DYNAMIC RELAXATION OF THE ELASTIC PROPERTIES OF HARD CARBON-FILMS

The effect of enhanced atomic mobility on the growth of hard carbon fi lms was examined. Tetrahedrally bonded amorphous carbon films were dep osited by condensing energetic carbon ions using an arc-discharge depo sition method. The deposition temperature varied between 50 and 400 de grees C. The dependence of elastic properties on deposition temperatur e was examined by determining the frequency-dependent propagation velo city of ultrasonic surface acoustic waves induced by a laser. A remark able decrease in elastic coefficient was revealed above the deposition temperature of 300 degrees C and complete relaxation was obtained at 400 degrees C. This observation was analysed by using a simple model w hich was in turn supported by molecular dynamics simulations. The rela xation turns out to be a thermally activated, dynamic process with an activation energy of 0.57 eV. Possible relaxation mechanisms associate d with the migration of atoms or defects on a growing surface are disc ussed. (C) 1997 American Institute of Physics.