simon-king

Dr Simon King


Research Fellow
EngD, BSc Hons

Biography

Areas of specialism

Electrospinning; Carbon Nanotubes; Graphene; Composite Materials; Raman Spectroscopy; Electron Microscopy

Affiliations and memberships

MInstP
Member of the Institute of Physics

Research projects

My publications

Publications

King S, McCafferty L, Stolojan V, Silva S (2015) Highly aligned arrays of super resilient carbon nanotubes by steam purification,Carbon 84 (1) pp. 130-137 PERGAMON-ELSEVIER SCIENCE LTD
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.
Stolojan V, McCafferty L, King S, Zhang W, Haq S, Silva S (2015) Decoration of multiwalled carbon nanotubes with protected iron nanoparticles,Carbon 84 pp. 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.
King Simon, Stolojan Vlad, Silva Ravi (2017) Large area uniform electrospun polymer nanofibres by balancing of the electrostatic field,Reactive and Functional Polymers 129 pp. 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.
King Simon G., Terrill Nicholas J., Goodwin Andrew J., Stevens Robert, Stolojan Vlad, Silva Ravi P. (2018) Probing of Polymer to Carbon Nanotube Surface Interactions within Highly Aligned Electrospun Nanofibers for Advanced Composites,Carbon 138 pp. 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 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.
King Simon, Castaldelli Evandro, McCaffterty Liam, Silva S Ravi P, Stolojan Vlad (2018) A Micro-Centrifugal Technique for Improved Assessment and Optimization of Nanomaterial Dispersions: The Case for Carbon Nanotubes,ACS Applied Nano Materials 1 (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.
Mirkhaydarov Bobur, Votsi Haris, Sahu Abhishek, Caroff Philippe, Young Paul R., Stolojan Vlad, King Simon, Ng Calvin C H, Devabhaktuni Vijaya, Tan Hoe H, Jagadish Chennupati, Aaen Peter, Shkunov Maxim (2019) Solution?Processed InAs Nanowire Transistors as Microwave Switches,Advanced Electronic Materials 5 (1) 1800323 Wiley
The feasibility of using self?assembled InAs nanowire bottom?gated field?effect transistors as radio?frequency and microwave switches by direct integration into a transmission line is demonstrated. This proof of concept is demonstrated as a coplanar waveguide (CPW) microwave transmission line, where the nanowires function as a tunable impedance in the CPW through gate biasing. The key to this switching capability is the high?performance, low impedance InAs nanowire transistor behavior with field?effect mobility of H300 cm2 V?1 s?1, on/off ratio of 103, and resistance modulation from only 50 © in the full accumulation mode, to H50 k© when the nanowires are depleted of charge carriers. The gate biasing of the nanowires within the CPW results in a switching behavior, exhibited by a H10 dB change in the transmission coefficient, S21, between the on/off switching states, over 5?33 GHz. This frequency range covers both the microwave and millimeter?wave bands dedicated to Internet of things and 5G applications. Demonstration of these switches creates opportunities for a new class of devices for microwave applications based on solution?processed semiconducting nanowires.
Le Borgne Brice, Chung Bo-Yan, Tas Mehmet O., King Simon G., Harnois Maxime, Sporea Radu A. (2019) Eco-Friendly Materials for Daily-Life Inexpensive Printed Passive Devices: Towards ?Do-It-Yourself? Electronics,Electronics 8 (6) MDPI
The need for the fabrication of a new generation of devices has developed with the next generation of ?home? engineers, which is resulting in an ever-increasing population interested in ?do-it-yourself? electronics and the Internet of Things. However, this new trend should not be done at the expense of the environment. Almost all previous studies, related to the low-temperature processing of devices, fail to highlight the extent of the impact that the synthesis of these technologies have on both the environment and human health. In addition, the substrates typically used, are also often associated with major drawbacks such as a lack of biodegradability. In this paper, we fabricate a simple RC filter using various domestically available printing techniques, utilising readily available materials such as: carbon soots (carbon black) as an electric conductor, and egg white (albumen) as a dielectric. These devices have been fabricated on both polyethylene terephthalate (PET) and paper, which demonstrated the same performances on both substrates and revealed that recyclable substrates can be used without compromise to the devices? performance. The filter was found to exhibit a cut-off frequency of 170 kHz, which made it suitable for high-frequency reception applications.