Stress-induced anisotropy of graphitelike amorphous carbon

Ellipsometry spectra of graphitelike amorphous carbon films on Si reveal a strong anisotropy of the optical constants in the 0.7–9.5eV photon-energy range. The films are optically uniaxial, with the optical axis oriented normal to the surface. This birefringence can be explained by ordering of the hexagonal graphene planes perpendicular to the substrate due to tensile stress, which was confirmed by transmission electron microscopy. All films show two peaks in the optical absorption, corresponding to the ordinary and extraordinary absorption peaks in graphite.