Influence of disorder on the density of π and σ states in hydrogenated amorphous carbon

The presence of both sp(2) and sp(3) hybridized carbon atoms, together with the tendency of spl atoms to gather into pi-bonded clusters with different bonding configurations, induce a particular type of disorder in hydrogenated amorphous carbon (a-C:H). To study the resulting effects on the density of both pi and sigma electronic states, we determined the optical absorption edge of plasma-enhanced chemical vapour deposition (PECVD) a-C:H films with optical gaps, E-04: varying from about 1.5 to about 3.5 eV, as well as their complex dielectric function at larger energies to 25 eV. We show that the determinant structural parameter for the electronic density of states is the local bonding configurations of the sp; carbon atoms. (C) 2000 Elsevier Science B.V. All rights reserved.