Approach interactions of scanned probes in dynamic pecking mode

Sharp, conical, metallic tips oriented perpendicular to the axis of a rod v ibrating in bending (pecking mode) are used as force sensors in scanned for ce probes and as optical scatterers in apertureless near-field optical micr oscopes. We have measured the displacement of such probes as a function of frequency and tip-sample separation during approach of the probe tip to a s olid-sample surface. We have also developed a nonlinear model describing th e attenuation of the probe motion during approach that takes into account t he variation of the force on the probe during each cycle of vibrational mot ion. The experimental data and the theory are in good agreement. The result s enable proper design of tip-sample-distance control systems, inference of material parameters, and an improved understanding of apertureless-near-fi eld-optical-microscope measurements. (C) 2001 American Institute of Physics .