Investigations of the corrosion protection of ultrathin a-C and a-C:N overcoats for magnetic storage devices

The thickness-dependent corrosion protection of carbon overcoats for magnetic hard disks can be analyzed by collecting X-ray absorption near edge structure (XANES) spectra at the Co L3-edge. Co is the main constituent of the protected magnetic media underneath. The spectra of the Co absorption edge display a strong peak for pure metallic, non-oxidized Co. This peak splits up into several sub-structures for oxidized Co. Therefore, XANES spectra provide a straightforward method to determine the overcoat thickness, leading to closed coverage and corrosion protection of the underlying material. A similar approach was carried out by X-ray photoelectron spectroscopy (XPS). Standard a-C:N overcoats deposited by magnetron sputtering (MS) were compared to a-C overcoats deposited by a novel filtered high current pulsed arc source (HCA) using a highly resolved imaging XPS system providing the combined measurement of XANES and XPS spectra in the same field of view. We determined that the HCA deposited a-C overcoats provide a closed coverage down to a layer thickness of 1.4 nm, whereas standard MS a-C:N overcoats do not cover the magnetic film completely until a thickness of 2–3 nm is reached.