Development of ZnO-based surface plasmon resonance gas sensor and analysis of UV irradiation effect on NO2 desorption from ZnO thin films

In order to perform a high throughput exploration of sensor materials using surface plasmon resonance (SPR), the gas sensing property of a ZnO/Au/SiO2 chip with SPR and the enhancing effect of UV irradiation on the desorption rate of NO2 from the ZnO surface were investigated. When the ZnO/Au/SiO2 chip was exposed to a high concentration of NO2 (1000 ppm), a large peak shift was observed in the SPR curve. However, this sensing signal for NO2 gas did not recover to the baseline. In the case of low-concentration NO2 (10 ppm), the peak shift of the SPR curve was lower than that in the case of the high-concentration gas, but recovery to the baseline was observed. From the X-ray photoelectron spectra for N 1s of the ZnO thin films exposed to 1000- and 10-ppm NO2, two chemisorption states—NO2- (403.7 eV) and NO3- (407 eV)—were confirmed. After the ZnO film was irradiated by UV rays, exposed to 10-ppm NO2, all peaks related to N 1s disappeared. However, in the case of the ZnO film exposed to 1000-ppm NO2, adsorbed NO3- remained on the surface of ZnO. From these results, it was found that UV irradiation effectively assisted NO2 desorption from the surface of the ZnO thin film exposed to 10-ppm NO2.