energy-dispersive X-ray spectroscopy, EDS

Energy-dispersive X-ray spectroscopy (EDS) is an element analysis method. Characteristic X-rays generated from a specimen are detected by a semiconductor detector and converted into electric signals. In the EDS analyzer, the pulse currents that are proportional to the energies of the detected characteristic X-rays are generated, and then these currents are measured with a multi-channel pulse-height analyzer. EDS has higher detection efficiency of X-rays than WDS, but the analyzing power of light elements is lower than WDS. (EDS cannot analyze elements from boron (B) on down.) Since the illumination current of the electron beam for EDS can be decreased from several pA to several nA compared with WDS, the beam damage to a specimen is small. Normally, the resolution of EDS is ～140 eV for Mn Kα emission at 5.9 keV. The resolution determined by statistical counting error is around the square root of energy E of the generated X-ray × √3. (The number of created electrons n is obtained as n～E/3 by taking the band gap energy as ～3 eV. Since the statistical error Δn is ～√n, the energy spread (error) is obtained to be ～Δn・3 = √E・√3.) Recently, an EDS detector that can resolve a beryllium (Be) peak has been developed. Its quantification accuracy is 0.5 to 5%. Compared with EPMA that uses analyzing crystals, EDS provides high spatial resolution, 100 times better than EPMA but shows 10 times worse quantification accuracy than EPMA. "EDX" is also used as the abbreviation of energy-dispersive X-ray spectroscopy.

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