| In recent years, with the rapid development of micro-electronics, micro mechanical and material science, imaging and detecting technology of micro/nano scale demand is becoming higher and higher. Traditional imaging and detection technology cannot meet us at the nanometer level within the scope of the observation and measurement. Imaging detection technology with nanometer level high resolution has become a challenge, and it affects us a lot in material microstructure and properties research. The resolution of Traditional acoustic and optical detection technology is low which can only reach micron grade. Atomic force microscopy and scanning probe microscope can only image the surface of the sample, but not the sub-surface or internal imaging of the sample.Ultrasonic atomic force microscope, which has nanoscale ultra high resolution and 3-d imaging ability, not only can be carried out on the sample surface imaging, but also can image the internal of the sample and measuring the sample of material mechanical properties such as elastic modulus and the contact stiffness. In this thesis, the following investigations on ultrasonic atomic force microscopy have been carried out:(1) related theory of ultrasonic atomic force microscopy are introduced, including samples of needlepoint contact theory, the local contact stiffness model; The dynamics of a cantilever beam theory model is set up to solve the free vibration state and contact with the sample characteristic equation and the resonance frequency of the cantilever beam system; Solve the contact tip sample contact rigidity according to the theory of Hertz model; Ultrasonic ultrasonic wave from the atomic force microscope is deduced for the sample from mixed with other impurities within the phase variation of the wave.Ultrasonic atomic force microscope is introduced how to measure the sample material elastic modulus method, and introduces the method of how to obtain the dynamic response of the beam according to the known samples under the condition of elastic modulus.(2) Established the finite element model of cantilever probe sample system simplified model, the dynamic characteristics of a cantilever beam under different status are analyzed by finite element simulation, including the cantilever beams under free vibration modal analysis and harmonic response analysis under loading. Free vibration modal analysis for a cantilever beam under the condition gets the first three order vibration mode and natural frequency. under the action of load harmonic response analysis analyzed the different effects of load, different contact stiffness, the influence of different tip position on the first resonance spectrum of cantilever, including the first resonant frequency and amplitude of the size effect. Get the first resonance frequency change due to the samples of different material samples of first resonance frequency and the same material in the tip into different depth of the sample.(3) established the simplified model which is in contact with the sample of the needle tip,and get the needlepoint samples contact surface contact stiffness distribution.with ANSYS finite element method for the static simulation. Simulation of different load and different depth of the internal structure and internal structure size, internal structure of different shape, different sample materials elastic modulus and other cases of tip and sample contact deformation and the change of the stiffness distribution, from the single quantity change to pinpoint the distribution of the contact stiffness of the sample;The changes of the center deformation and the contact stiffness of the tip sample contact surface are analyzed when the two quantities change to get their influences on the tip sample contact stiffness. |
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