Hong Seong Chul, Baek Ji-Hwan, Kim Jinwoo, Lee Hyeongseok, Lee Gwan-Hyoung
Department of Material Science and Engineering, Seoul National University, Seoul 08826, Republic of Korea.
ACS Nano. 2025 Aug 26;19(33):30487-30494. doi: 10.1021/acsnano.5c11757. Epub 2025 Aug 14.
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-MoS bilayers can be effectively engineered by tuning the CVD growth mode and substrate-induced strain. Specifically, MoS grown via conventional CVD (c-MoS) on rough SiO substrates forms multidomain structures with corrugated DWs, due to tensile strain arising from conformal adhesion and thermal expansion mismatch. In contrast, MoS synthesized by NaCl-assisted CVD (NA-MoS) via a vapor-liquid-solid (VLS) growth mode exhibits smooth surfaces and single-domain structures, regardless of substrate roughness. Furthermore, c-MoS 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-MoS and establish practical guidelines for synthesizing strain-relieved, single-domain ferroelectric TMD bilayers for future nanoelectronic applications.
菱面体堆叠的过渡金属二硫属化物（3R-TMDs）通过面内层间滑动表现出强大的铁电性，使其成为原子级薄非易失性存储器件的有前途的候选材料。然而，由于在通过化学气相沉积（CVD）合成或手动堆叠形成堆叠双层结构过程中出现的各种缺陷，控制由畴壁（DW）动力学支配的铁电畴分布仍然是一个重大挑战。这些缺陷包括衬底诱导的不稳定性、捕获的气泡和空间不均匀应变，所有这些都阻碍了均匀畴结构的实现。在这里，我们证明了通过调整CVD生长模式和衬底诱导应变，可以有效地设计3R-MoS双层中的畴结构。具体而言，在粗糙的SiO衬底上通过传统CVD（c-MoS）生长的MoS由于共形粘附和热膨胀失配产生的拉伸应变而形成具有波纹状DW的多畴结构。相比之下，通过NaCl辅助CVD（NA-MoS）经由气-液-固（VLS）生长模式合成的MoS，无论衬底粗糙度如何，都表现出光滑的表面和单畴结构。此外，在原子级平坦的蓝宝石上生长的c-MoS也形成单畴结构，证实了衬底形态和界面应变的关键作用。我们揭示畴的形成与累积的拉伸应变相关，拉伸应变随双层尺寸增加。我们的结果提供了对3R-MoS中畴壁形成的基本理解，并为合成用于未来纳米电子应用的应变缓解、单畴铁电TMD双层建立了实用指南。
