MECHANISM OF THE LOW-EJECTION-ENERGY (E,2E) REACTION ON A GRAPHITE SURFACE

We develop a theoretical model to describe a slow electron ejection fr om a crystal by electron impact at a moderate incident energy. The ele ctron impact ionization is considered within the first Born approximat ion. The projectile is treated as a plane wave whereas the target elec tron initial and final states are described by the bulk one-electron w ave functions in the momentum space representation. To allow the ioniz ed electron to escape from the crystal the final state in the bulk of the crystal is matched in energy and a parallel component of momentum by a plane wave in the vacuum. This theoretical model is used to simul ate the binding-energy spectra obtained by the grazing-angle reflectio n mode (e,2e) reaction on the surface of highly oriented pyrolytic gra phite.