The effect of enhanced atomic mobility on the growth of hard carbon films was examined. Tetrahedrally bonded amorphous carbon films were deposited by condensing energetic carbon ions using an arc-discharge deposition method. The deposition temperature varied between 50 and 400 °C. The dependence of elastic properties on deposition temperature was examined by determining the frequency-dependent propagation velocity of ultrasonic surface acoustic waves induced by a laser. A remarkable decrease in elastic coefficient was revealed above the deposition temperature of 300 °C and complete relaxation was obtained at 400 °C. This observation was analyzed by using a simple model which was in turn supported by molecular dynamics simulations. The relaxation turns out to be a thermally activated, dynamic process with an activation energy of 0.57 eV. Possible relaxation mechanisms associated with the migration of atoms or defects on a growing surface are discussed.
Hirvonen, J-P., Koskinen, J., Kaukonen, M., Nieminen, R., & Scheibe, H-J. (1997). Dynamic relaxation of the elastic properties of hard carbon films. Journal of Applied Physics, 81(11), 7248-7254. https://doi.org/10.1063/1.365322