DIET of metastable Kr∗ atoms via electron resonances in Kr/Ar alloy films

We report the electron-stimulated desorption of metastable Kr∗ atoms from films containing both argon and krypton. When Ar/Kr alloy films are deposited on a platinum surface, a narrow resonance feature is seen in the desorption yield at an incident electron energy of 10 eV; i.e., about 0.5 eV below the energy of the lowest bulk exciton states of the alloy. Desorption at 10 eV requires that krypton atoms be in close proximity to the platinum substrate since the resonance disappears when alloy films are deposited on a crystalline n-hexane film. Time-of-flight measurements show that the kinetic energies of desorbed krypton atoms are similar at incident electron energies of 10.1 eV and 15 eV, and indicate a similar mechanism for desorption at these energies. We attribute the new desorption feature to formation of a Kr− anionic state of the film (electron–exciton complex) which is transformed into a Kr∗ exciton by electron transfer into the metal. Desorption proceeds following exciton trapping at the film/vacuum interface.