Design Of The Tapping-mode Afm Based On Higher-order Resonance

Among the great varieties of SPMs, Atomic Force Microscopy(AFM) is most widely used. AFM can be used to observe many kinds of materials including conductors, semiconductors, nonconductors, which can be operated in air, liquid or vacuum. It performances well and its applicability is better. Base on the principle of AFM, a set of tapping-mode AFM based on higher-order resonance has been developed.The following is the primary design which has been completed. In the section of main structure of AFM, the base and the head design of tapping-mode AFM have been described in detail. In the base design, the paper describes the composition and operation principle of three-dimensional piezoelectric ceramic scanner which is the system's key component. Meanwhile, the paper designs the probe-sample approximation system, this system has achieved nanometer step through the screw micrometer head driven by the precision DC-motor. The emphases of head design are detection of silicon-cantilever probe deformation and design of laser alignment sector. In the section of tapping-mode probe driven unit, a driving method of tapping-mode probe based on DDS has been proposed, the probe driven circuit based on the AD9833 has been designed, and the output frequency characteristics and driving capability are discussed finally. Quadrant photoelectric detection unit, signal processing circuit unit, and DC voltage signal acquisition unit are designed according to the characteristics of the system signal in the control signal detection, processing and acquisition section. Finally, the paper describes the methods of key alignment in detail, tests the noise and the frequency response of each part of circuit system, and analyzes the performance of the whole system.The tapping-mode AFM based on higher-order resonance which has been developed in this paper has established a good platform for the future researches, such as the scanned image contrast of primary resonance probe and higher-order resonance probe, testing the higher-order resonance probe scanning technology's superiority.