THE INTERACTION OF WATER AND MN WITH SURFACES OF CACO3 - AN XPS STUDY

This paper reports an examination of the chemistry of single-crystal calcite (CaCO3) using x-ray photoelectron spectroscopy (XPS). The calcite cleavage surface was examined as freshly opened in vacuum and after several different treatments, including exposure to water vapor, covered with different amounts of evaporated Mn, ion sputtered and immersed in pure water. Clean and ion-sputtered calcite were not observed to react with water vapor. Ion sputtering caused significant changes to both oxygen and calcium bonding at the surface. However, immersion of sputtered calcite in water caused removal of the sputter damage and produced an XPS spectrum nearly indistinguishable from that of the fresh cleavage surface. The shapes and positions of the Mn and O peaks in the spectra of CaCO3 with submonolayer coverages of Mn indicate partial oxidation of the metal as deposited, presumably owing to reaction with the calcite surface. Immersion of the Mn-coated calcite in water caused further changes in the Mn peak, suggesting additional oxidation of the Mn.