Optical phase diagram of amorphous carbon films determined by spectroscopic ellipsometry

摘要

In this study we show how amorphous carbon films can be categorized using their optical properties which change according to their structure and composition. Hydrogenated and hydrogen free diamond- and graphite-like carbon films, characterized previously by several methods, were analyzed with spectroscopic ellipsometry in the 1.24-5 eV photon energy range. To model the measured Ψ and △ spectra the optical properties of the films were described with Tauc-Lorentz oscillator model, Gaussian line shape and Cauchy's dispersion relation. The results and the films are compared in terms of the highest refractive index (n_(max)) and the corresponding pho-rnton energy (E_(max)). When plotting E_(max) as a function of the maximal refractive index the data draw out a curved track. The data of different type films are located at different parts of the curve which are placed at corresponding positions for all models. Thus the trends derived with different modeling are the same, even though the optical properties of the films derived from ellipsometric measurements may slightly depend on the applied model. Hence this representation of the refractive index of a-C and a-C:H films can be utilized for qualitative analysis.