| With the development of nano-technology, scanning probe microscopy (SPM), especially atomic force microscopy (AFM), has been the most widely demanded and applied tools for researchers to pursue more ambitious goals, and has actually become the indispensable instruments for nano-scientists and engineers. Besides the stabilization of the instrument itself, the simplicity of its operation, the easiness of maintenance, the expansion of its application sphere and the trend of it becoming an industry have aroused more and more concerns.In this thesis, a new concept of digital AFM has been put forward, and a series of breakthrough of digital AFM has been gained based on the systematic research of its principle and method, which expands AFM's application sphere and lays good foundation for the popularization of AFM in China.On the basis of analyzing the current situation of AFM's research and application nationally and internationally, the paper makes thorough theoretical analysis into the defects of AFM made in China. The feedback control system of AFM and the action law of tip-sample feeding mechanism are emphatically analyzed in this thesis. We developed the new method of feedback control system which is implemented by incremental PID control, while another new method of feeding mechanism which is implemented by stepper motor based on the research of approximation law of tip-sample and kinds of other feeding mechanisms, which make AFM forward a long way on the technique function, automation and stability, which will help the atomic force microscopy expediently and effectively used in various scientific areas. And the development of digital AFM not only has important theoretical significations, but also has a great prospect for practical applications.The research content and achievements of this thesis are as follows:On the basis of the theoretical researches, we developed the new method of digital AFM. With the coming of the over-all digital time, the research of digital scanning probe microscopy has become increasingly important. At the present time, most SPM in China only stay on the level of analog quantity control, which is the intrinsic reason that the instrument can't be further refreshed. The digital technique, therefore, should be used in the AFM system, for increasing stability of the instrument itself, the simplicity of its operation, and the function of the instrument.We have constructed a digital PID feedback control system of AFM. At present, analogy PID control only with the merit of fast reaction speed, while the shortcomings are low precision, week ability of anti-interference, complex circuit construction, is widely used in most AFM in China. However a sensitive, highly active, precise, steady and reliable feedbackcontrol system is actively demanded in AFM system, recording to operating principle of AFM. Though the research of digital PID control of AFM has gain a certain development, the PID control is implemented by the technique of DSP, which not only increase the cost of AFM, but also has difficulty technique. We develop a new method of digital PID control in which AFM is implemented by the technique of computer. The control algorithms will be changed so long as change the programs in the computer, which brings a great flexibility. Some questions that aren't settled in the analogy PID for a long time, thus can be successfully resolved. Further more, the computer is formerly a part of the AFM system, which not only reduces the cost but also enhances the instrument's utility and simplification.A feeding mechanism, in the charge of stepper motor, adjusting the spacing interval between the sample and the tip has been accomplished. The computer is in control of the stepper motor driver to output impulse signals that are used to drive the stepper motor. The sample, therefore, is automatically moved to approach the tip, which not only enhances the simplicity of the operation, but also improves the automation of the system.A new sort of data acquisition board is used in the AFM system. And we optimized the so... |
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