Low-energy electron transmission method for measuring charge trapping in dielectric films

Abstract

We describe a method for investigating the trapping of low-energy electrons in thin dielectric films and at their surfaces. It is based on the shift in the zero-energy reference produced by charge trapping in the low-energy electron transmission (LEET) spectra of dielectric films. We show that this energy shift or retarding potential is linearly related to the amount of accumulated charges and the trapping cross section. The method has the unique feature of being able to determine the dependence of the trapping cross section on the energy of the charging electron beam in the range 0-30 eV. Its characteristics are illustrated in the investigation of surface charging of multilayer Kr films partially covered with O2 molecules. The results confirm the capacitor model and serve, via the energy dependence of trapping cross section, to determine the precise mechanism responsible for charging in the range 3-10 eV.