Adsorption of carbon monoxide on Au(1 1 0)-(1 × 2)

The adsorption of carbon monoxide on a gold (1 1 0)-(1 × 2) surface was studied between 28 and 300 K by means of TDS, UPS, ΔΦ, NEXAFS, and LEED. Below 150 K, CO adsorbs non-dissociatively with high initial sticking probability (S0=0.9 at 28 K). The isosteric heat of CO adsorption is 59 kJ/mol for ΘCO→0 and decreases strongly with coverage, indicating weak chemisorption and substantial CO–CO repulsion, in agreements with TDS results. Thermal desorption spectra show at least five desorption states corresponding to desorption energies between 38 and 8 kJ/mol. According to TDS, chemisorbed and physisorbed CO coexist in the first layer, a result that is corroborated by UV photoemission spectra. CO adsorption has a complex influence on ΔΦ and leads to a work function reduction of −0.95 eV at monolayer coverage. TDS and entropy measurements suggest that the state of chemisorbed CO at 160 K is best described by the model of a two-dimensional gas. No ordered CO overlayer structures were observed in the whole coverage and temperature range.