A study of oxygen gas adsorbed on ZnO nanorods by optical second harmonic generation

Abstract

ZnO nanorods have been applied to be a gas sensor as their high surface to volume ratio Oxygen absorption and desorption on ZnO nanorods should depend on the quality of surface and bulk ZnO nanorods In order to distinguish the contribution from the surface or bulk of ZnO nanorods there should be available tools to inspect the change amount of oxygen absorption on ZnO nanords through post-treatment Second harmonic generation (SHG) has high sensitivity on the surface variation and reflects to the actual amount of oxygen adsorption on ZnO nanorods In this work SHG is used to consist with the measurement of XPS PL and XRD for realizing the mechanism of gas sensor made of ZnO nanorods and the correlation between the surface or bulk quality of nanorods In order to study the mechanism of oxygen absorbed on ZnO nanorods we choose the three different annealing conditions by different annealing temperature and oxygen pressure in the annealing chabmer (1) changing the annealing temperature (room temperature 200℃ 400℃ and 600℃) in oxygen gas but fixing the annealing pressure (2) changing the annealing pressure (25 mTorr 55mTorr 130mTorr and 180mTorr) but fixing the annealing temperature (3) changing the annealing ambient (vacuum or oxygen) at (600℃ or 800℃) in which these annealing conditions were tuned to change the surface states or structure of zinc oxide nanorods When the surface states or structure of ZnO nanorods is changing the amounts of oxygen absorbed on the surface of ZnO nanorods will follow the change We use the PL spectrum and FWHM of (002) peak in XRD to study ZnO nanorods surface states and structure and the XPS spectrum and the changing of SHG intensity to measure the changing of amounts of oxygen absorbed on the ZnO nanorod surface which caused by irradiating UV light irradiation or exposing rich oxygen We compare these results of these measurements with each others and we obtain some relationships between the surface states or structure of ZnO nanorods and the amounts of ZnO nanorods surface oxygen We built the effective method to explain the amounts of ZnO nanorods surface oxygen and its states This result will be important influence to develop ZnO gas sensor because oxygen ions on the ZnO nanorods surface are the reaction center (the mechanism of gas sensor is that the surface oxygen ions react with the sensing gas and then change its characteristic)

Date of Award	2015 Jul 22
Original language	English
Supervisor	Kuang-Yao Lo (Supervisor)