semiconducting quantum dots. Selected CdSe quantum dots with absorption energies close to those of Ag and Au nanoparticles are chosen to construct model systems with ZnO to comprehend the role of ZnO's intrinsic defects and plasmonic excitation in realizing the spectrally selective luminescence enhancement. Excitation wavelength dependent photoluminescence spectra along with theoretical models quantifying the related transitions and plasmonic absorption reveal that a complex mechanism of charge transfer between the ZnO nanorods and metal nanoparticles or quantum dots is essential along with an optimal energy band alignment for realizing emission enhancement. The theoretical model presented also provides a direct method of quantifying the relative transition rate constants associated with various electronic transitions in ZnO and their change upon the incorporation of plasmonic nanoparticles. The results indicate that, while the presence of deep level defect states may facilitate the essential charge transfer process between ZnO and the plasmonic nanoparticles, their presence alone does not guarantee UV emission enhancement and strong plasmonic coupling between the two systems. The results offer clues to designing novel multicomponent systems with coupled plasmonic and charge transfer effects for applications in charge localization, energy harvesting, and luminescence enhancement, especially in electrically triggered nanophotonic applications. Published under license by AIP Publishing.

MAHESHANI PRABODHI ALWIS NANAYAKKARA, MATEUS GALLUCCI MASTEGHIN, Laura Basiricò, Ilaria Fratelli, Andrea Ciavatti, Rachel Kilbride, Sandra Jenatsch, THOMAS WEBB, FILIPE MASUCH RICHHEIMER, Sebastian Wood, Fernando A. Castro, Andrew J. Parnell, Beatrice Fraboni, IMALKA JAYAWARDENA, S RAVI PRADIP SILVA (2021)Molecular weight tuning of organic semiconductors for curved organic-inorganic hybrid X-ray detectors, In: Advanced Science Wiley

Curved X-ray detectors have the potential to revolutionise diverse sectors due to benefits such as reduced image distortion and vignetting compared to their planar counterparts. While the use of inorganic semiconductors for curved detectors are restricted by their brittle nature, organic-inorganic hybrid semiconductors which incorporated bismuth oxide nanoparticles in an organic bulk heterojunction consisting of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) are considered to be more promising in this regard. However, the influence of the P3HT molecular weight on the mechanical stability of curved, thick X-ray detectors remains less well understood. Herein, high P3HT molecular weights (>40 kDa) are identified to allow increased intermolecular bonding and chain entanglements, resulting in X-ray detectors that can be curved to a radius as low as 1.3 mm with low deviation in X-ray response under 100 repeated bending cycles while maintaining an industry-standard dark current of

MICHAEL GEORGE SPENCER, Marco SACCHI, JEREMY ALLAM, S. Ravi P. Silva (2022)Resonant Quenching of Photoluminescence in Porphyrin ? Nanocarbon Agglomerates, In: Cell reports physical science Elsevier

By adopting structural conformations with sub-nanometer precision, nature creates highly concentrated pigment-protein arrays to capture solar energy with high-efficiency. Synthetic analogues of such systems exhibit concentration dependent fluorescence quenching when approaching pigment concentrations of that seen in biological systems. Here we report on systems of acid functionalised multi-walled carbon nanotubes (o-MWCNT) and aminophenyl tetraporphyrins that create a novel synthetic pigment-scaffold complex. The complex does not follow the trend of typical fluorescence quenching. Our steady-state and time-resolved data suggest an optimal concentration that offers a luminescence enhancement compared to the expected standard Stern-Volmer quenching relationship. The quenching is modified by controlling 1 the pigment-distance via agglomerate size to near the upper limit for Dex-ter transfer of 10Å10˚10Å as confirmed by dynamic light scattering measurements and chromophore-chromophore nearest neighbour calculations. Our results highlight a potential synthetic complex with facile synthesis to investigate resonant electron transfer processes that do not follow traditional luminescence self-quenching relationships.

Bhaskar Dudem, Sontyana Adonijah Graham, R.D. Ishara G Dharmasena, S. Ravi P Silva, Jae Su Yu (2021)Natural silk-composite enabled versatile robust triboelectric nanogenerators for smart applications, In: Nano energy83105819 Elsevier

Strategies to maximize the surface charge density across triboelectric layers while protecting it from humidity are crucial in employing triboelectric nanogenerators (TENGs) for commercial/real-time applications. Herein, for the first time, we propose the utility of crystalline silk microparticles (SMPs) to improve the surface charge density in materials like polyvinyl alcohol to realise its applicability for TENG devices. Moreover, these SMPs are extracted from discarded Bombyx mori silkworm cocoons by facile, inexpensive, and single-step alkaline-hydrolysis treatment. We examine the performance of these composites with counter-materials composed of waste PTFE plastic cups to show reuse in recycled products. The processing cost of TENG developed from recycled materials is not only low but eco-friendly. The TENG performance as a function of the concentration of SMPs is investigated and compared with the composite's work-function and surface-potentials, with the distance-dependent electric field theoretical model employed to optimize the performance. Consequently, the optimized TENG exhibits maximum output voltage, current, charge, and power density of ∼280 V, 17.3 μA, 32.5 nC, and 14.4 W·m−2, respectively, creating a highly competitive energy harvester that can conform to the rigorous needs of wearables and mobile applications. Furthermore, the fully packaged silicone rubber device protects it from humidity and enables the device utility for practical applications with a soft, comfortable, and skin-friendly interface.

