Broadband optical properties of graphene by spectroscopic ellipsometry
Broadband optical properties of graphene by spectroscopic ellipsometry
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DOI：
10.1016/j.carbon.2015.12.007
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发表时间：
2016-04-01
期刊：
影响因子：
10.9
通讯作者：
Nguyen, Nhan V.
中科院分区：
文献类型：
--
作者：
Li, Wei;Cheng, Guangjun;Nguyen, Nhan V.
采用椭圆偏振光谱法在0.7 eV-9.0 eV能量范围内对化学气相沉积法生长的石墨烯的光学性质进行了高精度的测量。准确地获得了石墨烯的折射率（n）和消光系数（k），并与直接测量的透射率数据进行了比较。石墨烯的吸收在可见光范围内遵循公知的精细结构常数，在低于1 eV时变得更低，并且在4.8eV附近显示出强吸收峰。后者归因于布里渊区M点处货车霍韦奇点附近的共振激子。在6.4 eV处观察到更高的能量吸收峰，这是由于在布里渊区的伽马点处的sigma-to-sigma* 跃迁的激子效应。通过重复转移制造的多层石墨烯表现出与单层石墨烯相似的光学性质，并且4.8eV吸收峰表现出与层数目相关的峰位移，类似于剥离的AB堆叠的多层石墨烯。这封信中报道的宽带光学性质被认为是增强对石墨烯光学性质的理解，并将有利于石墨烯基光电器件的开发。(C)2015爱思唯尔有限公司版权所有。
The optical properties of chemical vapor deposition grown graphene were measured with high accuracy by spectroscopy ellipsometry in the energy range of 0.7 eV-9.0 eV, which is spectrally broader compared with those reported in literature. The refractive index (n) and extinction coefficient (k) of graphene were accurately obtained and compared with directly measured transmittance data. The absorption of graphene follows the well-known fine structure constant in the visible range, becomes lower below 1 eV, and shows a strong absorption peak around 4.8 eV. The latter was attributed to the resonant excitons near the van Hove singularity at the M point of the Brillouin zone. A higher energy absorption peak was observed at 6.4 eV resulting from the excitonic effect of the sigma-to-sigma* transition at the Gamma point of the Brillouin zone. The multi-layer graphene, fabricated by repeated transfer, exhibit similar optical properties to mono-layer graphene and the 4.8 eV absorption peak exhibits a layer-number dependent peak shift, similar to the exfoliated AB-stacked multi-layer graphene. The broadband optical properties reported in this letter are believed to enhance the understanding of the optical properties of graphene and will benefit the development of graphene-based optoelectronic devices. (C) 2015 Elsevier Ltd. All rights reserved.