Oxidation of gold by oxygen-ion sputtering

Adsorbed and implanted oxygen species produced by bombardment of a gold (1 1 0)-(1×2) surface with oxygen ions (O+/O2+) were characterized by thermal desorption spectroscopy (TDS), work function measurements (ΔΦ), and low-energy electron diffraction (LEED). TDS reveals four oxygen desorption states between 350 and 950 K, which are associated with chemisorbed atomic oxygen, oxygen atoms dissolved in the bulk, and gold oxide. The desorption energies are 204 kJ/mol (bulk oxygen), 158 kJ/mol (on-surface chemisorbed oxygen), and 103 kJ/mol (gold oxide). The relative TD signal intensities (and, to some extent, the desorption temperatures) depend strongly on the ion energy and, hence, on the penetration depth of the ions. As expected, higher ion energies favour occupation of bulk sites; lower energies promote formation of chemisorbed oxygen and surface gold oxide. Depth profiling was accomplished by titration with CO at 300 K. The work function of the oxygen-sputtered surface depends in a complex way on temperature. The on-surface oxygen species causes a suppression of the substrate LEED spots that is typical for oxygen chemisorption on gold.