Analytical electron microscope AEM

The uniqueness and desirability of EELS is realized when it is combined with the power of a TEM or STEM to form an Analytical Electron Microscope (AEM). This combination allows the analyst to perform spatially resolved nondestructive analysis with high-resolution imaging (< 3 A). Thus, not oiJy can the analyst observe the microstructure of interest (see the TEM article) but, by virtue of the focusing ability of the incident beam in the electron microscope, he or she can simultaneously analyze a specific region of interest. Lateral spatial resolutions of regions as small as 10 A in diameter are achievable with appropriate specimens and probe-forming optics in the electron microscope. 

The analytical electron microscope (AEM) is fitted with a spectrometer for X-ray microanalysis and also for electron energy-loss analysis (q.v. pp. 185). 

Various analytical techniques can be carried out in a transmission electron microscope. TEM is transformed into an analytical electron microscope (AEM) by adding an X-ray spectrometer as a detector [208]. The X-ray energy dispersive spectrometer (XEDS) is the only X-ray spectrometer currently used in TEMs. It is remarkably compact, efficient and sensitive. A combination of Si(Li) and Ge detectors can detect Ka lines from all the elements, from B to U. XEDS is limited in terms of its need for cooling, poor energy resolution, and many spectral artefacts. The spectral resolution of EDS in a TEM is typically 120-150 eV, hence this technique is not useful in the study of fine structural detail of the electronic structure of bonds. For quantitative X-ray analysis of thin Aims in TEM the so-called t-factor method is of great use [209],... 

Analytical electron microscopy (AEM) permits the determination of the elemental composition of a solid catalyst at the microscopic level by energy-dispersive detection of the electron-induced X-ray emission (EDX). Energy dispersive spectroscopy (EDS) is sensitive for elements with atomic numbers Z > 11. For lighter elements (Z < 11), electron energy loss spectroscopy (EELS) is applied. An example is shown in Figure 7 (bottom), which exhibits the elemental composition by EDX of two individual Pt/Rh particles on a carbon film. This analysis clearly demonstrates the heterogeneous composition of the alloy particles. 

Scanning transmission electron microscopy gives essentially the same type of results and has the same type of difficulties as the conventional TEM. There are two types of instruments, the dedicated STEMs, which generally have a UHV column, and the TEM based instruments mostly known as AEMs (analytical electron microscopes). A detailed comparison of STEM and TEM was given in Section 2.4.1.3. There are some advantages in using the STEM on polymer samples in particular it seems that thicker samples can be used. However, the added complexity and cost, combined with lower resolution in the AEM STEM mode, make it unlikely that either kind of instrument would be purchased for polymer studies. 

AEM analytical electron microscope (microscopy) Cl chemical ionization... 

The origins of analytical electron microscopy go back only about 15 years when the first x-ray spectra were obtained from submicron diameter areas of thin specimens in an electron microscope [1]. Characterization of catalyst materials using AEM is even more recent[2,3] but is currently a very active research area in several industrial and academic laboratories. The primary advantage of this technique for catalyst research is that it is the only technique that can yield chemical and structural information from individual submicron catalyst particles. 

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