Analytical Electron Microscopy

Abstract

Analytical electron microscopy (AEM) refers to a collection of spectroscopic techniques that are capable of providing structural, compositional, and bonding information about samples probed by an electron beam, typically inside a transmission electron microscope (TEM). Several AEM techniques are covered with particular attention given to the EDXS (energy-dispersive x-ray spectroscopy) microanalysis and EELS (electron energyloss spectroscopy) techniques. First, the different AEM techniques available in TEMs are surveyed and a parallel between EELS and EDXS is drawn. A fundamental description of the elastic and inelastic scattering events responsible for these signals is presented. The practical challenges related to electron optics and instrumentation capabilities are then discussed. Technical advances that have affected the performance of these AEM techniques are outlined, including successive generations and technologies of energy filters, monochromators, aberration correctors, and advanced energydispersive x-ray spectrometers. The different approaches of spectroscopic imaging with x-rays and energy-loss spectroscopy, the resolution limits, and the effects of electron-beam propagation are also described along with the types of information that can be extracted with electron-energyloss near-edge structures. After a review of dielectric theory and low-loss spectroscopy, examples of plasmonic imaging are presented. The review also draws attention to the many efforts to extend the limits of spatial resolution and the atomic-level chemical analyses of materials. Some important progress in the statistical analysis of signals and associated numerical methods is mentioned. The review also presents some novel developments in image capture, such as the pixelated detectors. Finally, the realm of phonon spectroscopy made possible through the latest instrumentation is also discussed.

Doping evolution of the Mott–Hubbard landscape in infinite-layer nickelates

“…In this work, we extract the electronic signatures of the Nd1−x Srx NiOy phases without contributions from extended defects by confining our spectroscopic measurements to crystallographically clean and fully reduced regions of each film using an angstrom-size STEM probe. The distinct characteristic shapes of EELS edges provide access to a wealth of rich chemical information (23)(24)(25)(26). To first approximation, the energy loss near-edge structure (ELNES) of core-loss spectra (edges at more than ∼100 eV) reflects the local density of unoccupied states for a specific element and angular momentum.…”

“…Small shifts in the absolute position of the EELS edge can similarly point to shifts or redistribution of unoccupied states. Because EELS probes the energy separation of the unoccupied and the core states, however, shifts in the EELS spectrum can also arise from changes in the core (rather than the unoccupied) level (26,27). Importantly, the effect of the core-hole created during the excitation process can significantly modify the ELNES and must be taken into account when considering comparisons to ground-state calculations.…”

A Review of Grain Boundary and Heterointerface Characterization in Polycrystalline Oxides by (Scanning) Transmission Electron Microscopy

“…Simply, a core-shell electron is excited and ejected from the atom, while an outer-shell electron replaces it; this energy difference is released as an X-ray. These characteristics X-rays are like fingerprints for each element and as a result, EDXS spectra are very useful to determine elemental composition of any sample [102]. Figure 15 exhibits a summarized illustration of X-ray signal generation, collection, data display and resulting quantification [102].…”

“…These characteristics X-rays are like fingerprints for each element and as a result, EDXS spectra are very useful to determine elemental composition of any sample [102]. Figure 15 exhibits a summarized illustration of X-ray signal generation, collection, data display and resulting quantification [102]. The methods for quantitative analysis of EDXS data is discussed below.…”

“…The transmission electron microscope (TEM) and scanning TEM (STEM) are powerful tools for directly imaging atomic arrangements, and quantitative chemical analysis down to the atomic scale. Books and review articles are written focusing on TEM [92][93][94][95][96][97], STEM [98][99][100][101], and the various analytical techniques available in both [93,[102][103][104][105]. A basic introduction to these techniques as they pertain to GB/HI characterization in polycrystalline oxides is provided here.…”