Boon Tong Goh

Synergistic effect of graphene as a co-catalyst for enhanced daylight-induced photocatalytic activity of Zn0.5Cd0.5S synthesized via an improved one-pot co-precipitation-hydrothermal strategy

In this study, a series of reduced graphene oxide (RGO)–Zn0.5Cd0.5S nanocomposites was synthesized via an improved one-step co-precipitation-hydrothermal strategy using thiourea as an organic S source. The experimental results demonstrated that thiourea facilitated heterogeneous nucleation of Zn0.5Cd0.5S and in situ growth of Zn0.5Cd0.5S nanocrystals on the RGO sheets via electrostatic attraction. Moreover, the addition of NaOH as a precipitating agent in the reaction environment was found to reduce the aggregation of Zn0.5Cd0.5S on the RGO sheets. Such an intimate interfacial contact between Zn0.5Cd0.5S and RGO resulted in well-dispersed nanoparticles decorated on RGO sheets. Photocatalytic performances of the RGO–Zn0.5Cd0.5S were evaluated by the degradation of Reactive Black 5 (RB5) under a low-power 15 W energy-saving daylight bulb at ambient conditions. Compared with pristine Zn0.5Cd0.5S, 20RGO–Zn0.5Cd0.5S (20 wt% of RGO) displayed an enhanced RB5 degradation of 97.4% with a rate constant of 0.0553 min−1 after 60 min of visible light irradiation. 20RGO–Zn0.5Cd0.5S exemplified a 1.3-fold enhancement after RGO incorporation relative to that for pristine Zn0.5Cd0.5S. The remarkable photocatalytic performance was ascribed to the efficient migration efficiency of the photoinduced electrons from Zn0.5Cd0.5S to RGO to inhibit the charge carrier recombination. Additionally, to systematically verify the role of each active species in the degradation of RB5, trapping experiments for radicals and holes were individually explored. It is confirmed that photogenerated ˙O2−, ˙OH and h+ were responsible for the degradation of RB5 in the 20RGO–Zn0.5Cd0.5S system. Lastly, a postulated visible-light photocatalytic mechanism for the RB5 degradation was discussed.

Influence of particle size on performance of a nickel oxide nanoparticle-based supercapacitor

The influence of the particle size of an active material on its performance as a supercapacitor electrode was reported. Nickel oxide nanoparticles (NiO NPs) with a uniform particle size were synthesized via a facile sol–gel method, and various sizes of NiO NPs (8, 12, and 22 nm) were achieved by calcination at various temperatures (300, 400, and 500 °C). TEM observations and XRD analysis were used to determine the particle size of the NiO NPs. The field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images showed flake-like morphologies, which consisted of interconnected nanoparticles with a porous channel to facilitate the diffusion of the electrolyte. The NiO NPs with an average particle size of 8 nm gave the highest specific capacitance value of 549 F g−1 at a scan rate of 1 mV s−1 compared to the NiO NPs with average particle sizes of 12 and 22 nm. These results suggest that the particle size of the NiO nanostructure plays an important role because of the presence of a higher number of active sites for a faradaic reaction.

Pressure dependent structural and optical properties of silicon carbide thin films deposited by hot wire chemical vapor deposition from pure silane and methane gases

Silicon carbide (SiC) thin films were deposited using hot wire chemical vapor deposition technique from silane (SiH4) and methane (CH4) gas precursors. The effect of deposition pressure on structural and optical properties of SiC films was investigated. Various spectroscopic methods including Fourier transform infrared spectroscopy, Raman scattering spectroscopy, Auger electron spectroscopy, and UV–Vis–NIR spectroscopy were used to study these properties. Films deposited at low deposition pressure were Si-rich, and were embedded with nano-crystals of silicon. These films showed strong absorption in the visible region and had low energy band gaps. Near stoichiometric SiC film, were formed at intermediate deposition pressure and these films were transparent in the visible region and exhibited a wide optical band gap. High deposition pressures caused inhomogeneity in the film as reflected by the increase in disorder parameter and low refractive index of the films. This was shown to be due to formation of sp2 carbon clusters in the film structure.

