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 $p(4\ifmmode\times\else\texttimes\fi{}4)$ phase, formed from the same ${\text{Ag}}_{6}$ and ${\text{Ag}}_{10}$ building blocks, (c) a $c(4\ifmmode\times\else\texttimes\fi{}8)$ 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 ${\text{Ag}}_{6}/{\text{Ag}}_{10}$ building block structures and the $c(4\ifmmode\times\else\texttimes\fi{}8)$ 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.