2-DIMENSIONAL BAND-GAP RESTRICTED DIFFUSION OF NEGATIVELY CHARGED EXCITONS IN RARE-GAS SOLIDS

We present measurements of electron stimulated desorption (ESD) yields of D-, obtained from sub-monolayer amounts of C2D6 physisorbed on rar e gas substrates; the latter consisting of alternating layers of Xe an d Kr adsorbed at 20 K on Pt. Negatively charged excitons (NCE), for ex ample, Xe- or Kr*-, which are produced by electron impact, may couple to dissociative anion states of C2D6, resulting in sharp resonance en hancements in the D-ESD yields. Our measurements suggest that resonant diffusion of the Xe NCEs can be restricted to a single Xe layer, by p lacing a Kr multilayer spacer between the Xe and the metal substrate. This is attributed to the 1.85 eV insulating band-gap difference at th e Xe-Kr interface. (C) 1997 Elsevier Science B.V.