CORRELATIONS BETWEEN IONIZATION RADIATION-DAMAGE AND CHARGING EFFECTSIN TRANSMISSION ELECTRON-MICROSCOPY

The goal of this paper is to correlate macroscopic positive charging o f electron-irradiated thin insulating specimens to atomic displacement s, migration and desorption effects. The leading role of the Auger pro cess is emphasized. It is shown that the electrons coming from the sur roundings cannot spontaneously compensate for Auger (and the secondary ) electron emissions with the result that electrons are missing in the uppermost states of the valence bands, At the steady state, the densi ty of missing electrons is correlated to the beam density and the elec trical resistivity of the specimen. For highly resistive specimens an expression for the etching rate is also suggested. This analysis expla ins some experimental results such as desorption of positively charged anions into the vacuum for ionic compounds or atomic displacement for covalent compounds. The influence of the crystalline or non-crystalli ne state of the specimen is considered. The role of coating the specim en foil with conductive layers is analyzed. The same analysis applies also to X-ray irradiation.