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Sample records for afm colloidal probe

  1. In situ hydrodynamic lateral force calibration of AFM colloidal probes.

    PubMed

    Ryu, Sangjin; Franck, Christian

    2011-11-01

    Lateral force microscopy (LFM) is an application of atomic force microscopy (AFM) to sense lateral forces applied to the AFM probe tip. Recent advances in tissue engineering and functional biomaterials have shown a need for the surface characterization of their material and biochemical properties under the application of lateral forces. LFM equipped with colloidal probes of well-defined tip geometries has been a natural fit to address these needs but has remained limited to provide primarily qualitative results. For quantitative measurements, LFM requires the successful determination of the lateral force or torque conversion factor of the probe. Usually, force calibration results obtained in air are used for force measurements in liquids, but refractive index differences between air and liquids induce changes in the conversion factor. Furthermore, in the case of biochemically functionalized tips, damage can occur during calibration because tip-surface contact is inevitable in most calibration methods. Therefore, a nondestructive in situ lateral force calibration is desirable for LFM applications in liquids. Here we present an in situ hydrodynamic lateral force calibration method for AFM colloidal probes. In this method, the laterally scanned substrate surface generated a creeping Couette flow, which deformed the probe under torsion. The spherical geometry of the tip enabled the calculation of tip drag forces, and the lateral torque conversion factor was calibrated from the lateral voltage change and estimated torque. Comparisons with lateral force calibrations performed in air show that the hydrodynamic lateral force calibration method enables quantitative lateral force measurements in liquid using colloidal probes.

  2. Probing the PEDOT:PSS/cell interface with conductive colloidal probe AFM-SECM

    NASA Astrophysics Data System (ADS)

    Knittel, P.; Zhang, H.; Kranz, C.; Wallace, G. G.; Higgins, M. J.

    2016-02-01

    Conductive colloidal probe Atomic Force-Scanning Electrochemical Microscopy (AFM-SECM) is a new approach, which employs electrically insulated AFM probes except for a gold-coated colloid located at the end of the cantilever. Hence, force measurements can be performed while biasing the conductive colloid under physiological conditions. Moreover, such colloids can be modified by electrochemical polymerization resulting, e.g. in conductive polymer-coated spheres, which in addition may be loaded with specific dopants. In contrast to other AFM-based single cell force spectroscopy measurements, these probes allow adhesion measurements at the cell-biomaterial interface on multiple cells in a rapid manner while the properties of the polymer can be changed by applying a bias. In addition, spatially resolved electrochemical information e.g., oxygen reduction can be obtained simultaneously. Conductive colloid AFM-SECM probes modified with poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) are used for single cell force measurements in mouse fibroblasts and single cell interactions are investigated as a function of the applied potential.Conductive colloidal probe Atomic Force-Scanning Electrochemical Microscopy (AFM-SECM) is a new approach, which employs electrically insulated AFM probes except for a gold-coated colloid located at the end of the cantilever. Hence, force measurements can be performed while biasing the conductive colloid under physiological conditions. Moreover, such colloids can be modified by electrochemical polymerization resulting, e.g. in conductive polymer-coated spheres, which in addition may be loaded with specific dopants. In contrast to other AFM-based single cell force spectroscopy measurements, these probes allow adhesion measurements at the cell-biomaterial interface on multiple cells in a rapid manner while the properties of the polymer can be changed by applying a bias. In addition, spatially resolved electrochemical

  3. Colloid-probe AFM studies of the interaction forces of proteins adsorbed on colloidal crystals.

    PubMed

    Singh, Gurvinder; Bremmell, Kristen E; Griesser, Hans J; Kingshott, Peter

    2015-04-28

    In recent years, colloid-probe AFM has been used to measure the direct interaction forces between colloidal particles of different size or surface functionality in aqueous media, as one can study different forces in symmerical systems (i.e., sphere-sphere geometry). The present study investigates the interaction between protein coatings on colloid probes and hydrophilic surfaces decorated with hexagonally close packed single particle layers that are either uncoated or coated with proteins. Controlled solvent evaporation from aqueous suspensions of colloidal particles (coated with or without lysozyme and albumin) produces single layers of close-packed colloidal crystals over large areas on a solid support. The measurements have been carried out in an aqueous medium at different salt concentrations and pH values. The results show changes in the interaction forces as the surface charge of the unmodified or modified particles, and ionic strength or pH of the solution is altered. At high ionic strength or pH, electrostatic interactions are screened, and a strong repulsive force at short separation below 5 nm dominates, suggesting structural changes in the absorbed protein layer on the particles. We also study the force of adhesion, which decreases with an increment in the salt concentration, and the interaction between two different proteins indicating a repulsive interaction on approach and adhesion on retraction. PMID:25758979

  4. Oscillatory structural forces due to nonionic surfactant micelles: data by colloidal-probe AFM vs theory.

    PubMed

    Christov, Nikolay C; Danov, Krassimir D; Zeng, Yan; Kralchevsky, Peter A; von Klitzing, Regine

    2010-01-19

    Micellar solutions of nonionic surfactants Brij 35 and Tween 20 are confined between two surfaces in a colloidal-probe atomic-force microscope (CP-AFM). The experimentally detected oscillatory forces due to the layer-by-layer expulsion of the micelles agree very well with the theoretical predictions for hard-sphere fluids. While the experiment gives parts of the stable branches of the force curve, the theoretical model allows reconstruction of the full oscillatory curve. Therewith, the strength and range of the ordering could be determined. The resulting aggregation number from the fits of the force curves for Brij 35 is close to 70 and exhibits a slight tendency to increase with the surfactant concentration. The last layer of micelles cannot be pressed out. The measured force-vs-distance curve has nonequilibrium portions, which represent "jumps" from one to another branch of the respective equilibrium oscillatory curve. In the case of Brij 35, at concentrations <150 mM spherical micelles are present and the oscillation period is close to the micelle diameter, slightly decreasing with the rise of concentration. For elongated micelles (at concentration 200 mM), no harmonic oscillations are observed anymore; instead, the period increases with the decrease of film thickness. In the case of Tween 20, the force oscillations are almost suppressed, which implies that the micelles of this surfactant are labile and are demolished by the hydrodynamic shear stresses due to the colloidal-probe motion. The comparison of the results for the two surfactants demonstrates that in some cases the micelles can be destroyed by the CP-AFM, but in other cases they can be stable and behave as rigid particles. This behavior correlates with the characteristic times of the slow micellar relaxation process for these surfactants.

  5. Exchangeable Colloidal AFM Probes for the Quantification of Irreversible and Long-Term Interactions

    PubMed Central

    Dörig, Pablo; Ossola, Dario; Truong, Anh Minh; Graf, Monika; Stauffer, Flurin; Vörös, János; Zambelli, Tomaso

    2013-01-01

    An original method is presented to study single-colloid interaction with a substrate in liquid environment. Colloids, either in solution or adsorbed on a surface, are fixed by suction against the aperture of a microchanneled atomic force microscopy cantilever. Their adhesion to the substrate is measured, followed by their release via a short overpressure surge. Such colloid exchange procedure allows for 1), the quick variation of differently functionalized colloids within the same experiment; 2), the investigation of long-term interactions by leaving the colloids on a surface for a defined time before detaching them; and 3), the inspection of irreversible interactions. After validation of the method by reproducing literature results obtained with traditional colloidal atomic force microscopy, the serial use of colloids with different surface functionalization was shown on a micropatterned surface. Finally, concanavalin A-coated colloids were allowed to adsorb on human embryonic kidney cells and then detached one by one. The adhesion between cells and colloids was up to 60 nN, whereas individual cells adhered with 20 nN to the glass substrate. A cellular elastic modulus of 0.8 kPa was determined using the attached colloid as indenter. PMID:23870267

  6. Exchangeable colloidal AFM probes for the quantification of irreversible and long-term interactions.

    PubMed

    Dörig, Pablo; Ossola, Dario; Truong, Anh Minh; Graf, Monika; Stauffer, Flurin; Vörös, János; Zambelli, Tomaso

    2013-07-16

    An original method is presented to study single-colloid interaction with a substrate in liquid environment. Colloids, either in solution or adsorbed on a surface, are fixed by suction against the aperture of a microchanneled atomic force microscopy cantilever. Their adhesion to the substrate is measured, followed by their release via a short overpressure surge. Such colloid exchange procedure allows for 1), the quick variation of differently functionalized colloids within the same experiment; 2), the investigation of long-term interactions by leaving the colloids on a surface for a defined time before detaching them; and 3), the inspection of irreversible interactions. After validation of the method by reproducing literature results obtained with traditional colloidal atomic force microscopy, the serial use of colloids with different surface functionalization was shown on a micropatterned surface. Finally, concanavalin A-coated colloids were allowed to adsorb on human embryonic kidney cells and then detached one by one. The adhesion between cells and colloids was up to 60 nN, whereas individual cells adhered with 20 nN to the glass substrate. A cellular elastic modulus of 0.8 kPa was determined using the attached colloid as indenter.

  7. Nano Mechanical Machining Using AFM Probe

    NASA Astrophysics Data System (ADS)

    Mostofa, Md. Golam

    Complex miniaturized components with high form accuracy will play key roles in the future development of many products, as they provide portability, disposability, lower material consumption in production, low power consumption during operation, lower sample requirements for testing, and higher heat transfer due to their very high surface-to-volume ratio. Given the high market demand for such micro and nano featured components, different manufacturing methods have been developed for their fabrication. Some of the common technologies in micro/nano fabrication are photolithography, electron beam lithography, X-ray lithography and other semiconductor processing techniques. Although these methods are capable of fabricating micro/nano structures with a resolution of less than a few nanometers, some of the shortcomings associated with these methods, such as high production costs for customized products, limited material choices, necessitate the development of other fabricating techniques. Micro/nano mechanical machining, such an atomic force microscope (AFM) probe based nano fabrication, has, therefore, been used to overcome some the major restrictions of the traditional processes. This technique removes material from the workpiece by engaging micro/nano size cutting tool (i.e. AFM probe) and is applicable on a wider range of materials compared to the photolithographic process. In spite of the unique benefits of nano mechanical machining, there are also some challenges with this technique, since the scale is reduced, such as size effects, burr formations, chip adhesions, fragility of tools and tool wear. Moreover, AFM based machining does not have any rotational movement, which makes fabrication of 3D features more difficult. Thus, vibration-assisted machining is introduced into AFM probe based nano mechanical machining to overcome the limitations associated with the conventional AFM probe based scratching method. Vibration-assisted machining reduced the cutting forces

  8. On CD-AFM bias related to probe bending

    NASA Astrophysics Data System (ADS)

    Ukraintsev, V. A.; Orji, N. G.; Vorburger, T. V.; Dixson, R. G.; Fu, J.; Silver, R. M.

    2012-03-01

    Critical Dimension AFM (CD-AFM) is a widely used reference metrology. To characterize modern semiconductor devices, very small and flexible probes, often 15 nm to 20 nm in diameter, are now frequently used. Several recent publications have reported on uncontrolled and significant probe-to-probe bias variation during linewidth and sidewall angle measurements [1,2]. Results obtained in this work suggest that probe bending can be on the order of several nanometers and thus potentially can explain much of the observed CD-AFM probe-to-probe bias variation. We have developed and experimentally tested one-dimensional (1D) and two-dimensional (2D) models to describe the bending of cylindrical probes. An earlier 1D bending model reported by Watanabe et al. [3] was refined. Contributions from several new phenomena were considered, including: probe misalignment, diameter variation near the carbon nanotube tip (CNT) apex, probe bending before snapping, distributed van der Waals-London force, etc. The methodology for extraction of the Hamaker probe-surface interaction energy from experimental probe bending data was developed. To overcome limitations of the 1D model, a new 2D distributed force (DF) model was developed. Comparison of the new model with the 1D single point force (SPF) model revealed about 27 % difference in probe bending bias between the two. A simple linear relation between biases predicted by the 1D SPF and 2D DF models was found. This finding simplifies use of the advanced 2D DF model of probe bending in various CD-AFM applications. New 2D and three-dimensional (3D) CDAFM data analysis software is needed to take full advantage of the new bias correction modeling capabilities.

  9. Structural and Mechanical Mechanisms of Ocular Tissues Probed by AFM

    NASA Astrophysics Data System (ADS)

    Ziebarth, Noël M.; Rico, Felix; Moy, Vincent T.

    In recent years, the atomic force microscope (AFM) has become an important tool in ophthalmic research. It has gained popularity largely because AFM is not restricted by the diffraction limits of light microscopy and can be applied to resolve images with molecular resolution. AFM is a minimally invasive technique and can be used to visualize molecular structures under near-physiological conditions. In addition, the AFM can be employed as a force apparatus to characterize the viscoelastic properties of biomaterials on the micron level and at the level of individual proteins. In this article, we summarize recent AFM studies of ocular tissues, while highlighting the great potential of AFM technology in ophthalmic research. Previous research demonstrates the versatility of the AFM as high resolution imaging technique and as a sensitive force apparatus for probing the mechanical properties of ocular tissues. The structural and mechanical properties of ocular tissues are of major importance to the understanding of the optomechanical functions of the human eye. In addition, AFM has played an important role in the development and characterization of ocular biomaterials, such as contact lenses and intraocular lenses. Studying ocular tissues using Atomic Force Microscopy has enabled several advances in ophthalmic research.

  10. Accurate noncontact calibration of colloidal probe sensitivities in atomic force microscopy.

    PubMed

    Chung, Koo-Hyun; Shaw, Gordon A; Pratt, Jon R

    2009-06-01

    The absolute force sensitivities of colloidal probes comprised of atomic force microscope, or AFM, cantilevers with microspheres attached to their distal ends are measured. The force sensitivities are calibrated through reference to accurate electrostatic forces, the realizations of which are described in detail. Furthermore, the absolute accuracy of a common AFM force calibration scheme, known as the thermal noise method, is evaluated. It is demonstrated that the thermal noise method can be applied with great success to colloidal probe calibration in air and in liquid to yield force measurements with relative standard uncertainties below 5%. Techniques to combine the electrostatics-based determination of the AFM force sensitivity with measurements of the colloidal probe's thermal noise spectrum to compute noncontact estimates of the displacement sensitivity and spring constant are also developed.

  11. Accurate noncontact calibration of colloidal probe sensitivities in atomic force microscopy

    SciTech Connect

    Chung, Koo-Hyun; Shaw, Gordon A.; Pratt, Jon R.

    2009-06-15

    The absolute force sensitivities of colloidal probes comprised of atomic force microscope, or AFM, cantilevers with microspheres attached to their distal ends are measured. The force sensitivities are calibrated through reference to accurate electrostatic forces, the realizations of which are described in detail. Furthermore, the absolute accuracy of a common AFM force calibration scheme, known as the thermal noise method, is evaluated. It is demonstrated that the thermal noise method can be applied with great success to colloidal probe calibration in air and in liquid to yield force measurements with relative standard uncertainties below 5%. Techniques to combine the electrostatics-based determination of the AFM force sensitivity with measurements of the colloidal probe's thermal noise spectrum to compute noncontact estimates of the displacement sensitivity and spring constant are also developed.

  12. Functionalized AFM probes for force spectroscopy: eigenmode shapes and stiffness calibration through thermal noise measurements.

    PubMed

    Laurent, Justine; Steinberger, Audrey; Bellon, Ludovic

    2013-06-01

    The functionalization of an atomic force microscope (AFM) cantilever with a colloidal bead is a widely used technique when the geometry between the probe and the sample must be controlled, particularly in force spectroscopy. But some questions remain: how does a bead glued at the end of a cantilever influence its mechanical response? And more importantly for quantitative measurements, can we still determine the stiffness of the AFM probe with traditional techniques?In this paper, the influence of the colloidal mass loading on the eigenmode shape and resonant frequency is investigated by measuring the thermal noise on rectangular AFM microcantilevers with and without beads attached at their extremities. The experiments are performed with a home-made ultra-sensitive AFM, based on differential interferometry. The focused beam from the interferometer probes the cantilever at different positions and the spatial shapes of the modes are determined up to the fifth resonance, without external excitation. The results clearly demonstrate that the first eigenmode is almost unchanged by mass loading. However the oscillation behavior of higher resonances presents a marked difference: with a particle glued at its extremity, the nodes of the modes are displaced towards the free end of the cantilever. These results are compared to an analytical model taking into account the mass and inertial moment of the load in an Euler-Bernoulli framework, where the normalization of the eigenmodes is explicitly worked out in order to allow a quantitative prediction of the thermal noise amplitude of each mode. A good agreement between the experimental results and the analytical model is demonstrated, allowing a clean calibration of the probe stiffness.

  13. Oxide nanocrystal based nanocomposites for fabricating photoplastic AFM probes

    NASA Astrophysics Data System (ADS)

    Ingrosso, Chiara; Martin-Olmos, Cristina; Llobera, Andreu; Innocenti, Claudia; Sangregorio, Claudio; Striccoli, Marinella; Agostiano, Angela; Voigt, Anja; Gruetzner, Gabi; Brugger, Jürgen; Perez-Murano, Francesc; Curri, Maria Lucia

    2011-11-01

    We report on the synthesis, characterization and application of a novel nanocomposite made of a negative tone epoxy based photoresist modified with organic-capped Fe2O3 nanocrystals (NCs). The mechanical properties of the nanocomposite drastically improve upon incorporation of a suitable concentration of NCs in the polymer, without deteriorating its photolithography performance. High aspect ratio 3D microstructures made of the nanocomposite have been fabricated with a uniform surface morphology and with a resolution down to few micrometres. The embedded organic-capped Fe2O3 NCs drastically increase the stiffness and hardness of the epoxy based photoresist matrix, making the final material extremely interesting for manufacturing miniaturized polymer based mechanical devices and systems. In particular, the nanocomposite has been used as structural material for fabricating photoplastic Atomic Force Microscopy (AFM) probes with integrated tips showing outstanding mechanical response and high resolution imaging performance. The fabricated probes consist of straight cantilevers with low stress-gradient and high quality factors, incorporating sharp polymeric tips. They present considerably improved performance compared to pure epoxy based photoresist AFM probes, and to commercial silicon AFM probes.We report on the synthesis, characterization and application of a novel nanocomposite made of a negative tone epoxy based photoresist modified with organic-capped Fe2O3 nanocrystals (NCs). The mechanical properties of the nanocomposite drastically improve upon incorporation of a suitable concentration of NCs in the polymer, without deteriorating its photolithography performance. High aspect ratio 3D microstructures made of the nanocomposite have been fabricated with a uniform surface morphology and with a resolution down to few micrometres. The embedded organic-capped Fe2O3 NCs drastically increase the stiffness and hardness of the epoxy based photoresist matrix, making the

  14. Scanning hall probe microscopy (SHPM) using quartz crystal AFM feedback.

    PubMed

    Dede, M; Urkmen, K; Girişen, O; Atabak, M; Oral, A; Farrer, I; Ritchie, D

    2008-02-01

    Scanning Hall Probe Microscopy (SHPM) is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains with high spatial and magnetic field resolution of approximately 50 nm and 7 mG/Hz(1/2) at room temperature. In the SHPM technique, scanning tunneling microscope (STM) or atomic force microscope (AFM) feedback is used to keep the Hall sensor in close proximity of the sample surface. However, STM tracking SHPM requires conductive samples; therefore the insulating substrates have to be coated with a thin layer of gold. This constraint can be eliminated with the AFM feedback using sophisticated Hall probes that are integrated with AFM cantilevers. However it is very difficult to micro fabricate these sensors. In this work, we have eliminated the difficulty in the cantilever-Hall probe integration process, just by gluing a Hall Probe chip to a quartz crystal tuning fork force sensor. The Hall sensor chip is simply glued at the end of a 32.768 kHz or 100 kHz Quartz crystal, which is used as force sensor. An LT-SHPM system is used to scan the samples. The sensor assembly is dithered at the resonance frequency using a digital Phase Locked Loop circuit and frequency shifts are used for AFM tracking. SHPM electronics is modified to detect AFM topography and the frequency shift, along with the magnetic field image. Magnetic domains and topography of an Iron Garnet thin film crystal, NdFeB demagnetised magnet and hard disk samples are presented at room temperature. The performance is found to be comparable with the SHPM using STM feedback.

  15. Nanoscale fabrication of a peptide layer using an AFM probe

    NASA Astrophysics Data System (ADS)

    Nakamura, Chikashi; Miyamoto, Chie; Obataya, Ikuo; Nakamura, Noriyuki; Miyake, Jun

    2004-12-01

    Scanning probe microscopy has been applied in many studies to manipulate atoms or molecules. In particular, force spectroscopy using an atomic force microscope (AFM) is a powerful tool to elucidate intermolecular or intramolecular interactions and provide mechanical information. If enzymes could retain their activity when immobilized on probes, not only could enzyme-substrate interactions be investigated but also the probes could be used for precise biomolecular manipulation at the nano-scale. In our study, a method based on "Enzymatic Nanolithography" was successfully performed in a buffered solution using Staphylococcal serine V8 protease and AFM. To estimate the fabricating activity of the protease immobilized on the AFM tip to peptides immobilized on a substrate, we designed and synthesized peptides that showed enzymatic action specific to the protease. When the protease digested the reporter peptide a quencher residue was released from the main flame of the peptide and resulted in fluorescence. In the designed 9 mer peptides, TAMRA functioned as a good quencher for FAM. After contact of the protease-immobilized tip to the reporter peptide layer, a fluorescent area was observed by microscopic imaging.

  16. Quantitative and Qualitative Examination of Particle-particle Interactions Using Colloidal Probe Nanoscopy

    PubMed Central

    D'Sa, Dexter; Chan, Hak-Kim; Kim, Hae-Won; Chrzanowski, Wojciech

    2014-01-01

    Colloidal Probe Nanoscopy (CPN), the study of the nano-scale interactive forces between a specifically prepared colloidal probe and any chosen substrate using the Atomic Force Microscope (AFM), can provide key insights into physical interactions present within colloidal systems. Colloidal systems are widely existent in several applications including, pharmaceuticals, foods, paints, paper, soil and minerals, detergents, printing and much more.1-3 Furthermore, colloids can exist in many states such as emulsions, foams and suspensions. Using colloidal probe nanoscopy one can obtain key information on the adhesive properties, binding energies and even gain insight into the physical stability and coagulation kinetics of the colloids present within. Additionally, colloidal probe nanoscopy can be used with biological cells to aid in drug discovery and formulation development. In this paper we describe a method for conducting colloidal probe nanoscopy, discuss key factors that are important to consider during the measurement, and show that both quantitative and qualitative data that can be obtained from such measurements. PMID:25080136

  17. Real time drift measurement for colloidal probe atomic force microscope: a visual sensing approach

    SciTech Connect

    Wang, Yuliang Bi, Shusheng; Wang, Huimin

    2014-05-15

    Drift has long been an issue in atomic force microscope (AFM) systems and limits their ability to make long time period measurements. In this study, a new method is proposed to directly measure and compensate for the drift between AFM cantilevers and sample surfaces in AFM systems. This was achieved by simultaneously measuring z positions for beads at the end of an AFM colloidal probe and on sample surface through an off-focus image processing based visual sensing method. The working principle and system configuration are presented. Experiments were conducted to validate the real time drift measurement and compensation. The implication of the proposed method for regular AFM measurements is discussed. We believe that this technique provides a practical and efficient approach for AFM experiments requiring long time period measurement.

  18. Diffusing colloidal probes of cell surfaces.

    PubMed

    Duncan, Gregg A; Fairbrother, D Howard; Bevan, Michael A

    2016-05-25

    Measurements and analyses are reported to quantify dynamic and equilibrium interactions between colloidal particles and live cell surfaces using dark field video microscopy. Two-dimensional trajectories of micron-sized polyethylene glycol (PEG)-coated silica colloids relative to adherent epithelial breast cancer cell perimeters are determined allowing measurement of position dependent diffusivities and interaction potentials. PEG was chosen as the material system of interest to assess non-specific interactions with cell surfaces and establishes a basis for investigation of specific interactions in future studies. Analysis of measured potential energies on cell surfaces reveals the spatial dependence in cell topography. With the measured cell topography and models for particle-cell surface hydrodynamic interactions, excellent agreement is obtained between theoretical and measured colloidal transport on cell surfaces. Quantitative analyses of association lifetimes showed that PEG coatings act to stabilize colloids above the cell surface through net repulsive, steric interactions. Our results demonstrate a self-consistent analysis of diffusing colloidal probe interactions due to conservative and non-conservative forces to characterize biophysical cell surface properties. PMID:27117575

  19. Diffusing colloidal probes of cell surfaces.

    PubMed

    Duncan, Gregg A; Fairbrother, D Howard; Bevan, Michael A

    2016-05-25

    Measurements and analyses are reported to quantify dynamic and equilibrium interactions between colloidal particles and live cell surfaces using dark field video microscopy. Two-dimensional trajectories of micron-sized polyethylene glycol (PEG)-coated silica colloids relative to adherent epithelial breast cancer cell perimeters are determined allowing measurement of position dependent diffusivities and interaction potentials. PEG was chosen as the material system of interest to assess non-specific interactions with cell surfaces and establishes a basis for investigation of specific interactions in future studies. Analysis of measured potential energies on cell surfaces reveals the spatial dependence in cell topography. With the measured cell topography and models for particle-cell surface hydrodynamic interactions, excellent agreement is obtained between theoretical and measured colloidal transport on cell surfaces. Quantitative analyses of association lifetimes showed that PEG coatings act to stabilize colloids above the cell surface through net repulsive, steric interactions. Our results demonstrate a self-consistent analysis of diffusing colloidal probe interactions due to conservative and non-conservative forces to characterize biophysical cell surface properties.

  20. Viscoelasticity of gelatin surfaces probed by AFM noise analysis.

    PubMed

    Benmouna, Farida; Johannsmann, Diethelm

    2004-01-01

    The viscoelastic properties of surfaces of swollen gelatin were investigated by analyzing the Brownian motion of an atomic force microscopy (AFM) cantilever in contact with the gel surface. A micron-sized glass sphere attached to the AFM cantilever is used as the dynamic probe. When the sphere approaches the gelatin surface, there is a static repulsive force without a jump into contact. The cantilever's Brownian movement is monitored in parallel, providing access to the dynamic sphere-surface interaction as quantified by the dynamic spring constant, kappa, and the drag coefficient, xi. Gelatin is used as a model substance for a variety of other soft surfaces, where the stiffness of the gel can be varied via the solvent quality, the bloom number, and the pH. The modulus derived from the static force-distance curve is in the kPa range, consistent with the literature. However, the dynamic spring constant as derived from the Brownian motion is much larger than the static differential spring constant dF/dz. On retraction, one observes a rather strong adhesion hysteresis. The strength of the bridge (as given by the dynamic spring constant and the drag coefficient) is very small. PMID:15745019

  1. Accurate flexural spring constant calibration of colloid probe cantilevers using scanning laser Doppler vibrometry.

    PubMed

    Gates, Richard S; Osborn, William A; Shaw, Gordon A

    2015-06-12

    Calibration of the flexural spring constant for atomic force microscope (AFM) colloid probe cantilevers provides significant challenges. The presence of a large attached spherical added mass complicates many of the more common calibration techniques such as reference cantilever, Sader, and added mass. Even the most promising option, AFM thermal calibration, can encounter difficulties during the optical lever sensitivity measurement due to strong adhesion and friction between the sphere and a surface. This may cause buckling of the end of the cantilever and hysteresis in the approach-retract curves resulting in increased uncertainty in the calibration. Most recently, a laser Doppler vibrometry thermal method has been used to accurately calibrate the normal spring constant of a wide variety of tipped and tipless commercial cantilevers. This paper describes a variant of the technique, scanning laser Doppler vibrometry, optimized for colloid probe cantilevers and capable of spring constant calibration uncertainties near ±1%.

  2. Improved in situ spring constant calibration for colloidal probe atomic force microscopy.

    PubMed

    McBride, Sean P; Law, Bruce M

    2010-11-01

    In colloidal probe atomic force microscopy (AFM) surface forces cannot be measured without an accurate determination of the cantilever spring constant. The effective spring constant k depends upon the cantilever geometry and therefore should be measured in situ; additionally, k may be coupled to other measurement parameters. For example, colloidal probe AFM is frequently used to measure the slip length b at solid/liquid boundaries by comparing the measured hydrodynamic force with Vinogradova slip theory (V-theory). However, in this measurement k and b are coupled, hence, b cannot be accurately determined without knowing k to high precision. In this paper, a new in situ spring constant calibration method based upon the residuals, namely, the difference between experimental force-distance data and V-theory is presented and contrasted with two other popular spring constant determination methods. In this residuals calibration method, V-theory is fitted to the experimental force-distance data for a range of systematically varied spring constants where the only adjustable parameter in V-theory is the slip length b. The optimal spring constant k is that value where the residuals are symmetrically displaced about zero for all colloidal probe separations. This residual spring constant calibration method is demonstrated by studying three different liquids (n-decanol, n-hexadecane, and n-octane) and two different silane coated colloidal probe-silicon wafer systems (n-hexadecyltrichlorosilane and n-dodecyltrichlorosilane).

  3. Improved in situ spring constant calibration for colloidal probe atomic force microscopy

    SciTech Connect

    McBride, Sean P.; Law, Bruce M.

    2010-11-15

    In colloidal probe atomic force microscopy (AFM) surface forces cannot be measured without an accurate determination of the cantilever spring constant. The effective spring constant k depends upon the cantilever geometry and therefore should be measured in situ; additionally, k may be coupled to other measurement parameters. For example, colloidal probe AFM is frequently used to measure the slip length b at solid/liquid boundaries by comparing the measured hydrodynamic force with Vinogradova slip theory (V-theory). However, in this measurement k and b are coupled, hence, b cannot be accurately determined without knowing k to high precision. In this paper, a new in situ spring constant calibration method based upon the residuals, namely, the difference between experimental force-distance data and V-theory is presented and contrasted with two other popular spring constant determination methods. In this residuals calibration method, V-theory is fitted to the experimental force-distance data for a range of systematically varied spring constants where the only adjustable parameter in V-theory is the slip length b. The optimal spring constant k is that value where the residuals are symmetrically displaced about zero for all colloidal probe separations. This residual spring constant calibration method is demonstrated by studying three different liquids (n-decanol, n-hexadecane, and n-octane) and two different silane coated colloidal probe-silicon wafer systems (n-hexadecyltrichlorosilane and n-dodecyltrichlorosilane).

  4. New developments at PTB in 3D-AFM with tapping and torsion AFM mode and vector approach probing strategy

    NASA Astrophysics Data System (ADS)

    Dai, G.; Hässler-Grohne, W.; Hüser, D.; Wolff, H.; Fluegge, J.; Bosse, H.

    2011-06-01

    A new 3D-AFM for true 3D measurements of nano structures has been developed at Physikalisch Technische-Bundesanstalt, the national metrology institute of Germany. In its configuration, two piezo actuators are applied to drive the AFM cantilever near its vertical and torsional resonant frequencies. In such a way, the AFM tip can probe the surface with a vertical and/or a lateral oscillation, offering high 3D probing sensitivity. For enhancing measurement flexibility as well as reducing tip wear, a so called "vector approach probing" (VAP) method has been applied. The sample is measured point by point using this method. At each probing point, the tip is approached towards the surface in its normal direction until the desired tip-sample interaction is detected and then immediately withdrawn from the surface. Preliminary experimental results show promising performance of the developed system. The measurement of a line structure of 800 nm height employing a super sharp AFM tip is performed, showing a repeatability of its 3D profiles of better than 1 nm (p-v). A single crystal critical dimension reference material (SCCDRM) having features with almost vertical sidewall is measured using a flared AFM tip. Results show that the feature has averaged left and right sidewall angles of 88.64° and 88.67deg;, respectively. However, the feature width non-uniformity may reach 10 nm within the measurement range of 1 μm. The standard deviation of the averaged middle CD values of 7 repeated measurements reaches 0.35 nm. In addition, an investigation of long term measurement stability is performed on a PTB photomask. The results shows that the 3D-AFM has a drift rate of about 0.00033 nm per line, which confirms the high measurement stability and the very low tip wear.

  5. Combining colloidal probe atomic force and reflection interference contrast microscopy to study the compressive mechanics of hyaluronan brushes.

    PubMed

    Attili, Seetharamaiah; Richter, Ralf P

    2012-02-14

    We describe a method that combines colloidal probe atomic force microscopy (AFM) and reflection interference contrast microscopy (RICM) to characterize the mechanical properties of thin and solvated polymer films. When analyzing polymer films, a fundamental problem in colloidal probe AFM experiments is to determine the distance at closest approach between the probe and the substrate on which the film is deposited. By combining AFM and RICM in situ, forces and absolute distances can be measured simultaneously. Using the combined setup, we quantify the compressive mechanics of films of the polysaccharide hyaluronan that is end-grafted to a supported lipid bilayer. The experimental data, and comparison with polymer theory, show that hyaluronan films are well-described as elastic, very soft and highly solvated polymer brushes. The data on these well-defined films should be a useful reference for the investigation of the more complex hyaluronan-rich coats that surround many living cells.

  6. Conductive probe AFM measurements of conjugated molecular wires.

    PubMed

    Ishida, Takao; Mizutani, Wataru; Liang, Tien-Tzu; Azehara, Hiroaki; Miyake, Koji; Sasaki, Shinya; Tokumoto, Hiroshi

    2003-12-01

    The electrical conduction of self-assembled monolayers (SAMs) made from conjugated molecules was measured using conductive probe atomic force microscopy (CP-AFM), with a focus on the molecular structural effect on conduction. First, the electrical conduction of SAMs made from phenylene oligomer SAMs was measured. The resistances through the monolayers increased exponentially with an increase in molecular length and the decay constants of transconductance beta were about 0.45 to 0.61 A(-1) measured at lower bias region. We further investigated the influence of applied load on the resistances. The resistances through terphenyl SAMs increased with an increase in the applied load up to 14 nN. Second, using an insertion technique into insulating alkanethiol SAMs, the electrical conduction of single conjugated terphenyl methanethiol and oligo(para-phenylenevinylene) (OPV) molecules embedded into insulating alkanethiol SAMs were measured. Electrical currents through these single molecules of OPVs were estimated to be larger than those through single terphenyl molecules, suggesting that the OPV structure can increase the electrical conduction of single molecules. Third, apparent negative differential resistance (NDR) was observed at higher bias measurements of SAMs. The appearance of NDR might be related to roughness of SAM surface, because apparent NDR was often observed on rough surfaces. In any case, the tip-molecule contact condition strongly affected carrier transport through metal tip/SAM/metal junction.

  7. AFM probes fabricated with masked maskless combined anisotropic etching and p+ surface doping

    NASA Astrophysics Data System (ADS)

    Han, Jianqiang; Li, Xinxin; Bao, Haifei; Zuo, Guomin; Wang, Yuelin; Feng, Fei; Yu, Zhenyin; Ge, Xiaohong

    2006-02-01

    The paper presents a newly developed high-yield micro-fabrication technology for single-crystalline silicon atomic force microscope (AFM) probes. Both the tips and the cantilevers are simultaneously formed by a masked-maskless combined anisotropic etching process. Compared to a conventional tip-to-cantilever sequential fabrication scheme, this tip-and-cantilever simultaneous formation can effectively increase fabrication yield by avoiding the tips damaged during the following processed photolithographic steps for defining the cantilevers. By heavy boron doping at the surface, the conductive AFM probe provides an electrical path to the electric ground of the AFM that helps to eliminate the electrostatic accumulation of charges and, therefore, eliminate undesirable electrostatic forces between the probes and the samples. A fabrication yield as high as 90% has been obtained for the AFM probes for 4 inch wafers. The tips after oxidation-sharpening treatment generally have a radius of 10-30 nm. The cantilever spring constant can be well controlled in the range of 0.025-40 N m-1. High-quality sample scanning results with the formed AFM probes are obtained with a slightly better resolution than that from commercial probes without surface conductive treatment.

  8. Fabrication of carbon nanotube AFM probes using the Langmuir-Blodgett technique.

    PubMed

    Lee, Jae-Hyeok; Kang, Won-Seok; Choi, Bung-Sam; Choi, Sung-Wook; Kim, Jae-Ho

    2008-09-01

    Carbon nanotube (CNT)-tipped atomic force microscopy (AFM) probes have shown a significant potential for obtaining high-resolution imaging of nanostructure and biological materials. In this paper, we report a simple method to fabricate single-walled carbon nanotube (SWNT) nanoprobes for AFM using the Langmuir-Blodgett (LB) technique. Thiophenyl-modified SWNTs (SWNT-SHs) through amidation of SWNTs in chloroform allowed to be spread and form a stable Langmuir monolayer at the water/air interface. A simple two-step transfer process was used: (1) dipping conventional AFM probes into the Langmuir monolayer and (2) lifting the probes from the water surface. This results in the attachment of SWNTs onto the tips of AFM nanoprobes. We found that the SWNTs assembled on the nanoprobes were well-oriented and robust enough to maintain their shape and direction even after successive scans. AFM measurements of a nano-porous alumina substrate and deoxyribonucleic acid using SWNT-modified nanoprobes revealed that the curvature diameter of the nanoprobes was less than 3 nm and a fine resolution was obtained than that from conventional AFM probes. We also demonstrate that the LB method is a scalable process capable of simultaneously fabricating a large number of SWNT-modified nanoprobes.

  9. The importance of correcting for variable probe-sample interactions in AFM-IR spectroscopy: AFM-IR of dried bacteria on a polyurethane film.

    PubMed

    Barlow, Daniel E; Biffinger, Justin C; Cockrell-Zugell, Allison L; Lo, Michael; Kjoller, Kevin; Cook, Debra; Lee, Woo Kyung; Pehrsson, Pehr E; Crookes-Goodson, Wendy J; Hung, Chia-Suei; Nadeau, Lloyd J; Russell, John N

    2016-08-01

    AFM-IR is a combined atomic force microscopy-infrared spectroscopy method that shows promise for nanoscale chemical characterization of biological-materials interactions. In an effort to apply this method to quantitatively probe mechanisms of microbiologically induced polyurethane degradation, we have investigated monolayer clusters of ∼200 nm thick Pseudomonas protegens Pf-5 bacteria (Pf) on a 300 nm thick polyether-polyurethane (PU) film. Here, the impact of the different biological and polymer mechanical properties on the thermomechanical AFM-IR detection mechanism was first assessed without the additional complication of polymer degradation. AFM-IR spectra of Pf and PU were compared with FTIR and showed good agreement. Local AFM-IR spectra of Pf on PU (Pf-PU) exhibited bands from both constituents, showing that AFM-IR is sensitive to chemical composition both at and below the surface. One distinct difference in local AFM-IR spectra on Pf-PU was an anomalous ∼4× increase in IR peak intensities for the probe in contact with Pf versus PU. This was attributed to differences in probe-sample interactions. In particular, significantly higher cantilever damping was observed for probe contact with PU, with a ∼10× smaller Q factor. AFM-IR chemical mapping at single wavelengths was also affected. We demonstrate ratioing of mapping data for chemical analysis as a simple method to cancel the extreme effects of the variable probe-sample interactions. PMID:27403761

  10. Development of a novel nanoindentation technique by utilizing a dual-probe AFM system

    PubMed Central

    Sahin, Ferat; Yablon, Dalia

    2015-01-01

    Summary A novel instrumentation approach to nanoindentation is described that exhibits improved resolution and depth sensing. The approach is based on a multi-probe scanning probe microscopy (SPM) tool that utilizes tuning-fork based probes for both indentation and depth sensing. Unlike nanoindentation experiments performed with conventional AFM systems using beam-bounce technology, this technique incorporates a second probe system with an ultra-high resolution for depth sensing. The additional second probe measures only the vertical movement of the straight indenter attached to a tuning-fork probe with a high spring constant and it can also be used for AFM scanning to obtain an accurate profiling. Nanoindentation results are demonstrated on silicon, fused silica, and Corning Eagle Glass. The results show that this new approach is viable in terms of accurately characterizing mechanical properties of materials through nanoindentation with high accuracy, and it opens doors to many other exciting applications in the field of nanomechanical characterization. PMID:26665072

  11. Coating of AFM probes with aquatic humic and non-humic NOM to study their adhesion properties.

    PubMed

    Aubry, Cyril; Gutierrez, Leonardo; Croue, Jean Philippe

    2013-06-01

    Atomic force microscopy (AFM) was used to study interaction forces between four Natural Organic Matter (NOM) samples of different physicochemical characteristics and origins and mica surface at a wide range of ionic strength. All NOM samples were strongly adsorbed on positively charged iron oxide-coated silica colloidal probe. Cross-sectioning by focused ion beam milling technique and elemental mapping by energy-filtered transmission electron microscopy indicated coating completeness of the NOM-coated colloidal probes. AFM-generated force-distance curves were analyzed to elucidate the nature and mechanisms of these interacting forces. Electrostatics and steric interactions were important contributors to repulsive forces during approach, although the latter became more influential with increasing ionic strength. Retracting force profiles showed a NOM adhesion behavior on mica consistent with its physicochemical characteristics. Humic-like substances, referred as the least hydrophilic NOM fraction, i.e., so called hydrophobic NOM, poorly adsorbed on hydrophilic mica due to their high content of ionized carboxyl groups and aromatic/hydrophobic character. However, adhesion force increased with increasing ionic strength, suggesting double layer compression. Conversely, polysaccharide-like substances showed high adhesion to mica. Hydrogen-bonding between hydroxyl groups on polysaccharide-like substances and highly electronegative elements on mica was suggested as the main adsorption mechanism, where the adhesion force decreased with increasing ionic strength. Results from this investigation indicated that all NOM samples retained their characteristics after the coating procedure. The experimental approach followed in this study can potentially be extended to investigate interactions between NOM and clean or fouled membranes as a function of NOM physicochemical characteristics and solution chemistry.

  12. A Novel Dog-Bone Oscillating AFM Probe with Thermal Actuation and Piezoresistive Detection †

    PubMed Central

    Xiong, Zhuang; Mairiaux, Estelle; Walter, Benjamin; Faucher, Marc; Buchaillot, Lionel; Legrand, Bernard

    2014-01-01

    In order to effectively increase the resonance frequency and the quality factor of atomic force microscope (AFM) probes, a novel oscillating probe based on a dog-bone shaped MEMS resonator was conceived, designed, fabricated and evaluated. The novel probe with 400 μm in length, 100 μm in width and 5 μm in thickness was enabled to feature MHz resonance frequencies with integrated thermal actuation and piezoresistive detection. Standard silicon micromachining was employed. Both electrical and optical measurements were carried out in air. The resonance frequency and the quality factor of the novel probe were measured to be 5.4 MHz and 4000 respectively, which are much higher than those (about several hundreds of kHz) of commonly used cantilever probes. The probe was mounted onto a commercial AFM set-up through a dedicated probe-holder and circuit board. Topographic images of patterned resist samples were obtained. It is expected that the resonance frequency and the measurement bandwidth of such probes will be further increased by a proper downscaling, thus leading to a significant increase in the scanning speed capability of AFM instruments. PMID:25365463

  13. A novel dog-bone oscillating AFM probe with thermal actuation and piezoresistive detection.

    PubMed

    Xiong, Zhuang; Mairiaux, Estelle; Walter, Benjamin; Faucher, Marc; Buchaillot, Lionel; Legrand, Bernard

    2014-01-01

    In order to effectively increase the resonance frequency and the quality factor of atomic force microscope (AFM) probes, a novel oscillating probe based on a dog-bone shaped MEMS resonator was conceived, designed, fabricated and evaluated. The novel probe with 400 μm in length, 100 μm in width and 5 μm in thickness was enabled to feature MHz resonance frequencies with integrated thermal actuation and piezoresistive detection. Standard silicon micromachining was employed. Both electrical and optical measurements were carried out in air. The resonance frequency and the quality factor of the novel probe were measured to be 5.4 MHz and 4000 respectively, which are much higher than those (about several hundreds of kHz) of commonly used cantilever probes. The probe was mounted onto a commercial AFM set-up through a dedicated probe-holder and circuit board. Topographic images of patterned resist samples were obtained. It is expected that the resonance frequency and the measurement bandwidth of such probes will be further increased by a proper downscaling, thus leading to a significant increase in the scanning speed capability of AFM instruments. PMID:25365463

  14. A novel dog-bone oscillating AFM probe with thermal actuation and piezoresistive detection.

    PubMed

    Xiong, Zhuang; Mairiaux, Estelle; Walter, Benjamin; Faucher, Marc; Buchaillot, Lionel; Legrand, Bernard

    2014-10-31

    In order to effectively increase the resonance frequency and the quality factor of atomic force microscope (AFM) probes, a novel oscillating probe based on a dog-bone shaped MEMS resonator was conceived, designed, fabricated and evaluated. The novel probe with 400 μm in length, 100 μm in width and 5 μm in thickness was enabled to feature MHz resonance frequencies with integrated thermal actuation and piezoresistive detection. Standard silicon micromachining was employed. Both electrical and optical measurements were carried out in air. The resonance frequency and the quality factor of the novel probe were measured to be 5.4 MHz and 4000 respectively, which are much higher than those (about several hundreds of kHz) of commonly used cantilever probes. The probe was mounted onto a commercial AFM set-up through a dedicated probe-holder and circuit board. Topographic images of patterned resist samples were obtained. It is expected that the resonance frequency and the measurement bandwidth of such probes will be further increased by a proper downscaling, thus leading to a significant increase in the scanning speed capability of AFM instruments.

  15. A rapid and automated relocation method of an AFM probe for high-resolution imaging

    NASA Astrophysics Data System (ADS)

    Zhou, Peilin; Yu, Haibo; Shi, Jialin; Jiao, Niandong; Wang, Zhidong; Wang, Yuechao; Liu, Lianqing

    2016-09-01

    The atomic force microscope (AFM) is one of the most powerful tools for high-resolution imaging and high-precision positioning for nanomanipulation. The selection of the scanning area of the AFM depends on the use of the optical microscope. However, the resolution of an optical microscope is generally no larger than 200 nm owing to wavelength limitations of visible light. Taking into consideration the two determinants of relocation—relative angular rotation and positional offset between the AFM probe and nano target—it is therefore extremely challenging to precisely relocate the AFM probe to the initial scan/manipulation area for the same nano target after the AFM probe has been replaced, or after the sample has been moved. In this paper, we investigate a rapid automated relocation method for the nano target of an AFM using a coordinate transformation. The relocation process is both simple and rapid; moreover, multiple nano targets can be relocated by only identifying a pair of reference points. It possesses a centimeter-scale location range and nano-scale precision. The main advantages of this method are that it overcomes the limitations associated with the resolution of optical microscopes, and that it is label-free on the target areas, which means that it does not require the use of special artificial markers on the target sample areas. Relocation experiments using nanospheres, DNA, SWCNTs, and nano patterns amply demonstrate the practicality and efficiency of the proposed method, which provides technical support for mass nanomanipulation and detection based on AFM for multiple nano targets that are widely distributed in a large area.

  16. A rapid and automated relocation method of an AFM probe for high-resolution imaging.

    PubMed

    Zhou, Peilin; Yu, Haibo; Shi, Jialin; Jiao, Niandong; Wang, Zhidong; Wang, Yuechao; Liu, Lianqing

    2016-09-30

    The atomic force microscope (AFM) is one of the most powerful tools for high-resolution imaging and high-precision positioning for nanomanipulation. The selection of the scanning area of the AFM depends on the use of the optical microscope. However, the resolution of an optical microscope is generally no larger than 200 nm owing to wavelength limitations of visible light. Taking into consideration the two determinants of relocation-relative angular rotation and positional offset between the AFM probe and nano target-it is therefore extremely challenging to precisely relocate the AFM probe to the initial scan/manipulation area for the same nano target after the AFM probe has been replaced, or after the sample has been moved. In this paper, we investigate a rapid automated relocation method for the nano target of an AFM using a coordinate transformation. The relocation process is both simple and rapid; moreover, multiple nano targets can be relocated by only identifying a pair of reference points. It possesses a centimeter-scale location range and nano-scale precision. The main advantages of this method are that it overcomes the limitations associated with the resolution of optical microscopes, and that it is label-free on the target areas, which means that it does not require the use of special artificial markers on the target sample areas. Relocation experiments using nanospheres, DNA, SWCNTs, and nano patterns amply demonstrate the practicality and efficiency of the proposed method, which provides technical support for mass nanomanipulation and detection based on AFM for multiple nano targets that are widely distributed in a large area. PMID:27559679

  17. Carbon nanotube/carbon nanotube composite AFM probes prepared using ion flux molding

    NASA Astrophysics Data System (ADS)

    Chesmore, Grace; Roque, Carrollyn; Barber, Richard

    The performance of carbon nanotube-carbon nanotube composite (CNT/CNT composite) atomic force microscopy (AFM) probes is compared to that of conventional Si probes in AFM tapping mode. The ion flux molding (IFM) process, aiming an ion beam at the CNT probe, aligns the tip to a desired angle. The result is a relatively rigid tip that is oriented to offset the cantilever angle. Scans using these probes reveal an improvement in image accuracy over conventional tips, while allowing higher aspect ratio imaging of 3D surface features. Furthermore, the lifetimes of CNT-CNT composite tips are observed to be longer than both conventional tips and those claimed for other CNT technologies. Novel applications include the imaging of embiid silk. Supported by the Clare Boothe Luce Research Scholars Award and Carbon Design Innovations.

  18. Imaging of a soft, weakly adsorbing, living cell with a colloid probe tapping atomic force microscope technique.

    PubMed

    McNamee, Cathy E; Pyo, Nayoung; Tanaka, Saaya; Kanda, Yoichi; Higashitani, Ko

    2006-01-15

    Here, we propose a new method to improve the atomic force microscopy (AFM) image resolution of soft samples, such as cells, in liquid. Attaching a colloid probe to a cantilever was seen improve the image resolution of a living cell in a physiological buffer solution, obtained by the normal tapping mode, when compared to an image obtained using a regular cantilever tip. This may be due to the averaging out of the cantilever tip swinging caused by the visco-elasticity of the cell. The resolution was best, when silica spheres with a 3.3 microm diameter were attached. Although larger spheres gave a resolution better than a bare cantilever tip, their resolution was less than that obtained for the 3.3 microm diameter silica colloid. This dependency of the image resolution on the colloid probe size may be a result of the increased macroscopic van der Waals attraction between the cell and probe, the decreased repulsive force dependence on the cantilever probe radius, and the decrease in resolution due to the increased probe size. The size of the colloid probe, which should be attached to the cantilever to give the best image resolution, would be the one that optimises the combined result of these facts. PMID:16406494

  19. Nanomechanical and topographical imaging of living cells by atomic force microscopy with colloidal probes

    SciTech Connect

    Puricelli, Luca; Galluzzi, Massimiliano; Schulte, Carsten; Podestà, Alessandro Milani, Paolo

    2015-03-15

    Atomic Force Microscopy (AFM) has a great potential as a tool to characterize mechanical and morphological properties of living cells; these properties have been shown to correlate with cells’ fate and patho-physiological state in view of the development of novel early-diagnostic strategies. Although several reports have described experimental and technical approaches for the characterization of cellular elasticity by means of AFM, a robust and commonly accepted methodology is still lacking. Here, we show that micrometric spherical probes (also known as colloidal probes) are well suited for performing a combined topographic and mechanical analysis of living cells, with spatial resolution suitable for a complete and accurate mapping of cell morphological and elastic properties, and superior reliability and accuracy in the mechanical measurements with respect to conventional and widely used sharp AFM tips. We address a number of issues concerning the nanomechanical analysis, including the applicability of contact mechanical models and the impact of a constrained contact geometry on the measured Young’s modulus (the finite-thickness effect). We have tested our protocol by imaging living PC12 and MDA-MB-231 cells, in order to demonstrate the importance of the correction of the finite-thickness effect and the change in Young’s modulus induced by the action of a cytoskeleton-targeting drug.

  20. High throughput nanofabrication of silicon nanowire and carbon nanotube tips on AFM probes by stencil-deposited catalysts.

    PubMed

    Engstrom, Daniel S; Savu, Veronica; Zhu, Xueni; Bu, Ian Y Y; Milne, William I; Brugger, Juergen; Boggild, Peter

    2011-04-13

    A new and versatile technique for the wafer scale nanofabrication of silicon nanowire (SiNW) and multiwalled carbon nanotube (MWNT) tips on atomic force microscope (AFM) probes is presented. Catalyst material for the SiNW and MWNT growth was deposited on prefabricated AFM probes using aligned wafer scale nanostencil lithography. Individual vertical SiNWs were grown epitaxially by a catalytic vapor-liquid-solid (VLS) process and MWNTs were grown by a plasma-enhanced chemical vapor (PECVD) process on the AFM probes. The AFM probes were tested for imaging micrometers-deep trenches, where they demonstrated a significantly better performance than commercial high aspect ratio tips. Our method demonstrates a reliable and cost-efficient route toward wafer scale manufacturing of SiNW and MWNT AFM probes. PMID:21446752

  1. Molecular Dynamic Simulations of Interaction of an AFM Probe with the Surface of an SCN Sample

    NASA Technical Reports Server (NTRS)

    Bune, Adris; Kaukler, William; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    Molecular dynamic (MD) simulations is conducted in order to estimate forces of probe-substrate interaction in the Atomic Force Microscope (AFM). First a review of available molecular dynamic techniques is given. Implementation of MD simulation is based on an object-oriented code developed at the University of Delft. Modeling of the sample material - succinonitrile (SCN) - is based on the Lennard-Jones potentials. For the polystyrene probe an atomic interaction potential is used. Due to object-oriented structure of the code modification of an atomic interaction potential is straight forward. Calculation of melting temperature is used for validation of the code and of the interaction potentials. Various fitting parameters of the probe-substrate interaction potentials are considered, as potentials fitted to certain properties and temperature ranges may not be reliable for the others. This research provides theoretical foundation for an interpretation of actual measurements of an interaction forces using AFM.

  2. Diamond-modified AFM probes: from diamond nanowires to atomic force microscopy-integrated boron-doped diamond electrodes.

    PubMed

    Smirnov, Waldemar; Kriele, Armin; Hoffmann, René; Sillero, Eugenio; Hees, Jakob; Williams, Oliver A; Yang, Nianjun; Kranz, Christine; Nebel, Christoph E

    2011-06-15

    In atomic force microscopy (AFM), sharp and wear-resistant tips are a critical issue. Regarding scanning electrochemical microscopy (SECM), electrodes are required to be mechanically and chemically stable. Diamond is the perfect candidate for both AFM probes as well as for electrode materials if doped, due to diamond's unrivaled mechanical, chemical, and electrochemical properties. In this study, standard AFM tips were overgrown with typically 300 nm thick nanocrystalline diamond (NCD) layers and modified to obtain ultra sharp diamond nanowire-based AFM probes and probes that were used for combined AFM-SECM measurements based on integrated boron-doped conductive diamond electrodes. Analysis of the resonance properties of the diamond overgrown AFM cantilevers showed increasing resonance frequencies with increasing diamond coating thicknesses (i.e., from 160 to 260 kHz). The measured data were compared to performed simulations and show excellent correlation. A strong enhancement of the quality factor upon overgrowth was also observed (120 to 710). AFM tips with integrated diamond nanowires are shown to have apex radii as small as 5 nm and where fabricated by selectively etching diamond in a plasma etching process using self-organized metal nanomasks. These scanning tips showed superior imaging performance as compared to standard Si-tips or commercially available diamond-coated tips. The high imaging resolution and low tip wear are demonstrated using tapping and contact mode AFM measurements by imaging ultra hard substrates and DNA. Furthermore, AFM probes were coated with conductive boron-doped and insulating diamond layers to achieve bifunctional AFM-SECM probes. For this, focused ion beam (FIB) technology was used to expose the boron-doped diamond as a recessed electrode near the apex of the scanning tip. Such a modified probe was used to perform proof-of-concept AFM-SECM measurements. The results show that high-quality diamond probes can be fabricated, which are

  3. High aspect ratio AFM Probe processing by helium-ion-beam induced deposition.

    PubMed

    Onishi, Keiko; Guo, Hongxuan; Nagano, Syoko; Fujita, Daisuke

    2014-11-01

    A Scanning Helium Ion Microscope (SHIM) is a high resolution surface observation instrument similar to a Scanning Electron Microscope (SEM) since both instruments employ finely focused particle beams of ions or electrons [1]. The apparent difference is that SHIMs can be used not only for a sub-nanometer scale resolution microscopic research, but also for the applications of very fine fabrication and direct lithography of surfaces at the nanoscale dimensions. On the other hand, atomic force microscope (AFM) is another type of high resolution microscopy which can measure a three-dimensional surface morphology by tracing a fine probe with a sharp tip apex on a specimen's surface.In order to measure highly uneven and concavo-convex surfaces by AFM, the probe of a high aspect ratio with a sharp tip is much more necessary than the probe of a general quadrangular pyramid shape. In this paper we report the manufacture of the probe tip of the high aspect ratio by ion-beam induced gas deposition using a nanoscale helium ion beam of SHIM.Gas of platinum organic compound was injected into the sample surface neighborhood in the vacuum chamber of SHIM. The decomposition of the gas and the precipitation of the involved metal brought up a platinum nano-object in a pillar shape on the normal commercial AFM probe tip. A SHIM system (Carl Zeiss, Orion Plus) equipped with the gas injection system (OmniProbe, OmniGIS) was used for the research. While the vacuum being kept to work, we injected platinum organic compound ((CH3)3(CH3C5H4)Pt) into the sample neighborhood and irradiated the helium ion beam with the shape of a point on the apex of the AFM probe tip. It is found that we can control the length of the Pt nano-pillar by irradiation time of the helium ion beam. The AFM probe which brought up a Pt nano-pillar is shown in Figure 1. It is revealed that a high-aspect-ratio Pt nano-pillar of ∼40nm diameter and up to ∼2000 nm length can be grown. In addition, for possible heating

  4. Analysis of time-resolved interaction force mode AFM imaging using active and passive probes.

    PubMed

    Giray Oral, Hasan; Parlak, Zehra; Levent Degertekin, F

    2012-09-01

    We present an in-depth analysis of time-resolved interaction force (TRIF) mode imaging for atomic force microscopy (AFM). A nonlinear model of an active AFM probe, performing simultaneous topography and material property imaging on samples with varying elasticity and adhesion is implemented in Simulink®. The model is capable of simulating various imaging modes, probe structures, sample material properties, tip-sample interaction force models, and actuation and feedback schemes. For passive AFM cantilevers, the model is verified by comparing results from the literature. As an example of an active probe, the force sensing integrated readout and active tip (FIRAT) probe is used. Simulation results indicate that the active and damped nature of FIRAT provides a significant level of control over the force applied to the sample, minimizing sample indentation and topography error. Active tip control (ATC) preserves constant contact time during force control for stable contact while preventing the loss of material property information such as elasticity and adhesive force. Simulation results are verified by TRIF mode imaging of the samples with both soft and stiff regions. PMID:22813887

  5. Probing incipient plasticity by indenting colloidal glasses

    NASA Astrophysics Data System (ADS)

    Rahmani, Y.; Koopman, R.; Denisov, D.; Schall, P.

