Nonuniform Distribution of Molecularly Thin Lubricant Caused by Inhomogeneous Buried Layers of Discrete Track Media

A method of estimating the thickness distribution on a surface with inhomogeneous buried layers is presented. It revealed that the lubricant distributes nonuniformly on discrete track media (DTM). First, the estimation method was theoretically developed. To balance the disjoining pressures of the lubricants in the track and off-track regions, the lubricant takes different film thicknesses in the two regions because the regions consist of different materials and have different intermolecular interactions. Formulating the balance of the disjoining pressures by using the theory for intermolecular force, we obtained the thicknesses in the two regions. Next, the validity of the theoretical estimation was experimentally verified. When a nonpolar lubricant was applied to a nanometer-thick oxide layer on a silicon surface, which was locally fabricated by probe oxidation, AFM images showed that the lubricant height in the oxide region decreased and the thickness distribution agreed well with that predicted by theory. Using the developed theory, we estimated the lubricant thicknesses on DTM. Even if lubricant is uniformly applied onto the disk, it moves from the off-track to track regions due to the pressure balance. Thus, the theory predicts that the lubricant is thicker in the track regions than the off-track region at equilibrium.