This article presents a Bayesian sparse modeling method to analyze extended x-ray absorption fine structure (EXAFS) data with basis functions built on two-body signals. This method does not require any structural model and allows us to evaluate regression coefficients proportional to the radial distribution functions of the respective elements and their errors and is very effective for analysis of EXAFS with weak absorption intensity and severe signal-to-noise ratios. As an application example, we used it to analyze the EXAFS of an yttrium oxyhydride (YOxHy) epitaxial thin film. These EXAFS data show weak absorption intensity and a severe signal-to-noise ratio due to the small amount of x-ray absorption in the thin film sample. However, this approach revealed that the radial distance ratio of the second neighbor yttrium to the first neighbor oxygen coincides with that of a tetrahedral configuration. This result demonstrates that the interstitial oxygen position is tetrahedral in the YOxHy thin film.
The synchrotron radiation experiments were performed using a JAEA experimental station at JAEA (QST) beamline BL14B1, SPring-8, with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2020A3648) and the JAEA Advanced Characterization Nanotechnology Platform under the remit of "Nanotechnology Platform" of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan (Grant No. JPMXP09A20AE0006). This work was supported by JST CREST (Grant Nos. JPMJCR1861, JPMJCR1761, and JPMJCR21O1), Japan; JST PRESTO (Grant Nos. JPMJPR17N2 and JPMJPR17N6), Japan; JSPS KAKENHI (Grant Nos. JP19H02596, JP19H04689, JP18H05513, and JP18H05514), Japan; and AGC, Inc. (Grant No. KC31AGC08p).
Publication: AIP Advances
Title: Bayesian sparse modeling of extended x-ray absorption fine structure to determine interstitial oxygen positions in yttrium oxyhydride epitaxial thin film
Authors: Hiroyuki Kumazoe*, Yasuhiko Igarashi, Fabio Iesari, Ryota Shimizu, Yuya Komatsu, Taro Hitosugi, Daiju Matsumura, Hiroyuki Saitoh, Kazunori Iwamitsu, Toshihiro Okajima, Yoshiki Seno, Masato Okada, Ichiro Akai*