Subnanometer scale tribological properties of nitrogen containing carbon coatings used in magnetic storage devices J.Continuity and topography of ultrathin diamond-like carbon films characterized by scanning electron microscopy/energy dispersive x-ray analysis and atomic force microscopy Carbon nitride films were grown on silicon and hard disk substrates using pulsed dc magnetron sputtering in a single-cathode deposition system. Substrates were mounted on a specially designed holder that allowed 45°tilt angle and substrate rotation about the surface normal up to 20 rpm. The influence of substrate bias, substrate tilt, and rotation on film growth and properties was studied. Films with the lowest rms surface roughness and corrosion performance were obtained at Ϫ100 V substrate bias with substrate tilt and rotation. Atomic force microscope scans over 10ϫ10 m 2 sampling areas showed that 50 nm thick CN x films prepared under these conditions have roughness almost four times lower than those prepared without substrate tilt and rotation. We observed a twofold reduction in corrosion damage for hard disk substrates with 1 nm thick CN x overcoats deposited with substrate tilt and rotation. This improved performance is likely a result of more efficient and uniform momentum transfer parallel to the surface during deposition in this configuration.

The influence of substrate rotary speed, species of reaction gases and flows on nanoindentation, nanoscratch fracture, and residual stress were explored on reactive sputtered nanoscale CrN/ZrN multilayered coatings. Hardness and critical fracture load as high as 32 GPa and 85 mN with desirable compressive stress were achieved for this model. A proper percentage of NH 3 in N 2 reaction gas was also proved to be of benefit to synthesize high-hard and fractureresistant CrN/ZrN coatings. The low-angle XRD patterns provided the layer modulation period of the coatings. A marked polycrystallite of two-cubic NaCl phase CrN + ZrN as well as probably hexagonal Cr 2 N with small modulation period corresponded to the enhanced mechanical properties.

Zr N ∕ Ti Al N multilayers with various modulation periods and ratios were grown by ion beam assisted deposition. The nanoscale multilayered modulation was confirmed by Auger electron spectroscopy. All multilayers possess higher hardness than the rule-of-mixture value of monolithic coatings. These properties critically depend on both modulation period and ratio. The multilayer with modulation period of 6.5nm and ratio of 2:3 displays the highest hardness (>30GPa) and critical fracture load (53.3mN). These improvements in properties are likely the result of nanoscale strain optimization as the evolution of layer crystallinity finally reaches the formation of (111) textures in all layers.

CN x / TiAlN multilayered coatings with different nanoscale modulation periods and ratio of CN x within each period were prepared by ion-beam-assisted deposition at room temperature. Auger electron spectroscopy ͑AES͒, x-ray diffraction ͑XRD͒, and nanoindenter and a profiler were used to characterize the microstructure and mechanical properties of the coatings. The low-angle XRD pattern and AES indicated a well-defined multilayered structure of the coating. Although monolithic CN x and TiAlN coatings formed amorphous and nanocrystalline structures, respectively, the CN x / TiAlN multilayers exhibited coherent epitaxial growth due to the mutual growth-promoting effect at small CN x layer thickness ͑Ͻ0.6 nm͒. At modulation period ⌳ = 2.83 nm and CN x thickness of 10% within each period, the multilayers exhibited strong TiAlN ͑111͒ and weak AlN ͑111͒ textures and showed the highest hardness ͑32 GPa͒, elastic modulus ͑409 GPa͒, and critical fracture load ͑65.7 mN͒.