Dielectric function and critical-point transitions in boron-doped graphite

Abstract

Optical reflectivity spectra of graphite substitutionally doped with 0.5-at.% boron were measured in the energy range 0.1-6.0 eV and analyzed by the Kramers-Kronig method to yield the $q=0$ dielectric function. A screened free-carrier plasma edge occurs at 0.5 eV, and the onset of interband transitions indicates a Fermi-level shift of 0.2 eV. Thermoreflectance spectra in the range 0.3-1.5 eV reveal changes in critical-point transitions which are consistent with the shift in Fermi energy. Both experiments can be understood in terms of a rigid-band model with spatially uniform charge density. This result is in contrast to the situation in dilute intercalation compounds, in which interlayer screening must be accounted for.