XPS Studies of ion-bombardment damage of transition metal sulfates

Radiation damage to the surfaces of transition metal sulfates under 1 keV argon ion bombardment has been investigated by photoelectron spectroscopy. The damage sequence appears to be related to the inertness of the metal. Near the beginning of the transition series (chromic and ferrous sulfate) and for the d¹⁰ closed-shell configuration (zinc sulfate) there is continuous loss of sulfur, eventually leaving behind the highly stable metal oxide on the surface. In contrast, for the sulfates near the end of the transition series, where the metal is more inert and its oxide less stable, the predominant process is reduction of the cation to the metallic state, accompanied by gradual reduction of sulfate to elemental sulfur. As expected, the behavior of the sulfates of transition metals in the middle of the series is intermediate between these two categories.