An AFM Study of corrosion on rigid magnetic disks

The corrosion susceptibility of a cobalt-based magnetic alloy as a function of overcoat film thickness at 20 °C and 50% relative humidity is investigated using atomic force microscopy. The overcoat films include ion beam-deposited nitrogenated carbon (IBDN), and sputter-deposited silicon carbide (SiC) and silicon nitride (SiN_x). In all cases, corrosion decreases with increasing overcoat film thickness. The critical overcoat film thickness for corrosion inhibition is approximately 25, 25 and 20 Å for IBDN, SiC and SiN_x, respectively. However, larger corrosion particles are found for IBDN and SiC with increasing thickness just below the critical thickness for coverage.