Contact to Sample Surface by Self-excited. Micro-cantilever Probe in AFM

AFM (atomic force microscope) has widely used in the fields of surface science, biological science, and so on. The measurement of biological samples requires the detection without contact between the samples and the micro-cantilever probe, because the contact damages the observation objects. The self-excitation technique for the micro-cantilever probe is a powerful tool for the detection in a liquid environment where the micro-cantilever has a very low quality factor Q. In the previous study, we propose an amplitude control method for a van der Pol type self-excited micro-cantilever probe by nonlinear feedback based on bifurcation control. In this presentation, we experimentally investigate the characteristics of detection depending on the magnitude of the response amplitude of the micro cantilever probe by using our own making AFM. We change the response steady state amplitude of the micro-cantilever probe by setting the nonlinear feedback gain to some values. Based on frequency modulation method, we detect the sample surface and discuss the effect of the magnitude of the amplitude on the performance in air. It is concluded from experimental results that the micro-cantilever probe with small amplitude under high gain nonlinear feedback control enhances the detection performance of AFM.