title: Growth from below: graphene bilayers on Ir(111).
abstract: We elucidate how graphene bilayers form on Ir(111). Low-energy electron diffraction (LEED) reveals that the two graphene layers are not always rotationally aligned. Monitoring this misalignment during growth shows that second-layer islands nucleate between the existing layer and the substrate. This mechanism occurs both when C segregates from the Ir and when elemental C is deposited from above. Low-energy electron microscopy (LEEM) and angle-resolved photoemission spectroscopy (ARPES) show that second-layer nucleation occurs preferentially under the first-layer rotational variants that are more weakly bound to the substrate. New-layer nucleation tends to occur inhomogeneously at substrate defects. Thus new-layer nucleation should be rapid on substrates that weakly bind graphene, making growth unstable toward mound formation initiated at substrate defects. In contrast, stronger binding permits layer-by-layer growth, as for Ru(0001). ARPES shows that bilayer graphene has two slightly p-doped π-bands. The work function of bilayer graphene is dominated by the orientation of the bottom layer.
authors.affiliation: Sandia National Laboratories, Livermore, California 94550, United States.
authors.forename: Shu
authors.initials: S
authors.lastname: Nie
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Walter
authors.forename: Norman C
authors.initials: NC
authors.lastname: Bartelt
authors.forename: Elena
authors.initials: E
authors.lastname: Starodub
authors.forename: Aaron
authors.initials: A
authors.lastname: Bostwick
authors.forename: Eli
authors.initials: E
authors.lastname: Rotenberg
authors.forename: Kevin F
authors.initials: KF
authors.lastname: McCarty
mesh_terms: D003460:Crystallization / Q000379:methods*; D006108:Graphite / Q000737:chemistry*; D007495:Iridium / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D013499:Surface Properties
chemical_list: D046911:Macromolecular Substances; D007495:Iridium; D006108:Graphite