Improved lithium-drifted silicon solid-state detectors allow detection and energy dispersion of x-rays of about 3 to 30 kiloelectron volts in the electron-microprobe x-ray analyzer. Energy resolution is sufficient to separate peaks of characteristic x-rays of elements adjacent in the periodic system at atomic number 20 and higher. The detected x-ray spectrum emitted from an unknown sample can be recorded with a multichannel analyzer in approximately 60 seconds.
On February 2, 1968, R. Fitzgerald, K. Keil, and K.F.J. Heinrich published a seminal paper in Science (159, 528-530) in which they described a solid-state Si(Li) energy dispersive spectrometer (EDS) for electron probe microanalysis (EPMA) with, initially, a resolution of 600 eV. This resolution was much improved over previous attempts to use either gas-filled proportional counters or solid-state devices for EDS to detect X-rays and was sufficient, for the first time, to make EDS a practically useful technique. It ushered in a new era not only in EPMA, but also in scanning electron microscopy, analytical transmission electron microscopy, X-ray fluorescence analysis, and X-ray diffraction. EDS offers many advantages over wavelength-dispersive crystal spectrometers, e.g., it has no moving parts, covers the entire X-ray energy range of interest to EPMA, there is no defocusing over relatively large distances across the sample, and, of particular interest to those who analyze complex minerals consisting of many elements, all X-ray lines are detected quickly and simultaneously.
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