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We demonstrate a solid phase reaction approach to synthesise transfer-free graphene on an insulating substrate by controlling the C diffusion process. Metal assisted crystallization by annealing of a C thin film was carried out to synthesise transfer-free graphene, in the presence of a top metal oxide and metal layer. Without the metal oxide layer, a large amount of C atoms diffused to the top of the metal surface and hence the formation of only small graphene domains was observed on the underneath of the metal layer. Introducing the metal oxide layer at the top surface, C diffusion was reduced and consequently the thin C film was crystallized to form large area graphene at the metal-insulating substrate interface. The metal oxide or metal catalyst layer was removed after graphene formation and transfer-free graphene was obtained directly on the base substrate. This finding shows that the thin metal oxide layer is critical to synthesise graphene with better quality and continuous domain structures.

Here, we report a controllable direct graphene growth process on an insulating substrate (SiO 2 /Si and sapphire) by the solid phase reaction of a polymer layer. Water soluble polyvinyl alcohol (PVA) was spin coated on the SiO 2 /Si substrate and graphitized in presence of a Ni catalyst cap layer. Graphene growth occurs with decomposition and dehydrogenation of the polymer layer with metal catalyzation. The role of gas atmosphere, temperature, thickness of polymer and catalyst layers are investigated in the solid phase reaction process for graphene nucleation and growth. Formation of graphene flakes directly on the substrate surface is confirmed by Raman spectroscopy, optical and atomic force microscopy analysis. The as-synthesized graphene flakes interconnect with each other to create a network like structure. In the growth process, decomposing the polymeric film at an elevated temperature, atomic carbon can diffuse and segregate at the Ni/substrate interface to create the graphene structure. The developed direct growth process of the graphene structure using a simple polymer by a solid phase reaction can be significant for device integration.