We report the observation of layer breathing mode (LBM) vibrations in few-layer graphene (FLG) samples of thickness from 2 to 6 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 identify the feature as the LOZO' 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.
@article{arxiv.1204.1702,
title = {Observation of out-of-plane vibrations in few-layer graphene},
author = {Chun Hung Lui and Leandro M. Malard and SukHyun Kim and Gabriel Lantz and François E. Laverge and Riichiro Saito and Tony F. Heinz},
journal= {arXiv preprint arXiv:1204.1702},
year = {2012}
}
Comments
17 pages, 7 figures, supplemental material included