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Sample records for dynamical force microscopy

  1. Dynamic force microscopy in liquids

    NASA Astrophysics Data System (ADS)

    Dreier, M.; Anselmetti, D.; Richmond, T.; Dammer, U.; Guentherodt, H.-J.

    1994-11-01

    We applied dynamic force microscopy in a liquid environment to silanized and derivatized glass surfaces, InGaAs, as well as to biological materials such as hexagonally packed intermediate layers of deinococcus radiodurans. The vertical and lateral resolution were estimated to be less than 1 A and 7 - 10 nm, respectively. Upon immersing the cantilever into water, the resonance frequency was found to be reduced by a factor of two and the Q factor was lowered to 20 - 30. The experimental working distance between sensor and sample was determined with approach curves indicating that the range of interaction in water is much shorter compared to air.

  2. Multiple impact regimes in liquid environment dynamic atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Melcher, John; Xu, Xin; Raman, Arvind

    2008-09-01

    A canonical assumption in dynamic atomic force microscopy is that the probe tip interacts with the sample once per oscillation cycle. We show this key ansatz breaks down for soft cantilevers in liquid environments. Such probes exhibit "drum roll" like dynamics with sequential bifurcations between oscillations with single, double, and triple impacts that can be clearly identified in the phase of the response. This important result is traced to a momentary excitation of the second flexural mode induced by tip-sample forces and low quality factors. Experiments performed on supported biological membranes in buffer solutions are used to demonstrate the findings.

  3. Microcantilevers with embedded accelerometers for dynamic atomic force microscopy

    SciTech Connect

    Shaik, Nurul Huda; Raman, Arvind; Reifenberger, Ronald G.

    2014-02-24

    The measurement of the intermittent interaction between an oscillating nanotip and the sample surface is a key challenge in dynamic Atomic Force Microscopy (AFM). Accelerometers integrated onto AFM cantilevers can directly measure this interaction with minimal cantilever modification but have been difficult to realize. Here, we design and fabricate high frequency bandwidth accelerometers on AFM cantilevers to directly measure the tip acceleration in commercial AFM systems. We demonstrate a simple way of calibrating such accelerometers and present experiments using amplitude modulated AFM on freshly cleaved mica samples in water to study the response of the accelerometer.

  4. Subharmonic Oscillations and Chaos in Dynamic Atomic Force Microscopy

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.; Cantrell, Sean A.

    2015-01-01

    The increasing use of dynamic atomic force microscopy (d-AFM) for nanoscale materials characterization calls for a deeper understanding of the cantilever dynamics influencing scan stability, predictability, and image quality. Model development is critical to such understanding. Renormalization of the equations governing d- AFM provides a simple interpretation of cantilever dynamics as a single spring and mass system with frequency dependent cantilever stiffness and damping parameters. The renormalized model is sufficiently robust to predict the experimentally observed splitting of the free-space cantilever resonance into multiple resonances upon cantilever-sample contact. Central to the model is the representation of the cantilever sample interaction force as a polynomial expansion with coefficients F(sub ij) (i,j = 0, 1, 2) that account for the effective interaction stiffness parameter, the cantilever-to-sample energy transfer, and the amplitude of cantilever oscillation. Application of the Melnikov method to the model equation is shown to predict a homoclinic bifurcation of the Smale horseshoe type leading to a cascade of period doublings with increasing drive displacement amplitude culminating in chaos and loss of image quality. The threshold value of the drive displacement amplitude necessary to initiate subharmonic generation depends on the acoustic drive frequency, the effective damping coefficient, and the nonlinearity of the cantilever-sample interaction force. For parameter values leading to displacement amplitudes below threshold for homoclinic bifurcation other bifurcation scenarios can occur, some of which lead to chaos.

  5. Dynamics of Bond Breaking Studied by Chemical Force Microscopy

    NASA Astrophysics Data System (ADS)

    Noy, Aleksandr; Zepeda, Salvador; Orme, Chris; Yeh, Yin; Deyoreo, Jim

    2000-03-01

    Intermolecular forces underline a variety of phenomena in chemical and in biological systems, such as cell adhesion, protein folding and molecular recognition in ligand-receptor pairs. Understanding the dynamics of these interactions is critical for modeling and controlling these processes. The advent of ultra-sensitive force measurement techniques has enabled direct measurement of the bond strength on the relevant length scales. Recent measurements have pointed out the importance of kinetic factors in bond strength and pointed out the necessity to explore the whole energy landscape of a chemical bond. Still, little is known about the response of the bond strength to the environmental variables such as temperature. The analysis of this response provides a way to determine thermodynamic characteristics of the binding interaction. We used chemical force microscopy to measure the temperature dependence of the interaction forces in a well-defined system presenting a finite number of identical bonds. The tip of the scanning probe microscope was modified with distinct chemical functionalities to give rise to the well-defined and uniform interactions with the sample surface. We will discuss the theoretical framework for interpretation of such measurements, as well as the relative importance of thermodynamic and kinetic factors affecting the bond strength in the presence of solvent medium. We also point out the differences in kinetics of bond breaking in single bond systems vs. multiple bond systems.

  6. Molecular dynamics simulation of amplitude modulation atomic force microscopy.

    PubMed

    Hu, Xiaoli; Egberts, Philip; Dong, Yalin; Martini, Ashlie

    2015-06-12

    Molecular dynamics (MD) simulations were used to model amplitude modulation atomic force microscopy (AM-AFM). In this novel simulation, the model AFM tip responds to both tip-substrate interactions and to a sinusoidal excitation signal. The amplitude and phase shift of the tip oscillation observed in the simulation and their variation with tip-sample distance were found to be consistent with previously reported trends from experiments and theory. These simulation results were also fit to an expression enabling estimation of the energy dissipation, which was found to be smaller than that in a corresponding experiment. The difference was analyzed in terms of the effects of tip size and substrate thickness. Development of this model is the first step toward using MD to gain insight into the atomic-scale phenomena that occur during an AM-AFM measurement.

  7. Laser Actuation of Cantilevers for Picometre Amplitude Dynamic Force Microscopy

    PubMed Central

    Evans, Drew R.; Tayati, Ponlawat; An, Hongjie; Lam, Ping Koy; Craig, Vincent S. J.; Senden, Tim J.

    2014-01-01

    As nanoscale and molecular devices become reality, the ability to probe materials on these scales is increasing in importance. To address this, we have developed a dynamic force microscopy technique where the flexure of the microcantilever is excited using an intensity modulated laser beam to achieve modulation on the picoscale. The flexure arises from thermally induced bending through differential expansion and the conservation of momentum when the photons are reflected and absorbed by the cantilever. In this study, we investigated the photothermal and photon pressure responses of monolithic and layered cantilevers using a modulated laser in air and immersed in water. The developed photon actuation technique is applied to the stretching of single polymer chains. PMID:24993548

  8. Identification of nanoscale dissipation processes by dynamic atomic force microscopy.

    PubMed

    Garcia, R; Gómez, C J; Martinez, N F; Patil, S; Dietz, C; Magerle, R

    2006-07-01

    Identification of energy-dissipation processes at the nanoscale is demonstrated by using amplitude-modulation atomic force microscopy. The variation of the energy dissipated on a surface by a vibrating tip as a function of its oscillation amplitude has a shape that singles out the dissipative process occurring at the surface. The method is illustrated by calculating the energy-dissipation curves for surface energy hysteresis, long-range interfacial interactions and viscoelasticity. The method remains valid with independency of the amount of dissipated energy per cycle, from 0.1 to 50 eV. The agreement obtained between theory and experiments performed on silicon and polystyrene validates the method.

  9. Direct observation of dynamic force propagation between focal adhesions of cells on microposts by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Okada, Akinori; Mizutani, Yusuke; Subagyo, Agus; Hosoi, Hirotaka; Nakamura, Motonori; Sueoka, Kazuhisa; Kawahara, Koichi; Okajima, Takaharu

    2011-12-01

    We investigated dynamic force propagation between focal adhesions of fibroblast cells cultured on polydimethylsiloxane micropost substrates, by atomic force microscopy. Live cells were mechanically modulated by the atomic force microscopy probe bound to cell apical surfaces at 0.01-0.5 Hz, while microposts served as a force sensor at basal surfaces. We observed that cells exhibited rheological behavior at the apical surface but had no apparent out-of-phase response at the basal surface, indicating that the dynamic force propagating through cytoskeletal filaments behaves in an elastic manner. Moreover, the direction of the propagated force was observed to be intimately associated with the prestress.

  10. Structure and Dynamics of Dinucleosomes Assessed by Atomic Force Microscopy

    DOE PAGES

    Filenko, Nina A.; Palets, Dmytro B.; Lyubchenko, Yuri L.

    2012-01-01

    Dynamics of nucleosomes and their interactions are important for understanding the mechanism of chromatin assembly. Internucleosomal interaction is required for the formation of higher-order chromatin structures. Although H1 histone is critically involved in the process of chromatin assembly, direct internucleosomal interactions contribute to this process as well. To characterize the interactions of nucleosomes within the nucleosome array, we designed a dinucleosome and performed direct AFM imaging. The analysis of the AFM data showed dinucleosomes are very dynamic systems, enabling the nucleosomes to move in a broad range along the DNA template. Di-nucleosomes in close proximity were observed, but their populationmore » was low. The use of the zwitterionic detergent, CHAPS, increased the dynamic range of the di-nucleosome, facilitating the formation of tight di-nucleosomes. The role of CHAPS and similar natural products in chromatin structure and dynamics is also discussed.« less

  11. Colloid probes with increased tip height for higher sensitivity in friction force microscopy and less cantilever damping in dynamic force microscopy.

    PubMed

    Schmutz, Jan-Erik; Schäfer, Marcus M; Hölscher, Hendrik

    2008-02-01

    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. PMID:18315335

  12. Quantification of surface displacements and electromechanical phenomena via dynamic atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Balke, Nina; Jesse, Stephen; Yu, Pu; Carmichael, Ben; Kalinin, Sergei V.; Tselev, Alexander

    2016-10-01

    Detection of dynamic surface displacements associated with local changes in material strain provides access to a number of phenomena and material properties. Contact resonance-enhanced methods of atomic force microscopy (AFM) have been shown capable of detecting ˜1-3 pm-level surface displacements, an approach used in techniques such as piezoresponse force microscopy, atomic force acoustic microscopy, and ultrasonic force microscopy. Here, based on an analytical model of AFM cantilever vibrations, we demonstrate a guideline to quantify surface displacements with high accuracy by taking into account the cantilever shape at the first resonant contact mode, depending on the tip-sample contact stiffness. The approach has been experimentally verified and further developed for piezoresponse force microscopy (PFM) using well-defined ferroelectric materials. These results open up a way to accurate and precise measurements of surface displacement as well as piezoelectric constants at the pm-scale with nanometer spatial resolution and will allow avoiding erroneous data interpretations and measurement artifacts. This analysis is directly applicable to all cantilever-resonance-based scanning probe microscopy (SPM) techniques.

  13. Quantification of surface displacements and electromechanical phenomena via dynamic atomic force microscopy.

    PubMed

    Balke, Nina; Jesse, Stephen; Yu, Pu; Ben Carmichael; Kalinin, Sergei V; Tselev, Alexander

    2016-10-21

    Detection of dynamic surface displacements associated with local changes in material strain provides access to a number of phenomena and material properties. Contact resonance-enhanced methods of atomic force microscopy (AFM) have been shown capable of detecting ∼1-3 pm-level surface displacements, an approach used in techniques such as piezoresponse force microscopy, atomic force acoustic microscopy, and ultrasonic force microscopy. Here, based on an analytical model of AFM cantilever vibrations, we demonstrate a guideline to quantify surface displacements with high accuracy by taking into account the cantilever shape at the first resonant contact mode, depending on the tip-sample contact stiffness. The approach has been experimentally verified and further developed for piezoresponse force microscopy (PFM) using well-defined ferroelectric materials. These results open up a way to accurate and precise measurements of surface displacement as well as piezoelectric constants at the pm-scale with nanometer spatial resolution and will allow avoiding erroneous data interpretations and measurement artifacts. This analysis is directly applicable to all cantilever-resonance-based scanning probe microscopy (SPM) techniques. PMID:27631885

  14. Quantification of surface displacements and electromechanical phenomena via dynamic atomic force microscopy.

    PubMed

    Balke, Nina; Jesse, Stephen; Yu, Pu; Ben Carmichael; Kalinin, Sergei V; Tselev, Alexander

    2016-10-21

    Detection of dynamic surface displacements associated with local changes in material strain provides access to a number of phenomena and material properties. Contact resonance-enhanced methods of atomic force microscopy (AFM) have been shown capable of detecting ∼1-3 pm-level surface displacements, an approach used in techniques such as piezoresponse force microscopy, atomic force acoustic microscopy, and ultrasonic force microscopy. Here, based on an analytical model of AFM cantilever vibrations, we demonstrate a guideline to quantify surface displacements with high accuracy by taking into account the cantilever shape at the first resonant contact mode, depending on the tip-sample contact stiffness. The approach has been experimentally verified and further developed for piezoresponse force microscopy (PFM) using well-defined ferroelectric materials. These results open up a way to accurate and precise measurements of surface displacement as well as piezoelectric constants at the pm-scale with nanometer spatial resolution and will allow avoiding erroneous data interpretations and measurement artifacts. This analysis is directly applicable to all cantilever-resonance-based scanning probe microscopy (SPM) techniques.

  15. Estimation of the shear force in transverse dynamic force microscopy using a sliding mode observer

    NASA Astrophysics Data System (ADS)

    Nguyen, Thang; Hatano, Toshiaki; Khan, Said G.; Zhang, Kaiqiang; Edwards, Christopher; Harniman, Robert; Burgess, Stuart C.; Antognozzi, Massimo; Miles, Mervyn; Herrmann, Guido

    2015-09-01

    In this paper, the problem of estimating the shear force affecting the tip of the cantilever in a Transverse Dynamic Force Microscope (TDFM) using a real-time implementable sliding mode observer is addressed. The behaviour of a vertically oriented oscillated cantilever, in close proximity to a specimen surface, facilitates the imaging of the specimen at nano-metre scale. Distance changes between the cantilever tip and the specimen can be inferred from the oscillation amplitudes, but also from the shear force acting at the tip. Thus, the problem of accurately estimating the shear force is of significance when specimen images and mechanical properties need to be obtained at submolecular precision. A low order dynamic model of the cantilever is derived using the method of lines, for the purpose of estimating the shear force. Based on this model, an estimator using sliding mode techniques is presented to reconstruct the unknown shear force, from only tip position measurements and knowledge of the excitation signal applied to the top of the cantilever. Comparisons to methods assuming a quasi-static harmonic balance are made.

  16. Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

    SciTech Connect

    Wang, R.; Williams, C. C.

    2015-09-15

    Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

  17. Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

    NASA Astrophysics Data System (ADS)

    Wang, R.; Williams, C. C.

    2015-09-01

    Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

  18. Dynamic nanoindentation by instrumented nanoindentation and force microscopy: a comparative review

    PubMed Central

    Kalfon-Cohen, Estelle

    2013-01-01

    Summary Viscoelasticity is a complex yet important phenomenon that drives material response at different scales of time and space. Burgeoning interest in nanoscale dynamic material mechanics has driven, and been driven by two key techniques: instrumented nanoindentation and atomic force microscopy. This review provides an overview of fundamental principles in nanoindentation, and compares and contrasts these two techniques as they are used for characterization of viscoelastic processes at the nanoscale. PMID:24367751

  19. Analysis of dynamic cantilever behavior in tapping mode atomic force microscopy.

    PubMed

    Deng, Wenqi; Zhang, Guang-Ming; Murphy, Mark F; Lilley, Francis; Harvey, David M; Burton, David R

    2015-10-01

    Tapping mode atomic force microscopy (AFM) provides phase images in addition to height and amplitude images. Although the behavior of tapping mode AFM has been investigated using mathematical modeling, comprehensive understanding of the behavior of tapping mode AFM still poses a significant challenge to the AFM community, involving issues such as the correct interpretation of the phase images. In this paper, the cantilever's dynamic behavior in tapping mode AFM is studied through a three dimensional finite element method. The cantilever's dynamic displacement responses are firstly obtained via simulation under different tip-sample separations, and for different tip-sample interaction forces, such as elastic force, adhesion force, viscosity force, and the van der Waals force, which correspond to the cantilever's action upon various different representative computer-generated test samples. Simulated results show that the dynamic cantilever displacement response can be divided into three zones: a free vibration zone, a transition zone, and a contact vibration zone. Phase trajectory, phase shift, transition time, pseudo stable amplitude, and frequency changes are then analyzed from the dynamic displacement responses that are obtained. Finally, experiments are carried out on a real AFM system to support the findings of the simulations. PMID:26303510

  20. Nonlinear Dynamics of Cantilever-Sample Interactions in Atomic Force Microscopy

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.; Cantrell, Sean A.

    2010-01-01

    The interaction of the cantilever tip of an atomic force microscope (AFM) with the sample surface is obtained by treating the cantilever and sample as independent systems coupled by a nonlinear force acting between the cantilever tip and a volume element of the sample surface. The volume element is subjected to a restoring force from the remainder of the sample that provides dynamical equilibrium for the combined systems. The model accounts for the positions on the cantilever of the cantilever tip, laser probe, and excitation force (if any) via a basis set of set of orthogonal functions that may be generalized to account for arbitrary cantilever shapes. The basis set is extended to include nonlinear cantilever modes. The model leads to a pair of coupled nonlinear differential equations that are solved analytically using a matrix iteration procedure. The effects of oscillatory excitation forces applied either to the cantilever or to the sample surface (or to both) are obtained from the solution set and applied to the to the assessment of phase and amplitude signals generated by various acoustic-atomic force microscope (A-AFM) modalities. The influence of bistable cantilever modes of on AFM signal generation is discussed. The effects on the cantilever-sample surface dynamics of subsurface features embedded in the sample that are perturbed by surface-generated oscillatory excitation forces and carried to the cantilever via wave propagation are accounted by the Bolef-Miller propagating wave model. Expressions pertaining to signal generation and image contrast in A-AFM are obtained and applied to amplitude modulation (intermittent contact) atomic force microscopy and resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM). The influence of phase accumulation in A-AFM on image contrast is discussed, as is the effect of hard contact and maximum nonlinearity regimes of A-AFM operation.

  1. Dynamic force microscopy simulator (dForce): A tool for planning and understanding tapping and bimodal AFM experiments

    PubMed Central

    Guzman, Horacio V; Garcia, Pablo D

    2015-01-01

    Summary We present a simulation environment, dForce, which can be used for a better understanding of dynamic force microscopy experiments. The simulator presents the cantilever–tip dynamics for two dynamic AFM methods, tapping mode AFM and bimodal AFM. It can be applied for a wide variety of experimental situations in air or liquid. The code provides all the variables and parameters relevant in those modes, for example, the instantaneous deflection and tip–surface force, velocity, virial, dissipated energy, sample deformation and peak force as a function of time or distance. The simulator includes a variety of interactions and contact mechanics models to describe AFM experiments including: van der Waals, Hertz, DMT, JKR, bottom effect cone correction, linear viscoelastic forces or the standard linear solid viscoelastic model. We have compared two numerical integration methods to select the one that offers optimal accuracy and speed. The graphical user interface has been designed to facilitate the navigation of non-experts in simulations. Finally, the accuracy of dForce has been tested against numerical simulations performed during the last 18 years. PMID:25821676

  2. Molecular Dynamics Simulation of Atomic Force Microscopy at the Water-Muscovite Interface: Hydration Layer Structure and Force Analysis.

    PubMed

    Kobayashi, Kazuya; Liang, Yunfeng; Amano, Ken-ichi; Murata, Sumihiko; Matsuoka, Toshifumi; Takahashi, Satoru; Nishi, Naoya; Sakka, Tetsuo

    2016-04-19

    With the development of atomic force microscopy (AFM), it is now possible to detect the buried liquid-solid interfacial structure in three dimensions at the atomic scale. One of the model surfaces used for AFM is the muscovite surface because it is atomically flat after cleavage along the basal plane. Although it is considered that force profiles obtained by AFM reflect the interfacial structures (e.g., muscovite surface and water structure), the force profiles are not straightforward because of the lack of a quantitative relationship between the force and the interfacial structure. In the present study, molecular dynamics simulations were performed to investigate the relationship between the muscovite-water interfacial structure and the measured AFM force using a capped carbon nanotube (CNT) AFM tip. We provide divided force profiles, where the force contributions from each water layer at the interface are shown. They reveal that the first hydration layer is dominant in the total force from water even after destruction of the layer. Moreover, the lateral structure of the first hydration layer transcribes the muscovite surface structure. It resembles the experimentally resolved surface structure of muscovite in previous AFM studies. The local density profile of water between the tip and the surface provides further insight into the relationship between the water structure and the detected force structure. The detected force structure reflects the basic features of the atomic structure for the local hydration layers. However, details including the peak-peak distance in the force profile (force-distance curve) differ from those in the density profile (density-distance curve) because of disturbance by the tip.

  3. Tracking Cytoskeletal Dynamics in Living Neurons via Combined Atomic Force and Fluorescence Microscopy

    NASA Astrophysics Data System (ADS)

    Spedden, Elise; Kaplan, David; Staii, Cristian

    2013-03-01

    Living cells are active mechanical structures which evolve within and in response to their local microenvironments. Various cell types possess different mechanical properties and respond uniquely to growth, environmental changes, and the application of chemical stimuli. Here we present a powerful approach which combines high resolution Atomic Force Microscopy with Fluorescence Microscopy to systematically obtain real-time micrometer and sub-micrometer resolution elasticity maps for live neuronal cells cultured on glass substrates. Through this approach we measure the topography, the elastic properties, and the dynamics of neuronal cells, and identify changes in cytoskeletal components during axonal growth, chemical modification, and changes in ambient temperature. We will also show high resolution elasticity measurements of the cell body and of axons/dendrites during growth, as well as identification of cytoskeletal components during cell growth and environmental changes.

  4. Optimization and calibration of atomic force microscopy sensitivity in terms of tip-sample interactions in high-order dynamic atomic force microscopy

    SciTech Connect

    Liu Yu; Guo Qiuquan; Nie Hengyong; Lau, W. M.; Yang Jun

    2009-12-15

    The mechanism of dynamic force modes has been successfully applied to many atomic force microscopy (AFM) applications, such as tapping mode and phase imaging. The high-order flexural vibration modes are recent advancement of AFM dynamic force modes. AFM optical lever detection sensitivity plays a major role in dynamic force modes because it determines the accuracy in mapping surface morphology, distinguishing various tip-surface interactions, and measuring the strength of the tip-surface interactions. In this work, we have analyzed optimization and calibration of the optical lever detection sensitivity for an AFM cantilever-tip ensemble vibrating in high-order flexural modes and simultaneously experiencing a wide range and variety of tip-sample interactions. It is found that the optimal detection sensitivity depends on the vibration mode, the ratio of the force constant of tip-sample interactions to the cantilever stiffness, as well as the incident laser spot size and its location on the cantilever. It is also found that the optimal detection sensitivity is less dependent on the strength of tip-sample interactions for high-order flexural modes relative to the fundamental mode, i.e., tapping mode. When the force constant of tip-sample interactions significantly exceeds the cantilever stiffness, the optimal detection sensitivity occurs only when the laser spot locates at a certain distance from the cantilever-tip end. Thus, in addition to the 'globally optimized detection sensitivity', the 'tip optimized detection sensitivity' is also determined. Finally, we have proposed a calibration method to determine the actual AFM detection sensitivity in high-order flexural vibration modes against the static end-load sensitivity that is obtained traditionally by measuring a force-distance curve on a hard substrate in the contact mode.

  5. Dynamics of a disturbed sessile drop measured by atomic force microscopy (AFM).

    PubMed

    McGuiggan, Patricia M; Grave, Daniel A; Wallace, Jay S; Cheng, Shengfeng; Prosperetti, Andrea; Robbins, Mark O

    2011-10-01

    A new method for studying the dynamics of a sessile drop by atomic force microscopy (AFM) is demonstrated. A hydrophobic microsphere (radius, r ∼ 20-30 μm) is brought into contact with a small sessile water drop resting on a polytetrafluoroethylene (PTFE) surface. When the microsphere touches the liquid surface, the meniscus rises onto it because of capillary forces. Although the microsphere volume is 6 orders of magnitude smaller than the drop, it excites the normal resonance modes of the liquid interface. The sphere is pinned at the interface, whose small (<100 nm) oscillations are readily measured with AFM. Resonance oscillation frequencies were measured for drop volumes between 5 and 200 μL. The results for the two lowest normal modes are quantitatively consistent with continuum calculations for the natural frequency of hemispherical drops with no adjustable parameters. The method may enable sensitive measurements of volume, surface tension, and viscosity of small drops.

  6. Dynamic nano-triboelectrification using torsional resonance mode atomic force microscopy

    PubMed Central

    Cai, Wei; Yao, Nan

    2016-01-01

    Understanding the mechanism of charge generation, distribution, and transfer between surfaces is very important for energy harvesting applications based on triboelectric effect. Here, we demonstrate dynamic nanotriboelectrification with torsional resonance (TR) mode atomic force microscopy (AFM). Experiments on rubbing the sample surface using TR mode for the generation of triboelectric charges and in-situ characterization of the charge distribution using scanning Kelvin probe microcopy (SKPM) were performed. This method allows the tip to perform lateral oscillation and maintains the tip-sample interaction in the attractive region to ensure high efficiency of the charge generation during the rubbing process. The measured efficiency of generating triboelectric charges can achieve ~10.53 times higher than conventional static/contact mode in the triboelectrification experiments. In addition to the charge generation, local discharging experiments were also performed. This work would provide a new method to generate patterned charges and also be helpful in understanding the mechanism of nanotriboelectrification. PMID:27302624

  7. Dynamic nano-triboelectrification using torsional resonance mode atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Cai, Wei; Yao, Nan

    2016-06-01

    Understanding the mechanism of charge generation, distribution, and transfer between surfaces is very important for energy harvesting applications based on triboelectric effect. Here, we demonstrate dynamic nanotriboelectrification with torsional resonance (TR) mode atomic force microscopy (AFM). Experiments on rubbing the sample surface using TR mode for the generation of triboelectric charges and in-situ characterization of the charge distribution using scanning Kelvin probe microcopy (SKPM) were performed. This method allows the tip to perform lateral oscillation and maintains the tip-sample interaction in the attractive region to ensure high efficiency of the charge generation during the rubbing process. The measured efficiency of generating triboelectric charges can achieve ~10.53 times higher than conventional static/contact mode in the triboelectrification experiments. In addition to the charge generation, local discharging experiments were also performed. This work would provide a new method to generate patterned charges and also be helpful in understanding the mechanism of nanotriboelectrification.

  8. Electrothermally driven high-frequency piezoresistive SiC cantilevers for dynamic atomic force microscopy

    SciTech Connect

    Boubekri, R.; Cambril, E.; Couraud, L.; Bernardi, L.; Madouri, A.; Portail, M.; Chassagne, T.; Moisson, C.; Zielinski, M.; Jiao, S.; Michaud, J.-F.; Alquier, D.; Bouloc, J.; Nony, L.; Bocquet, F.; Loppacher, C.

    2014-08-07

    Cantilevers with resonance frequency ranging from 1 MHz to 100 MHz have been developed for dynamic atomic force microscopy. These sensors are fabricated from 3C-SiC epilayers grown on Si(100) substrates by low pressure chemical vapor deposition. They use an on-chip method both for driving and sensing the displacement of the cantilever. A first gold metallic loop deposited on top of the cantilever is used to drive its oscillation by electrothermal actuation. The sensing of this oscillation is performed by monitoring the resistance of a second Au loop. This metallic piezoresistive detection method has distinct advantages relative to more common semiconductor-based schemes. The optimization, design, fabrication, and characteristics of these cantilevers are discussed.

  9. High-resolution dynamic atomic force microscopy in liquids with different feedback architectures

    PubMed Central

    Martínez-Martín, David; Jaafar, Miriam; Gómez-Herrero, Julio; Raman, Arvind

    2013-01-01

    Summary The recent achievement of atomic resolution with dynamic atomic force microscopy (dAFM) [Fukuma et al., Appl. Phys. Lett. 2005, 87, 034101], where quality factors of the oscillating probe are inherently low, challenges some accepted beliefs concerning sensitivity and resolution in dAFM imaging modes. Through analysis and experiment we study the performance metrics for high-resolution imaging with dAFM in liquid media with amplitude modulation (AM), frequency modulation (FM) and drive-amplitude modulation (DAM) imaging modes. We find that while the quality factors of dAFM probes may deviate by several orders of magnitude between vacuum and liquid media, their sensitivity to tip–sample forces can be remarkable similar. Furthermore, the reduction in noncontact forces and quality factors in liquids diminishes the role of feedback control in achieving high-resolution images. The theoretical findings are supported by atomic-resolution images of mica in water acquired with AM, FM and DAM under similar operating conditions. PMID:23503468

  10. Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space.

    PubMed

    Collins, Liam; Belianinov, Alex; Somnath, Suhas; Balke, Nina; Kalinin, Sergei V; Jesse, Stephen

    2016-08-12

    Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of materials and devices. In classical KPFM, which utilizes heterodyne detection and closed loop bias feedback, the cantilever response is down-sampled to a single measurement of the contact potential difference (CPD) per pixel. This level of detail, however, is insufficient for materials and devices involving bias and time dependent electrochemical events; or at solid-liquid interfaces, where non-linear or lossy dielectrics are present. Here, we demonstrate direct recovery of the bias dependence of the electrostatic force at high temporal resolution using General acquisition Mode (G-Mode) KPFM. G-Mode KPFM utilizes high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates. We show how G-Mode KPFM can be used to capture nanoscale CPD and capacitance information with a temporal resolution much faster than the cantilever bandwidth, determined by the modulation frequency of the AC voltage. In this way, G-Mode KPFM offers a new paradigm to study dynamic electric phenomena in electroactive interfaces as well as a promising route to extend KPFM to the solid-liquid interface.

  11. Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space

    PubMed Central

    Collins, Liam; Belianinov, Alex; Somnath, Suhas; Balke, Nina; Kalinin, Sergei V.; Jesse, Stephen

    2016-01-01

    Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of materials and devices. In classical KPFM, which utilizes heterodyne detection and closed loop bias feedback, the cantilever response is down-sampled to a single measurement of the contact potential difference (CPD) per pixel. This level of detail, however, is insufficient for materials and devices involving bias and time dependent electrochemical events; or at solid-liquid interfaces, where non-linear or lossy dielectrics are present. Here, we demonstrate direct recovery of the bias dependence of the electrostatic force at high temporal resolution using General acquisition Mode (G-Mode) KPFM. G-Mode KPFM utilizes high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates. We show how G-Mode KPFM can be used to capture nanoscale CPD and capacitance information with a temporal resolution much faster than the cantilever bandwidth, determined by the modulation frequency of the AC voltage. In this way, G-Mode KPFM offers a new paradigm to study dynamic electric phenomena in electroactive interfaces as well as a promising route to extend KPFM to the solid-liquid interface. PMID:27514987

  12. Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space.

    PubMed

    Collins, Liam; Belianinov, Alex; Somnath, Suhas; Balke, Nina; Kalinin, Sergei V; Jesse, Stephen

    2016-01-01

    Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of materials and devices. In classical KPFM, which utilizes heterodyne detection and closed loop bias feedback, the cantilever response is down-sampled to a single measurement of the contact potential difference (CPD) per pixel. This level of detail, however, is insufficient for materials and devices involving bias and time dependent electrochemical events; or at solid-liquid interfaces, where non-linear or lossy dielectrics are present. Here, we demonstrate direct recovery of the bias dependence of the electrostatic force at high temporal resolution using General acquisition Mode (G-Mode) KPFM. G-Mode KPFM utilizes high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates. We show how G-Mode KPFM can be used to capture nanoscale CPD and capacitance information with a temporal resolution much faster than the cantilever bandwidth, determined by the modulation frequency of the AC voltage. In this way, G-Mode KPFM offers a new paradigm to study dynamic electric phenomena in electroactive interfaces as well as a promising route to extend KPFM to the solid-liquid interface. PMID:27514987

  13. Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space

    NASA Astrophysics Data System (ADS)

    Collins, Liam; Belianinov, Alex; Somnath, Suhas; Balke, Nina; Kalinin, Sergei V.; Jesse, Stephen

    2016-08-01

    Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of materials and devices. In classical KPFM, which utilizes heterodyne detection and closed loop bias feedback, the cantilever response is down-sampled to a single measurement of the contact potential difference (CPD) per pixel. This level of detail, however, is insufficient for materials and devices involving bias and time dependent electrochemical events; or at solid-liquid interfaces, where non-linear or lossy dielectrics are present. Here, we demonstrate direct recovery of the bias dependence of the electrostatic force at high temporal resolution using General acquisition Mode (G-Mode) KPFM. G-Mode KPFM utilizes high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates. We show how G-Mode KPFM can be used to capture nanoscale CPD and capacitance information with a temporal resolution much faster than the cantilever bandwidth, determined by the modulation frequency of the AC voltage. In this way, G-Mode KPFM offers a new paradigm to study dynamic electric phenomena in electroactive interfaces as well as a promising route to extend KPFM to the solid-liquid interface.

  14. A method to provide rapid in situ determination of tip radius in dynamic atomic force microscopy.

    PubMed

    Santos, Sergio; Guang, Li; Souier, Tewfik; Gadelrab, Karim; Chiesa, Matteo; Thomson, Neil H

    2012-04-01

    We provide a method to characterize the tip radius of an atomic force microscopy in situ by monitoring the dynamics of the cantilever in ambient conditions. The key concept is that the value of free amplitude for which transitions from the attractive to repulsive force regimes are observed, strongly depends on the curvature of the tip. In practice, the smaller the value of free amplitude required to observe a transition, the sharper the tip. This general behavior is remarkably independent of the properties of the sample and cantilever characteristics and shows the strong dependence of the transitions on the tip radius. The main advantage of this method is rapid in situ characterization. Rapid in situ characterization enables one to continuously monitor the tip size during experiments. Further, we show how to reproducibly shape the tip from a given initial size to any chosen larger size. This approach combined with the in situ tip size monitoring enables quantitative comparison of materials measurements between samples. These methods are set to allow quantitative data acquisition and make direct data comparison readily available in the community.

  15. Molecular dynamics simulation of Lorentz force microscopy in magnetic nano-disks

    NASA Astrophysics Data System (ADS)

    Dias, R. A.; Mello, E. P.; Coura, P. Z.; Leonel, S. A.; Maciel, I. O.; Toscano, D.; Rocha, J. C. S.; Costa, B. V.

    2013-04-01

    In this paper, we present a molecular dynamics simulation to model the Lorentz force microscopy experiment. Experimentally, this technique consists in the scattering of electrons by magnetic structures in surfaces and gases. Here, we will explore the behavior of electrons colliding with nano-magnetic disks. The computational molecular dynamics experiment allows us to follow the trajectory of individual electrons all along the experiment. In order to compare our results with the experimental one reported in literature, we model the experimental electron detectors in a simplified way: a photo-sensitive screen is simulated in such way that it counts the number of electrons that collide at a certain position. The information is organized to give in grey scale the image information about the magnetic properties of the structure in the target. Computationally, the sensor is modeled as a square matrix in which we count how many electrons collide at each specific point after being scattered by the magnetic structure. We have used several configurations of the magnetic nano-disks to understand the behavior of the scattered electrons, changing the orientation direction of the magnetic moments in the nano-disk in several ways. Our results match very well with the experiments, showing that this simulation can become a powerful technique to help to interpret experimental results.

  16. Analysis of Adhesive Characteristics of Asphalt Based on Atomic Force Microscopy and Molecular Dynamics Simulation.

    PubMed

    Xu, Meng; Yi, Junyan; Feng, Decheng; Huang, Yudong; Wang, Dongsheng

    2016-05-18

    Asphalt binder is a very important building material in infrastructure construction; it is commonly mixed with mineral aggregate and used to produce asphalt concrete. Owing to the large differences in physical and chemical properties between asphalt and aggregate, adhesive bonds play an important role in determining the performance of asphalt concrete. Although many types of adhesive bonding mechanisms have been proposed to explain the interaction forces between asphalt binder and mineral aggregate, few have been confirmed and characterized. In comparison with chemical interactions, physical adsorption has been considered to play a more important role in adhesive bonding between asphalt and mineral aggregate. In this study, the silicon tip of an atomic force microscope was used to represent silicate minerals in aggregate, and a nanoscale analysis of the characteristics of adhesive bonding between asphalt binder and the silicon tip was conducted via an atomic force microscopy (AFM) test and molecular dynamics (MD) simulations. The results of the measurements and simulations could help in better understanding of the bonding and debonding procedures in asphalt-aggregate mixtures during hot mixing and under traffic loading. MD simulations on a single molecule of a component of asphalt and monocrystalline silicon demonstrate that molecules with a higher atomic density and planar structure, such as three types of asphaltene molecules, can provide greater adhesive strength. However, regarding the real components of asphalt binder, both the MD simulations and AFM test indicate that the colloidal structural behavior of asphalt also has a large influence on the adhesion behavior between asphalt and silicon. A schematic model of the interaction between asphalt and silicon is presented, which can explain the effect of aging on the adhesion behavior of asphalt. PMID:27115043

  17. Analysis of Adhesive Characteristics of Asphalt Based on Atomic Force Microscopy and Molecular Dynamics Simulation.

    PubMed

    Xu, Meng; Yi, Junyan; Feng, Decheng; Huang, Yudong; Wang, Dongsheng

    2016-05-18

    Asphalt binder is a very important building material in infrastructure construction; it is commonly mixed with mineral aggregate and used to produce asphalt concrete. Owing to the large differences in physical and chemical properties between asphalt and aggregate, adhesive bonds play an important role in determining the performance of asphalt concrete. Although many types of adhesive bonding mechanisms have been proposed to explain the interaction forces between asphalt binder and mineral aggregate, few have been confirmed and characterized. In comparison with chemical interactions, physical adsorption has been considered to play a more important role in adhesive bonding between asphalt and mineral aggregate. In this study, the silicon tip of an atomic force microscope was used to represent silicate minerals in aggregate, and a nanoscale analysis of the characteristics of adhesive bonding between asphalt binder and the silicon tip was conducted via an atomic force microscopy (AFM) test and molecular dynamics (MD) simulations. The results of the measurements and simulations could help in better understanding of the bonding and debonding procedures in asphalt-aggregate mixtures during hot mixing and under traffic loading. MD simulations on a single molecule of a component of asphalt and monocrystalline silicon demonstrate that molecules with a higher atomic density and planar structure, such as three types of asphaltene molecules, can provide greater adhesive strength. However, regarding the real components of asphalt binder, both the MD simulations and AFM test indicate that the colloidal structural behavior of asphalt also has a large influence on the adhesion behavior between asphalt and silicon. A schematic model of the interaction between asphalt and silicon is presented, which can explain the effect of aging on the adhesion behavior of asphalt.

  18. Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space

    DOE PAGES

    Balke, Nina; Kalinin, Sergei V.; Jesse, Stephen; Collins, Liam; Belianinov, Alex; Somnath, Suhas

    2016-08-12

    Kelvin probe force microscopy (KPFM) has provided deep insights into the role local electronic, ionic and electrochemical processes play on the global functionality of materials and devices, even down to the atomic scale. Conventional KPFM utilizes heterodyne detection and bias feedback to measure the contact potential difference (CPD) between tip and sample. This measurement paradigm, however, permits only partial recovery of the information encoded in bias- and time-dependent electrostatic interactions between the tip and sample and effectively down-samples the cantilever response to a single measurement of CPD per pixel. This level of detail is insufficient for electroactive materials, devices, ormore » solid-liquid interfaces, where non-linear dielectrics are present or spurious electrostatic events are possible. Here, we simulate and experimentally validate a novel approach for spatially resolved KPFM capable of a full information transfer of the dynamic electric processes occurring between tip and sample. General acquisition mode, or G-Mode, adopts a big data approach utilising high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates (> 4 MHz), providing a permanent record of the tip trajectory. We develop a range of methodologies for analysing the resultant large multidimensional datasets involving classical, physics-based and information-based approaches. Physics-based analysis of G-Mode KPFM data recovers the parabolic bias dependence of the electrostatic force for each cycle of the excitation voltage, leading to a multidimensional dataset containing spatial and temporal dependence of the CPD and capacitance channels. We use multivariate statistical methods to reduce data volume and separate the complex multidimensional data sets into statistically significant components that can then be mapped onto separate physical mechanisms. Overall, G-Mode KPFM offers a new paradigm to study

  19. Graphene on SiC(0001) inspected by dynamic atomic force microscopy at room temperature

    PubMed Central

    Telychko, Mykola; Berger, Jan; Majzik, Zsolt; Jelínek, Pavel

    2015-01-01

    Summary We investigated single-layer graphene on SiC(0001) by atomic force and tunneling current microscopy, to separate the topographic and electronic contributions from the overall landscape. The analysis revealed that the roughness evaluated from the atomic force maps is very low, in accord with theoretical simulations. We also observed that characteristic electron scattering effects on graphene edges and defects are not accompanied by any out-of-plane relaxations of carbon atoms. PMID:25977861

  20. Viewing dynamic interactions of proteins and a model lipid membrane with atomic force microscopy.

    PubMed

    Quinn, Anthony S; Rand, Jacob H; Wu, Xiao-Xuan; Taatjes, Douglas J

    2013-01-01

    The information covered in this chapter will present a model homogenous membrane preparation technique and dynamic imaging procedure that can be successfully applied to more than one type of lipid study and atomic force microscope (AFM) instrument setup. The basic procedural steps have been used with an Asylum Research MFP-3D BIO and the Bruker (formerly, Veeco) BioScope. The AFM imaging protocol has been supplemented by procedures (not to be presented in this chapter) of ellipsometry, standardized western blotting, and dot-blots to verify appropriate purity and activity of all experimental molecular components; excellent purity and activity level of the lipids, proteins, and drug(s) greatly influence the success of imaging experiments in the scanning probe microscopy field. The major goal of the chapter is to provide detailed procedures for sample preparation and operation of the Asylum Research MFP-3D BIO AFM. In addition, one should be cognizant that our comprehensive description in the use of the MFP-3D BIO's functions for successful image acquisitions and analyses is greatly enhanced by Asylum Research's (AR's) accompanying extensive manual(s), technical notes, and AR's users forum. Ultimately, the stepwise protocol and information will allow novice personnel to begin acquiring quality images for processing and analysis with minimal supervision.

  1. Dynamic behaviour of dagger-shaped cantilevers for atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Shen, Kangzhi; Hurley, Donna C.; Turner, Joseph A.

    2004-11-01

    Experimental techniques based on the atomic force microscope (AFM) have been developed for characterizing mechanical properties at the nanoscale and applied to a variety of materials and structures. Atomic force acoustic microscopy (AFAM) is one such technique that uses spectral information of the AFM cantilever as it vibrates in contact with a sample. In this paper, the dynamic behaviour of AFM cantilevers that have a dagger shape is investigated using a power-series method. Dagger-shaped cantilevers have plan-view geometry consisting of a rectangular section at the clamped end and a triangular section at the tip. Their geometry precludes modelling using closed-form expressions. The convergence of the series is demonstrated and the convergence radius is shown to be related to the given geometry. The accuracy and efficiency of the method are investigated by comparison with finite element results for several different cases. AFAM experiments are modelled by including a linear spring at the tip that represents the contact stiffness. The technique developed is shown to be very effective for inversion of experimental frequency information into contact stiffness results for AFAM. In addition, the sensitivities of the frequencies to the contact stiffness are discussed in terms of the various geometric parameters of the problem including the slope, the ratio of the rectangular to triangular lengths and the tip location. Calculations of contact stiffness from experimental data using this model are shown to be very good in comparison with other models. It is anticipated that this approach may be useful for other cantilever geometries as well, such that AFAM accuracy may be improved.

  2. Ultrasonic Force Microscopies

    NASA Astrophysics Data System (ADS)

    Kolosov, Oleg; Briggs, Andrew

    Ultrasonic Force Microscopy, or UFM, allows combination of two apparently mutually exclusive requirements for the nanomechanical probe—high stiffness for the efficient indentation and high mechanical compliance that brings force sensitivity. Somewhat inventively, UFM allows to combine these two virtues in the same cantilever by using indention of the sample at high frequency, when cantilever is very rigid, but detecting the result of this indention at much lower frequency. That is made possible due to the extreme nonlinearity of the nanoscale tip-surface junction force-distance dependence, that acts as "mechanical diode" detecting ultrasound in AFM. After introducing UFM principles, we discuss features of experimental UFM implementation, and the theory of contrast in this mode, progressing to quantitative measurements of contact stiffness. A variety of UFM applications ranging from semiconductor quantum nanostructures, graphene, very large scale integrated circuits, and reinforced ceramics to polymer composites and biological materials is presented via comprehensive imaging gallery accompanied by the guidance for the optimal UFM measurements of these materials. We also address effects of adhesion and topography on the elasticity imaging and the approaches for reducing artifacts connected with these effects. This is complemented by another extremely useful feature of UFM—ultrasound induced superlubricity that allows damage free imaging of materials ranging from stiff solid state devices and graphene to biological materials. Finally, we proceed to the exploration of time-resolved nanoscale phenomena using nonlinear mixing of multiple vibration frequencies in ultrasonic AFM—Heterodyne Force Microscopy, or HFM, that also include mixing of ultrasonic vibration with other periodic physical excitations, eg. electrical, photothermal, etc. Significant section of the chapter analyzes the ability of UFM and HFM to detect subsurface mechanical inhomogeneities, as well as

  3. Magnetic force microscopy

    PubMed Central

    Passeri, Daniele; Dong, Chunhua; Reggente, Melania; Angeloni, Livia; Barteri, Mario; Scaramuzzo, Francesca A; De Angelis, Francesca; Marinelli, Fiorenzo; Antonelli, Flavia; Rinaldi, Federica; Marianecci, Carlotta; Carafa, Maria; Sorbo, Angela; Sordi, Daniela; Arends, Isabel WCE; Rossi, Marco

    2014-01-01

    Magnetic force microscopy (MFM) is an atomic force microscopy (AFM) based technique in which an AFM tip with a magnetic coating is used to probe local magnetic fields with the typical AFM spatial resolution, thus allowing one to acquire images reflecting the local magnetic properties of the samples at the nanoscale. Being a well established tool for the characterization of magnetic recording media, superconductors and magnetic nanomaterials, MFM is finding constantly increasing application in the study of magnetic properties of materials and systems of biological and biomedical interest. After reviewing these latter applications, three case studies are presented in which MFM is used to characterize: (i) magnetoferritin synthesized using apoferritin as molecular reactor; (ii) magnetic nanoparticles loaded niosomes to be used as nanocarriers for drug delivery; (iii) leukemic cells labeled using folic acid-coated core-shell superparamagnetic nanoparticles in order to exploit the presence of folate receptors on the cell membrane surface. In these examples, MFM data are quantitatively analyzed evidencing the limits of the simple analytical models currently used. Provided that suitable models are used to simulate the MFM response, MFM can be used to evaluate the magnetic momentum of the core of magnetoferritin, the iron entrapment efficiency in single vesicles, or the uptake of magnetic nanoparticles into cells. PMID:25050758

  4. Finite element modeling of atomic force microscopy cantilever dynamics during video rate imaging

    SciTech Connect

    Howard-Knight, J. P.; Hobbs, J. K.

    2011-04-01

    A dynamic finite element model has been constructed to simulate the behavior of low spring constant atomic force microscope (AFM) cantilevers used for imaging at high speed without active feedback as in VideoAFM. The model is tested against experimental data collected at 20 frame/s and good agreement is found. The complex dynamics of the cantilever, consisting of traveling waves coming from the tip sample interaction, reflecting off the cantilever-substrate junction, and interfering with new waves created at the tip, are revealed. The construction of the image from this resulting nonequilibrium cantilever deflection is also examined. Transient tip-sample forces are found to reach values up to 260 nN on a calibration grid sample, and the maximum forces do not always correspond to the position of steepest features as a result of energy stored in the cantilever.

  5. Characterization of Probe Dynamic Behaviors in Critical Dimension Atomic Force Microscopy

    PubMed Central

    Feng, Shaw C.; Joung, Che Bong; Vorburger, Theodore V.

    2009-01-01

    This paper describes a detailed computational model of the interaction between an atomic force microscope probe tip and a sample surface. The model provides analyses of dynamic behaviors of the tip to estimate the probe deflections due to surface intermittent contact and the resulting dimensional biases and uncertainties. Probe tip and cantilever beam responses to intermittent contact between the probe tip and sample surface are computed using the finite element method. Intermittent contacts with a wall and a horizontal surface are computed and modeled, respectively. Using a 75 nm Critical Dimension (CD) tip as an example, the responses of the probe to interaction forces between the sample surface and the probe tip are shown in both time and frequency domains. In particular, interaction forces between the tip and both a vertical wall and a horizontal surface of a silicon sample are modeled using Lennard-Jones theory. The Snap-in and Snap-out of the probe tip in surface scanning are calculated and shown in the time domain. Based on the given tip-sample interaction force model, the calculation includes the compliance of the probe and dynamic forces generated by an excitation. Cantilever and probe tip deflections versus interaction forces in the time domain can be derived for both vertical contact with a plateau and horizontal contact with a side wall. Dynamic analysis using the finite element method and Lennard-Jones model provide a unique means to analyze the interaction of the probe and sample, including calculation of the deflection and the gap between the probe tip and the measured sample surface. PMID:27504222

  6. Probing charge screening dynamics and electrochemical processes at the solid-liquid interface with electrochemical force microscopy.

    PubMed

    Collins, Liam; Jesse, Stephen; Kilpatrick, Jason I; Tselev, Alexander; Varenyk, Oleksandr; Okatan, M Baris; Weber, Stefan A L; Kumar, Amit; Balke, Nina; Kalinin, Sergei V; Rodriguez, Brian J

    2014-05-20

    The presence of mobile ions complicates the implementation of voltage-modulated scanning probe microscopy techniques such as Kelvin probe force microscopy (KPFM). Overcoming this technical hurdle, however, provides a unique opportunity to probe ion dynamics and electrochemical processes in liquid environments and the possibility to unravel the underlying mechanisms behind important processes at the solid-liquid interface, including adsorption, electron transfer and electrocatalysis. Here we describe the development and implementation of electrochemical force microscopy (EcFM) to probe local bias- and time-resolved ion dynamics and electrochemical processes at the solid-liquid interface. Using EcFM, we demonstrate contact potential difference measurements, consistent with the principles of open-loop KPFM operation. We also demonstrate that EcFM can be used to investigate charge screening mechanisms and electrochemical reactions in the probe-sample junction. We further establish EcFM as a force-based imaging mode, allowing visualization of the spatial variability of sample-dependent local electrochemical properties.

  7. Strength by atomic force microscopy (AFM): Molecular dynamics of water layer squeezing on magnesium oxide

    NASA Astrophysics Data System (ADS)

    Kendall, K.; Dhir, Aman; Yong, Chin W.

    2010-11-01

    Localised strength testing of materials is often carried out in an atomic force microscope (AFM), as foreseen by Kelly in his book Strong Solids (Clarendon Press, Oxford, 1966). During AFM indentation experiments, contamination can strongly influence the observed strength and theoretical interpretation of the results is a major problem. Here, we use molecular dynamics computer modelling to describe the contact of NaCl and MgO crystal probes onto surfaces, comparable to an AFM experiment. Clean NaCl gave elastic, brittle behaviour in contact simulations at 300 K, whereas MgO was more plastic, leading to increased toughness. This paper also considers the strength of an oxide substrate contaminated by water molecules and tested by indentation with a pyramidal probe of oxide crystal. Recent theory on the effect of liquid contaminant layers on surface strength has been mainly focussed on Lennard Jones (LJ) molecules with some studies on alcohols and water, described by molecular dynamics, which allows the molecules to be squeezed out as the crystal lattice is deformed. In this work, we have focused on water by studying the forces between a magnesium oxide (MgO) atomic force microscope (AFM) probe and an MgO slab. Force versus separation has been plotted as the AFM probe was moved towards and away from the substrate. Simulation results showed that the water layers could be removed in steps, giving up to four force peaks. The last monolayer of water could not be squeezed out, even at pressures where MgO deformed plastically. Interestingly, with water present, strength was reduced, but more in tensile than compressive measurements. In conclusion, water contaminating the oxide surface in AFM strength testing is structured. Water layer squeezing removal can be predicted by molecular modelling, which may be verified by AFM experiments to show that water can influence the strength of perfect crystals at the nanometre scale.

  8. Kelvin probe force microscopy in liquid using electrochemical force microscopy

    PubMed Central

    Collins, Liam; Jesse, Stephen; Kilpatrick, Jason I; Tselev, Alexander; Okatan, M Baris; Kalinin, Sergei V

    2015-01-01

    Summary Conventional closed loop-Kelvin probe force microscopy (KPFM) has emerged as a powerful technique for probing electric and transport phenomena at the solid–gas interface. The extension of KPFM capabilities to probe electrostatic and electrochemical phenomena at the solid–liquid interface is of interest for a broad range of applications from energy storage to biological systems. However, the operation of KPFM implicitly relies on the presence of a linear lossless dielectric in the probe–sample gap, a condition which is violated for ionically-active liquids (e.g., when diffuse charge dynamics are present). Here, electrostatic and electrochemical measurements are demonstrated in ionically-active (polar isopropanol, milli-Q water and aqueous NaCl) and ionically-inactive (non-polar decane) liquids by electrochemical force microscopy (EcFM), a multidimensional (i.e., bias- and time-resolved) spectroscopy method. In the absence of mobile charges (ambient and non-polar liquids), KPFM and EcFM are both feasible, yielding comparable contact potential difference (CPD) values. In ionically-active liquids, KPFM is not possible and EcFM can be used to measure the dynamic CPD and a rich spectrum of information pertaining to charge screening, ion diffusion, and electrochemical processes (e.g., Faradaic reactions). EcFM measurements conducted in isopropanol and milli-Q water over Au and highly ordered pyrolytic graphite electrodes demonstrate both sample- and solvent-dependent features. Finally, the feasibility of using EcFM as a local force-based mapping technique of material-dependent electrostatic and electrochemical response is investigated. The resultant high dimensional dataset is visualized using a purely statistical approach that does not require a priori physical models, allowing for qualitative mapping of electrostatic and electrochemical material properties at the solid–liquid interface. PMID:25671164

  9. Kelvin probe force microscopy in liquid using electrochemical force microscopy.

    PubMed

    Collins, Liam; Jesse, Stephen; Kilpatrick, Jason I; Tselev, Alexander; Okatan, M Baris; Kalinin, Sergei V; Rodriguez, Brian J

    2015-01-01

    Conventional closed loop-Kelvin probe force microscopy (KPFM) has emerged as a powerful technique for probing electric and transport phenomena at the solid-gas interface. The extension of KPFM capabilities to probe electrostatic and electrochemical phenomena at the solid-liquid interface is of interest for a broad range of applications from energy storage to biological systems. However, the operation of KPFM implicitly relies on the presence of a linear lossless dielectric in the probe-sample gap, a condition which is violated for ionically-active liquids (e.g., when diffuse charge dynamics are present). Here, electrostatic and electrochemical measurements are demonstrated in ionically-active (polar isopropanol, milli-Q water and aqueous NaCl) and ionically-inactive (non-polar decane) liquids by electrochemical force microscopy (EcFM), a multidimensional (i.e., bias- and time-resolved) spectroscopy method. In the absence of mobile charges (ambient and non-polar liquids), KPFM and EcFM are both feasible, yielding comparable contact potential difference (CPD) values. In ionically-active liquids, KPFM is not possible and EcFM can be used to measure the dynamic CPD and a rich spectrum of information pertaining to charge screening, ion diffusion, and electrochemical processes (e.g., Faradaic reactions). EcFM measurements conducted in isopropanol and milli-Q water over Au and highly ordered pyrolytic graphite electrodes demonstrate both sample- and solvent-dependent features. Finally, the feasibility of using EcFM as a local force-based mapping technique of material-dependent electrostatic and electrochemical response is investigated. The resultant high dimensional dataset is visualized using a purely statistical approach that does not require a priori physical models, allowing for qualitative mapping of electrostatic and electrochemical material properties at the solid-liquid interface.

  10. Kelvin Probe Force Microscopy in liquid using Electrochemical Force Microscopy

    SciTech Connect

    Collins, Liam; Jesse, Stephen; Kilpatrick, J.; Tselev, Alexander; Okatan, Mahmut Baris; Kalinin, Sergei V.; Rodriguez, Brian

    2015-01-01

    Conventional closed loop-Kelvin probe force microscopy (KPFM) has emerged as a powerful technique for probing electric and transport phenomena at the solid-gas interface. The extension of KPFM capabilities to probe electrostatic and electrochemical phenomena at the solid–liquid interface is of interest for a broad range of applications from energy storage to biological systems. However, the operation of KPFM implicitly relies on the presence of a linear lossless dielectric in the probe-sample gap, a condition which is violated for ionically-active liquids (e.g., when diffuse charge dynamics are present). Here, electrostatic and electrochemical measurements are demonstrated in ionically-active (polar isopropanol, milli-Q water and aqueous NaCl) and ionically-inactive (non-polar decane) liquids by electrochemical force microscopy (EcFM), a multidimensional (i.e., bias- and time-resolved) spectroscopy method. In the absence of mobile charges (ambient and non-polar liquids), KPFM and EcFM are both feasible, yielding comparable contact potential difference (CPD) values. In ionically-active liquids, KPFM is not possible and EcFM can be used to measure the dynamic CPD and a rich spectrum of information pertaining to charge screening, ion diffusion, and electrochemical processes (e.g., Faradaic reactions). EcFM measurements conducted in isopropanol and milli-Q water over Au and highly ordered pyrolytic graphite electrodes demonstrate both sample- and solvent-dependent features. Finally, the feasibility of using EcFM as a local force-based mapping technique of material-dependent electrostatic and electrochemical response is investigated. The resultant high dimensional dataset is visualized using a purely statistical approach that does not require a priori physical models, allowing for qualitative mapping of electrostatic and electrochemical material properties at the solid–liquid interface.

  11. Kelvin Probe Force Microscopy in liquid using Electrochemical Force Microscopy

    DOE PAGES

    Collins, Liam; Jesse, Stephen; Kilpatrick, J.; Tselev, Alexander; Okatan, Mahmut Baris; Kalinin, Sergei V.; Rodriguez, Brian

    2015-01-01

    Conventional closed loop-Kelvin probe force microscopy (KPFM) has emerged as a powerful technique for probing electric and transport phenomena at the solid-gas interface. The extension of KPFM capabilities to probe electrostatic and electrochemical phenomena at the solid–liquid interface is of interest for a broad range of applications from energy storage to biological systems. However, the operation of KPFM implicitly relies on the presence of a linear lossless dielectric in the probe-sample gap, a condition which is violated for ionically-active liquids (e.g., when diffuse charge dynamics are present). Here, electrostatic and electrochemical measurements are demonstrated in ionically-active (polar isopropanol, milli-Q watermore » and aqueous NaCl) and ionically-inactive (non-polar decane) liquids by electrochemical force microscopy (EcFM), a multidimensional (i.e., bias- and time-resolved) spectroscopy method. In the absence of mobile charges (ambient and non-polar liquids), KPFM and EcFM are both feasible, yielding comparable contact potential difference (CPD) values. In ionically-active liquids, KPFM is not possible and EcFM can be used to measure the dynamic CPD and a rich spectrum of information pertaining to charge screening, ion diffusion, and electrochemical processes (e.g., Faradaic reactions). EcFM measurements conducted in isopropanol and milli-Q water over Au and highly ordered pyrolytic graphite electrodes demonstrate both sample- and solvent-dependent features. Finally, the feasibility of using EcFM as a local force-based mapping technique of material-dependent electrostatic and electrochemical response is investigated. The resultant high dimensional dataset is visualized using a purely statistical approach that does not require a priori physical models, allowing for qualitative mapping of electrostatic and electrochemical material properties at the solid–liquid interface.« less

  12. Cell adhesion force microscopy

    PubMed Central

    Sagvolden, G.; Giaever, I.; Pettersen, E. O.; Feder, J.

    1999-01-01

    The adhesion forces of cervical carcinoma cells in tissue culture were measured by using the manipulation force microscope, a novel atomic force microscope. The forces were studied as a function of time and temperature for cells cultured on hydrophilic and hydrophobic polystyrene substrates with preadsorbed proteins. The cells attached faster and stronger at 37°C than at 23°C and better on hydrophilic than on hydrophobic substrates, even though proteins adsorb much better to the hydrophobic substrates. Because cell adhesion serves to control several stages in the cell cycle, we anticipate that the manipulation force microscope can help clarify some cell-adhesion related issues. PMID:9892657

  13. High-resolution imaging of gold clusters on KBr(001) surfaces investigated by dynamic scanning force microscopy

    NASA Astrophysics Data System (ADS)

    Barth, Clemens; Henry, Claude R.

    2004-09-01

    Dynamic scanning force microscopy (dynamic SFM) images of (001) surfaces of KBr which have been prepared by cleavage and further decorated by nanometre-sized gold clusters in UHV are presented. During scanning we could achieve atomic resolution on the KBr substrate surface; however, the clusters mostly appeared as hemisphere-like or fuzzy objects exhibiting only a few details of their internal structure. We performed force spectroscopy measurements above single clusters which might point to a charging of the clusters. We anticipate that mainly a long-range electrostatic interaction between the cluster and the macroscopic tip apex determines the appearance of the clusters. Information on the interior of the clusters can be gained only for short tip-cluster distances in the presence of a short-range, chemical interaction between the cluster and the tip atoms closest to the surface.

  14. Dynamic modeling and simulation of rough cylindrical micro/nanoparticle manipulation with atomic force microscopy.

    PubMed

    Korayem, Moharam H; Badkoobeh Hezaveh, Hedieh; Taheri, Moein

    2014-12-01

    In this paper, the process of pushing rough cylindrical micro/nanoparticles on a surface with an atomic force microscope (AFM) probe is investigated. For this purpose, the mechanics of contact involving adhesion are studied first. Then, a method is presented for estimating the real area of contact between a rough cylindrical particle (whose surface roughness is described by the Rumpf and Rabinovich models) and a smooth surface. A dynamic model is then obtained for the pushing of rough cylindrical particles on a surface with an AFM probe. Afterwards, the process is simulated for different particle sizes and various roughness dimensions. Finally, by reducing the length of the cylindrical particle, the simulation condition is brought closer to the manipulation condition of a smooth spherical particle on a rough substrate, and the simulation results of the two cases are compared. Based on the simulation results, the critical force and time of manipulation diminish for rough particles relative to smooth ones. Reduction in the aspect ratio at a constant cross-section radius and the radius of asperities (height of asperities based on the Rabinovich model) results in an increase in critical force and time of manipulation.

  15. Gaining insight into the physics of dynamic atomic force microscopy in complex environments using the VEDA simulator

    NASA Astrophysics Data System (ADS)

    Kiracofe, Daniel; Melcher, John; Raman, Arvind

    2012-01-01

    Dynamic atomic force microscopy (dAFM) continues to grow in popularity among scientists in many different fields, and research on new methods and operating modes continues to expand the resolution, capabilities, and types of samples that can be studied. But many promising increases in capability are accompanied by increases in complexity. Indeed, interpreting modern dAFM data can be challenging, especially on complicated material systems, or in liquid environments where the behavior is often contrary to what is known in air or vacuum environments. Mathematical simulations have proven to be an effective tool in providing physical insight into these non-intuitive systems. In this article we describe recent developments in the VEDA (virtual environment for dynamic AFM) simulator, which is a suite of freely available, open-source simulation tools that are delivered through the cloud computing cyber-infrastructure of nanoHUB (www.nanohub.org). Here we describe three major developments. First, simulations in liquid environments are improved by enhancements in the modeling of cantilever dynamics, excitation methods, and solvation shell forces. Second, VEDA is now able to simulate many new advanced modes of operation (bimodal, phase-modulation, frequency-modulation, etc.). Finally, nineteen different tip-sample models are available to simulate the surface physics of a wide variety different material systems including capillary, specific adhesion, van der Waals, electrostatic, viscoelasticity, and hydration forces. These features are demonstrated through example simulations and validated against experimental data, in order to provide insight into practical problems in dynamic AFM.

  16. High-speed atomic force microscopy reveals structural dynamics of amyloid β1-42 aggregates.

    PubMed

    Watanabe-Nakayama, Takahiro; Ono, Kenjiro; Itami, Masahiro; Takahashi, Ryoichi; Teplow, David B; Yamada, Masahito

    2016-05-24

    Aggregation of amyloidogenic proteins into insoluble amyloid fibrils is implicated in various neurodegenerative diseases. This process involves protein assembly into oligomeric intermediates and fibrils with highly polymorphic molecular structures. These structural differences may be responsible for different disease presentations. For this reason, elucidation of the structural features and assembly kinetics of amyloidogenic proteins has been an area of intense study. We report here the results of high-speed atomic force microscopy (HS-AFM) studies of fibril formation and elongation by the 42-residue form of the amyloid β-protein (Aβ1-42), a key pathogenetic agent of Alzheimer's disease. Our data demonstrate two different growth modes of Aβ1-42, one producing straight fibrils and the other producing spiral fibrils. Each mode depends on initial fibril nucleus structure, but switching from one growth mode to another was occasionally observed, suggesting that fibril end structure fluctuated between the two growth modes. This switching phenomenon was affected by buffer salt composition. Our findings indicate that polymorphism in fibril structure can occur after fibril nucleation and is affected by relatively modest changes in environmental conditions. PMID:27162352

  17. Energy dissipation and dynamic response of an amplitude-modulation atomic-force microscopy subjected to a tip-sample viscous force.

    PubMed

    Lin, Shueei Muh

    2007-01-01

    In a common environment of atomic force microscopy (AFM), a damping force occurs between a tip and a sample. The influence of damping on the dynamic response of a cantilever must be significant. Moreover, accurate theory is very helpful for the interpretation of a sample's topography and properties. In this study, the effects of damping and nonlinear interatomic tip-sample forces on the dynamic response of an amplitude-formulation AFM are investigated. The damping force is simulated by using the conventional Kelvin-Voigt damping model. The interatomic tip-sample force is the attractive van der Waals force. For consistance with real measurement of a cantilever, the mathematical equations of the beam theory of an AM-AFM are built and its analytical solution is derived. Moreover, an AFM system is also simplified into a mass-spring-damper model. Its exact solution is simple and intuitive. Several relations among the damping ratio, the response ratio, the frequency shift, the energy dissipation and the Q-factor are revealed. It is found that the resonant frequencies and the phase angles determined by the two models are almost same. Significant differences in the resonant quality factors and the response ratios determined by using the two models are also found. Finally, the influences of the variations of several parameters on the error of measuring a sample's topography are investigated. PMID:16982149

  18. The emergence of multifrequency force microscopy.

    PubMed

    Garcia, Ricardo; Herruzo, Elena T

    2012-04-01

    In atomic force microscopy a cantilever with a sharp tip attached to it is scanned over the surface of a sample, and information about the surface is extracted by measuring how the deflection of the cantilever - which is caused by interactions between the tip and the surface - varies with position. In the most common form of atomic force microscopy, dynamic force microscopy, the cantilever is made to vibrate at a specific frequency, and the deflection of the tip is measured at this frequency. But the motion of the cantilever is highly nonlinear, and in conventional dynamic force microscopy, information about the sample that is encoded in the deflection at frequencies other than the excitation frequency is irreversibly lost. Multifrequency force microscopy involves the excitation and/or detection of the deflection at two or more frequencies, and it has the potential to overcome limitations in the spatial resolution and acquisition times of conventional force microscopes. Here we review the development of five different modes of multifrequency force microscopy and examine its application in studies of proteins, the imaging of vibrating nanostructures, measurements of ion diffusion and subsurface imaging in cells.

