Real-time microscopy of graphene growth on epitaxial metal films: role of template thickness and strain.

Epitaxial transition metal films have recently been introduced as substrates for the scalable synthesis of transferable graphene. Here, real-time microscopy is used to study graphene growth on epitaxial Ru films on sapphire. At high temperatures, high-quality graphene grows in macroscopic (>100 μm) domains to full surface coverage. Graphene nucleation and growth characteristics on thin (100 nm) Ru films are consistent with a pure surface chemical vapor deposition process, without detectable contributions from C segregation. Experiments on thicker (1 μm) films show a systematic suppression of the C uptake into the metal to levels substantially below those expected from bulk C solubility data, consistent with a strain-induced reduction of the C solubility due to gas bubbles acting as stressors in the epitaxial Ru films. The results identify two powerful approaches--i) limiting the template thickness and ii) tuning the interstitial C solubility via strain--for controlling graphene growth on metals with high C solubility, such as Ru, Pt, Rh, Co, and Ni.