Density of states and σ-π mixing in hydrogenated amorphous carbon films

In this work we analyse the real and imaginary parts of the complex dielectric functions of two a-C:H samples, which are available over a wide energy range (2-25 eV). Values of the Sp(3)/sp(2) ratios matching those determined by XANES can be obtained by an optical analysis of these data. provided that an asymmetric Gaussian density of states model (for pi-like states) and suitable matrix element values (for sigma-like states) are used. These results also suggest that bonding and anti-bonding states sitting similar to2 eV above and below Fermi level are not pure pi-states, but that some pi-sigma mixing is occurring. The origin and the effects of such a mixing are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.