Folded MoS2 bilayers with variable interfacial coupling revealed by Raman and Photoluminescence spectroscopy

The twisted bilayers of MoS2 with van der Waals coupling have attracted much attention of researchers for providing multiple degrees of freedom to engineer optical and electronic properties. In this work, partial monolayer MoS2 flakes are folded onto the monolayer MoS2 flake itself to form folded MoS2 bilayers during the chemical vapor deposition (CVD) growth process. Lattice vibrations and photon transitions of folded MoS2 bilayers with variable interfacial coupling are revealed by Raman and Photoluminescence (PL) spectroscopy. It is found that interlayer twist angle provides novel physical properties, e.g., the occurring of folded phonons and the evolution of exciton transitions, for promising application of optoelectronic devices.