Electron Energy Loss Spectroscopy (EELS)

A typical electron energy loss spectrum is shown below. It consists of three parts:

Zero-loss peak at 0 eV:
It mainly contains electrons that still have the original beam energy E₀, i.e., they have only interacted elastically or not at all with the specimen. In thin specimens, the intensity of the zero-loss beam is high, so that damage of the CCD chip can occur. Since there is no useful information in it, the zero-loss beam is often omitted during spectrum collection.

Low-loss region (< 100eV)
Here, the electrons that have induced plasmon oscillations occur. Since the plasmon generation is the most frequent inelastic interaction of electron with the sample, the intensity in this region is relatively high. Intensity and number of plasmon peaks increases with specimen thickness.

High-Loss region (> 100eV)
For the ionization of atoms, a specific minimum energy, the critical ionization energy E_C or ionization threshold, must be transferred from the incident electron to the expelled inner-shell electron, which leads to ionization edges in the spectrum at energy losses that are characteristic for an element. Thus, EELS is complementary to X-ray spectroscopy, and it can be utilized for qualitative and quantitative element analysis as well. In particular, the detection of light elements is a main task of EELS.
Compared to the plasmon generation, the inner-shell ionization is a much less probable process, leading to a low intensity of the peaks. In the high-loss region, the amount of inelastically scattered electrons drastically decreases with increasing energy loss, thus small peaks are superimposed on a strongly decreasing background (s. spectrum). Because of the low intensity, the representation of the high-loss region is often strongly enhanced (here: intensity gap at about 220 eV).

Generation of X-rays