Stiffness and Damping of Molecularly Thin PFPE Lubricant Bridging Between Magnetic Disk and Diamond Probe Tip

Spring constants and damping coefficients of a molecularly thin liquid bridge of PFPE lubricant intervening between a diamond probe tip and diamond like carbon (DLC) surface of a magnetic disk are identified through regression analysis of tip damping vibration. Perfluoropolyether (PFPE) lubricants having functional end groups were used to form the liquid bridge between the DLC surface and a probe tip with the notably small curvature radius of 0.1 μm. The tip was both retracted from and extended toward the disk surface at four different, progressive distances to attain varied elongation of the bridge, and was made to vibrate at each step to provide damping waveforms. By applying regression analysis to observed waveforms, the spring constant and the damping coefficient of the liquid bridge were identified. It is interesting to note that both the absolute value of the spring constant and the frequency-multiplied damping decrease with bridge elongation, and after reaching the minimum, those values begin to increase.