HARD DIAMOND-LIKE CARBON-FILMS PREPARED BY VARIOUS PHYSICAL VAPOR-DEPOSITION TECHNIQUES

Amorphous diamond-like carbon (DLC) films were prepared both by dual-ion-beam sputtering (DIBS) and by ion-beam-assisted d.c. magnetron sputtering (IBAM) of a graphite target under an argon atmosphere. The growing film was bombarded with 50-300 eV inert gas ions. Homogeneous, adherent films up to 0.8-mu-m thick were deposited on glass, steel and silicon substrates at a highest deposition rate of 5 nm min-1 observed with IBAM. This technique, as compared with DIBS, allowed the ion energy per deposited carbon atom to vary in a larger range and achieved a reduced stress level. The film properties were carefully examined and related to the process parameters in order to determine the growth conditions favouring DLC films with respect to poor quality carbon ones. The hardness reached 40 000 MPa and the morphology was very compact. The inert gas concentration rose from 1 to 2.5 at.% with film bombardment. The low hydrogen content (0.5-1 at.%) measured for DIBS films was increased to 10 at.% with IBAM. The density was strongly dependent on the ion bombardment parameters (ion energy, nature and flux). It ranged from 1.6 to 2.7 g cm-3 for the DIBS films and from 1.4 to 2.3 g cm-3 for the IBAM layers. Ball-on-disc tests performed in a laboratory environment pointed out a low friction coefficient varying from 0.08 to 0.1. Furthermore, the ion bombardment raised the optical indices.