Growth Kinetics of Graphene on Cu(111) Foils from Methane, Ethyne, Ethylene, and Ethane

Chemical vapor deposition of carbon precursors on Cu-based substrates at temperatures exceeding 1000 °C is currently a typical route for the scalable synthesis of large-area high-quality single-layer graphene (SLG) films. Using molecules with higher activities than CH₄ may afford lower growth temperatures that might yield fold- and wrinkle-free graphene. The kinetics of growth of graphene using hydrocarbons other than CH₄ are of interest to the scientific and industrial communities. We measured the growth rates of graphene islands on Cu(111) foils by using C₂H₂, C₂H₄, C₂H₆ and CH₄, respectively (each mixed with H₂). From such kinetics data we obtain the activation enthalpy (ΔH^≠) of graphene growth as shown in parentheses (C₂H₂ (0.93±0.09 eV); C₂H₄ (2.05±0.19 eV); C₂H₆ (2.50±0.11 eV); CH₄ (4.59±0.26 eV)); C₂H_y (y=2, 4, 6) show similar growth behavior but CH₄ is different. Computational fluid dynamics and density functional theory simulations suggest that C₂H_y differs from CH₄ due to different values of adsorption energy and the lifetime of relevant carbon precursors on the Cu(111) surface. Combining experimental and simulation results, we find that the rate determining step (RDS) is the dissociation of the first C-H bond of CH₄ molecules in the gas phase, while the RDS using C₂H_y is the first dehydrogenation of adsorbed C₂H_y that happens with assistance of H atoms adsorbed on the Cu(111) surface. By using C₂H₂ as the carbon precursor, high-quality single-crystal adlayer-free SLG films are achieved on Cu(111) foils at 900 °C.