¹Yoko Kebukawa,²Hanae Kobayashi,²Norio Urayama,²Naoki Baden,³Masashi Kondo,⁴Michael E. Zolensky,²Kensei Kobayashi
Proceedings of the National Academy of Sciences of the United States of America 116, 753-758 Link to Article [https://doi.org/10.1073/pnas.1816265116]
¹Faculty of Engineering, Yokohama National University, 240-8501 Yokohama, Japan;
²Nihon Thermal Consulting Co., Ltd., 160-0023 Tokyo, Japan
³Instrumental Analysis Center, Yokohama National University, 240-8501 Yokohama, Japan
⁴Astromaterials Research and Exploration Science, National Aeronautics and Space Administration Johnson Space Center, Houston, TX 77058

Organic matter in carbonaceous chondrites is distributed in fine-grained matrix. To understand pre- and postaccretion history of organic matter and its association with surrounding minerals, microscopic techniques are mandatory. Infrared (IR) spectroscopy is a useful technique, but the spatial resolution of IR is limited to a few micrometers, due to the diffraction limit. In this study, we applied the high spatial resolution IR imaging method to CM2 carbonaceous chondrites Murchison and Bells, which is based on an atomic force microscopy (AFM) with its tip detecting thermal expansion of a sample resulting from absorption of infrared radiation. We confirmed that this technique permits ∼30 nm spatial resolution organic analysis for the meteorite samples. The IR imaging results are consistent with the previously reported association of organic matter and phyllosilicates, but our results are at much higher spatial resolution. This observation of heterogeneous distributions of the functional groups of organic matter revealed its association with minerals at ∼30 nm spatial resolution in meteorite samples by IR spectroscopy.

¹Jordan A. Hachtel,^1,2Jingsong Huang,³Ilja Popovs,³Santa Jansone-Popova,^1,4Jong K. Keum,^1,2Jacek Jakowski,⁵Tracy C. Lovejoy,⁵Niklas Dellby,⁵Ondrej L. Krivanek,¹Juan Carlos Idrobo
Science 363, 525-528 Link to Article [DOI: 10.1126/science.aav5845]
¹Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
²Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
³Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
⁴Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
¹Nion R&D, Kirkland, WA 98034, USA.
Reprinted with permission from AAAS

The identification of isotopic labels by conventional macroscopic techniques lacks spatial resolution and requires relatively large quantities of material for measurements. We recorded the vibrational spectra of an α amino acid, l-alanine, with damage-free “aloof” electron energy-loss spectroscopy in a scanning transmission electron microscope to directly resolve carbon-site–specific isotopic labels in real space with nanoscale spatial resolution. An isotopic red shift of 4.8 ± 0.4 milli–electron volts in C–O asymmetric stretching modes was observed for ¹³C-labeled l-alanine at the carboxylate carbon site, which was confirmed by macroscopic infrared spectroscopy and theoretical calculations. The accurate measurement of this shift opens the door to nondestructive, site-specific, spatially resolved identification of isotopically labeled molecules with the electron microscope.