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Abstract
Surface roughness of commercially available thin film magnetic recording disks was investigated using scanning tunneling microscopy (STM). The height distributions of the disk surfaces were obtained and the bearing area curves were examined by using "probability scaling". The deviation of the height distributions from Gaussian behavior was determined and skewness as well as kurtosis of individual disk surfaces were calculated. The surface roughness data from scanning tunneling microscopy were compared with those obtained from optical non-contact profilometry, and the dependence of surface characterization on scan size and sample interval was examined.
An environmental test chamber, which allowed independent control of temperature, humidity, pressure and gas composition, was built to study the tribology of the head/disk interface. Constant speed drag tests were performed in air, nitrogen and carbon dioxide for lubricated and unlubricated disks in various environmental conditions, including very low and very high humidity and elevated temperature. It was found that gas composition affects the frictional behavior of unlubricated disks at low humidity but not at intermediate and high levels of humidity. In addition, it was found that unlubricated disks exhibit lower friction and longer lifetime at intermediate levels of humidity than at very low or high humidities. The frictional behavior of lubricated disks was also found to be strongly affected by relative humidity and temperature but not by gas composition. A qualitative model for the effect of water condensation on the frictional behavior of unlubricated and lubricated disks was developed. The model suggests that for unlubricated disks, adsorbed water acts as a lubricant, protecting the unlubricated disk surface from direct solid/solid contact and direct exposure to the environment. For lubricated disks, the interaction between adsorbed water and lubricant molecules appears to be responsible for the effect of humidity on friction. In addition to the study of the effect of humidity, the effect of temperature on the frictional behavior of the head/disk interface was investigated in terms of surface energy, lubricant viscosity and mobility.
A newly developed phosphazene lubricant was explored as a potential lubricant for thin film hard disks. Contact start/stop, stiction and drag tests were performed on five disks lubricated with a typical cyclic phosphazene lubricant, X-1p, with a thickness in the range of 0.3 nm to 0.7 nm. The coefficients of friction and stiction were found to increase initially, then level off and reach a steady state value without a further increase after 2000 contact start/stop (CSS) cycles. In addition, three groups of disks with different lubricant thickness were evaluated under different environmental conditions. It was found that X-1p performs well on thin film disks with a lubricant thickness of about 0.5 nm at ambient conditions, high humidity conditions and elevated temperature conditions. A comparison of the tribological performance was also made between the phosphazene and perfluoropolyether lubricants, and the difference in the performance was discussed in terms of lubricant molecular structures.
