Direct Growth of 2D Bilayers on Au(111) for Low-Coercive Sliding Ferroelectricity

Two-dimensional (2D) semiconductors directly grown on metal substrates can enable pristine and low-defect interfaces that are difficult to achieve through transfer-based fabrication. Although monolayer transition metal dichalcogenides (TMDs) have been widely synthesized on metals, controllable bilayer growth remains challenging owing to distinct thermodynamics and kinetics of second-layer growth on inert first-layer surfaces-a significant hurdle given their importance for interlayer-coupled functionalities like sliding ferroelectricity. Low-symmetry rhenium dichalcogenides (ReX₂, X = S, Se) are especially attractive because their weak interlayer coupling and multiple thermodynamically stable stacking configurations support low sliding barriers. Here, by optimizing precursor flux and growth kinetics, we achieved controlled chemical vapor deposition (CVD) growth of bilayer ReS₂ with well-defined parallel and antiparallel stacking directly on Au(111). As-grown parallel-stacked bilayers exhibit a large piezoelectric response (effective d_{33, eff} = 9.84 pm V^-1) and sliding ferroelectricity with an ultralow coercive voltage of approximately 2 V. Tip-defined ferroelectric tunnel junction and ferroelectric field-effect transistor measurements further support the ferroelectric interpretation. Comparative studies of as-grown, transferred, and exfoliated bilayers reveal that the cleaner, more conformal interface of the as-grown bilayers is associated with a lower coercive bias. This work establishes a scalable route for stacking-specific bilayer TMD growth on metal toward low-coercive sliding ferroelectricity.