Backscattering of 0·5-10 keV electrons from solid targets

Measurements have been made of electron backscattering in a range of incident beam energy from 0·5 to 10 keV. The variation of backscattering coefficient η with energy and angle of incidence, and the energy spectrum of backscattered electrons at incidence and take-off angles of 45°, have been measured. Results from carbon, aluminium-silicon, copper and silver were obtained at a pressure of approximately 10⁻⁸ Torr to make the effects of contamination under the electron beam negligible.

Various simple theories of the backscattering phenomenon which have been used successfully at higher energies are examined in an attempt to understand the processes producing the observed results. Although the theory of elastic scattering of electrons by atoms at low energies is complicated, it is found that a simple theory based on largeangle elastic collisions may explain the experimentally observed rise in η with fall in beam energy, when an accurate range-energy relationship is used. The variation of η with angle of beam incidence can be explained for low atomic number elements on a diffusion theory, but this explanation does not wholly explain the results for copper at low energies. The energy spectra cannot be predicted by any existing simple theory.