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ABSTRACT: In this chapter, we review the fundamentals of dynamic force microscopy (DFM) and dynamic force spectroscopy (DFS) focusing
on applications in ambient conditions. More specifically, we analyze the basic principles of the two important driving mechanisms
that are used in AFM imaging modes:the amplitude-modulation technique (“tapping mode”) and the frequency-modulation technique.
From this starting point, analytical descriptions of the two modes are developed. The theory is then applied in conjunction
with numerical simulations to various situations occurring while imaging in ambient conditions. Finally, we present methods
for the continuous measurement of the tip–sample interaction forces during the approach towards the sample surface using DFS.
12/2010: pages 71-94;
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07/2010; , ISBN: 9783527628155
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ABSTRACT: We report experiments of atomic stick-slip friction on graphite as an explicit function of surface temperature between 100 and 300 K under ultrahigh vacuum conditions. A statistical analysis of the individual stick-slip events as a function of the velocity reveals an agreement with the thermally activated Prandtl-Tomlinson model at all temperatures. Taking into account an explicit temperature-dependence of the attempt frequency all data points collapse onto one single master curve.
Physical Review Letters 06/2010; 104(25):256101. · 7.37 Impact Factor
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ABSTRACT: A spectral analysis method has been recently introduced by Stark et al (2002 Proc. Natl Acad. Sci. USA 99 8473-8) and implemented by Sahin et al (2007 Nat. Nanotechnol. 2 507-14) using a T-shaped cantilever design, the torsional harmonic cantilever (THC), which is capable of performing simultaneous tapping-mode atomic force microscopy imaging and force spectroscopy. Here we report on numerical simulations of the THC system using a simple dual-mass flexural-torsional model, which is applied in combination with Fourier data processing software to illustrate the spectroscopy process for quality factors corresponding to liquid, air and vacuum environments. We also illustrate the acquisition of enhanced topographical images and deformed surface contours under the application of uniform forces, and compare the results to those obtained with a previously reported linear dual-spring-mass model.
Nanotechnology 02/2010; 21(7):75702. · 3.98 Impact Factor
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ABSTRACT: The frequency-modulation (FM) mode was introduced in 1991 to increase the sensitivity of dynamic force microscopy in vacuum.
However, it is also possible to use this technique in air and liquids which has several advantages compared with the conventional
amplitude-modulation (AM) (“tapping”) mode. In this chapter, we review the fundamentals of the FM mode and analyze its basic
theoretical background. Finally, we present experimental results obtained in air and liquids and compare them with the conventional
AM technique.
12/2009: pages 3-21;
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ABSTRACT: Atomic resolution images in noncontact atomic force microscopy (NC-AFM) reflect planes of constant frequency shift. To draw
conclusions on the chemical activity at specific surface sites, however, the force acting between tip and sample should be
known locally rather than the frequency shift. This is not an easy translation due to the nonlinear nature of the relationship
between the two.
To overcome this problem, several groups have developed an extension to NC-AFM, dynamic force spectroscopy, which allows the
precise, distance-dependent measurement of tip–sample forces. The forces are determined from frequency shift vs. distance
curves by mathematical analysis. By combining many of these curves in a raster grid, the full three-dimensional surface force
field can be probed with atomic resolution as it extends into vacuum. This chapter reviews experiments performed on NiO, NaCl,
KBr, and graphite that illustrate the strengths and weaknesses of the different experimental approaches as well as the type
of results that can be obtained.
09/2009: pages 95-119;
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ABSTRACT: Experiments performed by friction force microscopy at atomic-scale surface steps on graphite, MoS2, and NaCl in ambient conditions are presented. Both step-down and step-up scans exhibit higher frictional forces at the edge, but distinguish in their load dependence: While the additional frictional force due to the step edge increases linearly with load if the tip has to jump a step up, it remains constant for downward jumps. This phenomenon represents a universal effect that can be explained in terms of a modified Prandtl-Tomlinson model featuring a Schwoebel-Ehrlich barrier at steps.
Physical Review Letters 01/2009; 101(24):246105. · 7.37 Impact Factor
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ABSTRACT: Tribology-the science of friction, wear and lubrication-is of great importance for all technical applications where moving bodies are in contact. Nonetheless, little progress has been made in finding an exact atomistic description of friction since Amontons proposed his empirical macroscopic laws over three centuries ago. The advent of new experimental tools such as the friction force microscope, however, enabled the investigation of frictional forces occurring at well-defined contacts down to the atomic scale. This research field has been established as nanotribology. In the present article, we review our current understanding of the principles of atomic-scale friction based on recent experiments using friction force microscopy.
Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 05/2008; 366(1869):1383-404. · 2.77 Impact Factor
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ABSTRACT: We present a method how to glue small spheres to atomic force microscope cantilevers. In difference to an often used approach where the sphere is glued to a tipless cantilever, we suggest to mount small spheres to a conventional cantilever with integrated tips modified by a focused ion beam. In this way it is possible to manufacture a spherical probe with increased tip height which enhances the sensitivity in friction force microscopy and reduces the cantilever damping in dynamic force microscopy. By milling cavities for the spheres at the tip apex the colloid particles can be attached at defined positions and contamination with glue can be prevented.
Review of Scientific Instruments 03/2008; 79(2 Pt 1):026103. · 1.37 Impact Factor
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01/2007: pages 75-97; , ISBN: 978-3-540-37315-5
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ABSTRACT: Point contact friction and adhesion between a silicon tip and an untreated silicon(111) wafer are measured as a function of sample temperature in ultrahigh vacuum by friction force microscopy. While the friction coefficient changes drastically in the temperature range from 50 K to room temperature, and shows a reproducible maximum near 100 K, the simultaneously recorded adhesion shows much less temperature dependence. Interestingly, the velocity dependence of friction shows a logarithmic increase below 150 K although it is nearly constant above 150 K. This peculiar behavior has profound consequences for tribological properties of devices manufactured from silicon.
