Electron-beam-induced reactions at surfaces

Abstract

It is well-known that the intense electron irradiation needed to record HREM images or micro-analytical spectra is liable to cause permanent microstructural changes in the specimen region undergoing observation or analysis. Beam-induced modifications at surfaces are even more likely because of the increased probability of permanent loss of material and the likelihood of reaction with constituents of the residual microscope vacuum. In this short review, we first survey the mechanisms available for beam-induced surface reactions, then briefly summarize recent observations of surface modifications and finally discuss their validity for surfaces relative to other reaction mechanisms described elsewhere. Since our primary interest here is in the possibilities for eliciting atomic-scale local information using HREM or microanalytical techniques, consideration is restricted to inorganic solids which are far less susceptible to damage by the electron beam than organic materials.Mechanisms. There are two basic mechanisms covered by the generic term “radiation damage” which could lead to electron-beam-induced surface reactions: ballistic or knock-on displacement whereby there is momentum exchange with an incident electron which may be sufficient to cause atomic displacement; and radiolytic processes which involve electron-electron interactions.