Electron transport for spectrum analysis and experiment design

A survey is presented on modeling the effects of electron transport on the energy and angular spectra of electrons emitted or reflected from non-crystalline solid surfaces and nanostructures. This is intended to aid in the quantitative interpretation of such spectra and should also provide a useful guideline for experiment design. A brief review of the most significant characteristics of the electron-solid interaction is given and the theory describing the energy dissipation and momentum relaxation of electrons in solids is outlined, which is based on the so-called Landau-Goudsmit-Saunderson (LGS) loss function. It is shown that the basis for true quantitative spectrum interpretation is provided by the collision statistics, i.e. the number of electrons arriving at the detector after participating in a given number of inelastic collisions, being equal to the partial intensities. By introducing an appropriate stochastic process for multiple scattering, the validity of the partial intensity approach (PIA) can be extended to the true slowing down regime making it possible, in a very simple way, to fully account for energy fluctuations in the limit of large energy losses. The LGS loss function thus provides a unified theoretical basis for electron spectroscopy and microscopy. The usefulness of the concept of the collision statistics, or partial intensities, for quantitative spectrum interpretation is illustrated by considering various examples of practical significance, including elastic peak electron spectroscopy (EPES), reflection electron energy loss spectroscopy (REELS), (hard) X-ray photoelectron emission ((HA)XPS), electron coincidence spectroscopy, the Auger electron backscattering factor and the ionization depth distribution. Finally, the relationship between the partial intensities and the emission depth is discussed, which allows one to combine the unique features of electron spectroscopy for investigation of chemical, electronic and magnetic properties of surfaces with a depth selectivity within the first few atomic layers of a solid. (C) 2009 Elsevier B.V. All rights reserved.