Density-of-states and optical properties in amorphous carbon thin films

In this paper we will link the local structure of amorphous carbon and the semi-empirical model which assumes the density of pi and pi* states as havi ng Gaussian shapes and to be symmetrical with respect to Fermi level. We wi ll show that the effect of charge transfer from sp(3) to sp(2) sites due th eir difference in electron-negativity, when coupled with the disorder effec t (taken into account by assuming a Gaussian distribution of the amount of charge transfer) lead to a sum of Gaussian symmetrical bands. Moreover, we will show that the sp2 pairs are responsible for most of the joint density- of-states (i.e. the imaginary part of the dielectric constant) in the visib le region. The limits of the approach will be discussed as well.