The sp3 bond fraction in carbon films prepared by mass-separated ion beam deposition

Amorphous carbon films were prepared by mass-separated ion beam deposition (MSIBD), and the sp(3) bond fraction was examined by electron energy loss spectroscopy. In previous studies, the carbon ion current was low, and the vacuum pressure during deposition was insufficient. There seems to be an influence of residual hydrogen gas, and damage to the film by the high-speed neutral species produced by the charge exchanging with residual gas molecules during ion transportation. In this study, an MSIBD system was developed with a high ion current density under ultra-high vacuum conditions. Typical carbon ion beam density was 0.2 mA/cm(2) at an energy of 100 eV under a vacuum pressure of 6 x 10(-7) Pa. The sp(3) bond fraction of the carbon film, which was prepared under a vacuum pressure of 10(-5) Pa during deposition, was 34%. However, that of the film prepared under 10(-7) Pa reached 83%. It was thought that the impact of the high-speed neutral carbon species on the films accounts for the degradation of the sp(3) bond fraction. The dependence of the sp(3) bond fraction on the carbon ion energy was examined. The maximum sp(3) bond fraction of 84% is obtained at an ion energy between 75 and 100 eV. (C) 2001 Elsevier Science B.V. All rights reserved.