Optical Properties Of Graphite Research Articles

Some optical properties of graphite from IR to millimetric wavelengths

Far infrared(FIR) data on the optical properties of graphite are presently lacking. An important step towards filling this gap was taken by Kuzmenko et al. (2008) who measured, on HOPG (Highly Oriented Pyrolitic Graphite) at normal incidence and from 10 to 300 K, the in-plane dielectric functions from 0.3 to 200 mum, and the reflectance between 0.3 and about 300 mum. We show here how, using recent developments of the electron theory of graphene, extended to graphite, it is possible to properly extrapolate the data farther even than 1000 mum, in effect all the way to Direct Current. The plasma frequency as well as the scattering rate of free electrons are shown to both decrease with T, but level off near 0 K, in agreement with theory. Along the way, we noticed significant discrepancies with the well-known and often used derivation of Philipp (1977) at room temperature, and also with previous data on temperature dependence and absorbance of graphitic material samples in different physical forms. Possible reasons for these discrepancies are discussed. Finally, the absorption efficiency of small graphitic spheres is deduced for the spectral range from 0.3 to 10000 mum. This may contribute to the discussion on model dust candidates for recently observed astronomical far infrared emissions.

Optical properties of graphite

Optical constants of graphite for ordinary and extraordinary waves are modeled with a modified Lorentz–Drude model with frequency-dependent damping. The model enables the shape of the spectral line to vary over a range of broadening functions with similar kernels and different wings, the broadening type being its adjustable parameter. The model parameters are determined by the acceptance-probability-controlled simulated annealing algorithm. Good agreement with the experimental data is obtained in the entire investigated spectral range (0.12–40 eV for ordinary wave and 2.1–40 eV for extraordinary wave). The significant discrepancies between the experimental data obtained by the reflectance measurements and the electron-energy-loss spectroscopy data are analyzed in details. Inconsistency in terms of unsatisfied Kramers–Kronig relations is discovered in the index of refraction data derived from reflectance measurements, and a method for correcting the data is proposed.

Highly Negative δ13C Values in Organic Carbon in the Mt. Roe #2 Palaeosol: Terrestrial Life at 2.765 Ga?

The ~13C value of organic carbon at the top of the Archaean Mt. Roe #2 palaeosol is l km. Near the sonthern end of the palaeosol exposure there is a thin (c. 50 cm) lens (c. 20 m x 20 m) of black material interposed between the normal white palaeosol and the overlying basalt. Petrographic microscopy and EPMA show that the white palaeosol layer and the black palaeosol lens both are nearly pure sericite with a small amount of quartz. In thin section the black palaeosol appears to be made up of palaeosol fragments c. 1 mm in diameter. The fragments have no preferred orientation, and probably represent the fragile upper surface of the soil. Some of the palaeosol fragments in the black palaeosol contain sheaves and layers of black material which have the optical properties of graphite. These sheaves and layers are reminiscent of algal/bacterial mat fragments. The 513C values of organic carbon in three samples from the black layer are -41.1%o, -40.8%o, and -40.3%0 PDB. These values are consistent with values found by Hayes (1994) for organic carbon in some late Archaean sediments and suggest that methanotrophic microorganisms colonized the Mt. Roe #2 palaeosol 2.765__.0.010 Ga. The methane these organisms needed could have been generated at the base of the mats during the bacterial degradation of organic matter. It might also have been derived from the ambient atmosphere. The isotopic and morphological observations presented above suggest that methanogens and methanotrophs lived on or near the surface of soils during the Archaean. If there was a methanotrophic

Erratum: Optical properties of graphite from first-principles calculations [Phys. Rev. B55, 4999 (1997)

Erratum: Optical properties of graphite from first-principles calculations [Phys. Rev. B<b>55</b>, 4999 (1997)

Optical properties of graphite from first-principles calculations

We present theoretical results for the frequency-dependent dielectric response, both for the electric field parallel and perpendicular to the c axis of graphite. The calculations are performed using a full-potential linear muffin-tin orbital method. Our calculations show fair agreement with experimental data and the different features observed are identified from interband transitions in various regions of the Brillouin zone. The anisotropy of the dielectric function is discussed in detail and shown to be due to the difference in the optical matrix elements for the two different polarizations, which is a result of the anisotropic crystallographic and electronic properties of graphite.

