Defect-mediated elastic resonances in He-atom scattering from single-crystal surfaces

Abstract

Experimental evidence for a new atom-surface resonant mechanism involving surface defects is presented. After an initial selective adsorption trapping into surface bound states of a NaCl ~001! surface, He atoms are subsequently scattered from surface defects back into the continuum. The inverse process also occurs: He atoms scatter from a defect and some of the amplitude enters the bound state eventually followed by selective desorption from the bound state via diffraction. For the 90°-scattering geometry used, the resonances show up as sharp peaks in the angular distributions of the quasielastic intensity between the diffraction peaks and are symmetric about the specular peak. A general description of the process is given which shows that it is a universal feature of any scattering system which can exhibit selective adsorption type resonances. @S0163-1829~98!00639-0#