Optical Properties of Graphite

Abstract

The complex dielectric constant $\epsilon \left(\omega \right)={\epsilon }_1+i{\epsilon }_2$ 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 $\pi$ bands. At higher energies, a broad absorption peak near 15 eV is associated with interband transitions involving the 3 $\sigma$ 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 $-\mathrm{Im}{\epsilon }^{-1\mathrm{}}$ 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 ${\gamma }_1$ of ≈0.4 eV.