Two-particle emission from LiF(1 0 0) upon photon, electron and positron excitation

Electron pairs simultaneously emitted from a solid surface upon excitation with photons (double photoemission or (?, 2e)) or electrons (e,2e) provide information about the electron correlation in the solid which is mediated by exchange and Coulomb interactions. Without the Pauli restriction, the correlation of a positron with many electrons in a solid is dominated by Coulomb interactions. We have therefore undertaken the first comparative study of electron-electron and positron-electron pair emission upon impact with low energy photons, electrons and positrons. The target surface chosen for this study was LiF(1 0 0), a wide band gap dielectric that allows for a simple kinematical interpretation of the energy distribution of emitted pairs. We present the first results and discuss insights into the mechanisms of pair emission upon positron, electron and photon impact. © 2009 IOP Publishing Ltd