ZnO nanowhiskers were formed by a simple oxidation of metallic zinc powder 99.9% at different temperatures from 400-900 °C for 2 hours on the silicon substrate. The result can be obtained after the thermal oxidation process, the ZnO nanowhiskers with different morphologies at different temperatures in which these morphologies and composition of ZnO nanostructures were characterized by scanning electron microscope, (SEM) and X-ray diffraction, XRD. It was found that the products were nanowhiskers, the structure are triangular shapes with average width of 10-50 nm at the root, 10-30 nm at the tip and length in the range of 1-3 μm was observed by SEM. Temperature in the range of 600-700 °C was suitable for the preparation of ZnO nanowhiskers. At higher temperature of 800 °C, the concentrations of ZnO structures become lower and stronger. At the oxidized temperature of 900 °C, ZnO nanowhiskers were not found and surface morphology become to porous. These results indicate that the oxidation rate is faster than the diffusion rate of Zn vapor on the surface of ZnO nuclei.
The ZnO/TiO2 heterojunction nanocomposites were synthesized via a thermal process. The morphology of the samples showed TiO2 nanoparticles with rang of 50 – 100 nm in diameter and ZnO nanoparticles with size of upper than 100 nm. The XRD patterns of ZnO/TiO2 nanocomposites indicate ZnO, anatase, and rutile phases. The current - voltage characteristics of ZnO and TiO2 nanoparticles, and ZnO/TiO2 heterojunction nanocomposites show behaviour of ohmic contact materials. The material sensitivity was measured under an ammonia atmosphere for 200 seconds at room temperature. The results showed maximum response of ZnO/TiO2 nanoparticles with 27.30 for 200 seconds.
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