Adhesion at a granular surface

The adhesion of an ultrathin carbon nitride (CN) coating to the surface of a two-phase CoPt–SiO2 granular film heterogeneous at the 10 nm scale has been studied using nanoscratch techniques. The nanoscratch resistance was found to depend sensitively on the volume fraction of the two phases. Both nanoscratch experiments and complementary electron microscopy observations indicate that CN adheres much more strongly to the SiO2 matrix than to the CoPt granules resulting in enhanced tribological performance in SiO2-rich films. The relative weakness of the CN/CoPt interface is correlated to the absence of interfacial metal nitride formation. The adhesion of the CN coating to the granular surface, the intrinsic mechanical properties of the underlying granular film (nanoindentation hardness and modulus), and the vertical rms surface roughness of the granular layer are all fundamentally changed as the CoPt content reaches the percolation threshold.