EELS is a powerful technique that provides compositional and chemical information from sub-nanometer areas in the sample. Due to the large interaction cross-sections and narrow angular distribution of the scattered electrons, EELS is a very sensitive and highly localized technique. The benefit of core-level EELS is its sensitivity to all elements in the periodic table (except atomic hydrogen). The deexcitation processes are competitive, resulting in near zero x-ray yield for low Z elements and near zero Auger yield for high Z elements. These processes reach parity (50/50 yield) around germanium (atomic number 32). In addition, EELS can probe the local density of states, making it uniquely suited to measure changes in local bonding at near-atomic resolution.

High-energy electrons interacting with the sample produce a myriad of signals. The elastic (including BSE) and inelastic interactions are the primary signals, while the other signals are secondary events caused by the sample relaxation after the inelastic scattering event. The EELS signal is strongly peaked in the forward direction, making near 100% collection efficiency possible.

Comparison Table

	EELS	EDS	XPS	Auger	CL
Probe → Signal	e- → e-	e- → \(\gamma\)	\(\gamma\) → e-	e- → e-	e- → \(hv\)
Spatial resolution More information	Å – µm	nm – mm	µm – mm	µm – mm	nm – mm
Compositional sensitivity More information	He – U 0.1 atm% typical	B – U 0.1 atm% typical	Li – U 0.01 atm% submonolayer	Li – U 0.1 atm% submonolayer	Sensitive to material properties rather than composition
Chemical sensitivity More information	Via edge shape and chemical shift	None	Via peak shape	Limited	Indirectly; linked to material properties
Ease of use (technique) More information	Requires setup of electron optics	Minimal setup	Ultra-high vacuum (UHV) handling	UHV handling Methods to reduce charging	Requires setup of spectrometer
Strengths	High signal-to-noise ratio (SNR) Chemical and composition data Atomic-level localization	Unlimited thickness High signal-to-background ratio (SBR)	Detects traces Detailed chemical information	Excellent low-Z detection SEM level spatial resolution	Very sensitive to mineral phases and doping Only process to probe optical emission
Limitations	Requires thin samples Some elements overlap	Non-local fluorescence Low Z- limits Limited thin-film SNR	Surface only Requires UHV >10 µm resolution	Surface only Requires UHV Conductive samples	Specific use cases

Note: e^- indicates electrons (~5 – 200 keV), \(\gamma\) indicates high-energy photons (UV – x-ray), and indicates optical photons (IR – Vis).

For more information on the cathodoluminescence technique, please visit WhatIsCL.info, an educational site.