Dynamics of carbon diffusion and segregation through nickel catalyst, investigated by in-situ XPS, during the growth of nitrogen-doped graphene
Résumé
The mechanisms of diffusion and segregation of carbon from a solid carbon-based film, through a nickel film catalyst, was investigated using in situ, time- and depth-resolved X-ray photoelectron spectroscopy. The graphene precursor was a carbon nitride amorphous film obtained by pulse laser deposition. Changes in both surface and bulk sensitive carbon components versus annealing time was investigated at temperatures between 200 °C and 500 °C. A model of carbon diffusion/segregation through the nickel film was implemented, enabling the quantitative description of the graphene growth. Carbon diffusion through the nickel film was shown to occur at low temperatures (200–300 °C) and to induce the growth of graphene domains. The fine microstructure and high density of defects in the nickel catalyst film accelerated the transport of carbon, faster than conventional bulk diffusion. At 500 °C, bulk diffusion of carbon occurred, due to the recovering of the nickel grain microstructure. The diffusion/segregation model developed in this study can be used as a support to a better control of the growth and quality of the graphene. Our interpretations are discussed in relation to similar approaches related to graphene growth by chemical vapor deposition.
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