Electron energy loss spectroscopy of ZnO nanocrystals with different oxygen vacancy concentrations

Abstract

ZnO nanocrystals with different oxygen vacancy concentrations were characterized by high-resolution electron energy loss spectroscopy (HREELS). ZnO nanocrystals show a decrease in green emission with increasing annealing temperature in an oxygen environment and which significantly quenches in a sample annealed at 400°C. O K and Zn L₃ pre-edge absorption structures of ZnO nanocrystals were studied by HREELS as a function of annealing temperature. Absorption edge peak broadening and variation in pre-edge absorption edge structure of Zn L₃ were observed in experimental electron energy loss spectroscopy spectra with different oxygen defect concentrations. All electron density functional theory (DFT) based (WIEN2k) calculation of electronic density of states and electron energy loss near edge structure were carried out with different oxygen vacancy concentrations and compared with experimental observations. Appearance of additional peaks in pre-edge electron energy loss structure with increasing oxygen vacancy is shown to be due to the oxygen defect states in the bandgap just below the conduction band.