Alkali-metal-plated graphite surfaces: He interaction and diffraction

Theoretical calculations and experimental data are reported for He scattering from a graphite surface covered with an alkali-metal overlayer. The computed interaction potential has a very shallow well depth (≤, 1 meV) in the case of a (2 × 2) layer. The predicted corrugation is also very small, corresponding to rather weak elastic diffraction beams. The calculated diffraction intensity is less than 2 percent of the specular intensity for a 17.4 meV He beam. No He diffraction was observed in the experiment on K, Rb, and Cs overlayers, indicating that these surfaces are even less corrugated than the calculation predicts.