  19. The emergence of multifrequency force microscopy.

    PubMed

    Garcia, Ricardo; Herruzo, Elena T

    2012-04-01

    In atomic force microscopy a cantilever with a sharp tip attached to it is scanned over the surface of a sample, and information about the surface is extracted by measuring how the deflection of the cantilever - which is caused by interactions between the tip and the surface - varies with position. In the most common form of atomic force microscopy, dynamic force microscopy, the cantilever is made to vibrate at a specific frequency, and the deflection of the tip is measured at this frequency. But the motion of the cantilever is highly nonlinear, and in conventional dynamic force microscopy, information about the sample that is encoded in the deflection at frequencies other than the excitation frequency is irreversibly lost. Multifrequency force microscopy involves the excitation and/or detection of the deflection at two or more frequencies, and it has the potential to overcome limitations in the spatial resolution and acquisition times of conventional force microscopes. Here we review the development of five different modes of multifrequency force microscopy and examine its application in studies of proteins, the imaging of vibrating nanostructures, measurements of ion diffusion and subsurface imaging in cells. PMID:22466857

  20. Photothermal excitation and laser Doppler velocimetry of higher cantilever vibration modes for dynamic atomic force microscopy in liquid

    SciTech Connect

    Nishida, Shuhei; Kobayashi, Dai; Sakurada, Takeo; Nakazawa, Tomonori; Hoshi, Yasuo; Kawakatsu, Hideki

    2008-12-15

    The authors present an optically based method combining photothermal excitation and laser Doppler velocimetry of higher cantilever vibration modes for dynamic atomic force microscopy in liquid. The frequency spectrum of a silicon cantilever measured in water over frequencies ranging up to 10 MHz shows that the method allows us to excite and detect higher modes, from fundamental to fifth flexural, without enhancing spurious resonances. By reducing the tip oscillation amplitude using higher modes, the average tip-sample force gradient due to chemical bonds is effectively increased to achieve high-spatial-resolution imaging in liquid. The method's performance is demonstrated by atomic resolution imaging of a mica surface in water obtained using the second flexural mode with a small tip amplitude of 99 pm; individual atoms on the surface with small height differences of up to 60 pm are clearly resolved.

  1. Tunneling magnetic force microscopy

    NASA Technical Reports Server (NTRS)

    Burke, Edward R.; Gomez, Romel D.; Adly, Amr A.; Mayergoyz, Isaak D.

    1993-01-01

    We have developed a powerful new tool for studying the magnetic patterns on magnetic recording media. This was accomplished by modifying a conventional scanning tunneling microscope. The fine-wire probe that is used to image surface topography was replaced with a flexible magnetic probe. Images obtained with these probes reveal both the surface topography and the magnetic structure. We have made a thorough theoretical analysis of the interaction between the probe and the magnetic fields emanating from a typical recorded surface. Quantitative data about the constituent magnetic fields can then be obtained. We have employed these techniques in studies of two of the most important issues of magnetic record: data overwrite and maximizing data-density. These studies have shown: (1) overwritten data can be retrieved under certain conditions; and (2) improvements in data-density will require new magnetic materials. In the course of these studies we have developed new techniques to analyze magnetic fields of recorded media. These studies are both theoretical and experimental and combined with the use of our magnetic force scanning tunneling microscope should lead to further breakthroughs in the field of magnetic recording.

  2. Deep atomic force microscopy

    SciTech Connect

    Barnard, H.; Drake, B.; Randall, C.; Hansma, P. K.

    2013-12-15

    The Atomic Force Microscope (AFM) possesses several desirable imaging features including the ability to produce height profiles as well as two-dimensional images, in fluid or air, at high resolution. AFM has been used to study a vast selection of samples on the scale of angstroms to micrometers. However, current AFMs cannot access samples with vertical topography of the order of 100 μm or greater. Research efforts have produced AFM scanners capable of vertical motion greater than 100 μm, but commercially available probe tip lengths are still typically less than 10 μm high. Even the longest probe tips are below 100 μm and even at this range are problematic. In this paper, we present a method to hand-fabricate “Deep AFM” probes with tips of the order of 100 μm and longer so that AFM can be used to image samples with large scale vertical topography, such as fractured bone samples.

  3. Dimensional and Mechanical Dynamics of Active and Stable Edges in Motile Fibroblasts Investigated by Using Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Rotsch, Christian; Jacobson, Ken; Radmacher, Manfred

    1999-02-01

    The atomic force microscope (AFM) was employed to investigate the extension and retraction dynamics of protruding and stable edges of motile 3T3 fibroblasts in culture. Such dynamics closely paralleled the results of earlier studies employing video microscopy that indicated that the AFM force-mapping technique does not appreciably perturb these dynamics. Force scans permitted height determinations of active and stable edges. Whereas the profiles of active edges are flat with average heights of 0.4-0.8 μ m, stable edges smoothly ascend to 2-3 μ m within about 6 μ m of the edge. In the region of the leading edge, the height fluctuates up to 50% (SD) of the mean value, much more than the stable edge; this fluctuation presumably reflects differences in underlying cytoskeletal activity. In addition, force mapping yields an estimate of the local Young's modulus or modulus of elasticity (E, the cortical stiffness). This stiffness will be related to "cortical tension," can be accurately calculated for the stable edges, and is ≈ 12 kPa in this case. The thinness of the leading edge precludes accurate estimation of the E values, but within 4 μ m of the margin it is considerably smaller than that for stable edges, which have an upper limit of 3-5 kPa. Although blebbing cannot absolutely be ruled out as a mechanism of extension, the data are consistent with an actin polymerization and/or myosin motor mechanism in which the average material properties of the extending margin would be nearly constant to the edge. Because the leading edge is softer than the stable edge, these data also are consistent with the notion that extension preferentially occurs in regions of lower cortical tension.

  4. Gaining insight into the physics of dynamic atomic force microscopy in complex environments using the VEDA simulator.

    PubMed

    Kiracofe, Daniel; Melcher, John; Raman, Arvind

    2012-01-01

    Dynamic atomic force microscopy (dAFM) continues to grow in popularity among scientists in many different fields, and research on new methods and operating modes continues to expand the resolution, capabilities, and types of samples that can be studied. But many promising increases in capability are accompanied by increases in complexity. Indeed, interpreting modern dAFM data can be challenging, especially on complicated material systems, or in liquid environments where the behavior is often contrary to what is known in air or vacuum environments. Mathematical simulations have proven to be an effective tool in providing physical insight into these non-intuitive systems. In this article we describe recent developments in the VEDA (virtual environment for dynamic AFM) simulator, which is a suite of freely available, open-source simulation tools that are delivered through the cloud computing cyber-infrastructure of nanoHUB (www.nanohub.org). Here we describe three major developments. First, simulations in liquid environments are improved by enhancements in the modeling of cantilever dynamics, excitation methods, and solvation shell forces. Second, VEDA is now able to simulate many new advanced modes of operation (bimodal, phase-modulation, frequency-modulation, etc.). Finally, nineteen different tip-sample models are available to simulate the surface physics of a wide variety different material systems including capillary, specific adhesion, van der Waals, electrostatic, viscoelasticity, and hydration forces. These features are demonstrated through example simulations and validated against experimental data, in order to provide insight into practical problems in dynamic AFM. PMID:22299957

  5. Interaction and dynamics of ambient water adlayers on graphite probed using AFM voltage nanolithography and electrostatic force microscopy.

    PubMed

    Gowthami, T; Kurra, Narendra; Raina, Gargi

    2014-04-18

    In this work, we report the impact of the interaction and dynamics of increasing ambient water adlayers on etch patterns on a hydrophobic highly oriented pyrolytic graphite (HOPG) surface obtained using atomic force microscopy (AFM) voltage nanolithography in contact mode by applying a positive bias to the sample. The changes in the dimensions of the etch patterns were investigated as a function of the increasing number of water adlayers present on the HOPG, which is varied by changing the time interval since HOPG cleavage. Changes in the width of the etch patterns and the surrounding water droplets were monitored with time, using intermittent-contact-mode AFM. Electrostatic force microscopy (EFM) has been employed to study the charged nature of the etch patterns and the neighboring water film with time. The width of the etch patterns made on freshly cleaved HOPG shows an increase of ∼33% over 48 h, whereas nine-day-old cleaved HOPG shows a 79% increase over the same period. No changes in the dimensions are observed while imaging in a nitrogen atmosphere soon after lithography. In ambient conditions, the EFM phase shift of the patterns shows a large change of ∼84-88% over 30 h. This study demonstrates the effect of the stored electrostatic energy of a polarized ice-like water adlayer, resulting in changes in the dimensions of the etch patterns long after lithography, whereas liquid-like water droplets do not affect the etch patterns.

  6. Interaction and dynamics of ambient water adlayers on graphite probed using AFM voltage nanolithography and electrostatic force microscopy.

    PubMed

    Gowthami, T; Kurra, Narendra; Raina, Gargi

    2014-04-18

    In this work, we report the impact of the interaction and dynamics of increasing ambient water adlayers on etch patterns on a hydrophobic highly oriented pyrolytic graphite (HOPG) surface obtained using atomic force microscopy (AFM) voltage nanolithography in contact mode by applying a positive bias to the sample. The changes in the dimensions of the etch patterns were investigated as a function of the increasing number of water adlayers present on the HOPG, which is varied by changing the time interval since HOPG cleavage. Changes in the width of the etch patterns and the surrounding water droplets were monitored with time, using intermittent-contact-mode AFM. Electrostatic force microscopy (EFM) has been employed to study the charged nature of the etch patterns and the neighboring water film with time. The width of the etch patterns made on freshly cleaved HOPG shows an increase of ∼33% over 48 h, whereas nine-day-old cleaved HOPG shows a 79% increase over the same period. No changes in the dimensions are observed while imaging in a nitrogen atmosphere soon after lithography. In ambient conditions, the EFM phase shift of the patterns shows a large change of ∼84-88% over 30 h. This study demonstrates the effect of the stored electrostatic energy of a polarized ice-like water adlayer, resulting in changes in the dimensions of the etch patterns long after lithography, whereas liquid-like water droplets do not affect the etch patterns. PMID:24651210

  7. Nanonet Force Microscopy for Measuring Cell Forces.

    PubMed

    Sheets, Kevin; Wang, Ji; Zhao, Wei; Kapania, Rakesh; Nain, Amrinder S

    2016-07-12

    The influence of physical forces exerted by or felt by cells on cell shape, migration, and cytoskeleton arrangement is now widely acknowledged and hypothesized to occur due to modulation of cellular inside-out forces in response to changes in the external fibrous environment (outside-in). Our previous work using the non-electrospinning Spinneret-based Tunable Engineered Parameters' suspended fibers has revealed that cells are able to sense and respond to changes in fiber curvature and structural stiffness as evidenced by alterations to focal adhesion cluster lengths. Here, we present the development and application of a suspended nanonet platform for measuring C2C12 mouse myoblast forces attached to fibers of three diameters (250, 400, and 800 nm) representing a wide range of structural stiffness (3-50 nN/μm). The nanonet force microscopy platform measures cell adhesion forces in response to symmetric and asymmetric external perturbation in single and cyclic modes. We find that contractility-based, inside-out forces are evenly distributed at the edges of the cell, and that forces are dependent on fiber structural stiffness. Additionally, external perturbation in symmetric and asymmetric modes biases cell-fiber failure location without affecting the outside-in forces of cell-fiber adhesion. We then extend the platform to measure forces of (1) cell-cell junctions, (2) single cells undergoing cyclic perturbation in the presence of drugs, and (3) cancerous single-cells transitioning from a blebbing to a pseudopodial morphology. PMID:27410747

  8. Dynamic shear force microscopy of viscosity in nanometer-confined hexadecane layers

    NASA Astrophysics Data System (ADS)

    Krass, Marc-Dominik; Nand Gosvami, Nitya; Carpick, Robert W.; Müser, Martin H.; Bennewitz, Roland

    2016-04-01

    Hexadecane exhibits pronounced molecular layering upon confinement to gaps of a few nanometer width which is discussed for its role in boundary lubrication. We have probed the mechanical properties of the confined layers with the help of an atomic force microscope, by quasi-static normal force measurements and by analyzing the lateral tip motion of a magnetically actuated torsional cantilever oscillation. The molecular layering is modeled by a oscillatory force curve and the tip approach is simulated assuming thermal equilibrium correlations in the liquid. The shear response of the confined layers reveals gradually increasing stiffness and viscous dissipation for a decreasing number of confined layers.

  9. Dynamic shear force microscopy of viscosity in nanometer-confined hexadecane layers.

    PubMed

    Krass, Marc-Dominik; Gosvami, Nitya Nand; Carpick, Robert W; Müser, Martin H; Bennewitz, Roland

    2016-04-01

    Hexadecane exhibits pronounced molecular layering upon confinement to gaps of a few nanometer width which is discussed for its role in boundary lubrication. We have probed the mechanical properties of the confined layers with the help of an atomic force microscope, by quasi-static normal force measurements and by analyzing the lateral tip motion of a magnetically actuated torsional cantilever oscillation. The molecular layering is modeled by a oscillatory force curve and the tip approach is simulated assuming thermal equilibrium correlations in the liquid. The shear response of the confined layers reveals gradually increasing stiffness and viscous dissipation for a decreasing number of confined layers. PMID:26931743

  10. Calibration of measurement sensitivities of multiple micro-cantilever dynamic modes in atomic force microscopy using a contact detection method

    SciTech Connect

    Liu Zhen; Jeong, Younkoo; Menq, Chia-Hsiang

    2013-02-15

    An accurate experimental method is proposed for on-spot calibration of the measurement sensitivities of multiple micro-cantilever dynamic modes in atomic force microscopy. One of the key techniques devised for this method is a reliable contact detection mechanism that detects the tip-surface contact instantly. At the contact instant, the oscillation amplitude of the tip deflection, converted to that of the deflection signal in laser reading through the measurement sensitivity, exactly equals to the distance between the sample surface and the cantilever base position. Therefore, the proposed method utilizes the recorded oscillation amplitude of the deflection signal and the base position of the cantilever at the contact instant for the measurement sensitivity calibration. Experimental apparatus along with various signal processing and control modules was realized to enable automatic and rapid acquisition of multiple sets of data, with which the calibration of a single dynamic mode could be completed in less than 1 s to suppress the effect of thermal drift and measurement noise. Calibration of the measurement sensitivities of the first and second dynamic modes of three micro-cantilevers having distinct geometries was successfully demonstrated. The dependence of the measurement sensitivity on laser spot location was also experimentally investigated. Finally, an experiment was performed to validate the calibrated measurement sensitivity of the second dynamic mode of a micro-cantilever.

  11. Calibration of measurement sensitivities of multiple micro-cantilever dynamic modes in atomic force microscopy using a contact detection method.

    PubMed

    Liu, Zhen; Jeong, Younkoo; Menq, Chia-Hsiang

    2013-02-01

    An accurate experimental method is proposed for on-spot calibration of the measurement sensitivities of multiple micro-cantilever dynamic modes in atomic force microscopy. One of the key techniques devised for this method is a reliable contact detection mechanism that detects the tip-surface contact instantly. At the contact instant, the oscillation amplitude of the tip deflection, converted to that of the deflection signal in laser reading through the measurement sensitivity, exactly equals to the distance between the sample surface and the cantilever base position. Therefore, the proposed method utilizes the recorded oscillation amplitude of the deflection signal and the base position of the cantilever at the contact instant for the measurement sensitivity calibration. Experimental apparatus along with various signal processing and control modules was realized to enable automatic and rapid acquisition of multiple sets of data, with which the calibration of a single dynamic mode could be completed in less than 1 s to suppress the effect of thermal drift and measurement noise. Calibration of the measurement sensitivities of the first and second dynamic modes of three micro-cantilevers having distinct geometries was successfully demonstrated. The dependence of the measurement sensitivity on laser spot location was also experimentally investigated. Finally, an experiment was performed to validate the calibrated measurement sensitivity of the second dynamic mode of a micro-cantilever.

  12. Analytical Model of the Nonlinear Dynamics of Cantilever Tip-Sample Surface Interactions for Various Acoustic-Atomic Force Microscopies

    NASA Technical Reports Server (NTRS)

    Cantrell, John H., Jr.; Cantrell, Sean A.

    2008-01-01

    A comprehensive analytical model of the interaction of the cantilever tip of the atomic force microscope (AFM) with the sample surface is developed that accounts for the nonlinearity of the tip-surface interaction force. The interaction is modeled as a nonlinear spring coupled at opposite ends to linear springs representing cantilever and sample surface oscillators. The model leads to a pair of coupled nonlinear differential equations that are solved analytically using a standard iteration procedure. Solutions are obtained for the phase and amplitude signals generated by various acoustic-atomic force microscope (A-AFM) techniques including force modulation microscopy, atomic force acoustic microscopy, ultrasonic force microscopy, heterodyne force microscopy, resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM), and the commonly used intermittent contact mode (TappingMode) generally available on AFMs. The solutions are used to obtain a quantitative measure of image contrast resulting from variations in the Young modulus of the sample for the amplitude and phase images generated by the A-AFM techniques. Application of the model to RDF-AFUM and intermittent soft contact phase images of LaRC-cp2 polyimide polymer is discussed. The model predicts variations in the Young modulus of the material of 24 percent from the RDF-AFUM image and 18 percent from the intermittent soft contact image. Both predictions are in good agreement with the literature value of 21 percent obtained from independent, macroscopic measurements of sheet polymer material.

  13. Spatiotemporal dynamics of the nuclear pore complex transport barrier resolved by high-speed atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Sakiyama, Yusuke; Mazur, Adam; Kapinos, Larisa E.; Lim, Roderick Y. H.

    2016-08-01

    Nuclear pore complexes (NPCs) are biological nanomachines that mediate the bidirectional traffic of macromolecules between the cytoplasm and nucleus in eukaryotic cells. This process involves numerous intrinsically disordered, barrier-forming proteins known as phenylalanine-glycine nucleoporins (FG Nups) that are tethered inside each pore. The selective barrier mechanism has so far remained unresolved because the FG Nups have eluded direct structural analysis within NPCs. Here, high-speed atomic force microscopy is used to visualize the nanoscopic spatiotemporal dynamics of FG Nups inside Xenopus laevis oocyte NPCs at timescales of ∼100 ms. Our results show that the cytoplasmic orifice is circumscribed by highly flexible, dynamically fluctuating FG Nups that rapidly elongate and retract, consistent with the diffusive motion of tethered polypeptide chains. On this basis, intermingling FG Nups exhibit transient entanglements in the central channel, but do not cohere into a tightly crosslinked meshwork. Therefore, the basic functional form of the NPC barrier is comprised of highly dynamic FG Nups that manifest as a central plug or transporter when averaged in space and time.

  14. Spring constant of a tuning-fork sensor for dynamic force microscopy

    PubMed Central

    Lange, Manfred; Schmuck, Merlin; Schmidt, Nico; Möller, Rolf

    2012-01-01

    Summary We present an overview of experimental and numerical methods to determine the spring constant of a quartz tuning fork in qPlus configuration. The simple calculation for a rectangular cantilever is compared to the values obtained by the analysis of the thermal excitation and by the direct mechanical measurement of the force versus displacement. To elucidate the difference, numerical simulations were performed taking account of the real geometry including the glue that is used to mount the tuning fork. PMID:23365793

  15. Study of fluid and transport properties of porous anodic aluminum membranes by dynamic atomic force microscopy.

    PubMed

    Wu, Chu; Leese, Hannah S; Mattia, Davide; Dagastine, Raymond R; Chan, Derek Y C; Tabor, Rico F

    2013-07-16

    Recent work on carbon nanotubes (CNT) has focused on their potential application in water treatment as a result of their predicted and observed enhanced flow rates. Recent work on the lesser-known porous anodic alumina membranes (PAAMs) has also shown flow enhancement, albeit at only a fraction of what has been observed in CNTs. Despite their potential applications, little research has been conducted on PAAMs' hydrodynamic properties, and in this Article we present experimental results and theoretical models that explore the fluid flow behavior around and through these membranes. The experiments were conducted using an atomic force microscope (AFM) that pushed a solid silica particle against PAAMs that were characterized with different pore diameters. Furthermore, the PAAMs were classified as either closed or open, with the latter allowing fluid to pass through. The theoretical model developed to describe the experimental data incorporates Derjaguin-Landau-Verwey-Overbeek (DLVO) effects, cantilever drag, and hydrodynamic forces. By using the slip boundary condition for the hydrodynamic forces, we were able to fit the model to experimental findings and also demonstrate that the difference between closed and open PAAMs was negligible. The slip lengths did not correspond to any physical feature of the PAAMs, but our model does provide a simple yet effective means of describing the hydrodynamics for not only PAAMs but for membranes in general. PMID:23750974

  16. Unraveling the Architecture and Structural Dynamics of Pathogens by High-Resolution in vitro Atomic Force Microscopy

    SciTech Connect

    Malkin, A J; Plomp, M; Leighton, T J; McPherson, A; Wheeler, K E

    2005-04-12

    Progress in structural biology very much depends upon the development of new high-resolution techniques and tools. Despite decades of study of viruses, bacteria and bacterial spores and their pressing importance in human medicine and biodefense, many of their structural properties are poorly understood. Thus, characterization and understanding of the architecture of protein surface and internal structures of pathogens is critical to elucidating mechanisms of disease, immune response, physicochemical properties, environmental resistance and development of countermeasures against bioterrorist agents. Furthermore, even though complete genome sequences are available for various pathogens, the structure-function relationships are not understood. Because of their lack of symmetry and heterogeneity, large human pathogens are often refractory to X-ray crystallographic analysis or reconstruction by cryo-electron microscopy (cryo-EM). An alternative high-resolution method to examine native structure of pathogens is atomic force microscopy (AFM), which allows direct visualization of macromolecular assemblies at near-molecular resolution. The capability to image single pathogen surfaces at nanometer scale in vitro would profoundly impact mechanistic and structural studies of pathogenesis, immunobiology, specific cellular processes, environmental dynamics and biotransformation.

  17. Molecular scale energy dissipation in oligothiophene monolayers measured by dynamic force microscopy.

    PubMed

    Martínez, Nicolas F; Kamiński, Wojciech; Gómez, Carlos J; Albonetti, Cristiano; Biscarini, Fabio; Pérez, Rubén; García, Ricardo

    2009-10-28

    We perform a combined experimental and theoretical approach to establish the atomistic origin of energy dissipation occurring while imaging a molecular surface with an amplitude modulation atomic force microscope. We show that the energy transferred by a single nano-asperity to a sexithiophene monolayer is about 0.15 eV/cycle. The configuration space sampled by the tip depends on whether it approaches or withdraws from the surface. The asymmetry arises because of the presence of energy barriers among different deformations of the molecular geometry. This is the source of the material contrast provided by the phase-shift images. PMID:19801766

  18. Molecular scale energy dissipation in oligothiophene monolayers measured by dynamic force microscopy.

    PubMed

    Martínez, Nicolas F; Kamiński, Wojciech; Gómez, Carlos J; Albonetti, Cristiano; Biscarini, Fabio; Pérez, Rubén; García, Ricardo

    2009-10-28

    We perform a combined experimental and theoretical approach to establish the atomistic origin of energy dissipation occurring while imaging a molecular surface with an amplitude modulation atomic force microscope. We show that the energy transferred by a single nano-asperity to a sexithiophene monolayer is about 0.15 eV/cycle. The configuration space sampled by the tip depends on whether it approaches or withdraws from the surface. The asymmetry arises because of the presence of energy barriers among different deformations of the molecular geometry. This is the source of the material contrast provided by the phase-shift images.

  19. Fidelity imaging for atomic force microscopy

    SciTech Connect

    Ghosal, Sayan Salapaka, Murti

    2015-01-05

    Atomic force microscopy is widely employed for imaging material at the nanoscale. However, real-time measures on image reliability are lacking in contemporary atomic force microscopy literature. In this article, we present a real-time technique that provides an image of fidelity for a high bandwidth dynamic mode imaging scheme. The fidelity images define channels that allow the user to have additional authority over the choice of decision threshold that facilitates where the emphasis is desired, on discovering most true features on the sample with the possible detection of high number of false features, or emphasizing minimizing instances of false detections. Simulation and experimental results demonstrate the effectiveness of fidelity imaging.

  20. Enhancing the optical lever sensitivity of microcantilevers for dynamic atomic force microscopy via integrated low frequency paddles.

    PubMed

    Shaik, Nurul Huda; Reifenberger, Ronald G; Raman, Arvind

    2016-05-13

    A method is presented to enhance the optical lever sensitivity in dynamic atomic force microscopy (AFM) by nearly an order of magnitude over a wide frequency bandwidth. This is achieved by fabricating or releasing a paddle with a soft hinge close to the free end of the AFM microcantilever such that the paddle resonance frequency is well below the fundamental resonance frequency of the microcantilever. We show a significant increase in signal to noise ratio when cantilever motion is observed at the paddle for AFM systems that are not limited by thermal noise. Also, any effects due to the excitation of the second eigenmode were decoupled by locating the paddle at the node of the second eigenmode. We use these probes for higher harmonic imaging in amplitude modulated AFM (AM-AFM) on a standard polymer blend made of polystyrene and low density polyethylene. We demonstrate significantly improved contrast in higher harmonic images when observing cantilever motion at the paddle. Thus this microcantilever design can improve significantly conventional cantilever performance for dynamic AFM and is compatible with low-cost, high yield microfabrication processes.

  1. Enhancing the optical lever sensitivity of microcantilevers for dynamic atomic force microscopy via integrated low frequency paddles.

    PubMed

    Shaik, Nurul Huda; Reifenberger, Ronald G; Raman, Arvind

    2016-05-13

    A method is presented to enhance the optical lever sensitivity in dynamic atomic force microscopy (AFM) by nearly an order of magnitude over a wide frequency bandwidth. This is achieved by fabricating or releasing a paddle with a soft hinge close to the free end of the AFM microcantilever such that the paddle resonance frequency is well below the fundamental resonance frequency of the microcantilever. We show a significant increase in signal to noise ratio when cantilever motion is observed at the paddle for AFM systems that are not limited by thermal noise. Also, any effects due to the excitation of the second eigenmode were decoupled by locating the paddle at the node of the second eigenmode. We use these probes for higher harmonic imaging in amplitude modulated AFM (AM-AFM) on a standard polymer blend made of polystyrene and low density polyethylene. We demonstrate significantly improved contrast in higher harmonic images when observing cantilever motion at the paddle. Thus this microcantilever design can improve significantly conventional cantilever performance for dynamic AFM and is compatible with low-cost, high yield microfabrication processes. PMID:27040811

  2. Enhancing the optical lever sensitivity of microcantilevers for dynamic atomic force microscopy via integrated low frequency paddles

    NASA Astrophysics Data System (ADS)

    Huda Shaik, Nurul; Reifenberger, Ronald G.; Raman, Arvind

    2016-05-01

    A method is presented to enhance the optical lever sensitivity in dynamic atomic force microscopy (AFM) by nearly an order of magnitude over a wide frequency bandwidth. This is achieved by fabricating or releasing a paddle with a soft hinge close to the free end of the AFM microcantilever such that the paddle resonance frequency is well below the fundamental resonance frequency of the microcantilever. We show a significant increase in signal to noise ratio when cantilever motion is observed at the paddle for AFM systems that are not limited by thermal noise. Also, any effects due to the excitation of the second eigenmode were decoupled by locating the paddle at the node of the second eigenmode. We use these probes for higher harmonic imaging in amplitude modulated AFM (AM–AFM) on a standard polymer blend made of polystyrene and low density polyethylene. We demonstrate significantly improved contrast in higher harmonic images when observing cantilever motion at the paddle. Thus this microcantilever design can improve significantly conventional cantilever performance for dynamic AFM and is compatible with low-cost, high yield microfabrication processes.

  3. Coupled molecular and cantilever dynamics model for frequency-modulated atomic force microscopy.

    PubMed

    Klocke, Michael; Wolf, Dietrich E

    2016-01-01

    A molecular dynamics model is presented, which adds harmonic potentials to the atomic interactions to mimic the elastic properties of an AFM cantilever. It gives new insight into the correlation between the experimentally monitored frequency shift and cantilever damping due to the interaction between tip atoms and scanned surface. Applying the model to ionic crystals with rock salt structure two damping mechanisms are investigated, which occur separately or simultaneously depending on the tip position. These mechanisms are adhesion hysteresis on the one hand and lateral excitations of the cantilever on the other. We find that the short range Lennard-Jones part of the atomic interaction alone is sufficient for changing the predominant mechanism. When the long range ionic interaction is switched off, the two damping mechanisms occur with a completely different pattern, which is explained by the energy landscape for the apex atom of the tip. In this case the adhesion hysteresis is always associated with a distinct lateral displacement of the tip. It is shown how this may lead to a systematic shift between the periodic patterns obtained from the frequency and from the damping signal, respectively. PMID:27335760

  4. Coupled molecular and cantilever dynamics model for frequency-modulated atomic force microscopy.

    PubMed

    Klocke, Michael; Wolf, Dietrich E

    2016-01-01

    A molecular dynamics model is presented, which adds harmonic potentials to the atomic interactions to mimic the elastic properties of an AFM cantilever. It gives new insight into the correlation between the experimentally monitored frequency shift and cantilever damping due to the interaction between tip atoms and scanned surface. Applying the model to ionic crystals with rock salt structure two damping mechanisms are investigated, which occur separately or simultaneously depending on the tip position. These mechanisms are adhesion hysteresis on the one hand and lateral excitations of the cantilever on the other. We find that the short range Lennard-Jones part of the atomic interaction alone is sufficient for changing the predominant mechanism. When the long range ionic interaction is switched off, the two damping mechanisms occur with a completely different pattern, which is explained by the energy landscape for the apex atom of the tip. In this case the adhesion hysteresis is always associated with a distinct lateral displacement of the tip. It is shown how this may lead to a systematic shift between the periodic patterns obtained from the frequency and from the damping signal, respectively.

  5. Coupled molecular and cantilever dynamics model for frequency-modulated atomic force microscopy

    PubMed Central

    Klocke, Michael

    2016-01-01

    Summary A molecular dynamics model is presented, which adds harmonic potentials to the atomic interactions to mimic the elastic properties of an AFM cantilever. It gives new insight into the correlation between the experimentally monitored frequency shift and cantilever damping due to the interaction between tip atoms and scanned surface. Applying the model to ionic crystals with rock salt structure two damping mechanisms are investigated, which occur separately or simultaneously depending on the tip position. These mechanisms are adhesion hysteresis on the one hand and lateral excitations of the cantilever on the other. We find that the short range Lennard-Jones part of the atomic interaction alone is sufficient for changing the predominant mechanism. When the long range ionic interaction is switched off, the two damping mechanisms occur with a completely different pattern, which is explained by the energy landscape for the apex atom of the tip. In this case the adhesion hysteresis is always associated with a distinct lateral displacement of the tip. It is shown how this may lead to a systematic shift between the periodic patterns obtained from the frequency and from the damping signal, respectively. PMID:27335760

  6. Filamentous Biopolymers on Surfaces: Atomic Force Microscopy Images Compared with Brownian Dynamics Simulation of Filament Deposition

    PubMed Central

    Mücke, Norbert; Klenin, Konstantin; Kirmse, Robert; Bussiek, Malte; Herrmann, Harald; Hafner, Mathias; Langowski, Jörg

    2009-01-01

    Nanomechanical properties of filamentous biopolymers, such as the persistence length, may be determined from two-dimensional images of molecules immobilized on surfaces. For a single filament in solution, two principal adsorption scenarios are possible. Both scenarios depend primarly on the interaction strength between the filament and the support: i) For interactions in the range of the thermal energy, the filament can freely equilibrate on the surface during adsorption; ii) For interactions much stronger than the thermal energy, the filament will be captured by the surface without having equilibrated. Such a ‘trapping’ mechanism leads to more condensed filament images and hence to a smaller value for the apparent persistence length. To understand the capture mechanism in more detail we have performed Brownian dynamics simulations of relatively short filaments by taking the two extreme scenarios into account. We then compared these ‘ideal’ adsorption scenarios with observed images of immobilized vimentin intermediate filaments on different surfaces. We found a good agreement between the contours of the deposited vimentin filaments on mica (‘ideal’ trapping) and on glass (‘ideal’ equilibrated) with our simulations. Based on these data, we have developed a strategy to reliably extract the persistence length of short worm-like chain fragments or network forming filaments with unknown polymer-surface interactions. PMID:19888472

  7. Energy dissipation in multifrequency atomic force microscopy.

    PubMed

    Pukhova, Valentina; Banfi, Francesco; Ferrini, Gabriele

    2014-01-01

    The instantaneous displacement, velocity and acceleration of a cantilever tip impacting onto a graphite surface are reconstructed. The total dissipated energy and the dissipated energy per cycle of each excited flexural mode during the tip interaction is retrieved. The tip dynamics evolution is studied by wavelet analysis techniques that have general relevance for multi-mode atomic force microscopy, in a regime where few cantilever oscillation cycles characterize the tip-sample interaction. PMID:24778976

  8. Prototype cantilevers for quantitative lateral force microscopy

    SciTech Connect

    Reitsma, Mark G.; Gates, Richard S.; Friedman, Lawrence H.; Cook, Robert F.

    2011-09-15

    Prototype cantilevers are presented that enable quantitative surface force measurements using contact-mode atomic force microscopy (AFM). The ''hammerhead'' cantilevers facilitate precise optical lever system calibrations for cantilever flexure and torsion, enabling quantifiable adhesion measurements and friction measurements by lateral force microscopy (LFM). Critically, a single hammerhead cantilever of known flexural stiffness and probe length dimension can be used to perform both a system calibration as well as surface force measurements in situ, which greatly increases force measurement precision and accuracy. During LFM calibration mode, a hammerhead cantilever allows an optical lever ''torque sensitivity'' to be generated for the quantification of LFM friction forces. Precise calibrations were performed on two different AFM instruments, in which torque sensitivity values were specified with sub-percent relative uncertainty. To examine the potential for accurate lateral force measurements using the prototype cantilevers, finite element analysis predicted measurement errors of a few percent or less, which could be reduced via refinement of calibration methodology or cantilever design. The cantilevers are compatible with commercial AFM instrumentation and can be used for other AFM techniques such as contact imaging and dynamic mode measurements.

  9. Nanorheology by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Li, Tai-De; Chiu, Hsiang-Chih; Ortiz-Young, Deborah; Riedo, Elisa

    2014-12-01

    We present an Atomic Force Microscopy (AFM) based method to investigate the rheological properties of liquids confined within a nanosize gap formed by an AFM tip apex and a solid substrate. In this method, a conventional AFM cantilever is sheared parallel to a substrate surface by means of a lock-in amplifier while it is approaching and retracting from the substrate in liquid. The normal solvation forces and lateral viscoelastic shear forces experienced by the AFM tip in liquid can be simultaneously measured as a function of the tip-substrate distance with sub-nanometer vertical resolution. A new calibration method is applied to compensate for the linear drift of the piezo transducer and substrate system, leading to a more precise determination of the tip-substrate distance. By monitoring the phase lag between the driving signal and the cantilever response in liquid, the frequency dependent viscoelastic properties of the confined liquid can also be derived. Finally, we discuss the results obtained with this technique from different liquid-solid interfaces. Namely, octamethylcyclotetrasiloxane and water on mica and highly oriented pyrolytic graphite.

  10. Nanorheology by atomic force microscopy.

    PubMed

    Li, Tai-De; Chiu, Hsiang-Chih; Ortiz-Young, Deborah; Riedo, Elisa

    2014-12-01

    We present an Atomic Force Microscopy (AFM) based method to investigate the rheological properties of liquids confined within a nanosize gap formed by an AFM tip apex and a solid substrate. In this method, a conventional AFM cantilever is sheared parallel to a substrate surface by means of a lock-in amplifier while it is approaching and retracting from the substrate in liquid. The normal solvation forces and lateral viscoelastic shear forces experienced by the AFM tip in liquid can be simultaneously measured as a function of the tip-substrate distance with sub-nanometer vertical resolution. A new calibration method is applied to compensate for the linear drift of the piezo transducer and substrate system, leading to a more precise determination of the tip-substrate distance. By monitoring the phase lag between the driving signal and the cantilever response in liquid, the frequency dependent viscoelastic properties of the confined liquid can also be derived. Finally, we discuss the results obtained with this technique from different liquid-solid interfaces. Namely, octamethylcyclotetrasiloxane and water on mica and highly oriented pyrolytic graphite. PMID:25554301

  11. Nanorheology by atomic force microscopy.

    PubMed

    Li, Tai-De; Chiu, Hsiang-Chih; Ortiz-Young, Deborah; Riedo, Elisa

    2014-12-01

    We present an Atomic Force Microscopy (AFM) based method to investigate the rheological properties of liquids confined within a nanosize gap formed by an AFM tip apex and a solid substrate. In this method, a conventional AFM cantilever is sheared parallel to a substrate surface by means of a lock-in amplifier while it is approaching and retracting from the substrate in liquid. The normal solvation forces and lateral viscoelastic shear forces experienced by the AFM tip in liquid can be simultaneously measured as a function of the tip-substrate distance with sub-nanometer vertical resolution. A new calibration method is applied to compensate for the linear drift of the piezo transducer and substrate system, leading to a more precise determination of the tip-substrate distance. By monitoring the phase lag between the driving signal and the cantilever response in liquid, the frequency dependent viscoelastic properties of the confined liquid can also be derived. Finally, we discuss the results obtained with this technique from different liquid-solid interfaces. Namely, octamethylcyclotetrasiloxane and water on mica and highly oriented pyrolytic graphite.

  12. Nanorheology by atomic force microscopy

    SciTech Connect

    Li, Tai-De; Chiu, Hsiang-Chih; Ortiz-Young, Deborah; Riedo, Elisa

    2014-12-15

    We present an Atomic Force Microscopy (AFM) based method to investigate the rheological properties of liquids confined within a nanosize gap formed by an AFM tip apex and a solid substrate. In this method, a conventional AFM cantilever is sheared parallel to a substrate surface by means of a lock-in amplifier while it is approaching and retracting from the substrate in liquid. The normal solvation forces and lateral viscoelastic shear forces experienced by the AFM tip in liquid can be simultaneously measured as a function of the tip-substrate distance with sub-nanometer vertical resolution. A new calibration method is applied to compensate for the linear drift of the piezo transducer and substrate system, leading to a more precise determination of the tip-substrate distance. By monitoring the phase lag between the driving signal and the cantilever response in liquid, the frequency dependent viscoelastic properties of the confined liquid can also be derived. Finally, we discuss the results obtained with this technique from different liquid-solid interfaces. Namely, octamethylcyclotetrasiloxane and water on mica and highly oriented pyrolytic graphite.

  13. Biomolecular interactions measured by atomic force microscopy.

    PubMed

    Willemsen, O H; Snel, M M; Cambi, A; Greve, J; De Grooth, B G; Figdor, C G

    2000-12-01

    Atomic force microscopy (AFM) is nowadays frequently applied to determine interaction forces between biological molecules. Starting with the detection of the first discrete unbinding forces between ligands and receptors by AFM only several years ago, measurements have become more and more quantitative. At the same time, theories have been developed to describe and understand the dynamics of the unbinding process and experimental techniques have been refined to verify this theory. In addition, the detection of molecular recognition forces has been exploited to map and image the location of binding sites. In this review we discuss the important contributions that have led to the development of this field. In addition, we emphasize the potential of chemically well-defined surface modification techniques to further improve reproducible measurements by AFM. This increased reproducibility will pave the way for a better understanding of molecular interactions in cell biology.

  14. Local viscoelastic properties of live cells investigated using dynamic and quasi-static atomic force microscopy methods.

    PubMed

    Cartagena, Alexander; Raman, Arvind

    2014-03-01

    The measurement of viscoelasticity of cells in physiological environments with high spatio-temporal resolution is a key goal in cell mechanobiology. Traditionally only the elastic properties have been measured from quasi-static force-distance curves using the atomic force microscope (AFM). Recently, dynamic AFM-based methods have been proposed to map the local in vitro viscoelastic properties of living cells with nanoscale resolution. However, the differences in viscoelastic properties estimated from such dynamic and traditional quasi-static techniques are poorly understood. In this work we quantitatively reconstruct the local force and dissipation gradients (viscoelasticity) on live fibroblast cells in buffer solutions using Lorentz force excited cantilevers and present a careful comparison between mechanical properties (local stiffness and damping) extracted using dynamic and quasi-static force spectroscopy methods. The results highlight the dependence of measured viscoelastic properties on both the frequency at which the chosen technique operates as well as the interactions with subcellular components beyond certain indentation depth, both of which are responsible for differences between the viscoelasticity property maps acquired using the dynamic AFM method against the quasi-static measurements.

  15. Dynamic Transmission Electron Microscopy

    SciTech Connect

    Evans, James E.; Jungjohann, K. L.; Browning, Nigel D.

    2012-10-12

    Dynamic transmission electron microscopy (DTEM) combines the benefits of high spatial resolution electron microscopy with the high temporal resolution of ultrafast lasers. The incorporation of these two components into a single instrument provides a perfect platform for in situ observations of material processes. However, previous DTEM applications have focused on observing structural changes occurring in samples exposed to high vacuum. Therefore, in order to expand the pump-probe experimental regime to more natural environmental conditions, in situ gas and liquid chambers must be coupled with Dynamic TEM. This chapter describes the current and future applications of in situ liquid DTEM to permit time-resolved atomic scale observations in an aqueous environment, Although this chapter focuses mostly on in situ liquid imaging, the same research potential exists for in situ gas experiments and the successful integration of these techniques promises new insights for understanding nanoparticle, catalyst and biological protein dynamics with unprecedented spatiotemporal resolution.

  16. Dynamic calibration of higher eigenmode parameters of a cantilever in atomic force microscopy by using tip–surface interactions

    DOE PAGES

    Borysov, Stanislav S.; Forchheimer, Daniel; Haviland, David B.

    2014-10-29

    Here we present a theoretical framework for the dynamic calibration of the higher eigenmode parameters (stiffness and optical lever inverse responsivity) of a cantilever. The method is based on the tip–surface force reconstruction technique and does not require any prior knowledge of the eigenmode shape or the particular form of the tip–surface interaction. The calibration method proposed requires a single-point force measurement by using a multimodal drive and its accuracy is independent of the unknown physical amplitude of a higher eigenmode.

  17. Ferromagnetic Resonance Force Microscopy Imaging

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Midzor, Melissa; Cross, Michael; Wigen, Philip; Hammel, Chris; Roukes, Michael

    2001-03-01

    Magnetic resonance force microscopy (MRFM) has been used to investigate magnetostatic waves on microscopic samples of YIG. This work elucidates the nature of scanned probe (local) imaging in ferromagnetically-coupled systems. Scanning was performed with a specially-designed ultrasharp tip with Permalloy (NiFe) deposited solely in the tip region, to yield a spatial sensitivity of <10um. This has provided the first direct imaging of fundamental and higher order magnetostatic modes in micromagnetic systems. The modal dependence upon applied field and sample size was measured and compares well with theoretical models. However, unlike traditional ferromagnetic resonance detection technique, MRFM not only serves as a non-perturbative detection tool of magnetostatic modes, but also can locally change their dispersion relations via the strong field gradients generated from the cantilever tip. As a result, when the tip is positioned closely to the YIG surface, certain modes of the magnetostatic waves are either enhanced or depressed, depending on their respective wavelengths. This corresponds to the fact when the tip is further away, the dispersion of the FMR modes is mainly determined by the sample size. As the tip moves closer to the surface, a new regime emerges where the FMR dispersion is dominated by the local magnetic field. A quantitative model based on DE theory is proposed, and it explains the main features of the observed tip influence on different magnetostatic modes.

  18. Nanopatterning by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Tang, Qian

    For the first time, we fabricated nanostructures of a ferroelectric polymer, poly(vinylidene fluoride-trifluorethylene) [P(VDF-TrFE)] on gold substrate via dip-pen nanolithography ink. Lines as thin as 32 nm and dot radius as small as 20 nm have been fabricated. The P(VDF-TrFE) molecules were well oriented on the gold substrate. The hydrophobic P(VDF-TrFE) produced a black contrast in the lateral force microscopy (LFM) images. The DPN-generated P(VDF-TrFE) patterns hold ferroelectric properties. The interaction between the P(VDF-TrFE) and the gold substrate was Van der Waals' interaction. The growth of dot radii/line-width was proportional to t1/2. We studied the influence of experimental conditions on dip-pen nanolithography. The results show: The transport rate of ink increased as the temperature increased for all of the inks. For P(VDF-TrFE), a deviation from Arrhenius plot at about 55°C was observed. It may be caused by a ferroelectric phase transition. Surface roughness influenced both the contrast in LFM images and the transport rate of ink. Surfaces with less roughness resulted in good contrast in LFM images, while rough surfaces resulted in poor contrast. The transport rate of ink increased as the roughness decreased; however, the extent of the influence was strongly ink-dependent. The influence of relative humidity depended on the solubility of the ink in water. The transport rate of hydrophilic inks increased as the relative humidity increased, while the transport rate of hydrophobic inks experienced small change as the relative humidity increased. At the same condition, a tip with a larger curvature radius could generate a larger pattern than a tip with a smaller curvature radius due to a bigger contact point or the formation of a meniscus with a larger size. The chemical affinity was also one of the key controlling parameters for DPN. It is necessary to consider the ink affinity to both the substrate and the tip when designing a new DPN system. We

  19. High-resolution elasticity maps and cytoskeletal dynamics of neurons measured by combined fluorescence and atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Staii, Cristian

    2014-03-01

    Detailed knowledge of mechanical parameters such as cell elasticity, stiffness of the growth substrate, or traction stresses generated during axonal extensions is essential for understanding the mechanisms that control neuronal growth. Here I present results obtained in my research group, which combine Atomic Force Microscopy and Fluorescence Microscopy measurements to produce systematic, high-resolution elasticity maps for different types of live neuronal cells cultured on glass or biopolymer-based substrates. We measure how the stiffness of neurons changes both during neurite outgrowth and upon chemical modification (disruption of the cytoskeleton) of the cell. We find a reversible local stiffening of the cell during growth, and show that the increase in local elastic modulus is primarily due to the formation of microtubules in the cell soma. We also report a reversible shift in the elastic modulus of the cortical neurons cytoskeleton with temperature, from tubulin dominated regions at 37C to actin dominated regions at 25C. We demonstrate that the dominant mechanism by which the elasticity of the neuronal soma changes in response to temperature is the contractile stiffening of the actin component of the cytoskeleton induced by the activity of myosin II motors. We acknowledge financial support from NSF grant CBET 1067093.

  20. Spatial distribution and dynamics of proton conductivity in fuel cell membranes: potential and limitations of electrochemical atomic force microscopy measurements.

    PubMed

    Aleksandrova, E; Hink, S; Hiesgen, R; Roduner, E

    2011-06-15

    The proton conductivity of a Nafion 112 membrane is measured with a high spatial resolution using electrochemical atomic force microscopy. Image analysis reveals an inhomogeneous conductivity distribution which is attributed to the limited connectivity of hydrophilic domains. This information relates to the micro-morphology which is due to phase separation of the hydrophobic polymer backbone and the hydrophilic pendant groups. The direct images relate to a different length scale and are complementary to the x-ray diffraction investigations which provide only average information. Furthermore, the measured current values reveal an interesting correlation with the size of the conductive areas. A bimodal conductivity distribution suggests that there are different mechanisms which contribute to the proton current in Nafion. Additionally, time dependence in local conductivity is found and interpreted in terms of redistribution of water in the membrane. A statistical analysis of the current distribution is performed and compared with theoretical simulations. Evidence is found for the existence of a critical current density. On a timescale of seconds the response of the conductive network is probed by applying voltage steps to the atomic force microscope tip.

  1. Super-Resolved Traction Force Microscopy (STFM).

    PubMed

    Colin-York, Huw; Shrestha, Dilip; Felce, James H; Waithe, Dominic; Moeendarbary, Emad; Davis, Simon J; Eggeling, Christian; Fritzsche, Marco

    2016-04-13

    Measuring small forces is a major challenge in cell biology. Here we improve the spatial resolution and accuracy of force reconstruction of the well-established technique of traction force microscopy (TFM) using STED microscopy. The increased spatial resolution of STED-TFM (STFM) allows a greater than 5-fold higher sampling of the forces generated by the cell than conventional TFM, accessing the nano instead of the micron scale. This improvement is highlighted by computer simulations and an activating RBL cell model system.

  2. Dynamic light scattering microscopy

    NASA Astrophysics Data System (ADS)

    Dzakpasu, Rhonda

    An optical microscope technique, dynamic light scattering microscopy (DLSM) that images dynamically scattered light fluctuation decay rates is introduced. Using physical optics we show theoretically that within the optical resolution of the microscope, relative motions between scattering centers are sufficient to produce significant phase variations resulting in interference intensity fluctuations in the image plane. The time scale for these intensity fluctuations is predicted. The spatial coherence distance defining the average distance between constructive and destructive interference in the image plane is calculated and compared with the pixel size. We experimentally tested DLSM on polystyrene latex nanospheres and living macrophage cells. In order to record these rapid fluctuations, on a slow progressive scan CCD camera, we used a thin laser line of illumination on the sample such that only a single column of pixels in the CCD camera is illuminated. This allowed the use of the rate of the column-by-column readout transfer process as the acquisition rate of the camera. This manipulation increased the data acquisition rate by at least an order of magnitude in comparison to conventional CCD cameras rates defined by frames/s. Analysis of the observed fluctuations provides information regarding the rates of motion of the scattering centers. These rates, acquired from each position on the sample are used to create a spatial map of the fluctuation decay rates. Our experiments show that with this technique, we are able to achieve a good signal-to-noise ratio and can monitor fast intensity fluctuations, on the order of milliseconds. DLSM appears to provide dynamic information about fast motions within cells at a sub-optical resolution scale and provides a new kind of spatial contrast.

  3. Coffee Cup Atomic Force Microscopy

    ERIC Educational Resources Information Center

    Ashkenaz, David E.; Hall, W. Paige; Haynes, Christy L.; Hicks, Erin M.; McFarland, Adam D.; Sherry, Leif J.; Stuart, Douglas A.; Wheeler, Korin E.; Yonzon, Chanda R.; Zhao, Jing; Godwin, Hilary A.; Van Duyne, Richard P.

    2010-01-01

    In this activity, students use a model created from a coffee cup or cardstock cutout to explore the working principle of an atomic force microscope (AFM). Students manipulate a model of an AFM, using it to examine various objects to retrieve topographic data and then graph and interpret results. The students observe that movement of the AFM…

  4. Robust atomic force microscopy using multiple sensors.

    PubMed

    Baranwal, Mayank; Gorugantu, Ram S; Salapaka, Srinivasa M

    2016-08-01

    Atomic force microscopy typically relies on high-resolution high-bandwidth cantilever deflection measurements based control for imaging and estimating sample topography and properties. More precisely, in amplitude-modulation atomic force microscopy (AM-AFM), the control effort that regulates deflection amplitude is used as an estimate of sample topography; similarly, contact-mode AFM uses regulation of deflection signal to generate sample topography. In this article, a control design scheme based on an additional feedback mechanism that uses vertical z-piezo motion sensor, which augments the deflection based control scheme, is proposed and evaluated. The proposed scheme exploits the fact that the piezo motion sensor, though inferior to the cantilever deflection signal in terms of resolution and bandwidth, provides information on piezo actuator dynamics that is not easily retrievable from the deflection signal. The augmented design results in significant improvements in imaging bandwidth and robustness, especially in AM-AFM, where the complicated underlying nonlinear dynamics inhibits estimating piezo motions from deflection signals. In AM-AFM experiments, the two-sensor based design demonstrates a substantial improvement in robustness to modeling uncertainties by practically eliminating the peak in the sensitivity plot without affecting the closed-loop bandwidth when compared to a design that does not use the piezo-position sensor based feedback. The contact-mode imaging results, which use proportional-integral controllers for cantilever-deflection regulation, demonstrate improvements in bandwidth and robustness to modeling uncertainties, respectively, by over 30% and 20%. The piezo-sensor based feedback is developed using H∞ control framework. PMID:27587128

  5. Robust atomic force microscopy using multiple sensors

    NASA Astrophysics Data System (ADS)

    Baranwal, Mayank; Gorugantu, Ram S.; Salapaka, Srinivasa M.

    2016-08-01

    Atomic force microscopy typically relies on high-resolution high-bandwidth cantilever deflection measurements based control for imaging and estimating sample topography and properties. More precisely, in amplitude-modulation atomic force microscopy (AM-AFM), the control effort that regulates deflection amplitude is used as an estimate of sample topography; similarly, contact-mode AFM uses regulation of deflection signal to generate sample topography. In this article, a control design scheme based on an additional feedback mechanism that uses vertical z-piezo motion sensor, which augments the deflection based control scheme, is proposed and evaluated. The proposed scheme exploits the fact that the piezo motion sensor, though inferior to the cantilever deflection signal in terms of resolution and bandwidth, provides information on piezo actuator dynamics that is not easily retrievable from the deflection signal. The augmented design results in significant improvements in imaging bandwidth and robustness, especially in AM-AFM, where the complicated underlying nonlinear dynamics inhibits estimating piezo motions from deflection signals. In AM-AFM experiments, the two-sensor based design demonstrates a substantial improvement in robustness to modeling uncertainties by practically eliminating the peak in the sensitivity plot without affecting the closed-loop bandwidth when compared to a design that does not use the piezo-position sensor based feedback. The contact-mode imaging results, which use proportional-integral controllers for cantilever-deflection regulation, demonstrate improvements in bandwidth and robustness to modeling uncertainties, respectively, by over 30% and 20%. The piezo-sensor based feedback is developed using H∞ control framework.

  6. Magnetic exchange force microscopy with atomic resolution.

    PubMed

    Kaiser, Uwe; Schwarz, Alexander; Wiesendanger, Roland

    2007-03-29

    The ordering of neighbouring atomic magnetic moments (spins) leads to important collective phenomena such as ferromagnetism and antiferromagnetism. A full understanding of magnetism on the nanometre scale therefore calls for information on the arrangement of spins in real space and with atomic resolution. Spin-polarized scanning tunnelling microscopy accomplishes this but can probe only conducting materials. Force microscopy can be used on any sample independent of its conductivity. In particular, magnetic force microscopy is well suited to exploring ferromagnetic domain structures. However, atomic resolution cannot be achieved because data acquisition involves the sensing of long-range magnetostatic forces between tip and sample. Magnetic exchange force microscopy has been proposed for overcoming this limitation: by using an atomic force microscope with a magnetic tip, it should be possible to detect the short-range magnetic exchange force between tip and sample spins. Here we show for a prototypical antiferromagnetic insulator, the (001) surface of nickel oxide, that magnetic exchange force microscopy can indeed reveal the arrangement of both surface atoms and their spins simultaneously. In contrast with previous attempts to implement this method, we use an external magnetic field to align the magnetic polarization at the tip apex so as to optimize the interaction between tip and sample spins. This allows us to observe the direct magnetic exchange coupling between the spins of the tip atom and sample atom that are closest to each other, and thereby demonstrate the potential of magnetic exchange force microscopy for investigations of inter-spin interactions at the atomic level.

  7. Ultrafast pump-probe force microscopy with nanoscale resolution

    NASA Astrophysics Data System (ADS)

    Jahng, Junghoon; Brocious, Jordan; Fishman, Dmitry A.; Yampolsky, Steven; Nowak, Derek; Huang, Fei; Apkarian, Vartkess A.; Wickramasinghe, H. Kumar; Potma, Eric Olaf

    2015-02-01

    We perform time-resolved pump-probe microscopy measurements by recording the local force between a sharp tip and the photo-excited sample as a readout mechanism for the material's nonlinear polarization. We show that the photo-induced force is sensitive to the same excited state dynamics as measured in an optical pump-probe experiment. Ultrafast pump-probe force microscopy constitutes a non-optical detection technique with nanoscale resolution that pushes pump-probe sensitivities close to the realm of single molecule studies.

  8. System analysis of force feedback microscopy

    SciTech Connect

    Rodrigues, Mario S.; Chevrier, Joël; Comin, Fabio

    2014-02-07

    It was shown recently that the Force Feedback Microscope (FFM) can avoid the jump-to-contact in Atomic force Microscopy even when the cantilevers used are very soft, thus increasing force resolution. In this letter, we explore theoretical aspects of the associated real time control of the tip position. We take into account lever parameters such as the lever characteristics in its environment, spring constant, mass, dissipation coefficient, and the operating conditions such as controller gains and interaction force. We show how the controller parameters are determined so that the FFM functions at its best and estimate the bandwidth of the system under these conditions.

  9. Theory of multifrequency atomic force microscopy.

    PubMed

    Lozano, Jose R; Garcia, Ricardo

    2008-02-22

    We develop a theory that explains the origin of the high force sensitivity observed in multifrequency force microscopy experiments. The ability of the microscope to extract complementary information on the surface properties is increased by the simultaneous excitation of several flexural cantilever modes. The force sensitivity in multifrequency operation is about 0.2 pN. The analytical model identifies the virial and the energy dissipated by the tip-surface forces as the parameters responsible for the material contrast. The agreement obtained among the theory, experiments and numerical simulations validates the model.

  10. Interfacial force microscopy: Application to polymer surfaces

    SciTech Connect

    HOUSTON,JACK E.; WINTER,R.M.

    2000-05-16

    Scanning-probe microscopies (SPM) are presently widely used in remarkably diverse applications and, as evidenced by this symposium these techniques are rapidly expanding into the important areas of polymer surfaces and interfaces. The Atomic Force Microscope (AFM) is presently the most widely used of the scanning-probe techniques. However, the AFM's range of application suffers from an inherent mechanical instability in its deflection force sensor. The instability problem has been overcome by the development of the Interfacial Force Microscope (IFM), which utilizes a force-feedback sensor concept. In the following, the authors present several examples of polymer applications to illustrate the utility of the IFM sensor concept.

  11. Imaging DNA Structure by Atomic Force Microscopy.

    PubMed

    Pyne, Alice L B; Hoogenboom, Bart W

    2016-01-01

    Atomic force microscopy (AFM) is a microscopy technique that uses a sharp probe to trace a sample surface at nanometre resolution. For biological applications, one of its key advantages is its ability to visualize substructure of single molecules and molecular complexes in an aqueous environment. Here, we describe the application of AFM to determine superstructure and secondary structure of surface-bound DNA. The method is also readily applicable to probe DNA-DNA interactions and DNA-protein complexes.

  12. Stochastic noise in atomic force microscopy.

    PubMed

    Labuda, Aleksander; Lysy, Martin; Paul, William; Miyahara, Yoichi; Grütter, Peter; Bennewitz, Roland; Sutton, Mark

    2012-09-01

    Having reached the quantum and thermodynamic limits of detection, atomic force microscopy (AFM) experiments are routinely being performed at the fundamental limit of signal to noise. A critical understanding of the statistical properties of noise leads to more accurate interpretation of data, optimization of experimental protocols, advancements in instrumentation, and new measurement techniques. Furthermore, accurate simulation of cantilever dynamics requires knowledge of stochastic behavior of the system, as stochastic noise may exceed the deterministic signals of interest, and even dominate the outcome of an experiment. In this article, the power spectral density (PSD), used to quantify stationary stochastic processes, is introduced in the context of a thorough noise analysis of the light source used to detect cantilever deflections. The statistical properties of PSDs are then outlined for various stationary, nonstationary, and deterministic noise sources in the context of AFM experiments. Following these developments, a method for integrating PSDs to provide an accurate standard deviation of linear measurements is described. Lastly, a method for simulating stochastic Gaussian noise from any arbitrary power spectral density is presented. The result demonstrates that mechanical vibrations of the AFM can cause a logarithmic velocity dependence of friction and induce multiple slip events in the atomic stick-slip process, as well as predicts an artifactual temperature dependence of friction measured by AFM. PMID:23030863

  13. Sensor for direct measurement of interaction forces in probe microscopy

    NASA Astrophysics Data System (ADS)

    Degertekin, F. L.; Onaran, A. G.; Balantekin, M.; Lee, W.; Hall, N. A.; Quate, C. F.

    2005-11-01

    We introduce a sensor for direct measurement of tip-sample interaction forces in probe microscopy. The sensor uses a micromachined membrane structure built on a transparent substrate with an integrated diffraction grating for optical interferometric detection, and a built-in electrostatic actuator. To demonstrate our concept for this sensor, we measured the force curves between an atomic force microscope (AFM) cantilever tip and a micromachined aluminum sensor membrane built on a quartz substrate. We also measured transient interaction forces exerted on the sensor membrane during each cycle of the vibrating AFM cantilever. These agree well with the temporal response of the sensor to a short force pulse applied by our integrated electrostatic actuator. With the addition of an integrated tip, this structure may be used for scanning probe microscopy with a bandwidth limited by the membrane dynamics.

  14. High-resolution high-speed dynamic mechanical spectroscopy of cells and other soft materials with the help of atomic force microscopy.

    PubMed

    Dokukin, M; Sokolov, I

    2015-07-28

    Dynamic mechanical spectroscopy (DMS), which allows measuring frequency-dependent viscoelastic properties, is important to study soft materials, tissues, biomaterials, polymers. However, the existing DMS techniques (nanoindentation) have limited resolution when used on soft materials, preventing them from being used to study mechanics at the nanoscale. The nanoindenters are not capable of measuring cells, nanointerfaces of composite materials. Here we present a highly accurate DMS modality, which is a combination of three different methods: quantitative nanoindentation (nanoDMA), gentle force and fast response of atomic force microscopy (AFM), and Fourier transform (FT) spectroscopy. This new spectroscopy (which we suggest to call FT-nanoDMA) is fast and sensitive enough to allow DMS imaging of nanointerfaces, single cells, while attaining about 100x improvements on polymers in both spatial (to 10-70 nm) and temporal resolution (to 0.7 s/pixel) compared to the current art. Multiple frequencies are measured simultaneously. The use of 10 frequencies are demonstrated here (up to 300 Hz which is a rather relevant range for biological materials and polymers, in both ambient conditions and liquid). The method is quantitatively verified on known polymers and demonstrated on cells and polymers blends. Analysis shows that FT-nanoDMA is highly quantitative. The FT-nanoDMA spectroscopy can easily be implemented in the existing AFMs.

  15. High-resolution high-speed dynamic mechanical spectroscopy of cells and other soft materials with the help of atomic force microscopy

    PubMed Central

    Dokukin, M.; Sokolov, I.

    2015-01-01

    Dynamic mechanical spectroscopy (DMS), which allows measuring frequency-dependent viscoelastic properties, is important to study soft materials, tissues, biomaterials, polymers. However, the existing DMS techniques (nanoindentation) have limited resolution when used on soft materials, preventing them from being used to study mechanics at the nanoscale. The nanoindenters are not capable of measuring cells, nanointerfaces of composite materials. Here we present a highly accurate DMS modality, which is a combination of three different methods: quantitative nanoindentation (nanoDMA), gentle force and fast response of atomic force microscopy (AFM), and Fourier transform (FT) spectroscopy. This new spectroscopy (which we suggest to call FT-nanoDMA) is fast and sensitive enough to allow DMS imaging of nanointerfaces, single cells, while attaining about 100x improvements on polymers in both spatial (to 10–70 nm) and temporal resolution (to 0.7s/pixel) compared to the current art. Multiple frequencies are measured simultaneously. The use of 10 frequencies are demonstrated here (up to 300 Hz which is a rather relevant range for biological materials and polymers, in both ambient conditions and liquid). The method is quantitatively verified on known polymers and demonstrated on cells and polymers blends. Analysis shows that FT-nanoDMA is highly quantitative. The FT-nanoDMA spectroscopy can easily be implemented in the existing AFMs. PMID:26218346

  16. Dynamic Interactions between a Silica Sphere and Deformable Interfaces in Organic Solvents Studied by Atomic Force Microscopy.

    PubMed

    Kuznicki, Natalie P; Harbottle, David; Masliyah, Jacob; Xu, Zhenghe

    2016-09-27

    Recent studies have successfully measured surface forces using atomic force microscope (AFM) and modeled surface deformations using the Stokes-Reynolds-Young-Laplace (SRYL) equations for particle-droplet, particle-bubble, droplet-droplet, and bubble-bubble systems in various solutions. The current work focuses on interactions between spherical silica particles and a viscoelastic interface of water droplets in crude oil. The self-assembly of surface active natural polyaromatic molecules (NPAMs) at the oil-water interface has previously been shown to change a viscous dominant oil-water interface to an elastic dominant interface upon aging, due to gradual formation of rigid interfacial networks. AFM was used to measure the interactions between a small silica sphere (D ≈ 8 μm) and a deformable water droplet (D ≈ 70 μm), which exhibits time-dependent interfacial viscoelasticity in NPAM solutions. Unlike the systems studied previously, the measured deformation shown as a repulsive force over the region of constant compliance could not be modeled adequately by the conventional SRYL equations which are applicable only to purely Laplacian interfaces. As the water droplet ages in NPAM solutions, a rigid "skin" forms at the oil-water interface, with the interface exhibiting increased elasticity. Over a short aging period (up to 15 min in NPAM-in-toluene solution), interfacial deformation is well predicted by the SRYL model. However, upon further exposure to the NPAM solution, droplet deformation is overpredicted by the model. Physical properties of this mechanical barrier as a function of interfacial aging were further investigated by measuring interfacial tension, dilatational rheology, and interfacial "crumpling" (non-smooth, non-Laplacian interface) upon droplet volume reduction. By introducing a viscoelasticity parameter to account for interfacial stiffening and using experimentally determined elasticity, we are able to correct this discrepancy and predict droplet

  17. Investigation of the depletion layer by scanning capacitance force microscopy with Kelvin probe force microscopy

    NASA Astrophysics Data System (ADS)

    Uruma, Takeshi; Satoh, Nobuo; Yamamoto, Hidekazu

    2016-08-01

    We have developed a scanning probe microscope (SPM) that combines atomic force microscopy (AFM) with both Kelvin probe force microscopy (KFM — to measure the surface potential) and scanning capacitance force microscopy (SCFM — to measure the differential capacitance). The surface physical characteristics of a commercial Si Schottky barrier diode (Si-SBD), with and without an applied reverse bias, were measured over the same area by our AFM/KFM/SCFM system. We thus investigated the discrete power device by calculating the depletion-layer width and drawing an energy-band diagram.

  18. Atomic force microscopy of biological samples

    SciTech Connect

    Doktycz, Mitchel John

    2010-01-01

    The ability to evaluate structural-functional relationships in real time has allowed scanning probe microscopy (SPM) to assume a prominent role in post genomic biological research. In this mini-review, we highlight the development of imaging and ancillary techniques that have allowed SPM to permeate many key areas of contemporary research. We begin by examining the invention of the scanning tunneling microscope (STM) by Binnig and Rohrer in 1982 and discuss how it served to team biologists with physicists to integrate high-resolution microscopy into biological science. We point to the problems of imaging nonconductive biological samples with the STM and relate how this led to the evolution of the atomic force microscope (AFM) developed by Binnig, Quate, and Gerber, in 1986. Commercialization in the late 1980s established SPM as a powerful research tool in the biological research community. Contact mode AFM imaging was soon complemented by the development of non-contact imaging modes. These non-contact modes eventually became the primary focus for further new applications including the development of fast scanning methods. The extreme sensitivity of the AFM cantilever was recognized and has been developed into applications for measuring forces required for indenting biological surfaces and breaking bonds between biomolecules. Further functional augmentation to the cantilever tip allowed development of new and emerging techniques including scanning ion-conductance microscopy (SICM), scanning electrochemical microscope (SECM), Kelvin force microscopy (KFM) and scanning near field ultrasonic holography (SNFUH).

  19. Reconstruction of electrostatic force microscopy images

    NASA Astrophysics Data System (ADS)

    Strassburg, E.; Boag, A.; Rosenwaks, Y.

    2005-08-01

    An efficient algorithm to restore the actual surface potential image from Kelvin probe force microscopy measurements of semiconductors is presented. The three-dimensional potential of the tip-sample system is calculated using an integral equation-based boundary element method combined with modeling the semiconductor by an equivalent dipole-layer and image-charge model. The derived point spread function of the measuring tip is then used to restore the actual surface potential from the measured image, using noise filtration and deconvolution algorithms. The model is then used to restore high-resolution Kelvin probe microscopy images of semiconductor surfaces.

