Real‐Time Microscopy of Graphene Growth on Epitaxial Metal Films: Role of Template Thickness and Strain

Abstract 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.