Interaction of Molecular Oxygen with Hexagonally Reconstructed Au (001) Surface

Kinetics of molecular oxygen / Au (001) surface interaction has been studied at high temperature and near atmospheric pressures of O2 gas with in situ x-ray scattering measurements. We find that the hexagonal reconstruction (hex) of Au (001) surface lifts to (1x1) in the presence of O2 gas, indicating that the (1x1) is more favored when some oxygen atoms present on the surface. The measured lifting rate constant vs. temperature is found to be highest at intermediate temperature exhibiting a 'volcano'-type behavior. At low temperature, the hex-to-(1x1) activation barrier (Eact = 1.3(3) eV) limits the lifting. At high temperature, oxygen adsorption energy (Eads = 1.6(2) eV) limits the lifting. The (1x1)-to-hex activation barrier (Ehex = 0.41(14) eV) is also obtained from hex recovery kinetics. The pressure-temperature (PT) surface phase diagram obtained in this study shows three regions: hex at low P and T, (1x1) at high P and T, and coexistence of the hex and (1x1) at the intermediate P and T.