  20. Confocal reference free traction force microscopy

    PubMed Central

    Bergert, Martin; Lendenmann, Tobias; Zündel, Manuel; Ehret, Alexander E.; Panozzo, Daniele; Richner, Patrizia; Kim, David K.; Kress, Stephan J. P.; Norris, David J.; Sorkine-Hornung, Olga; Mazza, Edoardo; Poulikakos, Dimos; Ferrari, Aldo

    2016-01-01

    The mechanical wiring between cells and their surroundings is fundamental to the regulation of complex biological processes during tissue development, repair or pathology. Traction force microscopy (TFM) enables determination of the actuating forces. Despite progress, important limitations with intrusion effects in low resolution 2D pillar-based methods or disruptive intermediate steps of cell removal and substrate relaxation in high-resolution continuum TFM methods need to be overcome. Here we introduce a novel method allowing a one-shot (live) acquisition of continuous in- and out-of-plane traction fields with high sensitivity. The method is based on electrohydrodynamic nanodrip-printing of quantum dots into confocal monocrystalline arrays, rendering individually identifiable point light sources on compliant substrates. We demonstrate the undisrupted reference-free acquisition and quantification of high-resolution continuous force fields, and the simultaneous capability of this method to correlatively overlap traction forces with spatial localization of proteins revealed using immunofluorescence methods. PMID:27681958

  1. Validation tool for traction force microscopy.

    PubMed

    Jorge-Peñas, A; Muñoz-Barrutia, A; de-Juan-Pardo, E M; Ortiz-de-Solorzano, C

    2015-01-01

    Traction force microscopy (TFM) is commonly used to estimate cells' traction forces from the deformation that they cause on their substrate. The accuracy of TFM highly depends on the computational methods used to measure the deformation of the substrate and estimate the forces, and also on the specifics of the experimental set-up. Computer simulations can be used to evaluate the effect of both the computational methods and the experimental set-up without the need to perform numerous experiments. Here, we present one such TFM simulator that addresses several limitations of the existing ones. As a proof of principle, we recreate a TFM experimental set-up, and apply a classic 2D TFM algorithm to recover the forces. In summary, our simulator provides a valuable tool to study the performance, refine experimentally, and guide the extraction of biological conclusions from TFM experiments. PMID:24697293

  2. Bacterial adhesion force quantification by fluidic force microscopy

    NASA Astrophysics Data System (ADS)

    Potthoff, Eva; Ossola, Dario; Zambelli, Tomaso; Vorholt, Julia A.

    2015-02-01

    Quantification of detachment forces between bacteria and substrates facilitates the understanding of the bacterial adhesion process that affects cell physiology and survival. Here, we present a method that allows for serial, single bacterial cell force spectroscopy by combining the force control of atomic force microscopy with microfluidics. Reversible bacterial cell immobilization under physiological conditions on the pyramidal tip of a microchanneled cantilever is achieved by underpressure. Using the fluidic force microscopy technology (FluidFM), we achieve immobilization forces greater than those of state-of-the-art cell-cantilever binding as demonstrated by the detachment of Escherichia coli from polydopamine with recorded forces between 4 and 8 nN for many cells. The contact time and setpoint dependence of the adhesion forces of E. coli and Streptococcus pyogenes, as well as the sequential detachment of bacteria out of a chain, are shown, revealing distinct force patterns in the detachment curves. This study demonstrates the potential of the FluidFM technology for quantitative bacterial adhesion measurements of cell-substrate and cell-cell interactions that are relevant in biofilms and infection biology.Quantification of detachment forces between bacteria and substrates facilitates the understanding of the bacterial adhesion process that affects cell physiology and survival. Here, we present a method that allows for serial, single bacterial cell force spectroscopy by combining the force control of atomic force microscopy with microfluidics. Reversible bacterial cell immobilization under physiological conditions on the pyramidal tip of a microchanneled cantilever is achieved by underpressure. Using the fluidic force microscopy technology (FluidFM), we achieve immobilization forces greater than those of state-of-the-art cell-cantilever binding as demonstrated by the detachment of Escherichia coli from polydopamine with recorded forces between 4 and 8 nN for many

  3. Resonance response of scanning force microscopy cantilevers

    SciTech Connect

    Chen, G.Y.; Warmack, R.J.; Thundat, T.; Allison, D.P. ); Huang, A. )

    1994-08-01

    A variational method is used to calculate the deflection and the fundamental and harmonic resonance frequencies of commercial V-shaped and rectangular atomic force microscopy cantilevers. The effective mass of V-shaped cantilevers is roughly half that calculated for the equivalent rectangular cantilevers. Damping by environmental gases, including air, nitrogen, argon, and helium, affects the frequency of maximum response and to a much greater degree the quality factor [ital Q]. Helium has the lowest viscosity, resulting in the highest [ital Q], and thus provides the best sensitivity in noncontact force microscopy. Damping in liquids is dominated by an increase in effective mass of the cantilever due to an added mass of the liquid being dragged with that cantilever.

  4. Atomically resolved force microscopy at room temperature

    SciTech Connect

    Morita, Seizo

    2014-04-24

    Atomic force microscopy (AFM) can now not only image individual atoms but also construct atom letters using atom manipulation method even at room temperature (RT). Therefore, the AFM is the second generation atomic tool following the scanning tunneling microscopy (STM). However the AFM can image even insulating atoms, and also directly measure/map the atomic force and potential at the atomic scale. Noting these advantages, we have been developing a bottom-up nanostructuring system at RT based on the AFM. It can identify chemical species of individual atoms and then manipulate selected atom species to the predesigned site one-by-one to assemble complex nanostructures consisted of multi atom species at RT. Here we introduce our results toward atom-by-atom assembly of composite nanostructures based on the AFM at RT including the latest result on atom gating of nano-space for atom-by-atom creation of atom clusters at RT for semiconductor surfaces.

  5. Automated force controller for amplitude modulation atomic force microscopy.

    PubMed

    Miyagi, Atsushi; Scheuring, Simon

    2016-05-01

    Atomic Force Microscopy (AFM) is widely used in physics, chemistry, and biology to analyze the topography of a sample at nanometer resolution. Controlling precisely the force applied by the AFM tip to the sample is a prerequisite for faithful and reproducible imaging. In amplitude modulation (oscillating) mode AFM, the applied force depends on the free and the setpoint amplitudes of the cantilever oscillation. Therefore, for keeping the applied force constant, not only the setpoint amplitude but also the free amplitude must be kept constant. While the AFM user defines the setpoint amplitude, the free amplitude is typically subject to uncontrollable drift, and hence, unfortunately, the real applied force is permanently drifting during an experiment. This is particularly harmful in biological sciences where increased force destroys the soft biological matter. Here, we have developed a strategy and an electronic circuit that analyzes permanently the free amplitude of oscillation and readjusts the excitation to maintain the free amplitude constant. As a consequence, the real applied force is permanently and automatically controlled with picoNewton precision. With this circuit associated to a high-speed AFM, we illustrate the power of the development through imaging over long-duration and at various forces. The development is applicable for all AFMs and will widen the applicability of AFM to a larger range of samples and to a larger range of (non-specialist) users. Furthermore, from controlled force imaging experiments, the interaction strength between biomolecules can be analyzed. PMID:27250433

  6. Force reconstruction from tapping mode force microscopy experiments.

    PubMed

    Payam, Amir F; Martin-Jimenez, Daniel; Garcia, Ricardo

    2015-05-01

    Fast, accurate, and robust nanomechanical measurements are intensely studied in materials science, applied physics, and molecular biology. Amplitude modulation force microscopy (tapping mode) is the most established nanoscale characterization technique of surfaces for air and liquid environments. However, its quantitative capabilities lag behind its high spatial resolution and robustness. We develop a general method to transform the observables into quantitative force measurements. The force reconstruction algorithm has been deduced on the assumption that the observables (amplitude and phase shift) are slowly varying functions of the tip-surface separation. The accuracy and applicability of the method is validated by numerical simulations and experiments. The method is valid for liquid and air environments, small and large free amplitudes, compliant and rigid materials, and conservative and non-conservative forces.

  7. First Steps in the Aggregation Process of Copolymers Based on Thymine Monomers: Characterization by Molecular Dynamics Simulations and Atomic Force Microscopy.

    PubMed

    Garay, A Sergio; Rodrigues, Daniel E; Fuselli, Antonela; Martino, Debora M; Passeggi, Mario C G

    2016-04-01

    Atomistic molecular dynamic simulations were performed to study the structure of isolated VBT-VBA (vinylbenzylthymine-vinylbenzyltriethylammonium chloride) copolymer chains in water at different monomeric species ratios (1:1 and 1:4). The geometric parameters of the structure that the copolymers form in equilibrium together with the basic interactions that stabilize them were determined. Atomic force microscopy (AFM) measurements of dried diluted concentrations of the two copolymers onto highly oriented pyrolytic graphite (HOPG) substrates were carried out to study their aggregation arrangement. The experiments show that both copolymers arrange in fiber-like structures. Comparing the diameters predicted by the simulation results and those obtained by AFM, it can be concluded that individual copolymers arrange in bunches of two chains, stabilized by contra-ions-copolymer interactions for the 1:1 copolymerization ratio at the ionic strength of our samples. In contrast, for the 1:4 system the individual copolymer chains do not aggregate in bunches. These results remark the relevance of the copolymerization ratio and ionic strength of the solvent in the mesoscopic structure of these materials.

  8. Manipulation of gold colloidal nanoparticles with atomic force microscopy in dynamic mode: influence of particle–substrate chemistry and morphology, and of operating conditions

    PubMed Central

    Darwich, Samer; Rao, Akshata; Gnecco, Enrico; Jayaraman, Shrisudersan; Haidara, Hamidou

    2011-01-01

    Summary One key component in the assembly of nanoparticles is their precise positioning to enable the creation of new complex nano-objects. Controlling the nanoscale interactions is crucial for the prediction and understanding of the behaviour of nanoparticles (NPs) during their assembly. In the present work, we have manipulated bare and functionalized gold nanoparticles on flat and patterned silicon and silicon coated substrates with dynamic atomic force microscopy (AFM). Under ambient conditions, the particles adhere to silicon until a critical drive amplitude is reached by oscillations of the probing tip. Beyond that threshold, the particles start to follow different directions, depending on their geometry, size and adhesion to the substrate. Higher and respectively, lower mobility was observed when the gold particles were coated with methyl (–CH3) and hydroxyl (–OH) terminated thiol groups. This major result suggests that the adhesion of the particles to the substrate is strongly reduced by the presence of hydrophobic interfaces. The influence of critical parameters on the manipulation was investigated and discussed viz. the shape, size and grafting of the NPs, as well as the surface chemistry and the patterning of the substrate, and finally the operating conditions (temperature, humidity and scan velocity). Whereas the operating conditions and substrate structure are shown to have a strong effect on the mobility of the particles, we did not find any differences when manipulating ordered vs random distributed particles. PMID:21977418

  9. Atomic structure of the ultrathin alumina on NiAl(110) and its antiphase domain boundaries as seen by frequency modulation dynamic force microscopy

    NASA Astrophysics Data System (ADS)

    Simon, G. H.; König, T.; Rust, H.-P.; Heyde, M.; Freund, H.-J.

    2009-09-01

    Atomically resolved frequency modulation dynamic force microscopy (FM-DFM) images of the ultrathin alumina film on NiAl(110) are presented. Images show in detail the surface unit cell, both types of antiphase domain boundaries (translation-related domain boundaries) and lateral displacements within these types of boundaries. Due to the loss of translational symmetry at the boundary, structures of even increased complexity are revealed. Lateral models for these local arrangements have been created on the basis of adjusted unit cell structures. FM-DFM produces on this surface a contrast of extraordinarily high surface sensitivity. It matches the topmost oxygen layer even with respect to topographic height, which adds the third dimension to the analysis. With this the antiphase domain boundaries are shown to be shallow depressions. Furthermore, new symmetry aspects have been found in the topography of these boundaries. The local structure of the film surface shows evidence of substrate influence in its topography and the domain boundary network shows indications that its growth behaviour is affected by this interaction in its very details beyond sheer appearance. Presented results can be linked to the relation between growth and structure of an emerging class of structurally related ultrathin alumina films.

  10. Dynamic Elastic Modulus of Porcine Articular Cartilage Determined at Two Different Levels of Tissue Organization by Indentation-Type Atomic Force Microscopy

    PubMed Central

    Stolz, Martin; Raiteri, Roberto; Daniels, A. U.; VanLandingham, Mark R.; Baschong, Werner; Aebi, Ueli

    2004-01-01

    Cartilage stiffness was measured ex vivo at the micrometer and nanometer scales to explore structure-mechanical property relationships at smaller scales than has been done previously. A method was developed to measure the dynamic elastic modulus, |E*|, in compression by indentation-type atomic force microscopy (IT AFM). Spherical indenter tips (radius = ∼2.5 μm) and sharp pyramidal tips (radius = ∼20 nm) were employed to probe micrometer-scale and nanometer-scale response, respectively. |E*| values were obtained at 3 Hz from 1024 unloading response curves recorded at a given location on subsurface cartilage from porcine femoral condyles. With the microsphere tips, the average modulus was ∼2.6 MPa, in agreement with available millimeter-scale data, whereas with the sharp pyramidal tips, it was typically 100-fold lower. In contrast to cartilage, measurements made on agarose gels, a much more molecularly amorphous biomaterial, resulted in the same average modulus for both indentation tips. From results of AFM imaging of cartilage, the micrometer-scale spherical tips resolved no fine structure except some chondrocytes, whereas the nanometer-scale pyramidal tips resolved individual collagen fibers and their 67-nm axial repeat distance. These results suggest that the spherical AFM tip is large enough to measure the aggregate dynamic elastic modulus of cartilage, whereas the sharp AFM tip depicts the elastic properties of its fine structure. Additional measurements of cartilage stiffness following enzyme action revealed that elastase digestion of the collagen moiety lowered the modulus at the micrometer scale. In contrast, digestion of the proteoglycans moiety by cathepsin D had little effect on |E*| at the micrometer scale, but yielded a clear stiffening at the nanometer scale. Thus, cartilage compressive stiffness is different at the nanometer scale compared to the overall structural stiffness measured at the micrometer and larger scales because of the fine

  11. High-Resolution Traction Force Microscopy

    PubMed Central

    Plotnikov, Sergey V.; Sabass, Benedikt; Schwarz, Ulrich S.; Waterman, Clare M.

    2015-01-01

    Cellular forces generated by the actomyosin cytoskeleton and transmitted to the extracellular matrix (ECM) through discrete, integrin-based protein assemblies, that is, focal adhesions, are critical to developmental morphogenesis and tissue homeostasis, as well as disease progression in cancer. However, quantitative mapping of these forces has been difficult since there has been no experimental technique to visualize nanonewton forces at submicrometer spatial resolution. Here, we provide detailed protocols for measuring cellular forces exerted on two-dimensional elastic substrates with a high-resolution traction force microscopy (TFM) method. We describe fabrication of polyacrylamide substrates labeled with multiple colors of fiducial markers, functionalization of the substrates with ECM proteins, setting up the experiment, and imaging procedures. In addition, we provide the theoretical background of traction reconstruction and experimental considerations important to design a high-resolution TFM experiment. We describe the implementation of a new algorithm for processing of images of fiducial markers that are taken below the surface of the substrate, which significantly improves data quality. We demonstrate the application of the algorithm and explain how to choose a regularization parameter for suppression of the measurement error. A brief discussion of different ways to visualize and analyze the results serves to illustrate possible uses of high-resolution TFM in biomedical research. PMID:24974038

  12. Periodicity in bimodal atomic force microscopy

    SciTech Connect

    Lai, Chia-Yun; Santos, Sergio Chiesa, Matteo; Barcons, Victor

    2015-07-28

    Periodicity is fundamental for quantification and the application of conservation principles of many important systems. Here, we discuss periodicity in the context of bimodal atomic force microscopy (AFM). The relationship between the excited frequencies is shown to affect and control both experimental observables and the main expressions quantified via these observables, i.e., virial and energy transfer expressions, which form the basis of the bimodal AFM theory. The presence of a fundamental frequency further simplifies the theory and leads to close form solutions. Predictions are verified via numerical integration of the equation of motion and experimentally on a mica surface.

  13. Applications for atomic force microscopy of DNA.

    PubMed

    Hansma, H G; Laney, D E; Bezanilla, M; Sinsheimer, R L; Hansma, P K

    1995-05-01

    Tapping mode atomic force microscopy (AFM) of DNA in propanol, dry helium, and aqueous buffer each have specific applications. Resolution is best in propanol, which precipitates and immobilizes the DNA and provides a fluid imaging environment where adhesive forces are minimized. Resolution on exceptional images of DNA appears to be approximately 2 nm, sufficient to see helix turns in detail, but the smallest substructures typically seen on DNA in propanol are approximately 6-10 nm in size. Tapping AFM in dry helium provides a convenient way of imaging such things as conformations of DNA molecules and positions of proteins on DNA. Images of single-stranded DNA and RecA-DNA complexes are presented. In aqueous buffer DNA molecules as small as 300 bp have been imaged even when in motion. Images are presented of the changes in shape and position of circular plasmid DNA molecules.

  14. Ultrastable Atomic Force Microscopy for Biophysics

    NASA Astrophysics Data System (ADS)

    Churnside, Allison B.

    Atomic force microscopy (AFM) is a multifunctional workhorse of nanoscience and molecular biophysics, but instrumental drift remains a critical issue that limits the precision and duration of experiments. We have significantly reduced the two most important types of drift: in position and in force. The first, position drift, is defined as uncontrolled motion between the tip and the sample, which occurs in all three dimensions. By scattering a laser off the apex of a commercial AFM tip, we locally measured and thereby actively controlled its three-dimensional position above a sample surface to <0.4 A (Deltaf = 0.01--10 Hz) in air at room temperature. With this enhanced stability, we demonstrated atomic-scale (˜1 A) tip-sample stability and registration over tens of minutes with a series of AFM images. The second type of drift is force drift. We found that the primary source of force drift for a popular class of soft cantilevers is their gold coating, even though they are coated on both sides to minimize drift. When the gold coating was removed through a simple chemical etch, this drift in deflection was reduced by more than an order of magnitude over the first 2 hours after wetting the tip. Removing the gold also led to ˜ 10-fold reduction in reflected light, yet short-term (0.1--10 s) force precision improved. With both position and force drift greatly reduced, the utility of the AFM is enhanced. These improvements led to several new AFM abilities, including a five-fold increase in the image signal-to-noise ratio; tip-registered, label-free optical imaging; registered tip return to a particular point on the sample; and dual-detection force spectroscopy, which enables a new extension clamp mode. We have applied these abilities to folding of both membrane and soluble proteins. In principle, the techniques we describe can be fully incorporated into many types of scanning probe microscopy, making this work a general improvement to scanning probe techniques.

  15. EDITORIAL: High-resolution noncontact atomic force microscopy High-resolution noncontact atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Pérez, Rubén; García, Ricardo; Schwarz, Udo

    2009-06-01

    original papers authored by many of the leading groups in the field with the goal of providing a well-balanced overview on the state-of-the-art in this rapidly evolving field. These papers, many of which are based on notable presentations given during the Madrid conference, feature highlights such as (1) the development of sophisticated force spectroscopy procedures that are able to map the complete 3D tip-sample force field on different surfaces; (2) the considerable resolution improvement of Kelvin probe force microscopy (reaching, in some cases, the atomic scale), which is accompanied by a thorough, quantitative understanding of the contrast observed; (3) the perfecting of atomic resolution imaging on insulating substrates, which helps reshape our microscopic understanding of surface properties and chemical activity of these surfaces; (4) the description of instrumental and methodological developments that pave the way to the atomic-scale characterization of magnetic and electronic properties of nanostructures, and last but not least (5) the extension of dynamic imaging modes to high-resolution operation in liquids, ultimately achieving atomic resolution. The latter developments are already having a significant impact in the highly competitive field of biological imaging under physiological conditions. This special issue of Nanotechnology would not have been possible without the highly professional support from Nina Couzin, Amy Harvey, Alex Wotherspoon and the entire Nanotechnology team at IOP Publishing. We are thankful for their help in pushing this project forward. We also thank the authors who have contributed their excellent original articles to this issue, the referees whose comments have helped make the issue an accurate portrait of this rapidly moving field, and the entire NC-AFM community that continues to drive NC-AFM to new horizons.

  16. Force-Mediated Kinetics of Single P-Selectin/Ligand Complexes Observed by Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Fritz, Jurgen; Katopodis, Andreas G.; Kolbinger, Frank; Anselmetti, Dario

    1998-10-01

    Leukocytes roll along the endothelium of postcapillary venules in response to inflammatory signals. Rolling under the hydrodynamic drag forces of blood flow is mediated by the interaction between selectins and their ligands across the leukocyte and endothelial cell surfaces. Here we present force-spectroscopy experiments on single complexes of P-selectin and P-selectin glycoprotein ligand-1 by atomic force microscopy to determine the intrinsic molecular properties of this dynamic adhesion process. By modeling intermolecular and intramolecular forces as well as the adhesion probability in atomic force microscopy experiments we gain information on rupture forces, elasticity, and kinetics of the P-selectin/P-selectin glycoprotein ligand-1 interaction. The complexes are able to withstand forces up to 165 pN and show a chain-like elasticity with a molecular spring constant of 5.3 pN nm-1 and a persistence length of 0.35 nm. The dissociation constant (off-rate) varies over three orders of magnitude from 0.02 s-1 under zero force up to 15 s-1 under external applied forces. Rupture force and lifetime of the complexes are not constant, but directly depend on the applied force per unit time, which is a product of the intrinsic molecular elasticity and the external pulling velocity. The high strength of binding combined with force-dependent rate constants and high molecular elasticity are tailored to support physiological leukocyte rolling.

  17. Effects of point substitutions on the structure of toxic Alzheimer's β-amyloid channels: atomic force microscopy and molecular dynamics simulations.

    PubMed

    Connelly, Laura; Jang, Hyunbum; Arce, Fernando Teran; Ramachandran, Srinivasan; Kagan, Bruce L; Nussinov, Ruth; Lal, Ratnesh

    2012-04-10

    Alzheimer's disease (AD) is a misfolded protein disease characterized by the accumulation of β-amyloid (Aβ) peptide as senile plaques, progressive neurodegeneration, and memory loss. Recent evidence suggests that AD pathology is linked to the destabilization of cellular ionic homeostasis mediated by toxic pores made of Aβ peptides. Understanding the exact nature by which these pores conduct electrical and molecular signals could aid in identifying potential therapeutic targets for the prevention and treatment of AD. Here using atomic force microscopy (AFM) and molecular dynamics (MD) simulations, we compared the imaged pore structures with models to predict channel conformations as a function of amino acid sequence. Site-specific amino acid (AA) substitutions in the wild-type Aβ(1-42) peptide yield information regarding the location and significance of individual AA residues to its characteristic structure-activity relationship. We selected two AAs that our MD simulation predicted to inhibit or permit pore conductance. The substitution of Phe19 with Pro has previously been shown to eliminate conductance in the planar lipid bilayer system. Our MD simulations predict a channel-like shape with a collapsed pore, which is supported by the AFM channel images. We suggest that proline, a known β-sheet breaker, creates a kink in the center of the pore and prevents conductance via blockage. This residue may be a viable target for drug development studies aiming to inhibit Aβ from inducing ionic destabilization toxicity. The substitution of Phe20 with Cys exhibits pore structures indistinguishable from the wild type in AFM images. MD simulations predict site 20 to face the solvated pore. Overall, the mutations support the previously predicted β-sheet-based channel structure.

  18. Rationalizing nanomaterial sizes measured by atomic force microscopy, flow field-flow fractionation, and dynamic light scattering: sample preparation, polydispersity, and particle structure.

    PubMed

    Baalousha, M; Lead, J R

    2012-06-01

    This study aims to rationalize the variability in the measured size of nanomaterials (NMs) by some of the most commonly applied techniques in the field of nano(eco)toxicology and environmental sciences, including atomic force microscopy (AFM), dynamic light scattering (DLS), and flow field-flow fractionation (FlFFF). A validated sample preparation procedure for size evaluation by AFM is presented, along with a quantitative explanation of the variability of measured sizes by FlFFF, AFM, and DLS. The ratio of the z-average hydrodynamic diameter (d(DLS)) by DLS and the particle height by AFM (d(AFM)) approaches 1.0 for monodisperse samples and increases with sample polydispersity. A polydispersity index of 0.1 is suggested as a suitable limit above which DLS data can no longer be interpreted accurately. Conversion of the volume particle size distribution (PSD) by FlFFF-UV to the number PSD reduces the differences observed between the sizes measured by FlFFF (d(FlFFF)) and AFM. The remaining differences in the measured sizes can be attributed to particle structure (sphericity and permeability). The ratio d(FlFFF)/d(AFM) approaches 1 for small ion-coated NMs, which can be described as hard spheres, whereas d(FlFFF)/d(AFM) deviates from 1 for polymer-coated NMs, indicating that these particles are permeable, nonspherical, or both. These findings improve our understanding of the rather scattered data on NM size measurements reported in the environmental and nano(eco)toxicology literature and provide a tool for comparison of the measured sizes by different techniques.

  19. Mechanical force analysis of peptide interactions using atomic force microscopy.

    PubMed

    Nakamura, Chikashi; Takeda, Seiji; Kageshima, Masami; Ito, Miyuki; Sugimoto, Naoki; Sekizawa, Kazuko; Miyake, Jun

    2004-01-01

    Some peptides have previously been reported to bind low molecular weight chemicals. One such peptide with the amino acid sequence His-Ala-Ser-Tyr-Ser was selectively screened from a phage library and bound to a cationic porphyrin, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphine (TMpyP), with a binding constant of 10(5) M(-1) (J. Kawakami, T. Kitano, and N. Sugimoto, Chemical Communications, 1999, pp. 1765-1766). The proposed binding was due to pi-electron stacking from two aromatic amino acids of histidine and tyrosine. In this study, the weak interactions between TMpyP and the peptide were further investigated by force curve analysis using atomic force microscopy (AFM). The mechanical force required to unbind the peptide-porphyrin complex was measured by vertical movement of the AFM tip. Peptide self-assembled monolayers were formed on both a gold-coated mica substrate and a gold-coated AFM tip. The TMpyPs could bind between the two peptide layers when the peptide-immobilized AFM tip contacted the peptide-immobilized substrate in solution containing TMpyP. In the retracting process a force that ruptured the interaction between TMpyPs and peptides was observed. The unbinding force values correlated to the concentration of TMpyP. A detection limit of 100 ng/mL porphyrin was obtained for the force measurement, and was similar to surface plasmon resonance sensor detection limits. Furthermore, we calculated the product of the observed force and the length of the molecular elongation to determine the work required to unbind the complexes. The obtained values of unbinding work were in a reasonable range compared to the binding energy of porphyrin-peptide.

  20. Dynamic imaging with electron microscopy

    ScienceCinema

    Campbell, Geoffrey; McKeown, Joe; Santala, Melissa

    2016-07-12

    Livermore researchers have perfected an electron microscope to study fast-evolving material processes and chemical reactions. By applying engineering, microscopy, and laser expertise to the decades-old technology of electron microscopy, the dynamic transmission electron microscope (DTEM) team has developed a technique that can capture images of phenomena that are both very small and very fast. DTEM uses a precisely timed laser pulse to achieve a short but intense electron beam for imaging. When synchronized with a dynamic event in the microscope's field of view, DTEM allows scientists to record and measure material changes in action. A new movie-mode capability, which earned a 2013 R&D 100 Award from R&D Magazine, uses up to nine laser pulses to sequentially capture fast, irreversible, even one-of-a-kind material changes at the nanometer scale. DTEM projects are advancing basic and applied materials research, including such areas as nanostructure growth, phase transformations, and chemical reactions.

  1. Dynamic imaging with electron microscopy

    SciTech Connect

    Campbell, Geoffrey; McKeown, Joe; Santala, Melissa

    2014-02-20

    Livermore researchers have perfected an electron microscope to study fast-evolving material processes and chemical reactions. By applying engineering, microscopy, and laser expertise to the decades-old technology of electron microscopy, the dynamic transmission electron microscope (DTEM) team has developed a technique that can capture images of phenomena that are both very small and very fast. DTEM uses a precisely timed laser pulse to achieve a short but intense electron beam for imaging. When synchronized with a dynamic event in the microscope's field of view, DTEM allows scientists to record and measure material changes in action. A new movie-mode capability, which earned a 2013 R&D 100 Award from R&D Magazine, uses up to nine laser pulses to sequentially capture fast, irreversible, even one-of-a-kind material changes at the nanometer scale. DTEM projects are advancing basic and applied materials research, including such areas as nanostructure growth, phase transformations, and chemical reactions.

  2. Force dependent metalloprotein conductance by conducting atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Zhao, Jianwei; Davis, Jason J.

    2003-09-01

    Our ability to analyse charge transport through a biological macromolecule, pertinent to our understanding not only of biological redox processes but also, for example, to our interpretation of tunnelling imaging, remains a significant practical and theoretical issue. Though much information can be gained by carrying out such examinations at a molecular level, there exist few methods where such controlled analyses are, in fact, feasible. Here we report on the electron transport characteristics of a blue copper metalloprotein as characterized at a refined level by conductive-probe atomic force microscopy. The modulation of this conductance with compressional force has also been examined. Though highly resistive, observations are consistent with the ability of the protein matrix to mediate appreciable tunnelling current. This work, then, paves the way for designed implementation of biomacromolecules into electronic devices.

  3. Investigating cell mechanics with atomic force microscopy

    PubMed Central

    Haase, Kristina; Pelling, Andrew E.

    2015-01-01

    Transmission of mechanical force is crucial for normal cell development and functioning. However, the process of mechanotransduction cannot be studied in isolation from cell mechanics. Thus, in order to understand how cells ‘feel’, we must first understand how they deform and recover from physical perturbations. Owing to its versatility, atomic force microscopy (AFM) has become a popular tool to study intrinsic cellular mechanical properties. Used to directly manipulate and examine whole and subcellular reactions, AFM allows for top-down and reconstitutive approaches to mechanical characterization. These studies show that the responses of cells and their components are complex, and largely depend on the magnitude and time scale of loading. In this review, we generally describe the mechanotransductive process through discussion of well-known mechanosensors. We then focus on discussion of recent examples where AFM is used to specifically probe the elastic and inelastic responses of single cells undergoing deformation. We present a brief overview of classical and current models often used to characterize observed cellular phenomena in response to force. Both simple mechanistic models and complex nonlinear models have been used to describe the observed cellular behaviours, however a unifying description of cell mechanics has not yet been resolved. PMID:25589563

  4. Investigating cell mechanics with atomic force microscopy.

    PubMed

    Haase, Kristina; Pelling, Andrew E

    2015-03-01

    Transmission of mechanical force is crucial for normal cell development and functioning. However, the process of mechanotransduction cannot be studied in isolation from cell mechanics. Thus, in order to understand how cells 'feel', we must first understand how they deform and recover from physical perturbations. Owing to its versatility, atomic force microscopy (AFM) has become a popular tool to study intrinsic cellular mechanical properties. Used to directly manipulate and examine whole and subcellular reactions, AFM allows for top-down and reconstitutive approaches to mechanical characterization. These studies show that the responses of cells and their components are complex, and largely depend on the magnitude and time scale of loading. In this review, we generally describe the mechanotransductive process through discussion of well-known mechanosensors. We then focus on discussion of recent examples where AFM is used to specifically probe the elastic and inelastic responses of single cells undergoing deformation. We present a brief overview of classical and current models often used to characterize observed cellular phenomena in response to force. Both simple mechanistic models and complex nonlinear models have been used to describe the observed cellular behaviours, however a unifying description of cell mechanics has not yet been resolved.

  5. Investigating cell mechanics with atomic force microscopy.

    PubMed

    Haase, Kristina; Pelling, Andrew E

    2015-03-01

    Transmission of mechanical force is crucial for normal cell development and functioning. However, the process of mechanotransduction cannot be studied in isolation from cell mechanics. Thus, in order to understand how cells 'feel', we must first understand how they deform and recover from physical perturbations. Owing to its versatility, atomic force microscopy (AFM) has become a popular tool to study intrinsic cellular mechanical properties. Used to directly manipulate and examine whole and subcellular reactions, AFM allows for top-down and reconstitutive approaches to mechanical characterization. These studies show that the responses of cells and their components are complex, and largely depend on the magnitude and time scale of loading. In this review, we generally describe the mechanotransductive process through discussion of well-known mechanosensors. We then focus on discussion of recent examples where AFM is used to specifically probe the elastic and inelastic responses of single cells undergoing deformation. We present a brief overview of classical and current models often used to characterize observed cellular phenomena in response to force. Both simple mechanistic models and complex nonlinear models have been used to describe the observed cellular behaviours, however a unifying description of cell mechanics has not yet been resolved. PMID:25589563

  6. Atomic Force Microscopy for Soil Analysis

    NASA Astrophysics Data System (ADS)

    gazze, andrea; doerr, stefan; dudley, ed; hallin, ingrid; matthews, peter; quinn, gerry; van keulen, geertje; francis, lewis

    2016-04-01

    Atomic Force Microscopy (AFM) is a high-resolution surface-sensitive technique, which provides 3-dimensional topographical information and material properties of both stiff and soft samples in their natural environments. Traditionally AFM has been applied to samples with low roughness: hence its use for soil analysis has been very limited so far. Here we report the optimization settings required for a standardization of high-resolution and artefact-free analysis of natural soil with AFM: soil immobilization, AFM probe selection, artefact recognition and minimization. Beyond topography, AFM can be used in a spectroscopic mode to evaluate nanomechanical properties, such as soil viscosity, stiffness, and deformation. In this regards, Bruker PeakForce-Quantitative NanoMechanical (QNM) AFM provides a fast and convenient way to extract physical properties from AFM force curves in real-time to obtain soil nanomechanical properties. Here we show for the first time the ability of AFM to describe the topography of natural soil at nanometre resolution, with observation of micro-components, such as clays, and of nano-structures, possibly of biotic origin, the visualization of which would prove difficult with other instrumentations. Finally, nanomechanical profiling has been applied to different wettability states in soil and the respective physical patterns are discussed.

  7. Bimodal frequency-modulated atomic force microscopy with small cantilevers.

    PubMed

    Dietz, Christian; Schulze, Marcus; Voss, Agnieszka; Riesch, Christian; Stark, Robert W

    2015-02-01

    Small cantilevers with ultra-high resonant frequencies (1-3 MHz) have paved the way for high-speed atomic force microscopy. However, their potential for multi-frequency atomic force microscopy is unexplored. Because small cantilevers have small spring constants but large resonant frequencies, they are well-suited for the characterisation of delicate specimens with high imaging rates. We demonstrate their imaging capabilities in a bimodal frequency modulation mode in constant excitation on semi-crystalline polypropylene. The first two flexural modes of the cantilever were simultaneously excited. The detected frequency shift of the first eigenmode was held constant for topographical feedback, whereas the second eigenmode frequency shift was used to map the local properties of the specimen. High-resolution images were acquired depicting crystalline lamellae of approximately 12 nm in width. Additionally, dynamic force curves revealed that the contrast originated from different interaction forces between the tip and the distinct polymer regions. The technique uses gentle forces during scanning and quantified the elastic moduli Eam = 300 MPa and Ecr = 600 MPa on amorphous and crystalline regions, respectively. Thus, multimode measurements with small cantilevers allow one to map material properties on the nanoscale at high resolutions and increase the force sensitivity compared with standard cantilevers.

  8. Analyzing Atmospheric Aerosol with Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Kong, W.; Hawkins, L. N.

    2013-12-01

    Aerosol-water interactions are poorly understood for complex organic particles and may be important for determining the radiative forcing of atmospheric aerosol. One factor that may limit water uptake by organic aerosol is the viscosity of the particles. High viscosity particles may have very low diffusion coefficients for water vapor (and VOCs), which may inhibit deliquescence on the timescale of cloud and fog formation. This may be especially true for oligomeric material formed in aqueous reactions. Atomic force microscopy (AFM) is a powerful technique that can measure morphology and material properties at high spatial resolution. We have used AFM to probe the material properties of atmospheric particles as well as simulated brown carbon particles to determine if either type of particle shows high viscosity behavior. AFM works by rastering across a small area (less than 100 microns) of the sample slides and recording the heights of the sample as well as the forces on the tip as it approaches the sample and retracts away. Using this information, we can determine the shape, volume, stiffness, adhesiveness, and viscosity of the particles. Using these methods, we were able to show that, in general, both synthetic brown carbon compounds-formed in aqueous reactions-and submicron size atmospheric aerosol particles are adhesive, stiff, and semi-solid, which indicates that the simulated brown carbon compounds are good proxies of aerosol particles in atmosphere. In addition, based on the force data from AFM, we found that molecules that compose these particles are rather large and that there are a good amount of interactions like attractions between them.

  9. Differential dynamic microscopy for anisotropic colloidal dynamics.

    PubMed

    Reufer, Mathias; Martinez, Vincent A; Schurtenberger, Peter; Poon, Wilson C K

    2012-03-13

    Differential dynamic microscopy (DDM) is a low-cost, high-throughput technique recently developed for characterizing the isotropic diffusion of spherical colloids using white-light optical microscopy. (1) We develop the theory for applying DDM to probe the dynamics of anisotropic colloidal samples such as various ordered phases, or particles interacting with an external field. The q-dependent dynamics can be measured in any direction in the image plane. We demonstrate the method on a dilute aqueous dispersion of anisotropic magnetic particles (hematite) aligned in a magnetic field. The measured diffusion coefficients parallel and perpendicular to the field direction are in good agreement with theoretical values. We show how these measurements allow us to extract the orientational order parameter S(2) of the system.

  10. Atomic force microscopy of Precambrian microscopic fossils.

    PubMed

    Kempe, André; Schopf, J William; Altermann, Wladyslaw; Kudryavtsev, Anatoliy B; Heckl, Wolfgang M

    2002-07-01

    Atomic force microscopy (AFM) is a technique used routinely in material science to image substances at a submicron (including nm) scale. We apply this technique to analysis of the fine structure of organic-walled Precambrian fossils, microscopic sphaeromorph acritarchs (cysts of planktonic unicellular protists) permineralized in approximately 650-million-year-old cherts of the Chichkan Formation of southern Kazakhstan. AFM images, backed by laser-Raman spectroscopic analysis of individual specimens, demonstrate that the walls of these petrified fossils are composed of stacked arrays of approximately 200-nm-sized angular platelets of polycyclic aromatic kerogen. Together, AFM and laser-Raman spectroscopy provide means by which to elucidate the submicron-scale structure of individual microscopic fossils, investigate the geochemical maturation of ancient organic matter, and, potentially, distinguish true fossils from pseudofossils and probe the mechanisms of fossil preservation by silica permineralization.

  11. High-frequency multimodal atomic force microscopy

    PubMed Central

    Nievergelt, Adrian P; Adams, Jonathan D; Odermatt, Pascal D

    2014-01-01

    Summary Multifrequency atomic force microscopy imaging has been recently demonstrated as a powerful technique for quickly obtaining information about the mechanical properties of a sample. Combining this development with recent gains in imaging speed through small cantilevers holds the promise of a convenient, high-speed method for obtaining nanoscale topography as well as mechanical properties. Nevertheless, instrument bandwidth limitations on cantilever excitation and readout have restricted the ability of multifrequency techniques to fully benefit from small cantilevers. We present an approach for cantilever excitation and deflection readout with a bandwidth of 20 MHz, enabling multifrequency techniques extended beyond 2 MHz for obtaining materials contrast in liquid and air, as well as soft imaging of delicate biological samples. PMID:25671141

  12. Atomic force microscopy of model lipid membranes.

    PubMed

    Morandat, Sandrine; Azouzi, Slim; Beauvais, Estelle; Mastouri, Amira; El Kirat, Karim

    2013-02-01

    Supported lipid bilayers (SLBs) are biomimetic model systems that are now widely used to address the biophysical and biochemical properties of biological membranes. Two main methods are usually employed to form SLBs: the transfer of two successive monolayers by Langmuir-Blodgett or Langmuir-Schaefer techniques, and the fusion of preformed lipid vesicles. The transfer of lipid films on flat solid substrates offers the possibility to apply a wide range of surface analytical techniques that are very sensitive. Among them, atomic force microscopy (AFM) has opened new opportunities for determining the nanoscale organization of SLBs under physiological conditions. In this review, we first focus on the different protocols generally employed to prepare SLBs. Then, we describe AFM studies on the nanoscale lateral organization and mechanical properties of SLBs. Lastly, we survey recent developments in the AFM monitoring of bilayer alteration, remodeling, or digestion, by incubation with exogenous agents such as drugs, proteins, peptides, and nanoparticles.

  13. Atomic Force Microscopy for DNA SNP Identification

    NASA Astrophysics Data System (ADS)

    Valbusa, Ugo; Ierardi, Vincenzo

    The knowledge of the effects of single-nucleotide polymorphisms (SNPs) in the human genome greatly contributes to better comprehension of the relation between genetic factors and diseases. Sequence analysis of genomic DNA in different individuals reveals positions where variations that involve individual base substitutions can occur. Single-nucleotide polymorphisms are highly abundant and can have different consequences at phenotypic level. Several attempts were made to apply atomic force microscopy (AFM) to detect and map SNP sites in DNA strands. The most promising approach is the study of DNA mutations producing heteroduplex DNA strands and identifying the mismatches by means of a protein that labels the mismatches. MutS is a protein that is part of a well-known complex of mismatch repair, which initiates the process of repairing when the MutS binds to the mismatched DNA filament. The position of MutS on the DNA filament can be easily recorded by means of AFM imaging.

  14. Full information acquisition in piezoresponse force microscopy

    SciTech Connect

    Somnath, Suhas Belianinov, Alexei E-mail: sergei2@ornl.gov Kalinin, Sergei V. E-mail: sergei2@ornl.gov Jesse, Stephen E-mail: sergei2@ornl.gov

    2015-12-28

    The information flow from the tip-surface junction to the detector electronics during the piezoresponse force microscopy (PFM) imaging is explored using the recently developed general mode (G-mode) detection. Information-theory analysis suggests that G-mode PFM in the non-switching regime, close to the first resonance mode, contains a relatively small (100–150) number of components containing significant information. The first two primary components are similar to classical PFM images, suggesting that classical lock-in detection schemes provide high veracity information in this case. At the same time, a number of transient components exhibit contrast associated with surface topography, suggesting pathway to separate the two. The number of significant components increases considerably in the non-linear and switching regimes and approaching cantilever resonances, precluding the use of classical lock-in detection and necessitating the use of band excitation or G-mode detection schemes. The future prospects of full information imaging in scanning probe microscopy are discussed.

  15. Atomic Force Microscopy Based Cell Shape Index

    NASA Astrophysics Data System (ADS)

    Adia-Nimuwa, Usienemfon; Mujdat Tiryaki, Volkan; Hartz, Steven; Xie, Kan; Ayres, Virginia

    2013-03-01

    Stellation is a measure of cell physiology and pathology for several cell groups including neural, liver and pancreatic cells. In the present work, we compare the results of a conventional two-dimensional shape index study of both atomic force microscopy (AFM) and fluorescent microscopy images with the results obtained using a new three-dimensional AFM-based shape index similar to sphericity index. The stellation of astrocytes is investigated on nanofibrillar scaffolds composed of electrospun polyamide nanofibers that has demonstrated promise for central nervous system (CNS) repair. Recent work by our group has given us the ability to clearly segment the cells from nanofibrillar scaffolds in AFM images. The clear-featured AFM images indicated that the astrocyte processes were longer than previously identified at 24h. It was furthermore shown that cell spreading could vary significantly as a function of environmental parameters, and that AFM images could record these variations. The new three-dimensional AFM-based shape index incorporates the new information: longer stellate processes and cell spreading. The support of NSF PHY-095776 is acknowledged.

  16. Atomic force microscopy study of tooth surfaces.

    PubMed

    Farina, M; Schemmel, A; Weissmüller, G; Cruz, R; Kachar, B; Bisch, P M

    1999-03-01

    Atomic force microscopy (AFM) was used to study tooth surfaces in order to compare the pattern of particle distribution in the outermost layer of the tooth surfaces. Human teeth and teeth from a rodent (Golden hamster), from a fish (piranha), and from a grazing mollusk (chiton) with distinct feeding habits were analyzed in terms of particle arrangement, packing, and size distribution. Scanning electron microscopy and transmission electron microscopy were used for comparison. It was found that AFM gives high-contrast, high-resolution images and is an important tool as a source of complementary and/or new structural information. All teeth were cleaned and some were etched with acidic solutions before analysis. It was observed that human enamel (permanent teeth) presents particles tightly packed in the outer surface, whereas enamel from the hamster (continuously growing teeth) shows particles of less dense packing. The piranha teeth have a thin cuticle covering the long apatite crystals of the underlying enameloid. This cuticle has a rough surface of particles that have a globular appearance after the brief acidic treatment. The similar appearance of the in vivo naturally etched tooth surface suggests that the pattern of globule distribution may be due to the presence of an organic material. Elemental analysis of this cuticle indicated that calcium, phosphorus, and iron are the main components of the structure while electron microdiffraction of pulverized cuticle particles showed a pattern consistent with hydroxyapatite. The chiton mineralized tooth cusp had a smooth surface in an unabraded region and a very rough structure with the magnetite crystals (already known to make part of the structure) protruding from the surface. It was concluded that the structures analyzed are optimized for efficiency in feeding mechanism and life span of the teeth.

  17. Nanoscale chemical imaging by photoinduced force microscopy

    PubMed Central

    Nowak, Derek; Morrison, William; Wickramasinghe, H. Kumar; Jahng, Junghoon; Potma, Eric; Wan, Lei; Ruiz, Ricardo; Albrecht, Thomas R.; Schmidt, Kristin; Frommer, Jane; Sanders, Daniel P.; Park, Sung

    2016-01-01

    Correlating spatial chemical information with the morphology of closely packed nanostructures remains a challenge for the scientific community. For example, supramolecular self-assembly, which provides a powerful and low-cost way to create nanoscale patterns and engineered nanostructures, is not easily interrogated in real space via existing nondestructive techniques based on optics or electrons. A novel scanning probe technique called infrared photoinduced force microscopy (IR PiFM) directly measures the photoinduced polarizability of the sample in the near field by detecting the time-integrated force between the tip and the sample. By imaging at multiple IR wavelengths corresponding to absorption peaks of different chemical species, PiFM has demonstrated the ability to spatially map nm-scale patterns of the individual chemical components of two different types of self-assembled block copolymer films. With chemical-specific nanometer-scale imaging, PiFM provides a powerful new analytical method for deepening our understanding of nanomaterials. PMID:27051870

  18. Nanoscale chemical imaging by photoinduced force microscopy.

    PubMed

    Nowak, Derek; Morrison, William; Wickramasinghe, H Kumar; Jahng, Junghoon; Potma, Eric; Wan, Lei; Ruiz, Ricardo; Albrecht, Thomas R; Schmidt, Kristin; Frommer, Jane; Sanders, Daniel P; Park, Sung

    2016-03-01

    Correlating spatial chemical information with the morphology of closely packed nanostructures remains a challenge for the scientific community. For example, supramolecular self-assembly, which provides a powerful and low-cost way to create nanoscale patterns and engineered nanostructures, is not easily interrogated in real space via existing nondestructive techniques based on optics or electrons. A novel scanning probe technique called infrared photoinduced force microscopy (IR PiFM) directly measures the photoinduced polarizability of the sample in the near field by detecting the time-integrated force between the tip and the sample. By imaging at multiple IR wavelengths corresponding to absorption peaks of different chemical species, PiFM has demonstrated the ability to spatially map nm-scale patterns of the individual chemical components of two different types of self-assembled block copolymer films. With chemical-specific nanometer-scale imaging, PiFM provides a powerful new analytical method for deepening our understanding of nanomaterials. PMID:27051870

  19. Imaging mechanisms of force detected FMR microscopy

    SciTech Connect

    Midzor, M. M.; Wigen, P. E.; Pelekhov, D.; Chen, W.; Hammel, P. C.; Roukes, M. L.

    2000-05-01

    We demonstrate spatial resolution of ferromagnetic resonance in a microscopic sample of YIG using ferromagnetic resonance force microscopy (FMRFM). Measurements were performed on a small single crystal YIG film grown on a GGG substrate, roughly rectangular in shape 20 {mu}mx{approx}150 {mu}m and 3 {mu}m thick. The perpendicular and parallel force geometries of FMRFM, in conjunction with an external bias field both parallel and perpendicular to the film, were used to scan the sample. This enabled the detection of strong signals, even at atmospheric pressure and room temperature. The fundamental and higher-order magnetostatic modes were observed to have 26-29 Gauss separation. The intensity of these modes exhibited spatial variation as the magnetic tip was scanned over the sample, and this behavior is qualitatively explained by DE theory. An improved fabrication method for magnet on cantilever was employed, which yielded a spatial resolution of 15 {mu}m. These results demonstrate the potential of FMRFM for investigating the spatial dependence of ferromagnetic resonance, and for studying the anisotropy fields and exchange coupling effects within multilayer films and small magnetic systems. (c) 2000 American Institute of Physics.

  20. Atomic force microscopy measurements of intermolecular binding forces.

    PubMed

    Misevic, Gradimir N; Karamanos, Yannis; Misevic, Nikola J

    2009-01-01

    Atomic force microscopy (AFM) measurements of intermolecular binding strength between a single pair of complementary cell adhesion molecules in physiological solutions provided the first quantitative evidence for their cohesive function. This novel AFM-based nanobiotechnology opens a molecular mechanic approach for studying structure- to function-related properties of any type of individual biological macromolecules. The presented example of Porifera cell adhesion glyconectin proteoglycans showed that homotypic carbohydrate to carbohydrate interactions between two primordial proteoglycans can hold the weight of 1,600 cells. Thus, glyconectin type carbohydrates, as the most peripheral cell surface molecules of sponges (today's simplest living Metazoa), are proposed to be the primary cell adhesive molecules essential for the evolution of the multicellularity.

  1. Dielectrophoretic immobilization of proteins: Quantification by atomic force microscopy.

    PubMed

    Laux, Eva-Maria; Knigge, Xenia; Bier, Frank F; Wenger, Christian; Hölzel, Ralph

    2015-09-01

    The combination of alternating electric fields with nanometer-sized electrodes allows the permanent immobilization of proteins by dielectrophoretic force. Here, atomic force microscopy is introduced as a quantification method, and results are compared with fluorescence microscopy. Experimental parameters, for example the applied voltage and duration of field application, are varied systematically, and the influence on the amount of immobilized proteins is investigated. A linear correlation to the duration of field application was found by atomic force microscopy, and both microscopical methods yield a square dependence of the amount of immobilized proteins on the applied voltage. While fluorescence microscopy allows real-time imaging, atomic force microscopy reveals immobilized proteins obscured in fluorescence images due to low S/N. Furthermore, the higher spatial resolution of the atomic force microscope enables the visualization of the protein distribution on single nanoelectrodes. The electric field distribution is calculated and compared to experimental results with very good agreement to atomic force microscopy measurements.

  2. Full information acquisition in piezoresponse force microscopy

    DOE PAGES

    Somnath, Suhas; Belianinov, Alex; Jesse, Stephen; Kalinin, Sergei V.

    2015-12-28

    The information flow from the tip-surface junction to the detector electronics during the piezoresponse force microscopy (PFM) imaging is explored using the recently developed general mode (G-mode) detection. Information-theory analysis suggests that G-mode PFM in the non-switching regime, close to the first resonance mode, contains a relatively small (100 - 150) number of components containing significant information. The first two primary components are similar to classical PFM images, suggesting that classical lock-in detection schemes provide high veracity information in this case. At the same time, a number of transient components exhibit contrast associated with surface topography, suggesting pathway to separatemore » the two. The number of significant components increases considerably in the non-linear and switching regimes and approaching to cantilever resonances, precluding the use of classical lock-in detection and necessitating the use of band excitation or G-mode detection schemes. As a result, the future prospects of full information imaging in SPM are discussed.« less

  3. Full information acquisition in piezoresponse force microscopy

    SciTech Connect

    Somnath, Suhas; Belianinov, Alex; Jesse, Stephen; Kalinin, Sergei V.

    2015-12-28

    The information flow from the tip-surface junction to the detector electronics during the piezoresponse force microscopy (PFM) imaging is explored using the recently developed general mode (G-mode) detection. Information-theory analysis suggests that G-mode PFM in the non-switching regime, close to the first resonance mode, contains a relatively small (100 - 150) number of components containing significant information. The first two primary components are similar to classical PFM images, suggesting that classical lock-in detection schemes provide high veracity information in this case. At the same time, a number of transient components exhibit contrast associated with surface topography, suggesting pathway to separate the two. The number of significant components increases considerably in the non-linear and switching regimes and approaching to cantilever resonances, precluding the use of classical lock-in detection and necessitating the use of band excitation or G-mode detection schemes. As a result, the future prospects of full information imaging in SPM are discussed.

  4. Investigating the glycocalyx using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Boren, Rebecca; Rafi, Adam; Farrell, Jessica; Peramo, Antonio; Garrett Matthews, W.

    2006-03-01

    The extracellular surfaces of the peripheral vascular system are coated with an outer filamentous layer of proteoglycan (PG) molecules, forming a brush-like structure known as the glycocalyx. The mechanical properties of PGs have become of increased interest due to their roles in a variety of interactions, including the adhesion of metastatic cells and their use as flow sensors. The goal of this project is to investigate the mechanical properties of the glycocalyx as a function of differing environmental conditions (i.e. pH, various ion concentrations, etc). We use as an experimental model of the glycocalyx an end-tethered brush of PGs oriented so that the protein backbone is upright, emulating their in vivo formation. We have developed a technique for patterning PG onto substrates allowing the exposure of the PG layer to different biologically relevant solvents. Resulting brush height changes will be measured using atomic force microscopy. The compression and extension of these PG molecules also will be measured and used to explain the imaged structures and the behaviors relevant to their biological function.

  5. Investigating bioconjugation by atomic force microscopy

    PubMed Central

    2013-01-01

    Nanotechnological applications increasingly exploit the selectivity and processivity of biological molecules. Integration of biomolecules such as proteins or DNA into nano-systems typically requires their conjugation to surfaces, for example of carbon-nanotubes or fluorescent quantum dots. The bioconjugated nanostructures exploit the unique strengths of both their biological and nanoparticle components and are used in diverse, future oriented research areas ranging from nanoelectronics to biosensing and nanomedicine. Atomic force microscopy imaging provides valuable, direct insight for the evaluation of different conjugation approaches at the level of the individual molecules. Recent technical advances have enabled high speed imaging by AFM supporting time resolutions sufficient to follow conformational changes of intricately assembled nanostructures in solution. In addition, integration of AFM with different spectroscopic and imaging approaches provides an enhanced level of information on the investigated sample. Furthermore, the AFM itself can serve as an active tool for the assembly of nanostructures based on bioconjugation. AFM is hence a major workhorse in nanotechnology; it is a powerful tool for the structural investigation of bioconjugation and bioconjugation-induced effects as well as the simultaneous active assembly and analysis of bioconjugation-based nanostructures. PMID:23855448

  6. Atomic force microscopy study of enamel remineralization

    PubMed Central

    Poggio, Claudio; Ceci, Matteo; Beltrami, Riccardo; Lombardini, Marco; Colombo, Marco

    2014-01-01

    Summary Aim The aim of the present in vitro study was the evaluation of two products: a CPP-ACP paste (GC Tooth Mousse, GC Corp.) and a desensitizing toothpaste (Colgate Sensitive Pro Relief, Colgate-Palmolive) on preventing enamel erosion produced by a soft drink (Coca Cola) by using Atomic Force Microscopy (AFM). Methods Thirty enamel specimens were assigned to 6 groups of 5 specimens each. 1: intact enamel, 2: enamel + soft drink, 3: intact enamel + Colgate Sensitive Pro Relief, 4: enamel + soft drink + Colgate Sensitive Pro Relief, 5: intact enamel + GC Tooth Mousse, 6: enamel + soft drink + GC Tooth Mousse. The surface of each specimen was imaged by AFM. The root mean-square roughness (Rrms) was obtained from the AFM images and the differences in the averaged values among the groups were analyzed by ANOVA test. Results Comparing groups 4 and 6 (soft drink + toothpastes) with group 2 (eroded enamel) a statistical difference (P<0.05) was registered, suggesting effectiveness in protecting enamel against erosion of the products investigated. Conclusions The use of new formulation toothpastes can prevent enamel demineralization. PMID:25506414

  7. Atomic force microscopy, lateral force microscopy, and transmission electron microscopy investigations and adhesion force measurements for elucidation of tungsten removal mechanisms

    SciTech Connect

    Stein, D.J.; Cecchi, J.L.; Hetherington, D.L.

    1999-09-01

    We investigated various interactions between alumina and tungsten films that occur during chemical mechanical polishing (CMP). Atomic force microscopy surface topography measurements of post-CMP tungsten indicate that the roughness of the tungsten is independent of polish pressure and rotation rate. Pure mechanical abrasion is therefore an unlikely mechanism of material removal during CMP. Transmission electron microscopy images corroborate these results. The adhesion force between alumina and tungsten was measured in solution. The adhesive force increased with KIO{sub 3} concentration. Friction forces were measured in solution using lateral force microscopy. The friction force in buffered solutions was independent of KIO{sub 3} concentration. These results indicate that interactions other than purely mechanical interactions exist during CMP. {copyright} {ital 1999 Materials Research Society.}

  8. Kelvin probe force microscopy in nonpolar liquids.

    PubMed

    Domanski, Anna L; Sengupta, Esha; Bley, Karina; Untch, Maria B; Weber, Stefan A L; Landfester, Katharina; Weiss, Clemens K; Butt, Hans-Jürgen; Berger, Rüdiger

    2012-10-01

    Work function changes of Au were measured by Kelvin probe force microscopy (KPFM) in the nonpolar liquid decane. As a proof of principle for the measurement in liquids, we investigated the work function change of an Au substrate upon hexadecanethiol chemisorption. To relate the measured contact potential difference (CPD) during the chemisorption of alkanethiols to a change of the work function, the influence of physisorbed decane must be taken into account. It is crucial that either the work function of the scanning probe microscope (SPM) tip or the sample surface remains constant throughout the reaction, since both contribute to the CPD. We describe two routes for determining the work function shift of Au coated with a monolayer of alkanethiols: In the first route, the SPM tips were taken as reference surfaces (constant tip work function). For this approach, we used Au(111) surfaces and kept the SPM tip ex situ during the adsorption process. In the second route, structured surfaces with reactive and inert parts were studied by KPFM (constant reference work function). For this route, we prepared nanometer sized Au structures by nanosphere lithography on SiO(x) substrates. Now, the SiO(x) served as the inert reference surface. The shifts in the work function after exposure to the hexadecanethiol (HDT) solution were determined to be ΔΦ(Au+HDT,decane-Au,air) = -1.33 eV ± 0.07 eV (route I) and ΔΦ(Au+HDT,decane-Au,air) = -1.46 eV ± 0.04 eV (route II). Both values are in excellent agreement with the work function shifts determined by ultraviolet photoemission spectroscopy (UPS) reported in literature. The presented procedures of measuring work function changes in decane open new ways to study local reactions at solid-liquid interfaces.

  9. Spatial spectrograms of vibrating atomic force microscopy cantilevers coupled to sample surfaces

    SciTech Connect

    Wagner, Ryan; Raman, Arvind; Proksch, Roger

    2013-12-23

    Many advanced dynamic Atomic Force Microscopy (AFM) techniques such as contact resonance, force modulation, piezoresponse force microscopy, electrochemical strain microscopy, and AFM infrared spectroscopy exploit the dynamic response of a cantilever in contact with a sample to extract local material properties. Achieving quantitative results in these techniques usually requires the assumption of a certain shape of cantilever vibration. We present a technique that allows in-situ measurements of the vibrational shape of AFM cantilevers coupled to surfaces. This technique opens up unique approaches to nanoscale material property mapping, which are not possible with single point measurements alone.

  10. Simultaneous Nanomechanical and Electrochemical Mapping: Combining Peak Force Tapping Atomic Force Microscopy with Scanning Electrochemical Microscopy.

    PubMed

    Knittel, Peter; Mizaikoff, Boris; Kranz, Christine

    2016-06-21

    Soft electronic devices play a crucial role in, e.g., neural implants as stimulating electrodes, transducers for biosensors, or selective drug-delivery. Because of their elasticity, they can easily adapt to their environment and prevent immunoreactions leading to an overall improved long-term performance. In addition, flexible electronic devices such as stretchable displays will be increasingly used in everyday life, e.g., for so-called electronic wearables. Atomic force microscopy (AFM) is a versatile tool to characterize these micro- and nanostructured devices in terms of their topography. Using advanced imaging techniques such as peak force tapping (PFT), nanomechanical properties including adhesion, deformation, and Young's modulus can be simultaneously mapped along with surface features. However, conventional AFM provides limited laterally resolved information on electrical or electrochemical properties such as the activity of an electrode array. In this study, we present the first combination of AFM with scanning electrochemical microscopy (SECM) in PFT mode, thereby offering spatially correlated electrochemical and nanomechanical information paired with high-resolution topographical data under force control (QNM-AFM-SECM). The versatility of this combined scanning probe approach is demonstrated by mapping topographical, electrochemical, and nanomechanical properties of gold microelectrodes and of gold electrodes patterned onto polydimethylsiloxane. PMID:27203837

  11. Simultaneous Nanomechanical and Electrochemical Mapping: Combining Peak Force Tapping Atomic Force Microscopy with Scanning Electrochemical Microscopy.

    PubMed

    Knittel, Peter; Mizaikoff, Boris; Kranz, Christine

    2016-06-21

    Soft electronic devices play a crucial role in, e.g., neural implants as stimulating electrodes, transducers for biosensors, or selective drug-delivery. Because of their elasticity, they can easily adapt to their environment and prevent immunoreactions leading to an overall improved long-term performance. In addition, flexible electronic devices such as stretchable displays will be increasingly used in everyday life, e.g., for so-called electronic wearables. Atomic force microscopy (AFM) is a versatile tool to characterize these micro- and nanostructured devices in terms of their topography. Using advanced imaging techniques such as peak force tapping (PFT), nanomechanical properties including adhesion, deformation, and Young's modulus can be simultaneously mapped along with surface features. However, conventional AFM provides limited laterally resolved information on electrical or electrochemical properties such as the activity of an electrode array. In this study, we present the first combination of AFM with scanning electrochemical microscopy (SECM) in PFT mode, thereby offering spatially correlated electrochemical and nanomechanical information paired with high-resolution topographical data under force control (QNM-AFM-SECM). The versatility of this combined scanning probe approach is demonstrated by mapping topographical, electrochemical, and nanomechanical properties of gold microelectrodes and of gold electrodes patterned onto polydimethylsiloxane.

  12. Accurate force spectroscopy in tapping mode atomic force microscopy in liquids

    NASA Astrophysics Data System (ADS)

    Xu, Xin; Melcher, John; Raman, Arvind

    2010-01-01

    Existing force spectroscopy methods in tapping mode atomic force microscopy (AFM) such as higher harmonic inversion [M. Stark, R. W. Stark, W. M. Heckl, and R. Guckenberger, Proc. Natl. Acad. Sci. U.S.A. 99, 8473 (2002)] or scanning probe acceleration microscopy [J. Legleiter, M. Park, B. Cusick, and T. Kowalewski, Proc. Natl. Acad. Sci. U.S.A. 103, 4813 (2006)] or integral relations [M. Lee and W. Jhe, Phys. Rev. Lett. 97, 036104 (2006); S. Hu and A. Raman, Nanotechnology 19, 375704 (2008); H. Hölscher, Appl. Phys. Lett. 89, 123109 (2006); A. J. Katan, Nanotechnology 20, 165703 (2009)] require and assume as an observable the tip dynamics in a single eigenmode of the oscillating microcantilever. We demonstrate that this assumption can distort significantly the extracted tip-sample interaction forces when applied to tapping mode AFM with soft cantilevers in liquid environments. This exception is due to the fact that under these conditions the second eigenmode is momentarily excited and the observed tip dynamics clearly contains contributions from the fundamental and second eigenmodes. To alleviate this problem, a simple experimental method is proposed to screen the second eigenmode contributions in the observed tip deflection signal to allow accurate tip-sample force reconstruction in liquids. The method is implemented experimentally to reconstruct interaction forces on polymer, bacteriorhodopsin membrane, and mica samples in buffer solutions.

  13. Spatial horizons in amplitude and frequency modulation atomic force microscopy.

    PubMed

    Font, Josep; Santos, Sergio; Barcons, Victor; Thomson, Neil H; Verdaguer, Albert; Chiesa, Matteo

    2012-04-01

    In dynamic atomic force microscopy (AFM) the cantilever is vibrated and its dynamics are monitored to probe the sample with nanoscale and atomic resolution. Amplitude and frequency modulation atomic force microscopy (AM-AFM and FM-AFM) have established themselves as the most powerful methods in the field. Nevertheless, it is still debatable whether one or the other technique is preferred in a given medium or experiment. Here, we quantitatively establish and compare the limitations in resolution of both techniques by introducing the concept of spatial horizon (SH) and quantifying it. The SH is the limiting spatial boundary beyond which collective atomic interactions do not affect the detection parameters of a given feedback system. We show that while an FM-AFM feedback can resolve a single atom or atomic defect where an AM feedback might fail, relative contrast is in fact equivalent for both feedback systems. That is, if the AM feedback could detect sufficiently small amplitude shifts and there was no noise, the detection of single atoms or atomic defects would be equivalent in AM-AFM and FM-AFM.

  14. Optical Force Probe Microscopy of the Pericellular Matrix

    NASA Astrophysics Data System (ADS)

    McLane, Louis T.; Chang, Patrick; Granqvist, Anna; Boehm, Heike; Kramer, Anthony; Curtis, Jennifer E.

    2012-02-01

    The pericellular matrix is a microns-thick grafted polymer film on the surface of cells. Its structure and mechanics influence processes as diverse as filtration, cell adhesion, proliferation, migration, cancer metastasis and possibly mechanotransduction. Optical force probe microscopy enables dynamic and equilibrium measurements of this polymer film on living cells. We show that equilibrium force measurements can be related to the osmotic pressure in the pericellular matrix, leading to a prediction of a spatially varying correlation length (mesh size) profile ranging from ˜100 nm at the cell surface to 1000 nm near the edge of the cell coat. Assuming the film is brush-like, comparison to polymer brush theory provides estimates of the equilibrium brush length and the grafting density at the surface. The equilibrium length is consistent with that observed during dynamic force measurements, and the grafting density is close to that of maximal packing for the large, space filling molecules in the system - i.e. tethered polymers populated by semi-flexible side chains with cross sections ˜80 x 400 nm^2.

  15. In-situ piezoresponse force microscopy cantilever mode shape profiling

    SciTech Connect

    Proksch, R.

    2015-08-21

    The frequency-dependent amplitude and phase in piezoresponse force microscopy (PFM) measurements are shown to be a consequence of the Euler-Bernoulli (EB) dynamics of atomic force microscope (AFM) cantilever beams used to make the measurements. Changes in the cantilever mode shape as a function of changes in the boundary conditions determine the sensitivity of cantilevers to forces between the tip and the sample. Conventional PFM and AFM measurements are made with the motion of the cantilever measured at one optical beam detector (OBD) spot location. A single OBD spot location provides a limited picture of the total cantilever motion, and in fact, experimentally observed cantilever amplitude and phase are shown to be strongly dependent on the OBD spot position for many measurements. In this work, the commonly observed frequency dependence of PFM response is explained through experimental measurements and analytic theoretical EB modeling of the PFM response as a function of both frequency and OBD spot location on a periodically poled lithium niobate sample. One notable conclusion is that a common choice of OBD spot location—at or near the tip of the cantilever—is particularly vulnerable to frequency dependent amplitude and phase variations stemming from dynamics of the cantilever sensor rather than from the piezoresponse of the sample.

