Structural characterization of ultrathin diamond-like carbon overcoats for high areal density magnetic recording

Abstract

This paper reports a comprehensive study on chemical structures of ultrathin diamond-like carbon (DLC) overcoats for high areal density magnetic recording. The DLC overcoats were fabricated in a range of thicknesses between 0.5 and 5.0 nm with Si interlayer on NiFe substrates using a pulsed filtered cathodic vacuum arc (PFCVA) technique. The overcoat thicknesses were accurately determined by high–resolution transmission electron microscopy and wavelength dispersive X-ray fluorescence techniques. The surface morphology, chemical composition, microstructure, and tribological properties were systematically investigated by atomic force microscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, Raman spectroscopy techniques, and a reciprocating wear test. The results showed that the surface morphologies of DLC overcoats were atomically smooth with a root mean square surface roughness below 0.23 nm. The DLC overcoats had high sp3 bonds fraction. However, as the overcoat thickness was thinner than 1 nm, the sp2 bonds fraction suddenly increased resulting in a significant increase in the coefficient of friction. The obtained results demonstrated the limitation of the thickness of the DLC overcoat fabricated by the PFCVA technique as a protective coating for high–density magnetic storage devices.