A practical vacuum sensor based on a ZnO nanowire array

We report a practical vacuum pressure sensor based on a ZnO nanowire array (NWA). An oriented single-crystal ZnO NWA was synthesized by electrodeposition. The device consists of two ITO glass plates coated with a ZnO NWA. Scanning electron microscopy (SEM) and the x-ray diffraction (XRD) pattern show that the as-grown ZnO NWAs are single-crystal and roughly oriented with the ZnO(002) plane parallel to the substrate. Through measuring the pressure dependent resistance of the sensor at different gas species and temperatures, we discovered that the resistance increases monotonically with vacuum pressure. This demonstrates that a practical vacuum sensor could be fabricated since measurements were carried out with a normal multimeter, with no need for the high sensitivity and costly equipment as routinely required in nanotechnology for extremely weak signals. Measurement at elevated temperature (300 deg. C) showed that the vacuum sensor is much stabler and more sensitive to O2 pressure. The principle of the device relates to the adsorbed oxygen species on the large surface area of a ZnO NWA to form a resistive depletion layer at the nanowire (NW) surface.