Electron energy-loss spectroscopy in the TEM

TLDR

EELS measures the kinetic energy loss of electrons after interaction with a specimen, providing structural and chemical information at near‑atomic resolution with typical energy resolution of ~1 eV that can improve to ~0.1 eV using a monochromator, and is comparable to techniques such as X‑ray absorption spectroscopy. The review surveys EELS instrumentation and the physics of kilovolt‑electron scattering in solids. EELS spectra reveal plasmon peaks, inner‑shell ionization edges, and fine structure linked to electronic densities of states, while spatial resolution is governed by factors such as radiation damage. EELS is applied to determine local specimen thickness, mechanical and electronic properties such as bandgap, and chemical composition.

Abstract

Electron energy-loss spectroscopy (EELS) is an analytical technique that measures the change in kinetic energy of electrons after they have interacted with a specimen. When carried out in a modern transmission electron microscope, EELS is capable of giving structural and chemical information about a solid, with a spatial resolution down to the atomic level in favourable cases. The energy resolution is typically 1 eV but can approach 0.1 eV if an electron-beam monochromator is used. This review provides an overview of EELS instrumentation and of the physics involved in the scattering of kilovolt electrons in solids. Features of the energy-loss spectrum are discussed, including plasmon peaks, inner-shell ionization edges and fine structure related to the electronic densities of states. Examples are given of the use of EELS for the measurement of local properties, including specimen thickness, mechanical and electronic properties (such as bandgap) and chemical composition. Factors that determine the spatial resolution of the analysis are outlined, including radiation damage to the specimen. Comparisons are made with related techniques, particularly x-ray absorption spectroscopy.