Roll-to-Roll Mechanical Exfoliation for Large-Area van der Waals Films with Preserved Crystallographic Alignment

Abstract

Anisotropic 2D materials such as black phosphorus (BP), GeS or CrSBr, exhibit direction-dependent optical and electronic properties that are highly desirable for polarization-sensitive detection, waveguiding, and directionally tuned transport. However, scalable fabrication of large-area films with preserved in-plane crystallographic alignment remains a key challenge. Here, a roll-to-roll-inspired mechanical exfoliation technique as a general, low-cost, and scalable strategy to produce large-area films of in-plane anisotropic van der Waals nanosheets is presented. Polarized transmittance measurements confirm the presence of predominant optical anisotropy across centimeter-scale areas, and scanning transmission electron microscopy (STEM) reveals that individual nanosheets exhibit consistent in-plane orientation at the nanoscale. Furthermore, anisotropic electronic devices are fabricated and demonstrate that the films inherit the direction-dependent conductivity of their constituent flakes. This method offers a broadly applicable route for integrating anisotropic nanosheets of 2D materials into scalable optoelectronic and sensing technologies.