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Energy dispersive and wavelength dispersive X-ray spectrometry are used to determine the composition of a specimen in a scanning electron microscope (SEM) by electron probe microanalysis (EPMA). A valuable completion for the SEM is analysis by X-ray fluorescence (XRFA). The main advantage of this method consists in its low detection limit. XRFA with a SEM uses the same spectrometers as for EPMA, necessary are only an additional X-ray source for the excitation of fluorescence spectra and software for their evaluation. Recent developments of smart low-power X-ray tubes and X-ray optical components enabled the construction of compact X-ray sources with focussing properties as add-on for a SEM. For quantitative XRFA the source spectrum has to be known. For its calculation the X-ray production yields Y have been measured for the commonly used tube target materials Mo, Rh and W. The excitation spectra were calculated for a variety of source types and compared with respect to the achievable photon flux and its spectral distribution.
X-ray Fluorescence (XRF) with a scanning electron microscope (SEM) is a valuable completion of the analytical capabilities of SEMs. Small and compact micro-focus x-ray sources are mounted to the microscope chamber, and the x-ray spectra are monitored with conventional EDS systems. Up to now the x-ray tubes used for the micro-focus x-ray sources are equipped with beryllium windows about 100 µm thick. The poly-capillary x-ray lenses have their transmission maximum at photon energies around 10 keV. It drops down in both low- and high-energy ranges. Hence, L-radiation from an Mo or Rh target will be strongly attenuated, and the excitation of fluorescence in the soft x-ray range becomes very ineffective. A new micro-focus x-ray source was developed. It is characterised by a lower self-absorption in the tube target, thin beryllium windows and an x-ray optics having a large distance between its foci and the maximum of transmission at about 5 keV. Thus K line fluorescence of light elements becomes effectively excited by the L-radiation from Mo or Rh tube targets. The detection limit for sodium oxide in glass was found to be below 1 mass%.