EDS
Energy Dispersive Spectrometry. This method utilizes a solid state detector that operates similarly to the gas-filled detector in the electron microprobe spectrometer, with important distinctions. In the solid state detector, the x-rays knock out electrons (specifically the photoelectric effect), producing electron-hole pairs, each part migrating to + or - surface of the voltage biased Si(Li) or Ge crystal. The number of electron-hole pairs is directly proportional to the x-ray energy, and a small pulse is generated. This is immediately amplified in an adjacent FET (field effect transistor), and then the signal proceeds to a pre-amp, and then to the processing and counting electronics. The result is a histogram of energy levels, or spectrum.
Many electron microprobes also have EDS detectors that are used to "fingerprint" materials prior to WDS analysis. EDS is also combined with WDS on some instruments for increasing the number of elements that can be elementally mapped. Probe for EPMA offers additional options for both acquiring elements for quantitative analysis, as well as acquiring and storing EDS spectra when each WDS measurement is made (useful for off-line data processing).