Kinetics and thermodynamics of carbon segregation and graphene growth on Ru(0 0 0 1)

• Published in: Carbon (New York) 2009-06, Vol.47 (7), p.1806-1813
• Main Authors: McCarty, Kevin F., Feibelman, Peter J., Loginova, Elena, Bartelt, Norman C.
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; Materials science; Physics; Specific materials
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2009.03.004

We measure the concentration of carbon adatoms on the Ru(0 0 0 1) 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.