Synthesis, Characterization And Application Of ZnO Whiskers

ZnO materials exhibit a wide range of electrical and optical properties that depend sensitively on both shape and size, and are of both fundamental and technological interest. We have demonstrated a simple vapor-phase approach to control growth of ZnO whiskers. Some types of ZnO whiskers with various shape and size, including tetrapod-like ZnO (T-ZnO) whiskers, one-dimensional whiskers (nanowires) and arrays etc., have been obtained by controlled growth process in our laboratory. The key for controlling the shape and size is the level of supersautration that controls ZnO nucleation and growth. The supersaturation in the reaction vessel strongly depends on the processing parameters.The structures of ZnO whiskers have been investigated by means of scanning electron microscope (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The growth mechanisms of various ZnO whiskers are proposed based on our experimental observations. Results show that T-ZnO whiskers grow in vapor-solid (VS) mechanism. T-ZnO whiskers grow in octa-twin model. Our experimental observation gives the direct evidence to the octahedral multiple twin nucleus model of T-ZnO whisker. ZnO nanowires and arrays deposited on Si substrate also grow in vapor-solid (VS) mechanism.The room temperature PL spectra of the ZnO whiskers show a narrow UV emission at 385nm and a broad green emission at 495nm. The green emission intensity in different structures is different, while their UV emission intensity is nearly the same. The difference in green emission intensity results from the different level of oxygen vacancies in ZnO structures. The green emission intensity in ZnO nanowires is decrease but the UV emission intensity keeps unchanged when the nanowires are annealed at 950℃ for an hour. It is obvious that optical property of the ZnO is tunable by controlling the oxygen vacancy concentration.The electrical resistivity of T-ZnOw/Polypropylene composites is decreased by using T-ZnO whiskers as the conductive additives. The conductive mechanisms are the combine of net conductive, tunnel effect and the charge concentrating effect at the needle's tips of the whiskers. The tensile strength of the composites is increase 50% compared to the PP matrix.