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Spectroscopic ellipsometry of graphene and an exciton-shifted van Hove peak in absorption

2010; American Physical Society; Volume: 81; Issue: 15 Linguagem: Inglês

10.1103/physrevb.81.155413

1550-235X

Vasyl G. Kravets, A. N. Grigorenko, Rahul R. Nair, Peter Blake, S. Anissimova, Kostya S. Novoselov, A. K. Geǐm,

Silicon Nanostructures and Photoluminescence

We demonstrate that optical transparency of any two-dimensional system with a symmetric electronic spectrum is governed by the fine structure constant and suggest a simple formula that relates a quasiparticle spectrum to an optical absorption of such a system. These results are applied to graphene deposited on a surface of oxidized silicon for which we measure ellipsometric spectra, extract optical constants of a graphene layer and reconstruct the electronic dispersion relation near the $K$ point using optical transmission spectra. We also present spectroscopic ellipsometry analysis of graphene placed on amorphous quartz substrates and report a pronounced peak in ultraviolet absorption at 4.6 eV because of a van Hove singularity in graphene's density of states. The peak is asymmetric and downshifted by 0.5 eV probably due to excitonic effects.