Fabrication of ZnO nanowires by vapor-phase deposition and their field emission properties

Unoriented ZnO nanowires are fabricated either on the surface of silicon wafer or at the tip of needle-like tungsten by vapor-phase deposition. Both the plane field emission and tip field emission of ZnO nanowires are studied using a field emission microscope. The results show that for unoriented ZnO nanowire thin films, the electric field intensities corresponding to the turn-on voltage and threshold voltage of field emission are 4.7 and 7.6 V/μm, which are much lower than those of aligned nanowire arrays. The enhancement of the field emission ability is attributed to the fact that the field-induced screening effect can be effectively avoided due to the widely spaced intervals that exist between the unoriented nanowires. The field emission of the tungsten tip also can be effectively improved by assembling ZnO nanowires on the tip, which presents a potential application of ZnO nanowire on the probe of electron microscopes with ultrahigh resolution.