STRUCTURE OF THE ZNO (000(1)OVER-BAR) SURFACE STUDIED BY X-RAY PHOTOELECTRON DIFFRACTION

The general ability of photoelectron diffraction (XPD) to investigate the surface structure of oxides is shown. The actual termination of a ZnO single crystal is determined, oriented along the basal plane, distinguishing between the two possible (0001) and (0001BAR) polar surfaces. The collected XPD curves have been compared with theoretical calculations. For all the transitions examined, the features of the XPD azimuthal curves were found to repeat for a period of 60-degrees, that is, the surface has an apparent sixfold symmetry which has been interpreted as being due to the presence of domains, separated by biatomic steps, equally distributed on the surface and rotated 60-degrees with respect to each other. The existence of two surface domains rotated 60-degrees was taken into account by averaging calculations for the two orientations. We tested two possible structural models, corresponding to the (0001) and to the (0001BAR) bulk termination structures, comparing the XPD azimuthal curves of the Zn 2p3/2, Zn 3p and O 1s transitions.