Low-Voltage-Driven Sensors Based on ZnO Nanowires for Room-Temperature Detection of NO₂ and CO Gases

Herein, we report the synthesis of pristine and Au-functionalized ZnO nanowires (NWs) for low power consumption (self-heated) gas sensors at room temperature. The ZnO NWs were produced via a vapor–liquid–solid growth technique, and Au layers with different thicknesses were sputter-deposited on the ZnO NWs, followed by subsequent annealing. Microscopic characterization methods demonstrated that ZnO NWs were successfully formed. Pristine ZnO NW gas sensors showed the best sensitivity toward either CO or NO2 gases at 300 and 350 °C, respectively. Also, the sensitivities of pristine ZnO NW gas sensors were tested toward NO2 gas under different applied voltages; the sensors revealed a good response and selectivity under an applied voltage of 7 V. Au-functionalized ZnO NW gas sensors exhibited the best response for CO gas at an applied voltage of 7 V and showed a much higher response relative to the pristine ZnO NWs. The sensing mechanisms for pristine and functionalized gas sensors are comprehensively discussed.