Giant Photoluminescence Enhancement and Carrier Dynamics in MoS2 Bilayers with Anomalous Interlayer Coupling

Abstract

Fundamental researches and explorations based on transition metal dichalcogenides (TMDCs) mainly focus on their monolayer counterparts, where optical densities are limited owing to the atomic monolayer thickness. Photoluminescence (PL) yield in bilayer TMDCs is much suppressed owing to indirect-bandgap properties. Here, optical properties are explored in artificially twisted bilayers of molybdenum disulfide (MoS2). Anomalous interlayer coupling and resultant giant PL enhancement are firstly observed in MoS2 bilayers, related to the suspension of the top layer material and independent of twisted angle. Moreover, carrier dynamics in MoS2 bilayers with anomalous interlayer coupling are revealed with pump-probe measurements, and the secondary rising behavior in pump-probe signal of B-exciton resonance, originating from valley depolarization of A-exciton, is firstly reported and discussed in this work. These results lay the groundwork for future advancement and applications beyond TMDCs monolayers.

Reconfiguring nucleation for CVD growth of twisted bilayer MoS2 with a wide range of twist angles

“…Compared with the 0°and 60°-TB-MoS 2 , the PL emission energies of A and B exciton exhibit a slight red shift (1.82-1.86 eV for A exciton and 1.92-1.96 eV for B exciton) in the ranges of 0°-20°and 60°-40°, while keep constant at around 20°-40°. This indicates that the direct excitonic transitions at K point is slightly sensitive to the twist angle, which is consistent with previous reports 13,19,35,47,49 . The relationship between the twist angles and energy disparity between the B and A excitons (E B À E A ) is shown in Fig.…”

CVD Synthesis of Twisted Bilayer WS2 with Tunable Second Harmonic Generation

“…The low yield, low success rate, defects such as wrinkles and bubbles, as well as polymer residue result in low quality and inhomogeneous interlayer coupling strength. [21][22][23] In contrast, the one-step CVD method provides a simple and convenient approach for the synthesis of high-quality TB-TMDCs. However, there is a substantial energy barrier caused by the rotations of the interlayers, which causes the formation of the AA and AB stacked TMDCs due to lower formation energy compared with other twist angles.…”