Abstract Low energy (few meV) acoustic phonon modes of graphene/Ir (111) have been measured using inelastic helium atom scattering (HAS). The data clearly show two vibrational modes with energies 4.6 and 7.2 meV at Γ ¯ with dispersionless branches due to Umklapp scattering. The phonons observed are not the ones expected for a free-standing graphene monolayer, in spite of the weak interaction between graphene and Ir (111). The measured parabolic dispersion of the flexural mode along the ΓM ¯ direction allows determining the bending rigidity κ = ( 0.80 ± 0.07 ) eV . Inelastic HAS measured at diffraction conditions proves that the moire superstructure results in localized phonon modes related to the upper and the lower regions of the graphene superstructure. Our study shows that inelastic HAS is suitable to resolve low-energy vibrations spatially localized on structures in the nanometer range.

中文翻译：

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通过非弹性原子散射解析石墨烯/Ir(111) 上的局域声子模式

摘要 石墨烯/Ir (111) 的低能量 (几 meV) 声学声子模式已使用非弹性氦原子散射 (HAS) 进行测量。数据清楚地显示了两种振动模式，在 Γ¯ 处能量为 4.6 和 7.2 meV，由于 Umklapp 散射具有无色散分支。尽管石墨烯和 Ir 之间的相互作用很弱，但观察到的声子不是独立的石墨烯单层所预期的声子（111）。沿 ΓM 方向测量的弯曲模式抛物线色散允许确定弯曲刚度 κ = (0.80 ± 0.07) eV。在衍射条件下测量的非弹性 HAS 证明莫尔超结构导致与石墨烯超结构的上部和下部区域相关的局部声子模式。