<title>Shear force characteristics and piezoelectric tip-sample distance control for NSOM</title>

Abstract

The shear force characteristics of NSOM (Near field scanning optical microscopy) probe is examined. The NSOM probe is modeled as a 2'nd order mass-spring-damper system driven by a harmonic force. The primary cause of the decrease in vibration amplitude is due to the damping force -- shear force -- between the surface and the probe. Using the model, damping constant and resonance frequency of the probe is calculated as a function of probe-sample distance. Detecting the amplitude and phase shift of the NSOM probe attached to the high Q- factor piezoelectric tuning fork, we can control the position of the NSOM probe about 0 to 50 nm above the sample. The feedback signal to regulate the probe-sample distance can be used independently for surface topography imaging. Three- dimensional view of the shear force image of a testing sample with the period of 1 micrometer will be shown.