Oxygen chemisorption on Au(1 1 0)-(1×2) I. Thermal desorption measurements

Oxygen chemisorption on Au(1 1 0)-(1×2) 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 (β2) and 490 K (β1). The β2 state desorbs at low coverages (Θ<0.35 ML) with a second-order kinetics, indicating associative O2 desorption, and with an activation energy of 140 kJ/mol. At higher coverages (0.35 ML<Θ<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 (β1) is observed, which we associate with gold oxide.