Fig. 1: Crystalline structure, X-ray diffraction, SEM images, element mappings, and XPS characterization of CoAs3 microcrystal.
a The final Rietveld refinement of XRD spectrum of CoAs3 polycrystals. (left insert) Structural model of CoAs3 (space group Im\(\bar{3}\)). Blue and green balls represent Co and As atoms, respectively. (right insert) SEM image of CoAs3 microcrystal. b–e SEM images (b) and element mappings of CoAs3 flake, showing a uniform distribution of Co + As (c), Co (d), and As (e) elements. The average Co:As atomic ratio determined by the energy-dispersive X-ray spectroscopy (EDX) spectra is close to 1:3, and no foreign elements were detected within the detection limit of the instrument; f–i Atomic-level TEM image and low-magnification scanning transmission electron microscopy (STEM) image. (insert) of CoAs3 microcrystals. The yellow rectangle at the top right of the insert graph indicates the area where the atomic-level TEM (f) and the selected-area electron diffraction (SAED) pattern (g) were measured. Red circles in (g) mark the primary diffraction spots. h, i Atomic-level TEM images of a CoAs3 crystal taken at different locations, where 4.2 Å corresponds to the distance to the nearest neighboring Co. j, k X-ray photoemission spectroscopy (XPS) spectra of j Co 2p and k As 3d for freshly prepared CoAs3 polycrystals. Source data for Fig. 1 are provided as a Source data file.
