The competition for graphene formation on Re(0001): A complex interplay between carbon segregation, dissolution and carburisation

We study the interplay between competitive substrate–C interaction processes occurring during chemical vapour deposition (CVD) of ethylene on Re (0 0 0 1). At T < 500 K dissociative ethylene adsorption leads to the formation of a dimer species, producing an ordered (4×2) structure. In the range 500–700 K, the formation of a high-quality single-layer of graphene is strongly opposed by the formation of a surface carbide characterised by C trimer units, and, at higher temperatures, by carbon dissolution into the bulk. Our experimental and theoretical results demonstrate that, under UHV conditions, the formation of a long-range ordered graphene layer on Re (0 0 0 1) without carbon bulk saturation is confined to a narrow window of growth parameters: substrate temperature, hydrocarbon gas pressure and exposure time. Our combined experimental and theoretical approach allowed us to validate a concept which had already been anticipated in some earlier works on Rh, Fe and Ni, namely that the epitaxial growth of graphene is not necessarily restricted to surfaces where carburisation is precluded, but could take place, under given appropriate conditions, also on other metallic substrates exhibiting a strong C–substrate interaction.