Bonding and hardness in nonhydrogenated carbon films with moderate sp(3) content

Amorphous carbon films with an sp(3) content up to 25% and a negligible amo unt of hydrogen have been grown by evaporation of graphite with concurrent Ar+ ion bombardment. The sp(3) content is maximized for Ar+ energies betwee n 200 and 300 eV following a subplantation mechanism. Higher ion energies d eteriorate the film due to sputtering and heating processes. The hardness o f the films increases in the optimal assisting range from 8 to 18 GPa, and is explained by crosslinking of graphitic planes through sp(3) connecting s ites. (C) 2000 American Institute of Physics. [S0021-8979(00)08911-8].