Applied Physics Letters 03/2006; 88(12):123108-123108-3. · 3.84 Impact Factor
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ABSTRACT: Atomic scale data obtained with atomic force microscopy (AFM) in the dynamic mode on graphite and a single-walled carbon nanotube (SWNT) are compared with simulations to relate the observed contrast to the real surface structure. The complete surface unit cell, and particularly the carbon site asymmetry on graphite, can be resolved in the attractive non-contact regime as well as in the weakly repulsive intermittent contact regime. On an SWNT, no carbon site asymmetry is present and the contrast above neighbouring carbon atoms in the attractive non-contact regime is symmetric. The experimental results can be qualitatively reproduced using a Lennard-Jones potential and a graphene layer with and without carbon site asymmetry to model the tip–sample interaction.
Nanotechnology 02/2005; 16(3):S134. · 3.98 Impact Factor
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ABSTRACT: Das Rasterkraftmikroskop hat gegenüber dem Rastertunnelmikroskop den Vorteil, dass es auch Oberflächen von nicht leitenden Materialien abbilden kann. Die moderne dynamische Rasterkraftmikroskopie erreicht im Nicht-Kontakt-Modus die Auflösung einzelner Atome und Fehlstellen. Das wurde an verschiedenen anorganischen und organischen Materialien demonstriert. Die dynamische Rasterkraftmikroskopie kann darüber hinaus auch Kräfte an Oberflächen auf der atomaren Skala ausmessen. Wegen dieser Vorteile wird sie voraussichtlich für die Oberflächenphysik wichtiger werden als das Rastertunnelmikroskop
Physik in unserer Zeit 07/2002; 33(4):178 - 182.
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Hendrik Hölscher
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ABSTRACT: An atomic force microscope mode is introduced to determine conservative and dissipative tip–sample interactions with high resolution in air. The proposed Q-controlled dynamic force spectroscopy is based on the measurement of frequency shift vs. amplitude and decay coefficient vs. amplitude curves by ringdown experiments. The numerical simulation demonstrates the accuracy of the method for the measurement of non-contact and contact forces in air. The basic principle, however, can be also applied in liquids or vacuum.
Surface Science. 515:517-522.
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ABSTRACT: The nature and the physical principles of dynamic force microscopy (DFM) performed in ultrahigh vacuum with fixed amplitudes much larger than the closest tip-sample distance are analyzed with a focus on the question which physical properties of the sample are actually measured. In a first part, we review conditions which essentially determine the achievable resolution in a scanning probe-based type of microscope. Then, the imaging process in a scanning force microscope is evaluated in the light of these conditions. Approximation of the nonlinear problem with a simple analytical model reveals that the frequency shift Δf which is recorded during DFM experiments is proportional to Δf∝Vint(D)/√λ(D), where Vint(D) represents the tip-sample potential at the point of closest approach D, and λ(D) a length which can be interpreted as decay length or range of Vint(z). The high accuracy of the derived relationship is demonstrated by comparison with other methods. Finally, we show why large oscillation amplitudes potentially enhance the stability of the measurement in comparison with very small amplitudes.
Phys. Rev. B. 62(19).
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ABSTRACT: We introduce a technique for measuring wear on the nano-scale by combining friction force and dynamic force microscopy. By measuring the resonance frequency of the cantilever after scratching over a sample surface we are able to detect the increase or decrease of the tip’s worn mass down to some picograms. Applying a recently developed technique to attach a small sphere to the upper end of the cantilever’s tip we are able to measure the nano-wear of several material combinations with this approach.
Wear.
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ABSTRACT: The present text reviews the fundamentals of amplitude-modulation atomic force microscopy (AM-AFM), which is frequently also referred to as dynamic force microscopy, non-contact atomic force microscopy, or “tapping mode” AFM. It is intended to address two different kinds of readerships. First, due to a thorough coverage of the theory necessary to explain the basic features observed in AM-AFM, it serves theoreticians that would like to gain overview on how nanoscale cantilevers interacting with the surrounding environment can be used to characterize nanoscale features and properties of suitable sample surfaces. On the other hand, it is designed to introduce experimentalists to the physics underlying AM-AFM measurements to a degree that is not too specialized, but sufficient to allow them measuring the quantities they need with optimized imaging parameters.More specifically, this article first covers the basics of the various driving mechanisms that are used in AFM imaging modes relying on oscillating cantilevers. From this starting point, an analytical theory of AM-AFM is developed, which also includes the effects of external resonance enhancement (“Q-Control”). This theory is then applied in conjunction with numerical simulations to various situations occurring while imaging in air or liquids. In particular, benefits and drawbacks of driving exactly at resonance frequency are examined as opposed to detuned driving. Finally, a new method for the continuous measurement of the tip–sample interaction force is discussed.
International Journal of Non-Linear Mechanics.
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ABSTRACT: In this paper, we review some of the most important results obtained with our low-temperature force microscope operated in ultrahigh vacuum. In particular, we stress the resolution capabilities on the atomic scale. After describing some recent modifications of our earlier published setup, we first compare quasi-atomic resolution in the contact mode with true-atomic resolution in the non-contact mode on graphite. On xenon, we demonstrate that weak Van der Waals interactions are sufficient to achieve atomic resolution. Thereafter, atomic scale contrast with ferromagnetic tips on nickel oxide, an insulating antiferromagnet, is discussed with respect to recent theoretical calculations regarding the detection of exchange forces. Finally, tip-induced relaxation is visualized by imaging a point defect on indium arsenide at different tip–sample distances.
Applied Surface Science 188:245-251. · 2.10 Impact Factor
