Electron Probe X-Ray Microanalyzer (EPMA)
About the lab
Electron Probe X-ray Microanalyzer
The Electron Probe X-ray Microanalyzer (EPMA) is used to determine the chemical composition of solid materials on a microscopic scale, down to volumes of a few cubic micrometers. Smaller particles can also be analyzed, although at considerably lower levels of accuracy).
The X-ray signal carries information about the chemical composition of the microvolume where it was generated. By means of an appropriate detection system, it is possible to eventually obtain qualitative (elements present) and quantitative (weight %) analyses. The detection of the X-rays is accomplished by means of crystal spectrometers (WDS, wavelength dispersive spectrometry) and solid state Si(Li) detectors (EDS, energy dispersive spectrometry). A computer and specialized software are also needed to achieve that end, ultimately making it possible to generate large volumes of high quality data, either in a manual or in an automatic, unattended mode.
Other signals typically utilized in an electron microprobe are Secondary Electrons (SE) and Backscattered Electrons (BSE). The SE emission intensity is most strongly modulated by surface topography, that of BSE by compositional variations. Both signals are collected while the beam is being scanned on a very small portion of the sample surface. The reconstruction of the spatial distribution of the collected signal intensity generates two-dimensional images (maps) displaying surface relief (SE) and compositional contrast (BSE). “Chemical maps” of the sample surface can similarly be obtained using the X-ray signal.
There are many web sites where you can read about EPMA, discussed in lesser or greater detail. Among those:
For links to other Cameca SX50 microprobe labs: