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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Electron probe microanalysis | 2/4 | https://en.wikipedia.org/wiki/Electron_probe_microanalysis | reference | science, encyclopedia | 2026-05-05T10:04:28.363360+00:00 | kb-cron |
== History ==
The electron microprobe (electron probe microanalyzer) developed from two technologies: electron microscopy, which uses a focused high energy electron beam to impact a target material, and X-ray spectroscopy, which identifies the photons scattered from the electron beam impact, with the energy/wavelength of the photons characteristic of the atoms excited by the incident electrons. Ernst Ruska and Max Knoll are associated with the prototype electron microscope in 1931. Henry Moseley was involved in the discovery of the direct relationship between the wavelength of X-rays and the identity of the atom from which it originated.
Several historical threads combined in the early development of electron beam microanalysis. One was the work of James Hillier and Richard Baker at RCA. In the early 1940s, they built an electron microprobe, combining an electron microscope and an energy loss spectrometer. A patent application was filed in 1944. Electron energy loss spectroscopy 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 concept 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. However, RCA had no interest in commercializing this invention.
A second thread developed in France in the late 1940s. In 1948–1950, Raimond 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, translated into English by Pol Duwez and David Wittry, 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 is considered the father of electron microprobe analysis.
The 1950s was a decade of great interest in electron beam X-ray microanalysis, following Castaing's presentations at the First European Microscopy Conference in Delft in 1949 and then at the National Bureau of Standards conference on Electron Physics in Washington, DC, in 1951, as well as at other conferences in the early to mid-1950s. Many researchers, mainly material scientists, developed their own experimental electron microprobes, sometimes starting from scratch, but many times using surplus electron microscopes.
Concurrently, Pol Duwez, a Belgian material scientist who fled the Nazis and settled at the California Institute of Technology (Caltech) and collaborated with Jesse DuMond, encountered André Guinier on a train in Europe in 1952, where he learned of Castaing's new instrument and the suggestion that Caltech build a similar instrument. David Wittry was hired to build such an instrument as his PhD thesis, which he completed in 1957. It became the prototype for the ARL EMX electron microprobe.
During the late 1950s and early 1960s there were over a dozen other laboratories in North America, the United Kingdom, Europe, Japan and the USSR developing electron beam X-ray microanalyzers.
The first commercial electron microprobe, the "MS85" was produced by CAMECA (France) in 1956.. It was soon followed in the early-mid 1960s by microprobes from other companies; however, all companies except CAMECA, JEOL and Shimadzu Corporation went out of business. Significant subsequent improvements and modifications to microprobes included the addition of solid state EDS detectors (1968) and the development of synthetic multilayer diffracting crystals for analysis of light elements (1984). One breakthrough of particular note, however, was the development, from the late 1950's onwards, of scanning microprobes; that is, devices which could scan the electron beam across a sample to make X-ray maps. These found great application in metallurgy, see section below.
Later, CAMECA pioneered manufacturing a shielded electron microprobe for nuclear applications. Several advances in CAMECA instruments in recent decades expanded the range of applications in metallurgy, electronics, geology, mineralogy, nuclear plants, trace elements, and dentistry.