Band structure and optical properties of graphite

We report the first ever calculation of the frequency dependent anisotropic dielectric function of graphite. We have used the LMTO-ASA method including the combined correction terms. On comparison with the experimental data, we find good agreement as far as the anisotropy is concerned. The individual ϵ ⊥( ω) and epsi; |( ω) are also in reasonable agreement with the data.

Optical properties and equilibrium temperatures of titanium-nitride-and graphite-coated Langmuir probes for space application

The equilibrium temperature of a coated Langmuir probe in space is determined by the optical properties of the coating and the geometry of the probe. In this investigation we report on the optical properties of graphite- and TiN-coated aluminium and titanium. Earlier results have shown that a TiN-coated sphere is preffered as a Langmuir probe for the Cassini satellite bound to Saturn owing to the hardness, chemical inertness and photoelectric stability of the TiN coating. The TiN coatings were prepared by high temperature nitriding of a titanium alloy in pure nitrogen gas. An epoxy-based graphite dispersion (DAG 213) was used to apply the graphite coating. The integrated total solar absorptance α s was calculated, for a spherical and a cylindrical probe, using measured total reflectance. Total hemispherical emittance ϵ H( T) of spherical samples was measured using a calorimetric method and compared with infrared reflectance measurements from 2 to 30 μm. The ratio α s ϵ H for graphite was determined to be 0.95−1.11 for spherical and cylindrical probes in the temperature interval 90−380 K. For TiN the ratio α s ϵ H is 2.64−4.64 for temperatures between 130 and 490 K. Equilibrium temperatures for spherical and cylindrical probes were estimated for solar constants at Venus, Earth and Saturn.

The optical properties of graphite under intense picosecond laser illumination

Picosecond laser ellipsometry has been used in the visible to estimate for the first time the index of refraction of highly oriented pyrolitic graphite samples at high temperatures. While recent experiments seem to indicate that molten graphite behaves in many respects as a metal, investigation of optical properties with picosecond laser pulses consistently shows a reduced reflectivity value as soon as the threshold value of laser fluence for surface melting is exceeded. This occurrence may be interpreted as a reduced conductivity of the liquid phase. The experimental conditions are discussed, and in particular, the possible occurrence of optically thick layers of matter in front of the hot surface during the measurements is evaluated.

Tabulated Optical Properties of Graphite and Silicate Grains: Erratum

Tabulated Optical Properties of Graphite and Silicate Grains: Erratum

Optical properties of graphite

SUMMARYReflectances of natural surfaces of fresh graphite peels parallel to the (0001) plane have been measured throughout the visible spectrum using only slightly modified microphotometric equipment and measuring procedures. There is satisfactory agreement between the level and trends of reflectances of graphites from different metamorphic environments throughout the spectrum, the maximum relative difference in the most difficult conditions in the blue region being approximately 4%. There is less good agreement between the dispersion curves of derived refractive and absorptive indices for which the maximum relative difference is as high as 12% in the red region. At 546 nm, the wavelength at which optical data in organic petrology are principally reported, relative errors below 1% for all the optical parameters were attained between samples. Values of Rair = 31.40%, Roil = 17.85%, n = 2.49 and k = 0.61 compare well with other recent estimates and although there is still not complete agreement between laboratories, the true constants for graphite at this wavelength must lie close to these values. The use of semi‐graphites as metamorphic indicators in a scale with graphite as the end‐point is considered, as are the implications on such a scale of the current use of natural surfaces for reflectance measurement, because of an inability of many laboratories to produce specularly polished surfaces of semi‐graphites and graphites of high uniform quality.

Optical properties of graphite and boron nitride

The energy bands of graphite and boron nitride have been calculated using the tight-binding approximation, with atomic potentials obtained by the SCF CNDO method. On the basis of the calculated bands some optical properties of the above materials are discussed. The optical absorption of the hot-pressed pyrolitic boron nitride was measured in the wavelength region from 25000 to 50000 cm-1 and the width of the forbidden gap was found to be 4.3 eV. Comparisons with the previous calculations have also been made.

