Spectroscopy of near-threshold electrons from surfaces

A time-of-flight technique for two-dimensional spectroscopy of near-threshold electrons from surfaces is described, and the properties of the method are illustrated using selected results from clean surfaces, and mono- and multilayer adsorbates. The analysis of two-dimensional data yields easy access to inner (bulk) and outer (surface) ionization edges and exciton series, for valence and core electron levels including satellite states, and to final state effects. Strong interaction between bulk and surface states is revealed in particular for samples with negative electron affinity. Core-level threshold electron spectra from monolayers adsorbed on metal surfaces exhibit strong substrate-mediated suppression of post-collision interaction-induced line broadening and shift, each of which can be quantitatively explained by image charge screening. Received: 27 April 1998/Accepted: 25 August 1998