Illuminating Invisible Grain Boundaries in Coalesced Single-Orientation WS₂ Monolayer Films

Engineering atomic-scale defects is crucial for realizing wafer-scale, single-crystalline transition metal dichalcogenide monolayers electronic devices. However, connecting to larger morphologies poses a significant challenge. Using electron microscopy and atomistic simulations, we provide insights into WS2 crystal growth mechanisms, providing direct link between synthetic conditions the microstructure. Dark-field TEM imaging of coalesced monolayer films illuminates defect arrays that atomic-resolution STEM identifies as translational grain boundaries. Imaging reveals have nearly single orientation with imperfectly stitched domains. Through ReaxFF reactive force field-based molecular dynamics observe two types mismatch discuss their atomic structures origin. Our results indicate from relatively fast rates. statistical analysis >1300 facets, demonstrate macrostructural features are constructed nanometer-scale building blocks, describing system across sub-{\AA}ngstrom multi-micrometer length scales.