SPACE-CHARGE AND PLASMA EFFECTS IN ZERO KINETIC-ENERGY (ZEKE) PHOTOELECTRON-SPECTROSCOPY

In photoelectron spectroscopy experiments it is generally assumed that the Coulomb force between charged particles is small compared with ex ternal fields, and that the free kinetic electrons will quickly leave the ions. This is the basis of the ZEKE photoelectron spectroscopy. Ho wever as the density of charged particles is increased, plasma physics effects begin to become important, and the kinetic electrons become t rapped by the net positive charge and move so as to set up a self-fiel d which can cancel any externally imposed electric fields. For high de nsities, fewer electrons than expected are able to escape the self-fie ld. The production of self-consistent electric fields is studied by me ans of particle-in-cell plasma simulations and by N-body trajectory ca lculations, and simple expressions are derived for when plasma physics effects become significant. An experimental illustration of plasma ef fects in ZEKE is presented. (C) 1997 American Institute of Physics.