Investigation of the electrochemical behavior of indium nitride thin films by plasma-assisted reactive evaporation

Indium nitride (InN) thin films were deposited on Si (111) substrate by plasma-assisted reactive evaporation with a variable radio frequency (RF) power supply. The effects of RF power on the structural, morphological, and optical properties of the films were investigated by X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray analysis, UV-vis transmittance, and micro Raman spectroscopy. The electrochemical behaviors of the InN thin films were investigated in 0.1 M KOH electrolyte towards electrochemical water splitting. Linear sweep voltammograms revealed that the anodic current decreases by increasing RF power for the growth of InN thin films. The charge transfer dynamics between the InN thin film and electrolyte interfaces during the electrochemical process were studied using electrochemical impedance spectroscopy (EIS). Variations in donor density and flat band potentials of the InN thin films were deduced from Mott–Schottky plots. Further, the electrocatalytic behavior of InN thin films was investigated with a K3[Fe(CN)6] redox probe. The good electrochemical behavior of InN thin films showed that this material could be a potential candidate for water splitting application.

Electroless Plating of Copper on Polyimide Film Modified by 50 Hz Plasma Graft Polymerization with 1-Vinylimidazole

This paper reports on the proof of concept work on the novel process of producing metalized polyimide (PI) film by coating a layer of copper (Cu) thin film on the surface of the PI film without using any adhesive. The method which is employed to produce a metalized PI film used in flexible printed circuit (FPC) is based on plasma graft polymerization of 1-vinlyimidazole (VIDz) on plasma pre-treated PI surface. The plasma grafted PI film (VIDz-g-PI) surfaces are characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). AFM results show that the PI film surface has been successfully treated and grafted with VIDz. As post-thermal treatment is known to promote adhesion strength between the metallic film and the PI surface, the effects of post-thermal treatment environment and temperature on the adhesion property of Cu plated VIDz-g-PI (Cu/VIDz-g-PI) are evaluated. Post-thermal treatment in air shows better adhesion strength than in vacuum. The adhesion strength decreases as the post-thermal treatment temperature is increased. In the present development work, the adhesion strength obtained has met the initial market targeted 9–10 N/cm adhesion strength. Samples obtained at a pre-selected plasma power and time window are able to maintain their adhesion strength after being subjected to ageing at 100 °C for 168 h.

Numerical investigation of the plasma-aided fabrication of stoichiometric InAs nanodots at early stage of the growth

Using numerical modeling of the plasma sheath and key surface processes, the plasma-aided fabrication of InAs nanodots is investigated at early stage of the growth. Roles of different plasma process parameters, such as electron temperature, electron number density, and ion-to-electron density ratio, in achieving the stoichiometric growth of the nanodots are explored and conditions to achieve a highly stoichiometric InAs composition are discussed. It is shown that the nanodots get larger with increasing the electron temperature and electron number density, whereas they shrink in size with increasing the ion-to-electron density ratio. Moreover, it is shown that with increase in the electron temperature and electron number density stoichiometric saturation state can be reached shortly, which this enables the fabrication of highly stoichiometric array of nanodots within shorter processing time. The results obtained can open a path toward nucleation and growth of an array of nanodots with desired structural co...

