Abstract
In the first part of experiment, amorphous SiO2 nanowires could be synthesized via carbothermal reduction at 1100 ℃ with Ar flow gas and Fe2O3/C mixed powders, and the ratio of source powders and the flux of Ar flow gas would significant influence the diameter, twisty shape, and density of SiO2 nanowires. Several ratio of Fe2O3/C mixed powders and different Ar flow rate were considered in this study, and it is observed that ultra-high density SiO2 nanowires with high aspect ratio are formed with a suitable ratio of source powders and Ar flux. The growth of SiO2 nanowires is originated by the reaction between SiO and O2 vapor and following the VS growth mechanism, while SiO vapor is formed by CO2 reacting with Si substrate as well as O2 vapor comes from the source powders. Furthermore, lots of neutral oxygen vacancy causes the SiO2 nanowires revealing the strong emitting peak of 450 nm in the cathodoluminescence analysis. In the second part of experiment, poly-crystal Ta2O5 nanowires can be synthesized via annealing SiO2 nanowires at 950℃ in a reductive Ta vapor ambient for 32 hours. To realize the formation process of Ta2O5 nanowires, the influence of different annealing was considered in this study. The Ta2O5 phase is formed by Ta reducing SiO2, and the formation of Ta2O5 nanowires starts with nucleation and grain growth of Ta2O5 crystal forming SiO2/Ta2O5 core-shell structure, and then continuous growth of shell layer. The growth process is dominated by diffusion through the ash layer control, and the diffusion of Ta atoms through shell layer would be the rate-controlling step of the diffusion controlled growth mechanism. In addition, Ta2O5 nanotubes could be synthesized by etching SiO2/Ta2O5 core-shell nanowires with dilute HF solution. It is also observed that the crystalline of Ta2O5 nanowires by vacuum annealing process rather than RTA process. Furthermore, the field-emission character and the cathodoluminescence (CL) property, resulting form the neutral oxygen vacancy, are considered in this study.