Dynamic Contact AFM Methods for Nanomechanical Properties

Hurley, Donna C.; Killgore, Jason P.

doi:10.1002/9781118723111.ch5

Cited by 15 publications

(23 citation statements)

References 76 publications

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“…An increasingly important application of the Atomic Force Microscope (AFM) is the characterization of viscoelastic materials and interfaces, such as cell membranes and tendons [1][2][3][4], polymer blends and composites [5][6][7][8][9][10][11], the liquid-gas and liquid-solid interfaces [12,13], and suspended membranes [14]. The present trend toward higher scanning speeds [15,16] and higher resolution mapping of mechanical properties [17,18] necessitates more rapid tip motion and therefore a larger viscous contribution to the tip-sample force.…”

Section: Introductionmentioning

confidence: 99%

Modeling and Measuring Viscoelasticity with Dynamic Atomic Force Microscopy

et al. 2018

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The interaction between a rapidly oscillating atomic force microscope tip and a soft material surface is described using both elastic and viscous forces with a moving surface model. We derive the simplest form of this model, motivating it as a way to capture the impact dynamics of the tip and sample with an interaction consisting of two components: interfacial or surface force, and bulk or volumetric force. Analytic solutions to the piece-wise linear model identify characteristic time constants, providing a physical explanation of the hysteresis observed in the measured dynamic force quadrature curves. Numerical simulation is used to fit the model to experimental data and excellent agreement is found with a variety of different samples. The model parameters form a dimensionless impact-rheology factor, giving a quantitative physical number to characterize a viscoelastic surface that does not depend on the tip shape or cantilever frequency.

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Section: Introductionmentioning

confidence: 99%

Modeling and Measuring Viscoelasticity with Dynamic Atomic Force Microscopy

et al. 2018

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“…The tip–sample interaction can be modeled by a vertical and a horizontal spring and a dashpot accounting for dissipative forces [ 16 , 26 ]. Yet, these sophisticated models lead to rather complex equations with a large number of parameters.…”

Section: Theorymentioning

confidence: 99%

“…The wavenumber for the free flexural mode n can be calculated from the following equation describing the vibration of a cantilever of length L in free space [ 16 , 27 ]:…”

Section: Theorymentioning

confidence: 99%

“…A crucial parameter is the location of the tip on the cantilever, which strongly influences the calculation of the contact stiffness. Several methods to obtain this parameter, such as direct measurement via scanning electron microscopy [ 14 ] or identification of the value for which two different modes of the same cantilever yield the same contact stiffness (“mode crossing” method), may lead to different values [ 16 ]. This is a major weakness of current analysis methods.…”

Section: Introductionmentioning

confidence: 99%

“…Additionally, as in other techniques dealing with mechanical properties, the radius of the tip needs to be known. Alternatively, a calibration sample can be used [ 16 ]. Yet, this presupposes the exact measurement of the elastic modulus of the calibration sample.…”

Section: Introductionmentioning

confidence: 99%

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Application of contact-resonance AFM methods to polymer samples

Friedrich

Cappella

2020

Beilstein J. Nanotechnol.

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Contact-resonance AFM (CR-AFM) has been used in recent years for the measurement of mechanical properties of rather stiff materials, such as ceramics or metals, but also of some polymers. Compared with other techniques providing information on the mechanical properties of a sample, notably force–distance curves, CR-AFM has a much shorter acquisition time. This compensates in part the incomplete theoretical understanding of the underlying physical phenomena and of factors influencing the measurements. A commonly used method to analyze CR data requires the determination of the relative position of the tip, the calculation of the normalized contact stiffness, and the use of a calibration sample for the calculation of the elastic modulus of the sample. In the present paper, we propose an alternative procedure, based on approximations of the equations describing the system, which allows one to determine the elastic modulus of the sample as a parameter of the fit of the CR frequency as a function of the load. After showing that CR modes including scanning under continuous contact wear and damage the sample and/or alter the surface roughness, the results of point CR measurements on bulk and thin films are presented. Though Young’s moduli of bulk polystyrene and poly(methyl methacrylate) could be determined through the presented analysis, it is concluded that CR measurements are not appropriate for polymer samples. Major drawbacks are the bad resolution for moduli lower than ca. 10 GPa and the lack of a comprehensive physical model accounting for many factors affecting the dynamic response of a cantilever in contact with a sample.

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