Dry release transfer of graphene and few-layer h-BN by utilizing thermoplasticity of polypropylene carbonate

We demonstrate the dry release transfer of single-layer and bi-layer graphene and few-layer h-BN by utilizing poly(propylene) carbonate (PPC) films. Because of the strong adhesion between PPC and 2D materials around room temperature, we demonstrate that single-layer to few-layer graphene, as well as few-layer h-BN can be fabricated on a spin-coated PPC film/SiO2/Si substrate via the mechanical exfoliation method. In addition, we show that these single-layer to few-layer crystals are clearly distinguishable using an optical microscope with the help of optical interference. Because of the thermoplastic properties of PPC film, the adhesion between the 2D materials and PPC significantly decreases at about 70？°C. Therefore, by tuning the temperature, the graphene and h-BN flakes on PPC can be easily dry-transferred onto another h-BN substrate. We demonstrate the fabrication of encapsulated h-BN/graphene/h-BN devices and graphene/few-layer h-BN/graphene vertical-tunnel-junction devices using this method. Our finding provides a simple method for constructing high-quality graphene and h-BN-based van der Waals heterostructures with a minimum amount of polymer contamination