Substrate wettability requirement for the direct transfer of graphene

The direct transfer method, wherein graphene is transferred from its growth metal to a soft substrate, is widely used to fabricate various devices, and the interfacial bonding condition between the substrate and the graphene is vital for transfer success. In this letter, we present a theoretical model to derive the wettability requirements of the soft substrate to sustain the direct transfer of graphene, and verify the theoretical analysis with experiments. We find that the surface energy components of the substrate have a crucial effect upon the graphene transfer, and that substrates possessing a strong polar surface energy are not suitable for transfer. The theoretical model predicts the critical water contact angle of the soft substrate for graphene transfer to be about 50 degrees, and the experiments measure it to be about 60 degrees. These results provide guidelines for choosing proper substrates to transfer graphene during the fabrication of graphene-based flexible devices. (C) 2015 AIP Publishing LLC.