title: Correlation between micrometer-scale ripple alignment and atomic-scale crystallographic orientation of monolayer graphene.
abstract: Deformation normal to the surface is intrinsic in two-dimensional materials due to phononic thermal fluctuations at finite temperatures. Graphene's negative thermal expansion coefficient is generally explained by such an intrinsic property. Recently, friction measurements on graphene exfoliated on a silicon oxide surface revealed an anomalous anisotropy whose origin was believed to be the formation of ripple domains. Here, we uncover the atomistic origin of the observed friction domains using a cantilever torsion microscopy in conjunction with angle-resolved photoemission spectroscopy. We experimentally demonstrate that ripples on graphene are formed along the zigzag direction of the hexagonal lattice. The formation of zigzag directional ripple is consistent with our theoretical model that takes account of the atomic-scale bending stiffness of carbon-carbon bonds and the interaction of graphene with the substrate. The correlation between micrometer-scale ripple alignment and atomic-scale arrangement of exfoliated monolayer graphene is first discovered and suggests a practical tool for measuring lattice orientation of graphene.
authors.affiliation: 1] Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul 143-701, Korea [2] Creative Research Center for Graphene Electronics, Electronics and Telecommunications Research Institute (ETRI), Daejeon 305-700, Korea.
authors.forename: Jin Sik
authors.initials: JS
authors.lastname: Choi
authors.affiliation: Department of Physics, University of Seoul, Seoul 130-743, Korea.
authors.forename: Young Jun
authors.initials: YJ
authors.lastname: Chang
authors.affiliation: Korea Institute for Advanced Study, Seoul 130-722, Korea.
authors.forename: Sungjong
authors.initials: S
authors.lastname: Woo
authors.affiliation: Korea Institute for Advanced Study, Seoul 130-722, Korea.
authors.forename: Young-Woo
authors.initials: YW
authors.lastname: Son
authors.affiliation: Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul 143-701, Korea.
authors.forename: Yeonggu
authors.initials: Y
authors.lastname: Park
authors.affiliation: Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul 143-701, Korea.
authors.forename: Mi Jung
authors.initials: MJ
authors.lastname: Lee
authors.affiliation: Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul 143-701, Korea.
authors.forename: Ik-Su
authors.initials: IS
authors.lastname: Byun
authors.affiliation: 1] Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul 143-701, Korea [2] Creative Research Center for Graphene Electronics, Electronics and Telecommunications Research Institute (ETRI), Daejeon 305-700, Korea.
authors.forename: Jin-Soo
authors.initials: JS
authors.lastname: Kim
authors.affiliation: Creative Research Center for Graphene Electronics, Electronics and Telecommunications Research Institute (ETRI), Daejeon 305-700, Korea.
authors.forename: Choon-Gi
authors.initials: CG
authors.lastname: Choi
authors.affiliation: Advanced Light Source (ALS), E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Aaron
authors.initials: A
authors.lastname: Bostwick
authors.affiliation: Advanced Light Source (ALS), E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Eli
authors.initials: E
authors.lastname: Rotenberg
authors.affiliation: Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul 143-701, Korea.
authors.forename: Bae Ho
authors.initials: BH
authors.lastname: Park