Unequal-Sphere Packing Model for Simulation of the Uniaxially Compressed Iodine Adlayer on Au(111)

Abstract

A simple unequal-sphere packing (USP) model, based on pure geometrical principles, was applied to study the centered-rectangular iodine c(p× 3)R30°adlayer on the Au(111) surface, well-known from surface X-ray structure (SXS), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM) experiments. To reproduce the exact patterns observed in experiments, two selective conditionssminimum average adsorbate height and minimum adlayer roughnessswere imposed. As a result, a series of adlayer patterns with c(p× 3)R30°symmetry (2.3 < p < 3), with precise structural details, including atomic registry and identification of the p-bisector as the most likely trajectory for the iodine adatom movement during the so-called uniaxial compression phenomenon, were identified. In addition, using the same model, the difference between the iodine adlayer arranged in hexagonal and centered-rectangular c(p× 3)R30°patterns, as in the case of Pt (111) and Au(111) surfaces, was investigated. Qualitative and quantitative comparison shows that iodine adatoms in these two arrangements differ significantly in atomic registry, distance from the substrate, and the adlayer corrugation. Our findings could be of special interest in the study of the nature of the iodine adatom bonding to different substrates (i.e., Au vs Pt).

Experimental structure determination of the chemisorbed overlayers of chlorine and iodine on Au{111}

“…Examples are the low-temperature oxidation of CO and CH 4 and the water-gas shift reaction on gold nanoparticles [1][2][3] , oxygenpromoted dissociation of O 2 on Au{111} 4 , or chlorine-promoted selectivity in the oxidation of olefins and mercury 1,4,5 . The selectivity-enhancing effect of chlorine in particular and the general importance of halogens in electrochemical reactions have prompted a number of experimental and theoretical studies on halogen adsorption on the close packed {111} surfaces of the group 1B coinage metals Cu, Ag and Au [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] .…”

“…1,4,5 The selectivity-enhancing effect of chlorine in particular and the general importance of halogens in electrochemical reactions have prompted a number of experimental and theoretical studies on halogen adsorption on the close-packed {111} surfaces of the group 1B coinage metals Cu, Ag and Au. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Chemisorbed Cl layers display well-ordered phases, which make structure determinations possible with a number of experimental techniques. The experimental studies agree that Cl prefers fcc adsorption sites on Cu and Ag{111}.…”

Classification of hexagonal adlayer arrangements by means of collective geometrical properties

“…We have recently shown that the I-Au͑111͒ system, which possesses structures with long periodicity, could also be described by our unequal-sphere packing model. 21 Moreover, additional parameters could be used for identification of the most likely structures in the case of different adsorbate-substrate systems.…”

Comment on “The Origin of Surface Stress Induced by Adsorption of Iodine on Gold”

“…Furthermore, the iodine monolayer on the Au(111) surface can form a large variety of structures, from the commensurate (√3×√3) R 30°, to uniaxially compressed c( p ×√3) R 30° with variable p , to rotated hexagonal ones. The formation of these monolayers has been attributed to a competition between the complex atom−surface and atom−atom interactions . Nevertheless, the authors do not comment on this fact, and consequently, it is not clear in the paper which monolayer symmetry the iodine possesses (i.e., no surface structure analysis was performed).…”

“…The formation of these monolayers has been attributed to a competition between the complex atom-surface and atom-atom interactions. 9 Nevertheless, the authors do not comment on this fact, and consequently, it is not clear in the paper which monolayer symmetry the iodine possesses (i.e., no surface structure analysis was performed). Finally, to obtain the hexagonal monolayer interaction energy, the authors multiply the pairwise interaction potential by 6 instead of the correct value of 3 (to avoid double counting for an atom i interacting with atom j).…”