    2013-01-01

    Glasses are lucrative engineering materials owing to their superior mechanical properties such as high strength and large elastic strain. A central question concerns incipient plasticity - the onset of permanent deformation - that is central to their relaxation, aging, yield and fracture. Here, we use an analogue of nano-indentation performed on a colloidal glass to obtain direct images of the incipient plasticity, allowing us to elucidate the onset of permanent deformation. We visualize the microscopic strain by following distorted nearest neighbor configurations, and observe a surprising hierarchical structure of deformation: at the onset of irreversible deformation, the strain acquires a robust fractal structure, and we measure its fractal dimension. These results give direct evidence that the onset of permanent deformation has the hallmarks of a critical point, in agreement with recent theoretical works.

  6. Nanomechanical probing of soft matter through hydrophobic AFM tips fabricated by two-photon polymerization

    NASA Astrophysics Data System (ADS)

    Suriano, Raffaella; Zandrini, Tommaso; De Marco, Carmela; Osellame, Roberto; Turri, Stefano; Bragheri, Francesca

    2016-04-01

    Atomic force microscopy (AFM) nanoindentation of soft materials is a powerful tool for probing mechanical properties of biomaterials. Though many results have been reported in this field over the last decade, adhesion forces between the tip and the sample hinder the elastic modulus measurement when hydrophilic soft samples are investigated. Here, two-photon polymerization (2PP) technology was used to fabricate hydrophobic perfluoropolyether-based AFM tips. The hydrophobic 2PP tips allowed us to overcome the limitations of commercial and functionalized tips as well as to successfully measure the elastic modulus of medically relevant soft materials in air. Our results obtained in the characterization of poly(dimethyl siloxane) and polyethylene glycol hydrogels showed lower adhesion forces over a larger measurement range when compared to measurements performed with commercial tips. The elastic moduli measured by means of hydrophobic 2PP AFM tips were also found to be comparable to those obtained using conventional techniques for macroscopic samples. We successfully showed that the hydrophobic AFM tips developed by this highly versatile technology enable the study of mechanical properties of soft matter, benefiting from reduced sample-tip interactions, and a custom-made shape and dimension of the tips.

  7. 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.

  8. Diffusing colloidal probes of protein-carbohydrate interactions.

    PubMed

    Eichmann, Shannon L; Meric, Gulsum; Swavola, Julia C; Bevan, Michael A

    2013-02-19

    We present diffusing colloidal probe measurements of weak, multivalent, specific protein-polysaccharide interactions mediated by a competing monosaccharide. Specifically, we used integrated evanescent wave and video microscopy methods to monitor the three-dimensional Brownian excursions of conconavilin A (ConA) decorated colloids interacting with dextran-functionalized surfaces in the presence of glucose. Particle trajectories were interpreted as binding lifetime histograms, binding isotherms, and potentials of mean force. Binding lifetimes and isotherms showed clear trends of decreasing ConA-dextran-specific binding with increasing glucose concentration, consistent with expectations. Net potentials were accurately captured by superposition of a short-range, glucose-independent ConA-dextran repulsion and a longer-range, glucose-dependent dextran bridging attraction modeled as a harmonic potential. For glucose concentrations greater than 100 mM, the net ConA-dextran potential was found to have only a nonspecific repulsion, similar to that of bovine serum albumin (BSA) decorated colloids over dextran determined in control experiments. Our results demonstrate the first use of optical microscopy methods to quantify the connections between potentials of mean force and the binding behavior of ConA-decorated colloids on dextran-functionalized surfaces.

  9. AFM investigation on surface damage caused by mechanical probing with small ruby spheres

    NASA Astrophysics Data System (ADS)

    Meli, Felix; Küng, Alain

    2007-02-01

    One challenge for today's coordinate metrology is fast and accurate 3D measurements on small objects. Mechanical probing is considered to be simple and accurate but limitations may arise from elastic and plastic deformations at the contact point. Understanding these limits quantitatively will help to avoid surface damage and measurement errors. Static and dynamic forces for single point probings and for scanning measurements were investigated in the present work using a metrology AFM and a micro-CMM. The obtained results were compared with theoretical predictions made by Hertz's theory. We found that the standard forces used by the METAS micro-CMM can be kept below the macroscopic damage threshold. On the other hand, plastic deformation of microscopic contact points which forms at the interface due to the surface roughness of the probe and sample is always present. Additionally, probe contamination by build-up of ductile metal on the probe surface was observed and probe wear on a hard sample was measured.

  10. Structure, cell wall elasticity and polysaccharide properties of living yeast cells, as probed by AFM

    NASA Astrophysics Data System (ADS)

    Alsteens, David; Dupres, Vincent; McEvoy, Kevin; Wildling, Linda; Gruber, Hermann J.; Dufrêne, Yves F.

    2008-09-01

    Although the chemical composition of yeast cell walls is known, the organization, assembly, and interactions of the various macromolecules remain poorly understood. Here, we used in situ atomic force microscopy (AFM) in three different modes to probe the ultrastructure, cell wall elasticity and polymer properties of two brewing yeast strains, i.e. Saccharomyces carlsbergensis and S. cerevisiae. Topographic images of the two strains revealed smooth and homogeneous cell surfaces, and the presence of circular bud scars on dividing cells. Nanomechanical measurements demonstrated that the cell wall elasticity of S. carlsbergensis is homogeneous. By contrast, the bud scar of S. cerevisiae was found to be stiffer than the cell wall, presumably due to the accumulation of chitin. Notably, single molecule force spectroscopy with lectin-modified tips revealed major differences in polysaccharide properties of the two strains. Polysaccharides were clearly more extended on S. cerevisiae, suggesting that not only oligosaccharides, but also polypeptide chains of the mannoproteins were stretched. Consistent with earlier cell surface analyses, these findings may explain the very different aggregation properties of the two organisms. This study demonstrates the power of using multiple complementary AFM modalities for probing the organization and interactions of the various macromolecules of microbial cell walls.

  11. Comparison and evaluation of immobilization methods for preparing bacterial probes using acidophilic bioleaching bacteria Acidithiobacillus thiooxidans for AFM studies.

    PubMed

    Diao, Mengxue; Taran, Elena; Mahler, Stephen M; Nguyen, Anh V

    2014-07-01

    We evaluated different strategies for constructing bacterial probes for atomic force microscopy studies of bioleaching Acidithiobacillus thiooxidans interacting with pyrite mineral surfaces. Of three available techniques, the bacterial colloidal probe technique is the most reliable and provides a versatile platform for quantifying true interactive forces between bioleaching microorganisms and mineral surfaces.

  12. Protein interactions with bottle-brush polymer layers: Effect of side chain and charge density ratio probed by QCM-D and AFM.

    PubMed

    Olanya, Geoffrey; Thormann, Esben; Varga, Imre; Makuska, Ricardas; Claesson, Per M

    2010-09-01

    Silica surfaces were coated with a range of cationic bottle-brush polymers with 45 units long poly(ethylene oxide) side chains, and their efficiency in reducing protein adsorption was probed by QCM-D, reflectometry and AFM. Preadsorbed layers formed by bottle-brush polymers with different side chain to charge ratio was exposed to two proteins with different net charge, lysozyme and BSA. The reduction in protein adsorption was found to depend on both the type of protein and on the nature of the polyelectrolyte layer. The most pronounced reduction in protein adsorption was achieved when the fraction of charged backbone segments was in the range 0.25-0.5 equivalent to a fraction of poly(ethylene oxide) side chains of 0.75-0.5. It was concluded that these polymers have enough electrostatic attachment points to ensure a strong binding to the surface, and at the same time a sufficient amount of poly(ethylene oxide) side chains to counteract protein adsorption. In contrast, a layer formed by a highly charged polyelectrolyte without side chains was unable to resists protein adsorption. On such a layer the adsorption of negatively charged BSA was strongly enhanced, and positively charged lysozyme adsorbed to a similar extent as to bare silica. AFM colloidal probe force measurement between silica surfaces with preadsorbed layers of bottle-brush polymers were conducted before and after exposure to BSA and lysozyme to gain insight into how proteins were incorporated in the bottle-brush polymer layers.

  13. Probing correlated current and force effects of nanoparticle charge states by hybrid STM-AFM

    NASA Astrophysics Data System (ADS)

    Suganuma, Y.; Trudeau, P.-E.; Dhirani, A.-A.

    2002-12-01

    By using an atomic force microscope (AFM) cantilever as a substrate for a scanning tunneling microscope (STM), we can simultaneously probe currents I and forces F in a tunnel junction as a function of bias voltage V. Measurements performed using gold-nanoparticle (NP) coated cantilevers under ambient conditions reveal correlated kinks in both I-V and F-V curves. Changes in background charge distributions, which have been problematic in controlling single charges in such systems, can be readily detected by the hybrid STM-AFM. To test whether we can statistically attribute observed kinks to Coulomb staircase phenomena, we have performed measurements using NP’s of different sizes. NP’s 4.8 and 2.5 nm in diameter exhibit kinks spaced on average 0.22 and 0.52 V apart, respectively. These values are in good agreement with a metallic sphere flat surface model for the STM tip NP capacitance and the orthodox model for single-electron tunneling.

  14. Conductive-probe AFM characterization of graphene sheets bonded to gold surfaces

    NASA Astrophysics Data System (ADS)

    Hauquier, Fanny; Alamarguy, David; Viel, Pascal; Noël, Sophie; Filoramo, Arianna; Huc, Vincent; Houzé, Frédéric; Palacin, Serge

    2012-01-01

    Conducting probe atomic force microscopy (CP-AFM) has been used to perform mechanical and electrical experiments on graphene layers bonded to polyaminophenylene (PAP) films grafted on gold substrates. This technique is a new approach for the characterization of graphene sheets and represents a complementary tool to Raman spectroscopy. The combination of friction and electrical imaging reveals that different stacked graphene sheets have been successfully distinguished from each other and from the underlying PAP films. Lateral force microscopy has shown that the friction is greatly reduced on graphene sheets in comparison with the organic coating. The electrical resistance images show very different local conduction properties which can be linked to the number of underlying graphene sheets. The resistance decreases very slowly when the normal load increases. Current-voltage curves display characteristics of metal-molecule-metal junctions.

  15. Forces between blank surfaces as measured by the colloidal probe technique and by optical tweezers--a comparison.

    PubMed

    Elmahdy, Mahdy M; Drechsler, Astrid; Gutsche, Christof; Synytska, Alla; Uhlmann, Petra; Kremer, Friedrich; Stamm, Manfred

    2009-11-17

    The well-established atomic force microscopy (AFM)-based colloidal probe technique (CPT) and optical tweezers (OT) are combined to measure the interaction forces between blank SiO(2) surfaces in aqueous ionic solutions (CaCl(2)) of varying concentration at pH 7. Spherical colloids (SiO(2), diameter approximately 4.63 +/- 0.05 microm) taken out of the same batch are used by both methods. In the case of CPT, a single colloid is glued to a cantilever, and the interaction forces with a plain SiO(2) surface are determined in dependence on the concentration of the surrounding medium. For the OT studies, two colloids (one fixed to a micropipet by capillary action, the other held with the optical trap) are approached to each other in nanometer steps, and the resulting forces are measured for the same media as in the CPT experiment. Both techniques fit well to each other and enable one to cover interaction energies ranging from 10(-5) to 1 mN/m. The experimental data are well described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory revealing that the effective surface charge density changes slightly with concentration.

  16. Double Layer of a Gold Electrode Probed by AFM Force Measurements.

    PubMed

    Barten, D; Kleijn, J M; Duval, J; Leeuwen, H P V; Lyklema, J; Cohen Stuart, M A

    2003-02-18

    Colloidal probe atomic force microscopy was used to determine the electric double layer interactions between a gold electrode and a spherical silica probe. The double layer properties of the gold/solution interface were varied through the pH and salt concentration of the electrolyte, as well as by externally applying an electric potential. The double layer potentials ψ(d) of the gold surface were obtained by fitting the force-distance curves according to the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory, using earlier obtained values for the double layer potential of the silica probe as input parameter. It was found that the gold electrode combines the features of reversible and polarizable interfaces; i.e., its charge and potential are determined by both the solution pH and the external potential. The pH dependence is attributed to proton adsorption and desorption from oxidic groups on the gold surface. In the potential range studied, ψ(d) varies linearly with the applied potential; the variation in ψ(d) is roughly 10% of that in the applied potential. The potential of zero force (the external potential at which ψ(d) = 0) varies with pH. The various features of the gold/electrolyte interface are described well by an amphifunctional double layer model. The results of this study form the basis of the interpretation of adsorption studies on gold as a function of pH and externally applied potential.

  17. Adhesion, stretching, and electrical charge assessment of dermatan sulfate molecules by colloidal probes.

    PubMed

    Gonzalez, Rodrigo; Caballero, Leonardo; Pavez, Jorge; Melo, Francisco

    2012-06-26

    Electrical and mechanical properties of dermatan sulfate (DS) molecules are studied in an aqueous environment as a function of pH. DS molecules linked at various points distributed on the surface of mica previously silanizated along with a suitable functionalized microsphere, attached to the cantilever of an atomic force microscope (AFM), provided suitable surfaces for testing interactions through the colloidal probe methodology. The repulsive force between the surfaces indicated that the charge of DS increases with pH as a result of the gradual deprotonation of acidic groups. Pulling experiments revealed increasing adhesion of DS to the monolayer as a function of pH, presumably due both to the electrical nature of the interaction between these molecules and the progressive increase of the charge of DS with pH. Serrations exhibited by the force in pulling experiments indicate that more than a single DS molecule is stretched at the same time. In addition, pulling force remained significant even at extensions that went beyond the average contour length of a single DS molecule, which suggests the existence of a significant link between DS molecules.

  18. Interaction Mechanism of Oil-in-Water Emulsions with Asphaltenes Determined Using Droplet Probe AFM.

    PubMed

    Shi, Chen; Zhang, Ling; Xie, Lei; Lu, Xi; Liu, Qingxia; Mantilla, Cesar A; van den Berg, Frans G A; Zeng, Hongbo

    2016-03-15

    Emulsions with interface-active components at the oil/water interface have long been of fundamental and practical interest in many fields. In this work, the interaction forces between two oil droplets in water in the absence/presence of asphaltenes were directly measured using droplet probe atomic force microscopy (AFM) and analyzed using a theoretical model based on Reynolds lubrication theory and the augmented Young-Laplace equation by including the effects of disjoining pressure. It was revealed that the interaction forces measured between two pristine oil droplets (i.e., toluene) could be well described by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, while an additional steric interaction should be included in the presence of asphaltenes in the oil. The surface interaction and the stability of oil droplets in aqueous solution were demonstrated to be significantly influenced by the asphaltenes concentration in oil, salt concentration, pH, and presence of divalent ions (Ca(2+)) in water. Adsorbed asphaltenes at the oil/water interface led to more negative surface potential of the oil/water interface and also induced steric repulsion between oil droplets, inhibiting the drop coalescence and stabilizing the oil-in-water emulsion. Lower pH of aqueous solution could lead to less negative surface potential and weaken the repulsion between oil droplets. Addition of divalent ions (Ca(2+)) was found to disrupt the protecting effects of adsorbed asphaltenes at oil/water interface and induce coalescence of oil droplets. Our results provide a useful methodology for quantifying the interaction forces and investigating the properties of asphaltenes at the oil/water interfaces and provide insights into the stabilization mechanism of oil-in-water emulsions due to asphaltenes in oil production and water treatment.

  19. Probing Ternary Solvent Effect in High V(oc) Polymer Solar Cells Using Advanced AFM Techniques.

    PubMed

    Li, Chao; Ding, Yi; Soliman, Mikhael; Lorenzo, Josie; Dhasmana, Nitesh; Chantharasupawong, Panit; Ievlev, Anton V; Gesquiere, Andre J; Tetard, Laurene; Thomas, Jayan

    2016-02-01

    This work describes a simple method to develop a high V(oc) low band gap PSCs. In addition, two new atomic force microscopy (AFM)-based nanoscale characterization techniques to study the surface morphology and physical properties of the structured active layer are introduced. With the help of ternary solvent processing of the active layer and C60 buffer layer, a bulk heterojunction PSC with V(oc) more than 0.9 V and conversion efficiency 7.5% is developed. In order to understand the fundamental properties of the materials ruling the performance of the PSCs tested, AFM-based nanoscale characterization techniques including Pulsed-Force-Mode AFM (PFM-AFM) and Mode-Synthesizing AFM (MSAFM) are introduced. Interestingly, MSAFM exhibits high sensitivity for direct visualization of the donor-acceptor phases in the active layer of the PSCs. Finally, conductive-AFM (cAFM) studies reveal local variations in conductivity in the donor and acceptor phases as well as a significant increase in photocurrent in the PTB7:ICBA sample obtained with the ternary solvent processing. PMID:26807919

  20. Probing Cytoskeletal Structures by Coupling Optical Superresolution and AFM Techniques for a Correlative Approach

    PubMed Central

    Chacko, Jenu Varghese; Zanacchi, Francesca Cella; Diaspro, Alberto

    2013-01-01

    In this article, we describe and show the application of some of the most advanced fluorescence superresolution techniques, STED AFM and STORM AFM microscopy towards imaging of cytoskeletal structures, such as microtubule filaments. Mechanical and structural properties can play a relevant role in the investigation of cytoskeletal structures of interest, such as microtubules, that provide support to the cell structure. In fact, the mechanical properties, such as the local stiffness and the elasticity, can be investigated by AFM force spectroscopy with tens of nanometers resolution. Force curves can be analyzed in order to obtain the local elasticity (and the Young's modulus calculation by fitting the force curves from every pixel of interest), and the combination with STED/STORM microscopy integrates the measurement with high specificity and yields superresolution structural information. This hybrid modality of superresolution-AFM working is a clear example of correlative multimodal microscopy. PMID:24027190

  1. Probing ternary solvent effect in high Voc polymer solar cells using advanced AFM techniques

    DOE PAGES

    Li, Chao; Soleman, Mikhael; Lorenzo, Josie; Dhasmana, Nitesh; Chantharasupawong, Panit; Ievlev, Anton; Gesquiere, Andre; Tetard, Laurene; Thomas, Jayan

    2016-01-25

    This work describes a simple method to develop a high Voc low band gap PSCs. In addition, two new atomic force microscopy (AFM)-based nanoscale characterization techniques to study the surface morphology and physical properties of the structured active layer are introduced. With the help of ternary solvent processing of the active layer and C60 buffer layer, a bulk heterojunction PSC with Voc more than 0.9 V and conversion efficiency 7.5% is developed. In order to understand the fundamental properties of the materials ruling the performance of the PSCs tested, AFM-based nanoscale characterization techniques including Pulsed-Force-Mode AFM (PFM-AFM) and Mode-Synthesizing AFMmore » (MSAFM) are introduced. Interestingly, MSAFM exhibits high sensitivity for direct visualization of the donor–acceptor phases in the active layer of the PSCs. Lastly, conductive-AFM (cAFM) studies reveal local variations in conductivity in the donor and acceptor phases as well as a significant increase in photocurrent in the PTB7:ICBA sample obtained with the ternary solvent processing.« less

  2. Diffusing Colloidal Probes of Protein and Synthetic Macromolecule Interactions

    PubMed Central

    Everett, W. Neil; Wu, Hung-Jen; Anekal, Samartha G.; Sue, Hung-Jue; Bevan, Michael A.

    2007-01-01

    A new approach is described for measuring kT and nanometer scale protein-protein and protein-synthetic macromolecule interactions. The utility of this method is demonstrated by measuring interactions of bovine serum albumin (BSA) and copolymers with exposed polyethyleneoxide (PEO) moieties adsorbed to hydrophobically modified colloids and surfaces. Total internal reflection and video microscopy are used to track three-dimensional trajectories of many single diffusing colloids that are analyzed to yield interaction potentials, mean-square displacements, and colloid-surface association lifetimes. A criterion is developed to identify colloids as being levitated, associated, or deposited based on energetic, spatial, statistical, and temporal information. Whereas levitation and deposition occur for strongly repulsive or attractive potentials, association is exponentially sensitive to weak interactions influenced by adsorbed layer architectures and surface heterogeneity. Systematic experiments reveal how BSA orientation and PEO molecular weight produce adsorbed layers that either conceal or expose substrate heterogeneities to generate a continuum of colloid-surface association lifetimes. These measurements provide simultaneous access to a broad range of information that consistently indicates purely repulsive BSA and PEO interactions and a role for surface heterogeneity in colloid-surface association. The demonstrated capability to measure nonspecific protein interactions provides a basis for future measurements of specific protein interactions. PMID:17098785

  3. Effect of AFM probe geometry on visco-hyperelastic characterization of soft materials

    NASA Astrophysics Data System (ADS)

    Boccaccio, Antonio; Lamberti, Luciano; Papi, Massimiliano; De Spirito, Marco; Pappalettere, Carmine

    2015-08-01

    Atomic force microscopy (AFM) nanoindentation is very suited for nano- and microscale mechanical characterization of soft materials. Although the structural response of polymeric networks that form soft matter depends on viscous effects caused by the relative slippage of polymeric chains, the usual assumption made in the AFM-based characterization is that the specimen behaves as a purely elastic material and viscous forces are negligible. However, for each geometric configuration of the AFM tip, there will be a limit indentation rate above which viscous effects must be taken into account to correctly determine mechanical properties. A parametric finite element study conducted on 12 geometric configurations of a blunt cone AFM tip (overall, the study included about 200 finite element analyses) allowed us to determine the limit indentation rate for each configuration. The selected tip dimensions cover commercially available products and account for changes in tip geometry caused by serial measurements. Nanoindentation rates cover typical experimental conditions set in AFM bio-measurements on soft matter. Viscous effects appear to be more significant in the case of sharper tips. This implies that, if quantitative data on sample viscosity are not available, using a rounded indenter and carrying out experiments below the limit indentation rate will allow errors in the determination of mechanical properties to be minimized.

  4. Quantitative atomic resolution force imaging on epitaxial graphene with reactive and nonreactive AFM probes.

    PubMed

    Boneschanscher, Mark P; van der Lit, Joost; Sun, Zhixiang; Swart, Ingmar; Liljeroth, Peter; Vanmaekelbergh, Daniël

    2012-11-27

    Atomic force microscopy (AFM) images of graphene and graphite show contrast with atomic periodicity. However, the contrast patterns vary depending on the atomic termination of the AFM tip apex and the tip-sample distance, hampering the identification of the atomic positions. Here, we report quantitative AFM imaging of epitaxial graphene using inert (carbon-monoxide-terminated) and reactive (iridium-terminated) tips. The atomic image contrast is markedly different with these tip terminations. With a reactive tip, we observe an inversion from attractive to repulsive atomic contrast with decreasing tip-sample distance, while a nonreactive tip only yields repulsive atomic contrast. We are able to identify the atoms with both tips at any tip-sample distance. This is a prerequisite for future structural and chemical analysis of adatoms, defects, and the edges of graphene nanostructures, crucial for understanding nanoscale graphene devices.

  5. Measuring the influence of solution chemistry on the adhesion of au nanoparticles to mica using colloid probe atomic force microscopy.

    PubMed

    Thio, Beng Joo Reginald; Lee, Jung-Hyun; Meredith, J Carson; Keller, Arturo A

    2010-09-01

    Engineered nanoparticles are used increasingly in numerous commercial products, leading to concerns over their environmental fate and ecotoxicity. We report the adaptation of colloid probe atomic force microscopy (AFM) to quantitatively determine the adhesive behavior of gold nanoparticles (Au NPs) with mica, chosen as a model for sand, in various water chemistries. Au NP-covered polystyrene (PS) beads were prepared by a combined swelling-heteroaggregation (CSH) technique prior to attachment to tipless AFM cantilevers. Force measurements were performed over a range of solution conditions (pH, ionic strength (IS), and natural organic matter (NOM) content). Plain PS beads with no Au NPs were used as controls. In general, adhesion of Au NP-PS beads to mica were found to increase as IS increased while a rise in pH led to a decrease in adhesion. Plain PS beads were not observed to adhere to mica in any of the experimental solution conditions, and the PS force curves were unaffected by changes in the pH and electrolyte concentrations. In the presence of NOM, pull-off forces for Au NP-PS beads increased in magnitude when NaCl was added. In addition, the experimental approach force curves were not successfully described by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. To reconcile the discrepancy between theory and experiment, an extended DLVO (xDLVO) empirical model was used to account for the contribution of non-DLVO interactions (known collectively as structural forces) between the Au NPs and mica surfaces.

  6. Mode coupling in a hanging-fiber AFM used as a rheological probe

    NASA Astrophysics Data System (ADS)

    Devailly, C.; Laurent, J.; Steinberger, A.; Bellon, L.; Ciliberto, S.

    2014-06-01

    We analyze the advantages and drawbacks of a method which measures the viscosity of liquids at microscales, using a thin glass fiber fixed on the tip of a cantilever of an ultra-low-noise Atomic Force Microscope (AFM). When the fiber is dipped into a liquid, the dissipation of the cantilever-fiber system, which is linked to the liquid viscosity, can be computed from the power spectral density of the thermal fluctuations of the cantilever deflection. The high sensitivity of the AFM allows us to show the existence and to develop a model of the coupling between the dynamics of the fiber and that of the cantilever. This model, which accurately fits the experimental data, gives also more insights into the dynamics of coupled microdevices in a viscous environment.

  7. Probing the surface of colloidal nanomaterials with potentiometry in situ.

    PubMed

    Fedin, Igor; Talapin, Dmitri V

    2014-08-13

    Colloidal nanomaterials represent an important branch of modern chemistry. However, we have very little understanding of molecular processes that occur at the nanocrystal (NC) surface during synthesis and post-synthetic modifications. Here we show that potentiometry can be used to study the surface of colloidal NCs under realistic reaction conditions. Potentiometric titrations of CdSe and InP nanostructures provide information on the active surface area, the affinity of ligands to the NC surface, and the surface reaction kinetics. These studies can be carried out at different temperatures in polar and nonpolar media for NCs of different sizes and shapes. In situ potentiometry can provide real-time feedback during synthesis of core-shell nanostructures.

  8. Laser light scattering as a probe of fractal colloid aggregates

    NASA Technical Reports Server (NTRS)

    Weitz, David A.; Lin, M. Y.

    1989-01-01

    The extensive use of laser light scattering is reviewed, both static and dynamic, in the study of colloid aggregation. Static light scattering enables the study of the fractal structure of the aggregates, while dynamic light scattering enables the study of aggregation kinetics. In addition, both techniques can be combined to demonstrate the universality of the aggregation process. Colloidal aggregates are now well understood and therefore represent an excellent experimental system to use in the study of the physical properties of fractal objects. However, the ultimate size of fractal aggregates is fundamentally limited by gravitational acceleration which will destroy the fractal structure as the size of the aggregates increases. This represents a great opportunity for spaceborne experimentation, where the reduced g will enable the growth of fractal structures of sufficient size for many interesting studies of their physical properties.

  9. In situ Stiffness Adjustment of AFM Probes by Two Orders of Magnitude

    PubMed Central

    de Laat, Marcel Lambertus Cornelis; Pérez Garza, Héctor Hugo; Ghatkesar, Murali Krishna

    2016-01-01

    The choice on which type of cantilever to use for Atomic Force Microscopy (AFM) depends on the type of the experiment being done. Typically, the cantilever has to be exchanged when a different stiffness is required and the entire alignment has to be repeated. In the present work, a method to adjust the stiffness in situ of a commercial AFM cantilever is developed. The adjustment is achieved by changing the effective length of the cantilever by electrostatic pull-in. By applying a voltage between the cantilever and an electrode (with an insulating layer at the point of contact), the cantilever snaps to the electrode, reducing the cantilever’s effective length. An analytical model was developed to find the pull-in voltage of the system. Subsequently, a finite element model was developed to study the pull-in behavior. The working principle of this concept is demonstrated with a proof-of-concept experiment. The electrode was positioned close to the cantilever by using a robotic nanomanipulator. To confirm the change in stiffness, the fundamental resonance frequency of the cantilever was measured for varying electrode positions. The results match with the theoretical expectations. The stiffness was adjusted in situ in the range of 0.2 N/m to 27 N/m, covering two orders of magnitude in one single cantilever. This proof-of-concept is the first step towards a micro fabricated prototype, that integrates the electrode positioning system and cantilever that can be used for actual AFM experiments. PMID:27077863

  10. A Unique Self-Sensing, Self-Actuating AFM Probe at Higher Eigenmodes

    PubMed Central

    Wu, Zhichao; Guo, Tong; Tao, Ran; Liu, Leihua; Chen, Jinping; Fu, Xing; Hu, Xiaotang

    2015-01-01

    With its unique structure, the Akiyama probe is a type of tuning fork atomic force microscope probe. The long, soft cantilever makes it possible to measure soft samples in tapping mode. In this article, some characteristics of the probe at its second eigenmode are revealed by use of finite element analysis (FEA) and experiments in a standard atmosphere. Although the signal-to-noise ratio in this environment is not good enough, the 2 nm resolution and 0.09 Hz/nm sensitivity prove that the Akiyama probe can be used at its second eigenmode under FM non-contact mode or low amplitude FM tapping mode, which means that it is easy to change the measuring method from normal tapping to small amplitude tapping or non-contact mode with the same probe and equipment. PMID:26580619

  11. AFM fluid delivery/liquid extraction surface sampling/electrostatic spray cantilever probe

    SciTech Connect

    Van Berkel, Gary J.

    2015-06-23

    An electrospray system comprises a liquid extraction surface sampling probe. The probe comprises a probe body having a liquid inlet and a liquid outlet, and having a liquid extraction tip. A solvent delivery conduit is provided for receiving solvent liquid from the liquid inlet and delivering the solvent liquid to the liquid extraction tip. An open liquid extraction channel extends across an exterior surface of the probe body from the liquid extraction tip to the liquid outlet. An electrospray emitter tip is in liquid communication with the liquid outlet of the liquid extraction surface sampling probe. A system for analyzing samples, a liquid junction surface sampling system, and a method of analyzing samples are also disclosed.

  12. Colloidal gold probe based rapid immunochromatographic strip assay for cortisol.

    PubMed

    Nara, Seema; Tripathi, Vinay; Singh, Harpal; Shrivastav, Tulsidas G

    2010-12-01

    A rapid and semi-quantitative immunochromatographic strip (ICS) test for cortisol analysis in serum was developed. The test strip was based on a competitive assay format. Colloidal gold nanoparticles were synthesized and coupled with cortisol-3-carboxymethyloxime-adipic acid dihydrazide-bovine serum albumin (F-3-CMO-ADH-BSA) antigen to directly compete with cortisol in human serum samples. F-3-CMO-ADH-BSA-gold label and uncoupled colloidal gold nanoparticles were appropriately characterized using UV-vis spectroscopy, transmission electron microscopy and atomic force microscopy. Anticortisol antibody raised against F-3-CMO-BSA immunogen in New Zealand white rabbits was coated on the NC membrane as test line. Anti-BSA antibody was used as control line. The lower detection limit of the ICS test was 30 ngmL(-1) with visual detection and was completed in 10 min. About 30 human serum samples were also analyzed by the developed strip test and their range of cortisol concentration was established. The developed ICS test is rapid, economic and user friendly. PMID:21056716

  13. Probing Dynamical Heterogeneity in Dense Colloidal Suspensions with Depletion Attraction

    NASA Astrophysics Data System (ADS)

    Brown, Zachery; Hogan, Gregory; Gratale, Matthew; Yodh, Arjun G.; Habdas, Piotr

    We directly observe the particle dynamics in dense colloidal suspensions. Using depletion attraction, we vary inter particle potential to study the reentrant glass transition. Confocal microscopy and particle tracking allow us to follow particle trajectories over time. By varying inter particle attraction strength for a fixed volume fraction of colloidal suspensions, we observe three qualitatively different states. Mean square displacement and long time diffusion constant vary with the depletant concentration and indicate a glass state for low attraction strengths, ergodic liquid state for moderate attraction strengths, and attractive arrested state for the highest attraction strengths. Variance in the self overlap function gives the four point susceptibility, a measure of dynamical heterogeneity over a range of length scales and lag times. Results show that the lag times corresponding to the most heterogeneous dynamics are longer for arrested states than for fluid states. The length scale that maximizes four point susceptibility across a range of attraction strengths exhibits a reentrant glass behavior similar to that of the long time diffusion constant. Z.B., G.H., and P.H. acknowledge financial support of the NSF RUI-1306990. M.G. and A.G.Y. acknowledge financial support of the NSF Grant DMR-1205463, NSF MRSEC Grant DMR-1120901, and NASA Grant NNX08AO0G.

  14. Simultaneous topographic and amperometric membrane mapping using an AFM probe integrated biosensor.

    PubMed

    Stanca, Sarmiza Elena; Csaki, Andrea; Urban, Matthias; Nietzsche, Sandor; Biskup, Christoph; Fritzsche, Wolfgang

    2011-02-15

    The investigation of the plasma membrane with intercorrelated multiparameter techniques is a prerequisite for understanding its function. Presented here, is a simultaneous electrochemical and topographic study of the cell membrane using a miniaturized amperometric enzymatic biosensor. The fabrication of this biosensor is also reported. The biosensor combines a scanning force microscopy (AFM) gold-coated cantilever and an enzymatic transducer layer of peroxidases (PODs). When these enzymes are brought in contact with the substrate, the specific redox reaction produces an electric current. The intensity of this current is detected simultaneously with the surface imaging. For sensor characterization, hydroquinone-2-carboxylic acid (HQ) is selected as an intrinsic source of H(2)O(2). HQ has been electrochemically regenerated by the reduction of antraquinone-2-carboxylic acid (AQ). The biosensor reaches the steady state value of the current intensity in 1 ± 0.2s.

  15. Scanning transmission x-ray microscopy as a novel tool to probe colloidal and photonic crystals.

    PubMed

    van Schooneveld, Matti M; Hilhorst, Jan; Petukhov, Andrei V; Tyliszczak, Tolek; Wang, Jian; Weckhuysen, Bert M; de Groot, Frank M F; de Smit, Emiel

    2011-03-21

    Photonic crystals consisting of nano- to micrometer-sized building blocks, such as multiple sorts of colloids, have recently received widespread attention. It remains a challenge, however, to adequately probe the internal crystal structure and the corresponding deformations that inhibit the proper functioning of such materials. It is shown that scanning transmission X-ray microscopy (STXM) can directly reveal the local structure, orientations, and even deformations in polystyrene and silica colloidal crystals with 30-nm spatial resolution. Moreover, STXM is capable of imaging a diverse range of crystals, including those that are dry and inverted, and provides novel insights complementary to information obtained by benchmark confocal fluorescence and scanning electron microscopy techniques.

  16. Molecular Adsorption on Nano Colloidal Particles Probed by Second Harmonic Generation

    NASA Astrophysics Data System (ADS)

    Jen, Shih-Hui; Dai, Hai-Lung

    2006-03-01

    It is shown that second-harmonic generation (SHG), detected at 90 degree angle from the fundamental beam propagation direction, can be used to probe molecular adsorption on spherical nano colloidal particles with diameter as small as 50 nm. Measurements done with the malachite green dye adsorbed on polystyrene particles with diameters ranging from 50 to 250 nm show that the SHG signal from these surface adsorbed molecules tilts toward larger scattering angles when the particle size becomes smaller. This phenomenon can be rigorously described by the nonlinear Rayleigh-Gans-Debye theory and used for measuring the density and adsorption free energy of molecules adsorbed on nanometer size colloidal particles.

  17. Integrin-Specific Mechanoresponses to Compression and Extension Probed by Cylindrical Flat-Ended AFM Tips in Lung Cells

    PubMed Central

    Acerbi, Irene; Luque, Tomás; Giménez, Alícia; Puig, Marta; Reguart, Noemi; Farré, Ramon; Navajas, Daniel; Alcaraz, Jordi

    2012-01-01

    Cells from lung and other tissues are subjected to forces of opposing directions that are largely transmitted through integrin-mediated adhesions. How cells respond to force bidirectionality remains ill defined. To address this question, we nanofabricated flat-ended cylindrical Atomic Force Microscopy (AFM) tips with ∼1 µm2 cross-section area. Tips were uncoated or coated with either integrin-specific (RGD) or non-specific (RGE/BSA) molecules, brought into contact with lung epithelial cells or fibroblasts for 30 s to form focal adhesion precursors, and used to probe cell resistance to deformation in compression and extension. We found that cell resistance to compression was globally higher than to extension regardless of the tip coating. In contrast, both tip-cell adhesion strength and resistance to compression and extension were the highest when probed at integrin-specific adhesions. These integrin-specific mechanoresponses required an intact actin cytoskeleton, and were dependent on tyrosine phosphatases and Ca2+ signaling. Cell asymmetric mechanoresponse to compression and extension remained after 5 minutes of tip-cell adhesion, revealing that asymmetric resistance to force directionality is an intrinsic property of lung cells, as in most soft tissues. Our findings provide new insights on how lung cells probe the mechanochemical properties of the microenvironment, an important process for migration, repair and tissue homeostasis. PMID:22384196

  18. Absorption Spectroscopy and Imaging from the Visible through Mid-IR with 20 nm Resolution Using AFM probes

    NASA Astrophysics Data System (ADS)

    Centrone, Andrea

    2015-03-01

    Correlated nanoscale composition and optical property maps are important to engineer nanomaterials in applications ranging from photovoltaics to sensing and therapeutics. Wavelengths (λs) from the visible to near-IR probe electronic transitions in materials, providing information regarding band gap and defects while light in mid-IR probes vibrational transitions and provide chemical composition. However, light diffraction limits the lateral resolution of conventional micro-spectroscopic techniques to approximately λ/2, which is insufficient to image nanomaterials. Additionally, the λ-dependent resolution impedes direct comparison of spectral maps from different spectral ranges. Photo Thermal Induced Resonance (PTIR) is a novel technique that circumvents light diffraction by employing an AFM tip as a local detector for measuring light absorption with λ-independent nanoscale resolution. Our PTIR setup combines an AFM microscope with three lasers providing λ-tunability from 500 nm to 16000 nm continuously. The AFM tip transduces locally the sample thermal expansion induced by light absorption into large cantilever oscillations. Local absorption spectra (electronic or vibrational) and maps are obtained recording the amplitude of the tip deflection as a function of λ and position, respectively. The working principles of the PTIR technique will be described first, and nano-patterned polymer samples will be used to evaluate its lateral resolution, sensitivity and linearity. Results show that the PTIR signal intensity is proportional to the local absorbed energy suggesting applicability of this technique for quantitative chemical analysis at nanoscale, at least for thin (less than 1000 nm thick) samples. Additionally, a λ-independent resolution as high as 20 nm is demonstrated across the whole spectral range. In the second part of the talk, PTIR will be applied to image the dark plasmonic resonance of gold Asymmetric Split Ring Resonators (A-SRRs) in the mid

  19. Probing Nanoscale Surface Enhanced Raman Scattering Fluctuation Dynamics using Correlated AFM and Confocal Ultramicroscopy

    SciTech Connect

    Suh, Yung D.; Schenter, Gregory K.; Zhu, Leyun; Lu, H PETER.

    2003-10-01

    We have studied the laser-excitation-intensity-dependent and Ag-nanocluster interstitial-site-dependent SERS intensity fluctuations under low molecule surface coverage of rhodamine 6G and cytochrome c. a new two-channel photon time-stamping system coupled with atomic force microscopic (AFM), Raman spectroscopic, and imaging microscopy was developed and applied to record Raman intensity fluctuation trajectories at sub-microsecond resolution correlated with in-situ characterization of the nanoparticle clusters. Our experimental results suggest that the nanoconfinement of the local electromagnetic-field enhancement and the interaction of the local field with the molecules, presumably under rotational motions, result in nano-Raman fluctuations. The SERS spectral fluctuation was pertinent to the nanoscale local enhancement and local interaction of the molecules with the surface when the number of molecules to contribute the microscopic Raman signal collected from a diffraction-limited focus spot. The SERS fluctuation dynamics were both photo-induced and spontaneous for rhodamine 6G, but only the photo-induced interstitial sites with heterogeneous geometries. To interpret the observed nano-SERS fluctuation dynamics, we used computer simulation of optical multiple scattering, based on multi-sphere scattering Mie theory, and rotational diffusion of molecules at an interstitial site, based on a random walk in orientation space.

  20. High-resolution noncontact AFM and Kelvin probe force microscopy investigations of self-assembled photovoltaic donor–acceptor dyads

    PubMed Central

    Schwartz, Pierre-Olivier; Biniek, Laure; Brinkmann, Martin; Leclerc, Nicolas; Zaborova, Elena

    2016-01-01

    Summary Self-assembled donor–acceptor dyads are used as model nanostructured heterojunctions for local investigations by noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). With the aim to probe the photo-induced charge carrier generation, thin films deposited on transparent indium tin oxide substrates are investigated in dark conditions and upon illumination. The topographic and contact potential difference (CPD) images taken under dark conditions are analysed in view of the results of complementary transmission electron microscopy (TEM) experiments. After in situ annealing, it is shown that the dyads with longer donor blocks essentially lead to standing acceptor–donor lamellae, where the acceptor and donor groups are π-stacked in an edge-on configuration. The existence of strong CPD and surface photo-voltage (SPV) contrasts shows that structural variations occur within the bulk of the edge-on stacks. SPV images with a very high lateral resolution are achieved, which allows for the resolution of local photo-charging contrasts at the scale of single edge-on lamella. This work paves the way for local investigations of the optoelectronic properties of donor–acceptor supramolecular architectures down to the elementary building block level. PMID:27335768

  1. High-resolution noncontact AFM and Kelvin probe force microscopy investigations of self-assembled photovoltaic donor-acceptor dyads.

    PubMed

    Grévin, Benjamin; Schwartz, Pierre-Olivier; Biniek, Laure; Brinkmann, Martin; Leclerc, Nicolas; Zaborova, Elena; Méry, Stéphane

    2016-01-01

    Self-assembled donor-acceptor dyads are used as model nanostructured heterojunctions for local investigations by noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). With the aim to probe the photo-induced charge carrier generation, thin films deposited on transparent indium tin oxide substrates are investigated in dark conditions and upon illumination. The topographic and contact potential difference (CPD) images taken under dark conditions are analysed in view of the results of complementary transmission electron microscopy (TEM) experiments. After in situ annealing, it is shown that the dyads with longer donor blocks essentially lead to standing acceptor-donor lamellae, where the acceptor and donor groups are π-stacked in an edge-on configuration. The existence of strong CPD and surface photo-voltage (SPV) contrasts shows that structural variations occur within the bulk of the edge-on stacks. SPV images with a very high lateral resolution are achieved, which allows for the resolution of local photo-charging contrasts at the scale of single edge-on lamella. This work paves the way for local investigations of the optoelectronic properties of donor-acceptor supramolecular architectures down to the elementary building block level. PMID:27335768

  2. Superresolution optical fluctuation imaging (SOFI) aided nanomanipulation of quantum dots using AFM for novel artificial arrangements of chemically functionalized colloidal quantum dots and plasmonic structures

    NASA Astrophysics Data System (ADS)

    Dopf, Katja; Heunisch, Sebastian; Schwab, Patrick; Moosmann, Carola; Habermehl, Anne; Lemmer, Uli; Eisler, Hans-Jürgen

    2014-05-01

    For single photon experiments or research on novel hybrid structures consisting of several colloidal quantum dots (Qdots) and plasmonic nanoparticles both the precise localization and the optical behavior of the emitters need to be correlated. Therefore, the gap between the high spatial resolution topography information that provides detailed localization of single Qdots and the diffraction limited fluorescence image needs to be overcome. In this paper, we demonstrate the combination of atomic force microscopy (AFM) with wide-field fluorescence microscopy improved by superresolution optical fluctuation imaging (SOFI). With this approach the topography and the superresolution image can be overlaid with sub-diffraction precision. Consequently, we discriminate between single Qdots that are optically active and dark ones. Additionally, the optical time-dependent behavior of molecular emitters can be selectively investigated. This method is, furthermore, useful for an advanced manipulation and characterization toolbox of Qdots in general. In summary, our findings represent an easily adaptable, highly reproducible and comparatively cheap subdiffraction limit imaging method and they facilitate the efficient selection of bright Qdots in a standard lab environment for proof-of-principle nanostructures containing Qdots and for nanomanipulation experiments.

  3. Detailed Observation of Multiphoton Emission Enhancement from a Single Colloidal Quantum Dot Using a Silver-Coated AFM Tip.

    PubMed

    Takata, Hiroki; Naiki, Hiroyuki; Wang, Li; Fujiwara, Hideki; Sasaki, Keiji; Tamai, Naoto; Masuo, Sadahiro

    2016-09-14

    The enhancement of multiphoton emission from a single colloidal nanocrystal quantum dot (NQD) interacting with a plasmonic nanostructure was investigated using a silver-coated atomic force microscopy tip (AgTip) as the plasmonic nanostructure. Using the AgTip, which exhibited a well-defined localized surface plasmon (LSP) resonance band, we controlled the spectral overlap and the distance between the single NQD and the AgTip. The emission behavior of the single NQD when approaching the AgTip at the nanometer scale was measured using off-resonance (405 nm) and resonance (465 nm) excitation of the LSP. We directly observed the conversion of the single-photon emission from a single NQD to multiphoton emission with reduction of the emission lifetime at both excitation wavelengths as the NQD-AgTip distance decreased, whereas a decrease and increase in the emission intensity were observed at 405 and 465 nm excitation, respectively. By combining theoretical analysis and the numerical simulation of the AgTip, we deduced that the enhancement of the multiphoton emission was caused by the quenching of the single-exciton state due to the energy transfer from the NQD to the AgTip and that the emission intensity was increased by enhancement of the excitation rate due to the electric field of the LSP on the AgTip. These results provide evidence that the photon statistics and the photon flux from the single NQD can be manipulated by the plasmonic nanostructure through control of the spectral overlap and the distance.

  4. Detailed Observation of Multiphoton Emission Enhancement from a Single Colloidal Quantum Dot Using a Silver-Coated AFM Tip.

    PubMed

    Takata, Hiroki; Naiki, Hiroyuki; Wang, Li; Fujiwara, Hideki; Sasaki, Keiji; Tamai, Naoto; Masuo, Sadahiro

    2016-09-14

    The enhancement of multiphoton emission from a single colloidal nanocrystal quantum dot (NQD) interacting with a plasmonic nanostructure was investigated using a silver-coated atomic force microscopy tip (AgTip) as the plasmonic nanostructure. Using the AgTip, which exhibited a well-defined localized surface plasmon (LSP) resonance band, we controlled the spectral overlap and the distance between the single NQD and the AgTip. The emission behavior of the single NQD when approaching the AgTip at the nanometer scale was measured using off-resonance (405 nm) and resonance (465 nm) excitation of the LSP. We directly observed the conversion of the single-photon emission from a single NQD to multiphoton emission with reduction of the emission lifetime at both excitation wavelengths as the NQD-AgTip distance decreased, whereas a decrease and increase in the emission intensity were observed at 405 and 465 nm excitation, respectively. By combining theoretical analysis and the numerical simulation of the AgTip, we deduced that the enhancement of the multiphoton emission was caused by the quenching of the single-exciton state due to the energy transfer from the NQD to the AgTip and that the emission intensity was increased by enhancement of the excitation rate due to the electric field of the LSP on the AgTip. These results provide evidence that the photon statistics and the photon flux from the single NQD can be manipulated by the plasmonic nanostructure through control of the spectral overlap and the distance. PMID:27501388

  5. Role of liver endothelium in the binding and uptake of ceruloplasmin: studies with colloidal gold probe

    SciTech Connect

    Kataoka, M.; Tavassoli, M.

    1985-02-01

    To determine the mode of uptake of ceruloplasmin (CP) by liver, the protein was labeled with colloidal gold and infused into the portal vein. In cold almost all probes bound to the sinusoidal endothelium, and at 37/sup 0/C internalization via a system of coated pits and vesicles occurred. Only rarely did the probe appear to bypass the endothelium, moving to the albuminal side through the gaps between endothelial cells. In the endothelial cytoplasm, the probe was seen in coated vesicles, endosomes, tubules, and large vesicles which may have formed by fusion of endosomes and tubules. Moreover, externalization of the probe to the abluminal side was noted, and this also occurred via a system of coated vesicles. The findings suggest that the uptake of CP in the liver may be primarily a transendothelial phenomenon (transcytosis).

  6. Probing Deviations From Traditional Colloid Filtration Theory by Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Bowman, R. S.; Reno, M. D.; Altman, S. J.

    2006-12-01

    Understanding colloid transport through saturated media is an integral component of predicting the fate and transport of groundwater contaminants. Developing sound predictive capabilities and establishing effective methodologies for remediation relies heavily on our ability to understand the physical and chemical mechanisms controlling colloid attachment and detachment. Colloid filtration theory (CFT) has been ubiquitously employed to describe particle advection, dispersion, and deposition in saturated media and predicts an exponential decrease in colloid concentration with travel distance from the source. Colloid depositional behavior can be further understood through consideration of Derjaguin Landau Verwey Overbeek (DLVO) interactions. Recent studies give evidence for significant deviations from traditional CFT in the presence of repulsive DLVO interactions. Deposition in the secondary energy minimum has been suggested as a mechanism to explain the observed deviations. This work reports on attempts to quantify the secondary energy minimum as predicted by DLVO theory using direct measurements obtained by atomic force microscopy. The colloid probe technique is used to directly measure the force of interaction between a single carboxylate modified polystyrene latex microsphere and a model collector surface in electrolyte solutions of varying ionic strength. Systematic variations in the size of the microsphere and the ionic strength of the electrolyte solutions yield force measurements that are compared to theoretical predictions and the experimental results of others. The importance of proper sample characterization and cleaning in obtaining meaningful measurements is emphasized. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04- 94AL85000.

  7. WGA-QD probe-based AFM detects WGA-binding sites on cell surface and WGA-induced rigidity alternation

    SciTech Connect

    Wang Xiaoping; He Dongmei; Cai Jiye Chen Tongsheng; Zou Feiyan; Li Yalan; Wu Yangzhe; Chen, Zheng W.; Chen Yong

    2009-02-06

    A strategy involving the conjugation of fluorescent quantum dot (QD) with wheat germ agglutinin (WGA) acting as fluorescent and topographic probes prior to cell surface staining is developed for fluorescence microscopy and atomic force microscopy (AFM). This strategy provided at least two advantages: (a) an amplified fluorescence of WGA-QD aggregates, strongly resistant to photobleaching, ensures repeated/real-time observations of the probe-labeled cells by fluorescence microscopy; (b) the enlarged size of WGA-QD probe makes it possible for labeled WGA to be distinguished from other membrane proteins by AFM. Here, the random distribution of WGA-binding sites on non-crosslinked cells and the uneven or polarized reorganization due to WGA-induced crosslinking on cell surfaces were studied using AFM-detectable WGA-QD probe. Moreover, we developed a method to rapidly detect the WGA-induced rigidity alternation of the whole cells, which is efficient and has the potentiality of being developed to a useful tool in clinical diagnosis.

  8. Simulation of CNT-AFM tip based on finite element analysis for targeted probe of the biological cell

    NASA Astrophysics Data System (ADS)

    Yousefi, Amin Termeh; Mahmood, Mohamad Rusop; Miyake, Mikio; Ikeda, Shoichiro

    2016-07-01

    Carbon nanotubes (CNTs) are potentially ideal tips for atomic force microscopy (AFM) due to the robust mechanical properties, nano scale diameter and also their ability to be functionalized by chemical and biological components at the tip ends. This contribution develops the idea of using CNTs as an AFM tip in computational analysis of the biological cell's. Finite element analysis employed for each section and displacement of the nodes located in the contact area was monitored by using an output database (ODB). This reliable integration of CNT-AFM tip process provides a new class of high performance nanoprobes for single biological cell analysis.

  9. Influence of the atmospheric humidity on the behaviour of silicon AFM probes in photon scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Benfedda, M.; Lahimer, S.; Bonnafe, J.

    1998-11-01

    The photon scanning tunneling microscopy (PSTM) allows to characterize the surface topography with high resolution. This microscopy exploits the exponential decay of the evanescent field achieved by the total internal reflection under the surface sample. When the distance between the sensor and the surface becomes small (sim 100 nm), the non propagating photons of the evanescent field can be converted into guided propagating mode of polaritons. A bulk Silicon probe is used in the AFM experiment as a sensor of van der Waals forces. The aim of this paper is to discuss the influence of the atmospheric humidity on the PSTM measurements. We have showed that the theoretical predictions of the dielectrical capture model (DCM) are very different from the experimental results when the humidity level is higher than a threshold value (30%). We present the results obtained with TE polarization, but the same behaviour is found with TM polarization. Although, in this paper we do not propose a theoretical model explaining the deviations between DCM values and experimental, however we found a validity threshold for our experimental results and we have emited the assumption that under high humidity level the pollution film presents on the sample surface slide during the displacement of the probe. La microscopie optique à effet tunnel (PSTM) est un outil de caractérisation de surface à haute résolution. Ce microscope exploite la décroissance du champ évanescent créé sur la surface de l'échantillon. Quand la distance entre le capteur et la surface est de quelques dizaines de nanomètres, les ondes évanescentes créées sur la surface sont converties en ondes propagatives et détectées en champ lointain. Le capteur est une sonde en silicium utilisée en microscopie à force atomique. Cet article montre l'influence des conditions atmosphériques sur les mesures PSTM. Il montre qu'au-delà d'un certain taux d'humidité (30%), les mesures ne sont plus valables et ne suivent

  10. Platinum-coated probes sliding at up to 100 mm s-1 against coated silicon wafers for AFM probe-based recording technology

    NASA Astrophysics Data System (ADS)

    Bhushan, Bharat; Kwak, Kwang Joo

    2007-08-01

    One of the new alternative information storage technologies being researched is based on the probe-based recording technique. In one technique, a phase-change medium is used, and the phase change is accomplished by applying either a high or low magnitude of current which heats the interface to different temperatures. Tip wear is a serious concern. For wear protection of the phase-change chalcogenide medium with a silicon substrate, diamond-like carbon (DLC) film with various lubricant overcoats was deposited on the recording layer surface. Nanowear properties of platinum (Pt)-coated probes with high electrical conductivity have been investigated in sliding against the coated medium using an atomic force microscope (AFM). A silicon grating sample and software to deconvolute tip shape were used to characterize the change in the tip shape and evaluate the tip radius and its wear volume. The nanowear experiments were performed at sliding velocities ranging from 0.1 to 100 mm s-1. Pt-coated tips on the lubricant-coated DLC film surfaces showed less sensitivity to the velocity and the load as compared to the unlubricated DLC film surfaces. In wear life threshold experiments, the threshold reaches a smaller sliding distance at higher loads. In high-temperature experiments at 80 °C, the wear rate is higher compared to that at 20 °C. The results suggest that the wear mechanism at low velocity appears to be primarily adhesive and abrasive. At high velocity, an additional wear mechanism of the tribochemical reaction is important.

  11. 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.

  12. Catalytic Scanning Probe Nanolithography (cSPL): Control of the AFM Parameters in Order to Achieve Sub-100-nm Spatially Resolved Epoxidation of Alkenes Grafted onto a Surface.

    PubMed

    Mesquita, Vincent; Botton, Julien; Valyaev, Dmitry A; François, Cyril; Patrone, Lionel; Balaban, Teodor Silviu; Abel, Mathieu; Parrain, Jean-Luc; Chuzel, Olivier; Clair, Sylvain

    2016-04-26

    Scanning probe lithography (SPL) appears to be a reliable alternative to the use of masks in traditional lithography techniques as it offers the possibility of directly producing specific chemical functionalities with nanoscale spatial control. We have recently extend the range of applications of catalytic SPL (cSPL) by introducing a homogeneous catalyst immobilized on the apex of a scanning probe. Here we investigate the importance of atomic force microscopy (AFM) physical parameters (applied force, writing speed, and interline distance) on the resultant chemical activity in this cSPL methodology through the direct topographic observation of nanostructured surfaces. Indeed, an alkene-terminated self-assembled monolayer (alkene-SAM) on a silicon wafer was locally epoxidized using a scanning probe tip with a covalently grafted manganese complex bearing the 1,4,7-triazacyclononane macrocycle as the ligand. In a post-transformation process, N-octylpiperazine was covalently grafted to the surface via a selective nucleophilic ring-opening reaction. With this procedure, we could write various patterns on the surface with high spatial control. The catalytic AFM probe thus appears to be very robust because a total area close to 500 μm(2) was patterned without any noticeable loss of catalytic activity. Finally, this methodology allowed us to reach a lower lateral line resolution down to 40 nm, thus being competitive and complementary to the other nanolithographical techniques for the nanostructuration of surfaces.

