Surface free energy of cubic boron nitride films deposited on nanodiamond

Thin and thick cubic boron nitride (cBN) films were grown on nanodiamond (nanoD), using radio-frequency magnetron sputtering and plasma-enhanced chemical vapor deposition. The chemical composition of the cBN surface layer was nearly stoichiometric, which yielded an essentially pure cubic phase. The root-mean-square roughness of the nanoD and cBN films varied from 4 to 37.5 nm, depending on the pretreatment, method of deposition, and film thickness. The surface free energy of the cBN films with respect to the nanoD was determined by the contact angle measurements. The surface free energy was affected by surface roughness, but the surface energy of nanodiamond was always slightly higher than that of cBN films. This relationship between the surface free energies has important implications for material compatibility and possible local heteroepitaxial growth of cBN on nanoD.