Design and control of tapping mode atomic force microscope in liquid utilizing optical pickup system

In this work, we propose a fluid tapping mode atomic force microscopy (AFM) implemented by a DVD pickup head. The use of DVD pickup head minimizes the volume of the hardware system, and thus reduces the measurement error caused by heat expansion. In order to realize the system mentioned above, we design a Q-controller to modulate the interaction force between the tip and the sample. Increasing the quality factor will overcome the problem with high damping ratio in the fluid which makes the probe hard to oscillate. Because of the reduction of the tip-sample force, the sample surface will not be hurt by the tip. Therefore, we can use the AFM to scan soft sample, and obtain more realistic topography. Traditionally, people use proportion-integration controller to control the system. Users need to tune this kind of controller manually, and hence the quality of the scan images is highly related to users´ experiences. To overcome this problem, we design an adaptive sliding-mode controller to improve the scanning capability and robustness.For testing the system capability, we will have a series of numerical simulations.