POTASSIUM-ADSORPTION-INDUCED PLASMON FREQUENCY-SHIFT IN GRAPHITE

A discrete energy loss feature has been observed after adsorption of small amounts of potassium on graphite at 90 K, the frequency of which increases markedly from about 50 meV at the lowest potassium coverage to 320 meV at a coverage of 0.1 ML. This feature is attributed to a surface plasmon mode. The shift in plasmon frequency allows an estimate, within the framework of a rigid band model for the graphite substrate, of the amount of charge transfer from the potassium layer as a function of coverage.