  16. Characterization of fragile nanostructures using scanning force microscopy

    NASA Astrophysics Data System (ADS)

    Buss, Michael Richard

    1998-12-01

    The possibility of using scanning force microscopy (SFM) to image monolayer arrays of nanometer diameter gold clusters on flat substrates has been investigated. A major difficulty in SFM studies of supported cluster arrays is the interaction force between the SFM probe and the clusters which results in the clusters moving on the substrate during imaging. The addition of a carbon nanotube to the tip of the SFM probe reduces this interaction force, resulting in stable, tapping mode height images of the supported cluster arrays. However, resolution of individual nanometer-size cluster in an array requires reduction of the endform radius of the nanotubes. In an attempt to reduce the effects of image dilation, the endform shape of the nanotube has been modified by spark etching. Also, metal atoms have been deposited onto the tip endform by sparking the tip of the nanotube by sparking the tip against a metal substrate and by electro-depositing metal onto the tip. Molecular dynamics (MD) simulations using embedded-atom-method (EAM) potentials have been used to model the compression behavior of nanometer-size gold clusters. The simulations examined the behavior of free and supported gold particles compressed with normal and shear forces. These results have been used to explain previously observed descrepencies between the calculated and measured elastic modulus of nanometer-size gold clusters.

  17. Force feedback microscopy based on an optical beam deflection scheme

    SciTech Connect

    Vitorino, Miguel V.; Rodrigues, Mario S.; Carpentier, Simon; Costa, Luca

    2014-07-07

    Force feedback microscopy circumvents the jump to contact in atomic force microscopy when using soft cantilevers and quantitatively measures the interaction properties at the nanoscale by simultaneously providing force, force gradient, and dissipation. The force feedback microscope developed so far used an optical cavity to measure the tip displacement. In this Letter, we show that the more conventional optical beam deflection scheme can be used to the same purpose. With this instrument, we have followed the evolution of the Brownian motion of the tip under the influence of a water bridge.

  18. Fast and gentle side approach for atomic force microscopy

    SciTech Connect

    Wessels, W. A.; Broekmaat, J. J.; Koster, G.; Rijnders, G.; Beerends, R. J. L.

    2013-12-15

    Atomic force microscopy is one of the most popular imaging tools with atomic resolution in different research fields. Here, a fast and gentle side approach for atomic force microscopy is proposed to image the same surface location and to reduce the time delay between modification and imaging without significant tip degradation. This reproducible approach to image the same surface location using atomic force microscopy shortly after, for example, any biological, chemical, or physical modification on a geometrically separated position has the potential to become widely used.

  19. Development and testing of hyperbaric atomic force microscopy (AFM) and fluorescence microscopy for biological applications.

    PubMed

    D'Agostino, D P; McNally, H A; Dean, J B

    2012-05-01

    A commercially available atomic force microscopy and fluorescence microscope were installed and tested inside a custom-designed hyperbaric chamber to provide the capability to study the effects of hyperbaric gases on biological preparations, including cellular mechanism of oxidative stress. In this report, we list details of installing and testing atomic force microscopy and fluorescence microscopy inside a hyperbaric chamber. The pressure vessel was designed to accommodate a variety of imaging equipment and ensures full functionality at ambient and hyperbaric conditions (≤85 psi). Electrical, gas and fluid lines were installed to enable remote operation of instrumentation under hyperbaric conditions, and to maintain viable biological samples with gas-equilibrated superfusate and/or drugs. Systems were installed for vibration isolation and temperature regulation to maintain atomic force microscopy performance during compression and decompression. Results of atomic force microscopy testing demonstrate sub-nanometre resolution at hyperbaric pressure in dry scans and fluid scans, in both contact mode and tapping mode. Noise levels were less when measurements were taken under hyperbaric pressure with air, helium (He) and nitrogen (N(2) ). Atomic force microscopy and fluorescence microscopy measurements were made on a variety of living cell cultures exposed to hyperbaric gases (He, N(2) , O(2) , air). In summary, atomic force microscopy and fluorescence microscopy were installed and tested for use at hyperbaric pressures and enables the study of cellular and molecular effects of hyperbaric gases and pressure per se in biological preparations.

  20. Nanometrology of delignified Populus using mode synthesizing atomic force microscopy

    SciTech Connect

    Tetard, Laurene; Passian, Ali; Farahi, R H; Davison, Brian H; Jung, S; Ragauskas, A J; Lereu, Aude; Thundat, Thomas George

    2011-01-01

    The study of the spatially resolved physical and compositional properties of materials at the nanoscale is increasingly challenging due to the level of complexity of biological specimens such as those of interest in bioenergy production. Mode synthesizing atomic force microscopy (MSAFM) has emerged as a promising metrology tool for such studies. It is shown that, by tuning the mechanical excitation of the probe-sample system, MSAFM can be used to dynamically investigate the multifaceted complexity of plant cells. The results are argued to be of importance both for the characteristics of the invoked synthesized modes and for accessing new features of the samples. As a specific system to investigate, we present images of Populus, before and after a holopulping treatment, a crucial step in the biomass delignification process.

  1. Unlocking higher harmonics in atomic force microscopy with gentle interactions

    PubMed Central

    Font, Josep; Verdaguer, Albert

    2014-01-01

    Summary In dynamic atomic force microscopy, nanoscale properties are encoded in the higher harmonics. Nevertheless, when gentle interactions and minimal invasiveness are required, these harmonics are typically undetectable. Here, we propose to externally drive an arbitrary number of exact higher harmonics above the noise level. In this way, multiple contrast channels that are sensitive to compositional variations are made accessible. Numerical integration of the equation of motion shows that the external introduction of exact harmonic frequencies does not compromise the fundamental frequency. Thermal fluctuations are also considered within the detection bandwidth of interest and discussed in terms of higher-harmonic phase contrast in the presence and absence of an external excitation of higher harmonics. Higher harmonic phase shifts further provide the means to directly decouple the true topography from that induced by compositional heterogeneity. PMID:24778948

  2. Unlocking higher harmonics in atomic force microscopy with gentle interactions.

    PubMed

    Santos, Sergio; Barcons, Victor; Font, Josep; Verdaguer, Albert

    2014-01-01

    In dynamic atomic force microscopy, nanoscale properties are encoded in the higher harmonics. Nevertheless, when gentle interactions and minimal invasiveness are required, these harmonics are typically undetectable. Here, we propose to externally drive an arbitrary number of exact higher harmonics above the noise level. In this way, multiple contrast channels that are sensitive to compositional variations are made accessible. Numerical integration of the equation of motion shows that the external introduction of exact harmonic frequencies does not compromise the fundamental frequency. Thermal fluctuations are also considered within the detection bandwidth of interest and discussed in terms of higher-harmonic phase contrast in the presence and absence of an external excitation of higher harmonics. Higher harmonic phase shifts further provide the means to directly decouple the true topography from that induced by compositional heterogeneity.

  3. Phase contrast and operation regimes in multifrequency atomic force microscopy

    SciTech Connect

    Santos, Sergio

    2014-04-07

    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)

  4. Calibration of frictional forces in atomic force microscopy

    SciTech Connect

    Ogletree, D.F.; Carpick, R.W.; Salmeron, M.

    1996-09-01

    The atomic force microscope can provide information on the atomic-level frictional properties of surfaces, but reproducible quantitative measurements are difficult to obtain. Parameters that are either unknown or difficult to precisely measure include the normal and lateral cantilever force constants (particularly with microfabricated cantilevers), the tip height, the deflection sensor response, and the tip structure and composition at the tip-surface contact. We present an {ital in} {ital situ} experimental procedure to determine the response of a cantilever to lateral forces in terms of its normal force response. This procedure is quite general. It will work with any type of deflection sensor and does not require the knowledge or direct measurement of the lever dimensions or the tip height. In addition, the shape of the tip apex can be determined. We also discuss a number of specific issues related to force and friction measurements using optical lever deflection sensing. We present experimental results on the lateral force response of commercially available V-shaped cantilevers. Our results are consistent with estimates of lever mechanical properties using continuum elasticity theory. {copyright} {ital 1996 American Institute of Physics.}

  5. Evaluation of Polymer-Filler Interaction Characteristics by Force Microscopy

    SciTech Connect

    Ratto, T; Saab, A

    2007-04-23

    Silicone polymers are frequently used as cushions and inserts between load bearing parts. In this capacity, they must act to position their associated parts and distribute mechanical force as appropriate. One type of failure is specific to silicones that are filled with high surface area particulates for purposes of tailoring the polymer compressive properties. Additives such as fumed silicon oxide are presumed to have a high degree of surface interaction with the polymer matrix, thus causing the polymer to stiffen and to display greater dimensional stability as a function of temperature. However, it has been observed that the compressive behavior of these materials is not always invariant over long times. There is evidence that suggests changes in humidity and temperature can irreversibly alter the silicone-filler interaction, thereby changing the overall characteristics of parts made from such materials. As before, changes in compressive or shear stability can have serious effects on the ability of these materials to effectively position precision parts or distribute high mechanical loads. We approach the analysis of the filled systems by creating controlled layers of silicone polymers attached to silicon oxide substrates. Straight chain vinyl-silicone polymers identical to those used in the formulation of pads for stockpile systems are chemically appended to a substrate surface, and cross-linked to form a three dimensional network. This type of structure serves as a model of silicone polymer coating a silicon oxide filler particle. We study these model systems first by using Atomic Force Microscopy (AFM) to image the samples with nanometer resolution, and then by measuring the forces of interactions between single model silica filler particles and polymer-coated surfaces. We use normal longitudinal force AFM to measure adhesion, and a relatively newly developed technique, lateral force AFM, to determine the frictional forces between the silica particles and the

  6. The Dynamic Force Table

    ERIC Educational Resources Information Center

    Geddes, John B.; Black, Kelly

    2008-01-01

    We examine an experimental apparatus that is used to motivate the connections between the basic properties of vectors, potential functions, systems of nonlinear equations, and Newton's method for nonlinear systems of equations. The apparatus is an adaptation of a force table where we remove the center-pin and allow the center-ring to move freely.…

  7. Atomic Force Microscopy of Biochemically Tagged DNA

    NASA Astrophysics Data System (ADS)

    Murray, Matthew N.; Hansma, Helen G.; Bezanilla, Magdalena; Sano, Takeshi; Ogletree, D. Frank; Kolbe, William; Smith, Casandra L.; Cantor, Charles R.; Spengler, Sylvia; Hansma, Paul K.; Salmeron, Miquel

    1993-05-01

    Small fragments of DNA of known length were made with the polymerase chain reaction. These fragments had biotin molecules covalently attached at their ends. They were subsequently labeled with a chimeric protein fusion between streptavidin and two immunoglobulin G-binding domains of staphyloccocal protein A. This tetrameric species was expected to bind up to four DNA molecules via their attached biotin moieties. The DNA-protein complex was deposited on mica and imaged with an atomic force microscope. The images revealed the protein chimera at the expected location at the ends of the strands of DNA as well as the expected dimers, trimers, and tetramers of DNA bound to a single protein.

  8. Single-molecule force spectroscopy: optical tweezers, magnetic tweezers and atomic force microscopy

    PubMed Central

    Neuman, Keir C.; Nagy, Attila

    2012-01-01

    Single-molecule force spectroscopy has emerged as a powerful tool to investigate the forces and motions associated with biological molecules and enzymatic activity. The most common force spectroscopy techniques are optical tweezers, magnetic tweezers and atomic force microscopy. These techniques are described and illustrated with examples highlighting current capabilities and limitations. PMID:18511917

  9. Microfluidics, Chromatography, and Atomic-Force Microscopy

    NASA Technical Reports Server (NTRS)

    Anderson, Mark

    2008-01-01

    A Raman-and-atomic-force microscope (RAFM) has been shown to be capable of performing several liquid-transfer and sensory functions essential for the operation of a microfluidic laboratory on a chip that would be used to perform rapid, sensitive chromatographic and spectro-chemical analyses of unprecedentedly small quantities of liquids. The most novel aspect of this development lies in the exploitation of capillary and shear effects at the atomic-force-microscope (AFM) tip to produce shear-driven flow of liquids along open microchannels of a microfluidic device. The RAFM can also be used to perform such functions as imaging liquids in microchannels; removing liquid samples from channels for very sensitive, tip-localized spectrochemical analyses; measuring a quantity of liquid adhering to the tip; and dip-pen deposition from a chromatographic device. A commercial Raman-spectroscopy system and a commercial AFM were integrated to make the RAFM so as to be able to perform simultaneous topographical AFM imaging and surface-enhanced Raman spectroscopy (SERS) at the AFM tip. The Raman-spectroscopy system includes a Raman microprobe attached to an optical microscope, the translation stage of which is modified to accommodate the AFM head. The Raman laser excitation beam, which is aimed at the AFM tip, has a wavelength of 785 nm and a diameter of about 5 m, and its power is adjustable up to 10 mW. The AFM is coated with gold to enable tip-localized SERS.

  10. Atomic force microscopy of polymeric liquid films

    NASA Astrophysics Data System (ADS)

    Mate, C. Mathew; Lorenz, Max R.; Novotny, V. J.

    1989-06-01

    We demonstrate the use of the atomic force microscope (AFM) for studying perfluoropolyether polymer liquid films as thin as ˜20 Å. With the AFM we are able to measure three distinct properties of the liquid film: (1) its thickness when the thickness of liquid on the AFM tip is taken into account, (2) the meniscus force acting on the AFM tip as a function of depth into the liquid film, and (3) the topography of the liquid/air interface. All three of these measurements can be done with a very high lateral resolution, ˜1000 Å, demonstrating the unique capability of AFM for studying liquid films. With AFM we have observed several interesting properties of these polymeric liquid films. First films thinner than ˜300 Å are fairly uniformly distributed, while films thicker than ˜300 Å slowly dewet the surface. Second, by measuring the meniscus radius of liquid in a micron sized hole on the surface, we can determine the disjoining pressure in a thin liquid film.

  11. Magnetic Resonance Force Microscopy Detected Long-Lived Spin Magnetization

    PubMed Central

    Chen, Lei; Longenecker, Jonilyn G.; Moore, Eric W.; Marohn, John A.

    2015-01-01

    Magnetic resonance force microscopy (MRFM), which combines magnetic resonance imaging with scanning probe microscopy together, is capable of performing ultra-sensitive detection of spin magnetization. In an attempt to observe dynamic nuclear polarization (DNP) in an MRFM experiment, which could possibly further improve its sensitivity towards a single proton spin, a film of perdeuterated polystyrene doped with a nitroxide electron-spin probe was prepared. A high-compliance cantilever with a 4 μm diameter magnetic tip was brought near the film at a temperature of 7.3 K and in a background magnetic field of ~0.6 T. The film was irradiated with 16.7 GHz microwaves while the resulting transient change in cantilever frequency was recorded in real time. In addition to observing the expected prompt change in cantilever frequency due to saturation of the nitroxide’s electron-spin magnetization, we observed a persistent cantilever frequency change. Based on its magnitude, lifetime, and field dependence, we tentatively attribute the persistent signal to polarized deuteron magnetization created via transfer of magnetization from electron spins. Further measurements of the persistent signal’s dependence on the cantilever amplitude and tip-sample separation are presented and explained by the cross-effect DNP mechanism in high magnetic field gradients. PMID:26097251

  12. Subsurface damage assessment with atomic force microscopy

    SciTech Connect

    Carr, J W; Fearon, E; Hutcheon, I D; Summers, L J

    1999-04-16

    The performance of transparent optics in high fluence applications is often dominated by inhomogeneities in the first few hundred nanometers of material. Defects undetectable with optical methods can cause catastrophic failures when used in critical applications where high strength, chemical or mechanical resistance or extreme smoothness is required. Not only are these defects substantially smaller than the wavelength of visible light, they are often concealed below a layer of glass-like material deposited during the polishing process. In high quality glass, the chemical and material properties of the outermost layer are modified by the grinding, lapping and polishing processes used in fabrication. Each succeeding step in a process is designed to remote damage from the previous operation. However, any force against the surface, no matter how slight will leave evidence of this damage. These processes invariably create dislocations, cracks and plastic deformation in the subsurface region.

  13. Surface Biology of DNA by Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Hansma, Helen G.

    2001-10-01

    The atomic force microscope operates on surfaces. Since surfaces occupy much of the space in living organisms, surface biology is a valid and valuable form of biology that has been difficult to investigate in the past owing to a lack of good technology. Atomic force microscopy (AFM) of DNA has been used to investigate DNA condensation for gene therapy, DNA mapping and sizing, and a few applications to cancer research and to nanotechnology. Some of the most exciting new applications for atomic force microscopy of DNA involve pulling on single DNA molecules to obtain measurements of single-molecule mechanics and thermodynamics.

  14. The unfolding of native laminin investigated by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Nemes, Cs.; Ramsden, J. J.; Rozlosnik, N.

    2002-10-01

    Atomic force microscopy has been used to directly measure the forces required to unfold individual domains of the extracellular matrix protein laminin. The approach-retraction cycles display a characteristic saw-tooth motif. Tooth heights and separations were used to establish a statistical relation between domain unfolding force and domain extension. The extensible domains of laminin require an unfolding force intermediate between previously established values for α-helical and β-sheet domains in other proteins. The relationship between unfolding force and extension for a given domain is not smooth; discrete steps are observed, interpreted as originating from the modularity of the protein structure.

  15. Numerical study of the hydrodynamic drag force in atomic force microscopy measurements undertaken in fluids.

    PubMed

    Méndez-Méndez, J V; Alonso-Rasgado, M T; Faria, E Correia; Flores-Johnson, E A; Snook, R D

    2014-11-01

    When atomic force microscopy (AFM) is employed for in vivo study of immersed biological samples, the fluid medium presents additional complexities, not least of which is the hydrodynamic drag force due to viscous friction of the cantilever with the liquid. This force should be considered when interpreting experimental results and any calculated material properties. In this paper, a numerical model is presented to study the influence of the drag force on experimental data obtained from AFM measurements using computational fluid dynamics (CFD) simulation. The model provides quantification of the drag force in AFM measurements of soft specimens in fluids. The numerical predictions were compared with experimental data obtained using AFM with a V-shaped cantilever fitted with a pyramidal tip. Tip velocities ranging from 1.05 to 105 μm/s were employed in water, polyethylene glycol and glycerol with the platform approaching from a distance of 6000 nm. The model was also compared with an existing analytical model. Good agreement was observed between numerical results, experiments and analytical predictions. Accurate predictions were obtained without the need for extrapolation of experimental data. In addition, the model can be employed over the range of tip geometries and velocities typically utilized in AFM measurements.

  16. Simultaneous topography and recognition imaging using force microscopy.

    PubMed

    Stroh, Cordula M; Ebner, Andreas; Geretschläger, Manfred; Freudenthaler, Günter; Kienberger, Ferry; Kamruzzahan, A S M; Smith-Gill, Sandra J; Gruber, Hermann J; Hinterdorfer, Peter

    2004-09-01

    We present a method for simultaneously recording topography images and localizing specific binding sites with nm positional accuracy by combining dynamic force microscopy with single molecule recognition force spectroscopy. For this we used lysozyme adsorbed to mica, the functionality of which was characterized by enzyme immunoassays. The topography and recognition images were acquired using tips that were magnetically oscillated during scanning and contained antibodies directed against lysozyme. For cantilevers with low Q-factor (approximately 1 in liquid) driven at frequencies below resonance, the surface contact only affected the downward deflections (minima) of the oscillations, whereas binding of the antibody on the tip to lysozyme on the surface only affected the upwards deflections (maxima) of the oscillations. The recognition signals were therefore well separated from the topographic signals, both in space (Delta z approximately 5 nm) and time (approximately 0.1 ms). Topography and recognition images were simultaneously recorded using a specially designed electronic circuit with which the maxima (U(up)) and the minima (U(down)) of each sinusoidal cantilever deflection period were depicted. U(down) was used for driving the feedback loop to record the height (topography) image, and U(up) provided the data for the recognition image. PMID:15345574

  17. Joseph F. Keithley Award: Force microscopy with subatomic spatial resolution

    NASA Astrophysics Data System (ADS)

    Giessibl, Franz

    2014-03-01

    For a long time, atomic force microscopy has been inferior to the scanning tunneling microscope (STM) in its spatial resolution, partially because measurements of small forces are more challenging than measurements of small currents. With the introduction of frequency modulation force microscopy, the static deflection measurement of a cantilever under a tip-sample force was replaced by a frequency measurement of an oscillating cantilever induced by an average force gradient. Atomic resolution of the challenging silicon reconstruction by frequency modulation atomic force microscopy has been demonstrated in 1995 using a silicon cantilever with a stiffness of k = 17 N/m and an oscillation amplitude of A = 34 nm. In 1996, a quartz cantilever (``qPlus sensor''), originally built from a quartz tuning fork from a wristwatch, has been proposed. At k = 1800 N/m, this quartz sensor is 100 times stiffer than the original Si cantilever, allowing stable oscillation amplitudes down to fractions of an atomic diameter. It has a high Q factor, simple piezoelectric readout, little frequency variation with temperature and allows to simply mount metal tips as used in STM. The demonstration of high spatial resolution, the detection of very small forces, the capability to perform simultaneous STM and AFM as well as the ease of use of the qPlus sensor has led to its adaptation in leading scanning probe microscopy laboratories worldwide as well as in a growing number of commercial scanning probe instruments.

  18. Measuring forces between protein fibers by microscopy.

    PubMed

    Jones, Christopher W; Wang, J C; Briehl, R W; Turner, M S

    2005-04-01

    We propose a general scheme for measuring the attraction between mechanically frustrated semiflexible fibers by measuring their thermal fluctuations and shape. We apply this analysis to a system of sickle hemoglobin (HbS) fibers that laterally attract one another. These fibers appear to "zip" together before reaching mechanical equilibrium due to the existence of cross-links into a dilute fiber network. We are also able to estimate the rigidities of the fibers. These rigidities are found to be consistent with sickle hemoglobin "single" fibers 20 nm in diameter, despite recent experiments indicating that fiber bundling sometimes occurs. Our estimate of the magnitude of the interfiber attraction for HbS fibers is in the range 8 +/- 7 kBT/microm, or 4 +/- 3 k(B)T/microm if the fibers are assumed, a priori to be single fibers (such an assumption is fully consistent with the data). This value is sufficient to bind the fibers, overcoming entropic effects, although extremely chemically weak. Our results are compared to models for the interfiber attraction that include depletion and van der Waals forces. This technique should also facilitate a similar analysis of other filamentous protein assembles in the future, including beta-amyloid, actin, and tubulin.

  19. Observation of DNA Molecules Using Fluorescence Microscopy and Atomic Force Microscopy

    ERIC Educational Resources Information Center

    Ito, Takashi

    2008-01-01

    This article describes experiments for an undergraduate instrumental analysis laboratory that aim to observe individual double-stranded DNA (dsDNA) molecules using fluorescence microscopy and atomic force microscopy (AFM). dsDNA molecules are observed under several different conditions to discuss their chemical and physical properties. In…

  20. Atom world based on nano-forces: 25 years of atomic force microscopy.

    PubMed

    Morita, Seizo

    2011-01-01

    Scanning tunneling microscopy (STM) has opened up the new nanoworlds of scanning probe microscopy. STM is the first-generation atomic tool that can image, evaluate and manipulate individual atoms and consequently can create nanostructures by true bottom-up methods based on atom-by-atom manipulation. Atomic force microscopy is a second-generation atomic tool that has followed the footsteps of STM, and which is now opening doors to a new atom world based on using nanoscale forces.

  1. Pump-probe Kelvin-probe force microscopy: Principle of operation and resolution limits

    SciTech Connect

    Murawski, J.; Graupner, T.; Milde, P. Raupach, R.; Zerweck-Trogisch, U.; Eng, L. M.

    2015-10-21

    Knowledge on surface potential dynamics is crucial for understanding the performance of modern-type nanoscale devices. We describe an electrical pump-probe approach in Kelvin-probe force microscopy that enables a quantitative measurement of dynamic surface potentials at nanosecond-time and nanometer-length scales. Also, we investigate the performance of pump-probe Kelvin-probe force microscopy with respect to the relevant experimental parameters. We exemplify a measurement on an organic field effect transistor that verifies the undisturbed functionality of our pump-probe approach in terms of simultaneous and quantitative mapping of topographic and electronic information at a high lateral and temporal resolution.

  2. Dynamic properties of force fields.

    PubMed

    Vitalini, F; Mey, A S J S; Noé, F; Keller, B G

    2015-02-28

    Molecular-dynamics simulations are increasingly used to study dynamic properties of biological systems. With this development, the ability of force fields to successfully predict relaxation timescales and the associated conformational exchange processes moves into focus. We assess to what extent the dynamic properties of model peptides (Ac-A-NHMe, Ac-V-NHMe, AVAVA, A10) differ when simulated with different force fields (AMBER ff99SB-ILDN, AMBER ff03, OPLS-AA/L, CHARMM27, and GROMOS43a1). The dynamic properties are extracted using Markov state models. For single-residue models (Ac-A-NHMe, Ac-V-NHMe), the slow conformational exchange processes are similar in all force fields, but the associated relaxation timescales differ by up to an order of magnitude. For the peptide systems, not only the relaxation timescales, but also the conformational exchange processes differ considerably across force fields. This finding calls the significance of dynamic interpretations of molecular-dynamics simulations into question.

  3. Microrheology of cells with magnetic force modulation atomic force microscopy.

    PubMed

    Rebêlo, L M; de Sousa, J S; Mendes Filho, J; Schäpe, J; Doschke, H; Radmacher, M

    2014-04-01

    We propose a magnetic force modulation method to measure the stiffness and viscosity of living cells using a modified AFM apparatus. An oscillating magnetic field makes a magnetic cantilever oscillate in contact with the sample, producing a small AC indentation. By comparing the amplitude of the free cantilever motion (A0) with the motion of the cantilever in contact with the sample (A1), we determine the sample stiffness and viscosity. To test the method, the frequency-dependent stiffness of 3T3 fibroblasts was determined as a power law k(s)(f) = α + β(f/f¯)(γ) (α = 7.6 × 10(-4) N m(-1), β = 1.0 × 10(-4) N m(-1), f¯ = 1 Hz, γ = 0.6), where the coefficient γ = 0.6 is in good agreement with rheological data of actin solutions with concentrations similar to those in cells. The method also allows estimation of the internal friction of the cells. In particular we found an average damping coefficient of 75.1 μN s m(-1) for indentation depths ranging between 1.0 μm and 2.0 μm. PMID:24651941

  4. Surface modifications with Lissajous trajectories using atomic force microscopy

    SciTech Connect

    Cai, Wei; Yao, Nan

    2015-09-14

    In this paper, we report a method for atomic force microscopy surface modifications with single-tone and multiple-resolution Lissajous trajectories. The tip mechanical scratching experiments with two series of Lissajous trajectories were carried out on monolayer films. The scratching processes with two scan methods have been illustrated. As an application, the tip-based triboelectrification phenomenon on the silicon dioxide surface with Lissajous trajectories was investigated. The triboelectric charges generated within the tip rubbed area on the surface were characterized in-situ by scanning Kelvin force microscopy. This method would provide a promising and cost-effective approach for surface modifications and nanofabrication.

  5. Silicon Carbide Epitaxial Films Studied by Atomic Force Microscopy

    NASA Technical Reports Server (NTRS)

    1996-01-01

    imaged. Away from local defects, step bunching was observed to yield step heights of hundreds of angstroms, with possible implications for the uniformity of dopants incorporated in SiC devices during fabrication. The quantitative topographic data from the AFM allow the relevant defect information to be extracted, such as the size and distribution of step bunching and the Burgers vector of screw dislocations. These atomic force microscopy results have furthered the understanding of the dynamic epitaxial SiC growth process. A model describing the observed hillock step bunching has been proposed. This cooperation between researchers involved in crystal growth, electronic device fabrication, and surface structural characterization is likely to continue as atomic force microscopy is used to improve SiC films for high-temperature electronic devices for NASA's advanced turbine engines and space power devices, as well as for future applications in the automotive industry.

  6. Atomic force microscopy and confocal laser scanning microscopy on the cytoskeleton of permeabilised and embedded cells.

    PubMed

    Meller, Karl; Theiss, Carsten

    2006-03-01

    We describe a technical method of cell permeabilisation and embedding to study the organisation and distribution of intracellular proteins with aid of atomic force microscopy and confocal laser scanning microscopy in identical areas. While confocal laser scanning microscopy is useful for the identification of certain proteins subsequent labelling with markers or antibodies, atomic force microscopy allows the observation of macromolecular structures in fixed and living cells. To demonstrate the field of application of this preparatory technique, cells were permeabilised, fixed, and the actin cytoskeleton was stained with phalloidin-rhodamine. Confocal laser scanning microscopy was used to show the organisation of these microfilaments, e.g. geodesic dome structures. Thereafter, cells were embedded in Durcupan water-soluble resin, followed by UV-polymerisation of resin at 4 degrees C. This procedure allowed intracellular visualisation of the cell nucleus or cytoskeletal elements by atomic force microscopy, for instance to analyse the globular organisation of actin filaments. Therefore, this method offers a great potential to combine both microscopy techniques in order to understand and interpret intracellular protein relations, for example, the biochemical and morphological interaction of the cytoskeleton. PMID:16360280

  7. The resistive switching in TiO2 films studied by conductive atomic force microscopy and Kelvin probe force microscopy

    NASA Astrophysics Data System (ADS)

    Du, Yuanmin; Kumar, Amit; Pan, Hui; Zeng, Kaiyang; Wang, Shijie; Yang, Ping; Wee, Andrew Thye Shen

    2013-08-01

    The resistive switching characteristics of TiO2 thin films were investigated using conductive atomic force microscopy (CAFM) and Kelvin probe force microscopy (KPFM). The as-prepared TiO2 thin films were modulated into higher and lower resistance states by applying a local electric field. We showed that the resistive switching results from charge injection and release assisted by electro-migration of oxygen ions. An integrated model combined with filamentary and interfacial effects was utilized to elucidate the experimentally observed phenomenon.

  8. Low temperature magnetic force microscopy on ferromagnetic and superconducting oxides

    NASA Astrophysics Data System (ADS)

    Sirohi, Anshu; Sheet, Goutam

    2016-05-01

    We report the observation of complex ferromagnetic domain structures on thin films of SrRuO3 and superconducting vortices in high temperature superconductors through low temperature magnetic force microscopy. Here we summarize the experimental details and results of magnetic imaging at low temperatures and high magnetic fields. We discuss these data in the light of existing theoretical concepts.

  9. Microbially influenced corrosion visualized by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Telegdi, J.; Keresztes, Z.; Pálinkás, G.; Kálmán, E.; Sand, W.

    Corrosion, biofilm formation and the adsorption of different, corrosion-enhancing microbes (such as Desulfovibrio desulfuricans, Thiobacillus ferrooxidans, Thiobacillus intermedius, Leptospirillum ferrooxidans, and mixed cultures) to different surfaces (iron, copper, pyrite) have been studied in aqueous environment by atomic force microscopy (AFM). It is one of the most effective on-line techniques for imaging surfaces (bacterial, metallic, etc.) with high resolution.

  10. Optical-force-induced artifacts in scanning probe microscopy.

    PubMed

    Kohlgraf-Owens, Dana C; Sukhov, Sergey; Dogariu, Aristide

    2011-12-15

    In the practice of near-field scanning probe microscopy, it is typically assumed that the distance regulation is independent of the optical signal. However, we demonstrate that these two signals are entangled due to the inherent action of optically induced force. This coupling leads to artifacts in both estimating the magnitude of optical fields and recording topographic maps.

  11. Nanoscale compression of polymer microspheres by atomic force microscopy.

    PubMed

    Tan, Susheng; Sherman, Robert L; Ford, Warren T

    2004-08-17

    Atomic force microscopy (AFM) was employed to probe the mechanical properties of surface-charged polystyrene microspheres with 1-12 mol% of vinylbenzyl(trimethyl)ammonium chloride (VBTA) units. On the basis of Hertz's theory of contact mechanics, compressive moduli between 1 and 2 GPa were measured by the analysis of force-displacement curves captured on the particles via the force-volume technique. The deformation of the top of the polystyrene particles by the AFM tip was used to calculate the surface modulus. The compressive moduli are slightly less than the moduli of polystyrene bulk materials. The modulus of the polystyrene microspheres increases with an increase of the VBTA content.

  12. Atomic force microscopy to study intermolecular forces and bonds associated with bacteria.

    PubMed

    Lower, Steven K

    2011-01-01

    Atomic force microscopy (AFM) operates on a very different principle than other forms of microscopy, such as optical microscopy or electron microscopy. The key component of an AFM is a cantilever that bends in response to forces that it experiences as it touches another surface. Forces as small as a few picoNewtons can be detected and probed with AFM. AFM has become very useful in biological sciences because it can be used on living cells that are immersed in water. AFM is particularly useful when the cantilever is modified with chemical groups (e.g. amine or carboxylic groups), small beads (e.g. glass or latex), or even a bacterium. This chapter describes how AFM can be used to measure forces and bonds between a bacterium and another surface. This paper also provides an example of the use of AFM on Staphylococcus aureus, a Gram-positive bacterium that is often associated with biofilms in humans.

  13. Non-contact atomic-level interfacial force microscopy

    SciTech Connect

    Houston, J.E.; Fleming, J.G.

    1997-02-01

    The scanning force microscopies (notably the Atomic Force Microscope--AFM), because of their applicability to nearly all materials, are presently the most widely used of the scanning-probe techniques. However, the AFM uses a deflection sensor to measure sample/probe forces which suffers from an inherent mechanical instability that occurs when the rate of change of the force with respect to the interfacial separation becomes equal to the spring constant of the deflecting member. This instability dramatically limits the breadth of applicability of AFM-type techniques to materials problems. In the course of implementing a DOE sponsored basic research program in interfacial adhesion, a self-balancing force sensor concept has been developed and incorporated into an Interfacial Force Microscopy (IFM) system by Sandia scientists. This sensor eliminates the instability problem and greatly enhances the applicability of the scanning force-probe technique to a broader range of materials and materials parameters. The impact of this Sandia development was recognized in 1993 by a Department of Energy award for potential impact on DOE programs and by an R and D 100 award for one of the most important new products of 1994. However, in its present stage of development, the IFM is strictly a research-level tool and a CRADA was initiated in order to bring this sensor technology into wide-spread availability by making it accessible in the form of a commercial instrument. The present report described the goals, approach and results of this CRADA effort.

  14. Note: Spring constant calibration of nanosurface-engineered atomic force microscopy cantilevers

    SciTech Connect

    Ergincan, O. Palasantzas, G.; Kooi, B. J.

    2014-02-15

    The determination of the dynamic spring constant (k{sub d}) of atomic force microscopy cantilevers is of crucial importance for converting cantilever deflection to accurate force data. Indeed, the non-destructive, fast, and accurate measurement method of the cantilever dynamic spring constant by Sader et al. [Rev. Sci. Instrum. 83, 103705 (2012)] is confirmed here for plane geometry but surface modified cantilevers. It is found that the measured spring constants (k{sub eff}, the dynamic one k{sub d}), and the calculated (k{sub d,1}) are in good agreement within less than 10% error.

  15. Note: spring constant calibration of nanosurface-engineered atomic force microscopy cantilevers.

    PubMed

    Ergincan, O; Palasantzas, G; Kooi, B J

    2014-02-01

    The determination of the dynamic spring constant (kd) of atomic force microscopy cantilevers is of crucial importance for converting cantilever deflection to accurate force data. Indeed, the non-destructive, fast, and accurate measurement method of the cantilever dynamic spring constant by Sader et al. [Rev. Sci. Instrum. 83, 103705 (2012)] is confirmed here for plane geometry but surface modified cantilevers. It is found that the measured spring constants (keff, the dynamic one kd), and the calculated (kd,1) are in good agreement within less than 10% error.

  16. Novel scanning force microscopy methods for investigation of transcription complexes

    NASA Astrophysics Data System (ADS)

    Guthold, Martin

    1997-11-01

    Scanning force microscopy (SFM) methods were developed to investigate the structure and the dynamics of E. coli transcription complexes. The described techniques will also be applicable to the study of other protein-nucleic acid complexes. First, the deposition process of DNA molecules onto a mica surface was investigated using polymer chain statistics. Conditions were found in which DNA molecules, and also protein-DNA complexes, are able to equilibrate on the surface. These findings imply that DNA and protein-DNA complexes attain a lowest energy state on the surface, and that meaningful structural information can, therefore, be obtained from the corresponding SFM images. Using these imaging conditions, SFM was then used to investigate various transcription complexes. The structures of crucial intermediates in the transcriptional activation of RNA polymeraseċsigma54 by NtrC were visualized and analyzed. Moreover, a new method was pioneered to identify the position of specific subunits in multi- protein assemblies. In this method, a specific subunit is tagged with a short piece of DNA which renders it easily recognizable in SFM images. This technique was employed to determine the positions of the two α subunits and the βsp/prime subunit in RNA polymerase-DNA complexes. Finally, SFM imaging in liquid was used to investigate the dynamics of the specific and non-specific interactions between RNA polymerase and DNA. Image sequences of an RNA polymerase actively transcribing a DNA template were obtained and analyzed. Image sequences of non-specific complexes were also obtained, and showed the RNA polymerase moving along the DNA in a one- dimensional random walk. The latter experiments provide some of the first direct evidence that RNA polymerase diffuses along DNA to facilitate promoter location. Chapters II, III, V and VI of this dissertation include material which has been previously published with co- authors. The co-authors are acknowledged at the beginning of

  17. Adhesive properties of Staphylococcus epidermidis probed by atomic force microscopy.

    PubMed

    Hu, Yifan; Ulstrup, Jens; Zhang, Jingdong; Molin, Søren; Dupres, Vincent

    2011-06-01

    Mapping of the surface properties of Staphylococcus epidermidis and of biofilm forming bacteria in general is a key to understand their functions, particularly their adhesive properties. To gain a comprehensive view of the structural and chemical properties of S. epidermidis, four different strains (biofilm positive and biofilm negative strains) were analyzed using in situ atomic force microscopy (AFM). Force measurements performed using bare hydrophilic silicon nitride tips disclosed similar adhesive properties for each strain. However, use of hydrophobic tips showed that hydrophobic forces are not the driving forces for adhesion of the four strains. Rather, the observation of sawtooth force-distance patterns on the surface of biofilm positive strains documents the presence of modular proteins such as Aap that may mediate cell adhesion. Treatment of two biofilm positive strains with two chemical inhibitor compounds leads to a loss of adhesion, suggesting that AFM could be a valuable tool to screen for anti-adhesion molecules.

  18. Simultaneous differential spinning disk fluorescence optical sectioning microscopy and nanomechanical mapping atomic force microscopy.

    PubMed

    Miranda, Adelaide; Martins, Marco; De Beule, Pieter A A

    2015-09-01

    Combined microscopy techniques offer the life science research community a powerful tool to investigate complex biological systems and their interactions. Here, we present a new combined microscopy platform based on fluorescence optical sectioning microscopy through aperture correlation microscopy with a Differential Spinning Disk (DSD) and nanomechanical mapping with an Atomic Force Microscope (AFM). The illumination scheme of the DSD microscope unit, contrary to standard single or multi-point confocal microscopes, provides a time-independent illumination of the AFM cantilever. This enables a distortion-free simultaneous operation of fluorescence optical sectioning microscopy and atomic force microscopy with standard probes. In this context, we discuss sample heating due to AFM cantilever illumination with fluorescence excitation light. Integration of a DSD fluorescence optical sectioning unit with an AFM platform requires mitigation of mechanical noise transfer of the spinning disk. We identify and present two solutions to almost annul this noise in the AFM measurement process. The new combined microscopy platform is applied to the characterization of a DOPC/DOPS (4:1) lipid structures labelled with a lipophilic cationic indocarbocyanine dye deposited on a mica substrate.

  19. Simultaneous differential spinning disk fluorescence optical sectioning microscopy and nanomechanical mapping atomic force microscopy.

    PubMed

    Miranda, Adelaide; Martins, Marco; De Beule, Pieter A A

    2015-09-01

    Combined microscopy techniques offer the life science research community a powerful tool to investigate complex biological systems and their interactions. Here, we present a new combined microscopy platform based on fluorescence optical sectioning microscopy through aperture correlation microscopy with a Differential Spinning Disk (DSD) and nanomechanical mapping with an Atomic Force Microscope (AFM). The illumination scheme of the DSD microscope unit, contrary to standard single or multi-point confocal microscopes, provides a time-independent illumination of the AFM cantilever. This enables a distortion-free simultaneous operation of fluorescence optical sectioning microscopy and atomic force microscopy with standard probes. In this context, we discuss sample heating due to AFM cantilever illumination with fluorescence excitation light. Integration of a DSD fluorescence optical sectioning unit with an AFM platform requires mitigation of mechanical noise transfer of the spinning disk. We identify and present two solutions to almost annul this noise in the AFM measurement process. The new combined microscopy platform is applied to the characterization of a DOPC/DOPS (4:1) lipid structures labelled with a lipophilic cationic indocarbocyanine dye deposited on a mica substrate. PMID:26429446

  20. Simultaneous differential spinning disk fluorescence optical sectioning microscopy and nanomechanical mapping atomic force microscopy

    SciTech Connect

    Miranda, Adelaide; De Beule, Pieter A. A.

    2015-09-15

    Combined microscopy techniques offer the life science research community a powerful tool to investigate complex biological systems and their interactions. Here, we present a new combined microscopy platform based on fluorescence optical sectioning microscopy through aperture correlation microscopy with a Differential Spinning Disk (DSD) and nanomechanical mapping with an Atomic Force Microscope (AFM). The illumination scheme of the DSD microscope unit, contrary to standard single or multi-point confocal microscopes, provides a time-independent illumination of the AFM cantilever. This enables a distortion-free simultaneous operation of fluorescence optical sectioning microscopy and atomic force microscopy with standard probes. In this context, we discuss sample heating due to AFM cantilever illumination with fluorescence excitation light. Integration of a DSD fluorescence optical sectioning unit with an AFM platform requires mitigation of mechanical noise transfer of the spinning disk. We identify and present two solutions to almost annul this noise in the AFM measurement process. The new combined microscopy platform is applied to the characterization of a DOPC/DOPS (4:1) lipid structures labelled with a lipophilic cationic indocarbocyanine dye deposited on a mica substrate.

  1. Dark-field differential dynamic microscopy.

    PubMed

    Bayles, Alexandra V; Squires, Todd M; Helgeson, Matthew E

    2016-02-28

    Differential dynamic microscopy (DDM) is an emerging technique to measure the ensemble dynamics of colloidal and complex fluid motion using optical microscopy in systems that would otherwise be difficult to measure using other methods. To date, DDM has successfully been applied to linear space invariant imaging modes including bright-field, fluorescence, confocal, polarised, and phase-contrast microscopy to study diverse dynamic phenomena. In this work, we show for the first time how DDM analysis can be extended to dark-field imaging, i.e. a linear space variant (LSV) imaging mode. Specifically, we present a particle-based framework for describing dynamic image correlations in DDM, and use it to derive a correction to the image structure function obtained by DDM that accounts for scatterers with non-homogeneous intensity distributions as they move within the imaging plane. To validate the analysis, we study the Brownian motion of gold nanoparticles, whose plasmonic structure allows for nanometer-scale particles to be imaged under dark-field illumination, in Newtonian liquids. We find that diffusion coefficients of the nanoparticles can be reliably measured by dark-field DDM, even under optically dense concentrations where analysis via multiple-particle tracking microrheology fails. These results demonstrate the potential for DDM analysis to be applied to linear space variant forms of microscopy, providing access to experimental systems unavailable to other imaging modes. PMID:26822331

  2. Atomic force microscopy investigation of electrochemically produced carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Miklósi, J.; Póczik, P.; Sytchev, I.; Papp, K.; Kaptay, G.; Nagy, P.; Kálmán, E.

    Carbon nanostructures have been synthesized in NaCl-MgCl2 and in NaCl-CaCl2 salt melts and the extracted material was investigated by tapping-mode atomic force microscopy (TM-AFM) and scanning electron microscopy. Some interesting new nanostructures were found and investigated as torus-shaped carbon structures with a ring diameter of 300-400 nm and 10-15 nm height. These tori are closely related to the wrapped SWNT rings described recently. They are probably formed during the electrolysis. A chain-like structure was also revealed.

  3. Protrusion force microscopy reveals oscillatory force generation and mechanosensing activity of human macrophage podosomes

    NASA Astrophysics Data System (ADS)

    Labernadie, Anna; Bouissou, Anaïs; Delobelle, Patrick; Balor, Stéphanie; Voituriez, Raphael; Proag, Amsha; Fourquaux, Isabelle; Thibault, Christophe; Vieu, Christophe; Poincloux, Renaud; Charrière, Guillaume M.; Maridonneau-Parini, Isabelle

    2014-11-01

    Podosomes are adhesion structures formed in monocyte-derived cells. They are F-actin-rich columns perpendicular to the substrate surrounded by a ring of integrins. Here, to measure podosome protrusive forces, we designed an innovative experimental setup named protrusion force microscopy (PFM), which consists in measuring by atomic force microscopy the deformation induced by living cells onto a compliant Formvar sheet. By quantifying the heights of protrusions made by podosomes onto Formvar sheets, we estimate that a single podosome generates a protrusion force that increases with the stiffness of the substratum, which is a hallmark of mechanosensing activity. We show that the protrusive force generated at podosomes oscillates with a constant period and requires combined actomyosin contraction and actin polymerization. Finally, we elaborate a model to explain the mechanical and oscillatory activities of podosomes. Thus, PFM shows that podosomes are mechanosensing cell structures exerting a protrusive force.

  4. Protrusion force microscopy reveals oscillatory force generation and mechanosensing activity of human macrophage podosomes.

    PubMed

    Labernadie, Anna; Bouissou, Anaïs; Delobelle, Patrick; Balor, Stéphanie; Voituriez, Raphael; Proag, Amsha; Fourquaux, Isabelle; Thibault, Christophe; Vieu, Christophe; Poincloux, Renaud; Charrière, Guillaume M; Maridonneau-Parini, Isabelle

    2014-01-01

    Podosomes are adhesion structures formed in monocyte-derived cells. They are F-actin-rich columns perpendicular to the substrate surrounded by a ring of integrins. Here, to measure podosome protrusive forces, we designed an innovative experimental setup named protrusion force microscopy (PFM), which consists in measuring by atomic force microscopy the deformation induced by living cells onto a compliant Formvar sheet. By quantifying the heights of protrusions made by podosomes onto Formvar sheets, we estimate that a single podosome generates a protrusion force that increases with the stiffness of the substratum, which is a hallmark of mechanosensing activity. We show that the protrusive force generated at podosomes oscillates with a constant period and requires combined actomyosin contraction and actin polymerization. Finally, we elaborate a model to explain the mechanical and oscillatory activities of podosomes. Thus, PFM shows that podosomes are mechanosensing cell structures exerting a protrusive force. PMID:25385672

  5. Submolecular Resolution Imaging of Molecules by Atomic Force Microscopy: The Influence of the Electrostatic Force.

    PubMed

    van der Lit, Joost; Di Cicco, Francesca; Hapala, Prokop; Jelinek, Pavel; Swart, Ingmar

    2016-03-01

    The forces governing the contrast in submolecular resolution imaging of molecules with atomic force microscopy (AFM) have recently become a topic of intense debate. Here, we show that the electrostatic force is essential to understand the contrast in atomically resolved AFM images of polar molecules. Specifically, we image strongly polarized molecules with negatively and positively charged tips. A contrast inversion is observed above the polar groups. By taking into account the electrostatic forces between tip and molecule, the observed contrast differences can be reproduced using a molecular mechanics model. In addition, we analyze the height dependence of the various force components contributing to the high-resolution AFM contrast.

  6. Submolecular Resolution Imaging of Molecules by Atomic Force Microscopy: The Influence of the Electrostatic Force

    NASA Astrophysics Data System (ADS)

    van der Lit, Joost; Di Cicco, Francesca; Hapala, Prokop; Jelinek, Pavel; Swart, Ingmar

    2016-03-01

    The forces governing the contrast in submolecular resolution imaging of molecules with atomic force microscopy (AFM) have recently become a topic of intense debate. Here, we show that the electrostatic force is essential to understand the contrast in atomically resolved AFM images of polar molecules. Specifically, we image strongly polarized molecules with negatively and positively charged tips. A contrast inversion is observed above the polar groups. By taking into account the electrostatic forces between tip and molecule, the observed contrast differences can be reproduced using a molecular mechanics model. In addition, we analyze the height dependence of the various force components contributing to the high-resolution AFM contrast.

  7. Intermodulation electrostatic force microscopy for imaging surface photo-voltage

    SciTech Connect

    Borgani, Riccardo Forchheimer, Daniel; Thorén, Per-Anders; Haviland, David B.; Bergqvist, Jonas; Inganäs, Olle

    2014-10-06

    We demonstrate an alternative to Kelvin Probe Force Microscopy for imaging surface potential. The open-loop, single-pass technique applies a low-frequency AC voltage to the atomic force microscopy tip while driving the cantilever near its resonance frequency. Frequency mixing due to the nonlinear capacitance gives intermodulation products of the two drive frequencies near the cantilever resonance, where they are measured with high signal to noise ratio. Analysis of this intermodulation response allows for quantitative reconstruction of the contact potential difference. We derive the theory of the method, validate it with numerical simulation and a control experiment, and we demonstrate its utility for fast imaging of the surface photo-voltage on an organic photo-voltaic material.

  8. Applications of Atomic Force Microscopy in Biophysical Chemistry of Cells

    PubMed Central

    Deng, Zhao; Lulevich, Valentin; Liu, Fu-tong; Liu, Gang-yu

    2014-01-01

    This article addresses the question of what information and new insights atomic force microscopy (AFM) provides that are of importance and relevance to cellular biophysical chemistry research. Three enabling aspects of AFM are discussed: (a) visualization of membrane structural features with nanometer resolution, such as microvilli, ridges, porosomes, lamellapodia, and filopodia; (b) revealing structural evolution associated with cellular signaling pathways by time-dependent and high-resolution imaging of the cellular membrane in correlation with intracellular components from simultaneous optical microscopy; and (c) qualitative and quantitative measurements of single cell mechanics by acquisition of force-deformation profiles and extraction of Young’s moduli for the membrane as well as cytoskeleton. A future prospective of AFM is also presented. PMID:20405961

  9. Structure of human chromosomes studied by atomic force microscopy.

    PubMed

    Tamayo, Javier

    2003-03-01

    In this work human chromosomes have been treated with RNase and pepsin to remove the layer of cellular material that covers the standard preparations on glass slides. This allows characterization of the topography of chromosomes at nanometer scale in air and in physiological solution by atomic force microscopy. Imaging of the dehydrated structure in air indicates radial arrangement of chromatin loops as the last level of DNA packing. However, imaging in liquid reveals a last level of organization consisting of a hierarchy of bands and coils. Additionally force curves between the tip and the chromosome in liquid are consistent with radial chromatin loops. These results and previous electron microscopy studies are analyzed, and a model is proposed for the chromosome structure in which radial loops and helical coils coexist.

  10. Atomic force microscopy force-distance curves with small amplitude ultrasonic modulation.

    PubMed

    Ma, Chengfu; Chen, Yuhang; Wang, Tian; Chu, Jiaru

    2015-01-01

    Force-distance curves were acquired on a highly oriented pyrolytic graphite (HOPG) specimen and a gold film specimen under ultrasonic modulation in atomic force microscopy (AFM). Measurements demonstrated that small amplitude ultrasonic oscillation of either the cantilever or the sample has significant impacts on the characteristics of force-distance curves. With the increase of excitation amplitude, the apparent pull-off force decreased gradually and the hysteresis between the approach and retraction curves reduced significantly. Furthermore, the decrease of the pull-off force was determined to be also relevant to the excitation frequency. With the assistance of contact resonance spectra, the pull-off force was verified to have a near-linear relationship with the cantilever contact oscillation amplitude. Theoretical analysis and subsequent numerical simulations well interpreted the experimental results. The emergence of large oscillating contact forces under ultrasonic modulation altered the force-distance curves, and such a mechanism was ascertained by further ultrasonic AFM imaging.

  11. Probing starch-iodine interaction by atomic force microscopy.

    PubMed

    Du, Xiongwei; An, Hongjie; Liu, Zhongdong; Yang, Hongshun; Wei, Lijuan

    2014-01-01

    We explored the interaction of iodine with three crystalline type starches, corn, potato, and sweet potato starches using atomic force microscopy. Results revealed that starch molecules aggregated through interaction with iodine solution as well as iodine vapor. Detailed fine structures such as networks, chains, and super-helical structures were found in iodide solution tests. The nanostructures formed due to iodine adsorption could help to understand the formation and properties of the starch-iodine complex.

  12. Probing starch-iodine interaction by atomic force microscopy.

    PubMed

    Du, Xiongwei; An, Hongjie; Liu, Zhongdong; Yang, Hongshun; Wei, Lijuan

    2014-01-01

    We explored the interaction of iodine with three crystalline type starches, corn, potato, and sweet potato starches using atomic force microscopy. Results revealed that starch molecules aggregated through interaction with iodine solution as well as iodine vapor. Detailed fine structures such as networks, chains, and super-helical structures were found in iodide solution tests. The nanostructures formed due to iodine adsorption could help to understand the formation and properties of the starch-iodine complex. PMID:24338992

  13. Transient response of tapping scanning force microscopy in liquids

    SciTech Connect

    Chen, G.Y.; Warmack, R.J. |; Oden, P.I.; Thundat, T.

    1996-03-01

    Tapping-mode scanning force microscopy in liquids is usually accomplished by acoustic excitation of the cantilever because of the strong viscous damping. Contact of the tip with the sample surface results in a damping of the cantilever amplitude with an anharmonic response. This interaction is modeled as a viscous-damped, one-dimensional harmonic oscillator periodically perturbed by an exponential surface potential. Experimental results verify the validity of the model. {copyright} {ital 1996 American Vacuum Society}

  14. Quantification of dissipation and deformation in ambient atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Santos, Sergio; Gadelrab, Karim R.; Barcons, Victor; Stefancich, Marco; Chiesa, Matteo

    2012-07-01

    A formalism to extract and quantify unknown quantities such as sample deformation, the viscosity of the sample and surface energy hysteresis in amplitude modulation atomic force microscopy is presented. Recovering the unknowns only requires the cantilever to be accurately calibrated and the dissipative processes occurring during sample deformation to be well modeled. The theory is validated by comparison with numerical simulations and shown to be able to provide, in principle, values of sample deformation with picometer resolution.

  15. Mechanical Forces Governing Tissue Dynamics

    NASA Astrophysics Data System (ADS)

    Edwards, Glenn

    2002-10-01

    We have refined a UV-laser microbeam to investigate the forces at play during morphogenesis, i.e. early biological development, in the fruit fly Drosophila (1). While the microbeam typically is used to ablate tissue with cellular spatial resolution, it has the capability for submicron and thus subcellular spatial resolution. The microbeam can be steered in two-dimensions and UV-laser dissection occurred in vivo while the tissue was imaged in real time using a (visible) laser-scanning confocal microscope. We investigated a morphogenic process, known as dorsal closure, in a genetically engineered strain of Drosophila where green fluorescent protein has been fused to a fragment of a native structural protein (2). This allowed us to visualize the fluorescing contours of two opposing, outer sheets of tissue closing over an inner tissue sheet. Time-lapse imaging captured the contours in native closure as well as in response to UV-laser dissection. Specific patterns of dissection essentially eliminated a selected force: by tracking the changes in contour geometry we estimated the relative magnitude of that force (mechanical jump). Using this approach we identified and characterized a set of forces governing tissue dynamics. We have developed a mechanical model for the dynamics of dorsal closure based on this data set. This model provides a theoretical framework for investigating defective closure in mutant flies. Dorsal closure is a model system for various aspects of cell movement in wound healing and vertebrate development. This research has been supported by the DoD MFEL Program as administered by the AFOSR and by the NIH. 1. M.S. Hutson, Y. Tokutake, M-S. Chang, J.W. Bloor, S. Venakides, D.P. Kiehart, and G.S. Edwards. "Laser dissection of morphogenetic dynamics in Drosophila dorsal closure." In preparation. 2. D.P. Kiehart, et al, J. Cell Biol. 149, 471 (2000).

  16. Multifrequency Force Microscopy of Helical Protein Assembly on a Virus

    PubMed Central

    Calò, Annalisa; Eleta-Lopez, Aitziber; Stoliar, Pablo; De Sancho, David; Santos, Sergio; Verdaguer, Albert; Bittner, Alexander M.

    2016-01-01

    High-resolution microscopy techniques have been extensively used to investigate the structure of soft, biological matter at the nanoscale, from very thin membranes to small objects, like viruses. Electron microscopy techniques allow for obtaining extraordinary resolution by averaging signals from multiple identical structures. In contrast, atomic force microscopy (AFM) collects data from single entities. Here, it is possible to finely modulate the interaction with the samples, in order to be sensitive to their top surface, avoiding mechanical deformations. However, most biological surfaces are highly curved, such as fibers or tubes, and ultimate details of their surface are in the vicinity of steep height variations. This limits lateral resolution, even when sharp probes are used. We overcome this problem by using multifrequency force microscopy on a textbook example, the Tobacco Mosaic Virus (TMV). We achieved unprecedented resolution in local maps of amplitude and phase shift of the second excited mode, recorded together with sample topography. Our data, which combine multifrequency imaging and Fourier analysis, confirm the structure deduced from averaging techniques (XRD, cryoEM) for surface features of single virus particles, down to the helical pitch of the coat protein subunits, 2.3 nm. Remarkably, multifrequency AFM images do not require any image postprocessing. PMID:26915629

  17. Polymer Filler Aging and Failure Studied by Lateral Force Microscopy

    SciTech Connect

    Ratto, T; Saab, A P

    2009-05-27

    In the present work, we study, via force microscopy, the basic physical interactions of a single bead of silica filler with a PDMS matrix both before and after exposure to gamma radiation. Our goal was to confirm our results from last year, and to explore force microscopy as a means of obtaining particle-scale polymer/filler interactions suitable for use as empirical inputs to a computational model consisting of an ensemble of silica beads embedded in a PDMS matrix. Through careful calibration of a conventional atomic force microscope, we obtained both normal and lateral force data that was fitted to yield adhesion, surface shear modulus, and friction of a 1 {micro}m silica bead in contact with PDMS layers of various thickness. Comparison of these terms before and after gamma exposure indicated that initially, radiation exposure lead to softening of the PDMS, but eventually resulted in stiffening. Simultaneously, adhesion between the polymer and silica decreased. This could indicate a serious failure path for filled PDMS exposed to radiation, whereby stiffening of the bulk polymer leads to loss of compressive elastic behavior, while a decrease in polymer filler adhesion results in an increased likelihood of stress failure under load. In addition to further testing of radiation damaged polymers, we also performed FEA modeling of silica beads in a silicone matrix using the shear modulus and adhesion values isolated from the force microscopy experiments as model inputs. The resulting simulation indicated that as a polymer stiffens due to impinging radiation, it also undergoes weakening of adhesion to the filler. The implication is that radiation induces a compound failure mode in filled polymer systems.

  18. Bimodal atomic force microscopy imaging of isolated antibodies in air and liquids.

    PubMed

    Martínez, N F; Lozano, J R; Herruzo, E T; Garcia, F; Richter, C; Sulzbach, T; Garcia, R

    2008-09-24

    We have developed a dynamic atomic force microscopy (AFM) method based on the simultaneous excitation of the first two flexural modes of the cantilever. The instrument, called a bimodal atomic force microscope, allows us to resolve the structural components of antibodies in both monomer and pentameric forms. The instrument operates in both high and low quality factor environments, i.e., air and liquids. We show that under the same experimental conditions, bimodal AFM is more sensitive to compositional changes than amplitude modulation AFM. By using theoretical and numerical methods, we study the material contrast sensitivity as well as the forces applied on the sample during bimodal AFM operation.

  19. Discrimination of DNA hybridization using chemical force microscopy.

    PubMed Central

    Mazzola, L T; Frank, C W; Fodor, S P; Mosher, C; Lartius, R; Henderson, E

    1999-01-01

    Atomic force microscopy (AFM) can be used to probe the mechanics of molecular recognition between surfaces. In the application known as "chemical force" microscopy (CFM), a chemically modified AFM tip probes a surface through chemical recognition. When modified with a biological ligand or receptor, the AFM tip can discriminate between its biological binding partner and other molecules on a heterogeneous substrate. The strength of the interaction between the modified tip and the substrate is governed by the molecular affinity. We have used CFM to probe the interactions between short segments of single-strand DNA (oligonucleotides). First, a latex microparticle was modified with the sequence 3'-CAGTTCTACGATGGCAAGTC and epoxied to a standard AFM cantilever. This DNA-modified probe was then used to scan substrates containing the complementary sequence 5'-GTCAAGATGCTACCGTTCAG. These substrates consisted of micron-scale, patterned arrays of one or more distinct oligonucleotides. A strong friction interaction was measured between the modified tip and both elements of surface-bound DNA. Complementary oligonucleotides exhibited a stronger friction than the noncomplementary sequences within the patterned array. The friction force correlated with the measured strength of adhesion (rupture force) for the tip- and array-bound oligonucleotides. This result is consistent with the formation of a greater number of hydrogen bonds for the complementary sequence, suggesting that the friction arises from a sequence-specific interaction (hybridization) of the tip and surface DNA. PMID:10354420

  20. Chemical Force Microscopy: Probing Chemical Origin of Interfacial Forces and Adhesion

    SciTech Connect

    Vezenov, D V; Noy, A; Ashby, P

    2005-03-21

    Experimental methods of measuring intermolecular interactions have had several recent developments which have improved our understanding of chemical forces. First, they allowed direct exploration of the role that different functionalities, solvents and environmental variables play in shaping the strength of intermolecular interactions. Chemical force microscopy approach, in particular, became an extremely effective tool for exploring the contributions of each of these factors. Second, CFM studies clearly debunked the naive notion that intermolecular interaction strength is determined only by the nature of the interacting groups. These studies showed that the interaction strength between two chemical species must always considered in context of the environment surrounding these species. Third, CFM studies highlighted the critical role solvent plays in shaping intermolecular interactions in condensed phases. Emerging kinetic view of the intermolecular interactions introduced a completely new paradigm for understanding these interactions. Kinetic modeling showed that the measured interactions strength depends not only on the energy landscape of the system, but also on the loading history prior to the bond break-up. This new paradigm refocused our attention to the energy landscape as a fundamental characteristic of the interaction. Moreover, dynamic force spectroscopy, derived from kinetic models, allowed direct characterization of the geometry of the potential energy barrier, while some other methods attempt to probe the equilibrium energy landscape directly. Further investigations of the interactions in different systems, especially interactions between biomolecules, will uncover many interesting characteristics of intermolecular potentials. These studies have the potential to reveal, for the first time, a true picture of the energy landscapes of adhesion processes in complex chemical and biological systems.

  1. A study of nanostructure magnetosolid Nd-Ho-Fe-Co-B materials via atomic force microscopy and magnetic force microscopy

    NASA Astrophysics Data System (ADS)

    Andreeva, N. V.; Filimonov, A. V.; Rudskoi, A. I.; Burkhanov, G. S.; Tereshina, I. S.; Politova, G. A.; Pelevin, I. A.

    2016-09-01

    Nanostructure Nd-Ho-Fe-Co-B alloys have been probed via atomic force microscopy and magnetic force microscopy (AFM and MFM, respectively). The ribbon samples with a thickness of ~30 μm are prepared via the rapid solidification on a rotating copper barrel. A part of samples has been subjected to hydration, whereas another one has undergone severe plastic deformation. AFM was mainly used to study the contact and free surface of ribbon samples. This has enabled us to establish the topography, structure, defects of both sides, morphology of magnetic inclusions of the initial quenched samples and the materials subjected to the subsequent external effects. The AFM and MFM data allowed the magnetic hysteresis properties of the bulk samples with the identical composition to be interpreted.

  2. Photothermally excited force modulation microscopy for broadband nanomechanical property measurements

    SciTech Connect

    Wagner, Ryan Killgore, Jason P.

    2015-11-16

    We demonstrate photothermally excited force modulation microscopy (PTE FMM) for mechanical property characterization across a broad frequency range with an atomic force microscope (AFM). Photothermal excitation allows for an AFM cantilever driving force that varies smoothly as a function of drive frequency, thus avoiding the problem of spurious resonant vibrations that hinder piezoelectric excitation schemes. A complication of PTE FMM is that the sub-resonance cantilever vibration shape is fundamentally different compared to piezoelectric excitation. By directly measuring the vibrational shape of the cantilever, we show that PTE FMM is an accurate nanomechanical characterization method. PTE FMM is a pathway towards the characterization of frequency sensitive specimens such as polymers and biomaterials with frequency range limited only by the resonance frequency of the cantilever and the low frequency limit of the AFM.

  3. Influence of Force Acting on Side Face of Carbon Nanotube in Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Akita, Seiji; Nishijima, Hidehiro; Kishida, Takayoshi; Nakayama, Yoshikazu

    2000-06-01

    We have examined the nanomechanics of a carbon nanotube by a manipulation technique using a scanning electron microscope. Young’s modulus of the nanotube, estimated from the buckling under force acting on the axial direction of the nanotube, agrees well with the value estimated from the bending under force acting on the side face. This indicates that the nanotube can be treated as an isotropic material in conventional mechanics. The adhesion force between the side face of the nanotube and a pit wall in a 4.7 GB digital versatile disk is estimated to be ˜10 nN using atomic force microscopy. This value is 160 times less than the value estimated using force curve measurement. This discrepancy is due to the finding that the value estimated from the force curve includes not only the adhesion but also the friction force.

  4. Correlative atomic force microscopy and localization-based super-resolution microscopy: revealing labelling and image reconstruction artefacts.

    PubMed

    Monserrate, Aitor; Casado, Santiago; Flors, Cristina

    2014-03-17

    Hybrid microscopy: A correlative microscopy tool that combines in situ super-resolution fluorescence microscopy based on single-molecule localization and atomic force microscopy is presented. Direct comparison with high- resolution topography allows the authors to improve fluorescence labeling and image analysis in super-resolution imaging.

  5. Detection of secondary phases in duplex stainless steel by magnetic force microscopy and scanning Kelvin probe force microscopy

    SciTech Connect

    Ramírez-Salgado, J.; Domínguez-Aguilar, M.A.; Castro-Domínguez, B.; Hernández-Hernández, P.; Newman, R.C.

    2013-12-15

    The secondary phase transformations in a commercial super duplex stainless steel were investigated by micro-chemical analyses and high resolution scanning probe microscopy. Energy dispersive X-ray and electron probe detected ferrite and austenite as well as secondary phases in unetched aged duplex stainless steel type 25Cr-7Ni-3Mo. Volta potential indicated that nitride and sigma appeared more active than ferrite, while secondary austenite and austenite presented a nobler potential. Reversal order in nobility is thought to be attributable to the potential ranking provided by oxide nature diversity as a result of secondary phase surface compositions on steel. After eutectoid transformation, secondary austenite was detected by electron probe microanalysis, whereas atomic force microscopy distinguished this phase from former austenite by image contrast. Magnetic force microscopy revealed a “ghosted” effect on the latter microstructure probably derived from metal memory reminiscence of mechanical polishing at passivity and long range magnetic forces of ferrite phase. - Highlights: • Nobility detection of secondary phases by SKPFM in DSS particles is not a straightforward procedure. • As Volta potential and contrast are not always consistent SKPFM surface oxides is thought played an important role in detection. • AFM distinguished secondary austenite from former austenite by image contrast though SEM required EPMA.

  6. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

    2016-09-01

    Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.

  7. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    PubMed Central

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

    2016-01-01

    Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained. PMID:27587276

  8. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy.

    PubMed

    Black, Jennifer M; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R; Guo, Daqiang; Okatan, M Baris; Dai, Sheng; Cummings, Peter T; Kalinin, Sergei V; Feng, Guang; Balke, Nina

    2016-01-01

    Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained. PMID:27587276

  9. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy.

    PubMed

    Black, Jennifer M; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R; Guo, Daqiang; Okatan, M Baris; Dai, Sheng; Cummings, Peter T; Kalinin, Sergei V; Feng, Guang; Balke, Nina

    2016-09-02

    Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.

