The electron energy loss spectroscopy known as (EELS) technique used with the transmission electron microscope

carloserp-2000 (68)in #steemstem • 7 years ago (edited)

Continuing the class of electronic microscopy, in general of the transmission electron microscope, today I will explain one of the characterization techniques that are performed in this type of microscope to analyze materials.

The study on TEM is extremely interesting, nowadays it is very important for the study of the science of materials. The electron energy loss spectroscopy known as (EELS) is a technique that is used for the chemical analysis of material surfaces using TEM.

This happens when an electron beam is mixed with the material, a part of the beam propagates elastically and ineslatically, that is, when this phenomenon happens they give us important information about the elastic diffusion and for this reason studies on new techniques have been originated of analysis of matariales.

Figure 1. Loss of electron energy due to the inelastic shock presented in this phenomenon.
Source

When an inelastic shock occurs, the electrons can lose energy due to this shock, this whole process is strictly related to the phenomenon, that is, you can obtain information with which electron the shock occurred, which atom and also what level of energy comes the shock produced. All this process is given in the EELS technique, in order to obtain chemical composition studies and other analyzes that I will show below.

In a TEM you can perform different studies of structural characterization at very small scales, that is the great advantage of this microscope, since with its high resolution you can observe the surfaces of the materials using little energy, thanks to the incorporation of the EELS that You could say that it is a very effective technique since you can use different detectors like the secondary and backscattered.

Which can be obtained from the EELS spectrum.

From the observation and respective analysis of the spectrum of a material can be determined different studies such as:

Oxidation states on the surface of certain compounds.
Number of coordination and position of symmetry in its structure.
Link and valence angles.
You can study the vibrational modes of atoms and molecules inserted in the crystal lattice.
As they scatter the low energy electrons on the surface of the material.
Chemical concentration of materials.
And different crystallographic characteristics.

Figure 2. Spectrum of analysis through the EELS.
Source

What is the technique.

Technique whereby a sample is bombarded with a beam of low energy electrons (E0 <10 eV), in order to measure the energy distribution of the reflected electrons. This distribution contains information corresponding to discrete energy losses of these reflected electrons due to the excitation of vibrational states and plasmons. It provides information on the type and geometric structure of the compounds on the surface of the sample.

cited text

As mentioned at the beginning the technique basically corresponds to its name and is that the electron due to the shock produced loses much of its energy, and that is why the scientists discovered this phenomenon and came to the conclusion that this technique is perfect to characterize said materials, because as the electron has little energy after the shock is very interesting to see the study of the material involved in this phenomenon.

Instrumentation required.

Vacuum chamber.
Source (electron gun).
Energy loss spectrometer - Analyzer.
Interpretation software.

It should be remembered that in the TEM technique a high vacuum chamber is used, that is, where air circulation does not flow, in this technique it is important to perform the assemblies well since it is a matter of characterizing very thin materials. mentions in my previous post in preparation of the samples, because they are very thin sheets the electrons during the collision will only suffer an inelastic collision.

Figure 3. Equipment used for electron loss spectroscopy (TEM-EELS).
Source

Main advantages of TEM-EELS.

What characterizes this technique is that you can study very small materials, its high resolution can obtain images up to 100 times closer than in your normal vision, which greatly facilitates the study of surfaces of samples.

Through equations we can obtain the volume and surface plasmons, and the low area of the curve through optical properties, which I will talk about later, is another technique for characterizing very different materials to the structural one.

Differences between the EELS and EDS.

The EELS presents a higher spatial resolution between the materials in comparison with the EDS.
The EELS uses little energy for characterization, the EDS more energy is needed to obtain the spectrum.
The EELS detects lighter elements and the heavier EDS.
The EELS has better energy resolution than the EDS.
And finally the EELS presents structural studies obtaining ideal information to observe its electronic structure or ordering of atoms inside the crystal.

I hope that my post will be of much help and of course be to your liking, later I will provide more information regarding this wonderful world of materials science.

in advance I want to thank the steemstem group for the support I received for my publications and the entire scientific community.

References.

Carlos Pagnini

#science #physics #semiconductor #steemiteducation