REFLECTION (E,2E) EXPERIMENTS - A NOVEL SURFACE SPECTROSCOPY

The possibility of using the grazing angle (e,2e) technique as a bindi ng energy and/or momentum spectroscopy of surface states rests on the accurate knowledge of the ionisation mechanism and on the capability o f achieving a sufficiently good energy resolution. Two possible mechan isms are envisaged that can generate pairs of correlated electrons in the reflection geometry: a single inelastic collision at large momentu m transfer or a double collision (elastic plus inelastic). In this pap er are presented the results of new (e,2e) experiments that allow to e lucidate the ionisation mechanism at intermediate energies (300 eV) an d asymmetric kinematics. The measurements, performed on highly oriente d pyrolitic graphite, also show that an overall energy resolution as g ood as 1.2 eV can be achieved.