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. KEY WORDS: magnetic hard disks; carbon overcoats; quartz crystal microbalance; water absorption; heat of absorption 1