Backscattering of 5–20 kev Electrons from Insulators and Metals

Abstract

Electron backscattering measurements were carried out on composite layers consisting of thin metal films deposited on base layers of widely different backscattering properties. At low primary energies the backscattered fraction η (energies >50 ev) is found to be characteristic of the surface film. When the electron energy is such that the range in the surface material is equal to twice its thickness, a marked change in η occurs. At sufficiently high energies, η approaches the value for the base layer. Measurements of η as a function of energy were made for layers of Al–Au, Al–Ag, and Al–C. These results led to a new method for measuring η for insulators using thin aluminum surface films (∼200 A) to avoid charging. Data on LiF, Zn₃ (PO₄)₂, KCl, RbBr, and TlI above ∼5 kev indicated agreement with the known values for metals of the same average atomic number, demonstrating that backscattering in the kev range and above is an atomic characteristic independent of the crystal structure or the conduction properties of the solid.