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

Abstract

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.

Commensurate monolayers on surfaces: Geometry and ground states

“…One expects lower energy structures to have higher symmetry, although this would require that the Fourier amplitudes be strictly decaying. Although this seems to be the case for some physisorption systems, 17,18 many examples of higher-order commensurate structures exist in the experimental literature on atomic and molecular adsorption, 5,9,11,13,21,22,[27][28][29] where the stability should be mainly determined by the contribution of the high-order Fourier terms. Furthermore, the knowledge of the Fourier amplitudes for any particular system ͑i.e., obtained from DFT calculations͒ could allow better interpretation of the translational symmetry of commensurate monolayers in addition to the fitting of the LEED spectra.…”

“…Even for one atom in the unit cell, the determination of the most stable adsorption site can pose severe difficulties, as it is evident from the long history of investigation of the most stable adsorption site for Xe on the Pt͑111͒ surface. 9 The identification of stable commensurate arrangements of a given monolayer-surface system is a highly relevant problem for basic science and technological applications as well. In this work, the procedure which can generate all rigid commensurate structures characterized by N ads Ͻϱ adsorbate and N sub substrate particles is presented.…”

Van Der Waals-Corrected Density Functional Theory Simulation of Adsorption Processes on Noble-Metal Surfaces: Xe on Ag(111), Au(111), and Cu(111)

“…in particular, for Xe a general tendency is found [6,[8][9][10][11] for adsorption on metallic surfaces in the low-coordination top sites (this behavior is attributed [6,16] to the delocalization of charge density that increases the Pauli repulsion effect at the hollow sites relative to the top site and lifts the potential well upwards both in energy and height).…”

“…Rare-gas adsorption on many close-packed metal surfaces, such as Ag(111), Al(111), Cu(111), Pd(111), Pt(111),.. have been extensively studied both experimentally [3][4][5][6] and theoretically [6][7][8][9][10][11][12][13][14][15]. Due to the non-directional character of the vdW interactions that should be dominant in physisorption processes, surface sites that maximize the coordination of the rare-gas adsorbate atom are expected to be the preferred ones, thus favoring the hollow adsorption site.…”

Accounting for van der Waals interactions between adsorbates and surfaces in density functional theory based calculations: selected examples

“…Although standard DFT methods cannot describe correctly the van der Waals attractive tail, the short range attraction felt by the adsorbate near the minima and the Pauli repulsion seem to be treated appropriately by these kinds of electronic structure methods. [10][11][12][13] In fact, cluster or periodic calculations employing either local density approach (LDA) or generalized gradient approach (GGA) were found to give a correct description of preferred adsorption sites of rare gases on close-packed metal surfaces (see the review of Diehl et al 14 and references there included). The interaction of molecules with solid surfaces also allows the confrontation of theory with experiment since, for instance, adsorption energies can be measured in desorption experiments and molecular structure on the surface and self-assembling can be ''visualized'' in scanning tunneling microscopy experiments and quantitatively determined by X-ray Photoelectron Spectroscopy (XPS) and similar techniques.…”