Abstract
Among the different spectroscopies applied to the study of graphite intercalation compounds (GIC), Auger electron spectroscopy (AES), and angle resolved photoemission spectroscopy show that the composition of the uppermost unit cell is different from the bulk composition. According to these measurements, donor compounds exhibit an increased intercalant concentration near the surface, while acceptor compounds at equilibrium exhibit two or three nearly pure graphite layers at the surface. We present here AES measurements for donor GIC (cesium compounds), and x-ray photoelectron spectroscopy and AES measurements for acceptor GIC (manganese chloride compounds). A simple model accounts for the observed surface concentration in both donor and acceptor compounds. The screening of a surface state involves an electrostatic energy, which depends on the Fermi level density of states in the most superficial unit cell or sandwich. The minimum of the free energy at equilibrium implies enrichment in cations and a depletion of anions near the surface of the compound.
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More From: Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films
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