We report on multiphonon Raman scattering in graphene samples. Higher-order combination modes involving three and four phonons are observed in single-layer, bilayer, and few-layer graphene samples prepared by mechanical exfoliation. The intensity of the higher-order phonon modes (relative to the G peak) is highest in single-layer graphene and decreases with increasing layers. In addition, all higher-order modes are observed to upshift in frequency almost linearly with increasing graphene layers, betraying the underlying interlayer van der Waals interactions.
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Rao et al. (2011) studied this question.
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