Microscopy analytical electron

Although electron microscopy is approached in this chapter as an analytical technique (a variant of XRF), it is essential to state at the outset that electron microscopy is far more versatile than this. Many standard descriptions of electron microscopy approach the subject from the microscopy end, regarding it as a higher resolution version of optical microscopy. Several texts, such as Goodhew et al. (2001), Reed (1993) and Joy et al. (1986), are devoted to the broad spectrum of analytical electron microscopy, but the emphasis here on the analytical capacity is justified in the context of a book on archaeological chemistry. 

As noted above, there are several ways of creating an inner shell vacancy which may de-excite via the emission of a characteristic X-ray. XRF uses a primary beam of X-rays, but suffers from the fact that the characteristic X-ray spectrum recorded from a solid sample contains a scattered version of the primary spectrum, increasing the background signal and therefore degrading analytical sensitivity. The use of an electron beam to create inner shell 

Principles and Characteristics In the late 1960s an alternative to the TEM imaging geometry was introduced by Crewe et al. [239], who used similar optics to produce a very small electron probe that was scanned in a raster over the area of interest. This high-resolution scanning transmission electron microscope (STEM) has become an 

Quantitative X-ray analysis in analytical electron microscopy is now a most straightforward technique. Matrix (interelement) correction procedures based upon first principles physical models provide great flexibility in examining unknown samples of arbitrary composition. According to Castaing [251,252]  

Possibilities and limitations of EPMA techniques for quantitative near-surface analysis and depth profiling were described [259]. Spatial distributions 

CRMs for electron microprobe analysis of carbon and nitrogen are available [260]. A major challenge for these materials is to obtain homogeneity at the micron level. ASTM Standard E 1508 describes quantitative analysis by EDS [261]. ISO Technical Committee TC202 has launched the standardisation project No. 15632 for the specification of an EDS spectrometer. 

AEM and X-ray emission specfioscopy were reviewed [262]. A monograph dealing with analytical electron microscopy has appeared [215]. Textbooks on X-ray spectrometry in elecfion beam insfiuments, particularly as it relates to the practice of EPMA and EDX, are available [263,263a]. 

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Joy D C 1986 The basic principles of EELS Principles of Analytical Electron Microscopy ed D C Joy, A D Romig Jr and J I Goldstein (New York Plenum)... 

The STEM instrument itself can produce highly focused high-intensity beams down to 2 A if a field-emission source is used. Such an instrument provides a higher spatial resolution compositional analysis than any other widely used technique, but to capitalize on this requires very thin samples, as stated above. EELS and EDS are the two composition techniques usually found on a STEM, but CL, and even AES are sometimes incorporated. In addition simultaneous crystallographic information can be provided by diffraction, as in the TEM, but with 100 times better spatial resolution. The combination of diffraction techniques and analysis techniques in a TEM or STEM is termed Analytical Electron Microscopy, AEM. A well-equipped analytical TEM or STEM costs well over 1,000,000. 

D. B. Williams. Practical Analytical Electron Microscopy in Materials Science. Verlag Chemie International, Weinheim, 1984. A good monograph discussing the use and applications of AEM, especially at intermediate voltages. The discussion on EDS is an excellent primer for using X-ray analysis on a TEM. 

Principles of Analytical Electron Microscopy (D. C. Joy, A. D. Romig, and J. I. Goldstein, eds.) Plenum Press, New York, 1986. Another book, more readily available, discussing all aspects of AEM. Approximately one-quarter of the book is devoted to EDS and a discussion of thin-film analysis in the TEM. 

I. Goldstein, eds.) Plenum Press, 1979. A good overview of analytical electron microscopy. 

N. J. Zaluzec, T. Schober, and B. W. Veal. In Analytical Electron Microscopy—1982 Proceedings of the Workshop at Vail Colorado. San Francisco Press, p. 191. 

Introduction to Analytical Electron Microscopy (J. J. Hren, J. I. Goldstein, and D. C. Joy, eds.) Plenum, New York, 1979. Somewhat dated text that is still useful for certain chapters including those of Cowley, Steeds, and Isaacson, et al. 

The combined use of energy-dispersive X-ray spectroscopy and TEM/STEM is a routine method of analytical electron microscopy enabling both qualitative and quantitative chemical analysis of interfaces and interlayers with high lateral resolution. Reso-... 

S. Amelincks, D. van Dyck, J. van Landuyt, G. van Tendeloo (eds.) Electron Microscopy Principles and Fundamentals,VCH Verlagsgesellschaft mbH, Weinheim 1997. 4-89 J. J. Hhen, j. I. Goldstein (eds.) Introduction to Analytical Electron Microscopy, Plenum Press, New York, 1979. 

In this chapter shock modification of powders (their specific area, x-ray diffraction lines, and point defects) measurements via analytical electron microscopy, magnetization and Mossbauer spectroscopy shock activation of catalysis, solution, solid-state chemical reactions, sintering, and structural transformations enhanced solid-state reactivity. 

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) permits elemental and structural data to be obtained from volumes of catalyst material vastly smaller in size than the pellet or fluidized particle typically used in industrial processes. Figure 1 shows three levels of analysis for catalyst materials. Composite catalyst vehicles in the 0.1 to lOim size range can be chemically analyzed in bulk by techniques such as electron microprobe, XRD, AA, NMR,... 

Analysis of individual catalyst particles less than IMm in size requires an analytical tool that focuses electrons to a small probe on the specimen. Analytical electron microscopy is usually performed with either a dedicated scanning transmission electron microscope (STEM) or a conventional transmission electron microscope (TEM) with a STEM attachment. These instruments produce 1 to 50nm diameter electron probes that can be scanned across a thin specimen to form an image or stopped on an image feature to perform an analysis. In most cases, an electron beam current of about 1 nanoampere is required to produce an analytical signal in a reasonable time. 

Figure 1. Three levels of analysis for catalyst materials, a) bulk analysis of an entire catalyst pellet, b) surface analysis and depth profiling from the surface inward, c) analytical electron microscopy of individual catalyst particles too small for analysis by other techniques.

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. 

Williams, D. B. "Practical Analytical Electron Microscopy in Materials Science," Philips Electronic Instruments Electron Optics Publishing, Mahwah, N.J., 1984. 

High Resolution Analytical Electron Microscopy (HRAEM) 129... 

HIGH RESOLUTION ANALYTICAL ELECTRON MICROSCOPY (HRAEM) 5.1.1 Interaction of Electrons with Matter... 

Michael, J.R. (1981) Practical Analytical Electron Microscopy in Materials Science, second Edition, Ed. Williams, D.B. p.83, Philips Electron Optics Publishing Group, Mahwah, NJ, 1987. 

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. 

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