Measurement of Adhesion Force and Elongation of Molecularly Thin Lubricant by Using Transient Response of SPM Cantilever

A novel method for identifying the adhesion force and dynamic elongation of molecularly thin lubricant coated over a DLC (diamond-like-carbon) surface was developed, in which those values were determined through the regression analysis of transient responses of an SPM (scanning probe microscopy) cantilever arising while separating from the target surface. The accuracy of measuring the cantilever displacement was greatly improved by mounting a silicon plate onto the cantilever as an optically reflective surface to produce a high quality image of the interference fringe pattern formed by Michelson interferometry. To analyze experimental transient vibration, a model to describe the separation process was introduced wherein the surface force decreases in proportion to the tip travel distance accompanying lubricant bridging. Based on this model, the adhesion force (contact force) and elongation of the lubricant were measured with varying retracting velocities. The results revealed that the contact force depends slightly on the velocity, and the lubricant elongates by several tens of times’ its original lubricant thickness.