Experimental investigations of nanotribology and its applications to the head-disk interface of magnetic recording

This dissertation focuses on experimental investigations of nanotribology and its applications to the head-disk interface of hard disk magnetic recording. The objectives are to obtain a better fundamental understanding of microscale tribological phenomena such as nano-friction, nano-wear and nano-fatigue wear, then to characterize ultra-thin films and study the possibility of no-wear sliding conditions for magnetic recording by the proposed techniques and observed mechanisms. A Point Contact Microscope and a Friction Force Microscope are used for the investigations. They can damage a tested surface by either indentation or scratch with a heavy load on one hand, and measure the surface topography in the nanometer scale with a light load on the other hand.; It is observed that there exist two distinct friction regimes on the friction versus normal loading force curve when a sharp diamond tip slides on a solid surface: a low friction regime that causes no detectable wear, and a high friction regime with significant wear. Based on the results presented it appears that a no-wear contact sliding condition is possible if the loading force at all asperity contacts remains below the critical load for wear initiation.; Various nano-wear mechanisms are identified when diamond tips are used to plow or cut sample surfaces by raster scan with normal loads larger than critical loads for wear initiation. On single-phase materials, the materials are removed layer by layer, and the wear depth is usually linear with the increase of wear cycles. The materials are also removed layer by layer on thin films deposited on harder substrates, but the wear rates in the films are different from those in the substrate materials. For thin films, deposited on softer substrates, the materials are removed layer by layer at the beginning. But when the wear depth is over one fifth of the film thickness, usually sudden collapse or film breakthroughs occur. For polycrystalline materials, the material is removed bit by bit under a light load, layer by layer with different wear rates on grains and grain boundaries under a medium load, and piece by piece under a large load.; Nano-fatigue wear tests indicate that under the same testing conditions no fatigue wear is detectable on some materials, but significant fatigue wear is produced on the other samples. "Negative wear", i.e., a frictional material build-up, is found on silicon. A curve of critical load for nano-fatigue wear initiation versus wear cycles is proposed and measured to quantitatively characterize nano-fatigue wear. It is observed that the critical load decreases linearly with the logarithm of wear cycles, and there exists an endurance limit, where the decrease of critical load is not significant.; The proposed nanotribological characterization techniques are employed to evaluate the effects of hydrogen concentration on the mechanical and tribological properties of hydrogenated carbon films, which are widely used as protection overcoats on thin film magnetic disks. The effects of film thickness and substrate are also investigated. The results show that these characterization methods are very effective in determining properties of ultra thin films for the purpose of optimizing fabrication process parameters.