This work reports a successful electron-electron coincidence experiment performed in grazing-angle reflection geometry. (e,2e) measurements with a 300-eV impact energy have been carried out on a clean highly oriented pyrolytic graphite surface and the feasibility of binding-energy spectroscopy with quasimomentum discrimination has been established. Evidence is given that direct impact ionization of the valence electrons is the dominant ionization mechanism in the highly asymmetric kinematics used here.

• Received 30 January 1995

DOI:https://doi.org/10.1103/PhysRevB.51.10252