Phase transition of dissociatively adsorbed oxygen on Ag(001)

Abstract

We show that dissociative oxygen adsorption on Ag͑001͒ induces below room temperature a missing row 2ͱ2ϫͱ2 reconstruction of the substrate. As demonstrated by the analysis of the photoelectron diffraction patterns, the oxygen atoms sit thereby in a c(2ϫ2) arrangement in the previous fourfold hollow sites nearly coplanar with the Ag atoms, while rows of substrate atoms are removed along the ͓100͔ directions. Annealing the crystal above 350 K restores the p(1ϫ1) symmetry and the oxygen moves to 0.6 Å above the fourfold hollow site. It becomes then more oxidic in nature, as demonstrated by the shift of the O 1s level from 530.3 eV to 528.3 eV. The phase transition affects also the O 2s and O 2p levels as well as the surface component of Ag 3d 5/2 . The vibrational frequency of the oxygen adatoms against the surface decreases at the phase transition, in accord with the larger adsorption distance. The higher temperature phase is active towards CO and C 2 H 4 oxidation, while the low-temperature phase is not. When cooling the sample below room temperature the reconstructed phase is restored. The time constant of this process as well as the chemical reactivity of the high-temperature phase are weakly reproducible since they depend on the previous history, i.e., presumably on the subsurface oxygen content of the sample.

The silver–oxygen system in catalysis: new insights by near ambient pressure X-ray photoelectron spectroscopy

“…Among all species, Oa 1 was found to be related to the highest amount of Ag d+ , confirming its oxidic nature as already pointed out by many authors. The relatively flat feature around 2.0 eV in the VB spectrum agrees well with UPS 10,32 and XPS 38,55 spectra reported by other authors for O species with the same core-level BE. The disappearance of Oa 1 at high temperatures ( Fig.…”

MgO∕Ag(001)interface structure and STM images from first principles

“…It has been seen experimentally that O atoms are above the hollow site at about 0.6 Å out of the Ag surface. 34 This value is rather similar to our estimate, 0.5 Å for the O adsorbed on Ag(001) for the MgO/O/Ag system. When MgO is deposited on top of the preoxidized structure the presence of the interstitial O gives rise to a larger distance from the surface metal atoms to both anions and cations of the MgO layer.…”

The effect of common gases on nucleation of metal islands: The role of oxygen in Ag(100) homoepitaxy

“…An upper limit on the coverage of oxygen in our experiments is probably given by the work of Rocca et al, wherein the coverage was estimated from vibrational experiments to be about 0.04 ML at 250 K on Ag͑100͒, after an O 2,g exposure of 1000 L. 24 The coverage of oxygen on our surface is too low to be detectable with Auger electron spectroscopy.…”