  10. Surface characterization by atomic force microscopy of sterilized PLGA microspheres.

    PubMed

    Dorati, Rossella; Patrini, Maddalena; Perugini, Paola; Pavanetto, Franca; Stella, Angiolino; Modena, Tiziana; Genta, Ida; Conti, Bice

    2006-03-01

    Atomic force microscopy (AFM) is recognized a suitable and powerful technique for surface and morphological analysis. Even if until now this technique has not been frequently used in the pharmaceutical field, it can contribute to an accurate morphologic characterization of microspheres and nanospheres. In this work, atomic force microscopy has been used to perform the surface characterization of sterilized microspheres. The aim is to investigate the morphologic modifications induced by gamma irradiation on poly(lactide-co-glycolide) microspheres loaded with ovalbumin and to compare the results obtained by AFM to those obtained by scanning electron microscopy (SEM). The results obtained show that, with respect to SEM, AFM can give some additional information regarding the modifications induced by gamma-irradiation on microspheres surface morphology. The significant changes in surface roughness after irradiation are indicative of damage due to gamma-irradiation. The unchanged surface roughness values calculated for microspheres containing PEG in their matrix, suggest that this polymer exerts a protective effect towards gamma-irradiation. PMID:16754370

  11. Use of Atomic Force Microscopy and Transmission Electron Microscopy for Correlative Studies of Bacterial Capsules▿ †

    PubMed Central

    Stukalov, Oleg; Korenevsky, Anton; Beveridge, Terry J.; Dutcher, John R.

    2008-01-01

    Bacteria can possess an outermost assembly of polysaccharide molecules, a capsule, which is attached to their cell wall. We have used two complementary, high-resolution microscopy techniques, atomic force microscopy (AFM) and transmission electron microscopy (TEM), to study bacterial capsules of four different gram-negative bacterial strains: Escherichia coli K30, Pseudomonas aeruginosa FRD1, Shewanella oneidensis MR-4, and Geobacter sulfurreducens PCA. TEM analysis of bacterial cells using different preparative techniques (whole-cell mounts, conventional embeddings, and freeze-substitution) revealed capsules for some but not all of the strains. In contrast, the use of AFM allowed the unambiguous identification of the presence of capsules on all strains used in the present study, including those that were shown by TEM to be not encapsulated. In addition, the use of AFM phase imaging allowed the visualization of the bacterial cell within the capsule, with a depth sensitivity that decreased with increasing tapping frequency. PMID:18606791

  12. Sub-cellular structure studied by combined atomic force-fluorescence microscopy

    NASA Astrophysics Data System (ADS)

    Trache, Andreea

    2009-03-01

    A novel experimental technique that integrates atomic force microscopy (AFM) with fluorescence imaging was used to study the role of extracellular matrix proteins in cellular organization. To understand the mechanism by which living cells sense mechanical forces, and how they respond and adapt to their environment, we developed a new technology able to investigate cellular behavior at sub-cellular level that integrates an AFM with total internal reflection fluorescence (TIRF) microscopy and fast-spinning disk (FSD) confocal microscopy. Live smooth muscle cells exhibited differences in focal adhesions and actin pattern depending on the extracellular matrix used for substrate coating. Data obtained by using the AFM-optical imaging integrated technique offer novel quantitative information that allows understanding the fundamental processes of cellular reorganization in response to extracellular matrix modulation. The integrated microscope presented here is broadly applicable across a wide range of molecular dynamic studies in any adherent live cells.

  13. Local Mechanical Properties by Atomic Force Microscopy Nanoindentations

    NASA Astrophysics Data System (ADS)

    Tranchida, Davide; Piccarolo, Stefano

    The analysis of mechanical properties on a nanometer scale is a useful tool for combining information concerning texture organization obtained by microscopy with the properties of individual components. Moreover, this technique promotes the understanding of the hierarchical arrangement in complex natural materials as well in the case of simpler morphologies arising from industrial processes. Atomic Force Microscopy (AFM) can bridge morphological information, obtained with outstanding resolution, to local mechanical properties. When performing an AFM nanoindentation, the rough force curve, i.e., the plot of the voltage output from the photodiode vs. the voltage applied to the piezo-scanner, can be translated into a curve of the applied load vs. the penetration depth after a series of preliminary determinations and calibrations. However, the analysis of the unloading portion of the force curves collected for polymers does not lead to a correct evaluation of Young's modulus. The high slope of the unloading curves is not linked to an elastic behavior, as would be expected, but rather to a viscoelastic effect. This can be argued on the basis that the unloading curves are superimposed on the loading curves in the case of an ideal elastic behavior, as for rubbers, or generally in the case of materials with very short relaxation times. In contrast, when the relaxation time of the sample is close to or even much larger than the indentation time scale, very high slopes are recorded.

  14. Quantitative electrostatic force microscopy with sharp silicon tips

    NASA Astrophysics Data System (ADS)

    Fumagalli, L.; Edwards, M. A.; Gomila, G.

    2014-12-01

    Electrostatic force microscopy (EFM) probes are typically coated in either metal (radius ˜ 30 nm) or highly-doped diamond (radius ˜ 100 nm). Highly-doped silicon probes, which offer a sharpened and stable tip apex (radius ˜ 1-10 nm) and are usually used only in standard atomic force microscopy, have been recently shown to allow enhanced lateral resolution in quantitative EFM and its application for dielectric constant measurement. Here we present the theoretical modelling required to quantitatively interpret the electrostatic force between these sharpened tips and samples. In contrast to a sphere-capped cone geometry used to describe metal/diamond-coated tips, modelling a sharpened silicon tip requires a geometry comprised of a cone with two different angles. Theoretical results are supported by experimental measurements of metallic substrates and ˜10 nm radius dielectric nanoparticles. This work is equally applicable to EFM and other electrical scanned probe techniques, where it allows quantifying electrical properties of nanomaterials and 3D nano-objects with higher resolution.

  15. Adhesion Forces between Lewis(X) Determinant Antigens as Measured by Atomic Force Microscopy.

    PubMed

    Tromas, C; Rojo, J; de la Fuente, J M; Barrientos, A G; García, R; Penadés, S

    2001-01-01

    The adhesion forces between individual molecules of Lewis(X) trisaccharide antigen (Le(X) ) have been measured in water and in calcium solution by using atomic force microscopy (AFM, see graph). These results demonstrate the self-recognition capability of this antigen, and reinforce the hypothesis that carbohydrate-carbohydrate interaction could be considered as the first step in the cell-adhesion process in nature. PMID:12203646

  16. Adhesion Forces between Lewis(X) Determinant Antigens as Measured by Atomic Force Microscopy.

    PubMed

    Tromas, C; Rojo, J; de la Fuente, J M; Barrientos, A G; García, R; Penadés, S

    2001-01-01

    The adhesion forces between individual molecules of Lewis(X) trisaccharide antigen (Le(X) ) have been measured in water and in calcium solution by using atomic force microscopy (AFM, see graph). These results demonstrate the self-recognition capability of this antigen, and reinforce the hypothesis that carbohydrate-carbohydrate interaction could be considered as the first step in the cell-adhesion process in nature.

  17. Peering at Brain Polysomes with Atomic Force Microscopy.

    PubMed

    Lunelli, Lorenzo; Bernabò, Paola; Bolner, Alice; Vaghi, Valentina; Marchioretto, Marta; Viero, Gabriella

    2016-01-01

    The translational machinery, i.e., the polysome or polyribosome, is one of the biggest and most complex cytoplasmic machineries in cells. Polysomes, formed by ribosomes, mRNAs, several proteins and non-coding RNAs, represent integrated platforms where translational controls take place. However, while the ribosome has been widely studied, the organization of polysomes is still lacking comprehensive understanding. Thus much effort is required in order to elucidate polysome organization and any novel mechanism of translational control that may be embedded. Atomic force microscopy (AFM) is a type of scanning probe microscopy that allows the acquisition of 3D images at nanoscale resolution. Compared to electron microscopy (EM) techniques, one of the main advantages of AFM is that it can acquire thousands of images both in air and in solution, enabling the sample to be maintained under near physiological conditions without any need for staining and fixing procedures. Here, a detailed protocol for the accurate purification of polysomes from mouse brain and their deposition on mica substrates is described. This protocol enables polysome imaging in air and liquid with AFM and their reconstruction as three-dimensional objects. Complementary to cryo-electron microscopy (cryo-EM), the proposed method can be conveniently used for systematically analyzing polysomes and studying their organization. PMID:27023752

  18. Atom inlays performed at room temperature using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Sugimoto, Yoshiaki; Abe, Masayuki; Hirayama, Shinji; Oyabu, Noriaki; Custance, Óscar; Morita, Seizo

    2005-02-01

    The ability to manipulate single atoms and molecules laterally for creating artificial structures on surfaces is driving us closer to the ultimate limit of two-dimensional nanoengineering. However, experiments involving this level of manipulation have been performed only at cryogenic temperatures. Scanning tunnelling microscopy has proved, so far, to be a unique tool with all the necessary capabilities for laterally pushing, pulling or sliding single atoms and molecules, and arranging them on a surface at will. Here we demonstrate, for the first time, that it is possible to perform well-controlled lateral manipulations of single atoms using near-contact atomic force microscopy even at room temperature. We report the creation of 'atom inlays', that is, artificial atomic patterns formed from a few embedded atoms in the plane of a surface. At room temperature, such atomic structures remain stable on the surface for relatively long periods of time.

  19. Parylene insulated probes for scanning electrochemical-atomic force microscopy.

    PubMed

    Derylo, Maksymilian A; Morton, Kirstin C; Baker, Lane A

    2011-11-15

    Scanning electrochemical-atomic force microscopy (SECM-AFM) is a powerful technique that can be used to obtain in situ information related to electrochemical phenomena at interfaces. Fabrication of probes to perform SECM-AFM experiments remains a challenge. Herein, we describe a method for formation of microelectrodes at the tip of commercial conductive AFM probes and demonstrate application of these probes to SECM-AFM. Probes were first insulated with a thin parylene layer, followed by subsequent exposure of active electrodes at the probe tips by mechanical abrasion of the insulating layer. Characterization of probes was performed by electron microscopy and cyclic voltammetry. In situ measurement of localized electrochemical activity with parylene-coated probes was demonstrated through measurement of the diffusion of Ru(NH)(6)(3+) across a porous membrane.

  20. Atomic force microscopy of living and fixed Xenopus laevis embryos.

    PubMed

    Efremov, Yu M; Pukhlyakova, E A; Bagrov, D V; Shaitan, K V

    2011-12-01

    Xenopus laevis embryos are a rather simple and at the same time a very interesting animal model, which is widely used for research in developmental biology. Intensive coordinated cell movements take place during the multi-cellular organism development. Little is known of the cellular, molecular and biomechanical mechanisms of these movements. The conceptual framework for analysis of cell interactions within integrated populations is poorly developed. We have used atomic force microscopy (AFM) to observe the surface of fixed X. laevis embryos at different stages of their development. We have developed a new sample preparation protocol for these observations. The obtained images were compared with scanning electronic microscopy (SEM) data. Cell rearrangement during morphogenesis in vivo was also visualized by AFM. In the current paper we discuss facilities and challenges of using this technique for further embryo researching.

  1. Amplitude modulation atomic force microscopy, is acoustic driving in liquid quantitatively reliable?

    PubMed

    Liu, Fei; Zhao, Cunlu; Mugele, Frieder; van den Ende, Dirk

    2015-09-25

    Measuring quantitative tip-sample interaction forces in dynamic atomic force microscopy in fluids is challenging because of the strong damping of the ambient viscous medium and the fluid-mediated driving forces. This holds in particular for the commonly used acoustic excitation of the cantilever oscillation. Here we present measurements of tip-sample interactions due to conservative DLVO and hydration forces and viscous dissipation forces in aqueous electrolytes using tips with radii varying from typical 20 nm for the DLVO and hydration forces, to 1 μm for the viscous dissipation. The measurements are analyzed using a simple harmonic oscillator model, continuous beam theory with fluid-mediated excitation and thermal noise spectroscopy (TNS). In all cases consistent conservative forces, deviating less than 40% from each other, are obtained for all three approaches. The DLVO forces are even within 5% of the theoretical expectations for all approaches. Accurate measurements of dissipative forces within 15% of the predictions of macroscopic fluid dynamics require the use of TNS or continuous beam theory including fluid-mediated driving. Taking this into account, acoustic driving in liquid is quantitatively reliable. PMID:26335613

  2. Amplitude modulation atomic force microscopy, is acoustic driving in liquid quantitatively reliable?

    NASA Astrophysics Data System (ADS)

    Liu, Fei; Zhao, Cunlu; Mugele, Frieder; van den Ende, Dirk

    2015-09-01

    Measuring quantitative tip-sample interaction forces in dynamic atomic force microscopy in fluids is challenging because of the strong damping of the ambient viscous medium and the fluid-mediated driving forces. This holds in particular for the commonly used acoustic excitation of the cantilever oscillation. Here we present measurements of tip-sample interactions due to conservative DLVO and hydration forces and viscous dissipation forces in aqueous electrolytes using tips with radii varying from typical 20 nm for the DLVO and hydration forces, to 1 μm for the viscous dissipation. The measurements are analyzed using a simple harmonic oscillator model, continuous beam theory with fluid-mediated excitation and thermal noise spectroscopy (TNS). In all cases consistent conservative forces, deviating less than 40% from each other, are obtained for all three approaches. The DLVO forces are even within 5% of the theoretical expectations for all approaches. Accurate measurements of dissipative forces within 15% of the predictions of macroscopic fluid dynamics require the use of TNS or continuous beam theory including fluid-mediated driving. Taking this into account, acoustic driving in liquid is quantitatively reliable.

  3. Local rheology of human neutrophils investigated using atomic force microscopy.

    PubMed

    Lee, Yong J; Patel, Dipika; Park, Soyeun

    2011-01-01

    During the immune response, neutrophils display localized mechanical events by interacting with their environment through the micro-vascular transit, trans-endothelial, and trans-epithelial migration. Nano-mechanical studies of human neutrophils on localized nano-domains could provide the essential information for understanding their immune responsive functions. Using the Atomic Force Microscopy (AFM)-based micro-rheology, we have investigated rheological properties of the adherent human neutrophils on local nano-domains. We have applied the modified Hertz model to obtain the viscoelastic moduli from the relatively thick body regions of the neutrophils. In addition, by using more advanced models to account for the substrate effects, we have successfully characterized the rheological properties of the thin leading and tail regions as well. We found a regional difference in the mechanical compliances of the adherent neutrophils. The central regions of neutrophils were significantly stiffer (1,548 ± 871 Pa) than the regions closer to the leading edge (686 ± 801 Pa), while the leading edge and the tail (494 ± 537 Pa) regions were mechanically indistinguishable. The frequency-dependent elastic and viscous moduli also display a similar regional difference. Over the studied frequency range (100 to 300 Hz), the complex viscoelastic moduli display the partial rubber plateau behavior where the elastic moduli are greater than the viscous moduli for a given frequency. The non-disparaging viscous modulus indicates that the neutrophils display a viscoelastic dynamic behavior rather than a perfect elastic behavior like polymer gels. In addition, we found no regional difference in the structural damping coefficient between the leading edge and the cell body. Thus, we conclude that despite the lower loss and storage moduli, the leading edges of the human neutrophils display partially elastic properties similar to the cell body. These results suggest that the lower elastic moduli

  4. Local rheology of human neutrophils investigated using atomic force microscopy.

    PubMed

    Lee, Yong J; Patel, Dipika; Park, Soyeun

    2011-01-01

    During the immune response, neutrophils display localized mechanical events by interacting with their environment through the micro-vascular transit, trans-endothelial, and trans-epithelial migration. Nano-mechanical studies of human neutrophils on localized nano-domains could provide the essential information for understanding their immune responsive functions. Using the Atomic Force Microscopy (AFM)-based micro-rheology, we have investigated rheological properties of the adherent human neutrophils on local nano-domains. We have applied the modified Hertz model to obtain the viscoelastic moduli from the relatively thick body regions of the neutrophils. In addition, by using more advanced models to account for the substrate effects, we have successfully characterized the rheological properties of the thin leading and tail regions as well. We found a regional difference in the mechanical compliances of the adherent neutrophils. The central regions of neutrophils were significantly stiffer (1,548 ± 871 Pa) than the regions closer to the leading edge (686 ± 801 Pa), while the leading edge and the tail (494 ± 537 Pa) regions were mechanically indistinguishable. The frequency-dependent elastic and viscous moduli also display a similar regional difference. Over the studied frequency range (100 to 300 Hz), the complex viscoelastic moduli display the partial rubber plateau behavior where the elastic moduli are greater than the viscous moduli for a given frequency. The non-disparaging viscous modulus indicates that the neutrophils display a viscoelastic dynamic behavior rather than a perfect elastic behavior like polymer gels. In addition, we found no regional difference in the structural damping coefficient between the leading edge and the cell body. Thus, we conclude that despite the lower loss and storage moduli, the leading edges of the human neutrophils display partially elastic properties similar to the cell body. These results suggest that the lower elastic moduli

  5. Atomic force microscopy analysis of cell volume regulation.

    PubMed

    Spagnoli, Chiara; Beyder, Arthur; Besch, Stephen; Sachs, Frederick

    2008-09-01

    Cells swell in response a hypoosmotic challenge. By converting osmotic pressure to hydrostatic pressure at the cell membrane via van't Hoff's law, and converting that to tension via Laplace's law one predicts that the cell membrane should stretch and become stiff. We tested this prediction using the atomic force microscopy. During osmotic swelling cells did not become stiff and generally became softer. This result contradicts the assumption of the cell membrane as the constraining element in osmotic stress but is consistent with the cytoskeleton acting as a cross-linked gel. Models of the cells' response to osmotic stress must include energy terms for three-dimensional stresses. PMID:18851074

  6. Cooling crystallization experiments observed by in situ scanning force microscopy

    NASA Astrophysics Data System (ADS)

    Kipp, S.; Lacmann, R.

    1996-03-01

    The change in surface morphology of potassium nitrate and potassium alum has been studied in situ by means of scanning force microscopy. The supersaturation and undersaturation were varied in a cooling crystallizer under flow conditions. To keep the crystal growth rate of potassium nitrate low, the specific additive DOW FAX 3B2 had been used in different concentrations. The crystal growth rate of both systems could be determined and the growth and dissolution surface morphologies of potassium alum exhibited structures similar to those of microscopic measurements.

  7. Measuring the elasticity of plant cells with atomic force microscopy.

    PubMed

    Braybrook, Siobhan A

    2015-01-01

    The physical properties of biological materials impact their functions. This is most evident in plants where the cell wall contains each cell's contents and connects each cell to its neighbors irreversibly. Examining the physical properties of the plant cell wall is key to understanding how plant cells, tissues, and organs grow and gain the shapes important for their respective functions. Here, we present an atomic force microscopy-based nanoindentation method for examining the elasticity of plant cells at the subcellular, cellular, and tissue level. We describe the important areas of experimental design to be considered when planning and executing these types of experiments and provide example data as illustration.

  8. Probing Persistence in DNA Curvature Properties with Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Moukhtar, J.; Fontaine, E.; Faivre-Moskalenko, C.; Arneodo, A.

    2007-04-01

    We elaborate on a mean-field extension of the wormlike chain model that accounts for the presence of long-range correlations (LRC) in the intrinsic curvature disorder of genomic DNA, the stronger the LRC, the smaller the persistence length. The comparison of atomic force microscopy imaging of straight, uncorrelated virus and correlated human DNA fragments with DNA simulations confirms that the observed decrease in persistence length for human DNA more likely results from a sequence-induced large-scale intrinsic curvature than from some increased flexibility.

  9. Atomic force microscopy to detect internal live processes in insects

    NASA Astrophysics Data System (ADS)

    Dokukin, M. E.; Guz, N. V.; Vasilyev, S.; Sokolov, I.

    2010-01-01

    Here we report on the use of atomic force microscopy (AFM) to study surface oscillations coming from internal live processes of insects. With a specially designed AFM stage to keep an insect motion partially restricted, the AFM can record internal oscillations on different parts of the insect. We demonstrate the method for a fly, mosquito, and lady beetle. We show that AFM can provide information about the spectral behavior that has not been studied so far, 10-600 Hz range, detecting amplitudes down to subnanometer level.

  10. Image contrast reversals in contact resonance atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Ma, Chengfu; Chen, Yuhang; Wang, Tian

    2015-02-01

    Multiple image contrast inversions are observed along with the increase of modulation frequency for contact resonance atomic force microscopy (CR-AFM) imaging of a highly oriented pyrolytic graphite (HOPG) specimen. Analysis of the contact vibrational spectra indicates that the inversions can be attributed to structure-induced variations of tip-sample contact mechanics. Contact stiffness and damping at HOPG step edges exhibit significant increases relative to those in the flat regions. For quantitative evaluation of mechanical properties in CR-AFM, coupling effects of the surface geometry must be considered.

  11. Nanoscale resolution microchannel flow velocimetry by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Piorek, Brian; Mechler, Ádám; Lal, Ratnesh; Freudenthal, Patrick; Meinhart, Carl; Banerjee, Sanjoy

    2006-10-01

    The velocity of a microchannel flow was determined by atomic force microscopy (AFM) using a 50nm wide "whisker," which was partially submerged and scanned transverse to the flow while drag was recorded. A peaked, near parabolic, flow velocity profile was found. Particle image velocity (PIV) measurements using 70nm diameter quantum-dot-coated polystyrene spheres confirmed the shape of the AFM-measured velocity profile. AFM-based nanometer resolution velocimetry confirms that the drag-velocity relationship for the whisker remains consistent over a wide range of shear values and appears to successfully resolve submicron scale flows, which are beyond the limits of conventional PIV measurements.

  12. Image contrast reversals in contact resonance atomic force microscopy

    SciTech Connect

    Ma, Chengfu; Chen, Yuhang Wang, Tian

    2015-02-15

    Multiple image contrast inversions are observed along with the increase of modulation frequency for contact resonance atomic force microscopy (CR-AFM) imaging of a highly oriented pyrolytic graphite (HOPG) specimen. Analysis of the contact vibrational spectra indicates that the inversions can be attributed to structure-induced variations of tip-sample contact mechanics. Contact stiffness and damping at HOPG step edges exhibit significant increases relative to those in the flat regions. For quantitative evaluation of mechanical properties in CR-AFM, coupling effects of the surface geometry must be considered.

  13. Chemical Force Microscopy of Chemical and Biological Interactions

    SciTech Connect

    Noy, A

    2006-01-02

    Interactions between chemical functionalities define outcomes of the vast majority of important events in chemistry, biology and materials science. Chemical Force Microscopy (CFM)--a technique that uses direct chemical functionalization of AFM probes with specific functionalities--allows researchers to investigate these important interactions directly. We review the basic principles of CFM, some examples of its application, and theoretical models that provide the basis for understanding the experimental results. We also emphasize application of modern kinetic theory of non-covalent interactions strength to the analysis of CFM data.

  14. Visualisation of xanthan conformation by atomic force microscopy.

    PubMed

    Moffat, Jonathan; Morris, Victor J; Al-Assaf, Saphwan; Gunning, A Patrick

    2016-09-01

    Direct visual evidence obtained by atomic force microscopy demonstrates that when xanthan is adsorbed from aqueous solution onto the heterogeneously charged substrate mica, its helical conformation is distorted. Following adsorption it requires annealing for several hours to restore its ordered helical state. Once the helix state reforms, the AFM images obtained showed clear resolution of the periodicity with a value of 4.7nm consistent with the previously predicted models. In addition, the images also reveal evidence that the helix is formed by a double strand, a clarification of an ambiguity of the xanthan ultrastructure that has been outstanding for many years. PMID:27185152

  15. CO tip functionalization in subatomic resolution atomic force microscopy

    SciTech Connect

    Kim, Minjung; Chelikowsky, James R.

    2015-10-19

    Noncontact atomic force microscopy (nc-AFM) employing a CO-functionalized tip displays dramatically enhanced resolution wherein covalent bonds of polycyclic aromatic hydrocarbon can be imaged. Employing real-space pseudopotential first-principles calculations, we examine the role of CO in functionalizing the nc-AFM tip. Our calculations allow us to simulate full AFM images and ascertain the enhancement mechanism of the CO molecule. We consider two approaches: one with an explicit inclusion of the CO molecule and one without. By comparing our simulations to existing experimental images, we ascribe the enhanced resolution of the CO functionalized tip to the special orbital characteristics of the CO molecule.

  16. Atomic-force microscopy: Rhodopsin dimers in native disc membranes

    NASA Astrophysics Data System (ADS)

    Fotiadis, Dimitrios; Liang, Yan; Filipek, Slawomir; Saperstein, David A.; Engel, Andreas; Palczewski, Krzysztof

    2003-01-01

    In vertebrate retinal photoreceptors, the rod outer-segment disc membranes contain densely packed rhodopsin molecules for optimal light absorption and subsequent amplification by the visual signalling cascade, but how these photon receptors are organized with respect to each other is not known. Here we use infrared-laser atomic-force microscopy to reveal the native arrangement of rhodopsin, which forms paracrystalline arrays of dimers in mouse disc membranes. The visualization of these closely packed rhodopsin dimers in native membranes gives experimental support to earlier inferences about their supramolecular structure and provides insight into how light signalling is controlled.

  17. Understanding the plasmonics of nanostructured atomic force microscopy tips

    NASA Astrophysics Data System (ADS)

    Sanders, A.; Bowman, R. W.; Zhang, L.; Turek, V.; Sigle, D. O.; Lombardi, A.; Weller, L.; Baumberg, J. J.

    2016-10-01

    Structured metallic tips are increasingly important for optical spectroscopies such as tip-enhanced Raman spectroscopy, with plasmonic resonances frequently cited as a mechanism for electric field enhancement. We probe the local optical response of sharp and spherical-tipped atomic force microscopy (AFM) tips using a scanning hyperspectral imaging technique to identify the plasmonic behaviour. Localised surface plasmon resonances which radiatively couple with far-field light are found only for spherical AFM tips, with little response for sharp AFM tips, in agreement with numerical simulations of the near-field response. The precise tip geometry is thus crucial for plasmon-enhanced spectroscopies, and the typical sharp cones are not preferred.

  18. Nanoindentation of Pseudomonas aeruginosa bacterial biofilm using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Baniasadi, Mahmoud; Xu, Zhe; Gandee, Leah; Du, Yingjie; Lu, Hongbing; Zimmern, Philippe; Minary-Jolandan, Majid

    2014-12-01

    Bacterial biofilms are a source of many chronic infections. Biofilms and their inherent resistance to antibiotics are attributable to a range of health issues including affecting prosthetic implants, hospital-acquired infections, and wound infection. Mechanical properties of biofilm, in particular, at micro- and nano-scales, are governed by microstructures and porosity of the biofilm, which in turn may contribute to their inherent antibiotic resistance. We utilize atomic force microscopy (AFM)-based nanoindentation and finite element simulation to investigate the nanoscale mechanical properties of Pseudomonas aeruginosa bacterial biofilm. This biofilm was derived from human samples and represents a medically relevant model.

  19. Atomic force microscopy of electrospun organic-inorganic lipid nanofibers

    NASA Astrophysics Data System (ADS)

    Zhang, Jinhong; Cohn, Celine; Qiu, Weiguo; Zha, Zhengbao; Dai, Zhifei; Wu, Xiaoyi

    2011-09-01

    An organic-inorganic hybridization strategy has been proposed to synthesize polymerizable lipid-based materials for the creation of highly stable lipid-mimetic nanostructures. We employ atomic force microscopy (AFM) to analyze the surface morphology and mechanical property of electrospun cholesteryl-succinyl silane (CSS) nanofibers. The AFM nanoindentation of the CSS nanofibers reveals elastic moduli of 55.3 ± 27.6 to 70.8 ± 35 MPa, which is significantly higher than the moduli of natural phospholipids and cholesterols. The study shows that organic-inorganic hybridization is useful in the design of highly stable lipid-based materials.

  20. Note: On the deconvolution of Kelvin probe force microscopy data.

    PubMed

    Blümel, A; Plank, H; Klug, A; Fisslthaler, E; Sezen, M; Grogger, W; List, E J W

    2010-05-01

    In Kelvin probe force microscopy (KPFM) proper interpretation of the data is often difficult because the measured surface potential is affected by the interaction of the cantilever with the sample. In this work, the tip's interaction with a modeled surface potential distribution was simulated, leading to a calculated KPFM image. Although simplified, the calculation is capable of showing the influence of the cantilever in the correct qualitative manner, proven by a comparison with experimental data. Additionally, a deconvolution was performed on the simulated image, showing that for simple geometries revealing the "real" surface potential data is possible in principle. PMID:20515184

  1. Cryogel micromechanics unraveled by atomic force microscopy-based nanoindentation.

    PubMed

    Welzel, Petra B; Friedrichs, Jens; Grimmer, Milauscha; Vogler, Steffen; Freudenberg, Uwe; Werner, Carsten

    2014-11-01

    Cell-instructive physical characteristics of macroporous scaffolds, developed for tissue engineering applications, often remain difficult to assess. Here, an atomic force microscopy-based nanoindentation approach is adapted to quantify the local mechanical properties of biohybrid glycosaminoglycan-poly(ethylene glycol) cryogels. Resulting from cryoconcentration effects upon gel formation, cryogel struts are observed to feature a higher stiffness compared to the corresponding bulk hydrogel materials. Local Young's moduli, porosity, and integral moduli of the cryogel scaffolds are compared in dependence on gel formation parameters. The results provide valuable insights into the cryogelation process and a base for adjusting physical characteristics of the obtained cryogel scaffolds, which can critically influence the cellular response.

  2. Band excitation Kelvin probe force microscopy utilizing photothermal excitation

    SciTech Connect

    Collins, Liam E-mail: liq1@ORNL.gov; Rodriguez, Brian J.; Jesse, Stephen; Balke, Nina; Kalinin, Sergei; Li, Qian E-mail: liq1@ORNL.gov

    2015-03-09

    A multifrequency open loop Kelvin probe force microscopy (KPFM) approach utilizing photothermal as opposed to electrical excitation is developed. Photothermal band excitation (PthBE)-KPFM is implemented here in a grid mode on a model test sample comprising a metal-insulator junction with local charge-patterned regions. Unlike the previously described open loop BE-KPFM, which relies on capacitive actuation of the cantilever, photothermal actuation is shown to be highly sensitive to the electrostatic force gradient even at biases close to the contact potential difference (CPD). PthBE-KPFM is further shown to provide a more localized measurement of true CPD in comparison to the gold standard ambient KPFM approach, amplitude modulated KPFM. Finally, PthBE-KPFM data contain information relating to local dielectric properties and electronic dissipation between tip and sample unattainable using conventional single frequency KPFM approaches.

  3. Monitoring molecular beacon/DNA interactions using atomic force microscopy.

    PubMed

    Jin, Yan; Wang, Kemin; Tan, Weihong; Wu, Ping; Wang, Qing; Huang, Hongmei; Huang, Shasheng; Tang, Zhiwen; Guo, Qiuping

    2004-10-01

    The molecular beacon (MB) is a new fluorescence probe containing a single-stranded oligonucleotide with a probe sequence embedded in complementary sequences that form a hairpin stem. Due to the inherent fluorescent signal transduction mechanism, an MB functions as a sensitive probe with a high signal-to-background ratio for real-time monitoring and provides a variety of exciting opportunities in DNA, RNA, and protein studies. To better understand the properties of MBs, the specific interactions between MB and target DNA (complementary and one-base mismatch) have been directly investigated by atomic force microscopy. The interaction force between a linear DNA probe and the target DNA was also detected and compared to that between MB and target DNA. The results demonstrate the high specificity of the MB/target DNA compared to the linear DNA/target DNA interaction.

  4. Taking Nanomedicine Teaching into Practice with Atomic Force Microscopy and Force Spectroscopy

    ERIC Educational Resources Information Center

    Carvalho, Filomena A.; Freitas, Teresa; Santos, Nuno C.

    2015-01-01

    Atomic force microscopy (AFM) is a useful and powerful tool to study molecular interactions applied to nanomedicine. The aim of the present study was to implement a hands-on atomic AFM course for graduated biosciences and medical students. The course comprises two distinct practical sessions, where students get in touch with the use of an atomic…

  5. Estimating the transfer function of the cantilever in atomic force microscopy: A system identification approach

    NASA Astrophysics Data System (ADS)

    Stark, Martin; Guckenberger, Reinhard; Stemmer, Andreas; Stark, Robert W.

    2005-12-01

    Dynamic atomic force microscopy (AFM) offers many opportunities for the characterization and manipulation of matter on the nanometer scale with a high temporal resolution. The analysis of time-dependent forces is basic for a deeper understanding of phenomena such as friction, plastic deformation, and surface wetting. However, the dynamic characteristics of the force sensor used for such investigations are determined by various factors such as material and geometry of the cantilever, detection alignment, and the transfer characteristics of the detector. Thus, for a quantitative investigation of surface properties by dynamic AFM an appropriate system identification procedure is required, characterizing the force sensor beyond the usual parameters spring constant, quality factor, and detection sensitivity. Measurement of the transfer function provides such a characterization that fully accounts for the dynamic properties of the force sensor. Here, we demonstrate the estimation of the transfer function in a bandwidth of 1MHz from experimental data. To this end, we analyze the signal of the vibrations induced by snap-to-contact and snap-off-contact events. For the free cantilever, we determine both a parameter-free estimate [empirical transfer function estimate (ETFE)] and a parametric estimate of the transfer function. For the surface-coupled cantilever the ETFE is obtained. These identification procedures provide an intrinsic calibration as they dispense largely with a priori knowledge about the force sensor.

  6. Combining confocal microscopy with precise force-scope optical tweezers

    NASA Astrophysics Data System (ADS)

    Richardson, Andrew C.; Reihani, Nader; Oddershede, Lene B.

    2006-08-01

    We demonstrate an example of 'confocal-tweezers' wherein confocal images and precise optical force measurements, using photodiodes, are obtained simultaneously in the x-y plane without moving the objective lens. The optical trap is produced using a 1.064μm cw laser and is combined with Leica's TCS SP5 broadband confocal microscope to trap and image living cells. The unique method by which the confocal images are created facilitates the acquisition of images in areas far from the trapping location. In addition, because the scanning process involves moving galvanic mirrors independently of the objective, the trap is held stable in position and is not subject to any error in position for the x-y scan. We have successfully trapped and confocally imaged 80nm gold colloids, 150nm gold colloids and 1μm polystyrene beads whilst making quantitative measurements of the force applied by the trap on each bead. To the best of our knowledge this is the first time that anyone has combined precise force measuring optical tweezers with confocal microscopy. We also discuss some of the technical challenges involved in advancing the experimental set up to make quantitative force measurements in combination with 3D stacking. Having proven the potential of this system in 2D, we hope to develop it further to investigate the nano-mechanics of cell division through the attachment of gold beads to fluorescently labelled organelles in S. pombe yeast cells.

  7. Quantifying mineral surface energy by scanning force microscopy.

    PubMed

    Sauerer, Bastian; Stukan, Mikhail; Abdallah, Wael; Derkani, Maryam H; Fedorov, Maxim; Buiting, Jan; Zhang, Zhenyu J

    2016-06-15

    Fundamental understanding of the wettability of carbonate formations can potentially be applied to the development of oil recovery strategies in a complex carbonate reservoir. In the present study, surface energies of representative carbonate samples were evaluated by direct quantitative force measurements, using scanning force microscopy (SFM) at sub-micron scale, to develop a reliable method to predict reservoir wettability. Local adhesion force measurements were conducted on appropriate calcite and dolomite samples and performed in air as well as in the presence of polar and nonpolar fluids. This study demonstrated that, by comparing measurements of adhesion forces between samples of the same mineral in different fluids, it is feasible to determine the surface energy of a given mineral as well as its polar and nonpolar components. The derived values are in agreement with literature. A proof-of-principle protocol has been established to quantify surface energy using SFM-based adhesion measurements. This novel methodology complements the conventional contact angle measurement technique, where surface energy can only be examined at large length scale. The reported methodology has great potential for further optimization into a new standard method for fast and accurate surface energy determination, and hence provides a new tool for reservoir rock wettability characterization. PMID:27054773

  8. Atomically resolved graphitic surfaces in air by atomic force microscopy.

    PubMed

    Wastl, Daniel S; Weymouth, Alfred J; Giessibl, Franz J

    2014-05-27

    Imaging at the atomic scale using atomic force microscopy in biocompatible environments is an ongoing challenge. We demonstrate atomic resolution of graphite and hydrogen-intercalated graphene on SiC in air. The main challenges arise from the overall surface cleanliness and the water layers which form on almost all surfaces. To further investigate the influence of the water layers, we compare data taken with a hydrophilic bulk-silicon tip to a hydrophobic bulk-sapphire tip. While atomic resolution can be achieved with both tip materials at moderate interaction forces, there are strong differences in force versus distance spectra which relate to the water layers on the tips and samples. Imaging at very low tip-sample interaction forces results in the observation of large terraces of a naturally occurring stripe structure on the hydrogen-intercalated graphene. This structure has been previously reported on graphitic surfaces that are not covered with disordered adsorbates in ambient conditions (i.e., on graphite and bilayer graphene on SiC, but not on monolayer graphene on SiC). Both these observations indicate that hydrogen-intercalated graphene is close to an ideal graphene sample in ambient environments.

  9. Atomically resolved graphitic surfaces in air by atomic force microscopy.

    PubMed

    Wastl, Daniel S; Weymouth, Alfred J; Giessibl, Franz J

    2014-05-27

    Imaging at the atomic scale using atomic force microscopy in biocompatible environments is an ongoing challenge. We demonstrate atomic resolution of graphite and hydrogen-intercalated graphene on SiC in air. The main challenges arise from the overall surface cleanliness and the water layers which form on almost all surfaces. To further investigate the influence of the water layers, we compare data taken with a hydrophilic bulk-silicon tip to a hydrophobic bulk-sapphire tip. While atomic resolution can be achieved with both tip materials at moderate interaction forces, there are strong differences in force versus distance spectra which relate to the water layers on the tips and samples. Imaging at very low tip-sample interaction forces results in the observation of large terraces of a naturally occurring stripe structure on the hydrogen-intercalated graphene. This structure has been previously reported on graphitic surfaces that are not covered with disordered adsorbates in ambient conditions (i.e., on graphite and bilayer graphene on SiC, but not on monolayer graphene on SiC). Both these observations indicate that hydrogen-intercalated graphene is close to an ideal graphene sample in ambient environments. PMID:24746062

  10. Comparative study of clinical pulmonary surfactants using atomic force microscopy.

    PubMed

    Zhang, Hong; Fan, Qihui; Wang, Yi E; Neal, Charles R; Zuo, Yi Y

    2011-07-01

    Clinical pulmonary surfactant is routinely used to treat premature newborns with respiratory distress syndrome, and has shown great potential in alleviating a number of neonatal and adult respiratory diseases. Despite extensive study of chemical composition, surface activity, and clinical performance of various surfactant preparations, a direct comparison of surfactant films is still lacking. In this study, we use atomic force microscopy to characterize and compare four animal-derived clinical surfactants currently used throughout the world, i.e., Survanta, Curosurf, Infasurf and BLES. These modified-natural surfactants are further compared to dipalmitoyl phosphatidylcholine (DPPC), a synthetic model surfactant of DPPC:palmitoyl-oleoyl phosphatidylglycerol (POPG) (7:3), and endogenous bovine natural surfactant. Atomic force microscopy reveals significant differences in the lateral structure and molecular organization of these surfactant preparations. These differences are discussed in terms of DPPC and cholesterol contents. We conclude that all animal-derived clinical surfactants assume a similar structure of multilayers of fluid phospholipids closely attached to an interfacial monolayer enriched in DPPC, at physiologically relevant surface pressures. This study provides the first comprehensive survey of the lateral structure of clinical surfactants at various surface pressures. It may have clinical implications on future application and development of surfactant preparations.

  11. Nanomechanics of Cells and Biomaterials Studied by Atomic Force Microscopy.

    PubMed

    Kilpatrick, Jason I; Revenko, Irène; Rodriguez, Brian J

    2015-11-18

    The behavior and mechanical properties of cells are strongly dependent on the biochemical and biomechanical properties of their microenvironment. Thus, understanding the mechanical properties of cells, extracellular matrices, and biomaterials is key to understanding cell function and to develop new materials with tailored mechanical properties for tissue engineering and regenerative medicine applications. Atomic force microscopy (AFM) has emerged as an indispensable technique for measuring the mechanical properties of biomaterials and cells with high spatial resolution and force sensitivity within physiologically relevant environments and timescales in the kPa to GPa elastic modulus range. The growing interest in this field of bionanomechanics has been accompanied by an expanding array of models to describe the complexity of indentation of hierarchical biological samples. Furthermore, the integration of AFM with optical microscopy techniques has further opened the door to a wide range of mechanotransduction studies. In recent years, new multidimensional and multiharmonic AFM approaches for mapping mechanical properties have been developed, which allow the rapid determination of, for example, cell elasticity. This Progress Report provides an introduction and practical guide to making AFM-based nanomechanical measurements of cells and surfaces for tissue engineering applications.

  12. High resolution atomic force microscopy of double-stranded RNA

    NASA Astrophysics Data System (ADS)

    Ares, Pablo; Fuentes-Perez, Maria Eugenia; Herrero-Galán, Elías; Valpuesta, José M.; Gil, Adriana; Gomez-Herrero, Julio; Moreno-Herrero, Fernando

    2016-06-01

    Double-stranded (ds) RNA mediates the suppression of specific gene expression, it is the genetic material of a number of viruses, and a key activator of the innate immune response against viral infections. The ever increasing list of roles played by dsRNA in the cell and its potential biotechnological applications over the last decade has raised an interest for the characterization of its mechanical properties and structure, and that includes approaches using Atomic Force Microscopy (AFM) and other single-molecule techniques. Recent reports have resolved the structure of dsDNA with AFM at unprecedented resolution. However, an equivalent study with dsRNA is still lacking. Here, we have visualized the double helix of dsRNA under near-physiological conditions and at sufficient resolution to resolve the A-form sub-helical pitch periodicity. We have employed different high-sensitive force-detection methods and obtained images with similar spatial resolution. Therefore, we show here that the limiting factors for high-resolution AFM imaging of soft materials in liquid medium are, rather than the imaging mode, the force between the tip and the sample and the sharpness of the tip apex.Double-stranded (ds) RNA mediates the suppression of specific gene expression, it is the genetic material of a number of viruses, and a key activator of the innate immune response against viral infections. The ever increasing list of roles played by dsRNA in the cell and its potential biotechnological applications over the last decade has raised an interest for the characterization of its mechanical properties and structure, and that includes approaches using Atomic Force Microscopy (AFM) and other single-molecule techniques. Recent reports have resolved the structure of dsDNA with AFM at unprecedented resolution. However, an equivalent study with dsRNA is still lacking. Here, we have visualized the double helix of dsRNA under near-physiological conditions and at sufficient resolution to

  13. Low temperature scanning force microscopy using piezoresistive cantilevers

    NASA Astrophysics Data System (ADS)

    Meiser, P.; Koblischka, M. R.; Hartmann, U.

    2015-08-01

    A low temperature dynamic scanning force microscope has been constructed using commercially available piezoresistive cantilevers that can be coated with a ferromagnetic material for MFM application. The setup is able to work in a temperature range from room temperature down to 1.5 K. The performance of the piezoresistive cantilevers has been investigated under different working conditions. Topographic as well as magnetic images of a magnetite thin film sample have been taken at 50 and 4.2 K confirming the proper operation of the microscope at cryogenic temperatures. Furthermore, force-distance-curves taken on thin lead films at 4.2 K demonstrate the levitation forces between the magnetized cantilever tip and the superconducting films. Flux lines were generated by the magnetized cantilever tip itself when approaching the sample. It has also been shown that the microscope is sensitive to the detection of single magnetic flux lines penetrating the lead films.

  14. Imaging of DNA and Protein–DNA Complexes with Atomic Force Microscopy

    PubMed Central

    Lyubchenko, Yuri L.; Shlyakhtenko, Luda S.

    2016-01-01

    This article reviews atomic force microscopy (AFM) studies of DNA structure and dynamics and protein–DNA complexes, including recent advances in the visualization of protein–DNA complexes with the use of cutting-edge, high-speed AFM. Special emphasis is given to direct nanoscale visualization of dynamics of protein–DNA complexes. In the area of DNA structure and dynamics, structural studies of local non-B conformations of DNA and the interplay of local and global DNA conformations are reviewed. The application of time-lapse AFM nanoscale imaging of DNA dynamics is illustrated by studies of Holliday junction branch migration. Structure and dynamics of protein–DNA interactions include problems related to site-specific DNA recombination, DNA replication, and DNA mismatch repair. Studies involving the structure and dynamics of chromatin are also described. PMID:27278886

  15. Enhanced quality factors and force sensitivity by attaching magnetic beads to cantilevers for atomic force microscopy in liquid

    NASA Astrophysics Data System (ADS)

    Hoof, Sebastian; Nand Gosvami, Nitya; Hoogenboom, Bart W.

    2012-12-01

    Dynamic-mode atomic force microscopy (AFM) in liquid remains complicated due to the strong viscous damping of the cantilever resonance. Here, we show that a high-quality resonance (Q >20) can be achieved in aqueous solution by attaching a microgram-bead at the end of the nanogram-cantilever. The resulting increase in cantilever mass causes the resonance frequency to drop significantly. However, the force sensitivity—as expressed via the minimum detectable force gradient—is hardly affected, because of the enhanced quality factor. Through the enhancement of the quality factor, the attached bead also reduces the relative importance of noise in the deflection detector. It can thus yield an improved signal-to-noise ratio when this detector noise is significant. We describe and analyze these effects for a set-up that includes magnetic actuation of the cantilevers and that can be easily implemented in any AFM system that is compatible with an inverted optical microscope.

  16. Quality of corneal lamellar cuts quantified using atomic force microscopy

    PubMed Central

    Ziebarth, Noël M.; Dias, Janice; Hürmeriç, Volkan; Shousha, Mohamed Abou; Yau, Chiyat Ben; Moy, Vincent T.; Culbertson, William; Yoo, Sonia H.

    2012-01-01

    PURPOSE To quantify the cut quality of lamellar dissections made with the femtosecond laser using atomic force microscopy (AFM). SETTING Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA. DESIGN Experimental study. METHODS Experiments were performed on 3 pairs of human cadaver eyes. The cornea was thinned to physiologic levels by placing the globe, cornea side down, in 25% dextran for 24 hours. The eyes were reinflated to normal pressures by injecting a balanced salt solution into the vitreous cavity. The eyes were placed in a holder, the epithelium was removed, and the eyes were cut with a Visumax femtosecond laser. The energy level was 180 nJ for the right eye and 340 nJ for the left eye of each pair. The cut depths were 200 μm, 300 μm, and 400 μm, with the cut depth maintained for both eyes of each pair. A 12.0 mm trephination was then performed. The anterior portion of the lamellar surface was placed in a balanced salt solution and imaged with AFM. As a control, the posterior surface was placed in 2% formalin and imaged with environmental scanning electron microscopy (SEM). Four quantitative parameters (root-mean-square deviation, average deviation, skewness, kurtosis) were calculated from the AFM images. RESULTS From AFM, the 300 μm low-energy cuts were the smoothest. Similar results were seen qualitatively in the environmental SEM images. CONCLUSION Atomic force microscopy provided quantitative information on the quality of lamellar dissections made using a femtosecond laser, which is useful in optimizing patient outcomes in refractive and lamellar keratoplasty surgeries. PMID:23141078

  17. Atomic Force Microscopy to Study Mechanics of Living Mitotic Mammalian Cells

    NASA Astrophysics Data System (ADS)

    Toyoda, Yusuke; Stewart, Martin P.; Hyman, Anthony A.; Müller, Daniel J.

    2011-08-01

    While biochemical pathways within mitotic cells have been intensively studied, the mechanics of dividing cells is only poorly understood. In our recent report, an experimental system combining fluorescence and atomic force microscopy was set up to study dynamics of mitotic rounding of mammalian cells. We show that cells have a rounding pressure that increases upon mitotic entry. Using specific inhibitors or perturbations, we revealed biological processes required for force generation that underpin the cell rounding shape change during mitosis. The significance of the finding and an outlook are discussed.

  18. Exploring Local Electrostatic Effects with Scanning Probe Microscopy: Implications for Piezoresponse Force Microscopy and Triboelectricity

    SciTech Connect

    Balke, Nina; Maksymovych, Petro; Jesse, Stephen; Kravchenko, Ivan I.; Li, Qian; Kalinin, Sergei V.

    2014-09-25

    The implementation of contact mode Kelvin probe force microscopy (KPFM) utilizes the electrostatic interactions between tip and sample when the tip and sample are in contact with each other. Surprisingly, the electrostatic forces in contact are large enough to be measured even with tips as stiff as 4.5 N/m. As for traditional non-contact KPFM, the signal depends strongly on electrical properties of the sample, such as the dielectric constant, and the tip-properties, such as the stiffness. Since the tip is in contact with the sample, bias-induced changes in the junction potential between tip and sample can be measured with higher lateral and temporal resolution compared to traditional non-contact KPFM. Significant and reproducible variations of tip-surface capacitance are observed and attributed to surface electrochemical phenomena. Lastly, observations of significant surface charge states at zero bias and strong hysteretic electromechanical responses at non-ferroelectric surface have significant implications for fields such as triboelectricity and piezoresponse force microscopy.

  19. Exploring Local Electrostatic Effects with Scanning Probe Microscopy: Implications for Piezoresponse Force Microscopy and Triboelectricity

    DOE PAGES

    Balke, Nina; Maksymovych, Petro; Jesse, Stephen; Kravchenko, Ivan I.; Li, Qian; Kalinin, Sergei V.

    2014-09-25

    The implementation of contact mode Kelvin probe force microscopy (KPFM) utilizes the electrostatic interactions between tip and sample when the tip and sample are in contact with each other. Surprisingly, the electrostatic forces in contact are large enough to be measured even with tips as stiff as 4.5 N/m. As for traditional non-contact KPFM, the signal depends strongly on electrical properties of the sample, such as the dielectric constant, and the tip-properties, such as the stiffness. Since the tip is in contact with the sample, bias-induced changes in the junction potential between tip and sample can be measured with highermore » lateral and temporal resolution compared to traditional non-contact KPFM. Significant and reproducible variations of tip-surface capacitance are observed and attributed to surface electrochemical phenomena. Lastly, observations of significant surface charge states at zero bias and strong hysteretic electromechanical responses at non-ferroelectric surface have significant implications for fields such as triboelectricity and piezoresponse force microscopy.« less

  20. Atomic force microscopy measurement of leukocyte-endothelial interaction.

    PubMed

    Zhang, Xiaohui; Chen, Aileen; De Leon, Dina; Li, Hong; Noiri, Eisei; Moy, Vincent T; Goligorsky, Michael S

    2004-01-01

    Leukocyte adhesion to vascular endothelium is a key initiating step in the pathogenesis of many inflammatory diseases. In this study, we present real-time force measurements of the interaction between monocytic human promyelocytic leukemia cells (HL-60) cells and a monolayer of human umbilical vein endothelial cells (HUVECs) by using atomic force microscopy (AFM). The detachment of HL-60-HUVEC conjugates involved a series of rupture events with force transitions of 40-100 pN. The integrated force of these rupture events provided a quantitative measure of the adhesion strength on a whole cell level. The AFM measurements revealed that HL-60 adhesion is heightened in the borders formed by adjacent HUVECs. The average force and mechanical work required to detach a single HL-60 from the borders of a tumor necrosis factor-alpha-activated HUVEC layer were twice as high as those of the HUVEC bodies. HL-60 adhesion to the monolayer was significantly reduced by a monoclonal antibody against beta1-integrins and partially inhibited by antibodies against selectins ICAM-1 and VCAM-1 but was not affected by anti-alphaVbeta3. Interestingly, adhesion was also inhibited in a dose-dependent manner (IC50 approximately 100 nM) by a cyclic arginine-glycine-aspartic acid (cRGD) peptide. This effect was mediated via interfering with the VLA-4-VCAM-1 binding. In parallel measurements, transmigration of HL-60 cells across a confluent HUVEC monolayer was inhibited by the cRGD peptide and by both anti-beta1 and anti-alphaVbeta3 antibodies. In conclusion, these data demonstrate the role played by beta1-integrins in leukocyte-endothelial adhesion and transmigration and the role played by alphaVbeta3 in transmigration, thus underscoring the high efficacy of cRGD peptide in blocking both the adhesion and transmigration of monocytes. PMID:12969892

  1. Dynamic Force Measurement with Strain Gauges

    ERIC Educational Resources Information Center

    Lee, Bruce E.

    1974-01-01

    Discusses the use of four strain gauges, a Wheatstone bridge, and an oscilloscope to measure forces dynamically. Included is an example of determining the centripetal force of a pendulum in a general physics laboratory. (CC)

  2. Simultaneous Scanning Ion Conductance Microscopy and Atomic Force Microscopy with Microchanneled Cantilevers

    NASA Astrophysics Data System (ADS)

    Ossola, Dario; Dorwling-Carter, Livie; Dermutz, Harald; Behr, Pascal; Vörös, János; Zambelli, Tomaso

    2015-12-01

    We combined scanning ion conductance microscopy (SICM) and atomic force microscopy (AFM) into a single tool using AFM cantilevers with an embedded microchannel flowing into the nanosized aperture at the apex of the hollow pyramid. An electrode was positioned in the AFM fluidic circuit connected to a second electrode in the bath. We could thus simultaneously measure the ionic current and the cantilever bending (in optical beam deflection mode). First, we quantitatively compared the SICM and AFM contact points on the approach curves. Second, we estimated where the probe in SICM mode touches the sample during scanning on a calibration grid and applied the finding to image a network of neurites on a Petri dish. Finally, we assessed the feasibility of a double controller using both the ionic current and the deflection as input signals of the piezofeedback. The experimental data were rationalized in the framework of finite elements simulations.

  3. Simultaneous Scanning Ion Conductance Microscopy and Atomic Force Microscopy with Microchanneled Cantilevers.

    PubMed

    Ossola, Dario; Dorwling-Carter, Livie; Dermutz, Harald; Behr, Pascal; Vörös, János; Zambelli, Tomaso

    2015-12-01

    We combined scanning ion conductance microscopy (SICM) and atomic force microscopy (AFM) into a single tool using AFM cantilevers with an embedded microchannel flowing into the nanosized aperture at the apex of the hollow pyramid. An electrode was positioned in the AFM fluidic circuit connected to a second electrode in the bath. We could thus simultaneously measure the ionic current and the cantilever bending (in optical beam deflection mode). First, we quantitatively compared the SICM and AFM contact points on the approach curves. Second, we estimated where the probe in SICM mode touches the sample during scanning on a calibration grid and applied the finding to image a network of neurites on a Petri dish. Finally, we assessed the feasibility of a double controller using both the ionic current and the deflection as input signals of the piezofeedback. The experimental data were rationalized in the framework of finite elements simulations. PMID:26684144

  4. Atomic force microscopy application in biological research: a review study.

    PubMed

    Vahabi, Surena; Nazemi Salman, Bahareh; Javanmard, Anahita

    2013-06-01

    Atomic force microscopy (AFM) is a three-dimensional topographic technique with a high atomic resolution to measure surface roughness. AFM is a kind of scanning probe microscope, and its near-field technique is based on the interaction between a sharp tip and the atoms of the sample surface. There are several methods and many ways to modify the tip of the AFM to investigate surface properties, including measuring friction, adhesion forces and viscoelastic properties as well as determining the Young modulus and imaging magnetic or electrostatic properties. The AFM technique can analyze any kind of samples such as polymers, adsorbed molecules, films or fibers, and powders in the air whether in a controlled atmosphere or in a liquid medium. In the past decade, the AFM has emerged as a powerful tool to obtain the nanostructural details and biomechanical properties of biological samples, including biomolecules and cells. The AFM applications, techniques, and -in particular- its ability to measure forces, are not still familiar to most clinicians. This paper reviews the literature on the main principles of the AFM modality and highlights the advantages of this technique in biology, medicine, and- especially- dentistry. This literature review was performed through E-resources, including Science Direct, PubMed, Blackwell Synergy, Embase, Elsevier, and Scholar Google for the references published between 1985 and 2010.

  5. Nanoscale dielectric microscopy of non-planar samples by lift-mode electrostatic force microscopy

    NASA Astrophysics Data System (ADS)

    Van Der Hofstadt, M.; Fabregas, R.; Biagi, M. C.; Fumagalli, L.; Gomila, G.

    2016-10-01

    Lift-mode electrostatic force microscopy (EFM) is one of the most convenient imaging modes to study the local dielectric properties of non-planar samples. Here we present the quantitative analysis of this imaging mode. We introduce a method to quantify and subtract the topographic crosstalk from the lift-mode EFM images, and a 3D numerical approach that allows for extracting the local dielectric constant with nanoscale spatial resolution free from topographic artifacts. We demonstrate this procedure by measuring the dielectric properties of micropatterned SiO2 pillars and of single bacteria cells, thus illustrating the wide applicability of our approach from materials science to biology.

  6. Nanoscale dielectric microscopy of non-planar samples by lift-mode electrostatic force microscopy.

    PubMed

    Van Der Hofstadt, M; Fabregas, R; Biagi, M C; Fumagalli, L; Gomila, G

    2016-10-01

    Lift-mode electrostatic force microscopy (EFM) is one of the most convenient imaging modes to study the local dielectric properties of non-planar samples. Here we present the quantitative analysis of this imaging mode. We introduce a method to quantify and subtract the topographic crosstalk from the lift-mode EFM images, and a 3D numerical approach that allows for extracting the local dielectric constant with nanoscale spatial resolution free from topographic artifacts. We demonstrate this procedure by measuring the dielectric properties of micropatterned SiO2 pillars and of single bacteria cells, thus illustrating the wide applicability of our approach from materials science to biology. PMID:27597315

  7. Nanoscale dielectric microscopy of non-planar samples by lift-mode electrostatic force microscopy.

    PubMed

    Van Der Hofstadt, M; Fabregas, R; Biagi, M C; Fumagalli, L; Gomila, G

    2016-10-01

    Lift-mode electrostatic force microscopy (EFM) is one of the most convenient imaging modes to study the local dielectric properties of non-planar samples. Here we present the quantitative analysis of this imaging mode. We introduce a method to quantify and subtract the topographic crosstalk from the lift-mode EFM images, and a 3D numerical approach that allows for extracting the local dielectric constant with nanoscale spatial resolution free from topographic artifacts. We demonstrate this procedure by measuring the dielectric properties of micropatterned SiO2 pillars and of single bacteria cells, thus illustrating the wide applicability of our approach from materials science to biology.

  8. Easy and direct method for calibrating atomic force microscopy lateral force measurements.

    PubMed

    Liu, Wenhua; Bonin, Keith; Guthold, Martin

    2007-06-01

    We have designed and tested a new, inexpensive, easy-to-make and easy-to-use calibration standard for atomic force microscopy (AFM) lateral force measurements. This new standard simply consists of a small glass fiber of known dimensions and Young's modulus, which is fixed at one end to a substrate and which can be bent laterally with the AFM tip at the other end. This standard has equal or less error than the commonly used method of using beam mechanics to determine a cantilever's lateral force constant. It is transferable, thus providing a universal tool for comparing the calibrations of different instruments. It does not require knowledge of the cantilever dimensions and composition or its tip height. This standard also allows direct conversion of the photodiode signal to force and, thus, circumvents the requirement for a sensor response (sensitivity) measurement.

  9. Combined atomic force microscopy and voltage pulse technique to accurately measure electrostatic force

    NASA Astrophysics Data System (ADS)

    Inami, Eiichi; Sugimoto, Yoshiaki

    2016-08-01

    We propose a new method of extracting electrostatic force. The technique is based on frequency modulation atomic force microscopy (FM-AFM) combined with a voltage pulse. In this method, the work that the electrostatic field does on the oscillating tip is measured through the cantilever energy dissipation. This allows us to directly extract capacitive forces including the longer range part, to which the conventional FM-AFM is insensitive. The distance-dependent contact potential difference, which is modulated by local charges distributed on the surfaces of the tip and/or sample, could also be correctly obtained. In the absence of local charges, our method can perfectly reproduce the electrostatic force as a function of the distance and the bias voltage. Furthermore, we demonstrate that the system serves as a sensitive sensor enabling us to check the existence of the local charges such as trapped charges and patch charges.

  10. Easy and direct method for calibrating atomic force microscopy lateral force measurements

    PubMed Central

    Liu, Wenhua; Bonin, Keith; Guthold, Martin

    2010-01-01

    We have designed and tested a new, inexpensive, easy-to-make and easy-to-use calibration standard for atomic force microscopy (AFM) lateral force measurements. This new standard simply consists of a small glass fiber of known dimensions and Young’s modulus, which is fixed at one end to a substrate and which can be bent laterally with the AFM tip at the other end. This standard has equal or less error than the commonly used method of using beam mechanics to determine a cantilever’s lateral force constant. It is transferable, thus providing a universal tool for comparing the calibrations of different instruments. It does not require knowledge of the cantilever dimensions and composition or its tip height. This standard also allows direct conversion of the photodiode signal to force and, thus, circumvents the requirement for a sensor response (sensitivity) measurement. PMID:17614616

  11. Young's moduli of surface-bound liposomes by atomic force microscopy force measurements.

    PubMed

    Brochu, Heïdi; Vermette, Patrick

    2008-03-01

    Mechanical properties of layers of intact liposomes attached by specific interactions on solid surfaces were studied by atomic force microscopy (AFM) force measurements. Force-distance measurements using colloidal probe tips were obtained over liposome layers and used to calculate Young's moduli by using the Hertz contact theory. A classical Hertz model and a modified Hertz one have been used to extract Young's moduli from AFM force curves. The modified model, proposed by Dimitriadis, is correcting for the finite sample thickness since Hertz's classical model is assuming that the sample is infinitely thick. Values for Young's moduli of 40 and 8 kPa have been obtained using the Hertz model for one and three layers of intact liposomes, respectively. Young's moduli of approximately 3 kPa have been obtained using the corrected Hertz model for both one and three layers of surface-bound liposomes. Compression work performed by the colloidal probe to compress these liposome layers has also been calculated.

  12. Primate lens capsule elasticity assessed using Atomic Force Microscopy.

    PubMed

    Ziebarth, Noël M; Arrieta, Esdras; Feuer, William J; Moy, Vincent T; Manns, Fabrice; Parel, Jean-Marie

    2011-06-01

    The purpose of this project is to measure the elasticity of the human and non-human primate lens capsule at the microscopic scale using Atomic Force Microscopy (AFM). Elasticity measurements were performed using AFM on the excised anterior lens capsule from 9 cynomolgus monkey (5.9-8.0 years), 8 hamadryas baboon (2.8-10.1 years), and 18 human lenses (33-79 years). Anterior capsule specimens were obtained by performing a 5 mm continuous curvilinear capsulorhexis and collecting the resulting disk of capsular tissue. To remove the lens epithelial cells the specimen was soaked in 0.1% trypsin and 0.02% EDTA for 5 min, washed, and placed on a Petri dish and immersed in DMEM. Elasticity measurements of the capsule were performed with a laboratory-built AFM system custom designed for force measurements of ophthalmic tissues. The capsular specimens were probed with an AFM cantilever tip to produce force-indentation curves for each specimen. Young's modulus was calculated from the force-indentation curves using the model of Sneddon for a conical indenter. Young's modulus of elasticity was 20.1-131 kPa for the human lens capsule, 9.19-117 kPa for the cynomolgus lens capsule, and 13.1-62.4 kPa for the baboon lens capsule. Young's modulus increased significantly with age in humans (p = 0.03). The age range of the monkey and baboon samples was not sufficient to justify an analysis of age dependence. The capsule elasticity of young humans (<45 years) was not statistically different from that of the monkey and baboon. In humans, there is an increase in lens capsule stiffness at the microscale that could be responsible for an increase in lens capsule bulk stiffness.

  13. Model based control of dynamic atomic force microscope

    SciTech Connect

    Lee, Chibum; Salapaka, Srinivasa M.

    2015-04-15

    A model-based robust control approach is proposed that significantly improves imaging bandwidth for the dynamic mode atomic force microscopy. A model for cantilever oscillation amplitude and phase dynamics is derived and used for the control design. In particular, the control design is based on a linearized model and robust H{sub ∞} control theory. This design yields a significant improvement when compared to the conventional proportional-integral designs and verified by experiments.

  14. Model based control of dynamic atomic force microscope.

    PubMed

    Lee, Chibum; Salapaka, Srinivasa M

    2015-04-01

    A model-based robust control approach is proposed that significantly improves imaging bandwidth for the dynamic mode atomic force microscopy. A model for cantilever oscillation amplitude and phase dynamics is derived and used for the control design. In particular, the control design is based on a linearized model and robust H(∞) control theory. This design yields a significant improvement when compared to the conventional proportional-integral designs and verified by experiments.

  15. Development of eddy current microscopy for high resolution electrical conductivity imaging using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Nalladega, V.; Sathish, S.; Jata, K. V.; Blodgett, M. P.

    2008-07-01

    We present a high resolution electrical conductivity imaging technique based on the principles of eddy current and atomic force microscopy (AFM). An electromagnetic coil is used to generate eddy currents in an electrically conducting material. The eddy currents generated in the conducting sample are detected and measured with a magnetic tip attached to a flexible cantilever of an AFM. The eddy current generation and its interaction with the magnetic tip cantilever are theoretically modeled using monopole approximation. The model is used to estimate the eddy current force between the magnetic tip and the electrically conducting sample. The theoretical model is also used to choose a magnetic tip-cantilever system with appropriate magnetic field and spring constant to facilitate the design of a high resolution electrical conductivity imaging system. The force between the tip and the sample due to eddy currents is measured as a function of the separation distance and compared to the model in a single crystal copper. Images of electrical conductivity variations in a polycrystalline dual phase titanium alloy (Ti-6Al-4V) sample are obtained by scanning the magnetic tip-cantilever held at a standoff distance from the sample surface. The contrast in the image is explained based on the electrical conductivity and eddy current force between the magnetic tip and the sample. The spatial resolution of the eddy current imaging system is determined by imaging carbon nanofibers in a polymer matrix. The advantages, limitations, and applications of the technique are discussed.

  16. Note: Electrical resolution during conductive atomic force microscopy measurements under different environmental conditions and contact forces

    SciTech Connect

    Lanza, M.; Porti, M.; Nafria, M.; Aymerich, X.; Whittaker, E.; Hamilton, B.

    2010-10-15

    Conductive atomic force microscopy experiments on gate dielectrics in air, nitrogen, and UHV have been compared to evaluate the impact of the environment on topography and electrical measurements. In current images, an increase of the lateral resolution and a reduction of the conductivity were observed in N{sub 2} and, especially, in UHV (where current depends also on the contact force). Both effects were related to the reduction/elimination of the water layer between the tip and the sample in N{sub 2}/UHV. Therefore, since current measurements are very sensitive to environmental conditions, these factors must be taken into consideration when comparisons between several experiments are performed.

  17. Calibration of lateral force measurements in atomic force microscopy with a piezoresistive force sensor

    SciTech Connect

    Xie Hui; Vitard, Julien; Haliyo, Sinan; Regnier, Stephane

    2008-03-15

    We present here a method to calibrate the lateral force in the atomic force microscope. This method makes use of an accurately calibrated force sensor composed of a tipless piezoresistive cantilever and corresponding signal amplifying and processing electronics. Two ways of force loading with different loading points were compared by scanning the top and side edges of the piezoresistive cantilever. Conversion factors between the lateral force and photodiode signal using three types of atomic force microscope cantilevers with rectangular geometries (normal spring constants from 0.092 to 1.24 N/m and lateral stiffness from 10.34 to 101.06 N/m) were measured in experiments using the proposed method. When used properly, this method calibrates the conversion factors that are accurate to {+-}12.4% or better. This standard has less error than the commonly used method based on the cantilever's beam mechanics. Methods such of this allow accurate and direct conversion between lateral forces and photodiode signals without any knowledge of the cantilevers and the laser measuring system.

