Fig. 5: Surface analysis and theoretical model of the SiCuOx layer for the high-temperature oxidation resistance.

a Paired annular dark-field (ADF) images and the corresponding E_xy maps for the surface part of the sioxed SCCF. The atomic resolution cross-sectional ADF-STEM images were obtained for the [\(1\bar{1}\)0] orientation, and the strain maps were obtained by geometric phase analysis (GPA). The reference area used to calculate the relative strain is marked by the white box in the map. The irrelevant complex patterns of the carbon film are shaded in gray for clarity. b Out-of-plane projected atomic distance (PAD) map of the sioxed SCCF. The schematic at the top left represents the PAD (A and H = B·cosθ) measurement. Note that the magnitude of the PAD map is expressed by false colors corresponding to the bottom color scale bar for visualization, representing the difference between the measured PADs and the values (A = 2.23 Å and H = 2.11 Å) of bulk Cu. c, d Histograms showing the PAD distribution of A (in-plane distance) and H (out-of-plane distance), obtained for the three regions marked I–III. Gaussian fits are represented by solid lines, while dashed lines denote the mean values of each region. Reproducibility was confirmed through additional measurements conducted on the Si-treated sample prepared from a different batch. e Schematic diagram of the structure of the sioxed Cu(111) thin film. f Structural model of the SiCuOx skin layer showing the side (top) and top (bottom) views. For clarity, the top view was generated after making a crosscut along the dotted line. Brown, red, and violet spheres represent Cu, O, and Si atoms, respectively. Small white spheres represent O atoms in the amorphous SiO₂ layer. g Energy profiles of O atoms penetrating the pristine and sioxed SCCF surfaces. Path 1–4 represent slightly different paths the O atoms can take penetrating the sioxed SCCF surfaces. The solid black line denotes the SCCF surface, delineating the boundary between the external and internal structures. The dashed line indicates the region where SiCuOx has formed. Source data are provided as a Source Data file.