Optical Properties of Evolutionary Grown Layers of Carbon Nanowalls Analyzed by Spectroscopic Ellipsometry

Carbon nanowalls (CNWs), vertically standing graphene sheets, grown by the radical injection plasma-enhanced chemical vapor deposition system were analyzed by spectroscopic ellipsometry. The refractive indexes (n), extinction coefficients (k), and optical band gaps (Eg) of evolutionary growth layers were evaluated using the Tauc?Lorentz model with the effective medium approximation. It was observed that an amorphous carbon interfacial layer with n of 1.9?2.0 was formed prior to the growth of CNWs with n of 1.2?1.5. Moreover, the imaginary parts of complex dielectric functions analyzed using the Tauc?Lorentz model indicate the possibility that the CNWs have semiconducting features.