Conduction-band density of states in solid argon revealed by low-energy-electron backscattering from thin films: Role of the electron mean free path.

Abstract

The results of high-resolution low-energy (1--14 eV)-electron inelastic backscattering experiments on thin solid rare-gas films deposited on a metal substrate have recently been shown to provide an almost direct measurement of the electronic conduction-band density of states (DOS) of those solids. In order to gain more insight into this phenomenon, the variation with film thickness of the backscattered current from solid films of Ar is analyzed with a three-dimensional electron transport model. From this analysis, we determine the electron mean free path (\ensuremath{\lambda}) as well as film-vacuum interface terms that characterize the entrance and exit of the electrons. A comparison of the energy dependence of those parameters to that of the calculated DOS of solid argon shows that 1/\ensuremath{\lambda} and the DOS are strongly correlated over the whole electron-energy range investigated. In contrast, the interface terms are found to reflect only partly the electronic DOS. It thus appears that the ability of the experimental results to reveal the DOS can be attributed mainly to the role played by the electron mean free path in the reflectivity of the studied films. We also find that electron scatterings in the bulk of the film must be anisotropic (with a preference for forward scattering) to account for the observed distributions of energy losses.