Cantilever Dynamics And Imaging Analysis Of Atomic Force Microscope In Liquid

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.