Electron Energy Loss Microscopy

An electron spectrometer is placed below the standard column in a TEM or STEM for EELS. In TEM, a defining aperture or slit selects the region contributing to the spectrum, while in STEM the probe naturally controls the area being analyzed. A ID electron detector can collect the EELS data from a point, and a 2D detector can collect data from a line. These techniques are sometimes called PEELS, for parallel 

as early systems had a single point detector, requiring the spectrum to be scanned. In any case, scanning the spot or line over the sample can form a 3D image in x, y and energy, which is usually called a spectrum image. 

Note that the shapes of the two carbon peaks are quite different in Fig. 6.16. This relates to the different chemical bonding in the two polymers in principle this information can be used in analysis, but it has been shown in PMMA that chemical changes due to electron beam damage rapidly alter the peak structure [339]. For many polymers, the low energy loss region may not contain any distinct features for use in analysis or imaging, but aromatic compounds do have a peak at about 7 eV, which has been used to identify polystyrene in a polystyrene/ polybutadiene / poly(methyl methacrylate) sample [340]. 

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A. J. Bevolo. Scanning Electron Microscopy. 1985, vol. 4, p. 1449. (Scanning Electron Microscopy, Inc. Elk Grove Village, IL) Thorough exposition of the principles and applications of reflected electron energy-loss microscopy (REELM) as well as a comparison to other techniques, such as SAM, EDS and SEM. 

REELM Reflection Electron Energy-Loss Microscopy... 

EELS, chiefly as a tool for ultramicroanalysis, will also be discussed with the aid of some recently studied examples. Electron energy loss microscopy will also be briefly mentioned. 

Several structural characterisations of carbon nanotubes (CNTs) with the cylindrical graphite are reviewed from the viewpoint of transmission electron microscopy (TEM). Especially, electron energy loss spectroscopy (EELS) by using an energy-fdtered TEM is applied to reveal the dependence of fine structure of EELS on the diameter and the anisotropic features of CNTs. 

Analytical electron microscopy permits structural and chemical analyses of catalyst areas nearly 1000 times smaller than those studied by conventional bulk analysis techniques. Quantitative x-ray analyses of bismuth molybdates are shown from lOnm diameter regions to better than 5% relative accuracy for the elements 61 and Mo. Digital x-ray images show qualitative 2-dimensional distributions of elements with a lateral spatial resolution of lOnm in supported Pd catalysts and ZSM-5 zeolites. Fine structure in CuLj 2 edges from electron energy loss spectroscopy indicate d>ether the copper is in the form of Cu metal or Cu oxide. These techniques should prove to be of great utility for the analysis of active phases, promoters, and poisons. 

Analytical electron microscopy (AEM) can use several signals from the specimen to analyze volumes of catalyst material about a thousand times smaller than conventional techniques. X-ray emission spectroscopy (XES) is the most quantitative mode of chemical analyse in the AEM and is now also useful as a high resolution elemental mapping technique. Electron energy loss spectroscopy (EELS) vftiile not as well developed for quantitative analysis gives additional chemical information in the fine structure of the elemental absorption edges. EELS avoids the problem of spurious x-rays generated from areas of the spectrum remote from the analysis area. 

I. Kottke and F. Martin. Demonstration of aluminium in polyphosphate of Laccaria amethystea (Bolt, ex Hooker) Murr. by means of electron energy loss spectroscopy. J. Microscopy 174 225 (1994). 

High resolution analytical electron microscopy (HRAEM) is not confined to surface analysis, and applications of this as well Auger (AES) and electron energy loss (EELS) spectroscopies are described. 

High-Resolution Electron Microscopy and Electron Energy Loss Spectroscopy... 

Lichtenberger O, Neumann D. Analytical electron microscopy as a powerful tool in plant cell biology examples using electron energy loss spectroscopy and x-ray microanalysis. Eur J Cell Biol 1997 73 378-386. 

Oleshko, V. et al., High resolution electron microscopy and electron energy-loss spectroscopy of giant palladium clusters, Z. Phys. D., 34, 283, 1995. 

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