Nano-resolution TXM–EXAFS Imaging: Two-dimensional Visualization of Local Atomic Structural Parameters in Heterogeneous Systems

[Background] The combination of synchrotron-based transmission X-ray microscopy (TXM) and X-ray absorption spectroscopy (XAS) is a vital approach for investigating chemical and structural heterogeneity in materials. While TXM-XANES imaging enables high-spatial-resolution mapping of elemental valence states, its capability to resolve local atomic-scale structures, such as bond lengths and coordination numbers, remains limited. [Purpose] This study aims to develop a two-dimensional extended X-ray absorption fine structure (EXAFS) imaging method with nano-resolution at the BL18B beamline of the Shanghai Synchrotron Radiation Facility (SSRF), in order to visualize local atomic structural parameters in heterogeneous systems. [Methods] Firstly, the energy collection range was extended to the EXAFS region (8900–9300 eV), and TXM image stacks were acquired from both spatially separated and mixed Cu/CuO samples. Then, a custom-developed MATLAB script was employed for batch processing of all pixels, performing sequential steps including E-k transformation, k³-weighting, and Fourier transformation to obtain the radial distribution function in R-space for each pixel. Finally, Gaussian fitting was applied to extract the position and intensity of the first coordination shell peak, and spatial correlation analysis between chemical composition and local structural parameters was conducted by integrating the results with linear combination fitting from the XANES region. [Results] Analysis of the separated samples revealed that the first-shell peak position for Cu (Cu–Cu) is0.216 ± 0.009 nm, and that for CuO (Cu–O) is 0.149 ± 0.013 nm , consistent with theoretical expectations and validating the accuracy of the TXM-EXAFS method at the single-pixel scale (50 nm). For the mixed sample, the average first-shell peak position was 0.209 ± 0.008 nm, indicating a dominant metallic Cu phase. Moreover, the two-dimensional distributions of both the peak position and intensity showed clear spatial correlation with the Cu/CuO composition maps, quantitatively revealing the correlations between chemical composition and local atomic structural parameters. [Conclusions] This study establishes a TXM-EXAFS imaging method with a spatial resolution of 50 nm, successfully achieving two-dimensional visualization of local atomic structural parameters in the Cu/CuO system. By integrating chemical imaging with coordination environment analysis, the method provides a quantitative tool for investigating microstructural heterogeneity in complex material systems and advances synchrotron-based multimodal imaging toward atomic-scale structural characterization.