Large Oscillatory Forces Generated by Interfacial Water Under Lateral Modulation Between Two Hydrophilic Surfaces

We observed remarkable oscillatory forces with amplitude of 60-90 nN and periodicity of 3-4 water molecule diameters in an ambient environment between two silicon surfaces as the tip-sample distance decreased using the cantilever-based optical interfacial force microscope with lateral modulation. As the humidity increased, the oscillatory forces changed from being large at lower relative humidities, below 40, to progressively becoming smaller as the humidity went higher than 40. The frequency of oscillatory forces increased with the existence of lateral tip-modulation and with the slower approaching tip-speed. Its starting point distance has been found to originate from the topographic water structure.