Christopher T. G. Smith, Michal Delkowki, Jose V. Anguita, David C. Cox, Catherine Haas, S. Ravi P. Silva (2021)Complete Atomic Oxygen and UV Protection for Polymer and Composite Materials in a Low Earth Orbit, In: ACS Applied Materials and Interfaces13(5)pp. 6670-6677 American Chemical Society

With the realization of larger and more complex space installations, an increase in the surface area exposed to atomic oxygen (AO) and ultraviolet (UV) effects is expected, making structural integrity of space structures essential for future development. In a low Earth orbit (LEO), the effects of AO and UV degradation can have devastating consequences for polymer and composite structures in satellites and space installations. Composite materials such as carbon fiber-reinforced polymer (CFRP) or polymer materials such as polyetherimide and polystyrene are widely used in satellite construction for various applications including structural components, thermal insulation, and importantly radio frequency (RF) assemblies. In this paper, we present a multilayered material protection solution, a multilayered protection barrier, that mitigates the effects of AO and UV without disrupting the functional performance of tested assemblies. This multilayered protection barrier deposited via a custom-built plasma-enhanced chemical vapor deposition (PECVD) system is designed so as to deposit all necessary layers without breaking vacuum to maximize the adhesion to the surface of the substrate and to ensure no pinhole erosion is present. In the multilayer solution, a moisture and outgassing barrier (MOB) is coupled with an AO and UV capping layer to provide complete protection.

James R. Clark, Ying Chen, Steven Hinder, S. Ravi P. Silva (2017)Highly Sensitive Dopamine Detection Using a Bespoke Functionalised Carbon Nanotube Microelectrode Array, In: Electroanalysis29(10)pp. 2365-2376 Wiley

Understanding how the brain works requires developing advanced tools that allow measurement of bioelectrical and biochemical signals, including how they propagate between neurons. The introduction of nanomaterials as electrode materials has improved the impedance and sensitivity of microelectrode arrays (MEAs), allowing high quality recordings of single cells insitu using electrode diameters of

Simon G. King, Liam McCafferty, Mehmet O. Tas, Kaspar Snashall, Jeng Shiung Chen, Maxim Shkunov, Vlad Stolojan, S. Ravi P. Silva (2020)Low-Cost Catalyst Ink for Simple Patterning and Growth of High-Quality Single- and Double-Walled Carbon Nanotubes, In: ACS Applied Materials and Interfaces12(10)pp. 11898-11906 American Chemical Society

Research into carbon nanotubes (CNTs) has been a hot topic for almost 3 decades, and it is now that we are beginning to observe the impact of advanced applictions of this nanomaterial in areas such as electronics. Currently, in order to mass produce CNT devices, either large-scale synthesis, followed by numerous energy-intensive processing steps or photolithography processes, including several sputter-deposition steps, are required to pattern this material to fabricate functional devices. In the work reported here, through the utilization of a universal catalyst precursor (cyclopentadienyl iron dicarbonyl dimer) and the optimization of solution parameters, patterned high-quality vertically aligned arrays of single- and few-walled CNTs have been synthesized via various inexpensive, commercially scalable methods such as inkjet printing, stamp printing, spray painting, and even handwriting. The two-step process of precursor printing, followed immediately by CNT growth, results in CNTs with a Raman I-D/I-G ratio of 0.073, demonstrating very high-quality nanotubes. This process eliminates time-consuming and costly CNT post processing techniques or the deposition of numerous substrate barrier and catalyst layers to achieve device manufacturing. As a result, this method has the potential to provide a route for the large-scale synthesis of high-quality single- and few-walled CNTs that can be applied in industrial settings.

LYNN TUMILTY, M. Prabodhi A. Nanayakkara , Lidija Matjačić , Sebastian Wood, Filipe Richheimer , Fernando A. Castro, Sandra Jenatsch, Simon Züfle, Rachel Kilbride, Andrew J. Parnell, Mateus G. Masteghin, Hashini M. Thirimanne, Andrew Nisbet, K. D. G. Imalka Jayawardena, S. Ravi P. Silva (2020)Ultra-Low Dark Current Organic-Inorganic Hybrid X-Ray Detectors, In: Advanced functional materials2008482 Wiley
R. D. I. G. Dharmasena, K. D. G. I. Jayawardena, Zakaria Saadi, Xuhui Yao, R. M. I. Bandara, Yunlong Zhao, S. Ravi P. Silva (2019)Energy Scavenging and Powering E-Skin Functional Devices, In: Proceedings of the IEEE107(10)pp. 2118 - 2136 Institute of Electrical and Electronics Engineers (IEEE)

