Scratch behavior of re-structured carbon coating by oxygen plasma etching technology for magnetic disk application

• ECR oxygen plasma etching was developed to prepare ultrathin carbon coatings.
• Scratch resistance of the carbon coating after oxygen plasma etching was improved.
• Oxygen plasma etching re-structured the coating in terms of the increase in sp3 bond.
• Re-structured overcoat on magnetic disk had good scratch behavior and smooth surface.

An oxygen plasma etching technology to prepare ultrathin carbon coatings for magnetic disk in electron cyclotron resonance (ECR) plasma system was developed. In the preparation process, as-deposited carbon coatings were etched by oxygen plasma to obtain re-structured carbon coatings. Scratch behaviors of the as-deposited and re-structured carbon coatings on silicon substrates were evaluated by atomic force microscope (AFM) scratch test. It was found that the scratch resistance of the re-structured carbon coating was improved. Then X-ray photoelectron spectroscopy (XPS) analysis showed that after oxygen plasma etching, the CC (sp2) content decreased from 55% to 17%, the CC (sp3) content increased from 33% to 58% and the CO content increased from 7% to 18%. It indicated that the oxygen plasma etching induced the increase of the sp3 bonding carbon, which contributed to the improved scratch resistance. Further transmission electron microscope (TEM) observation was conducted and the rising of the scratch resistance was inferred to be caused by the formation of the interlayer cross-linking after preferentially breaking the sp2 bond. Based on the above results, the ultrathin re-structured carbon coatings by oxygen plasma etching were prepared on uncoated magnetic disk substrates and showed a better scratch behavior and a comparable surface roughness in comparison with the commercial magnetic disk.