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Concept
Electron microprobe
Summary
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, when a conventional accelerating voltage of 15-20 kV is used. The concentrations of elements from lithium to plutonium may be measured at levels as low as 100 parts per million (ppm), material dependent, although with care, levels below 10 ppm are possible. The ability to quantify lithium by EPMA became a reality in 2008.
The electron microprobe, also known as the electron probe microanalyzer, developed utilizing two technologies: electron microscopy — the use of a focused high energy electron beam to interact with a target material, and X-ray spectroscopy — identification of the photons resulting from electron beam interaction with the target, with the energy/wavelength of the photons being characteristic of the atoms excited by the incident electrons. The names of Ernst Ruska and Max Knoll are associated with the first prototype electron microscope in 1931. The name of Henry Moseley is associated with the discovery of the direct relationship between the wavelength of X-rays and the identity of the atom from which it originated.
There have been at several historical threads to electron beam microanalytical technique. One was developed by 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.
Official source
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