转角多层石墨烯层间耦合的共振拉曼光谱研究

Interface Coupling in Twisted Multilayer Graphene by Resonant Raman Spectroscopy

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。

The C and LB modes of t（m＋n）LG are studied systematically by Raman spectros- copy. In the t（m＋n）LG,the C modes of nLG and mLG and LBMs of （m＋n）LG are ob- served. We fit the positions of C and LB modes by an improved linear chain model. We find the interlayer shear coupling at the twisted interface is - 20% of that at Bernal stacked inter- faces,but the layer breathing coupling at the twisted interface is closed to that of Bernal in- terface. Moreover, the next-fiearest interlayer interaction, which is 9 % of the nearest interlay- er interaction,must be considered for LBMs. The Raman intensity of the C,LB and G modes is significantly enhanced in t（m＋n）LGs for specific excitation energies. This behavior is as- signed to the resonance between van Hove singularities in the joint density of states of all op- tically allowed transitions in twisted multilayer samples and the laser excitation energy, dur- ing the optical absorption and emission steps of the Raman process. Beyond tMLGs, the inter- layer interaction of other heterostructures can also be measured by Raman spectroscopy.