Abstract
Direct growth of spherical graphene with large surface area is important for various applications in sensor technology. However, the preparation of transfer-free graphene on different substrates is still a challenge. This study presents a novel approach for the transfer-free graphene growth directly on cemented carbide. The used simple thermal annealing induces an in-situ transformation of magnetron-sputtered amorphous silicon carbide films into the graphene matrix. The study reveals the role of Co, a binding phase in cemented carbides, in Si sublimation process, and its interplay with the annealing temperature in development of the graphene matrix. A detailed physico-chemical characterisation was performed by structural (XRD analysis and Raman spectroscopy with mapping studies), morphological (SEM) and chemical (EDS) analyses. The optimal bilayer graphene matrix with hollow graphene spheres on top readily grows at 1000 °C. Higher annealing temperature critically decreases the amount of Si, which yields an increased number of the graphene layers and formation of multi-layer graphene (MLG). The proposed action mechanism involves silicidation of Co during thermal treatment, which influences the existing chemical form of Co, and thus, the graphene formation and variations in a number of the formed graphene layers.
Highlights
Direct growth of spherical graphene with large surface area is important for various applications in sensor technology
Surface Ni-silicidation reaction is an effective mean for preparation of few-layer graphene (FLG) by controlled thermal annealing of SiC crystals, which was successfully demonstrated in Ni/6H-SiC (0001) system, with the best graphene structure obtained at 800 °C6
The question that arises here is related to control of carbon diffusion process since it affects number and quality of graphene layers; formation of the top CoO layer is critical for the synthesis of a high-quality graphene layer[10]
Summary
Direct growth of spherical graphene with large surface area is important for various applications in sensor technology. Metal-catalysed graphene growth from SiC followed by a simple but controlled annealing step is a useful approach towards the synthesis of large area graphene layer. There are no acceptable methods to synthesise in-situ a graphene layer on the cemented carbide surface, especially in regards to following aspects: (1) using readily available a-SiC instead of costly SiC single-crystal as carbon source, (2) the impact of annealing temperature on the number of produced graphene layers and (3) the understanding of Si atoms role in graphene growth and change in the number of graphene layers. If the mechanism of Si acting is not identified, the graphene layercannot be directly grown from a-SiC
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