Electronic skins (e-skins), which can seamlessly adapt and adhere to the body to mimic the functionality of human skin, are a rapidly emerging research area. Such e-skins have the potential to revolutionize artificial prosthetics, robotics, human-machine interfacing, and health monitoring applications. Powering the e-skin is a critical challenge at present due to strict performance criteria, including flexibility, stretchability, mobility, and autonomous operation. One of the most promising approaches to overcome some of these challenges is to scavenge energy from the human body's movements and its surrounding environment. This paper outlines some of the key potential developments that enable energy harvesting through mechanical, thermal affects, and low light sources, as well as energy management and storage technologies, which could lead toward the construction of autonomous e-skin modules and self-powered sensing systems.

José V. Anguita, TR Pozegic, Muhammad Ahmad, S. Ravi P. Silva (2021)Layer-by-Layer Growth of Graphene Sheets over Selected Areas for Semiconductor Device Applications, In: ACS Applied Nano Materials4(5)pp. 5211-5219 American Chemical Society

We report an in situ imaging method and use it to reveal the mechanism for the formation of extended size sheets of graphene (carpets) in few-layer graphene using the solid-state process, taking place via a layer-by-layer growth mechanism, which can result in a stack of separate individual layers of graphene. This mechanism is revealed by an imaging method that allows the use of conventional (unmodified) scanning electron microscopy to image graphene growth in situ and in real time. With this dynamic imaging, we reveal for the first time the dynamics of flake nucleation and growth and show the dynamics of flake coalescence to form extended size polycrystalline graphene carpets, allowing one to deduce a growth model. This growth method produces graphene flakes with Raman spectral characteristics that closely resemble those from exfoliated flakes obtained using the “Scotch-tape” method. The material is highly electronically intrinsic, with I 2D/I G ratios as high as 5. The kinetics of electronic interconnectivity between flakes during blanket formation is imaged dynamically using a doping level contrast in an electron microscope in real time. Furthermore, the observations reveal that it is possible to maximize the time between the formation of each individual blanket, up to several minutes, thus facilitating the production of multiple decoupled graphene layers of precise thickness. This allows one to control the number of layers produced even when using catalysts of high activity and high-carbon solubility such as Fe.

Ankit Kumar Singh, Nandita Jaiswal, Ida Tiwari, Muhammad Ahmad, S. Ravi P. Silva (2023)Electrochemical biosensors based on in situ grown carbon nanotubes on gold microelectrode array fabricated on glass substrate for glucose determination, In: Mikrochimica Acta190(55) Springer

We herein report a highly sensitive electrochemical sensor for glucose detection using carbon nanotubes grown in-situ at low temperatures on photolithographically defined gold microelectrode arrays printed on glass substrate (CNTs/Au MEA). One of the main advantages of the present design is its potential to monitor 64 samples individually for the detection of glucose. The selectivity of the fabricated MEA towards glucose detection is dramatically maintained via modification of CNTs/Au MEA by immobilizing glucose oxidase (GOx) enzyme in the matrix of poly (paraphenylenediamine) (GOx/poly (p-PDA)/CNTs/Au MEA). The electrocatalytic and electrochemical response of the proposed sensing platform towards glucose determination were examined via cyclic voltammetry and electrochemical impedance spectroscopy. The developed impedimetric biosensor exhibits a good linear response towards glucose detection i.e., 0.2-27.5 µM with sensitivity and detection limits of 168.03 kΩ-1M-1 and 0.2 ± 0.0014 μM, respectively. The proposed glucose biosensor shows excellent reproducibility, good anti-interference property and was successfully tested in blood serum samples. Further, applicability of the proposed sensor was successfully validated through HPLC. These results supported the viability of using such devices for the simultaneous detection of multiple electroactive biomolecules of physiological relevance.

Ioannis Vangelidis, Anna Theodosi, MJ Beliatis, KK Gandhi, Argiris Laskarakis, Panos Patsalas, S Logothetidis, S. Ravi P. Silva, Elefterios Lidorikis (2018)Plasmonic Organic Photovoltaics: Unraveling Plasmonic Enhancement for Realistic Cell Geometries, In: ACS photonics5(4)pp. 1440-1452 American Chemical Society

Incorporating plasmonic nanoparticles in organic photovoltaic (OPV) devices can increase the optical thickness of the organic absorber layer while keeping its physical thickness small. However, trade-offs between various structure parameters have caused contradictions regarding the effectiveness of plasmonics in the literature, that have somewhat stunted the progressing of a unified theoretical understanding for practical applications. We examine the optical enhancement mechanisms of practical PCDTBT:PC70BM OPV cells incorporating metal nano particles. The plasmonic near- and far-field contributions are differentiated, with spectrum- and space-wide current enhancements found in the plasmon scattering regime and spectrum- and space-specific current enhancements in the near-field regime. A remarkable system complexity is revealed, where the plasmonic enhancement trends change and even reverse by simple changes in the device geometry. This accounts for many of the contradictory results published in the literature on plasmonic effects in OPVs. By exploring the full structural parameter phase-space we are able to now propose a unified representation that intuitively explains literature findings and trends. Our results show that an already optimized PCDTBT:PC70BM cell can be further optically enhanced by plasmonic effects by at least 20% with the incorporation of Ag nanoparticles.

