Atom-Precision Synthesis of MoS₂/WS₂ Lateral Heterostructures for Prolonged Excitonic Lifetime

Transition metal dichalcogenide (TMD) lateral heterostructures provide unique platforms to study nanoscale physics, but progress is limited by the difficulty of producing high-quality interfaces, which require atomic-precision growth rather than simple stacking. We report a controllable two-step chemical vapor deposition (CVD) process for directed epitaxy growth of MoS₂/WS₂ monolayer lateral heterostructures. Atom-resolution scanning tunneling microscopy measurements demonstrate an atomically sharp, defect-free MoS₂/WS₂ interface formed along the sulfur zigzag edge of MoS₂, indicating an atomic-substitution-nucleation growth mechanism. Domain sizes of both MoS₂ and WS₂ can be precisely tuned from several to hundreds of micrometers. The zig-zag interface creates an intermediate energy level at the junction, prolonging photogenerated carrier recombination lifetimes, in agreement with theoretical band-structure calculations. This work establishes a scalable synthesis route to high-quality TMDs lateral heterostructures with an atomic-scale shape interface and tunable domain sizes, accelerating the applications in electronic and optoelectronic devices.