Strain-Mediated Control of Domain Structures in 3R-MoS₂ Bilayers Synthesized by Vapor–Liquid–Solid Growth in Chemical Vapor Deposition

Rhombohedrally stacked transition metal dichalcogenides (3R-TMDs) exhibit robust ferroelectricity enabled by in-plane interlayer sliding, positioning them as promising candidates for atomically thin nonvolatile memory devices. However, controlling the distribution of ferroelectric domains, which is governed by domain wall (DW) dynamics, remains a major challenge due to various imperfections that arise during the formation of stacked bilayer structures, by either CVD synthesis or manual stacking. These include substrate-induced instabilities, trapped bubbles, and spatially inhomogeneous strain, all of which hinder the realization of uniform domain structures. Here, we demonstrate domain structures in 3R-MoS₂ bilayers can be effectively engineered by tuning the CVD growth mode and substrate-induced strain. Specifically, MoS₂ grown via conventional CVD (c-MoS₂) on rough SiO₂ substrates forms multidomain structures with corrugated DWs, due to tensile strain arising from conformal adhesion and thermal expansion mismatch. In contrast, MoS₂ synthesized by NaCl-assisted CVD (NA-MoS₂) via a vapor-liquid-solid (VLS) growth mode exhibits smooth surfaces and single-domain structures, regardless of substrate roughness. Furthermore, c-MoS₂ grown on an atomically flat sapphire also forms single-domain structures, confirming the critical role of substrate morphology and interfacial strain. We reveal that domain formation is correlated with the accumulated tensile strain, which increases with bilayer size. Our results provide a fundamental understanding of domain wall formation in 3R-MoS₂ and establish practical guidelines for synthesizing strain-relieved, single-domain ferroelectric TMD bilayers for future nanoelectronic applications.