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An original approach to a conventional sputtering process was examined where ta-C and a-C:N films were grown using a single low energy Kaufmann ion source and both a target and a substrate were positioned at the grazing angles to the incoming ions. In this configuration the ions (Xe and N) simultaneously bombarded the target and the growing film that was nucleating on Si substrate. The Xe and N ion energies were varied from 0.2 keV to a maximum of 1.0 keV.
In conventional sputtering, bombardment of a graphite target with energetic ions causes the release of carbon ions and neutrals with sputtering yields proportional to the energy of the incoming ions, their types and incident angles. There was a hypothesis that by positioning a substrate at grazing angles to the central axis of the ion beam the additional energy provided will be beneficial to formation of sp3 bonding in ta-C and rich N-sp3 C bonded sites in a-C:N films.
Theoretical atomic scale molecular dynamic simulation for Xe and N ions interacting with a pyrolytic graphite target was performed using SRIM prior to experiments. Experimental results revealed that it was not possible to fabricate quality ta-C but only sp2 rich polymeric a-C films when bombarded by Xe, nor quality a-C:N films but only films with N-sp and N-sp2 C bonded sites when bombarded by N ions. The failure to fabricate quality films was attributed to a secondary resputtering process. However, ta-C and a-C:N films were still synthesised when the substrate was positioned parallel to the axis of the ion beam flux. At this arrangement the increase of incident ion energy promotes sp3 and N-sp3 bonding formation in ta-C and a-C:N films. The optimal angle of the target to the axis of the ion beam flux was found to be 30 deg. The increase of ion beam energy to the experimental maximum of 1.0 keV resulted in higher sp3 fraction of up to 40 % in ta-C films and higher contribution from N-sp3 bonded sites a-C:N films.
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