Dispersed Au atoms, supported on TiO2(1 1 0)

The agglomeration behavior of 0.05 ML of Au deposited as Au+ at 1 eV impact energy on rutile TiO2(1 1 0) was investigated by a combination of ion scattering, X-ray photoelectron spectroscopy (XPS), CO adsorption, and CO temperature-programmed desorption (TPD). Samples were studied over the temperature range between 115 K and 800 K, and on both near-stoichiometric UHV-annealed TiO2, and TiO2 with a high density of oxygen vacancies created by He+ bombardment. At low temperatures, Au is atomically dispersed, shifting into complexes with oxygen vacancies for Tanneal around room temperature, and finally agglomerating into small clusters for Tanneal ⩾ 450 K. CO adsorbed on dispersed atoms results in nearly 1 eV shift in the Au 4f binding energy to higher energy, and CO desorption peaking at 280 K. CO adsorbs more weakly on Au–vacancy complexes and on Au in clusters, as indicated by both TPD and XPS. Comparisons with experiments depositing thermal Au, and implications for size-selected CO oxidation on Aun/TiO2 are discussed.