HIGH FREQUENCY ANALYSIS OF A NON-CONTACT ATOMIC FORCE MICROSCOPY MICROCANTILEVER

The AFM imaging systems typically operate in three open-loop modes which are non-contact, contact, and tapping or intermittent. In this paper the high frequency analysis of a non-contact atomic force microscopy microcantilever has been discussed. In non-contact mode a moving cantilever slightly away from the sample surface is used. The cantilever is excited at or near its natural resonant frequency. Simplification of this problem is often realized by modeling the cantilever as a one-degree-of-freedom system such that the higher-order flexural modes are neglected. This lumped model has been successful in advancing material property measurement techniques, but for increasing the accuracy, three different model of one, two and three degree of freedom systems have been used. Important differences in the linear behavior of the lumped and distributed systems were found whenever the excitation frequency was near to or above the natural frequency of the first flexural mode. It has been shown that as a consequence of the difference in drive-point impedance, the effects of interaction stiffness and interaction damping are distinctly different in distributed and lumped systems. The influence of the lateral tip-sample force and the difference between the amplitude and the slope at the end of the beam, which cannot be modeled by a lumped model, were shown to be considerable. It has been concluded that the three degree of freedom model can better predict the dynamical behavior of AFM cantilevers against the one and two degree of freedom models and also with lumped models, viscous damping modeling and analytical solution derivation can be done easily which is not simply possible for distributed model.