Epitaxial Growth\nof Monolayer WS<sub>2</sub> Single\nCrystals on Au(111) Toward Direct Surface-Enhanced Raman Spectroscopy\nDetection

The epitaxial growth of wafer-scale two-dimensional (2D)\nsemiconducting\ntransition metal dichalcogenides (STMDCs) single crystals is the key\npremise for their applications in next-generation electronics. Despite\nsignificant advancements, some fundamental factors affecting the epitaxy\ngrowth have not been fully uncovered, e.g., interface coupling strength,\nadlayer-substrate lattice matching, substrate step-edge-guiding effects,\netc. Herein, we develop a model system to tackle these issues concurrently,\nand realize the epitaxial growth of wafer-scale monolayer tungsten\ndisulfide (WS<sub>2</sub>) single crystals on the Au(111) substrate.\nThis epitaxial system is featured with good adlayer-substrate lattice\nmatching, obvious step-edge-guiding effect for the unidirectionally\naligned nucleation/growth, and relatively weaker interfacial interaction\nthan that of monolayer MoS<sub>2</sub>/Au(111), as evidenced by the\nevolution of a uniform Moiré pattern and an intrinsic band\ngap, according to on-site scanning tunneling microscopy/spectroscopy\n(STM/STS) characterizations and density functional theory calculations.\nIntriguingly, the unidirectionally aligned monolayer WS<sub>2</sub> domains along the Au(111) steps can behave as ultrasensitive templates\nfor surface-enhanced Raman scattering detection of organic molecules,\ndue to the obvious charge transfer occurred at substrate step edges.\nThis work should hereby deepen our understanding of the epitaxy mechanism\nof 2D STMDCs on single-crystal substrates, and propel their wafer-scale\nproduction and applications in various cutting-edge fields.