title: Real-time observation of epitaxial graphene domain reorientation.
abstract: Graphene films grown by vapour deposition tend to be polycrystalline due to the nucleation and growth of islands with different in-plane orientations. Here, using low-energy electron microscopy, we find that micron-sized graphene islands on Ir(111) rotate to a preferred orientation during thermal annealing. We observe three alignment mechanisms: the simultaneous growth of aligned domains and dissolution of rotated domains, that is, 'ripening'; domain boundary motion within islands; and continuous lattice rotation of entire domains. By measuring the relative growth velocity of domains during ripening, we estimate that the driving force for alignment is on the order of 0.1 meV per C atom and increases with rotation angle. A simple model of the orientation-dependent energy associated with the moiré corrugation of the graphene sheet due to local variations in the graphene-substrate interaction reproduces the results. This work suggests new strategies for improving the van der Waals epitaxy of 2D materials.
authors.affiliation: 1] Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California 94720, USA [2] Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Paul C
authors.initials: PC
authors.lastname: Rogge
authors.affiliation: Sandia National Laboratory, Livermore, California 94550, USA.
authors.forename: Konrad
authors.initials: K
authors.lastname: Thürmer
authors.affiliation: Sandia National Laboratory, Livermore, California 94550, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Foster
authors.affiliation: Sandia National Laboratory, Livermore, California 94550, USA.
authors.forename: Kevin F
authors.initials: KF
authors.lastname: McCarty
authors.affiliation: 1] Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California 94720, USA [2] Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Oscar D
authors.initials: OD
authors.lastname: Dubon
authors.affiliation: Sandia National Laboratory, Livermore, California 94550, USA.
authors.forename: Norman C
authors.initials: NC
authors.lastname: Bartelt