Localized Liquid-Phase Synthesis of Porous SnO Nanotubes on MEMS Platform for Low-Power, High Performance Gas Sensors.

We have developed highly sensitive, low-power gas sensors through the novel integration method of porous SnO nanotubes (NTs) on a micro-electro-mechanical-systems (MEMS) platform. As a template material, ZnO nanowires (NWs) were directly synthesized on beam-shaped, suspended microheaters through an in situ localized hydrothermal reaction induced by local thermal energy around the Joule-heated area. Also, the liquid-phase deposition process enabled the formation of a porous SnO thin film on the surface of ZnO NWs and simultaneous etching of the ZnO core, eventually to generate porous SnO NTs. Because of the localized synthesis of SnO NTs on the suspended microheater, very low power for the gas sensor operation (<6 mW) has been realized. Moreover, the sensing performance (e.g., sensitivity and response time) of synthesized SnO NTs was dramatically enhanced compared to that of ZnO NWs. In addition, the sensing performance was further improved by forming SnO-ZnO hybrid nanostructures due to the heterojunction effect.