Plasma based nitrogen ion implantation to hydrogenated diamond-like carbon films

Surface modification of hydrogenated diamond-like carbon films prepared by C7H8 plasma is carried out by the implantation of nitrogen ions in pure nitrogen plasmas, changing the modification time from 0 to 30 min. A negative high voltage pulse with a value of 10 kV, a width of 10 µs, and a repetition rate of 2 kHz is applied to the substrate. The electrical resistivity decreases from 2.1 Ωcm to 0.08 Ωcm with increasing the modification time. The film hardness also decreases from about 11 GPa to about 7.5 GPa. The near surface region in the films modified by the nitrogen implantation is expected to contain the relative nitrogen content of about 10%, based on the results of X-ray photoelectron spectroscopy (XPS). The XPS measurements in the depth direction show that the nitrogen content depends on the modification time and the depth of nitrogen implantation is approximately 20 nm or more at the modification time longer than 18 min. The relative content of carbon increases from 80% on the surface to 99% except for the content of hydrogen and sp2 C bond is always dominant in the XPS. The estimated resistivity of the nitrogen ion implanted layer decreases to 0.008-0.013 Ωcm with increasing the modification time.