Comparison Spectra for Calcite by XPS

Calcite is a common component of soil and a natural mineral sometimes found in the form of large high quality single crystals. The interactions of calcite with ions in ground water affects their transport in the environment. Consequently, understanding the surface chemistry of calcite is important for environmental remediation research. To establish the nature of a clean calcite surface, single-crystal rhombohedral calcite (CaCO3) was cleaved in vacuum to expose the (101¯4) plane for x-ray photoelectron spectroscopy analysis. Survey and multiplex spectra were obtained under standard operating conditions with a Perkin-Elmer Physical Electronics 550 spectrometer. An adventitious carbon peak, from a cleavage surface exposed to the environment, was used to measure surface charging and allow determination of binding energies for calcite C 1s, O 1s, and Ca 2p3/2 photopeaks. Two forms of C were observed on the vacuum cleaved specimen: a “carbonate” and a “carbide” peak.