The Experts below are selected from a list of 228882 Experts worldwide ranked by ideXlab platform
Ricardo Garcia - One of the best experts on this subject based on the ideXlab platform.
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high resolution imaging of antibodies by tapping mode atomic force microscopy attractive and repulsive tip Sample Interaction regimes
Biophysical Journal, 2000Co-Authors: Alvaro San Paulo, Ricardo GarciaAbstract:A force microscope operated with an amplitude modulation feedback (usually known as tapping-mode atomic force microscope) has two tip-Sample Interaction regimes, attractive and repulsive. We have studied the performance of those regimes to imaging single antibody molecules. The attractive Interaction regime allows determination of the basic morphologies of the antibodies on the support. More importantly, this regime is able to resolve the characteristic Y-shaped domain structure of antibodies and the hinge region between domains. Imaging in the repulsive Interaction regime is associated with the irreversible deformation of the molecules. This causes a significant loss in resolution and contrast. Two major physical differences distinguish the repulsive Interaction regime from the attractive Interaction regime: the existence of tip-Sample contact and the strength of the forces involved.
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attractive and repulsive tip Sample Interaction regimes in tapping mode atomic force microscopy
Physical Review B, 1999Co-Authors: Ricardo Garcia, Alvaro San PauloAbstract:Attractive and repulsive tip-Sample Interaction regimes of a force microscope operated with an amplitude modulation feedback were investigated as a function of tip-Sample separation, free amplitude, and Sample properties. In the attractive regime, a net attractive force dominates the amplitude reduction while in the repulsive regime the amplitude reduction is dominated by a net repulsive force. The transition between both regimes may be smooth or steplike, depending on free amplitude and Sample properties. A steplike discontinuity is always a consequence of the existence of two oscillation states for the same conditions. Stiff materials and small free amplitudes give rise to steplike transitions while the use of large free amplitudes produce smooth transitions. Simulations performed on compliant Samples showed cases where the cantilever dynamics is fully controlled by a net attractive force. Phase-shift measurements provide a practical method to determine the operating regime. Finally, we discuss the influence of those regimes in data acquisition and image interpretation.
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phase contrast and surface energy hysteresis in tapping mode scanning force microsopy
Surface and Interface Analysis, 1999Co-Authors: Ricardo Garcia, Javier Tamayo, Alvaro San PauloAbstract:Phase imaging is one of the most attractive features of tapping mode scanning force microscopy operation. In this paper we analyse the relationship between phase contrast imaging and the energy loss due to tip-Sample Interaction forces. An analytical relationship is obtained between the phase shift and the energy loss. Experiments performed on graphite are in agreement with the analytical expression.
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relationship between phase shift and energy dissipation in tapping mode scanning force microscopy
Applied Physics Letters, 1998Co-Authors: Javier Tamayo, Ricardo GarciaAbstract:Force curves taken during a load–unload cycle show the presence of a hysteresis loop. The area enclosed by the loop is used to measure the energy dissipated by the tip-Sample Interaction in tapping-mode scanning force microscopy. The values of the energy loss obtained from force curves are compared with the results derived from a model based on phase shift measurements. The agreement obtained between both methods demonstrates that for the same operating conditions, the higher the phase shift the larger the amount of energy dissipated by the tip-Sample Interaction. It also confirms the prediction that phase-contrast images can only arise if there are tip-Sample inelastic Interactions.
A. M. Baró - One of the best experts on this subject based on the ideXlab platform.
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Tip-Sample Interaction in tapping-mode scanning force microscopy
Physical Review B, 2000Co-Authors: P. J. De Pablo, Jaime Colchero, Julio Gómez-herrero, M. Luna, A. M. BaróAbstract:Tip-Sample Interaction in intermittent contact scanning force microscopy, also called tapping mode, is experimentally studied to determine under which conditions tip-Sample contact is established. Force vs distance curves are made while the cantilever is oscillating at its resonance frequency. Cantilevers with different force constants driven at different oscillation amplitudes have been used. In addition, Samples with different hardness, such as silicon oxide, glass, and highly orientated pyrolytic graphite were taken as Sample surface. From the analysis of the data we conclude that by choosing appropriate operating conditions, tip-Sample contact can be avoided. This operating regime is of general interest in scanning force microscopy, since it allows imaging of even the softest Samples.