Microfluidic paper-based analytical devices for potential use in quantitative and direct detection of disease biomarkers in clinical analysis

Clinicians, working in the health-care diagnostic systems of developing countries, currently face the challenges of rising costs, increased number of patient visits, and limited resources. A significant trend is using low-cost substrates to develop microfluidic devices for diagnostic purposes. Various fabrication techniques, materials, and detection methods have been explored to develop these devices. Microfluidic paper-based analytical devices (μPADs) have gained attention for sensing multiplex analytes, confirming diagnostic test results, rapid sample analysis, and reducing the volume of samples and analytical reagents. μPADs, which can provide accurate and reliable direct measurement without sample pretreatment, can reduce patient medical burden and yield rapid test results, aiding physicians in choosing appropriate treatment. The objectives of this review are to provide an overview of the strategies used for developing paper-based sensors with enhanced analytical performances and to discuss the current challenges, limitations, advantages, disadvantages, and future prospects of paper-based microfluidic platforms in clinical diagnostics. μPADs, with validated and justified analytical performances, can potentially improve the quality of life by providing inexpensive, rapid, portable, biodegradable, and reliable diagnostics.

Gold catalysed growth of silicon nanowires and core–shell heterostructures via solid–liquid–solid process and galvanic displacement

Abstract Silicon nanowires (SiNWs) were first synthesised using Au coated p type Si (100) substrate via the solid–liquid–solid (SLS) process. The growth parameters were selectively varied to achieve various stages of growth for studying their effects on the morphology and microstructures of the nanowires (NWs). The SLS growth of SiNWs is discussed in the context of the experimental conditions used. Straight NWs of large aspect ratios, good crystallinity and morphology were generally obtained at a growth temperature of 1000°C along with some worm-like amorphous structures. Te–Si NW core–shell structures were subsequently obtained via post-growth galvanic displacement of the SiNWs in an acidic HF electrolyte containing ions. The core–shell structures obtained were decorated with Te nanoparticles. This increases the NW surface areas and should have great potential in non-reflecting, photovoltaic and thermoelectric applications. Growth study on the SiNWs and Te–Si core–shell structures is presented using various microscopy, diffraction and probe based techniques for structural, morphological and chemical characterisations.

Synthesis and characterization of self-assembled, high aspect ratio nm-scale columnar silicon structures

The aim of this work is to synthesize nm-scale columnar structures in Si principally for solar cell applications. These structures are also desirable as templates for heteroepitaxial growth of SixGe1-x. A nanostructured layer is instrumental in facilitating pseudomorphic heteroepitaxial growth of SixGe1-x layers since it can help reduce lattice mismatch as well as thermal expansion mismatch, thus, leading to Si-based high efficiency solar cells at lower cost. A simple yet promising method was chosen to synthesize randomly distributed, nm-scale columnar structures. This metal assisted chemical etching (MACE) technique uses metal-induced oxidation of silicon to anisotropic trenches. Preliminary results indicate that nm-scale columns as characterized by field emission scanning microscopy (FE-SEM) consist of fine pores running parallel to the wafer surface and deeply etched anisotropic columns perpendicular to the surface. All etching work was carried out on (100) orientation Si wafers. Results indicate strong dependence on solution concentration both in terms of profile and etch rate. Optical characterization based on spectral reflectance and transmission measurements have been employed in characterizing the nm-scale surfaces. Initial studies indicate low reflectance and high absorption with increasing depth of the nanostructures.

Effect of Rapid Thermal Annealing Time on the Structural and Optical Properties of Layered Structured SiOx/Au/SiOx Film

In this work, layer structured silicon suboxide/gold/silicon suboxide (SiOx/Au/SiOx) films were prepared by using plasma enhanced chemical vapor deposition assisted with hot wire evaporation technique. Post rapid thermal annealing (RTA) process was done on the as-prepared films for 100, 500 and 700s at constant temperature of 800oC in vacuum ambient. Effects of RTA process on the structural and morphological properties of films were studied using FE-SEM, depth profiling and XRD measurement. While, surface plasmon resonance (SPR) phenomenon exhibited by Au particles was investigated via the optical absorption spectra. SPR signals can be exhibited by sample annealed for longer time duration. Individual Au islands tend to form the spherical shape as a whole. Diffusion of Au particles towards the surface of SiOx film is temperature dependent and crystallite size of Au enlarges with the rapid thermal annealing time.