Electronic and mechanical coupling in twisted MoS₂ bilayer. (a) Schematics of MoS₂ bilayers with different stacking configurations. Green spheres are Mo atoms; yellow sphere are S atoms. (a) Optical images of a MoS₂ monolayer and twisted bilayers with different twist angles. (c) Photoluminescence and (d) Raman spectra of MoS₂ monolayer and bilayers with different twist angles. Reprinted with permission from Ref. [80]. Copyright 2014, Nature Publishing Group.