The properties of amorphous carbon (a-C) deposited using a filtered cathodic vacuum arc as a function of the ion energy and substrate temperature are reported. Thesp3fraction was found to strongly depend on the ion energy, giving a highlysp3bondeda-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 withsp2fraction. The dependence of the electronic properties are discussed in terms of models of the electronic structure ofa-C. The structure ofta-C was also strongly dependent on the deposition temperature, changing sharply tosp2above a transition temperature,T1, of ≈200 °C. Furthermore,T1was found to decrease with increasing ion energy. Most film properties, such as compressive stress and plasmon energy, were correlated to thesp3fraction. 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 ofsp2sites. We attribute the variation in film properties with the deposition temperature to diffusion of interstitials to the surface aboveT1due to thermal activation, leading to the relaxation of density in context of a growth model. ©1997 American Institute of Physics.