In general, the
hardness is closely related with sp3 fraction. In the other words,
higher sp3 fraction, higher hardness. The friction coefficient is
closely related with sp2 fraction i.e. higher sp2 fraction, lower
friction coefficient. Thus, the CrCN coating (10 sccm) may possess
the highest hardness and lowest friction coefficient among these
coatings. Fig. 3c illustrates the N1s core level spectra and the fitting
curves of the coating, where the N1s peak is deconvolved into three
peaks with binding energies of 397.8 eV, 399.3 eV and 400.5 eV,
which corresponds to Cr–N, N–C, NQC, respectively [34–36]. This
indicates that the amorphous CNx is formed in the CrCN coatings
after carbon atoms were incorporated. To sum up, it can be seen
from the image there exist CrN, Cr2N, Cr7C3 and Cr2O3 phase in the
CrCN coating, which are consistent with the XRD analysis.