Optical and sensor properties of ZnO nanostructure grown by thermal oxidation in dry or wet nitrogen

Zn films on glass were oxidized at 390°C in dry or wet N₂. As-prepared ZnO oxides were characterized by a scanning electron microscope (SEM), an X-ray diffractometer (XRD), a transmission electron microscope (TEN) and photoluminescence (PL) measurements. Gold electrodes were deposited on ZnO films to obtain ZnO gas sensors, which were characterized by exposure to ethanol at room temperature. The results show that the specimen oxidized in dry N₂ exhibits a sharp PL peak at 380 nm whereas that oxidized in wet N₂ exhibits a broad peak at 490 nm. The sensors demonstrate significant sensitivity to ethanol vapor at room temperature with a detection limit of 200 ppm for the sensor with ZnO oxidized in wet N₂. Recovery for the sensor with ZnO oxidized in wet N₂ can be achieved by illumination with natural light. However, for the sensor with ZnO oxidized in dry N₂, ultraviolet (UV) radiation is needed for recovery.