ELECTRONIC AGING AND RELATED ELECTRON INTERACTIONS IN THIN-FILM DIELECTRICS

Hot electrons generated in dielectrics subjected to high electrical field strengths can produce highly reactive chemical species which contribute to the aging process. The interaction of such low energy (0 to 15 eV) electrons near the surface of dielectrics can be investigated in experiments combining cryogenic thin film deposition and high-resolution low-energy electron-beam techniques. These experiments are described in the present review. Examples of the results obtained with thin film atomic and molecular solids are used to illustrate the basic mechanisms which control the electron-dielectric interactions and provide a description of the basic degradation processes involved during 'electronic' aging. It is shown that elastic and quasi-elastic scattering of hot electrons in dielectrics can be described in terms of band structure parameters whereas inelastic scattering is often governed by the formation of transient anions. These anions can decay by stabilisation, by producing vibrationally and electronically excited molecules, or by dissociating into a stable anion and a neutral radical. These latter species usually initiate other reactions with nearby molecules causing further chemical damage. It is shown that the damage caused by transient anions can be controlled by modifying its molecular environment.