Influence of ion energy and substrate temperature on the optical and electronic properties of tetrahedral amorphous carbon (ta-C) films

The properties of amorphous carbon (a-C) deposited using a filtered cathodic vacuum are as a function of the ion energy and substrate temperature are reported. The sp(3) fraction was found to strongly depend on the ion energy, giving a highly sp(3) bonded a-C denoted as tetrahedral amorphous carbon (ta-C) at ion energies around 100 eV. The optical band gap was found to follow similar trends to other diamondlike carbon films, varying almost linearly with sp(2) fraction. The dependence of the electronic properties are discussed in terms of models of the electronic structure of a-C. The structure of ta-C was also strongly dependent on the deposition temperature, changing sharply to sp(2) above a transition temperature, T-1, of approximate to 200 degrees C. Furthermore, T-1 was found to decrease with increasing ion energy. Most film properties, such as compressive stress and plasmon energy, were correlated to the sp(3) fraction. However, the optical and electrical properties were found to undergo a more gradual transition with the deposition temperature which we attribute to the medium range order of sp(2) sites. We attribute the variation in film properties with the deposition temperature to diffusion of interstitials to the surface above T-1 due to thermal activation, leading to the relaxation of density in context of a growth model. (C) 1997 American Institute of Physics.