Niobium Atom Chains in Monolayer Tungsten Disulfide

Atom chains (ACs), being the smallest one-dimensional (1D) structures, exhibit intriguing topological quantum phases due to their unique 1D atomic and electronic structures. So far, ACs have been primarily grown inside a confined 1D space, e.g., carbon nanotubes, or realized along interfaces in two-dimensional (2D) materials with less controlled geometry or size. Direct growth of single or few-atom-thick metal ACs on a relatively large scale remains elusive. Herein, we successfully grow single or few-atom-thick Nb-ACs embedded in monolayer WS 2 via a two-step chemical vapor deposition (CVD) method. The Nb-ACs directly grow along the edges of the pregrown monolayer WS 2 under low-temperature conditions with limited Nb precursor supply. Atomic-resolution annular dark field scanning transmission electron microscopy (ADF-STEM) reveals that the Nb-ACs largely concentrate on subnanometer-width regions and extend up to micron scales. These Nb-ACs maintain the epitaxy alignment with the WS 2 lattice in the absence of structural defects or dislocations. Density functional theory (DFT) calculations reveal that the presence of Nb-ACs enhances the metallic property, transforms the direct bandgap to an indirect bandgap, and induces valley polarization in monolayer WS 2 due to the metallic nature and symmetry breaking caused by 1D features. Our study sheds light on growing confined 1D ACs and paves an alternative approach for tuning the electronic structures of monolayer 2D materials via 1D anisotropic doping.