OPTICAL-CONSTANTS OF HYDROGENATED AND UNHYDROGENATED AMORPHOUS-CARBON IN THE 0.5-12-EV RANGE

The real and imaginary parts of the refractive index have been obtained in a wide energy range (0.5-12 eV) for films (0.2-0.3 mu m thick) of amorphous carbon with different hydrogen contents (0-40 at. %) to obtain more insight into the electronic structure of these materials. Reflectance and transmittance measurements have been processed with two different approaches in the low- and high-energy parts of the spectra. The results are compared with the known optical properties of bulk diamond and graphite to obtain the ratio between trigonal and tetrahedral carbon atoms. It was found that the number of trigonal carbon sites increases from 20% to 80%, decreasing the hydrogen concentration from 40 to 15 at.%.