Intercalation from the Depths: Growth of a Metastable Chromium Carbide between Epitaxial Graphene and Ni(111) by Carbon Segregation from the Bulk

The intercalation of atoms or small molecules underneath graphene epitaxially grown on single metal surfaces is a widely exploited method for modifying the interaction between the carbon monolayer and the substrate. Despite it would be highly desirable to expand the class of the intercalants by including also metal compounds such as oxides, nitrides, or carbides, their use as decoupling layers is a much more challenging task. Here, we demonstrate that it is possible to intercalate an ultrathin layer of Cr-carbide at the graphene/Ni(111) interface by using the carbon dissolved in the bulk of the substrate as a reservoir. Auger electron spectroscopy reveals that Cr deposition on the graphene/Ni(111) interface triggers C segregation from the Ni bulk, while the graphene layer floats on top of the growing film. Scanning tunneling microscopy shows the presence of a periodic superstructure on the surface, due to a coincidence lattice at the graphene/carbide boundary or alternatively to a dislocation network developing at the carbide/Ni(111) interface. Scanning tunneling spectra normalized to the total conductance indicate that the density of states around the Fermi level depends linearly on the energy, suggesting that the graphene layer is electronically decoupled from the Cr-carbide film.