Scratching resistance of diamond-like carbon coatings in the subnanometer regime

In order to examine the scratching resistance of ultrathin hydrogenated amo rphous carbon (a-C:H) coatings used in magnetic storage devices, a large nu mber of scratches with reproducible residual groove depths well below 1 nm has been examined. All measurements were carried out with an atomic force m icroscope and diamond-tipped cantilevers. The analysis of such shallow scra tches is made possible by means of an image processing procedure which mini mizes surface roughness effects using subtraction imaging. This method was applied to a series of sputter-deposited, fully aged, unlubricated amorphou s coatings with different hydrogenations. For low hydrogen content in the s puttering gas, the scratching resistance decreased with an increasing amoun t of hydrogen, in accordance with many other experiments. In contrast, an u nusual slight improvement of the scratching resistance for a further increa se of hydrogenation was obtained. (C) 1999 American Institute of Physics. [ S0003-6951(99)00734-2].