Angle-resolved X-ray photoelectron spectroscopic study of the interface chemistry between ultra-thin a-C overcoat and the magnetic layer on magnetic thin film disks

Abstract

Abstract Ultra-thin amorphous carbon (a-C) overcoats of different thicknesses were sputtered on magnetic thin-film disks. The chemistry at the interface of the carbon overcoat and the magnetic layer was studied using Angle-Resolved X-ray Photoelectron Spectroscopy (ARXPS). For a-C overcoats thinner than 20 A, the interface was found to consist of metal carbides, metal oxides, and carbon–metal–oxygen complexes, most likely carbonyls. In marked contrast, a clean transition from metals to carbon with thin metal carbides at the interface was found for the 40 A a-C overcoat. The evolution of the C 1s, Co 2p, Ta 4f, and O 1s spectra as a function of carbon thickness and polar angle suggests that the carbon films form in a layer-by-layer fashion. The oxygen from the ambient can diffuse through carbon films when the carbon thickness is ≤20 A, and leads to the formation of metal oxides and carbonyls at the carbon–metal interface. Overlayer thickness of ∼40 A effectively inhibits oxygen diffusion and thus leaves the magnetic layer fully intact. This ∼40 A carbon thickness points to a required minimum coverage necessary to maintain a functionally viable magnetic hard disk as well as other systems that use carbon overcoats on polished metal substrates.