New Method for Range Measurements of Low-Energy Electrons in Solids

Abstract

A new method for determining the range of low-energy electrons in solids is described and compared with older techniques. In the new method, the material under study is deposited on a thick layer of greatly different electron backscattering characteristics. When the incident electrons have just sufficient energy to penetrate to the support and return to the surface, a marked change in the backscattered fraction occurs. In this manner, the need for very thin organic supporting films of unknown stopping power is avoided. Range-energy data from 1 to 15 kev for films of aluminum on a gold substrate obtained by this technique are found to agree with the data obtained by the use of cathode luminescence to detect electron penetration. The technique was applied to thin films of gold in the energy region from 2 to 15 kev. It was found that the practical ranges in mg/cm2 for gold and aluminum were the same below 10 kev, unlike the situation in the mev region where the effective penetration into Al is about twice that for Au due to the importance of nuclear scattering in a high Z element. Good agreement is found with the Bohr-Bethe theory for aluminum at all energies and for Au below ∼10 kev.