Low Power Consumption Gas Sensor Created from Silicon Nanowires/TiO2 Core-Shell Heterojunctions.

Silicon nanowires/TiO2 (SiNWs/TiO2) array with core-shell nanostructure was created by sol-gel and drop-casting methods. The hybrid material displayed excellent sensing performance for CH4 detection at room temperature. The chemiresistor sensor has a linear response toward CH4 gas in the 30-120 ppm range with a detection limit of 20 ppm, which is well below most CH4 sensors reported before. The enhanced gas sensing performance at room temperature was attributed to the creation of heterojunctions that form a depletion layer at the interface of SiNWs and TiO2 layer. Adsorption of oxygen and corresponding gas analyte on TiO2 layer could induce the change of depletion layer thickness and consequently the width of the SiNWs conductive channel, leading to a sensitive conductive response toward gas analyte. Compared to conventional metal oxide gas sensors, the room temperature gas sensors constructed from SiNWs/TiO2 do not need an additional heating device and work at power at the μW level. The low power consumption feature is of great importance for sensing devices, if they are widely deployed and connected to the Internet of Things. The innovation of room temperature sensing materials may push forward the integration of gas sensing element with wireless device.