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Electron microprobe
An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. It works similarly to a scanning electron microscope: the sample is bombarded with an electron beam, emitting x-rays at wavelengths characteristic to the elements being analyzed. This enables the abundances of elements present within small sample volumes (typically 10-30 cubic micrometers or less) to be determined.〔Wittry, David B. (1958). "Electron Probe Microanalyzer", (US Patent No 2916621 ), Washington, DC: U.S. Patent and Trademark Office.〕 The concentrations of elements from beryllium to plutonium can be measured at levels as low as 100 parts per million (ppm). Recent models of EMPAs can accurately measure elemental concentrations of approximately 10 ppm.
== History ==
In 1944, MIT built an electron microprobe, combining an electron microscope and an energy-loss spectrometer. Electron energy-loss spectrometry is very good for light element analysis and they obtained spectra of C-Kα, N-Kα and O-Kα radiation. In 1947, Hiller patented the idea of using an electron beam to produce analytical X-rays, but never constructed a working model. His design proposed using Bragg diffraction from a flat crystal to select specific X-ray wavelengths and a photographic plate as a detector.
In 1948-1950, Raymond Castaing, supervised by André Guinier, built the first electron “microsonde électronique” (electron microprobe) at ONERA. This microprobe produced an electron beam diameter of 1-3 μm with a beam current of ~10 nanoamperes (nA) and used a Geiger counter to detect the X-rays produced from the sample. However, the Geiger counter could not distinguish X-rays produced from specific elements and in 1950, Castaing added a quartz crystal between the sample and the detector to permit wavelength discrimination. He also added an optical microscope to view the point of beam impact. The resulting microprobe was described in Castaing's 1951 PhD Thesis, in which he laid the foundations of the theory and application of quantitative analysis by electron microprobe, establishing the theoretical framework for the matrix corrections of absorption and fluorescence effects. Castaing (1921-1999) is considered the "father" of electron microprobe analysis.
CAMECA (France) produced the first commercial microprobe, the “MS85,” in 1956. It was soon followed by many microprobes from other companies; however, all companies except CAMECA and JEOL, are now out of business. In addition, many researchers build electron microprobes in their labs. Significant subsequent improvements and modifications to microprobes included scanning the electron beam to make X-ray maps (1960), the addition of solid state EDS detectors (1968) and the development of synthetic multilayer diffracting crystals for analysis of light elements (1984). Latter, CAMECA became also the pioneer on manufacturing a shielded version of the electron microprobe for nuclear applications. Several new advances in CAMECA instruments in the last decades allowed them to expand their range of applications on metallurgy, electronics, geology, mineralogy, nuclear plants, trace elements, dentistry, etc.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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