Photoemission Studies of the Oxidation of Strontium

The oxidation of strontium has been studied by ultraviolet photoelectron spectroscopy. Minimal oxidation produces a relatively sharp peak (width about 0.5 eV) in the energy distribution curves originating from a state 5.0 eV below the Fermi level; this state is seen to broaden strongly into a band as the ${\mathrm{O}}^{--}$ concentration increases and ${\mathrm{O}}^{--}$-${\mathrm{O}}^{--}$ overlap occurs. The metallic component of the emission appears to originate from a thin layer near the surface and is little affected by the oxidation.