LAUSR

Biaxial p-SnO/n-ZnO heterostructured (nanowiresaverage length of 10 µm) were grown on a glass substrate using a chemical vapor deposition (CVD) system. These nanowires had spherical ball tips, andthe size of the SnO part increased gradually from the top to the bottom of the nanowire, but the corresponding size of ZnO varied slightly. The Sn-Zn alloy formed in the tips resulted in catalytic growth of the ZnO nanowires via the vapor-liquid-solid (VLS) mechanism. A possible growth mechanism of the p-SnO/n-ZnO biaxial nanowires was discussed based on the subsequent growth process: the VLS catalyticgrowth of the ZnO nanowire and subsequent epitaxial SnO growth on the sidewall of the pre-grown ZnO nanowire. An epitaxial relationship, (001)SnO//(110)ZnO and [110]SnO//[002]ZnO, was observed in the biaxial p-SnO/n-ZnOheterostructured nanowires. The gas sensing properties of the as synthesized p-SnO/n-ZnO nanowires were investigated. The results show that the device exhibit a good performance to ppb-level NO2 at room temperature (25 °C) without light illumination. The limit of detection of NO2 for the p-SnO/n-ZnO sensor is 50 ppb. Moreover, the NO2 sensing properties of the p-SnO/n-ZnO device was investigated under various relative humidity (RH). Finally, the NO2 sensing mechanism of the p-SnO/n-ZnO nanowires was proposed and discussed.