Sensitive boron detection with a table-top wavelength dispersive spectrometer

Boron has many applications in science and industry yet there don't exist any easy-to-use X-ray fluorescence analysis techniques to detect low concentrations of boron in a sample. Wavelength dispersive X-ray spectrometry (WDX) after excitation by scanning electron microscope (SEM-WDX) combines high spatial resolution obtained with an electron microprobe and a spectrometer with sub-eV energy resolution, and high sensitivity in the soft X-ray range. The sensitivity necessary for low concentration boron detection is achieved by a wide sagittal acceptance, high diffraction efficiency and the focussing effect of the used reflection zone plate (RZP). The RZP and a CCD camera form a compact WDX spectrometer (309 × 156 × 165 mm3), suitable for tabletop laboratory setups and as an add-on to beamlines at large-scale facilities. In order to test the detection limit for boron, three samples were measured: Duran glass with ~ 9 at% boron, Si (55 %) / Ge (45 %) with 1 at% boron implantation and Si (55 %) / Ge (45 %) with 0.1 at% boron implantation. After optimising the setup, a signal to noise (S/N) ratio of 7.2 was achieved at 0.1 at% boron, indicating a detection limit of 500 ppm for the current setup. Effects of radiation damage and energy shifts depending on the boron binding state were observed as well.