The rediscovery of one-dimensional (1D) and quasi-1D (q-1D) van der Waals (vdW) crystals ushered the realization of nascent physical properties in 1D that are suitable for applications in photonics, electronics, and sensing. However, despite renewed interest in the creation and understanding of the physical properties of 1D and q-1D vdW crystals, the lack of accessible synthetic pathways for growing well-defined nanostructures that extend across several length scales remains. Using the highly anisotropic 1D vdW NbS3-I crystal as a model phase, we present a catalyst-free and bottom-up synthetic approach to access ultralong nanowires, with lengths reaching up to 7.9 mm and with uniform thicknesses ranging from 13 to 160 nm between individual nanowires. Control over the synthetic parameters enabled the modulation of intra- and interchain growth modalities to selectively yield only 1D nanowires or quasi-2D nanoribbons. Comparative synthetic and density functional theory (DFT) studies with a closely related nondimerized phase, ZrS3, show that the unusual preferential growth along 1D can be correlated to the strongly anisotropic bonding and dimeric nature of NbS3-I.

The fine-tuning of topologically protected states in quantum materials holds great promise for novel electronic devices. However, there are limited methods that allow for the controlled and efficient modulation of the crystal lattice while simultaneously monitoring the changes in the electronic structure within a single sample. Here, we apply significant and controllable strain to high-quality HfTe₅ samples and perform electrical transport measurements to reveal the topological phase transition from a weak topological insulator phase to a strong topological insulator phase. After applying high strain to HfTe₅ and converting it into a strong topological insulator, we found that the resistivity of the sample increased by 190,500% and that the electronic transport was dominated by the topological surface states at cryogenic temperatures. Our results demonstrate the suitability of HfTe₅ as a material for engineering topological properties, with the potential to generalize this approach to study topological phase transitions in van der Waals materials and heterostructures.