Microstructure and optical properties of V2O5-capped ZnO nanorods

초록

V2O5-capped ZnO nanorods were fabricated on Si substrates using a two-step process: thermal evaporation of a mixture of ZnO and graphite powders and sputter-deposition of V2O5. Scanning electron microscopy (SEM), transmission electron spectroscopy (TEM), and X-ray diffraction, and Pholuminescence (PL) spectroscopy analyses were systematically carried to investigate the microstructure and optical properties of the nanostructures. The ZnO nanorods were 80-200 nm in diameter and a few tens of micrometers in length. The as-synthesized ZnO was monocrystalline whereas the V2O5 capping layer was amorphous. The XRD analysis revealed that the capping layer was partially recrystallized by annealing. The as-synthesized ZnO nanowires have a strong near-band edge (NBE) emission band centered at around 375 nm and a very weak broad deep level (DL) emission band centered at around 540 nm. The NBE and DL emission intensities strongly depend on the thickness of the V2O5-capping layer. Both the NBE and deep level emissions were slightly increased in intensity by capping the ZnO rods with V2O5 of a proper thickness (equivalent to the sputtering time of 20 min). However, the DL emission was substantially increased and the emission band was shifted from 540 to 460 nm by annealing in an oxidation atmosphere. The mechanism for the changes in the PL by capping and postannealing have been discussed.