Electronically Induced Desorption and Luminescence from Multilayer Argon Films

Abstract

The rare gas solids provide special opportunities for study of desorption induced by electronic transitions (DIET) because so much is already known about the processes of electronic excitation and decay in the bulk of these weakly bonded low-temperature systems [1]. Their importance was evident in ion induced sputtering work of OLLERHEAD, et al [2] on xenon and BESENBACHER, et al [3] on argon and in electron induced sputtering of neon by BORGESEN, et al [4] and argon by COLETTI, et al [5]. We have concentrated on the study of solid argon and report on it here. We have examined both the ejection of neutral argon atoms from the surface and the emission of ultraviolet light from the full thickness of the films. These reflect the non-radiative and radiative parts of the decay of electronic excitation starting with Ar⁺ -electron (hole-electron) pairs. A part of this work has been reported by REIMANN et al [6]. Using the particularly simple conditions of uniform excitation throughout the film thicknesses that are provided by MeV light ions, we have been able to deduce diffusion lengths for excitons as well as surface and interface boundary conditions for these efficient carriers of electronic excitation. It is clear that the desorption observed does not arise solely or even dominantly from electronic excitation in the surface monolayer of multi-layer films. It arises instead from electronic excitation generated in tide bulk of the film and diffusion of the excited species over distances ^~200Å. In the electronic deexcitation chain of these excited species there are repulsive, non-radiative, energy releases which produce desorption when the releases occur within ^~10Å of the surface.

Work at the University of Virginia was supported in part by NSF Grant DRM-82-1555.