Muhammad Ahmed

Dr Muhammad Ahmad

Research Fellow
+44 (0)1483 686099
08 ATI 02

Academic and research departments

Advanced Technology Institute.



Research interests


JD Carey, M Ahmad, JV Anguita, V Stolojan, T Corless, SRP Silva (2020)Data for 'High Quality Carbon Nanotubes on Conductive Substrates Grown at Low Temperatures' University of Surrey
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.

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

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.

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.

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.

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.

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.

M Ahmad, JV Anguita, V Stolojan, JD Carey, SR Silva (2013)Efficient coupling of optical energy for rapid catalyzed nanomaterial growth: high-quality carbon nanotube synthesis at low substrate temperatures., In: ACS Appl Mater Interfaces5(9)pp. 3861-3866

The synthesis of high-quality nanomaterials depends on the efficiency of the catalyst and the growth temperature. To produce high-quality material, high-growth temperatures (often up to 1000 °C) are regularly required and this can limit possible applications, especially where temperature sensitive substrates or tight thermal budgets are present. In this study, we show that high-quality catalyzed nanomaterial growth at low substrate temperatures is possible by efficient coupling of energy directly into the catalyst particles by an optical method. We demonstrate that using this photothermal-based chemical vapor deposition method that rapid growth (under 4 min, which includes catalyst pretreatment time) of high-density carbon nanotubes can be grown at substrate temperatures as low as 415 °C with proper catalyst heat treatment. The growth process results in nanotubes that are high quality, as judged by a range of structural, Raman, and electrical characterization techniques, and are compatible with the requirements for interconnect technology.

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.

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.

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.