High-energy optical conductivity of graphene determined by reflection contrast spectroscopy

Fei, Zhe; Shi, Yi; Peng, Lin; Gao, Feng; Liu, Yu; Sheng, L.; Wang, Baigeng; Zhang, Rong; Zheng, Yu‐Xiang

doi:10.1103/physrevb.78.201402

Cited by 29 publications

(39 citation statements)

References 17 publications

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“…Such a change is conceivable in space, as ω p is intimately linked to the electrical conductivity, which is very sensitive to the heat treatment previously suffered by the material (Robertson 1986). Alternatively, the feature location may be controlled through , which is notoriously subject to experimental errors of measurement (see Jellison, Hun & Lee 2007) and was recently shown to strongly depend on the distance between graphene planes (Marinopoulos, Reining & Olevano 2002;Fei et al 2008). Thus, calculations show that changing its value by a factor of 1/2 or 2 shifts the feature to 2070 and 2210 Å, respectively; the required adjustment may thus fall within the limits of measurement errors and structural variations.…”

Section: T H E M O D E L C a R R I E Rmentioning

confidence: 99%

A polycrystalline graphite model for the 2175 Å interstellar extinction band

Papoular

2009

Monthly Notices of the Royal Astronomical Society

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A random, hydrogen‐free, assembly of microscopic sp2 carbon chips, forming a macroscopically homogeneous and isotropic solid, is proposed as a model carrier for the ultraviolet (UV) interstellar extinction band. The validity of this model is based on the calculation of the Bruggeman average dielectric function of a mixture of the known parallel and perpendicular dielectric functions of graphite. The π absorption feature of Rayleigh‐sized spheres of this mixture falls near 4.6 μm−1 (2175 Å), but its width is 1.5 μm−1, somewhat larger than the astronomically observed average, 1 μm−1. This is confirmed by measurements of the reflectance of an industrial material, polycrystalline graphite. A better fit to the interstellar feature position and width is obtained with a hypothetical material, having the same dielectric functions as natural graphite, except for less extended wings of the π resonance. Physically, this could result from changes in the electronic band structure due to previous thermal histories. In this model, the Frölich feature central wavelength depends only on the π resonance frequency, while its width depends only on the damping constant of the same resonance. This explains the range of observed feature widths at constant feature wavelength.

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Section: T H E M O D E L C a R R I E Rmentioning

confidence: 99%

A polycrystalline graphite model for the 2175 Å interstellar extinction band

Papoular

2009

Monthly Notices of the Royal Astronomical Society

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“…11 Furthermore, the flattening of the π bands at energies away from the Dirac point is responsible for the strong peak in the spectrum at higher energies (of the order of 5 eV) which is associated with optical transitions between states of the Van Hove singularities. 8,12,13 Finally, a method to control the intermediate excited states in inelastic light scattering experiments has also been reported, revealing the important role of quantum interference in Raman scattering. 14 This intense experimental work has been accompanied by a series of theoretical studies which have treated the problem of the optical conductivity at different levels of approximation.…”

Section: Introductionmentioning

confidence: 99%

Optical conductivity of disordered graphene beyond the Dirac cone approximation

et al. 2011

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In this paper we systemically study the optical conductivity and density of states of disordered graphene beyond the Dirac cone approximation. The optical conductivity of graphene is computed by using the Kubo formula, within the framework of a full π -band tight-binding model. Different types of noncorrelated and correlated disorder are considered, such as random or Gaussian potentials, random or Gaussian nearest-neighbor hopping parameters, randomly distributed vacancies or their clusters, and randomly adsorbed hydrogen atoms or their clusters. For a large enough concentration of resonant impurities, an additional peak in the optical conductivity is found, associated with transitions between the midgap states and the Van Hove singularities of the main π band. We further discuss the effect of doping on the spectrum, and find that small amounts of resonant impurities are enough to obtain a background contribution to the conductivity in the infrared part of the spectrum, in agreement with recent experiments.

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“…13 Compared with the absorption measurement, 11 the contrast measurement can be performed on any substrate, with better spatial resolution of micrometer scale, 28 and do not need suspended samples. The graphene samples are fabricated by micromechanical cleavage and transferred to the SiO 2 /Si substrate.…”

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confidence: 99%

Stacking-Dependent Optical Conductivity of Bilayer Graphene

et al. 2010

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The optical conductivities of graphene layers are strongly dependent on their stacking orders. Our first-principle calculations show that, while the optical conductivities of single-layer graphene (SLG) and bilayer graphene (BLG) with Bernal stacking are almost frequency-independent in the visible region, the optical conductivity of twisted bilayer graphene (TBG) is frequency-dependent, giving rise to additional absorption features due to the band folding effect. Experimentally, we obtain from contrast spectra the optical conductivity profiles of BLG with different stacking geometries. Some TBG samples show additional features in their conductivity spectra, in full agreement with our calculation results, while a few samples give universal conductivity values similar to that of SLG. We propose that those variations of optical conductivity spectra of TBG samples originate from the difference between the commensurate and incommensurate stackings. Our results reveal that the optical conductivity measurements of graphene layers indeed provide an efficient way to select graphene films with desirable electronic and optical properties, which would greatly help the future application of those large-scale misoriented graphene films in photonic devices.

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High-energy optical conductivity of graphene determined by reflection contrast spectroscopy

Cited by 29 publications

References 17 publications

A polycrystalline graphite model for the 2175 Å interstellar extinction band

A polycrystalline graphite model for the 2175 Å interstellar extinction band

Optical conductivity of disordered graphene beyond the Dirac cone approximation

Stacking-Dependent Optical Conductivity of Bilayer Graphene

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