Twisted bilayer graphene (tBLG) provides an opportunity to control the optoelectronic properties of graphene owing to the relative orientation (θ)-induced van Hove singularities (vHs). However, how different environments affect vHs behaviors of various tBLGs and their Raman resonance window is not clear. A study of the optical vHs properties of tBLGs on a quartz substrate, prepared by chemical vapor deposition, was carried out using simultaneous reflection and Raman imaging techniques according to the presence of ubiquitous residual amorphous carbon (RAC). The results show that the presence of RAC exhibits a narrower vHs peak width and resonance Raman windows of tBLG as compared to that without RAC, due to the absence of charge-inhomogeneous interactions from bare substrate. In addition, the background-subtracted vHs peak reflectances from various θ values at a specific laser energy are proportional to the measured G-band enhancement factor (GEF). The comparison reveals the detailed optical and Raman resonance windows of various tBLGs in both environments. Extension of the approach to twisted fewlayer graphenes reveals the different vHs peak behaviors including broadening, intensification, and splitting governed by θ-, along with layer number-dependent band structure hybridization.
Bibliographical noteFunding Information:
The authors thank Y. Li for sheet conductivity calculations. This research was supported financially by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology ( NRF-2014R1A1A2055572 ), and in part by the Yonsei University Future-Leading Research Initiative of 2014 ( 2014-22-0123 ).
All Science Journal Classification (ASJC) codes
- Materials Science(all)