  18. A decade of piezoresponse force microscopy: progress, challenges, and opportunities.

    PubMed

    Kalinin, Sergei V; Rar, Andrei; Jesse, Stephen

    2006-12-01

    Coupling between electrical and mechanical phenomena is a near-universal characteristic of inorganic and biological systems alike, with examples ranging from piezoelectricity in ferroelectric perovskites to complex, electromechanical couplings in electromotor proteins in cellular membranes. Understanding electromechanical functionality in materials such as ferroelectric nanocrystals and thin films, relaxor ferroelectrics, and biosystems requires probing these properties on the nanometer level of individual grain, domain, or protein fibril. In the last decade, piezoresponse force microscopy (PFM) was established as a powerful tool for nanoscale imaging, spectroscopy, and manipulation of ferroelectric materials. Here, we present principles and recent advances in PFM, including vector and frequency-dependent imaging of piezoelectric materials, briefly review applications for ferroelectric materials, discuss prospects for electromechanical imaging of local crystallographic and molecular orientations and disorder, and summarize future challenges and opportunities for PFM emerging in the second decade since its invention. PMID:17186903

  19. Destabilization induced by electropermeabilization analyzed by atomic force microscopy.

    PubMed

    Chopinet, Louise; Roduit, Charles; Rols, Marie-Pierre; Dague, Etienne

    2013-09-01

    Electropermeabilization is a physical method that uses electric field pulses to deliver molecules into cells and tissues. Despite its increasing interest in clinics, little is known about plasma membrane destabilization process occurring during electropermeabilization. In this work, we took advantage of atomic force microscopy to directly visualize the consequences of electropermeabilization in terms of membrane reorganization and to locally measure the membrane elasticity. We visualized transient rippling of membrane surface and measured a decrease in membrane elasticity by 40%. Our results obtained both on fixed and living CHO cells give evidence of an inner effect affecting the entire cell surface that may be related to cytoskeleton destabilization. Thus, AFM appears as a useful tool to investigate basic process of electroporation on living cells in absence of any staining or cell preparation.

  20. Atomic-force microscopy of submicron films of electroactive polymer

    NASA Astrophysics Data System (ADS)

    Karamov, D. D.; Kornilov, V. M.; Lachinov, A. N.; Kraikin, V. A.; Ionova, I. A.

    2016-07-01

    Atomic-force microscopy is used to study the supramolecular structure of submicron films of electroactive thermally stable polymer (polydiphenylenephthalide (PDP)). It has been demonstrated that PDP films produced using centrifuging are solid homogeneous films with thicknesses down to several nanometers, which correspond to two or three monomolecular layers. The film volume is structurized at thicknesses greater than 100 nm. The study of the rheological properties of solutions used for film production yields a crossover point that separates the domains of strongly diluted and semidiluted solutions. A transition from the globular structure to the associate structure is observed in films that are produced using solutions with a boundary concentration. A model of the formation of polymer film that involves the presence of associates in the original solution is discussed.

  1. Molecular resolution imaging of macromolecular crystals by atomic force microscopy.

    PubMed Central

    Kuznetsov YuG; Malkin, A J; Land, T A; DeYoreo, J J; Barba, A P; Konnert, J; McPherson, A

    1997-01-01

    Atomic force microscopy (AFM) images at the molecular level have been obtained for a number of different protein and virus crystals. They can be utilized in some special cases to obtain information useful to crystal structure analyses by x-ray diffraction. In particular, questions of space group enantiomer, the packing of molecules within a unit cell, the number of molecules per asymmetric unit, and the dispositions of multiple molecules within the asymmetric unit may be resolved. In addition, because of the increasing sensitivity and resolution of the AFM technique, some molecular features of very large asymmetric units may be within reach. We describe here high-resolution studies, using AFM, to visualize individual molecules and viruses in their crystal lattices. These investigations included fungal lipase, lysozyme, thaumatin, canavalin, and satellite tobacco mosaic virus (STMV). Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 8 PMID:9129839

  2. Atomic force microscopy spring constant determination in viscous liquids.

    PubMed

    Pirzer, Tobias; Hugel, Thorsten

    2009-03-01

    The spring constant of cantilever in atomic force microscopy (AFM) is often calibrated from thermal noise spectra. Essential for accurate implementation of this "thermal noise method" is an appropriate fitting function and procedure. Here, we survey the commonly used fitting functions and examine their applicability in a range of environments. We find that viscous liquid environments are extremely problematic due to the frequency dependent nature of the damping coefficient. The deviations from the true spring constant were sometimes more than 100% when utilizing the fit routines built into the three investigated commercial AFM instruments; similar problems can arise with homebuilt AFMs. We discuss the reasons for this problem, especially the limits of the fitting process. Finally, we present a thermal noise based procedure and an improved fit function to determine the spring constant with AFMs in fluids of various viscosities. PMID:19334955

  3. Optical interference artifacts in contact atomic force microscopy images.

    PubMed

    Méndez-Vilas, A; González-Martin, M L; Nuevo, M J

    2002-08-01

    Atomic force microscopy images are usually affected by different kinds of artifacts due to either the microscope design and operation mode or external environmental factors. Optical interferences between the laser light reflected off the top of the cantilever and the light scattered by the surface in the same direction is one of the most frequent sources of height artifact in contact (and occasionally non-contact) images. They are present when imaging highly reflective surfaces, or even when imaging non-reflective materials deposited onto reflective ones. In this study interference patterns have been obtained with a highly polished stainless steel planchet. The influence of these artifacts in surface roughness measurements is discussed, and a semi-quantitative method based on the fast Fourier transform technique is proposed to remove the artifacts from the images. This method improves the results obtained by applying the usual flattening routines.

  4. Atomic force microscopy spring constant determination in viscous liquids

    SciTech Connect

    Pirzer, Tobias; Hugel, Thorsten

    2009-03-15

    The spring constant of cantilever in atomic force microscopy (AFM) is often calibrated from thermal noise spectra. Essential for accurate implementation of this 'thermal noise method' is an appropriate fitting function and procedure. Here, we survey the commonly used fitting functions and examine their applicability in a range of environments. We find that viscous liquid environments are extremely problematic due to the frequency dependent nature of the damping coefficient. The deviations from the true spring constant were sometimes more than 100% when utilizing the fit routines built into the three investigated commercial AFM instruments; similar problems can arise with homebuilt AFMs. We discuss the reasons for this problem, especially the limits of the fitting process. Finally, we present a thermal noise based procedure and an improved fit function to determine the spring constant with AFMs in fluids of various viscosities.

  5. A Decade of Piezoresponse Force Microscopy: Progress, Challenges, and Opportunities

    SciTech Connect

    Kalinin, Sergei V; Rar, Andrei; Jesse, Stephen

    2006-01-01

    Coupling between electrical and mechanical phenomena is a near-universal characteristic of inorganic and biological systems alike, with examples ranging from piezoelectricity in ferroelectric perovskites to complex, electromechanical couplings in electromotor proteins in cellular membranes. Understanding electromechanical functionality in materials such as ferroelectric nanocrystals and thin films, relaxor ferroelectrics, and biosystems requires probing these properties on the nanometer level of individual grain, domain, or protein fibril. In the last decade, piezoresponse force microscopy (PFM) was established as a powerful tool for nanoscale imaging, spectroscopy, and manipulation of ferroelectric materials. Here, we present principles and recent advances in PFM, including vector and frequency-dependent imaging of piezoelectric materials, briefly review applications for ferroelectric materials, discuss prospects for electromechanical imaging of local crystallographic and molecular orientations and disorder, and summarize future challenges and opportunities for PFM emerging in the second decade since its invention.

  6. Extremely sharp carbon nanocone probes for atomic force microscopy imaging

    NASA Astrophysics Data System (ADS)

    Chen, I.-Chen; Chen, Li-Han; Ye, Xiang-Rong; Daraio, Chiara; Jin, Sungho; Orme, Christine A.; Quist, Arjan; Lal, Ratnesh

    2006-04-01

    A simple and reliable catalyst patterning technique combined with electric-field-guided growth is utilized to synthesize a sharp and high-aspect-ratio carbon nanocone probe on a tipless cantilever for atomic force microscopy. A single carbon nanodot produced by an electron-beam-induced deposition serves as a convenient chemical etch mask for catalyst patterning, thus eliminating the need for complicated, resist-based, electron-beam lithography for a nanoprobe fabrication. A gradual, sputtering-induced size reduction and eventual removal of the catalyst particle at the probe tip during electric-field-guided growth creates a sharp probe with a tip radius of only a few nanometers. These fabrication processes are amenable for the wafer-scale synthesis of multiple probes. High resolution imaging of three-dimensional features and deep trenches, and mechanical durability enabling continuous operation for many hours without noticeable image deterioration have been demonstrated.

  7. Nanoscale imaging of Bacillus thuringiensis flagella using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Gillis, Annika; Dupres, Vincent; Delestrait, Guillaume; Mahillon, Jacques; Dufrêne, Yves F.

    2012-02-01

    Because bacterial flagella play essential roles in various processes (motility, adhesion, host interactions, secretion), studying their expression in relation to function is an important challenge. Here, we use atomic force microscopy (AFM) to gain insight into the nanoscale surface properties of two wild-type and four mutant strains of Bacillus thuringiensis exhibiting various levels of flagellation. We show that, unlike AFM in liquid, AFM in air is a simple and reliable approach to observe the morphological details of the bacteria, and to quantify the density and dimensions of their flagella. We found that the amount of flagella expressed by the six strains, as observed at the nanoscale, correlates with their microscopic swarming motility. These observations provide novel information on flagella expression in Gram-positive bacteria and demonstrate the power of AFM in genetic studies for the fast assessment of the phenotypic characteristics of bacterial strains altered in cell surface appendages.Because bacterial flagella play essential roles in various processes (motility, adhesion, host interactions, secretion), studying their expression in relation to function is an important challenge. Here, we use atomic force microscopy (AFM) to gain insight into the nanoscale surface properties of two wild-type and four mutant strains of Bacillus thuringiensis exhibiting various levels of flagellation. We show that, unlike AFM in liquid, AFM in air is a simple and reliable approach to observe the morphological details of the bacteria, and to quantify the density and dimensions of their flagella. We found that the amount of flagella expressed by the six strains, as observed at the nanoscale, correlates with their microscopic swarming motility. These observations provide novel information on flagella expression in Gram-positive bacteria and demonstrate the power of AFM in genetic studies for the fast assessment of the phenotypic characteristics of bacterial strains altered in

  8. A novel self-sensing technique for tapping-mode atomic force microscopy

    SciTech Connect

    Ruppert, Michael G.; Moheimani, S. O. Reza

    2013-12-15

    This work proposes a novel self-sensing tapping-mode atomic force microscopy operation utilizing charge measurement. A microcantilever coated with a single piezoelectric layer is simultaneously used for actuation and deflection sensing. The cantilever can be batch fabricated with existing micro electro mechanical system processes. The setup enables the omission of the optical beam deflection technique which is commonly used to measure the cantilever oscillation amplitude. Due to the high amount of capacitive feedthrough in the measured charge signal, a feedforward control technique is employed to increase the dynamic range from less than 1 dB to approximately 35 dB. Experiments show that the conditioned charge signal achieves excellent signal-to-noise ratio and can therefore be used as a feedback signal for atomic force microscopy imaging.

  9. A novel self-sensing technique for tapping-mode atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Ruppert, Michael G.; Moheimani, S. O. Reza

    2013-12-01

    This work proposes a novel self-sensing tapping-mode atomic force microscopy operation utilizing charge measurement. A microcantilever coated with a single piezoelectric layer is simultaneously used for actuation and deflection sensing. The cantilever can be batch fabricated with existing micro electro mechanical system processes. The setup enables the omission of the optical beam deflection technique which is commonly used to measure the cantilever oscillation amplitude. Due to the high amount of capacitive feedthrough in the measured charge signal, a feedforward control technique is employed to increase the dynamic range from less than 1 dB to approximately 35 dB. Experiments show that the conditioned charge signal achieves excellent signal-to-noise ratio and can therefore be used as a feedback signal for atomic force microscopy imaging.

  10. Distinguishing magnetic and electrostatic interactions by a Kelvin probe force microscopy–magnetic force microscopy combination

    PubMed Central

    Jaafar, Miriam; Iglesias-Freire, Oscar; Serrano-Ramón, Luis; Ibarra, Manuel Ricardo; de Teresa, Jose Maria

    2011-01-01

    Summary The most outstanding feature of scanning force microscopy (SFM) is its capability to detect various different short and long range interactions. In particular, magnetic force microscopy (MFM) is used to characterize the domain configuration in ferromagnetic materials such as thin films grown by physical techniques or ferromagnetic nanostructures. It is a usual procedure to separate the topography and the magnetic signal by scanning at a lift distance of 25–50 nm such that the long range tip–sample interactions dominate. Nowadays, MFM is becoming a valuable technique to detect weak magnetic fields arising from low dimensional complex systems such as organic nanomagnets, superparamagnetic nanoparticles, carbon-based materials, etc. In all these cases, the magnetic nanocomponents and the substrate supporting them present quite different electronic behavior, i.e., they exhibit large surface potential differences causing heterogeneous electrostatic interaction between the tip and the sample that could be interpreted as a magnetic interaction. To distinguish clearly the origin of the tip–sample forces we propose to use a combination of Kelvin probe force microscopy (KPFM) and MFM. The KPFM technique allows us to compensate in real time the electrostatic forces between the tip and the sample by minimizing the electrostatic contribution to the frequency shift signal. This is a great challenge in samples with low magnetic moment. In this work we studied an array of Co nanostructures that exhibit high electrostatic interaction with the MFM tip. Thanks to the use of the KPFM/MFM system we were able to separate the electric and magnetic interactions between the tip and the sample. PMID:22003461

  11. Study of the Depletion Force using Total Internal Reflection Microscopy

    NASA Astrophysics Data System (ADS)

    Walz, John Y.

    1998-03-01

    The depletion force between colloidal particles arises in dispersions in which a nonadsorbing species (e.g., polymer, micelles, or other small particles) is present in solution with the particles. When the separation distance between two particles becomes sufficiently small, the polymer is excluded from the gap, producing a concentration difference between the gap and bulk solution. An osmotic pressure difference is created, such that the higher pressure in the bulk creates a net attraction between the particles. Our research has focused on the depletion effect produced by nonadsorbing polyelectrolyte species. We first developed a force-balance model, in which the net interparticle force is calculated as the sum of the forces produced by the surrounding polyelectrolyte species. This model showed that in addition to the attractive depletion force, the interparticle force can actually be repulsive at larger separations, resulting from an order of the nonadsorbing species. In addition, both the magnitude and range of the force in charged systems was substantially larger than that in nonionic systems. We then performed experimental measurement of the force using the optical technique of total internal reflection microscopy (TIRM). Here, the net interaction energy between a single colloidal particle and flat plate was measured in aqueous solutions containing the nonadsorbing species. In TIRM, an evanescent wave is formed at the plate/fluid interface using a visible laser beam. The particle scatters the light from this wave (termed frustrated total internal reflection), and because of the exponentially- decaying wave intensity, the scattering intensity varies exponentially with separation distance. Measurement of this intensity thus provides a sensitive method for monitoring the separation distance of the particle as it undergoes Brownian motion. If the scattering intensity is measured for a sufficiently long period of time, a probability distribution of separation

  12. Enhanced efficiency in the excitation of higher modes for atomic force microscopy and mechanical sensors operated in liquids

    SciTech Connect

    Penedo, M. Hormeño, S.; Fernández-Martínez, I.; Luna, M.; Briones, F.; Raman, A.

    2014-10-27

    Recent developments in dynamic Atomic Force Microscopy where several eigenmodes are simultaneously excited in liquid media are proving to be an excellent tool in biological studies. Despite its relevance, the search for a reliable, efficient, and strong cantilever excitation method is still in progress. Herein, we present a theoretical modeling and experimental results of different actuation methods compatible with the operation of Atomic Force Microscopy in liquid environments: ideal acoustic, homogeneously distributed force, distributed applied torque (MAC Mode™), photothermal and magnetostrictive excitation. From the analysis of the results, it can be concluded that magnetostriction is the strongest and most efficient technique for higher eigenmode excitation when using soft cantilevers in liquid media.

  13. Introduction to Atomic Force Microscopy (AFM) in Biology.

    PubMed

    Kreplak, Laurent

    2016-01-01

    The atomic force microscope (AFM) has the unique capability of imaging biological samples with molecular resolution in buffer solution over a wide range of time scales from milliseconds to hours. In addition to providing topographical images of surfaces with nanometer- to angstrom-scale resolution, forces between single molecules and mechanical properties of biological samples can be investigated from the nano-scale to the micro-scale. Importantly, the measurements are made in buffer solutions, allowing biological samples to "stay alive" within a physiological-like environment while temporal changes in structure are measured-e.g., before and after addition of chemical reagents. These qualities distinguish AFM from conventional imaging techniques of comparable resolution, e.g., electron microscopy (EM). This unit provides an introduction to AFM on biological systems and describes specific examples of AFM on proteins, cells, and tissues. The physical principles of the technique and methodological aspects of its practical use and applications are also described. © 2016 by John Wiley & Sons, Inc. PMID:27479503

  14. Tribology studies of organic thin films by scanning force microscopy

    SciTech Connect

    Bar, G.; Rubin, S.; Parikh, A.N.; Swanson, B.I.; Zawodzinski, T.A.

    1996-06-01

    The use of organic thin films as lubricants on solid surfaces is important in many modern technologies including magnetic storage and micromachines. Langmuir-Blodgett (LB) films and self-assembled monolayers (SAMs) are attractive candidates for lubricant layers and for model studies of lubrication because of their strong adsorption to the surface. The recent interest on the properties of LB films and SAMs has been also motivated by their potential applications in sensors, non-linear optical devices, lithography and microelectronics. Using the micro-contact printing method the authors prepared patterned SAMs consisting of methyl-terminated alkanethiols of different chain lengths. The samples were characterized using lateral force microscopy (LFM) and the force modulation technique (FMT). In general, higher friction is observed over the short chain regions than over the long chain regions when a low or moderate load is applied to the SFM tip. For such cases the high friction (short chain) regions are also ``softer`` as measured by FMT. A high loads, a reversal of the image contrast is observed and the short chain regions show a lower friction than the long chain regions. This image contrast is reversible upon reduction of the applied load.

  15. Single-Crystal Diamond Nanowire Tips for Ultrasensitive Force Microscopy.

    PubMed

    Tao, Y; Degen, C L

    2015-12-01

    We report the fabrication, integration, and assessment of sharp diamond tips for ultrasensitive force microscopy experiments. Two types of tips, corresponding to the upper and lower halves of a diamond nanowire, were fabricated by top-down plasma etching from a single-crystalline substrate. The lower, surface-attached halves can be directly integrated into lithographically defined nanostructures, like cantilevers. The upper, detachable halves result in diamond nanowires with a tunable diameter (50-500 nm) and lengths of a few microns. Tip radii were around 10 nm and tip apex angles around 15°. We demonstrate the integration of diamond nanowires for use as scanning tips onto ultrasensitive pendulum-style silicon cantilevers. We find the noncontact friction and frequency jitter to be exceptionally low, with no degradation in the intrinsic mechanical quality factor (Q ≈ 130,000) down to tip-to-surface distances of about 10 nm. Our results are an encouraging step toward further improvement of the sensitivity and resolution of force-detected magnetic resonance imaging. PMID:26517172

  16. On mapping subangstrom electron clouds with force microscopy.

    PubMed

    Wright, C Alan; Solares, Santiago D

    2011-11-01

    In 2004 Hembacher et al. (Science 2004, 305, 380-383) reported simultaneous higher-harmonics atomic force mocroscopy (AFM)/scanning tunneling microscopy (STM) images acquired while scanning a graphite surface with a tungsten tip. They interpreted the observed subatomic features in the AFM images as the signature of lobes of increased electron density at the tungsten tip apex. Although these intriguing images have stirred controversy, an in-depth theoretical feasibility study has not yet been produced. Here we report on the development of a method for simulating higher harmonics AFM images and its application to the same system. Our calculations suggest that four lobes of increased electron density are expected to be present at a W(001) tip apex atom and that the corresponding higher harmonics AFM images of graphite can exhibit 4-fold symmetry features. Despite these promising results, open questions remain since the calculated amplitudes of the higher harmonics generated by the short-range forces are on the order of hundredths of picometers, leading to very small corrugations in the theoretical images. Additionally, the complex, intermittent nature of the tip-sample interaction, which causes constant readjustment of the tip and sample orbitals as the tip approaches and retracts from the surface, prevents a direct quantitative connection between the electron density and the AFM image features.

  17. Cross-talk compensation in atomic force microscopy.

    PubMed

    Onal, Cagdas D; Sümer, Bilsay; Sitti, Metin

    2008-10-01

    In this work, calibration and correction of cross-talk in atomic force microscopy (AFM) is demonstrated. Several reasons and effects of this inherent problem on experimental results are discussed. We propose a general procedure that can be used on most AFM systems to compensate for cross-talk on the cantilever bending and twisting signals. The method utilizes two initial experiments on a flat surface to achieve an affine transformation between the measured signals and the actual signals. Using this transformation directly on the voltage signals allows us to remove the detrimental effects of cross-talk on AFM-based force measurement experiments. The achieved transformation matrix can be turned into a simple circuit and applied online, by users who have access to the raw signals in the AFM head. As a case study, a lateral deflection based mechanical characterization test for a poly(methyl methacrylate) microfiber that is suspended on a trench is investigated in terms of the effectiveness of the cross-talk compensation.

  18. Cross-talk compensation in atomic force microscopy

    SciTech Connect

    Onal, Cagdas D.; Suemer, Bilsay; Sitti, Metin

    2008-10-15

    In this work, calibration and correction of cross-talk in atomic force microscopy (AFM) is demonstrated. Several reasons and effects of this inherent problem on experimental results are discussed. We propose a general procedure that can be used on most AFM systems to compensate for cross-talk on the cantilever bending and twisting signals. The method utilizes two initial experiments on a flat surface to achieve an affine transformation between the measured signals and the actual signals. Using this transformation directly on the voltage signals allows us to remove the detrimental effects of cross-talk on AFM-based force measurement experiments. The achieved transformation matrix can be turned into a simple circuit and applied online, by users who have access to the raw signals in the AFM head. As a case study, a lateral deflection based mechanical characterization test for a poly(methyl methacrylate) microfiber that is suspended on a trench is investigated in terms of the effectiveness of the cross-talk compensation.

  19. Segmented nanofibers of spider dragline silk: atomic force microscopy and single-molecule force spectroscopy.

    PubMed

    Oroudjev, E; Soares, J; Arcdiacono, S; Thompson, J B; Fossey, S A; Hansma, H G

    2002-04-30

    Despite its remarkable materials properties, the structure of spider dragline silk has remained unsolved. Results from two probe microscopy techniques provide new insights into the structure of spider dragline silk. A soluble synthetic protein from dragline silk spontaneously forms nanofibers, as observed by atomic force microscopy. These nanofibers have a segmented substructure. The segment length and amino acid sequence are consistent with a slab-like shape for individual silk protein molecules. The height and width of nanofiber segments suggest a stacking pattern of slab-like molecules in each nanofiber segment. This stacking pattern produces nano-crystals in an amorphous matrix, as observed previously by NMR and x-ray diffraction of spider dragline silk. The possible importance of nanofiber formation to native silk production is discussed. Force spectra for single molecules of the silk protein demonstrate that this protein unfolds through a number of rupture events, indicating a modular substructure within single silk protein molecules. A minimal unfolding module size is estimated to be around 14 nm, which corresponds to the extended length of a single repeated module, 38 amino acids long. The structure of this spider silk protein is distinctly different from the structures of other proteins that have been analyzed by single-molecule force spectroscopy, and the force spectra show correspondingly novel features.

  20. Physical mechanisms of megahertz vibrations and nonlinear detection in ultrasonic force and related microscopies

    SciTech Connect

    Bosse, J. L.; Huey, B. D.; Tovee, P. D.; Kolosov, O. V.

    2014-04-14

    Use of high frequency (HF) vibrations at MHz frequencies in Atomic Force Microscopy (AFM) advanced nanoscale property mapping to video rates, allowed use of cantilever dynamics for mapping nanomechanical properties of stiff materials, sensing μs time scale phenomena in nanostructures, and enabled detection of subsurface features with nanoscale resolution. All of these methods critically depend on the generally poor characterized HF behaviour of AFM cantilevers in contact with a studied sample, spatial and frequency response of piezotransducers, and transfer of ultrasonic vibrations between the probe and a specimen. Focusing particularly on Ultrasonic Force Microscopy (UFM), this work is also applicable to waveguide UFM, heterodyne force microscopy, and near-field holographic microscopy, all methods that exploit nonlinear tip-surface force interactions at high frequencies. Leveraging automated multidimensional measurements, spectroscopic UFM (sUFM) is introduced to investigate a range of common experimental parameters, including piezotransducer excitation frequency, probed position, ultrasonic amplitude, cantilever geometry, spring constant, and normal force. Consistent with studies of influence of each of these factors, the data-rich sUFM signatures allow efficient optimization of ultrasonic-AFM based measurements, leading to best practices recommendations of using longer cantilevers with lower fundamental resonance, while at the same time increasing the central frequency of HF piezo-actuators, and only comparing results within areas on the order of few μm{sup 2} unless calibrated directly or compared with in-the-imaged area standards. Diverse materials such as Si, Cr, and photoresist are specifically investigated. This work thereby provides essential insight into the reliable use of MHz vibrations with AFM and provides direct evidence substantiating phenomena such as sensitivity to adhesion, diminished friction for certain ultrasonic conditions, and the

  1. Atomic species identification at the (101) anatase surface by simultaneous scanning tunnelling and atomic force microscopy

    PubMed Central

    Stetsovych, Oleksandr; Todorović, Milica; Shimizu, Tomoko K.; Moreno, César; Ryan, James William; León, Carmen Pérez; Sagisaka, Keisuke; Palomares, Emilio; Matolín, Vladimír; Fujita, Daisuke; Perez, Ruben; Custance, Oscar

    2015-01-01

    Anatase is a pivotal material in devices for energy-harvesting applications and catalysis. Methods for the accurate characterization of this reducible oxide at the atomic scale are critical in the exploration of outstanding properties for technological developments. Here we combine atomic force microscopy (AFM) and scanning tunnelling microscopy (STM), supported by first-principles calculations, for the simultaneous imaging and unambiguous identification of atomic species at the (101) anatase surface. We demonstrate that dynamic AFM-STM operation allows atomic resolution imaging within the material's band gap. Based on key distinguishing features extracted from calculations and experiments, we identify candidates for the most common surface defects. Our results pave the way for the understanding of surface processes, like adsorption of metal dopants and photoactive molecules, that are fundamental for the catalytic and photovoltaic applications of anatase, and demonstrate the potential of dynamic AFM-STM for the characterization of wide band gap materials. PMID:26118408

  2. Force interactions between magnetite, silica, and bentonite studied with atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Dobryden, I.; Potapova, E.; Holmgren, A.; Weber, H.; Hedlund, J.; Almqvist, N.

    2015-04-01

    Iron ore pellets consist of variety of mineral particles and are an important refined product used in steel manufacturing. Production of high-quality pellets requires good understanding of interactions between different constituents, such as magnetite, gangue residues, bentonite, and additives. Much research has been reported on magnetite, silica, and bentonite surface properties and their effect on pellet strength but more scant with a focus on a fundamental particle-particle interaction. To probe such particle interaction, atomic force microscopy (AFM) using colloidal probe technique has proven to be a suitable tool. In this work, the measurements were performed between magnetite-magnetite, bentonite-magnetite, silica-bentonite, and silica-magnetite particles in 1 mM CaCl2 solution at various pH values. The interaction character, i.e., repulsion or attraction, was determined by measuring and analyzing AFM force curves. The observed quantitative changes in interaction forces were in good agreement with the measured zeta-potentials for the particles at the same experimental conditions. Particle aggregation was studied by measuring the adhesion force. Absolute values of adhesion forces for different systems could not be compared due to the difference in particle size and contact geometry. Therefore, the relative change of adhesion force between pH 6 and 10 was used for comparison. The adhesion force decreased for the magnetite-magnetite and bentonite-silica systems and slightly increased for the magnetite-bentonite system at pH 10 as compared to pH 6, whereas a pronounced decrease in adhesion force was observed in the magnetite-silica system. Thus, the presence of silica particles on the magnetite surface could have a negative impact on the interaction between magnetite and bentonite in balling due to the reduction of the adhesion force.

  3. Multidimensional traction force microscopy reveals out-of-plane rotational moments about focal adhesions.

    PubMed

    Legant, Wesley R; Choi, Colin K; Miller, Jordan S; Shao, Lin; Gao, Liang; Betzig, Eric; Chen, Christopher S

    2013-01-15

    Recent methods have revealed that cells on planar substrates exert both shear (in-plane) and normal (out-of-plane) tractions against the extracellular matrix (ECM). However, the location and origin of the normal tractions with respect to the adhesive and cytoskeletal elements of cells have not been elucidated. We developed a high-spatiotemporal-resolution, multidimensional (2.5D) traction force microscopy to measure and model the full 3D nature of cellular forces on planar 2D surfaces. We show that shear tractions are centered under elongated focal adhesions whereas upward and downward normal tractions are detected on distal (toward the cell edge) and proximal (toward the cell body) ends of adhesions, respectively. Together, these forces produce significant rotational moments about focal adhesions in both protruding and retracting peripheral regions. Temporal 2.5D traction force microscopy analysis of migrating and spreading cells shows that these rotational moments are highly dynamic, propagating outward with the leading edge of the cell. Finally, we developed a finite element model to examine how rotational moments could be generated about focal adhesions in a thin lamella. Our model suggests that rotational moments can be generated largely via shear lag transfer to the underlying ECM from actomyosin contractility applied at the intracellular surface of a rigid adhesion of finite thickness. Together, these data demonstrate and probe the origin of a previously unappreciated multidimensional stress profile associated with adhesions and highlight the importance of new approaches to characterize cellular forces. PMID:23277584

  4. Three-dimensional atomic force microscopy: interaction force vector by direct observation of tip trajectory.

    PubMed

    Sigdel, Krishna P; Grayer, Justin S; King, Gavin M

    2013-11-13

    The prospect of a robust three-dimensional atomic force microscope (AFM) holds significant promise in nanoscience. Yet, in conventional AFM, the tip-sample interaction force vector is not directly accessible. We scatter a focused laser directly off an AFM tip apex to rapidly and precisely measure the tapping tip trajectory in three-dimensional space. This data also yields three-dimensional cantilever spring constants, effective masses, and hence, the tip-sample interaction force components via Newton's second law. Significant lateral forces representing 49 and 13% of the normal force (Fz = 152 ± 17 pN) were observed in common tapping mode conditions as a silicon tip intermittently contacted a glass substrate in aqueous solution; as a consequence, the direction of the force vector tilted considerably more than expected. When addressing the surface of a lipid bilayer, the behavior of the force components differed significantly from that observed on glass. This is attributed to the lateral mobility of the lipid membrane coupled with its elastic properties. Direct access to interaction components Fx, Fy, and Fz provides a more complete view of tip dynamics that underlie force microscope operation and can form the foundation of a three-dimensional AFM in a plurality of conditions.

  5. Computational model for noncontact atomic force microscopy: energy dissipation of cantilever.

    PubMed

    Senda, Yasuhiro; Blomqvist, Janne; Nieminen, Risto M

    2016-09-21

    We propose a computational model for noncontact atomic force microscopy (AFM) in which the atomic force between the cantilever tip and the surface is calculated using a molecular dynamics method, and the macroscopic motion of the cantilever is modeled by an oscillating spring. The movement of atoms in the tip and surface is connected with the oscillating spring using a recently developed coupling method. In this computational model, the oscillation energy is dissipated, as observed in AFM experiments. We attribute this dissipation to the hysteresis and nonconservative properties of the interatomic force that acts between the atoms in the tip and sample surface. The dissipation rate strongly depends on the parameters used in the computational model. PMID:27420398

  6. Computational model for noncontact atomic force microscopy: energy dissipation of cantilever.

    PubMed

    Senda, Yasuhiro; Blomqvist, Janne; Nieminen, Risto M

    2016-09-21

    We propose a computational model for noncontact atomic force microscopy (AFM) in which the atomic force between the cantilever tip and the surface is calculated using a molecular dynamics method, and the macroscopic motion of the cantilever is modeled by an oscillating spring. The movement of atoms in the tip and surface is connected with the oscillating spring using a recently developed coupling method. In this computational model, the oscillation energy is dissipated, as observed in AFM experiments. We attribute this dissipation to the hysteresis and nonconservative properties of the interatomic force that acts between the atoms in the tip and sample surface. The dissipation rate strongly depends on the parameters used in the computational model.

  7. Drive-amplitude-modulation atomic force microscopy: From vacuum to liquids

    PubMed Central

    Jaafar, Miriam; Cuenca, Mariano; Melcher, John; Raman, Arvind

    2012-01-01

    Summary We introduce drive-amplitude-modulation atomic force microscopy as a dynamic mode with outstanding performance in all environments from vacuum to liquids. As with frequency modulation, the new mode follows a feedback scheme with two nested loops: The first keeps the cantilever oscillation amplitude constant by regulating the driving force, and the second uses the driving force as the feedback variable for topography. Additionally, a phase-locked loop can be used as a parallel feedback allowing separation of the conservative and nonconservative interactions. We describe the basis of this mode and present some examples of its performance in three different environments. Drive-amplutide modulation is a very stable, intuitive and easy to use mode that is free of the feedback instability associated with the noncontact-to-contact transition that occurs in the frequency-modulation mode. PMID:22563531

  8. Computational model for noncontact atomic force microscopy: energy dissipation of cantilever

    NASA Astrophysics Data System (ADS)

    Senda, Yasuhiro; Blomqvist, Janne; Nieminen, Risto M.

    2016-09-01

    We propose a computational model for noncontact atomic force microscopy (AFM) in which the atomic force between the cantilever tip and the surface is calculated using a molecular dynamics method, and the macroscopic motion of the cantilever is modeled by an oscillating spring. The movement of atoms in the tip and surface is connected with the oscillating spring using a recently developed coupling method. In this computational model, the oscillation energy is dissipated, as observed in AFM experiments. We attribute this dissipation to the hysteresis and nonconservative properties of the interatomic force that acts between the atoms in the tip and sample surface. The dissipation rate strongly depends on the parameters used in the computational model.

  9. Localization and force analysis at the single virus particle level using atomic force microscopy

    SciTech Connect

    Liu, Chih-Hao; Horng, Jim-Tong; Chang, Jeng-Shian; Hsieh, Chung-Fan; Tseng, You-Chen; Lin, Shiming

    2012-01-06

    Highlights: Black-Right-Pointing-Pointer Localization of single virus particle. Black-Right-Pointing-Pointer Force measurements. Black-Right-Pointing-Pointer Force mapping. -- Abstract: Atomic force microscopy (AFM) is a vital instrument in nanobiotechnology. In this study, we developed a method that enables AFM to simultaneously measure specific unbinding force and map the viral glycoprotein at the single virus particle level. The average diameter of virus particles from AFM images and the specificity between the viral surface antigen and antibody probe were integrated to design a three-stage method that sets the measuring area to a single virus particle before obtaining the force measurements, where the influenza virus was used as the object of measurements. Based on the purposed method and performed analysis, several findings can be derived from the results. The mean unbinding force of a single virus particle can be quantified, and no significant difference exists in this value among virus particles. Furthermore, the repeatability of the proposed method is demonstrated. The force mapping images reveal that the distributions of surface viral antigens recognized by antibody probe were dispersed on the whole surface of individual virus particles under the proposed method and experimental criteria; meanwhile, the binding probabilities are similar among particles. This approach can be easily applied to most AFM systems without specific components or configurations. These results help understand the force-based analysis at the single virus particle level, and therefore, can reinforce the capability of AFM to investigate a specific type of viral surface protein and its distributions.

  10. Development of Tuning Fork Based Probes for Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Jalilian, Romaneh; Yazdanpanah, Mehdi M.; Torrez, Neil; Alizadeh, Amirali; Askari, Davood

    2014-03-01

    This article reports on the development of tuning fork-based AFM/STM probes in NaugaNeedles LLC for use in atomic force microscopy. These probes can be mounted on different carriers per customers' request. (e.g., RHK carrier, Omicron carrier, and tuning fork on a Sapphire disk). We are able to design and engineer tuning forks on any type of carrier used in the market. We can attach three types of tips on the edge of a tuning fork prong (i.e., growing Ag2Ga nanoneedles at any arbitrary angle, cantilever of AFM tip, and tungsten wire) with lengths from 100-500 μm. The nanoneedle is located vertical to the fork. Using a suitable insulation and metallic coating, we can make QPlus sensors that can detect tunneling current during the AFM scan. To make Qplus sensors, the entire quartz fork will be coated with an insulating material, before attaching the nanoneedle. Then, the top edge of one prong is coated with a thin layer of conductive metal and the nanoneedle is attached to the fork end of the metal coated prong. The metal coating provides electrical connection to the tip for tunneling current readout and to the electrodes and used to read the QPlus current. Since the amount of mass added to the fork is minimal, the resonance frequency spectrum does not change and still remains around 32.6 KHz and the Q factor is around 1,200 in ambient condition. These probes can enhance the performance of tuning fork based atomic microscopy.

  11. Long-tip high-speed atomic force microscopy for nanometer-scale imaging in live cells

    PubMed Central

    Shibata, Mikihiro; Uchihashi, Takayuki; Ando, Toshio; Yasuda, Ryohei

    2015-01-01

    Visualization of morphological dynamics of live cells with nanometer resolution under physiological conditions is highly desired, but challenging. It has been demonstrated that high-speed atomic force microscopy is a powerful technique for visualizing dynamics of biomolecules under physiological conditions. However, application of high-speed atomic force microscopy for imaging larger objects such as live mammalian cells has been complicated because of the collision between the cantilever and samples. Here, we demonstrate that attaching an extremely long (~3 μm) and thin (~5 nm) tip by amorphous carbon to the cantilever allows us to image the surface structure of live cells with the spatiotemporal resolution of nanometers and seconds. We demonstrate that long-tip high-speed atomic force microscopy is capable of imaging morphogenesis of filopodia, membrane ruffles, pit formation, and endocytosis in COS-7, HeLa cells and hippocampal neurons. PMID:25735540

  12. Long-tip high-speed atomic force microscopy for nanometer-scale imaging in live cells

    NASA Astrophysics Data System (ADS)

    Shibata, Mikihiro; Uchihashi, Takayuki; Ando, Toshio; Yasuda, Ryohei

    2015-03-01

    Visualization of morphological dynamics of live cells with nanometer resolution under physiological conditions is highly desired, but challenging. It has been demonstrated that high-speed atomic force microscopy is a powerful technique for visualizing dynamics of biomolecules under physiological conditions. However, application of high-speed atomic force microscopy for imaging larger objects such as live mammalian cells has been complicated because of the collision between the cantilever and samples. Here, we demonstrate that attaching an extremely long (~3 μm) and thin (~5 nm) tip by amorphous carbon to the cantilever allows us to image the surface structure of live cells with the spatiotemporal resolution of nanometers and seconds. We demonstrate that long-tip high-speed atomic force microscopy is capable of imaging morphogenesis of filopodia, membrane ruffles, pit formation, and endocytosis in COS-7, HeLa cells and hippocampal neurons.

  13. The effect of adhesion on the contact radius in atomic force microscopy indentation.

    PubMed

    Sirghi, L; Rossi, F

    2009-09-01

    The effect of adhesion on nanoscale indentation experiments makes the interpretation of force-displacement curves acquired in these experiments very difficult. The indentation force results from the addition of adhesive and elastic forces at the indenter-sample contact. The evolution of the two forces during the indentation is determined by the variation of the indenter-sample contact radius. In the present work the variation of contact radius during atomic force microscopy (AFM) indentation of elastic and adhesive samples with conical indenters (AFM tips) is indirectly determined by measurements of the contact dynamic stiffness. For weak sample deformations, the contact radius is determined mainly by the adhesion force and indenter apex radius. For strong sample deformations, the contact radius increases linearly with the increase of the indenter displacement, the slope of this linear dependence being in agreement with Sneddon's theory of indentation (Sneddon 1965 Int. J. Eng. Sci. 3 47). Based on these results, a theoretical expression of indentation force dependence on displacement is found. This expression allows for determination of the thermodynamic work of adhesion at the indenter-sample interface and the sample elasticity modulus.

  14. Novel Combination of Atomic Force Microscopy and Epifluorescence Microscopy for Visualization of Leaching Bacteria on Pyrite▿

    PubMed Central

    Mangold, Stefanie; Harneit, Kerstin; Rohwerder, Thore; Claus, Günter; Sand, Wolfgang

    2008-01-01

    Bioleaching of metal sulfides is an interfacial process comprising the interactions of attached bacterial cells and bacterial extracellular polymeric substances with the surface of a mineral sulfide. Such processes and the associated biofilms can be investigated at high spatial resolution using atomic force microscopy (AFM). Therefore, we visualized biofilms of the meso-acidophilic leaching bacterium Acidithiobacillus ferrooxidans strain A2 on the metal sulfide pyrite with a newly developed combination of AFM with epifluorescence microscopy (EFM). This novel system allowed the imaging of the same sample location with both instruments. The pyrite sample, as fixed on a shuttle stage, was transferred between AFM and EFM devices. By staining the bacterial DNA with a specific fluorescence dye, bacterial cells were labeled and could easily be distinguished from other topographic features occurring in the AFM image. AFM scanning in liquid caused deformation and detachment of cells, but scanning in air had no effect on cell integrity. In summary, we successfully demonstrate that the new microscopic system was applicable for visualizing bioleaching samples. Moreover, the combination of AFM and EFM in general seems to be a powerful tool for investigations of biofilms on opaque materials and will help to advance our knowledge of biological interfacial processes. In principle, the shuttle stage can be transferred to additional instruments, and combinations of AFM and EFM with other surface-analyzing devices can be proposed. PMID:18039818

  15. Carrier density distribution in silicon nanowires investigated by scanning thermal microscopy and Kelvin probe force microscopy.

    PubMed

    Wielgoszewski, Grzegorz; Pałetko, Piotr; Tomaszewski, Daniel; Zaborowski, Michał; Jóźwiak, Grzegorz; Kopiec, Daniel; Gotszalk, Teodor; Grabiec, Piotr

    2015-12-01

    The use of scanning thermal microscopy (SThM) and Kelvin probe force microscopy (KPFM) to investigate silicon nanowires (SiNWs) is presented. SThM allows imaging of temperature distribution at the nanoscale, while KPFM images the potential distribution with AFM-related ultra-high spatial resolution. Both techniques are therefore suitable for imaging the resistance distribution. We show results of experimental examination of dual channel n-type SiNWs with channel width of 100 nm, while the channel was open and current was flowing through the SiNW. To investigate the carrier distribution in the SiNWs we performed SThM and KPFM scans. The SThM results showed non-symmetrical temperature distribution along the SiNWs with temperature maximum shifted towards the contact of higher potential. These results corresponded to those expressed by the distribution of potential gradient along the SiNWs, obtained using the KPFM method. Consequently, non-uniform distribution of resistance was shown, being a result of non-uniform carrier density distribution in the structure and showing the pinch-off effect. Last but not least, the results were also compared with results of finite-element method modeling.

  16. Spectral analysis of irregular roughness artifacts measured by atomic force microscopy and laser scanning microscopy.

    PubMed

    Chen, Yuhang; Luo, Tingting; Ma, Chengfu; Huang, Wenhao; Gao, Sitian

    2014-12-01

    Atomic force microscopy (AFM) and laser scanning microscopy (LSM) measurements on a series of specially designed roughness artifacts were performed and the results characterized by spectral analysis. As demonstrated by comparisons, both AFM and LSM can image the complex structures with high resolution and fidelity. When the surface autocorrelation length increases from 200 to 500 nm, the cumulative power spectral density spectra of the design, AFM and LSM data reach a better agreement with each other. The critical wavelength of AFM characterization is smaller than that of LSM, and the gap between the measured and designed critical wavelengths is reduced with an increase in the surface autocorrelation length. Topography measurements of surfaces with a near zero or negatively skewed height distribution were determined to be accurate. However, obvious discrepancies were found for surfaces with a positive skewness owing to more severe dilations of either the solid tip of the AFM or the laser tip of the LSM. Further surface parameter evaluation and template matching analysis verified that the main distortions in AFM measurements are tip dilations while those in LSM are generally larger and more complex.

  17. Nanomechanical Characterization of Bacillus anthracis Spores by Atomic Force Microscopy

    PubMed Central

    Burggraf, Larry W.; Xing, Yun

    2016-01-01

    ABSTRACT The study of structures and properties of bacterial spores is important to understanding spore formation and biological responses to environmental stresses. While significant progress has been made over the years in elucidating the multilayer architecture of spores, the mechanical properties of the spore interior are not known. Here, we present a thermal atomic force microscopy (AFM) study of the nanomechanical properties of internal structures of Bacillus anthracis spores. We developed a nanosurgical sectioning method in which a stiff diamond AFM tip was used to cut an individual spore, exposing its internal structure, and a soft AFM tip was used to image and characterize the spore interior on the nanometer scale. We observed that the elastic modulus and adhesion force, including their thermal responses at elevated temperatures, varied significantly in different regions of the spore section. Our AFM images indicated that the peptidoglycan (PG) cortex of Bacillus anthracis spores consisted of rod-like nanometer-sized structures that are oriented in the direction perpendicular to the spore surface. Our findings may shed light on the spore architecture and properties. IMPORTANCE A nanosurgical AFM method was developed that can be used to probe the structure and properties of the spore interior. The previously unknown ultrastructure of the PG cortex of Bacillus anthracis spores was observed to consist of nanometer-sized rod-like structures that are oriented in the direction perpendicular to the spore surface. The variations in the nanomechanical properties of the spore section were largely correlated with its chemical composition. Different components of the spore materials showed different thermal responses at elevated temperatures. PMID:26969703

  18. Analysis of force-deconvolution methods in frequency-modulation atomic force microscopy

    PubMed Central

    Illek, Esther; Giessibl, Franz J

    2012-01-01

    Summary In frequency-modulation atomic force microscopy the direct observable is the frequency shift of an oscillating cantilever in a force field. This frequency shift is not a direct measure of the actual force, and thus, to obtain the force, deconvolution methods are necessary. Two prominent methods proposed by Sader and Jarvis (Sader–Jarvis method) and Giessibl (matrix method) are investigated with respect to the deconvolution quality. Both methods show a nontrivial dependence of the deconvolution quality on the oscillation amplitude. The matrix method exhibits spikelike features originating from a numerical artifact. By interpolation of the data, the spikelike features can be circumvented. The Sader–Jarvis method has a continuous amplitude dependence showing two minima and one maximum, which is an inherent property of the deconvolution algorithm. The optimal deconvolution depends on the ratio of the amplitude and the characteristic decay length of the force for the Sader–Jarvis method. However, the matrix method generally provides the higher deconvolution quality. PMID:22496997

  19. Combined frequency modulated atomic force microscopy and scanning tunneling microscopy detection for multi-tip scanning probe microscopy applications.

    PubMed

    Morawski, Ireneusz; Spiegelberg, Richard; Korte, Stefan; Voigtländer, Bert

    2015-12-01

    A method which allows scanning tunneling microscopy (STM) tip biasing independent of the sample bias during frequency modulated atomic force microscopy (AFM) operation is presented. The AFM sensor is supplied by an electronic circuit combining both a frequency shift signal and a tunneling current signal by means of an inductive coupling. This solution enables a control of the tip potential independent of the sample potential. Individual tip biasing is specifically important in order to implement multi-tip STM/AFM applications. An extensional quartz sensor (needle sensor) with a conductive tip is applied to record simultaneously topography and conductivity of the sample. The high resonance frequency of the needle sensor (1 MHz) allows scanning of a large area of the surface being investigated in a reasonably short time. A recipe for the amplitude calibration which is based only on the frequency shift signal and does not require the tip being in contact is presented. Additionally, we show spectral measurements of the mechanical vibration noise of the scanning system used in the investigations. PMID:26724038

  20. Combined frequency modulated atomic force microscopy and scanning tunneling microscopy detection for multi-tip scanning probe microscopy applications

    SciTech Connect

    Morawski, Ireneusz; Spiegelberg, Richard; Korte, Stefan; Voigtländer, Bert

    2015-12-15

    A method which allows scanning tunneling microscopy (STM) tip biasing independent of the sample bias during frequency modulated atomic force microscopy (AFM) operation is presented. The AFM sensor is supplied by an electronic circuit combining both a frequency shift signal and a tunneling current signal by means of an inductive coupling. This solution enables a control of the tip potential independent of the sample potential. Individual tip biasing is specifically important in order to implement multi-tip STM/AFM applications. An extensional quartz sensor (needle sensor) with a conductive tip is applied to record simultaneously topography and conductivity of the sample. The high resonance frequency of the needle sensor (1 MHz) allows scanning of a large area of the surface being investigated in a reasonably short time. A recipe for the amplitude calibration which is based only on the frequency shift signal and does not require the tip being in contact is presented. Additionally, we show spectral measurements of the mechanical vibration noise of the scanning system used in the investigations.

  1. Electric force microscopy of semiconductors: Theory of cantilever frequency fluctuations and noncontact friction

    SciTech Connect

    Lekkala, Swapna; Marohn, John A.; Loring, Roger F.

    2013-11-14

    An electric force microscope employs a charged atomic force microscope probe in vacuum to measure fluctuating electric forces above the sample surface generated by dynamics of molecules and charge carriers. We present a theoretical description of two observables in electric force microscopy of a semiconductor: the spectral density of cantilever frequency fluctuations (jitter), which are associated with low-frequency dynamics in the sample, and the coefficient of noncontact friction, induced by higher-frequency motions. The treatment is classical-mechanical, based on linear response theory and classical electrodynamics of diffusing charges in a dielectric continuum. Calculations of frequency jitter explain the absence of contributions from carrier dynamics to previous measurements of an organic field effect transistor. Calculations of noncontact friction predict decreasing friction with increasing carrier density through the suppression of carrier density fluctuations by intercarrier Coulomb interactions. The predicted carrier density dependence of the friction coefficient is consistent with measurements of the dopant density dependence of noncontact friction over Si. Our calculations predict that in contrast to the measurement of cantilever frequency jitter, a noncontact friction measurement over an organic semiconductor could show appreciable contributions from charge carriers.

  2. Electric force microscopy of semiconductors: theory of cantilever frequency fluctuations and noncontact friction.

    PubMed

    Lekkala, Swapna; Marohn, John A; Loring, Roger F

    2013-11-14

    An electric force microscope employs a charged atomic force microscope probe in vacuum to measure fluctuating electric forces above the sample surface generated by dynamics of molecules and charge carriers. We present a theoretical description of two observables in electric force microscopy of a semiconductor: the spectral density of cantilever frequency fluctuations (jitter), which are associated with low-frequency dynamics in the sample, and the coefficient of noncontact friction, induced by higher-frequency motions. The treatment is classical-mechanical, based on linear response theory and classical electrodynamics of diffusing charges in a dielectric continuum. Calculations of frequency jitter explain the absence of contributions from carrier dynamics to previous measurements of an organic field effect transistor. Calculations of noncontact friction predict decreasing friction with increasing carrier density through the suppression of carrier density fluctuations by intercarrier Coulomb interactions. The predicted carrier density dependence of the friction coefficient is consistent with measurements of the dopant density dependence of noncontact friction over Si. Our calculations predict that in contrast to the measurement of cantilever frequency jitter, a noncontact friction measurement over an organic semiconductor could show appreciable contributions from charge carriers.

  3. Electric force microscopy of semiconductors: theory of cantilever frequency fluctuations and noncontact friction.

    PubMed

    Lekkala, Swapna; Marohn, John A; Loring, Roger F

    2013-11-14

    An electric force microscope employs a charged atomic force microscope probe in vacuum to measure fluctuating electric forces above the sample surface generated by dynamics of molecules and charge carriers. We present a theoretical description of two observables in electric force microscopy of a semiconductor: the spectral density of cantilever frequency fluctuations (jitter), which are associated with low-frequency dynamics in the sample, and the coefficient of noncontact friction, induced by higher-frequency motions. The treatment is classical-mechanical, based on linear response theory and classical electrodynamics of diffusing charges in a dielectric continuum. Calculations of frequency jitter explain the absence of contributions from carrier dynamics to previous measurements of an organic field effect transistor. Calculations of noncontact friction predict decreasing friction with increasing carrier density through the suppression of carrier density fluctuations by intercarrier Coulomb interactions. The predicted carrier density dependence of the friction coefficient is consistent with measurements of the dopant density dependence of noncontact friction over Si. Our calculations predict that in contrast to the measurement of cantilever frequency jitter, a noncontact friction measurement over an organic semiconductor could show appreciable contributions from charge carriers. PMID:24320286

  4. Combined X-ray Microfluorescence and Atomic Force Microscopy Studies of Mg Distribution in Whole Cells

    SciTech Connect

    Lagomarsino, S.; Farruggia, G.; Trapani, V.; Mastrototaro, L.; Wolf, F.; Cedola, A.; Fratini, M.; Notargiacomo, A.; Bukreeva, I.; McNulty, I.; Vogt, S.; Kim, S.; Legnini, D.; Maier, J. A. M.

    2011-09-09

    We present in this paper a novel methodology that combines scanning x-ray fluorescencee microscopy and atomic force microscopy. The combination of these two techniques allows the determination of a concentration map of Mg in whole (not sectioned) cells.

  5. Intermyofilament dynamics of myocytes revealed by second harmonic generation microscopy.

    PubMed

    Prent, Nicole; Green, Chantal; Greenhalgh, Catherine; Cisek, Richard; Major, Arkady; Stewart, Bryan; Barzda, Virginijus

    2008-01-01

    Drosophila melanogaster larva myocytes are imaged with second harmonic generation (SHG) microscopy undergoing forced stretching and rhythmic contractions to determine the nature of the SHG signal. During stretching, double peaked SHG profiles of the anisotropic (A-) bands evolve into single peaks with a higher SHG intensity. The dip in the intensity profile at the center of the A-band is attributed to destructive interference from out-of-phase second harmonic radiating myosin molecules that, in the central region of myofilaments, are arranged antiparallel. An intensity increase at the center of the A-band appears during forced stretching due to a small, less than 100 nm, intermyofilament separation of the antiparallel myosin molecules leading to constructive interference of the SHG radiation. In addition, the same phenomenon occurs during periodic contractions of the myocyte, where an SHG intensity increase with the lengthening of sarcomeres is observed. The SHG intensity dependence on sarcomere length can be used for imaging myocyte contractions with low resolution microscopy, and can be applied for the development of diagnostic tools where monitoring of muscle contraction dynamics is required.

  6. A quantitative lateral force Microscopy study of the dolomite (104)-water interface.

    SciTech Connect

    Higgins, S. R.; Hu, X.; Fentert, P.; Wright State Univ.

    2007-08-14

    The friction and lateral stiffness of the contact between an atomic force microscopy (AFM) probe tip and an atomically flat dolomite (104) surface were investigated in contact with two aqueous solutions that were in equilibrium and supersaturated with respect to dolomite, respectively. The two aqueous solutions yielded negligible differences in friction at the native dolomite-water interface. However, the growth of a Ca-rich film from the supersaturated solution, revealed by X-ray reflectivity measurements, altered the probe-dolomite contact region sufficiently to observe distinct friction forces on the native dolomite and the film-covered surface regions. Quantitative friction-load relationships demonstrated three physically distinct load regimes for applied loads up to 200 nN. Similar friction forces were observed on both surfaces below 50 nN load and above 100 nN load. The friction forces on the two surfaces diverged at intermediate loads. Quantitative measurements of dynamic friction forces at low load were consistent with the estimated energy necessary to dehydrate the surface ions, whereas differences in mechanical properties of the Ca-rich film and dolomite surfaces were evidently important above 50 nN load. Attempts to fit the quantitative stiffness-load data using a Hertzian contact mechanical model based on bulk material properties yielded physically unrealistic fitting coefficients, suggesting that the interfacial contact region must be explicitly considered in describing the static and dynamic contact mechanics of this and similar systems.

  7. Simulating photoconductive atomic-force microscopy on disordered photovoltaic materials

    NASA Astrophysics Data System (ADS)

    Blakesley, James C.; Castro, Fernando A.

    2015-04-01

    We present a tool for simulating photoconductive atomic-force microscopy (Pc-AFM) on bulk heterojunction (BHJ) materials with a minimal set of empirical parameters. The simulation is a master-equation solution of a three-dimensional hopping charge transport model which includes donor-acceptor domain morphology, energetic and spatial disorder, exciton transport and splitting, charge-pair generation and recombination, and tip-substrate electrostatics. A simplifying aspect of the model is that electron transport, hole transport, and electron-hole recombination are treated as the same electron-transfer process. The model recreates realistic bulk recombination rates, without requiring short-range Coulombic effects to be calculated. We demonstrate the tool by simulating line scans of a Pc-AFM tip passing over the surface of a buried or exposed acceptor cluster in a BHJ film. The simulations confirm experimental observations that such defects can be detected by open-circuit mode Pc-AFM imaging, even when the clusters are buried below the surface.

  8. Medical applications of atomic force microscopy and Raman spectroscopy.

    PubMed

    Choi, Samjin; Jung, Gyeong Bok; Kim, Kyung Sook; Lee, Gi-Ja; Park, Hun-Kuk

    2014-01-01

    This paper reviews the recent research and application of atomic force microscopy (AFM) and Raman spectroscopy techniques, which are considered the multi-functional and powerful toolkits for probing the nanostructural, biomechanical and physicochemical properties of biomedical samples in medical science. We introduce briefly the basic principles of AFM and Raman spectroscopy, followed by diagnostic assessments of some selected diseases in biomedical applications using them, including mitochondria isolated from normal and ischemic hearts, hair fibers, individual cells, and human cortical bone. Finally, AFM and Raman spectroscopy applications to investigate the effects of pharmacotherapy, surgery, and medical device therapy in various medicines from cells to soft and hard tissues are discussed, including pharmacotherapy--paclitaxel on Ishikawa and HeLa cells, telmisartan on angiotensin II, mitomycin C on strabismus surgery and eye whitening surgery, and fluoride on primary teeth--and medical device therapy--collagen cross-linking treatment for the management of progressive keratoconus, radiofrequency treatment for skin rejuvenation, physical extracorporeal shockwave therapy for healing of Achilles tendinitis, orthodontic treatment, and toothbrushing time to minimize the loss of teeth after exposure to acidic drinks.

  9. Actuation of atomic force microscopy microcantilevers using contact acoustic nonlinearities

    SciTech Connect

    Torello, D.; Degertekin, F. Levent

    2013-11-15

    A new method of actuating atomic force microscopy (AFM) cantilevers is proposed in which a high frequency (>5 MHz) wave modulated by a lower frequency (∼300 kHz) wave passes through a contact acoustic nonlinearity at the contact interface between the actuator and the cantilever chip. The nonlinearity converts the high frequency, modulated signal to a low frequency drive signal suitable for actuation of tapping-mode AFM probes. The higher harmonic content of this signal is filtered out mechanically by the cantilever transfer function, providing for clean output. A custom probe holder was designed and constructed using rapid prototyping technologies and off-the-shelf components and was interfaced with an Asylum Research MFP-3D AFM, which was then used to evaluate the performance characteristics with respect to standard hardware and linear actuation techniques. Using a carrier frequency of 14.19 MHz, it was observed that the cantilever output was cleaner with this actuation technique and added no significant noise to the system. This setup, without any optimization, was determined to have an actuation bandwidth on the order of 10 MHz, suitable for high speed imaging applications. Using this method, an image was taken that demonstrates the viability of the technique and is compared favorably to images taken with a standard AFM setup.

  10. DNA fragmentation induced by ionizing radiation - Atomic Force Microscopy study .

    NASA Astrophysics Data System (ADS)

    Gudowska-Nowak, E.; Psonka, K.; Elsaesser, Th.; Brons, S.; Taucher-Scholz, G.

    DNA as a carrier of genetic information is considered to be the critical target for radiation induced damage Especially severe are DNA double-strand breaks DSBs formed when breaks occur in both strands of the molecule The DSBs production is determined by the spatial distribution of ionization events dependent on the physical properties of the energy deposition and the chemical environment of the DNA According to theoretical predictions high LET charged particle radiation induces lesions in close proximity forming so called clustered damage in the DNA Atomic Force Microscopy AFM was newly established as a technique allowing the direct visualization of DNA fragments resulting from DSBs induced in small DNA molecules plasmids by ionizing radiation We have used AFM to visualize the DNA fragmentation induced by heavy ions high LET radiation and to compare it to the fragmentation pattern obtained after X-rays low LET radiation Plasmid supercoiled DNA was irradiated in vitro with X-rays and 3 9 MeV u Ni ions within a dose range 0 -- 3000 Gy Afterwards the samples were analyzed using AFM which allowed the detection and length measurement of individual fragments with a nanometer resolution Recording of the length of the induced fragments allowed to distinguish between molecules broken by a single DSB or by multiple DSBs The fragment length distributions were derived for different doses and different radiation qualities The first results of the measurement of radiation-induced DNA fragmentation show an influence of radiation quality on

  11. Atomic force microscopy of differential weathering in real time

    SciTech Connect

    Heaton, J.S.; Engstrom, R.C. . Dept. of Chemistry)

    1994-04-01

    Differential weathering of a rock sample was observed in-situ using atomic force microscopy (AFM). The sample contained fayalite intergrown with veins of magnetite and serpentine. Analyses consisted of polishing the sample with alumina and recording AFM scans periodically during subsequent exposure to nitric acid. Immediately after polishing, serpentine areas were recessed compared to fayalite and magnetite, which were similar in height. As weathering proceeded, both serpentine and magnetite areas protruded from the fayalite surface, and no significant change in the relative heights of magnetite and serpentine features was observed. This suggests that serpentine is less resistant to mechanical weathering than fayalite or magnetite but that serpentine and magnetite are both more resistant to chemical weathering than fayalite. Differential weathering rates between fayalite and magnetite, on the order of a few unit cells per minute, were determined in various nitric acid concentrations by measuring the difference in height between the two minerals as a function of time. A dissolution rate law for fayalite was determined by comparing the rates for different concentrations of nitric acid and assuming the dissolution of magnetite was negligible compared to that of fayalite. The rate law from this study is Rate = 7.7* [HNO[sub 3

  12. Atomic Force Microscopy of Arrays of Asymmetrical DNA Motifs

    SciTech Connect

    Sherman, W.B.; Mudalige, T.K.

    2012-03-21

    DNA can easily be assembled into wide and relatively flat nanostructures that lend themselves to study via Atomic Force Microscopy (AFM). It is often important to know which side of an assembly the AFM is imaging. This is particularly crucial for characterizing nanomachines, where the movement must be measured relative to fiducial features visible to the AFM. We have developed a cheap and simple technique for building DNA arrays with distinguishable sides, a technique requiring 10 or fewer strands - dozens or hundreds of strands fewer than used for these purposes previously. Our approach involves constructing arrays out of DNA tiles that have low apparent symmetry when imaged via AFM. We have surveyed the effects of varying degrees of motif asymmetry in AFM micrographs. Even at resolutions where the individual tiles cannot be resolved (either because of sub-optimal tip quality, or very gentle tapping by the AFM tip) the larger scale features of the arrays have predictable structures that allow the determination of which side of the array is facing up. We have used this information to verify that DNA hairpins attached to either the up- or down-facing side of an array on mica can be detected in AFM height scans. We have also characterized differences in appearance between hairpins attached to different sides of the arrays.

  13. Conductive-probe atomic force microscopy characterization of silicon nanowire

    PubMed Central

    2011-01-01

    The electrical conduction properties of lateral and vertical silicon nanowires (SiNWs) were investigated using a conductive-probe atomic force microscopy (AFM). Horizontal SiNWs, which were synthesized by the in-plane solid-liquid-solid technique, are randomly deployed into an undoped hydrogenated amorphous silicon layer. Local current mapping shows that the wires have internal microstructures. The local current-voltage measurements on these horizontal wires reveal a power law behavior indicating several transport regimes based on space-charge limited conduction which can be assisted by traps in the high-bias regime (> 1 V). Vertical phosphorus-doped SiNWs were grown by chemical vapor deposition using a gold catalyst-driving vapor-liquid-solid process on higly n-type silicon substrates. The effect of phosphorus doping on the local contact resistance between the AFM tip and the SiNW was put in evidence, and the SiNWs resistivity was estimated. PMID:21711623

  14. Magnetic resonance force microscopy and a solid state quantum computer.

    SciTech Connect

    Pelekhov, D. V.; Martin, I.; Suter, A.; Reagor, D. W.; Hammel, P. C.

    2001-01-01

    A Quantum Computer (QC) is a device that utilizes the principles of Quantum Mechanics to perform computations. Such a machine would be capable of accomplishing tasks not achievable by means of any conventional digital computer, for instance factoring large numbers. Currently it appears that the QC architecture based on an array of spin quantum bits (qubits) embedded in a solid-state matrix is one of the most promising approaches to fabrication of a scalable QC. However, the fabrication and operation of a Solid State Quantum Computer (SSQC) presents very formidable challenges; primary amongst these are: (1) the characterization and control of the fabrication process of the device during its construction and (2) the readout of the computational result. Magnetic Resonance Force Microscopy (MRFM)--a novel scanning probe technique based on mechanical detection of magnetic resonance-provides an attractive means of addressing these requirements. The sensitivity of the MRFM significantly exceeds that of conventional magnetic resonance measurement methods, and it has the potential for single electron spin detection. Moreover, the MRFM is capable of true 3D subsurface imaging. These features will make MRFM an invaluable tool for the implementation of a spin-based QC. Here we present the general principles of MRFM operation, the current status of its development and indicate future directions for its improvement.

  15. Atomic force microscopy investigation of the giant mimivirus

    SciTech Connect

    Kuznetsov, Yuri G.; Xiao Chuan; Sun Siyang; Raoult, Didier; Rossmann, Michael; McPherson, Alexander

    2010-08-15

    Mimivirus was investigated by atomic force microscopy in its native state following serial degradation by lysozyme and bromelain. The 750-nm diameter virus is coated with a forest of glycosylated protein fibers of lengths about 140 nm with diameters 1.4 nm. Fibers are capped with distinctive ellipsoidal protein heads of estimated Mr = 25 kDa. The surface fibers are attached to the particle through a layer of protein covering the capsid, which is in turn composed of the major capsid protein (MCP). The latter is organized as an open network of hexagonal rings with central depressions separated by 14 nm. The virion exhibits an elaborate apparatus at a unique vertex, visible as a star shaped depression on native particles, but on defibered virions as five arms of 50 nm width and 250 nm length rising above the capsid by 20 nm. The apparatus is integrated into the capsid and not applied atop the icosahedral lattice. Prior to DNA release, the arms of the star disengage from the virion and it opens by folding back five adjacent triangular faces. A membrane sac containing the DNA emerges from the capsid in preparation for fusion with a membrane of the host cell. Also observed from disrupted virions were masses of distinctive fibers of diameter about 1 nm, and having a 7-nm periodicity. These are probably contained within the capsid along with the DNA bearing sac. The fibers were occasionally observed associated with toroidal protein clusters interpreted as processive enzymes modifying the fibers.

  16. Recognizing and avoiding artifacts in atomic force microscopy imaging.

    PubMed

    Canale, Claudio; Torre, Bruno; Ricci, Davide; Braga, Pier Carlo

    2011-01-01

    Atomic force microscopy (AFM) measurements could be affected by different kinds of artifacts; some of them derive from the improper use of the instrument and can be avoided by setting the correct experimental parameters and conditions. In other cases, distortions of the images acquired by AFM are intrinsically related to the operating principle of the instrument itself and to the kind of interactions taken into account for the reconstruction of the sample topography. A perfect knowledge of all the artifacts that can perturb AFM measurements is fundamental to avoid misleading interpretations of the results. In this chapter, all the most common sources of artifact are presented, and strategies to avoid them are proposed.Subheading 1 is a brief introduction to the chapter. In Subheading 2, the artifacts due to the interactions between the sample and the AFM tip are presented. Subheading 3 is focused on the deformations due to the AFM scanner nonlinear movements. The interaction with the environment surrounding the instrument can affect the quality of the AFM results and the environmental instability are discussed in Subheading 4. Subheading 5 shows the effects of an incorrect setting of the feedback gains or other parameters. Subheading 6 aims on the artifacts that can be produced by the improper use of the image processing software. Subheading 7 is a short guide on the test that can be done to easily recognize some of the artifacts previously described.

