Dimensionally resolved nanostructures of an atomically precise and optically active 1D van der Waals helix

Inorganic freestanding helices are rare and are sought-after for their unusual physical states endowed by chirality. To this end, III-VI-VII solids have emerged as a distinct class of ternary 1D van der Waals (vdW) crystals which bear atomically precise helical motifs. However, the physical understanding of the instrinsic and size-dependent properties of these materials is limited by the lack of synthetic strategies to directly access freestanding nanocrystals in high volumes. Using GaSI as a representative phase, we present a bottom-up strategy to grow high yields of ultrathin nanostructures based on this helical materials class. With this strategy, we were able to grow single crystals of 1D nanowires with thicknesess in the 10 to 100 nm range at high temperature conditions, as well as quasi-2D nanoribbons at lower temperatures. We establish the band gap of the nanowires in the UV region and demonstrate the persistence of nonlinear optical behavior originating from the non-centrosymmetric crystal structure of GaSI. Inspired by these results, we probe the effect of chirality on the electronic structure of hypothetical single chains of GaSI from first principles and show the pronounced handedness-dependent and chirality-driven spin polarization at the single helix regime.