Oxygen chemisorption on Au(110)-(1 x 2) I. Thermal desorption measurements

Oxygen chemisorption on Au(110)-(1 x 2) was induced by electron bombardment (500 eV) of physisorbed oxygen molecules at 28 K. TDS reveals the successive occupation of two desorption states around 550 K (beta(2)) and 490 K (beta(1)). The beta(2) state desorbs at low coverages (Theta < 0.35 ML) with a second-order kinetics, indicating associative O-2 desorption, and with an activation energy of 140 kJ/mol. At higher coverages (0.35 ML < Theta < 1.0 ML), desorption is dominated by an autocatalytic behaviour resulting in a high-temperature shift and a narrow peak width. The TD spectra of the submonolayer range were simulated on the basis of a kinetic model that includes formation of oxygen islands and desorption from a phase equilibrium between two-dimensional condensed and gas phases. As the coverage exceeds 1.0 ML, another desorption state (beta(1)) is observed, which we associate with gold oxide. (C) 2002 Elsevier Science B.V. All rights reserved.