Stacking sequence dependence of graphene layers on SiC (0001−)—Experimental and theoretical investigation

Abstract

Different stacking sequences of graphene are investigated using a combination of experimental and theoretical methods. High-resolution transmission electron microscopy (HRTEM) of the stacking sequence of several layers of graphene, formed on the C-terminated 4H-SiC (0001−) surface, was used to determine the stacking sequence and the interlayer distances. These data prove that the three metastable multilayer graphene configurations exist: AB, AA, and ABC. In accordance, those three cases were considered theoretically, using density functional theory (DFT) calculations comparing properties of graphene, both free-standing and positioned on the SiC (0001−) substrate. Total energies were calculated, the most stable structure was identified, and the electronic band structure was obtained. These results were compared with results obtained for a graphene single layer, having six or three H atoms attached to the carbon ring. It was found that sixfold symmetry leads to linear dispersion relations and threefold symmetry leads to hyperbolic dispersion relations. Thus the type of dispersion relation, i.e., linear versus hyperbolic, is independent of the number of graphene layers or the interlayer coupling but depends on the graphene symmetry. Similarly, it was shown that a linear dispersion relation is obtained in the presence of the SiC substrate, and also for various distances between adjacent carbon layers for AA stacking.