摘要 :
Experiments and theoretical calculations of conservative forces measured by frequency modulation atomic force microscopy (FM-AFM) in vacuum are generally in reasonable agreement. This contrasts with dissipative forces, where exper...
展开
Experiments and theoretical calculations of conservative forces measured by frequency modulation atomic force microscopy (FM-AFM) in vacuum are generally in reasonable agreement. This contrasts with dissipative forces, where experiment and theory often disagree by several orders of magnitude. These discrepancies have repeatedly been attributed to instrumental artifacts, the cause of which remains elusive. We demonstrate that the frequency response of the piezoacoustic cantilever excitation system, traditionally assumed flat, can actually lead to surprisingly large apparent damping by the coupling of the frequency shift to the drive-amplitude signal, typically referred to as the "dissipation" signal. Our theory predicts large quantitative and qualitative variability observed in dissipation spectroscopy experiments, contrast inversion at step edges and in atomic-scale dissipation imaging, as well as changes in the power-law relationship between the drive signal and bias voltage in dissipation spectroscopy. The magnitude of apparent damping can escalate by more than an order of magnitude at cryogenic temperatures. We present a simple nondestructive method for correcting this source of apparent damping, which will allow dissipation measurements to be reliably and quantitatively compared to theoretical models.
收起
摘要 :
In this work we report a comprehensive experimental and computational study of the dynamical behavior of the tapping mode atomic force microscope (AFM) probe in interaction with the force field of a sample surface. To address the ...
展开
In this work we report a comprehensive experimental and computational study of the dynamical behavior of the tapping mode atomic force microscope (AFM) probe in interaction with the force field of a sample surface. To address the nonlinear nature of the probe dynamics, we apply describing function method. We established that the corner frequency of the low pass describing function of the probe is sensitive to the modulation amplitude and is generally higher than predicted by linear — force gradient — approximation. We show that large tip apex radii and high values of surface Young's moduli can introduce a resonant amplitude transfer, which could lead to image distortion and system instabilities. We demonstrate that the oscillating amplitude of the probe far from the surface and during imaging, and the ratio of these two (setpoint) have an influence on the describing function of the probe similar to that of the quality factor. Accordingly, expert control of these parameters is as effective as active Q control in improving the imaging bandwidth of the tapping mode AFM.
收起
摘要 :
In this paper we quantitatively compare different electrostatic models, which describe the interaction between the tip of an electrically biased atomic force microscopy cantilever and a conducting flat substrate. The models by Hud...
展开
In this paper we quantitatively compare different electrostatic models, which describe the interaction between the tip of an electrically biased atomic force microscopy cantilever and a conducting flat substrate. The models by Hudlet et al. [Eur. Phys. J. B 2, 5 (1998)] and Colchero et al. [Phys. Rev. B 64, 245403 (2001)] provide excellent descriptions of the experimental force, for tip parameters close to their typical values, although an accurate treatment of the electrostatic force contribution due to the cantilever is still missing. We introduce it here, together with a correction function which accounts for the tilting angle between the cantilever and surface, and confirm it with several experiments. Since the electrostatic force acting between a cantilever and a surface can be accurately tuned, force measurements with a defined voltage are also suitable for calibrating cantilever spring constants.
收起
摘要 :
Direct time-varying tip-sample force measurements by torsional harmonic cantilevers facilitate detailed investigations of the cantilever dynamics in tapping-mode atomic force microscopy. Here, we report experimental evidence that ...
展开
Direct time-varying tip-sample force measurements by torsional harmonic cantilevers facilitate detailed investigations of the cantilever dynamics in tapping-mode atomic force microscopy. Here, we report experimental evidence that the mathematical relation
收起
摘要 :
Power dissipation, as measured in dynamic force microscopy, is usually considered to be proportional to the energy lost in the contact process through the oscillation period. In the presence of adhesion hysteresis, the dissipation...
展开
Power dissipation, as measured in dynamic force microscopy, is usually considered to be proportional to the energy lost in the contact process through the oscillation period. In the presence of adhesion hysteresis, the dissipation is not triggered in each oscillation and only a fraction of the cycles contributes to the dissipated power. We derive a simple analytical closed expression for the dissipated power versus the oscillation amplitude which is in good agreement with the results of numerical simulations. Our theoretical and numerical results predict the existence of two possible dissipation regimes. In the first one, the power dissipated is linear with the energy dissipated by the substrate as expected. In the second regime, a beating pattern appears, causing the fraction of cycles undergoing hysteresis to be inversely proportional to the energy dissipated. As a consequence, the measured power dissipation is a function of a characteristic dissipation length and it is not proportional to the energy lost in a single adhesion process.
