Thickness dependence of properties and structure of ultrathin tetrahedral amorphous carbon films: A molecular dynamics simulation

Molecular dynamics simulation was performed to investigate the effect of thickness on the properties and structure of ultrathin tetrahedral amorphous carbon films (ta-C). The present simulation showed that both the density and residual compressive stress decreased with increasing the thickness of ultrathin ta-C films, which was in agreement with the experimental results. The gradient of properties with the thickness was dependent on the incident kinetic energy of deposited atoms; when the incident kinetic energy was 10 eV/atom, the slower gradient was observed. Further structural analysis indicated that the critical relaxation of highly distorted bond angles was responsible for the reduction of residual compressive stress in the films deposited at 10 eV/atom, while the joint relaxation of both the distorted bond angles and CC bond length led to the fast release of residual compressive stress in the films deposited at 70 eV/atom.