title: Observation of layer-breathing mode vibrations in few-layer graphene through combination Raman scattering.
abstract: We report the observation of layer-breathing mode (LBM) vibrations in few-layer graphene (FLG) samples of thickness from two to six layers, exhibiting both Bernal (AB) and rhombohedral (ABC) stacking order. The LBM vibrations are identified using a Raman combination band lying around 1720 cm(-1). From double resonance theory, we assign the feature as the LO+ZO' combination mode of the out-of-plane LBM (ZO') and the in-plane longitudinal optical mode (LO). The LOZO' Raman band is found to exhibit multiple peaks with a unique line shape for each layer thickness and stacking order. These complex line shapes of the LOZO'-mode arise both from the material-dependent selection of different phonons in the double-resonance Raman process and from the detailed structure of the different branches of LBM in FLG.
authors.affiliation: Department of Physics, Columbia University, 538 West 120th Street, New York, New York 10027, USA.
authors.forename: Chun Hung
authors.initials: CH
authors.lastname: Lui
authors.forename: Leandro M
authors.initials: LM
authors.lastname: Malard
authors.forename: SukHyun
authors.initials: S
authors.lastname: Kim
authors.forename: Gabriel
authors.initials: G
authors.lastname: Lantz
authors.forename: François E
authors.initials: FE
authors.lastname: Laverge
authors.forename: Riichiro
authors.initials: R
authors.lastname: Saito
authors.forename: Tony F
authors.initials: TF
authors.lastname: Heinz