Fig. 2: Nitrogen and oxidized carbon enrichment at the organo–mineral interface.
From: Organo–organic and organo–mineral interfaces in soil at the nanometer scale
High-resolution cryo-electron imaging and spectroscopy of an organo–mineral interface in a volcanic soil sample. a Annular dark-field (ADF) scanning transmission electron microscopy (STEM) image of organo–mineral interface and adjacent organic matter region, showing the location of electron energy-loss spectroscopy (EELS) data collection across and adjacent to an aluminum (Al) mineral with layered structure. b, c Average carbon (b) and nitrogen (c) K-edge EELS (black line) and individual spectra (gray lines) for either five points (A–E) across the organo–mineral interface or three EELS point scans within the adjacent OM region. For both b and c, spectra are shown unsmoothed and normalized to the maximum carbon intensity. In b, dotted vertical line indicates peak at 288.1 eV, putatively identified as carboxylic/carbonyl groups with substituted or adjacent N31,32. Lower (284.0–286.5 eV) (y) and higher (286.6–289.0 eV) (x) energy regions are indicated by shaded boxes. Ratio x/y indicates the ratio of integrated EELS intensity within each region, normalized to total carbon integrated area (280.0–315.0 eV). Between the adjacent region and interface, the x/y ratio increased by an average 33% (Supplementary Table 2), indicating an increase in oxidized C at the organo–mineral interface compared to the adjacent C region. In addition, the ratio of integrated total carbon (280.0–315.0 eV) to total nitrogen (395.0–430.0 eV) decreased by an average 88% between the adjacent C region and the organo–mineral interface region.
