Measurement of nanotribological properties of molecularry thin lubricant by using optical fiber probe

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A novel method for measuring dynamic shear force at a high shear rate with precise gap control has been developed to clarify the rheological properties of confined perfluoropolyether lubricant. We call this new method "fiber wobbling method". In this method, an optical fiber is used as a probe and measuring amplitude and phase shift of the fiber shearing a lubricant film provides the rheological properties. The fiber wobbling method requires highly sensitive force sensing due to the small shear force generated by thin liquid films. In this study, we have demonstrated that a highly sensitive shear force measurement method with a minimum detection force of the order of sub-nN. This method uses an optical fiber probe as a microlens and measures the displacement of the laser spot on a position sensitive detector. In addition, we have demonstrated that a double-ended tuning fork-based force sensor is feasible to detect vertical force during sliding.