Electron stimulated desorption from molecules on a noble gas solid: an analysis of cluster and island formation upon deposition

Desorption of negative fragment ions following low energy electron impact t o a two monolayer (ML) adsorbate of CHF2Cl is studied. Results are compared for a deposition of the 2 ML quantity directly on a monocrystaline gold su bstrate with that on the surface of a Xe film as a spacer to the metal. The desorption intensity (Cl-, F-) is strongly suppressed when going from the metal to the rare gas film. For a uniformly covered surface one would expec t the opposite behaviour, namely an enhanced desorption from molecules on t he rare gas spacer. We interpret this observation by cluster and island for mation on the rare gas film after CHF2Cl deposition. A general analysis of cluster and island format for the fluorchloromethanes on a rare gas surface is performed. (Int J Mass Spectrom 205 (2001) 331-337) (C) 2001 Elsevier S cience B.V.