The Study Of Several Key Technologies In The Precision Control Of The Scanning Probe

The atomic force microscopy (AFM) is an important tool for micro-nanoscalecharacterization, measurement and manipulation. It has a wide range of applicationsin various fields, such as biology, physics, chemistry, materials, semiconductorindustry and etc since its invention, resulting from its sub-nanometer resolution. It isstill a challenge to obtain highly efficient, highly precise and accurate results for theAFM. The paper is centered with several key technologies in the precision control ofthe scanning probe. The experimental systems are built and a series of researchmethods are proposed to improve its imaging efficiency and accuracy in theapplication fields of imaging; the protein caliper method is reported in the applicationfields of single-molecule manipulation to realize the measurement accuracy of theproteins. The results of the research successfully realize the precisely controlling ofthe scanning probe. And the research shows new insights for the high-speed AFM andprecision measurement in single-molecue AFM. The main content of the paper arelisted as the following:1. The theory on the precison control of the scanning probe, including the modelof the cantilever, the performance of the piezo actuator, the function of the feedbackcontroller in Z direction, the rate of the acquisition system and so on, is systematicallyanalyzed. The factors affecting the measurement efficiency and the accuracy aresummarized.2. The resonant frequency of the piezo actuator is tested. The sinusoidal scanningmethod, combined with the new linear displacement correction method, is proposed.The new scanning technology can avoid the resonant perfomance of the piezo in highfrequency，improve the scanning rate and ensure the image resolution in XYdirections.3. The limitations of the feedback controller in the Z direction to the scanning rateare analyzed. The intelligent fuzzy PI controller is applied as the feedback controller.The controller can automatically select appropriate proportional and integralparameters according to the surface topography of the sample, corresponding to theincrease of the controller’s bandwidth.4. The system identification of the Z system is done and the rate adaptive controlmethod is put forward to accelerate the dynamic response of the Z feedback system.The control error in the Z direction can be linked with the scanning rate of the XY directions. So the scanning rate can be adaptive to the surface topography of thesample. The method can allocate the imaging time in each scanning point reasonablely.The image acquisition time is up to20s from the original100s, which is a significantadvancement.5. The protein caliper method is reported for the application of the AFM in thefield of single-molecule force spectroscopy. The differential testing method isdeveloped to achieve the different setups’s length per amino acid, which is a fixedvalue. Then the length is set as a caliper to calibrate the displacement of the AFMs inZ direction, in order to eliminate systematic errors that occur while using differentsetups. The method can help researchers achieve highly precise and accurate lengthchange measurements using different setups in protein mechanics studies. The methodimproves the accuracy of single protein force spectroscopy measurements. It providesa precise and accurate means of measuring force-induced protein conformationalchanges. And it improves the efficiency in data analysis.