Silica Particle-Mediated Growth of Single Crystal Graphene Ribbons on Cu(111) Foil

The authors report the growth of micrometer-long single-crystal graphene ribbons (GRs) (tapered when grown above 900 degrees C, but uniform width when grown in the range 850 degrees C to 900 degrees C) using silica particle seeds on single crystal Cu(111) foil. Tapered graphene ribbons grow strictly along the Cu direction on Cu(111) and polycrystalline copper (Cu) foils. Silica particles on both Cu foils form (semi-)molten Cu-Si-O droplets at growth temperatures, then catalyze nucleation and drive the longitudinal growth of graphene ribbons. Longitudinal growth is likely by a vapor-liquid-solid (VLS) mechanism but edge growth (above 900 degrees C) is due to catalytic activation of ethylene (C2H4) and attachment of C atoms or species ("vapor solid" or VS growth) at the edges. It is found, based on the taper angle of the graphene ribbon, that the taper angle is determined by the growth temperature and the growth rates are independent of the particle size. The activation enthalpy (1.73 +/- 0.03 eV) for longitudinal ribbon growth on Cu(111) from ethylene is lower than that for VS growth at the edges of the GRs (2.78 +/- 0.15 eV) and for graphene island growth (2.85 +/- 0.07 eV) that occurs concurrently.