Initial steps towards lithium quantification by electron probe microanalysis
Résumé
Electron probe microanalysis (EPMA) has established itself as a reliable and widely used technique for non-destructive and precise material characterization in diverse scientific and industrial applications. Despite the growing interest in lithium (Li) and the need for accurate non-destructive analysis at a micron scale, the quantification of Li using EPMA faces persistent challenges. Although recently developed periodic multilayers allow spectroscopy in the energy range around the characteristic Li K emission (~50 eV) [1,2], the detection and quantification of Li using a commercialized microprobe equipped with a bent crystal spectrometer without diffraction gratings has not been successfully performed yet.
The complexity of Li detection is due to several factors: the fluorescence yield of Li is low, i.e., few characteristic photons are produced by the decays of the Li 1s core hole, favoring the emission of Auger electrons. Further, the energy of the emitted photons is extremely low, causing strong absorption and weak photon intensity detection. Moreover, the emission undergoes chemical shift and peak-shape changes as the Li K emission band (2p – 1s transition) involves valence electrons, which introduces a dependency on the density of states (DOS) in the valence band [3,4]. This makes the technique highly sensitive to the chemical state of lithium atoms, complicating quantitative analysis further.
This work presents promising results of quantitative EPMA of Li in different materials, including battery compounds, metal alloys and ceramics with Li concentrations down to 4 %. The advances were facilitated by the integration of a new detection system, combined with improvements on the quantification procedure using real standards and correction programs adapted to low-voltage EPMA.
While additional investigation is required, these first results are promising for researchers focusing on lithium characterization. We demonstrate that EPMA emerges as a potential candidate for quantitative Li analysis, even if the Li is contained in heavy matrices with elements showing emission bands in the same spectral range as Li. This novel Li quantification method can be more accessible than techniques employing synchrotron radiation and is a cost-effective alternative to detection using a scanning electron microscope or an electron microprobe equipped with diffraction gratings.
[1] Polkonikov, V., Chkhalo, N., Pleshkov, R., Giglia, A., Rividi, N., Brackx, E., Le Guen, K., Ismail, I., Jonnard, P., Periodic Multilayer for X-ray Spectroscopy in the Li K Range. Appl. Sci. 2021, 11, 6385. https://doi.org/10.3390/app11146385
[2] Hassebi, K.; Meltchakov, E.; Delmotte, F.; Giglia, A.; Jonnard, P. Sc/SiC/Al Multilayer Optimization for Li K Spectroscopy. Appl. Sci. 2024, 14, 956. https://doi.org/10.3390/app14030956
[3] Schweizer, P., Brackx, E., Jonnard, P., X-Ray Spectrom. 2022, 51 (4), 403. https://doi.org/10.1002/xrs.3290 [4] Hassebi, K., Le Guen, K., Rividi, N., Verlaguet, A., Jonnard, P., X-Ray Spectrom 2023, 52(6), 330. https://doi.org/10.1002/xrs.3329