Yussof Wahab

The Effect of V/III Ratio on the Crystal Structure of Gallium Arsenide Nanowires

Gallium arsenide (GaAs) nanowires were grown vertically on GaAs (111)B substrate by gold particle-assisted using metal-organic chemical vapour deposition. Transmission electron microscopy and X-Ray diffraction analysis were carried out to investigate the effects of V/III ratio and nanowire diameter on structural properties and crystallinity changes. Results show that GaAs nanowires grow preferably in the wurtzite crystal structure than zinc blende structure with increasing V/III ratio. Additionally, XRD studies have revealed that wurtzite nanowires show prominent peaks especially at (222) orientation. The optimum V/III ratio was found to be 166 with less defect structure, uniform diameter and peak prominence. The nanowires with high quality are needed in solar cells technology for energy trapping with maximum capacity.Keywords : Nanowire; crystal structure; Gallium arsenide; Vapor Liquid Solid

Conductivity of Yittria-Stabilized Zirconia Nanostructure Electrolyte for Solid Oxide Fuel Cell Application by Using RF Magnetron Sputtering

Yttria-stabilized zirconia (YSZ) thin films were deposited successfully using RF magnetron sputtering. The substrate had been used are sapphire glass. A pure ceramic of Zr-Y is synthesized and processed into a planar magnetron target which is reactively sputtered with an Argon-Oxygen gas mixture to form Zr-Y-O nanostructure. The aim of this research is to study the conductivity and roughness YSZ thin film by using RF magnetron sputtering by varying the temperature deposition parameter. By lowering the YSZ thin film into nanostructure would enable for SOFC to be operate at lower temperature below 400°C. The YSZ nanostructure were controlled by varying the deposition parameters, including the deposition temperature and the substrate used. The crystalline of YSZ structure at 100W and temperature 300°C. The surface morphology of the films proved that at 300°C temperature rate deposition showed optimum growth morphology and density of YSZ thin films. Besides, the high deposition subtrate temperature affected the thickness of YSZ thin film at 80nm by using surface profiler. A higher rate of deposition is achievable when the sputtering mode of the Zr-Y target is metallic as opposed to oxide. YSZ is synthesizing to obtain the optimum thin film for SOFC application.

Effect of annealing temperature on platinum/YSZ thin film fabricated using RF and DC magnetron sputtering

This research aims to study the growth and the effect of annealing temperature on the structural properties of Platinum/YSZ/Platinum thin film. The thin films were prepared by RF and DC magnetron sputtering method utilized platinum as electrodes (anode and cathode) and YSZ as electrolyte. Two temperatures of annealing (400 and 600 °C) were conducted onto Platinum/YSZ/Platinum thin film for comparison in this study. Crystalline phase, microstructure and thickness of thin films were evaluated using X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscope (FE-SEM) technique. Results show that Pt/YSZ/Pt thin film without post-annealing gives a better morphology and crystal phase.

Influence of substrate orientation on the structural properties of GaAs nanowires in MOCVD

In this study, the effect of substrate orientation on the structural properties of GaAs nanowires grown by a metal organic chemical vapor deposition has been investigated. Gold colloids were used as catalyst to initiate the growth of nanowiresby the vapour-liquid-solid (VLS) mechanism. From the field-emission scanning electron microscopy (FE-SEM), the growth of the nanowires were at an elevation angle of 90°, 60°, 65° and 35° with respect to the GaAs substrate for (111)B, (311)B, (110) and (100) orientations respectively. The preferential NW growth direction is always B. High-resolution transmission electron microscope (HRTEM) micrograph showed the NWs that grew on the GaAs(111)B has more structural defects when compared to others. Energy dispersive X-ray analysis (EDX) indicated the presence of Au, Ga and As. The bigger diameter NWs dominates the (111)B substrate surface.

Electrical Characteristics of Photovoltaic Cell Module by Simulation

This paper emphasizes on the model verification of the electrical performance of a Photovoltaic (PV) cell module by MATLAB/Simulink simulation. The developed model can then be used to predict the PV cell behavior under different physical and environmental parameters such as solar irradiation, ambient temperature, series resistor, shunt resistor, diode saturation current and cell arrangement. Photovoltaic cell model is used for comparing the electrical characteristics for this modeling process. Kyocera PV module is used as the module specification, whereby a PV model can be easily generalized to predict the output current, power characteristics and the maximum power point tracking.

Interdependencies of Critical Radius, Critical Energy and Surface Energy (CRESE) in Silicon Self-Assembled Nanodots

The interdependence parameters in the growth of silicon self-assembled nanodots are investigated. Accordingly, the critical radius, critical energy change and surface energy can be interpreted in terms of cubic function, where it produced a critical surface energy uf067NS* and the corresponding r* and uf044G*, called a CRESE point at a fixed growth temperature T when solved mathematically. It is defined as a limiting point at which equilibrium of the critical parameters take place at a constant temperature. Experiments were performed on the samples of amorphous silicon nanodots fabricated onto different non-crystalline substrates. A further analysis on the uf067NS*-T plots revealed inverse linear relationships which converged at a CID point (uf067o*,T*) when projected near the solidification temperature of silicon. The results suggested strong influence of atomic bonding at the nucleus-surface interface combined with higher surface roughness. In conclusion, there exists an equilibrium condition among the growth parameters which stabilizes the growth of amorphous silicon nanodots, as well as the existence of CRESE’s ideal destination (CID).

Photoluminescence Studies of Silicon Self-Assembled Quantum Dots

Silicon self-assembled nanodots have been fabricated on corning (7059) and quartz glass substrates using a magnetron sputtering method at different experimental conditions, including the deposition time, RF power and substrate temperature. It was observed that, as the deposition time increases, PL intensities increased with deposition time. However, the full width at half maximum of individual spectra was observed to decrease with time. This occurs because the nature of PL is such that an improvement in the number of carriers (electron and holes) results in enhanced PL intensities. An increase in the deposition time allows more silicon attached to substrate and forming the nanodots, thus increasing the number of atoms as well as carriers. The effect of RF power was indicated by increasing trends in PL intensities. Higher deposition power appeared to increase the ratio of Si atomic concentration and, hence, an increasing number of silicon nanodots. On the other hand, the results showed that, the PL intensity decreased as the substrate temperatures were increased caused by an activated non-radiative recombination process and decrease of crystal quality. It was also observed that the peak of PL wavelength centered at 693 nm or 1.78eV energy bandgap did not differ much from those peaks obtained by varying the RF power and substrate temperature. The suggested that deposition time up to 5 min, RF power of 200 W and substrate temperature of 400°C as optimum conditions for the growth of dome-shaped silicon nanodots, with sizes between 40-80 nm. Generally the shifts in PL intensities are attributed to the structural changes which occurs during the growth processes