Electron Probe Microanalysis point analysis

Because X-ray counting rates are relatively low, it typically requires 100 seconds or more to accumulate adequate counting statistics for a quantitative analysis. As a result, the usual strategy in applying electron probe microanalysis is to make quantitative measurements at a limited collection of points. Specific analysis locations are selected with the aid of a rapid imaging technique, such as an SEM image prepared with backscattered electrons, which are sensitive to compositional variations, or with the associated optical microscope. 

Electron beam probe microanalysis, developed by Castaing (1951), is a method of the nondestructive elemental analysis from an area only 1 pm in diameter at the surface of a solid specimen. A beam of electrons is collimated into a fine pencil of 1-pm cross section and directed at a specimen surface exactly on the spot to be analyzed. This electron bombardment excites characteristic X-rays essentially from a point source and at intensities considerably higher than with fluorescent excitation. The limit of detectability (in a 1-pm sized region) is about 10 g. The relative accuracy is 1-2% if the concentration is greater than a few percentages and adequate standards are available. 

Energy-dispersive X-ray (EDX) spectroscopy utilizes the characteristic spectrum of X-rays that is emitted by a sample, following initial excitation by the high-energy electron beam. Information about the elemental composition of the sample can be obtained, where the spatial resolution is determined by the probe size, any beam broadening occurring within the specimen, and the effects of any backscattered electrons on the specimen around the point of analysis. EDX is relatively simple and can be used to provide rapid qualitative microanalysis. Quantitative elemental analysis can also be achieved, with an... 

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