Coincidence, Resonant, and High‐Energy Electron Spectroscopies – Resonant Auger, Electron Coincidence for Surface Analysis

Electron spectroscopic methods are powerful and efficient tools for characterization of chemical and electronic structures of surface and interface layers of solids. The electron spectroscopic methods most widely applied for surface chemical analysis, the X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) are providing information on the elemental composition of the surface and interface layers, as well as on the chemical state of the components. In addition, these techniques can offer possibilities for depth-resolved and/or laterally resolved analysis in a nondestructive (up to several nanometers depth) or destructive (in combination with ion sputtering, up to several hundred nanometers depth) way. Quantitative surface chemical analytical applications of these methods are greatly helped by physical quantities characterizing electron transport, which can be derived from reflection electron energy loss spectroscopic (REELS) studies of given materials. There are, however, a plenty of opportunities available how to improve the sensitivity, selectivity, and information depth of these techniques. Among these, the coincidence techniques help to identify the physical processes leading to specific structures in the experimental electron spectra, clean up the spectra from unwanted contributions of interfering processes, and limit the depth of analytical information. The resonant excitation can yield unprecedented chemical state selectivity and can greatly improve the detection limit for particular species while providing unique information on the electronic structure in the proximity of the excited atom. High-energy-resolution spectroscopy of high-energy electrons induced by hard X-rays from solids allows to get an insight into deeper subsurface regions owing to the much increased information depth for energetic electrons, and in addition to the possibility for collecting information on the bulk chemical and electronic structures without interfering effects because of the presence of the surface, this spectroscopy provides a nondestructive access to the chemical state-resolved composition at deeply buried interfaces. This article intends to give a brief review on selected electron–electron coincidence techniques, resonant Auger electron spectroscopic methods, and high-energy electron spectroscopic methods, namely, the hard X-ray photoelectron spectroscopy (HAXPES), focusing on the principle and specific instrumentation of the techniques, the underlying physics of the fundamental processes utilized, the analytical information provided, and important fields of applications. These highly sensitive, selective, and uniquely informative electron spectroscopic methods are expected to be used increasingly in studies of sophisticated novel materials of great practical importance, especially in fields of nanotechnology, micro- and nanoelectronics, nano-biotechnology, nanomedicine, and development of novel solar cells.