  13. The jump-into-contact effect in biased AFM probes on dielectric films and its application to quantify the dielectric permittivity of thin layers

    NASA Astrophysics Data System (ADS)

    Revilla, Reynier I.

    2016-07-01

    The jump-into-contact (JIC) phenomenon in biased atomic force microscopy (AFM) probes on dielectric films is studied. The influence of the film thickness on the position at which the AFM tip collapses irreversibly into the sample surface was theoretically analyzed using a widely accepted analytical expression of the probe-sample electrostatic interaction force. It was demonstrated that for relatively high values of voltage (V > 10-20 V) applied between the probe and the substrate the cantilever deflection at the JIC is independent of the dielectric film thickness for thin-ultrathin layers (h < 10-50 nm). Under the same conditions the z-piezo distance at the JIC follows approximately a linear behavior with the film thickness. Based on this effect an empirical model was formulated to estimate the dielectric permittivity of thin/ultrathin dielectric films using the jump-into-contact distance. The procedure was successfully applied on thin PVD-SiO2 films, obtaining good agreement with a dielectric constant value previously reported for the same material.

  14. The origin of the "snap-in" in the force curve between AFM probe and the water/gas interface of nanobubbles.

    PubMed

    Song, Yang; Zhao, Binyu; Zhang, Lijuan; Lü, Junhong; Wang, Shuo; Dong, Yaming; Hu, Jun

    2014-02-24

    The long-range attractive force or "snap-in" is an important phenomenon usually occurring when a solid particle interacts with a water/gas interface. By using PeakForce quantitative nanomechanics the origin of snap-in in the force curve between the atomic force microscopy (AFM) probe and the water/gas interface of nanobubbles has been investigated. The snap-in frequently happened when the probe was preserved for a certain time or after being used for imaging solid surfaces under atmospheric conditions. In contrast, imaging in liquids rarely induced a snap-in. After a series of control experiments, it was found that the snap-in can be attributed to hydrophobic interactions between the water/gas interface and the AFM probe, which was either modified or contaminated with hydrophobic material. The hydrophobic contamination could be efficiently removed by a conventional plasma-cleaning treatment, which prevents the occurring of the snap-in. In addition, the adsorption of sodium dodecyl sulfate onto the nanobubble surface changed the water/gas interface into hydrophilic, which also eliminated the snap-in phenomenon.

  15. The jump-into-contact effect in biased AFM probes on dielectric films and its application to quantify the dielectric permittivity of thin layers.

    PubMed

    Revilla, Reynier I

    2016-07-01

    The jump-into-contact (JIC) phenomenon in biased atomic force microscopy (AFM) probes on dielectric films is studied. The influence of the film thickness on the position at which the AFM tip collapses irreversibly into the sample surface was theoretically analyzed using a widely accepted analytical expression of the probe-sample electrostatic interaction force. It was demonstrated that for relatively high values of voltage (V > 10-20 V) applied between the probe and the substrate the cantilever deflection at the JIC is independent of the dielectric film thickness for thin-ultrathin layers (h < 10-50 nm). Under the same conditions the z-piezo distance at the JIC follows approximately a linear behavior with the film thickness. Based on this effect an empirical model was formulated to estimate the dielectric permittivity of thin/ultrathin dielectric films using the jump-into-contact distance. The procedure was successfully applied on thin PVD-SiO2 films, obtaining good agreement with a dielectric constant value previously reported for the same material.

  16. The jump-into-contact effect in biased AFM probes on dielectric films and its application to quantify the dielectric permittivity of thin layers.

    PubMed

    Revilla, Reynier I

    2016-07-01

    The jump-into-contact (JIC) phenomenon in biased atomic force microscopy (AFM) probes on dielectric films is studied. The influence of the film thickness on the position at which the AFM tip collapses irreversibly into the sample surface was theoretically analyzed using a widely accepted analytical expression of the probe-sample electrostatic interaction force. It was demonstrated that for relatively high values of voltage (V > 10-20 V) applied between the probe and the substrate the cantilever deflection at the JIC is independent of the dielectric film thickness for thin-ultrathin layers (h < 10-50 nm). Under the same conditions the z-piezo distance at the JIC follows approximately a linear behavior with the film thickness. Based on this effect an empirical model was formulated to estimate the dielectric permittivity of thin/ultrathin dielectric films using the jump-into-contact distance. The procedure was successfully applied on thin PVD-SiO2 films, obtaining good agreement with a dielectric constant value previously reported for the same material. PMID:27199351

  17. Qplus AFM driven nanostencil.

    PubMed

    Grévin, B; Fakir, M; Hayton, J; Brun, M; Demadrille, R; Faure-Vincent, J

    2011-06-01

    We describe the development of a novel setup, in which large stencils with suspended silicon nitride membranes are combined with atomic force microscopy (AFM) regulation by using tuning forks. This system offers the possibility to perform separate AFM and nanostencil operations, as well as combined modes when using stencil chips with integrated tips. The flexibility and performances are demonstrated through a series of examples, including wide AFM scans in closed loop mode, probe positioning repeatability of a few tens of nanometer, simultaneous evaporation of large (several hundred of micron square) and nanoscopic metals and fullerene patterns in static, multistep, and dynamic modes. This approach paves the way for further developments, as it fully combines the advantages of conventional stenciling with the ones of an AFM driven shadow mask. PMID:21721701

  18. Review and perspectives of AFM application on the study of deformable drop/bubble interactions.

    PubMed

    Wang, Wei; Li, Kai; Ma, Mengyu; Jin, Hang; Angeli, Panagiota; Gong, Jing

    2015-11-01

    The applications of Atomic Force Microscopy (AFM) on the study of dynamic interactions and film drainage between deformable bodies dispersed in aqueous solutions are reviewed in this article. Novel experimental designs and recent advances in experimental methodologies are presented, which show the advantage of using AFM as a tool for probing colloidal interactions. The effects of both DLVO and non-DLVO forces on the colloid stabilization mechanism are discussed. Good agreement is found between the force - drop/bubble deformation behaviour revealed by AFM measurements and the theoretical modeling of film drainage process, giving a convincing explanation of the occurrence of certain phenomenon. However, the behaviour and shape of deformable drops as they approach or retract is still not well resolved. In addition, when surfactants are present further research is needed on the absorption of surfactant molecules into the interfaces, their mobility and the effects on interfacial film properties.

  19. Predicting physical stability in pressurized metered dose inhalers via dwell and instantaneous force colloidal probe microscopy.

    PubMed

    D'Sa, Dexter; Chan, Hak-Kim; Chrzanowski, Wojciech

    2014-09-01

    Colloidal probe microscopy (CPM) is a quantitative predictive tool, which can offer insight into particle behavior in suspension pressurized metered dose inhalers (pMDIs). Although CPM instantaneous force measurements, which involve immediate retraction of the probe upon sample contact, can provide information on inter-particle attractive forces, they lack the ability to appropriately imitate all critical particle pMDI interactions (e.g., particle re-dispersion after prolonged pMDI storage). In this paper, two novel dwell force techniques - indentation and deflection dwell - were employed to mimic long-term particle interactions present in pMDIs, using particles of various internal structures and a model liquid propellant (2H,3H perfluoropentane) as a model system. Dwell measurements involve particle contact for an extended period of time. In deflection dwell mode the probe is held at a specific position, while in indentation dwell mode the probe is forced into the sample with a constant force for the entirety of the contact time. To evaluate the applicability of CPM to predict actual pMDI physical stability, inter-particle force measurements were compared with qualitative and quantitative bulk pMDI measurement techniques (visual quality and light scattering). Measured instantaneous attractive (snap-in) and adhesive (max-pull) forces decreased as a function of increasing surface area, while adhesive forces measured by indentation dwell decreased as a function of dwell contact time for particles containing voids. Instantaneous force measurements provided information on the likelihood of floccule formation, which was predictive of partitioning rates, while indentation dwell force measurements were predictive of formulation re-dispersibility after prolonged storage. Dwell force measurements provide additional information on particle behavior within a pMDI not obtainable via instantaneous measurements. PMID:25058596

  20. The jump-into-contact effect in biased AFM probes on dielectric films and its application to quantify the dielectric permittivity of thin layers

    NASA Astrophysics Data System (ADS)

    Revilla, Reynier I.

    2016-07-01

    The jump-into-contact (JIC) phenomenon in biased atomic force microscopy (AFM) probes on dielectric films is studied. The influence of the film thickness on the position at which the AFM tip collapses irreversibly into the sample surface was theoretically analyzed using a widely accepted analytical expression of the probe–sample electrostatic interaction force. It was demonstrated that for relatively high values of voltage (V > 10–20 V) applied between the probe and the substrate the cantilever deflection at the JIC is independent of the dielectric film thickness for thin–ultrathin layers (h < 10–50 nm). Under the same conditions the z–piezo distance at the JIC follows approximately a linear behavior with the film thickness. Based on this effect an empirical model was formulated to estimate the dielectric permittivity of thin/ultrathin dielectric films using the jump-into-contact distance. The procedure was successfully applied on thin PVD–SiO2 films, obtaining good agreement with a dielectric constant value previously reported for the same material.

  1. 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.

  2. 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

  3. Optical systems modeling and experimental realization of pump and probe technique: investigation of nonlinear absorption in colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Smirnov, A.; Golinskaya, A.; Ezhova, K.; Kozlova, M.; Dneprovskii, V.

    2016-04-01

    Two optical systems modeling of laser and broadband radiation focusing, that is necessary for realization of the pump and probe method, was carried out in this work. Modeling was utilized to construct experimental setup for transmission spectra measuring of studied sample by probe nanosecond broadband radiation (coumarin photoluminescence) depending on the intensity of the nanosecond laser pump pulses. The saturation effect of absorption and the induced charge Stark-effect coexistence and predominate issue of these effects are determined by power of optical excitation. In dependence of tuning of excitation radiation frequency from basic exciton transition frequency nonlinear effects in colloidal CdSe/ZnS quantum dots has been investigated.

  4. Using AFM to probe the complexation of DNA with anionic lipids mediated by Ca(2+): the role of surface pressure.

    PubMed

    Luque-Caballero, Germán; Martín-Molina, Alberto; Sánchez-Treviño, Alda Yadira; Rodríguez-Valverde, Miguel A; Cabrerizo-Vílchez, Miguel A; Maldonado-Valderrama, Julia

    2014-04-28

    Complexation of DNA with lipids is currently being developed as an alternative to classical vectors based on viruses. Most of the research to date focuses on cationic lipids owing to their spontaneous complexation with DNA. Nonetheless, recent investigations have revealed that cationic lipids induce a large number of adverse effects on DNA delivery. Precisely, the lower cytotoxicity of anionic lipids accounts for their use as a promising alternative. However, the complexation of DNA with anionic lipids (mediated by cations) is still in early stages and is not yet well understood. In order to explore the molecular mechanisms underlying the complexation of anionic lipids and DNA we proposed a combined methodology based on the surface pressure-area isotherms, Gibbs elasticity and Atomic Force Microscopy (AFM). These techniques allow elucidation of the role of the surface pressure in the complexation and visualization of the interfacial aggregates for the first time. We demonstrate that the DNA complexes with negatively charged model monolayers (DPPC/DPPS 4 : 1) only in the presence of Ca(2+), but is expelled at very high surface pressures. Also, according to the Gibbs elasticity plot, the complexation of lipids and DNA implies a whole fluidisation of the monolayer and a completely different phase transition map in the presence of DNA and Ca(2+). AFM imaging allows identification for the first time of specific morphologies associated with different packing densities. At low surface coverage, a branched net like structure is observed whereas at high surface pressure fibers formed of interfacial aggregates appear. In summary, Ca(2+) mediates the interaction between DNA and negatively charged lipids and also the conformation of the ternary system depends on the surface pressure. Such observations are important new generic features of the interaction between DNA and anionic lipids. PMID:24668321

  5. Influence of Nanoscale Surface Roughness on Colloidal Force Measurements.

    PubMed

    Zou, Yi; Jayasuriya, Sunil; Manke, Charles W; Mao, Guangzhao

    2015-09-29

    Forces between colloidal particles determine the performances of many industrial processes and products. Colloidal force measurements conducted between a colloidal particle AFM probe and particles immobilized on a flat substrate are valuable in selecting appropriate surfactants for colloidal stabilization. One of the features of inorganic fillers and extenders is the prevalence of rough surfaces-even the polymer latex particles, often used as model colloidal systems including the current study, have rough surfaces albeit at a much smaller scale. Surface roughness is frequently cited as the reason for disparity between experimental observations and theoretical treatment but seldom verified by direct evidence. This work reports the effect of nanoscale surface roughness on colloidal force measurements carried out in the presence of surfactants. We applied a heating method to reduce the mean surface roughness of commercial latex particles from 30 to 1 nm. We conducted force measurements using the two types of particles at various salt and surfactant concentrations. The surfactants used were pentaethylene glycol monododecyl ether, Pluronic F108, and a styrene/acrylic copolymer, Joncryl 60. In the absence of the surfactant, nanometer surface roughness affects colloidal forces only in high salt conditions when the Debye length becomes smaller than the surface roughness. The adhesion is stronger between colloids with higher surface roughness and requires a higher surfactant concentration to be eliminated. The effect of surface roughness on colloidal forces was also investigated as a function of the adsorbed surfactant layer structure characterized by AFM indentation and dynamic light scattering. We found that when the layer thickness exceeds the surface roughness, the colloidal adhesion is less influenced by surfactant concentration variation. This study demonstrates that surface roughness at the nanoscale can influence colloidal forces significantly and should be taken

  6. Extraordinary adhesion of phenylboronic acid derivatives of polyvinylamine to wet cellulose: a colloidal probe microscopy investigation.

    PubMed

    Notley, Shannon M; Chen, Wei; Pelton, Robert

    2009-06-16

    Typically, the adhesion between cellulose surfaces under aqueous conditions is very poor. Often, adsorbed polymers such as polyvinylamine (PVAm) are used to increase the wet strength; however, this provides only a minimal increase in the adhesion energy. Here, the adhesion between cellulose surfaces with adsorbed layers of phenylboronic acid derivatized polyvinylamine has been studied using colloidal probe microscopy as a function of pH. The adhesion due to the phenylboronic acid (PBA) groups grafted on the polyvinylamine backbone is almost 30 times greater, providing a new, exciting class of polymers using covalent linkages to improve the strength of the joint between cellulose surfaces. The measured surface forces on approach provided key information on the molecular conformation of the polymers at the cellulose-solution interface. At low pH, the three polymers tested, PVAm, PVAm-Ph (with pendant phenol groups), and PVAm-PBA (with phenylboronic acid groups) all had a relatively flat conformation at the interface, which is in agreement with the predictions based upon theory for highly charged polyelectrolytes adsorbing to an oppositely charged interface. With increasing pH, the charge on the polymers is reduced, eventually resulting in a more expansive conformation at the interface at pH 10 and above with the development of a steric interaction force. The onset of this steric force correlates well with the observed significant increase in the pull-off force upon separation of the cellulose surfaces. Furthermore, a greater increase in the adhesion was observed for PVAm-PBA in agreement with previous studies using macroscopic cellulose surfaces. This is attributed to the formation of boronic acid esters between the polymer and the cis diol groups on the cellulose surface.

  7. Surface forces of colloidal particles from micrometer to nanometer

    NASA Astrophysics Data System (ADS)

    Cho, Jeong-Min

    2003-10-01

    Surface forces of colloidal particles play critical roles in the macroscopic behavior of particulate systems such as dispersion and coagulation, adhesion and coating, and the rheological behavior of ceramic slurries. As particle size is decreased from micrometer to nanometer range, surface forces are increasingly important. Polyelectrolytes are the chemical additives commonly used to efficiently control the stabilization of the colloidal system. Their conformations on the solid surfaces as well as the interactions between the adsorbed polyelectrolytes are important issues in colloidal processing. Most experimental and theoretical approaches to the surface forces are based on particle sizes in the micrometer range. However, nanoparticles at close proximity or high solids loading are expected to show different behavior than what can be estimated from conventional theories such as continuum or mean field theories. My study examined the effect of pH, ionic strength, and molecular weight of the polyelectrolytes on the surface forces of colloidal particles by the interplay with the adsorption, turbidity, and direct surface force measurement in terms of the conformation on the solid surfaces. The colloid probe technique based on atomic force microscopy (AFM) is well established for micron size particles; and could be extended for nanosize particles by using carbon nanotubes as proximal probes. Nanotubes with their high aspect ratio avoid the contribution from cone shapes that happens with AFM tips. The difference in particle size significantly influences surface forces for sterically dispersed colloidal systems.

  8. Probing the enhancement mechanisms of SERS with p-aminothiophenol molecules adsorbed on self-assembled gold colloidal nanoparticles

    NASA Astrophysics Data System (ADS)

    Baia, M.; Toderas, F.; Baia, L.; Popp, J.; Astilean, S.

    2006-04-01

    Gold colloidal nanoparticles were immobilized upon a glass substrate and their morphology and optical properties are analyzed with TEM and UV-Vis absorption spectroscopy. The substrate suitability for surface-enhanced Raman spectroscopy (SERS) in visible and near-infrared spectral region is demonstrated with four excitation lines using p-aminothiophenol. The SERS spectra of probing molecules exhibit a clear signature of electromagnetic and charge-transfer enhancement mechanisms, which critically depend on the laser lines. The large tunability of surface plasmon excitation combined with the advantage of highly chemical affinity to gold of probe molecules recommends this SERS-active system as a useful model for probing the mechanisms of Raman enhancement.

  9. Application of colloid probe atomic force microscopy to the adhesion of thin films of viscous and viscoelastic silicone fluids.

    PubMed

    Bowen, James; Cheneler, David; Andrews, James W; Avery, Andrew R; Zhang, Zhibing; Ward, Michael C L; Adams, Michael J

    2011-09-20

    The adhesive characteristics of thin films (0.2-2 μm) of linear poly(dimethylsiloxane) (PDMS) liquids with a wide range of molecular weights have been measured using an atomic force microscope with a colloid probe (diameters 5 and 12 μm) for different separation velocities. The data were consistent with a residual film in the contact region having a thickness of ∼6 nm following an extended dwell time before separation of the probe. It was possible to estimate the maximum adhesive force as a function of the capillary number, Ca, by applying existing theoretical models based on capillary interactions and viscous flow except at large values of Ca in the case of viscoelastic fluids, for which it was necessary to develop a nonlinear viscoelastic model. The compliance of the atomic force microscope colloid beam was an important factor in governing the retraction velocity of the probe and therefore the value of the adhesive force, but the inertia of the beam and viscoelastic stress overshoot effects were not significant in the range of separation velocities investigated.

  10. Probing deviations from traditional colloid filtration theory by atomic forces microscopy.

    SciTech Connect

    Reno, Marissa Devan

    2005-12-01

    Colloid transport through saturated media is an integral component of predicting the fate and transport of groundwater contaminants. Developing sound predictive capabilities and establishing effective methodologies for remediation relies heavily on our ability to understand the pertinent physical and chemical mechanisms. Traditionally, colloid transport through saturated media has been described by classical colloid filtration theory (CFT), which predicts an exponential decrease in colloid concentration with travel distance. Furthermore, colloid stability as determined by Derjaguin-Landau-Veney-Overbeek (DLVO) theory predicts permanent attachment of unstable particles in a primary energy minimum. However, recent studies show significant deviations from these traditional theories. Deposition in the secondary energy minimum has been suggested as a mechanism by which observed deviations can occur. This work investigates the existence of the secondary energy minimum as predicted by DLVO theory using direct force measurements obtained by Atomic Forces Microscopy. Interaction energy as a function of separation distance between a colloid and a quartz surface in electrolyte solutions of varying ionic strength are obtained. Preliminary force measurements show promise and necessary modifications to the current experimental methodology have been identified. Stringent surface cleaning procedures and the use of high-purity water for all injectant solutions is necessary for the most accurate and precise measurements. Comparisons between direct physical measurements by Atomic Forces Microscopy with theoretical calculations and existing experimental findings will allow the evaluation of the existence or absence of a secondary energy minimum.

  11. Probing droplets with biological colloidal suspensions on smart surfaces by synchrotron radiation micro- and nano-beams

    NASA Astrophysics Data System (ADS)

    Marinaro, G.; Accardo, A.; Benseny-Cases, N.; Burghammer, M.; Castillo-Michel, H.; Cotte, M.; Dante, S.; De Angelis, F.; Di Cola, E.; Di Fabrizio, E.; Hauser, C.; Riekel, C.

    2016-01-01

    Droplets with colloidal biological suspensions evaporating on substrates with defined wetting properties generate confined environments for initiating aggregation and self-assembly processes. We describe smart micro- and nanostructured surfaces, optimized for probing single droplets and residues by synchrotron radiation micro- and nanobeam diffraction techniques. Applications are presented for Ac-IVD and β-amyloid (1-42) peptides capable of forming cross-β sheet structures. Complementary synchrotron radiation FTIR microspectroscopy addresses secondary structure formation. The high synchrotron radiation source brilliance enables fast raster-scan experiments.

  12. Picosecond-to-nanosecond dynamics of plasmonic nanobubbles from pump-probe spectral measurements of aqueous colloidal gold nanoparticles.

    PubMed

    Katayama, Tetsuro; Setoura, Kenji; Werner, Daniel; Miyasaka, Hiroshi; Hashimoto, Shuichi

    2014-08-12

    The photothermal generation of nanoscale vapor bubbles around noble metal nanoparticles is of significant interest, not only in understanding the underlying mechanisms responsible for photothermal effects, but also to optimize photothermal effects in applications such as photothermal cancer therapies. Here, we describe the dynamics in the 400-900 nm regime of the formation and evolution of nanobubbles around colloidal gold nanoparticles using picosecond pump-probe optical measurements. From excitations of 20-150 nm colloidal gold nanoparticles with a 355 nm, 15 ps laser, time-dependent optical extinction signals corresponding to nanobubble formation were recorded. The extinction spectra associated with nanobubbles of different diameters were simulated by considering a concentric spherical core-shell model within the Mie theory framework. In the simulations, we assumed an increase in particle temperature. From temporal changes in the experimental data of transient extinctions, we estimated the temporal evolution of the nanobubble diameter. Corrections to bubble-free temperature effects on the transient extinction decays were applied in these experiments by suppressing bubble formation using pressures as high as 60 MPa. The results of this study suggest that the nanobubbles generated around a 60 nm-diameter gold nanoparticle using a fluence of 5.2 mJ cm(-2) had a maximum diameter of 260 ± 40 nm, and a lifetime of approximately 10 ns. The combination of fast transient extinction spectral measurements and spectral simulations provides insights into plasmonic nanobubble dynamics.

  13. Colloidal Disorder-Order Transition Experiment Probes Particle Interactions in Microgravity

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Everything in the universe is made up of the same basic building blocks - atoms. All physical properties of matter such as weight, hardness, and color are determined by the kind of atoms present and the way they interact with each other. The Colloidal Disorder-Order Transition (CDOT) shuttle flight experiment tested fundamental theories that model atomic interactions. The experiment was part of the Second United States Microgravity Laboratory (USML-2) aboard the Space Shuttle Columbia, which flew from October 20 to November 5, 1995.

  14. Near-wall colloidal dynamics probed by evanescent-wave dynamic light scattering

    NASA Astrophysics Data System (ADS)

    Blawzdziewicz, J.; Wajnryb, E.; Lang, P.; Young, Y.-N.; Dhont, J. K. G.; Cichocki, B.

    2009-11-01

    We present theoretical, numerical, and experimental investigations of evane-scent-wave dynamic light scattering (EWDLS) in a wall-bounded colloidal suspension of spheres. The first cummulant γ1 representing the initial decay of the time autocorrelation function of the scattered field is expressed in terms of the hydrodynamic tensor Hw(,q) describing response of the suspension to a spatially varying harmonic force damped exponentially away from the wall. The wavelength of the harmonic spatial variation corresponds to the scattering vector q in the EWDLS experiments, and the exponential decay is characterized by the decay length &-1circ; of the evanescent wave. The hydrodynamic tensor Hw is evaluated using viral expansion at low densities and numerical simulations at higher densities. A complex non-isotropic structure of the tensor Hw(,q) reflects the hydrodynamic particle-wall coupling and wall-induced short range suspension ordering. Our theory and simulations agree well with the results of EWDLS experiments.

  15. Colloidal quantum dots as probes of excitation field enhancement in photonic antennas.

    PubMed

    Aouani, Heykel; Itzhakov, Stella; Gachet, David; Devaux, Eloïse; Ebbesen, Thomas W; Rigneault, Hervé; Oron, Dan; Wenger, Jérôme

    2010-08-24

    Optical antennas are essential devices to interface light to nanoscale volumes and locally enhance the electromagnetic intensity. Various experimental methods can be used to quantify the antenna amplification on the emission process, yet characterizing the antenna amplification at the excitation frequency solely is a challenging task. Such experimental characterization is highly needed to fully understand and optimize the antenna response. Here, we describe a novel experimental tool to directly measure the antenna amplification on the excitation field independently of the emission process. We monitor the transient emission dynamics of colloidal quantum dots and show that the ratio of doubly to singly excited state photoluminescence decay amplitudes is an accurate tool to quantify the local excitation intensity amplification. This effect is demonstrated on optical antennas made of polystyrene microspheres and gold nanoapertures, and supported by numerical computations. The increased doubly excited state formation on nanoantennas realizes a new demonstration of enhanced light-matter interaction at the nanoscale.

  16. Use of Pyrene Spectroscopic Probes in the Study of Colloidal Systems.

    PubMed

    Campbell; Somasundaran

    2000-09-01

    The interfacial behavior of polyethylene oxide (PEO) end-labeled with the often-used fluorescent probe pyrene was monitored to asess the effect of use of such hydrophobic probes on system behavior. Mixtures of labeled and unlabeled PEO were adsorbed on silica and the resulting suspension properties noted. The suspension behavior was found to be markedly different, depending on the ratio of labeled-to-unlabeled PEO employed. While it was "safe" to use pyrene probes in amounts of 3% or less for spectroscopic investigation of PEO effects, it was found that ratios equal to, or greater than, 1 : 3 produced anomalous behavior of the silica suspensions. This was manifested in the form of decreased suspension stability, as evidenced by significantly higher settling rates. Similar experiments using free pyrene revealed that these effects could be attributed to the chemical attachment of the pyrene probe to the polyethylene oxide chain. Fluorescence spectroscopy was used to simultaneously monitor the behavior of the adsorbed polyethylene oxide molecules. These results were used to explain the observed suspension behavior as a function of the labeled-to-unlabeled polymer mixing ratio. Bridging effects facilitated by hydrophobic interaction between pyrene end groups is proposed as the reason for the observed phenomena. Copyright 2000 Academic Press.

  17. Probing self assembly in biological mixed colloids by SANS, deuteration and molecular manipulation

    SciTech Connect

    Hjelm, R.P.; Thiyagarajan, P.; Hoffman, A.; Alkan-Onyuksel, H.

    1994-12-31

    Small-angle neutron scattering was used to obtain information on the form and molecular arrangement of particles in mixed colloids of bile salts with phosphatidylcholine, and bile salts with monoolein. Both types of systems showed the same general characteristics. The particle form was highly dependent on total lipid concentration. At the highest concentrations the particles were globular mixed micelles with an overall size of 50{Angstrom}. As the concentration was reduced the mixed micelles elongated, becoming rodlike with diameter about 50{Angstrom}. The rods had a radial core-shell structure in which the phosphatidylcholine or monoolein fatty tails were arranged radially to form the core with the headgroups pointing outward to form the shell. The bile salts were at the interface between the shell and core with the hydrophilic parts facing outward as part of the shell. The lengths of the rods increased and became more polydispersed with dilution. At sufficiently low concentrations the mixed micelles transformed into single bilayer vesicles. These results give insight on the physiological function of bile and on the rules governing the self assembly of bile particles in the hepatic duct and the small intestine.

  18. Surfaces of colloidal PbSe nanocrystals probed by thin-film positron annihilation spectroscopy

    SciTech Connect

    Chai, L.; Schut, H.; Schaarenburg, L. C. van; Eijt, S. W. H.; Al-Sawai, W.; Barbiellini, B.; Bansil, A.; Gao, Y.; Houtepen, A. J.; Mijnarends, P. E.; Huis, M. A. van; Ravelli, L.; Egger, W.; Kaprzyk, S.

    2013-08-01

    Positron annihilation lifetime spectroscopy and positron-electron momentum density (PEMD) studies on multilayers of PbSe nanocrystals (NCs), supported by transmission electron microscopy, show that positrons are strongly trapped at NC surfaces, where they provide insight into the surface composition and electronic structure of PbSe NCs. Our analysis indicates abundant annihilation of positrons with Se electrons at the NC surfaces and with O electrons of the oleic ligands bound to Pb ad-atoms at the NC surfaces, which demonstrates that positrons can be used as a sensitive probe to investigate the surface physics and chemistry of nanocrystals inside multilayers. Ab initio electronic structure calculations provide detailed insight in the valence and semi-core electron contributions to the positron-electron momentum density of PbSe. Both lifetime and PEMD are found to correlate with changes in the particle morphology characteristic of partial ligand removal.

  19. AFM cantilever vibration detection with a transmitted electron beam

    NASA Astrophysics Data System (ADS)

    Woehl, Taylor; Wagner, Ryan; Keller, Robert; Killgore, Jason

    Cantilever oscillations for dynamic atomic force microscopy (AFM) are conventionally measured with an optical lever system. The speed of AFM cantilevers can be increased by decreasing the size of the cantilever; however, the fastest AFM cantilevers are currently nearing the smallest size that can be detected with the current optical lever approach. Here we demonstrate an electron detection scheme in an SEM for detecting AFM cantilever oscillations. An oscillating AFM tip is positioned perpendicular to the propagation direction of a stationary ~ 1 nm diameter electron probe, and the oscillatory change in electron scattering resulting from the changing thickness of the electron irradiated area of the AFM tip is detected with a transmitted electron detector positioned below the AFM tip. We perform frequency sweep and ring-down experiments to determine the first resonant frequency and Q factor of an AFM cantilever.

  20. Waveguides in colloidal nanosuspensions

    NASA Astrophysics Data System (ADS)

    López-Peña, Luis A.; Salazar-Romero, Yadira; Terborg, Roland A.; Hernández-Cordero, Juan; Torres, Juan P.; Volke-Sepúlveda, K.

    2014-09-01

    We present and discuss a set of experiments based on the application of the nonlinear properties of colloidal nanosuspensions to induce waveguides with a high-power CW laser beam (wavelength 532nm) and its use for controlling an additional probe beam. The probe is a CW laser of a different wavelength (632nm), whose power is well below the critical value to induce nonlinear effects in the colloidal medium. We also discuss a technique for the characterization of the induced waveguides.

  1. 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

  2. Showing particles their place: deterministic colloid immobilization by gold nanomeshes.

    PubMed

    Stelling, Christian; Mark, Andreas; Papastavrou, Georg; Retsch, Markus

    2016-08-14

    The defined immobilization of colloidal particles on a non-close packed lattice on solid substrates is a challenging task in the field of directed colloidal self-assembly. In this contribution the controlled self-assembly of polystyrene beads into chemically modified nanomeshes with a high particle surface coverage is demonstrated. For this, solely electrostatic interaction forces were exploited by the use of topographically shallow gold nanomeshes. Employing orthogonal functionalization, an electrostatic contrast between the glass surface and the gold nanomesh was introduced on a sub-micron scale. This surface charge contrast promotes a highly site-selective trapping of the negatively charged polystyrene particles from the liquid phase. AFM force spectroscopy with a polystyrene colloidal probe was used to rationalize this electrostatic focusing effect. It provides quantitative access to the occurring interaction forces between the particle and substrate surface and clarifies the role of the pH during the immobilization process. Furthermore, the structure of the non-close packed colloidal monolayers can be finely tuned by varying the ionic strength and geometric parameters between colloidal particles and nanomesh. Therefore one is able to specifically and selectively adsorb one or several particles into one individual nanohole. PMID:27416921

  3. Application of the Johnson-Kendall-Roberts model in AFM-based mechanical measurements on cells and gel.

    PubMed

    Efremov, Yu M; Bagrov, D V; Kirpichnikov, M P; Shaitan, K V

    2015-10-01

    The force-distance curves (FCs) obtained by the atomic force microscope (AFM) with colloid probes contain information about both the viscoelastic properties and adhesion of a sample. Here, we processed both the approach and retraction parts of FCs obtained on polyacrylamide gels (in water or PBS) and Vero cells (in a culture medium). The Johnson-Kendall-Roberts model was applied to the retraction curves to account for the adhesion. The effects of loading rate, holding time and indentation depth on adhesion force and Young's modulus, calculated from approach and retraction curves, were studied. It was shown that both bulk and local interfacial viscoelasticity can affect the observed approach-retraction hysteresis and measured parameters. The addition of 1% bovine serum albumin (BSA) decreased adhesion of the probe to the PAA gel surface, so interfacial viscoelasticity effects were diminished. On the contrary, the adhesiveness of Vero cells increased after BSA addition, indicating the complex nature of the cell-probe interaction.

  4. USE OF FLUORESCENT POLYCYLIC AROMATIC HYDROCARBON PROBES IN STUDYING THE IMPACT OF COLLOIDS ON POLLUTANT TRANSPORT IN GROUNDWATER

    EPA Science Inventory

    A fluorescence-quenching method was developed to assess the hydrophobic organic pollutant binding potential of organic colloids (OC) in unaltered natural waters. This method allows (1) direct assessment of the importance of OC-enhanced pollutant transport for environmental sam- p...

  5. Measuring protein isoelectric points by AFM-based force spectroscopy using trace amounts of sample.

    PubMed

    Guo, Shifeng; Zhu, Xiaoying; Jańczewski, Dominik; Lee, Serina Siew Chen; He, Tao; Teo, Serena Lay Ming; Vancso, G Julius

    2016-09-01

    Protein charge at various pH and isoelectric point (pI) values is important in understanding protein function. However, often only trace amounts of unknown proteins are available and pI measurements cannot be obtained using conventional methods. Here, we show a method based on the atomic force microscope (AFM) to determine pI using minute quantities of proteins. The protein of interest is immobilized on AFM colloidal probes and the adhesion force of the protein is measured against a positively and a negatively charged substrate made by layer-by-layer deposition of polyelectrolytes. From the AFM force-distance curves, pI values with an estimated accuracy of ±0.25 were obtained for bovine serum albumin, myoglobin, fibrinogen and ribonuclease A over a range of 4.7-9.8. Using this method, we show that the pI of the 'footprint' of the temporary adhesive proteins secreted by the barnacle cyprid larvae of Amphibalanus amphitrite is in the range 9.6-9.7. PMID:27454881

  6. Measuring protein isoelectric points by AFM-based force spectroscopy using trace amounts of sample

    NASA Astrophysics Data System (ADS)

    Guo, Shifeng; Zhu, Xiaoying; Jańczewski, Dominik; Lee, Serina Siew Chen; He, Tao; Teo, Serena Lay Ming; Vancso, G. Julius

    2016-09-01

    Protein charge at various pH and isoelectric point (pI) values is important in understanding protein function. However, often only trace amounts of unknown proteins are available and pI measurements cannot be obtained using conventional methods. Here, we show a method based on the atomic force microscope (AFM) to determine pI using minute quantities of proteins. The protein of interest is immobilized on AFM colloidal probes and the adhesion force of the protein is measured against a positively and a negatively charged substrate made by layer-by-layer deposition of polyelectrolytes. From the AFM force-distance curves, pI values with an estimated accuracy of ±0.25 were obtained for bovine serum albumin, myoglobin, fibrinogen and ribonuclease A over a range of 4.7-9.8. Using this method, we show that the pI of the ‘footprint’ of the temporary adhesive proteins secreted by the barnacle cyprid larvae of Amphibalanus amphitrite is in the range 9.6-9.7.

  7. Measuring protein isoelectric points by AFM-based force spectroscopy using trace amounts of sample

    NASA Astrophysics Data System (ADS)

    Guo, Shifeng; Zhu, Xiaoying; Jańczewski, Dominik; Lee, Serina Siew Chen; He, Tao; Teo, Serena Lay Ming; Vancso, G. Julius

    2016-09-01

    Protein charge at various pH and isoelectric point (pI) values is important in understanding protein function. However, often only trace amounts of unknown proteins are available and pI measurements cannot be obtained using conventional methods. Here, we show a method based on the atomic force microscope (AFM) to determine pI using minute quantities of proteins. The protein of interest is immobilized on AFM colloidal probes and the adhesion force of the protein is measured against a positively and a negatively charged substrate made by layer-by-layer deposition of polyelectrolytes. From the AFM force–distance curves, pI values with an estimated accuracy of ±0.25 were obtained for bovine serum albumin, myoglobin, fibrinogen and ribonuclease A over a range of 4.7–9.8. Using this method, we show that the pI of the ‘footprint’ of the temporary adhesive proteins secreted by the barnacle cyprid larvae of Amphibalanus amphitrite is in the range 9.6–9.7.

  8. Combined nano-SIMS/AFM/EBSD analysis and atom probe tomography, of carbon distribution in austenite/ε-martensite high-Mn steels.

    PubMed

    Seol, Jae-Bok; Lee, B-H; Choi, P; Lee, S-G; Park, C-G

    2013-09-01

    We introduce a new experimental approach for the identification of the atomistic position of interstitial carbon in a high-Mn binary alloy consisting of austenite and ε-martensite. Using combined nano-beam secondary ion mass spectroscopy, atomic force microscopy and electron backscatter diffraction analyses, we clearly observe carbon partitioning to austenite. Nano-beam secondary ion mass spectroscopy and atom probe tomography studies also reveal carbon trapping at crystal imperfections as identified by transmission electron microscopy. Three main trapping sites can be distinguished: phase boundaries between austenite and ε-martensite, stacking faults in austenite, and prior austenite grain boundaries. Our findings suggest that segregation and/or partitioning of carbon can contribute to the austenite-to-martensite transformation of the investigated alloy.

  9. Probing the structural dependency of photoinduced properties of colloidal quantum dots using metal-oxide photo-active substrates

    SciTech Connect

    Patty, Kira; Campbell, Quinn; Hamilton, Nathan; West, Robert G.; Sadeghi, Seyed M.; Mao, Chuanbin

    2014-09-21

    We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.

  10. Colloidal Phenomena.

    ERIC Educational Resources Information Center

    Russel, William B.; And Others

    1979-01-01

    Described is a graduate level engineering course offered at Princeton University in colloidal phenomena stressing the physical and dynamical side of colloid science. The course outline, reading list, and requirements are presented. (BT)

  11. Showing particles their place: deterministic colloid immobilization by gold nanomeshes

    NASA Astrophysics Data System (ADS)

    Stelling, Christian; Mark, Andreas; Papastavrou, Georg; Retsch, Markus

    2016-07-01

    The defined immobilization of colloidal particles on a non-close packed lattice on solid substrates is a challenging task in the field of directed colloidal self-assembly. In this contribution the controlled self-assembly of polystyrene beads into chemically modified nanomeshes with a high particle surface coverage is demonstrated. For this, solely electrostatic interaction forces were exploited by the use of topographically shallow gold nanomeshes. Employing orthogonal functionalization, an electrostatic contrast between the glass surface and the gold nanomesh was introduced on a sub-micron scale. This surface charge contrast promotes a highly site-selective trapping of the negatively charged polystyrene particles from the liquid phase. AFM force spectroscopy with a polystyrene colloidal probe was used to rationalize this electrostatic focusing effect. It provides quantitative access to the occurring interaction forces between the particle and substrate surface and clarifies the role of the pH during the immobilization process. Furthermore, the structure of the non-close packed colloidal monolayers can be finely tuned by varying the ionic strength and geometric parameters between colloidal particles and nanomesh. Therefore one is able to specifically and selectively adsorb one or several particles into one individual nanohole.The defined immobilization of colloidal particles on a non-close packed lattice on solid substrates is a challenging task in the field of directed colloidal self-assembly. In this contribution the controlled self-assembly of polystyrene beads into chemically modified nanomeshes with a high particle surface coverage is demonstrated. For this, solely electrostatic interaction forces were exploited by the use of topographically shallow gold nanomeshes. Employing orthogonal functionalization, an electrostatic contrast between the glass surface and the gold nanomesh was introduced on a sub-micron scale. This surface charge contrast promotes a

  12. Contact nanomechanical measurements with the AFM

    NASA Astrophysics Data System (ADS)

    Geisse, Nicholas

    2013-03-01

    The atomic force microscope (AFM) has found broad use in the biological sciences largely due to its ability to make measurements on unfixed and unstained samples under liquid. In addition to imaging at multiple spatial scales ranging from micro- to nanometer, AFMs are commonly used as nanomechanical probes. This is pertinent for cell biology, as it has been demonstrated that the geometrical and mechanical properties of the extracellular microenvironment are important in such processes as cancer, cardiovascular disease, muscular dystrophy, and even the control of cell life and death. Indeed, the ability to control and quantify these external geometrical and mechanical parameters arises as a key issue in the field. Because AFM can quantitatively measure the mechanical properties of various biological samples, novel insights to cell function and to cell-substrate interactions are now possible. As the application of AFM to these types of problems is widened, it is important to understand the performance envelope of the technique and its associated data analyses. This talk will discuss the important issues that must be considered when mechanical models are applied to real-world data. Examples of the effect of different model assumptions on our understanding of the measured material properties will be shown. Furthermore, specific examples of the importance of mechanical stimuli and the micromechanical environment to the structure and function of biological materials will be presented.

  13. Nanoscale structural features determined by AFM for single virus particles.

    PubMed

    Chen, Shu-wen W; Odorico, Michael; Meillan, Matthieu; Vellutini, Luc; Teulon, Jean-Marie; Parot, Pierre; Bennetau, Bernard; Pellequer, Jean-Luc

    2013-11-21

    In this work, we propose "single-image analysis", as opposed to multi-image averaging, for extracting valuable information from AFM images of single bio-particles. This approach allows us to study molecular systems imaged by AFM under general circumstances without restrictions on their structural forms. As feature exhibition is a resolution correlation, we have performed AFM imaging on surfaces of tobacco mosaic virus (TMV) to demonstrate variations of structural patterns with probing resolution. Two AFM images were acquired with the same tip at different probing resolutions in terms of pixel width, i.e., 1.95 and 0.49 nm per pixel. For assessment, we have constructed an in silico topograph based on the three-dimensional crystal structure of TMV as a reference. The prominent artifacts observed in the AFM-determined shape of TMV were attributed to tip convolutions. The width of TMV rod was systematically overestimated by ~10 nm at both probing resolutions of AFM. Nevertheless, the effects of tip convolution were less severe in vertical orientation so that the estimated height of TMV by AFM imaging was in close agreement with the in silico X-ray topograph. Using dedicated image processing algorithms, we found that at low resolution (i.e., 1.95 nm per pixel), the extracted surface features of TMV can be interpreted as a partial or full helical repeat (three complete turns with ~7.0 nm in length), while individual protein subunits (~2.5 nm) were perceivable only at high resolution. The present study shows that the scales of revealed structural features in AFM images are subject to both probing resolution and processing algorithms for image analysis. PMID:24056758

  14. Attractive forces between hydrophobic solid surfaces measured by AFM on the first approach in salt solutions and in the presence of dissolved gases.

    PubMed

    Azadi, Mehdi; Nguyen, Anh V; Yakubov, Gleb E

    2015-02-17

    Interfacial gas enrichment of dissolved gases (IGE) has been shown to cover hydrophobic solid surfaces in water. The atomic force microscopy (AFM) data has recently been supported by molecular dynamics simulation. It was demonstrated that IGE is responsible for the unexpected stability and large contact angle of gaseous nanobubbles at the hydrophobic solid-water interface. Here we provide further evidence of the significant effect of IGE on an attractive force between hydrophobic solid surfaces in water. The force in the presence of dissolved gas, i.e., in aerated and nonaerated NaCl solutions (up to 4 M), was measured by the AFM colloidal probe technique. The effect of nanobubble bridging on the attractive force was minimized or eliminated by measuring forces on the first approach of the AFM probe toward the flat hydrophobic surface and by using high salt concentrations to reduce gas solubility. Our results confirm the presence of three types of forces, two of which are long-range attractive forces of capillary bridging origin as caused by either surface nanobubbles or gap-induced cavitation. The third type is a short-range attractive force observed in the absence of interfacial nanobubbles that is attributed to the IGE in the form of a dense gas layer (DGL) at hydrophobic surfaces. Such a force was found to increase with increasing gas saturation and to decrease with decreasing gas solubility.

  15. Laser-driven phase transitions in aqueous colloidal gold nanoparticles under high pressure: picosecond pump-probe study.

    PubMed

    Hashimoto, Shuichi; Katayama, Tetsuro; Setoura, Kenji; Strasser, Michael; Uwada, Takayuki; Miyasaka, Hiroshi

    2016-02-14

    Pump-probe transient extinction spectroscopy was used to analyze 355 nm picosecond laser heating-induced phenomena in 60 nm-diameter aqueous gold nanoparticles (AuNPs) under a high pressure of 60 MPa. Kinetic spectroscopy revealed that a supercritical layer surrounding the AuNP nucleated with a lifetime of approximately 1 ns during its dynamic expansion and decay for a fluence of 19.6 mJ cm(-2). Moreover, in the post-mortem transmission electron micrographs we observed a number of fragments, a small percentage of size-reduced cores, and erupted particles among the intact particles after 60 shots, suggesting that evaporation occurred under laser illumination. The particle temperature calculation indicated that evaporation begins with a liquid droplet AuNP surrounded by a supercritical layer at temperatures below the boiling point of gold. By applying high pressure, we obtained a clear picture of the evaporation event, which was not possible at ambient pressure because bubble formation caused particle temperatures to rise uncontrollably. In this study, we shed light on the critical role of the supercritical layer formed around the AuNP under high pressure during laser-induced evaporation. PMID:26812175

  16. Probing effects of polymer adsorption in colloidal particle suspensions by light scattering as relevant for the aquatic environment: An overview.

    PubMed

    Tiraferri, Alberto; Borkovec, Michal

    2015-12-01

    Modification of particle surfaces by adsorption of polymers is a process that governs particle behavior in aqueous environmental systems. The present article briefly reviews the current understanding of the adsorption mechanisms and the properties of the resulting layers, and it discusses two environmentally relevant cases of particle modification by polymers. In particular, the discussion focuses on the usefulness of methods based on light scattering to probe such adsorbed layers together with the resulting properties of the particle suspensions, and it highlights advantages and disadvantages of these techniques. Measurement of the electrophoretic mobility allows to follow the development of the adsorption layer and to characterize the charge of the modified particles. At saturation, the surface charge is governed by the charge of the adsorbed film. Dynamic light scattering provides information on the film thickness and on the behavior of the modified suspensions. The charge and the structure of the adsorbed layer influence the stability of the particles, as well as the applicability of the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). This fundamental knowledge is presented in the light of environmental systems and its significance for applied systems is underlined. In particular, the article discusses two examples of environmental processes involving adsorption of polymers, namely, the modification of particles by natural adsorption of humic substances and the tailoring of surface properties of iron-based particles used to remediate contaminated aquifers.

  17. Ultrafast optical pump-probe spectroscopy is used to reveal the coexistence of coupled antiferromagnetic (AFM)/ferroelectric (FE) and ferromagnetic (FM) orders in multiferroic TbMnO3 films, which can guide researchers in creating new kinds of multiferroic materials.

    SciTech Connect

    Qi, Jingbo; Zhu, Jianxin; Trugman, Stuart A.; Taylor, Antoinette; Jia, Quanxi; Prasankumar, Rohit

    2012-07-06

    , experimental techniques capable of dynamically unraveling the interplay between these degrees of freedom on an ultrafast timescale are needed. Here, we use ultrafast optical pump-probe spectroscopy to reveal coexisting coupled magnetic orders in epitaxial TMO thin films grown on (001)-STO, which were not observed in previous work. Our temperature (T)-dependent transient differential reflectivity ({Delta}R/R) measurements show clear signatures of sinusoidal AFM, spiral AFM (FE) and FM phases developing as the film thickness changes. We carry out first-principle density functional theory (DFT) calculations to explain the coupling between AFM/FE and FM orders. These results reveal that the coupling between different magnetic orders observed in our multiferroic TMO thin films may offer greater control of functionality as compared to bulk single crystal multiferroics.

  18. Colloid update.

    PubMed

    Argalious, Maged Y

    2012-01-01

    This update aims to provide an evidence based review of natural and synthetic colloids with a special emphasis on the various generations of the synthetic colloid hydroxyethyl starch. The effect of 1(st), 2(nd) and 3(rd) generation hetastarches on bleeding, coagulopathy, acute kidney injury and mortality will be discussed. The results of randomised controlled trials addressing morbidity and mortality outcomes of colloid versus crystalloid resuscitation in critically ill patients will be described. In addition, the rationale and evidence behind early goal directed fluid therapy (EGDFT) including a practical approach to assessment of dynamic measures of fluid responsiveness will be presented.

  19. Colloidal polypyrrole

    DOEpatents

    Armes, Steven P.; Aldissi, Mahmoud

    1990-01-01

    Processable electrically conductive latex polymer compositions including colloidal particles of an oxidized, polymerized aromatic heterocyclic monomer, a stabilizing effective amount of a vinyl pyridine-containing polymer and dopant anions and a method of preparing such polymer compositions are disclosed.

  20. Hexadecapolar Colloids

    DOE PAGES

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-02-11

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and forbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms’ displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. We describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Becausemore » of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and report the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.« less

  1. Hexadecapolar colloids

    PubMed Central

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-01-01

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously. PMID:26864184

  2. A simple and 'green' synthesis of polymer-based silver colloids and their antibacterial properties.

    PubMed

    Bo, Lili; Yang, Wu; Chen, Miao; Gao, Jinzhang; Xue, Qunji

    2009-01-01

    Stable silver colloids were prepared using polyethylene glycol (PEG) as an environment friendly reduction agent and stabilizer, and with H2O as solvent. The Ag colloids were characterized by UV/VIS spectroscopy, transmission electron microscopy (TEM), and atom force microscopy (AFM). TEM and AFM of the sample showed uniform and monodispersive particle distribution in the colloids. The particle size is found to be less than 10 nm. The antibacterial activity of the Ag colloids was also studied. The results showed that the sample had high antibacterial activity toward Gram-positive and Gram-negative bacteria, and fungi.

  3. Novel Polymer Linkers for Single Molecule AFM Force Spectroscopy

    PubMed Central

    Tong, Zenghan; Mikheikin, Andrey; Krasnoslobodtsev, Alexey; Lv, Zhengjian; Lyubchenko, Yuri L.

    2013-01-01

    Flexible polymer linkers play an important role in various imaging and probing techniques that require surface immobilization, including atomic force microscopy (AFM). In AFM force spectroscopy, polymer linkers are necessary for the covalent attachment of molecules of interest to the AFM tip and the surface. The polymer linkers tether the molecules and provide their proper orientation in probing experiments. Additionally, the linkers separate specific interactions from nonspecific short-range adhesion and serve as a reference point for the quantitative analysis of single molecule probing events. In this report, we present our results on the synthesis and testing of a novel polymer linker and the identification of a number of potential applications for its use in AFM force spectroscopy experiments. The synthesis of the linker is based on the well-developed phosphoramidate (PA) chemistry that allows the routine synthesis of linkers with predetermined lengths and PA composition. These linkers are homogeneous in length and can be terminated with various functional groups. PA linkers with different functional groups were synthesized and tested in experimental systems utilizing different immobilization chemistries. We probed interactions between complementary DNA oligonucleotides; DNA and protein complexes formed by the site-specific binding protein SfiI; and interactions between amyloid peptide (Aβ42). The results of the AFM force spectroscopy experiments validated the feasibility of the proposed approach for the linker design and synthesis. Furthermore, the properties of the tether (length, functional groups) can be adjusted to meet the specific requirements for different force spectroscopy experiments and system characteristics, suggesting that it could be used for a large number of various applications. PMID:23624104

  4. Intrinsically high-Q dynamic AFM imaging in liquid with a significantly extended needle tip

    NASA Astrophysics Data System (ADS)

    Minary-Jolandan, Majid; Tajik, Arash; Wang, Ning; Yu, Min-Feng

    2012-06-01

    Atomic force microscope (AFM) probe with a long and rigid needle tip was fabricated and studied for high Q factor dynamic (tapping mode) AFM imaging of samples submersed in liquid. The extended needle tip over a regular commercially available tapping-mode AFM cantilever was sufficiently long to keep the AFM cantilever from submersed in liquid, which significantly minimized the hydrodynamic damping involved in dynamic AFM imaging of samples in liquid. Dynamic AFM imaging of samples in liquid at an intrinsic Q factor of over 100 and an operational frequency of over 200 kHz was demonstrated. The method has the potential to be extended to acquire viscoelastic material properties and provide truly gentle imaging of soft biological samples in physiological environments.

  5. Cells mechanics with AFM: problems and solutions

    NASA Astrophysics Data System (ADS)

    Sokolov, Igor; Dokukin, Maxim; Guz, Nataliia

    2012-02-01

    Atomic force microscopy (AFM) is used to study mechanics of cells. Cell is far from being a homogeneous medium. This creates a number of problems which will be discussed as well as the ways to solve them. We will focus on the following problems: 1. Cellular surface brush (microvilli, glycocalyx..) surrounds cells. A simple model to separate the brush and cell deformation will be overviewed. 2. Problem of nonlinearity of stress-strain relation. Although unsolved, this may indirectly tested: the rigidity modulus should be reasonably independent of penetration. We will show that it can be achieved when using relatively dull AFM probes (the radii of microns) only. 3. Heterogeneity of cell surface. Cells are not homogeneous over the surface. We will discuss the question how many points is enough to characterize the cell. We will exemplify the above with human cervical epithelial cells. We will demonstrate that without proper consideration of the above problems, the error in defining the modulus of rigidity can easily reach an order of magnitude.

  6. Examination of dentin surface using AFM (our experience).

    PubMed

    Zapletalová, Zdenka; Kubínek, Roman; Vůjtek, Milan; Novotný, Radko

    2004-01-01

    Atomic force microscopy (AFM) as one the technique of Scanning Probe Microscopy is useful for imaging of surface structure. This method can yield three-dimensional high-resolution topographic images of sample surfaces by using a scanning technique for conductors and insulators on atomic scale. It is based upon mapping of atomic-forces on a surface of an investigated sample. The method is useful not only in physics and chemistry; it can be also applied in biological fields. Special construction of AFM scanner enables to follow biological samples in liquid environments. Artifacts caused by dehydration of samples are removed this way. Dentin of human teeth is a vital hydrated tissue. It is strongly sensitive to dehydration and drying that are commonly used in preparation of samples in examinations by Scanning Electron Microscopy (SEM). We describe our experience in examination of dentin surfaces of extracted human third molars using contact method of AFM under moist conditions.

  7. AFM of biological complexes: what can we learn?

    PubMed Central

    Gaczynska, Maria; Osmulski, Pawel A.

    2009-01-01

    The term “biological complexes” broadly encompasses particles as diverse as multisubunit enzymes, viral capsids, transport cages, molecular nets, ribosomes, nucleosomes, biological membrane components and amyloids. The complexes represent a broad range of stability and composition. Atomic force microscopy offers a wealth of structural and functional data about such assemblies. For this review, we choose to comment on the significance of AFM to study various aspects of biology of selected nonmembrane protein assemblies. Such particles are large enough to reveal many structural details under the AFM probe. Importantly, the specific advantages of the method allow for gathering dynamic information about their formation, stability or allosteric structural changes critical for their function. Some of them have already found their way to nanomedical or nanotechnological applications. Here we present examples of studies where the AFM provided pioneering information about the biology of complexes, and examples of studies where the simplicity of the method is used toward the development of potential diagnostic applications. PMID:19802337

  8. Liquid contact resonance AFM: analytical models, experiments, and limitations

    NASA Astrophysics Data System (ADS)

    Parlak, Zehra; Tu, Qing; Zauscher, Stefan

    2014-11-01

    Contact resonance AFM (CR-AFM) is a scanning probe microscopy technique that utilizes the contact resonances of the AFM cantilever for concurrent imaging of topography and surface stiffness. The technique has not been used in liquid until recently due to analytical and experimental difficulties, associated with viscous damping of cantilever vibrations and fluid loading effects. To address these difficulties, (i) an analytical approach for contact resonances in liquid is developed, and (ii) direct excitation of the contact resonances is demonstrated by actuating the cantilever directly in a magnetic field. By implementing the analytical approach and the direct actuation through magnetic particles, quantitative stiffness imaging on surfaces with a wide range of stiffness can be achieved in liquid with soft cantilevers and low contact forces.

