Characterisation of oxygen plasma-modified mica surfaces using XPS and AFM

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Atomic force microscopy (AFM), together with X-ray photoelectron spectroscopy (XPS), has been used to investigate the microstructure of air-cleaved mica surfaces modified by an oxygen RF plasma discharge run under a range of different conditions. The dramatic changes in the topography and the chemical composition in the mica surfaces processed are found to depend strongly on the plasma etching parameters used. At relatively low power levels (≤150 W), the main oxygen plasma interaction with the mica surface is energy-dependent physical etching enhanced by structure-dependent chemical processes. The formation of the regular topographical features observed is attributed mainly to lattice anisotropy of and the defects in the mica surface. When the oxygen plasma power level is above 150 W, the dome-shaped features formed on the treated mica surfaces are determined mainly by the power-enhanced non-selective sputter etching by energetic plasma species, coupled with the local re-deposition of involatile sputter products and reorganisation of such residues on the surfaces concerned. The effects of oxygen pressure and etching time on the morphology of the processed mica surface have also been investigated. XPS analysis revealed that the oxygen plasma etching can cause a build-up of oxygen species on the treated mica surface while the aluminium and silicon present are decreased significantly. Moreover, the changes observed in atomic abundances in the processed mica surface depend strongly on the etching parameters involved.