Determination of ZnO(0001) surface termination by x-ray photoelectron spectroscopy at photoemission angles of 0° and 70°

We present an XPS method to determine the termination of the ZnO(0001) surface. By measuring O 1s and Zn 2p(3/2) core-level x-ray photoelectron spectra at photoemission angles of 0degrees and 70degrees and comparing the intensity ratio (I-O1s/I-Zn2p3)(0=0)/(I-O1s/I-Zn2p3)(0=70), the Zn and O termination can be distinguished. Calculations show that these two terminations have intensity ratios differing by similar to17%. This difference is not affected by a contamination layer provided that the contamination layer thickness is the same for these two differently terminated surfaces. Although this determination method prefers a clean ZnO(0001) surface (in situ measurement), it seems also feasible for surfaces with known contamination layer thickness (ex situ measurement). We have measured ex situ ZnO(0001)-Zn, ZnO(0001)-O single crystals and an epitaxial ZnO film deposited on Al2O3(0001). The measured intensity ratios of the first two samples agree with the calculated values for a 0.2 and 0.26 nm contamination layer, respectively. The intensity ratio and the O 1s contamination component intensity of the epitaxial ZnO film are close to those of the ZnO(0001)-Zn single crystal thus pointing at Zn termination of the film. Copyright (C) 2004 John Wiley Sons, Ltd.