Reversible Loss of Bernal Stacking during the Deformation of Few-Layer Graphene in Nanocomposites

Rashid Jalil,Robert J Young,Jonathan A Hinks,Lei Gong,Ibtsam Riaz,Jamie H Warner,Li Li,Kostya S Novoselov,Feng Ding,Ian A Kinloch,Ziwei Xu,Sarah J Haigh

doi:10.1021/nn402830f

Rashid Jalil, Robert J Young + Show 10 more

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https://doi.org/10.1021/nn402830f

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Abstract

The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (∼0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed.

Highlights

Graphene is currently inspiring a whole range of research activities in a number of scientific areas such as physics and materials science because of its interesting and unusual electronic and mechanical properties.[1,2] Excitement was generated originally because monolayer graphene was the world's first 2D atomic crystal and the thinnest material every produced.[3]
Scanning tunneling microscopy (STM)[22] and spectroscopy are useful techniques to understand the effect of stacking upon the electronic structure of few-layer graphene as they can simultaneously measure the local twist angle, the Fermi velocity and the degree of interlayer coupling.[23]
It is well established that Raman spectroscopy is one of the most versatile methods of both characterizing graphene and following its deformation in nanocomposites.24À26 Strong, well-defined resonance Raman spectra are obtained even from single atomic graphene layers and the technique can be used relatively to differentiate between monolayer, bilayer, trilayer and few-layer material, from the shape and position of the 2D Raman band.27À29 It is found that the positions of the Raman bands in graphene shift with stress30À39 and that such stressinduced Raman band shifts can be used to determine the stress in the material and so determine its effective Young's modulus.[38]

Summary

Introduction

Graphene is currently inspiring a whole range of research activities in a number of scientific areas such as physics and materials science because of its interesting and unusual electronic and mechanical properties.[1,2] Excitement was generated originally because monolayer graphene was the world's first 2D atomic crystal and the thinnest material every produced.[3]. It is possible to distinguish between ABA Bernal-stacked or ABC rhombohedral stacked trilayer material from the form of the 2D Raman band.[18,19] Synchrotron-based infrared absorption spectroscopy has been employed to show that the electronic structure of mechanically exfoliated few-layer graphene in which there is either ABA or ABC stacking depends strongly upon the stacking sequence.[21] Scanning tunneling microscopy (STM)[22] and spectroscopy are useful techniques to understand the effect of stacking upon the electronic structure of few-layer graphene as they can simultaneously measure the local twist angle, the Fermi velocity and the degree of interlayer coupling.[23] It has been found for CVD-grown material that the low energy carriers start to exhibit Landau level spectra characteristic of massless Dirac fermions for twist angles of over about 3° and that above 20° the layers effectively decouple with their electronic properties becoming similar to those of single-layer graphene.[23]. This has been modeled in terms of poorer stress transfer between the inner graphene layers than between the polymer matrix and the outer graphene layers.[26]

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