ß-Ga2O3 Nanostructures: Chemical Vapor Deposition Growth Using Thermally Dewetted Au Nanoparticles as Catalyst and Characterization.

ß-Ga2O3 nanostructures, including nanowires (NWs), nanosheets (NSHs), and nanorods (NRs), were synthesized using thermally dewetted Au nanoparticles as catalyst in a chemical vapor deposition process. The morphology of the as-grown ß-Ga2O3 nanostructures depends strongly on the growth temperature and time. Successful growth of ß-Ga2O3 NWs with lengths of 7-25 µm, NSHs, and NRs was achieved. It has been demonstrated that the vapor-liquid-solid mechanism governs the NW growth, and the vapor-solid mechanism occurs in the growth of NSHs and NRs. The X-ray diffraction analysis showed that the as-grown nanostructures were highly pure single-phase ß-Ga2O3. The bandgap of the ß-Ga2O3 nanostructures was determined to lie in the range of 4.68-4.74 eV. Characteristic Raman peaks were observed with a small blue and red shift, both of 1-3 cm-1, as compared with those from the bulk, indicating the presence of internal strain and defects in the as-grown ß-Ga2O3 nanostructures. Strong photoluminescence emission in the UV-blue spectral region was obtained in the ß-Ga2O3 nanostructures, regardless of their morphology. The UV (374-377 nm) emission is due to the intrinsic radiative recombination of self-trapped excitons present at the band edge. The strong blue (404-490 nm) emissions, consisting of five bands, are attributed to the presence of the complex defect states in the donor (VO) and acceptor (VGa or VGa-O). These ß-Ga2O3 nanostructures are expected to have potential applications in optoelectronic devices such as tunable UV-Vis photodetectors.

Pulsed laser-induced dewetting and thermal dewetting of Ag thin films for the fabrication of Ag nanoparticles.

Two different dewetting methods, namely pulsed laser-induced dewetting (PLiD)-a liquid-state dewetting process and thermal dewetting (TD)-a solid-state dewetting process, have been systematically explored for Ag thin films (1.9-19.8 nm) on Si substrates for the fabrication of Ag nanoparticles (NPs) and the understanding of dewetting mechanisms. The effect of laser fluence and irradiation time in PLiD and temperature and duration in TD were investigated. A comparison of the produced Ag NP size distributions using the two methods of PLiD and TD has shown that both produce Ag NPs of similar size with better size uniformity for thinner films (<6 nm), whereas TD produced bigger Ag NPs for thicker films (≥8-10 nm) as compared to PLiD. As the film thickness increases, the Ag NP size distributions from both PLiD and TD show a deviation from the unimodal distributions, leading to a bimodal distribution. The PLiD process is governed by the mechanism of nucleation and growth of holes due to the formation of many nano-islands from the Volmer-Weber growth of thin films during the sputtering process. The investigation of thickness-dependent NP size in TD leads to the understanding of void initiation due to pore nucleation at the film-substrate interface. Furthermore, the linear dependence of NP size on thickness in TD provides direct evidence of fingering instability, which leads to the branched growth of voids.