Thermodynamically Driven Tilt Grain Boundaries of Monolayer Crystals Using Catalytic Liquid Alloys

Grain boundaries (GBs) of two-dimensional (2D) materials host unique atomic defects that reveal novel properties, but deterministic control of the defect structures has not been achieved. Here, we report selective formations of dislocation cores at GBs of monolayer (ML) MoS₂ by vapor-liquid-solid (VLS) growth with Na-Mo-O eutectic alloys. The alloys function as a growth catalyst and provide Mo-rich chemical environments during the growth, which guide the formation of pentagon-heptagon defects with Mo-Mo homo-elemental bond (Mo 5|7) by yield &gt; 95 %. In particular, we found that GBs with high tilt angle (<i>θ_t</i> &gt; 34°) relieve strains by deformation-twining, instead of forming a dense arrays of defects including derivatives of S 5|7 defects. Polycrystalline MoS₂ films grown by VLS mode present about 8 times higher photoluminescence (PL) intensity than the films grown by vapor-solid-solid (VSS) mode. Density-functional theory (DFT) calculations suggest that the enhancement of PL intensity is associated with suppression of S 5|7 donor-type derivatives and electron doping. Using eutectic alloys will be useful to precisely determine atomic defects of various polycrystalline 2D films for engineering the material properties.