Surface chemical characterization and surface diffraction effects of real margarite (001): An angle-resolved XPS investigation

The (001) surface of natural pure margarite was chemically characterized by angle-resolved Xray photoelectron spectroscopy (ARXPS). The extreme surfac e sensitivity of ARXPS permits concluding that the chemical composition of the near-surface region differs from the bulk because of the strong anisotr opy of the margarite structure. Depth profiling was carried out by angle re solved spectroscopy that is a non destructive measuring technique. More gra zing polar angles sample increasingly superficial layers of the margarite. The topmost layers are made up of C, due to the mineral/atmosphere interact ion. At low grazing angles the concentration of Si increases, and both Al a nd Ca decreases; therefore we conclude that the tetrahedral sheet is the to pmost monolayer. Repulsion between the octahedral and tetrahedral sheets is probably responsible for the cleavage. Photoelectron diffraction effects a re also clearly evidenced by Si, Ca, and Al. Single-scattering cluster calc ulations were performed in simulating scanned angle core emission. The calc ulated patterns do not show a reasonable agreement with experimental data.