Michal Delkowski, José Virgilio Anguita, Christopher Toby Gibb Smith, S. Ravi P. Silva (2023)Multifunctional Nanostructures with Controllable Band Gap Giving Highly Stable Infrared Emissivity for Smart Thermal Management, In: ACS Nano American Chemical Society

Thermal control is essential to guarantee the optimal performance of most advanced electronic devices or systems. In space, orbital satellites face the issues of high thermal gradients, heating, and different thermal loads mediated by differential illumination from the Sun. Todaýs state-of-the-art thermal control systems provide protection; however, they are bulky and restrict the mass and power budgets for payloads. Here, we develop a lightweight optical superlattice nanobarrier structure to provide a smart thermal control solution. The structure consists of a moisture and outgassing physical barrier (MOB) coupled with atomic oxygen (AO)-UV protection functionality. The nanobarrier exhibits transmission and reflection of light by controlling the optical gap of individual layers to enable high infrared emissivity and variable solar absorptivity (minimum Δα = 0.30) across other wavelengths. The multifunctional coating can be applied to heat-sensitive substrates by means of a bespoke room-temperature process. We demonstrate enhanced stability, energy-harvesting capability, and power savings by facilitating the radiation cooling and facility for active self-reconfiguration in orbit. In this way, the reduction of the operating temperature from ∼120 to ∼60 °C on space-qualified and nonmechanically controlled composite structures is also demonstrated.

Yuren Xiang, Yameng Cao, Wenqiang Yang, Rui Hu, Sebastian Wood, Bowei Li, Qin Hu, Fan Zhang, Jujie He, Mozhgan Yavari, Jinlai Zhao, Yunlong Zhao, Jun Song, Junle Qu, Rui Zhu, Thomas P Russell, S. Ravi P Silva, Wei Zhang (2021)Laser‐induced recoverable fluorescence quenching of perovskite films at a microscopic grain‐scale, In: Energy & environmental materials (Hoboken, N.J.) Wiley

Understanding the fundamental properties of metal halide perovskite materials is driving the development of novel optoelectronic applications. Here, we report the observation of a recoverable laser-induced fluorescence quenching phenomenon in perovskite films with a microscopic grain-scale restriction, accompanied by spectral variations. This fluorescence quenching depends on the laser intensity and the dwell time under Auger recombination dominated conditions. These features indicate that the perovskite lattice deformation may take the main responsibility for the transient, show a new aspect to understand halide perovskite photo-stability. We further modulate this phenomenon by adjusting the charge carrier recombination and extraction, revealing that efficient carrier transfer can improve the bleaching resistance of perovskite grains. Our results provide future opportunities to attain high-performance devices by tuning the perovskite lattice disorder and harvesting the energetic carriers.

Bowei Li, Victoria Ferguson, S. Ravi P. Silva, Wei Zhang (2018)Defect Engineering towards Highly Efficient and Stable Perovskite Solar Cells, In: Advanced Materials Interfaces5(22)1800326 Wiley

Metal halide perovskite solar cells are emerging candidates amongst the next-generation thin-film photovoltaic devices with extremely low fabrication cost and high power conversion efficiency. Defects (both in the bulk material and at the interfaces) are recognized as one of the most fundamental reasons for the compromised device performance and long-term stability of perovskite solar cells. In this review article, the authors analyze the possible origins of the defects formation in metal halide perovskites, followed by the rationalization of various approaches being utilized to reduce the density of defects. The authors demonstrate that defect engineering, including adding dopants in the precursor solutions, interface passivation, or other physical treatments (thermal or light stress), is an essential way to further boost the device performance and enhance their long-term stability. The authors note that although the exact mechanisms of defect elimination in some approaches are yet to be elucidated, the research on defect engineering is expected to have enormous impact on next wave of device performance optimization of metal halide perovskite solar cells toward Shockley–Queisser limit.

