Quantification of nanomechanical properties of surfaces by higher harmonic monitoring in amplitude modulated AFM imaging (original) (raw)
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We present a combined theoretical and experimental study of the dependence of resonant higher harmonics of rectangular cantilevers of an atomic force microscope (AFM) as a function of relevant parameters such as the cantilever force constant, tip radius and free oscillation amplitude as well as the stiffness of the sample's surface. The simulations reveal a universal functional dependence of the amplitude of the 6th harmonic (in resonance with the 2nd flexural mode) on these parameters, which can be expressed in terms of a gun-shaped function. This analytical expression can be regarded as a practical tool for extracting qualitative information from AFM measurements and it can be extended to any resonant harmonics. The experiments confirm the predicted dependence in the explored 3–45 N/m force constant range and 2–345 GPa sample's stiffness range. For force constants around 25 N/m, the amplitude of the 6th harmonic exhibits the largest sensitivity for ultrasharp tips (tip radius below 10 nm) and polymers (Young's modulus below 20 GPa). 883
Measuring the Size Dependence of Young's Modulus Using Force Modulation Atomic Force Microscopy
The Journal of Physical Chemistry A, 2006
The dependence of the local Young's modulus of organic thin films on the size of the domains at the nanometer scale is systematically investigated. Using atomic force microscopy (AFM) based imaging and lithography, nanostructures with designed size, shape, and functionality are preengineered, e.g., nanostructures of octadecanethiols inlaid in decanethiol self-assembled monolayers (SAMs). These nanostructures are characterized using AFM, followed by force modulation spectroscopy and microscopy measurements. Young's modulus is then extracted from these measurements using a continuum mechanics model. The apparent Young's modulus is found to decrease nonlinearly with the decreasing size of these nanostructures. This systematic study presents conclusive evidence of the size dependence of elasticity in the nanoregime. The approach utilized may be applied to study the size-dependent behavior of various materials and other mechanical properties. † Part of the special issue "William Hase Festschrift".
New modes for subsurface atomic force microscopy through nanomechanical coupling
Nature Nanotechnology, 2010
Non-destructive, nanoscale characterization techniques are needed to understand both synthetic and biological materials. The atomic force microscope uses a force-sensing cantilever with a sharp tip to measure the topography and other properties of surfaces 1,2 . As the tip is scanned over the surface it experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample. Here we show that an atomic force microscope can obtain a range of surface and subsurface information by making use of the nonlinear nanomechanical coupling between the probe and the sample. This technique, which is called mode-synthesizing atomic force microscopy, relies on multi-harmonic forcing of the sample and the probe. A rich spectrum of first-and higherorder couplings is discovered, providing a multitude of new operational modes for force microscopy, and the capabilities of the technique are demonstrated by examining nanofabricated samples and plant cells 3,4 .
Materials Characterization, 2002
Soft cantilevers, although having good force sensitivity, have found limited use for investigating materials' nanomechanical properties by conventional force modulation (FM) and intermittent contact (IC) atomic force microscopy. This is due to the low forces and small indentations that these cantilevers are able to exert on the surface, and to the high amplitudes required to overcome adhesion to the surface. In this paper, it is shown that imaging of local elastic properties of surface and subsurface layers can be carried out by employing electrostatic forcing of the cantilever. In addition, by mechanically exciting the higher vibration modes in contact with the surface and monitoring the phase of vibrations, the contrast due to local surface elasticity is obtained.
IEEE Transactions on Control Systems Technology, 2019
The ability of the atomic force microscope (AFM) to resolve highly accurate interaction forces, has made it an increasingly popular tool for determining nanomechanical properties of soft samples. Traditionally, elasticity is determined by gathering force-distance curves. More recently, dynamic properties such as viscoelasticity can be determined by relating the observables to sample properties, either by single-or multifrequency modulation of the cantilever. In this article, a model-based technique for resolving nanomechanical properties is presented. Both the sample and cantilever are represented by dynamic models. A recursive least squares method is then employed to identify the unknown parameters of the sample model, thus revealing its nanomechanical properties. Two sample models are presented in this article, demonstrating the ability to swap sample models to best suit the material being studied. The method has been experimentally implemented on a commercial AFM for online estimation of elastic moduli, spring constants and damping coefficients. Additionally, the experimental results demonstrate the capability of measuring time-or space-varying parameters using the presented approach.
Higher-Harmonic Force Detection in Dynamic Force Microscopy
2007
In atomic force microscopy, a force-sensing cantilever probes a sample and thereby creates a topographic image of its surface. The simplest implementation uses the static deflection of the cantilever to probe the forces. More recently, dynamic operation modes have been introduced. The dynamic modes either work at a constant oscillation frequency and sense the amplitude variations caused by tip-sample forces (amplitude-modulation or tapping mode) or operate at a constant amplitude and varying frequency (frequency-modulation mode). Here, we report on new operational concepts that capture the higher harmonics in either amplitude-modulation or frequency-modulation mode. Higher-harmonic detection in AM force microscopy allows the measurement of time-resolved tip-sample forces that contain detailed information about the material characteristics of the sample, while higher-harmonic detection in small-amplitude frequency-modulation mode allows a significant improvement in spatial resolution, in particular when operating in vacuum at low temperatures.
Langmuir, 2000
In atomic force microscopy, tapping-mode (also called intermittent contact mode) operation is known for its ability to image soft materials without inducing severe damage. For soft materials, the determination of the relative contributions of the topography and the local mechanical properties to the recorded image is of primary importance. In this paper, we report a systematic comparison between images and approachretract curve data. We show that this experimental comparison allows the origin of the contrast that produces the image to be straightforwardly evaluated. The method provides an unambiguous quantitative measurement of the contribution of the local mechanical response to the image. To achieve this goal, experimental results are recorded on a model system, a triblock copolymer, with a nanophase separation between elastomer and glassy domains. In this particular case, we show that most of the contrast in the height and phase images is due to variations of the local mechanical properties.