Characterization and field-emission properties of needle-like zinc oxide nanowires grown vertically on conductive zinc oxide films

Needle-like ZnO nanowires with high density are grown uniformly and vertically over an entire Ga-doped conductive ZnO film at 550degreesC. The nanowires are grown preferentially in the c-axis direction. The X-ray diffraction (XRD) theta-scan curve shows a full width at half maximum (FWHM) value of 2degrees. The indicates that the c-axis of the nanorods are along the normal direction of the substrate surface. The investigation using high-resolution transmission electron microspray (HRTEM) confirmed that each nanowire is a single crystal. A room-temperature photoluminescence (PL) spectrum of the wires consists of a string and sharp UV emission band at 380 nm and at 380 nm and a weak and broad green-yellow band. It reveals a low concentration of oxygen vacancies in the ZnO nanowires and their high optical quality. Filed electron emission from the wires was also investigated. The turn-on field for the ZnO nanowires reached 0.1 mA cm(-2) at a bias filed of 24 V mum(-1).