title: Strain Relaxation of Graphene Layers by Cu Surface Roughening.
abstract: The surface morphology of copper (Cu) often changes after the synthesis of graphene by chemical vapor deposition (CVD) on a Cu foil, which affects the electrical properties of graphene, as the Cu step bunches induce the periodic ripples on graphene that significantly disturb electrical conduction. However, the origin of the Cu surface reconstruction has not been completely understood yet. Here, we show that the compressive strain on graphene induced by the mismatch of thermal expansion coefficient with Cu surface can be released by forming periodic Cu step bunching that depends on graphene layers. Atomic force microscopy (AFM) images and the Raman analysis show the noticeably longer and higher step bunching of Cu surface under multilayer graphene and the weaker biaxial compressive strain on multilayer graphene compared to monolayer. We found that the surface areas of Cu step bunches under multilayer and monolayer graphene are increased by ∼1.41% and ∼0.77% compared to a flat surface, respectively, indicating that the compressive strain on multilayer graphene can be more effectively released by forming the Cu step bunching with larger area and longer periodicity. We believe that our finding on the strain relaxation of graphene layers by Cu step bunching formation would provide a crucial idea to enhance the electrical performance of graphene electrodes by controlling the ripple density of graphene.
authors.affiliation: Department of Chemistry, Seoul National University , Seoul 151-747, Republic of Korea.|Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University , Seoul 08826, Republic of Korea.
authors.forename: Jin Hyoun
authors.initials: JH
authors.lastname: Kang
authors.affiliation: Department of Chemistry, Seoul National University , Seoul 151-747, Republic of Korea.|Advanced Nano-Surface Research Group, Korea Basic Science Institute , Gwahak-ro, Yuseong-gu, Daejeon 34133, Republic of Korea.
authors.forename: Joonhee
authors.initials: J
authors.lastname: Moon
authors.affiliation: Program in Nano Science and Technology, Graduate School of Convergence Science and Technology, Seoul National University , Seoul 08826, Republic of Korea.
authors.forename: Dong Jin
authors.initials: DJ
authors.lastname: Kim
authors.affiliation: Advanced Nano-Surface Research Group, Korea Basic Science Institute , Gwahak-ro, Yuseong-gu, Daejeon 34133, Republic of Korea.
authors.forename: Yooseok
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Seoul National University , Seoul 151-747, Republic of Korea.
authors.forename: Insu
authors.initials: I
authors.lastname: Jo
authors.affiliation: Advanced Nano-Surface Research Group, Korea Basic Science Institute , Gwahak-ro, Yuseong-gu, Daejeon 34133, Republic of Korea.
authors.forename: Cheolho
authors.initials: C
authors.lastname: Jeon
authors.affiliation: Advanced Nano-Surface Research Group, Korea Basic Science Institute , Gwahak-ro, Yuseong-gu, Daejeon 34133, Republic of Korea.
authors.forename: Jouhahn
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Chemistry, Seoul National University , Seoul 151-747, Republic of Korea.|Program in Nano Science and Technology, Graduate School of Convergence Science and Technology, Seoul National University , Seoul 08826, Republic of Korea.
authors.forename: Byung Hee
authors.initials: BH
authors.lastname: Hong
keywords: AFM; Cu step bunching; Raman spectroscopy; graphene; strain relaxation