Electron Energy Loss Spectroscopy - Variants

Variants

There are several basic flavors of EELS, primarily classified by the geometry and by the kinetic energy of the incident electrons (typically measured in kiloelectron-volts, or keV). Probably the most common today is transmission EELS, in which the kinetic energies are typically 100 to 300 keV and the incident electrons pass entirely through the material sample. Usually this occurs in a transmission electron microscope (TEM), although some dedicated systems exist which enable extreme resolution in terms of energy and momentum transfer at the expense of spatial resolution.

Other flavors include reflection EELS (including reflection high-energy electron energy-loss spectroscopy (RHEELS), typically at 10 to 30 keV) and aloof EELS (sometimes called near-field EELS, in which the electron beam does not in fact strike the sample but instead interacts with it via the long-ranged Coulomb interaction; aloof EELS is particularly sensitive to surface properties but is limited to very small energy losses such as those associated with surface plasmons or direct interband transitions).

Within transmission EELS, the technique is further subdivided into valence EELS (which measures plasmons and interband transitions) and inner-shell ionization EELS (which provides much the same information as x-ray absorption spectroscopy, but from much smaller volumes of material). The dividing line between the two, while somewhat ill-defined, is in the vicinity of 50 eV energy loss.

High resolution electron energy loss spectroscopy, in which the electron beam is 1eV to 10eV, and highly monochromatic.