Determination of energy spectra of backscattered electrons by use of Everhart's theory

Everhart's theory on the backscatter of electrons from solids is extended so as to yield the backscatter coefficient as a function of the retarding potential rejecting backscattered electrons having energies below a certain fraction of the energy of the primaries. From this function an analytical expression is obtained for the energy spectra of backscattered electrons with the atomic number of the target material as a parameter. Limited comparisons with experiments are included. The theory is found to give reasonable agreement with electron backscatter experiments for primary electron energies above about 1 keV and target materials having atomic numbers up to about 40. The upper energy limit of perhaps 100 keV is set by the relative importance of bremsstrahlung and relativistic effects which are not included in the Thomson-Whiddington law. Theoretical energy spectra display observed behavior of measured spectra under variation of the atomic number of the target. Energy spectra obtained from this theory give results which are in rather good agreement with experiment for backscattered electrons having energies in the range of about 0.25 to 0.90 of the energy of primary electrons