Theory of phase spectroscopy in bimodal atomic force microscopy

Lozano, Jose R.; García, Ricardo García

doi:10.1103/physrevb.79.014110

Cited by 115 publications

(97 citation statements)

References 49 publications

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“…Conventional theory that relates phase contrast, a key observable in dAFM, to tip-sample dissipation assumes that the cantilever motion can be described by using a single spatial eigenmode with, perhaps, higher harmonic temporal content. In ambient environments, high quality factors eliminate the energy propagation between eigenmodes, even in the case of bimodal (2-frequency) excitation (31,32). We have shown that this assumption breaks down when soft cantilevers are used in liquids where the dynamics are naturally multimodal due to the momentary excitation of higher eigenmodes.…”

Section: Resultsmentioning

confidence: 95%

Origins of phase contrast in the atomic force microscope in liquids

Melcher

Carrasco

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

109

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We study the physical origins of phase contrast in dynamic atomic force microscopy (dAFM) in liquids where low-stiffness microcantilever probes are often used for nanoscale imaging of soft biological samples with gentle forces. Under these conditions, we show that the phase contrast derives primarily from a unique energy flow channel that opens up in liquids due to the momentary excitation of higher eigenmodes. Contrary to the common assumption, phase-contrast images in liquids using soft microcantilevers are often maps of short-range conservative interactions, such as local elastic response, rather than tip-sample dissipation. The theory is used to demonstrate variations in local elasticity of purple membrane and bacteriophage φ29 virions in buffer solutions using the phase-contrast images.atomic force microscopy | liquid environments | energy dissipation | higher eigenmodes | momentary excitation D ynamic atomic force microscopy (dAFM) is an essential experimental tool for the study of conservative and dissipative forces on surfaces at nanometer length scales, which has major implications for the physics of biomolecular interactions, chemical bond kinetics, adhesion, wetting and capillary action, friction and elasticity on material surfaces (1, 2). dAFM techniques have been developed to distinguish between dissipative (friction, viscoelastic, bond breaking, surface hysteresis, capillary condensation) and conservative (elastic, magnetic, electrostatic) forces between a sharp oscillating tip and the surface. In amplitude-modulated AFM (AM-AFM) phase-contrast imaging, the variation in the phase of the oscillating probe tip with respect to the drive signal is mapped over the sample. For the past decade phase contrast has been intimately connected with variation in tip-sample dissipation over the sample (2-6). Phase-contrast imaging is widely recognized as perhaps the most important AM-AFM mode for the measurement of compositional contrast.The connection between phase contrast and tip-sample dissipation rests on the assumption that the cantilever dynamics can be modeled by a single eigenmode (point-mass) oscillator. With this assumption, the tip-sample dissipation can be equated to the difference between work input to the oscillator and energy dissipated into a surrounding viscous medium (4, 5). This theory forms the bedrock upon which phase-contrast imaging is currently based, at least under ambient and vacuum conditions. dAFM is now a well-known and broadly extended technique for nanoscale imaging and force spectroscopy in the biology community (7-10). Because the natural medium for the study of biological samples is liquid, it is of fundamental importance to develop a proper description of the different working modes of dAFM when the probe and sample are immersed in liquids. In particular, there is little work on understanding the origins of phase contrast in liquids (6) where soft cantilevers (stiffness 1 N/m) with low-quality factors (Q 5) are routinely used for the imaging of soft biological samples. It is im...

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Section: Resultsmentioning

confidence: 95%

Origins of phase contrast in the atomic force microscope in liquids

Melcher

Carrasco

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

109

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“…This expression is equivalent to those derived by others 23,24 but its interpretation here leads to key results relating to energy transfer and phase contrast as discussed below. In standard AM AFM the fundamental phase shift / 1 might lie above or below 90 in what defines two distinct force regimes, 25 i.e., the attractive and the repulsive regimes, where the average tip-sample force F AV is attractive or repulsive, respectively.…”

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confidence: 72%

Phase contrast and operation regimes in multifrequency atomic force microscopy

Santos

2014

Applied Physics Letters

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In amplitude modulation atomic force microscopy the attractive and the repulsive force regimes induce phase shifts above and below 90°, respectively. In the more recent multifrequency approach, however, multiple operation regimes have been reported and the theory should be revisited. Here, a theory of phase contrast in multifrequency atomic force microscopy is developed and discussed in terms of energy transfer between modes, energy dissipation and the kinetic energy and energy transfer associated with externally driven harmonics. The single frequency virial that controls the phase shift might undergo transitions in sign while the average force (modal virial) remains positive (negative). © 2014 AIP Publishing LLC.Peer ReviewedPostprint (published version

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“…To study the effect of energy dissipation in the bimodal phase contrast, in addition the above conservative force, we introduce the following non-conservative interaction [47]: (7) The power dissipated in the sample for each mode is calculated by [47] (8) Figure 3a,b show the dependence of versus A 1 /A 01 when the tip-sample interaction includes non-conservative interactions. The phase shift increases by reducing the A 1 /A 01 -ratio until a maximum is reached for ratios below 0.2.…”

Section: Materials and Cantilever-tip Parametersmentioning

confidence: 99%

Optimization of phase contrast in bimodal amplitude modulation AFM

Damircheli¹,

Payam²,

García³

2016

Nano Online

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Bimodal force microscopy has expanded the capabilities of atomic force microscopy (AFM) by providing high spatial resolution images, compositional contrast and quantitative mapping of material properties without compromising the data acquisition speed. In the first bimodal AFM configuration, an amplitude feedback loop keeps constant the amplitude of the first mode while the observables of the second mode have not feedback restrictions (bimodal AM). Here we study the conditions to enhance the compositional contrast in bimodal AM while imaging heterogeneous materials. The contrast has a maximum by decreasing the amplitude of the second mode. We demonstrate that the roles of the excited modes are asymmetric. The operational range of bimodal AM is maximized when the second mode is free to follow changes in the force. We also study the contrast in trimodal AFM by analyzing the kinetic energy ratios. The phase contrast improves by decreasing the energy of second mode relative to those of the first and third modes.1072

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Theory of phase spectroscopy in bimodal atomic force microscopy

Cited by 115 publications

References 49 publications

Origins of phase contrast in the atomic force microscope in liquids

Origins of phase contrast in the atomic force microscope in liquids

Phase contrast and operation regimes in multifrequency atomic force microscopy

Optimization of phase contrast in bimodal amplitude modulation AFM

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