Determination of surface exciton energies by velocity resolved atomic desorption

We have developed a new method for determining surface exciton band energies in alkali halides based on velocity-resolved atomic desorption (VRAD). Using this new method, we predict the surface exciton energies for KI, KBr, KCl, and NaCl within ±0.15 eV. Our data, the measured and calculated shifts of the surface exciton energies with respect to the bulk excitons, combined with the available EELS data for alkali fluorides, demonstrate a universal linear correlation with the inverse inter-atomic distance in these materials. The results suggest that surface excitons exist in all alkali halides and their excitation energies can be predicted from the known bulk exciton energies and the obtained correlation plot.