Discrimination between domain wall and uniformly incommensurate structures by surface extended x-ray absorption fine structure: Adsorption of chlorine on Ag{110}

Abstract

A well-established problem in surface structure determination is the experimental difficulty in distinguishing a uniformly incommensurate structure from a domain wall structure. Surface extended x-ray absorption fine structure (SEXAFS), as a local structural probe, should provide an unambiguous means of making the distinction. We have studied chlorine adsorbed on Ag{110} by SEXAFS at several coverages. The Cl–Ag nearest-neighbor distance, 2.56±0.04 Å, is found to be substantially shorter than on the {111} and {100} faces, and is independent of coverage. At θ=0.75 an incommensurate phase is formed. A multishell analysis (up to 5.6 Å) allowed a complete structural determination and has, for the first time, confirmed our expectation. The Cl–Cl spacing unambiguously favors a domain wall structure. Structural models have been tested by laser simulation experiments, and by kinematic analysis of the low-energy electron diffraction data.

Halogen Phases on Pd(110): Compression Structures, Domain Walls, and Corrosion

“…Instead, domain walls are formed, as one would expect if an incommensurate overlayer were modulated by the periodic potential of the substrate. 19,20 A similar conclusion was drawn by Holmes et al 21 for Cl on Ag(110) based on surface extended X-ray absorption.…”

“…A further remarkable result is the general occurrence of compression structures for all of the halogens on a variety of fcc(110) substrates, namely, Pd, 12 Cu, 18,24,25 Ag, 21,31,32 and Au. 33,34 The notable exception is the Pt(110) surface, on which specific new adsorption sites are populated as the coverage exceeds 0.5 ML.…”

“…A further remarkable result is the general occurrence of compression structures for all of the halogens on a variety of fcc(110) substrates, namely, Pd, Cu, ,, Ag, ,, and Au. , The notable exception is the Pt(110) surface, on which specific new adsorption sites are populated as the coverage exceeds 0.5 ML. This is true for all halogens, even though, up to 0.5 ML, Cl and Br occupy preferably short-bridge sites, whereas I adsorbs in long-bridge sites.…”

Determination of an Adlayer Bonding Transition by Surface Extended X-Ray-Absorption Fine-Structure Spectroscopy: Cesium Adsorbed on Ag {111}

“…Other systems have shown no variation in distance, and our own highprecision SEXAFS study of CI adsorption on Ag{lll} and on Ag{ll0} gave a Cl-Ag distance that was constant, within experimental error of 0.01 A, at two different coverages. 24,25 Dipole-dipole repulsions still occur for increasing density of CI adatoms, but the interatomic distance is unchanged. The differences between electronegative adsorbates and the alkali metals may be explained by the energy of the adsorbate resonance.…”

Structure of thec(2×2)-Br/Pt(110) surface

“…In most previous studies, the structure was deduced from qualitative low energy electron diffraction ͑LEED͒ [6][7][8][9][10][11] or scanning tunneling microscopy ͑STM͒. 3,[12][13][14][15][16] Adsorption site analysis was carried out mainly by surface extended x-ray-absorption fine structure ͑SEXAFS͒, [17][18][19][20][21][22][23] whereas quantitative structure determinations by LEED ͑Refs. 24 -26͒ or first-principles calculations 27,28 are sparse.…”