Facile fabrication of twisted MoS₂ bilayers by direct bonding

When stacking two-dimensional (2D) materials with a lattice mismatch and/or a small twist, moiré superlattice emerges with fascinating electronic and optical properties. The fabrication of such stacked 2D materials usually requires multiple transfer and stack processes, assisted by a certain transfer medium which needs to be removed afterwards, and it is very challenging to maintain pristine and clean surfaces/interfaces for these stacked structures. In this work, we report a facile direct bonding method for fabrication of twisted MoS₂ bilayers with ultra-clean surfaces/interfaces. Novel interlayer interactions are revealed in the as-fabricated high-quality samples, leading to twist-angle related dispersion behavior of various Raman modes, such as layer breathing modes, shear modes and E_2g modes, as well as indirect bandgap excitons. Field-effect transistors (FETs) of twisted MoS₂ bilayers also exhibit angle-dependent performance, which could be attributed to the band structure evolution. This facile method holds significance for the future integration of pre-designed multilayer 2D materials and paves a way to explore underlying physical mechanisms and potential applications.