M. Caragiu

Observation of top-site adsorption for Xe on Cu(111)

Abstract A low-energy electron diffraction study of Cu(111)–(√3×√3)R30°–Xe at 50 K indicates that Xe atoms occupy the top sites. The equilibrium Xe–Cu interlayer spacing is 3.60±0.08 A and the spacings of the three top Cu layers are essentially bulk-like. The Xe–Cu spacing agrees well with estimates based on hard-sphere packing. Top-site adsorption for Xe on Cu(111) was unexpected on the basis of previous experimental and theoretical results for noble gas adsorption on metal surfaces. This result is discussed in the light of earlier studies of physisorbed atoms, anticorrugated potentials in He-atom scattering, and possible links to alkali metal adsorption.

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.

The coverage dependence of the adsorption structures of Cs on Ag(111)

Abstract The structures of five different submonolayer commensurate phases of Cs on Ag(111) have been determined by low energy electron diffraction (LEED). This paper presents the results of two of these studies: for the primitive (2 3 ×2 3 )R30° and ( 7 × 7 )R19° structures which form at coverages of 1/12 and 1/7 respectively. The adsorption site was found to be the fcc hollow in both cases. These structures are accompanied by a substrate rumple which has the effect of allowing the Cs atoms to push deeper into the substrate. The structures determined here, along with the earlier structure determinations of three other submonolayer phases, indicate that the CsAg bond length does not change over the coverage range from 1/12 to the monolayer saturation coverage of 1/3.