Image-potential states and energy-loss satellites in inverse photoemission spectra

Abstract

$k$-resolved inverse photoemission spectra taken on Ni(001) and Cu(001) show a weak peak at an apparent energy within a bulk band gap and close to the vacuum level. Comparisons with the energy-loss function $|\mathrm{Im}(\frac{1}{\ensuremath{\epsilon}})|$ show that it may be due to an energy-loss satellite. Surface states associated with the long-range nature of the image potential are also expected to occur at the observed energies, and may therefore also be responsible.