Quantitative Compositional Mapping with the Electron Probe Microanalyzer

Abstract

Of all the techniques of electron probe microanalysis, the one that has undergone the least change over the history of the field is the technique of producing an image of the distribution of the elemental constituents of a sample, which can be termed compositional mapping. Even today with the dominance of computers for digital data collection and processing in the microprobe laboratory, most compositional mapping is still carried out with an analog procedure that is little changed from the “dot mapping” or “area scanning” technique described by Cosslett and Duncumb in 1956 [1]. The dot mapping procedure can be summarized as follows: (1) As in conventional scanning electron imaging, the beam on the cathode ray tube (CRT) is scanned in synchronism with the beam on the specimen. (2) When the beam is at a particular position on the specimen and an x-ray photon is detected with either a wavelength-dispersive (WDS) or an energy dispersive spectrometer (EDS), the corresponding beam location on the CRT is marked by adjusting the current to excite the phosphor to full brightness. (3) The white dots produced on the CRT display are continuously recorded by photographing the screen to produce the dot map.