Nanotribological properties of ultra-thin carbon coatings for magnetic storage devices

Abstract

In the magnetic storage industry ultra-thin amorphous carbon coatings are commonly used to protect read/write head and magnetic media against corrosion and mechanical damage. In our work, the mechanical properties of different carbon coatings produced with magnetron-sputtering (MS) and filtered high-current pulsed arc (HCA) are compared by using an AFM-based scratching technique. The presented method allows the generation and analyzation of very shallow scratches with residual depths of only a few Ångstroms and even below. This enables a determination of the scratch resistance of ultra-thin coatings even in the nanometer range widely independent from the hardness of the substrate. A comparison to X-ray reflectivity measurements exhibits a clear correlation between the scratch resistance and the mass density of the investigated coatings. It is shown that a variation of the film thicknesses from 5 to 2 nm has very different effects on their mechanical properties and strongly depends on the deposition technique and temperature. In tribological respect it turns out that the HCA films are superior to the MS films even if prepared at typical disk deposition temperatures of approximately 200 °C.