Characterization of reordered (001) Au surfaces by positive−ion−channeling spectroscopy, LEED, and AES

An extensive investigation of the atomic arrangement on the (001) Au surface has been performed using the techniques of positive−ion−channeling spectroscopy (PICS), LEED, and AES. Both the normal surface in which the Au atoms are ordered in a square array and the reordered surface where it is proposed that the topmost layer of Au atoms are ordered in a hexagonal array have been examined. LEED and AES have been used in determining that the normal atomic arrangement producing the (1×1) LEED pattern is observed only when contamination is present, while the reordered surface producing the complex (5×20) LEED pattern is observed on surfaces which are atomically clean. The yield and energy distributions of 1 MeV 4He+ ions scattered from the oriented Au crystals have been used to determine the number of effective monolayers constituting the normal and reordered surfaces. Single alignment surface peaks and minimum yields have been determined, and experimental data are compared with predictions made by computer simulation calculations. It is found that the surface peak from the reordered surface is larger by an amount corresponding to ? 1 monolayer; this implies that only one extra hexagonal layer of atoms exists on the clean surface.