title: Probing graphene grain boundaries with optical microscopy.
abstract: Grain boundaries in graphene are formed by the joining of islands during the initial growth stage, and these boundaries govern transport properties and related device performance. Although information on the atomic rearrangement at graphene grain boundaries can be obtained using transmission electron microscopy and scanning tunnelling microscopy, large-scale information regarding the distribution of graphene grain boundaries is not easily accessible. Here we use optical microscopy to observe the grain boundaries of large-area graphene (grown on copper foil) directly, without transfer of the graphene. This imaging technique was realized by selectively oxidizing the underlying copper foil through graphene grain boundaries functionalized with O and OH radicals generated by ultraviolet irradiation under moisture-rich ambient conditions: selective diffusion of oxygen radicals through OH-functionalized defect sites was demonstrated by density functional calculations. The sheet resistance of large-area graphene decreased as the graphene grain sizes increased, but no strong correlation with the grain size of the copper was revealed, in contrast to a previous report. Furthermore, the influence of graphene grain boundaries on crack propagation (initialized by bending) and termination was clearly visualized using our technique. Our approach can be used as a simple protocol for evaluating the grain boundaries of other two-dimensional layered structures, such as boron nitride and exfoliated clays.
authors.affiliation: Sungkyunkwan Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 440-746, South Korea.
authors.forename: Dinh Loc
authors.initials: DL
authors.lastname: Duong
authors.forename: Gang Hee
authors.initials: GH
authors.lastname: Han
authors.forename: Seung Mi
authors.initials: SM
authors.lastname: Lee
authors.forename: Fethullah
authors.initials: F
authors.lastname: Gunes
authors.forename: Eun Sung
authors.initials: ES
authors.lastname: Kim
authors.forename: Sung Tae
authors.initials: ST
authors.lastname: Kim
authors.forename: Heetae
authors.initials: H
authors.lastname: Kim
authors.forename: Quang Huy
authors.initials: QH
authors.lastname: Ta
authors.forename: Kang Pyo
authors.initials: KP
authors.lastname: So
authors.forename: Seok Jun
authors.initials: SJ
authors.lastname: Yoon
authors.forename: Seung Jin
authors.initials: SJ
authors.lastname: Chae
authors.forename: Young Woo
authors.initials: YW
authors.lastname: Jo
authors.forename: Min Ho
authors.initials: MH
authors.lastname: Park
authors.forename: Sang Hoon
authors.initials: SH
authors.lastname: Chae
authors.forename: Seong Chu
authors.initials: SC
authors.lastname: Lim
authors.forename: Jae Young
authors.initials: JY
authors.lastname: Choi
authors.forename: Young Hee
authors.initials: YH
authors.lastname: Lee