The hardness,elastic modulus, and structure of several amorphouscarbonfilms on silicon prepared by cathodic‐arc deposition with substrate pulse biasing have been examined using nanoindentation, energy loss spectroscopy (EELS), and cross‐sectional transmission electron microscopy. EELS analysis shows that the highest sp 3 contents (85%) and densities (3.00 g/cm3) are achieved at incident ion energies of around 120 eV. The hardness and elastic modulus of the films with the highest sp 3 contents are at least 59 and 400 GPa, respectively. These values are conservative lower estimates due to substrate influences on the nanoindentation measurements. The films are predominantly amorphous with a ∼20 nm surface layer which is structurally different and softer than the bulk.