Graphitic carbon grown on fluorides by molecular beam epitaxy

We study the growth mechanism of carbon molecules supplied by molecular beam epitaxy on fluoride substrates (MgF₂, CaF₂, and BaF₂). All the carbon layers form graphitic carbon with different crystallinities depending on the cation. Especially, the growth on MgF₂ results in the formation of nanocrystalline graphite (NCG). Such dependence on the cation is a new observation and calls for further systematic studies with other series of substrates. At the same growth temperature, the NCG on MgF₂ has larger clusters than those on oxides. This is contrary to the general expectation because the bond strength of the carbon-fluorine bond is larger than that of the carbon-oxygen bond. Our results show that the growth of graphitic carbon does not simply depend on the chemical bonding between the carbon and the anion in the substrate.