Jing Gui

Water Adsorption on Lubricated a-CHx in Humid Environments

Humidity influences the tribological performance of the head-disk interface in magnetic data storage devices. In this work a quartz crystal microbalance was used to measure the uptake of water on amorphous hydrogenated carbon (a-CHx) films at room temperature and pressures of water corresponding to relative humidities of ∼25%. These experiments have used a-CHx films of varying thickness with and without lubricant. The lubricants used included Fomblin Z-03, Z-disoc, and Z-tetraol deposited on the surfaces of a-CHx films of various thickness. The amount of water adsorbed on the unlubricated a-CHx films is roughly independent of a-CHx film thickness. The presence of the lubricant reduces the amount of adsorbed water; however, the amount of water adsorbed in the presence of a lubricant does not depend significantly on the type of lubricant. These observations imply that water is adsorbed on the surfaces of the lubricant or the a-CHx film rather than being absorbed in their bulk.

Effect of Humidity on Lubricated Carbon Overcoats

An apparatus has been designed and built to measure the adsorption of contaminants on the surfaces of lubricated carbon overcoats such as those used on magnetic data storage media. The device is based on a quartz crystal microbalance housed in a high vacuum chamber and can be used to make rapid measurements of both the amounts and the rates of contaminant adsorption from the gas phase during exposure. Initial measurements of the adsorption of water during exposure to water vapor indicate that at room temperature and moderate humidity levels (∼50% RH) the amount of water on a surface is of the order of one adsorbed monolayer. Adsorption and desorption is remarkably rapid indicating that equilibrium with ambient humidity is reached on timescales of minutes. Finally, the comparison of H2O and D2O adsorption indicates that the adsorbed water either forms a hydrogen bonded network on the surface or is hydrogen bonded to some species exposed at the surface of the carbon overcoat.

High resolution electron energy loss spectroscopy study of Fomblin Z-tetraol thin filmsa)

High resolution electron energy loss spectroscopy has been used to obtain vibrational spectra of Fomblin Z-tetraol lubricant films on a commercial magnetic hard disk. The energy loss intensities of the ν(CF2) stretching mode are roughly independent of scattering angle up to angles of Δθ<14° indicating that they are excited by impact scattering. As a consequence there is little information that can be gleaned from the spectra about molecular orientation on the surface. A negative ion resonance enhances the energy loss cross section of the ν(CF2) stretching mode at the impact energy of EI=4eV. It is possible that this resonance is associated with the known sensitivity of fluorocarbons to electron induced dissociation. Annealing the disk sample to T=700K causes a dramatic decrease in the intensity of C–F stretching modes and an increase of the loss features due to C–H stretching. This indicates that the Fomblin Z-tetraol has decomposed and is exposing the a‐CHx overcoat on the magnetic media surface.