Optical Constants Of Graphite Research Articles

Universal layer number in graphite

Graphene absorbs light in accordance with the fine-structure constant α ≃ 1/137. The α value is universal in the sense that it is unrelated to material parameters but solely related to the elementary charge, which is a fundamental constant governing the coupling of light and matter. A new universality governed only by α has yet to be discovered in graphene optics. However, since α is a dimensionless quantity, it can be anticipated that the reciprocal of α appears as a characteristic number of layers in the light absorptance of an N-layer graphene. Here, we report that this number is 2/πα. We show simultaneously that for light in the infrared to visible range, an N-layer graphene with N above 1500 may be regarded as graphite. This also enables us to obtain the simplest expression for the optical constants of graphite, which is written in terms of α and interlayer distance only.

A study of vibrational states in condensed carbon-based media

The spectra of the optical constants n(v) and κ(v) of a strongly absorbing object, graphite, having a high concentration and mobility of free carriers, are calculated by the methods of classical dispersion analysis. The problem of detection and identification of vibrational states of the substance against an intense nonselective absorption is considered. The calculated spectra of the optical constants of graphite are compared with the analogous data obtained from the spectrum of attenuated total internal reflection in the range of the vibrational E1u mode of a quasi-single crystal of graphite, the Raman spectrum of the sample, and the background spectrum of graphite structures.

Optical properties from reflection electron energy loss spectroscopy

The optical constants of graphite (highly oriented pyrolitic graphite) and Kapton (Dupont de Nemours) polymer, pyromellitic dianhydride-oxy dyaniline (PMDA-ODA), over the 0–40 eV energy range, have been obtained by reflection electron energy loss spectroscopy (REELS) measurements. Raw data handling procedures, such as background subtraction, elastic peak elimination and the evaluation of the double-scattering contribution, are discussed. The influence of surface plasmons on the experimental line shapes is also considered in order to deduce the importance of surface effects in the REELS experiment. The pure Im(−1/ε) loss function is therefore obtained by a conventional Kramers-Kronig analysis giving the optical constants of the samples. The REELS-deduced optical constants are compared with those obtained by a conventional wide-range reflectivity spectrum, showing a very good agreement. No relaxation of dipole selection rules has been observed for the primary energy used (1.2 keV), thus justifying the retention of the optical limit assumption ( q → 0).

Transition Radiation and Optical Properties of Evaporated Carbon Foil*,†

The light emitted from an electron-irradiated self-supported foil (334±30 Å) of evaporated carbon has been investigated experimentally. Normally incident, 1-μA electron beams having monochromatic energies of 297, 423, 632 keV and 1.10 MeV were used. These correspond to β2 values of 0.6, 0.7, 0.8, and 0.9, respectively, where β = ν/c, and ν is the velocity of the incident electrons. The absolute photon intensity emitted in the 2200–5800-Å spectral region was measured with a calibrated optical system. The results were analyzed with respect to wavelength of emitted radiation, forward angle of emission, θ (15° and 30°), and degree of polarization (parallel and perpendicular to the plane of the incident electrons and observed light). The transition-radiation contribution determined from the parallel-polarized component has been compared with the generalized theory of Ritchie and Eldridge, using the optical constants of graphite and glassy carbon. From this comparison and a best-fit calculation, the optical constants for the carbon film throughout the 2200–5800-Å spectral region have been derived. The derived constants indicate that the carbon film has optical properties between those of graphite and glassy (amorphous) carbon. The results obtained stress the importance of measuring the optical constants of a given carbon film for any experiment in which they are needed.

Interstellar Dust—Reply to Duley's Criticisms

DULEY' second1 criticism of our hypothesis of graphite-iron-silicate grain mixtures2,3 contains further errors and misrepresentations of our statements. We wish to refer here to a few crucial facts which seem to have been overlooked by Duley1,4 and which invalidate his contention that the interstellar extinction curve does not provide additional evidence to support either graphite or silicate grains. The suggestion that a fit to the observed extinction curve on the basis of graphite, iron and silicate grains is confined to the adoption of the special set of values 0.06, 0.02 and 0.15 µm for their respective mean radii is incorrect. In our original paper2 we stated clearly that r (graphite)=0.045–0.07 µm, r (iron)≤0.02 µm and r (silicate)=0.15–0.18 µm are the requirements necessary to obtain good agreement with the observations. A wide range of relative proportions of the three grain species and several different types of size distributions2,3,5,6 have been shown to provide satisfactory fits to the available astronomical data. It should be stressed that the optical constants of graphite are such that the observed optical extinction curve and the ultraviolet hump at λ2200 A could be reproduced for a wide range of particle sizes. Iron and silicates in our model play a less important part at optical wavelengths so that constraints on their sizes and proportions relative to graphite are less rigorously specified by the optical extinction data.

Determination of Longitudinal and Transverse Optical Constants of Absorbing Uniaxial Crystals–Optical Anisotropy of Graphite

Equations relating the minimum values of the refractive and attenuation indices to the longitudinal and transverse optical constants are developed. The longitudinal optical constants of graphite are thus obtained

136. The optical constants of graphite in the ultraviolet-visible spectrum determined by reflectance from single crystal faces

136. The optical constants of graphite in the ultraviolet-visible spectrum determined by reflectance from single crystal faces

133. The optical constants of graphite in the infrared spectrum determined by transmission through ultrathin crystals

133. The optical constants of graphite in the infrared spectrum determined by transmission through ultrathin crystals

132. The optical constants of graphite in the ultraviolet-visible spectrum determined by transmission through ultrathin crystals

132. The optical constants of graphite in the ultraviolet-visible spectrum determined by transmission through ultrathin crystals