Electron Probe Microanalysiswith Cryogenic Detectors

Abstract

Electron probe X-ray microanalysis (EPMA) is based upon the use of a focused, high current density electron beam, 5 to 30 keV in energy, to excite characteristic X-rays from a picogram mass of a solid target. X-ray spectral measurements are currently performed with the broad bandpass semiconductor energy dispersive X-ray spectrometry (Si-EDS) and/or the high resolution crystal diffraction wavelength dispersive spectrometry (WDS). The strengths and weaknesses of WDS and EDS are mutually complementary. Nevertheless, existing EPMA/WDS/EDS technology has limitations which become extreme when applied to the newly emerging field of low voltage microanalysis, where the beam energy is less than 5 keV. The microcalorimeter EDS provides both high spectral resolution and energy dispersive operational character, two key features of the ideal spectrometer for EPMA. The NIST prototype microcalorimeter EDS achieves impressive performance for EPMA in terms of resolving key elemental interferences, detecting chemical state induced peak shifts, high sensitivity, and applicability to low voltage microanalysis. Further technical developments should extend these capabilities, and commercialization will bring the advantages of the microcalorimeter EDS to critical applications.