  9. Fibrinogen monolayer characterization by colloid deposition.

    PubMed

    Nattich-Rak, Małgorzata; Adamczyk, Zbigniew; Wasilewska, Monika; Sadowska, Marta

    2013-09-24

    Colloid particle deposition was applied to characterize bovine and human fibrinogen (Fb) monolayers on mica produced by controlled adsorption under diffusion transport at pH 3.5. The surface concentration of Fb was determined by AFM enumeration of single molecules adsorbed over the substrate surface. The electrokinetic properties of Fb monolayers for various ionic strength were studied using the in situ streaming potential measurements. It was shown that Fb adsorbs irreversibly on mica for a broad range of ionic strength of 4 × 10(-4) to 0.15 M, NaCl. The overcharging of initially negative mica surface occurred for fibrinogen surface concentrations higher than 1400 μm(-2). The orientation of fibrinogen molecules in the monolayers was evaluated by the colloid deposition method involving negatively charged polystyrene latex microspheres, 820 nm in diameter. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential was observed, which contradicts the mean-field DLVO predictions. Measurable deposition was observed even at low ionic strength where the minimum approach distance of latex particles to the interface exceeds 70 nm (for 6 × 10(-4) M NaCl). This confirms that, at this pH, fibrinogen molecules adsorb end-on on mica assuming extended conformations with the positive charge located mostly in the end part of the αA chains. This agrees with previous experimental and theoretical results discussed in the literature (Santore, M. M.; Wertz Ch. F. Protein spreading kinetics at liquid-solid interfaces via an adsorption probe method. Langmuir 2005, 21, 10172-10178 (experimental); Adamczyk, Z.; Barbasz, J.; Cieśla, M.; Mechanisms of fibrinogen adsorption at solid substrates. Langmuir, 2011, 25, 6868-6878 (theoretical)). This unusual latex deposition on Fb monolayers was quantitatively interpreted in terms of the model developed in ref 55 (Jin, X.; Wang, N. H. L.; Tarjus, G.; Talbot, J. Irreversible adsorption on nonuniform

  10. Growth behaviour and mechanical properties of PLL/HA multilayer films studied by AFM.

    PubMed

    Uzüm, Cagri; Hellwig, Johannes; Madaboosi, Narayanan; Volodkin, Dmitry; von Klitzing, Regine

    2012-01-01

    Scanning- and colloidal-probe atomic force microscopy were used to study the mechanical properties of poly(L-lysine)/hyaluronan (PLL/HA)(n) films as a function of indentation velocity and the number of polymer deposition steps n. The film thickness was determined by two independent AFM-based methods: scratch-and-scan and newly developed full-indentation. The advantages and disadvantages of both methods are highlighted, and error minimization techniques in elasticity measurements are addressed. It was found that the film thickness increases linearly with the bilayer number n, ranging between 400 and 7500 nm for n = 12 and 96, respectively. The apparent Young's modulus E ranges between 15 and 40 kPa and does not depend on the indenter size or the film bilayer number n. Stress relaxation measurements show that PLL/HA films have a viscoelastic behaviour, regardless of their thickness. If indentation is performed several times at the same lateral position on the film, a viscous/plastic deformation takes place.

  11. 3D force and displacement sensor for SFA and AFM measurements.

    PubMed

    Kristiansen, Kai; McGuiggan, Patricia; Carver, Greg; Meinhart, Carl; Israelachvili, Jacob

    2008-02-19

    A new device has been designed, and a prototype built and tested, that can simultaneously measure the displacements and/or the components of a force in three orthogonal directions. The "3D sensor" consists of four or eight strain gauges attached to the four arms of a single cross-shaped force-measuring cantilever spring. Finite element modeling (FEM) was performed to optimize the design configuration to give desired sensitivity of force, displacement, stiffness, and resonant frequency in each direction (x, y, and z) which were tested on a "mesoscale" device and found to agree with the predicted values to within 4-10%. The device can be fitted into a surface forces apparatus (SFA), and a future smaller "microscale" microfabricated version can be fitted into an atomic force microscope (AFM) for simultaneous measurements of the normal and lateral (friction) forces between a tip (or colloidal bead probe) and a surface, and the topography of the surface. Results of the FEM analysis are presented, and approximate equations derived using linear elasticity theory are given for the sensitivity in each direction. Initial calibrations and measurements of thin film rheology (lubrication forces) using the "mesoscale" prototype show the device to function as expected.

  12. Crystallographic order and decomposition of [MnIII6CrIII]3+ single-molecule magnets deposited in submonolayers and monolayers on HOPG studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin probe force microscopy in UHV.

    PubMed

    Gryzia, Aaron; Volkmann, Timm; Brechling, Armin; Hoeke, Veronika; Schneider, Lilli; Kuepper, Karsten; Glaser, Thorsten; Heinzmann, Ulrich

    2014-01-01

    Monolayers and submonolayers of [MnIII6CrIII]3+ single-molecule magnets (SMMs) adsorbed on highly oriented pyrolytic graphite (HOPG) using the droplet technique characterized by non-contact atomic force microscopy (nc-AFM) as well as by Kelvin probe force microscopy (KPFM) show island-like structures with heights resembling the height of the molecule. Furthermore, islands were found which revealed ordered 1D as well as 2D structures with periods close to the width of the SMMs. Along this, islands which show half the heights of intact SMMs were observed which are evidences for a decomposing process of the molecules during the preparation. Finally, models for the structure of the ordered SMM adsorbates are proposed to explain the observations.

  13. Colloidal polyaniline

    DOEpatents

    Armes, Steven P.; Aldissi, Mahmoud

    1990-01-01

    Processable electrically conductive latex polymer compositions including colloidal particles of an oxidized, polymerized amino-substituted aromatic monomer, a stabilizing effective amount of a random copolymer containing amino-benzene type moieties as side chain constituents, and dopant anions, and a method of preparing such polymer compositions are provided.

  14. AFM nanoscale indentation in air of polymeric and hybrid materials with highly different stiffness

    NASA Astrophysics Data System (ADS)

    Suriano, Raffaella; Credi, Caterina; Levi, Marinella; Turri, Stefano

    2014-08-01

    In this study, nanomechanical properties of a variety of polymeric materials was investigated by means of AFM. In particular, selecting different AFM probes, poly(methyl methacrylate) (PMMA), polydimethylsiloxane (PDMS) bulk samples, sol-gel hybrid thin films and hydrated hyaluronic acid hydrogels were indented in air to determine the elastic modulus. The force-distance curves and the indentation data were found to be greatly affected by the cantilever stiffness and by tip geometry. AFM indentation tests show that the choice of the cantilever spring constant and of tip shape is crucially influenced by elastic properties of samples. When adhesion-dominated interactions occur between the tip and the surface of samples, force-displacement curves reveal that a suitable functionalization of AFM probes allows the control of such interactions and the extraction of Young' modulus from AFM curves that would be otherwise unfeasible. By applying different mathematical models depending on AFM probes and materials under investigation, the values of Young's modulus were obtained and compared to those measured by rheological and dynamic mechanical analysis or to literature data. Our results show that a wide range of elastic moduli (10 kPa-10 GPa) can be determined by AFM in good agreement with those measured by conventional macroscopic measurements.

  15. In Situ Probing of Cholesterol in Astrocytes at the Single Cell Level using Laser Desorption Ionization Mass Spectrometric Imaging with Colloidal Silver

    SciTech Connect

    Perdian, D.C.; Cha, Sangwon; Oh, Jisun; Sakaguchi, Donald S.; Yeung, Edward S.; and Lee, Young Jin

    2010-03-18

    Mass spectrometric imaging has been utilized to localize individual astrocytes and to obtain cholesterol populations at the single-cell level in laser desorption ionization (LDI) with colloidal silver. The silver ion adduct of membrane-bound cholesterol was monitored to detect individual cells. Good correlation between mass spectrometric and optical images at different cell densities indicates the ability to perform single-cell studies of cholesterol abundance. The feasibility of quantification is confirmed by the agreement between the LDI-MS ion signals and the results from a traditional enzymatic fluorometric assay. We propose that this approach could be an effective tool to study chemical populations at the cellular level.

  16. High-speed AFM for Studying Dynamic Biomolecular Processes

    NASA Astrophysics Data System (ADS)

    Ando, Toshio

    2008-03-01

    Biological molecules show their vital activities only in aqueous solutions. It had been one of dreams in biological sciences to directly observe biological macromolecules (protein, DNA) at work under a physiological condition because such observation is straightforward to understanding their dynamic behaviors and functional mechanisms. Optical microscopy has no sufficient spatial resolution and electron microscopy is not applicable to in-liquid samples. Atomic force microscopy (AFM) can visualize molecules in liquids at high resolution but its imaging rate was too low to capture dynamic biological processes. This slow imaging rate is because AFM employs mechanical probes (cantilevers) and mechanical scanners to detect the sample height at each pixel. It is quite difficult to quickly move a mechanical device of macroscopic size with sub-nanometer accuracy without producing unwanted vibrations. It is also difficult to maintain the delicate contact between a probe tip and fragile samples. Two key techniques are required to realize high-speed AFM for biological research; fast feedback control to maintain a weak tip-sample interaction force and a technique to suppress mechanical vibrations of the scanner. Various efforts have been carried out in the past decade to materialize high-speed AFM. The current high-speed AFM can capture images on video at 30-60 frames/s for a scan range of 250nm and 100 scan lines, without significantly disturbing week biomolecular interaction. Our recent studies demonstrated that this new microscope can reveal biomolecular processes such as myosin V walking along actin tracks and association/dissociation dynamics of chaperonin GroEL-GroES that occurs in a negatively cooperative manner. The capacity of nanometer-scale visualization of dynamic processes in liquids will innovate on biological research. In addition, it will open a new way to study dynamic chemical/physical processes of various phenomena that occur at the liquid-solid interfaces.

  17. Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission

    SciTech Connect

    Wawrzynczyk, Dominika; Szeremeta, Janusz; Samoc, Marek; Nyk, Marcin

    2015-11-01

    Spectrally resolved nonlinear optical properties of colloidal InP@ZnS core-shell quantum dots of various sizes were investigated with the Z-scan technique and two-photon fluorescence excitation method using a femtosecond laser system tunable in the range from 750 nm to 1600 nm. In principle, both techniques should provide comparable results and can be interchangeably used for determination of the nonlinear optical absorption parameters, finding maximal values of the cross sections and optimizing them. We have observed slight differences between the two-photon absorption cross sections measured by the two techniques and attributed them to the presence of non-radiative paths of absorption or relaxation. The most significant value of two-photon absorption cross section σ{sub 2} for 4.3 nm size InP@ZnS quantum dot was equal to 2200 GM, while the two-photon excitation action cross section σ{sub 2}Φ was found to be 682 GM at 880 nm. The properties of these cadmium-free colloidal quantum dots can be potentially useful for nonlinear bioimaging.

  18. Characterization of single 1.8-nm Au nanoparticle attachments on AFM tips for single sub-4-nm object pickup

    NASA Astrophysics Data System (ADS)

    Cheng, Hui-Wen; Chang, Yuan-Chih; Tang, Song-Nien; Yuan, Chi-Tsu; Tang, Jau; Tseng, Fan-Gang

    2013-11-01

    This paper presents a novel method for the attachment of a 1.8-nm Au nanoparticle (Au-NP) to the tip of an atomic force microscopy (AFM) probe through the application of a current-limited bias voltage. The resulting probe is capable of picking up individual objects at the sub-4-nm scale. We also discuss the mechanisms involved in the attachment of the Au-NP to the very apex of an AFM probe tip. The Au-NP-modified AFM tips were used to pick up individual 4-nm quantum dots (QDs) using a chemically functionalized method. Single QD blinking was reduced considerably on the Au-NP-modified AFM tip. The resulting AFM tips present an excellent platform for the manipulation of single protein molecules in the study of single protein-protein interactions.

  19. Soil colloidal behavior

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Recent understanding that organic and inorganic contaminants are often transported via colloidal particles has increased interest in colloid science. The primary importance of colloids in soil science stems from their surface reactivity and charge characteristics. Characterizations of size, shape,...

  20. Using short-lived nuclides of the U- and Th-series to probe the kinetics of colloid migration in forested soils

    NASA Astrophysics Data System (ADS)

    Rihs, Sophie; Prunier, Jonathan; Thien, Bruno; Lemarchand, Damien; Pierret, Marie-Claire; Chabaux, François

    2011-12-01

    The recent chemical dynamics of a podzolic forest soil section (from the Strengbach watershed, France) was investigated using U- and Th-series nuclides. Analyses of ( 238U), ( 230Th), ( 226Ra), ( 232Th), ( 228Ra) and ( 228Th) activities in the soil particles, the seepage waters, and the mature leaves of the beech trees growing on this soil were performed by TIMS or gamma spectrometry. The simultaneous analysis of the different soil ( sl) compartments allows to demonstrate that a preferential Th leaching over Ra must be assumed to explain the ( 226Ra/ 230Th), ( 228Ra/ 232Th) and ( 228Th/ 228Ra) disequilibria recorded in the soil particles. The overall Ra- and Th- transfer schemes are entirely consistent with the prevailing acido-complexolysis weathering mechanism in podzols. Using a continuous open-system leaching model, the ( 226Ra/ 230Th) and ( 228Ra/ 232Th) disequilibria measured in the different soil layers enable dating of the contemporary processes occurring in this soil. In this way, we have determined that a preferential Th-leaching from the shallow Ah horizon, due to a strong complexation with organic colloids, began fairly recently (18 years ago at most). The continual increase in pH recorded in precipitations over the last 20 years is assumed to be the cause of this enhanced organic complexation. A lower soil horizon (50-60 cm) is also affected by preferential Th leaching, though lasting over several centuries at least, with a much smaller leaching rate. The migration of Th isotopes through this soil section might hence be used as a tracer for the organic colloids migration and the induced radioactive disequilibria demonstrate to be useful for assessing the colloidal migration kinetics in a forested soil. Ra and Th isotopic ratios also appear to be valuable tracers of some mineral-water-plant interactions occurring in soil. The ( 228Ra/ 226Ra) ratio enables discrimination of the Ra flux originating from leaf degradation from that originating from mineral

  1. Development of a 3D-AFM for true 3D measurements of nanostructures

    NASA Astrophysics Data System (ADS)

    Dai, Gaoliang; Häßler-Grohne, Wolfgang; Hüser, Dorothee; Wolff, Helmut; Danzebrink, Hans-Ulrich; Koenders, Ludger; Bosse, Harald

    2011-09-01

    The development of advanced lithography requires highly accurate 3D metrology methods for small line structures of both wafers and photomasks. Development of a new 3D atomic force microscopy (3D-AFM) with vertical and torsional oscillation modes is introduced in this paper. In its configuration, the AFM probe is oscillated using two piezo actuators driven at vertical and torsional resonance frequencies of the cantilever. In such a way, the AFM tip can probe the surface with a vertical and a lateral oscillation, offering high 3D probing sensitivity. In addition, a so-called vector approach probing (VAP) method has been applied. The sample is measured point-by-point using this method. At each probing point, the tip is approached towards the surface until the desired tip-sample interaction is detected and then immediately withdrawn from the surface. Compared to conventional AFMs, where the tip is kept continuously in interaction with the surface, the tip-sample interaction time using the VAP method is greatly reduced and consequently the tip wear is reduced. Preliminary experimental results show promising performance of the developed system. A measurement of a line structure of 800 nm height employing a super sharp AFM tip could be performed with a repeatability of its 3D profiles of better than 1 nm (p-v). A line structure of a Physikalisch-Technische Bundesanstalt photomask with a nominal width of 300 nm has been measured using a flared tip AFM probe. The repeatability of the middle CD values reaches 0.28 nm (1σ). A long-term stability investigation shows that the 3D-AFM has a high stability of better than 1 nm within 197 measurements taken over 30 h, which also confirms the very low tip wear.

  2. Electrochemical fabrication of graphene nanomesh via colloidal templating.

    PubMed

    Mangadlao, J D; de Leon, A C C; Felipe, M J L; Advincula, R C

    2015-05-01

    A simple electrochemical fabrication of graphene nanomesh (GNM) via colloidal templating is reported for the first time. The process involves the arraying of polystyrene (PS) spheres onto a CVD-deposited graphene, electro-deposition of carbazole units, removal of the PS template and electrochemical oxidative etching. The GNM was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy.

  3. Hydrodynamic effects in fast AFM single-molecule force measurements.

    PubMed

    Janovjak, Harald; Struckmeier, Jens; Müller, Daniel J

    2005-02-01

    Atomic force microscopy (AFM) allows the critical forces that unfold single proteins and rupture individual receptor-ligand bonds to be measured. To derive the shape of the energy landscape, the dynamic strength of the system is probed at different force loading rates. This is usually achieved by varying the pulling speed between a few nm/s and a few microm/s, although for a more complete investigation of the kinetic properties higher speeds are desirable. Above 10 microm/s, the hydrodynamic drag force acting on the AFM cantilever reaches the same order of magnitude as the molecular forces. This has limited the maximum pulling speed in AFM single-molecule force spectroscopy experiments. Here, we present an approach for considering these hydrodynamic effects, thereby allowing a correct evaluation of AFM force measurements recorded over an extended range of pulling speeds (and thus loading rates). To support and illustrate our theoretical considerations, we experimentally evaluated the mechanical unfolding of a multi-domain protein recorded at 30 microm/s pulling speed. PMID:15257425

  4. Near-Field Spectroscopy with Nanoparticles Deposited by AFM

    NASA Technical Reports Server (NTRS)

    Anderson, Mark S.

    2008-01-01

    An alternative approach to apertureless near-field optical spectroscopy involving an atomic-force microscope (AFM) entails less complexity of equipment than does a prior approach. The alternative approach has been demonstrated to be applicable to apertureless near-field optical spectroscopy of the type using an AFM and surface enhanced Raman scattering (SERS), and is expected to be equally applicable in cases in which infrared or fluorescence spectroscopy is used. Apertureless near-field optical spectroscopy is a means of performing spatially resolved analyses of chemical compositions of surface regions of nanostructured materials. In apertureless near-field spectroscopy, it is common practice to utilize nanostructured probe tips or nanoparticles (usually of gold) having shapes and dimensions chosen to exploit plasmon resonances so as to increase spectroscopic-signal strengths. To implement the particular prior approach to which the present approach is an alternative, it is necessary to integrate a Raman spectrometer with an AFM and to utilize a special SERS-active probe tip. The resulting instrumentation system is complex, and the tasks of designing and constructing the system and using the system to acquire spectro-chemical information from nanometer-scale regions on a surface are correspondingly demanding.

  5. Insight into mechanics of AFM tip-based nanomachining: bending of cantilevers and machined grooves

    NASA Astrophysics Data System (ADS)

    Al-Musawi, R. S. J.; Brousseau, E. B.; Geng, Y.; Borodich, F. M.

    2016-09-01

    Atomic force microscope (AFM) tip-based nanomachining is currently the object of intense research investigations. Values of the load applied to the tip at the free end of the AFM cantilever probe used for nanomachining are always large enough to induce plastic deformation on the specimen surface contrary to the small load values used for the conventional contact mode AFM imaging. This study describes an important phenomenon specific for AFM nanomachining in the forward direction: under certain processing conditions, the deformed shape of the cantilever probe may change from a convex to a concave orientation. The phenomenon can principally change the depth and width of grooves machined, e.g. the grooves machined on a single crystal copper specimen may increase by 50% on average following such a change in the deformed shape of the cantilever. It is argued that this phenomenon can take place even when the AFM-based tool is operated in the so-called force-controlled mode. The study involves the refined theoretical analysis of cantilever probe bending, the analysis of experimental signals monitored during the backward and forward AFM tip-based machining and the inspection of the topography of produced grooves.

  6. Insight into mechanics of AFM tip-based nanomachining: bending of cantilevers and machined grooves.

    PubMed

    Al-Musawi, R S J; Brousseau, E B; Geng, Y; Borodich, F M

    2016-09-23

    Atomic force microscope (AFM) tip-based nanomachining is currently the object of intense research investigations. Values of the load applied to the tip at the free end of the AFM cantilever probe used for nanomachining are always large enough to induce plastic deformation on the specimen surface contrary to the small load values used for the conventional contact mode AFM imaging. This study describes an important phenomenon specific for AFM nanomachining in the forward direction: under certain processing conditions, the deformed shape of the cantilever probe may change from a convex to a concave orientation. The phenomenon can principally change the depth and width of grooves machined, e.g. the grooves machined on a single crystal copper specimen may increase by 50% on average following such a change in the deformed shape of the cantilever. It is argued that this phenomenon can take place even when the AFM-based tool is operated in the so-called force-controlled mode. The study involves the refined theoretical analysis of cantilever probe bending, the analysis of experimental signals monitored during the backward and forward AFM tip-based machining and the inspection of the topography of produced grooves. PMID:27532247

  7. A homogeneous and "off-on" fluorescence aptamer-based assay for chloramphenicol using vesicle quantum dot-gold colloid composite probes.

    PubMed

    Miao, Yang-Bao; Ren, Hong-Xia; Gan, Ning; Zhou, You; Cao, Yuting; Li, Tianhua; Chen, Yinji

    2016-07-27

    In this work, a novel homogeneous and signal "off-on" aptamer based fluorescence assay was successfully developed to detect chloramphenicol (CAP) residues in food based on the fluorescence resonance energy transfer (FRET). The vesicle nanotracer was prepared through labeling single stranded DNA binding protein (SSB) on limposome-CdSe/ZnS quantum dot (SSB/L-QD) complexes. It was worth mentioning that the signal tracer (SSB/L-QD) with vesicle shape, which was fabricated being encapsulated with a number of quantum dots and SSB. The nanotracer has excellent signal amplification effects. The vesicle composite probe was formed by combining aptamer labeled nano-gold (Au-Apt) and SSB/L-QD. Which based on SSB's specific affinity towards aptamer. This probe can't emit fluoresce which is in "off" state because the signal from SSB/L-QD as donor can be quenched by the Au-aptas acceptor. When CAP was added in the composite probe solution, the aptamer on the Au-Apt can be preferentially bounded with CAP then release from the composite probe, which can turn the "off" signal of SSB/L-QD tracer into "on" state. The assay indicates excellent linear response to CAP from 0.001 nM to 10 nM and detection limit down to 0.3 pM. The vesicle probes with size of 88 nm have strong signal amplification. Because a larger number of QDs can be labeled inside the double phosphorus lipid membrane. Besides, it was employed to detect CAP residues in the milk samples with results being agreed well with those from ELISA, verifying its accuracy and reliability. PMID:27251948

  8. The extended wedge method: Atomic force microscope friction calibration for improved tolerance to instrument misalignments, tip offset, and blunt probes

    SciTech Connect

    Khare, H. S.; Burris, D. L.

    2013-05-15

    One of the major challenges in understanding and controlling friction is the difficulty in bridging the length and time scales of macroscale contacts and those of the single asperity interactions they comprise. While the atomic force microscope (AFM) offers a unique ability to probe tribological surfaces in a wear-free single-asperity contact, instrument calibration challenges have limited the usefulness of this technique for quantitative nanotribological studies. A number of lateral force calibration techniques have been proposed and used, but none has gained universal acceptance due to practical considerations, configuration limitations, or sensitivities to unknowable error sources. This paper describes a simple extension of the classic wedge method of AFM lateral force calibration which: (1) allows simultaneous calibration and measurement on any substrate, thus eliminating prior tip damage and confounding effects of instrument setup adjustments; (2) is insensitive to adhesion, PSD cross-talk, transducer/piezo-tube axis misalignment, and shear-center offset; (3) is applicable to integrated tips and colloidal probes; and (4) is generally applicable to any reciprocating friction coefficient measurement. The method was applied to AFM measurements of polished carbon (99.999% graphite) and single crystal MoS{sub 2} to demonstrate the technique. Carbon and single crystal MoS{sub 2} had friction coefficients of {mu}= 0.20 {+-} 0.04 and {mu}= 0.006 {+-} 0.001, respectively, against an integrated Si probe. Against a glass colloidal sphere, MoS{sub 2} had a friction coefficient of {mu}= 0.005 {+-} 0.001. Generally, the measurement uncertainties ranged from 10%-20% and were driven by the effect of actual frictional variation on the calibration rather than calibration error itself (i.e., due to misalignment, tip-offset, or probe radius).

  9. The extended wedge method: atomic force microscope friction calibration for improved tolerance to instrument misalignments, tip offset, and blunt probes.

    PubMed

    Khare, H S; Burris, D L

    2013-05-01

    One of the major challenges in understanding and controlling friction is the difficulty in bridging the length and time scales of macroscale contacts and those of the single asperity interactions they comprise. While the atomic force microscope (AFM) offers a unique ability to probe tribological surfaces in a wear-free single-asperity contact, instrument calibration challenges have limited the usefulness of this technique for quantitative nanotribological studies. A number of lateral force calibration techniques have been proposed and used, but none has gained universal acceptance due to practical considerations, configuration limitations, or sensitivities to unknowable error sources. This paper describes a simple extension of the classic wedge method of AFM lateral force calibration which: (1) allows simultaneous calibration and measurement on any substrate, thus eliminating prior tip damage and confounding effects of instrument setup adjustments; (2) is insensitive to adhesion, PSD cross-talk, transducer/piezo-tube axis misalignment, and shear-center offset; (3) is applicable to integrated tips and colloidal probes; and (4) is generally applicable to any reciprocating friction coefficient measurement. The method was applied to AFM measurements of polished carbon (99.999% graphite) and single crystal MoS2 to demonstrate the technique. Carbon and single crystal MoS2 had friction coefficients of μ = 0.20 ± 0.04 and μ = 0.006 ± 0.001, respectively, against an integrated Si probe. Against a glass colloidal sphere, MoS2 had a friction coefficient of μ = 0.005 ± 0.001. Generally, the measurement uncertainties ranged from 10%-20% and were driven by the effect of actual frictional variation on the calibration rather than calibration error itself (i.e., due to misalignment, tip-offset, or probe radius).

  10. Microrheology using a custom-made AFM

    NASA Astrophysics Data System (ADS)

    Kosgodagan Acharige, Sebastien; Benzaquen, Michael; Steinberger, Audrey

    In the past few years, a new method was developed to measure local properties of liquids (X. Xiong et al., Phys. Rev. E 80, 2009). This method consists of gluing a micron-sized glass fiber at the tip of an AFM cantilever and probing the liquid with it. In ENS Lyon, this method was perfected (C. Devailly et al., EPL, 106 5, 2014) with the help of an interferometer developped in the same laboratory (L. Bellon et al., Opt. Commun. 207 49, 2002 and P. Paolino et al., Rev. Sci. Instrum. 84, 2013), which background noise can reach 10-14 m /√{ Hz } . This method allows us to measure a wide range of viscosities (1 mPa . s to 500 mPa . s) of transparent and opaque fluids using a small sample volume ( 5 mL). In this presentation, I will briefly describe the interferometer developped in ENS Lyon, then explain precisely the microrheology measurements and then compare the experimental results to a model developped by M. Benzaquen. This work is supported financially by the ANR project NANOFLUIDYN (Grant Number ANR-13-BS10-0009).

  11. Quantitative nano-mechanics of biological cells with AFM

    NASA Astrophysics Data System (ADS)

    Sokolov, Igor

    2013-03-01

    The importance of study of living cells is hard to overestimate. Cell mechanics is a relatively young, yet not a well-developed area. Besides just a fundamental interest, large practical need has emerged to measure cell mechanics quantitatively. Recent studies revealed a significant correlation between stiffness of biological cells and various human diseases, such as cancer, malaria, arthritis, and even aging. However, really quantitative studies of mechanics of biological cells are virtually absent. It is not even clear if the cell, being a complex and heterogeneous object, can be described by the elastic modulus at all. Atomic force microscopy (AFM) is a natural instrument to study properties of cells in their native environments. Here we will demonstrate that quantitative measurements of elastic modulus of cells with AFM are possible. Specifically, we will show that the ``cell body'' (cell without ``brush'' surface layer, a non-elastic layer surrounding cells) typically demonstrates the response of a homogeneous elastic medium up to the deformation of 10-20%, but if and only if a) the cellular brush layer is taken into account, b) rather dull AFM probes are used. This will be justified with the help of the strong condition of elastic behavior of material: the elastic modulus is shown to be independent on the indentation depth. We will also demonstrate that an attempt either to ignore the brush layer or to use sharp AFM probes will result in the violation of the strong condition, which implies impossibility to use the concept of the elastic modulus to describe cell mechanics in such experiments. Examples of quantitative measurements of the Young's modulus of the cell body and the cell brush parameters will be given for various cells. Address when submitting: Clarkson University, Potsdam, NY 13699

  12. EDITORIAL: Colloidal suspensions Colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Petukhov, Andrei; Kegel, Willem; van Duijneveldt, Jeroen

    2011-05-01

    Special issue in honour of Henk Lekkerkerker's 65th birthday Professor Henk N W Lekkerkerker is a world-leading authority in the field of experimental and theoretical soft condensed matter. On the occasion of his 65th birthday in the summer of 2011, this special issue celebrates his many contributions to science. Henk Lekkerkerker obtained his undergraduate degree in chemistry at the University of Utrecht (1968) and moved to Calgary where he received his PhD in 1971. He moved to Brussels as a NATO fellow at the Université Libre de Bruxelles and was appointed to an assistant professorship (1974), an associate professorship (1977) and a full professorship (1980) in physical chemistry at the Vrije Universiteit Brussel. In 1985 he returned to The Netherlands to take up a professorship at the Van 't Hoff Laboratory, where he has been ever since. He has received a series of awards during his career, including the Onsager Medal (1999) of the University of Trondheim, the Bakhuys Roozeboom Gold Medal (2003) of the Royal Dutch Academy of Arts and Sciences (KNAW), the ECIS-Rhodia European Colloid and Interface Prize (2003), and the Liquid Matter Prize of the European Physical Society (2008). He was elected a member of KNAW in 1996, was awarded an Academy Chair position in 2005, and has held several visiting lectureships. Henk's work focuses on phase transitions in soft condensed matter, and he has made seminal contributions to both the theoretical and experimental aspects of this field. Here we highlight three major themes running through his work, and a few selected publications. So-called depletion interactions may lead to phase separation in colloid-polymer mixtures, and Henk realised that the partitioning of polymer needs to be taken into account to describe the phase behaviour correctly [1]. Colloidal suspensions can be used as model fluids, with the time- and length-scales involved leading to novel opportunities, notably the direct observation of capillary waves at a

  13. EDITORIAL: Colloidal suspensions Colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Petukhov, Andrei; Kegel, Willem; van Duijneveldt, Jeroen

    2011-05-01

    Special issue in honour of Henk Lekkerkerker's 65th birthday Professor Henk N W Lekkerkerker is a world-leading authority in the field of experimental and theoretical soft condensed matter. On the occasion of his 65th birthday in the summer of 2011, this special issue celebrates his many contributions to science. Henk Lekkerkerker obtained his undergraduate degree in chemistry at the University of Utrecht (1968) and moved to Calgary where he received his PhD in 1971. He moved to Brussels as a NATO fellow at the Université Libre de Bruxelles and was appointed to an assistant professorship (1974), an associate professorship (1977) and a full professorship (1980) in physical chemistry at the Vrije Universiteit Brussel. In 1985 he returned to The Netherlands to take up a professorship at the Van 't Hoff Laboratory, where he has been ever since. He has received a series of awards during his career, including the Onsager Medal (1999) of the University of Trondheim, the Bakhuys Roozeboom Gold Medal (2003) of the Royal Dutch Academy of Arts and Sciences (KNAW), the ECIS-Rhodia European Colloid and Interface Prize (2003), and the Liquid Matter Prize of the European Physical Society (2008). He was elected a member of KNAW in 1996, was awarded an Academy Chair position in 2005, and has held several visiting lectureships. Henk's work focuses on phase transitions in soft condensed matter, and he has made seminal contributions to both the theoretical and experimental aspects of this field. Here we highlight three major themes running through his work, and a few selected publications. So-called depletion interactions may lead to phase separation in colloid-polymer mixtures, and Henk realised that the partitioning of polymer needs to be taken into account to describe the phase behaviour correctly [1]. Colloidal suspensions can be used as model fluids, with the time- and length-scales involved leading to novel opportunities, notably the direct observation of capillary waves at a

  14. AFM tip effect on a thin liquid film.

    PubMed

    Ledesma-Alonso, R; Legendre, D; Tordjeman, Ph

    2013-06-25

    We study the interaction between an AFM probe and a liquid film deposited over a flat substrate. We investigate the effects of the physical and geometrical parameters, with a special focus on the film thickness E, the probe radius R, and the distance D between the probe and the free surface. Deformation profiles have been calculated from the numerical simulations of the Young-Laplace equation by taking into account the probe/liquid and the liquid/substrate interactions, characterized by the Hamaker constants, Hpl and Hls. We demonstrate that the deformation of a shallow film is determined by a particular characteristic length λF = (2πγE(4)/Hls)(1/2), resulting from the balance between the capillary force (γ is the surface tension) and the van der Waals liquid/substrate attraction. For the case of a bulk liquid, the extent of the interface deformation is simply controlled by the capillary length λC = (γ/Δρg)(1/2). These trends point out two asymptotic regimes, which in turn are bounded by two characteristic film thicknesses Eg = (Hls/2πΔρg)(1/4) and Eγ = (R(2)Hls/2πγ)(1/4). For E > Eg, the bulk behavior is recovered, and for E < Eγ, we show the existence of a particular shallow film regime in which a localized tip effect is observed. This tip effect is characterized by the small magnitude of the deformation and an important restriction of its radial extent λF localized below the probe. In addition, we have found that the film thickness has a significant effect on the threshold separation distance Dmin below which the irreversible jump-to-contact process occurs: Dmin is probe radius-dependent for the bulk whereas it is film-thickness-dependent for shallow films. These results have an important impact on the optimal AFM scanning conditions. PMID:23721486

  15. 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.

  16. Resonance Frequency Analysis for Surface-Coupled AFM Cantilever in Liquids

    SciTech Connect

    Mirman, B; Kalinin, Sergei V

    2008-01-01

    Shifts in the resonance frequencies of surface-coupled atomic force microscope (AFM) probes are used as the basis for the detection mechanisms in a number of scanning probe microscopy techniques including atomic force acoustic microscopy (AFAM), force modulation microscopy, and resonance enhanced piezoresponse force microscopy (PFM). Here, we analyze resonance characteristics for AFM cantilever coupled to surface in liquid environment, and derive approximate expressions for resonant frequencies as a function of vertical and lateral spring constant of the tip-surface junction. This analysis provides a simplified framework for the interpretation of AFAM and PFM data in ambient, liquid, and vacuum environments.

  17. Photophysics of carbon-60 colloids

    NASA Astrophysics Data System (ADS)

    Clements, Andrew F.

    The goal of this dissertation is to study the photophysics of suspensions of colloidal C60 particles to determine if their nonlinear optical (NLO) response is superior in any way to benchmark NLO materials such as molecular solutions of C60 and carbon black suspensions (CBS). C60 in molecular form is known to exhibit strong reverse saturable absorption (RSA) and it is posited that colloidal particles composed of many C60 molecules would maintain some degree of RSA behavior upon association, although some quenching is to be expected. CBS is known to have an NLO response that is dominated by nonlinear scattering resulting from a phase change due to heating of the carbon black particles by absorbed energy. Colloidal C 60 particles that are many nanometers in diameter are similar to CBS, so it is posited that they would also have a nonlinear scattering mechanism contributing to their NLO response. Three samples of C60 colloids are characterized by several techniques, along with two carbon black suspensions and one molecular solution of C60. Transmission electron microscopy is used to determine morphology. Femtosecond pump-probe spectroscopy is used to determine the absorption spectrum and the relaxation kinetics of the first excited singlet state. Nanosecond laser flash photolysis is used to determine the absorption spectrum and the relaxation kinetics of the first excited triplet state. Z-scan is used to determine triplet-triplet absorption cross-sections. An experiment is performed to determine the percentage of the input energy that is transmitted, scattered, or absorbed by each sample. Computer modeling is performed to compare the experimental results to theory. Results show that all materials that exhibit nonlinear scattering have a constant extinction coefficient in the nonlinear regime, implying a characteristic size for the scattering centers that is independent of input energy. Quenching processes in C60 colloids are found to be morphology dependent, with more

  18. Fabrication of cone-shaped boron doped diamond and gold nanoelectrodes for AFM-SECM

    NASA Astrophysics Data System (ADS)

    Avdic, A.; Lugstein, A.; Wu, M.; Gollas, B.; Pobelov, I.; Wandlowski, T.; Leonhardt, K.; Denuault, G.; Bertagnolli, E.

    2011-04-01

    We demonstrate a reliable microfabrication process for a combined atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM) measurement tool. Integrated cone-shaped sensors with boron doped diamond (BDD) or gold (Au) electrodes were fabricated from commercially available AFM probes. The sensor formation process is based on mature semiconductor processing techniques, including focused ion beam (FIB) machining, and highly selective reactive ion etching (RIE). The fabrication approach preserves the geometry of the original AFM tips resulting in well reproducible nanoscaled sensors. The feasibility and functionality of the fully featured tips are demonstrated by cyclic voltammetry, showing good agreement between the measured and calculated currents of the cone-shaped AFM-SECM electrodes.

  19. Fabrication of cone-shaped boron doped diamond and gold nanoelectrodes for AFM-SECM.

    PubMed

    Avdic, A; Lugstein, A; Wu, M; Gollas, B; Pobelov, I; Wandlowski, T; Leonhardt, K; Denuault, G; Bertagnolli, E

    2011-04-01

    We demonstrate a reliable microfabrication process for a combined atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM) measurement tool. Integrated cone-shaped sensors with boron doped diamond (BDD) or gold (Au) electrodes were fabricated from commercially available AFM probes. The sensor formation process is based on mature semiconductor processing techniques, including focused ion beam (FIB) machining, and highly selective reactive ion etching (RIE). The fabrication approach preserves the geometry of the original AFM tips resulting in well reproducible nanoscaled sensors. The feasibility and functionality of the fully featured tips are demonstrated by cyclic voltammetry, showing good agreement between the measured and calculated currents of the cone-shaped AFM-SECM electrodes.

  20. Fabrication of cone-shaped boron doped diamond and gold nanoelectrodes for AFM-SECM.

    PubMed

    Avdic, A; Lugstein, A; Wu, M; Gollas, B; Pobelov, I; Wandlowski, T; Leonhardt, K; Denuault, G; Bertagnolli, E

    2011-04-01

    We demonstrate a reliable microfabrication process for a combined atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM) measurement tool. Integrated cone-shaped sensors with boron doped diamond (BDD) or gold (Au) electrodes were fabricated from commercially available AFM probes. The sensor formation process is based on mature semiconductor processing techniques, including focused ion beam (FIB) machining, and highly selective reactive ion etching (RIE). The fabrication approach preserves the geometry of the original AFM tips resulting in well reproducible nanoscaled sensors. The feasibility and functionality of the fully featured tips are demonstrated by cyclic voltammetry, showing good agreement between the measured and calculated currents of the cone-shaped AFM-SECM electrodes. PMID:21368355

  1. Colloidal Dispersions

    NASA Astrophysics Data System (ADS)

    Russel, W. B.; Saville, D. A.; Schowalter, W. R.

    1992-03-01

    The book covers the physical side of colloid science from the individual forces acting between submicron particles suspended in a liquid through the resulting equilibrium and dynamic properties. The relevant forces include Brownian motion, electrostatic repulsion, dispersion attraction, both attraction and repulsion due to soluble polymer, and viscous forces due to relative motion between the particles and the liquid. The balance among Brownian motion and the interparticle forces decides the questions of stability and phase behavior. Imposition of external fields produces complex effects, i.e. electrokinetic phenomena (electric field), sedimentation (gravitational field), diffusion (concentration/chemical potential gradient), and non-Newtonian rheology (shear field). The treatment aims to impart a sound, quantitative understanding based on fundamental theory and experiments with well-characterized model systems. This broad grasp of the fundamentals lends insight and helps to develop the intuitive sense needed to isolate essential features of technological problems and design critical experiments. Some exposure to fluid mechanics, statistical mechanics, and electricity and magnetism is assumed, but each subject is reintroduced in a self-contained manner.

  2. Charge dynamics at heterojunctions for PbS/ZnO colloidal quantum dot solar cells probed with time-resolved surface photovoltage spectroscopy

    NASA Astrophysics Data System (ADS)

    Spencer, B. F.; Leontiadou, M. A.; Clark, P. C. J.; Williamson, A. I.; Silly, M. G.; Sirotti, F.; Fairclough, S. M.; Tsang, S. C. E.; Neo, D. C. J.; Assender, H. E.; Watt, A. A. R.; Flavell, W. R.

    2016-02-01

    Time-resolved laser-pump X-ray-photoemission-probe spectroscopy of a ZnO ( 10 1 ¯ 0 ) substrate with and without PbS quantum dots (QDs) chemically linked to the surface is performed, using laser photon energies resonant with and below the band gap energy of the substrate (λ = 372 and 640 nm, hν = 3.33 and 1.94 eV). Charge injection from the photoexcited QDs to ZnO is demonstrated through the change in the surface photovoltage of the ZnO substrate observed when the heterojunction is illuminated with 1.94 eV radiation. The measured carrier dynamics are limited by the persistent photoconductivity of ZnO, giving dark carrier lifetimes of the order of 200 μs in a depletion layer at the interface. The chemical specificity of soft X-rays is used to separately measure the charge dynamics in the quantum dots and the substrate, yielding evidence that the depletion region at the interface extends into the PbS QD layer.

  3. Colloids: current recommendations.

    PubMed

    Chan, Daniel L

    2008-05-01

    Colloids are increasingly becoming considered indispensable in the management of critically ill patients. Typical indications for colloid administration include patients with tissue edema, hypovolemia, and low oncotic pressure. Current guidelines for the use of colloids in veterinary patients balance the purported benefits of colloid fluid administration with the potential risks, such as volume overload and coagulation disturbances. This article focuses primarily on hydroxyethyl starches, because they are the most commonly used colloid in veterinary practice, and because recent advances in colloid therapy have been achieved with this colloid. Newer colloids have been modified to limit effects on the coagulation system, and they may be used to modulate the inflammatory response, which could prove to be particularly useful in the management of critically ill patients. A better understanding of how different fluids influence the host response may enable us to explore new applications of fluid replacement therapy beyond simply replenishing volume deficits.

  4. ezAFM: A low cost Atomic Force Microscope(AFM)

    NASA Astrophysics Data System (ADS)

    Celik, Umit; Celik, Kubra; Aslan, Husnu; Kehribar, Ihsan; Dede, Munir; Ozgur Ozer, H.; Oral, Ahmet

    2012-02-01

    A low cost AFM, ezAFM is developed for educational purposes as well as research. Optical beam deflection method is used to measure the deflection of cantilever. ezAFM scanner is built using voice coil motors (VCM) with ˜50x50x6 μm scan area. The microscope uses alignment free cantilevers, which minimizes setup times. FPGA based AFM feedback Control electronics is developed. FPGA technology allows us to drive all peripherals in parallel. ezAFM Controller is connected to PC by USB 2.0 interface as well as Wi-Fi. We have achieved <5nm lateral and ˜0.01nm vertical resolution. ezAFM can image single atomic steps in HOPG and mica. An optical microscope with <3 μm resolution is also integrated into the system. ezAFM supports different AFM operation modes such as dynamic mode, contact mode, lateral force microscopy. Advanced modes like magnetic force microscopy and electric force microscopy will be implemented later on. The new ezAFM system provides, short learning times for student labs, quick setup and easy to transport for portable applications with the best price/performance ratio. The cost of the system starts from 15,000, with system performance comparable with the traditional AFM systems.

  5. Colloidal Nanoantennas for Hyperspectral Chemical Mapping.

    PubMed

    Dill, Tyler J; Rozin, Matthew J; Palani, Stephen; Tao, Andrea R

    2016-08-23

    Tip-enhanced Raman spectroscopy enables access to chemical information with nanoscale spatial resolution and single-molecule sensitivities by utilizing optical probes that are capable of confining light to subwavelength dimensions. Because the probes themselves possess nanoscale features, they are notoriously difficult to fabricate, and more critically, can result in poor reproducibility. Here, we demonstrate high-performance, predictable, and readily tunable nanospectroscopy probes that are fabricated by self-assembly. Shaped metal nanoparticles are organized into dense layers and deposited onto scanning probe tips. When coupled to a metal surface, these probes behave like nanoantenna by supporting a strong optical resonance, producing dramatic Raman field enhancements in the range of 10(8)-10(9) with sub-50 nm spatial resolution. In contrast to other nanospectroscopy probes, our colloidal probes can be fabricated in a scalable fashion with a batch-to-batch reproducibility of ∼80% and serve as an important demonstration of bottom-up engineering. PMID:27454680

  6. AFM and electroanalytical studies of synthetic oligonucleotide hybridization.

    PubMed

    Chiorcea Paquim, A-M; Diculescu, V C; Oretskaya, T S; Oliveira Brett, A M

    2004-11-15

    The first and most important step in the development and manufacture of a sensitive DNA-biosensor for hybridization detection is the immobilization procedure of the nucleic acid probe on the transducer surface, maintaining its mobility and conformational flexibility. MAC Mode AFM images were used to demonstrate that oligonucleotide (ODN) molecules adsorb spontaneously at the electrode surface. After adsorption, the ODN layers were formed by molecules with restricted mobility, as well as by superposed molecules, which can lead to reduced hybridization efficiency. The images also showed the existence of pores in the adsorbed ODN film that revealed large parts of the electrode surface, and enabled non-specific adsorption of other ODNs on the uncovered areas. Electrostatic immobilization onto a clean glassy carbon electrode surface was followed by hybridization with complementary sequences and by control experiments with non-complementary sequences, studied using differential pulse voltammetry. The data obtained showed that non-specific adsorption strongly influenced the results, which depended on the sequence of the ODNs. In order to reduce the contribution of non-specific adsorbed ODNs during hybridization experiments, the carbon electrode surface was modified. After modification, the AFM images showed an electrode completely covered by the ODN probe film, which prevented the undesirable binding of target ODN molecules to the electrode surface. The changes of interfacial capacitance that took place after hybridization or control experiments showed the formation of a mixed multilayer that strongly depended on the local environment of the immobilized ODN.

  7. What Is a Colloid?

    ERIC Educational Resources Information Center

    Lamb, William G.

    1985-01-01

    Describes the properties of colloids, listing those commonly encountered (such as whipped cream, mayonnaise, and fog). Also presents several experiments using colloids and discusses "Silly Putty," a colloid with viscoelastic properties whose counterintuitive properties result from its mixture of polymers. (DH)

  8. Development and application of multiple-probe scanning probe microscopes.

    PubMed

    Nakayama, Tomonobu; Kubo, Osamu; Shingaya, Yoshitaka; Higuchi, Seiji; Hasegawa, Tsuyoshi; Jiang, Chun-Sheng; Okuda, Taichi; Kuwahara, Yuji; Takami, Kazuhiro; Aono, Masakazu

    2012-04-01

    In the research of advanced materials based on nanoscience and nanotechnology, it is often desirable to measure nanoscale local electrical conductivity at a designated position of a given sample. For this purpose, multiple-probe scanning probe microscopes (MP-SPMs), in which two, three or four scanning tunneling microscope (STM) or atomic force microscope (AFM) probes are operated independently, have been developed. Each probe in an MP-SPM is used not only for observing high-resolution STM or AFM images but also for forming an electrical contact enabling nanoscale local electrical conductivity measurement. The world's first double-probe STM (DP-STM) developed by the authors, which was subsequently modified to a triple-probe STM (TP-STM), has been used to measure the conductivities of one-dimensional metal nanowires and carbon nanotubes and also two-dimensional molecular films. A quadruple-probe STM (QP-STM) has also been developed and used to measure the conductivity of two-dimensional molecular films without the ambiguity of contact resistance between the probe and sample. Moreover, a quadruple-probe AFM (QP-AFM) with four conductive tuning-fork-type self-detection force sensing probes has been developed to measure the conductivity of a nanostructure on an insulating substrate. A general-purpose computer software to control four probes at the same time has also been developed and used in the operation of the QP-AFM. These developments and applications of MP-SPMs are reviewed in this paper.

  9. Development and Application of Multiple-Probe Scanning Probe Microscopes

    SciTech Connect

    Nakayama, T.; Kubo, O.; Shingaya, Y.; Higuchi, S.; Hasegawa, T.; Jiang, C. S.; Okuda, T.; Kuwahara, Y.; Takami, K.; Aono, M.

    2012-04-03

    the research of advanced materials based on nanoscience and nanotechnology, it is often desirable to measure nanoscale local electrical conductivity at a designated position of a given sample. For this purpose, multiple-probe scanning probe microscopes (MP-SPMs), in which two, three or four scanning tunneling microscope (STM) or atomic force microscope (AFM) probes are operated independently, have been developed. Each probe in an MP-SPM is used not only for observing high-resolution STM or AFM images but also for forming an electrical contact enabling nanoscale local electrical conductivity measurement. The world's first double-probe STM (DP-STM) developed by the authors, which was subsequently modified to a triple-probe STM (TP-STM), has been used to measure the conductivities of one-dimensional metal nanowires and carbon nanotubes and also two-dimensional molecular films. A quadruple-probe STM (QP-STM) has also been developed and used to measure the conductivity of two-dimensional molecular films without the ambiguity of contact resistance between the probe and sample. Moreover, a quadruple-probe AFM (QP-AFM) with four conductive tuning-fork-type self-detection force sensing probes has been developed to measure the conductivity of a nanostructure on an insulating substrate. A general-purpose computer software to control four probes at the same time has also been developed and used in the operation of the QP-AFM. These developments and applications of MP-SPMs are reviewed in this paper.

  10. Electrohydrodynamically patterned colloidal crystals

    NASA Technical Reports Server (NTRS)

    Hayward, Ryan C. (Inventor); Poon, Hak F. (Inventor); Xiao, Yi (Inventor); Saville, Dudley A. (Inventor); Aksay, Ilhan A. (Inventor)

    2003-01-01

    A method for assembling patterned crystalline arrays of colloidal particles using ultraviolet illumination of an optically-sensitive semiconducting anode while using the anode to apply an electronic field to the colloidal particles. The ultraviolet illumination increases current density, and consequently, the flow of the colloidal particles. As a result, colloidal particles can be caused to migrate from non-illuminated areas of the anode to illuminated areas of the anode. Selective illumination of the anode can also be used to permanently affix colloidal crystals to illuminated areas of the anode while not affixing them to non-illuminated areas of the anode.

  11. Microfluidic colloid filtration

    PubMed Central

    Linkhorst, John; Beckmann, Torsten; Go, Dennis; Kuehne, Alexander J. C.; Wessling, Matthias

    2016-01-01

    Filtration of natural and colloidal matter is an essential process in today’s water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a “cake layer” – often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level. PMID:26927706

  12. Saturated Zone Colloid Transport

    SciTech Connect

    H. Viswanathan; P. Reimus

    2003-09-05

    Colloid retardation is influenced by the attachment and detachment of colloids from immobile surfaces. This analysis demonstrates the development of parameters necessary to estimate attachment and detachment of colloids and, hence, retardation in both fractured tuff and porous alluvium. Field and experimental data specific to fractured tuff are used for the analysis of colloid retardation in fractured tuff. Experimental data specific to colloid transport in alluvial material from Yucca Mountain as well as bacteriophage field studies in alluvial material, which are thought to be good analogs for colloid transport, are used to estimate attachment and detachment of colloids in the alluvial material. There are no alternative scientific approaches or technical methods for calculating these retardation factors.

  13. Microfluidic colloid filtration

    NASA Astrophysics Data System (ADS)

    Linkhorst, John; Beckmann, Torsten; Go, Dennis; Kuehne, Alexander J. C.; Wessling, Matthias

    2016-03-01

    Filtration of natural and colloidal matter is an essential process in today’s water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a “cake layer” – often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level.

  14. Microfluidic colloid filtration.

    PubMed

    Linkhorst, John; Beckmann, Torsten; Go, Dennis; Kuehne, Alexander J C; Wessling, Matthias

    2016-01-01

    Filtration of natural and colloidal matter is an essential process in today's water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a "cake layer"--often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level. PMID:26927706

  15. Effective Forces Between Colloidal Particles

    NASA Technical Reports Server (NTRS)

    Tehver, Riina; Banavar, Jayanth R.; Koplik, Joel

    1999-01-01

    Colloidal suspensions have proven to be excellent model systems for the study of condensed matter and its phase behavior. Many of the properties of colloidal suspensions can be investigated with a systematic variation of the characteristics of the systems and, in addition, the energy, length and time scales associated with them allow for experimental probing of otherwise inaccessible regimes. The latter property also makes colloidal systems vulnerable to external influences such as gravity. Experiments performed in micro-ravity by Chaikin and Russell have been invaluable in extracting the true behavior of the systems without an external field. Weitz and Pusey intend to use mixtures of colloidal particles with additives such as polymers to induce aggregation and form weak, tenuous, highly disordered fractal structures that would be stable in the absence of gravitational forces. When dispersed in a polarizable medium, colloidal particles can ionize, emitting counterions into the solution. The standard interaction potential in these charged colloidal suspensions was first obtained by Derjaguin, Landau, Verwey and Overbeek. The DLVO potential is obtained in the mean-field linearized Poisson-Boltzmann approximation and thus has limited applicability. For more precise calculations, we have used ab initio density functional theory. In our model, colloidal particles are charged hard spheres, the counterions are described by a continuum density field and the solvent is treated as a homogeneous medium with a specified dielectric constant. We calculate the effective forces between charged colloidal particles by integrating over the solvent and counterion degrees of freedom, taking into account the direct interactions between the particles as well as particle-counterion, counterion-counterion Coulomb, counterion entropic and correlation contributions. We obtain the effective interaction potential between charged colloidal particles in different configurations. We evaluate two

  16. Active microrheology in a colloidal glass

    NASA Astrophysics Data System (ADS)

    Gruber, M.; Abade, G. C.; Puertas, A. M.; Fuchs, M.

    2016-10-01

    We study the dynamics of a probe particle driven by a constant force through a colloidal glass of hard spheres. This nonequilibrium and anisotropic problem is investigated using a new implementation of the mode-coupling approximation with multiple relaxation channels and Langevin dynamics simulations. A force threshold is found, below which the probe remains localized, while above it the probe acquires a finite velocity. We focus on the localized regime, comparing theory and simulations concerning the dynamics in the length scale of the cage and the properties of the transition to the delocalized regime, such as the critical power-law decay of the probe correlation function. Probe van Hove functions predicted by the theory show exponential tails reminiscent of an intermittent dynamics of the probe. This scenario is microscopically supported by simulations.

  17. Pair Potential of Charged Colloidal Stars

    NASA Astrophysics Data System (ADS)

    Huang, F.; Addas, K.; Ward, A.; Flynn, N. T.; Velasco, E.; Hagan, M. F.; Dogic, Z.; Fraden, S.

    2009-03-01

    We report on the construction of colloidal stars: 1μm polystyrene beads grafted with a dense brush of 1μm long and 10 nm wide charged semiflexible filamentous viruses. The pair interaction potentials of colloidal stars are measured using an experimental implementation of umbrella sampling, a technique originally developed in computer simulations in order to probe rare events. The influence of ionic strength and grafting density on the interaction is measured. Good agreements are found between the measured interactions and theoretical predictions based upon the osmotic pressure of counterions.

  18. Saturated Zone Colloid Transport

    SciTech Connect

    H. S. Viswanathan

    2004-10-07

    This scientific analysis provides retardation factors for colloids transporting in the saturated zone (SZ) and the unsaturated zone (UZ). These retardation factors represent the reversible chemical and physical filtration of colloids in the SZ. The value of the colloid retardation factor, R{sub col} is dependent on several factors, such as colloid size, colloid type, and geochemical conditions (e.g., pH, Eh, and ionic strength). These factors are folded into the distributions of R{sub col} that have been developed from field and experimental data collected under varying geochemical conditions with different colloid types and sizes. Attachment rate constants, k{sub att}, and detachment rate constants, k{sub det}, of colloids to the fracture surface have been measured for the fractured volcanics, and separate R{sub col} uncertainty distributions have been developed for attachment and detachment to clastic material and mineral grains in the alluvium. Radionuclides such as plutonium and americium sorb mostly (90 to 99 percent) irreversibly to colloids (BSC 2004 [DIRS 170025], Section 6.3.3.2). The colloid retardation factors developed in this analysis are needed to simulate the transport of radionuclides that are irreversibly sorbed onto colloids; this transport is discussed in the model report ''Site-Scale Saturated Zone Transport'' (BSC 2004 [DIRS 170036]). Although it is not exclusive to any particular radionuclide release scenario, this scientific analysis especially addresses those scenarios pertaining to evidence from waste-degradation experiments, which indicate that plutonium and americium may be irreversibly attached to colloids for the time scales of interest. A section of this report will also discuss the validity of using microspheres as analogs to colloids in some of the lab and field experiments used to obtain the colloid retardation factors. In addition, a small fraction of colloids travels with the groundwater without any significant retardation

  19. Comparison of the cohesion-adhesion balance approach to colloidal probe atomic force microscopy and the measurement of Hansen partial solubility parameters by inverse gas chromatography for the prediction of dry powder inhalation performance.

