Experimental and theoretical study of oxygen adsorption structures on Ag(111)

Abstract

The oxidized Ag(111) surface has been studied by a combination of experimental and theoretical methods, scanning tunneling microscopy, x-ray photoelectron spectroscopy, and density functional theory. A large variety of different surface structures is found, depending on the detailed preparation conditions. The observed structures fall into four classes: (a) individually chemisorbed atomic oxygen atoms, (b) three different oxygen overlayer structures, including the well-known p(4x4) phase, formed from the same Ag₆ and Ag₁₀ building blocks, (c) a c(4x8) structure not previously observed, and (d) at higher oxygen coverages structures characterized by stripes along the high-symmetry directions of the Ag(111) substrate. Our analysis provides a detailed explanation of the atomic-scale geometry of the Ag₆/Ag₁₀ building block structures and the c(4x8) and stripe structures are discussed in detail. The observation of many different and co-existing structures implies that the O/Ag(111) system is characterized by a significantly larger degree of complexity than previously anticipated, and this will impact our understanding of oxidation catalysis processes on Ag catalysts

Oxidation of Ethylene on Oxygen Reconstructed Silver Surfaces

“…Such results have similarly been predicted by ab initio calculations suggesting that silver surfaces are covered with oxygen-induced surface reconstructions at the oxygen chemical potentials typical for epoxidation under industrial conditions, while a low coverage of oxygen adatoms on an unreconstructed Ag surface is only stable at lower oxygen chemical potentials [9,15]. However, due to the long-standing difficulty associated with resolving the structure of some of these 4 surface reconstructions [16][17][18][19], we know of no complete theoretical study of their behavior in epoxidation. Thus, their role remains unclear.…”

Antibacterial activity of silver nanoparticles: A surface science insight

“…This has been attributed to an easier dissolution of [111] facets of silver, leading to a faster Ag + release and thus a higher activity for nanoparticles that exhibit more of these facets. The exact reason why Ag [111] facets are easier to dissolve remains to be investigated, but this effect could be due to differences in the solvation and arrangement of the ligands on this type of facets, or to an instability of Ag 2 O layer on Ag [111], with the preferential formation of suboxides layer [68].…”

“…The oxidative dissolution process of Ag NPs is thus likely to involves reaction of O 2 at the Ag surface, followed by the formation of a layer of AgO x (OH) y (the exact nature of the oxide layer could differ from the common bulk Ag 2 O due to size effects, ligand influence and epitaxial constraints) [68]. According to Sotiriou et al [101], this oxide layer comprises only between one and two atomic layers of Ag atoms, while the core is still constituted of metallic silver.…”

Thermally Selective Formation of Subsurface Oxygen in Ag(111) and Consequent Surface Structure

“…However, a causal link between surface preparation and surface oxide structure(s) remains undeveloped (5,7). Furthermore, it is not altogether clear how the various surface structures are tied to the 'electrophilic oxygen' species believed to be active in the partial oxidation reactions (2).…”

“…Oxygen species described by various authors have included chemisorbed oxygen (21,26), which is both weakly and strongly bound to the surface (27)(28), O γ (29), nucleophilic and electrophilic oxygen (12), oxygen in the bulk, and O sub (4,26,30). The surface structures thus far identified or proposed include p(4×4) (9,31), c(3×5√3), p(4×5√3) (32), (7x√3) (2), c(4×8) (7), p(√3×3√3)R30° (33), and striped (7,32) 5 structures as well as p(7×7) (34), AgO, and Ag 2 O oxide structures (1). As yet, there is little correlation between the oxidant, temperature, or flux, and the resultant surface structure.…”