Broadband Optical Properties of Graphene by Spectroscopic Ellipsometry
Wei Li, Nhan V. Nguyen, Guangjun Cheng, Angela R. Hight Walker, David J. Gundlach, Yiran Liang, boyuan Tian, Xuelei Liang, Lianmao Peng
The broadband (0.7 eV to 9.0 eV) optical properties of chemical-vapor-deposition (CVD) grown graphene are determined by spectroscopic ellipsometry. The optical absorption follows the fine structure constant in the energy range from 1.0 eV to 2.0 eV, but deviates to lower below 1 eV. A strong absorption peak is observed at 4.6 eV which is dominated by resonant excitons near the van Hove singularity at M point of the Brillouin zone. A higher energy peak at 6.4 eV is regarded as a result from the excitonic effect of σ-to-σ* transition at Γ point of the Brillouin zone. The dielectric function of multi-layered CVD graphene fabricated by layer transfer was also investigated. We found that the multi-layered graphene resembles the characteristics of CVD single-layer graphene and exfoliated multilayer graphene, leading to a prospect of new potential device applications.