Relationships between the optical and Raman behavior of van Hove singularity in twisted bi- and fewlayer graphenes and environmental effects

详细信息    查看全文

• 作者：Eunhye Koo ; Somin Kim ; Sang-Yong Ju ; ^{syju@yonsei.ac.kr" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Twisted fewlayer graphene ; van Hove singularity ; Substrate effect ; Charge inhomogeneity ; Reflection spectroscopy ; Widefield Raman imaging
• 刊名：Carbon
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：111
• 期：Complete
• 页码：238-247
• 全文大小：2539 K

文摘

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.