Synthesis and Characterization of TiO2-sheathed ZnO nanowires

초록

In recent years, one-dimensional (1D) nanostructures have been extensively investigated due to their interesting properties and potential applications in electronics and optoelectronics. In particular, extensive research into coaxial one-dimensional (1D) nanostructures consisting of different materials in the radial direction has been carried out due to their potential applications in electronic and optoelectronic device applications owing to a couple of important reasons. One reason is that the coaxial 1D nanostructures can realize various tailor-made functions by fabricating heterojunction nanodevices or depositing multilayers with different chemical compositions in the radial direction. Another is that we can protect them from oxidation or contamination and passivation of interface states abundant at the surface of 1D nanostructures. Much more work has been done for the latter purpose in the synthesis of the radial heterostructures by coating the semiconductor cores with oxide materials. In this study, ZnO nanowires have been grown by thermal evaporation of ZnO powders on Si (100) substrates coated with gold (Au) thin films. The ZnO nanowires by using vapor-liquid-solid (VLS) mechanism were 30 – 60 nm in diameter and up to 200nm in length. We also have prepared ZnO/TiO2 coaxial nanowires by metal organic chemical vapor deposition (MOCVD) of TiO2 onto the nanowires. Transmission electron microscopy (TEM) and X–ray diffraction (XRD) analysis results indicate that the ZnO-cores and the TiO2 shells of the annealed coaxial nanowires are of a single crystalline nature with wurtzite and simple tetragonal structures, respectively. TiO2 coating slightly increases the photoluminescence (PL) emission intensity of ZnO nanowires. The PL emission of the TiO2-sheathed ZnO nanowires can be considerably enhanced by thermal annealing and are found to strongly depend on the annealing atmosphere. In particular, the PL emission intensity of the ZnO/TiO2 coaxial nanowire