Rosnita Muhammad

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

Structure and electrical characterization of gallium arsenide nanowires with different V/III ratio growth parameters

Gallium arsenide (GaAs) nanowires were grown vertically on GaAs(111)B substrate by gold-assisted using metal-organic chemical vapour deposition. Field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and conductivity atomic force microscopy (CAFM) analysis were carried out to investigate the effects of V/III ratio on structural properties and current-voltage changes in the wires. Results show that GaAs NWs grow preferably in the wurtzite crystal structure than zinc blende crystal structure with increasing V/III ratio. Additionally, CAFM studies have revealed that zincblende nanowires indicate ohmic characteristic compared to oscillation current occurred for wurtzite structures. The GaAs NWs with high quality structures are needed in solar cells technology for trapping energy that directly converts of sunlight into electricity with maximum capacity.

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.

Growth of Copper Nanowires by Using Thermal Oxidation for Solid Oxide Fuel Cell

Tuning high density nanostructures by simple and economic method may contribute towards the development of solid oxide fuel cells. Copper oxide nanowires grown on Cu foil by thermal oxidation at relative low operating temperature from 400°C are characterized by using x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), atomic force morphology (AFM), conductive-AFM (C-AFM), and field emission scanning electron microscopy (FESEM). The role of oxidizing temperature and time on structural and electrical properties are studied. The formation of nanowires is confirmed by X-Ray diffraction pattern with the presence of copper oxide. The electrical conductivity of the nanowires was ranging from 0.2x105 S m-1 to 0.8x105 S m-1are determined from conductive atomic force microscopy. The oxidation time strongly influence the morphology and chemical composition of the nanowires. Field emission scanning electron microscopy reveals the growth mechanism of copper nanowires formation is based on vapour-solid (VS) mechanism. Herein, the successfully growth of CuO nanowire are directly from Cu foil to overcome the mismatching stress between the substrate and the oxide layer. Optimum parameters are studied to make better electrolyte performance in the applications of solid oxide fuel cell (SOFC).

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.

Growth of ZnO Nanowires by Vapour Solid Mechanism

The growth of zinc oxide nanowires is further investigated by thermal evaporation method and is discussed with respect to vapour-solid (V-S) growth mechanism. In this paper, ZnO nanowires were synthesized on glass substrate without the use of any catalyst with a constant flow of argon gas 1.36 psig and oxygen gas of 0.34 psig. Zinc powder of 99.99% purity is placed in a horizontal furnace and exposed to temperature of 600°C for 90 minutes. The surface morphology of the deposited zinc oxide is investigated by the atomic force microscopy (AFM) images and it was found that the deposited ZnO has a rough surface while field-emission scanning electron microscopy (FESEM) confirms the morphology of the ZnO nanowires. Photoluminescence (PL) spectra indicate that the optical quality of the deposited structure is potentially excellent with high energy excitonic emission close to the band edge which is assigned to the surface exciton in ZnO at 3.4eV.

Morphological of Yttrium Stabilized Zirconia (YSZ) Thin Film of Electrolyte in Solid Oxide Fuel Cell Application

Recently, the performance of solid oxide fuel cell is focused on lowering operating temperature (400°C-650°C). To achieve the goal, the thickness of commonly used electrolyte, YSZ was reduced. The dip-coating technique was used for preparing dense YSZ electrolyte thin films on glass substrate. The suspensions were prepared by sol-gel method. Polyvinyl alcohol (PVA) and polyethylene glycol (PEG) was used as a ceramic binder and plasticizer, respectively. Crystalline structure and morphology of thin films were analyze by X-ray diffraction (XRD) and Atomic Force Microscope (AFM). The XRD reveals that crystallization of YSZ phase does not occur at any sintering temperature but can only have a small peak at 2θ = 30° as the thickness of layer increase. The roughness and morphology of the film with different thickness were observed. The roughness increased as the thickness increased.

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.

Effect of gas flow rate on structural properties of zinc oxide nanowires grown by vapor-solid mechanism

ZnO nanowires have been grown on pre-coated (ZnO thin film) silicon (100) substrates with special attention on the effect of gas flow rate. The samples were fabricated using a simple thermal evaporation method within a horizontal quartz tube under controlled supply of Ar and O2 gas where ZnO powder source were previously weighed and heated at 960 °C for 2 h, allowing the reactant vapors to deposit onto substrate to form the nanowires. FESEM images revealed the randomly-oriented nanowires in which the shapes varied with increasing gas flow rates from varied from 90 to 130 sccm. According, both diameter and aspect ratio of the nanowires was observed to shift at 110 sccm where optimum growth condition was expected at this gas flow rate. From EDX spectrum analysis, ZnO nanowires appeared to have uniform composition and purity and confirming the hexagonal wurtzite crystal structure. These measured parameters in combination with unique properties made the possibility of ZnO nanowires potentially useful for functional nanodevices.

The effect of annealing process on the colloidal golds and gallium arsenide nanowires

Nanowires as a one dimensional building block have generated a lot of interests due to their unique physical properties and potential to revolutionize broad areas of nanotechnology. For successful applications, precise knowledge about the effect of the various growth parameters is essential. In this study, we report the effects of annealing process on colloidal gold and GaAs nanowires using metal‐organic chemical vapor deposition. AFM observation showed that the annealing process of colloidal gold, the substrate surface was attacked with a pit left behind where Au and Ga dissolved to form eutectic alloy. The morphological studies using FE‐SEM of the as‐annealed GaAs nanowire showed the direction of the GaAs nanowire to be 35° inclined from the surface but grown almost perpendicular to the substrate when the annealing process was omitted from the MOCVD growth process flow. TEM studies showed that the GaAs nanowires grown on orientation substrate without annealing process have less crystal latti...