VEELS is short for Valence Electron Energy Loss Spectrometry and deals with th low loss part of the energy loss spectrum in the range of 0-50 eV.
VEELS is used for detecting bandgaps or for characterizing optical properties of materials. Because of the high operation voltage of a TEM which accelerates the electrons to 0.7 times the speed of light, relativistic effects can be observed in the loss spectrum hampering the determination of bandgaps and optical properties.
The theory of VEELS based on Maxwell's theory was described by Erhard Kröger (Zeitschrift für Physik, 216 (1968), S. 115-135), but was forgotten throughout the years. The reason might ly in the bad spatial and energy resolution available experimentally in the late 60s of the 20th century. Todays instruments achieve both, excellent spatial and fantastic energy resolutions. The team of USTEM re-described in 2004 these relativistic effects and presented first results at the international EELS workshop EDGE 2005 in Grundlsee, Austria, (Cerenkov losses in valence EELS, M. Stöger-Pollach et. al, opens an external URL in a new window). Since then retardation losses are a hot topic in EELS research.
93Citations: "Čerenkov losses: A limit for bandgap determination and Kramers-Kronig analysis", Stöger-Pollach, et al., Micron (2006), pp. 396-402
88Citations: "Optical properties and bandgaps from low loss EELS: Pitfalls and solutions", Stöger-Pollach, Micron (2008), pp. 1092-1110