以光學讀取頭系統實現之輕敲式液相原子力顯微鏡設計與控制

Abstract

In this thesis, we propose a fluid tapping mode atomic force microscopy (AFM) implemented by a DVD pickup head. The use of DVD pickup head replaces the quadrant photodiode and complex light path system of traditional optical-lever technique and minimizes the volume of the measuring system. In addition, a piezoelectric tube is used as a scanner which can perform three-dimensional motion. Both achievements make the AFM system more compact. Therefore, the measurement error caused by heat expansion will be reduced. Through adjusting the light path system and applying the controller, we can correctly measure the displacement of the probe in vertical direction in different condition. 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 caused by high damping ratio in the fluid which makes the probe hard to oscillate. Because of the tip-sample force reduction, the sample surface will not be hurt by the tip. Therefore, we can use the AFM to scan soft samples, and obtain more realistic topography. Traditionally, people use proportion-integration controllers to control the system. Users need to tune this kind of controller manually, and hence the quality of 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 have conducted a series of experiments.