A combined LEED, AES and XPS study of the ZnO {0001} polar surfaces: I. LEED, AES and XPS of contaminated surfaces

Abstract

The {0001} polar surfaces of ZnO single crystals have first been examined after a chemical treatment involving HCl and H 3PO 4 and a 24 hr bakeout at 250 °C. The impurities detected on the (000 1 )-O surface with AES were carbon, chlorine, phosphorus and to a lesser extent sulphur. On the (0001)-Zn surface, carbon, chlorine and sulphur were the dominant impurities, while the phosphorus signal was less important. These results were confirmed by XPS measurements on frehsly etched surfaces. The AES spectra were recorded as distribution curves N( E). Averaging, curve-fitting and related numerical techniques were used to obtain high resolution spectra, enabling the identification of the phosphorus L 1-transitions. The etched surfaces were cleaned progressively using argon ion bombardment and ohmic heating. It has been consistently observed that the clean surfaces exhibit primitive (1 × 1) structures. Superstructures such as ( 3 × 3 ) on the (000 1 )-O surface, and (4 3 × 4 3 ) and (3 × 3) on the (0001)-Zn surface, were repeatedly observed at discrete spots of contaminated surfaces. A clear correlation with impurities as observed by AES however could not be found. Facetting was observed after prolonged heating.