Shuai Huang, YS TANG, Yang Dang, Xu Xu, Qingfeng Dong, B Kang, S. Ravi P. Silva (2018)Low-Temperature Solution-Processed Mg:SnO2 Nanoparticles as an Effective Cathode Interfacial Layer for Inverted Polymer Solar Cell, In: ACS sustainable chemistry & engineering6(5)pp. 6702-6710 American Chemical Society

An efficient inverted polymer solar cell (PSC)-based on bulk heterojunction composites of poly(3-hexylthiophene) (P3HT) and phenyl C-61-butryricacid methyl ester (PCBM) has been demonstrated by incorporating facile low temperature solution -processed Mg-doped SnO2 (Mg:SnO2) nanoparticles as the cathode interfacial layer. Compared to the pure SnO2, the PSCs based on Mg:SnO2 interfacial layer exhibits excellent properties with a power conversion efficiency (PCE) of up to 4.08%, increased from 2.77%, corresponding to a significant 47.29% PCE enhancement. The improved photovoltaic performance is ascribed to the increased electron mobility, elevated electrical conductivity and optimized surface morphology, which makes it an excellent growth platform for a flat and high quality photoactive layer. Furthermore, we show the Mg:SnO2 interfacial layers to dramatically improve the electron extraction and effectively suppress the photogenerated carrier recombination. The low-temperature solution-processed SnO2 with Mg doping is proposed as ideal interfacial contender for PSCs and other organic electronic devices requiring electron transport layers.

Yang Dang, S Shen, Yunhe Wang, Xiangwei Qu, Shuai Huang, Qingfeng Dong, S. Ravi P. Silva, B Kang (2018)Hole Extraction Enhancement for Efficient Polymer Solar Cells with Boronic Acid Functionalized Carbon Nanotubes doped Hole Transport Layers, In: ACS sustainable chemistry & engineering6(4)pp. 5122-5131 American Chemical Society

Boronic acid functionalized multiwalled carbon nanotubes (bf-MWCNTs) were synthesized via a facile low temperature process and introduced in PEDOT:PSS as the composite hole transport layer (HTL), which improved the power conversion efficiency (PCE) of polymer solar cells (PSCs). The devices utilized PCDTBT:PC71BM active layers had achieved an optimal PCE of 6.953%, leading to 28% enhancement comparing to the device based on pristine PEDOT:PSS HTL. The PEDOT:PSS:bf-MWCNTs composite HTLs exhibited remarkable enhancement on hole mobility and electrical conductivity, which were beneficial to the hole extraction and transport on interface. Meanwhile, the work function (WF) of HTLs had an increase after bf-MWCNTs doping, which was matched with the highest occupied molecular orbital (HOMO) of the donor material, further improving the hole transport. Therefore, the incorporation of bf-MWCNTs efficiently improved the hole extraction and transport from active layer to the electrode.

Cameron C. L Underwood, J. David Carey, S. Ravi P Silva (2021)Nonlinear Band Gap Dependence of Mixed Pb–Sn 2D Ruddlesden–Popper PEA2Pb1–x Sn x I4 Perovskites, In: The Journal of Physical Chemistry Letters12(5)pp. 1501-1506 American Chemical Society

Two-dimensional (2D) Ruddlesden–Popper perovskites (RPPs) of the form PEA2Pb1–x Sn x I4 can be used as the tunable active layer in photovoltaics, as the passivating layer for 3D perovskite photovoltaics or in light emitting diodes. Here, we show a nonlinear band gap behavior with Sn content in mixed phase 2D RPPs. Density functional theory calculations (with and without spin–orbit coupling) are employed to study the effects of the short-range ordering of Pb and Sn in PEA2Pb1–x Sn x I4 compositions with x = 0, 0.25, 0.5, 0.75, and 1. Analysis of the partial density of states shows that the energy mismatch of the Pb 6s and Sn 5s states in the valence band maximum determines the nonlinearity of the band gap, leading to a bowing parameter of 0.35–0.38 eV. This research provides a critical insight for the design of future metal alloy 2D perovskite materials. The positions of the tunable energy band discontinuity may point to intraband transitions of interest to device engineers.

S. O. Adeyemo, S Kar, SHASHINI MANOORI SILVA, IMALKA JAYAWARDENA, S. Ravi P. Silva, H. J. Joyce High Charge Carrier Mobilities and Long Diffusion Lengths in Tin Based Metal Halide Perovskite

Tin (Sn)-based perovskites are promising for lower band gap and tandem solar cells due to their red-shifted band gap towards the infrared region. However, Sn based hybrid metal halide perovskite is well known to suffer rapid photoconductivity decay due to the oxidation of Sn 2+ to Sn 4+ under atmospheric oxygen. Here, the charge carrier dynamics of tin based metal halide perovskite is investigated using optical pump-terahertz probe (OPTP) spectroscopy. Also, the performance of the perovskite films at different annealing temperatures is compared and the best performing temperature is identified. The Sn based perovskite films exhibited a remarkable charge carrier mobility and diffusion length.

GY Chen, Vlad Stolojan, David Cox, C Giusca, S Silva (2006)Growth of tungsten oxide nanowires using simple thermal heating, In: 2006 IEEE Conference on Emerging Technologies - Nanoelectronicspp. 376-378

Tungsten oxide nanowires are grown directly on tungsten wires and plates using thermal heating in an acetylene and nitrogen mixture. By heating the tungsten in nitrogen ambient, single crystal tungsten oxide nanowires can be synthesized via a self-assembly mechanism. It was found that the yield can be significantly increased with the addition of acetylene, which also results in thinner nanowires, as compared to nanowires synthesized in an oxidizing ambient. The tungsten oxide nanowires are 5 to 15 nm in diameter and hundreds of nanometers in length. In some cases, the use of acetylene and nitrogen process gas would result in tungsten oxide nanowires samples that appear visually,transparent. Comparison of the growth using the acetylene/nitrogen or then air/nitrogen mixtures is carried out. A possible synthesis mechanism, taking into account the effect of hydrocarbon addition is proposed.