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adsorption of water on solid surfaces studied by scanning force microscopy
Langmuir, 2000Co-Authors: A Gil, Jaime Colchero, M. Luna, And J Gomezherrero, A. M. BaróAbstract:Tip−Sample Interaction of an oscillating tip near a surface is determined. The experimental results show that the presence of the surface can be detected without mechanically touching the surface. By adjusting the appropriate operating conditions of a scanning force microscope setup, tip−Sample contact can be avoided during imaging at atmospheric pressure. This allows study of even the softest Samples. In the present work, we demonstrate that molecularly thin water films can be imaged with nanometer resolution on different substrates such as mica, gold, and highly oriented pyrolitic graphite. Correspondingly, scanning force microscopy can be used to investigate wetting properties of liquids with very high spatial resolution.
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jumping mode scanning force microscopy
Applied Physics Letters, 1998Co-Authors: P. J. De Pablo, Jaime Colchero, Julio Gomezherrero, A. M. BaróAbstract:In this letter, we present a new scanning probe microscopy mode, jumping mode, which allows the simultaneous measurement of the topography and of some other physical property of the Sample. Essentially, at each image point first the topography of the Sample is measured during a feedback phase of a cycle, and then the tip–Sample Interaction is evaluated in real time as the tip is moved away and towards the Sample. Since the lateral motion is done out of contact the method is free, or nearly free, of shear forces. The general advantages of jumping mode are discussed. Finally, two different applications of this mode are presented. In addition to the topography, the first application measures the adhesion between the tip and the Sample, while the second determines the corresponding electrostatic Interaction.
Alvaro San Paulo - One of the best experts on this subject based on the ideXlab platform.
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high resolution imaging of antibodies by tapping mode atomic force microscopy attractive and repulsive tip Sample Interaction regimes
Biophysical Journal, 2000Co-Authors: Alvaro San Paulo, Ricardo GarciaAbstract:A force microscope operated with an amplitude modulation feedback (usually known as tapping-mode atomic force microscope) has two tip-Sample Interaction regimes, attractive and repulsive. We have studied the performance of those regimes to imaging single antibody molecules. The attractive Interaction regime allows determination of the basic morphologies of the antibodies on the support. More importantly, this regime is able to resolve the characteristic Y-shaped domain structure of antibodies and the hinge region between domains. Imaging in the repulsive Interaction regime is associated with the irreversible deformation of the molecules. This causes a significant loss in resolution and contrast. Two major physical differences distinguish the repulsive Interaction regime from the attractive Interaction regime: the existence of tip-Sample contact and the strength of the forces involved.
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attractive and repulsive tip Sample Interaction regimes in tapping mode atomic force microscopy
Physical Review B, 1999Co-Authors: Ricardo Garcia, Alvaro San PauloAbstract:Attractive and repulsive tip-Sample Interaction regimes of a force microscope operated with an amplitude modulation feedback were investigated as a function of tip-Sample separation, free amplitude, and Sample properties. In the attractive regime, a net attractive force dominates the amplitude reduction while in the repulsive regime the amplitude reduction is dominated by a net repulsive force. The transition between both regimes may be smooth or steplike, depending on free amplitude and Sample properties. A steplike discontinuity is always a consequence of the existence of two oscillation states for the same conditions. Stiff materials and small free amplitudes give rise to steplike transitions while the use of large free amplitudes produce smooth transitions. Simulations performed on compliant Samples showed cases where the cantilever dynamics is fully controlled by a net attractive force. Phase-shift measurements provide a practical method to determine the operating regime. Finally, we discuss the influence of those regimes in data acquisition and image interpretation.
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phase contrast and surface energy hysteresis in tapping mode scanning force microsopy
Surface and Interface Analysis, 1999Co-Authors: Ricardo Garcia, Javier Tamayo, Alvaro San PauloAbstract:Phase imaging is one of the most attractive features of tapping mode scanning force microscopy operation. In this paper we analyse the relationship between phase contrast imaging and the energy loss due to tip-Sample Interaction forces. An analytical relationship is obtained between the phase shift and the energy loss. Experiments performed on graphite are in agreement with the analytical expression.
Arvind Raman - One of the best experts on this subject based on the ideXlab platform.
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theoretical basis of parametric resonance based atomic force microscopy
Physical Review B, 2009Co-Authors: Gyan Prakash, Arvind Raman, R ReifenbergerAbstract:Parametric resonance underpins the physics of swings, resonant surface waves, and particle traps. There is increasing interest in its potential applications in atomic force microscopy (AFM). In this paper, the dynamics of parametrically resonant microcantilevers for high sensitivity imaging and force spectroscopy applications is investigated theoretically. Detailed numerical parametric-resonance simulations are performed to understand how the microcantilever amplitude varies with tip-Sample separation, the tip-Sample Interaction, and the scanning dynamics of a microcantilever probe. We find three key advantages of a parametrically resonant microcantilever for AFM applications: (a) the reduction in ringing effects near feature edges that occur for high-$Q$ microcantilevers; (b) an increase in the scanning speed while maintaining a low tip-Sample Interaction force while imaging; and (c) an enhanced sensitivity to long-range magnetic and electrostatic force gradients acting between the tip and the Sample. Experimental results are presented with an aim to clearly identify the advantages and disadvantages that parametric resonance offers for scanning probe applications.
