Layer breathing modes in few-layer graphene

TL;DR

This paper reports the direct observation of layer breathing modes in few-layer graphene, revealing how interlayer coupling influences out-of-plane vibrations across different layer thicknesses.

Contribution

It provides experimental evidence of layer breathing modes in graphene and models their frequencies using a simple nearest-plane coupling approach.

Findings

Distinct LBMs observed in 2-20 layer graphene

Raman bands show layer-dependent multi-peak features

Frequencies fit a simple nearest-plane coupling model

Abstract

Layer-layer coupling plays a critical role in defining the physical properties of few-layer graphene (FLG). With respect to vibrations, the interlayer coupling is predicted to create a set of N-1 finite frequency, out-of-plane interlayer modes in N-layer graphene. Unlike the widely studied in-plane vibrations, the properties of these layer-breathing modes (LBMs) are defined by the layer-layer interactions. Here we report direct observation of the distinct LBMs for graphene of thicknesses from 2 to 20 layers through electronically resonant overtone Raman bands observed in the range of 80 - 300 cm-1. The Raman bands exhibit multi-peak features that are unique for graphene samples of each layer thickness up to 20 layers. The frequencies of the set of layer breathing modes for all samples can be described within a simple model of nearest plane coupling.