Scanned-probe lateral-force determination of fluid-dynamic effects near a solid surface in air

A calibrated method for the experimental determination of dynamic lateral force using a scanned probe in air has been applied to the measurement of force vs distance as the probe tip approaches a solid surface. The probe is a fused silica fiber vibrated with its axis perpendicular to the surface in a configuration commonly used for distance regulation in near-field scanned optical microscopes. Quantitative agreement of a fluid-dynamic model with the approach data demonstrates that the effects of fluids between the probe and the surface dominate the force on the probe in the optical far field. A two-layer fluid model indicates that fluid-dynamic effects must also be considered in lateral-force determination in the optical near field. (C) 1996 American Institute of Physics.