Extended Data Fig. 9: Effect of defects in the low-index-plane-exposed seeds on the morphology of 432 helicoid III.

a, Characterization of twin boundary defects in seed nanoparticles. Twin boundaries were observed as bright lines in a single nanoparticle by scanning TEM imaging. Nanoparticles with a single twin and fivefold twins are indicated in red and yellow, respectively. b, Defect-induced morphology deformation of 432 helicoid III. SEM (left), TEM (middle) and selected-area electron diffraction (SAED; right) images are shown for an ideal 432 helicoid III (i), an irregular achiral nanoparticle (ii) and an irregular nanoparticle with broken 432 symmetry (iii). In the case of the irregular achiral particle (ii), several diffraction spots that deviate from the regular diffraction pattern of the 〈100〉 zone (red) show polycrystalline character. In case of the particle with partially broken symmetry (iii), dark-field TEM images originating from diffraction spots 1 and 2 are also shown on the right, and demonstrate different crystallographic orientations in a single nanoparticle. We believe that the irregular, non-homogeneous shapes represented by ii and iii may originate from the twin boundary defects in seeds. By decreasing the population of twinned seeds, we expect that the g-factor can be further increased.