No abstract

An ultrathin bilayer overcoat of silicon nitride and carbon (SiNx/C) providing low friction, high wear resistance, and high corrosion resistance is proposed for future generation hard disk media. The 16 Å thick SiNx/C overcoat consists of an atomically thin SiNx underlayer (4 Å) and a carbon layer (12 Å), fabricated by reactive magnetron sputtering and filtered cathodic vacuum arc (FCVA), respectively. When compared with monolithic overcoats of FCVA-deposited carbon (16 Å) and sputtered SiNx (16 Å), the SiNx/C bilayer overcoat demonstrated the best tribological performance with a coefficient of friction < 0.2. Despite showing marginally less electrochemical corrosion protection than monolithic SiNx, its ability to protect the magnetic media from corrosion/oxidation was better than that of an ∼27 Å thick commercial hard disk overcoat and 16 Å thick monolithic FCVA-deposited carbon. From X-ray photoelectron spectroscopy and Raman spectroscopy analyses, it was found that the introduction of the 4 Å SiNx underlayer facilitated higher sp(3) hybridization within the carbon layer by acting as a barrier and promoted the formation of strong bonds at the SiNx/C and the SiNx/media interfaces by acting as an adhesion layer. The higher sp(3) carbon content is expected to improve the thermal stability of the overcoat, which is extremely important for future hard disk drives employing heat assisted magnetic recording (HAMR).

Depositing an ultra-thin tetrahedral amorphous carbon (ta-C) protective coating on the surface of the recording heads in magnetic tape drives can improve the tribological problems at the head/tape interface. In this work the effect of pre-treatment of the surface of AlTiC substrate (main bearing surface of head in contact with tape) by C+ ions of moderate energy (smaller than 400 eV) on the structural and tribo-mechanical behaviours of the coated surfaces is studied. Sample preparation consisted of two separate stages of surface pre-treatment and deposition of the protective film, and was done by means of filtered cathodic vacuum arc. Structure of the ta-C film and its interface with the substrate were studied by transmission electron microscopy and time-of-flight secondary ion mass spectrometry depth profiling. The results revealed the formation of a broader, dense atomically mixed layer at the ta-C film–substrate interface of the pre-treated samples comparing with that of the samples without pre-treatment. Chemical characterization of thin diamond-like carbon coatings was conducted by means of x-ray photoelectron spectroscopy and the surface pre-treatment was found to have a remarkable effect on increasing the sp3 hybridization fraction in the ta-C overcoat. Nano-tribological properties of the treated surfaces were examined using ball-on-flat wear test at very low load (20 mN). There was a good correlation between the surface and structure characteristics of the film, and the tribological results and the pre-treated surfaces presented a very low coefficient of friction and higher wear life. The experimental results demonstrate the effectiveness of bombardment of the surface with C+ ions of moderate ion energy to improve the structural and tribo-mechanical properties of the protective ta-C films on the magnetic head substrate material.

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.

No abstract