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inverting amplitude and phase to reconstruct tip Sample Interaction forces in tapping mode atomic force microscopy
Nanotechnology, 2008Co-Authors: Shuiqing Hu, Arvind RamanAbstract:Quantifying the tip–Sample Interaction forces in amplitude-modulated atomic force microscopy (AM-AFM) has been an elusive yet important goal in nanoscale imaging, manipulation and spectroscopy using the AFM. In this paper we present a general theory for the reconstruction of tip–Sample Interaction forces using integral equations for AM-AFM and Chebyshev polynomial expansions. This allows us to reconstruct the tip–Sample Interactions using standard amplitude and phase versus distance curves acquired in AM-AFM regardless of tip oscillation amplitude and in both the net attractive and repulsive regimes of oscillation. Systematic experiments are performed to reconstruct Interaction forces on polymer Samples to demonstrate the power of the theoretical approach.
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equivalent point mass models of continuous atomic force microscope probes
Applied Physics Letters, 2007Co-Authors: John Melcher, Arvind RamanAbstract:The theoretical foundations of dynamic atomic force microscopy (AFM) are based on point-mass models of continuous, micromechanical oscillators with nanoscale tips that probe local tip-Sample Interaction forces. In this letter, the authors present the conditions necessary for a continuous AFM probe to be faithfully represented as a point-mass model, and derive the equivalent point-mass model for a general eigenmode of arbitrarily shaped AFM probes based on the equivalence of kinetic, strain, and tip-Sample Interaction energies. They also demonstrate that common formulas in dynamic AFM change significantly when these models are used in place of the traditional ad hoc point-mass models.
R Wiesendanger - One of the best experts on this subject based on the ideXlab platform.
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magnetic sensitive force microscopy
Nano Today, 2008Co-Authors: A Schwarz, R WiesendangerAbstract:High-resolution magnetic imaging down to the atomic scale is of utmost importance to understand magnetism on the nanoscale and below. Here we report on recent advances in force microscopy based techniques from our laboratory, namely magnetic force microscopy and magnetic exchange force microscopy. The former is a well established technique for studying ferromagnetic domain patterns by sensing the long-range magnetostatic tip-Sample Interaction relatively far above the surface. In contrast, the latter is a novel and promising tool capable of detecting spin configurations with atomic resolution by probing the short-range magnetic exchange Interaction at very small tip-Sample distances. Data acquisition schemes and tip preparation methods are evaluated on Sample systems to illustrate and compare sensitivity and spatial resolution of both methods.
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measurement of conservative and dissipative tip Sample Interaction forces with a dynamic force microscope using the frequency modulation technique
Physical Review B, 2001Co-Authors: Hendrik Holscher, Bernd Gotsmann, Wolf Allers, Udo D Schwarz, Harald Fuchs, R WiesendangerAbstract:The measurement principle of dynamic-force microscopy using the frequency-modulation (FM) detection scheme is investigated by analytical as well as numerical approaches. As the detection method is based on the properties of a self-driven oscillator, we discuss the main differences from an externally driven oscillator. We then derive an analytical expression, which clarifies how the measured quantities of the FM technique, the frequency shift, and the gain factor (or ``excitation amplitude'') are influenced by the time (``phase'') shift. Introducing a very general tip-Sample force law, we show that the frequency shift is determined by the mean tip-Sample force whereas the gain factor is directly related to dissipative processes like hysteresis or viscous damping.
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calculation of the frequency shift in dynamic force microscopy
Applied Surface Science, 1999Co-Authors: Hendrik Holscher, Udo D Schwarz, R WiesendangerAbstract:Abstract A theoretical study of the quality and the range of validity of different numerical and analytical methods to calculate the frequency shift in dynamic force microscopy is presented. By comparison with exact results obtained by the numerical solution of the equation of motion, it is demonstrated that the commonly used interpretation of the frequency shift as a measure for the force gradient of the tip–Sample Interaction force is only valid for very small oscillation amplitudes and leads to misinterpretations in most practical cases. Perturbation theory, however, allows the derivation of useful analytic approximations.
