  We investigated the impact of surface oxygen on the ion yield for He$^+$ ions
scattered from different single crystalline surfaces in low-energy ion
scattering. Initially clean Al(111) and Ta(111) were exposed to molecular
oxygen and ion spectra for different oxidation stages and different primary
energies were recorded. A comparison of ion yields normalized to the
differential scattering cross section as well as experimental factors allows
obtaining information about the influence of oxygen on charge exchange
processes. The decrease in the ion yield of both metals with exposure cannot be
explained by different surface coverages exclusively, but requires the
neutralization efficiency to be dependent on the chemical structure of the
surface. For Ta, additionally, a different energy dependency of the ion yield
obtained in the metal and oxide occurs. The ion yield for O shows in both
surfaces a significantly weaker energy dependency than the investigated metals.