  17. Experimental issues in magnetic force microscopy of nanoparticles

    NASA Astrophysics Data System (ADS)

    Angeloni, L.; Passeri, D.; Reggente, M.; Rossi, M.; Mantovani, D.; Lazzaro, L.; Nepi, F.; De Angelis, F.; Barteri, M.

    2015-06-01

    The development of magnetic nanoparticles for biomedical applications requires a detailed characterization of their magnetic properties, with relation not only to their chemical structure, but also their morphology and size. Magnetic force microscopy (MFM), thanks to its nanometric lateral resolution and its capability to detect weak magnetic fields, appears as a powerful tool for the characterization of the magnetic properties of single nanoparticles, together with their morphological characteristics. Nevertheless, the application of MFM to the quantitative measurements of magnetic properties at the nanoscale is still an open issue because of a certain incongruence between experimental data and existing theoretical models of the tip-sample magnetic interactions. In this work, MFM data acquired on different magnetic nanoparticles in different experimental conditions (magnetized and not magnetized probes, out-of-field and in-field measurements) are analyzed, with the aim of individuating the possible phenomena affecting MFM measurements. These include topography-induced artifacts resulting from the tip-sample capacitive coupling, which we propose here for the first time. In case of measurements performed in presence of an external magnetic field, much more intense MFM signals were detected as it produces the saturation of the magnetization of the nanoparticles, which is not completely obtained by the sole stray field produced by the tip. Nevertheless, even in in-field measurements, the results evidenced the presence of significant electrostatic effects in MFM images, which, therefore, appear as an important factor to be taken into account for the quantitative interpretation of MFM data.

  18. Nanoscale study of cartilage surfaces using atomic force microscopy.

    PubMed

    Wang, Meiling; Peng, Zhongxiao; Watson, Jolanta A; Watson, Gregory S; Yin, Ling

    2012-12-01

    Articulating cartilage wear plays an important role in cartilage degeneration and osteoarthritis (OA) progression. This study investigated the changes of mechanical properties and surface roughness of sheep cartilages with wear progression at a nanometre scale. Young sheep's rear legs were subjected to a series of wear tests to generate worn cartilage samples to simulate the OA progression. Atomic force microscopy (AFM) was used to determine the effective indentation modulus and to measure the surface morphology of moist cartilage surfaces. The study has found that the mean effective indentation modulus values of worn cartilages were lower than that of healthy cartilage as the control sample. A medium-to-strong correlation between the effective indentation modulus values and the OA grades has been found. The relation between surface topography and effective indentation modulus values of the cartilage surfaces with OA progression was weakly correlated. The method established in this study can be implemented to investigate the effective indentation modulus values of clinical osteoarthritic cartilages and to assist in the understanding and assessment of OA.

  19. Atomic force microscopy study of biaxially oriented polypropylene films

    NASA Astrophysics Data System (ADS)

    Nie, H.-Y.; Walzak, M. J.; McIntyre, N. S.

    2004-08-01

    Atomic force microscopy (AFM) uses a very sharp pointed mechanical probe to collect real-space morphological information of solid surfaces. AFM was used in this study to image the surface morphology of a biaxially oriented polypropylene film. The polymer film is characterized by a nanometer-scale, fiberlike network structure, which reflects the drawing process used during the fabrication of the film. AFM was used to study polymer-surface treatment to improve wettability by exposing the polymer to ozone with or without ultraviolet (UV) irradiation. Surface-morphology changes observed by AFM are the result of the surface oxidation induced by the treatment. Due to the topographic features of the polymer film, the fiberlike structure has been used to check the performance of the AFM tip. An AFM image is a mixture of the surface morphology and the shape of the AFM tip. Therefore, it is important to check the performance of a tip to ensure that the AFM image collected reflects the true surface features of the sample, rather than contamination on the AFM tip.

  20. Atomic Force Microscopy Study of Atherosclerosis Progression in Arterial Walls.

    PubMed

    Timashev, Peter S; Kotova, Svetlana L; Belkova, Galina V; Gubar'kova, Ekaterina V; Timofeeva, Lidia B; Gladkova, Natalia D; Solovieva, Anna B

    2016-04-01

    Cardiovascular disease remains the leading cause of mortality worldwide. Here we suggest a novel approach for tracking atherosclerosis progression based on the use of atomic force microscopy (AFM). Using AFM, we studied cross-sections of coronary arteries with the following types of lesions: Type II-thickened intima; Type III-thickened intima with a lipid streak; Type IV-fibrotic layer over a lipid core; Type Va-unstable fibrotic layer over a lipid core; Type Vc-very thick fibrotic layer. AFM imaging revealed that the fibrotic layer of an atherosclerotic plaque is represented by a basket-weave network of collagen fibers and a subscale network of fibrils that become looser with atherosclerosis progression. In an unstable plaque (Type Va), packing of the collagen fibers and fibrils becomes even less uniform than that at the previous stages, while a stable fibrotic plaque (Vc) has significantly tighter packing. Such alterations of the collagen network morphology apparently, led to deterioration of the Type Va plaque mechanical properties, that, in turn, resulted in its instability and propensity to rupture. Thus, AFM may serve as a useful tool for tracking atherosclerosis progression in the arterial wall tissue. PMID:26843417

  1. Recent Progress in Molecular Recognition Imaging Using Atomic Force Microscopy.

    PubMed

    Senapati, Subhadip; Lindsay, Stuart

    2016-03-15

    Atomic force microscopy (AFM) is an extremely powerful tool in the field of bionanotechnology because of its ability to image single molecules and make measurements of molecular interaction forces with piconewton sensitivity. It works in aqueous media, enabling studies of molecular phenomenon taking place under physiological conditions. Samples can be imaged in their near-native state without any further modifications such as staining or tagging. The combination of AFM imaging with the force measurement added a new feature to the AFM technique, that is, molecular recognition imaging. Molecular recognition imaging enables mapping of specific interactions between two molecules (one attached to the AFM tip and the other to the imaging substrate) by generating simultaneous topography and recognition images (TREC). Since its discovery, the recognition imaging technique has been successfully applied to different systems such as antibody-protein, aptamer-protein, peptide-protein, chromatin, antigen-antibody, cells, and so forth. Because the technique is based on specific binding between the ligand and receptor, it has the ability to detect a particular protein in a mixture of proteins or monitor a biological phenomenon in the native physiological state. One key step for recognition imaging technique is the functionalization of the AFM tips (generally, silicon, silicon nitrides, gold, etc.). Several different functionalization methods have been reported in the literature depending on the molecules of interest and the material of the tip. Polyethylene glycol is routinely used to provide flexibility needed for proper binding as a part of the linker that carries the affinity molecule. Recently, a heterofunctional triarm linker has been synthesized and successfully attached with two different affinity molecules. This novel linker, when attached to AFM tip, helped to detect two different proteins simultaneously from a mixture of proteins using a so-called "two

  2. Mechanical properties of poly(dimethylsiloxane)-block-poly(2-methyloxazoline) polymersomes probed by atomic force microscopy.

    PubMed

    Jaskiewicz, Karmena; Makowski, Marcin; Kappl, Michael; Landfester, Katharina; Kroeger, Anja

    2012-08-28

    Poly(dimethylsiloxane)-block-poly(2-methyloxazoline) (PDMS-b-PMOXA) vesicles were characterized by a combination of dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), and atomic force microscopy imaging and force spectroscopy (AFM). From DLS data, a hydrodynamic radius of ~150 nm was determined, and cryo-TEM micrographs revealed a bilayer thickness of ~16 nm. In AFM experiments on a silicon wafer substrate, adsorption led to a stable spherical caplike conformation of the polymersomes, whereas on mica, adsorption resulted also in vesicle fusion and formation of bilayer patches or multilayer stacks. This indicates a delicate balance between the mechanical stability of PDMS-b-PMOXA polymersomes on one hand and the driving forces for spreading on the other. A Young's modulus of 17 ± 11 MPa and a bending modulus of 7 ± 5 × 10(-18) J were derived from AFM force spectroscopy measurements. Therefore, the elastic response of the PDMS-b-PMOXA polymersomes to external stimuli is much closer to that of lipid vesicles compared to other types of polymersomes, such as polystyrene-block-poly(acrylic acid) (PS-b-PAA).

  3. Preparation and Friction Force Microscopy Measurements of Immiscible, Opposing Polymer Brushes

    PubMed Central

    de Beer, Sissi; Kutnyanszky, Edit; Müser, Martin H.; Vancso, G. Julius

    2014-01-01

    Solvated polymer brushes are well known to lubricate high-pressure contacts, because they can sustain a positive normal load while maintaining low friction at the interface. Nevertheless, these systems can be sensitive to wear due to interdigitation of the opposing brushes. In a recent publication, we have shown via molecular dynamics simulations and atomic force microscopy experiments, that using an immiscible polymer brush system terminating the substrate and the slider surfaces, respectively, can eliminate such interdigitation. As a consequence, wear in the contacts is reduced. Moreover, the friction force is two orders of magnitude lower compared to traditional miscible polymer brush systems. This newly proposed system therefore holds great potential for application in industry. Here, the methodology to construct an immiscible polymer brush system of two different brushes each solvated by their own preferred solvent is presented. The procedure how to graft poly(N-isopropylacrylamide) (PNIPAM) from a flat surface and poly(methyl methacrylate) (PMMA) from an atomic force microscopy (AFM) colloidal probe is described. PNIPAM is solvated in water and PMMA in acetophenone. Via friction force AFM measurements, it is shown that the friction for this system is indeed reduced by two orders of magnitude compared to the miscible system of PMMA on PMMA solvated in acetophenone. PMID:25590429

  4. Preparation and friction force microscopy measurements of immiscible, opposing polymer brushes.

    PubMed

    de Beer, Sissi; Kutnyanszky, Edit; Müser, Martin H; Vancso, G Julius

    2014-12-24

    Solvated polymer brushes are well known to lubricate high-pressure contacts, because they can sustain a positive normal load while maintaining low friction at the interface. Nevertheless, these systems can be sensitive to wear due to interdigitation of the opposing brushes. In a recent publication, we have shown via molecular dynamics simulations and atomic force microscopy experiments, that using an immiscible polymer brush system terminating the substrate and the slider surfaces, respectively, can eliminate such interdigitation. As a consequence, wear in the contacts is reduced. Moreover, the friction force is two orders of magnitude lower compared to traditional miscible polymer brush systems. This newly proposed system therefore holds great potential for application in industry. Here, the methodology to construct an immiscible polymer brush system of two different brushes each solvated by their own preferred solvent is presented. The procedure how to graft poly(N-isopropylacrylamide) (PNIPAM) from a flat surface and poly(methyl methacrylate) (PMMA) from an atomic force microscopy (AFM) colloidal probe is described. PNIPAM is solvated in water and PMMA in acetophenone. Via friction force AFM measurements, it is shown that the friction for this system is indeed reduced by two orders of magnitude compared to the miscible system of PMMA on PMMA solvated in acetophenone.

  5. Atomic force microscopy imaging of viscoelastic properties in toughened polypropylene resins

    NASA Astrophysics Data System (ADS)

    Nysten, Bernard; Legras, Roger; Costa, Jean-Louis

    1995-11-01

    The bulk morphology of two toughened polypropylene/(ethylene propylene)copolymer resins (PP/EP) presenting different impact resistances has been studied by means of different atomic force microscopy techniques: contact atomic force microscopy, lateral force microscopy (LFM), and force modulation microscopy (FMM). The three techniques reveal two different morphologies as observed in transmission electronic microscopy. In LFM, a higher friction force is observed on the rubbery phase which has the lower Young's modulus confirming the relationship between friction force and elastic properties. In force modulation, the elastic moduli is found to be much lower on the EP nodules in both resins. FMM also reveals that the difference of viscous response between the PP matrix and the EP nodules is much lower in the resin which is less impact resistant.

  6. Photonic Torque Microscopy of the Nonconservative Force Field for Optically Trapped Silicon Nanowires.

    PubMed

    Irrera, Alessia; Magazzù, Alessandro; Artoni, Pietro; Simpson, Stephen H; Hanna, Simon; Jones, Philip H; Priolo, Francesco; Gucciardi, Pietro Giuseppe; Maragò, Onofrio M

    2016-07-13

    We measure, by photonic torque microscopy, the nonconservative rotational motion arising from the transverse components of the radiation pressure on optically trapped, ultrathin silicon nanowires. Unlike spherical particles, we find that nonconservative effects have a significant influence on the nanowire dynamics in the trap. We show that the extreme shape of the trapped nanowires yields a transverse component of the radiation pressure that results in an orbital rotation of the nanowire about the trap axis. We study the resulting motion as a function of optical power and nanowire length, discussing its size-scaling behavior. These shape-dependent nonconservative effects have implications for optical force calibration and optomechanics with levitated nonspherical particles.

  7. Local Force Interactions and Image Contrast Reversal on Graphite Observed with Noncontact Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Dagdeviren, Omur; Goetzen, Jan; Altman, Eric; Schwarz, Udo

    Surface interactions of graphene-based nanostructures remain a topic of considerable interest in nanotechnology. Similarly, tip-dependent imaging contrasts have attracted attention as they allow conclusions to be made about the surface's chemical structure and local reactivity. In this talk, we present noncontact atomic force microscopy data recorded in the attractive regime on highly oriented pyrolytic graphite that reveals image contrast reversal for the first time. While larger tip-sample separations feature bright spots on atomic sites, the maximum of the tip-sample interaction flips to the hollow site positions upon further approach, which represents the contrast predominantly observed in previous studies during attractive-mode imaging. This cross over of the local chemical interaction is confirmed in force spectroscopy experiments. The results will be discussed in light of recent theoretical simulations that have predicted the occurrence of such contrast reversal for specific tip terminations.

  8. Fast time-resolved electrostatic force microscopy: Achieving sub-cycle time resolution.

    PubMed

    Karatay, Durmus U; Harrison, Jeffrey S; Glaz, Micah S; Giridharagopal, Rajiv; Ginger, David S

    2016-05-01

    The ability to measure microsecond- and nanosecond-scale local dynamics below the diffraction limit with widely available atomic force microscopy hardware would enable new scientific studies in fields ranging from biology to semiconductor physics. However, commercially available scanning-probe instruments typically offer the ability to measure dynamics only on time scales of milliseconds to seconds. Here, we describe in detail the implementation of fast time-resolved electrostatic force microscopy using an oscillating cantilever as a means to measure fast local dynamics following a perturbation to a sample. We show how the phase of the oscillating cantilever relative to the perturbation event is critical to achieving reliable sub-cycle time resolution. We explore how noise affects the achievable time resolution and present empirical guidelines for reducing noise and optimizing experimental parameters. Specifically, we show that reducing the noise on the cantilever by using photothermal excitation instead of piezoacoustic excitation further improves time resolution. We demonstrate the discrimination of signal rise times with time constants as fast as 10 ns, and simultaneous data acquisition and analysis for dramatically improved image acquisition times. PMID:27250430

  9. Scanning force microscopy as a tool for fracture studies

    SciTech Connect

    Thome, F.; Goeken, M.; Grosse Gehling, M.; Vehoff, H.

    1999-08-01

    Dynamic simulations of the fracture toughness as a function of the orientation and temperature were carried out and compared with experimental results obtained by in-situ loading pre-cracked NiAl single crystals inside a scanning force microscope (SFM). In order to compare the simulations with the experiments the problem of the short crack with dislocations was solved for general loading and arbitrary slip line directions. The stress and strain field obtained could be directly connected to FEM calculations which allowed the examination of the stability of micro cracks at notches. The effect of different fracture conditions for biaxial loading were studied in detail. The dynamic simulation yielded predictions of K{sub IC}, slip line length and dislocation distributions as a function of loading rate, temperature and orientation. These predictions were tested by in-situ loading NiAl single crystals inside a SFM at various temperatures. The local COD, slip line length and apparent dislocation distribution at the surface were measured as a function of the applied load and the temperature. The experiments clearly demonstrated that dislocations emit from the crack tip before unstable crack jumps occur. The local COD could be directly related to the number of dislocations emitted from the crack tip. With increasing temperature the number of dislocations and the local COD increased before unstable crack jumps or final fracture occurred.

  10. Probing the limits of the Derjaguin approximation with scanning force microscopy.

    PubMed

    Todd, Brian A; Eppell, Steven J

    2004-06-01

    We have measured the interaction force between a silicon nitride scanning force microscopy (SFM) probe and the basal plane of highly oriented pyrolitic graphite as a function of pH and ionic concentration in aqueous solutions. Forces in the range +/- 50 pN were reconstructed from measured signals using dynamical analysis of the cantilever. We modeled the force-separation data using a flat plate electric double-layer interaction and assumed the Derjaguin approximation to adapt the flat plate geometry for the SFM probe shape. Measured forces were well modeled by the theory at high ionic concentrations (10 and 100 mM), where Debye lengths were 3.0 and 0.96 nm, respectively. The theory failed to model forces at a lower ionic concentration (1 mM), where the Debye length was 9.6 nm. To investigate this, we calibrated the SFM probe geometry using blind reconstruction and obtained an apex radius of 7 nm. This value suggested that failure of the theory was due to an invalidation of the Derjaguin approximation at long Debye lengths, where the characteristic length scale for the interaction was larger than the size of the SFM probe. The errors were reduced by replacing the Derjaguin approximation with a surface element integration. The result experimentally demonstrates the limitations of the Derjaguin approximation for predicting interactions of nanoscale colloids.

  11. Stochastic friction force mechanism of energy dissipation in noncontact atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Kantorovich, L. N.

    2001-12-01

    The tip-surface interaction in noncontact atomic force microscopy (NC-AFM) leads to energy dissipation, which has been used as another imaging mechanism of surface topography with atomic resolution. In this paper, using a rigorous approach based on the coarse graining method of (classical) nonequilibrium statistical mechanics, we derive the Fokker-Planck equation for the tip distribution function and then the Langevin equation (equation of motion) for the tip. We show that the latter equation contains a friction force leading to the energy dissipation. The friction force is related to the correlation function of the fluctuating tip-surface force in agreement with earlier treatments by other methods. Using a simple model of a plane surface in which only one surface atom interacts directly with the tip (it, however, interacts with other surface atoms), we calculate the friction coefficient and the corresponding dissipation energy as a function of the tip position. In our model all surface atoms are allowed to relax. Nevertheless, our calculations qualitatively agree with a previous much simpler treatment by Gauthier and Tsukada [Phys. Rev. B 60, 11 716 (1999)] that, at least for the plain terraces, the calculated dissipation energies appear to be much smaller than observed in experiments. We also demonstrate the validity of the Markovian approximation in studying the NC-AFM system.

  12. Direct force measurement of single DNA-peptide interactions using atomic force microscopy.

    PubMed

    Chung, Ji W; Shin, Dongjin; Kwak, June M; Seog, Joonil

    2013-06-01

    The selective interactions between DNA and miniature (39 residues) engineered peptide were directly measured at the single-molecule level by using atomic force microscopy. This peptide (p007) contains an α-helical recognition site similar to leucine zipper GCN4 and specifically recognizes the ATGAC sequence in the DNA with nanomolar affinity. The average rupture force was 42.1 pN, which is similar to the unbinding forces of the digoxigenin-antidigoxigenin complex, one of the strongest interactions in biological systems. The single linear fit of the rupture forces versus the logarithm of pulling rates showed a single energy barrier with a transition state located at 0.74 nm from the bound state. The smaller koff compared with that of other similar systems was presumably due to the increased stability of the helical structure by putative folding residues in p007. This strong sequence-specific DNA-peptide interaction has a potential to be utilized to prepare well-defined mechanically stable DNA-protein hybrid nanostructures.

  13. Taking nanomedicine teaching into practice with atomic force microscopy and force spectroscopy.

    PubMed

    Carvalho, Filomena A; Freitas, Teresa; Santos, Nuno C

    2015-12-01

    Atomic force microscopy (AFM) is a useful and powerful tool to study molecular interactions applied to nanomedicine. The aim of the present study was to implement a hands-on atomic AFM course for graduated biosciences and medical students. The course comprises two distinct practical sessions, where students get in touch with the use of an atomic force microscope by performing AFM scanning images of human blood cells and force spectroscopy measurements of the fibrinogen-platelet interaction. Since the beginning of this course, in 2008, the overall rating by the students was 4.7 (out of 5), meaning a good to excellent evaluation. Students were very enthusiastic and produced high-quality AFM images and force spectroscopy data. The implementation of the hands-on AFM course was a success, giving to the students the opportunity of contact with a technique that has a wide variety of applications on the nanomedicine field. In the near future, nanomedicine will have remarkable implications in medicine regarding the definition, diagnosis, and treatment of different diseases. AFM enables students to observe single molecule interactions, enabling the understanding of molecular mechanisms of different physiological and pathological processes at the nanoscale level. Therefore, the introduction of nanomedicine courses in bioscience and medical school curricula is essential.

  14. Mapping of surface-immobilized DNA with force-based atomic force microscopy.

    PubMed

    Lee, Yoonhee; Kwon, Sung Hong; Kim, Youngkyu; Lee, Jong-Bong; Park, Joon Won

    2013-04-16

    Single-stranded 50-mer, 100-mer, and 150-mer DNAs were immobilized on a surface, and force-based atomic force microscopy (AFM) was employed to examine their behavior. A complementary 20-mer probe DNA on an AFM tip was used for the measurements. High-resolution maps were generated, and relevant parameters, including the force, stretching distance, unbinding probability, cluster size, and degree of distortion, were analyzed. Due to thermal drift, the cluster shape became increasingly distorted as the scan speed was decreased and as the map area was reduced. The cluster radius increased with the number of base (N), and the radius was proportional to N(0.6) (r = 0.977) and N(0.53) (r = 0.991). Due to the effect of the pulling angle, the apparent values of the stretching distance and the unbinding force decreased as the AFM probe was moved away from the center position; these values can be described as a function of sin θ.

  15. Taking nanomedicine teaching into practice with atomic force microscopy and force spectroscopy.

    PubMed

    Carvalho, Filomena A; Freitas, Teresa; Santos, Nuno C

    2015-12-01

    Atomic force microscopy (AFM) is a useful and powerful tool to study molecular interactions applied to nanomedicine. The aim of the present study was to implement a hands-on atomic AFM course for graduated biosciences and medical students. The course comprises two distinct practical sessions, where students get in touch with the use of an atomic force microscope by performing AFM scanning images of human blood cells and force spectroscopy measurements of the fibrinogen-platelet interaction. Since the beginning of this course, in 2008, the overall rating by the students was 4.7 (out of 5), meaning a good to excellent evaluation. Students were very enthusiastic and produced high-quality AFM images and force spectroscopy data. The implementation of the hands-on AFM course was a success, giving to the students the opportunity of contact with a technique that has a wide variety of applications on the nanomedicine field. In the near future, nanomedicine will have remarkable implications in medicine regarding the definition, diagnosis, and treatment of different diseases. AFM enables students to observe single molecule interactions, enabling the understanding of molecular mechanisms of different physiological and pathological processes at the nanoscale level. Therefore, the introduction of nanomedicine courses in bioscience and medical school curricula is essential. PMID:26628660

  16. Calculation of the effect of tip geometry on noncontact atomic force microscopy using a qPlus sensor.

    PubMed

    Stirling, Julian; Shaw, Gordon A

    2013-01-01

    In qPlus atomic force microscopy the tip length can in principle approach the length of the cantilever. We present a detailed mathematical model of the effects this has on the dynamic properties of the qPlus sensor. The resulting, experimentally confirmed motion of the tip apex is shown to have a large lateral component, raising interesting questions for both calibration and force-spectroscopy measurements.

  17. Calculation of the effect of tip geometry on noncontact atomic force microscopy using a qPlus sensor

    PubMed Central

    Shaw, Gordon A

    2013-01-01

    Summary In qPlus atomic force microscopy the tip length can in principle approach the length of the cantilever. We present a detailed mathematical model of the effects this has on the dynamic properties of the qPlus sensor. The resulting, experimentally confirmed motion of the tip apex is shown to have a large lateral component, raising interesting questions for both calibration and force-spectroscopy measurements. PMID:23400392

  18. Noncontact estimation of intercellular breaking force using a femtosecond laser impulse quantified by atomic force microscopy

    PubMed Central

    Hosokawa, Yoichiroh; Hagiyama, Man; Iino, Takanori; Murakami, Yoshinori; Ito, Akihiko

    2011-01-01

    When a femtosecond laser pulse (fsLP) is focused through an objective lens into a culture medium, an impulsive force (fsLP-IF) is generated that propagates from the laser focal point (Of) in a micron-sized space. This force can detach individual adherent cells without causing considerable cell damage. In this study, an fsLP-IF was reflected in the vibratory movement of an atomic force microscopy (AFM) cantilever. Based on the magnitude of the vibration and the geometrical relationship between Of and the cantilever, the fsLP-IF generated at Of was calculated as a unit of impulse [N-s]. This impulsive force broke adhesion molecule-mediated intercellular interactions in a manner that depended on the adhesion strength that was estimated by the cell aggregation assay. The force also broke the interactions between streptavidin-coated microspheres and a biotin-coated substrate with a measurement error of approximately 7%. These results suggest that fsLP-IF can be used to break intermolecular and intercellular interactions and estimate the adhesion strength. The fsLP-IF was used to break intercellular contacts in two biologically relevant cultures: a coculture of leukocytes seeded over on an endothelial cell monolayer, and a polarized monolayer culture of epithelial cells. The impulses needed to break leukocyte–endothelial and interepithelial interactions, which were calculated based on the geometrical relationship between Of and the adhesive interface, were on the order of 10-13 and 10-12 N-s, respectively. When the total impulse at Of is well-defined, fsLP-IF can be used to estimate the force required to break intercellular adhesions in a noncontact manner under biologically relevant conditions. PMID:21245358

  19. Quantitative assessment of contact and non-contact lateral force calibration methods for atomic force microscopy.

    PubMed

    Tran Khac, Bien Cuong; Chung, Koo-Hyun

    2016-02-01

    Atomic Force Microscopy (AFM) has been widely used for measuring friction force at the nano-scale. However, one of the key challenges faced by AFM researchers is to calibrate an AFM system to interpret a lateral force signal as a quantifiable force. In this study, five rectangular cantilevers were used to quantitatively compare three different lateral force calibration methods to demonstrate the legitimacy and to establish confidence in the quantitative integrity of the proposed methods. The Flat-Wedge method is based on a variation of the lateral output on a surface with flat and changing slopes, the Multi-Load Pivot method is based on taking pivot measurements at several locations along the cantilever length, and the Lateral AFM Thermal-Sader method is based on determining the optical lever sensitivity from the thermal noise spectrum of the first torsional mode with a known torsional spring constant from the Sader method. The results of the calibration using the Flat-Wedge and Multi-Load Pivot methods were found to be consistent within experimental uncertainties, and the experimental uncertainties of the two methods were found to be less than 15%. However, the lateral force sensitivity determined by the Lateral AFM Thermal-Sader method was found to be 8-29% smaller than those obtained from the other two methods. This discrepancy decreased to 3-19% when the torsional mode correction factor for an ideal cantilever was used, which suggests that the torsional mode correction should be taken into account to establish confidence in Lateral AFM Thermal-Sader method.

  20. Characterization of protein immobilization on nanoporous gold using atomic force microscopy and scanning electron microscopy

    NASA Astrophysics Data System (ADS)

    Tan, Yih Horng; Schallom, John R.; Ganesh, N. Vijaya; Fujikawa, Kohki; Demchenko, Alexei V.; Stine, Keith J.

    2011-08-01

    Nanoporous gold (NPG), made by dealloying low carat gold alloys, is a relatively new nanomaterial finding application in catalysis, sensing, and as a support for biomolecules. NPG has attracted considerable interest due to its open bicontinuous structure, high surface-to-volume ratio, tunable porosity, chemical stability and biocompatibility. NPG also has the attractive feature of being able to be modified by self-assembled monolayers. Here we use scanning electron microscopy (SEM) and atomic force microscopy (AFM) to characterize a highly efficient approach for protein immobilization on NPG using N-hydroxysuccinimide (NHS) ester functionalized self-assembled monolayers on NPG with pore sizes in the range of tens of nanometres. Comparison of coupling under static versus flow conditions suggests that BSA (Bovine Serum Albumin) and IgG (Immunoglobulin G) can only be immobilized onto the interior surfaces of free standing NPG monoliths with good coverage under flow conditions. AFM is used to examine protein coverage on both the exterior and interior of protein modified NPG. Access to the interior surface of NPG for AFM imaging is achieved using a special procedure for cleaving NPG. AFM is also used to examine BSA immobilized on rough gold surfaces as a comparative study. In principle, the general approach described should be applicable to many enzymes, proteins and protein complexes since both pore sizes and functional groups present on the NPG surfaces are controllable.Nanoporous gold (NPG), made by dealloying low carat gold alloys, is a relatively new nanomaterial finding application in catalysis, sensing, and as a support for biomolecules. NPG has attracted considerable interest due to its open bicontinuous structure, high surface-to-volume ratio, tunable porosity, chemical stability and biocompatibility. NPG also has the attractive feature of being able to be modified by self-assembled monolayers. Here we use scanning electron microscopy (SEM) and atomic force

  1. Nanocharacterization of bio-silica using atomic force and ultrasonic force microscopy

    NASA Astrophysics Data System (ADS)

    Gill, Vinaypreet S.; Hallinan, Kevin P.; Brar, N. S.

    2005-04-01

    Nanotechnology has become central to our research efforts to fabricate relatively smaller size devices, which are more versatile than their older and larger predecessors. Silica is a very important material in this regard. Recently, a new biomimetically inspired path to silica production has been demonstrated. This processing technique was inspired from biological organisms, such as marine diatoms, which produce silica at ambient conditions and almost neutral ph with beautiful control over location and structure. Recently, several researchers have demonstrated that positional control of silica formed could be achieved by application of an electric field to locate charged enzymes responsible for the bio catalytic condensation of silica from solution. Secondly, chemical and physical controls of silica structural morphology were achievable. Atomic Force Microscopy (AFM) and Ultrasonic Force Microscopy (UFM) techniques are employed for the first time to provide both substantially improved resolution of the morphology and relative measurement of the modulus of elasticity of the structures. In particular, these measurements reveal the positive impact of a shear flow field present during the silica formation on both the "ordering" of the structure and the mechanical properties.

  2. Characterization and Detection of Biological Weapons with Atomic Force Microscopy

    SciTech Connect

    Malkin, A J; Plomp, M; Leighton, T J; McPherson, A

    2006-09-25

    Critical gaps exist in our capabilities to rapidly characterize threat agents which could be used in attacks on facilities and military forces. DNA-based PCR and immunoassay-based techniques provide unique identification of species, strains and protein signatures of pathogens. However, differentiation between naturally occurring and weaponized bioagents and the identification of formulation signatures are beyond current technologies. One of the most effective and often the only definitive means to identify a threat agent is by its direct visualization. Atomic force microscopy (AFM) is a rapid imaging technique that covers the size range of most biothreat agents (several nanometers to tens of microns), is capable of resolving pathogen morphology and structure, and could be developed into a portable device for biological weapons (BW) field characterization. AFM can detect pathogens in aerosol, liquid, surface and soil samples while concomitantly acquiring their weaponization and threat agent digital signatures. BW morphological and structural signatures, including modifications to pathogen microstructural architecture and topology that occur during formulation and weaponization, provide the means for their differentiation from crude or purified unformulated agent, processing signatures, as well as assessment of their potential for dispersion, inhalation and environmental persistence. AFM visualization of pathogen morphology and architecture often provides valuable digital signatures and allows direct detection and identification of threat agents. We have demonstrated that pathogens, spanning the size range from several nanometers for small agricultural satellite viruses to almost half micron for pox viruses, and to several microns for bacteria and bacterial spores, can be visualized by AFM under physiological conditions to a resolution of {approx}20-30 {angstrom}. We have also demonstrated that viruses from closely related families could be differentiated by AFM on

  3. Thin-foil magnetic force system for high-numerical-aperture microscopy

    PubMed Central

    Fisher, J. K.; Cribb, J.; Desai, K. V.; Vicci, L.; Wilde, B.; Keller, K.; Taylor, R. M.; Haase, J.; Bloom, K.; O'Brien, E. Timothy; Superfine, R.

    2006-01-01

    Forces play a key role in a wide range of biological phenomena from single-protein conformational dynamics to transcription and cell division, to name a few. The majority of existing microbiological force application methods can be divided into two categories: those that can apply relatively high forces through the use of a physical connection to a probe and those that apply smaller forces with a detached probe. Existing magnetic manipulators utilizing high fields and high field gradients have been able to reduce this gap in maximum applicable force, but the size of such devices has limited their use in applications where high force and high-numerical-aperture (NA) microscopy must be combined. We have developed a magnetic manipulation system that is capable of applying forces in excess of 700 pN on a 1 μm paramagnetic particle and 13 nN on a 4.5 μm paramagnetic particle, forces over the full 4π sr, and a bandwidth in excess of 3 kHz while remaining compatible with a commercially available high-NA microscope objective. Our system design separates the pole tips from the flux coils so that the magnetic-field geometry at the sample is determined by removable thin-foil pole plates, allowing easy change from experiment to experiment. In addition, we have combined the magnetic manipulator with a feedback-enhanced, high-resolution (2.4 nm), high-bandwidth (10 kHz), long-range (100 μm xyz range) laser tracking system. We demonstrate the usefulness of this system in a study of the role of forces in higher-order chromosome structure and function. PMID:16858495

  4. In situ mechanical characterization of the cell nucleus by atomic force microscopy.

    PubMed

    Liu, Haijiao; Wen, Jun; Xiao, Yun; Liu, Jun; Hopyan, Sevan; Radisic, Milica; Simmons, Craig A; Sun, Yu

    2014-04-22

    The study of nuclear mechanical properties can provide insights into nuclear dynamics and its role in cellular mechanotransduction. While several methods have been developed to characterize nuclear mechanical properties, direct intracellular probing of the nucleus in situ is challenging. Here, a modified AFM (atomic force microscopy) needle penetration technique is demonstrated to mechanically characterize cell nuclei in situ. Cytoplasmic and nuclear stiffness were determined based on two different segments on the AFM indentation curves and were correlated with simultaneous confocal Z-stack microscopy reconstructions. On the basis of direct intracellular measurement, we show that the isolated nuclei from fibroblast-like cells exhibited significantly lower Young's moduli than intact nuclei in situ. We also show that there is in situ nucleus softening in the highly metastatic bladder cancer cell line T24 when compared to its less metastatic counterpart RT4. This technique has potential to become a reliable quantitative measurement tool for intracellular mechanics studies.

  5. α-amylase crystal growth investigated by in situ atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Astier, J. P.; Bokern, D.; Lapena, L.; Veesler, S.

    2001-06-01

    The growth behavior of porcine pancreatic α-amylase at defined supersaturation has been investigated by means of temperature controlled in situ atomic force microscopy (AFM). The step velocities measured by AFM were in overall agreement with the normal growth rates of an individual face measured by optical microscopy. In addition, highly local growth dynamics could be visualized. Imaging in tapping mode revealed crystalline amylase aggregates attached to the basal face and their subsequent incorporation into growing terraces producing a macrodefect. At high supersaturation ( β=1.6) 2-D nucleation was found to be the dominating growth mechanism, whereas at lower supersaturation ( β=1.3) the growth process appears to be defect controlled (spiral growth). The analysis of step heights on 2-D nucleation islands (monomolecular protein layers) and growth steps (two molecules in height) in combination with results from light scattering experiments suggest that a single protein molecule is the basic growth unit.

  6. Characterization of photodeposited selenium planar structures by scanning force microscopy

    NASA Astrophysics Data System (ADS)

    Peled, A.; Baranauskas, V.; Rodrigues, C.; Art-Weisman, D.; Grantman, L.; Friesem, A. A.

    1995-06-01

    This article describes the results of a surface morphology study of photodeposited thin film devices of Selenium by scanning force microscopy (SFM). First, the structures of the photodeposited films were investigated at device level dimensions of the order of visible wavelength. Specifically, ultrathin sinusoidal holographic gratings with spatial periods in the range 480-514 nm were visually identified from SFM nanograph images. Second, grain level structural investigation was performed using image processing techniques such as filtering and one- and two-dimensional Fourier transforms analysis. The variation of the surface grain structure was sampled across the Gaussian profiles of the laser photodeposited patterns. It was found that the random amorphous clustering at the perimeter of the deposited structures becomes progressively grainy towards the center, creating protrusions above the surface with trigonal Selenium (t-Se) crystalline features. Third, performing image enhancement analysis at high magnification—the nanometer level structure was investigated for amorphous Selenium (a-Se) and the laser thermally induced structural transformations of the a-Se films. It was found that the atomic solid-state structure of a-Se films, previously deduced only by indirect methods, consists mainly of a random mixture of Sex branched chains containing also a small concentration of imperfect ring structures characteristic of the α- and β-monoclinic phases. The triclinic crystalline phase (t-Se) was identified in the center of the laser overheated regions of the film Gaussian profile. The results enable us to conclude about the debate in the literature regarding the crystalline and amorphous structure of Selenium thin films.

  7. Dielectric fluctuations in force microscopy: noncontact friction and frequency jitter.

    PubMed

    Yazdanian, Showkat M; Marohn, John A; Loring, Roger F

    2008-06-14

    Electric force microscopy, in which a charged probe oscillates tens to hundreds of nanometers above a sample surface, provides direct mechanical detection of relaxation in molecular materials. Noncontact friction, the damping of the probe's motions, reflects the dielectric function at the resonant frequency of the probe, while fluctuations in the probe frequency are induced by slower molecular motions. We present a unified theoretical picture of both measurements, which relates the noncontact friction and the power spectrum of the frequency jitter to dielectric properties of the sample and to experimental geometry. Each observable is related to an equilibrium correlation function associated with electric field fluctuations, which is determined by two alternative, complementary strategies for a dielectric continuum model of the sample. The first method is based on the calculation of a response function associated with the polarization of the dielectric by a time-varying external charge distribution. The second approach employs a stochastic form of Maxwell's equations, which incorporate a fluctuating electric polarization, to compute directly the equilibrium correlation function in the absence of an external charge distribution. This approach includes effects associated with the propagation of radiation. In the experimentally relevant limit that the tip-sample distance is small compared to pertinent wavelengths of radiation, the two methods yield identical results. Measurements of the power spectrum of frequency fluctuations of an ultrasensitive cantilever together with measurements of the noncontact friction over a poly(methylmethacrylate) film are used to estimate the minimum experimentally detectable frequency jitter. The predicted jitter for this polymer is shown to exceed this threshold, demonstrating the feasibility of the measurement. PMID:18554042

  8. Controlled evaluation of silver nanoparticle dissolution using atomic force microscopy.

    PubMed

    Kent, Ronald D; Vikesland, Peter J

    2012-07-01

    Incorporation of silver nanoparticles (AgNPs) into an increasing number of consumer products has led to concern over the potential ecological impacts of their unintended release to the environment. Dissolution is an important environmental transformation that affects the form and concentration of AgNPs in natural waters; however, studies on AgNP dissolution kinetics are complicated by nanoparticle aggregation. Herein, nanosphere lithography (NSL) was used to fabricate uniform arrays of AgNPs immobilized on glass substrates. Nanoparticle immobilization enabled controlled evaluation of AgNP dissolution in an air-saturated phosphate buffer (pH 7.0, 25 °C) under variable NaCl concentrations in the absence of aggregation. Atomic force microscopy (AFM) was used to monitor changes in particle morphology and dissolution. Over the first day of exposure to ≥10 mM NaCl, the in-plane AgNP shape changed from triangular to circular, the sidewalls steepened, the in-plane radius decreased by 5-11 nm, and the height increased by 6-12 nm. Subsequently, particle height and in-plane radius decreased at a constant rate over a 2-week period. Dissolution rates varied linearly from 0.4 to 2.2 nm/d over the 10-550 mM NaCl concentration range tested. NaCl-catalyzed dissolution of AgNPs may play an important role in AgNP fate in saline waters and biological media. This study demonstrates the utility of NSL and AFM for the direct investigation of unaggregated AgNP dissolution. PMID:22191460

  9. Voltage-dependent membrane displacements measured by atomic force microscopy.

    PubMed

    Mosbacher, J; Langer, M; Hörber, J K; Sachs, F

    1998-01-01

    Cells use polar molecules in the membrane to sense changes in the transmembrane potential. The opening of voltage-gated ion channels and membrane bending due to the inverse flexoelectric effect are two examples of such electromechanical coupling. We have looked for membrane motions in an electric field using atomic (or scanning) force microscopy (AFM) with the intent of studying voltage-dependent conformational changes of ion channels. Voltage-clamped HEK293 cells were either untransfected controls or transfected with Shaker K+ channels. Using a +/- 10-mV peak-peak AC carrier stimulus, untransfected cells moved 0.5-15 nm normal to the plane of the membrane. These movements tracked the voltage at frequencies >1 kHz with a phase lead of 60-120 degrees, as expected of a displacement current. The movement was outward with depolarization, but the holding potential only weakly influenced the amplitude of the movement. In contrast, cells transfected with a noninactivating mutant of Shaker K+channels showed similar movements, but these were sensitive to the holding potential; decreasing with depolarization between -80 and 0 mV. Searching for artifactual origins of these movements, we used open or sealed pipettes and AFM cantilever placements just above the cells. These results were negative, suggesting that the observed movements were produced by the cell membrane rather than by movement of the patch pipette, or by acoustic or electrical interactions of the membrane with the AFM tip. In control cells, the electrical motor may arise from the flexoelectric effect, where changes in potential induce changes in curvature. In transfected cells, it appears that channel-specific movements also occurred. These experiments demonstrate that the AFM may be able to exploit voltage-dependent movements as a source of contrast for imaging membrane components. The electrically induced motility will cause twitching during action potentials, and may have physiological consequences. PMID

  10. Controlled evaluation of silver nanoparticle dissolution using atomic force microscopy.

    PubMed

    Kent, Ronald D; Vikesland, Peter J

    2012-07-01

    Incorporation of silver nanoparticles (AgNPs) into an increasing number of consumer products has led to concern over the potential ecological impacts of their unintended release to the environment. Dissolution is an important environmental transformation that affects the form and concentration of AgNPs in natural waters; however, studies on AgNP dissolution kinetics are complicated by nanoparticle aggregation. Herein, nanosphere lithography (NSL) was used to fabricate uniform arrays of AgNPs immobilized on glass substrates. Nanoparticle immobilization enabled controlled evaluation of AgNP dissolution in an air-saturated phosphate buffer (pH 7.0, 25 °C) under variable NaCl concentrations in the absence of aggregation. Atomic force microscopy (AFM) was used to monitor changes in particle morphology and dissolution. Over the first day of exposure to ≥10 mM NaCl, the in-plane AgNP shape changed from triangular to circular, the sidewalls steepened, the in-plane radius decreased by 5-11 nm, and the height increased by 6-12 nm. Subsequently, particle height and in-plane radius decreased at a constant rate over a 2-week period. Dissolution rates varied linearly from 0.4 to 2.2 nm/d over the 10-550 mM NaCl concentration range tested. NaCl-catalyzed dissolution of AgNPs may play an important role in AgNP fate in saline waters and biological media. This study demonstrates the utility of NSL and AFM for the direct investigation of unaggregated AgNP dissolution.

  11. Surface potential measurement of fullerene derivative/copper phthalocyanine on indium tin oxide electrode by Kelvin probe force microscopy

    NASA Astrophysics Data System (ADS)

    Satoh, Nobuo; Yamaki, Michio; Noda, Kei; Katori, Shigetaka; Kobayashi, Kei; Matsushige, Kazumi; Yamada, Hirofumi

    2015-08-01

    We have investigated the organic semiconductor thin films deposited by vacuum evaporation deposition using intersecting metal shadow masks on indium tin oxide (ITO) electrode/glass substrates to simulate organic solar cells by simultaneous observation with dynamic force microscopy (DFM)/Kelvin-probe force microscopy (KFM). The energy band diagram was depicted by simultaneously obtaining topographic and surface potential images of the same area using DFM/KFM. We considered the charge behavior at the interface having band bending in the phenyl-C61-butyric acid methyl ester (PCBM) film.

  12. Exploring nanoscale electrical and electronic properties of organic and polymeric functional materials by atomic force microscopy based approaches.

    PubMed

    Palermo, Vincenzo; Liscio, Andrea; Palma, Matteo; Surin, Mathieu; Lazzaroni, Roberto; Samorì, Paolo

    2007-08-28

    Beyond imaging, atomic force microscopy (AFM) based methodologies enable the quantitative investigation of a variety of physico-chemical properties of (multicomponent) materials with a spatial resolution of a few nanometers. This Feature Article is focused on two AFM modes, i.e. conducting and Kelvin probe force microscopies, which allow the study of electrical and electronic properties of organic thin films, respectively. These nanotools provide a wealth of information on (dynamic) characteristics of tailor-made functional architectures, opening pathways towards their technological application in electronics, catalysis and medicine.

  13. Probing biofouling resistant polymer brush surfaces by atomic force microscopy based force spectroscopy.

    PubMed

    Schön, Peter; Kutnyanszky, Edit; ten Donkelaar, Bas; Santonicola, M Gabriella; Tecim, Tugba; Aldred, Nick; Clare, Anthony S; Vancso, G Julius

    2013-02-01

    The protein repellency and biofouling resistance of zwitterionic poly(sulfobetaine methacrylate)(pSBMA) brushes grafted via surface initiated polymerization (SIP) from silicon and glass substrata was assessed using atomic force microscopy (AFM) adherence experiments. Laboratory settlement assays were conducted with cypris larvae of the barnacle Balanus amphitrite. AFM adherence includes the determination of contact rupture forces when AFM probe tips are withdrawn from the substratum. When the surface of the AFM tip is modified, adherence can be assessed with chemical specifity using a method known as chemical force microscopy (CFM). In this study, AFM tips were chemically functionalized with (a) fibronectin- here used as model for a nonspecifically adhering protein - and (b) arginine-glycine-aspartic acid (RGD) peptide motifs covalently attached to poly(methacrylic acid) (PMAA) brushes as biomimics of cellular adhesion receptors. Fibronectin functionalized tips showed significantly reduced nonspecific adhesion to pSBMA-modified substrata compared to bare gold (2.3±0.75 nN) and octadecanethiol (ODT) self-assembled monolayers (1.3±0.75 nN). PMAA and PMAA-RGD modified probes showed no significant adhesion to pSBMA modified silicon substrata. The results gathered through AFM protein adherence studies were complemented by laboratory fouling studies, which showed no adhesion of cypris larvae of Balanus amphitrite on pSBMA. With regard to its unusually high non-specific adsorption to a wide variety of materials the behavior of fibronectin is analogous to the barnacle cyprid temporary adhesive that also binds well to surfaces differing in polarity, charge and free energy. The antifouling efficacy of pSBMA may, therefore, be directly related to the ability of this surface to resist nonspecific protein adsorption. PMID:23138001

  14. Improvements in fundamental performance of liquid-environment atomic force microscopy with true atomic resolution

    NASA Astrophysics Data System (ADS)

    Miyata, Kazuki; Miyazawa, Keisuke; Akrami, Seyed Mohammad Reza; Fukuma, Takeshi

    2015-08-01

    Recently, there have been significant advancements in liquid-environment atomic force microscopy (AFM) with true atomic resolution. The technical advancements are followed by a rapid expansion of its application area. Examples include subnanometer-scale imaging of biological systems and three-dimensional measurements of water distributions (i.e., hydration structures) and fluctuating surface structures. However, to continue this progress, we should improve the fundamental performance of liquid-environment dynamic-mode AFM. The present AFM technique does not allow real-time imaging of atomic-scale dynamic phenomena at a solid-liquid interface. This has hindered atomic-level understanding of crystal growth and dissolution, catalytic reactions and metal corrosion processes. Improvement in force sensitivity is required not only for such a high-speed imaging but also for various surface property measurements using a high-resolution AFM technique. In this review, we summarize recent works on the improvements in the force sensitivity and operation speed of atomic-resolution dynamic-mode AFM for liquid-environment applications.

  15. Magnetic resonance force microscopy of paramagnetic electron spins at millikelvin temperatures.

    PubMed

    Vinante, A; Wijts, G; Usenko, O; Schinkelshoek, L; Oosterkamp, T H

    2011-12-06

    Magnetic resonance force microscopy (MRFM) is a powerful technique to detect a small number of spins that relies on force detection by an ultrasoft magnetically tipped cantilever and selective magnetic resonance manipulation of the spins. MRFM would greatly benefit from ultralow temperature operation, because of lower thermomechanical noise and increased thermal spin polarization. Here we demonstrate MRFM operation at temperatures as low as 30 mK, thanks to a recently developed superconducting quantum interference device (SQUID)-based cantilever detection technique, which avoids cantilever overheating. In our experiment, we detect dangling bond paramagnetic centres on a silicon surface down to millikelvin temperatures. Fluctuations of such defects are supposedly linked to 1/f magnetic noise and decoherence in SQUIDs, as well as in several superconducting and single spin qubits. We find evidence that spin diffusion has a key role in the low-temperature spin dynamics.

  16. Fast, high-resolution surface potential measurements in air with heterodyne Kelvin probe force microscopy

    NASA Astrophysics Data System (ADS)

    Garrett, Joseph L.; Munday, Jeremy N.

    2016-06-01

    Kelvin probe force microscopy (KPFM) adapts an atomic force microscope to measure electric potential on surfaces at nanometer length scales. Here we demonstrate that Heterodyne-KPFM enables scan rates of several frames per minute in air, and concurrently maintains spatial resolution and voltage sensitivity comparable to frequency-modulation KPFM, the current spatial resolution standard. Two common classes of topography-coupled artifacts are shown to be avoidable with H-KPFM. A second implementation of H-KPFM is also introduced, in which the voltage signal is amplified by the first cantilever resonance for enhanced sensitivity. The enhanced temporal resolution of H-KPFM can enable the imaging of many dynamic processes, such as such as electrochromic switching, phase transitions, and device degredation (battery, solar, etc), which take place over seconds to minutes and involve changes in electric potential at nanometer lengths.

  17. High Resolution Electromechanical Imaging of Ferroelectric Materials in a Liquid Environment by Piezoresponse Force Microscopy

    SciTech Connect

    Rodriguez, Brian J; Jesse, Stephen; Baddorf, Arthur P; Kalinin, Sergei V

    2006-01-01

    High-resolution imaging of ferroelectric materials using piezoresponse force microscopy (PFM) is demonstrated in an aqueous environment. The elimination of both long-range electrostatic forces and capillary interactions results in a localization of the ac field to the tip-surface junction and allows the tip-surface contact area to be controlled. This approach results in spatial resolutions approaching the limit of the intrinsic domain-wall width. Imaging at frequencies corresponding to high-order cantilever resonances minimizes the viscous damping and added mass effects on cantilever dynamics and allows sensitivities comparable to ambient conditions. PFM in liquids will provide novel opportunities for high-resolution studies of ferroelectric materials, imaging of soft polymer materials, and imaging of biological systems in physiological environments on, ultimately, the molecular level.

  18. Resonance frequency-retuned quartz tuning fork as a force sensor for noncontact atomic force microscopy

    SciTech Connect

    Ooe, Hiroaki; Sakuishi, Tatsuya; Arai, Toyoko; Nogami, Makoto; Tomitori, Masahiko

    2014-07-28

    Based on a two-prong type quartz tuning fork, a force sensor with a high Q factor, which we call a retuned fork sensor, was developed for non-contact atomic force microscopy (nc-AFM) with atomic resolution. By cutting a small notch and attaching an AFM tip to one prong, its resonance frequency can be retuned to that of the other intact prong. In balancing the two prongs in this manner, a high Q factor (>50 000 in ultrahigh vacuum) is obtained for the sensor. An atomic resolution image of the Si(111)-7 × 7 surface was demonstrated using an nc-AFM with the sensor. The dependence of the Q factor on resonance frequency of the sensor and the long-range force between tip and sample were measured and analyzed in view of the various dissipation channels. Dissipation in the signal detection circuit turned out to be mainly limited by the total Q factor of the nc-AFM system.

  19. Resonance frequency-retuned quartz tuning fork as a force sensor for noncontact atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Ooe, Hiroaki; Sakuishi, Tatsuya; Nogami, Makoto; Tomitori, Masahiko; Arai, Toyoko

    2014-07-01

    Based on a two-prong type quartz tuning fork, a force sensor with a high Q factor, which we call a retuned fork sensor, was developed for non-contact atomic force microscopy (nc-AFM) with atomic resolution. By cutting a small notch and attaching an AFM tip to one prong, its resonance frequency can be retuned to that of the other intact prong. In balancing the two prongs in this manner, a high Q factor (>50 000 in ultrahigh vacuum) is obtained for the sensor. An atomic resolution image of the Si(111)-7 × 7 surface was demonstrated using an nc-AFM with the sensor. The dependence of the Q factor on resonance frequency of the sensor and the long-range force between tip and sample were measured and analyzed in view of the various dissipation channels. Dissipation in the signal detection circuit turned out to be mainly limited by the total Q factor of the nc-AFM system.

  20. Reliable measurements of interfacial slip by colloid probe atomic force microscopy. II. Hydrodynamic force measurements.

    PubMed

    Zhu, Liwen; Attard, Phil; Neto, Chiara

    2011-06-01

    Here we report a new study on the boundary conditions for the flow of a simple liquid in a confined geometry obtained by measuring hydrodynamic drainage forces with colloid probe atomic force microscopy (AFM). In this work, we provide experimental data obtained using a best practice experimental protocol and fitted with a new theoretical calculation (Zhu, L.; Attard, P.; Neto, C. Langmuir 2010, submitted for publication, preceding paper). We investigated the hydrodynamic forces acting on a silica colloid probe approaching a hydrophobized silicon surface in a single-component viscous Newtonian liquid (di-n-octylphthalate), a partially wetting system. The measured average slip lengths were in the range of 24-31 nm at approach velocities of between 10 and 80 μm/s. Using our experimental approach, the presence of nanoparticle contaminants in the system can be indentified, which is important because it has been shown that nanoparticles lead to a large apparent slip length. Under our stringent control of experimental conditions, the measurement of the slip length is reproducible and independent of the spring constant of the cantilever.

  1. Microfluidic-assisted atomic force microscopy for the mechanical characterization of soft biological materials

    NASA Astrophysics Data System (ADS)

    Mosier, Aaron P.

    Viable methods for bacterial biofilm remediation require a fundamental understanding of biofilm mechanical properties and their dependence on dynamic environmental conditions. Mechanical test data, quantifying elasticity or adhesion, may be used to perform physical modeling of biofilm behavior, thus enabling the development of novel remediation strategies. To achieve real-time, dynamic measurements of these properties, a novel analysis platform consisting of a microfluidic flowcell device has been designed and fabricated for in situ analysis using atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). The flowcell consists of microfluidic channels for biofilm establishment that are then converted into an open architecture, laminar flow channel for AFM measurement in a liquid environment. Computational fluid dynamics (CFD) was used to profile fluid conditions within the device during biofilm establishment. The validity of the AFM nanoindentation measurement mechanism was confirmed in the context of the system through the elastic characterization of several non-living reference materials. Force-mode AFM was used to measure the elastic properties of mature Pseudomonas aeruginosa PAO1 biofilms and observe a dynamic response to a chemical antagonist. Elastic moduli ranging from 0.58 to 2.61 kPa were determined for the mature biofilm, which fall within the range of moduli previously reported by optical, rheometric, and microindentation techniques. A modified version of the flowcell was employed to perform similar elastic characterization of mouse submandibular glands (SMGs), demonstrating the adaptability of the system to perform ex situ analyses of a broader set of biological materials. These results demonstrate the validity of the microfluidic flowcell system as an effective platform for future investigations of the mechanical and morphological response of biofilms and other soft biomaterials to dynamic environmental conditions.

  2. Structure and stability of semiconductor tip apexes for atomic force microscopy.

    PubMed

    Pou, P; Ghasemi, S A; Jelinek, P; Lenosky, T; Goedecker, S; Perez, R

    2009-07-01

    The short range force between the tip and the surface atoms, that is responsible for atomic-scale contrast in atomic force microscopy (AFM), is mainly controlled by the tip apex. Thus, the ability to image, manipulate and chemically identify single atoms in semiconductor surfaces is ultimately determined by the apex structure and its composition. Here we present a detailed and systematic study of the most common structures that can be expected at the apex of the Si tips used in experiments. We tackle the determination of the structure and stability of Si tips with three different approaches: (i) first principles simulations of small tip apexes; (ii) simulated annealing of a Si cluster; and (iii) a minima hopping study of large Si tips. We have probed the tip apexes by making atomic contacts between the tips and then compared force-distance curves with the experimental short range forces obtained with dynamic force spectroscopy. The main conclusion is that although there are multiple stable solutions for the atomically sharp tip apexes, they can be grouped into a few types with characteristic atomic structures and properties. We also show that the structure of the last atomic layers in a tip apex can be both crystalline and amorphous. We corroborate that the atomically sharp tips are thermodynamically stable and that the tip-surface interaction helps to produce the atomic protrusion needed to get atomic resolution.

  3. Tribology of diamond-like carbon films from generic fabrication routes investigated by lateral force microscopy

    NASA Astrophysics Data System (ADS)

    Crossley, Alison; Johnston, Colin; Watson, Gregory S.; Myhra, Sverre

    1998-08-01

    The tribological characteristics of diamond-like carbon (DLC) films have been studied by lateral force microscopy (LFM). Specimens from two fabrication routes, ion-beam assisted deposition and chemical vapour deposition, have been investigated. Thick (micrometres) and thin (a few nanometres) films from both routes have been considered, as have the service environments of ambient air and vacuum. Lateral force data were calculated from `friction loops', obtained as functions of load, surface topography, scan speed and service environment. An identical methodology and LFM probe were used throughout the series of measurements in order to ensure internal consistency, and the validity of the methodology was checked against measurements on epitaxially grown Si. A linear dependence was observed between lateral force and force loading up to ca 0022-3727/31/16/003/img8, in accord with a multi-asperity model, thus allowing determination of coefficients of friction that ranged from 0.05 to 0.15. The results showed that adhesive interactions contributed up to 0022-3727/31/16/003/img9 to the overall dynamic load. Meniscus interaction played a minor role in comparison to that from tribo-generated electrostatic forces. The experiments show that LFM methodologies have value and relevance to the science and technology of tribology, especially when the required spatial resolution cannot be obtained with the traditional macroscopic techniques.

  4. Undulator with dynamic compensation of magnetic forces

    DOEpatents

    Gluskin, Efim; Trakhtenberg, Emil; Xu, Joseph Z.

    2016-05-31

    A method and apparatus for implementing dynamic compensation of magnetic forces for undulators are provided. An undulator includes a respective set of magnet arrays, each attached to a strongback, and placed on horizontal slides and positioned parallel relative to each other with a predetermined gap. Magnetic forces are compensated by a set of compensation springs placed along the strongback. The compensation springs are conical springs having exponential-force characteristics that substantially match undulator magnetic forces independently of the predetermined gap. The conical springs are positioned along the length of the magnets.

  5. Imaging dielectric relaxation in nanostructured polymers by frequency modulation electrostatic force microscopy

    NASA Astrophysics Data System (ADS)

    Riedel, C.; Sweeney, R.; Israeloff, N. E.; Arinero, R.; Schwartz, G. A.; Alegria, A.; Tordjeman, Ph.; Colmenero, J.

    2010-05-01

    We have developed a method for imaging the temperature-frequency dependence of the dynamics of nanostructured polymer films with spatial resolution. This method provides images with dielectric compositional contrast well decoupled from topography. Using frequency-modulation electrostatic-force-microscopy, we probe the local frequency-dependent (0.1-100 Hz) dielectric response through measurement of the amplitude and phase of the force gradient in response to an oscillating applied electric field. When the phase is imaged at fixed frequency, it reveals the spatial variation in dielectric losses, i.e., the spatial variation in molecular/dipolar dynamics, with 40 nm lateral resolution. This is demonstrated by using as a model system; a phase separated polystyrene/polyvinyl-acetate (PVAc) blend. We show that nanoscale dynamic domains of PVAc are clearly identifiable in phase images as those which light-up in a band of temperature, reflecting the variations in the molecular/dipolar dynamics approaching the glass transition temperature of PVAc.

  6. Atomic Force Microscopy of Red-Light Photoreceptors Using PeakForce Quantitative Nanomechanical Property Mapping

    PubMed Central

    Kroeger, Marie E.; Sorenson, Blaire A.; Thomas, J. Santoro; Stojković, Emina A.; Tsonchev, Stefan; Nicholson, Kenneth T.

    2014-01-01

    Atomic force microscopy (AFM) uses a pyramidal tip attached to a cantilever to probe the force response of a surface. The deflections of the tip can be measured to ~10 pN by a laser and sectored detector, which can be converted to image topography. Amplitude modulation or “tapping mode” AFM involves the probe making intermittent contact with the surface while oscillating at its resonant frequency to produce an image. Used in conjunction with a fluid cell, tapping-mode AFM enables the imaging of biological macromolecules such as proteins in physiologically relevant conditions. Tapping-mode AFM requires manual tuning of the probe and frequent adjustments of a multitude of scanning parameters which can be challenging for inexperienced users. To obtain high-quality images, these adjustments are the most time consuming. PeakForce Quantitative Nanomechanical Property Mapping (PF-QNM) produces an image by measuring a force response curve for every point of contact with the sample. With ScanAsyst software, PF-QNM can be automated. This software adjusts the set-point, drive frequency, scan rate, gains, and other important scanning parameters automatically for a given sample. Not only does this process protect both fragile probes and samples, it significantly reduces the time required to obtain high resolution images. PF-QNM is compatible for AFM imaging in fluid; therefore, it has extensive application for imaging biologically relevant materials. The method presented in this paper describes the application of PF-QNM to obtain images of a bacterial red-light photoreceptor, RpBphP3 (P3), from photosynthetic R. palustris in its light-adapted state. Using this method, individual protein dimers of P3 and aggregates of dimers have been observed on a mica surface in the presence of an imaging buffer. With appropriate adjustments to surface and/or solution concentration, this method may be generally applied to other biologically relevant macromolecules and soft materials. PMID

  7. Exploring the electronic and mechanical properties of protein using conducting atomic force microscopy.

    PubMed

    Zhao, Jianwei; Davis, Jason J; Sansom, Mark S P; Hung, Andrew

    2004-05-01

    In interfacing man-made electronic components with specifically folded biomacromolecules, the perturbative effects of junction structure on any signal generated should be considered. We report herein on the electron-transfer characteristics of the blue copper metalloprotein, azurin, as characterized at a refined level by conducting atomic force microscopy (C-AFM). Specifically, the modulation of current-voltage (I-V) behavior with compressional force has been examined. In the absence of assignable resonant electron tunneling within the confined bias region, from -1 to 1 V, the I-V behavior was analyzed with a modified Simmons formula. To interpret the variation of tunneling barrier height and barrier length obtained by fitting with the modified Simmons formula, an atom packing density model associated with protein mechanical deformation was proposed and simulated by molecular dynamics. The barrier heights determined at the minimum forces necessary for stable electrical contact correlate reasonably well with those estimated from bulk biophysical (electroanalytical and photochemical) experiments previously reported. At higher forces, the tunnel barrier decreases to fall within the range observed with saturated organic systems. Molecular dynamics simulations revealed changes in secondary structure and atomic density of the protein with respect to compression. At low compression, where transport measurements are made, secondary structure is retained, and atomic packing density is observed to increase linearly with force. These predictions, and those made at higher compression, are consistent with both experimentally observed modulations of tunneling barrier height with applied force and the applicability of the atom packing density model of electron tunneling in proteins to molecular-level analyses.

  8. Low-temperature dynamics of ferroelectric domains in PbZr{sub 0.3}Ti{sub 0.7}O{sub 3} epitaxial thin films studied by piezoresponse force microscopy

    SciTech Connect

    Andreeva, N. V.; Vakulenko, A. F.; Filimonov, A. V.; Rudskoy, A. I.; Petraru, A.; Soni, R.; Kohlstedt, H.; Vakhrushev, S. B.; Pertsev, N. A.

    2015-10-12

    Dynamics of domain boundaries is expected to change drastically at low absolute temperatures but direct experimental information for this temperature range is still lacking. To clarify the mechanism of low-temperature domain dynamics, we studied the growth of ferroelectric domains in the temperature range 4.2–295 K using the out-of-plane piezoresponse mode of a cryogenic atomic force microscope (AFM). Nanoscale 180° domains were created in epitaxial PbZr{sub 0.3}Ti{sub 0.7}O{sub 3} films by applying short voltage pulses between the conductive AFM tip brought into contact with the bare film surface and the bottom LaSr{sub 0.7}Mn{sub 0.3}O{sub 3} electrode. A quantitative analysis of acquired piezoresponse images enabled us to determine the in-plane domain size as a function of the writing voltage and pulse duration. It is found that at all studied temperatures the dependence of this size on the pulse duration can be fitted by a logarithmic function, which indicates that the domain-wall velocity exponentially depends on the driving electric field. The theoretical analysis of experimental data shows that the observed low-temperature domain dynamics is consistent with the creep of domain boundaries occurring in the presence of defects and structural nanoheterogeneities.

  9. Tip-bias-induced domain evolution in PMN-PT transparent ceramics via piezoresponse force microscopy

    NASA Astrophysics Data System (ADS)

    Zhao, K. Y.; Zhao, W.; Zeng, H. R.; Yu, H. Z.; Ruan, W.; Xu, K. Q.; Li, G. R.

    2015-05-01

    Piezoresponse force microscopy (PFM) was employed to investigate ferroelectric domain structures and their dynamic behavior of lead magnesium niobate-lead titanate [Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT)] transparent ceramics under an tip-bias-induced electric field. A remarkable effect of fluctuation of PT content on the domain configurations and domain dynamic response in PMN-PT transparent ferroelectric ceramics were found by PFM. Comparing with PMN-10%PT and PMN-20%PT, the reversed polarization of macrodomain area in PMN-35%PT and PMN-25%PT exhibits a relatively higher response behavior and better polarization retention performance under the PFM tip-bias-induced electric field, which correspond to their unique macroscopic electro-optic properties.

  10. Atomic force microscopy measurements reveal multiple bonds between Helicobacter pylori blood group antigen binding adhesin and Lewis b ligand.

    PubMed

    Parreira, P; Shi, Q; Magalhaes, A; Reis, C A; Bugaytsova, J; Borén, T; Leckband, D; Martins, M C L

    2014-12-01

    The strength of binding between the Helicobacter pylori blood group antigen-binding adhesin (BabA) and its cognate glycan receptor, the Lewis b blood group antigen (Le(b)), was measured by means of atomic force microscopy. High-resolution measurements of rupture forces between single receptor-ligand pairs were performed between the purified BabA and immobilized Le(b) structures on self-assembled monolayers. Dynamic force spectroscopy revealed two similar but statistically different bond populations. These findings suggest that the BabA may form different adhesive attachments to the gastric mucosa in ways that enhance the efficiency and stability of bacterial adhesion.

  11. Robust high-resolution imaging and quantitative force measurement with tuned-oscillator atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Dagdeviren, Omur E.; Götzen, Jan; Hölscher, Hendrik; Altman, Eric I.; Schwarz, Udo D.

    2016-02-01

    Atomic force microscopy (AFM) and spectroscopy are based on locally detecting the interactions between a surface and a sharp probe tip. For highest resolution imaging, noncontact modes that avoid tip-sample contact are used; control of the tip’s vertical position is accomplished by oscillating the tip and detecting perturbations induced by its interaction with the surface potential. Due to this potential’s nonlinear nature, however, achieving reliable control of the tip-sample distance is challenging, so much so that despite its power vacuum-based noncontact AFM has remained a niche technique. Here we introduce a new pathway to distance control that prevents instabilities by externally tuning the oscillator’s response characteristics. A major advantage of this operational scheme is that it delivers robust position control in both the attractive and repulsive regimes with only one feedback loop, thereby providing an easy-to-implement route to atomic resolution imaging and quantitative tip-sample interaction force measurement.

  12. A calibration method for lateral forces for use with colloidal probe force microscopy cantilevers

    SciTech Connect

    Quintanilla, M. A. S.; Goddard, D. T.

