Dispersion relations and optical properties of amorphous carbons

A dispersion model based on two Tauc-Lorentz oscillators (2-TL), to describe the pi-pi* and sigma-sigma* transitions, is applied to a wide variety of amorphous carbons grown by various vapor deposition techniques. The application of identical analysis to the various samples enables the quantitative comparison between various forms of amorphous carbon. The model is applied to spectroscopic ellipsometry data and can describe accurately the optical properties of all amorphous carbons. A validation is performed based on wide-range electron energy-loss spectroscopy spectra. This approach, universal for all carbons, extends the single TL model and can determine accurately the energy position of the pi-pi* transition and estimate fairly the sigma-sigma* transitions in addition to the E-g; these parameters as well as the refractive index are correlated to the sp(3) content and density of all amorphous carbons. (C) 2007 Elsevier B.V. All rights reserved.