Dose-rate dependence of electron-induced mass loss from organic specimens

Electron energy-loss measurements on thin films of collodion at low temperatures (90 K) show that the characteristic electron dose D_e for mass loss first increases and then decreases with increasing dose rate (current density). This behaviour is explained in terms of the limited diffusion rates at low specimen temperature and the heating effect of the electron beam, and can be approximately modelled using a simple computer program. For a small-diameter electron probe, the increase in D_e can be several orders of magnitude, suggesting a substantial advantage of STEM (in comparison to fixed-beam TEM) for examining beam-sensitive specimens.