DC Cox, V Stolojan, G Chen, SR Silva, AG Cullis, PA Midgley (2008)In situ Observation of the Growth of Tungsten Oxide Nanostructures, In: MICROSCOPY OF SEMICONDUCTING MATERIALS 2007120pp. 277-280
GY Chen, CHP Poa, Vlad Stolojan, S Silva (2006)Novel approach to low substrate temperature synthesis of carbon nanotubes, In: 2006 IEEE Conference on Emerging Technologies - Nanoelectronicspp. 254-257

We present a novel approach, which will potentially allow for low-temperature-substrate synthesis of carbon nanotubes using direct-current plasma-enhanced chemical vapour deposition. The approach utilizes top-down plasma heating rather than conventional heating from a conventional substrate heater under the electrode. In this work, a relatively thick titanium layer is used as a thermal barrier to create a temperature gradient between the Ni catalyst surface and the substrate. We describe the growth properties as a function of the bias voltage and the hydrocarbon concentrations. The heating during growth is provided solely by the plasma, which is dependent only on the process conditions, which dictate the power density and the cooling of the substrate, plus now the thermal properties of the "barrier layer". This novel approach of using plasma heating and thermal barrier allows for the synthesis of carbon nanotubes at low substrate temperature conditions to be attained with suitable cooling schemes.

Giulio Ruffini, Stephen Dunne, Esteve Farres, Paul C P Watts, Ernest Mendoza, S Ravi P Silva, Carles Grau, Josep Marco-Pallares, Lluis Fuentemilla, Bjorn Vandecasteele (2006)ENOBIO - First Tests of a Dry Electrophysiology Electrode Using Carbon Nanotubes

We describe the development and first tests of ENOBIO, a dry electrode sensor concept for biopotential applications. In the proposed electrodes the tip of the electrode is covered with a forest of multi-walled Carbon Nanotubes (CNTs) that can be coated with Ag/AgCl to provide ionic–electronic transduction. The CNT brushlike structure is to penetrate the outer layers of the skin improving electrical contact as well as increase the contact surface area. In this paper we report the results of the first tests of this concept—immersion on saline solution and pig skin signal detection. These indicate performance on a par with state of the art researchoriented wet electrodes.

JD Carey, Simon Henley, E Mendoza, CE Giusca, AADT Adikaari, S Silva (2004)Formation of three dimensional Ni nanostructures for large area catalysts, In: DP Taylor, J Liu, D McIlroy, L Merhari, JB Pendry, JT Borenstein, P Grodzinski, LP Lee, ZL Wang (eds.), NANOENGINEERED ASSEMBLIES AND ADVANCED MICRO/NANOSYSTEMS820pp. 357-362

The formation of Ni nanostructures to act as catalysts in the growth of carbon nanotubes is reported. The changes in the surface morphology of Ni produced by three methods - thermal evaporation and annealing of thin films, pulsed laser ablation and annealing of Ni, and the use of metal containing macromolecules - have been investigated by atomic force microscopy and scanning electron microscopy. In the case of thermal annealing of thin metal films in the temperature range 300-500oC we observe an increase in the mean diameter of the islands formed, accompanied by a reduction in the mean island density with increasing temperature. We attribute this effect to mass transport of weakly bound individual Ni atoms and/or small island clusters across the surface to form larger isolated islands, in a process similar to Ostwald ripening. Using a pulsed KrF excimer laser for ablation of a Ni target we show that nanometre smooth Ni thin films can be produced provided a sufficient number of laser shots is used. The surface morphology of these smooth films can then be altered by laser annealing to form Ni droplets. It is found that the mean diameter of the Ni droplets depends not only on the initial Ni thickness but also the laser fluence. It is also found that the nanostructuring of the film depends on the presence of an oxide under layer, with a higher fluence required on thinner oxides and no nanostructuring observed on bare Si. Finally, we show that Ni nanostructuring can be formed by suitable annealing of a Ni containing aqueous dendrimer solutions.

R. C. Smith, JD Carey, C. H. P. Poa, D. C. Cox, S. R. P. Silva (2004)Electron field emission from room temperature grown carbon nanofibers, In: Journal of Applied Physics95pp. 3153-3157

The observation of field induced electron emission from room temperature grown carbon nanofibers at low (5 V/µm) macroscopic electric fields is reported. The nanofibers were deposited using methane as a source gas in a conventional rf plasma enhanced chemical vapor deposition reactor using a Ni metal catalyst previously subjected to an Ar plasma treatment. Analysis of the scanning electron microscopy images of the nanofibers show them to possess an average diameter of 300 nm and that the nanofibers are observed to be radially dispersed over an area of 50 µm in diameter. No evidence of hysteresis in the current-voltage characteristic or conditioning of the emitters is observed. The mechanism for emission at low fields is attributed to field enhancement at the tips rather than from the surrounding amorphous carbon film which is shown to have a higher threshold field (20 V/µm) for emission.

