31 research outputs found
Emerging Applications of Novel Nanoparticles (Ed. by N Balakrishnan)
No full textThis book is a comprehensive and modern guide on emerging nanoparticles and their diverse applications in engineering, medicine, food safety, transportation, energy, agriculture, and environmental sustainability. Written by leading researchers from all over the world, it is designed to cover the full range of nanoparticles as well as provide in-depth detail regarding their development, characterization, processing, and synthesis. The book is divided into two sections: the first covers the development of advanced nanoparticles and the second is dedicated to their variety of cutting-edge applications. The authors also cover the unique properties and green synthesis of nanoparticles as well as their use as nanobiosensors, nanopesticide, nanofertilizer, and as energy storage and conversion devices, just to name a few. This book provides readers with insight onto the broad scope of computational, theoretical, and experimental research on novel nanoparticles and their applications. It is ideal for both young and experienced researchers and industry professionals in the field of nanotechnology
Symmetric double-layer capacitor with natural rubber and sodium salt-based solid polymer electrolyte and reduced graphene oxide electrodes
No full textSolid polymer electrolytes (SPEs) are the key to improving electrochemical devices’ energy density and safety. In recent years, natural polymers have received tremendous attention due to the latest advances in green technology for a sustainable future. Herein, SPEs based on 49 % methyl grafted natural rubber (MG49-NR) and sodium trifluoromethanesulfonate (Na(CF3SO3) – NaTF) salt were prepared and characterized to optimize their performance. The composition MG49-NR: NaTF = 1:0.5 (by weight) shows the highest room temperature conductivity (σRT) of 7.52 × 10− 4 S cm− 1. This optimized electrolyte is purely an ionic conductor with an activation energy (Ea) of 0.29 eV. The optimized electrolyte was used to fabricate double-layer capacitors by sandwiching it between two identical reduced graphene oxide (rGO) electrodes. The fabricated double-layer capacitors show a maximum single electrode specific capacitance (Csc) of 42.5 F g− 1 from the cyclic voltammetry (CV) test. Moreover, the charge storage mechanism utterly takes place via non-faradaic reactions which is evidenced by cyclic voltammograms. Furthermore, the electrochemical impedance spectroscopy (EIS) test shows the capacitive features are dominant at low frequencies. Performance of the double-layer capacitor during 10,000 charge anddischarge cycles at a constant current density of 0.05 A g− 1 shows a fast drop of single electrode specific discharge capacitance (Csd) at the beginning, but it started to saturate after the 5000th cycle proving the good stability of the capacitor. These findings are relevant to expanding the functionalities of SPE-based double-layer capacitors in green technologies
Coherent Phonons in van der Waals MoSe2/WSe2 Heterobilayers
No full textThe increasing role of two-dimensional (2D) devices requires the development of new techniques for ultrafast control of physical properties in 2D van der Waals (vdW) nanolayers. A special feature of heterobilayers assembled from vdW monolayers is femtosecond separation of photoexcited electrons and holes between the neighboring layers, resulting in the formation of Coulomb force. Using laser pulses, we generate a 0.8 THz coherent breathing mode in MoSe2/WSe2 heterobilayers, which modulates the thickness of the heterobilayer and should modulate the photogenerated electric field in the vdW gap. While the phonon frequency and decay time are independent of the stacking angle between the MoSe2 and WSe2 monolayers, the amplitude decreases at intermediate angles, which is explained by a decrease in the photogenerated electric field between the layers. The modulation of the vdW gap by coherent phonons enables a new technology for the generation of THz radiation in 2D nanodevices with vdW heterobilayers
Low-temperature growth of metal chalcogenide semiconductors
No full textMetal chalcogenides exhibit a variety of intriguing properties and promising applications. However, a significant challenge in utilising these materials for electronic devices lies in producing high quality thin films. Chemical vapour deposition (CVD) is a scalable technique that can produce extraordinarily high-quality thin films which are nanometres in thickness, over large areas. High growth temperatures are often required in order to synthesise the best quality materials which hinder the use of CVD techniques for commercial thin film manufacture. This work centres on the development, optimisation and use of low-temperature CVD growth systems to grow metal chalcogenides films and two-dimensional materials utilising both aerosol-assisted chemical vapour deposition (AACVD) and salt-assisted chemical vapour deposition (SA-CVD), respectively. This enables film deposition to occur at lower temperatures when compared to existing reported traditional CVD methods, using single source dithiocarbamate precursors and halide salts. To synthesise metal sulfide, oxide and selenide semiconductors, that are suitable for a wide range of uses, such as optoelectronic, thermoelectric and catalytic applications. Thus, this could offer exciting opportunities for scalable renewable energy research by determining if low-temperature CVD methods can produce high quality films, that are comparable to their existing high temperature counterparts. In this project, materials morphology, crystal quality, lattice strain and structural composition were explored through various characterisation techniques, including Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray (EDX) analysis. The research has proven that low-temperature chemical vapour deposition methods can be utilized to produce high quality molybdenum, zinc and tin chalcogenide semiconductors, which are suitable for optoelectronic and thermoelectric devices and also show great promise for catalysing hydrogen evolution reactions. This mean we are one step closer to a highly efficient, low-cost clean energy future
