the cross-sectional microstructure of the NFC films used in our study. As can be seen,
the film is essentially featureless, tightly bonded to its substrate, and very smooth on the surface.
Micro-laser Raman spectroscopy has confirmed that the NFC coating was of a high-quality carbon film
with both the sp3-bonded diamond and sp2-bonded graphitic carbon. Mircrohardness test measurements
have shown that it had a Vickers hardness value of 1650 +1 20 kg/mm2.