Fig. 6: The enantioselective synthesis of octahedron-helicoid Au@Ag NPs.

a Schematic illustration for the synthesis of octahedron-helicoid Au@Ag NPs. The yellow, pink, and translucent models represent the Au NP, Ag-based NPs with octahedral profiles, and chiral SiO₂ nanoshells, respectively. b, c SEM images of (b) 0.07-L- and (c) 0.07-D-octahedron-helicoid Au@Ag NPs. d SAED pattern of a single octahedron-helicoid Au@Ag@SiO₂ NP along the [100] zone axis. e HRTEM image of edge-on surface corresponding to the red box in inset of (d). f HAADF-STEM and (g) corresponding EDX elemental mapping of a single octahedron-helicoid Au@Ag@SiO₂ NP. The red and yellow colors denote Au and Ag, respectively. h–m SEM images of individual (h, j, l) 0.07-L- and (i, k, m) 0.07-D-octahedron-helicoid Au@Ag NP viewed from (h, i) [100], (j, k) [111], and (l, m) [110] axes. n Chiroptical signal reversal of helicoid Au@Ag NPs within the same chiral template regulated by the facet formation. The g-factor spectra and geometric models, and the corresponding intensity difference distribution of local electric fields of L- (orange line, orange model with red-orange concaves) and D-cube-Au@Ag NPs (blue line, orange model with blue concaves), L- (purple line, pink model with purple concaves), and D-octahedron-Au@Ag NPs (green line, pink model with green concaves). The intensity difference distributions of local electric fields are presented with the color map from blue (−2.0) to red (2.0). Scale bars: b, c 200 nm. d 5 nm⁻¹. Inset: 100 nm. e 2 nm. f, g 100 nm. h–n 100 nm. Source data are provided as a Source Data file.