Novel encapsulation methods for X-ray crystallography
No full textNovel crystal encapsulation methods were developed for use in X-ray crystallography to protect vulnerable crystals from degradation or dehydration, whilst minimising background scatter. Graphene with a backing of poly(methyl methacrylate) (PMMA), and 2-hydroxyethyl methacrylate resin (HEMA), were used in various combinations to encapsulate sucrose crystals (C12H22O11). Purpose-designed 3D printed holders and adaptations of standard manufactured mounts were developed. The crystals were analysed using single-crystal X-ray crystallography before and after exposure to a very high relative humidity water vapour for 72 hours. Some samples, where the encapsulation was incomplete or insufficiently thick did not survive, but those that did showed that both graphene and HEMA resin, individually or in combination, could protect these crystals with no degradation. Development of these methods could be particularly useful for room-temperature analysis of large biological molecules, which require synchrotron light and may exhibit altered or restricted behaviours when cryocooled. However, careful selection of the resin will be needed to ensure compatibility, and handling methods for the graphene require further improvement
Novel approaches to the fabrication of nanoscale devices
No full textThis thesis describes the effects of a post-growth hydrogenation on as-grown samples and device structures based on III-N-V and III-V semiconductor compounds. The spectral response of quantum wells (QWs) or superlattices (SLs) are tuned by the control dissociation of N-H complexes using a focused laser beam (photon assisted dissociation) or by thermal annealing. These approaches could be implemented in other materials and heterostructure devices, and offer the advantage of enabling an accurate control of the spectral response of a device using a layer compound with a single N- concentration. A focused laser beam is also used to diffuse hydrogen from the p-type contact layer towards the III-N-V superlattice in the intrinsic region of a p-i-n diode, thus creating preferential injection paths for the carriers and creating nanoscale light emitting diodes. Opportunities for realizing a movable micron size-light emitting diode (-LED) are also demonstrated.\ud
\ud
Moreover, room temperature electroluminescence from semiconductor junctions formed from combinations of n-InSe, p-InSe, p-GaSe and n-In2O3 is demonstrated. These p-n junctions are fabricated using mechanical exfoliation of Bridgman-grown crystals and a simple mechanical contact method or thermal annealing. These results demonstrate the technological potential of mechanically formed heterojunctions and homojunctions of direct band gap layered GaSe and InSe compounds with an optical response over an extended wavelength range, from the near-infrared to the visible spectrum. These layered crystals could be combined in different sequences of layer stacking, thus offering exciting opportunities for new structures and devices
Novel approaches to the fabrication of nanoscale devices
No full textThis thesis describes the effects of a post-growth hydrogenation on as-grown samples and device structures based on III-N-V and III-V semiconductor compounds. The spectral response of quantum wells (QWs) or superlattices (SLs) are tuned by the control dissociation of N-H complexes using a focused laser beam (photon assisted dissociation) or by thermal annealing. These approaches could be implemented in other materials and heterostructure devices, and offer the advantage of enabling an accurate control of the spectral response of a device using a layer compound with a single N- concentration. A focused laser beam is also used to diffuse hydrogen from the p-type contact layer towards the III-N-V superlattice in the intrinsic region of a p-i-n diode, thus creating preferential injection paths for the carriers and creating nanoscale light emitting diodes. Opportunities for realizing a movable micron size-light emitting diode (-LED) are also demonstrated.
Moreover, room temperature electroluminescence from semiconductor junctions formed from combinations of n-InSe, p-InSe, p-GaSe and n-In2O3 is demonstrated. These p-n junctions are fabricated using mechanical exfoliation of Bridgman-grown crystals and a simple mechanical contact method or thermal annealing. These results demonstrate the technological potential of mechanically formed heterojunctions and homojunctions of direct band gap layered GaSe and InSe compounds with an optical response over an extended wavelength range, from the near-infrared to the visible spectrum. These layered crystals could be combined in different sequences of layer stacking, thus offering exciting opportunities for new structures and devices
Oxidation of InSe
No full textData collection on the effects of thermal and laser annealing on the electronic properties of InS
Quantum confinement and photoresponsivity of β-In2Se3 nanosheets grown by physical vapour transport
No full textWe demonstrate that β-In2Se3 layers with thickness ranging from 2.8 – 100 nm can be grown on SiO2/Si, mica and graphite using a physical vapour transport method. The β-In2Se3 layers are chemically stable at room temperature and exhibit a blue-shift of the photoluminescence emission when the layer thickness is reduced, due to strong quantum confinement of carriers by the physical boundaries of the material. The layers are characterized using Raman spectroscopy and X-ray diffraction from which we confirm lattice constants c = 28.310.05 Å and a = 3.990.02 Å. In addition, these layers show high photoresponsivity of up to ~ 2×103 A/W at a wavelength of 633 nm, with rise and decay times of 0.6 ms and 2.5 ms, respectively, confirming the potential of the as-grown layers for high sensitivity, fast photodetectors
