IMAGING MATERIAL PROPERTIES BY RESONANT TAPPING-FORCE MICROSCOPY - A MODEL INVESTIGATION

The interaction of a cantilever performing a forced oscillation with a sample in a tapping-mode scanning force microscope is investigated wi thin a simple model. The tip together with the cantilever is modeled a s a periodically driven, damped harmonic oscillator. The viscoelastic sample is described by a friction force acting on the tip while it is in contact and a harmonic potential. The penetration of the probe and the phase shift of the oscillator due to contact with the sample are c alculated for various sample parameters. In particular, an approximate solution of the model equations for the phase shift is presented. Mor eover, a relation between the elastic constant of the model and the el astic modulus of a material is presented.