posted on 2023-12-29, 07:29authored byMayu Morita, Hiroharu Yui, Shu-hei Urashima, Morihiko Onose, Shintaro Komatani, Izumi Nakai, Yoshinari Abe, Yasuko Terada, Hisashi Homma, Kazuko Motomura, Kiyohiro Ichida, Tetsuya Yokoyama, Kazuhide Nagashima, Jérôme Aléon, Conel M. O’D. Alexander, Sachiko Amari, Yuri Amelin, Ken-ichi Bajo, Martin Bizzarro, Audrey Bouvier, Richard W. Carlson, Marc Chaussidon, Byeon-Gak Choi, Nicolas Dauphas, Andrew M. Davis, Wataru Fujiya, Ryota Fukai, Ikshu Gautam, Makiko K. Haba, Yuki Hibiya, Hiroshi Hidaka, Peter Hoppe, Gary R. Huss, Tsuyoshi Iizuka, Trevor R. Ireland, Akira Ishikawa, Shoichi Itoh, Noriyuki Kawasaki, Noriko T. Kita, Kouki Kitajima, Thorsten Kleine, Sasha Krot, Ming-Chang Liu, Yuki Masuda, Frédéric Moynier, Ann Nguyen, Larry Nittler, Andreas Pack, Changkun Park, Laurette Piani, Liping Qin, Tommaso Di Rocco, Sara S. Russell, Naoya Sakamoto, Maria Schönbächler, Lauren Tafla, Haolan Tang, Kentaro Terada, Tomohiro Usui, Sohei Wada, Meenakshi Wadhwa, Richard J. Walker, Katsuyuki Yamashita, Qing-Zhu Yin, Shigekazu Yoneda, Edward D. Young, Ai-Cheng Zhang, Tomoki Nakamura, Hiroshi Naraoka, Takaaki Noguchi, Ryuji Okazaki, Kanako Sakamoto, Hikaru Yabuta, Masanao Abe, Akiko Miyazaki, Aiko Nakato, Masahiro Nishimura, Tatsuaki Okada, Toru Yada, Kasumi Yogata, Satoru Nakazawa, Takanao Saiki, Satoshi Tanaka, Fuyuto Terui, Yuichi Tsuda, Sei-ichiro Watanabe, Makoto Yoshikawa, Shogo Tachibana, Hisayoshi Yurimoto
Characterization
of the elemental distribution of samples
with
rough surfaces has been strongly desired for the analysis of various
natural and artificial materials. Particularly for pristine and rare
analytes with micrometer sizes embedded on specimen surfaces, non-invasive
and matrix effect-free analysis is required without surface polishing
treatment. To satisfy these requirements, we proposed a new method
employing the sequential combination of two imaging modalities, i.e.,
microenergy-dispersive X-ray fluorescence (micro-XRF) and Raman micro-spectroscopy.
The applicability of the developed method is tested by the quantitative
analysis of cation composition in micrometer-sized carbonate grains
on the surfaces of intact particles sampled directly from the asteroid
Ryugu. The first step of micro-XRF imaging enabled a quick search
for the sparsely scattered and micrometer-sized carbonates by the
codistributions of Ca2+ and Mn2+ on the Mg2+- and Fe2+-rich phyllosilicate matrix. The following
step of Raman micro-spectroscopy probed the carbonate grains and analyzed
their cation composition (Ca2+, Mg2+, and Fe2+ + Mn2+) in a matrix effect-free manner via the
systematic Raman shifts of the lattice modes. The carbonates were
basically assigned to ferroan dolomite bearing a considerable amount
of Fe2+ + Mn2+ at around 10 atom %. These results
are in good accordance with the assignments reported by scanning electron
microscopy–energy-dispersive X-ray spectroscopy, where the
thin-sectioned and surface-polished Ryugu particles were applicable.
The proposed method requires neither sectioning nor surface polishing;
hence, it can be applied to the remote sensing apparatus on spacecrafts
and planetary rovers. Furthermore, the non-invasive and matrix effect-free
characterization will provide a reliable analytical tool for quantitative
analysis of the elemental distribution on the samples with surface
roughness and chemical heterogeneity at a micrometer scale, such as
art paintings, traditional crafts with decorated shapes, as well as
sands and rocks with complex morphologies in nature.