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我们通过共振拉曼光谱测量了转角多层石墨烯的层间振动模式:剪切模和呼吸模。根据改进的线性模型,我们发现在转角多层石墨烯界面处的层间呼吸耦合与正常Bernal堆垛多层石墨烯的强度相当。此结果明显不同于层间剪切耦合,后者在转角多层石墨烯界面处的层间剪切耦合减弱到了正常Bernal堆垛多层石墨烯的20%。另外,我们首次发现层间呼吸耦合存在着次近邻原子层之间的相互作用,其强度为最近邻的9%。我们发现当采用与界面层间旋转角度相对应的激发光时,转角多层石墨烯的拉曼信号得到极大的增强。为此,我们引入光学跃迁允许的电子联合态密度的概念,通过理论计算,我们发现这种联合态密度的极大值决定了拉曼信号共振线型的激发光能量极值。本研究表明,层间振动模式是探测二维层状异质层间耦合的有效手段,为其在器件应用方面的研究奠定了基础。
We measured the interlaminar vibrational modes of corner multi-layer graphene by resonance Raman spectroscopy: shear mode and respiration mode. Based on the improved linear model, we found that the layer-to-layer respiratory coupling at the corner multi-layer graphene interface is comparable to that of a normal Bernal stacked multilayer graphene. This result is significantly different from that of interlaminar shear coupling, where the interlaminar shear coupling at the corner multi-graphene interface weakened to 20% of that of a normal Bernal stacked multilayer graphene. In addition, we find for the first time that the inter-layer respiratory coupling has the interaction between the next nearest atomic layers and its intensity is 9% of the nearest neighbor. We have found that the Raman signal of the corner multi-layer graphene is greatly enhanced when using the excitation light corresponding to the rotation angle between the interface layers. For this reason, we introduce the concept of electronic united density of states allowed by optical transition. By theoretical calculations, we find that the maximum of the combined state density determines the extremal energy of the excitation light of the Raman signal. This study shows that the inter-layer vibration mode is an effective method to detect the coupling between two-dimensional layered heterogeneous layers, which lays the foundation for its application in device research.