Diameter dependence of the electronic structure of ZnO nanorods determined by x-ray absorption spectroscopy and scanning photoelectron microscopy

O K-, ZnL3, and K-edges x-ray absorption near-edge structure (XANES) spectra and scanning photoelectron microscopy (SPEM) spectra were obtained for ZnO nanorods with various diameters. The analysis of the XANES spectra revealed increased numbers of O 2p and Zn 4p unoccupied states with the downsizing of the nanorods which reflects the enhancement of surface states when the diameter is decreased. Valence-band photoemission spectra show a significant narrowing of the valence band for the 45 nm diameter nanorod. The Zn 3d intensities in the Zn 3d SPEM spectra are drastically diminished for all nanorods as compared to the ZnO reference film, which can be interpreted as a reduction in density of itinerant final states or in transition probability. (C) 2004 American Institute of Physics.