Optical properties of carbon thin films containing nanoparticles

The incorporation of carbon nanoparticles in the forms of nanotubes and bucky onions have shown to improve the mechanical properties of amorphous carbon (a-C) thin films. In this paper we report on the change in the optical properties of a-C films containg nanoparticles. The optical band gap, index of refraction and extinction coefficient are studied. The optical band gap in highly tetrahedral amorphous carbon (ta-C) is found to be around 2 eV. It decreases almost linearly with the sp(2) fraction. It is theorized that the clustering of the sp(2) sites leads to a reduction in the band gap. In this paper, we study the influence of large sp(2) clusters in forms of graphitic nanoparticles on the optical of ta-C. We find that the optical gap remains around 1.8 eV even with the large inclusions of clustered nanoparticles. Furthermore, the gap remains close to 1.8 eV even when the sp(2) fraction in the amorphous matrix is increased. The index of refraction however is found to decrease with the sp(2) fraction indicating a reduction in density.