Kalbac Martin, Frank Otakar, Kong Jing, Sanchez-Yamagishi Javier, Watanabe Kenji, Taniguchi Takashi, Jarillo-Herrero Pablo, Dresselhaus Mildred S
†J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejškova 3, CZ-18223 Prague 8, Czech Republic.
‡Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
J Phys Chem Lett. 2012 Mar 15;3(6):796-9. doi: 10.1021/jz300176a. Epub 2012 Mar 6.
We report an unusual enhancement of the Raman signal of the G mode in a twisted graphene bilayer (2-LG) on a hexagonal single-crystalline boron nitride substrate. We used an isotopically engineered 2-LG, where the top layer was composed of (13)C atoms and the bottom layer of (12)C atoms. Consequently, it was possible by Raman spectroscopy to distinguish between the enhancement coming from the top and bottom layers. The enhancement of the G mode was, however, found to be similar for the top and bottom layers, and this enhancement effect was observed only at certain locations on the substrate. The experiment with two different laser excitation energies showed that the location of the enhanced spots is dependent on the laser excitation energy. Therefore our results suggest that the enhancement comes from new states in the electronic structure, which are a consequence of a local specific rotation of the grains in graphene layers.
我们报道了在六方单晶氮化硼衬底上的扭曲双层石墨烯（2-LG）中，G 模式拉曼信号出现异常增强的现象。我们使用了同位素工程化的 2-LG，其中顶层由（13）C 原子组成，底层由（12）C 原子组成。因此，通过拉曼光谱可以区分来自顶层和底层的增强信号。然而，发现 G 模式在顶层和底层的增强情况相似，并且这种增强效应仅在衬底上的某些位置观察到。用两种不同激光激发能量进行的实验表明，增强斑点的位置取决于激光激发能量。因此，我们的结果表明，这种增强来自电子结构中的新状态，这是石墨烯层中晶粒局部特定旋转的结果。
