The Research On Bimodal Atomic Force Microscopy Based On A Tuning Fork Probe

The development of the probe is an important improvement to the bimodal atomic force microscope(AFM),which is widely used in the simultaneous measurement of morphological,and material,properties.The probe can obtain better signal to noise ratio(SNR)and higher sensitivity through the change of its shape or sensing manner.Typical tuning fork probes,which adhere the tip to one of the tuning fork's prongs directly,have high sensitivity and high quality factor caused by the high stiffness of the tuning fork prong which otherwise easily destroys soft samples.The Akiyama probe,which symmetrically couples a long,soft,U-shaped cantilever to a quartz tuning fork,retains the advantages of these probes,overcomes the shortcoming caused by the high stiffness,and thus avoids the likely damage during scanning soft samples.However,the application of this probe is limited by little development in the principle of its complex structure.In this article,the research focuses on the fundamental of the Akiyama probe used as a bimodal AFM's sensor.A bimodal AFM system based on the Akiyama probe is built for scanning samples.The operating modes of the probe are realized and analyzed.A method to quantitatively analyze the power dissipation between the tip and the sample is proposed.The main work contains:1?The development,theories and challenges of the bimodal AFM are introduced.The advantages and difficulties of using tuning fork probes in the bimodal AFM are analyzed.The feasibility of building a bimodal AFM based on the new tuning fork probe with several advantages is discussed.2?A bimodal AFM system based on the new probe in different operating modes is designed and built.The parameters in the test are confirmed.The formation and impact on the output signal of the parasitic capacitance are studied.A realistic method to reduce the influence of the parasitic capacitance is mentioned.The resonance frequency and the quality factor shift caused by the change of temperature are measured.The best morphology imaging mode is analyzed and confirmed.The four operating modes are tested in the bimodal AFM system.The results show that the optimal operating mode is AM-OL mode that can analyze the power dissipation quantificationally.3?A multistage coupling model of the probe is built.The meanings and measuring methods of the coupling factors are mentioned.The relation between the electrical output's eigenfrequencies and the effective force gradient is inferred.The second eigenfrequency is insensitive to the effective force gradient.Finite element analysis is used to verify the model.4?Instead of the phase,the amplitude of the second eigenmode signal is used to analyze the power dissipation quantificationally.This method avoids the nonmonotonicity of the sine and simplifies the measurement.With the tests on a special sample,the method is repeatable.