▎ 摘　　要

Layer-layer coupling plays a critical role in defining the physical properties of few-layer graphene. With respect to vibrations, for each layer thickness N, interlayer coupling creates a set of N - 1 out-of-plane layer breathing modes (ZO') with finite frequencies at the zone center. Unlike the widely studied intralayer vibrations, the properties of these layer breathing modes (LBMs) are defined by the layer-layer interactions. Here we report the observation of distinct LBMs for Bernal stacked graphene of layer thicknesses N = 2-20 through measurement of electronically resonant overtone Raman bands. The Raman bands exhibit multipeak features that are unique for graphene samples of each layer thickness. The frequencies can be described well using a simple linear-chain model based on nearest-neighbor couplings between the layers. DOI: 10.1103/PhysRevB.87.121404