Measurement of Optical Functions of Highly Oriented Pyrolytic Graphite in the Visible

Abstract

The spectroscopic dielectric functions of highly oriented pyrolytic graphite (HOPG) are determined at 9 different wavelengths from 405 to 750 nm (3.06 to 1.65 eV). This determination is made on the basis of two ellipsometry measurements: 1) Standard ellipsometry measurements are performed on HOPG with the c-axis perpendicular to the sample surface, and 2) Two-modulator generalized ellipsometry microscope (2-MGEM) measurements are performed on HOPG cut and polished such that the c-axis is parallel to the sample surface. Both the ordinary and extraordinary complex dielectric functions show non-zero absorption throughout the observed spectral range, while the ordinary dielectric function shows Drude-like behavior at longer wavelengths. From this, it can be concluded that graphite is metallic for visible light polarized parallel to the graphene planes, but acts more as a semiconductor or semimetal for visible light polarized perpendicular to the graphene planes. The 2-MGEM technique can also be used to generate images of the diattenuation, retardation, and direction of the principal axis.