13. Soft X-Ray Fluorescence Spectroscopy

Abstract

Publisher Summary This chapter discusses the characteristic features of soft x-ray fluorescence (SXF) spectroscopy, specialized spectrometers and detectors that have been developed for measuring very weak spectra, and some typical experimental results. X-ray fluorescence spectra are produced when x-rays are used to excite characteristic x-ray emission spectra of a particular element. Very low yields for radiative transitions in the soft x-ray spectral range made SXF impractical before the advent of powerful synchrotron sources. Consequently, the history of SXF spectroscopy is provided by the measurement of soft x-ray emission (SXE) spectra excited by energetic electrons. Soft x-rays are strongly absorbed requiring windowless operation from a source to sample to spectrometer and detector and the use of reflective optics. Normal incidence reflectance is very low, requiring the use of grazing incidence optics and the accommodation or correction of the large aberrations that this implies. The single most important constraint on SXF spectroscopy, however, is the low radiative yield, which results from the fact that holes in shallow core levels are filled more efficiently by nonradiative than by radiative processes. This fact prevented the development of intense conventional sources using e-beam excitation and limited the development of SXE spectroscopies before the advent of modern synchrotron sources. Another major advantage of photon excitation of emission spectra is that it eliminates the bremsstrahlung background radiation associated with the scattering of energetic electrons.