    PubMed

    Jones, Matthew D; Buckton, Graham

    2016-07-25

    The abilities of the cohesive-adhesive balance approach to atomic force microscopy (AFM) and the measurement of Hansen partial solubility parameters by inverse gas chromatography (IGC) to predict the performance of carrier-based dry powder inhaler (DPI) formulations were compared. Five model drugs (beclometasone dipropionate, budesonide, salbutamol sulphate, terbutaline sulphate and triamcinolone acetonide) and three model carriers (erythritol, α-lactose monohydrate and d-mannitol) were chosen, giving fifteen drug-carrier combinations. Comparison of the AFM and IGC interparticulate adhesion data suggested that they did not produce equivalent results. Comparison of the AFM data with the in vitro fine particle delivery of appropriate DPI formulations normalised to account for particle size differences revealed a previously observed pattern for the AFM measurements, with a slightly cohesive AFM CAB ratio being associated with the highest fine particle fraction. However, no consistent relationship between formulation performance and the IGC data was observed. The results as a whole highlight the complexity of the many interacting variables that can affect the behaviour of DPIs and suggest that the prediction of their performance from a single measurement is unlikely to be successful in every case.

  20. Comparison of the cohesion-adhesion balance approach to colloidal probe atomic force microscopy and the measurement of Hansen partial solubility parameters by inverse gas chromatography for the prediction of dry powder inhalation performance.

    PubMed

    Jones, Matthew D; Buckton, Graham

    2016-07-25

    The abilities of the cohesive-adhesive balance approach to atomic force microscopy (AFM) and the measurement of Hansen partial solubility parameters by inverse gas chromatography (IGC) to predict the performance of carrier-based dry powder inhaler (DPI) formulations were compared. Five model drugs (beclometasone dipropionate, budesonide, salbutamol sulphate, terbutaline sulphate and triamcinolone acetonide) and three model carriers (erythritol, α-lactose monohydrate and d-mannitol) were chosen, giving fifteen drug-carrier combinations. Comparison of the AFM and IGC interparticulate adhesion data suggested that they did not produce equivalent results. Comparison of the AFM data with the in vitro fine particle delivery of appropriate DPI formulations normalised to account for particle size differences revealed a previously observed pattern for the AFM measurements, with a slightly cohesive AFM CAB ratio being associated with the highest fine particle fraction. However, no consistent relationship between formulation performance and the IGC data was observed. The results as a whole highlight the complexity of the many interacting variables that can affect the behaviour of DPIs and suggest that the prediction of their performance from a single measurement is unlikely to be successful in every case. PMID:27265314

  1. Influence of smectite suspension structure on sheet orientation in dry sediments: XRD and AFM applications.

    PubMed

    Zbik, Marek S; Frost, Ray L

    2010-06-15

    The structure-building phenomena within clay aggregates are governed by forces acting between clay particles. Measurements of such forces are important to understand in order to manipulate the aggregate structure for applications such as dewatering of mineral processing tailings. A parallel particle orientation is required when conducting XRD investigation on the oriented samples and conduct force measurements acting between basal planes of clay mineral platelets using atomic force microscopy (AFM). To investigate how smectite clay platelets were oriented on silicon wafer substrate when dried from suspension range of methods like SEM, XRD and AFM were employed. From these investigations, we conclude that high clay concentrations and larger particle diameters (up to 5 microm) in suspension result in random orientation of platelets in the substrate. The best possible laminar orientation in the clay dry film, represented in the XRD 001/020 intensity ratio of 47 was obtained by drying thin layers from 0.02 wt.% clay suspensions of the natural pH. Conducted AFM investigations show that smectite studied in water based electrolytes show very long-range repulsive forces lower in strength than electrostatic forces from double-layer repulsion. It was suggested that these forces may have structural nature. Smectite surface layers rehydrate in water environment forms surface gel with spongy and cellular texture which cushion approaching AFM probe. This structural effect can be measured in distances larger than 1000 nm from substrate surface and when probe penetrate this gel layer, structural linkages are forming between substrate and clay covered probe. These linkages prevent subsequently smooth detachments of AFM probe on way back when retrieval. This effect of tearing new formed structure apart involves larger adhesion-like forces measured in retrieval. It is also suggested that these effect may be enhanced by the nano-clay particles interaction.

  2. 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.

  3. Hydration states of AFm cement phases

    SciTech Connect

    Baquerizo, Luis G.; Matschei, Thomas; Scrivener, Karen L.; Saeidpour, Mahsa; Wadsö, Lars

    2015-07-15

    The AFm phase, one of the main products formed during the hydration of Portland and calcium aluminate cement based systems, belongs to the layered double hydrate (LDH) family having positively charged layers and water plus charge-balancing anions in the interlayer. It is known that these phases present different hydration states (i.e. varying water content) depending on the relative humidity (RH), temperature and anion type, which might be linked to volume changes (swelling and shrinkage). Unfortunately the stability conditions of these phases are insufficiently reported. This paper presents novel experimental results on the different hydration states of the most important AFm phases: monocarboaluminate, hemicarboaluminate, strätlingite, hydroxy-AFm and monosulfoaluminate, and the thermodynamic properties associated with changes in their water content during absorption/desorption. This data opens the possibility to model the response of cementitious systems during drying and wetting and to engineer systems more resistant to harsh external conditions.

  4. Dynamic Assembly of Magnetic Colloidal Vortices.

    PubMed

    Mohorič, Tomaž; Kokot, Gašper; Osterman, Natan; Snezhko, Alexey; Vilfan, Andrej; Babič, Dušan; Dobnikar, Jure

    2016-05-24

    Magnetic colloids in external time-dependent fields are subject to complex induced many-body interactions governing their self-assembly into a variety of equilibrium and out-of-equilibrium structures such as chains, networks, suspended membranes, and colloidal foams. Here, we report experiments, simulations, and theory probing the dynamic assembly of superparamagnetic colloids in precessing external magnetic fields. Within a range of field frequencies, we observe dynamic large-scale structures such as ordered phases composed of precessing chains, ribbons, and rotating fluidic vortices. We show that the structure formation is inherently coupled to the buildup of torque, which originates from internal relaxation of induced dipoles and from transient correlations among the particles as a result of short-lived chain formation. We discuss in detail the physical properties of the vortex phase and demonstrate its potential in particle-coating applications. PMID:27128501

  5. SU-8 hollow cantilevers for AFM cell adhesion studies

    NASA Astrophysics Data System (ADS)

    Martinez, Vincent; Behr, Pascal; Drechsler, Ute; Polesel-Maris, Jérôme; Potthoff, Eva; Vörös, Janos; Zambelli, Tomaso

    2016-05-01

    A novel fabrication method was established to produce flexible, transparent, and robust tipless hollow atomic force microscopy (AFM) cantilevers made entirely from SU-8. Channels of 3 μm thickness and several millimeters length were integrated into 12 μm thick and 40 μm wide cantilevers. Connected to a pressure controller, the devices showed high sealing performance with no leakage up to 6 bars. Changing the cantilever lengths from 100 μm to 500 μm among the same wafer allowed the targeting of various spring constants ranging from 0.5 to 80 N m-1 within a single fabrication run. These hollow polymeric AFM cantilevers were operated in the optical beam deflection configuration. To demonstrate the performance of the device, single-cell force spectroscopy experiments were performed with a single probe detaching in a serial protocol more than 100 Saccharomyces cerevisiae yeast cells from plain glass and glass coated with polydopamine while measuring adhesion forces in the sub-nanoNewton range. SU-8 now offers a new alternative to conventional silicon-based hollow cantilevers with more flexibility in terms of complex geometric design and surface chemistry modification.

  6. SU-8 hollow cantilevers for AFM cell adhesion studies

    NASA Astrophysics Data System (ADS)

    Martinez, Vincent; Behr, Pascal; Drechsler, Ute; Polesel-Maris, Jérôme; Potthoff, Eva; Vörös, Janos; Zambelli, Tomaso

    2016-05-01

    A novel fabrication method was established to produce flexible, transparent, and robust tipless hollow atomic force microscopy (AFM) cantilevers made entirely from SU-8. Channels of 3 μm thickness and several millimeters length were integrated into 12 μm thick and 40 μm wide cantilevers. Connected to a pressure controller, the devices showed high sealing performance with no leakage up to 6 bars. Changing the cantilever lengths from 100 μm to 500 μm among the same wafer allowed the targeting of various spring constants ranging from 0.5 to 80 N m‑1 within a single fabrication run. These hollow polymeric AFM cantilevers were operated in the optical beam deflection configuration. To demonstrate the performance of the device, single-cell force spectroscopy experiments were performed with a single probe detaching in a serial protocol more than 100 Saccharomyces cerevisiae yeast cells from plain glass and glass coated with polydopamine while measuring adhesion forces in the sub-nanoNewton range. SU-8 now offers a new alternative to conventional silicon-based hollow cantilevers with more flexibility in terms of complex geometric design and surface chemistry modification.

  7. Analysis of colloid transport

    SciTech Connect

    Travis, B.J.; Nuttall, H.E.

    1985-12-31

    The population balance methodology is described and applied to the transport and capture of polydispersed colloids in packed columns. The transient model includes particle growth, capture, convective transport, and dispersion. We also follow the dynamic accumulation of captured colloids on the solids. The multidimensional parabolic partial differential equation was solved by a recently enhanced method of characteristics technique. This computational technique minimized numerical dispersion and is computationally very fast. The FORTRAN 77 code ran on a VAX-780 in less than a minute and also runs on an IBM-AT using the Professional FORTRAN compiler. The code was extensively tested against various simplified cases and against analytical models. The packed column experiments by Saltelli et al. were re-analyzed incorporating the experimentally reported size distribution of the colloid feed material. Colloid capture was modeled using a linear size dependent filtration function. The effects of a colloid size dependent filtration factor and various initial colloid size distributions on colloid migration and capture were investigated. Also, we followed the changing colloid size distribution as a function of position in the column. Some simple arguments are made to assess the likelihood of colloid migration at a potential NTS Yucca Mountain waste disposal site. 10 refs., 3 figs., 1 tab.

  8. UZ Colloid Transport Model

    SciTech Connect

    M. McGraw

    2000-04-13

    The UZ Colloid Transport model development plan states that the objective of this Analysis/Model Report (AMR) is to document the development of a model for simulating unsaturated colloid transport. This objective includes the following: (1) use of a process level model to evaluate the potential mechanisms for colloid transport at Yucca Mountain; (2) Provide ranges of parameters for significant colloid transport processes to Performance Assessment (PA) for the unsaturated zone (UZ); (3) Provide a basis for development of an abstracted model for use in PA calculations.

  9. AFM-assisted fabrication of thiol SAM pattern with alternating quantified surface potential

    PubMed Central

    2011-01-01

    Thiol self-assembled monolayers (SAMs) are widely used in many nano- and bio-technology applications. We report a new approach to create and characterize a thiol SAMs micropattern with alternating charges on a flat gold-coated substrate using atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). We produced SAMs-patterns made of alternating positively charged, negatively charged, and hydrophobic-terminated thiols by an automated AFM-assisted manipulation, or nanografting. We show that these thiol patterns possess only small topographical differences as revealed by AFM, and distinguished differences in surface potential (20-50 mV), revealed by KPFM. The pattern can be helpful in the development of biosensor technologies, specifically for selective binding of biomolecules based on charge and hydrophobicity, and serve as a model for creating surfaces with quantified alternating surface potential distribution. PMID:21711703

  10. Study on water-dispersible colloids in saline-alkali soils by atomic force microscopy and spectrometric methods.

    PubMed

    Liu, Zhiguo; Xu, Fengjie; Zu, Yuangang; Meng, Ronghua; Wang, Wenjie

    2016-06-01

    Recent studies have revealed that water-dispersible colloids play an important role in the transport of nutrients and contaminants in soils. In this study, water-dispersible colloids extracted from saline-alkali soils have been characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV absorption spectra. AFM observation indicated that the water-dispersible colloids contain some large plates and many small spherical particles. XRD, XPS, and UV absorption measurement revealed that the water-dispersible colloids are composed of kaolinite, illite, calcite, quartz and humic acid. In addition, UV absorption measurement demonstrated that the humic acids are associated with clay minerals. Water-dispersible colloids in the saline-alkali soils after hydrolyzed polymaleic anhydride treatment and an agricultural soil (nonsaline-alkali soil) were also investigated for comparison. The obtained results implied that the saline-alkali condition facilitates the formation of a large quantity of colloids. The use of AFM combined with spectrometric methods in the present study provides new knowledge on the colloid characteristics of saline-alkali soils. Microsc. Res. Tech. 79:525-531, 2016. © 2016 Wiley Periodicals, Inc.

  11. Magnetic Assisted Colloidal Pattern Formation

    NASA Astrophysics Data System (ADS)

    Yang, Ye

    Pattern formation is a mysterious phenomenon occurring at all scales in nature. The beauty of the resulting structures and myriad of resulting properties occurring in naturally forming patterns have attracted great interest from scientists and engineers. One of the most convenient experimental models for studying pattern formation are colloidal particle suspensions, which can be used both to explore condensed matter phenomena and as a powerful fabrication technique for forming advanced materials. In my thesis, I have focused on the study of colloidal patterns, which can be conveniently tracked in an optical microscope yet can also be thermally equilibrated on experimentally relevant time scales, allowing for ground states and transitions between them to be studied with optical tracking algorithms. In particular, I have focused on systems that spontaneously organize due to particle-surface and particle-particle interactions, paying close attention to systems that can be dynamically adjusted with an externally applied magnetic or acoustic field. In the early stages of my doctoral studies, I developed a magnetic field manipulation technique to quantify the adhesion force between particles and surfaces. This manipulation technique is based on the magnetic dipolar interactions between colloidal particles and their "image dipoles" that appear within planar substrate. Since the particles interact with their own images, this system enables massively parallel surface force measurements (>100 measurements) in a single experiment, and allows statistical properties of particle-surface adhesion energies to be extracted as a function of loading rate. With this approach, I was able to probe sub-picoNewton surface interactions between colloidal particles and several substrates at the lowest force loading rates ever achieved. In the later stages of my doctoral studies, I focused on studying patterns formed from particle-particle interaction, which serve as an experimental model of

  12. An approach towards 3D sensitive AFM cantilevers

    NASA Astrophysics Data System (ADS)

    Koops, Richard; Fokkema, Vincent

    2014-04-01

    The atomic force microscope (AFM) tapping mode is a highly sensitive local probing technique that is very useful to study and measure surface properties down to the atomic scale. The tapping mode is mostly implemented using the resonance of the first bending mode of the cantilever and therefore provides sensitivity mainly along the direction of this oscillation. Driven by the semiconductor industry, there is an increasing need for accurate measurements of nanoscale structures for side wall characterization by AFM that requires additional sensitivity in the lateral direction. The conventional tapping mode has been augmented by various authors, for example by tilting the cantilever system (Cho et al 2011 Rev. Sci. Instrum. 82 023707) to access the sidewall or using a torsion mode (Dai et al 2011 Meas. Sci. Technol. 22 094009) of the cantilever to provide additional lateral sensitivity. These approaches however trade lateral sensitivity for vertical sensitivity or still lack sensitivity in the remaining lateral direction. We present an approach towards true 3D sensitivity for AFM cantilevers based on simultaneous excitation and optical detection of multiple cantilever resonance modes along three axes. Tuning the excitation of the cantilever to specific frequencies provides a mechanism to select only those cantilever modes that have the desired characteristics. Additionally, cantilever engineering has been used to design and create a substructure within the cantilever that has been optimized for specific resonance behavior around 4 MHz. In contrast to the conventional approach of using a piezo to actuate the cantilever modulation, we present results on photo-thermal excitation using an intensity modulated low-power laser source. By tightly focusing the excitation spot on the cantilever we were able to attain a deflection efficiency of 0.7 nm µW-1 for the first bending mode. The presented approach results in an efficient all optical excitation and deflection detection

  13. AFM Bio-Mechanical Investigation of the Taxol Treatment of Breast Cancer Cells

    NASA Astrophysics Data System (ADS)

    Smith, Dylan; Patel, Dipika; Monjaraz, Fernando; Park, Soyeun

    2009-10-01

    Cancerous cells are known to be softer and easier to deform than normal cells. Changes in mechanical properties originate from the alteration of the actin cytoskeleton. The mechanism of cancer treatment using Taxol is related to the stabilization of microtubules. It has been shown that Taxol binds to polymerized tublin, stabilizes it against disassembly, and consequently inhibits cell division. An accurate quantitative study still lacks to relate the microtubule stabilizing effect with the cellular mechanical properties. We utilized our AFM to study changes in elastic properties of treated breast cancer cells. The AFM has several advantages for precise force measurements on a localized region with nanometer lateral dimension. In previous AFM studies, measurable contributions from the underlying hard substrate have been an obstacle to accurately determine the properties on thin samples. We modified our AFM tip to obtain the exact deformation profile as well as reducing the high stresses produced. We have probed depth profiles of mechanical properties of the taxol-treated and untreated cells by varying the indentation depth of the AFM-nanoindenting experiments.

  14. Adsorption Behavior of Cellulose and Its Derivatives toward Ag(I) in Aqueous Medium: An AFM, Spectroscopic, and DFT Study.

    PubMed

    Zhu, Chuantao; Dobryden, Illia; Rydén, Jens; Öberg, Sven; Holmgren, Allan; Mathew, Aji P

    2015-11-17

    The aim of this study was to develop a fundamental understanding of the adsorption behavior of metal ions on cellulose surfaces using experimental techniques supported by computational modeling, taking Ag(I) as an example. Force interactions among three types of cellulose microspheres (native cellulose and its derivatives with sulfate and phosphate groups) and the silica surface in AgNO3 solution were studied with atomic force microscopy (AFM) using the colloidal probe technique. The adhesion force between phosphate cellulose microspheres (PCM) and the silica surface in the aqueous AgNO3 medium increased significantly with increasing pH while the adhesion force slightly decreased for sulfate cellulose microspheres (SCM), and no clear adhesion force was observed for native cellulose microspheres (CM). The stronger adhesion enhancement for the PCM system is mainly attributed to the electrostatic attraction between Ag(I) and the negative silica surface. The observed force trends were in good agreement with the measured zeta potentials. The scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analyses confirmed the presence of silver on the surface of cellulose microspheres after adsorption. This study showed that PCM with a high content of phosphate groups exhibited a larger amount of adsorbed Ag(I) than CM and SCM and possible clustering of Ag(I) to nanoparticles. The presence of the phosphate group and a wavenumber shift of the P-OH vibration caused by the adsorption of silver ions on the phosphate groups were further confirmed with computational studies using density functional theory (DFT), which gives support to the above findings regarding the adsorption and clustering of Ag(I) on the cellulose surface decorated with phosphate groups as well as IR spectra.

  15. Interface colloidal robotic manipulator

    DOEpatents

    Aronson, Igor; Snezhko, Oleksiy

    2015-08-04

    A magnetic colloidal system confined at the interface between two immiscible liquids and energized by an alternating magnetic field dynamically self-assembles into localized asters and arrays of asters. The colloidal system exhibits locomotion and shape change. By controlling a small external magnetic field applied parallel to the interface, structures can capture, transport, and position target particles.

  16. Difference in cellular mechanics of cancer and normal cervical cells as seen with the AFM

    NASA Astrophysics Data System (ADS)

    Sokolov, Igor; Iyer, Swaminathan; Subba-Rao, Venkatesh; Woodworth, Craig

    2006-03-01

    Oncogenically transformed cells differ from their normal counter parts in many aspects, including organization and the amount of cytoskeleton. Consequently it is natural to expect to see the difference in cellular mechanics. Here we will present the study of such differences by using atomic force microscopy (AFM) in-vitro. So far the present research is the first study of mechanics of cervical cells, and the third comparative study of differences between mechanics of cancer and normal cells down with the help of AFM. Using a micron size silica ball as the AFM probe, we presumably do not overstress the cell surface as it can be in the case of the sharp AFM tip, and consequently, we may use the classical Hertz model. In contrast to the reported previously studies (bladder and fibroblast cells), we found that oncogenically transformed cervical cells are more rigid than the normal cells. The reason for such difference will be discussed. To demonstrate the complexity of the problem, we study cell mechanics in detail. The Young's modulus of rigidity clearly shows two separate regions of rigidity depending on the depth of the probe penetration. There may be two alternative explanations of the difference in rigidity of this top layer: it is either the cell membrane layer or detected long-range (presumably steric) forces due to the molecular ``brush'' of glycocalyx molecules. Experiments and modal calculations will be presented to choose between these two possibilities.

  17. AFM nanoindentations of diatom biosilica surfaces.

    PubMed

    Losic, Dusan; Short, Ken; Mitchell, James G; Lal, Ratnesh; Voelcker, Nicolas H

    2007-04-24

    Diatoms have intricately and uniquely nanopatterned silica exoskeletons (frustules) and are a common target of biomimetic investigations. A better understanding of the diatom frustule structure and function at the nanoscale could provide new insights for the biomimetic fabrication of nanostructured ceramic materials and lightweight, yet strong, scaffold architectures. Here, we have mapped the nanoscale mechanical properties of Coscinodiscus sp. diatoms using atomic force microscopy (AFM)-based nanoindentation. Mechanical properties were correlated with the frustule structures obtained from high-resolution AFM and scanning electron microscopy (SEM). Significant differences in the micromechanical properties for the different frustule layers were observed. A comparative study of other related inorganic material including porous silicon films and free-standing membranes as well as porous alumina was also undertaken.

  18. Detection of Pathogens Using AFM and SPR

    NASA Astrophysics Data System (ADS)

    Vaseashta, Ashok

    2005-03-01

    A priori detection of pathogens in food and water has become a subject of paramount importance. Several recent incidents have resulted in the government passing stringent regulations for tolerable amounts of contamination of food products. Identification and/or monitoring of bacterial contamination in food are critical. The conventional methods of pathogen detection require time-consuming steps to arrive disembark at meaningful measurement in a timely manner as the detection time exceeds the time in which perishable food recycles through the food chain distribution. The aim of this presentation is to outline surface plasmon resonance (SPR) and atomic force microscopy (AFM) as two methods for fast detect6ion of pathogens. Theoretical basis of SPR and experimental results of SPR and AFM on E. coli O157:H7 and prion are presented.

  19. If mechanics of cells can be described by elastic modulus in AFM indentation experiments?

    NASA Astrophysics Data System (ADS)

    Sokolov, Igor; Dokukin, Maxim; Guz, Nataliia; Kalaparthi, Vivekanand

    2014-03-01

    We study the question if cells, being highly heterogeneous objects, can be described with an elastic modulus (the Young's modulus) in a self-consistent way. We analyze the elastic modulus using indentation done with AFM of human cervical epithelial cells. Both sharp (cone) and dull AFM probes were used. The indentation data collected were processed through different elastic models. The cell was considered as a homogeneous elastic medium which had either smooth spherical boundary (Hertz/Sneddon models) or the boundary covered with a layer of glycocalyx and membrane protrusions (``brush'' models). Validity of these approximations was investigated. Specifically, we tested the independence of the elastic modulus of the indentation depth, which is assumed in these models. We demonstrate that only one model shows consistency with treating cells as homogeneous elastic medium, the bush model when processing the indentation data collected with the dull probe. The elastic modulus demonstrates strong depth dependence in all other three models. We conclude that it is possible to describe the elastic properties of the cell body by means of an effective elastic modulus in a self-consistent way when using the brush model to analyze data collected with a dull AFM probe.

  20. Understanding the TERS Effect with On-line Tunneling and Force Feedback Using Multiprobe AFM/NSOM with Raman Integration

    NASA Astrophysics Data System (ADS)

    Lewis, Aaron; Dekhter, Rimma; Hamra, Patricia; Bar-David, Yossi; Taha, Hesham

    Tip enhanced Raman scattering (TERS) has evolved in several directions over the past years. The data from this variety of methodologies has now accumulated to the point that there is a reasonable possibility of evolving an understanding of the underlying cause of the resulting effects that could be the origin of the various TERS enhancement processes. The objective of this presentation is to use the results thus far with atomic force microscopy (AFM) probes with noble metal coating, etching, transparent gold nanoparticles with and without a second nanoparticle [Wang and Schultz, ANALYST 138, 3150 (2013)] and tunneling feedback probes [R. Zhang et. al., NATURE 4 9 8, 8 2 (2013)]. We attempt at understanding this complex of results with AFM/NSOM multiprobe techniques. Results indicate that TERS is dominated by complex quantum interactions. This produces a highly confined and broadband plasmon field with all k vectors for effective excitation. Normal force tuning fork feedback with exposed tip probes provides an excellent means to investigate these effects with TERS probes that we have shown can circumvent the vexing problem of jump to contact prevalent in conventional AFM methodology and permit on-line switching between tunneling and AFM feedback modes of operation.

  1. AFM studies of semicrystalline polymer/inorganic nanocomposites

    NASA Astrophysics Data System (ADS)

    Strawhecker, Kenneth E.

    2002-01-01

    The aims of this work are to elucidate the effects of interaction strength on the crystallization of a polymer near an inorganic surface; connect filler induced polymer crystallinity with resulting property changes, especially for strongly interacting (i.e. hydrogen bonding) systems; and to devise atomic force microscopy (AFM) methods for probing the crystallinity and properties of polymer/layered silicate systems at the nanometer level. Three inorganically filled systems were studied: (1) poly(vinyl alcohol) (PVA), (2) poly(ethylene oxide) (PEO), and (3) polypropylene (PP). Since it has the strongest, interactions, the PVA system is investigated first. AFM is used in conjunction with x-ray diffraction and differential scanning calorimetry (DSC) to show that strong polymer/filler interactions can promote a different crystalline structure and a different morphology than those seen in the bulk. The study then proceeds to the weakly interacting PEO/inorganic system where it is found that the inorganic layers disrupt crystalline morphology, but do not change the crystal structure. Furthermore, crystallization always occurs in volumes away from the inorganic filler. The third system (neutral interactions), PP/inorganic is then discussed. The three systems are compared with each other, and is found that the crystalline morphology and structure is highly dependent upon the strength of interaction between the polymer and filler. Due to its far-reaching morphology changes, the strongly interacting system was chosen for property studies. The composite structure study revealed a coexistence of exfoliated and intercalated MMT layers, especially for low and moderate silicate loadings. The inorganic layers promote a new crystalline phase different than the one of the respective neat PVA, characterized by higher melting temperature and a different crystal structure. This new crystal phase reflects on the composite materials properties, which have mechanical, thermal, and water

  2. BOREAS AFM-6 Surface Meteorological Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from the National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) collected surface meteorological data from 21 May to 20 Sep 1994 near the Southern Study Area-Old Jack Pine (SSA-OJP) tower site. The data are in tabular ASCII files. The surface meteorological data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  3. Accurate calibration and uncertainty estimation of the normal spring constant of various AFM cantilevers.

    PubMed

    Song, Yunpeng; Wu, Sen; Xu, Linyan; Fu, Xing

    2015-03-10

    Measurement of force on a micro- or nano-Newton scale is important when exploring the mechanical properties of materials in the biophysics and nanomechanical fields. The atomic force microscope (AFM) is widely used in microforce measurement. The cantilever probe works as an AFM force sensor, and the spring constant of the cantilever is of great significance to the accuracy of the measurement results. This paper presents a normal spring constant calibration method with the combined use of an electromagnetic balance and a homemade AFM head. When the cantilever presses the balance, its deflection is detected through an optical lever integrated in the AFM head. Meanwhile, the corresponding bending force is recorded by the balance. Then the spring constant can be simply calculated using Hooke's law. During the calibration, a feedback loop is applied to control the deflection of the cantilever. Errors that may affect the stability of the cantilever could be compensated rapidly. Five types of commercial cantilevers with different shapes, stiffness, and operating modes were chosen to evaluate the performance of our system. Based on the uncertainty analysis, the expanded relative standard uncertainties of the normal spring constant of most measured cantilevers are believed to be better than 2%.

  4. High spatial resolution surface imaging and analysis of fungal cells using SEM and AFM.

    PubMed

    Kaminskyj, Susan G W; Dahms, Tanya E S

    2008-06-01

    We review the use of scanning electron microscopy (SEM), atomic force microscopy (AFM) and force spectroscopy (FS) for probing the ultrastructure, chemistry, physical characteristics and motion of fungal cells. When first developed, SEM was used to image fixed/dehydrated/gold coated specimens, but here we describe more recent SEM developments as they apply to fungal cells. CryoSEM offers high resolution for frozen fungal samples, whereas environmental SEM allows the analysis of robust samples (e.g. spores) under ambient conditions. Dual beam SEM, the most recently developed, adds manipulation capabilities along with element detection. AFM has similar lateral and better depth resolution compared to SEM, and can image live cells including growing fungal hyphae. FS can analyze cell wall chemistry, elasticity and dynamic cell characteristics. The integration of AFM with optical microscopy will allow examination of individual molecules or cellular structures in the context of fungal cell architecture. SEM and AFM are complementary techniques that are clarifying our understanding of fungal biology. PMID:18068995

  5. Single-Molecule Studies of Integrins by AFM-Based Force Spectroscopy on Living Cells

    NASA Astrophysics Data System (ADS)

    Eibl, Robert H.

    The characterization of cell adhesion between two living cells at the single-molecule level, i.e., between one adhesion receptor and its counter-receptor, appears to be an experimental challenge. Atomic force microscopy (AFM) can be used in its force spectroscopy mode to determine unbinding forces of a single pair of adhesion receptors, even with a living cell as a probe. This chapter provides an overview of AFM force measurements of the integrin family of cell adhesion receptors and their ligands. A focus is given to major integrins expressed on leukocytes, such as lymphocyte function-associated antigen 1 (LFA-1) and very late antigen 4 (VLA-4). These receptors are crucial for leukocyte trafficking in health and disease. LFA-1 and VLA-1 can be activated within the bloodstream from a low-affinity to a high-affinity receptor by chemokines in order to adhere strongly to the vessel wall before the receptor-bearing leukocytes extravasate. The experimental considerations needed to provide near-physiological conditions for a living cell and to be able to measure adequate forces at the single-molecule level are discussed in detail. AFM technology has been developed into a modern and extremely sensitive tool in biomedical research. It appears now that AFM force spectroscopy could enter, within a few years, medical applications in diagnosis and therapy of cancer and autoimmune diseases.

  6. Spherical colloidal photonic crystals.

    PubMed

    Zhao, Yuanjin; Shang, Luoran; Cheng, Yao; Gu, Zhongze

    2014-12-16

    CONSPECTUS: Colloidal photonic crystals (PhCs), periodically arranged monodisperse nanoparticles, have emerged as one of the most promising materials for light manipulation because of their photonic band gaps (PBGs), which affect photons in a manner similar to the effect of semiconductor energy band gaps on electrons. The PBGs arise due to the periodic modulation of the refractive index between the building nanoparticles and the surrounding medium in space with subwavelength period. This leads to light with certain wavelengths or frequencies located in the PBG being prohibited from propagating. Because of this special property, the fabrication and application of colloidal PhCs have attracted increasing interest from researchers. The most simple and economical method for fabrication of colloidal PhCs is the bottom-up approach of nanoparticle self-assembly. Common colloidal PhCs from this approach in nature are gem opals, which are made from the ordered assembly and deposition of spherical silica nanoparticles after years of siliceous sedimentation and compression. Besides naturally occurring opals, a variety of manmade colloidal PhCs with thin film or bulk morphology have also been developed. In principle, because of the effect of Bragg diffraction, these PhC materials show different structural colors when observed from different angles, resulting in brilliant colors and important applications. However, this angle dependence is disadvantageous for the construction of some optical materials and devices in which wide viewing angles are desired. Recently, a series of colloidal PhC materials with spherical macroscopic morphology have been created. Because of their spherical symmetry, the PBGs of spherical colloidal PhCs are independent of rotation under illumination of the surface at a fixed incident angle of the light, broadening the perspective of their applications. Based on droplet templates containing colloidal nanoparticles, these spherical colloidal PhCs can be

  7. Mean-field microrheology of a very soft colloidal suspension: Inertia induces shear thickening.

    PubMed

    Démery, Vincent

    2015-06-01

    Colloidal suspensions have a rich rheology and can exhibit shear thinning as well as shear thickening. Numerical simulations recently suggested that shear-thickening may be attributed to the inertia of the colloids, besides the hydrodynamic interactions between them. Here, we consider the ideal limit of a dense bath of soft colloids following an underdamped Langevin dynamics. We use a mean-field equation for the colloidal density to get an analytical expression of the drag force felt by a probe pulled at constant velocity through the suspension. Our results show that inertia can indeed induce shear thickening by allowing density waves to propagate through the suspension.

  8. Structural insight into iodide uptake by AFm phases.

    PubMed

    Aimoz, Laure; Wieland, Erich; Taviot-Guého, Christine; Dähn, Rainer; Vespa, Marika; Churakov, Sergey V

    2012-04-01

    The ability of cement phases carrying positively charged surfaces to retard the mobility of (129)I, present as iodide (I(-)) in groundwater, was investigated in the context of safe disposal of radioactive waste. (125)I sorption experiments on ettringite, hydrotalcite, chloride-, carbonate- and sulfate-containing AFm phases indicated that calcium-monosulfate (AFm-SO(4)) is the only phase that takes up trace levels of iodide. The structures of AFm phases prepared by coprecipitating iodide with other anions were investigated in order to understand this preferential uptake mechanism. X-ray diffraction (XRD) investigations showed a segregation of monoiodide (AFm-I(2)) and Friedel's salt (AFm-Cl(2)) for I-Cl mixtures, whereas interstratifications of AFm-I(2) and hemicarboaluminate (AFm-OH-(CO(3))(0.5)) were observed for the I-CO(3) systems. In contrast, XRD measurements indicated the formation of a solid solution between AFm-I(2) and AFm-SO(4) for the I-SO(4) mixtures. Extended X-ray absorption fine structure spectroscopy showed a modification of the coordination environment of iodine in I-CO(3) and in I-SO(4) samples compared to pure AFm-I(2). This is assumed to be due to the introduction of stacking faults in I-CO(3) samples on one hand and due to the presence of sulfate and associated space-filling water molecules as close neighbors in I-SO(4) samples on the other hand. The formation of a solid solution between AFm-I(2) and AFm-SO(4), with a short-range mixing of iodide and sulfate, implies that AFm-SO(4) bears the potential to retard (129)I. PMID:22376086

  9. Bacterial adhesion to protein-coated surfaces: An AFM and QCM-D study

    NASA Astrophysics Data System (ADS)

    Strauss, Joshua; Liu, Yatao; Camesano, Terri A.

    2009-09-01

    Bacterial adhesion to biomaterials, mineral surfaces, or other industrial surfaces is strongly controlled by the way bacteria interact with protein layers or organic matter and other biomolecules that coat the materials. Despite this knowledge, many studies of bacterial adhesion are performed under clean conditions, instead of in the presence of proteins or organic molecules. We chose fetal bovine serum (FBS) as a model protein, and prepared FBS films on quartz crystals. The thickness of the FBS layer was characterized using atomic force microscopy (AFM) imaging under liquid and quartz crystal microbalance with dissipation (QCM-D). Next, we characterized how the model biomaterial surface would interact with the nocosomial pathogen Staphylococcus epidermidis. An AFM probe was coated with S. epidermidis cells and used to probe a gold slide that had been coated with FBS or another protein, fibronectin (FN). These experiments show that AFM and QCM-D can be used in complementary ways to study the complex interactions between bacteria, proteins, and surfaces.

  10. 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.

  11. Interactions between colloidal particles in the presence of an ultrahighly charged amphiphilic polyelectrolyte.

    PubMed

    Yu, Danfeng; Yang, Hui; Wang, Hui; Cui, Yingxian; Yang, Guang; Zhang, Jian; Wang, Jinben

    2014-12-01

    A novel amphiphilic polyelectrolyte denoted as PAGC8 and a traditional amphiphilic polyelectrolyte denoted as PASC8 were prepared. PAGC8 consisted of gemini-type surfactant segment based on 1,3-bis (N,N-dimethyl-N-octylammonium)-2-propyl acrylate dibromide, while PASC8 incorporated acryloyloxyethyl-N,N-dimethyl-N-dodecylammonium bromide as single chain surfactant units within its repeat unit structure. Turbidity, stability, and zeta potential measurements were performed in the presence of PAGC8 and PASC8, respectively, to evaluate their effectiveness in inducing solid/liquid separations. It was found that the maximum transmittance was observed before the zeta potential values reached the isoelectric point, implying that not only charge neutralization but also charge-patch mechanism contributed to the separation process. Colloid probe atomic force microscopy technique was introduced to directly determine the interactions between surfaces in the presence of ultrahighly charged amphiphilic polyelectrolyte. On the basis of the AFM results, we have successfully interpreted the influence of the charge density of the polyelectrolytes on the phase stability. Electrostatic interaction played the dominant role in the flocculation processes, although both electrostatic interaction and hydrophobic effect provided contributions to the colloidal dispersions. The attractions upon surfaces approach in the case of PAGC8 were significantly larger than that of PASC8 due to the higher charge density. The strong peeling events upon retraction in the presence of PAGC8 implied that the hydrophobic effect was stronger than that of PASC8, which displayed the loose pulling events. A strong attraction was identified at shorter separation distances for both systems. However, these interactions cannot be successfully described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloid stability due to the participation of charge-patch and strong hydrophobic effect. To account for the

  12. Entropic attractions in colloid-polymer solutions

    NASA Astrophysics Data System (ADS)

    Verma, Ritu

    We explore the depletion attractions that arise between hard colloidal spheres immersed in a non-adsorbing polymeric solution of DNA molecules. Using a scanning optical tweezer we were able to spatially confine colloidal particles along a line and quantitatively examine the interaction potential between two 1.25 m m silica spheres moving in various complex fluids. At fixed DNA concentration, we found that the range and depth of the inter-particle potentials did not change for background salt concentrations between 0.1 and 20 mM. Then we fixed the background salt concentration at 10 mM, and measured the inter-particle potentials as a function of DNA concentration. The potentials obtained display variations in depth and range that are consistent with scaling behavior expected for semi-flexible polymers near the theta point. In particular we clearly observe the crossover from a dilute solution of Gaussian coils to the weakly fluctuating semi-dilute regime dominated by two-point collisions. We also quantitatively test the Asakura-Oosawa Model for these systems and show how it can be used in both the dilute as well as the semi-dilute regime. We also explore the dynamics of colloidal particles in background DNA solutions. We find that the Stokes-Einstein picture breaks down in these complex fluids as the size ratio of the probe particle to the characteristic polymer length scale is decreased. We explain these deviations in terms of the changes in the microenvironment caused by the presence of the depletion cavity. The colloidal spheres were also used to probe the transition time scales from the viscoelastic regime to the purely viscous regime.

  13. Anisotropic Model Colloids

    NASA Astrophysics Data System (ADS)

    van Kats, C. M.

    2008-10-01

    The driving forces for fundamental research in colloid science are the ability to manage the material properties of colloids and to unravel the forces that play a role between colloids to be able to control and understand the processes where colloids play an important role. Therefore we are searching for colloidal materials with specific physical properties to better understand our surrounding world.Until recently research in colloid science was mainly focused on spherical (isotropic) particles. Monodisperse spherical colloids serve as a model system as they exhibit similar phase behaviour as molecular and atomic systems. Nevertheless, in many cases the spherical shape is not sufficient to reach the desired research goals. Recently the more complex synthesis methods of anisotropic model colloids has strongly developed. This thesis should be regarded as a contribution to this research area. Anisotropic colloids can be used as a building block for complex structures and are expected not only to lead to the construction of full photonic band gap materials. They will also serve as new, more realistic, models systems for their molecular analogues. Therefore the term ‘molecular colloids” is sometimes used to qualify these anisotropic colloidal particles. In the introduction of this thesis, we give an overview of the main synthesis techniques for anisotropic colloids. Chapter 2 describes the method of etching silicon wafers to construct monodisperse silicon rods. They subsequently were oxidized and labeled (coated) with a fluorescent silica layer. The first explorative phase behaviour of these silica rods was studied. The particles showed a nematic ordering in charge stabilized suspensions. Chapter 3 describes the synthesis of colloidal gold rods and the (mesoporous) silica coating of gold rods. Chapter 4 describes the physical and optical properties of these particles when thermal energy is added. This is compared to the case where the particles are irradiated with

  14. [AFM fishing of proteins under impulse electric field].

    PubMed

    Ivanov, Yu D; Pleshakova, T O; Malsagova, K A; Kaysheva, A L; Kopylov, A T; Izotov, A A; Tatur, V Yu; Vesnin, S G; Ivanova, N D; Ziborov, V S; Archakov, A I

    2016-05-01

    A combination of (atomic force microscopy)-based fishing (AFM-fishing) and mass spectrometry allows to capture protein molecules from solutions, concentrate and visualize them on an atomically flat surface of the AFM chip and identify by subsequent mass spectrometric analysis. In order to increase the AFM-fishing efficiency we have applied pulsed voltage with the rise time of the front of about 1 ns to the AFM chip. The AFM-chip was made using a conductive material, highly oriented pyrolytic graphite (HOPG). The increased efficiency of AFM-fishing has been demonstrated using detection of cytochrome b5 protein. Selection of the stimulating pulse with a rise time of 1 ns, corresponding to the GHz frequency range, by the effect of intrinsic emission from water observed in this frequency range during water injection into the cell. PMID:27562998

  15. [AFM fishing of proteins under impulse electric field].

    PubMed

    Ivanov, Yu D; Pleshakova, T O; Malsagova, K A; Kaysheva, A L; Kopylov, A T; Izotov, A A; Tatur, V Yu; Vesnin, S G; Ivanova, N D; Ziborov, V S; Archakov, A I

    2016-05-01

    A combination of (atomic force microscopy)-based fishing (AFM-fishing) and mass spectrometry allows to capture protein molecules from solutions, concentrate and visualize them on an atomically flat surface of the AFM chip and identify by subsequent mass spectrometric analysis. In order to increase the AFM-fishing efficiency we have applied pulsed voltage with the rise time of the front of about 1 ns to the AFM chip. The AFM-chip was made using a conductive material, highly oriented pyrolytic graphite (HOPG). The increased efficiency of AFM-fishing has been demonstrated using detection of cytochrome b5 protein. Selection of the stimulating pulse with a rise time of 1 ns, corresponding to the GHz frequency range, by the effect of intrinsic emission from water observed in this frequency range during water injection into the cell.

  16. Accurate and precise calibration of AFM cantilever spring constants using laser Doppler vibrometry.

    PubMed

    Gates, Richard S; Pratt, Jon R

    2012-09-21

    Accurate cantilever spring constants are important in atomic force microscopy both in control of sensitive imaging and to provide correct nanomechanical property measurements. Conventional atomic force microscope (AFM) spring constant calibration techniques are usually performed in an AFM. They rely on significant handling and often require touching the cantilever probe tip to a surface to calibrate the optical lever sensitivity of the configuration. This can damage the tip. The thermal calibration technique developed for laser Doppler vibrometry (LDV) can be used to calibrate cantilevers without handling or touching the tip to a surface. Both flexural and torsional spring constants can be measured. Using both Euler-Bernoulli modeling and an SI traceable electrostatic force balance technique as a comparison we demonstrate that the LDV thermal technique is capable of providing rapid calibrations with a combination of ease, accuracy and precision beyond anything previously available.

  17. Surface electrical properties of stainless steel fibres: An AFM-based study

    NASA Astrophysics Data System (ADS)

    Yin, Jun; D'Haese, Cécile; Nysten, Bernard

    2015-03-01

    Atomic force microscopy (AFM) electrical modes were used to study the surface electrical properties of stainless steel fibres. The surface electrical conductivity was studied by current sensing AFM and I-V spectroscopy. Kelvin probe force microscopy was used to measure the surface contact potential. The oxide film, known as passivation layer, covering the fibre surface gives rise to the observation of an apparently semiconducting behaviour. The passivation layer generally exhibits a p-type semiconducting behaviour, which is attributed to the predominant formation of chromium oxide on the surface of the stainless steel fibres. At the nanoscale, different behaviours are observed from points to points, which may be attributed to local variations of the chemical composition and/or thickness of the passivation layer. I-V curves are well fitted with an electron tunnelling model, indicating that electron tunnelling may be the predominant mechanism for electron transport.

  18. High precision attachment of silver nanoparticles on AFM tips by dielectrophoresis.

    PubMed

    Leiterer, Christian; Wünsche, Erik; Singh, Prabha; Albert, Jens; Köhler, Johann M; Deckert, Volker; Fritzsche, Wolfgang

    2016-05-01

    AFM tips are modified with silver nanoparticles using an AC electrical field. The used technique works with sub-micron precision and also does not require chemical modification of the tip. Based on the electrical parameters applied in the process, particle density and particle position on the apex of the tip can be adjusted. The feasibility of the method is proven by subsequent tip-enhanced Raman spectroscopy (TERS) measurements using the fabricated tips as a measurement probe. Since this modification process itself does not require any lithographic processing, the technique can be easily adapted to modify AFM tips with a variety of nanostructures with pre-defined properties, while being parallelizable for a potential commercial application.

  19. Characterization and Optimization of Quartz Tuning Fork-Based Force Sensors for Combined STM/AFM

    NASA Astrophysics Data System (ADS)

    Castellanos-Gomez, Andres; Agraït, Nicolás; Rubio-Bollinger, Gabino

    This chapter will be divided in two main parts. In the first one, we will show a detailed analysis of the dynamics of quartz tuning fork resonators which are being increasingly used in scanning probe microscopy as force sensors. We will also show that a coupled harmonic oscillators model, which includes a finite coupling between the prongs, is in remarkable agreement with the observed motion of the tuning forks. Relevant parameters for the tuning fork performance such as the effective spring constant can be obtained from our analysis. In the second one, we will present an implementation of a quartz tuning fork supplemented with optimized tips based on carbon fibers. The remarkable electrical and mechanical properties of carbon fiber make these tips more suitable for combined and/or simultaneous STM and AFM than conventional metallic tips. The fabrication and the characterization of these carbon fiber tips as well as their performance in STM/AFM will be detailed.

  20. BOREAS AFM-6 Boundary Layer Height Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) site. This data set provides boundary layer height information over the site. The data were collected from 21 May 1994 to 20 Sep 1994 and are stored in tabular ASCII files. The boundary layer height data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  1. BOREAS AFM-06 Mean Wind Profile Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from the National Oceanic and Atmospheric Administration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) tower from 21 May 1994 to 20 Sep 1994. The data set provides wind profiles at 38 heights, containing the variables of wind speed; wind direction; and the u-, v-, and w-components of the total wind. The data are stored in tabular ASCII files. The mean wind profile data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  2. BOREAS AFM-06 Mean Temperature Profile Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from the National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) tower from 21 May 1994 to 20 Sep 1994. The data set provides temperature profiles at 15 heights, containing the variables of virtual temperature, vertical velocity, the speed of sound, and w-bar. The data are stored in tabular ASCII files. The mean temperature profile data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  3. Synthesis and optical properties of Au decorated colloidal tungsten oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Tahmasebi, Nemat; Mahdavi, Seyed Mohammad

    2015-11-01

    In this study, colloidal tungsten oxide nanoparticles were fabricated by pulsed laser ablation of tungsten target using the first harmonic of a Nd:YAG laser (1064 nm) in deionized water. After ablation, a 0.33 g/lit HAuCl4 aqueous solution was added into as-prepared colloidal nanoparticles. In this process, Au3+ ions were reduced to decorate gold metallic state (Au0) onto colloidal tungsten oxide nanoparticles surface. The morphology and chemical composition of the synthesized nanoparticles were studied by AFM, XRD, TEM and XPS techniques. UV-Vis analysis reveals a distinct absorption peak at ∼530 nm. This peak can be attributed to the surface plasmon resonance (SPR) of Au and confirms formation of gold state. Moreover, X-ray photoelectron spectroscopy reveals that Au ions' reduction happens after adding HAuCl4 solution into as-prepared colloidal tungsten oxide nanoparticles. Transmission electron microscope shows that an Au shell has been decorated onto colloidal WO3 nanoparticles. Noble metal decorated tungsten oxide nanostructure could be an excellent candidate for photocatalysis, gas sensing and gasochromic applications. Finally, the gasochromic behavior of the synthesized samples was investigated by H2 and O2 gases bubbling into the produced colloidal Au/WO3 nanoparticles. Synthesized colloidal nanoparticles show excellent coloration contrast (∼80%) through NIR spectra.

  4. Study of the Conformational Changes of Chlorophyll a (Chl a) Colloids with the Atomic Force Microscope.

    PubMed

    Boussaad; Tazi; Leblanc

    1999-01-15

    Atomic force microscopic (AFM) images of chlorophyll a (Chl a) colloids deposited onto mica and Au(111) present two different shapes. The colloids appear as clouds on mica and as large chains on Au(111). This difference in topography is attributed to different interactions between the colloids and the substrate. The real-time changes occurring during the electrodeposition of the colloids are also monitored. For an applied electric field intensity varying between 5 x 10(3) and 25 x 10(4) V/m, the colloids are opened and flattened relative to a deposition in the absence of an electric field and the drop method. However, when these films are exposed to ethanol vapors, disaggregation occurrs. These changes indicate that the association of Chl a dimers can form nanocrystals with large size distribution: 45-100 nm. Arrangement of nanocrystals in colloids is a characteristic feature of microcrystalline Chl a. The interaction between the colloids and H2O can also provoke aggregate dissociation. Copyright 1999 Academic Press.

  5. Implications of the contact radius to line step (CRLS) ratio in AFM for nanotribology measurements.

    PubMed

    Helt, James M; Batteas, James D

    2006-07-01

    Investigating the mechanisms of defect generation and growth at surfaces on the nanometer scale typically requires high-resolution tools such as the atomic force microscope (AFM). To accurately assess the kinetics and activation parameters of defect production over a wide range of loads (F(z)), the AFM data should be properly conditioned. Generally, AFM wear trials are performed over an area defined by the length of the slow (L(sscan)) and fast scan axes. The ratio of L(sscan) to image resolution (res, lines per image) becomes an important experimental parameter in AFM wear trials because it defines the magnitude of the line step (LS = L(sscan)/res), the distance the AFM tip steps along the slow scan axis. Comparing the contact radius (a) to the line step (LS) indicates that the overlap of successive scans will result unless the contact radius-line step ratio (CRLS) is < or =(1)/(2). If this relationship is not considered, then the scan history (e.g., contact frequency) associated with a single scan is not equivalent at different loads owing to the scaling of contact radius with load (a proportional variant F(z)(1/3)). Here, we present a model in conjunction with empirical wear tests on muscovite mica to evaluate the effects of scan overlap on surface wear. Using the Hertz contact mechanics definition of a, the CRLS model shows that scan overlap pervades AFM wear trials even under low loads. Such findings indicate that simply counting the number of scans (N(scans)) in an experiment underestimates the full history conveyed to the surface by the tip and translates into an error in the actual extent to which a region on the surface is contacted. Utilizing the CRLS method described here provides an approach to account for image scan history accurately and to predict the extent of surface wear. This general model also has implications for any AFM measurement where one wishes to correlate scan-dependent history to image properties as well as feature resolution in scanned

  6. Implications of the contact radius to line step (CRLS) ratio in AFM for nanotribology measurements.

    PubMed

    Helt, James M; Batteas, James D

    2006-07-01

    Investigating the mechanisms of defect generation and growth at surfaces on the nanometer scale typically requires high-resolution tools such as the atomic force microscope (AFM). To accurately assess the kinetics and activation parameters of defect production over a wide range of loads (F(z)), the AFM data should be properly conditioned. Generally, AFM wear trials are performed over an area defined by the length of the slow (L(sscan)) and fast scan axes. The ratio of L(sscan) to image resolution (res, lines per image) becomes an important experimental parameter in AFM wear trials because it defines the magnitude of the line step (LS = L(sscan)/res), the distance the AFM tip steps along the slow scan axis. Comparing the contact radius (a) to the line step (LS) indicates that the overlap of successive scans will result unless the contact radius-line step ratio (CRLS) is < or =(1)/(2). If this relationship is not considered, then the scan history (e.g., contact frequency) associated with a single scan is not equivalent at different loads owing to the scaling of contact radius with load (a proportional variant F(z)(1/3)). Here, we present a model in conjunction with empirical wear tests on muscovite mica to evaluate the effects of scan overlap on surface wear. Using the Hertz contact mechanics definition of a, the CRLS model shows that scan overlap pervades AFM wear trials even under low loads. Such findings indicate that simply counting the number of scans (N(scans)) in an experiment underestimates the full history conveyed to the surface by the tip and translates into an error in the actual extent to which a region on the surface is contacted. Utilizing the CRLS method described here provides an approach to account for image scan history accurately and to predict the extent of surface wear. This general model also has implications for any AFM measurement where one wishes to correlate scan-dependent history to image properties as well as feature resolution in scanned

  7. Direct observation of hydration of TiO 2 on Ti using electrochemical AFM: freely corroding versus potentiostatically held

    NASA Astrophysics Data System (ADS)

    Bearinger, Jane P.; Orme, Christine A.; Gilbert, Jeremy L.

    2001-10-01

    Hydration of titanium/titanium oxide surfaces under freely corroding and potentiostatically held conditions has been characterized using electrochemical atomic force microscopy (EC AFM). In contrast to conventional high vacuum techniques, AFM enables measurement of morphological surface structure in the in situ hydrated state. Electrochemical probes in the imaging environment further enable acquisition of electrical characteristics during AFM imaging. Experiments were performed on etched, electropolished commercially pure titanium. As noted by direct observation and corroborated by power spectral density (Fourier analysis) measurements, oxide domes cover the titanium surface and grow laterally during hydration. Applied potential altered the growth rate. Under open circuit potential conditions, growth proceeded approximately six times faster than under a -1 V applied voltage ( 1098±52 nm2/ min ± versus 184.84±19 nm2/min). Film growth increased electrical resistance and lowered interfacial capacitance based on step polarization impedance spectroscopy tests.

  8. Viscosity of colloidal suspensions

    SciTech Connect

    Cohen, E.G.D.; Schepper, I.M. de

    1995-12-31

    Simple expressions are given for the effective Newtonian viscosity as a function of concentration as well as for the effective visco-elastic response as a function of concentration and imposed frequency, of monodisperse neutral colloidal suspensions over the entire fluid range. The basic physical mechanisms underlying these formulae are discussed. The agreement with existing experiments is very good.

  9. Physics of Colloids in Space-2 (PCS-2)

    NASA Technical Reports Server (NTRS)

    Sankaran, Subramanian; Gasser, Urs; Manley, Suliana; Valentine, Megan; Prasad, Vikram; Rudhardt, Daniel; Bailey, Arthur; Dinsmore, Anthony; Segre, Phil; Doherty, Michael P.

    2001-01-01

    The Physics of Colloids-2 (PCS-2) experiment is aimed at investigating the basic physical properties of several types of colloidal suspensions. The three broad classes of colloidal systems of interest are binary colloids, colloid-polymer mixtures, and fractal gels. The objective is to understand their phase behavior as well as the kinetics of the phase transitions in the absence of gravity. The nucleation, growth, and morphology characteristics of the crystals and gels that form would be studied using confocal microscopy. These will be observed directly with excellent time resolution, and therefore extensive information about the different phases and their growth mechanisms will be gained. With the laser tweezers, it will be possible to measure the strength of these structures and to modify them in a controlled way, and the spectrophotometer will provide the possibility to probe their optical properties. We believe that this experiment will provide the basis for future 'colloid engineering' in which complicated structures with novel properties (e.g., photonic crystals) will be grown by controlled self-assembly.

  10. Assembly of colloidal strings in a simple fluid flow

    NASA Astrophysics Data System (ADS)

    Abe, Yu; Francis, Lorraine; Cheng, Xiang

    Colloidal particles self-assemble into ordered structures ranging from face- and body-centered cubic crystals to binary ionic crystals and to kagome lattices. Such diverse micron-scale structures are of practical importance for creating photonic materials and also of fundamental interest for probing equilibrium and non-equilibrium statistical mechanics. As a particularly interesting example, 1D colloidal strings provide a unique system for investigating non-equilibrium dynamics of crystal lattices. Here, we report a simple experimental method for constructing 1D colloidal crystals, where colloidal particles self-assemble into flow-aligned string structures near solid boundary under unidirectional flows. Using fast confocal microscopy, we explore the degree of particle alignment as functions of flow rate, particle concentrations, wetting properties of solid boundary and ionic strength of solvent. Through our systematic experiments, we show that these colloidal strings arise from hydrodynamic coupling, facilitated by electrostatic attractions between particles and the boundary. Compared with previous methods, our work provides a much simpler experimental procedure for assembling a large number of colloidal strings.

  11. Improving the Lateral Resolution of Quartz Tuning Fork-Based Sensors in Liquid by Integrating Commercial AFM Tips into the Fiber End

    PubMed Central

    Gonzalez, Laura; Martínez-Martín, David; Otero, Jorge; de Pablo, Pedro José; Puig-Vidal, Manel; Gómez-Herrero, Julio

    2015-01-01

    The use of quartz tuning fork sensors as probes for scanning probe microscopy is growing in popularity. Working in shear mode, some methods achieve a lateral resolution comparable with that obtained with standard cantilevered probes, but only in experiments conducted in air or vacuum. Here, we report a method to produce and use commercial AFM tips in electrically driven quartz tuning fork sensors operating in shear mode in a liquid environment. The process is based on attaching a standard AFM tip to the end of a fiber probe which has previously been sharpened. Only the end of the probe is immersed in the buffer solution during imaging. The lateral resolution achieved is about 6 times higher than that of the etched microfiber on its own. PMID:25594596

  12. Improving the lateral resolution of quartz tuning fork-based sensors in liquid by integrating commercial AFM tips into the fiber end.

    PubMed

    Gonzalez, Laura; Martínez-Martín, David; Otero, Jorge; de Pablo, Pedro José; Puig-Vidal, Manel; Gómez-Herrero, Julio

    2015-01-14

    The use of quartz tuning fork sensors as probes for scanning probe microscopy is growing in popularity. Working in shear mode, some methods achieve a lateral resolution comparable with that obtained with standard cantilevered probes, but only in experiments conducted in air or vacuum. Here, we report a method to produce and use commercial AFM tips in electrically driven quartz tuning fork sensors operating in shear mode in a liquid environment. The process is based on attaching a standard AFM tip to the end of a fiber probe which has previously been sharpened. Only the end of the probe is immersed in the buffer solution during imaging. The lateral resolution achieved is about 6 times higher than that of the etched microfiber on its own.

