Synthesis of graphene-based nanostructures by microwave surface-wave plasma

This work was focused on the study of the direct and selective synthesis of free-standing graphene nanostructures, as N-graphene and composite of graphene or N-graphene and metal-based nanoparticles. The synthesis was performed using an argon microwave-induced plasma, sustained by surface waves at atmospheric pressure conditions. The different nanostructures produced were characterized and compared to understand the relation between the synthesis parameters and the carbon-based nanostructures behavior. The synthesis method consists of injecting carbon/nitrogen precursors into the plasma environment where they are subsequently decomposed into atomic/molecular carbon/nitrogen species. These, by flowing to the post-plasma zone, where the temperature drops, agglomerate and nucleate to the solid structures. For the synthesis of the composite nanostructures, metal-based solid agglomerates were dragged by an upstream Ar flow and injected into the mild plasma zone. The type and quality of the produced structures are controlled by a few parameters, such as the precursors and background gas fluxes, the type of precursors used, and the microwave power. In the first part of the work pure graphene samples were produced with different precursor injections (ethanol and methane) and different power. Therefore, the samples were characterized by XRD analysis. While in the second part N-graphene, N-graphene with MnO/ MnS nanoparticles and graphene with FeO nanoparticles were produced and characterized. A deeper analysis on morphological, structural and chemical properties of the samples were performed by HRTEM, SEM, XRD, XPS and Raman spectroscopy.