On the energy dissipation process in incoherent electron scattering

Abstract

The energy dissipation process in non-crystalline solids for electron beam techniques is reviewed. The characteristics for the interaction of the probe electron with the electronic as well as the ionic subsystem of a solid are discussed, corresponding to inelastic and elastic scattering, respectively. Since the energy dissipation process is responsible for the energy and angular spectrum of techniques such as transmission electron microscopy (TEM), electron probe microanalysis (EPMA), (reflection) electron energy loss spectroscopy ((R)EELS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), and the like, quantitative spectrum interpretation requires a sound theoretical description of multiple scattering processes. The theory of non-coherent multiple scattering is outlined using a Boltzmann-type kinetic equation as a starting point. The only assumption made is that the elastic interaction can be represented by a static spherically symmetric potential. This leads to a simple and general expression for the generalized loss function describing the energy losses and deflections experienced by a particle as a function of the pathlength travelled in the solid. The loss function is found to be governed by the collision statistics, on the one hand and the fluctuations of the energy loss and deflection angle, on the other hand and in this way provides a sound basis for rigorous quantitative spectrum analysis. Decomposition of experimental spectra is straightforward if different types of inelastic scattering are uncorrelated, a requirement that is fulfilled if only one of the considered processes takes place in a region in space whose dimension exceeds the elastic mean free path. Spectrum analysis procedures on this basis are discussed for selected techniques including EELS in the TEM, reflection EELS, X-ray production in EPMA and decomposition of photoelectron spectra in XPS.