Effect of disk roughness and carbon impact energy on corrosion protection of magnetic recording films

Hard disks with different roughness levels have been coated with hydrogenated and/or nitrogenated carbon using magnetron sputtering and plasma beam based carbon guns. The plasma beam is generated by means of the self bias effect of an asymmetric, magnetically enhanced rf glow discharge. Acetylene is used in the sub-μbar pressure range. The ion impact energy was approx. 190 eV/carbon atom, as opposed to typically <10 eV for the sputtered atoms. Hard disks have been coated with 2–10 nm a-C:H. They were subjected to a hot–wet environment for 4 days. The corrosion was measured by the cobalt extraction test. For either mode of deposition it was confirmed that disk surface roughness considerably affects the corrosion protection achieved by the respective carbon top coat. Plasma beam deposition yielded a better corrosion protection than sputtering.