Effects of SiO2 coating and thermal annealing on the structure and optical properties of ZnO nanowires

초록

It is essential to passivate of 1D nanostructures with insulating materials to avoid crosstalking between the building blocks of complex nanoscale circuits as well as to protect them from contamination and oxidation. Passivation also offers many advantages such as substantial reduction of surface densities, prevention of the surface from adsorption of unwanted species, prevention of unnecessary charge injection, and partial screening of the external fields. In particular, passivation of nanowires is required in fabrication of field effect transistors and sensor devices based on nanowires. Various techniques have been reported to be used to form passivation layers on the 1D nanowire cores. We have fabricated ZnO-core/SiO2-shell one-dimensional nanostructures by coating the ZnO nanowires with SiO2. ZnO nanowires were synthesized by thermal evaporation of ZnO powders and then coated with SiO2 by using a sputtering technique. We performed scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDXS), and photoluminescence (PL) spectroscopy to characterize the of ZnO-core/ SiO2-shell coaxial nanowires. TEM and XRD analyses revealed that the ZnO cores and the SiO2 shells had crystalline face-centered cubic (fcc) and amorphous structures, respectively. Photoluminescence (PL) measurement at room temperature shows that ZnO nanorods have a strong ultraviolet (UV) emission (3.26 eV) and a weak broad emission centered at around 2.46 eV in the green region. It is also found that the UV emission intensity of ZnO nanowires can be increased by coating them with a SiO2 layer with an appropriate thickness. The PL properties of the ZnO-core/SiO2-shell nanowires strongly depend on the annealing atmosphere. The UV emission intensity has been slightly increased by annealing in a reducing atmosphere and the emission peak position has been red-shifted. In contrast, the UV emission intensity has been increas