  13. Large-Scale Fabrication of Carbon Nanotube Probe Tips For Atomic Force Microscopy Critical Dimension Imaging Applications

    NASA Technical Reports Server (NTRS)

    Ye, Qi Laura; Cassell, Alan M.; Stevens, Ramsey M.; Meyyappan, Meyya; Li, Jun; Han, Jie; Liu, Hongbing; Chao, Gordon

    2004-01-01

    Carbon nanotube (CNT) probe tips for atomic force microscopy (AFM) offer several advantages over Si/Si3N4 probe tips, including improved resolution, shape, and mechanical properties. This viewgraph presentation discusses these advantages, and the drawbacks of existing methods for fabricating CNT probe tips for AFM. The presentation introduces a bottom up wafer scale fabrication method for CNT probe tips which integrates catalyst nanopatterning and nanomaterials synthesis with traditional silicon cantilever microfabrication technology. This method makes mass production of CNT AFM probe tips feasible, and can be applied to the fabrication of other nanodevices with CNT elements.

  14. COLLOIDS. Colloidal matter: Packing, geometry, and entropy.

    PubMed

    Manoharan, Vinothan N

    2015-08-28

    Colloidal particles with well-controlled shapes and interactions are an ideal experimental system for exploring how matter organizes itself. Like atoms and molecules, these particles form bulk phases such as liquids and crystals. But they are more than just crude analogs of atoms; they are a form of matter in their own right, with complex and interesting collective behavior not seen at the atomic scale. Their behavior is affected by geometrical or topological constraints, such as curved surfaces or the shapes of the particles. Because the interactions between the particles are often short-ranged, we can understand the effects of these constraints using geometrical concepts such as packing. The geometrical viewpoint gives us a window into how entropy affects not only the structure of matter, but also the dynamics of how it forms. PMID:26315444

  15. Cellular mechanoadaptation to substrate mechanical properties: contributions of substrate stiffness and thickness to cell stiffness measurements using AFM.

    PubMed

    Vichare, Shirish; Sen, Shamik; Inamdar, Mandar M

    2014-02-28

    Mechanosensing by adherent cells is usually studied by quantifying cell responses on hydrogels that are covalently linked to a rigid substrate. Atomic force microscopy (AFM) represents a convenient way of characterizing the mechanoadaptation response of adherent cells on hydrogels of varying stiffness and thickness. Since AFM measurements reflect the effective cell stiffness, therefore, in addition to measuring real cytoskeletal alterations across different conditions, these measurements might also be influenced by the geometry and physical properties of the substrate itself. To better understand how the physical attributes of the gel influence AFM stiffness measurements of cells, we have used finite element analysis to simulate the indentation of cells of various spreads resting on hydrogels of varying stiffness and thickness. Consistent with experimental results, our simulation results indicate that for well spread cells, stiffness values are significantly over-estimated when experiments are performed on cells cultured on soft and thin gels. Using parametric studies, we have developed scaling relationships between the effective stiffness probed by AFM and the bulk cell stiffness, taking cell and tip geometry, hydrogel properties, nuclear stiffness and cell contractility into account. Finally, using simulated mechanoadaptation responses, we have demonstrated that a cell stiffening response may arise purely due to the substrate properties. Collectively, our results demonstrate the need to take hydrogel properties into account while estimating cell stiffness using AFM indentation. PMID:24651595

  16. Colloidal Double Quantum Dots

    PubMed Central

    2016-01-01

    Conspectus Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole–dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single

  17. BOREAS AFM-07 SRC Surface Meteorological Data

    NASA Technical Reports Server (NTRS)

    Osborne, Heather; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Young, Kim; Wittrock, Virginia; Shewchuck, Stan; Smith, David E. (Technical Monitor)

    2000-01-01

    The Saskatchewan Research Council (SRC) collected surface meteorological and radiation data from December 1993 until December 1996. The data set comprises Suite A (meteorological and energy balance measurements) and Suite B (diffuse solar and longwave measurements) components. Suite A measurements were taken at each of ten sites, and Suite B measurements were made at five of the Suite A sites. The data cover an approximate area of 500 km (North-South) by 1000 km (East-West) (a large portion of northern Manitoba and northern Saskatchewan). The measurement network was designed to provide researchers with a sufficient record of near-surface meteorological and radiation measurements. The data are provided in tabular ASCII files, and were collected by Aircraft Flux and Meteorology (AFM)-7. The surface meteorological and radiation data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  18. Multimodal Plasmonics in Fused Colloidal Networks

    PubMed Central

    Teulle, Alexandre; Bosman, Michel; Girard, Christian; Gurunatha, Kargal L.; Li, Mei; Mann, Stephen; Dujardin, Erik

    2014-01-01

    Harnessing the optical properties of noble metals down to the nanometer-scale is a key step towards fast and low-dissipative information processing. At the 10-nm length scale, metal crystallinity and patterning as well as probing of surface plasmon (SP) properties must be controlled with a challenging high level of precision. Here, we demonstrate that ultimate lateral confinement and delocalization of SP modes are simultaneously achieved in extended self-assembled networks comprising linear chains of partially fused gold nanoparticles. The spectral and spatial distributions of the SP modes associated with the colloidal superstructures are evidenced by performing monochromated electron energy loss spectroscopy with a nanometer-sized electron probe. We prepare the metallic bead strings by electron beam-induced interparticle fusion of nanoparticle networks. The fused superstructures retain the native morphology and crystallinity but develop very low energy SP modes that are capable of supporting long range and spectrally tunable propagation in nanoscale waveguides. PMID:25344783

  19. Multimodal plasmonics in fused colloidal networks.

    PubMed

    Teulle, Alexandre; Bosman, Michel; Girard, Christian; Gurunatha, Kargal L; Li, Mei; Mann, Stephen; Dujardin, Erik

    2015-01-01

    Harnessing the optical properties of noble metals down to the nanometre scale is a key step towards fast and low-dissipative information processing. At the 10-nm length scale, metal crystallinity and patterning as well as probing of surface plasmon properties must be controlled with a challenging high level of precision. Here, we demonstrate that ultimate lateral confinement and delocalization of surface plasmon modes are simultaneously achieved in extended self-assembled networks comprising linear chains of partially fused gold nanoparticles. The spectral and spatial distributions of the surface plasmon modes associated with the colloidal superstructures are evidenced by performing monochromated electron energy-loss spectroscopy with a nanometre-sized electron probe. We prepare the metallic bead strings by electron-beam-induced interparticle fusion of nanoparticle networks. The fused superstructures retain the native morphology and crystallinity but develop very low-energy surface plasmon modes that are capable of supporting long-range and spectrally tunable propagation in nanoscale waveguides.

  20. Statistical analysis of AFM topographic images of self-assembled quantum dots

    SciTech Connect

    Sevriuk, V. A.; Brunkov, P. N. Shalnev, I. V.; Gutkin, A. A.; Klimko, G. V.; Gronin, S. V.; Sorokin, S. V.; Konnikov, S. G.

    2013-07-15

    To obtain statistical data on quantum-dot sizes, AFM topographic images of the substrate on which the dots under study are grown are analyzed. Due to the nonideality of the substrate containing height differences on the order of the size of nanoparticles at distances of 1-10 {mu}m and the insufficient resolution of closely arranged dots due to the finite curvature radius of the AFM probe, automation of the statistical analysis of their large dot array requires special techniques for processing topographic images to eliminate the loss of a particle fraction during conventional processing. As such a technique, convolution of the initial matrix of the AFM image with a specially selected matrix is used. This makes it possible to determine the position of each nanoparticle and, using the initial matrix, to measure their geometrical parameters. The results of statistical analysis by this method of self-assembled InAs quantum dots formed on the surface of an AlGaAs epitaxial layer are presented. It is shown that their concentration, average size, and half-width of height distribution depend strongly on the In flow and total amount of deposited InAs which are varied within insignificant limits.

  1. The Influence of Gravity on Nucleation, Growth, Stability and Structure in Crystallizing Colloidal Suspensions

    NASA Technical Reports Server (NTRS)

    Gast, Alice P.

    1996-01-01

    Our goal is to understand the dynamics of particles within colloidal crystals. In particular, we focus on the influence of the cell walls and gravity on the particle dynamics. In this study, we will use a novel light scattering experiment, known as diffusing wave spectroscopy, to probe particle motions in turbid suspensions. This is a noninvasive experimental probe of interparticle dynamics.

  2. Magnetic domain structure investigation of Bi: YIG-thin films by combination of AFM and cantilever-based aperture SNOM

    NASA Astrophysics Data System (ADS)

    Vysokikh, Yu E.; Shelaev, A. V.; Prokopov, A. R.; Shevyakov, V. I.; Krasnoborodko, S. Yu

    2016-08-01

    We present the results of magnetic domain structure investigation by combination of atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM). Special hollow-pyramid AFM cantilevers with aperture was used. This combination allows us use same probe for both topography and domain structure visualization of Bi -substituted ferrite garnet films of micro- and nano-meter thickness. Samples were excited through aperture by tightly focused linearly polarized laser beam. Magneto-optical effect rotates polarization of transmitted light depend on domain orientation. Visualization of magnetic domains was performed by detecting cross polarized component of transmitted light. SNOM allows to obtain high resolution magnetic domain image and prevent sample from any disturbance by magnetic probe. Same area SNOM and MFM images are presented.

  3. Equilibrium Shape of Colloidal Crystals.

    PubMed

    Sehgal, Ray M; Maroudas, Dimitrios

    2015-10-27

    Assembling colloidal particles into highly ordered configurations, such as photonic crystals, has significant potential for enabling a broad range of new technologies. Facilitating the nucleation of colloidal crystals and developing successful crystal growth strategies require a fundamental understanding of the equilibrium structure and morphology of small colloidal assemblies. Here, we report the results of a novel computational approach to determine the equilibrium shape of assemblies of colloidal particles that interact via an experimentally validated pair potential. While the well-known Wulff construction can accurately capture the equilibrium shape of large colloidal assemblies, containing O(10(4)) or more particles, determining the equilibrium shape of small colloidal assemblies of O(10) particles requires a generalized Wulff construction technique which we have developed for a proper description of equilibrium structure and morphology of small crystals. We identify and characterize fully several "magic" clusters which are significantly more stable than other similarly sized clusters.

  4. DNA-coated AFM cantilevers for the investigation of cell adhesion and the patterning of live cells

    SciTech Connect

    Hsiao, Sonny C.; Crow, Ailey K.; Lam, Wilbur A.; Bertozzi, Carolyn R.; Fletcher, Daniel A.; Francis, Matthew B.

    2008-08-01

    Measurement of receptor adhesion strength requires the precise manipulation of single cells on a contact surface. To attach live cells to a moveable probe, DNA sequences complementary to strands displayed on the plasma membrane are introduced onto AFM cantilevers (see picture, bp=base pairs). The strength of the resulting linkages can be tuned by varying the length of DNA strands, allowing for controlled transport of the cells.

  5. Enhanced adhesion of bioinspired nanopatterned elastomers via colloidal surface assembly

    PubMed Central

    Akerboom, Sabine; Appel, Jeroen; Labonte, David; Federle, Walter; Sprakel, Joris; Kamperman, Marleen

    2015-01-01

    We describe a scalable method to fabricate nanopatterned bioinspired dry adhesives using colloidal lithography. Close-packed monolayers of polystyrene particles were formed at the air/water interface, on which polydimethylsiloxane (PDMS) was applied. The order of the colloidal monolayer and the immersion depth of the particles were tuned by altering the pH and ionic strength of the water. Initially, PDMS completely wetted the air/water interface outside the monolayer, thereby compressing the monolayer as in a Langmuir trough; further application of PDMS subsequently covered the colloidal monolayers. PDMS curing and particle extraction resulted in elastomers patterned with nanodimples. Adhesion and friction of these nanopatterned surfaces with varying dimple depth were studied using a spherical probe as a counter-surface. Compared with smooth surfaces, adhesion of nanopatterned surfaces was enhanced, which is attributed to an energy-dissipating mechanism during pull-off. All nanopatterned surfaces showed a significant decrease in friction compared with smooth surfaces. PMID:25392404

  6. New AFM Techniques for Investigating Molecular Growth Mechanisms of Protein Crystals

    NASA Technical Reports Server (NTRS)

    Li, Huayu; Nadarajah, Arunan; Konnert, John H.; Pusey, Marc L.

    1998-01-01

    Atomic Force Microscopy (AFM) has emerged as a powerful technique for investigating protein crystal growth. Earlier AFM studies were among the first to demonstrate that these crystals grew by dislocation and 2D nucleation growth mechanisms [1]. These investigations were restricted to the micron range where only surface features, such as dislocation hillocks and 2D islands are visible. Most AFM instruments can scan at higher resolutions and have the potential to resolve individual protein molecules at nanometer ranges. Such scans are essential for determining the molecular packing arrangements on crystal faces and for probing the growth process at the molecular level. However, at this resolution the AFM tip influences the image produced, with the resulting image being a convolution of the tip shape and the surface morphology [2]. In most studies this problem is resolved by deconvoluting the image to obtain the true surface morphology. Although deconvolution routines work reasonably well for simple one- dimensional shapes, for complex surfaces this approach does not produce accurate results. In this study we devised a new approach which takes advantage of the precise molecular order of crystal surfaces, combined with the knowledge of individual molecular shapes from the crystallographic data of the protein and the AFM tip shape. This information is used to construct expected theoretical AFM images by convoluting the tip shape with the constructed crystal surface shape for a given surface packing arrangement. By comparing the images from actual AFM scans with the constructed ones for different possible surface packing arrangements, the correct packing arrangement can be conclusively determined. This approach was used in this study to determine the correct one from two possible packing arrangements on (I 10) faces of tetragonal lysozyme crystals. Another novel AFM technique was also devised to measure the dimension of individual growth units of the crystal faces

  7. Raman and AFM study of gamma irradiated plastic bottle sheets

    NASA Astrophysics Data System (ADS)

    Ali, Yasir; Kumar, Vijay; Sonkawade, R. G.; Dhaliwal, A. S.

    2013-02-01

    In this investigation, the effects of gamma irradiation on the structural properties of plastic bottle sheet are studied. The Plastic sheets were exposed with 1.25MeV 60Co gamma rays source at various dose levels within the range from 0-670 kGy. The induced modifications were followed by micro-Raman and atomic force microscopy (AFM). The Raman spectrum shows the decrease in Raman intensity and formation of unsaturated bonds with an increase in the gamma dose. AFM image displays rough surface morphology after irradiation. The detailed Raman analysis of plastic bottle sheets is presented here, and the results are correlated with the AFM observations.

  8. Raman and AFM study of gamma irradiated plastic bottle sheets

    SciTech Connect

    Ali, Yasir; Kumar, Vijay; Dhaliwal, A. S.; Sonkawade, R. G.

    2013-02-05

    In this investigation, the effects of gamma irradiation on the structural properties of plastic bottle sheet are studied. The Plastic sheets were exposed with 1.25MeV {sup 60}Co gamma rays source at various dose levels within the range from 0-670 kGy. The induced modifications were followed by micro-Raman and atomic force microscopy (AFM). The Raman spectrum shows the decrease in Raman intensity and formation of unsaturated bonds with an increase in the gamma dose. AFM image displays rough surface morphology after irradiation. The detailed Raman analysis of plastic bottle sheets is presented here, and the results are correlated with the AFM observations.

  9. Contact resonances of U-shaped atomic force microscope probes

    NASA Astrophysics Data System (ADS)

    Rezaei, E.; Turner, J. A.

    2016-01-01

    Recent approaches used to characterize the elastic or viscoelastic properties of materials with nanoscale resolution have focused on the contact resonances of atomic force microscope (CR-AFM) probes. The experiments for these CR-AFM methods involve measurement of several contact resonances from which the resonant frequency and peak width are found. The contact resonance values are then compared with the noncontact values in order for the sample properties to be evaluated. The data analysis requires vibration models associated with the probe during contact in order for the beam response to be deconvolved from the measured spectra. To date, the majority of CR-AFM research has used rectangular probes that have a relatively simple vibration response. Recently, U-shaped AFM probes have created much interest because they allow local sample heating. However, the vibration response of these probes is much more complex such that CR-AFM is still in its infancy. In this article, a simplified analytical model of U-shaped probes is evaluated for contact resonance applications relative to a more complex finite element (FE) computational model. The tip-sample contact is modeled using three orthogonal Kelvin-Voigt elements such that the resonant frequency and peak width of each mode are functions of the contact conditions. For the purely elastic case, the frequency results of the simple model are within 8% of the FE model for the lowest six modes over a wide range of contact stiffness values. Results for the viscoelastic contact problem for which the quality factor of the lowest six modes is compared show agreement to within 13%. These results suggest that this simple model can be used effectively to evaluate CR-AFM experimental results during AFM scanning such that quantitative mapping of viscoelastic properties may be possible using U-shaped probes.

  10. Preparation of silver colloids with improved uniformity and stable surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Meng, Wei; Hu, Fang; Jiang, Xiaohong; Lu, Lude

    2015-02-01

    Silver colloids of uniform shape and size are prepared by a two-step reduction. Small silver particles form initially by the rapid reduction of silver nitrate with sodium citrate at 100°C and then grow at 92°C. The reaction processes and resulting silver colloids are characterized by transmission electron microscopy, ultraviolet-visible absorption spectrophotometry, zeta-potential measurements, and Ag+ concentration analysis. The surface-enhanced Raman scattering (SERS) activity of the silver colloids is then investigated, using crystal violet (CV) as a SERS probe. The silver colloids exhibit uniform shape and size and stable SERS activity. The average size of the silver particles is 47 nm (14% relative standard deviation), while the average sizes of the silver colloids prepared at 100°C and 92°C are 41 (30%) and 71 nm (33%), respectively.

  11. AFM Investigation of mechanical properties of dentin

    SciTech Connect

    Cohen, Sidney R; Apter, Nathan; Jesse, Stephen; Kalinin, Sergei V; Barlam, David; Peretz, Adi Idit; Ziskind, Daniel; Wagner, H. Daniel

    2008-01-01

    Mechanical properties of peritubular dentin were investigated using scanning probe microscopy techniques, namely Nanoindentation and Band Excitation. Particular attention was directed to the possible existence of a gradient in these properties moving outward from the tubular lumen to the junction with the intertubular dentin. Finite element analysis showed that the influence of the boundaries is small relative to the effects observed. Thus, these results strongly support the concept of a lowering of modulus and hardness from the tubular exterior to its periphery, which appear to correlate with graded changes in the mineral content.

  12. Measurement of Cationic and Intracellular Modulation of Integrin Binding Affinity by AFM-Based Nanorobot

    PubMed Central

    Patterson, Kevin C.; Yang, Ruiguo; Zeng, Bixi; Song, Bo; Wang, Shouye; Xi, Ning; Basson, Marc D.

    2013-01-01

    Integrins are dynamic transmembrane cation-dependent heterodimers that both anchor cells in position and transduce signals into and out of cells. We used an atomic force microscope (AFM)-based nanorobotic system to measure integrin-binding forces in intact human intestinal epithelial Caco-2 cells. The AFM-based nanorobot enables human-directed, high-accuracy probe positioning and site-specific investigations. Functionalizing the AFM probe with an arginine-glycine-aspartate (RGD)-containing sequence (consensus binding sequence for integrins) allowed us to detect a series of peptide-cell membrane interactions with a median binding force of 115.1 ± 4.9 pN that were not detected in control interactions. Chelating divalent cations from the culture medium abolished these interactions, as did inhibiting intracellular focal adhesion kinase (FAK) using Y15. Adding 1 mM Mg2+ to the medium caused a rightward shift in the force-binding curve. Adding 1 mM Ca2+ virtually abolished the RGD-membrane specific interactions and blocked the Mg2+ effects. Cell adhesion assays demonstrated parallel effects of divalent cations and the FAK inhibitor on cell adhesion. These results demonstrate direct modulation of integrin-binding affinity by both divalent cations and intracellular signal inhibition. Additionally, three binding states (nonspecific, specific inactivated, and specific activated) were delineated from affinity measurements. Although other research has assumed that this process of integrin conformational change causes altered ligand binding, in this work we directly measured these three states in individual integrins in a physiologically based study. PMID:23823222

  13. A detailed guideline for the fabrication of single bacterial probes used for atomic force spectroscopy.

    PubMed

    Thewes, Nicolas; Loskill, Peter; Spengler, Christian; Hümbert, Sebastian; Bischoff, Markus; Jacobs, Karin

    2015-12-01

    The atomic force microscope (AFM) evolved as a standard device in modern microbiological research. However, its capability as a sophisticated force sensor is not used to its full capacity. The AFM turns into a unique tool for quantitative adhesion research in bacteriology by using "bacterial probes". Thereby, bacterial probes are AFM cantilevers that provide a single bacterium or a cluster of bacteria as the contact-forming object. We present a step-by-step protocol for preparing bacterial probes, performing force spectroscopy experiments and processing force spectroscopy data. Additionally, we provide a general insight into the field of bacterial cell force spectroscopy.

  14. A detailed guideline for the fabrication of single bacterial probes used for atomic force spectroscopy.

    PubMed

    Thewes, Nicolas; Loskill, Peter; Spengler, Christian; Hümbert, Sebastian; Bischoff, Markus; Jacobs, Karin

    2015-12-01

    The atomic force microscope (AFM) evolved as a standard device in modern microbiological research. However, its capability as a sophisticated force sensor is not used to its full capacity. The AFM turns into a unique tool for quantitative adhesion research in bacteriology by using "bacterial probes". Thereby, bacterial probes are AFM cantilevers that provide a single bacterium or a cluster of bacteria as the contact-forming object. We present a step-by-step protocol for preparing bacterial probes, performing force spectroscopy experiments and processing force spectroscopy data. Additionally, we provide a general insight into the field of bacterial cell force spectroscopy. PMID:26701715

  15. Dry powder inhaler: influence of humidity on topology and adhesion studied by AFM.

    PubMed

    Bérard, V; Lesniewska, E; Andrès, C; Pertuy, D; Laroche, C; Pourcelot, Y

    2002-01-31

    In the dry powder inhalers (DPIs), the adhesion results of the interactions between the active substance and the excipient. The carrier and the micronized drug particle morphologies are believed to affect the delivery of the drug. In this work, the couple studied was the lactose monohydrate and micronized zanamivir, used for the treatment of influenza. In a first approach, observations by scanning electron microscopy (SEM) have shown that the relative humidity (RH) greatly influenced the zanamivir amount fixed on the lactose monohydrate surface. This paper deals with the direct measurement in controlled atmosphere by atomic force microscopy (AFM) of the forces and the interaction ranges between a zanamivir probe and a lactose substrate. Selected zanamivir crystals were attached to the standard AFM probe. Different RH have been used in order to determine influent parameters permitting to identify the nature of adhesion forces between them. This study demonstrated that the increase of RH modified progressively the surface topology of the two components and increased the adhesion force.

  16. Comparison of CD measurements of an EUV photomask by EUV scatterometry and CD-AFM

    NASA Astrophysics Data System (ADS)

    Scholze, Frank; Soltwisch, Victor; Dai, Gaoliang; Henn, Mark-Alexander; Gross, Hermann

    2013-09-01

    EUV scatterometry is a potential high-throughput measurement method for the characterization of EUV photomask structures. We present a comparison of angle resolved extreme ultraviolet (EUV) scatterometry and critical dimension atomic force microscope (CD-AFM) as a reference metrology for measurements of geometrical parameters like line width (CD), height and sidewall angle of EUV photomask structures. The structures investigated are dense and semidense bright and dark lines with different nominal CDs between 140 nm and 540 nm. The results show excellent linearity of the critical dimension measured with both methods within a range of only 1.8 nm and an offset of the absolute values below 3 nm. A maximum likelihood estimation (MLE) method is used to reconstruct the shape parameters and to estimate their uncertainties from the measured scattering efficiencies. The newly developed CD-AFM at PTB allows versatile measurements of parameters such as height, CD, sidewall angle, line edge/width roughness, corner rounding, and pitch. It applies flared tips to probe steep and even undercut sidewalls and employs a new vector approaching probing (VAP) strategy which enables very low tip wear and high measurement flexibility. Its traceability is ensured by a set of calibrated step-height and reference CD standards.

  17. Differences in crystal habitus of natural and synthetic colloids

    NASA Astrophysics Data System (ADS)

    Wieczorek, Arkadiusz K.; Händel, Matthias; Totsche, Kai Uwe

    2014-05-01

    The formation of colloids from natural aqueous solutions is influenced by a multitude of biogeochemical and physicochemical processes and the presence of a large diversity of geogen and biogen, inorganic and organic solution phase components. A thereby frequently neglected class of components is the dissolved and colloidal phase organic matter (DOM). As DOM will interact with other solution phase components, we hypothesize that nanosized and colloidal particles formed in DOM bearing solutions may differ from synthetic precipitates either by size, shape, crystal habitus, crystallinity, composition or combinations of that. To investigate this, we analyzed natural colloidal particles collected from a limestone aquifer of the Upper Muschelkalk formation at Hainich National Park, Thuringia, Germany. Major groundwater components are Ca2+, Mg2+, Na+, SO42-, Cl-, HCO3- , and about 1 ppm of total organic carbon (TOC) in dissolved and colloidal form. Synthetic nanoparticles were precipitated from a series of oversaturated solutions containing single or mixtures of the following salts CaSO4, MgSO4, Ca(HCO3)2 NaCl typical for limestone environments. The solutions were produced with both natural groundwater and pure water (milli-Q). Droplets of such produced colloidal suspension were pipetted on silicon wafers and subject to air drying. The wafers were then analyzed by scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). We found that particles from oversaturated CaSO4 solution in pure water precipitate as large needle shaped crystals, whereas precipitates from CaSO4 solution in natural water were much smaller and showed a rosette like shape - similar in size and shape to gypsum crystals collected from the limestone formation water. Similar differences we found for other aqueous solution compositions. From this pilot study we presume that even minute amounts of dissolved and colloidal phase organic matter in

  18. Nonequilibrium Equation of State in Suspensions of Active Colloids

    NASA Astrophysics Data System (ADS)

    Ginot, Félix; Theurkauff, Isaac; Levis, Demian; Ybert, Christophe; Bocquet, Lydéric; Berthier, Ludovic; Cottin-Bizonne, Cécile

    2015-01-01

    Active colloids constitute a novel class of materials composed of colloidal-scale particles locally converting chemical energy into motility, mimicking micro-organisms. Evolving far from equilibrium, these systems display structural organizations and dynamical properties distinct from thermalized colloidal assemblies. Harvesting the potential of this new class of systems requires the development of a conceptual framework to describe these intrinsically nonequilibrium systems. We use sedimentation experiments to probe the nonequilibrium equation of state of a bidimensional assembly of active Janus microspheres and conduct computer simulations of a model of self-propelled hard disks. Self-propulsion profoundly affects the equation of state, but these changes can be rationalized using equilibrium concepts. We show that active colloids behave, in the dilute limit, as an ideal gas with an activity-dependent effective temperature. At finite density, increasing the activity is similar to increasing adhesion between equilibrium particles. We quantify this effective adhesion and obtain a unique scaling law relating activity and effective adhesion in both experiments and simulations. Our results provide a new and efficient way to understand the emergence of novel phases of matter in active colloidal suspensions.

  19. Crystalloid and colloid therapy.

    PubMed

    Fielding, Langdon

    2014-08-01

    Fluid therapy is a cornerstone of emergency medicine, but equine practitioners should be aware of recent developments that have modified previous recommendations. First, new emphasis on the avoidance of hyperchloremia suggests that crystalloids with a lower chloride concentration may be more appropriate for use. Second, modifications to the understanding of the Starling equation suggest that the benefits of colloids may be more limited than previously thought. In addition, the negative effects of fluid overload on morbidity and mortality are becoming increasingly recognized. Although more specific research in horses is needed, these principles are likely to apply across all species.

  20. Multiarm Star Polymers as Model Soft Colloids

    NASA Astrophysics Data System (ADS)

    Vlassopoulos, Dimitris

    2010-03-01

    Over the last decade, star polymers emerged as a useful model colloids that interpolate between polymers and hard sphere colloids. Together with microgels, they represent two benchmark soft colloidal systems, their internal structure being the key difference. Indeed, in the case of stars with open structure, the arms can interpenetrate in dense suspensions. The latter feature, that can be probed experimentally, is responsible for a number of interesting structural and dynamic properties of star polymers that set them apart from microgels. In this talk we present the basic properties of star polymers and focus on their extraordinary behavior in the highly concentrated regime, which is typically glassy. Our rheological and scattering experiments demonstrate unique features of the star glasses. Here we discuss two major ones: (i) Aging after pre-shear (the so-called rejuvenation) proceeds via a two-step process, associated with a fast arm engagement and a slow cooperative (cage) rearrangement. Remarkably, at extremely long times a steady state is observed and the terminal time in these systems can be experimentally accessible (and hence tailored at molecular level), as a consequence of the arms fluctuations. (ii) Multiple glassy states can be obtained when mixing stars with polymers or with other stars. Simultaneous theoretical and simulations work suggests that the softness is at the core of this unexpected behavior where depletion gives rise to glass melting and eventually re-entrant glasses are formed. Construction of a state diagram suggests kinetic pathways for tailoring the flow of soft colloids. These examples outline the importance of particle architecture on colloidal properties. Stars are a representative of a large class of hairy particles. The parallel important developments in mode coupling theory and its verses provide much needed predictive tools and rationalization for a number of phenomena such as those discussed here, as well as the complex

  1. Colloid solutions: a clinical update.

    PubMed

    Niemi, Tomi T; Miyashita, Ryo; Yamakage, Michiaki

    2010-12-01

    Albumin, dextran, gelatin, and hydroxyethyl starch (HES) solutions are colloids that efficiently expand the circulating blood volume. The administration of colloids restores the intravascular volume with minimal risk of tissue edema in comparison with crystalloid solutions alone. However, colloids are always given for surgical and critically ill patients. The type of the colloid, volumes applied, aggressiveness of fluid resuscitation, and the volume status at the initial phase of administration determine their clinical responses. The outcome after fluid resuscitation with various colloids in critically ill patients seems to be comparable according to systematic reviews. A randomized, adequately powered clinical trial comparing modern nonprotein colloid to albumin is still lacking. Rapidly degradable HES solutions have good hemodynamic effects, and the risk of adverse renal and coagulation effects, as well as allergic reactions, is minimal. The current investigation has also shown the beneficial effect of HES solution (especially HES 130/0.4) on inflammatory response, postoperative nausea and vomiting, and postoperative outcome. The indication of colloids with an assessment of the degree of hypovolemia and safety profiles should thus be taken into consideration before colloid administration.

  2. Adsorption-induced colloidal aggregation

    NASA Astrophysics Data System (ADS)

    Law, B. M.; Petit, J.-M.; Beysens, D.

    1998-03-01

    Reversible colloidal aggregation in binary liquid mixtures has been studied for a number of years. As the phase separation temperature of the liquid mixture is approached the thickness of an adsorption layer around the colloidal particles increases. Beysens and coworkers have demonstrated experimentally that this adsorption layer is intimately connected with the aggregation of the colloidal particles, however, no definitive theory has been available which can explain all of the experimental observations. In this contribution we describe an extension of the Derjaguin, Landau, Verwey, and Overbeek theory of colloidal aggregation which takes into account the presence of the adsorption layer and which more realistically models the attractive dispersion interactions. This modified theory can quantitatively account for many of the observed experimental features such as the characteristics of the aggregated state, the general shape of the aggregation line, and the temperature dependence of the second virial coefficient for a lutidine-water mixture containing a small volume fraction of silica colloidal particles.

  3. Study of modification methods of probes for critical-dimension atomic-force microscopy by the deposition of carbon nanotubes

    SciTech Connect

    Ageev, O. A.; Bykov, Al. V.; Kolomiitsev, A. S.; Konoplev, B. G.; Rubashkina, M. V.; Smirnov, V. A.; Tsukanova, O. G.

    2015-12-15

    The results of an experimental study of the modification of probes for critical-dimension atomicforce microscopy (CD-AFM) by the deposition of carbon nanotubes (CNTs) to improve the accuracy with which the surface roughness of vertical walls is determined in submicrometer structures are presented. Methods of the deposition of an individual CNT onto the tip of an AFM probe via mechanical and electrostatic interaction between the probe and an array of vertically aligned carbon nanotubes (VACNTs) are studied. It is shown that, when the distance between the AFM tip and a VACNT array is 1 nm and the applied voltage is within the range 20–30 V, an individual carbon nanotube is deposited onto the tip. On the basis of the results obtained in the study, a probe with a carbon nanotube on its tip (CNT probe) with a radius of 7 nm and an aspect ratio of 1:15 is formed. Analysis of the CNT probe demonstrates that its use improves the resolution and accuracy of AFM measurements, compared with the commercial probe, and also makes it possible to determine the roughness of the vertical walls of high-aspect structures by CD-AFM. The results obtained can be used to develop technological processes for the fabrication and reconditioning of special AFM probes, including those for CD-AFM, and procedures for the interoperational express monitoring of technological process parameters in the manufacturing of elements for micro- and nanoelectronics and micro- and nanosystem engineering.

  4. Elastic modulus of polypyrrole nanotubes: AFM measurement

    NASA Astrophysics Data System (ADS)

    Cuenot, Stéphane; Demoustier-Champagne, Sophie; Nysten, Bernard

    2001-03-01

    Polypyrrole nanotubes were electrochemically synthesized within the pores of nanoporous track-etched membranes. After dissolution of the template membrane, they were dispersed on PET membranes. Their tensile elastic modulus was measured by probing them in three points bending using an atomic force microscope. The elastic modulus was deduced from force-curve measurements. In this communication, the effect of the synthesis temperature and of the nanotube diameter will be presented. Especially it will be shown that the elastic modulus strongly increases when the nanotube outer diameter is reduced from 160 nm down to 35 nm. These results are in good agreement with previous results showing that the electrical conductivity of polypyrrole nanotubes increases by more than one order of magnitude when the diameter decreases in the same range. These behaviors could be explained by a larger ratio of well-oriented defect-free polymer chains in smaller tubes.

  5. Cytosolic delivery of materials with endosome-disrupting colloids

    DOEpatents

    Helms, Brett A.; Bayles, Andrea R.

    2016-03-15

    A facile procedure to deliver nanocrystals to the cytosol of live cells that is both rapid and general. The technique employs a unique cationic core-shell polymer colloid that directs nanocrystals to the cytosol of living cells within a few hours of incubation. The present methods and compositions enable a host of advanced applications arising from efficient cytosolic delivery of nanocrystal imaging probes: from single particle tracking experiments to monitoring protein-protein interactions in live cells for extended periods.

  6. Linking of Sensor Molecules with Amino Groups to Amino-Functionalized AFM Tips

    PubMed Central

    2011-01-01

    The measuring tip of an atomic force microscope (AFM) can be upgraded to a specific biosensor by attaching one or a few biomolecules to the apex of the tip. The biofunctionalized tip is then used to map cognate target molecules on a sample surface or to study biophysical parameters of interaction with the target molecules. The functionality of tip-bound sensor molecules is greatly enhanced if they are linked via a thin, flexible polymer chain. In a typical scheme of tip functionalization, reactive groups are first generated on the tip surface, a bifunctional cross-linker is then attached with one of its two reactive ends, and finally the probe molecule of interest is coupled to the free end of the cross-linker. Unfortunately, the most popular functional group generated on the tip surface is the amino group, while at the same time, the only useful coupling functions of many biomolecules (such as antibodies) are also NH2 groups. In the past, various tricks or detours were applied to minimize the undesired bivalent reaction of bifunctional linkers with adjacent NH2 groups on the tip surface. In the present study, an uncompromising solution to this problem was found with the help of a new cross-linker (“acetal-PEG-NHS”) which possesses one activated carboxyl group and one acetal-protected benzaldehyde function. The activated carboxyl ensures rapid unilateral attachment to the amino-functionalized tip, and only then is the terminal acetal group converted into the amino-reactive benzaldehyde function by mild treatment (1% citric acid, 1–10 min) which does not harm the AFM tip. As an exception, AFM tips with magnetic coating become demagnetized in 1% citric acid. This problem was solved by deprotecting the acetal group before coupling the PEG linker to the AFM tip. Bivalent binding of the corresponding linker (“aldehyde-PEG-NHS”) to adjacent NH2 groups on the tip was largely suppressed by high linker concentrations. In this way, magnetic AFM tips could be

  7. Direct visualization of the interfacial position of colloidal particles and their assemblies.

    PubMed

    Vogel, N; Ally, J; Bley, K; Kappl, M; Landfester, K; Weiss, C K

    2014-06-21

    A method for direct visualization of the position of nanoscale colloidal particles at air-water interfaces is presented. After assembling hard (polystyrene, poly(methyl methacrylate), silica) or soft core-shell gold-hydrogel composite (Au@PNiPAAm) colloids at the air-water interface, butylcyanoacrylate is introduced to the interface via the gas phase. Upon contact with water, an anionic polymerization reaction of the monomer is initiated and a film of poly(butylcyanoacrylate) (PBCA) is generated, entrapping the colloids at their equilibrium position at the interface. We apply this method to investigate the formation of complex, binary assembly structures directly at the interface, to visualize soft, nanoscale hydrogel colloids in the swollen state, and to visualize and quantify the equilibrium position of individual micro- and nanoscale colloids at the air-water interface depending of the amount of charge present on the particle surface. We find that the degree of deprotonation of the carboxyl group shifts the air-water contact angle, which is further confirmed by colloidal probe atomic force microscopy. Remarkably, the contact angles determined for individual colloidal particles feature a significant distribution that greatly exceeds errors attributable to the size distribution of the colloids. This finding underlines the importance of accessing soft matter on an individual particle level.

  8. Improved Process for Fabricating Carbon Nanotube Probes

    NASA Technical Reports Server (NTRS)

    Stevens, R.; Nguyen, C.; Cassell, A.; Delzeit, L.; Meyyappan, M.; Han, Jie

    2003-01-01

    An improved process has been developed for the efficient fabrication of carbon nanotube probes for use in atomic-force microscopes (AFMs) and nanomanipulators. Relative to prior nanotube tip production processes, this process offers advantages in alignment of the nanotube on the cantilever and stability of the nanotube's attachment. A procedure has also been developed at Ames that effectively sharpens the multiwalled nanotube, which improves the resolution of the multiwalled nanotube probes and, combined with the greater stability of multiwalled nanotube probes, increases the effective resolution of these probes, making them comparable in resolution to single-walled carbon nanotube probes. The robust attachment derived from this improved fabrication method and the natural strength and resiliency of the nanotube itself produces an AFM probe with an extremely long imaging lifetime. In a longevity test, a nanotube tip imaged a silicon nitride surface for 15 hours without measurable loss of resolution. In contrast, the resolution of conventional silicon probes noticeably begins to degrade within minutes. These carbon nanotube probes have many possible applications in the semiconductor industry, particularly as devices are approaching the nanometer scale and new atomic layer deposition techniques necessitate a higher resolution characterization technique. Previously at Ames, the use of nanotube probes has been demonstrated for imaging photoresist patterns with high aspect ratio. In addition, these tips have been used to analyze Mars simulant dust grains, extremophile protein crystals, and DNA structure.

  9. Colloids in Acute Burn Resuscitation.

    PubMed

    Cartotto, Robert; Greenhalgh, David

    2016-10-01

    Colloids have been used in varying capacities throughout the history of formula-based burn resuscitation. There is sound experimental evidence that demonstrates colloids' ability to improve intravascular colloid osmotic pressure, expand intravascular volume, reduce resuscitation requirements, and limit edema in unburned tissue following a major burn. Fresh frozen plasma appears to be a useful and effective immediate burn resuscitation fluid but its benefits must be weighed against its costs, and risks of viral transmission and acute lung injury. Albumin, in contrast, is less expensive and safer and has demonstrated ability to reduce resuscitation requirements and possibly limit edema-related morbidity. PMID:27600123

  10. Two-dimensional dipolar nematic colloidal crystals.

    PubMed

    Skarabot, M; Ravnik, M; Zumer, S; Tkalec, U; Poberaj, I; Babic, D; Osterman, N; Musevic, I

    2007-11-01

    We study the interactions and directed assembly of dipolar nematic colloidal particles in planar nematic cells using laser tweezers. The binding energies for two stable configurations of a colloidal pair with homeotropic surface alignment are determined. It is shown that the orientation of the dipolar colloidal particle can efficiently be controlled and changed by locally quenching the nematic liquid crystal from the laser-induced isotropic phase. The interaction of a single colloidal particle with a single colloidal chain is determined and the interactions between pairs of colloidal chains are studied. We demonstrate that dipolar colloidal chains self-assemble into the two-dimensional (2D) dipolar nematic colloidal crystals. An odd-even effect is observed with increasing number of colloidal chains forming the 2D colloidal crystal. PMID:18233658

  11. AFM investigation of Martian soil simulants on micromachined Si substrates.

    PubMed

    Vijendran, S; Sykulska, H; Pike, W T

    2007-09-01

    The micro and nanostructures of Martian soil simulants with particles in the micrometre-size range have been studied using a combination of optical and atomic force microscopy (AFM) in preparation for the 2007 NASA Phoenix Mars Lander mission. The operation of an atomic force microscope on samples of micrometre-sized soil particles is a poorly investigated area where the unwanted interaction between the scanning tip and loose particles results in poor image quality and tip contamination by the sample. In order to mitigate these effects, etched silicon substrates with a variety of features have been used to facilitate the sorting and gripping of particles. From these experiments, a number of patterns were identified that were particularly good at isolating and immobilizing particles for AFM imaging. This data was used to guide the design of micromachined substrates for the Phoenix AFM. Both individual particles as well as aggregates were successfully imaged, and information on sizes, shapes and surface morphologies were obtained. This study highlights both the strengths and weaknesses of AFM for the potential in situ investigation of Martian soil and dust. Also presented are more general findings of the limiting operational constraints that exist when attempting the AFM of high aspect ratio particles with current technology. The performance of the final designs of the substrates incorporated on Phoenix will be described in a later paper. PMID:17760618

  12. Visualizing dislocation nucleation by indenting colloidal crystals.

    PubMed

    Schall, Peter; Cohen, Itai; Weitz, David A; Spaepen, Frans

    2006-03-16

    The formation of dislocations is central to our understanding of yield, work hardening, fracture, and fatigue of crystalline materials. While dislocations have been studied extensively in conventional materials, recent results have shown that colloidal crystals offer a potential model system for visualizing their structure and dynamics directly in real space. Although thermal fluctuations are thought to play a critical role in the nucleation of these defects, it is difficult to observe them directly. Nano-indentation, during which a small tip deforms a crystalline film, is a common tool for introducing dislocations into a small volume that is initially defect-free. Here, we show that an analogue of nano-indentation performed on a colloidal crystal provides direct images of defect formation in real time and on the single particle level, allowing us to probe the effects of thermal fluctuations. We implement a new method to determine the strain tensor of a distorted crystal lattice and we measure the critical dislocation loop size and the rate of dislocation nucleation directly. Using continuum models, we elucidate the relation between thermal fluctuations and the applied strain that governs defect nucleation. Moreover, we estimate that although bond energies between particles are about fifty times larger in atomic systems, the difference in attempt frequencies makes the effects of thermal fluctuations remarkably similar, so that our results are also relevant for atomic crystals.

  13. Confocal imaging of confined quiescent and flowing colloid-polymer mixtures.

    PubMed

    Pandey, Rahul; Spannuth, Melissa; Conrad, Jacinta C

    2014-05-20

    The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed assembly(1-3), drug delivery(4), improved hydrocarbon recovery(5-7), and flowable electrodes for energy storage(8). Suspensions containing fluorescent colloids and non-adsorbing polymers are appealing model systems, as the ratio of the polymer radius of gyration to the particle radius and concentration of polymer control the range and strength of the interparticle attraction, respectively. By tuning the polymer properties and the volume fraction of the colloids, colloid fluids, fluids of clusters, gels, crystals, and glasses can be obtained(9). Confocal microscopy, a variant of fluorescence microscopy, allows an optically transparent and fluorescent sample to be imaged with high spatial and temporal resolution in three dimensions. In this technique, a small pinhole or slit blocks the emitted fluorescent light from regions of the sample that are outside the focal volume of the microscope optical system. As a result, only a thin section of the sample in the focal plane is imaged. This technique is particularly well suited to probe the structure and dynamics in dense colloidal suspensions at the single-particle scale: the particles are large enough to be resolved using visible light and diffuse slowly enough to be captured at typical scan speeds of commercial confocal systems(10). Improvements in scan speeds and analysis algorithms have also enabled quantitative confocal imaging of flowing suspensions(11-16,37). In this paper, we demonstrate confocal microscopy experiments to probe the confined phase behavior and flow properties of colloid-polymer mixtures. We first prepare colloid-polymer mixtures that are density- and refractive-index matched. Next, we report a standard protocol for imaging quiescent dense colloid-polymer mixtures under varying confinement in thin wedge-shaped cells. Finally, we demonstrate a protocol

  14. Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

    PubMed Central

    Conrad, Jacinta C.

    2014-01-01

    The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed assembly1-3, drug delivery4, improved hydrocarbon recovery5-7, and flowable electrodes for energy storage8. Suspensions containing fluorescent colloids and non-adsorbing polymers are appealing model systems, as the ratio of the polymer radius of gyration to the particle radius and concentration of polymer control the range and strength of the interparticle attraction, respectively. By tuning the polymer properties and the volume fraction of the colloids, colloid fluids, fluids of clusters, gels, crystals, and glasses can be obtained9. Confocal microscopy, a variant of fluorescence microscopy, allows an optically transparent and fluorescent sample to be imaged with high spatial and temporal resolution in three dimensions. In this technique, a small pinhole or slit blocks the emitted fluorescent light from regions of the sample that are outside the focal volume of the microscope optical system. As a result, only a thin section of the sample in the focal plane is imaged. This technique is particularly well suited to probe the structure and dynamics in dense colloidal suspensions at the single-particle scale: the particles are large enough to be resolved using visible light and diffuse slowly enough to be captured at typical scan speeds of commercial confocal systems10. Improvements in scan speeds and analysis algorithms have also enabled quantitative confocal imaging of flowing suspensions11-16,37. In this paper, we demonstrate confocal microscopy experiments to probe the confined phase behavior and flow properties of colloid-polymer mixtures. We first prepare colloid-polymer mixtures that are density- and refractive-index matched. Next, we report a standard protocol for imaging quiescent dense colloid-polymer mixtures under varying confinement in thin wedge-shaped cells. Finally, we demonstrate a protocol for

  15. Colloid labelled with radionuclide and method

    DOEpatents

    Atcher, R.W.; Hines, J.J.

    1990-11-13

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints. No Drawings

  16. Colloid labelled with radionuclide and method

    DOEpatents

    Atcher, Robert W.; Hines, John J.

    1990-01-01

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints.

  17. Method of making colloid labeled with radionuclide

    DOEpatents

    Atcher, Robert W.; Hines, John J.

    1991-01-01

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints.

  18. Optimization of phase contrast in bimodal amplitude modulation AFM.

    PubMed

    Damircheli, Mehrnoosh; Payam, Amir F; Garcia, Ricardo

    2015-01-01

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

  19. Optimization of phase contrast in bimodal amplitude modulation AFM

    PubMed Central

    Damircheli, Mehrnoosh; Payam, Amir F

    2015-01-01

    Summary Bimodal force microscopy has expanded the capabilities of atomic force microscopy (AFM) by providing high spatial resolution images, compositional contrast and quantitative mapping of material properties without compromising the data acquisition speed. In the first bimodal AFM configuration, an amplitude feedback loop keeps constant the amplitude of the first mode while the observables of the second mode have not feedback restrictions (bimodal AM). Here we study the conditions to enhance the compositional contrast in bimodal AM while imaging heterogeneous materials. The contrast has a maximum by decreasing the amplitude of the second mode. We demonstrate that the roles of the excited modes are asymmetric. The operational range of bimodal AM is maximized when the second mode is free to follow changes in the force. We also study the contrast in trimodal AFM by analyzing the kinetic energy ratios. The phase contrast improves by decreasing the energy of second mode relative to those of the first and third modes. PMID:26114079

  20. Mounting of Escherichia coli spheroplasts for AFM imaging.

    SciTech Connect

    Sullivan, Claretta J; Morrell-Falvey, Jennifer L; Allison, David P; Doktycz, Mitchel John

    2005-11-01

    The cytoplasmic membrane of Escherichia coli (E. coli) is the location of numerous, chemically specific transporters and recognition elements. Investigation of this membrane in vivo by atomic force microscopy (AFM) requires removal of the cell wall and stable immobilization of the spheroplast. AFM images demonstrate that spheroplasts can be secured with warm gelatin applied to the mica substrate just before the addition of a spheroplast suspension. The resulting preparation can be repeatedly imaged by AFM over the course of several hours. Confocal fluorescence imaging confirms the association of the spheroplasts with the gelatin layer. Gelatin molecules are known to reorder into a network after heating. Entrapment within this gelatin network is believed to be responsible for the immobilization of spheroplasts on mica.

  1. Cell visco-elasticity measured with AFM and optical trapping at sub-micrometer deformations.

    PubMed

    Nawaz, Schanila; Sánchez, Paula; Bodensiek, Kai; Li, Sai; Simons, Mikael; Schaap, Iwan A T

    2012-01-01

    The measurement of the elastic properties of cells is widely used as an indicator for cellular changes during differentiation, upon drug treatment, or resulting from the interaction with the supporting matrix. Elasticity is routinely quantified by indenting the cell with a probe of an AFM while applying nano-Newton forces. Because the resulting deformations are in the micrometer range, the measurements will be affected by the finite thickness of the cell, viscous effects and even cell damage induced by the experiment itself. Here, we have analyzed the response of single 3T3 fibroblasts that were indented with a micrometer-sized bead attached to an AFM cantilever at forces from 30-600 pN, resulting in indentations ranging from 0.2 to 1.2 micrometer. To investigate the cellular response at lower forces up to 10 pN, we developed an optical trap to indent the cell in vertical direction, normal to the plane of the coverslip. Deformations of up to two hundred nanometers achieved at forces of up to 30 pN showed a reversible, thus truly elastic response that was independent on the rate of deformation. We found that at such small deformations, the elastic modulus of 100 Pa is largely determined by the presence of the actin cortex. At higher indentations, viscous effects led to an increase of the apparent elastic modulus. This viscous contribution that followed a weak power law, increased at larger cell indentations. Both AFM and optical trapping indentation experiments give consistent results for the cell elasticity. Optical trapping has the benefit of a lower force noise, which allows a more accurate determination of the absolute indentation. The combination of both techniques allows the investigation of single cells at small and large indentations and enables the separation of their viscous and elastic components. PMID:23028915

  2. Emergent behavior in active colloids

    NASA Astrophysics Data System (ADS)

    Zöttl, Andreas; Stark, Holger

    2016-06-01

    Active colloids are microscopic particles, which self-propel through viscous fluids by converting energy extracted from their environment into directed motion. We first explain how artificial microswimmers move forward by generating near-surface flow fields via self-phoresis or the self-induced Marangoni effect. We then discuss generic features of the dynamics of single active colloids in bulk and in confinement, as well as in the presence of gravity, field gradients, and fluid flow. In the third section, we review the emergent collective behavior of active colloidal suspensions, focusing on their structural and dynamic properties. After summarizing experimental observations, we give an overview of the progress in modeling collectively moving active colloids. While active Brownian particles are heavily used to study collective dynamics on large scales, more advanced methods are necessary to explore the importance of hydrodynamic and phoretic particle interactions. Finally, the relevant physical approaches to quantify the emergent collective behavior are presented.

  3. Colloidal caterpillars for cargo transportation.

    PubMed

    Sasaki, Yuji; Takikawa, Yoshinori; Jampani, V S R; Hoshikawa, Hikaru; Seto, Takafumi; Bahr, Christian; Herminghaus, Stephan; Hidaka, Yoshiki; Orihara, Hiroshi

    2014-11-28

    Tunable transport of tiny objects in fluid systems is demanding in diverse fields of science such as drug delivery, active matter far from equilibrium, and lab-on-a-chip applications. Here, we report the directed motion of colloidal particles and self-assembled colloidal chains in a nematic liquid crystal matrix using electrohydrodynamic convection (EHC) rolls. The asymmetric distortion of the molecular orientation around the particles results - for single particles - in a hopping motion from one EHC roll to the next and - for colloidal chains - in a caterpillar-like motion in the direction perpendicular to the roll axes. We demonstrate the use of colloidal chains as microtraction engines for the transport of various types of microcargo.

  4. Impact of gravity, collector surface roughness and fracture orientation on colloid retention kinetics in an artificial fracture.

    PubMed

    Stoll, M; Huber, F M; Darbha, G K; Schill, E; Schäfer, T

    2016-08-01

    The interaction of monodisperse fluorescent carboxylated polystyrene colloids (25nm and 1000nm diameter) with a cut granodiorite surface (Grimsel granodiorite; Switzerland) and with acrylic glass is investigated both experimentally and numerically. Colloid transport experiments are conducted in a parallel plate type fracture flow cell with an aperture of 0.75mm at pH5 under low ionic strength (1mM NaCl) and under laminar flow (7mL/h) conditions. The study focuses on the effect of residence time, colloid size, collector material and fracture orientation on colloid retention. Long colloid residence times are achieved by stop-flow experiments. Using atomic force microscopy and, more specifically, the colloid probe technique surface roughness and force distance information of the collector material (granodiorite or acrylic glass) as a function of probe size (cantilever) are obtained. The experiments are modeled using COMSOL Multiphysics® (2-D numerical simulations). The experimental and the modeled results lead to the conclusion that large colloids (1000nm diameter) undergo sedimentation and deposition on the surface during stop-flow. Collector interaction is not affected by the surface roughness variation. Contrariwise, for the investigated 25nm colloids sedimentation does not play a role under the experimental conditions and collector interaction is triggered by surface inhomogeneities such as surface roughness. PMID:27174623

  5. Impact of gravity, collector surface roughness and fracture orientation on colloid retention kinetics in an artificial fracture.

    PubMed

    Stoll, M; Huber, F M; Darbha, G K; Schill, E; Schäfer, T

    2016-08-01

    The interaction of monodisperse fluorescent carboxylated polystyrene colloids (25nm and 1000nm diameter) with a cut granodiorite surface (Grimsel granodiorite; Switzerland) and with acrylic glass is investigated both experimentally and numerically. Colloid transport experiments are conducted in a parallel plate type fracture flow cell with an aperture of 0.75mm at pH5 under low ionic strength (1mM NaCl) and under laminar flow (7mL/h) conditions. The study focuses on the effect of residence time, colloid size, collector material and fracture orientation on colloid retention. Long colloid residence times are achieved by stop-flow experiments. Using atomic force microscopy and, more specifically, the colloid probe technique surface roughness and force distance information of the collector material (granodiorite or acrylic glass) as a function of probe size (cantilever) are obtained. The experiments are modeled using COMSOL Multiphysics® (2-D numerical simulations). The experimental and the modeled results lead to the conclusion that large colloids (1000nm diameter) undergo sedimentation and deposition on the surface during stop-flow. Collector interaction is not affected by the surface roughness variation. Contrariwise, for the investigated 25nm colloids sedimentation does not play a role under the experimental conditions and collector interaction is triggered by surface inhomogeneities such as surface roughness.

  6. CD-AFM reference metrology at NIST and SEMATECH

    NASA Astrophysics Data System (ADS)

    Dixson, Ronald; Fu, Joseph; Orji, Ndubuisi; Guthrie, William; Allen, Richard; Cresswell, Michael

    2005-05-01

    The National Institute of Standards and Technology (NIST) and SEMATECH have been working together to improve the traceability of critical dimension atomic force microscope (CD-AFM) dimensional metrology in semiconductor manufacturing. A major component of this collaboration has been the implementation of a Reference Measurement System (RMS) at SEMATECH using a current generation CD-AFM. An earlier tool, originally used at SEMATECH, has now been installed at NIST. Uncertainty budgets were developed for pitch, height, and CD measurements using both tools. At present, the standard uncertainties are approximately 0.2 % for pitch measurements and 0.4% for step height measurements. Prior to the current work, CD AFM linewidth measurements were limited to a standard uncertainty of about 5 nm. However, this limit can now be significantly reduced. This reduction results from the completion of the NIST/SEMATECH collaboration on the development of single crystal critical dimension reference materials (SCDDRM). A new generation of these reference materials was released to SEMATECH Member Companies during late 2004. The SEMATECH RMS was used to measure the linewidths of selected features on the distributed specimens. To reduce the uncertainty in tip width calibration, a separate transfer experiment was performed in which samples were measured by CD-AFM and then sent for high resolution transmission electron microscopy (HRTEM). In this manner, CD-AFM could be used to transfer the HRTEM width information to the distributed samples. Consequently, we are now able to reduce the limit on the standard uncertainty (k = 1) of CD-AFM width measurements to 1 nm.

  7. Characterizing the local optoelectronic performance of organic solar cells with scanning-probe microscopy

    NASA Astrophysics Data System (ADS)

    Coffey, David C.

