A new device for high-resolution Li K X-ray spectroscopy using an electron microprobe

Lithium is one of the key elements in today's materials and battery industry, and the interest in non-destructive characterization techniques at a micron scale for materials containing lithium is steadily increasing. The electron microprobe is a reliable and accessible analysis tool widely used for this purpose, but performing X-ray emission spectroscopy in the low-energy range is still challenging.

In this work, we demonstrate that spectroscopy in the Li K energy range is feasible by integrating a new detection system composed of a multilayer and ultra-thin separation windows into a commercial wavelength dispersive spectrometer of a microprobe. The detection system is described in detail, and the results, in form of spectra showing the Li K emission in LiF and in a ternary quasicrystalline sample, are presented and analyzed. In LiF the emission band is centered at 54.5 eV and has varying intensities for different beam exposure times. The spectra obtained in the ternary quasicrystal clearly demonstrate that the detection system has sufficient energy resolution to separate the Li emission band and the Al $L_{2,3}$ and Cu $M_{2,3}$ emission bands, enabling chemical state analysis by comparing the shapes of the emissions. To our knowledge, this is the first time such a detection system, implemented in a WDS spectrometer and enabling the acquisition of different Li K spectra in various compounds has been described in detail. This kind of system can be used for Li quantification using a common procedure in electron probe microanalysis.