Electronic Band Structure and Optical Properties of Graphite from a Variational Approach

The electronic band structure of graphite has been calculated from an ab initio variational approach using a linear-combination of atomic-orbitals (LCAO) basis of Bloch states, including nonspherical terms in the one-electron crystal potential. Matrix elements of the Hamiltonian are evaluated directly without any tight-binding approximations. The optical transitions deduced from the energy bands calculated using a single-layer crystal model agree nicely with recent polarized-light reflectance measurements. Details of the band structure are calculated for the three-dimensional Brillouin zone and related to the results obtained using the single-layer crystal structure. The results are encouraging, not only from the standpoint that the method employed is an ab initio approach with no special a priori assumptions, but also because the band structure is quite insensitive to the particulars of the crystal potential function.

Optical Properties of Graphite in the Far-Infrared Region

The transverse dielectric function e = e 1 + i e 2 of graphite for the electromagnetic wave normally incident on the trigonal plane is calculated on the basis of the band structure for the far-infrared region where the effects of free carriers and the spin orbit coupling are predominant. In the absorption spectrum there appears van Hove singularity arising from the transition between the two degenerate bands near point K of the Brillouin zone split by the effect of spin orbit coupling, but no observable structures from the vicinity of point H . The plasma due to free carriers is markedly affected by the interband effect. The strength of spin orbit coupling λ 33 z is not determined definitely from the experiment available, but is estimated as 0.004eV (at point H ) or 0.0055eV (at point K ) as one of possible values.

Band structure and optical properties of graphite and of the layer compounds GaS and GaSe

The band structure of graphite and of the layer compounds GaS and GaSe is computed by using the tight-binding approach in a semi-empirical way. The band structure is related to the basic properties of these compounds and some features of the optical excitation spectrum are explained. We show that the reason why graphite is a semi-metal and GaS and GaSe are semiconductors can be understood in the two-dimensional approximation and is due to the existence of the inversion symmetry in the former case. The absorption edge in GaS corresponds to indirect transitions between the statesΓ1+ andP1+, while in GaSe it corresponds to direct transitions between the statesΓ1+ andΓ3+. Sharp peaks ine2(0,ω) are attributed to saddle point singularities in the joint density of states. The effect on the optical properties produced by a change in the polarization of light is discussed.

Optical properties of graphite in the infrared region

The optical properties of graphite in the infrared region were studied theoretically on the basis of the Slonczewskii-Weiss band model of π-electrons in graphite. The calculated conductivity of graphite with a large value of γ 1=0.4 eV is in good agreement with the experimental result obtained by Taft and Philipp, though a larger value of γ 1 is not favorable to fit the reflectance measured by Boyle and Nozieres.

9. Optical properties of graphite

9. Optical properties of graphite

Optical Properties of Graphite

The complex dielectric constant $\ensuremath{\epsilon}(\ensuremath{\omega})={\ensuremath{\epsilon}}_{1}+i{\ensuremath{\epsilon}}_{2}$ and associated functions are derived by application of the Kramers-Kronig relation to reflectance data for graphite obtained in the energy range to 26 eV. It is possible to divide the optical properties into two spectral regions. In the range 0 to 9 eV, intra- and interband transitions involve mainly the $\ensuremath{\pi}$ bands. At higher energies, a broad absorption peak near 15 eV is associated with interband transitions involving the 3 $\ensuremath{\sigma}$ electrons per atom. This viewpoint is strongly supported by evaluation of the sum rules for ${n}_{\mathrm{eff}}$. Plasma resonances which produce peaks in the energy-loss function $\ensuremath{-}\mathrm{Im}{\ensuremath{\epsilon}}^{\ensuremath{-}1}$ at 7 and 25 eV are identified and described physically. At low energies, structure in the reflectance curve near 0.8 eV is attributed to the onset of transitions between the ${E}_{2}$ and ${E}_{3}$ bands at the point $K$. This yields a value for ${\ensuremath{\gamma}}_{1}$ of \ensuremath{\approx}0.4 eV.

Optical Properties of Graphite in the Region 1100 to 3000 Å

Optical Properties of Graphite in the Region 1100 to 3000 Å