Modification of tetrahedral amorphous carbon film by concurrent Ar ion bombardment during deposition

The surface morphology, mechanical and optical properties of tetrahedral amorphous carbon (ta-C) films by concurrent Ar ion bombardment during filtered cathodic vacuum arc (FCVA) deposition are investigated. The Ar ions were produced by an RF ion beam source at different ion energies ranging from 60 eV to 500 eV, in order to study the Ar ion-induced modification of ta-C films. Atomic force microscopy shows that all films are atomically smooth, with roughnesses (RMS) ranging from 0.17 to 0.43 nm. A rougher film surface has been attributed to a higher Ar ion energy. The compressive stress in the ta-C films ranges from 6.6 to 11.2 GPa and the microhardness from 34 to 67 GPa. A lower compressive stress and microhardness were observed at a higher Ar ion energy. The optical absorption spectrum shows that the edge has shifted to the lower photon energy side with the increasing Ar ion energy. The optical band gap decreases from 2.61 to 1.52 eV as the Ar ion energy is increased from 60 eV to 500 eV. The compressive stress, microhardness, optical absorption and optical band gap information suggests that the sp²-bonded carbon atoms in the sp³ matrix increase with the increasing Ar ion energy.