收起
摘要 :
We have developed a method referred to as three-dimensional scanning force microscopy (3D-SFM) which enables us to visualize water distribution at a solid-liquid interface with an atomic-scale resolution in less than 1 min. The 3D...
展开
We have developed a method referred to as three-dimensional scanning force microscopy (3D-SFM) which enables us to visualize water distribution at a solid-liquid interface with an atomic-scale resolution in less than 1 min. The 3D-SFM image obtained at a mica-water interface visualizes 3D distributions of adsorbed water molecules above the center of hexagonal cavities and the laterally distributed hydration layer. The atomically resolved 3D-SFM image showing mirror symmetry suggests the existence of surface relaxation of the cleaved mica surface next to the aqueous environment.
收起
摘要 :
Microcantilever beams are versatile force sensors used for, among others, microaccelerometry, microelec-tromechanical systems, and surface force measurements, the most prominent application being atomic force microscopic imaging a...
展开
Microcantilever beams are versatile force sensors used for, among others, microaccelerometry, microelec-tromechanical systems, and surface force measurements, the most prominent application being atomic force microscopic imaging and force spectroscopy. Bending of the cantilever is used for simple force measurements, while changes in the amplitude or frequency of the fundamental resonance are used to detect small interaction forces or brief perturbations. Spring constants needed for quantitative measurements are determined by "reversing" the force measurements, using either Hooke's law or the oscillation of the beam. The equality of the Hookian and the oscillating spring constant is generally assumed; however, consistent differences in experimental results suggest otherwise. In this work, we introduce a theoretical formula to describe the relationship between these two spring constants for an Euler-Bernoulli beam. We show that the two spring constants are not equal, although the percentage difference stays in the range of a single digit. We derive a general formula for the determination of effective spring constants of arbitrary eigenmodes of the cantilever beam. We demonstrate that all overtones can be treated with a linear spring - effective mass approach, where the mass remains the same for higher eigenmodes.
收起
摘要 :
Nanomachining of thin polymer resist films with an atomic force microscope (AFM) is a promising route for the fabrication of nanoscale devices. In order to enhance the controllability of the nanomachining process an in-plane acous...
展开
Nanomachining of thin polymer resist films with an atomic force microscope (AFM) is a promising route for the fabrication of nanoscale devices. In order to enhance the controllability of the nanomachining process an in-plane acoustic wave is coupled to the sample support. This enhances the intermittent force exerted by the AFM tip. The lateral resolution reached by this method is only limited by the physical size of the AFM tip to dimensions far below the light diffraction limit. The main process parameters are the frequency and magnitude of the acoustic wave, and the preloading force. In this work, the feasibility of acoustical force lithography and the influence of the relevant parameters are investigated.
收起
摘要 :
THE ATOMIC FORCE MICROSCOPE (AFM) has become a powerful tool for investigating biomolecules since its invention in 1986. DNA, which plays an important role in molecular biology, is under intensive study using AFM. The investigatio...
展开
THE ATOMIC FORCE MICROSCOPE (AFM) has become a powerful tool for investigating biomolecules since its invention in 1986. DNA, which plays an important role in molecular biology, is under intensive study using AFM. The investigation includes DNA morphology and DNA interaction with other molecules, which broadens our understanding of life processes and mechanisms.
收起
摘要 :
This paper presents the modeling and design of a novel magnetically actuated compliant micromanipulator based on the atomic force microscope (AFM) probe. The manipulator can control the Z -position of the tip and its orientation a...
展开
This paper presents the modeling and design of a novel magnetically actuated compliant micromanipulator based on the atomic force microscope (AFM) probe. The manipulator can control the Z -position of the tip and its orientation about the longitudinal axis. It enables sensitive interaction with the sample along two axes and is therefore a useful 3-D tool for metrology and manipulation at the micro/nanoscale. The model for the actuation scheme is first presented. Subsequently, the quasi-static and dynamic lumped parameter models of the two-axis manipulator are developed. The developed models are used to propose a systematic procedure to design the probe. The design is evaluated by means of finite-element analysis, and the results are compared with the prediction of the lumped parameter model. Finally, the manipulator is fabricated, and the experimentally measured dynamics is shown to agree well with the results of modeling and simulation.
收起
原文获取