Abstract
We proposed application of van der Pol-type self-excited oscillation as the method to excite the probe-cantilever in AFM. The van der Pol-type self-excited oscillation presents the advantage that the oscillation frequency always coincides with the natural frequency of the probe-cantilever. Furthermore, it has another advantage: we can suppress the steady state amplitude of the cantilever to an extremely low level thanks to the nonlinear feedback effect, while maintaining stable self-excited oscillation. The quality of images obtained using vdP-AFM is comparable to that of pictures obtained using contact-mode AFM. Moreover, the non-contact state is maintained during themeasurement experiments. In each case, the distance between the sample and the probe-cantilever is greater than the vibration amplitude of the cantilever. This fact confirms results of the non-contact observation.
