Femtosecond electron dynamics on solid surfaces probed by low energy ion scattering and stimulated desorption of secondary ions

Abstract

Abstract The cations emission from condensed matter surfaces has been investigated on the basis of localization and delocalization of valence hole(s) in the femtosecond timescale. The yield of scattered H + ( E 0 =100 eV), though negligibly small from the Pt(1 1 1) substrate, increases markedly when Ar is adsorbed on it, indicating the localization of a valence (H + 1s) hole on the physisorbed Ar layer. However, the yield of H + scattered from a thick H 2 O layer is considerably small relative to that from Ar and CO layers. The delocalized nature of a valence hole in water ice is caused by some covalency in hydrogen bonds. Hydrated protons, H + (H 2 O) n , n =1,2,…,10, are emitted efficiently in electron stimulated desorption from water molecules adsorbed on the Ar layer; the ion yields are highest at the initial adsorption stage and decay steeply with increasing coverage. Coulombic repulsion between the hydrated protons confined in physisorbed nanoclusters is responsible for the explosive ion emission.