Simulation Of Probe Dynamic Behaviors In Multimodal Amplitude Modulation Atomic Force Microscopy

Multimodal amplitude modulation atomic force microscopy(AM-AFM)is one of the most widely used modes in the field of multifrequency atomic force microscopy.It is possible to simultaneously acquire the nanoscale topography,mechanical,electrical,magnetic properties and more information of the sample by exciting two or more eigenmodes of the probe microcantilever in multimodal amplitude modulation atomic force microscopy.It is of great significance to study the dynamic behavior of probe for obtaining high contrast images,optimizing topographical imaging and quantifying mechanical properties of samples in multimodal amplitude modulation atomic force microscopy.The dynamic behavior of probe is studied by numerical simulation in multimodal amplitude modulation atomic force microscopy,the work is mainly carried out in the following aspects:(1)The probe is equivalent to a point mass model,the dynamic responses for different modes of the probe microcantilever is studied and the sensitivity of different modes to the changes of the mechanical properties of the sample is analyzed.The results show that the higher mode phase can provide higher sensitivity to the change of the viscosity coefficient of the sample,and can significantly reduce the bistable effect of the probe.(2)The Euler-Bernoulli beam model is used to describe the microcantilever of the probe,the dynamic behavior of the probe and its imaging stability and contrast under different modes combination are studied.The research results show that: When the first eigenmode is the dominant mode,the higher the order of the additional mode is,the smaller the amplitude and phase variation will be on the transition between different interaction regimes.When the second eigenmode is the dominant mode,the imaging of the high modulus sample in the replusive regime will cause a strong subharmonic response,resulting in the instability of the probe motion.When the third mode is the dominant mode and the additional mode is the lower mode,the phase variation after the interaction regime is very small.The contrast study shows that the excitation scheme with the first mode as the dominant mode and the second mode as the additional mode has higher sensitivity to the change of the viscosity coefficient of the sample and lower peak repulsive force.(3)The effects of modal free amplitude and the mechanical properties of samples on the topographical imaging errors are analyzed in bimodal amplitude modulation atomic force microscopy.The results show that when the free amplitude of the second mode is small,the increase of the viscosity coefficient causes the first modal amplitude to decrease,which leads to the higher topography.When the free amplitude of the second mode is larger than a certain threshold,the increase of viscosity coefficient will lead to the increase of the first modal amplitude,resulting in the lower height of the topography.The smaller the sample modulus is,the smaller the amplitude response of the first mode will be,resulting in a higher topography,and the increase of the first modal amplitude will be affected by the change of the viscosity coefficient of the sample.(4)The Hertz model and Tatara model are used to study the probe dynamic behavior of the bimodal amplitude modulation atomic force microscopy in the liquid environment,and compare it to the dynamic behavior of the probe in the air environment,and the imaging contrast is analyzed in the liquid environment.The results show that the momentary excitation of the second mode by the interaction force between the tip and sample makes it difficult for the second mode to reach the steady state oscillation.The phase of the second mode is more sensitive to the change of the sample modulus.