Density-of-States and Optical Properties in Amorphous Carbon Thin Films

Abstract

In this paper we will link the local structure of amorphous carbon and the semi-empirical model which assumes the density of π and π* states as having Gaussian shapes and to be symmetrical with respect to Fermi level. We will show that the effect of charge transfer from sp3 to sp2 sites due their difference in electron-negativity, when coupled with the disorder effect (taken into account by assuming 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 visible region. The limits of the approach will be discussed as well.