Brief Introduction To Electron Probe Microanalysis (EPMA)
Electron Probe Microanalysis (EPMA) is an elemental analysis technique which uses a focused beam of high energy electrons (5 - 30 KeV) to non-destructively ionize a solid specimen surface (including thin films and particles) for inducing emission of characteristic x-rays (0.1 - 15 KeV). The spatial resolution of x-ray microanalysis of thick specimens is limited to a volume with dimensions of approximately 1 micrometer due to electron scattering effects. This volume may be even larger for low energy emission lines that can still be excited by lower energy electrons that have been highly scattered a significant distance from the impinging beam on the specimen surface.
Quantitative matrix (interelement) correction procedures based on first principle physical models provide great flexibility and accuracy in analyzing unknown samples of arbitrary composition. Spatial distribution of elemental constituents can be visualized quantitatively by digital composition maps and displayed in gray scale or false color.
These quantitative procedures have been demonstrated to produce error distributions characterized by a standard deviation of less than 3% relative when the samples are in the ideal form of a metallographically polished bulk solid. Standards utilized in these analyses are in the form of pure elements or simple compounds (e.g., MgO or GaP). This analytical approach provides great versatility in the analysis of multi-element unknowns of virtually any composition, with the significant exception of very light elements (atomic numbers less than 6). Detection limits are of the order of 100 ppm with wavelength dispersive spectrometry and 1000 ppm with energy dispersive spectrometry. Typical applications include metallurgical studies, failure analysis, thin film, particulate analysis, mineral analysis, ceramic analysis, anthropological studies, art history and many others.
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