Synthesis and Gas Sensing Properties of ZnO Nanostructures

We report on the gas sensing properties of ZnO nanostructures synthesized using a simple method combined with sputtering and subsequent thermal oxidation of sputtered metallic films in dry air. By controlling the sputtering condition, we achieved polycrystalline wurtzite ZnO films with a flower-like structure consisting of nanoflakes with a thickness of similar to 20 nm and a wire-like structure having a width of 100 - 150 nm and a length of several microns for deposition temperatures of room temperature and 150 degrees C, respectively. From gas sensing measurements for NH3, CO, and H-2 in dry air, the gas sensors based on ZnO wire-like thin films showed quite better responses than those based on ZnO flower-like thin films. The ZnO wire-like thin film gas sensors exhibited a high sensitivity to NH3 with a maximum sensitivity as high as similar to 300% for 20 ppm NH3 at an operating temperature of 200 degrees C and a detection limit of 2 ppm. In addition, the ZnO wire-like thin film gas sensors also displayed good responses to CO and H-2 exposures. These results illustrate that the ZnO wire-like thin films are very promising for low-cost, high-performance gas sensors.