Study the mechanism of oxygen gas absorbed on ZnO nanorods by second harmonic generation
Feng-Ming Chang1*, Chi-Wei Yang1, Sanjaya Brahma1, Kuang-Yao Lo1
1物理系, 國立成功大學, 台南市, Taiwan
* presenting author:Feng-Ming Chang,
Semiconductor oxide (SMO) nanostructure is widely used to be gas sensors since their large ratio of surface to volume and easy fabricate. The efficiency and identification of SMO should be improved in further application. The mechanism of SMO is based on the redox reaction between the chemical absorption on the surface and the target gas. Many works focused on the mechanism of SMO and following efficiency discussion. In this work, we perform the second harmonic generation (SHG) measurement to analysis the causes of oxygen desorption and adsorption on ZnO nanorods by irradiating UV light and exposing to rich oxygen environment. As the additional double frequent contribution generated from the electrical enhanced SHG which is the third order nonlinearity and cased by built-in field of the depletion region, there is a obvious index to analyze the amount of oxygen adsorption or desorption on ZnO nanorods. The ability of oxygen adsorbed on ZnO nanorods is dependent on the defects and quality of ZnO nanorods. More post-annealing treatments were performed on ZnO nanorods to provide varied quality of ZnO nanorods which were inspected by X-ray diffraction, Photoluminescence and X-ray photoelectron spectroscopy. We observed that obvious SHG change after UV irradiation and then exposing to rich oxygen pressure due to the defects amount on ZnO nanorods. The density of adsorbed site on the surface of ZnO nanorods is limited by the quality of ZnO nanorods, and its value will determine the oxygen amount of desorption under UV light irradiation and sequent expose to air, respectively.

Keywords: ZnO, nano-rod, SHG