Effect of pretreatment of Si interlayer by energetic C⁺ ions on the improved nanotribological properties of magnetic head overcoat

A thin layer of silicon has been used to improve the adhesion between amorphous carbon coatings and different substrates. However, the mechanism responsible for this improved adhesion to ceramic substrates, especially the Al₂O₃-TiC (AlTiC) substrate of magnetic recording heads, has not been well studied. In this work, this mechanism was investigated by conducting simulation and experimental tests. A tetrahedral amorphous carbon (ta-C) overcoat was deposited on Si-coated ceramic substrates by using filtered cathodic vacuum arc (FCVA) at ion energy of 100 eV. The chemical structure of the ta-C overcoats and interlayers as well as the nanotribological properties of the ta-C coated AlTiC substrate were studied by means of XPS analysis, nanoscratch and ball-on-flat tests. The formation of a Si-C network between the Si interlayer and ta-C overcoat as well as the formation of Al–O–Si and Si–O–C bonds between the interlayer and the substrate were found to be the two main phenomena which strongly bond the ta-C film to its ceramic substrate. Prior to deposition of the ta-C overcoat, surface of the Si interlayer was bombarded (pretreated) by C⁺ ions with ion energy of 350 eV. Effect of this pretreatment on the structure and tribological properties of the coated surfaces was also studied. The results revealed that pretreatment of the Si interlayer by energetic C⁺ ions is an effective way to form a mixed interface and enhance the formation of a larger number of strong chemical bonds between the substrate and the overcoat which improves the adhesion of the overcoat to the substrate. In addition, this method increased the sp³ content of the ta-C film which further improves the wear resistance and durability of the coating.