Kinetics and thermodynamics of carbon segregation and graphene growth on Ru(0001)

Details Kinetics and thermodynamics of carbon segregation and graphene growth on Ru(0001) Kinetics and thermodynamics of carbon segregation and graphene growth on Ru(0001)

2009-04-07

arxiv.org/abs/0904.1039v1

CARBON Volume: 47 Issue: 7 Pages: 1806-1813 Published: JUN 2009

Physics

Condensed Matter

Materials Science

Scientific paper

10.1016/j.carbon.2009.03.004

We measure the concentration of carbon adatoms on the Ru(0001) surface that are in equilibrium with C atoms in the crystal's bulk by monitoring the electron reflectivity of the surface while imaging. During cooling from high temperature, C atoms segregate to the Ru surface, causing graphene islands to nucleate. Using low-energy electron microscopy (LEEM), we measure the growth rate of individual graphene islands and, simultaneously, the local concentration of C adatoms on the surface. We find that graphene growth is fed by the supersaturated, two-dimensional gas of C adatoms rather than by direct exchange between the bulk C and the graphene. At long times, the rate at which C diffuses from the bulk to the surface controls the graphene growth rate. The competition among C in three states - dissolved in Ru, as an adatom, and in graphene - is quantified and discussed. The adatom segregation enthalpy determined by applying the simple Langmuir-McLean model to the temperature-dependent equilibrium concentration seriously disagrees with the value calculated from first-principles. This discrepancy suggests that the assumption in the model of non-interacting C is not valid.

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