Double electron emission from surfaces via low-energy positrons

Abstract

We have studied the electron pair emission process from surfaces due to the impact of a primary low-energy positron. The existence of this process implies a two-step scattering event. We find that the electron pair intensity is on the same scale as the positron-electron pair intensity. This suggests that a significant contribution of the pair intensity is actually due to the emission of three particles, of which two are detected. We also observe a strong material dependence of the coincidence intensity. Similarly to our previous studies with primary electron excitation or photon absorption, NiO is the material that displays the highest coincidence rates. We also note that the electron pair intensity scales with the single electron rate. This was also observed in electron pair emission with primary photons or electrons. This suggests that the coincidence intensity may provide a measure of the electron correlation strength.