5:15 PM - 6:45 PM
[MZZ45-P04] Multi-element-XANES of PFIB sections of meteorite by complementary application of scanning transmission X-ray microscopy and full-field transmission X-ray microscopy
Keywords:Scanning Transmission X-ray Microscopy, Transmission X-ray Microscopy, Carbonaceous Chondrite, pFIB, Organics-Mineral Associations
Introduction: In-situ analytical techniques, which enables a direct observation of organic-mineral associations in geological and planetary samples, have been recently developed. Synchrotron-based scanning transmission X-ray microscopy (STXM) provides the elemental distributions and chemical states within samples with a high spatial resolution (< 30 nm) through the transmission X-ray images obtained by two-dimensional scanning of the sample (Kilcoyne et al. 2003). On the other hand, Full-field Transmission X-ray microscopy (TXM) installs a zone plate to magnify the sample image onto a detector for providing chemical states from a larger-area of samples in shorter acquisition time (Tamenori and Hoshino 2018). TXM has been traditionally used for imaging at the synchrotron facilities in Japan, while it has been infrequently used for chemical characterization. In this study, for maximizing our understanding on the organic-mineral associations in extraterrestrial samples, STXM and TXM were complementarily applied to measure C-, O-, Fe-, Mg-XANES of plasma-FIB (PFIB) sections of carbonaceous chondrite and to investigate some technical issues to solve for TXM in development.
Samples and Methods: Two PFIB sections of Orgueil carbonaceous CI chondrite (350 nm thickness, 50 μm × 25 μm) were prepared by FEI Helios PFIB G4, at Carnegie Institution of Science. The image stack data of the pFIB meteorite samples were acquired at 0.1 eV/sec in the energy ranges of O- (520-560 eV), Fe- (700-730 eV), and Mg- (1295-1350 eV) XANES by TXM, BL27SU, SPring-8. The field of view of TXM is 40 μm × 40 μm. Afterward, C-, O-, Fe-, Mg-XANES spectra of the same samples were acquired by STXM, BL19A, Photon Factory, KEK.
Results and Discussion: From the O- and Fe-XANES spectra of Orgueil PFIB samples by TXM, oxide grains within phyllosilicate matrix were tentatively identified. The subsequent STXM measurement of the oxides revealed that some oxide grains have framboidal textures. The framboidal oxides are identified as magnetite (Fe3O4), based on the x-ray absorptions corresponding to O 2p hybridized with Fe 3d (~530 eV), O2p hybridized with Fe4s and 4p, (~541 eV), electron backscattering by O in configuration originated from the crystalline structure of magnetite (~547 eV) from the O-XANES spectra. Those peaks were not observed from the spectra obtained by TXM. The spectral shapes of O-XANES were also different between TXM and STXM.
Several hundred-nanometer-sized carbon-rich grains and diffuse carbon within the phyllosilicate matrix were observed from the carbon elemental maps of the sample acquired by STXM. The C-XANES spectra of any C-rich regions were similar to insoluble organic matter (IOM) from primitive carbonaceous chondrites in terms of the typical three peaks of aromatic C=C (~285 eV), aromatic ketone C=C-C=O (~286 eV), and carboxyl C=O group (~288.5 eV). In addition to the IOM-like spectra, aromatic-rich spectra were locally observed. Broader spectra with relatively high abundance of aliphatic carbon were also observed at the rim of the framboidal magnetite.
Although there is a room for improvement of the energy calibration methods of TXM, this study shows a potential to understand the whole truth of chemical distributions in geological and planetary samples by complimentary application of TXM and STXM.
Samples and Methods: Two PFIB sections of Orgueil carbonaceous CI chondrite (350 nm thickness, 50 μm × 25 μm) were prepared by FEI Helios PFIB G4, at Carnegie Institution of Science. The image stack data of the pFIB meteorite samples were acquired at 0.1 eV/sec in the energy ranges of O- (520-560 eV), Fe- (700-730 eV), and Mg- (1295-1350 eV) XANES by TXM, BL27SU, SPring-8. The field of view of TXM is 40 μm × 40 μm. Afterward, C-, O-, Fe-, Mg-XANES spectra of the same samples were acquired by STXM, BL19A, Photon Factory, KEK.
Results and Discussion: From the O- and Fe-XANES spectra of Orgueil PFIB samples by TXM, oxide grains within phyllosilicate matrix were tentatively identified. The subsequent STXM measurement of the oxides revealed that some oxide grains have framboidal textures. The framboidal oxides are identified as magnetite (Fe3O4), based on the x-ray absorptions corresponding to O 2p hybridized with Fe 3d (~530 eV), O2p hybridized with Fe4s and 4p, (~541 eV), electron backscattering by O in configuration originated from the crystalline structure of magnetite (~547 eV) from the O-XANES spectra. Those peaks were not observed from the spectra obtained by TXM. The spectral shapes of O-XANES were also different between TXM and STXM.
Several hundred-nanometer-sized carbon-rich grains and diffuse carbon within the phyllosilicate matrix were observed from the carbon elemental maps of the sample acquired by STXM. The C-XANES spectra of any C-rich regions were similar to insoluble organic matter (IOM) from primitive carbonaceous chondrites in terms of the typical three peaks of aromatic C=C (~285 eV), aromatic ketone C=C-C=O (~286 eV), and carboxyl C=O group (~288.5 eV). In addition to the IOM-like spectra, aromatic-rich spectra were locally observed. Broader spectra with relatively high abundance of aliphatic carbon were also observed at the rim of the framboidal magnetite.
Although there is a room for improvement of the energy calibration methods of TXM, this study shows a potential to understand the whole truth of chemical distributions in geological and planetary samples by complimentary application of TXM and STXM.