Microprobe electron

Table 7.8 contains values of p,/p for the common target elements employed in X-ray work. A more extensive set of mass absorption coefficients for K, L, and M emission lines within the wavelength range from 0.7 to 12 A is contained in Heinrich s paper in T. D. McKinley, K. F. J. Heinrich, and D. B. Wittry (eds.). The Electron Microprobe, Wiley, New York, 1966, pp. 351-377. This article should be consulted to ascertain the probable accuracy of the values and for a compilation of coefficients and exponents employed in the computations. 

Edx is based on the emission of x-rays with energies characteristic of the atom from which they originate in Heu of secondary electron emission. Thus, this technique can be used to provide elemental information about the sample. In the sem, this process is stimulated by the incident primary beam of electrons. As will be discussed below, this process is also the basis of essentially the same technique but performed in an electron spectrometer. When carried out this way, the technique is known as electron microprobe analysis (ema). 

Electron Microprobe A.na.Iysis, Electron microprobe analysis (ema) is a technique based on x-ray fluorescence from atoms in the near-surface region of a material stimulated by a focused beam of high energy electrons (7—9,30). Essentially, this method is based on electron-induced x-ray emission as opposed to x-ray-induced x-ray emission, which forms the basis of conventional x-ray fluorescence (xrf) spectroscopy (31). The microprobe form of this x-ray fluorescence spectroscopy was first developed by Castaing in 1951 (32), and today is a mature technique. Primary beam electrons with energies of 10—30 keV are used and sample the material to a depth on the order of 1 pm. X-rays from all elements with the exception of H, He, and Li can be detected. 

K. L. WiUiams, A.n Introduction to X-Ray Spectromety X-Ray F/uorescence and Electron Microprobe Mnalysis AHen Unwin, Boston, Mass., 1987. 

Polymer—Cp—MCl complexes have been formed with the Cp-group covalendy bound to a polystyrene bead. The metal complex is uniformly distributed throughout the bead, as shown by electron microprobe x-ray fluorescence. Olefin hydrogenation catalysts were then prepared by reduction with butyl hthium (262). 

Not only is topographical information produced in the SEM, but information concerning the composition near surface regions of the material is provided as well. There are also a number of important instruments closely related to the SEM, notably the electron microprobe (EMP) and the scanning Auger microprobe (SAM). Both of these instruments, as well as the TEM, are described in detail elsewhere in this volume. 

Electron Probe Microanalysis, EPMA, as performed in an electron microprobe combines EDS and WDX to give quantitative compositional analysis in the reflection mode from solid surfaces together with the morphological imaging of SEM. The spatial resolution is restricted by the interaction volume below the surface, varying from about 0.2 pm to 5 pm. Flat samples are needed for the best quantitative accuracy. Compositional mapping over a 100 x 100 micron area can be done in 15 minutes for major components Z> 11), several hours for minor components, and about 10 hours for trace elements. 

Quantitative Electron-Probe Microanalysis. (V. D. Scott and G. Love, eds.) John Wiley Sons, New York, 1983. Taken from a short course on the electron microprobe for scientists working in the field. A thorough discussion of EDS and WDS is given, including experimental conditions and specimen requirements. The ZAF correction factors are treated extensively, and statistics, computer programs and Monte Carlo methods are explained in detail. Generally, a very useftd book. 

With a special optical system at the sample chamber, combined with an imagir system at the detector end, it is possible to construct two-dimensional images of the sample displayed in the emission of a selected Raman line. By imaging from their characteristic Raman lines, it is possible to map individual phases in the multiphase sample however, Raman images, unlike SEM and electron microprobe images, have not proved sufficiently useful to justify the substantial cost of imaging optical systems. 

Scanning Electron Microscopy Scanning Electron Microprobe Secondary Electron Miscroscopy Secondary Electron Backscatteted Electron... 

S. J. B. Reed in Electron Microprobe Analysis, Cambridge University Press, London, 1975. 

J Electron microprobe analysis. The instrument which I shall introduce here is, in my view, the most important development in characterisation since the 1939-1945 War. It has completely transformed the study of microstructure in its compositional perspective. 

Duncumb, P. (2000) Proceedings of Symposium Fifty Years of Electron Microprobe Analysis . August 1999, Microscopy and Microanalysis. 

