Cleavage mechanism and surface chemical characterization of phengitic Muscovite and Muscovite as constrained by X-Ray Photoelectron Spectroscopy
Freshly cleaved (001) natural muscovite was chemically characterized by X-ray Photoelectron Spectroscopy (XPS). The investigated muscovite crystals have composition ranging from pure end member to phengitic muscovite. XPS provides experimental evidence that the chemical composition of the near-surface region differs from the bulk. This difference is not due to analytical problems, but to extreme surface sensitivity of XPS. Depth profiling was also carried out after tilting of 60° or 70° of the sample along an axis perpendicular to . After tilting of phengitic muscovite, the concentration of Al increases and of K decreases, and therefore Al is the topmost monolayer. Repulsion between the octahedral and tetrahedral sheets, stacking faults or more probably interlayered phases (gibbsite-like) are responsible for the cleavage. Possible perturbations of surface chemistry due to X-ray radiation and Ar+ ion sputtering have also been investigated. X-ray radiation is negligeable, but Ar+ ion sputtering introduces important structural modifications, perturbation of the chemical environment of elements and minor chemical variations.