Fabrication And Investigation Of Gan Nanostructures And Their Applications In Ammonia Gas Sensing

Dalam kerja ini, nanodawai GaN, GaN berliang (PGaN), dan pengesan gas ammonia (NH3) telah difabrikasi dan dikaji. Sampel nanodawai GaN dalam kerja ini ditumbuh dengan kaedah pemendapan wap kimia (CVD), yang bermod pertumbuhan wapcecair-pepejal (VLS). Untuk pengajian nanodawai GaN, tumpuan diberi terhadap mekanisma pertumbuhan VLS, terutamanya kesan pemangkin logam. In this work, gallium nitride (GaN) nanowires, porous GaN (PGaN), and ammonia (NH3) gas sensors have been fabricated and studied. The GaN nanowires samples in this work were grown using chemical vapour deposition (CVD) method, additionally employing vapour-liquid-solid (VLS) growth mode

On The Investigations Of Chip-On-Board Ultra-Violet Sensor By Screen Printing Of Gan Powder

In this work, the characteristics of a chip-on-board screen printed GaN UV sensor was investigated. On the sensing material, GaN powders were obtained through ammonolysis of Ga2O3 at 1000°C under NH3 flow. The XRD result revealed the polycrystalline nature of hexagonal wurtzite GaN. For the fabrication of the UV sensor platform, soft-lithography was employed in patterning a copper clad board. About 20 pairs of interdigitated electrodes with 127 m spacing were produced. For the screen printing process, GaN powder is mixed with PVP binder, subsequently deposited on the electrode pairs. The overall UV sensor showed three times of changes in sensing current upon illumination. The preliminary works showed the possibility of simple designing and fabricating process of a GaN based UV sensor

Characteristics Of Titanium Dioxide Nanotubes Annealed Under Various Conditions And Quenched Using Liquid Nitrogen

This paper presents the effects of the different annealing treatments and quenching conditions on the characteristics of titanium dioxide nanotubes (TNTs), which were synthesised successfully via two-step anodization. The X-ray diffraction (XRD) showed that TNTs annealed and quenched using liquid nitrogen (N2) exhibited significant dissimilarities in the phase transition and plane dominance, as compared to that of air quenched. It also revealed that the liquid N2 quenching was capable of suppressing the phase transition of anatase into rutile. Apart from that, the elemental analysis showed that liquid N2 quenching led to Leidenfrost effect, which had affected the Ti:O ratio of the TNTs significantly. Morphologically, the use of controllable water vapour/N2 was found to be able to preserve the nanotubular structures, even at the high annealing temperature of 850 °C. From the optical aspect, the bandgap energy of all samples were found to decrease when the annealing temperatures increased, regardless of the annealing and quenching conditions. Particularly, the crystal structure of TNTs was found to exert greater effect on their bandgap energy, as compared to that of crystallite size when the annealing temperatures were varied between 650 °C and 850 °C

Improvement of Porous GaN-Based UV Photodetector with Graphene Cladding

This work presents the role of graphene in improving the performance of a porous GaN-based UV photodetector. The porous GaN-based photodetector, with a mean pore diameter of 35 nm, possessed higher UV sensitivity, about 95% better compared to that of the as-received (non-porous) photodetector. In addition, it exhibits a lower magnitude of leakage current at dark ambient, about 70.9 μA, compared to that of the as-received photodetector with 13.7 mA. However, it is also highly resistive in nature due to the corresponding electrochemical process selectively dissolute doped regions. Herein, two types of graphene, derived from CVD and the electrochemical exfoliation (EC) process, were cladded onto the porous GaN region. The formation of a graphene/porous GaN interface, as evident from the decrease in average distance between defects as determined from Raman spectroscopy, infers better charge accumulation and conductance, which significantly improved UV sensing. While the leakage current shows little improvement, the UV sensitivity was greatly enhanced, by about 460% and 420% for CVD and EC cladded samples. The slight difference between types of graphene was attributed to the coverage area on porous GaN, where CVD-grown graphene tends to be continuous while EC-graphene relies on aggregation to form films