The adsorption sites of rare gases on metallic surfaces: a review

During the past six years, the adsorption geometries of several rare gases in structures having several different symmetries on a variety of substrates were determined using low-energy electron diffraction (LEED). In most of these studies, a preference is found for the rare gas atoms to adsorb in the low-coordination sites. Only in the case of adsorption on graphite has a clear preference for a high-coordination site for a rare gas atom been found. This unexpected behaviour is not yet completely understood, although recent density functional theory (DFT) calculations for these and similar surfaces suggest that this is a general phenomenon. This paper reviews the early studies that were presages of the discovery of top site adsorption for rare gases, the discovery itself, and the present state of understanding of this curiosity. It also details some of the features of the LEED experiments and analysis that are specific to the case of rare gas adsorption