Stacking-controllable interlayer coupling and symmetric configuration of multilayered MoS2

The stacking order in layered transition-metal dichalcogenides (TMDCs) induces variations in the electronic and interlayer couplings. Therefore, controlling the stacking orientations when synthesizing TMDCs is desirable but remains a significant challenge. Here, we developed and showed the growth kinetics of different shapes and stacking orders in as-grown multi-stacked MoS 2 crystals and revealed the stacking-order-induced interlayer separations, spin–orbit couplings (SOCs), and symmetry variations. Raman spectra in AA(A…)-stacked crystals demonstrated blueshifted out-of-plane (A 1g ) and in-plane (E 2g 1 ) phonon frequencies, representing a greater reduction of the van der Waals gap compared to conventional AB(A…)-stacking. Our observations, together with first-principles calculations, revealed distinct excitonic phenomena due to various stacking orientations. As a result, the photoluminescence emission was improved in the AA(A…)-stacking configuration. Additionally, calculations showed that the valence-band maxima (VBM) at the K point of the AA(A…)-stacking configuration was separated into multiple sub-bands, indicating the presence of stronger SOC. We demonstrated that AA(A…)-stacking emitted an intense second-harmonic signal (SHG) as a fingerprint of the more augmented non-centrosymmetric stacking and enabled SOC-induced splitting at the VBM. We further highlighted the superiority of four-wave mixing-correlated SHG microscopy to quickly resolve the symmetries and multi-domain crystalline phases of differently shaped crystals. Our study based on crystals with different shapes and multiple stacking configurations provides a new avenue for development of future optoelectronic devices. Transition-metal dichalcogenides: Bringing layers into line A method for investigating the relative alignment of stacks of two-dimensional layers has been developed by researchers in Korea. Two-dimensional materials, those just a single atom thick, have a host of unusual electronic and optical properties. Placing two-dimensional materials on top of each other to create thicker films offers a way to engineer further novel materials, but the properties of these stacks depend crucially on the relative orientation of each layer. Jong-Hyun Ahn from Yonsei University and colleagues synthesized stacks of molybdenum disulfide monolayers with various angular alignments using a technique called atmospheric-pressure chemical vapor deposition. They then characterized the structures opt