Fig. 3: Composition of organic features and the organo–organic interface.
From: Organo–organic and organo–mineral interfaces in soil at the nanometer scale
High-resolution imaging and spectroscopy of organo–organic features and their interface by cryo-scanning transmission electron microscopy and electron energy-loss spectroscopy (cryo-STEM-EELS). a Overview low-magnification (5 kx) annular dark-field (ADF) STEM image of cryo-focused ion beam (cryo-FIB) thin section of organic-rich volcanic soil. The approximate region indicated by a box was used for subsequent electron energy-loss spectroscopy (EELS) mapping of carbon (C) and nitrogen (N). b EELS elemental map showing the patchy distribution of low-N features in the high-N matrix. c Patchy distribution of organic matter (OM) features micrometers in size, shown with EELS maps of the two distinct carbon (C) bonding environments, as revealed by carbon K-edge multivariate curve resolution (MCR) component fits (component spectra are shown in f). d Nanometer-scale EELS C K-edge MCR component map of the interface between two OM patches (component spectra shown in g). For c, d, the cyan color channel contrast and brightness were auto-adjusted in ImageJ71. e Raw EELS data for representative lower N (top spectrum) and higher N (bottom spectrum) regions in (b). Spectra show the high C K-edge (~280.0 eV) intensity relative to N (~400.0 eV) and O (~530.0 eV) intensities. f, g Normalized (maximum = 1) C K-edge MCR component spectra corresponding to (c, d), with a distinctive transition from ~285.0 eV in component 1 (assigned to aromatic C=C bonds) to higher-energy features (~286.3–287.0 eV) in component 2. Features in spectra are shown by dotted vertical lines. Spectra are shown as raw (unsmoothed) MCR fit outputs normalized to the maximum output value.
