ZnO single nanowire gas sensor: A platform to investigate the sensitization of Pt

Platinum (Pt) has been extensively used as a catalyst in metal oxide semiconductor (MOS) gas sensors. However, a clear understanding on the size effect of Pt sensitization is still missing. Herein, we establish a ZnO single nanowire sensor as a platform to investigate the sensitization of Pt catalyst. Pt has been loaded on ZnO nanowires by both atomic layer deposition (ALD) and solution method to realize delicate control over the size and loading mount. With increasing ALD cycles, the Pt size increases from single atom to an average of 11.86 nm and the sensor resistance shows a decrease. The nanowire sensor with a medium Pt loading (0.61 at%) with a size of 3.95 nm shows the best response of 7.01 to 20 ppm NO2, revealing a 5-fold enhancement compared to pristine ZnO. The sensor operating temperature shows a remarkable decrease from 310 to 220 degrees C due to Pt sensitization. A control sensor with almost identical Pt loading of 0.59 at% and size of 4.98 nm prepared by solution impregnation displays a response of 5.04 to 20 ppm NO2, but showing much slower response and recovery. Our findings determinate the crucial effect of Pt size in chemical sensors.