Co-sputtering C-Gu thin film synthesis: microstructural study of copper precipitates encapsulated into a carbon matrix

Co-sputtered C-Cu thin film depositions have been performed in the temperat ure range 80-873 K, the atomic carbon concentration varying from 16% to 96% . To characterize the microstructure of the C-Cu thin films, transmission e lectron microscopy, extended X-ray absorption fine structure and grazing in cidence small angle X-ray scattering experiments have been used. During the deposition process, a demixing occurs of the carbon and copper species due to their very low solubilities that leads to the formation of nanometric c opper precipitates homogeneously distributed in a more or less graphitic ma trix. These precipitates have an elongated shape in the direction of the th in film growth. When the deposition was performed at 273 K for copper atomi c concentrations C-Cu > 55%, as well as for all thin films synthesized at 5 73 K whatever the C-Cu value, the formation of graphene layers parallel to the surface of the copper precipitates was observed so that an encapsulatio n of the Gu aggregates in carbon cages occurs. We propose that surface diff usion of the different species occurring during the deposition process lead s to the demixing of carbon and copper. Thus, we suggest that the copper ac ts as a catalyst for graphitization of carbon to explain the formation of s uch structures at temperatures as low as those used in these experiments.