Quantitative nanoscale mapping of the Mn redox states in silicates by scanning transmission X-ray microscopy at the Mn L2,3-edges

Abstract

We present a novel analytical protocol for quantifying and mapping Mn oxidation states in silicates at the nanoscale. Based on X-ray Absorption Near Edge Structure spectra of the Mn L_2,3-edges (630–660 eV) acquired thanks to a Scanning transmission X-ray microscope available at various Synchrotron facilities, we calibrate two equations using reference Mn-bearing samples to precisely determine the Mn mean valence. We detail the spectra processing and the methodology for deriving quantitative Mn redox maps from the proposed calibrations, with a high spatial resolution (20–30 nm). Furthermore, we explore the potential for coupling Mn and Fe L_2,3-edge redox calibrations over the 630–730 eV energy range. The effectiveness of these calibrations, the coupling of MnFe results, and the subsequent redox mapping are evaluated through two case studies, showcasing the benefits of this non-destructive approach.