Observation of Low Energy Raman Modes in Twisted Bilayer Graphene
Observation of Low Energy Raman Modes in Twisted Bilayer Graphene
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DOI：
10.1021/nl4013387
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发表时间：
2013-08-01
期刊：
影响因子：
10.8
通讯作者：
Chen, Yong P.
中科院分区：
文献类型：
--
作者：
He, Rui;Chung, Ting-Fung;Chen, Yong P.
在用化学气相沉积法生长的扭曲双层石墨烯中观察到两个低于100 cm（-1）的新的拉曼模。这两个模式被观察到在一个小的扭曲角的范围内，在该范围内的G拉曼峰的强度被强烈增强，这表明这些低能量模式和G拉曼模式共享相同的共振增强机制，作为扭曲角的函数。类似于94 cm（-1）模式（用532 nm激光激发测量）被分配给由扭曲双层石墨烯晶格介导的基本层呼吸振动（ZO'模式），其缺乏长程平移对称性。该模式的频率和线宽对旋转角的依赖性可以通过双共振拉曼过程来解释，该过程不同于先前识别的由扭曲双层石墨烯超晶格激活的拉曼过程。该依赖性还揭示了两个石墨烯层的电子带重叠的强烈影响。在类似于52 cm（-1）处的另一种新模式，先前在双层石墨烯系统中未观察到，暂时归因于扭转模式，其中底部和顶部石墨烯层在平面中异相旋转。
Two new Raman modes below 100 cm(-1) are observed in twisted bilayer graphene grown by chemical vapor deposition. The two modes are observed in a small range of twisting angle at which the intensity of the G Raman peak is strongly enhanced, indicating that these low energy modes and the G Raman mode share the same resonance enhancement mechanism, as a function of twisting angle. The similar to 94 cm(-1) mode (measured with a 532 nm laser excitation) is assigned to the fundamental layer breathing vibration (ZO' mode) mediated by the twisted bilayer graphene lattice, which lacks long-range translational symmetry. The dependence of this mode's frequency and line width on the rotational angle can be explained by the double resonance Raman process that is different from the previously identified Raman processes activated by twisted bilayer graphene superlattice. The dependence also reveals the strong impact of electronic-band overlaps of the two graphene layers. Another new mode at similar to 52 cm(-1), not observed previously in the bilayer graphene system, is tentatively attributed to a torsion mode in which the bottom and top graphene layers rotate out-of-phase in the plane.