課題番号 ：S-16-MS-2009
利用形態 ：機器利用
利用課題名（日本語） ：STXMを用いた隕石有機物のその場分析
Program Title (English) ：In-situ analyses of organic matter in meteorites by STXM
利用者名（日本語） ：癸生川陽子1), 内村絵梨花2)
Username (English) ：Y. Kebukawa1), E. Uchimura2)
所属名（日本語） ：1) 横浜国立大学大学院工学研究院, 2) 横浜国立大学理工学部
Affiliation (English) ：1) Faculty of Engineering, Yokohama National University, 2) School of Engineering Science, Yokohama National University

１．概要（Summary ）
Murchison隕石及びフミン酸（隕石有機物のアナログ物質）のウルトラミクロトーム超薄切片について，C,N,O-XANES分析を行った。FIBにより作成した同試料とスペクトルを比較し，試料準備方法によるC,N,O-XANESスペクトルへの影響を評価した。また，フミン酸試料については，C,N,O-X線吸収スペクトルのフィッティングにより，N/C比及びO/C比を求め，同試料の元素分析値と比較し，X線吸収スペクトルから元素組成比を求めるうえでの問題点を評価した。

２．実験（Experimental）
We prepared ~100 nm-thick thin sections of Murchison meteorite and humic acid (IHSS standard Leonardite humic acid, as an analog of organic matter in meteorites) using a focused ion beam (FIB) and an ultramicrotome (UMT) equipped with a diamond knife. For UMT, the sample grains were mixed with sulfur powder and heated to melt the sulfur (~150°C for less than one minute). Solidified sulfur droplet was attached to an epoxy stub. The ultramicrotomed sections were transferred to SiO-coated TEM grids and gently heated until the sulfur sublimed off. C, N, O-XANES spectra were obtained at BL4U, UVSOR.

３．結果と考察（Results and Discussion）
C-XANES spectra of the Murchison show some differences between UMT and FIB. Ketone C=O appeared only in FIB sample and C-O (alcohol, ether) appeared only in UMT sample. Ketone might be increased due to FIB beam damage, while C-O in UMT sample might be a contamination during sample preparation. Note that the Murchison has some heterogeneity so we examined C-XANES from several different locations. While humic acid prepared in either UMT or FIB showed no significant difference in C-XANES, indicating that slight damage/contamination affects when one intend to detect small amount of organic matter embedded in mineral matrix.
Elemental abundances of humic acid was calculated using computational fit of C-, N-, and O-XANES spectra using the method described in Cody et al. [1]. The O/C ratio obtained with XANES are underestimated compared to elemental composition data for the humic acid standard provided by International Humic Substances Society (IHSS) [2]. These results indicate that XANES data interpretations must be made with cautions.

４．その他・特記事項（Others）
[1] G. D. Cody et al., Meteorit. Planet. Sci. 43 (2008) [2] http://www.humicsubstances.org

５．論文・学会発表（Publication/Presentation）
(1) 内村絵梨花，平成28年度横浜国立大学卒業論文(2017).

６．関連特許（Patent）
なし。