Spectroscopy of characteristic energy loss by electrons

Characteristic energy losses by electrons cover a wide range from 10 ⁻³ to 10 ⁴ eV and can occur as a result of various scattering processes, such as:

• excitation of deep levels (100-10 ⁴ eV);
• excitation of plasmons and electronic interband transitions (1-100 eV);
• excitation of vibrations of surface atoms and adsorbate (10–3–1 eV).

The term "spectroscopy of characteristic energy loss by electrons (SHEEL)" has a dual meaning. On the one hand, it is used as a generic term for denoting methods for analyzing energy loss by electrons in the whole range from 10 ⁻³ to 10 ⁴ eV.

On the other hand, it has a narrower meaning for designating the method for studying the characteristic losses of only the second group, with energies in the range from a few eV to several tens of eV, associated with the excitation of plasmons and electronic interband transitions. In this case, the first group of losses is the subject of deep-level CPEE spectroscopy, and the third group is a high-resolution spectroscopy of characteristic electron energy losses . The most frequent use of the SPS method (precisely in the narrow sense) is associated with the solution of such tasks as determining the density of electrons participating in plasma oscillations and chemical analysis of samples, including the analysis of the distribution of elements over depth.

The technique was developed by J. Hiller and R. F. Baker in the mid-1940s ^[1] , but it was not widely used in the next 50 years. And only in the 1990s began to spread due to the improvement of vacuum technology and microscopes.

EELS are often considered complementary to EMF (EDX) , which is another common spectroscopic technique available on a variety of electron microscopes. EMF is good for determining the atomic composition of substances, is easy to use and somewhat more sensitive to heavy elements. CETS is historically a more difficult technique, but, in principle, capable of measuring the atomic composition, chemical bonds, valence and properties of the conduction band, surface properties, etc. SHEPEE is preferable to work with relatively small atomic numbers, where the edge of the absorption band is sharper It is easier to determine and experimentally available (at high absorption energy (> 3 keV) the signal is very weak).

EELS allows you to quickly and accurately measure locally the thickness of the sample in TEM. ^[2] The following procedure is most effective: ^[3]

• Measure the EELS spectrum in the energy range of −5..200 eV (more is better). Such a measurement can be made in a short exposure time (milliseconds), so that it can be carried out on substances unstable under aileron beam.
• Spectrum analysis: select the zero-loss peak (ZLP) and calculate its integral value ( I ₀ ) and integral value of the whole spectrum ( I ).
• Thickness t = mfp * ln (I / I ₀ ) . Where mfp is the average mean free path of inelastically scattered electrons, tabular value. ^[four]

The spatial resolution in this method is limited to the plasmon localization (~ 1 nm), ^[2] that is, thickness maps can be obtained in STEM with a resolution of ~ 1 nm.

• Energetically Filtered Transmission Electron Microscopy
• Transmission electron microscope

• Oura K., Lifshits V. G., Saranin A. A., et al. Introduction to Surface Physics, Ed. V.I. Sergienko. - M .: Science, 2006. - 490 p.
• Egerton, RF Electron Energy Loss Spectroscopy in the Electron Microscope. - 2nd. - New York: Plenum, 1996. - ISBN 978-0-306-45223-9 .