Fabrication methods. (a) Top: illustration of CVD growth of vertical WS₂/MoS₂ bilayers. Bottom: schematic illustration, optical image, and scanning electron microscopy image of vertical WS₂/MoS₂ bilayers. Reprinted with permission from Ref. [16]. Copyright 2016, Nature Publishing Group. (b) Schematic illustration of ‘tear & stack’ technique, which is essentially a modified dry transfer method to fabricate clean interface with accurate twist angle. Reprinted with permission from Ref. [17]. Copyright 2016, American Physical Society. (c) Schematic illustration and AFM images of the twist-angle-tunable graphene/hBN heterostructures. Reprinted with permission from Ref. [22]. Copyright 2018, American Association for the Advancement of Science. (d) Top: AFM images of graphene/hBN heterostructures before (left) and after (right) annealing. Bottom: AFM images of graphene/hBN heterostructures. They are obtained initially (left), after AFM tip control (middle), and after long-time annealing (right), respectively. Reprinted with permission from Ref. [23]. Copyright 2016, Nature Publishing Group. Reprinted with permission from Ref. [21]. Copyright 2016, American Physical Society.