Thorough Search Analysis of Extended X-ray Absorption Fine Structure Data for Complex Molecules and Nanomaterials Applications
Daiki Kido, Yohei Uemura, Yuki Wakisaka, Hiroko Ariga-Miwa, Satoru Takakuasgi, Kiyotaka Asakura
Abstract
Extended X-ray absorption fine structure (EXAFS) plays an important role in the surface science and nanotechnology to characterize the non-crystalline materials using the curve fitting (CF) analysis. However, the CF has problems such as correlation between the structural parameters, the dependence on initial parameters, and the limitation of degree of freedom when EXAFS is applied to the complex system. In this paper, we propose a thorough search (TS) method to solve these problems. We analyzed EXAFS data for molybdenum oxide (α-MoO3) using the TS method. MO3 possesses a well-defined but complex local structure in which a central molybdenum (Mo) atom is surrounded by six oxygen (O) atoms. In CF analysis, the correlations of these six Mo—O bonds make it very difficult to derive reliable structural parameters from EXAFS data. In the TS analysis, the structural parameters regarded as a point (𝒫) were surveyed thoroughly over a certain range. The goodness of fit was evaluated by R-factor. All 𝒫 with R-factors less than a certain value were accepted. The accepted points 𝒫 made a domain in which it was assumed that all points 𝒫 in the domain should occur with equal probability and consequently their averages were used as representative structural parameters. If multiple independent domains were obtained, they were all regarded as possible candidates and the TS analysis provided possible structural parameters. The feasibility and advantages of the TS method were compared with the CF analysis and the micro reverse Monte Carlo method.