Mapping the excited-state bands above the vacuum level with VLEED: principles, results for Cu, and the connection to photoemission

Experimental photoelectron spectra are usually interpreted using rather crude approximations for the upper states into which the electrons are excited. Better knowledge about these excited states could substantially improve the accuracy of valence band mapping by photoelectron spectroscopy. We here demonstrate that VLEED measurements are ideally suited for accurate determination of the desired upper states. This is illustrated by model calculations including absorption and self-energy corrections. The close correspondence between so-called irregularity points of the excited-state bands and the total electron reflectivity is established, which opens up the possibility for direct mapping of irregularity points by comparison with experimental VLEED spectra, and for fitting of the whole excited-state bands between these points. The proposed scheme is finally used to determine the excited-state bands of Cu along from measurements on Cu(111).