S. J. Henley, JD Carey, S. R. P. Silva (2004)Room temperature photoluminescence from nanostructured amorphous carbon, In: Applied Physics Letters85pp. 6236-6238

Visible room-temperature photoluminescence (PL) was observed from hydrogen-free nanostructured amorphous carbon films deposited by pulsed laser ablation in different background pressures of argon (PAr). By varying PAr from 5 to 340 mTorr, the film morphology changed from smooth to rough and at the highest pressures, low-density filamentary growth was observed. Over the same pressure regime an increase in the ordering of sp2 bonded C content was observed using visible Raman spectroscopy. The origin of the PL is discussed in terms of improved carrier localization within an increased sp2 rich phase.

RC Smith, JD Carey, DC Cox, SRP Silva (2007)In-situ field emission characterisation of multi walled carbon nanotubes, In: Technical Digest of the 20th International Vacuum Nanoelectronics Conference, IVNC 07pp. 94-95
R. C. Smith, JD Carey, S. R. P. Silva (2004)Simulation of field enhancement effects in carbon nanotubes, In: Technical Digest of the 17th International Vacuum Nanoelectronics Conference, 2004

Simulations of electric field enhancement factor, beta, for isolated metallic carbon nanotubes (CNT) are reported. We show that beta is dependent not only on the geometry of the tubes, but also on the location of the anode electrode. We also highlight the effect of field screening due to boundary conditions of the simulation package. Finally, we give an expression for beta as a function of CNT height, radius, and anode to cathode separation.

We report prediction of selected physical properties (e.g. glass transition temperature, moduli and thermal degradation temperature) using molecular dynamics simulations for a difunctional epoxy monomer (the diglycidyl ether of bisphenol A) when cured with p-3,30 -dimethylcyclohexylamine to form a dielectric polymer suitable for microelectronic applications. Plots of density versus temperature show decreases in density within the same temperature range as experimental values for the thermal degradation and other thermal events determined using e.g. dynamic mechanical thermal analysis. Empirical characterisation data for a commercial example of the same polymer are presented to validate the network constructed. Extremely close agreement with empirical data is obtained: the simulated value for the glass transition temperature for the 60 C cured epoxy resin (simulated conversion a = 0.70; experimentally determined a = 0.67 using Raman spectroscopy) is ca. 70–85 C, in line with the experimental temperature range of 60–105 C (peak maximum 85 C). The simulation is also able to mimic the change in processing temperature: the simulated value for the glass transition temperature for the 130 C cured epoxy resin (simulated a = 0.81; experimentally determined a = 0.73 using Raman and a = 0.85 using DSC) is ca. 105–130 C, in line with the experimental temperature range of 110–155 C (peak maximum 128 C). This offers the possibility of optimising the processing parameters in silico to achieve the best final properties, reducing labour- and material-intensive empirical testing. 2013

S. R. P. Silva, JD Carey, G. Y. Chen, D. C. Cox, R. D. Forrest, C. H. Poa, R. C. Smith, Y. F. Tang, J. M. Shannon (2004)Nanoengineering of materials for field emission display technologies, In: IEE Proceedings in Circuits, Devices and Systems51pp. 489-496

The holy grail in terms of flat panel displays has been an inexpensive process for the production of large area 'hang on the wall' television that is based on an emissive technology. Electron field emission displays, in principle, should be able to give high quality pictures with good colour saturation, and, if suitable technologies for the production of cathodes over large areas were to be made available, at low cost. This requires a process technology where temperatures must be maintained below 450/spl deg/C throughout the entire production cycle to be consistent with the softening temperature of display glass. In this paper we propose three possible routes for nanoscale engineering of large area cathodes using low temperature processing that can be integrated into a display technology. The first process is based on carbon nanotube-polymer composites that can be screen printed over large areas and show electron field emission properties comparable with some of the best aligned nanotube arrays. The second process is based on the large area growth of carbon nanofibres directly onto substrates held at temperatures ranging from room temperature to 300/spl deg/C, thereby making it possible to use inexpensive substrates. The third process is based on the use of excimer laser processing of amorphous silicon for the production of lithography-free large area three terminal nanocrystalline silicon substrates. Each route has its own advantages and flexibility in terms of incorporation into an existing display technology. The harnessing of these synergies will be highlighted together with the properties of the cathodes developed for the differing technologies.

