Fingerprinting materials oxidation using laser-induced XUV spectroscopy (LIXS)

Laser-induced XUV spectroscopy (LIXS) is an emerging plasma-based microanalytical technique that offers access to the early, "background-uncontaminated" (pristine) stages of laser-induced plasma evolution. In this study, the capability of LIXS to resolve not only the elemental composition but also the oxidation state of complex materials is investigated, i.e., by exploiting radiative recombination dynamics. Using a spatial-filtered detection scheme, the evolution of plasma emission was tracked, revealing characteristic spectral features associated with electron recombination into unoccupied s or d atomic orbitals. The latter retain a distinct fingerprint of the parent material's oxidation state. Preliminary experiments on LiF, Al, and Ni served to calibrate the relationship between expansion kinetics, emission time delay, and atomic structure. Reference samples, including lithium manganese oxides with well-defined stoichiometries, were used to correlate LIXS spectral fingerprints to manganese oxidation levels. The results indicate that, contrary to the observations for the thermalized LIBS plasma, the LIXS laser plasma does not erase information on the material's stoichiometry. Instead, the recombination features in the XUV region directly reflect the electronic configuration of the parent material. This work introduces LIXS as a novel route for rapid, stoichiometry-sensitive mapping of oxidation states, with immediate applications in the quality control of energy materials and battery components. The approach lays the foundation for the development of oxidation-specific plasma spectroscopy, extending the analytical power of laser ablation far beyond elemental analysis.