    2007-12-01

    Conjugated polymers, small molecules, and colloidal semiconductor nanocrystals are promising materials for use in low-cost, thin-film solar cells. The photovoltaic performance of these materials, however, is highly dependent on film structure, and directly correlating local film structures with device performance remains challenging. This dissertation describes several techniques we have developed to probe and control the local optoelectronic properties of organic semiconducting films. First, with an aim of rapidly fabricating photovoltaic films with varying morphology, we demonstrate that Dip-Pen Nanolithography (DPN) can be used to control nanoscale phase separation with sub-150 nm lateral resolution in polymer films that are 20--80 nm thick. This control is based on writing monolayer chemical templates that nucleate phase separation, and we use this technique to study heterogeneous nucleation in thin films. Second, we use time-resolved electrostatic force microscopy (trEFM) to measure photoexcited charge in polymer films with a resolution of 100 nm and 100 mus. We show that such data can predict the external quantum efficiencies of polymer photodiodes, and can thus link device performance with local optoelectronic properties. When applied to the study of blended polyfluorene films, we show that domain centers can buildup charge faster then domain interfaces, which indicates that polymer/polymer blend devices should be modeled as having impure donor/acceptor domains. Third, we use photoconductive atomic force microscopy (pcAFM) to map local photocurrents with 20 nm-resolution in polymer/fullerene solar cells- achieving an order of magnitude better resolution than previous techniques. We present photocurrent maps under short-circuit conditions (zero applied bias), as well as under various applied voltages. We find significant variations in the short-circuit current between regions that appear identical in AFM topography. These variations occur from one domain to

  8. Mechanical Failure in Colloidal Gels

    NASA Astrophysics Data System (ADS)

    Kodger, Thomas Edward

    When colloidal particles in a dispersion are made attractive, they aggregate into fractal clusters which grow to form a space-spanning network, or gel, even at low volume fractions. These gels are crucial to the rheological behavior of many personal care, food products and dispersion-based paints. The mechanical stability of these products relies on the stability of the colloidal gel network which acts as a scaffold to provide these products with desired mechanical properties and to prevent gravitational sedimentation of the dispersed components. Understanding the mechanical stability of such colloidal gels is thus of crucial importance to predict and control the properties of many soft solids. Once a colloidal gel forms, the heterogeneous structure bonded through weak physical interactions, is immediately subject to body forces, such as gravity, surface forces, such as adhesion to a container walls and shear forces; the interplay of these forces acting on the gel determines its stability. Even in the absence of external stresses, colloidal gels undergo internal rearrangements within the network that may cause the network structure to evolve gradually, in processes known as aging or coarsening or fail catastrophically, in a mechanical instability known as syneresis. Studying gel stability in the laboratory requires model colloidal system which may be tuned to eliminate these body or endogenous forces systematically. Using existing chemistry, I developed several systems to study delayed yielding by eliminating gravitational stresses through density matching and cyclic heating to induce attraction; and to study syneresis by eliminating adhesion to the container walls, altering the contact forces between colloids, and again, inducing gelation through heating. These results elucidate the varied yet concomitant mechanisms by which colloidal gels may locally or globally yield, but then reform due to the nature of the physical, or non-covalent, interactions which form

  9. Re-shaping colloidal clusters

    NASA Astrophysics Data System (ADS)

    Kraft, Daniela

    2015-03-01

    Controlling the geometry and yield of anisotropic colloidal particles remains a challenge for hierarchical self-assembly. I will discuss a synthetic strategy for fabricating colloidal clusters by creating order in randomly aggregated polymer spheres using surface tension and geometrical constraints. The technique can be extended to a variety of charge-stabilized polymer spheres and offers control over the cluster size distribution. VENI grant from The Netherlands Organization for Scientific Research (NWO).

  10. Mapping individual cosmid DNAs by direct AFM imaging.

    PubMed

    Allison, D P; Kerper, P S; Doktycz, M J; Thundat, T; Modrich, P; Larimer, F W; Johnson, D K; Hoyt, P R; Mucenski, M L; Warmack, R J

    1997-05-01

    Individual cosmid clones have been restriction mapped by directly imaging, with the atomic force microscope (AFM), a mutant EcoRI endonuclease site-specifically bound to DNA. Images and data are presented that locate six restriction sites, predicted from gel electrophoresis, on a 35-kb cosmid isolated from mouse chromosome 7. Measured distances between endonuclease molecules bound to lambda DNA, when compared to known values, demonstrate the accuracy of AFM mapping to better than 1%. These results may be extended to identify other important site-specific protein-DNA interactions, such as transcription factor and mismatch repair enzyme binding, difficult to resolve by current techniques.

  11. Thermo-magnetic behaviour of AFM-MFM cantilevers

    NASA Astrophysics Data System (ADS)

    Kumar, M.; Arinero, R.; Bergez, W.; Tordjeman, Ph

    2015-08-01

    Atomic force microscopy (AFM) experiments were performed to study the behaviour of AFM cantilevers under an external magnetic field B and temperature field produced by a coil with an iron core. Four cantilever types were studied. Forces were measured for different B values and at various coil-to-cantilever separation distances. The results were analysed on the basis of a phenomenological model. This model contains the contribution of two terms, one monopole-monopole interaction at short distance, and one apparent paramagnetic interaction in \

  12. GPIM AF-M315E Propulsion System

    NASA Technical Reports Server (NTRS)

    Spores, Ronald A.; Masse, Robert; Kimbrel, Scott; McLean, Chris

    2014-01-01

    The NASA Space Technology mission Directorate's (STMD) Green Propellant Infusion Mission (GPIM) Technology Demonstration Mission (TDM) will demonstrate an operational AF-M315E green propellant propulsion system. Aerojet-Rocketdyne is responsible for the development of the propulsion system payload. This paper statuses the propulsion system module development, including thruster design and system design; Initial test results for the 1N engineering model thruster are presented. The culmination of this program will be high-performance, green AF-M315E propulsion system technology at TRL 7+, with components demonstrated to TRL 9, ready for direct infusion to a wide range of applications for the space user community.

  13. BOREAS AFM-04 Twin Otter Aircraft Flux Data

    NASA Technical Reports Server (NTRS)

    MacPherson, J. Ian; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Desjardins, Raymond L.; Smith, David E. (Technical Monitor)

    2000-01-01

    The BOREAS AFM-5 team collected and processed data from the numerous radiosonde flights during the project. The goals of the AFM-05 team were to provide large-scale definition of the atmosphere by supplementing the existing AES aerological network, both temporally and spatially. This data set includes basic upper-air parameters collected from the network of upper-air stations during the 1993, 1994, and 1996 field campaigns over the entire study region. The data are contained in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884) or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  14. Aggregation of Heterogeneously Charged Colloids.

    PubMed

    Dempster, Joshua M; Olvera de la Cruz, Monica

    2016-06-28

    Patchy colloids are attractive as programmable building blocks for metamaterials. Inverse patchy colloids, in which a charged surface is decorated with patches of the opposite charge, are additionally noteworthy as models for heterogeneously charged biological materials such as proteins. We study the phases and aggregation behavior of a single charged patch in an oppositely charged colloid with a single-site model. This single-patch inverse patchy colloid model shows a large number of phases when varying patch size. For large patch sizes we find ferroelectric crystals, while small patch sizes produce cross-linked gels. Intermediate values produce monodisperse clusters and unusual worm structures that preserve finite ratios of area to volume. The polarization observed at large patch sizes is robust under extreme disorder in patch size and shape. We examine phase-temperature dependence and coexistence curves and find that large patch sizes produce polarized liquids, in contrast to mean-field predictions. Finally, we introduce small numbers of unpatched charged colloids. These can either suppress or encourage aggregation depending on their concentration and the size of the patches on the patched colloids. These effects can be exploited to control aggregation and to measure effective patch size.

  15. Insulated Conducting Cantilevered Nanotips and Two-Chamber Recording System for High Resolution Ion Sensing AFM

    NASA Astrophysics Data System (ADS)

    Meckes, Brian; Arce, Fernando Teran; Connelly, Laura S.; Lal, Ratnesh

    2014-03-01

    Biological membranes contain ion channels, which are nanoscale pores allowing controlled ionic transport and mediating key biological functions underlying normal/abnormal living. Synthetic membranes with defined pores are being developed to control various processes, including filtration of pollutants, charge transport for energy storage, and separation of fluids and molecules. Although ionic transport (currents) can be measured with single channel resolution, imaging their structure and ionic currents simultaneously is difficult. Atomic force microscopy enables high resolution imaging of nanoscale structures and can be modified to measure ionic currents simultaneously. Moreover, the ionic currents can also be used to image structures. A simple method for fabricating conducting AFM cantilevers to image pore structures at high resolution is reported. Tungsten microwires with nanoscale tips are insulated except at the apex. This allows simultaneous imaging via cantilever deflections in normal AFM force feedback mode as well as measuring localized ionic currents. These novel probes measure ionic currents as small as picoampere while providing nanoscale spatial resolution surface topography and is suitable for measuring ionic currents and conductance of biological ion channels.

  16. An innovative method and experiment for fabricating bulgy shape nanochannel using AFM

    NASA Astrophysics Data System (ADS)

    Lin, Zone-Ching; Jheng, Hao-Yuan; Ding, Hao-Yang

    2015-08-01

    The paper proposes using atomic force microscopy (AFM) and the concept of specific down force energy (SDFE) to establish an innovative offset cycle cutting method for fabricating a bulgy shape nanochannel on a single-crystal silicon substrate. In the offset cycle cutting method, cutting is performed at a constant down force in all cutting passes. After the first cutting pass, the AFM probe is offset rightward for the second pass and subsequently offset leftward to the middle (i.e., between the positions of the first two cutting passes) for the third cutting pass. Applying a step-by-step method to modify the offset distance and approach the defined SDFE value, this study determined the depth of the middle cutting pass and smaller values of upward bulginess and downward indentation at the bottom of the nanochannel. The nanochannel width can be increased by increasing the number of offset cycle cutting passes. In addition, by applying the proposed method, this study involved a simulation and experiment concerning the cutting path plan of bulgy shape nanochannels. Furthermore, using a small down force along the burr path is proposed for reducing burr height. The results of the simulation and experiment were compared to verify the feasibility of the method.

  17. Insulated Conducting Cantilevered Nanotips and Two-Chamber Recording System for High Resolution Ion Sensing AFM

    PubMed Central

    Meckes, Brian; Arce, Fernando Teran; Connelly, Laura S.; Lal, Ratnesh

    2014-01-01

    Biological membranes contain ion channels, which are nanoscale pores allowing controlled ionic transport and mediating key biological functions underlying normal/abnormal living. Synthetic membranes with defined pores are being developed to control various processes, including filtration of pollutants, charge transport for energy storage, and separation of fluids and molecules. Although ionic transport (currents) can be measured with single channel resolution, imaging their structure and ionic currents simultaneously is difficult. Atomic force microscopy enables high resolution imaging of nanoscale structures and can be modified to measure ionic currents simultaneously. Moreover, the ionic currents can also be used to image structures. A simple method for fabricating conducting AFM cantilevers to image pore structures at high resolution is reported. Tungsten microwires with nanoscale tips are insulated except at the apex. This allows simultaneous imaging via cantilever deflections in normal AFM force feedback mode as well as measuring localized ionic currents. These novel probes measure ionic currents as small as picoampere while providing nanoscale spatial resolution surface topography and is suitable for measuring ionic currents and conductance of biological ion channels. PMID:24663394

  18. Spin Dynamics and Quantum Tunneling in Fe8 Nanomagnet and in AFM Rings by NMR

    SciTech Connect

    Seung-Ho-Baek

    2004-12-19

    In this thesis, our main interest has been to investigate the spin dynamics and quantum tunneling in single molecule magnets (SMMs), For this we have selected two different classes of SMMs: a ferrimagnetic total high spin S = 10 cluster Fe8 and antiferromagnetic (AFM) ring-type clusters. For Fe8, our efforts have been devoted to the investigation of the quantum tunneling of magnetization in the very low temperature region. The most remarkable experimental finding in Fe8 is that the nuclear spin-lattice relaxation rate (1/T{sub l}) at low temperatures takes place via strong collision mechanism, and thus it allows to measure directly the tunneling rate vs T and H for the first time. For AFM rings, we have shown that 1/T{sub l} probes the thermal fluctuations of the magnetization in the intermediate temperature range. We find that the fluctuations are dominated by a single characteristic frequency which has a power law T-dependence indicative of fluctuations due to electron-acoustic phonon interactions.

  19. AFM characterization of spin coated carboxylated polystyrene nanospheres/xyloglucan layers on mica and silicon.

    PubMed

    Lubambo, Adriana F; Lucyszyn, Neoli; Petzhold, Cesar L; Sierakowski, Maria-R; Schreiner, Wido H; Saul, Cyro K

    2013-03-01

    Self-assembled nano-arrays have a potential application as solid-phase diagnostics in many biomedical devices. The easiness of its production is directly connected to manufacture cost reduction. In this work, we present self-assembled structures starting from spin coated thin films of carboxylated polystyrene (PSC) and xyloglucan (XG) mixtures on both mica and silicon substrates. AFM images showed PSC nanospheres on top of a homogeneous layer of XG, for both substrates. The average nanosphere diameter fluctuated for a constant speed and it was likely to be independent of the component proportions on the mixture within a range of 30-50% (v/v) PSC. It was also observed that the largest diameters were found at the center of the sample and the smallest at the border. The detected nanospheres were also more numerous at the border. This behavior presents a similarity to spin coated colloidal dispersions. We observed that the average nanosphere diameter on mica substrates was bigger than the nanosphere diameters obtained on top of silicon substrates, under the same conditions. This result seems to be possibly connected to different mixture-surface interactions. PMID:23465925

  20. Scanning Probe Evaluation of Electronic, Mechanical and Structural Material Properties

    NASA Astrophysics Data System (ADS)

    Virwani, Kumar

    2011-03-01

    We present atomic force microscopy (AFM) studies of a range of properties from three different classes of materials: mixed ionic electronic conductors, low-k dielectrics, and polymer-coated magnetic nanoparticles. (1) Mixed ionic electronic conductors are being investigated as novel diodes to drive phase-change memory elements. Their current-voltage characteristics are measured with direct-current and pulsed-mode conductive AFM (C-AFM). The challenges to reliability of the C-AFM method include the electrical integrity of the probe, the sample and the contacts, and the minimization of path capacitance. The role of C-AFM in the optimization of these electro-active materials will be presented. (2) Low dielectric constant (low-k) materials are used in microprocessors as interlayer insulators, a role directly affected by their mechanical performance. The mechanical properties of nanoporous silicate low-k thin films are investigated in a comparative study of nanomechanics measured by AFM and by traditional nanoindentation. Both methods are still undergoing refinement as reliable analytical tools for determining nanomechanical properties. We will focus on AFM, the faster of the two methods, and its developmental challenges of probe shape, cantilever force constant, machine compliance and calibration standards. (3) Magnetic nanoparticles are being explored for their use in patterned media for magnetic storage. Current methods for visualizing the core-shell structure of polymer-coated magnetic nanoparticles include dye-staining the polymer shell to provide contrast in transmission electron microscopy. AFM-based fast force-volume measurements provide direct visualization of the hard metal oxide core within the soft polymer shell based on structural property differences. In particular, the monitoring of adhesion and deformation between the AFM tip and the nanoparticle, particle-by-particle, provides a reliable qualitative tool to visualize core-shell contrast without the use

  1. Photodoping of Colloidal Nanocrystals

    NASA Astrophysics Data System (ADS)

    Cohn, Alicia W.

    This dissertation addresses various aspects of photodoping colloidal nanocrystals. Photodoped ZnO nanocrystals were found to be versatile tuneable reducers using both quantum confinement and band-gap engineering with Mg2+ doping to change the conduction band potential. Using photoluminescence of the visible trap and magnetic circular dichroism spectroscopy of Mg2+ and Mn2+ co-doped ZnO, Mg2+ was shown to change the potential of both the conduction and valence band in a ratio of 0.68:0.32. The hole scavenging reaction using ethanol as the hole scavenger was investigated using continuous-wave and time resolved photoluminescence of the visible trap state of ZnO. The reaction was found to occur between the valence band hole and with a rate of > 15 ps-1. Quenching of the ZnO visible trap luminescence upon photodoping was shown to be due to trap/electron Auger process while the concomitant enhancement of the UV band-gap emission was hypothesized to be due to a reduction in non-radiative processes due to extra electrons in the conduction-band. The trap/electron Auger process in ZnO nanocrystals was further characterized by a size-dependence and shown to scale with R2. Another previously unknown Auger size dependence was measured in CdSe/ZnS trions and shown to scale with R4.3.

  2. Consolidation of colloidal suspensions

    SciTech Connect

    Shih, Wei-Heng; Kim, Seong Il; Shih, Wan Y.; Aksay, I.A. ); Schilling, C.H. Pacific Northwest Lab., Richland, WA )

    1990-08-01

    A key step in the processing of ceramics is the consolidation of powders into engineered shapes. Colloidal processing uses solvents (usually water) and dispersants to break up powder agglomerates in suspension and thereby reduce the pore size in a consolidated compact. However, agglomeration and particle rearrangement leading to pore enlargement can still occur during drying. Therefore, it is beneficial to consolidate the compact as densely as possible during the suspension stage. The consolidation techniques of pressure filtration and centrifugation were studied and the results are reported in this paper. In particular, the steady-state pressure- density relationship was studied, and information was obtained regarding the consolidation process, the microstructure, and the average density profile of consolidated cakes. Recently, we performed Monte Carlo simulations on a cluster-cluster aggregation model with restructuring, and found the exponential relationship between pressure and density is indeed the result of the breaking up of the fractal structural units. Furthermore, we calculated density profiles from the bottom to the top of the consolidated cakes by solving the local static force balance equation in the continuum particulate network. 11 refs., 3 figs.

  3. Bilayer Incorporated Influenza A M2 Single Molecule Time-Dependent AFM Studies

    NASA Astrophysics Data System (ADS)

    Hughes, Travis; Bradley, Strongin; Davis, Robert; Vijayvergiya, Viksita; Busath, David

    2004-03-01

    We report the observation of Influenza A M2 incorporated in a DPPC supported planar bilayer (SPB) on mica, formed by use of a modified vesicle fusion method from proteoliposomes using contact mode Atomic Force Microscopy (AFM). Incubation of proteoliposomes in a hypertonic solution and increased DPPC:M2 weight ratios improved SPB formation by M2/DPPC proteoliposomes. M2's extra-bilayer domains were observed as particles estimated to protrude 1-1.5 nm above the bilayer surface and < 4nm in diameter. Movement of M2 independent of the probe tip was observed with a calculated lateral diffusion coefficient of ˜5 × 10-14cm2/s and a mobile fraction of ˜80%. Protein- protein interaction was also observed.

  4. Green Rust: Structure, Redox Reaction Mechanisms, Transformation and Colloidal Behaviour

    NASA Astrophysics Data System (ADS)

    Stipp, S.; Skovbjerg, L.; Christiansen, B.; Hansson, E.; Utsunomiya, S.; Schild, D.; Geckeis, H.; Ewing, R.

    2006-05-01

    Green rust (GR) forms where pH is neutral to basic, iron concentration is high and oxidation potential provides a small amount of Fe(III). GR is best known from metallic iron corrosion but it has also been reported in soil. It typically forms nano-particles, so surface area is high. It has a layered structure and is reactive, adsorbing species on its surface, providing exchange of interlayer ions, and allowing reaction of redox active species. Corroding stainless-steel canisters in a concrete and steel radioactive waste repository would offer geochemical conditions for GR formation. We used surface-sensitive and high resolution techniques (atomic force microscopy, AFM, transmission electron microscopy, TEM, X-ray photoelectron spectroscopy, XPS) to supplement data from traditional methods (X-ray diffraction, XRD, and wet chemistry). The purpose was to refine structural and compositional parameters for green rust sulfate; to define trace component uptake mechanisms; and to assess potential mobility of GR colloids and thus, sorbed radionuclides. Green rust reduced dissolved Np(V), Cr(VI) and Se(VI), rapidly decreasing solution concentration. High resolution TEM and AFM images showed that chromate penetrates GR interlayers to a distance of about 100 nm from crystal edges. It reduces to Cr(III), blocking further movement and GR transforms topotactically to Cr- goethite, thus immobilising the contaminant in a phase significantly less soluble than pure goethite. Further oxidation results in dissolution of GR and growth of more Cr-goethite. In-situ AFM imaging showed that GR can nucleate and grow both in solution and on minerals typical of fractures in granite, i.e. graphite, muscovite, biotite, quartz and amorphous silica. Particles are more likely to stick to each other or to a substrate than to remain monodispersed.

  5. Lateral Tip Control Effects in CD-AFM Metrology: The Large Tip Limit

    PubMed Central

    Dixson, Ronald G.; Orji, Ndubuisi G.; Goldband, Ryan S.

    2016-01-01

    Sidewall sensing in critical dimension atomic force microscopes (CD-AFMs) usually involves continuous lateral dithering of the tip or the use of a control algorithm and fast response piezo actuator to position the tip in a manner that resembles touch-triggering of coordinate measuring machine (CMM) probes. All methods of tip position control, however, induce an effective tip width that may deviate from the actual geometrical tip width. Understanding the influence and dependence of the effective tip width on the dither settings and lateral stiffness of the tip can improve the measurement accuracy and uncertainty estimation for CD-AFM measurements. Since CD-AFM typically uses tips that range from 15 nm to 850 nm in geometrical width, the behavior of effective tip width throughout this range should be understood. The National Institute of Standards and Technology (NIST) has been investigating the dependence of effective tip width on the dither settings and lateral stiffness of the tip, as well as the possibility of material effects due to sample composition. For tip widths of 130 nm and lower, which also have lower lateral stiffness, the response of the effective tip width to lateral dither is greater than for larger tips. However, we have concluded that these effects will not generally result in a residual bias, provided that the tip calibration and sample measurement are performed under the same conditions. To validate that our prior conclusions about the dependence of effective tip width on lateral stiffness are valid for large CD-tips, we recently performed experiments using a very large non-CD tip with an etched plateau of approximately 2 μm width. The effective lateral stiffness of these tips is at least 20 times greater than typical CD-AFM tips, and these results supported our prior conclusions about the expected behavior for larger tips. The bottom-line importance of these latest observations is that we can now reasonably conclude that a dither slope of 3 nm

  6. 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

  7. AFM Structural Characterization of Drinking Water Biofilm under Physiological Conditions

    EPA Science Inventory

    Due to the complexity of mixed culture drinking water biofilm, direct visual observation under in situ conditions has been challenging. In this study, atomic force microscopy (AFM) revealed the three dimensional morphology and arrangement of drinking water relevant biofilm in air...

  8. Structural investigations on native collagen type I fibrils using AFM

    SciTech Connect

    Strasser, Stefan; Zink, Albert; Janko, Marek; Heckl, Wolfgang M.; Thalhammer, Stefan . E-mail: stefan.thalhammer@gsf.de

    2007-03-02

    This study was carried out to determine the elastic properties of single collagen type I fibrils with the use of atomic force microscopy (AFM). Native collagen fibrils were formed by self-assembly in vitro characterized with the AFM. To confirm the inner assembly of the collagen fibrils, the AFM was used as a microdissection tool. Native collagen type I fibrils were dissected and the inner core uncovered. To determine the elastic properties of collagen fibrils the tip of the AFM was used as a nanoindentor by recording force-displacement curves. Measurements were done on the outer shell and in the core of the fibril. The structural investigations revealed the banding of the shell also in the core of native collagen fibrils. Nanoindentation experiments showed the same Young's modulus on the shell as well as in the core of the investigated native collagen fibrils. In addition, the measurements indicate a higher adhesion in the core of the collagen fibrils compared to the shell.

  9. 3D Color Digital Elevation Map of AFM Sample

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This color image is a three dimensional (3D) view of a digital elevation map of a sample collected by NASA's Phoenix Mars Lander's Atomic Force Microscope (AFM).

    The image shows four round pits, only 5 microns in depth, that were micromachined into the silicon substrate, which is the background plane shown in red. This image has been processed to reflect the levelness of the substrate.

    A Martian particle only one micrometer, or one millionth of a meter, across is held in the upper left pit.

    The rounded particle shown at the highest magnification ever seen from another world is a particle of the dust that cloaks Mars. Such dust particles color the Martian sky pink, feed storms that regularly envelop the planet and produce Mars' distinctive red soil.

    The particle was part of a sample informally called 'Sorceress' delivered to the AFM on the 38th Martian day, or sol, of the mission (July 2, 2008). The AFM is part of Phoenix's microscopic station called MECA, or the Microscopy, Electrochemistry, and Conductivity Analyzer.

    The AFM was developed by a Swiss-led consortium, with Imperial College London producing the silicon substrate that holds sampled particles.

    The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  10. Patterned when wet: environment-dependent multifunctional patterns within amphiphilic colloidal crystals.

    PubMed

    Brozell, Adrian M; Muha, Michelle A; Abed-Amoli, Arian; Bricarello, Daniel; Parikh, Atul N

    2007-12-01

    A simple integration of molecular and colloidal self-assembly approaches with photopatterning is shown to produce multifunctional patterns of amphiphilic colloidal crystals. These crystals display binary spatial patterns of wettability by water and a single photonic stop-band in air. Upon exposure to water, the uniform stop-band is replaced by a pattern of coexisting stop-bands that reflect the underlying pattern of surface wetting. These hydration-dependent photonic patterns within single colloidal crystals form because of near-complete water rejection from the three-dimensionally disposed nanoscale interstices in hydrophobic regions and its exclusive permeation within the hydrophilic regions. This water permeation pattern is further structured by the three-dimensional (3D) distribution and contiguity of the nanoscale interstices between individual colloids, allowing 3D patterned organization of functional units in secondary self-assembly processes, as illustrated using quantum dots, metal nanoparticles, and fluorescent probes.

  11. A Model for Step Height, Edge Slope and Linewidth Measurements Using AFM

    NASA Astrophysics Data System (ADS)

    Zhao, Xuezeng; Vorburger, Theodore V.; Fu, Joseph; Song, John; Nguyen, Cattien V.

    2003-09-01

    Nano-scale linewidth measurements are performed in semiconductor manufacturing and in the data storage industry and will become increasingly important in micro-mechanical engineering. With the development of manufacturing technology in recent years, the sizes of linewidths are steadily shrinking and are in the range of hundreds of nanometers. As a result, it is difficult to achieve accurate measurement results for nanometer scale linewidth, primarily because of the interaction volume of electrons in materials for an SEM probe or the tip size of an AFM probe. However, another source of methods divergence is the mathematical model of the line itself. In order to reduce the methods divergences caused by different measurement methods and instruments for an accurate determination of nanometer scale linewidth parameters, a metrological model and algorithm are proposed for linewidth measurements with AFM. The line profile is divided into 5 parts with 19 sections and 20 key derived points. Each section is fitted by a least squares straight line, so that the profile can be represented by a set of straight lines and 6 special points, or by a 20×2 matrix of fitted points and a 6×2 matrix of starter points. According to the algorithm, WT and WTF, WM and WMF, WB and WBF represent the widths at the top, the middle and the bottom of the line profile before and after the least squares fitting, respectively. AL and AR represent the left and right sidewall angles, and H represents the step height of the line profile. Based on this algorithm, software has been developed using MATLAB for the calculation of width and height parameters of the line profile. A NIST nanometer scale linewidth artifact developed at NIST's Electronics and Electrical Engineering Laboratory (EEEL) was measured using a commercial AFM with nanotube tips. The measured linewidth profiles are analyzed using our model, algorithm and software. The model developed in this paper is straightforward to understand, and

  12. Elastic properties of hollow colloidal particles

    NASA Astrophysics Data System (ADS)

    Zoldesi, C. I.; Ivanovska, I. L.; Quilliet, C.; Wuite, G. J. L.; Imhof, A.

    2008-11-01

    The elastic properties of micrometer-sized hollow colloidal particles obtained by emulsion templating are probed by nanoindentation measurements in which point forces are applied to solvent-filled particles supported on a flat substrate. We show that the shells respond linearly up to forces of 7-21nN , where the indentation becomes of the order of the shell thickness (20-40nm) . In the linear region, the particle deformation is reversible. The measured Young’s modulus (˜200MPa) is comparable to values for stiff rubbers or soft polymers. At larger applied force, we observe a crossover into a nonlinear regime, where the shells assume a buckled shape. Here, the force increases approximately as the square root of the indentation, in agreement with the theory of elasticity of thin shells. We also observe permanent deformation of the shells after probing them repetitively beyond the linear regime. Finally, the measured elastic properties of the shells nicely explain their spontaneous buckling in solution and due to drying.

  13. Colloidal transition-metal-doped ZnO quantum dots.

    PubMed

    Radovanovic, Pavle V; Norberg, Nick S; McNally, Kathryn E; Gamelin, Daniel R

    2002-12-25

    Methods for introducing new magnetic, optical, electronic, photophysical, or photochemical properties to semiconductor nanocrystals are attracting intense applications-oriented interest. In this communication, we report the preparation and electronic absorption spectroscopy of colloidal ZnO DMS-QDs. Our synthetic procedure involves modification of literature methods known to yield highly crystalline and relatively monodisperse nanocrystals of pure ZnO to allow introduction of transition-metal dopants. We use ligand-field electronic absorption spectroscopy as a dopant-specific optical probe to monitor dopant incorporation during nanocrystal growth and to verify internal substitutional doping in Co2+:ZnO and Ni2+:ZnO DMS-QDs. To the best of our knowledge, these are the first free-standing oxide DMS-QDs reported. The synthesis of colloidal oxide DMS-QDs introduces a new category of magnetic semiconductor materials available for detailed physical study and application in nanotechnology.

  14. Crack formation and prevention in colloidal drops

    NASA Astrophysics Data System (ADS)

    Kim, Jin Young; Cho, Kun; Ryu, Seul-A.; Kim, So Youn; Weon, Byung Mook

    2015-08-01

    Crack formation is a frequent result of residual stress release from colloidal films made by the evaporation of colloidal droplets containing nanoparticles. Crack prevention is a significant task in industrial applications such as painting and inkjet printing with colloidal nanoparticles. Here, we illustrate how colloidal drops evaporate and how crack generation is dependent on the particle size and initial volume fraction, through direct visualization of the individual colloids with confocal laser microscopy. To prevent crack formation, we suggest use of a versatile method to control the colloid-polymer interactions by mixing a nonadsorbing polymer with the colloidal suspension, which is known to drive gelation of the particles with short-range attraction. Gelation-driven crack prevention is a feasible and simple method to obtain crack-free, uniform coatings through drying-mediated assembly of colloidal nanoparticles.

  15. Crack formation and prevention in colloidal drops

    PubMed Central

    Kim, Jin Young; Cho, Kun; Ryu, Seul-a; Kim, So Youn; Weon, Byung Mook

    2015-01-01

    Crack formation is a frequent result of residual stress release from colloidal films made by the evaporation of colloidal droplets containing nanoparticles. Crack prevention is a significant task in industrial applications such as painting and inkjet printing with colloidal nanoparticles. Here, we illustrate how colloidal drops evaporate and how crack generation is dependent on the particle size and initial volume fraction, through direct visualization of the individual colloids with confocal laser microscopy. To prevent crack formation, we suggest use of a versatile method to control the colloid-polymer interactions by mixing a nonadsorbing polymer with the colloidal suspension, which is known to drive gelation of the particles with short-range attraction. Gelation-driven crack prevention is a feasible and simple method to obtain crack-free, uniform coatings through drying-mediated assembly of colloidal nanoparticles. PMID:26279317

  16. EDITORIAL: Colloidal dispersions in external fields Colloidal dispersions in external fields

    NASA Astrophysics Data System (ADS)

    Löwen, Hartmut

    2012-11-01

    , Ojeda-Lopez M A and Arauz-Lara J L 2012 J. Phys. Condens. Matter 24 464126 [31]Leferink op Reinink A B G M, van den Pol E, Byelov D V, Petukhov A V and Vroege G J 2012 J. Phys. Condens. Matter 24 464127 [32]Taylor S L, Evans R and Royall C P 2012 J. Phys. Condens. Matter 24 464128 [33]Toner J, Tu Y H and Ramaswamy S 2012 J. Phys. Condens. Matter 24 464110 [34]Schmitz R and Dünweg B 2005 J. Phys. Condens. Matter 318 170 [35]Cates M E 2012 Rep. Prog. Phys. 75 042601 [36]Tarama M and Ohta T 2012 J. Phys. Condens. Matter 24 464129 [37]Wensink H H and Löwen H 2012 J. Phys. Condens. Matter 24 464130 Colloidal dispersions in external fields contents Colloidal dispersions in external fieldsHartmut Löwen Depletion induced clustering in mixtures of colloidal spheres and fd-virusD Guu, J K G Dhont, G A Vliegenthart and M P Lettinga Advanced rheological characterization of soft colloidal model systemsS Gupta, S K Kundu, J Stellbrink, L Willner, J Allgaier and D Richter Conformational and dynamical properties of ultra-soft colloids in semi-dilute solutions under shear flowSunil P Singh, Dmitry A Fedosov, Apratim Chatterji, Roland G Winkler and Gerhard Gompper Transient dynamics in dense colloidal suspensions under shear: shear rate dependenceM Laurati, K J Mutch, N Koumakis, J Zausch, C P Amann, A B Schofield, G Petekidis, J F Brady, J Horbach, M Fuchs and S U Egelhaaf Force-induced diffusion in microrheologyCh J Harrer, D Winter, J Horbach, M Fuchs and Th Voigtmann Micro-macro-discrepancies in nonlinear microrheology: I. Quantifying mechanisms in a suspension of Brownian ellipsoidsRyan J DePuit and Todd M Squires Micro-macro discrepancies in nonlinear microrheology: II. Effect of probe shapeRyan J DePuit and Todd M Squires Viscosity of electrolyte solutions: a mode-coupling theoryClaudio Contreras-Aburto and Gerhard Nägele Electro-kinetics of charged-sphere suspensions explored by integral low-angle super-heterodyne laser Doppler velocimetryThomas Palberg, Tetyana K

  17. Entropy favours open colloidal lattices.

    PubMed

    Mao, Xiaoming; Chen, Qian; Granick, Steve

    2013-03-01

    Burgeoning experimental and simulation activity seeks to understand the existence of self-assembled colloidal structures that are not close-packed. Here we describe an analytical theory based on lattice dynamics and supported by experiments that reveals the fundamental role entropy can play in stabilizing open lattices. The entropy we consider is associated with the rotational and vibrational modes unique to colloids interacting through extended attractive patches. The theory makes predictions of the implied temperature, pressure and patch-size dependence of the phase diagram of open and close-packed structures. More generally, it provides guidance for the conditions at which targeted patchy colloidal assemblies in two and three dimensions are stable, thus overcoming the difficulty in exploring by experiment or simulation the full range of conceivable parameters.

  18. Synthesis and Characterization of Supramolecular Colloids.

    PubMed

    Vilanova, Neus; De Feijter, Isja; Voets, Ilja K

    2016-01-01

    Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical properties for applications in photonics, drug delivery and coating technology. Here we present a new family of colloidal building blocks, coined supramolecular colloids, whose self-assembly is controlled through surface-functionalization with a benzene-1,3,5-tricarboxamide (BTA) derived supramolecular moiety. Such BTAs interact via directional, strong, yet reversible hydrogen-bonds with other identical BTAs. Herein, a protocol is presented that describes how to couple these BTAs to colloids and how to quantify the number of coupling sites, which determines the multivalency of the supramolecular colloids. Light scattering measurements show that the refractive index of the colloids is almost matched with that of the solvent, which strongly reduces the van der Waals forces between the colloids. Before photo-activation, the colloids remain well dispersed, as the BTAs are equipped with a photo-labile group that blocks the formation of hydrogen-bonds. Controlled deprotection with UV-light activates the short-range hydrogen-bonds between the BTAs, which triggers the colloidal self-assembly. The evolution from the dispersed state to the clustered state is monitored by confocal microscopy. These results are further quantified by image analysis with simple routines using ImageJ and Matlab. This merger of supramolecular chemistry and colloidal science offers a direct route towards light- and thermo-responsive colloidal assembly encoded in the surface-grafted monolayer. PMID:27168201

  19. Carbon Nanotube Tip Probes: Stability and Lateral Resolution in Scanning Probe Microscopy and Application to Surface Science to Semiconductors

    NASA Technical Reports Server (NTRS)

    Nguyen, Cattien V.; Chao, Kuo-Jen; Stevens, Ramsey M. D.; Delzeit, Lance; Cassell, Alan; Han, Jie; Meyyappan, M.; Arnold, James (Technical Monitor)

    2001-01-01

    In this paper we present results on the stability and lateral resolution capability of carbon nanotube (CNT) scanning probes as applied to atomic force microscopy (AFM). Surface topography images of ultra-thin films (2-5 nm thickness) obtained with AFM are used to illustrate the lateral resolution capability of single-walled carbon nanotube probes. Images of metal films prepared by ion beam sputtering exhibit grain sizes ranging from greater than 10 nm to as small as approximately 2 nm for gold and iridium respectively. In addition, imaging stability and lifetime of multi-walled carbon nanotube scanning probes are studied on a relatively hard surface of silicon nitride (Si3N4). AFM images Of Si3N4 surface collected after more than 15 hrs of continuous scanning show no detectable degradation in lateral resolution. These results indicate the general feasibility of CNT tips and scanning probe microscopy for examining nanometer-scale surface features of deposited metals as well as non-conductive thin films. AFM coupled with CNT tips offers a simple and nondestructive technique for probing a variety of surfaces, and has immense potential as a surface characterization tool in integrated circuit manufacturing.

  20. Colloids and Nucleation

    NASA Technical Reports Server (NTRS)

    Ackerson, Bruce

    1997-01-01

    The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range

  1. Simultaneous AFM nano-patterning and imaging for photomask repair

    NASA Astrophysics Data System (ADS)

    Keyvani, Aliasghar; Tamer, Mehmet S.; van Es, Maarten H.; Sadeghian, Hamed

    2016-03-01

    In this paper we present a new AFM based nano-patterning technique that can be used for fast defect repairing of high resolution photomasks and possibly other high-speed nano-patterning applications. The proposed method works based on hammering the sample with tapping mode AFM followed by wet cleaning of the residuals. On the area where a specific pattern should be written, the tip-sample interaction force is tuned in a controlled manner by changing the excitation frequency of the cantilever without interrupting the imaging process. Using this method several patterns where transferred to different samples with imaging speed. While the pattern was transferred to the sample in each tracing scan line, the patterned sample was imaged in retracing scan line, thus the outcome was immediately visible during the experiment.

  2. BOREAS AFM-5 Level-1 Upper Air Network Data

    NASA Technical Reports Server (NTRS)

    Barr, Alan; Hrynkiw, Charmaine; Newcomer, Jeffrey A. (Editor); Hall, Forrest G. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-5 team collected and processed data from the numerous radiosonde flights during the project. The goals of the AFM-05 team were to provide large-scale definition of the atmosphere by supplementing the existing Atmospheric Environment Service (AES) aerological network, both temporally and spatially. This data set includes basic upper-air parameters collected from the network of upper-air stations during the 1993, 1994, and 1996 field campaigns over the entire study region. The data are contained in tabular ASCII files. The level-1 upper-air network data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files also are available on a CD-ROM (see document number 20010000884).

  3. Insights into Epoxy Network Nanostructural Heterogeneity Using AFM-IR.

    PubMed

    Morsch, Suzanne; Liu, Yanwen; Lyon, Stuart B; Gibbon, Simon R

    2016-01-13

    The first direct observation of a chemically heterogeneous nanostructure within an epoxy resin is reported. Epoxy resins comprise the matrix component of many high performance composites, coatings and adhesives, yet the molecular network structure that underpins the performance of these industrially essential materials is not well understood. Internal nodular morphologies have repeatedly been reported for epoxy resins analyzed using SEM or AFM, yet the origin of these features remains a contentious subject, and epoxies are still commonly assumed to be chemically homogeneous. Uniquely, in this contribution we use the recently developed AFM-IR technique to eliminate previous differences in interpretation, and establish that nodule features correspond to heterogeneous network connectivity within an epoxy phenolic formulation.

  4. MDI: integrity index of cytoskeletal fibers observed by AFM

    NASA Astrophysics Data System (ADS)

    Manghi, Massimo; Bruni, Luca; Croci, Simonetta

    2016-06-01

    The Modified Directional Index (MDI) is a form factor of the angular spectrum computed from the 2D Fourier transform of an image marking the prevalence of rectilinear features throughout the picture. We study some properties of the index and we apply it to AFM images of cell cytoskeleton regions featuring patterns of rectilinear nearly parallel actin filaments as in the case of microfilaments grouped in bundles. The analysis of AFM images through MDI calculation quantifies the fiber directionality changes which could be related to fiber damages. This parameter is applied to the images of Hs 578Bst cell line, non-tumoral and not immortalized human epithelial cell line, irradiated with X-rays at doses equivalent to typical radiotherapy treatment fractions. In the reported samples, we could conclude that the damages are mainly born to the membrane and not to the cytoskeleton. It could be interesting to test the parameter also using other kinds of chemical or physical agents.

  5. LET Spectrum Measurements In CR-39 PNTD With AFM

    SciTech Connect

    Johnson, C. E.; DeWitt, J. M.; Benton, E. R.; Yasuda, N.; Benton, E. V.

    2011-06-01

    Energetic protons, neutrons, and heavy ions undergoing collisions with target nuclei of varying Z can produce residual heavy recoil fragments via intra-nuclear cascade/evaporation reactions. The particles produced in these non-elastic collisions generally have such extremely short range ({approx}<10 {mu}m) that they cannot be directly observed by conventional detection methods including CR-39 plastic nuclear track detector (PNTD) that has been chemically etched for analysis by standard visible light microscopy. However, high-LET recoil fragments having range on the order of several cell diameters can be produced in tissue during radiotherapy using proton and carbon beams. We have developed a method to analyze short-range, high-LET tracks in CR-39 plastic nuclear track detector (PNTD) using short duration chemical etching ({approx}<1 {mu}m) following by automated atomic force microscope (AFM) scanning. The post-scan data processing used in this work was based on semi-automated matrix analysis opposed to traditional grey-scale image analysis. This method takes advantage of the 3-D data obtained via AFM to achieve robust discrimination of nuclear tracks from other features inherently present in the post-etch detector surface. Through automation of AFM scanning, sufficient AFM scan frames were obtained to attain an LET spectrum spanning the LET range from 200-1500 keV/{mu}m. In addition to our experiments, simulations were carried out with the Monte Carlo transport code, FLUKA. To demonstrate this method, CR-39 PNTD was exposed to the proton therapy beam at Loma Linda University Medical Center (LLUMC) at 60 and 230 MeV. Additionally, detectors were exposed to 1 GeV protons at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL). For these exposures CR-39 PNTD, Al and Cu target foils were used between detector layers.

  6. LET Spectrum Measurements In CR-39 PNTD With AFM

    NASA Astrophysics Data System (ADS)

    Johnson, C. E.; DeWitt, J. M.; Benton, E. R.; Yasuda, N.; Benton, E. V.

    2011-06-01

    Energetic protons, neutrons, and heavy ions undergoing collisions with target nuclei of varying Z can produce residual heavy recoil fragments via intra-nuclear cascade/evaporation reactions. The particles produced in these non-elastic collisions generally have such extremely short range (˜<10 μm) that they cannot be directly observed by conventional detection methods including CR-39 plastic nuclear track detector (PNTD) that has been chemically etched for analysis by standard visible light microscopy. However, high-LET recoil fragments having range on the order of several cell diameters can be produced in tissue during radiotherapy using proton and carbon beams. We have developed a method to analyze short-range, high-LET tracks in CR-39 plastic nuclear track detector (PNTD) using short duration chemical etching (˜<1 μm) following by automated atomic force microscope (AFM) scanning. The post-scan data processing used in this work was based on semi-automated matrix analysis opposed to traditional grey-scale image analysis. This method takes advantage of the 3-D data obtained via AFM to achieve robust discrimination of nuclear tracks from other features inherently present in the post-etch detector surface. Through automation of AFM scanning, sufficient AFM scan frames were obtained to attain an LET spectrum spanning the LET range from 200-1500 keV/μm. In addition to our experiments, simulations were carried out with the Monte Carlo transport code, FLUKA. To demonstrate this method, CR-39 PNTD was exposed to the proton therapy beam at Loma Linda University Medical Center (LLUMC) at 60 and 230 MeV. Additionally, detectors were exposed to 1 GeV protons at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL). For these exposures CR-39 PNTD, Al and Cu target foils were used between detector layers.

  7. LET spectrum measurements in Cr-39 PNTD with AFM

    SciTech Connect

    Johnson, Carl Edward; De Witt, Joel M; Benton, Eric R; Yasuda, Nakahiro; Benton, Eugene V

    2010-01-01

    Energetic protons, neutrons, and heavy ions undergoing collisions with target nuclei of varying Z can produce residual heavy recoil fragments via intra-nuclear cascade/evaporation reactions. The particles produced in these non-elastic collisions generally have such extremely short range ({approx}< 10 {mu}m) that they cannot be directly observed by conventional detection methods including CR-39 plastic nuclear track detector (PNTD) that has been chemically etched for analysis by standard visible light microscopy. However, high-LET recoil fragments having range on the order of several cell diameters can be produced in tissue during radiotherapy using proton and carbon beams. We have developed a method to analyze short-range, high-LET tracks in CR-39 plastic nuclear track detector (PNTD) using short duration chemical etching ({approx}< 1 {mu}m) followed by automated atomic force microscope (AFM) scanning. The post-scan data processing used in this work was based on semi-automated matrix analysis opposed to traditional grey-scale image analysis. This method takes advantage of the 3-D data obtained via AFM to achieve robust discrimination of nuclear tracks from other features. Through automation of AFM scanning, sufficient AFM scan frames were obtained to attain an LET spectrum spanning the LET range from 200-1500 keV/{mu}m. In addition to our experiments, simulations were carried out with the Monte Carlo transport code, FLUKA. To demonstrate this method, CR-39 PNTD was exposed to the proton therapy beam at Loma Linda University Medical Center (LLUMC) at 60 and 230 MeV. Additionally, detectors were exposed to I GeV protons at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL). For these exposures CR-39 PNTD, Al and Cu target foils were used between detector layers.

  8. Using 2D Correlation Analysis to Enhance Spectral Information Available from Highly Spatially Resolved AFM-IR Spectra.

    PubMed

    Marcott, Curtis; Lo, Michael; Hu, Qichi; Kjoller, Kevin; Boskey, Adele; Noda, Isao

    2014-07-01

    The recent combination of atomic force microscopy and infrared spectroscopy (AFM-IR) has led to the ability to obtain IR spectra with nanoscale spatial resolution, nearly two orders-of-magnitude better than conventional Fourier transform infrared (FT-IR) microspectroscopy. This advanced methodology can lead to significantly sharper spectral features than are typically seen in conventional IR spectra of inhomogeneous materials, where a wider range of molecular environments are coaveraged by the larger sample cross section being probed. In this work, two-dimensional (2D) correlation analysis is used to examine position sensitive spectral variations in datasets of closely spaced AFM-IR spectra. This analysis can reveal new key insights, providing a better understanding of the new spectral information that was previously hidden under broader overlapped spectral features. Two examples of the utility of this new approach are presented. Two-dimensional correlation analysis of a set of AFM-IR spectra were collected at 200-nm increments along a line through a nucleation site generated by remelting a small spot on a thin film of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). There are two different crystalline carbonyl band components near 1720 cm(-1) that sequentially disappear before a band at 1740 cm(-1) due to more disordered material appears. In the second example, 2D correlation analysis of a series of AFM-IR spectra spaced every 1 micrometer of a thin cross section of a bone sample measured outward from an osteon center of bone growth. There are many changes in the amide I and phosphate band contours, suggesting changes in the bone structure are occurring as the bone matures.

  9. Combined single cell AFM manipulation and TIRFM for probing the molecular stability of multilayer fibrinogen matrices

    PubMed Central

    Christenson, W.; Yermolenko, I.; Plochberger, B.; Camacho-Alanis, F.; Ros, A.; Ugarova, T.P.; Ros, R.

    2014-01-01

    Adsorption of fibrinogen on various surfaces produces a nanoscale multilayer matrix, which strongly reduces the adhesion of platelets and leukocytes with implications for hemostasis and blood compatibility of biomaterials. The nonadhesive properties of fibrinogen matrices are based on their extensibility, ensuing the inability to transduce strong mechanical forces via cellular integrins and resulting in weak intracellular signaling. In addition, reduced cell adhesion may arise from the weaker associations between fibrinogen molecules in the superficial layers of the matrix. Such reduced stability would allow integrins to pull fibrinogen molecules out of the matrix with comparable or smaller forces than required to break integrin–fibrinogen bonds. To examine this possibility, we developed a method based on the combination of total internal reflection fluorescence microscopy, single cell manipulation with an atomic force microscope and microcontact printing to study the transfer of fibrinogen molecules out of a matrix onto cells. We calculated the average fluorescence intensities per pixel for wild-type HEK 293 (HEK WT) and HEK 293 cells expressing leukocyte integrin Mac-1 (HEK Mac-1) before and after contact with multilayered matrices of fluorescently labeled fibrinogen. For contact times of 500 s, HEK Mac-1 cells show a median increase of 57% of the fluorescence intensity compared to 6% for HEKWT cells. The results suggest that the integrin Mac-1-fibrinogen interactions are stronger than the intermolecular fibrinogen interactions in the superficial layer of the matrix. The low mechanical stability of the multilayer fibrinogen surface may contribute to the reduced cell adhesive properties of fibrinogen-coated substrates. We anticipate that the described method can be applied to various cell types to examine their integrin-mediated adhesion to the extracellular matrices with a variable protein composition. PMID:24239757

  10. Reflection-mode TERS on Insulin Amyloid Fibrils with Top-Visual AFM Probes.

    PubMed

    Moretti, Manola; Proietti Zaccaria, Remo; Descrovi, Emiliano; Das, Gobind; Leoncini, Marco; Liberale, Carlo; De Angelis, Francesco; Di Fabrizio, Enzo

    2013-03-01

    Tip-enhanced Raman spectroscopy provides chemical information while raster scanning samples with topographical detail. The coupling of atomic force microscopy and Raman spectroscopy in top illumination optical setup is a powerful configuration to resolve nanometer structures while collecting reflection mode backscattered signal. Here, we theoretically calculate the field enhancement generated by TER spectroscopy with top illumination geometry and we apply the technique to the characterization of insulin amyloid fibrils. We experimentally confirm that this technique is able to enhance the Raman signal of the polypeptide chain by a factor of 10(5), thus revealing details down to few molecules resolution.

  11. Combining AFM and Acoustic Probes to Reveal Changes in the Elastic Stiffness Tensor of Living Cells

    PubMed Central

    Nijenhuis, Nadja; Zhao, Xuegen; Carisey, Alex; Ballestrem, Christoph; Derby, Brian

    2014-01-01

    Knowledge of how the elastic stiffness of a cell affects its communication with its environment is of fundamental importance for the understanding of tissue integrity in health and disease. For stiffness measurements, it has been customary to quote a single parameter quantity, e.g., Young’s modulus, rather than the minimum of two terms of the stiffness tensor required by elasticity theory. In this study, we use two independent methods (acoustic microscopy and atomic force microscopy nanoindentation) to characterize the elastic properties of a cell and thus determine two independent elastic constants. This allows us to explore in detail how the mechanical properties of cells change in response to signaling pathways that are known to regulate the cell’s cytoskeleton. In particular, we demonstrate that altering the tensioning of actin filaments in NIH3T3 cells has a strong influence on the cell's shear modulus but leaves its bulk modulus unchanged. In contrast, altering the polymerization state of actin filaments influences bulk and shear modulus in a similar manner. In addition, we can use the data to directly determine the Poisson ratio of a cell and show that in all cases studied, it is less than, but very close to, 0.5 in value. PMID:25296302

  12. Analytical model for the deformation of a fluid-fluid interface beneath an AFM probe.

    PubMed

    Quinn, Daniel B; Feng, Jie; Stone, Howard A

    2013-02-01

    We present an analytical solution for the shape of a fluid-fluid interface near a nanoscale solid sphere, which is a configuration motivated by common measurements with an atomic force microscope. The forces considered are surface tension, gravity, and the van der Waals attraction. The nonlinear governing equation has been solved previously using the method of matched asymptotic expansions, and this requires that the surface tension forces far exceed those of gravity, i.e., the Bond number is much less than one. We first present this method using a physically relevant scaling of the equations, then offer a new analytical solution valid for all Bond numbers. We show that one configuration with a large effective Bond number, and thus one requiring our new solution, is a nanothick liquid film spread over a solid substrate. The scaling implications of both analytical methods are considered, and both are compared with numerical solutions of the full equation.

  13. Spectrophotometric probe

    DOEpatents

    Prather, William S.; O'Rourke, Patrick E.

    1994-01-01

    A support structure bearing at least one probe for making spectrophotometric measurements of a fluid using a source of light and a spectrophotometer. The probe includes a housing with two optical fibers and a planoconvex lens. A sleeve bearing a mirror surrounds the housing. The lens is separated from the mirror by a fixed distance, defining an interior space for receiving a volume of the fluid sample. A plurality of throughholes extending through the sleeve communicate between the sample volume and the exterior of the probe, all but one hole bearing a screen. A protective jacket surrounds the probe. A hollow conduit bearing a tube is formed in the wall of the probe for venting any air in the interior space when fluid enters. The probe is held at an acute angle so the optic fibers carrying the light to and from the probe are not bent severely on emergence from the probe.

  14. Spectrophotometric probe

    DOEpatents

    Prather, W.S.; O'Rourke, P.E.

    1994-08-02

    A support structure is described bearing at least one probe for making spectrophotometric measurements of a fluid using a source of light and a spectrophotometer. The probe includes a housing with two optical fibers and a planoconvex lens. A sleeve bearing a mirror surrounds the housing. The lens is separated from the mirror by a fixed distance, defining an interior space for receiving a volume of the fluid sample. A plurality of throughholes extending through the sleeve communicate between the sample volume and the exterior of the probe, all but one hole bearing a screen. A protective jacket surrounds the probe. A hollow conduit bearing a tube is formed in the wall of the probe for venting any air in the interior space when fluid enters. The probe is held at an acute angle so the optic fibers carrying the light to and from the probe are not bent severely on emergence from the probe. 3 figs.

  15. Confocal Raman-AFM, A New Tool for Materials Research

    NASA Astrophysics Data System (ADS)

    Schmidt, Ute

    2005-03-01

    Characterization of heterogeneous systems, e.g. polymers, on the nanometer scale continues to grow in importance and to impact key applications in the field of materials science, nanotechnology and catalysis. The development of advanced polymeric materials for such applications requires detailed information about the physical and chemical properties of these materials on the nanometer scale. However, some details about the phase-separation process in polymers are difficult to study with conventional characterization techniques due to the inability of these methods to chemically differentiate materials with good spatial resolution, without damage, staining or preferential solvent washing. The CR-AFM is a breakthrough in microscopy. It combines three measuring techniques in one instrument: a high resolution confocal optical microscope, an extremely sensitive Raman spectroscopy system, and an Atomic Force Microscope. Using this instrument, the high spatial and topographical resolution obtained with an AFM can be directly linked to the chemical information gained by Confocal Raman spectroscopy. To demonstrate the capabilities of this unique combination of measuring techniques, polymer blend films, spin coated on glass substrates, have been characterized. AFM measurements reveal the structural and mechanical properties of the films, whereas Raman spectral images show the chemical composition of the blends.