S. J. Henley, C. H. P. Poa, A. A. D. T. Adikaari, C. E. Giusca, JD Carey, S. R. P. Silva (2004)Excimer laser nanostructuring of nickel thin films for the catalytic growth of carbon nanotubes, In: Applied Physics Letters84pp. 4035-4037

Pulse laser ablation and subsequent laser nanostructuring at room temperature has been employed to produce nanostructured Ni on SiO2/Si substrates for catalytic growth of carbon nanotubes. The resultant nanostructured surface is seen to consist of nanometer sized hemispherical droplets whose mean diameter is controlled by the initial metal thickness, which in turn is readily controlled by the number of laser pulses. Vertically aligned multiwall carbon nanotube mats were then grown using conventional plasma enhanced chemical vapor deposition. We show that within a single processing technique it is possible to produce the initial metal-on-oxide thin film to a chosen thickness but also to be able to alter the morphology of the film to desired specifications at low macroscopic temperatures using the laser parameters. The influence of the underlying oxide is also explored to explain the mechanism of nanostructuring of the Ni catalyst.

SM Lyth, Simon Henley, S Silva (2007)Laser ablation of thin carbon nanotube films on glass substrates as transparent field emitters, In: EIGHTH IEEE INTERNATIONAL VACUUM ELECTRONICS CONFERENCEpp. 329-330 IEEE

This paper reports the transparent field-emitters, produced by spin-coating acid-oxidised multiwall carbon nanotubes (o-MWNT) onto indium tin oxide (ITO)-coated glass slides via an o-MWNT ink. We report substantial changes in the morphology of the o-MWNT layer and an improvement in the FE properties after exposing the films to laser pulses of differing intensity. It is envisaged that this technique could be scaled up as an industrial process for producing truly large area, transparent and cheap FE substrates.

AP Burden, E Mendoza, SRP Silva, GAJ Amaratunga (1998)The stability of nitrogen-containing amorphous carbon films after annealing at moderate temperatures, In: DIAMOND AND RELATED MATERIALS7(2-5)pp. 495-498
Daniel Sebastia-Saez, Tomas Ramirez Reina, Ravi Silva, Harvey Arellano-Garcia (2019)Synthesis and characterisation of n-octacosane@silica nano-capsules for thermal storage applications, In: International Journal of Energy Research Wiley

This work reports the synthesis and characterisation of a core-shell n-octacosane@silica nano-encapsulated phase-change material obtained via interfacial hydrolysis and poly-condensation of tetraethyl orthosilicate in mini-emulsion. Silica has been used as the encapsulating material because of its thermal advantages relative to synthesised polymers. The material presents excellent heat storage potential, with a measured latent heat varying between 57.1 and 89 kJ∙kg-1 (melting point between 58 and 64°C) and a small particle size (between ~565 and ~227 nm). Degradation of the n-octacosane core starts between 150 and 180°C. Also, the use of silica as shell material gives way to a heat conductivity of 0.796 W∙m-1∙K-1 (greater than that of nano-encapsulated materials with polymeric shell). Charge/discharge cycles have been successfully simulated at low pressure to prove the suitability of the nano-powder as phase-change material. Further investigations will be carried out in the future regarding the use of the synthesised material in thermal applications involving nanofluids.

X Guo, SRP Silva (2006)Capacitive compensation to suppress sample-and-hold non-idealities in switched-current AMOLED pixel circuits, In: IDW '06: PROCEEDINGS OF THE 13TH INTERNATIONAL DISPLAY WORKSHOPS, VOLS 1-3pp. 829-832
Muhammad Ahmad, Sembukuttiarachilage Ravi Silva (2015)A method for graphene and carbon nanotube growth

A layer stack for growing graphene or carbon nanotubes (CNTs) is described. The layer stack comprises a substrate, a protective layer, and an attachment surface disposed therebetween. The protective layer is configured to allow carbon diffusion therethrough to the attachment surface, such that graphene or CNTs grow therefrom. L'invention concerne un empilement de couches pour la croissance de graphène ou de nanotubes de carbone (CNT). L'empilement de couches comprend un substrat, une couche de protection, et une surface de fixation disposée entre les deux. La couche de protection est conçue de manière à permettre la diffusion de carbone à travers celle-ci vers la surface de fixation, de telle sorte que le graphène ou des nanotubes de carbone se développent à partir de celle-ci.

G Ruffini, S Dunne, E Farres, J Marco-Pallares, C Ray, E Mendoza, R Silva, C Grau (2006)A dry electrophysiology electrode using CNT arrays, In: SENSORS AND ACTUATORS A-PHYSICAL132(1)pp. 34-41
D Carey, R Smith, R Silva, R Murphy, W Blau, J Coleman (2007)Transport and field emission in carbon nanotube - polymer composite cathodes, In: 2007 IEEE 20TH INTERNATIONAL VACUUM NANOELECTRONICS CONFERENCEpp. 165-166
Y Hayashi, T Fujita, T Tokunaga, K Kaneko, T Butler, N Rupesinghe, JD Carey, SRP Silva, GAJ Amaratunga (2007)Encapsluation of Co and Pd multi-metal nanowires inside multiwalled carbon nanotubes by microwave plasma chemical vapor deposition, In: DIAMOND AND RELATED MATERIALS16(4-7)pp. 1200-1203
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