Ion Bombardment Induced Changes in Oxide-Metal Interactions Studied by Photoelectron Spectroscopy

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We have studied the influence of ion bombardment on the surfaces of MgO and Al2O3 single crystals. The two oxides were sputtered with low energy Ar+ ions, and x-ray photoelectron spectroscopy was used to analyze surface compositions and chemical interactions with metallic adsorbates. Expected changes in surface compositions have been calculated mathematically using first principle formulation from existing literature. The resulting effects on XPS spectra have been predicted based on concentration profile models and agree with experimental observations. Changes in surface oxygen activity were studied by evaporating Ni on these surfaces at an extremely slow rate and analyzing what fraction of the first monolayer was oxidized on adsorption. This fraction, used as a measure of surface oxygen activity, was substantially reduced in Al2O3 on sputtering, but remained practically unchanged for MgO. The amount of these changes matches reasonably well with calculated changes in surface oxygen fraction. Based on these results, the relation between ion bombardment and interfacial bonding has been discussed.



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