Dresden 2017 – wissenschaftliches Programm
CPP 29.7: Vortrag
Dienstag, 21. März 2017, 15:30–15:45, ZEU 250
Mechanical response of soft materials at the nanoscale and the moving-surface model — •Per-Anders Thoren, Riccardo Borgani, Daniel Forchheimer, and David B. Haviland — Nanostructure Physics, KTH Royal Institute of Technology, Stockholm, Sweden
The Atomic Force Microscope (AFM) is ideal for characterization of surfaces and interfaces at the nano-scale. Despite many different measuring techniques, understanding the interaction between the AFM tip and the surface of soft materials is challenging. In most cases a Hertzian contact-mechanics model is used, where only the elastic deformation of an indented surface is considered. This approach might be justified for stiff samples, but not for soft viscoelastic materials. We present a dynamic model of both the cantilever and the soft viscoelastic surface. The strong adhesion force and finite relaxation of the surface gives rise to distinct features in the oscillation amplitude dependence of the cantilevers dynamic force quadratures. These dynamic force curves are easily obtained from multi-frequency AFM measurements without assuming a particular interaction model, and they separately reveal the conservative and dissipative character of the tip-surface interaction. Numerical simulation of our nonlinear moving-surface model compares extremely well to the measured force quadratures, allowing us to extract the relaxation time of the viscoelastic surface.
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