Spontaneous and electron-induced adsorption of oxygen on Au(110)-(1 x 2)

The interaction of dioxygen with a gold(1 1 0)-(1 x 2) surface has been investigated between 28 and 700 K by means of thermal desorption spectroscopy (TDS), UV photoelectron spectroscopy (UPS), work function measurements (DeltaPhi), low-energy electron diffraction (LEED), and near-edge X-ray absorption spectroscopy (NEXAFS). It proves that Au-unlike most of the other metals including its congeners Cu and Ag-does not spontaneously dissociate physisorbed molecular oxygen. Rather, additional activation of the physisorbed O-2 either by electron or by photon impact is required to make the oxygen chemisorb. Below 50 K, dioxygen adsorbs readily with a binding energy <12 kJ/mol, causing a work function decrease of DeltaPhi = 0.22 eV at Theta = 1.0 ML. TDS reveals three molecular desorption states with first-order kinetics around 51 and 45 K (first layer), and at 37 K (second layer). A zeroth-order peak around 34 K corresponds to multilayer desorption. Both UPS and NEXAFS exhibit signals typical for physisorbed O-2. Irradiation of physisorbed O-2 layers with low-energy electrons or UV photons produces chemisorbed oxygen, providing a convenient possibility for the preparation of chemisorbed oxygen adlayers. The chemisorbed oxygen species is characterized by a single desorption state above 500 K, with second-order kinetics at low coverages (Theta < 0.25 ML) suggesting adsorbed oxygen atoms. A desorption energy of 140 +/- 3 kJ/mol was determined. Another desorption peak around 490 K and at coverages >1.0 ML is associated with the decomposition of an oxidic species. LEED observations reveal that chemisorbed oxygen destroys the long-range order of the An substrate surface. Our results provide possible explanations for the 'beam damage' often observed in UPS/LEED experiments with adsorbed dioxygen. (C) 2002 Elsevier Science B.V. All rights reserved.