    2008-02-15

    A calibration method is described for colloidal probe cantilevers that enables friction force measurements obtained using lateral force microscopy (LFM) to be quantified. The method is an adaptation of the lever method of Feiler et al. [A. Feiler, P. Attard, and I. Larson, Rev. Sci. Instum. 71, 2746 (2000)] and uses the advantageous positioning of probe particles that are usually offset from the central axis of the cantilever. The main sources of error in the calibration method are assessed, in particular, the potential misalignment of the long axis of the cantilever that ideally should be perpendicular to the photodiode detector. When this is not taken into account, the misalignment is shown to have a significant effect on the cantilever torsional stiffness but not on the lateral photodiode sensitivity. Also, because the friction signal is affected by the topography of the substrate, the method presented is valid only against flat substrates. Two types of particles, 20 {mu}m glass beads and UO{sub 3} agglomerates attached to silicon tapping mode cantilevers were used to test the method against substrates including glass, cleaved mica, and UO{sub 2} single crystals. Comparisons with the lateral compliance method of Cain et al. [R. G. Cain, S. Biggs, and N. W. Page, J. Colloid Interface Sci. 227, 55 (2000)] are also made.

  13. High-resolution atomic force microscopy and spectroscopy of native membrane proteins

    NASA Astrophysics Data System (ADS)

    Bippes, Christian A.; Muller, Daniel J.

    2011-08-01

    Membranes confining cells and cellular compartments are essential for life. Membrane proteins are molecular machines that equip cell membranes with highly sophisticated functionality. Examples of such functions are signaling, ion pumping, energy conversion, molecular transport, specific ligand binding, cell adhesion and protein trafficking. However, it is not well understood how most membrane proteins work and how the living cell regulates their function. We review how atomic force microscopy (AFM) can be applied for structural and functional investigations of native membrane proteins. High-resolution time-lapse AFM imaging records membrane proteins at work, their oligomeric state and their dynamic assembly. The AFM stylus resembles a multifunctional toolbox that allows the measurement of several chemical and physical parameters at the nanoscale. In the single-molecule force spectroscopy (SMFS) mode, AFM quantifies and localizes interactions in membrane proteins that stabilize their folding and modulate their functional state. Dynamic SMFS discloses fascinating insights into the free energy landscape of membrane proteins. Single-cell force spectroscopy quantifies the interactions of live cells with their environment to single-receptor resolution. In the future, technological progress in AFM-based approaches will enable us to study the physical nature of biological interactions in more detail and decipher how cells control basic processes.

  14. Force dynamics in fixed-ratio schedules.

    PubMed

    Pinkston, Jonathan W; McBee, Lindsey N

    2014-03-01

    Fixed-ratio schedules are widely used in behavioral research. Although fixed-ratio schedules often conjure up relationships to work and effort, little is known about effort-related measures in these schedules. Early research had shown that force and effort of operant behavior vary systematically during the execution of ratio schedules, and the goal of the present study was to revisit early research on force dynamics in fixed-ratio schedules. Four rats earned sucrose by pressing an isometric force transducer. Presses produced sucrose after ten or twenty responses. In general, the force of responses increased then decreased systematically across the ratio. The possibility that decreases in force during ratio execution was due to a trade-off with the differential reinforcement of short inter-response times (IRT) was investigated in an additional condition where sucrose was made available according to a tandem fixed-ratio 19 inter-response (IRT)> t schedule. The tandem IRT requirement did not eliminate decreasing trends in force across the ratio; unexpectedly, the tandem requirement did eliminate increases in force early in the ratio, which may reflect sequence-level organization operating in the control of force dynamics. PMID:24315798

  15. Modeling and boundary force control of microcantilevers utilized in atomic force microscopy for cellular imaging and characterization

    NASA Astrophysics Data System (ADS)

    Eslami, Sohrab

    This dissertation undertakes the theoretical and experimental developments microcantilevers utilized in Atomic Force Microscopy (AFM) with applications to cellular imaging and characterization. The capability of revealing the inhomogeneties or interior of ultra-small materials has been of most interest to many researchers. However, the fundamental concept of signal and image formation remains unexplored and not fully understood. For his, a semi-empirical nonlinear force model is proposed to show that virtual frequency generation, regarded as the simplest synthesized subsurface probe, occurs optimally when the force is tuned to the van der Waals form. This is the first-time observation of a novel theoretical dynamic multi-frequency force microscopy that has not been already reported. Owing to the broad applications of microcantilevers in the nanoscale imaging and microscopic techniques, there is an essential feeling to study and propose a comprehensive model of such systems. Therefore, in the theoretical part of this dissertation, a distributed-parameters representation modeling of the microcantilever along with a general interaction force comprising of two attractive and repulsive components with general amplitude and power terms is studied. This model is investigated in a general 2D Cartesian coordinate to consider the motions of the probe with a tip mass. There is an excitation at the microcantilever's base such that the end of the beam is subject to the proposed general force. These forces are very sensitive to the amplitude and power terms of these parts; on the other hand, atomic intermolecular force is a function of the distance such that this distance itself is also a function of the interaction force that will result in a nonlinear implicit equation. From a parametric study in the probe-sample excitation, it is shown that the predicted behavior of the generated difference-frequency oscillation amplitude agrees well with experimental measurements. Following

  16. Carbon Nanotube Atomic Force Microscopy for Proteomics and Biological Forensics

    SciTech Connect

    Noy, A; De Yoreo, J J; Malkin, A J

    2002-01-01

    The Human Genome Project was focused on mapping the complete genome. Yet, understanding the structure and function of the proteins expressed by the genome is the real end game. But there are approximately 100,000 proteins in the human body and the atomic structure has been determined for less than 1% of them. Given the current rate at which structures are being solved, it will take more than one hundred years to complete this task. The rate-limiting step in protein structure determination is the growth of high-quality single crystals for X-ray diffraction. Synthesis of the protein stock solution as well as X-ray diffraction and analysis can now often be done in a matter of weeks, but developing a recipe for crystallization can take years and, especially in the case of membrane proteins, is often completely unsuccessful. Consequently, techniques that can either help to elucidate the factors controlling macromolecular crystallization, increase the amount of structural information obtained from crystallized macromolecules or eliminate the need for crystallization altogether are of enormous importance. In addition, potential applications for those techniques extend well beyond the challenges of proteomics. The global spread of modern technology has brought with it an increasing threat from biological agents such as viruses. As a result, developing techniques for identifying and understanding the operation of such agents is becoming a major area of forensic research for DOE. Previous to this project, we have shown that we can use in situ atomic force microscopy (AFM) to image the surfaces of growing macromolecular crystals with molecular resolution (1-5) In addition to providing unprecedented information about macromolecular nucleation, growth and defect structure, these results allowed us to obtain low-resolution phase information for a number of macromolecules, providing structural information that was not obtainable from X-ray diffraction(3). For some virus systems

  17. Compensator design for improved counterbalancing in high speed atomic force microscopy

    PubMed Central

    Bozchalooi, I. S.; Youcef-Toumi, K.; Burns, D. J.; Fantner, G. E.

    2011-01-01

    High speed atomic force microscopy can provide the possibility of many new scientific observations and applications ranging from nano-manufacturing to the study of biological processes. However, the limited imaging speed has been an imperative drawback of the atomic force microscopes. One of the main reasons behind this limitation is the excitation of the AFM dynamics at high scan speeds, severely undermining the reliability of the acquired images. In this research, we propose a piezo based, feedforward controlled, counter actuation mechanism to compensate for the excited out-of-plane scanner dynamics. For this purpose, the AFM controller output is properly filtered via a linear compensator and then applied to a counter actuating piezo. An effective algorithm for estimating the compensator parameters is developed. The information required for compensator design is extracted from the cantilever deflection signal, hence eliminating the need for any additional sensors. The proposed approach is implemented and experimentally evaluated on the dynamic response of a custom made AFM. It is further assessed by comparing the imaging performance of the AFM with and without the application of the proposed technique and in comparison with the conventional counterbalancing methodology. The experimental results substantiate the effectiveness of the method in significantly improving the imaging performance of AFM at high scan speeds. PMID:22128989

  18. Monitoring ligand-receptor interactions by photonic force microscopy

    PubMed Central

    Jeney, Sylvia; Mor, Flavio; Koszali, Roland; Forró, László; Moy, Vincent T.

    2011-01-01

    We introduce a method for the acquisition of single molecule force measurements of ligand —receptor interactions using the photonic force microscope (PFM). Biotin-functionalized beads, manipulated with an optical trap, and a streptavidin-functionalized coverslip were used to measure the effect of different pulling forces on the lifetime of individual streptavidin-biotin complexes. By optimizing the design of the optical trap and selection of the appropriate bead size, pulling forces in excess of 50 pN were achieved. Based on the amplitude of three dimensional (3D) thermal position fluctuations of the attached bead, we were able to select for a bead-coverslip interaction that was mediated by a single streptavidin-biotin complex. Moreover, the developed experimental system was greatly accelerated by automation of data acquisition and analysis. In force-dependent kinetic measurements carried out between streptavidin and biotin, we observed that the streptavidin-biotin complex exhibited properties of a catch bond with the lifetime increasing 10 fold when the pulling force increased from 10 to 20 pN. We also show that silica beads were more appropriate than polystyrene beads for the force measurements as polystyrene tethers, longer than 200 nm, could be extracted from the beads. PMID:20516583

  19. Low Temperature Force Microscopy on a Deeply Embedded Two Dimensional Electron Gas

    NASA Astrophysics Data System (ADS)

    Hedberg, James Augustin

    2011-12-01

    Experimental physics in the low temperature limit has consistently produced major advances for condensed matter research. Likewise, scanning probe microscopy offers a unique view of the nanometer scale features that populate the quantum landscape. This work discusses the merger of the two disciplines via the development of the Ultra Low Temperature Scanning Probe Microscope, the ULT-SPM. We focus on the novel characterization of an exotic condensed matter system: a deeply buried two dimensional electron gas with a cleaved edge overgrowth geometry. By coupling the dynamics of the force sensing probe microscope to the electrostatics of the electron gas, we can remotely and non-invasively measure charge transport features which are normally only observable using physically contacted electrodes. Focusing on the quantum Hall regime, we can exploit the high sensitivity of the local force sensor to study spatially dependent phenomena associated with electronic potential distributions. The instrument shows promise for many exciting experiments in which low temperatures, high magnetic fields, and local measurements are critical. Designed for operation at 50 mK, in magnetic fields reaching 16 T, many components of the instrument are not commercially available and were therefore designed and constructed in- house. As such, the intricate details of its design, construction and operation are documented thoroughly. This includes: the microscope assembly, the modular components such as the scan head and coarse motors, the electronics developed for controlling the instrument, and the general integration into the low temperature infrastructure. A quartz tuning fork is used as the force sensor in this instrument, enabling a wide selection between different modes of operation, the most relevant being electrostatic force microscopy. Noise limits are investigated and matched sources of experimental noise are identified. Detailed schematics of the instrument are also included.

  20. Piezoelectric force microscopy of crystalline oxide-semiconductor heterostructures

    SciTech Connect

    Marshall, M. S. J.; Kumah, D.; Reiner, J. W.; Maksymovych, Petro; Baddorf, Arthur P; Ahn, Charles H.; Walker, F. J.

    2012-01-01

    Thin films of epitaxial SrTiO{sub 3} grown on silicon exhibit compressive in-plane strain that may stabilize ferroelectricity in this normally non-ferroelectric material. We investigate this possibility by using an ultra-high vacuum atomic force microscope to measure the local force response of coherently strained SrTiO{sub 3} films on silicon to an applied ac electric field. The observed cantilever response is different in regions that were previously written with positive and negative voltages, but the frequency dependence of this response indicates that the dominant forces are related to electrostatic charging rather than ferroelectricity.

  1. Piezoelectric force microscopy of crystalline oxide-semiconductor heterostructures

    SciTech Connect

    Marshall, M. S. J.; Kumah, D. P.; Reiner, J. W.; Ahn, C. H.; Walker, F. J.; Baddorf, A. P.

    2012-09-03

    Thin films of epitaxial SrTiO{sub 3} grown on silicon exhibit compressive in-plane strain that may stabilize ferroelectricity in this normally non-ferroelectric material. We investigate this possibility by using an ultra-high vacuum atomic force microscope to measure the local force response of coherently strained SrTiO{sub 3} films on silicon to an applied ac electric field. The observed cantilever response is different in regions that were previously written with positive and negative voltages, but the frequency dependence of this response indicates that the dominant forces are related to electrostatic charging rather than ferroelectricity.

  2. G-mode magnetic force microscopy: Separating magnetic and electrostatic interactions using big data analytics

    NASA Astrophysics Data System (ADS)

    Collins, Liam; Belianinov, Alex; Proksch, Roger; Zuo, Tingting; Zhang, Yong; Liaw, Peter K.; Kalinin, Sergei V.; Jesse, Stephen

    2016-05-01

    In this work, we develop a full information capture approach for Magnetic Force Microscopy (MFM), referred to as generalized mode (G-Mode) MFM. G-Mode MFM acquires and stores the full data stream from the photodetector, captured at sampling rates approaching the intrinsic photodiode limit. The data can be subsequently compressed, denoised, and analyzed, without information loss. Here, G-Mode MFM is implemented and compared to the traditional heterodyne-based MFM on model systems, including domain structures in ferromagnetic Yttrium Iron Garnet and the electronically and magnetically inhomogeneous high entropy alloy, CoFeMnNiSn. We investigate the use of information theory to mine the G-Mode MFM data and demonstrate its usefulness for extracting information which may be hidden in traditional MFM modes, including signatures of nonlinearities and mode-coupling phenomena. Finally, we demonstrate detection and separation of magnetic and electrostatic tip-sample interactions from a single G-Mode image, by analyzing the entire frequency response of the cantilever. G-Mode MFM is immediately implementable on any atomic force microscopy platform and as such is expected to be a useful technique for probing spatiotemporal cantilever dynamics and mapping material properties, as well as their mutual interactions.

  3. Atomic force microscopy studies of alkali halide surfaces nanostructured by DIET

    NASA Astrophysics Data System (ADS)

    Goryl, M.; Such, B.; Krok, F.; Meisel, K.; Kolodziej, J. J.; Szymonski, M.

    2005-11-01

    We report on surface topography modification of single crystal alkali halides due to creation of the excitonic states by keV electron irradiation. The DIET—structured surfaces have been studied with nanometer scale resolution by means of a dynamic (non-contact) atomic force microscopy (DFM) in UHV. The force microscopy studies reveal that randomly spread rectangular pits of monolayer depth in the topmost layer of the crystal are formed during irradiation. Growth and coalescence of the pits lead to almost layer-by-layer desorption mode. It is demonstrated that varying surface topography affects the yield of both the halogen and the alkali atom desorption component, as well as velocity spectrum of desorbing halogen atoms (thermal versus non-thermal ratio). We propose a model in which periodic changes of the surface topography with the increasing electron fluence (from initially flat to rough at about half monolayer desorbed, back to flat after a complete monolayer removal) are modulating the surface recombination probability for the excited F-centers. By controlling the population of traps in the bulk these surface processes are causing modulation of the diffusion range of mobile defects migrating from the bulk of the material towards its surface and the bulk recombination probabilities of F- and H-centres.

  4. Three-dimensional force microscopy of cells in biopolymer networks.

    PubMed

    Steinwachs, Julian; Metzner, Claus; Skodzek, Kai; Lang, Nadine; Thievessen, Ingo; Mark, Christoph; Münster, Stefan; Aifantis, Katerina E; Fabry, Ben

    2016-02-01

    We describe a technique for the quantitative measurement of cell-generated forces in highly nonlinear three-dimensional biopolymer networks that mimic the physiological situation of living cells. We computed forces of MDA-MB-231 breast carcinoma cells from the measured network deformations around the cells using a finite-element approach based on a constitutive equation that captures the complex mechanical properties of diverse biopolymers such as collagen gels, fibrin gels and Matrigel. Our measurements show that breast carcinoma cells cultured in collagen gels generated nearly constant forces regardless of the collagen concentration and matrix stiffness. Furthermore, time-lapse force measurements showed that these cells migrated in a gliding motion with alternating phases of high and low contractility, elongation, migratory speed and persistence. PMID:26641311

  5. Universal aspects of brittle fracture, adhesion, and atomic force microscopy

    NASA Technical Reports Server (NTRS)

    Banerjea, Amitava; Ferrante, John; Smith, John R.

    1989-01-01

    This universal relation between binding energy and interatomic separation was originally discovered for adhesion at bimetallic interfaces involving the simple metals Al, Zn, Mg, and Na. It is shown here that the same universal relation extends to adhesion at transition-metal interfaces. Adhesive energies have been computed for the low-index interfaces of Al, Ni, Cu, Ag, Fe, and W, using the equivalent-crystal theory (ECT) and keeping the atoms in each semiinfinite slab fixed rigidly in their equilibrium positions. These adhesive energy curves can be scaled onto each other and onto the universal adhesion curve. The effect of tip shape on the adhesive forces in the atomic-force microscope (AFM) is studied by computing energies and forces using the ECT. While the details of the energy-distance and force-distance curves are sensitive to tip shape, all of these curves can be scaled onto the universal adhesion curve.

  6. Bacterial turgor pressure can be measured by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Arnoldi, Markus; Fritz, Monika; Bäuerlein, Edmund; Radmacher, Manfred; Sackmann, Erich; Boulbitch, Alexei

    2000-07-01

    We report a study of the deformability of a bacterial wall with an atomic force microscope (AFM). A theoretical expression is derived for the force exerted by the wall on the cantilever as a function of the depths of indentation generated by the AFM tip. Evidence is provided that this reaction force is a measure for the turgor pressure of the bacterium. The method was applied to magnetotactic bacteria of the species Magnetospirillum gryphiswaldense. Force curves were generated on the substrate and on the bacteria while scanning laterally. With the mechanical properties so gained we obtained the spring constant of the bacterium as a whole. Making use of our theoretical results we determined the turgor pressure to be in the range of 85 to 150 kPa.

  7. Protein crystals as scanned probes for recognition atomic force microscopy.

    PubMed

    Wickremasinghe, Nissanka S; Hafner, Jason H

    2005-12-01

    Lysozyme crystal growth has been localized at the tip of a conventional silicon nitride cantilever through seeded nucleation. After cross-linking with glutaraldehyde, lysozyme protein crystal tips image gold nanoparticles and grating standards with a resolution comparable to that of conventional tips. Force spectra between the lysozyme crystal tips and surfaces covered with antilysozyme reveal an adhesion force that drops significantly upon blocking with free lysozyme, thus confirming that lysozyme crystal tips can detect molecular recognition interactions.

  8. An Undergraduate Nanotechnology Engineering Laboratory Course on Atomic Force Microscopy

    ERIC Educational Resources Information Center

    Russo, D.; Fagan, R. D.; Hesjedal, T.

    2011-01-01

    The University of Waterloo, Waterloo, ON, Canada, is home to North America's first undergraduate program in nanotechnology. As part of the Nanotechnology Engineering degree program, a scanning probe microscopy (SPM)-based laboratory has been developed for students in their fourth year. The one-term laboratory course "Nanoprobing and Lithography"…

  9. Visualizing Nano-Electromechanics by Vector Piezoresponse Force Microscopy

    SciTech Connect

    Rodriguez, Brian J; Jesse, Stephen; Baddorf, Arthur P; Kalinin, Sergei V; Gruverman, A.

    2005-01-01

    This is a detailed examination of the electro-mechanical and elastic coupling that occurs in the scanning probe microscopy of electro-active materials. This research is useful to detecting, imaging and understanding the orientation of nanoscale electromechanical anisotropies in material. This method has been applied to piezo electric and ferro electric thin films as well as biological samples.

  10. Morphological discretion of basidiospores of the puffball mushroom Calostoma by electron and atomic force microscopy.

    PubMed

    Kim, Misun; Kim, Ki Woo; Jung, Hack Sung

    2007-10-01

    Comparative morphology among species of the genus Calostoma, including C. cinnabarina, C. ravenelii, and C. japonicum, was investigated by scanning electron microscopy and atomic force microscopy. Spore morphology of cinnabarina and C. ravenelii showed no dramatic differences by light microcopy and scanning electron microscopy. To differentiate these species, atomic force microscopy was employed. Quantitative analysis of the surface roughness basidiospores revealed subtle differences in height fluctuation at the nanometer scale between the species of Calostoma. Basidiospores of C. cinnabarina had a relatively rougher surface than those of C. ravenelii at 2.0 x 2.0 micro m2 scan areas. PMID:18156793

  11. High-aspect ratio metal tips attached to atomic force microscopy cantilevers with controlled angle, length, and radius for electrostatic force microscopy.

    PubMed

    Cockins, Lynda; Miyahara, Yoichi; Stomp, Romain; Grutter, Peter

    2007-11-01

    We demonstrate a method to fabricate a high-aspect ratio metal tip attached to microfabricated cantilevers with controlled angle, length, and radius, for use in electrostatic force microscopy. A metal wire, after gluing it into a guiding slot that is cut into the cantilever, is shaped into a long, thin tip using a focused ion beam. The high-aspect ratio results in considerable reduction of the capacitive force between tip body and sample when compared to a metal coated pyramidal tip.

  12. Noninvasive determination of optical lever sensitivity in atomic force microscopy

    SciTech Connect

    Higgins, M.J.; Proksch, R.; Sader, J.E.; Polcik, M.; Mc Endoo, S.; Cleveland, J.P.; Jarvis, S.P.

    2006-01-15

    Atomic force microscopes typically require knowledge of the cantilever spring constant and optical lever sensitivity in order to accurately determine the force from the cantilever deflection. In this study, we investigate a technique to calibrate the optical lever sensitivity of rectangular cantilevers that does not require contact to be made with a surface. This noncontact approach utilizes the method of Sader et al. [Rev. Sci. Instrum. 70, 3967 (1999)] to calibrate the spring constant of the cantilever in combination with the equipartition theorem [J. L. Hutter and J. Bechhoefer, Rev. Sci. Instrum. 64, 1868 (1993)] to determine the optical lever sensitivity. A comparison is presented between sensitivity values obtained from conventional static mode force curves and those derived using this noncontact approach for a range of different cantilevers in air and liquid. These measurements indicate that the method offers a quick, alternative approach for the calibration of the optical lever sensitivity.

  13. Kelvin probe force microscopy of metallic surfaces used in Casimir force measurements

    NASA Astrophysics Data System (ADS)

    Behunin, R. O.; Dalvit, D. A. R.; Decca, R. S.; Genet, C.; Jung, I. W.; Lambrecht, A.; Liscio, A.; López, D.; Reynaud, S.; Schnoering, G.; Voisin, G.; Zeng, Y.

    2014-12-01

    Kelvin probe force microscopy at normal pressure was performed by two different groups on the same Au-coated planar sample used to measure the Casimir interaction in a sphere-plane geometry. The obtained voltage distribution was used to calculate the separation dependence of the electrostatic pressure Pres(D ) in the configuration of the Casimir experiments. In the calculation it was assumed that the potential distribution in the sphere has the same statistical properties as the measured one, and that there are no correlation effects on the potential distributions due to the presence of the other surface. The result of this calculation, using the currently available knowledge, is that Pres(D ) does not explain the magnitude or the separation dependence of the difference Δ P (D ) between the measured Casimir pressure and the one calculated using a Drude model for the electromagnetic response of Au. We discuss in the conclusions the points which have to be checked out by future work, including the influence of pressure and a more accurate determination of the patch distribution, in order to confirm these results.

  14. Probe-rotating atomic force microscopy for determining material properties

    SciTech Connect

    Lee, Sang Heon

    2014-03-15

    In this paper, we propose a probe-rotating atomic force microscope that enables scan in an arbitrary direction in the contact imaging mode, which is difficult to achieve using a conventional atomic force microscope owing to the orientation-dependent probe and the inability to rotate the probe head. To enable rotation of the probe about its vertical axis, we employed a compact and light probe head, the sensor of which is made of an optical disk drive pickup unit. Our proposed mechanical configuration, operating principle, and control system enables axial and lateral scan in various directions.

  15. Atomic Force Microscopy on Its Way to Adolescence

    NASA Astrophysics Data System (ADS)

    Giessibl, Franz J.

    2003-12-01

    When the atomic force microscope (AFM) was introduced in 1986, its potential to resolve surfaces with true atomic resolution was already proposed. However, substantial problems had to be overcome before atomic resolution became possible by AFM. Today, true atomic resolution by AFM is standard practice. This article discusses the influence of the cantilever stiffness and — amplitude on noise and short-range force sensitivity and introduces a sensor operating at near optimal conditions (qPlus sensor). The data achieved with this optimized sensing technology show substructures within single atom images, attributed to atomic orbitals.

  16. Stereological characterization of the {gamma}' particles in a nickel base superalloy: Comparison between transmission electron microscopy and atomic force microscopy techniques

    SciTech Connect

    Risbet, M. Feaugas, X.; Guillemer-Neel, C.; Clavel, M.

    2008-09-15

    Critical comparison of transmission electron microscopy and atomic force microscopy techniques was provided concerning size measurements of {gamma}' precipitates in a nickel-base superalloy. The divergence between results is explained in terms of the resolution limit for atomic force microscopy, linked both to the tip dimension and the diameter of the investigated particles.

  17. Detection of atomic force microscopy cantilever displacement with a transmitted electron beam

    NASA Astrophysics Data System (ADS)

    Wagner, R.; Woehl, T. J.; Keller, R. R.; Killgore, J. P.

    2016-07-01

    The response time of an atomic force microscopy (AFM) cantilever can be decreased by reducing cantilever size; however, the fastest AFM cantilevers are currently nearing the smallest size that can be detected with the conventional optical lever approach. Here, we demonstrate an electron beam detection scheme for measuring AFM cantilever oscillations. The oscillating AFM tip is positioned perpendicular to and in the path of a stationary focused nanometer sized electron beam. As the tip oscillates, the thickness of the material under the electron beam changes, causing a fluctuation in the number of scattered transmitted electrons that are detected. We demonstrate detection of sub-nanometer vibration amplitudes with an electron beam, providing a pathway for dynamic AFM with cantilevers that are orders of magnitude smaller and faster than the current state of the art.

  18. Current status and perspectives in atomic force microscopy-based identification of cellular transformation

    PubMed Central

    Dong, Chenbo; Hu, Xiao; Dinu, Cerasela Zoica

    2016-01-01

    Understanding the complex interplay between cells and their biomechanics and how the interplay is influenced by the extracellular microenvironment, as well as how the transforming potential of a tissue from a benign to a cancerous one is related to the dynamics of both the cell and its surroundings, holds promise for the development of targeted translational therapies. This review provides a comprehensive overview of atomic force microscopy-based technology and its applications for identification of cellular progression to a cancerous phenotype. The review also offers insights into the advancements that are required for the next user-controlled tool to allow for the identification of early cell transformation and thus potentially lead to improved therapeutic outcomes. PMID:27274238

  19. In situ atomic force microscopy imaging of electrodeposition of mixed layers of copper/cuprous oxide

    SciTech Connect

    Bonnefont, A.; Kostecki, R.; McLarnon, F.; Arrayet, J.C.; Servant, L.; Argoul, F.

    1999-11-01

    In situ atomic force microscopy (AFM) was applied to the dynamic characterization of the growth of mixed Cu/Cu{sub 2}O layers obtained by galvanostatic electrodeposition from alkaline Cu(II) lactate solutions. The correlation of the cathode potential profile with the average topographic profiles computed from the AFM images provided evidence for two transitions in the deposit growth during which the average growth velocity underwent rapid accelerations, the first one corresponding to zero interfacial concentration (Sand's time) and the second one to the emergence of the oscillations by a smooth transition. Despite its temporal resolution, the AFM technique could not capture the details of a single oscillation, but it proved to be quite adequate for tracking the general evolution of the electrode surface.

  20. Local raster scanning for high-speed imaging of biopolymers in atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Chang, Peter I.; Huang, Peng; Maeng, Jungyeoul; Andersson, Sean B.

    2011-06-01

    A novel algorithm is described and illustrated for high speed imaging of biopolymers and other stringlike samples using atomic force microscopy. The method uses the measurements in real-time to steer the tip of the instrument to localize the scanning area over the sample of interest. Depending on the sample, the scan time can be reduced by an order of magnitude or more while maintaining image resolution. Images are generated by interpolating the non-raster data using a modified Kriging algorithm. The method is demonstrated using physical simulations that include actuator and cantilever dynamics, nonlinear tip-sample interactions, and measurement noise as well as through scanning experiments in which a two-axis nanopositioning stage is steered by the algorithm using simulated height data.

  1. Nanoscale monitoring of drug actions on cell membrane using atomic force microscopy

    PubMed Central

    Li, Mi; Liu, Lian-qing; Xi, Ning; Wang, Yue-chao

    2015-01-01

    Knowledge of the nanoscale changes that take place in individual cells in response to a drug is useful for understanding the drug action. However, due to the lack of adequate techniques, such knowledge was scarce until the advent of atomic force microscopy (AFM), which is a multifunctional tool for investigating cellular behavior with nanometer resolution under near-physiological conditions. In the past decade, researchers have applied AFM to monitor the morphological and mechanical dynamics of individual cells following drug stimulation, yielding considerable novel insight into how the drug molecules affect an individual cell at the nanoscale. In this article we summarize the representative applications of AFM in characterization of drug actions on cell membrane, including topographic imaging, elasticity measurements, molecular interaction quantification, native membrane protein imaging and manipulation, etc. The challenges that are hampering the further development of AFM for studies of cellular activities are aslo discussed. PMID:26027658

  2. A serial-kinematic nanopositioner for high-speed atomic force microscopy

    SciTech Connect

    Wadikhaye, Sachin P. Yong, Yuen Kuan; Reza Moheimani, S. O.

    2014-10-15

    A flexure-guided serial-kinematic XYZ nanopositioner for high-speed Atomic Force Microscopy is presented in this paper. Two aspects influencing the performance of serial-kinematic nanopositioners are studied in this work. First, mass reduction by using tapered flexures is proposed to increased the natural frequency of the nanopositioner. 25% increase in the natural frequency is achieved due to reduced mass with tapered flexures. Second, a study of possible sensor positioning in a serial-kinematic nanopositioner is presented. An arrangement of sensors for exact estimation of cross-coupling is incorporated in the proposed design. A feedforward control strategy based on phaser approach is presented to mitigate the dynamics and nonlinearity in the system. Limitations in design approach and control strategy are discussed in the Conclusion.

  3. Magnetically-modulated atomic force microscopy for analysis of soft matter systems.

    PubMed

    Kageshima, Masami

    2012-11-01

    Experimental method of studying viscoelasticity, a common idea to understand properties of microscopic biological soft matter systems, especially single biopolymer chains, using atomic force microscopy (AFM) with magnetically- driven cantilever is surveyed. The experimental setup of applying well-characterized excitation to the cantilever and the analysis method to derive the viscoelasticity of the system under study are briefly introduced. Examples of measuring viscoelasticity of single peptide molecule and single titin molecule are shown. Considering the close relation of viscoelasticity and the time-scale for nonequilibrium dynamics in soft matter, extension of the method to a frequency-resolved analysis is attempted. A result of measuring viscoelasticity spectrum of a single dextran chain is shown. Challenges in further progress of the method are also described. PMID:22039807

  4. Photonic Torque Microscopy of the Nonconservative Force Field for Optically Trapped Silicon Nanowires.

    PubMed

    Irrera, Alessia; Magazzù, Alessandro; Artoni, Pietro; Simpson, Stephen H; Hanna, Simon; Jones, Philip H; Priolo, Francesco; Gucciardi, Pietro Giuseppe; Maragò, Onofrio M

    2016-07-13

    We measure, by photonic torque microscopy, the nonconservative rotational motion arising from the transverse components of the radiation pressure on optically trapped, ultrathin silicon nanowires. Unlike spherical particles, we find that nonconservative effects have a significant influence on the nanowire dynamics in the trap. We show that the extreme shape of the trapped nanowires yields a transverse component of the radiation pressure that results in an orbital rotation of the nanowire about the trap axis. We study the resulting motion as a function of optical power and nanowire length, discussing its size-scaling behavior. These shape-dependent nonconservative effects have implications for optical force calibration and optomechanics with levitated nonspherical particles. PMID:27280642

  5. Mechanisms of protein and virus crystal growth: An atomic force microscopy study of Canavalin crystallization

    SciTech Connect

    Land, T.A.; De Yoreo, J.J.; Malkin, A.J.; Kutznesov, Y.G.; McPherson, A.

    1995-03-10

    The evolution of surface morphology and step dynamics during growth of single crystals of the protein Canavalin and of the cubic satellite tobacco mosaic virus crystals (STMV) have been investigated by in situ atomic force microscopy. These two crystals were observed to grow by very different mechanisms. Growth of Canavalin occurs on complex vicinal hillocks formed by multiple, independently acting screw dislocations. Small cluster were observed on the terraces. STMV on the other hand, was observed to grow by 2D nucleation of islands. No dislocations were found on the crystal. The results are used to determine the growth mechanisms and estimate fundamental materials parameters. The images also illustrate the important mechanism of defect incorporation and provide insight to the processes that limit the growth rate and uniformity of these crystals.

  6. Elastic modulus measurements at variable temperature: Validation of atomic force microscopy techniques

    NASA Astrophysics Data System (ADS)

    Natali, Marco; Reggente, Melania; Passeri, Daniele; Rossi, Marco

    2016-06-01

    The development of polymer-based nanocomposites to be used in critical thermal environments requires the characterization of their mechanical properties, which are related to their chemical composition, size, morphology and operating temperature. Atomic force microscopy (AFM) has been proven to be a useful tool to develop techniques for the mechanical characterization of these materials, thanks to its nanometer lateral resolution and to the capability of exerting ultra-low loads, down to the piconewton range. In this work, we demonstrate two techniques, one quasi-static, i.e., AFM-based indentation (I-AFM), and one dynamic, i.e., contact resonance AFM (CR-AFM), for the mechanical characterization of compliant materials at variable temperature. A cross-validation of I-AFM and CR-AFM has been performed by comparing the results obtained on two reference materials, i.e., low-density polyethylene (LDPE) and polycarbonate (PC), which demonstrated the accuracy of the techniques.

  7. Forced synchronization of autonomous dynamical Boolean networks

    SciTech Connect

    Rivera-Durón, R. R. Campos-Cantón, E.; Campos-Cantón, I.; Gauthier, Daniel J.

    2015-08-15

    We present the design of an autonomous time-delay Boolean network realized with readily available electronic components. Through simulations and experiments that account for the detailed nonlinear response of each circuit element, we demonstrate that a network with five Boolean nodes displays complex behavior. Furthermore, we show that the dynamics of two identical networks display near-instantaneous synchronization to a periodic state when forced by a common periodic Boolean signal. A theoretical analysis of the network reveals the conditions under which complex behavior is expected in an individual network and the occurrence of synchronization in the forced networks. This research will enable future experiments on autonomous time-delay networks using readily available electronic components with dynamics on a slow enough time-scale so that inexpensive data collection systems can faithfully record the dynamics.

  8. Forced synchronization of autonomous dynamical Boolean networks.

    PubMed

    Rivera-Durón, R R; Campos-Cantón, E; Campos-Cantón, I; Gauthier, Daniel J

    2015-08-01

    We present the design of an autonomous time-delay Boolean network realized with readily available electronic components. Through simulations and experiments that account for the detailed nonlinear response of each circuit element, we demonstrate that a network with five Boolean nodes displays complex behavior. Furthermore, we show that the dynamics of two identical networks display near-instantaneous synchronization to a periodic state when forced by a common periodic Boolean signal. A theoretical analysis of the network reveals the conditions under which complex behavior is expected in an individual network and the occurrence of synchronization in the forced networks. This research will enable future experiments on autonomous time-delay networks using readily available electronic components with dynamics on a slow enough time-scale so that inexpensive data collection systems can faithfully record the dynamics.

  9. The Effects of Orthophosphate in Drinking Water on the Initial Copper Corrosion Using Atomic Force Microscopy

    EPA Science Inventory

    Corroding of copper piping used in household drinking water plumbing may potentially impacts consumer’s health and economics. Copper corrosion studies conducted on newly corroding material with atomic force microscopy (AFM) may be particularly useful in understanding the impact ...

  10. The Use of Contact Mode Atomic Force Microscopy in Aqueous Medium for Structural Analysis of Spinach Photosynthetic Complexes1[OPEN

    PubMed Central

    Phuthong, Witchukorn; Huang, Zubin; Wittkopp, Tyler M.; Sznee, Kinga; Heinnickel, Mark L.; Dekker, Jan P.; Frese, Raoul N.; Prinz, Fritz B.; Grossman, Arthur R.

    2015-01-01

    To investigate the dynamics of photosynthetic pigment-protein complexes in vascular plants at high resolution in an aqueous environment, membrane-protruding oxygen-evolving complexes (OECs) associated with photosystem II (PSII) on spinach (Spinacia oleracea) grana membranes were examined using contact mode atomic force microscopy. This study represents, to our knowledge, the first use of atomic force microscopy to distinguish the putative large extrinsic loop of Photosystem II CP47 reaction center protein (CP47) from the putative oxygen-evolving enhancer proteins 1, 2, and 3 (PsbO, PsbP, and PsbQ) and large extrinsic loop of Photosystem II CP43 reaction center protein (CP43) in the PSII-OEC extrinsic domains of grana membranes under conditions resulting in the disordered arrangement of PSII-OEC particles. Moreover, we observed uncharacterized membrane particles that, based on their physical characteristics and electrophoretic analysis of the polypeptides associated with the grana samples, are hypothesized to be a domain of photosystem I that protrudes from the stromal face of single thylakoid bilayers. Our results are interpreted in the context of the results of others that were obtained using cryo-electron microscopy (and single particle analysis), negative staining and freeze-fracture electron microscopy, as well as previous atomic force microscopy studies. PMID:26220954

  11. The Use of Contact Mode Atomic Force Microscopy in Aqueous Medium for Structural Analysis of Spinach Photosynthetic Complexes.

    PubMed

    Phuthong, Witchukorn; Huang, Zubin; Wittkopp, Tyler M; Sznee, Kinga; Heinnickel, Mark L; Dekker, Jan P; Frese, Raoul N; Prinz, Fritz B; Grossman, Arthur R

    2015-10-01

    To investigate the dynamics of photosynthetic pigment-protein complexes in vascular plants at high resolution in an aqueous environment, membrane-protruding oxygen-evolving complexes (OECs) associated with photosystem II (PSII) on spinach (Spinacia oleracea) grana membranes were examined using contact mode atomic force microscopy. This study represents, to our knowledge, the first use of atomic force microscopy to distinguish the putative large extrinsic loop of Photosystem II CP47 reaction center protein (CP47) from the putative oxygen-evolving enhancer proteins 1, 2, and 3 (PsbO, PsbP, and PsbQ) and large extrinsic loop of Photosystem II CP43 reaction center protein (CP43) in the PSII-OEC extrinsic domains of grana membranes under conditions resulting in the disordered arrangement of PSII-OEC particles. Moreover, we observed uncharacterized membrane particles that, based on their physical characteristics and electrophoretic analysis of the polypeptides associated with the grana samples, are hypothesized to be a domain of photosystem I that protrudes from the stromal face of single thylakoid bilayers. Our results are interpreted in the context of the results of others that were obtained using cryo-electron microscopy (and single particle analysis), negative staining and freeze-fracture electron microscopy, as well as previous atomic force microscopy studies.

  12. Applications of atomic force microscopy to the studies of biomaterials in biomolecular systems

    NASA Astrophysics Data System (ADS)

    Ma, Xiang

    Atomic force microscopy (AFM) is a unique tool for the studies of nanoscale structures and interactions. In this dissertation, I applied AFM to study transitions among multiple states of biomaterials in three different microscopic biomolecular systems: MukB-dependent DNA condensation, holdfast adhesion, and virus elasticity. To elucidate the mechanism of MukB-dependent DNA condensation, I have studied the conformational changes of MukB proteins as indicators for the strength of interactions between MukB, DNA and other molecular factors, such as magnesium and ParC proteins, using high-resolution AFM imaging. To determine the physical origins of holdfast adhesion, I have investigated the dynamics of adhesive force development of the holdfast, employing AFM force spectroscopy. By measuring rupture forces between the holdfast and the substrate, I showed that the holdfast adhesion is strongly time-dependent and involves transformations at multiple time scales. Understanding the mechanisms of adhesion force development of the holdfast will be critical for future engineering of holdfasts properties for various applications. Finally, I have examined the elasticity of self-assembled hepatitis B virus-like particles (HBV VLPs) and brome mosaic virus (BMV) in response to changes of pH and salinity, using AFM nanoindentation. The distributions of elasticity were mapped on a single particle level and compared between empty, RNA- and gold-filled HBV VLPs. I found that a single HBV VLP showed heterogeneous distribution of elasticity and a two-step buckling transition, suggesting a discrete property of HBV capsids. For BMV, I have showed that viruses containing different RNA molecules can be distinguished by mechanical measurements, while they are indistinguishable by morphology. I also studied the effect of pH on the elastic behaviors of three-particle BMV and R3/4 BMV. This study can yield insights into RNA presentation/release mechanisms, and could help us to design novel drug

  13. Joining patch-clamp and atomic force microscopy techniques for studying black lipid bilayers

    NASA Astrophysics Data System (ADS)

    Ovalle-García, Erasmo; Ortega-Blake, Iván

    2007-08-01

    An experimental protocol that enables the direct characterization of freestanding lipid bilayers through a combination of atomic force microscopy and single channel recording is presented. The method consists of producing a 15μm diameter pore in a 3μm thick Mylar film that delimits two vessels. The micropore was done by a glass microneedle. >L-α-phosphatidylcholine bilayers were routinely painted on the pore, observed by atomic force microscopy, and tested with gramicidin D ion channels.

  14. Frequency-dependent viscoelasticity measurement by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Yang, Nan; Wong, Kenneth Kar Ho; de Bruyn, John R.; Hutter, Jeffrey L.

    2009-02-01

    We demonstrate a new technique for investigating viscoelastic properties of soft materials using the atomic force microscope. A small oscillatory voltage is added to the deflection signal of the atomic force microscope causing a vertical oscillatory sample motion. Monitoring the amplitude and phase of this motion allows determination of the viscous and elastic moduli of the sample as a function of frequency during contact imaging. This technique is applied to suspended poly(vinyl alcohol) nanofibers and poly(vinyl alcohol) hydrogels, giving results similar to those measured using traditional static methods. However, the moduli of both the fibers and the hydrogels show a significant frequency dependence. The Young's modulus of the fibers increases with frequency, while for the viscoelastic hydrogels, the storage modulus dominates the mechanical response at low frequency whereas the loss modulus dominates at high frequency.

  15. Universal aspects of adhesion and atomic force microscopy

    NASA Technical Reports Server (NTRS)

    Banerjea, Amitava; Smith, John R.; Ferrante, John

    1990-01-01

    Adhesive energies are computed for flat and atomically sharp tips as a function of the normal distance to the substrate. The dependence of binding energies on tip shape is investigated. The magnitudes of the binding energies for the atomic force microscope are found to depend sensitively on tip material, tip shape and the sample site being probed. The form of the energy-distance curve, however, is universal and independent of these variables, including tip shape.

  16. Multifunctional hydrogel nano-probes for atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Lee, Jae Seol; Song, Jungki; Kim, Seong Oh; Kim, Seokbeom; Lee, Wooju; Jackman, Joshua A.; Kim, Dongchoul; Cho, Nam-Joon; Lee, Jungchul

    2016-05-01

    Since the invention of the atomic force microscope (AFM) three decades ago, there have been numerous advances in its measurement capabilities. Curiously, throughout these developments, the fundamental nature of the force-sensing probe--the key actuating element--has remained largely unchanged. It is produced by long-established microfabrication etching strategies and typically composed of silicon-based materials. Here, we report a new class of photopolymerizable hydrogel nano-probes that are produced by bottom-up fabrication with compressible replica moulding. The hydrogel probes demonstrate excellent capabilities for AFM imaging and force measurement applications while enabling programmable, multifunctional capabilities based on compositionally adjustable mechanical properties and facile encapsulation of various nanomaterials. Taken together, the simple, fast and affordable manufacturing route and multifunctional capabilities of hydrogel AFM nano-probes highlight the potential of soft matter mechanical transducers in nanotechnology applications. The fabrication scheme can also be readily utilized to prepare hydrogel cantilevers, including in parallel arrays, for nanomechanical sensor devices.

  17. Multifunctional hydrogel nano-probes for atomic force microscopy

    PubMed Central

    Lee, Jae Seol; Song, Jungki; Kim, Seong Oh; Kim, Seokbeom; Lee, Wooju; Jackman, Joshua A.; Kim, Dongchoul; Cho, Nam-Joon; Lee, Jungchul

    2016-01-01

    Since the invention of the atomic force microscope (AFM) three decades ago, there have been numerous advances in its measurement capabilities. Curiously, throughout these developments, the fundamental nature of the force-sensing probe—the key actuating element—has remained largely unchanged. It is produced by long-established microfabrication etching strategies and typically composed of silicon-based materials. Here, we report a new class of photopolymerizable hydrogel nano-probes that are produced by bottom-up fabrication with compressible replica moulding. The hydrogel probes demonstrate excellent capabilities for AFM imaging and force measurement applications while enabling programmable, multifunctional capabilities based on compositionally adjustable mechanical properties and facile encapsulation of various nanomaterials. Taken together, the simple, fast and affordable manufacturing route and multifunctional capabilities of hydrogel AFM nano-probes highlight the potential of soft matter mechanical transducers in nanotechnology applications. The fabrication scheme can also be readily utilized to prepare hydrogel cantilevers, including in parallel arrays, for nanomechanical sensor devices. PMID:27199165

  18. Multifunctional hydrogel nano-probes for atomic force microscopy.

    PubMed

    Lee, Jae Seol; Song, Jungki; Kim, Seong Oh; Kim, Seokbeom; Lee, Wooju; Jackman, Joshua A; Kim, Dongchoul; Cho, Nam-Joon; Lee, Jungchul

    2016-05-20

    Since the invention of the atomic force microscope (AFM) three decades ago, there have been numerous advances in its measurement capabilities. Curiously, throughout these developments, the fundamental nature of the force-sensing probe-the key actuating element-has remained largely unchanged. It is produced by long-established microfabrication etching strategies and typically composed of silicon-based materials. Here, we report a new class of photopolymerizable hydrogel nano-probes that are produced by bottom-up fabrication with compressible replica moulding. The hydrogel probes demonstrate excellent capabilities for AFM imaging and force measurement applications while enabling programmable, multifunctional capabilities based on compositionally adjustable mechanical properties and facile encapsulation of various nanomaterials. Taken together, the simple, fast and affordable manufacturing route and multifunctional capabilities of hydrogel AFM nano-probes highlight the potential of soft matter mechanical transducers in nanotechnology applications. The fabrication scheme can also be readily utilized to prepare hydrogel cantilevers, including in parallel arrays, for nanomechanical sensor devices.

  19. Shrinking of ultrathin polyelectrolyte multilayer capsules upon annealing: A confocal laser scanning microscopy and scanning force microscopy study

    NASA Astrophysics Data System (ADS)

    Leporatti, S.; Gao, C.; Voigt, A.; Donath, E.; Möhwald, H.

    Heating-induced morphological changes of micrometer size capsules prepared by step-wise deposition of oppositely charged polyelectrolytes onto melamine formaldehyde (MF) latex particles and biological cells with subsequent dissolution of the core have been investigated by confocal laser scanning microscopy (CLSM) and scanning force microscopy (SFM). For poly(styrenesulfonate-Na salt)/poly(allylamine hydrochloride) polyelectrolyte capsules a remarkable heating-induced shrinking is observed. An increase of the wall thickness corresponding to the capsule diameter decrease is found. The morphology of these microcapsules after temperature treatment is characterized. The thickening of the polyelectrolyte multilayer is interpreted in terms of a configurational entropy increase via polyanion-polycation bond rearrangement.

  20. Characterization of gold nanoparticle films: Rutherford backscattering spectroscopy, scanning electron microscopy with image analysis, and atomic force microscopy

    SciTech Connect

    Lansåker, Pia C. Niklasson, Gunnar A.; Granqvist, Claes G.; Hallén, Anders

    2014-10-15

    Gold nanoparticle films are of interest in several branches of science and technology, and accurate sample characterization is needed but technically demanding. We prepared such films by DC magnetron sputtering and recorded their mass thickness by Rutherford backscattering spectroscopy. The geometric thickness d{sub g}—from the substrate to the tops of the nanoparticles—was obtained by scanning electron microscopy (SEM) combined with image analysis as well as by atomic force microscopy (AFM). The various techniques yielded an internally consistent characterization of the films. In particular, very similar results for d{sub g} were obtained by SEM with image analysis and by AFM.

  1. Interfacial aqueous solutions dielectric constant measurements using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Teschke, O.; Ceotto, G.; de Souza, E. F.

    2000-08-01

    The exchange of the volume of a region of the electric double layer of a mica surface immersed in aqueous solutions, with a dielectric constant ɛDL, by a nanosized radius tip, with a dielectric constant ɛTip, is responsible for the repulsion at large distances from the surface (starting at ˜100 nm, diffuse layer) and followed by an attraction when the tip is immersed in the inner layer (˜10 nm). The calculated dielectric constant as a function of the distance to the charged interface obtained by fitting the force versus distance curves, allows the mapping of the inner layer dielectric constant profiles with a nanometer resolution.

  2. Characterization of the motion of membrane proteins using high-speed atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Casuso, Ignacio; Khao, Jonathan; Chami, Mohamed; Paul-Gilloteaux, Perrine; Husain, Mohamed; Duneau, Jean-Pierre; Stahlberg, Henning; Sturgis, James N.; Scheuring, Simon

    2012-08-01

    For cells to function properly, membrane proteins must be able to diffuse within biological membranes. The functions of these membrane proteins depend on their position and also on protein-protein and protein-lipid interactions. However, so far, it has not been possible to study simultaneously the structure and dynamics of biological membranes. Here, we show that the motion of unlabelled membrane proteins can be characterized using high-speed atomic force microscopy. We find that the molecules of outer membrane protein F (OmpF) are widely distributed in the membrane as a result of diffusion-limited aggregation, and while the overall protein motion scales roughly with the local density of proteins in the membrane, individual protein molecules can also diffuse freely or become trapped by protein-protein interactions. Using these measurements, and the results of molecular dynamics simulations, we determine an interaction potential map and an interaction pathway for a membrane protein, which should provide new insights into the connection between the structures of individual proteins and the structures and dynamics of supramolecular membranes.

  3. Characterization of the motion of membrane proteins using high-speed atomic force microscopy.

    PubMed

    Casuso, Ignacio; Khao, Jonathan; Chami, Mohamed; Paul-Gilloteaux, Perrine; Husain, Mohamed; Duneau, Jean-Pierre; Stahlberg, Henning; Sturgis, James N; Scheuring, Simon

    2012-08-01

    For cells to function properly, membrane proteins must be able to diffuse within biological membranes. The functions of these membrane proteins depend on their position and also on protein-protein and protein-lipid interactions. However, so far, it has not been possible to study simultaneously the structure and dynamics of biological membranes. Here, we show that the motion of unlabelled membrane proteins can be characterized using high-speed atomic force microscopy. We find that the molecules of outer membrane protein F (OmpF) are widely distributed in the membrane as a result of diffusion-limited aggregation, and while the overall protein motion scales roughly with the local density of proteins in the membrane, individual protein molecules can also diffuse freely or become trapped by protein-protein interactions. Using these measurements, and the results of molecular dynamics simulations, we determine an interaction potential map and an interaction pathway for a membrane protein, which should provide new insights into the connection between the structures of individual proteins and the structures and dynamics of supramolecular membranes. PMID:22772862

  4. High-speed atomic force microscopy shows that annexin V stabilizes membranes on the second timescale.

    PubMed

    Miyagi, Atsushi; Chipot, Christophe; Rangl, Martina; Scheuring, Simon

    2016-09-01

    Annexins are abundant cytoplasmic proteins that can bind to negatively charged phospholipids in a Ca(2+)-dependent manner, and are known to play a role in the storage of Ca(2+) and membrane healing. Little is known, however, about the dynamic processes of protein-Ca(2+)-membrane assembly and disassembly. Here we show that high-speed atomic force microscopy (HS-AFM) can be used to repeatedly induce and disrupt annexin assemblies and study their structure, dynamics and interactions. Our HS-AFM set-up is adapted for such biological applications through the integration of a pumping system for buffer exchange and a pulsed laser system for uncaging caged compounds. We find that biochemically identical annexins (annexin V) display different effective Ca(2+) and membrane affinities depending on the assembly location, providing a wide Ca(2+) buffering regime while maintaining membrane stabilization. We also show that annexin is membrane-recruited and forms stable supramolecular assemblies within ∼5 s in conditions that are comparable to a membrane lesion in a cell. Molecular dynamics simulations provide atomic detail of the role played by Ca(2+) in the reversible binding of annexin to the membrane surface. PMID:27271964

  5. High-speed atomic force microscopy shows that annexin V stabilizes membranes on the second timescale

    NASA Astrophysics Data System (ADS)

    Miyagi, Atsushi; Chipot, Christophe; Rangl, Martina; Scheuring, Simon

    2016-09-01

    Annexins are abundant cytoplasmic proteins that can bind to negatively charged phospholipids in a Ca2+-dependent manner, and are known to play a role in the storage of Ca2+ and membrane healing. Little is known, however, about the dynamic processes of protein-Ca2+-membrane assembly and disassembly. Here we show that high-speed atomic force microscopy (HS-AFM) can be used to repeatedly induce and disrupt annexin assemblies and study their structure, dynamics and interactions. Our HS-AFM set-up is adapted for such biological applications through the integration of a pumping system for buffer exchange and a pulsed laser system for uncaging caged compounds. We find that biochemically identical annexins (annexin V) display different effective Ca2+ and membrane affinities depending on the assembly location, providing a wide Ca2+ buffering regime while maintaining membrane stabilization. We also show that annexin is membrane-recruited and forms stable supramolecular assemblies within ˜5 s in conditions that are comparable to a membrane lesion in a cell. Molecular dynamics simulations provide atomic detail of the role played by Ca2+ in the reversible binding of annexin to the membrane surface.

  6. High-speed atomic force microscopy shows that annexin V stabilizes membranes on the second timescale

    NASA Astrophysics Data System (ADS)

    Miyagi, Atsushi; Chipot, Christophe; Rangl, Martina; Scheuring, Simon

    2016-09-01

    Annexins are abundant cytoplasmic proteins that can bind to negatively charged phospholipids in a Ca2+-dependent manner, and are known to play a role in the storage of Ca2+ and membrane healing. Little is known, however, about the dynamic processes of protein–Ca2+–membrane assembly and disassembly. Here we show that high-speed atomic force microscopy (HS-AFM) can be used to repeatedly induce and disrupt annexin assemblies and study their structure, dynamics and interactions. Our HS-AFM set-up is adapted for such biological applications through the integration of a pumping system for buffer exchange and a pulsed laser system for uncaging caged compounds. We find that biochemically identical annexins (annexin V) display different effective Ca2+ and membrane affinities depending on the assembly location, providing a wide Ca2+ buffering regime while maintaining membrane stabilization. We also show that annexin is membrane-recruited and forms stable supramolecular assemblies within ∼5 s in conditions that are comparable to a membrane lesion in a cell. Molecular dynamics simulations provide atomic detail of the role played by Ca2+ in the reversible binding of annexin to the membrane surface.

  7. Mapping power-law rheology of living cells using multi-frequency force modulation atomic force microscopy

    SciTech Connect

    Takahashi, Ryosuke; Okajima, Takaharu

    2015-10-26

    We present multi-frequency force modulation atomic force microscopy (AFM) for mapping the complex shear modulus G* of living cells as a function of frequency over the range of 50–500 Hz in the same measurement time as the single-frequency force modulation measurement. The AFM technique enables us to reconstruct image maps of rheological parameters, which exhibit a frequency-dependent power-law behavior with respect to G{sup *}. These quantitative rheological measurements reveal a large spatial variation in G* in this frequency range for single cells. Moreover, we find that the reconstructed images of the power-law rheological parameters are much different from those obtained in force-curve or single-frequency force modulation measurements. This indicates that the former provide information about intracellular mechanical structures of the cells that are usually not resolved with the conventional force measurement methods.

  8. Probing effective slippage on superhydrophobic stripes by atomic force microscopy.

    PubMed

    Nizkaya, Tatiana V; Dubov, Alexander L; Mourran, Ahmed; Vinogradova, Olga I

    2016-08-17

    While the effective slippage of water past superhydrophobic surfaces has been studied over a decade, theoretical predictions have never been properly confirmed by experiments. Here we measure a drag force on a sphere approaching a plane decorated by superhydrophobic grooves and compare the results with the predictions of semi-analytical theory developed here, which employs the gas cushion model to calculate the local slip length at the gas sectors. We demonstrate that at intermediate and large (compared to a texture period) separations the half-sum of longitudinal and transverse effective slip lengths can be deduced from the force-distance curve by using the known analytical theory of hydrodynamic interaction of a sphere with a homogeneous slipping plane. This half-sum is shown to depend on the fraction of gas sectors and its value is in excellent agreement with theoretical predictions. At small distances the half-sum of effective longitudinal and transverse slip lengths becomes separation-dependent, and is in quantitative agreement with the predictions of our semi-analytical theory. PMID:27476481

  9. Probing effective slippage on superhydrophobic stripes by atomic force microscopy.

    PubMed

    Nizkaya, Tatiana V; Dubov, Alexander L; Mourran, Ahmed; Vinogradova, Olga I

    2016-08-17

    While the effective slippage of water past superhydrophobic surfaces has been studied over a decade, theoretical predictions have never been properly confirmed by experiments. Here we measure a drag force on a sphere approaching a plane decorated by superhydrophobic grooves and compare the results with the predictions of semi-analytical theory developed here, which employs the gas cushion model to calculate the local slip length at the gas sectors. We demonstrate that at intermediate and large (compared to a texture period) separations the half-sum of longitudinal and transverse effective slip lengths can be deduced from the force-distance curve by using the known analytical theory of hydrodynamic interaction of a sphere with a homogeneous slipping plane. This half-sum is shown to depend on the fraction of gas sectors and its value is in excellent agreement with theoretical predictions. At small distances the half-sum of effective longitudinal and transverse slip lengths becomes separation-dependent, and is in quantitative agreement with the predictions of our semi-analytical theory.

  10. Applications of Traction Force Microscopy in Measuring Adhesion Molecule Dependent Cell Contractility

    ERIC Educational Resources Information Center

    Mann, Cynthia Marie

    2009-01-01

    This work describes the use of polyacrylamide hydrogels as controlled elastic modulus substrates for single cell traction force microscopy studies. The first section describes the use of EDC/NHS chemistry to convalently link microbeads to the hydrogel matrix for the purpose of performing long-term traction force studies (7 days). The final study…

  11. Note: Artificial neural networks for the automated analysis of force map data in atomic force microscopy

    SciTech Connect

    Braunsmann, Christoph; Schäffer, Tilman E.

    2014-05-15

    Force curves recorded with the atomic force microscope on structured samples often show an irregular force versus indentation behavior. An analysis of such curves using standard contact models (e.g., the Sneddon model) would generate inaccurate Young's moduli. A critical inspection of the force curve shape is therefore necessary for estimating the reliability of the generated Young's modulus. We used a trained artificial neural network to automatically recognize curves of “good” and of “bad” quality. This is especially useful for improving the analysis of force maps that consist of a large number of force curves.

  12. Theoretical models for surface forces and adhesion and their measurement using atomic force microscopy.

    PubMed

    Leite, Fabio L; Bueno, Carolina C; Da Róz, Alessandra L; Ziemath, Ervino C; Oliveira, Osvaldo N

    2012-10-08

    The increasing importance of studies on soft matter and their impact on new technologies, including those associated with nanotechnology, has brought intermolecular and surface forces to the forefront of physics and materials science, for these are the prevailing forces in micro and nanosystems. With experimental methods such as the atomic force spectroscopy (AFS), it is now possible to measure these forces accurately, in addition to providing information on local material properties such as elasticity, hardness and adhesion. This review provides the theoretical and experimental background of afs, adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution.

  13. Theoretical Models for Surface Forces and Adhesion and Their Measurement Using Atomic Force Microscopy

    PubMed Central

    Leite, Fabio L.; Bueno, Carolina C.; Da Róz, Alessandra L.; Ziemath, Ervino C.; Oliveira, Osvaldo N.

    2012-01-01

    The increasing importance of studies on soft matter and their impact on new technologies, including those associated with nanotechnology, has brought intermolecular and surface forces to the forefront of physics and materials science, for these are the prevailing forces in micro and nanosystems. With experimental methods such as the atomic force spectroscopy (AFS), it is now possible to measure these forces accurately, in addition to providing information on local material properties such as elasticity, hardness and adhesion. This review provides the theoretical and experimental background of AFS, adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution. PMID:23202925

  14. Real-time high dynamic range laser scanning microscopy.

    PubMed

    Vinegoni, C; Leon Swisher, C; Fumene Feruglio, P; Giedt, R J; Rousso, D L; Stapleton, S; Weissleder, R

    2016-01-01

    In conventional confocal/multiphoton fluorescence microscopy, images are typically acquired under ideal settings and after extensive optimization of parameters for a given structure or feature, often resulting in information loss from other image attributes. To overcome the problem of selective data display, we developed a new method that extends the imaging dynamic range in optical microscopy and improves the signal-to-noise ratio. Here we demonstrate how real-time and sequential high dynamic range microscopy facilitates automated three-dimensional neural segmentation. We address reconstruction and segmentation performance on samples with different size, anatomy and complexity. Finally, in vivo real-time high dynamic range imaging is also demonstrated, making the technique particularly relevant for longitudinal imaging in the presence of physiological motion and/or for quantification of in vivo fast tracer kinetics during functional imaging. PMID:27032979

  15. Real-time high dynamic range laser scanning microscopy

    PubMed Central

    Vinegoni, C.; Leon Swisher, C.; Fumene Feruglio, P.; Giedt, R. J.; Rousso, D. L.; Stapleton, S.; Weissleder, R.

    2016-01-01

    In conventional confocal/multiphoton fluorescence microscopy, images are typically acquired under ideal settings and after extensive optimization of parameters for a given structure or feature, often resulting in information loss from other image attributes. To overcome the problem of selective data display, we developed a new method that extends the imaging dynamic range in optical microscopy and improves the signal-to-noise ratio. Here we demonstrate how real-time and sequential high dynamic range microscopy facilitates automated three-dimensional neural segmentation. We address reconstruction and segmentation performance on samples with different size, anatomy and complexity. Finally, in vivo real-time high dynamic range imaging is also demonstrated, making the technique particularly relevant for longitudinal imaging in the presence of physiological motion and/or for quantification of in vivo fast tracer kinetics during functional imaging. PMID:27032979

  16. Real-time high dynamic range laser scanning microscopy

    NASA Astrophysics Data System (ADS)

    Vinegoni, C.; Leon Swisher, C.; Fumene Feruglio, P.; Giedt, R. J.; Rousso, D. L.; Stapleton, S.; Weissleder, R.

    2016-04-01

    In conventional confocal/multiphoton fluorescence microscopy, images are typically acquired under ideal settings and after extensive optimization of parameters for a given structure or feature, often resulting in information loss from other image attributes. To overcome the problem of selective data display, we developed a new method that extends the imaging dynamic range in optical microscopy and improves the signal-to-noise ratio. Here we demonstrate how real-time and sequential high dynamic range microscopy facilitates automated three-dimensional neural segmentation. We address reconstruction and segmentation performance on samples with different size, anatomy and complexity. Finally, in vivo real-time high dynamic range imaging is also demonstrated, making the technique particularly relevant for longitudinal imaging in the presence of physiological motion and/or for quantification of in vivo fast tracer kinetics during functional imaging.

  17. Nonlinear dynamic phase contrast microscopy for microfluidic and microbiological applications

    NASA Astrophysics Data System (ADS)

    Denz, C.; Holtmann, F.; Woerdemann, M.; Oevermann, M.

    2008-08-01

    In live sciences, the observation and analysis of moving living cells, molecular motors or motion of micro- and nano-objects is a current field of research. At the same time, microfluidic innovations are needed for biological and medical applications on a micro- and nano-scale. Conventional microscopy techniques are reaching considerable limits with respect to these issues. A promising approach for this challenge is nonlinear dynamic phase contrast microscopy. It is an alternative full field approach that allows to detect motion as well as phase changes of living unstained micro-objects in real-time, thereby being marker free, without contact and non destructive, i.e. fully biocompatible. The generality of this system allows it to be combined with several other microscope techniques such as conventional bright field or fluorescence microscopy. In this article we will present the dynamic phase contrast technique and its applications in analysis of micro organismic dynamics, micro flow velocimetry and micro-mixing analysis.

  18. Combining nanoscale optical phenomena with atomic force microscopy for cellular studies

    NASA Astrophysics Data System (ADS)

    Amini, Sina; Sun, Zhe; Meininger, Gerald A.; Meissner, Kenith E.

    2012-03-01

    Evanescent Waves (EWs) and Förster Resonance Energy Transfer (FRET) concepts combined with Atomic Force Microscopy (AFM) have been used for imaging and sensing. For the proposed EW microscopy system, Quantum Dot (QD) embedded Polystyrene microspheres are mounted on AFM cantilevers. When excited by laser, QDs luminescence couples to the Whispering Gallery Modes (WGMs) in the periphery of the microsphere. The resultant EWs extend on the order of 100 nm from the surface of the microsphere. These EWs decay exponentially and are explored as a tool to excite fluorescent labeled trans-membrane and near-membrane proteins. For the FRET system, QD coated silica microspheres are conjugated with fibronectin and mounted on AFM cantilevers. Moving the sphere down to the surface of the RFP-αv integrin tagged cells, fibronectins on the microsphere surface bind to integrins on the cell surface and FRET is observed between the QDs (donor) and RFP (acceptor). The detected fluorescence for the imaging system and the FRET efficiency for the sensing system are both functions of cell surface protein density. These innovative nanoscale imaging and sensing systems can be used to obtain unique dynamic data from living cells to improve understanding of cell adhesion and mechanobiology in cells.

  19. Studying early stages of fibronectin fibrillogenesis in living cells by atomic force microscopy

    PubMed Central

    Gudzenko, Tetyana; Franz, Clemens M.

    2015-01-01

    Fibronectin (FN) is an extracellular matrix protein that can be assembled by cells into large fibrillar networks, but the dynamics of FN remodeling and the transition through intermediate fibrillar stages are incompletely understood. Here we used a combination of fluorescence microscopy and time-lapse atomic force microscopy (AFM) to visualize initial stages of FN fibrillogenesis in living fibroblasts at high resolution. Initial FN nanofibrils form within <5 min of cell–matrix contact and subsequently extend at a rate of 0.25 μm/min at sites of cell membrane retraction. FN nanofibrils display a complex linear array of globular features spaced at varying distances, indicating the coexistence of different conformational states within the fibril. In some cases, initial fibrils extended in discrete increments of ∼800 nm during a series of cyclical membrane retractions, indicating a stepwise fibrillar extension mechanism. In presence of Mn2+, a known activator of integrin adhesion to FN, fibrillogenesis was accelerated almost threefold to 0.68 μm/min and fibrillar dimensions were increased, underlining the importance of integrin activation for early FN fibrillogenesis. FN fibrillogenesis visualized by time-lapse AFM thus provides new structural and mechanistic insight into initial steps of cell-driven FN fibrillogenesis. PMID:26371081

  20. Atomic force microscopy using ZnO whisker tip

    NASA Astrophysics Data System (ADS)

    Kado, H.; Yokoyama, K.; Tohda, T.

    1992-06-01

    We have developed an atomic force microscope (AFM) using a zinc oxide (ZnO) whisker crystal as a probing tip. The ZnO whisker crystal is tetrapodal in shape, with each leg having a length of 5-30 μm, a radius of curvature less than 10 nm, and a cone half angle of 1°-2°. Polyimide thin films rubbed with cloths as liquid-crystal aligning films were employed for AFM imaging. Due to the needle shape of the probing tip, the AFM was able to resolve the tiny grooves (3-5 nm deep, 60-80 nm apart) on these films more clearly than that using a conventional pyramidal tip. The new AFM will be available for precise evaluation of surfaces on which fine structures are microfabricated in nanometer scale.