Tribological and mechanical properties of CN ultra-thin overcoat films and their influence on the underlying magnetic media

Ultra-thin nitrogenated carbon overcoats have attractive tribological properties that make them favorable for protective coatings for rigid magnetic disks. The wear characteristics of the overcoat are clearly influenced by the nitrogen content and thickness of the overcoat. In addition, as the magnetic media thickness is reduced to approximately 10 nm for future extraordinarily high density recording, the influence of the ultra-thin overcoat on media magnetic properties may become important. In this study the main parameters of interest were the nitrogen content and the overcoat film thickness. These two parameters were systematically varied to evaluate their influence on both the tribological performance of the overcoat. The nitrogenated overcoats, with thicknesses ranging from 2 to 10 nm, were all deposited on a 20 nm thick layer of Co. The tribological and mechanical properties of the overcoats were evaluated with the use of nanoindentation and nanowear test procedures. The vertical resolution, approximately 1 nm, of the Nano Indenter II allowed examination of tribological properties of ultra-thin films on the order of 2 nm in thickness. Several important properties of the overcoats have been determined as a function of nitrogen content and overcoat film thickness. Included among these are the adhesion of the overcoat to the magnetic layer as well as the surface roughness and the coefficient of friction.