Fig. 2: Microstructure of CF and TACN samples.

SEM image of a CF and b TACN-1. SEM image of TACN-1 c outer surface and d inner surface. SEM images of cross-section and corresponding elemental distributions e, f TACN-1 and g, h TACN-2. HAADF-STEM image of TACN-1 i inner side of the shell and j, k surface. l iDPC-STEM image of the surface of TACN-1. The experiments were repeated three times independently with similar results.