【作者】 牛顿；

【导师】 黄文浩； 陈宇航；

【作者基本信息】 中国科学技术大学 ， 机械电子工程， 2011， 硕士

【摘要】 原子力显微镜柔性的工作环境以及对各种样品良好的适应性,使得它在生物科学、材料科学、物理化学等众多领域有着重要应用。科技的飞速发展,对于原子力显微镜提出了更高要求。而相对于真空和大气环境下较为充分的研究,液相原子力显微镜的研究显得不足,特别是作为阐明成像传感机理、合理解释数据基础的原子力显微镜悬臂梁的动态特性亟需深入的研究。本文围绕液相原子力显微镜悬臂梁的动态特性,综合利用实验、理论与有限元仿真,进行了以下几个方面的工作:1.压电激励原子力显微镜悬臂梁在液体中自由振动时,频率响应曲线中干扰峰的产生原因与其消除。实验结果表明,激励悬臂梁的压电陶瓷自身的共振与压电陶瓷-悬臂梁的接触界面对干扰峰的产生起主导作用;而通过在压电陶瓷与悬臂梁接触界面间添加弹性吸振层能够简单有效地消除由接触界面产生的干扰峰。2.液体中原子力显微镜悬臂梁靠近平整基底过程中的动态特性。结果显示,去离子水中悬臂梁在靠近平整基底过程中存在两种典型的振动行为,分别对应于小自由振动振幅下的约束水膜主导作用和大自由振幅下的排斥针尖样品作用力主导作用。3.液体中原子力显微镜悬臂梁靠近一定结构基底过程中的动态特性。3D模式显示,水中光栅结构约束的水膜对悬臂梁的振动有明显影响。即便在相同设定条件下,探针在光栅台阶单元和槽单元的振动状态也可能不同。4.结合实验,本文建立了悬臂梁振动的质量-弹簧-阻尼模型,分析了约束水膜和流体阻尼的作用与性质,并进行了相应的系统和有限元仿真,均与实验符合良好。本文从自由振动、靠近平整样品到靠近一定结构样品,研究了原子力显微镜悬臂梁在液体中的振动特性,进而选择合适样品进行成像,分析了悬臂梁动态特性、主要成像参数对液相原子力显微镜成像的影响。这些结果对于阐明液相原子力显微镜成像传感机理、合理解释原子力显微镜数据有一定意义。更多还原

【Abstract】 Atomic force microscopes (AFMs) have wide applications in the biology, physics, chemistry, materials and other fields for its applicability to different samples and working environments. Science developments put forwards higher demands for the AFMs. However, compared to the application in air, less is known when AFM is operated in liquids, especially cantilever dynamics, which is the background for the understanding of the imaging mechanism and reasonable explanations of the acquired data. In this paper, combined with methods of experiments, theory modeling and finite element simulation, works as following conducted:1. Origin and elimination of spurious peaks in the frequency response curves for free vibrating piezo-driven AFM cantilevers in liquid. It was found that the spurious peaks are dominated by two main factors, i.e., the intrinsic resonance of the shaker-piezo and the contact interface between the cantilever base and the shaker-piezo. Clean resonance curves could be obtained effectively with elastic film added in the interface.2. Cantilever dynamics when the probe is vibrating near a flat substrate in liquid. Results show that there are typically two general dynamic types of behavior in deionized water when the probe approaches to the flat substrate, which cooresponding to the dominating function of the confined water film when small free amplitude is applied and the repulsive tip-substrate force when free amplitude is large enough.3. Cantilever dynamics when the probe is vibrating near the structured substrate in liquid. 3D mode experiments show that the oscillation characteristics can be systematically deviated on the step element and the bottom element of the grating even with the same controlling parameters. Different amounts of hydrodynamic contributions are presented on different microstructures.4. Based on the experiments, mass-spring-damper model of the cantilever vibration is established. Functions and qualities of the confined water film and the fluid damping are analized. Corresponding system and finite element simulations are conducted, which show well consistent with the experiments.With the combination of experiments, theory modeling and finite element simulation, from free vibration state to oscillating near flat substrate and then near structured substrate, AFM cantilever dynamics and its influence on imaging in liquid were studied. Researches of the cantilever dynamics are of significance for the accurate understanding of the AFM imaging and sensing mechanism and reasonable explanation of the acquired AFM data.更多还原