Interaction of graphene with intercalated Al: The process of intercalation and specific features of the electronic structure of the system

This paper reports on a study of the process of Al intercalation underneath a graphene monolayer formed on the Ni(111) surface by propylene cracking. Graphene formed on Ni(111) is known to be strongly coupled to the substrate; however, we have been able to show that Al intercalation underneath a graphene monolayer eventually results in blocking of this interaction and the formation of an electronic structure similar to that of quasi-freestanding graphene. As a result, the dispersion relation of the π states of graphene is linear at the К point of the Brillouin zone, with the Dirac point located in the region of the Fermi level. Thereat, an energy gap opens at the Fermi level near the K ¯ point between the cones of occupied π and unoccupied π* states of graphene. There are no features in the spectra that would signal a partial filling of the π* states and clearly detectable charge transfer between the graphene and the intercalated Al. A detailed analysis of the process by which Al intercalates underneath the graphene monolayer revealed that intercalation of Al differs somewhat from that of other (for instance, noble) metals. The intercalated Al is observed to dissolve and subsequently, alloy with the Ni substrate. Only if the concentration of Al intercalated underneath the graphene is high enough, will it accumulate on the interface directly under the graphene monolayer and form, in the near-surface region, an alloy with a prevalent concentration of Al; the stage at which the strong binding of graphene to the Ni substrate becomes blocked.