Stacking-Dependent Interlayer Coupling in Trilayer MoS₂ with Broken Inversion Symmetry

Abstract

The stacking configuration in few-layer two-dimensional (2D) materials results in different structural symmetries and layer-to-layer interactions, and hence it provides a very useful parameter for tuning their electronic properties. For example, ABA-stacking trilayer graphene remains semimetallic similar to that of monolayer, while ABC-stacking is predicted to be a tunable band gap semiconductor under an external electric field. Such stacking dependence resulting from many-body interactions has recently been the focus of intense research activities. Here we demonstrate that few-layer MoS2 samples grown by chemical vapor deposition with different stacking configurations (AA, AB for bilayer; AAB, ABB, ABA, AAA for trilayer) exhibit distinct coupling phenomena in both photoluminescence and Raman spectra. By means of ultralow-frequency (ULF) Raman spectroscopy, we demonstrate that the evolution of interlayer interaction with various stacking configurations correlates strongly with layer-breathing mode (LBM) vibrations. Our ab initio calculations reveal that the layer-dependent properties arise from both the spin-orbit coupling (SOC) and interlayer coupling in different structural symmetries. Such detailed understanding provides useful guidance for future spintronics fabrication using various stacked few-layer MoS2 blocks.

Stacking-controllable interlayer coupling and symmetric configuration of multilayered MoS2

“…11 In this process, the temperature was identified as a key parameter affecting the growth kinetics of the CVDbased MoS 2 synthesis with a positive correlation between the growth rate and film thickness. [9][10][11][12][13][14] To date, stacking of up to three layers of MoS 2 with various orientations has only been obtained by CVD at high temperatures (⩾850°C). [11][12][13][14] In conventional CVD synthesis, high-order stacking is only possible at high temperatures.…”

“…[9][10][11][12][13][14] To date, stacking of up to three layers of MoS 2 with various orientations has only been obtained by CVD at high temperatures (⩾850°C). [11][12][13][14] In conventional CVD synthesis, high-order stacking is only possible at high temperatures. In contrast, in this research, our approach involves growing MoS 2 stacked crystals with high stacking orders (AAA and ABA) at the lowest possible temperature.…”

“…Stacking of MoS 2 crystals can be categorized in three groups: (a) repeated-layer piling with the same orientation, as in AA(A…); (b) repeated-layer piling with alternating orientations, as in AB(AB…); and (c) a mixed-layer piling with false order in the abovementioned stacking orders, such as AAB… or AABB… 11 Intensive scanning transmission electron microscopy analysis has proven the existence of an AA(A…)-type arrangement in 3R-phase crystals possessing broken inversion symmetry, whereas AB(A…)-type stacking can form a 2H-phase similar to that of natural crystals, where the net symmetry of the inversion depends whether there is an odd or even number of layers. [10][11][12][13]16,17 Moreover, the remaining stacking order, such as A (BB…) or AA(BA...), with a false order of either AB(A...) or AA(A...) gives rise to a combination of 2H and 3R-phases.…”

“…[10][11][12][13]16,17 Moreover, the remaining stacking order, such as A (BB…) or AA(BA...), with a false order of either AB(A...) or AA(A...) gives rise to a combination of 2H and 3R-phases. Note that these stacking orientations tune the electronic properties by engineering interlayer distances and structural symmetry.…”

“…Note that these stacking orientations tune the electronic properties by engineering interlayer distances and structural symmetry. 3,11,13 In particular, the spin-orbit coupling (SOC) effect, valley polarization, and representative nonlinear optical properties, such as second-harmonic generation (SHG), are highly affected by the stacking configuration and subsequent structural symmetry. [3][4][5]11,16,17 To the best of our knowledge, few studies of stacking-orientation-controlled samples of more than three layers and subsequent characterization with PL and Raman spectroscopy have been conducted.…”