Anisotropy-Driven Crystallization of Dimensionally Resolved Quasi-1D van der Waals Nanostructures

Unusual behavior in solids emerge from the complex interplay between crystalline order, composition, and dimensionality. In crystals comprising of weakly-bound one-dimensional (1D) or quasi-1D (q-1D) chains, properties such as charge density waves, topologically protected states, and indirect-to-direct band gap crossovers have been predicted to arise. However, the experimental demonstration of many of these nascent physics in 1D or q-1D van der Waals (vdW) crystals is obscured by the highly anisotropic bonding between the chains, stochasticity of top-down exfoliation, and lack of synthetic strategies to control bottom-up growth. Herein, we report the directed crystallization of a model q-1D vdW phase, Sb2S3, into dimensionally resolved nanostructures. We demonstrate the uncatalyzed growth of highly crystalline Sb2S3 nanowires, nanoribbons, and quasi-2D nanosheets with thicknesses in the range of 10 to 100 nm from the bottom-up crystallization of [Sb4S6]n chains. We found that dimensionally resolved nanostructures emerge from two distinct chemical vapor growth pathways defined by diverse covalent intra-chain and anisotropic vdW inter-chain interactions and precise precursor ratios. At sub-100 nm nanostructure thicknesses, we observe the hardening of phonon modes, blue-shifting of optical band gaps, and emergence of a new high-energy photoluminescence peak, suggesting a confinement-induced indirect-to-direct optical band gap crossover. The directional growth of weakly bound 1D ribbons or chains into well-resolved nanocrystalline morphologies provides opportunities to develop ordered nanostructures and hierarchical assemblies that are suitable for a wide range of optoelectronic and quantum devices.