Correlation of surface, mechanical and microproperties of tetrahedral amorphous carbon films deposited under different magnetic confinement conditions
The effect of using a magnetic field to confine and focus the carbon plasma in a filtered cathodic vacuum arc (FCVA) deposition system was investigated in the preparation of tetrahedrally bonded amorphous carbon (ta-C) thin films. The design of the magnetic field was such that the plasma can be confined into a high-density focussed spot of 2 cm diameter or de-focussed into a wide beam of 10 cm diameter. The microstructural, optical, tribological and surface properties of the ta-C films grown in the high-density magnetic field were subsequently studied in detail. Under a high-density magnetic field, ta-C thin films were deposited on Si and quartz substrates. Laser-induced surface acoustic wave (L-SAW) measurements confirmed an increase in the Youngs Modulus and the bulk density of these films as compared to ta-C films deposited under no or low magnetic field [Phys. Rev. B 48 (1993) 4777; J. Appl. Phys. 79 (1996) 7239]. XPS results showed a high >85% sp3 content on the surface while combined EELS and Raman measurements showed high and constant sp3 content of >85% in bulk of all deposited films. An increase in optical bandgap was observed, from 3.6 to 3.9 eVas the density of the plasma (and hence, the films) was increased. In addition, the overall surface free energy was also observed to decrease from 44 to 40 dyn/cm. This confirms that under a high external magnetic field, the carbon plasma is confined and focussed, and is thus able to deposit highly densified ta-C thin films with high optical bandgap and low sp2 defect density. Tribological measurements showed that by comparing the high-density ta-C films with lower density ta-C films, the former have a better adhesion to the substrate, as well as a better coefficient of friction and wear rate.