Electron Probe X-Ray Microanalysis EPMA

Electron Probe X-Ray Microanalysis (EPMA) is a spatially resolved, quantitative elemental analysis technique based on the generation of characteristic X rays by a focused beam of energetic electrons. EPMA is used to measure the concentrations of elements (beryllium to the actinides) at levels as low as 100 parts per million (ppm) and to determine lateral distributions by mapping. The modern EPMA instrument consists of several key components  

1 An electron-optical column capable of forming a beam rangii in diameter from nm to nm and carrying a current ranging from pA to jA 

2 An energy-dispersive X-ray spectrometer and at least one wavelength-dispersive X-ray spectrometer 

3 An optical microscope for precise positioning of the specimen relative to the X-ray spectrometers 

4 A vacuum system capable of operating at pressures ranging from 10 to 10 Pa 

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X-ray microanalysis techniques— in particular, electron probe x-ray microanalysis (EPXMA or EPMA) and SEM coupled with energy dispersive spectrometers (EDS, EDX) are, by far, one of the surface analysis techniques most extensively used in the field of art and art conservation, and they have actually become routine methods of analyzing art and archaeological objects and monitoring conservation treatments [34, 61, 63]. 

The powders of zeolites of various trademarks are used to produce petroleum-refining catalysts. In this connection, it is very important to have complete information concerning not only chemical composition and distribution of impurity elements, but also shape, surface, stmcture and sizes of particles. It allows a more detailed analysis of the physical-chemical characteristics of catalysts, affecting their activity at different stages of technological process. One prospective for solving these tasks is X-ray microanalysis with an electron probe (EPMA). 

Figure 5.27. A summary of the relationship between the spatial resolution and the MMF for X-ray microanalysis in several electron-probe instruments (references given). The two shaded areas represent the ranges of future EPMA microanalysis predicted by Newbury et al. (1999) and the future AEM microanalysis estimated by Williams et al. (2002). (Reproduced by permission of Williams et al., 2002.)...

EPMA Electron probe microanalysis Electron Characteristic x-ray... 

Acronyms SEM scanning electron microscopy, SEMPA scanning electron microscopy with polarisation analysis, EDX energy dispersive X-ray analysis, EPMA electron probe microanalysis, STkM scanning Auger microscopy. 

Electron probe microanalysis is used for characterising surface morphology and for microanalysis of inhomogeneous samples and small volumes. Bet-zold [136] has discussed the use of EPMA for the determination of plastics, fillers, reinforcing materials, pigments, stabilisers, etc. X-ray microanalysis (Br, Mo, Sb, Ti) has been used for determining flame retardant content in ABS granules before and after extraction [265]. Also EPMA analysis of automobile paint was described [158]. EPMA of a film surface of stored PE/4,4 -thiobis(3-methyl-6-r-butylphenol) has revealed that only material within exuded, crystalline platelets contained sulfur [266]. 

The elemental composition of the fish otoliths is a potential source of the useful information to recreate environment history of the individual fish in some of the species. In-depth study of the chemical composition of the otolith center (formed eaidy in fish life) and otolith edge (formed later in fish life) ensures chronological and environmental information stored in the otoliths [1]. This infoiTnation may be achieved by X-ray electron probe microanalysis (EPMA). EPMA is the analytical method to determine the elemental composition of different otolith s parts, their sizes varying from ten up to some tens of microns. 

The complex of the following destmctive and nondestmctive analytical methods was used for studying the composition of sponges inductively coupled plasma mass-spectrometry (ICP-MS), X-ray fluorescence (XRF), electron probe microanalysis (EPMA), and atomic absorption spectrometry (AAS). Techniques of sample preparation were developed for each method and their metrological characteristics were defined. Relative standard deviations for all the elements did not exceed 0.25 within detection limit. The accuracy of techniques elaborated was checked with the method of additions and control methods of analysis. 

There are three types of electron microscopes commonly used for microanalysis. These are the scanning electron microscope (SEM) with X-ray detectors, the electron probe microanalyser (EPMA), which is essentially a purpose built analytical microscope of the SEM type, and transmission microscopes (TEM and STEM) fitted with X-ray detectors. In a TEM, compositional information may also be obtained by... 

As indicated in Fig. 7.2, X-rays are among the by-products in an electron microscope. Already at the beginning of this century, people knew that matter emits X-rays when it is bombarded with electrons. The explanation of the phenomenon came with the development of quantum mechanics. Nowadays, it is the basis for determining composition on the submicron scale and, with still increasing spatial resolution, is used in the technique referred to as Electron Microprobe Analysis (EMA), Electron Probe Microanalysis (EPMA) or Energy Dispersive Analysis of X-rays (EDAX, EDX) [21]. 

To understand the wear mechanism in valve train wear tests, samples of the worn tappet surface were analyzed for surface elements by electron probe microanalysis (EPMA) and X-ray photo electron spectroscopy (XPS). Results of EPMA analysis of the worn surface in terms of concentration of phosphorus and sulfur atoms for oil with primary ZnDDP without MoDTC, showed an increase of zinc and sulfur intensity after 100 hrs of test time, in spite of decreasing phosphorus intensity. Examination of the worn surface by XPS with primary and secondary ZDDP with addition of MoDTC showed the presence of MoS2 in the tribofilm. Using mixtures of ZDDP and MoDTC, the friction coefficient is reduced, and wear is comparable to that of using ZDDP alone (Kasrai et ah, 1997). 

The compound layer formed in the transition zone between nickel and bismuth was investigated metallographically, by X-rays and electron probe microanalysis (EPMA). X-ray patterns were taken both from the cross-sections in the planes parallel to the initial Ni-Bi interface (after successive removal of the specimen material and polishing its surface) and the powdered phases using Cu Ka radiation. Two methods of obtaining X-ray patterns were employed. Firstly, X-ray photographs were obtained in a 57.3 mm inner diameter Debye-Scherrer camera. Secondly, use was made of a DRON-3 diffractometer to record X-ray diffractograms. 

Electron microprobes permit chemical microanalysis as well as SEM and BSE detection, often referred to as analytical electron microscopy (AEM), or electron probe microanalysis (EPMA)56 57. This is because another product of the surface interaction with an incident electron beam is X-ray photons which have wavelengths and energies dependent on element identity and on the electron shell causing the emission. Analysis of these photons can give a local chemical analysis of the surface. Resolution of 1 pm is attainable. Two types of X-ray spectrometer can be employed ... 

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