Controllable Sliding Transfer of Wafer‐Size Graphene

The successful isolation of high‐quality single‐layer or few‐layer graphene by mechanical exfoliation has unleashed a flurry of research activities in 2D carbon worldwide over the past few years.1, 2, 3, 4, 5 The ease of production and low cost make exfoliation of graphite the most popular route to prepare graphene whenever and wherever possible.6, 7, 8 However, this generally involves using either an adhesive tape to attach to the surface of graphite and using force to vertically peel off the tape plus graphene layers attached1, 7, 8 or by rubbing the surface of graphite against another material to slide off graphene sheets from the bulk.6, 9 Thus, this technique fails to provide sufficient output yield, large size and layer‐number homogeneity for many applications owing to multiple cleavage planes and strong interlayer van der Waals interactions in the normal direction.8 Moreover, the produced material often contains exfoliating agent remnants such as glues due to the pre‐press to obtain compact contact and the following violent peeling to achieve separation, and micromechanical action may induce strains on the graphene layer during adherence on a substrate and introduce various types of defects, including atomic vacancies, wrinkles or cracks, and microscopic corrugation. These inhomogeneities and defects may lower the electrical performance of graphene devices since they break translational or rotational symmetry.10, 11 Some studies have been conducted to improve the controllability of the exfoliation process. Instead of adhesive tape which relies on enforced press to achieve full contact, a zinc layer was implemented over the multilayer flakes of graphite to realize better contact via refined sputtering process and was subsequently mildly removed in diluted hydrochloric acid, which resulted in the controllable removal of a single atomic layer of carbon material, one layer at a time.12 The procedure can be repeated to remove additional carbon layers, nevertheless, this improved transfer method can be quite cumbersome and still fails to achieve the whole uniformity of the as‐obtained graphene. In conclusion, the core problem lies in the strong layer interaction of exfoliated layers and the improper mode to apply force, which hampers the controllability of graphene transferred onto target substrates. Accordingly, we attempt to design an innovative transfer method based on uniform graphene on an easily exfoliated support via applying a sliding force parallel to the interfacial shear slip, which not only inherits the simplicity of traditional mechanical cleavage but also improves the interface contact and lowers the exfoliation energy, thus improves its controllability of uniformity and size.