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 ∼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 .deg. C, respectively. From gas sensing measurements for NH3, CO, and H2 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 ∼300% for 20 ppm NH3 at an operating temperature of 200 .deg. 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 H2 exposures. These results illustrate that the ZnO wire-like thin films are very promising for low-cost, high-performance gas sensors.