Evaluation of scanning transmission X-ray microscopy at the Mn L2,3-edges as a potential probe for manganese redox state in natural silicates

Determining the Mn valence variation at nanometer scale will be an important advance in study of heterogeneous natural silicates. Here, potential scanning transmission X-ray microscopy L2,3-edges (640–655 eV) as a probe for manganese redox state is evaluated. For this purpose, several Mn-silicates (rhodonite, ardennite, piemontite, Mn4+-silicate, jacobsite) were analysed to identify spectral parameters most sensitive valence, regardless coordination environment, crystal field strength, nature and length metal–ligand bonds, intra-atomic Coulomb spin–orbit interactions. Two suitable empirical calibrations are thus proposed, linking two peak intensity ratios: one ratio intensities from energy points L2 (at 651.7 655.2 eV), point L3 641.6 eV). Thank them, first quantitative maps constructed, with high spatial resolution (<40 nm pixel size), opening way exhaustive crystallochemical studies silicates containing different valences.