Research On Key Technologies Of The High-speed Atomic Force Microscope

Atomic force microscope(AFM)is an important tool for characterizing surfaces at micro and nanoscale.It has been widely used in basic research and semiconductor industry.However,with the development of the research in various fields,the slow imaging rate of AFM limits its application.Although many schemes have been established to improve imaging rate,these schemes often sacrifice other performances in pursuit of rate.In this paper,the existing structure and the time delay of key components of AFM are analyzed comprehensively,and the factors that restrict the imaging rate and other performances are analyzed.On this basis,a more universal highspeed atomic force microscope(HS-AFM)is prepared in this paper.By optimizing the load distribution of the scanners,the carrying capacity,the scanning range,and the imaging rate of the designed HS-AFM are balanced.The system can image a 40 g sample with an 80 Hz scan rate and a 15 μm scan range.The main achievements of this work are listed in the following:1.The working principle of each component in the AFM system was analyzed in detail,and the key components that have the great influence on the imaging rate and carrying capacity of the system were concluded.2.An X-YZ combined scanning high-speed AFM was presented.In this system,the separation design of the X-scanner and the AFM head makes the system suitable for high-speed imaging of the large-mass samples.The designed optical beam deflection method can ensure that the focus spot effectively tracks the movement of the cantilever,and this is important for wide-range imaging.3.A magnetic probe holder and the corresponding adjustment method were designed.The designed method can be used for laser alignment without adjusting the components in the optical beam detector.It simplifies the installation process of the probe,improves the usability of the instrument,and can avoid the degradation of the dynamic performance of the Z scanner.4.According to the requirements of high-speed scanning imaging,the improved schemes were designed for two raster-scanning methods,respectively.To improve the applicability of triangular raster scanning method for high-speed scanning,a scanning scheme with a moving average filter and background subtraction was proposed,which significantly reduces the imaging oscillation distortion caused by the higher harmonic of the triangular wave.To improve the applicability of sinusoidal raster scanning method for high-speed scanning,a velocity-dependent adaptive PI control algorithm was designed.In the controller,the feedback parameters were correlated with the linear velocity between the tip and sample,so that the system can automatically adjust the feedback parameters according to the different linear velocities and reduce the tracking errors caused by the different linear velocities.5.The performance of the designed system was systematically evaluated.The influence of each error source on the measurement results and the noise level of the system were measured.The response time of the key components in the system and the feedback bandwidth of the system were tested.The measurement accuracy of highspeed imaging of the system was evaluated.The results show that the maximum scanning range of the system is 15 μm×15 μm,the maximum line-scan rate is 100 Hz,and when the mass of the sample is about 40 g,the system can obtain a relatively real sample topography at 80 Hz scan rate,in this case the corresponding velocity between the tip and sample is 2.4 mm/s.