Szummer, A., Szklarska-Smialowska, Z. and Janik-Czachor, M., Electron Microprobe Study of the Corrosion Pits Nucleation of Fe-16Cr Single Crystals , Corros. Sci., 8, 827... 

Szklarska-Smialowska, Z., Electron Microprobe Study of the Effect of Sulphide Inclusions on the Nucleation of Corrosion Pits in Stainless Steels , Br. Corros. J., S, 159 (1970) Weinstein, M. and Speirs, K., Mechanisms of Chloride-activated Pitting Corrosion of Martensitic Stainless Steels , J. Electrochem. Soc., 117, 256 (1970)... 

Soluble pigments The most important pigments in this class are the metallic chromates, which range in solubilities from 17 0 to 0-00005 g/1 CrO . An examination has recently been carried out of the mechanism of inhibition by chromate ions and it has been shown by chemical analysis of the stripped film, Mdssbauer spectroscopy and electron microprobe analysis that the air-formed film is reinforced with a more protective material in the form of a chromium-containing spinel (Chapter 17). The situation is, however, complicated by the possibility that some chromates, particularly the basic ones, may inhibit through the formation of soaps. There is evidence that lead chromate can function in this way. 

The x-ray emission electron-microprobe is a sufficiently complex spectrograph system to make naming it a problem. The name used here has been chosen because it emphasizes the three salient characteristics of... 

Fig. 9-14. Schematic diagram of the essential elements of an x-ray emission electron-microprobe. (After Castaing and Guinier, Anal. Chem., 25, 724.)...

For additional information about the x-ray emission electron-microprobe, the reader will do well to consult Birks and Brooks,11 who built a simplified probe that gave satisfactory results. They examined both metallic and nonmetallic materials, the surface of the latter being covered by evaporation with about 50 A of manganese or copper to provide sufficient electrical conductivity. Figure 9-15 illustrates an application... 

The short wavelength of x-rays naturally makes them difficult to focus. Electrons, on the other hand, can rather easily be controlled to give beams a few square microns in cross section, a fact that made possible the x-ray emission electron-microprobe (9.9). Clearly, such a concentrated electron beam striking one side of a suitable thin target can give rise to an x-ray spot on the other, and this spot can be small enough to be regarded as a point source of x-rays. 

The apparatus has also been made into an x-ray emission electron-microprobe (9.9) by replacing the target with a transparent section of a rock or mineral sample. The spot being excited could be located easily by viewing it through the sample with an optical microscope. 

The fine-focus electron optical system of the General Electric X-ray Microscope has been used as the basis for an x-ray emission electron-microprobe.9 10... 

X-ray emission electron-microprobe, 261-265, 292, 294, 295 development by Castaing, 261 schematic diagram, 263 simplified, researches of Birks and Brooks with use of, 264, 265 X-ray emission lines, characteristic, chemical influences on, 37-40 effect on analytical-line ratios, 189-191... 

Other instruments which have been devised for microstructure examination include the X-ray microscope, with greater resolving power than the EM (Ref 41), and the electron microprobe, capable of indicating subtle changes in composition over small specimen areas (Refs 57 62)... 

The characteristic feature of solid—solid reactions which controls, to some extent, the methods which can be applied to the investigation of their kinetics, is that the continuation of product formation requires the transportation of one or both reactants to a zone of interaction, perhaps through a coherent barrier layer of the product phase or as a monomolec-ular layer across surfaces. Since diffusion at phase boundaries may occur at temperatures appreciably below those required for bulk diffusion, the initial step in product formation may be rapidly completed on the attainment of reaction temperature. In such systems, there is no initial delay during nucleation and the initial processes, perhaps involving monomolec-ular films, are not readily identified. The subsequent growth of the product phase, the main reaction, is thereafter controlled by the diffusion of one or more species through the barrier layer. Microscopic observation is of little value where the phases present cannot be unambiguously identified and X-ray diffraction techniques are more fruitful. More recently, the considerable potential of electron microprobe analyses has been developed and exploited. 

Scanning electron microscopy and replication techniques provide information concerning the outer surfaces of the sample only. Accurate electron microprobe analyses require smooth surfaces. To use these techniques profitably, it is therefore necessary to incorporate these requirements into the experimental design, since the interfaces of interest are often below the external particle boundary. To investigate the zones of interest, two general approaches to sample preparation have been used. 

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