In this work, we report unusual properties of amorphous carbon films prepared by ion beam-assisted deposition using different noble gases (neon, argon, and krypton). Independent of the noble gas ions used, the intrinsic compressive stress and plasmon energy increase sharply with the assisting ion beam energies up to 100 eV. Above this energy, the material properties depend on the mass of the ion. The highest values of stress (similar to 12 Cpa) and plasmon energy associated with the C1s core electron (29.5 eV) are of the same order of magnitude as those reported for highly tetrahedral amorphous carbon films. Structural results, however, indicate that the material is composed of a hard, highly stressed, and locally dense graphite-like network, i.e., a predominantly sp(2)-bonded material. It is suggested that, the ion bombardment compacts the film structure by reducing the interplanar cluster distances, generating high compressive stress and high local density. The differences in the properties of the films introduced by Ne, Ar, and Kr bombarding ions are also discussed. (C) 2001 American Vacuum Society.193971975