Spectroscopic Signatures of AA′ and AB Stacking of Chemical Vapor Deposited Bilayer MoS₂

Abstract

Prominent resonance Raman and photoluminescence spectroscopic differences between AA′ and AB stacked bilayer molybdenum disulfide (MoS2) grown by chemical vapor deposition are reported. Bilayer MoS2 islands consisting of the two stacking orders were obtained under identical growth conditions. Resonance Raman and photoluminescence spectra of AA′ and AB stacked bilayer MoS2 were obtained on Au nanopyramid surfaces under strong plasmon resonance. Both resonance Raman and photoluminescence spectra show distinct features indicating clear differences in interlayer interaction between these two phases. The implication of these findings on device applications based on spin and valley degrees of freedom will be discussed.

Stacking-controllable interlayer coupling and symmetric configuration of multilayered MoS2

“…The observed PL spectra for the indirect band gaps of the CVD-grown AA and AB bilayers indicate the interlayer electronic coupling strength, while the slightly broadened bandwidth of AA suggests stronger interlayer coupling. 12,42 Next, the valence-band splitting (VBS) of the MoS 2 crystals was studied as a function of the layer-number thickness and stacking-order configuration. Essentially, the amount of VBS was measured as the distance between the A-and B-peak energies observed in the PL or absorption spectra.…”

“…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.…”

“…[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.…”

“…[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. [10][11][12][13]18 Furthermore, studying the nonlinear optical properties, such as SHG or four-wave mixing (FWM), as a function of the layer number and stacking orientation of the multi-stacked crystals grown by CVD have scarcely been sought. [4][5][6] The minute variations of the band structures according to the geometry and order of stacking are sufficient to modulate the nonlinear optical susceptibility, and hence, versatile MoS 2 crystals synthesized by CVD play a crucial role in understanding fundamental optoelectronic properties.…”