Using sputtering parameters to mitigate argon ion sputtering induced reduction of nickel in XPS

Argon ion sputtering for depth profiling in XPS results in the preferential sputtering of oxygen in certain oxide systems. Preferential oxygen removal results in the chemical reduction of the associated cation which is observed in spectra collected following sputtering. Characterizing the effects of different sputtering parameters and developing methods to account for and to minimize changes to chemical state during sputtering would allow for greater confidence in the qualitative and quantitative analysis of the chemical states observed after sputtering. In this study argon ion sputtering was performed with monatomic and clustered argon ions on thermally oxidized NiO. Parameters for monatomic and cluster sputtering were varied to observe their effects on the induced reduction. Results show that extensive reduction is experienced for monatomic sputtering irrespective of the energy and current chosen. For cluster argon ion sputtering, reduction was mitigated when selecting either large cluster sizes or low cluster energies. Sputtering for long periods of time with low energy clusters was observed to result in the removal of surface contaminants without concomitant reduction of the nickel oxide.