Is scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS) quantitative? Effect of specimen shape

摘要

The extraordinary throughput of the silicon drift detector energy dispersive x-ray spectrometer (SDD-EDS) enables collection of EDS spectra with much higher integrated counts within practical time periods, e.g., 100 s or less, compared to past experience with the Si(Li)-EDS. Such high count SDD spectra, containing one million to ten million counts, yield characteristic peak intensities with relative standard deviation below 0.25%, a precision similar to that achieved with wavelength dispersive spectrometry (WDS), the "gold standard" of microprobe analysis, but at lower dose because of the greater solid angle of the SDD-EDS. Such high count SDD-EDS spectra also enable more accurate quantification, nearly indistinguishable from WDS for major and minor constituents when the WDS unknown-to-standard intensity ratio ("k-value") protocol is followed. A critical requirement to satisfy this measurement protocol is that the specimen must be a highly polished bulk target. The geometric character of specimens examined in the scanning electron microscope (SEM) often deviates greatly from the ideal flat bulk target but EDS spectra can still be readily obtained and analyzed. The influence of geometric factors such as local inclination and surface topography on the accuracy of quantitative EDS analysis is examined. Normalized concentration values are subject to very large errors, as high as a factor of 10, as a result of deviation of the specimen geometry from the ideal flat bulk target.