Electronic structure of ZnO nanorods studied by angle-dependent x-ray absorption spectroscopy and scanning photoelectron microscopy

Angle-dependent x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy measurements were performed to differentiate local electronic structures at the tips and sidewalls of highly aligned ZnO nanorods. The overall intensity of the O K-edge XANES spectra is greatly enhanced for small photon incident angles. In contrast, the overall intensity of the Zn K-edge XANES is much less sensitive to the photon incident angle. Both valence-band photoemission and O K-edge XANES spectra show substantial enhancement of O 2p derived states near the valence band maximum and conduction band minimum, respectively. The spatially resolved Zn 3d core level spectra from tip and sidewall regions show the lack of chemical shift. All the results consistently suggest that the tip surfaces of the highly aligned ZnO nanorods are terminated by O ions and the nanorods are oriented in the [0001̄] direction.