2-ELECTRON COINCIDENCE SPECTROSCOPY OF SCATTERING EVENTS AT SURFACES

We report on the first successful two-electron coincidence experiment at solid surfaces in a back-reflection geometry. We found that two-electron coincident electron emission events exist, and that they require a certain threshold energy of the primary electron (relative to the Fermi level) which is not equal to twice the work function of the sample surface [W(100)] as one might expect from the energy conservation law. We give evidence that we observe at low primary energy single electron-electron scattering events between the primary electron and a valence-band electron and give a semiquantitative estimate of the relative probability of such events.