Single and polycrystalline graphene on Rh(111) following different growth mechanisms.

Graphene grown on the same substrate but under different growth conditions may evolve diverse characteristics and disparate growth mechanisms. To explore this issue, graphene is prepared on Rh(111) by both ultrahigh vacuum and ambient-pressure chemical vapor deposition methods and the different growth behaviors, the atomic-scale structures, and the stacking geometry are analysed, mainly by virtue of scanning tunneling microscope. Interestingly, with ultrahigh vacuum chemical vapor deposition growth at 600 °C, a template growth of graphene by the Rh(111) lattice is obtained, reflected with the formation of a uniform graphene moiré. In comparison, with the ambient-pressure chemical vapor deposition at 1000 °C by different quenching processes, monolayer and randomly stacked few-layer polycrystalline graphene is achieved, probably directed by combined surface catalysis and segregation mechanisms. In this case, strong and weak interactions between graphene and Rh substrates are suggested, with the samples prepared under vacuum and ambient-pressure conditions, respectively. This work is expected to contribute greatly to the exploration of interactions between graphene and a substrate, as well as the segregation mechanism of graphene growth on polycrystalline transitional metal substrates.