Extended Data Fig. 3: Transmission electron microscopy analysis.

a Scanning electron micrograph of an additional helical Co₃Sn₂S₂ sample, prepared using the identical fabrication process, but made thinner to facilitate the transmission imaging. The scale bar is 1 μm. b Thickness map obtained from electron energy-loss spectroscopy (EELS). The inset shows a line profile taken from the top to bottom of the helix, as indicated by the dashed white rectangle, showing a central thickness of ~ 300 nm, tapering to below 150 nm at the edges, making these areas suitable for high-resolution TEM imaging. The scale bar is 500 nm. c TEM image at the outer edge of the example spiral. A ~ 4 nm thick layer consisting of a mixture of amorphous and polycrystalline phases is observed, caused by the ion beam damage during FIB fabrication. The scale bar is 10 nm. d High-resolution TEM image of the region marked by the blue square in c. Clear ordered lattice fringes are observed within the bulk of the helix, confirming the preservation of the single crystalline structure, and indicating that the core Co₃Sn₂S₂ material remains largely unaffected by the FIB fabrication. The scale bar is 5 nm.