Water adsorption on lubricated fullerene-like CNx films

Humidity influences the tribological performance of the head–disk interface in magnetic data storage devices. In this work we compare the uptake of water of amorphous hydrogenated carbon (a-CHy) and carbon nitride (a-CNx) films, widely used as protective overcoats in computer disk drive systems, with two types of amorphous non-hydrogenated carbon (a-C and a-Csp2) films, and fullerene-like carbon nitride (FL-CNx) films. Carbon films were deposited on quartz crystal substrates by reactive dc magnetron sputtering in Ar/N2 discharges. After deposition, some of the films were coated with a 2-nm-thick layer of Z-tetraol, a lubricant used in hard disk devices. A quartz crystal microbalance placed in a vacuum chamber was used to measure the adsorption of water at room temperature and at pressures of water corresponding to relative humidities in the range RH = 0 to 90%. Water adsorption and desorption is fast, indicating that equilibrium with ambient humidity is reached on time scales of minutes, much faster than the time scales for fluctuations in ambient humidity. The amount of water adsorbed on the non-lubricated amorphous carbon films is significantly higher than that on the fullerene-like films. The presence of the lubricant influences water adsorption but its impact differs on different carbon films.