Simultaneous Measurement of Film Deformation and Friction Force During Shearing of Molecularly Thin Lubricants

The shearing deformation of the lubricant film was measured by using two-stage imaging ellipsometric microscope (TIEM) combined with an optical-fiber-based friction force measurement method. The TIEM enables high-lateral-resolution and real-time measurements of the thickness distribution of the nanometer-thick lubricant films during shearing. By adding a relay lenses illumination system and a high-power LED light source to the TIEM, a thickness resolution of 0.14 nm was achieved. The results of an experiment using this apparatus demonstrated that the asynchronous component of the probe oscillation, which is induced by friction force between the probe and lubricant or disk and corresponds to acoustic emission avalanches in the head-disk interface of hard disk drives, can occur when the probe is in contact with the lubricant film. The time constant of replenishment of the sheared lubricant film was of the order of hundreds of microseconds, which is much shorter than the timescale of diffusion phenomena.