Insight into the Thermodynamics of Graphene Growth on Copper
Peter Leidinger, Sebastian Günther
Abstract
High-precision thermodynamic data were derived for single-layer graphene growth on Cu by measuring an increase or decrease in graphene flake size during chemical vapor deposition (CVD) in a reactive CH4/H2 atmosphere. An immediate flake shape change was observed when crossing the thermodynamic equilibrium of graphene formation, which was used as a sensitive criterion when systematically varying the CVD parameters during growth at 975–1080 °C. Extraction of the reaction enthalpy (ΔRH° = 91.8 ± 2.4 kJ·mol–1) and entropy (ΔRS° = 108.0 ± 1.8 J·mol–1·K–1) provides the anchoring point highly needed for calibration of experimental reactor studies or theoretical work. Comparing the Gibbs free energy with the thermodynamic data of graphite formation verifies that self-limiting single-layer graphene growth on copper occurs purely kinetically. Thermodynamics always favors the formation of multilayer graphene. Identifying the CVD parameter space where multilayer graphene is formed while single-layer graphene decays will foster the development of future synthesis strategies. The gained knowledge is transferable to other CVD-based graphene growth systems.