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The process schematics for the metal-catalyzed crystallization of a-C to graphene by thermal annealing.
Raman spectra of (a) a-C (40 nm) and (b) the resulting graphene layer after Ni-catalyzed crystallization (Ni thickness ). Excitation laser wavelength was 632.8 nm.
Raman spectra showing quality vs temperature dependence for (a) nickel catalyst and (b) cobalt catalyst. Graphene can form within a range of temperatures, although appears to be optimal. Insets show representative optical images after annealing at 750 and , showing relatively uniform surface coverage. The thickness of the initial a-C layer was 40 nm.
(a) AFM image of a transferred graphene sheet on a substrate. (b) Graphene (and graphite) thickness vs initial a-C thickness. Samples were annealed at for 15 min with a 300 nm Ni catalyst layer.
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