Bimodal atomic force microscopy (AFM) is an important branch of multi-frequency AFM, which can simultaneously obtain the surface morphology and properties of samples. However, the atomic-scale phenomena in the vibration process of bimodal AFM have not been observed due to the absence of atomic-scale model. In this paper, the molecular dynamics (MD) simulations are used to model bimodal AFM. A double springs oscillator model is used to describe the first two vibration mode of the AFM cantilever. By applying dual-frequencies excitation, the dynamics of the model tip and the tip-substrate interactions are observed. The amplitude, phase shift and the average force change of the tip obtained in the simulation were found to be consistent with the continuum simulation results. The effect of different amplitude ratios on the vibration response of the tip is analyzed and validated by experiments. This novel model makes it possible to simulate two vibration modes of cantilever at atomic scale in bimodal AFM.

中文翻译：

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双峰原子力显微镜的分子动力学模拟

双峰原子力显微镜（AFM）是多频原子力显微镜的一个重要分支，可以同时获得样品的表面形貌和性质。然而，由于缺乏原子尺度模型，双峰原子力显微镜振动过程中的原子尺度现象尚未被观察到。在本文中，分子动力学 (MD) 模拟用于模拟双峰 AFM。双弹簧振荡器模型用于描述 AFM 悬臂的前两种振动模式。通过应用双频激发，观察模型尖端和尖端-基板相互作用的动力学。发现模拟中获得的尖端的幅度、相移和平均力变化与连续介质模拟结果一致。通过实验分析和验证了不同振幅比对尖端振动响应的影响。这种新颖的模型可以在双峰 AFM 中在原子尺度上模拟悬臂的两种振动模式。