Effect of humidity on the interactions between probes and ultra-thin liquid lubricant films in an environmentally controlled atomic force microscope

To achieve a magnetic recording density of 1 Tb/in², the required head-disk spacing is expected to be less than 2–3 nm. However, a critical issue in achieving such an ultra-low spacing is the dynamic instability of the head-disk interface (HDI), that is, the experimentally observed hysteresis of the flying sliders. It is important to clarify the interactive forces between the sliders and disk surfaces in a nanometer HDI. In addition, the adhesive forces between the thermally protruding magnetic head writer pole tip, which exists in the most commercially available recording head, and the lubricant film have also become very important. Therefore, in this study, the interactions between the probes of an environmentally controlled atomic force microscope (AFM) and ultra-thin liquid lubricant films were studied as a model experiment, resulting in the acquisition of fundamental knowledge related to the adhesive forces as well as the slider hysteresis. Subsequently, the effect of humidity on the force curve characteristics was investigated by varying the lubricant film thickness. As a result, it was found that the probe touchdown occurred earlier as the humidity increased, with its driving force suggested to be the force of the lubricant meniscus formed on the AFM probe. The probe touchdown occurred earlier for lubricants with a higher mobility. The adhesive force gradually increased with the humidity and was at its minimum for a one monolayer film thickness, independent of the lubricant materials. On the other hand, the elongation of the lubricant meniscus increased with the humidity. Therefore, the probe takeoff occurred later as the humidity increased. Accordingly, the hysteresis increased with the humidity and was mainly dependent on the elongation of the meniscus.