  16. Nanoscale rippling on polymer surfaces induced by AFM manipulation

    PubMed Central

    2015-01-01

    Summary Nanoscale rippling induced by an atomic force microscope (AFM) tip can be observed after performing one or many scans over the same area on a range of materials, namely ionic salts, metals, and semiconductors. However, it is for the case of polymer films that this phenomenon has been widely explored and studied. Due to the possibility of varying and controlling various parameters, this phenomenon has recently gained a great interest for some technological applications. The advent of AFM cantilevers with integrated heaters has promoted further advances in the field. An alternative method to heating up the tip is based on solvent-assisted viscoplastic deformations, where the ripples develop upon the application of a relatively low force to a solvent-rich film. An ensemble of AFM-based procedures can thus produce nanoripples on polymeric surfaces quickly, efficiently, and with an unprecedented order and control. However, even if nanorippling has been observed in various distinct modes and many theoretical models have been since proposed, a full understanding of this phenomenon is still far from being achieved. This review aims at summarizing the current state of the art in the perspective of achieving control over the rippling process on polymers at a nanoscale level. PMID:26733086

  17. Programmable, isothermal disassembly of DNA-linked colloidal particles

    NASA Astrophysics Data System (ADS)

    Tison, Christopher Kirby

    Colloidal particles serve as useful building blocks for materials applications ranging from controlled hand-gap materials to rationally designed drug delivery systems. Thus, developing approaches to direct the assembly and disassembly of sub-micron sized particles will be paramount to further advances in materials science engineering. This project focuses on using programmable and reversible binding between oligonucleotide strands to assemble and then disassemble polystyrene colloidal particles. It is shown that DNA-mediated assembly can be reversed at a fixed temperature using secondary oligonucleotide strands to competitively displace the primary strands linking particles together. It was found that (1) titrating the surface density of hybridizing probe strands and (2) adjusting the base length difference between primary and secondary target strands was key to successful isothermal disassembly. In order to titrate the surface density of primary probe-target duplexes, colloidal particles were conjugated with mixtures of probe strands and "diluent" strands in order to minimize the number of DNA linkages between particles. To reduce the steric interference of the diluent strands to hybridization events, diluent strands were clipped with a restriction enzyme in select cases. Kinetics studies revealed that a four to six base-length difference between primary and secondary target strands resulted in extensive competitive hybridization at secondary oligonucleotide concentrations as low as 10 nM. Importantly, it was found that the timing for release of either DNA alone or DNA-conjugated nanoparticles could be tuned through choices in the DNA sequences and concentration. Lastly, competitive hybridization was explored in select studies to drive the "shedding" of PEGylated DNA targets from microspheres to reveal underlying adhesive groups or ligands on the particle surface. Unlike prior work relying on elevated temperatures to melt DNA-linkages, this work presents an

  18. Colloid characterization and quantification in groundwater samples

    SciTech Connect

    K. Stephen Kung

    2000-06-01

    This report describes the work conducted at Los Alamos National Laboratory for studying the groundwater colloids for the Yucca Mountain Project in conjunction with the Hydrologic Resources Management Program (HRMP) and the Underground Test Area (UGTA) Project. Colloidal particle size distributions and total particle concentration in groundwater samples are quantified and characterized. Colloid materials from cavity waters collected near underground nuclear explosion sites by HRMP field sampling personnel at the Nevada Test Site (NTS) were quantified. Selected colloid samples were further characterized by electron microscope to evaluate the colloid shapes, elemental compositions, and mineral phases. The authors have evaluated the colloid size and concentration in the natural groundwater sample that was collected from the ER-20-5 well and stored in a 50-gallon (about 200-liter) barrel for several months. This groundwater sample was studied because HRMP personnel have identified trace levels of radionuclides in the water sample. Colloid results show that even though the water sample had filtered through a series of Millipore filters, high-colloid concentrations were identified in all unfiltered and filtered samples. They had studied the samples that were diluted with distilled water and found that diluted samples contained more colloids than the undiluted ones. These results imply that colloids are probably not stable during the storage conditions. Furthermore, results demonstrate that undesired colloids have been introduced into the samples during the storage, filtration, and dilution processes. They have evaluated possible sources of colloid contamination associated with sample collection, filtrating, storage, and analyses of natural groundwaters. The effects of container types and sample storage time on colloid size distribution and total concentration were studied to evaluate colloid stability by using J13 groundwater. The data suggests that groundwater samples

  19. Colloidal Assembly via Shape Complementarity

    SciTech Connect

    Macfarlane, Robert John; Mirkin, Chad A.

    2010-07-15

    A simple method for selectively assembling colloidal particles with depletion forces is achieved using the concept of shape complementarity, reminiscent of Fischer's “lock and key” enzyme model. A spherical particle can fit inside a second particle with an indentation of similar size and shape, allowing access to a large variety of assembled structures.

  20. Sonochemical synthesis of iron colloids

    SciTech Connect

    Suslick, K.S.; Fang, M.; Hyeon, T.

    1996-11-27

    We present here a new method for the preparation of stable ferromagnetic colloids of iron using high-intensity ultrasound to sonochemically decompose volatile organometallic compounds. These colloids have narrow size distributions centered at a few nanometers and are found to be superparamagnetic. In conclusion, a simple synthetic method has been discovered to produce nanosized iron colloid using high-intensity ultrasound. Nanometer iron particles dispersed in polyvinylpyrrolidone (PVP) matrix or stabilized by adsorption of oleic acid have been synthesized by sonochemical decomposition of Fe(CO){sub 5}. Transmission electron micrographs show that the iron particles have a relatively narrow range in size from 3 to 8 nm for polyvinylpyrrolidone, while oleic acid gives an even more uniform distribution at 8 nm. magnetic measurements revealed that these nanometer iron particles are superparamagnetic with a saturation magnetization of 101 emu/g (Fe) at 290 K. This work is easily extended to colloids of other metals and to alloys of two or more metals, simply by using multiple volatile precursors. 29 refs., 4 figs.

  1. Dynamics of evaporative colloidal patterning

    NASA Astrophysics Data System (ADS)

    Kaplan, C. Nadir; Wu, Ning; Mandre, Shreyas; Aizenberg, Joanna; Mahadevan, L.

    2015-09-01

    Drying suspensions often leave behind complex patterns of particulates, as might be seen in the coffee stains on a table. Here, we consider the dynamics of periodic band or uniform solid film formation on a vertical plate suspended partially in a drying colloidal solution. Direct observations allow us to visualize the dynamics of band and film deposition, where both are made of multiple layers of close packed particles. We further see that there is a transition between banding and filming when the colloidal concentration is varied. A minimal theory of the liquid meniscus motion along the plate reveals the dynamics of the banding and its transition to the filming as a function of the ratio of deposition and evaporation rates. We also provide a complementary multiphase model of colloids dissolved in the liquid, which couples the inhomogeneous evaporation at the evolving meniscus to the fluid and particulate flows and the transition from a dilute suspension to a porous plug. This allows us to determine the concentration dependence of the bandwidth and the deposition rate. Together, our findings allow for the control of drying-induced patterning as a function of the colloidal concentration and evaporation rate.

  2. Microbial effects on colloidal agglomeration

    SciTech Connect

    Hersman, L.

    1995-11-01

    Colloidal particles are known to enhance the transport of radioactive metals through soil and rock systems. This study was performed to determine if a soil microorganism, isolated from the surface samples collected at Yucca Mountain, NV, could affect the colloidal properties of day particles. The agglomeration of a Wyoming bentonite clay in a sterile uninoculated microbial growth medium was compared to the agglomeration in the medium inoculated with a Pseudomonas sp. In a second experiment, microorganisms were cultured in the succinate medium for 50 h and removed by centrifugation. The agglomeration of the clay in this spent was compared to sterile uninoculated medium. In both experiments, the agglomeration of the clay was greater than that of the sterile, uninoculated control. Based on these results, which indicate that this microorganism enhanced the agglomeration of the bentonite clay, it is possible to say that in the presence of microorganisms colloidal movement through a rock matrix could be reduced because of an overall increase in the size of colloidal particle agglomerates. 32 refs.

  3. Physics of Colloids in Space

    NASA Technical Reports Server (NTRS)

    Weitz, Dave; Weeks, Eric; Gasser, Urs; Dinsmore, Tony; Mawley, Suliana; Segre, Phil; Cipelletti, Lucia

    2000-01-01

    This talk will present recent results from ground-based research to support the "Physics of Colloids in Space" project which is scheduled to fly in the ISS approximately one year from now. In addition, results supporting future planned flights will be discussed.

  4. Solid colloidal optical wavelength filter

    DOEpatents

    Alvarez, Joseph L.

    1992-01-01

    A solid colloidal optical wavelength filter includes a suspension of spheal particles dispersed in a coagulable medium such as a setting plastic. The filter is formed by suspending spherical particles in a coagulable medium; agitating the particles and coagulable medium to produce an emulsion of particles suspended in the coagulable medium; and allowing the coagulable medium and suspended emulsion of particles to cool.

  5. Escherichia coli as a model active colloid: A practical introduction.

    PubMed

    Schwarz-Linek, Jana; Arlt, Jochen; Jepson, Alys; Dawson, Angela; Vissers, Teun; Miroli, Dario; Pilizota, Teuta; Martinez, Vincent A; Poon, Wilson C K

    2016-01-01

    The flagellated bacterium Escherichia coli is increasingly used experimentally as a self-propelled swimmer. To obtain meaningful, quantitative results that are comparable between different laboratories, reproducible protocols are needed to control, 'tune' and monitor the swimming behaviour of these motile cells. We critically review the knowledge needed to do so, explain methods for characterising the colloidal and motile properties of E. coli cells, and propose a protocol for keeping them swimming at constant speed at finite bulk concentrations. In the process of establishing this protocol, we use motility as a high-throughput probe of aspects of cellular physiology via the coupling between swimming speed and the proton motive force. PMID:26310235

  6. Colonoscopic preoperative localization using submucosal injection of radiolabelled colloid

    PubMed Central

    Cho, Carolyn; Jain, Sanjiv; Pilbeam, Mark; Tait, Noel; Thomson, Andrew

    2008-01-01

    Malignant colonic polyps can be removed endoscopically but surgical resection is sometimes required. However, the polypectomy site can be difficult to locate. Current methods use various tattooing agents, with varying degrees of success. A new technique using pre-operative injection of technetium-99m-labelled antimony colloid, with intraoperative localization using a handheld gamma probe, is described. Although unsuccessful in terms of localizing a previously partially resected polyp, the technique itself proved safe and simple, and has some advantages over other endoscopic approaches. PMID:18629395

  7. Plasticity of a Colloidal Polycrystal under Cyclic Shear

    NASA Astrophysics Data System (ADS)

    Tamborini, Elisa; Cipelletti, Luca; Ramos, Laurence

    2014-08-01

    We use confocal microscopy and time-resolved light scattering to investigate plasticity in a colloidal polycrystal, following the evolution of the network of grain boundaries as the sample is submitted to thousands of shear deformation cycles. The grain boundary motion is found to be ballistic, with a velocity distribution function exhibiting nontrivial power law tails. The shear-induced dynamics initially slow down, similarly to the aging of the spontaneous dynamics in glassy materials, but eventually reach a steady state. Surprisingly, the crossover time between the initial aging regime and the steady state decreases with increasing probed length scale, hinting at a hierarchical organization of the grain boundary dynamics.

  8. Plasticity of a colloidal polycrystal under cyclic shear.

    PubMed

    Tamborini, Elisa; Cipelletti, Luca; Ramos, Laurence

    2014-08-15

    We use confocal microscopy and time-resolved light scattering to investigate plasticity in a colloidal polycrystal, following the evolution of the network of grain boundaries as the sample is submitted to thousands of shear deformation cycles. The grain boundary motion is found to be ballistic, with a velocity distribution function exhibiting nontrivial power law tails. The shear-induced dynamics initially slow down, similarly to the aging of the spontaneous dynamics in glassy materials, but eventually reach a steady state. Surprisingly, the crossover time between the initial aging regime and the steady state decreases with increasing probed length scale, hinting at a hierarchical organization of the grain boundary dynamics. PMID:25170734

  9. Escherichia coli as a model active colloid: A practical introduction.

    PubMed

    Schwarz-Linek, Jana; Arlt, Jochen; Jepson, Alys; Dawson, Angela; Vissers, Teun; Miroli, Dario; Pilizota, Teuta; Martinez, Vincent A; Poon, Wilson C K

    2016-01-01

    The flagellated bacterium Escherichia coli is increasingly used experimentally as a self-propelled swimmer. To obtain meaningful, quantitative results that are comparable between different laboratories, reproducible protocols are needed to control, 'tune' and monitor the swimming behaviour of these motile cells. We critically review the knowledge needed to do so, explain methods for characterising the colloidal and motile properties of E. coli cells, and propose a protocol for keeping them swimming at constant speed at finite bulk concentrations. In the process of establishing this protocol, we use motility as a high-throughput probe of aspects of cellular physiology via the coupling between swimming speed and the proton motive force.

  10. Field induced anisotropic cooperativity in a magnetic colloidal glass

    NASA Astrophysics Data System (ADS)

    Wandersman, E.; Chushkin, Y.; Dubois, E.; Dupuis, V.; Robert, A.; Perzynski, R.

    The translational dynamics in a repulsive colloidal glass-former is probed by time-resolved X-ray Photon Correlation Spectroscopy. In this dense dispersion of charge-stabilized and magnetic nanoparticles, the interaction potential can be tuned, from quasi-isotropic to anisotropic by applying an external magnetic field. Structural and dynamical anisotropies are reported on interparticle lengthscales associated with highly anisotropic cooperativity, almost two orders of magnitude larger in the field direction than in the perpendicular direction and in zero field.

  11. Nonequilibrium interfaces in colloidal fluids

    NASA Astrophysics Data System (ADS)

    Bier, Markus; Arnold, Daniel

    2013-12-01

    The time-dependent structure, interfacial tension, and evaporation of an oversaturated colloid-rich (liquid) phase in contact with an undersaturated colloid-poor (vapor) phase of a colloidal dispersion is investigated theoretically during the early-stage relaxation, where the interface is relaxing towards a local equilibrium state while the bulk phases are still out of equilibrium. Since systems of this type exhibit a clear separation of colloidal and solvent relaxation time scales with typical times of interfacial tension measurements in between, they can be expected to be suitable for analogous experimental studies, too. The major finding is that, irrespective of how much the bulk phases differ from two-phase coexistence, the interfacial structure and the interfacial tension approach those at two-phase coexistence during the early-stage relaxation process. This is a surprising observation since it implies that the relaxation towards global equilibrium of the interface is not following but preceding that of the bulk phases. Scaling forms for the local chemical potential, the flux, and the dissipation rate exhibit qualitatively different leading order contributions depending on whether an equilibrium or a nonequilibrium system is considered. The degree of nonquilibrium between the bulk phases is found to not influence the qualitative relaxation behavior (i.e., the values of power-law exponents), but to determine the quantitative deviation of the observed quantities from their values at two-phase coexistence. Whereas the underlying dynamics differs between colloidal and molecular fluids, the behavior of quantities such as the interfacial tension approaching the equilibrium values during the early-stage relaxation process, during which nonequilibrium conditions of the bulk phases are not changed, can be expected to occur for both types of systems.

  12. Electrical characterization of FIB processed metal layers for reliable conductive-AFM on ZnO microstructures

    NASA Astrophysics Data System (ADS)

    Pea, M.; Maiolo, L.; Giovine, E.; Rinaldi, A.; Araneo, R.; Notargiacomo, A.

    2016-05-01

    We report on the conductive-atomic force microscopy (C-AFM) study of metallic layers in order to find the most suitable configuration for electrical characterization of individual ZnO micro-pillars fabricated by focused ion beam (FIB). The electrical resistance between the probe tip and both as deposited and FIB processed metal layers (namely, Cr, Ti, Au and Al) has been investigated. Both chromium and titanium evidenced a non homogenous and non ohmic behaviour, non negligible scanning probe induced anodic oxidation associated to electrical measurements, and after FIB milling they exhibited significantly higher tip-sample resistance. Aluminium had generally a more apparent non conductive behaviour. Conversely, gold films showed very good tip-sample conduction properties being less sensitive to FIB processing than the other investigated metals. We found that a reliable C-AFM electrical characterization of ZnO microstructures obtained by FIB machining is feasible by using a combination of metal films as top contact layer. An Au/Ti bilayer on top of ZnO was capable to sustain the FIB fabrication process and to form a suitable ohmic contact to the semiconductor, allowing for reliable C-AFM measurement. To validate the consistency of this approach, we measured the resistance of ZnO micropillars finding a linear dependence on the pillar height, as expected for an ohmic conductor, and evaluated the resistivity of the material. This procedure has the potential to be downscaled to nanometer size structures by a proper choice of metal films type and thickness.

  13. CaO as drop-in colloidal catalysts for the synthesis of higher polyglycerols.

    PubMed

    Kirby, Fiona; Nieuwelink, Anne-Eva; Kuipers, Bonny W M; Kaiser, Anton; Bruijnincx, Pieter C A; Weckhuysen, Bert M

    2015-03-23

    Glycerol is an attractive renewable building block for the synthesis of polyglycerols, which find application in the cosmetic and pharmaceutical industries. The selective etherification of glycerol to higher oligomers was studied in the presence of CaO colloids and the data are compared with those obtained from NaOH and CaO. The materials were prepared by dispersing CaO, CaCO3 , or Ca(OH)2 onto a carbon nanofiber (CNF) support. Colloidal nanoparticles were subsequently dispensed from the CNF into the reaction mixture to give CaO colloids that have a higher activity than equimolar amounts of bulk CaO and NaOH. Optimization of the reaction conditions allowed us to obtain a product with Gardner color number <2, containing no acrolein and minimal cyclic byproducts. The differences in the CaO colloids originating from CNF and bulk CaO were probed using light scattering and conductivity measurements. The results confirmed that the higher activity of the colloids originating from CaO/CNF was due to their more rapid formation and smaller size compared with colloids from bulk CaO. We thus have developed a practical method for the synthesis of polyglycerols containing low amounts of Ca.

  14. CaO as Drop-In Colloidal Catalysts for the Synthesis of Higher Polyglycerols

    PubMed Central

    Kirby, Fiona; Nieuwelink, Anne-Eva; Kuipers, Bonny W M; Kaiser, Anton; Bruijnincx, Pieter C A; Weckhuysen, Bert M

    2015-01-01

    Glycerol is an attractive renewable building block for the synthesis of polyglycerols, which find application in the cosmetic and pharmaceutical industries. The selective etherification of glycerol to higher oligomers was studied in the presence of CaO colloids and the data are compared with those obtained from NaOH and CaO. The materials were prepared by dispersing CaO, CaCO3, or Ca(OH)2 onto a carbon nanofiber (CNF) support. Colloidal nanoparticles were subsequently dispensed from the CNF into the reaction mixture to give CaO colloids that have a higher activity than equimolar amounts of bulk CaO and NaOH. Optimization of the reaction conditions allowed us to obtain a product with Gardner color number <2, containing no acrolein and minimal cyclic byproducts. The differences in the CaO colloids originating from CNF and bulk CaO were probed using light scattering and conductivity measurements. The results confirmed that the higher activity of the colloids originating from CaO/CNF was due to their more rapid formation and smaller size compared with colloids from bulk CaO. We thus have developed a practical method for the synthesis of polyglycerols containing low amounts of Ca. PMID:25684403

  15. Distorted colloidal arrays as designed template

    NASA Astrophysics Data System (ADS)

    Yu, Ye; Zhou, Ziwei; Möhwald, Helmuth; Ai, Bin; Zhao, Zhiyuan; Ye, Shunsheng; Zhang, Gang

    2015-01-01

    In this paper, a novel type of colloidal template with broken symmetry was generated using commercial, inductively coupled plasma reactive ion etching (ICP-RIE). With proper but simple treatment, the traditional symmetric non-close-packed colloidal template evolves into an elliptical profile with high uniformity. This unique feature can add flexibility to colloidal lithography and/or other lithography techniques using colloidal particles as building blocks to fabricate nano-/micro-structures with broken symmetry. Beyond that the novel colloidal template we developed possesses on-site tunability, i.e. the transformability from a symmetric into an asymmetric template. Sandwich-type particles with eccentric features were fabricated utilizing this tunable template. This distinguishing feature will provide the possibility to fabricate structures with unique asymmetric features using one set of colloidal template, providing flexibility and broad tunability to enable nano-/micro-structure fabrication with colloidal templates.

  16. Glass/Jamming Transition in Colloidal Aggregation

    NASA Technical Reports Server (NTRS)

    Segre, Philip N.; Prasad, Vikram; Weitz, David A.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    We have studied colloidal aggregation in a model colloid plus polymer system with short-range attractive interactions. By varying the colloid concentration and the strength of the attraction, we explored regions where the equilibrium phase is expected to consist of colloidal crystallites in coexistance with colloidal gas (i.e. monomers). This occurs for moderate values of the potential depth, U approximately equal to 2-5 kT. Crystallization was not always observed. Rather, over an extended sub-region two new metastable phases appear, one fluid-like and one solid-like. These were examined in detail with light scattering and microscopy techniques. Both phases consist of a near uniform distribution of small irregular shaped clusters of colloidal particles. The dynamical and structural characteristics of the ergodic-nonergodic transition between the two phases share much in common with the colloidal hard sphere glass transition.

  17. Direct visualization of the interfacial position of colloidal particles and their assemblies

    NASA Astrophysics Data System (ADS)

    Vogel, N.; Ally, J.; Bley, K.; Kappl, M.; Landfester, K.; Weiss, C. K.

    2014-05-01

    A method for direct visualization of the position of nanoscale colloidal particles at air-water interfaces is presented. After assembling hard (polystyrene, poly(methyl methacrylate), silica) or soft core-shell gold-hydrogel composite (Au@PNiPAAm) colloids at the air-water interface, butylcyanoacrylate is introduced to the interface via the gas phase. Upon contact with water, an anionic polymerization reaction of the monomer is initiated and a film of poly(butylcyanoacrylate) (PBCA) is generated, entrapping the colloids at their equilibrium position at the interface. We apply this method to investigate the formation of complex, binary assembly structures directly at the interface, to visualize soft, nanoscale hydrogel colloids in the swollen state, and to visualize and quantify the equilibrium position of individual micro- and nanoscale colloids at the air-water interface depending of the amount of charge present on the particle surface. We find that the degree of deprotonation of the carboxyl group shifts the air-water contact angle, which is further confirmed by colloidal probe atomic force microscopy. Remarkably, the contact angles determined for individual colloidal particles feature a significant distribution that greatly exceeds errors attributable to the size distribution of the colloids. This finding underlines the importance of accessing soft matter on an individual particle level.A method for direct visualization of the position of nanoscale colloidal particles at air-water interfaces is presented. After assembling hard (polystyrene, poly(methyl methacrylate), silica) or soft core-shell gold-hydrogel composite (Au@PNiPAAm) colloids at the air-water interface, butylcyanoacrylate is introduced to the interface via the gas phase. Upon contact with water, an anionic polymerization reaction of the monomer is initiated and a film of poly(butylcyanoacrylate) (PBCA) is generated, entrapping the colloids at their equilibrium position at the interface. We apply

  18. A review of the application of atomic force microscopy (AFM) in food science and technology.

    PubMed

    Liu, Shaoyang; Wang, Yifen

    2011-01-01

    Atomic force microscopy (AFM) is a powerful nanoscale analysis technique used in food area. This versatile technique can be used to acquire high-resolution sample images and investigate local interactions in air or liquid surroundings. In this chapter, we explain the principles of AFM and review representative applications of AFM in gelatin, casein micelle, carrageenan, gellan gum, starch, and interface. We elucidate new knowledge revealed with AFM as well as ways to use AFM to obtain morphology and rheology information in different food fields.

  19. PREFACE: NC-AFM 2006: Proceedings of the 9th International Conference on Non-contact Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Tomitori, Masahiko; Onishi, Hiroshi

    2007-02-01

    The advent of scanning probe microscopy (SPM) in the 1980s has significantly promoted nanoscience and nanotechnology. In particular, non-contact atomic force microscopy (NC-AFM), one of the SPM family, has unique capabilities with high spatial resolution for nanoscale measurements in vacuum, air and liquids. In the last decade we have witnessed the rapid progress of NC-AFM with improved performance and increasing applications. A series of NC-AFM international conferences have greatly contributed to this field. Initiated in Osaka in 1998, the NC-AFM meeting has been followed by annual conferences at Pontresina, Hamburg, Kyoto, Montreal, Dingle, Seattle and Bad Essen. The 9th conference was held in Kobe, Japan, 16-20 July 2006. This special issue of Nanotechnology contains the outstanding contributions of the conference. During the meeting delegates learnt about a number of significant advances. Topics covered atomic resolution imaging of metals, semiconductors, insulators, ionic crystals, oxides, molecular systems, imaging of biological materials in various environments and novel instrumentation. Work also included the characterization of electronic and magnetic properties, tip and cantilever fabrication and characterization, atomic distinction based on analysis of tip-sample interaction, atomic scale manipulation, fabrication of nanostructures using NC-AFM, and related theories and simulations. We are greatly impressed by the increasing number of applications, and convinced that NC-AFM and related techniques are building a bridge to a future nano world, where quantum phenomena will dominate and nano devices will be realized. In addition, a special session on SPM road maps was held as a first trial in the field, where the future prospects of SPM were discussed enthusiastically. The overall success of the NC-AFM 2006 conference was due to the efforts of many individuals and groups with respect to scientific and technological progress, as well as the international

  20. Statistical Physics of Colloidal Dispersions.

    NASA Astrophysics Data System (ADS)

    Canessa, E.

    Available from UMI in association with The British Library. Requires signed TDF. This thesis is concerned with the equilibrium statistical mechanics of colloidal dispersions which represent useful model systems for the study of condensed matter physics; namely, charge stabilized colloidal dispersions and polymer stabilized colloidal dispersions. A one-component macroparticle approach is adopted in order to treat the macroscopic and microscopic properties of these systems in a simple and comprehensive manner. The thesis opens with the description of the nature of the colloidal state before reviewing some basic definitions and theory in Chapter II. In Chapter III a variational theory of phase equilibria based on the Gibbs-Bogolyobov inequality is applied to sterically stabilized colloidal dispersions. Hard spheres are chosen as the reference system for the disordered phases while an Einstein model is used for the ordered phases. The new choice of pair potential, taken for mathematical convenience, is a superposition of two Yukawa functions. By matching a double Yukawa potential to the van der Waals attractive potential at different temperatures and introducing a purely temperature dependent coefficient to the repulsive part, a rich variety of observed phase separation phenomena is qualitatively described. The behaviour of the potential is found to be consistent with a small decrease of the polymer layer thickness with increasing temperature. Using the same concept of a collapse transition the non-monotonic second virial coefficient is also explained and quantified. It is shown that a reduction of the effective macroparticle diameter with increasing temperature can only be partially examined from the point of view of a (binary-) polymer solution theory. This chapter concludes with the description of the observed, reversible, depletion flocculation behaviour. This is accomplished by using the variational formalism and by invoking the double Yukawa potential to allow

  1. Colloidal aspects of texture perception.

    PubMed

    van Vliet, Ton; van Aken, George A; de Jongh, Harmen H J; Hamer, Rob J

    2009-08-30

    Recently, considerable attention has been given to the understanding of texture attributes that cannot directly be related to physical properties of food, such as creamy, crumbly and watery. The perception of these attributes is strongly related to the way the food is processed during food intake, mastication, swallowing of it and during the cleaning of the mouth after swallowing. Moreover, their perception is modulated by the interaction with other basic attributes, such as taste and aroma attributes (e.g. sourness and vanilla). To be able to link the composition and structure of food products to more complicated texture attributes, their initial physical/colloid chemical properties and the oral processing of these products must be well understood. Understanding of the processes in the mouth at colloidal length scales turned out to be essential to grasp the interplay between perception, oral physiology and food properties. In view of the huge differences in physical chemical properties between food products, it is practical to make a distinction between solid, semi-solid, and liquid food products. The latter ones are often liquid dispersions of emulsion droplets or particles in general. For liquid food products for instance flow behaviour and colloidal stability of dispersed particles play a main role in determining their textural properties. For most solid products stiffness and fracture behaviour in relation to water content are essential while for semi-solids a much larger range of mechanical properties will play a role. Examples of colloidal aspects of texture perception will be discussed for these three categories of products based on selected sensory attributes and/or relevant colloidal processes. For solid products some main factors determining crispness will be discussed. For crispiness of dry cellular solid products these are water content and the architecture of the product at mesoscopic length scales (20-1000 microm). In addition the distribution of

  2. In situ observation of biomolecules patterned on a PEG-modified Si surface by scanning probe lithography.

    PubMed

    Choi, Inhee; Kang, Sung Koo; Lee, Jeongjin; Kim, Younghun; Yi, Jongheop

    2006-09-01

    A Si(100) wafer was modified with methoxy-poly(ethylene glycol) (M-PEG silane) via a self-assembly technique and nano-/micro-sized patterns were then fabricated by scanning probe lithography. The protrusive silicon dioxide pattern was more reactive compared to the non-patterned area, i.e. the PEG deposited area. To demonstrate the feasibility of the submicron patterning of protein based on the anodic oxidation of the Si surface by atomic force microscopy (AFM), streptavidin labelled with Au-colloidal particle and non-labelled streptavidin were site-selectively immobilized on the patterned areas. The streptavidin-patterned surface produced by these procedures can be utilized for the detection of biotinylated materials, such as an antibody and an antigen. A patterned silicon surface is the basis of biosensing devices, in which the patterned areas serve as sensing elements that directly interact with bioanalytes, while the background of the substrate remains passive to the deposition of analytes, thus resulting in a high signal-to-noise ratio.

  3. Solvent-mediated repair and patterning of surfaces by AFM

    SciTech Connect

    Elhadj, S; Chernov, A; De Yoreo, J

    2007-10-30

    A tip-based approach to shaping surfaces of soluble materials with nanometer-scale control is reported. The proposed method can be used, for example, to eliminate defects and inhomogeneities in surface shape, repair mechanical or laser-induced damage to surfaces, or perform 3D lithography on the length scale of an AFM tip. The phenomenon that enables smoothing and repair of surfaces is based on the transport of material from regions of high- to low-curvature within the solution meniscus formed in a solvent-containing atmosphere between the surface in question and an AFM tip scanned over the surface. Using in situ AFM measurements of the kinetics of surface remodeling on KDP (KH{sub 2}PO{sub 4}) crystals in humid air, we show that redistribution of solute material during relaxation of grooves and mounds is driven by a reduction in surface free energy as described by the Gibbs-Thomson law. We find that the perturbation from a flat interface evolves according to the diffusion equation where the effective diffusivity is determined by the product of the surface stiffness and the step kinetic coefficient. We also show that, surprisingly, if the tip is instead scanned over or kept stationary above an atomically flat area of the surface, a convex structure is formed with a diameter that is controlled by the dimensions of the meniscus, indicating that the presence of the tip and meniscus reduces the substrate chemical potential beneath that of the free surface. This allows one to create nanometer-scale 3D structures of arbitrary shape without the removal of substrate material or the use of extrinsic masks or chemical compounds. Potential applications of these tip-based phenomena are discussed.

  4. Image Analysis and Length Estimation of Biomolecules Using AFM

    PubMed Central

    Sundstrom, Andrew; Cirrone, Silvio; Paxia, Salvatore; Hsueh, Carlin; Kjolby, Rachel; Gimzewski, James K.; Reed, Jason; Mishra, Bud

    2014-01-01

    There are many examples of problems in pattern analysis for which it is often possible to obtain systematic characterizations, if in addition a small number of useful features or parameters of the image are known a priori or can be estimated reasonably well. Often, the relevant features of a particular pattern analysis problem are easy to enumerate, as when statistical structures of the patterns are well understood from the knowledge of the domain. We study a problem from molecular image analysis, where such a domain-dependent understanding may be lacking to some degree and the features must be inferred via machine-learning techniques. In this paper, we propose a rigorous, fully automated technique for this problem. We are motivated by an application of atomic force microscopy (AFM) image processing needed to solve a central problem in molecular biology, aimed at obtaining the complete transcription profile of a single cell, a snapshot that shows which genes are being expressed and to what degree. Reed et al. (“Single molecule transcription profiling with AFM,” Nanotechnology, vol. 18, no. 4, 2007) showed that the transcription profiling problem reduces to making high-precision measurements of biomolecule backbone lengths, correct to within 20–25 bp (6–7.5 nm). Here, we present an image processing and length estimation pipeline using AFM that comes close to achieving these measurement tolerances. In particular, we develop a biased length estimator on trained coefficients of a simple linear regression model, biweighted by a Beaton–Tukey function, whose feature universe is constrained by James–Stein shrinkage to avoid overfitting. In terms of extensibility and addressing the model selection problem, this formulation subsumes the models we studied. PMID:22759526

  5. Colloid dispersion on the pore scale.

    PubMed

    Baumann, Thomas; Toops, Laura; Niessner, Reinhard

    2010-02-01

    Dispersion describes the spreading of a tracer or contaminant in an aquifer. Detailed knowledge of dispersion is the key to successful risk assessment in case of groundwater pollution or groundwater protection. The dispersion of colloids on the pore scale is controlled by flow velocity, ionic strength, colloid size, colloid concentration, and colloid-matrix interactions. The objective of this study was to provide quantitative data and to assess the scale dependency of colloid dispersion on the pore scale. The positions of carboxylated polystyrene microspheres (1 microm, 0.5 microm) were recorded during transport experiments in silicon micromodels with three pore topologies. The positions were combined into particle trajectories revealing the flow path of individual colloids. More than thousand trajectories were evaluated for each experiment to obtain the dispersivity of the colloids for flow distances between 10 and 1000 microm. All experiments were run at high Peclet numbers. The pore scale dispersivity was on the order of 8-30% of the flow distance with pure water, dependent on the heterogeneity of the pore topology. The dispersivity was positively correlated with the ionic strength and inversely correlated with the colloid size and the flow velocity. A coating of the micromodel surface with humic acid also increased dispersivity. The quantitative data set presented here supports the theoretical framework for colloid transport and allows to parametrize colloid transport on the pore scale.

  6. What happens when pharmaceuticals meet colloids.

    PubMed

    Xing, Yingna; Chen, Xijuan; Zhuang, Jie; Chen, Xin

    2015-12-01

    Pharmaceuticals (PCs) have been widely detected in natural environment due to agricultural application of reclaimed water, sludge and animal wastes. Their potential risks to various ecosystems and even to human health have caused great concern; however, little was known about their environmental behaviors. Colloids (such as clays, metal oxides, and particulate organics) are kind of substances that are active and widespread in the environment. When PCs meet colloids, their interaction may influence the fate, transport, and toxicity of PCs. This review summarizes the progress of studies on the role of colloids in mediating the environmental behaviors of PCs. Synthesized results showed that colloids can adsorb PCs mainly through ion exchange, complexation and non-electrostatic interactions. During this process the structure of colloids and the stability of PCs may be changed. The adsorbed PCs may have higher risks to induce antibiotic resistance; besides, their transport may also be altered considering they have great chance to move with colloids. Solution conditions (such as pH, ionic strength, and cations) could influence these interactions between PCs and colloids, as they can change the forms of PCs and alter the primary forces between PCs and colloids in the solution. It could be concluded that PCs in natural soils could bind with colloids and then co-transport during the processes of irrigation, leaching, and erosion. Therefore, colloid-PC interactions need to be understood for risk assessment of PCs and the best management practices of various ecosystems (such as agricultural and wetland systems). PMID:26427370

  7. Colloid dispersion on the pore scale.

    PubMed

    Baumann, Thomas; Toops, Laura; Niessner, Reinhard

    2010-02-01

    Dispersion describes the spreading of a tracer or contaminant in an aquifer. Detailed knowledge of dispersion is the key to successful risk assessment in case of groundwater pollution or groundwater protection. The dispersion of colloids on the pore scale is controlled by flow velocity, ionic strength, colloid size, colloid concentration, and colloid-matrix interactions. The objective of this study was to provide quantitative data and to assess the scale dependency of colloid dispersion on the pore scale. The positions of carboxylated polystyrene microspheres (1 microm, 0.5 microm) were recorded during transport experiments in silicon micromodels with three pore topologies. The positions were combined into particle trajectories revealing the flow path of individual colloids. More than thousand trajectories were evaluated for each experiment to obtain the dispersivity of the colloids for flow distances between 10 and 1000 microm. All experiments were run at high Peclet numbers. The pore scale dispersivity was on the order of 8-30% of the flow distance with pure water, dependent on the heterogeneity of the pore topology. The dispersivity was positively correlated with the ionic strength and inversely correlated with the colloid size and the flow velocity. A coating of the micromodel surface with humic acid also increased dispersivity. The quantitative data set presented here supports the theoretical framework for colloid transport and allows to parametrize colloid transport on the pore scale. PMID:20042215

  8. What happens when pharmaceuticals meet colloids.

    PubMed

    Xing, Yingna; Chen, Xijuan; Zhuang, Jie; Chen, Xin

    2015-12-01

    Pharmaceuticals (PCs) have been widely detected in natural environment due to agricultural application of reclaimed water, sludge and animal wastes. Their potential risks to various ecosystems and even to human health have caused great concern; however, little was known about their environmental behaviors. Colloids (such as clays, metal oxides, and particulate organics) are kind of substances that are active and widespread in the environment. When PCs meet colloids, their interaction may influence the fate, transport, and toxicity of PCs. This review summarizes the progress of studies on the role of colloids in mediating the environmental behaviors of PCs. Synthesized results showed that colloids can adsorb PCs mainly through ion exchange, complexation and non-electrostatic interactions. During this process the structure of colloids and the stability of PCs may be changed. The adsorbed PCs may have higher risks to induce antibiotic resistance; besides, their transport may also be altered considering they have great chance to move with colloids. Solution conditions (such as pH, ionic strength, and cations) could influence these interactions between PCs and colloids, as they can change the forms of PCs and alter the primary forces between PCs and colloids in the solution. It could be concluded that PCs in natural soils could bind with colloids and then co-transport during the processes of irrigation, leaching, and erosion. Therefore, colloid-PC interactions need to be understood for risk assessment of PCs and the best management practices of various ecosystems (such as agricultural and wetland systems).

  9. Application of ESEM to environmental colloids.

    PubMed

    Nuttall, H E; Kale, R

    1993-08-01

    Environmental colloids are toxic or radioactive particles suspended in ground or surface water. These hazardous particles can facilitate and accelerate the transport of toxicants and enhance the threat to humans by exposure to pathogenic substances. The chemical and physical properties of hazardous colloids have not been well characterized nor are there standard colloid remediation technologies to prevent their deleterious effects. Colloid characterization requires measurement of their size distribution, zeta potential, chemical composition, adsorption capacity, and morphology. The environmental scanning electron microscope (ESEM) by ElectroScan, Inc., analyzes particle sizes, composition, and morphology. It is also used in this study to identify the attachment of colloids onto packing or rock surfaces in our development of a colloid remediation process. The ESEM has confirmed the composition of groundwater colloids in our studies to be generally the same material as the surrounding rock. The morphology studies have generally shown that colloids are simply small pieces of the rock surface that has exfoliated into the surrounding water. However, in general, the source and chemical composition of groundwater colloids is site dependent. We have found that an ESEM works best as a valuable analysis tool within a suite of colloid characterization instruments.

  10. Chancellor Water Colloids: Characterization and Radionuclide Association

    SciTech Connect

    Abdel-Fattah, Amr I.

    2012-06-18

    Concluding remarks about this paper are: (1) Gravitational settling, zeta potential, and ultrafiltration data indicate the existence of a colloidal phase of both the alpha and beta emitters in the Chancellor water; (2) The low activity combined with high dispersion homogeneity of the Chancellor water indicate that both alpha and beta emitters are not intrinsic colloids; (3) Radionuclides in the Chancellor water, particularly Pu, coexist as dissolved aqueous and sorbed phases - in other words the radionuclides are partitioned between the aqueous phase and the colloidal phase; (4) The presence of Pu as a dissolved species in the aqueous phase, suggests the possibility of Pu in the (V) oxidation state - this conclusion is supported by the similarity of the k{sub d} value of Pu determined in the current study to that determined for Pu(V) sorbed onto smectite colloids, and the similar electrokinetic behavior of the Chancellor water colloids to smectite colloids; (5) About 50% of the Pu(V) is in the aqueous phase and 50% is sorbed on colloids (mass concentration of colloids in the Chancellor water is 0.12 g/L); (6) The k{sub d} of the Pu and the beta emitters (fission products) between aqueous and colloidal phases in the Chancellor water is {approx}8.0 x 10{sup 3} mL/g using two different activity measurement techniques (LSC and alpha spectroscopy); (7) The gravitational settling and size distributions of the association colloids indicate that the properties (at least the physical ones) of the colloids to which the alpha emitters are associated with seem to be different that the properties of the colloids to which the beta emitters are associated with - the beta emitters are associated with very small particles ({approx}50 - 120 nm), while the alpha emitters are associated with relatively larger particles; and (8) The Chancellor water colloids are extremely stable under the natural pH and ionic strength conditions, indicating high potential for transport in the

  11. Theoretical modelling of AFM for bimetallic tip-substrate interactions

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Ferrante, John

    1991-01-01

    Recently, a new technique for calculating the defect energetics of alloys based on Equivalent Crystal Theory was developed. This new technique successfully predicts the bulk properties for binary alloys as well as segregation energies in the dilute limit. The authors apply this limit for the calculation of energy and force as a function of separation of an atomic force microscope (AFM) tip and substrate. The study was done for different combinations of tip and sample materials. The validity of the universality discovered for the same metal interfaces is examined for the case of different metal interactions.

  12. The Advancing State of AF-M315E Technology

    NASA Technical Reports Server (NTRS)

    Masse, Robert; Spores, Ronald A.; McLean, Chris

    2014-01-01

    The culmination of twenty years of applied research in hydroxyl ammonium nitrate (HAN)-based monopropellants, the NASA Space Technology mission Directorate's (STMD) Green Propellant Infusion Mission (GPIM) will achieve the first on-orbit demonstration of an operational AF-M315E green propellant propulsion system by the end of 2015. Following an contextual overview of the completed flight design of the GPIM propellant storage and feed system, results of first operation of a flight-representative heavyweight 20-N engineering model thruster (to be conducted in mid-2014) are presented with performance comparisons to prior lab model (heavyweight) test articles.

  13. Dendronized iron oxide colloids for imaging the sentinel lymph node

    NASA Astrophysics Data System (ADS)

    Jouhannaud, J.; Garofalo, A.; Felder-Flesch, D.; Pourroy, G.

    2015-03-01

    Various methods have been used in medicine for more than one century to explore the lymphatic system. Radioactive colloids (RuS labelled with 99mTc) or/and Vital Blue dye are injected around the primary tumour and detected by means of nuclear probe or visual colour inspection respectively. The simultaneous clinical use of both markers (dye and radionuclide) improves the sensitivity of detection close to 100%. Superparamagnetic iron oxides (SPIOs) are currently receiving much attention as strong T2 weighted magnetic resonance imaging contrast agents that can be potentially used for preoperative localization of sentinel nodes, but also for peroperative detection of sentinel node using hand-held probes. In that context, we present the elaboration of dendronized iron oxide nanoparticles elaborated at the Institute of Physics and Chemistry of Materials of Strasbourg.

  14. Electrokinetic properties of polymer colloids

    NASA Technical Reports Server (NTRS)

    Micale, F. J.; Fuenmayor, D. Y.

    1986-01-01

    The surface of polymer colloids, especially polystyrene latexes, were modified for the purpose of controlling the electrokinetic properties of the resulting colloids. Achievement required a knowledge of electrical double layer charging mechanism, as a function of the electrolyte conditions, at the polymer/water interface. The experimental approach is to control the recipe formulation in the emulsion polymerization process so as to systematically vary the strong acid group concentration on the surface of the polymer particles. The electrophoretic mobility of these model particles will then be measured as a function of surface group concentration and as a function of electrolyte concentration and type. An effort was also made to evaluate the electrophoretic mobility of polystyrene latexes made in space and to compare the results with latexes made on the ground.

  15. Biaxial ferromagnetic liquid crystal colloids.

    PubMed

    Liu, Qingkun; Ackerman, Paul J; Lubensky, Tom C; Smalyukh, Ivan I

    2016-09-20

    The design and practical realization of composite materials that combine fluidity and different forms of ordering at the mesoscopic scale are among the grand fundamental science challenges. These composites also hold a great potential for technological applications, ranging from information displays to metamaterials. Here we introduce a fluid with coexisting polar and biaxial ordering of organic molecular and magnetic colloidal building blocks exhibiting the lowest symmetry orientational order. Guided by interactions at different length scales, rod-like organic molecules of this fluid spontaneously orient along a direction dubbed "director," whereas magnetic colloidal nanoplates order with their dipole moments parallel to each other but pointing at an angle to the director, yielding macroscopic magnetization at no external fields. Facile magnetic switching of such fluids is consistent with predictions of a model based on competing actions of elastic and magnetic torques, enabling previously inaccessible control of light. PMID:27601668

  16. Colloidal silica films for high-capacity DNA arrays

    NASA Astrophysics Data System (ADS)

    Glazer, Marc Irving

    The human genome project has greatly expanded the amount of genetic information available to researchers, but before this vast new source of data can be fully utilized, techniques for rapid, large-scale analysis of DNA and RNA must continue to develop. DNA arrays have emerged as a powerful new technology for analyzing genomic samples in a highly parallel format. The detection sensitivity of these arrays is dependent on the quantity and density of immobilized probe molecules. We have investigated substrates with a porous, "three-dimensional" surface layer as a means of increasing the surface area available for the synthesis of oligonucleotide probes, thereby increasing the number of available probes and the amount of detectable bound target. Porous colloidal silica films were created by two techniques. In the first approach, films were deposited by spin-coating silica colloid suspensions onto flat glass substrates, with the pores being formed by the natural voids between the solid particles (typically 23nm pores, 35% porosity). In the second approach, latex particles were co-deposited with the silica and then pyrolyzed, creating films with larger pores (36 nm), higher porosity (65%), and higher surface area. For 0.3 mum films, enhancements of eight to ten-fold and 12- to 14-fold were achieved with the pure silica films and the films "templated" with polymer latex, respectively. In gene expression assays for up to 7,000 genes using complex biological samples, the high-capacity films provided enhanced signals and performed equivalently or better than planar glass on all other functional measures, confirming that colloidal silica films are a promising platform for high-capacity DNA arrays. We have also investigated the kinetics of hybridization on planar glass and high-capacity substrates. Adsorption on planar arrays is similar to ideal Langmuir-type adsorption, although with an "overshoot" at high solution concentration. Hybridization on high-capacity films is

  17. Dynamics of hard sphere colloidal dispersions

    NASA Technical Reports Server (NTRS)

    Zhu, J. X.; Chaikin, Paul M.; Phan, S.-E.; Russel, W. B.

    1994-01-01

    Our objective is to perform on homogeneous, fully equilibrated dispersions the full set of experiments characterizing the transition from fluid to solid and the properties of the crystalline and glassy solid. These include measurements quantifying the nucleation and growth of crystallites, the structure of the initial fluid and the fully crystalline solid, and Brownian motion of particles within the crystal, and the elasticity of the crystal and the glass. Experiments are being built and tested for ideal microgravity environment. Here we describe the ground based effort, which exploits a fluidized bed to create a homogeneous, steady dispersion for the studies. The differences between the microgravity environment and the fluidized bed is gauged by the Peclet number Pe, which measures the rate of convection/sedimentation relative to Brownian motion. We have designed our experiment to accomplish three types of measurements on hard sphere suspensions in a fluidized bed: the static scattering intensity as a function of angle to determine the structure factor, the temporal autocorrelation function at all scattering angles to probe the dynamics, and the amplitude of the response to an oscillatory forcing to deduce the low frequency viscoelasticity. Thus the scattering instrument and the colloidal dispersion were chosen such as that the important features of each physical property lie within the detectable range for each measurement.

  18. Dynamics of cracking in drying colloidal sheets.

    PubMed

    Sengupta, Rajarshi; Tirumkudulu, Mahesh S

    2016-04-01

    Colloidal dispersions are known to display a fascinating network of cracks on drying. We probe the fracture mechanics of free-standing films of aqueous polymer-particle dispersions. Thin films of the dispersion are cast between a pair of plain steel wires and allowed to dry under ambient conditions. The strain induced on the particle network during drying is relieved by cracking. The stress which causes the films to crack has been calculated by measuring the deflection of the wires. The critical cracking stress varied inversely to the two-thirds' power of the film thickness. We also measure the velocity of the tip of a moving crack. The motion of a crack has been modeled as a competition between the release of the elastic energy stored in the particle network, the increase in surface energy as a result of the growth of a crack, the rate of viscous dissipation of the interstitial fluid and the kinetic energy associated with a moving crack. There is fair agreement between the measured crack velocities and predictions.

  19. Dynamics of cracking in drying colloidal sheets.

    PubMed

    Sengupta, Rajarshi; Tirumkudulu, Mahesh S

    2016-04-01

    Colloidal dispersions are known to display a fascinating network of cracks on drying. We probe the fracture mechanics of free-standing films of aqueous polymer-particle dispersions. Thin films of the dispersion are cast between a pair of plain steel wires and allowed to dry under ambient conditions. The strain induced on the particle network during drying is relieved by cracking. The stress which causes the films to crack has been calculated by measuring the deflection of the wires. The critical cracking stress varied inversely to the two-thirds' power of the film thickness. We also measure the velocity of the tip of a moving crack. The motion of a crack has been modeled as a competition between the release of the elastic energy stored in the particle network, the increase in surface energy as a result of the growth of a crack, the rate of viscous dissipation of the interstitial fluid and the kinetic energy associated with a moving crack. There is fair agreement between the measured crack velocities and predictions. PMID:26924546

  20. Phases transitions and interfaces in temperature-sensitive colloidal systems

    NASA Astrophysics Data System (ADS)

    Nguyen, Duc; Schall, Peter

    2013-03-01

    Colloids are widely used because of their exceptional properties. Beside their own applications in food, petrol, cosmetics and drug industries, photonic, optical filters and chemical sensor, they are also known as powerful model systems to study molecular phase behavior. Here, we examine both aspects of colloids using temperature-sensitive colloidal systems to fully investigate colloidal phase behavior and colloidal assembly.

  1. Electrocoagulation of colloidal biogenic selenium.

    PubMed

    Staicu, Lucian C; van Hullebusch, Eric D; Lens, Piet N L; Pilon-Smits, Elizabeth A H; Oturan, Mehmet A

    2015-02-01

    Colloidal elemental selenium (Se(0)) adversely affects membrane separation processes and aquatic ecosystems. As a solution to this problem, we investigated for the first time the removal potential of Se(0) by electrocoagulation process. Colloidal Se(0) was produced by a strain of Pseudomonas fluorescens and showed limited gravitational settling. Therefore, iron (Fe) and aluminum (Al) sacrificial electrodes were used in a batch reactor under galvanostatic conditions. The best Se(0) turbidity removal (97 %) was achieved using iron electrodes at 200 mA. Aluminum electrodes removed 96 % of colloidal Se(0) only at a higher current intensity (300 mA). At the best Se(0) removal efficiency, electrocoagulation using Fe electrode removed 93 % of the Se concentration, whereas with Al electrodes the Se removal efficiency reached only 54 %. Due to the less compact nature of the Al flocs, the Se-Al sediment was three times more voluminous than the Se-Fe sediment. The toxicity characteristic leaching procedure (TCLP) test showed that the Fe-Se sediment released Se below the regulatory level (1 mg L(-1)), whereas the Se concentration leached from the Al-Se sediment exceeded the limit by about 20 times. This might be related to the mineralogical nature of the sediments. Electron scanning micrographs showed Fe-Se sediments with a reticular structure, whereas the Al-Se sediments lacked an organized structure. Overall, the results obtained showed that the use of Fe electrodes as soluble anode in electrocoagulation constitutes a better option than Al electrodes for the electrochemical sedimentation of colloidal Se(0).

  2. Colloidal assembly by ice templating.

    PubMed

    Kumaraswamy, Guruswamy; Biswas, Bipul; Choudhury, Chandan Kumar

    2016-01-01

    We investigate ice templating of aqueous dispersions of polymer coated colloids and crosslinkers, at particle concentrations far below that required to form percolated monoliths. Freezing the aqueous dispersions forces the particles into close proximity to form clusters, that are held together as the polymer chains coating the particles are crosslinked. We observe that, with an increase in the particle concentration from about 10(6) to 10(8) particles per ml, there is a transition from isolated single particles to increasingly larger clusters. In this concentration range, most of the colloidal clusters formed are linear or sheet like particle aggregates. Remarkably, the cluster size distribution for clusters smaller than about 30 particles, as well as the size distribution of linear clusters, is only weakly dependent on the dispersion concentration in the range that we investigate. We demonstrate that the main features of cluster formation are captured by kinetic simulations that do not consider hydrodynamics or instabilities at the growing ice front due to particle concentration gradients. Thus, clustering of colloidal particles by ice templating dilute dispersions appears to be governed only by particle exclusion by the growing ice crystals that leads to their accumulation at ice crystal boundaries.

  3. Colloidal dynamics near an interface

    NASA Astrophysics Data System (ADS)

    Mani, Madhav; Manoharan, Vinothan; Brenner, Michael; Kaz, David; McGorty, Ryan

    2010-11-01

    Although the equilibrium state of a colloidal particle at an interface is well understood, the dynamics associated with the approach to equilibrium is not. Recent high-resolution experiments have shown that the dynamics are richer than expected. This part of the study focuses on the evolution of the system after the initiation of a contact-line. We model the dynamics associated with the three degrees of motion in this regime, the center of mass (c.o.m.) of the colloid, the location of the contact-line and the dynamic contact-angle. Following Nikolov et al. (Journal of Colloid and Interface Science - 112,1,1986), we derive the statements of force balance by taking variations of an energy functional. Appealing to a balance of power we are able to derive the dynamical laws. Associated with the degrees of motion are three modes of dissipation corresponding to a moving c.o.m., a moving contact-line and an evolving contact angle. We derive an asymptotically valid model for the system, which we integrate numerically and compare to experiments.

  4. Nanostructured colloidal crystals from forced hydrolysis methods.

    PubMed

    Otal, Eugenio H; Granada, Mara; Troiani, Horacio E; Cánepa, Horacio; Walsöe de Reca, Noemí E

    2009-08-18

    In this work, an original route for ZnO nanostructured spherical colloids and their assembly into colloidal crystals are presented. The temporal evolution of crystal size and shape was followed by X-ray diffraction and the colloids size distribution by scanning electron microscopy. These spherical colloids showed a change in their size dispersion with aging time. Early stage suspensions, with a narrow size distribution, were settled to the bottom and dried with a slow evaporation rate to obtain colloidal crystals. This original route provides a new material for future applications in opalline photonic crystals, with a dielectric constant higher than that of classical materials (silica and latex). Moreover, this route means an improvement of previously reported data from the literature since it involves a one-pot strategy and room-temperature colloid assembly.

  5. Crystallization of DNA-coated colloids

    PubMed Central

    Wang, Yu; Wang, Yufeng; Zheng, Xiaolong; Ducrot, Étienne; Yodh, Jeremy S.; Weck, Marcus; Pine, David J.

    2015-01-01

    DNA-coated colloids hold great promise for self-assembly of programmed heterogeneous microstructures, provided they not only bind when cooled below their melting temperature, but also rearrange so that aggregated particles can anneal into the structure that minimizes the free energy. Unfortunately, DNA-coated colloids generally collide and stick forming kinetically arrested random aggregates when the thickness of the DNA coating is much smaller than the particles. Here we report DNA-coated colloids that can rearrange and anneal, thus enabling the growth of large colloidal crystals from a wide range of micrometre-sized DNA-coated colloids for the first time. The kinetics of aggregation, crystallization and defect formation are followed in real time. The crystallization rate exhibits the familiar maximum for intermediate temperature quenches observed in metallic alloys, but over a temperature range smaller by two orders of magnitude, owing to the highly temperature-sensitive diffusion between aggregated DNA-coated colloids. PMID:26078020

  6. Crystallization of DNA-coated colloids.

    PubMed

    Wang, Yu; Wang, Yufeng; Zheng, Xiaolong; Ducrot, Étienne; Yodh, Jeremy S; Weck, Marcus; Pine, David J

    2015-06-16

    DNA-coated colloids hold great promise for self-assembly of programmed heterogeneous microstructures, provided they not only bind when cooled below their melting temperature, but also rearrange so that aggregated particles can anneal into the structure that minimizes the free energy. Unfortunately, DNA-coated colloids generally collide and stick forming kinetically arrested random aggregates when the thickness of the DNA coating is much smaller than the particles. Here we report DNA-coated colloids that can rearrange and anneal, thus enabling the growth of large colloidal crystals from a wide range of micrometre-sized DNA-coated colloids for the first time. The kinetics of aggregation, crystallization and defect formation are followed in real time. The crystallization rate exhibits the familiar maximum for intermediate temperature quenches observed in metallic alloys, but over a temperature range smaller by two orders of magnitude, owing to the highly temperature-sensitive diffusion between aggregated DNA-coated colloids.

  7. Dynamic DNA Interactions with Functionalized Colloids

    NASA Astrophysics Data System (ADS)

    Zhang, Lu; Zhu, Yingxi Elaine

    2009-03-01

    Many biomedical processes, such as protein adsorption, DNA hybridization and enzyme reactivity, are intimately related to their interactions with surfaces and complex ionic environments, yet the details of biomacromolecular interaction remain insufficiently understood. In this work, we use confocal laser scanning microscopy to examine the interaction between DNA molecules and functionalized colloidal particles in aqueous suspension. We observe an intriguing attractive interaction between DNAs and carboxyl-functionalized silica particles of varied sizes from 50 nm to 3 um, resulting in complex DNA-colloid aggregation with a strong dependence on DNA/colloid size ration and ionic strength. As colloidal size becomes larger than DNA dimensions, colloidal doublets and triplets with adsorbed DNAs are observed at high DNA concentration and ionic strength. The intriguing DNA-colloid complex structures are further confirmed by SEM and appear stable for at least 2 weeks.

  8. AFM analysis of bleaching effects on dental enamel microtopography

    NASA Astrophysics Data System (ADS)

    Pedreira de Freitas, Ana Carolina; Espejo, Luciana Cardoso; Botta, Sergio Brossi; Teixeira, Fernanda de Sa; Luz, Maria Aparecida A. Cerqueira; Garone-Netto, Narciso; Matos, Adriana Bona; Salvadori, Maria Cecilia Barbosa da Silveira

    2010-02-01

    The purpose of this in vitro study was to test a new methodology to evaluate the effects of 35% hydrogen peroxide agent on the microtopography of sound enamel using an atomic force microscope (AFM). The buccal sound surfaces of three extracted human lower incisors were used, without polishing the surfaces to maintain them with natural morphology. These unpolished surfaces were subjected to bleaching procedure with 35% hydrogen peroxide that consisted of 4 applications of the bleaching agent on enamel surfaces for 10 min each application. Surface images were obtained in a 15 μm × 15 μm area using an AFM. The roughness (Ra and RMS) and the power spectral density (PSD) were obtained before and after the bleaching treatment. As results we could inquire that the PSD analyses were very suitable to identifying the morphological changes on the surfaces, while the Ra and RMS parameters were insufficient to represent the morphological alterations promoted by bleaching procedure on enamel. The morphological wavelength in the range of visible light spectrum (380-750 nm) was analyzed, showing a considerable increase of the PSD with the bleaching treatment.

  9. Analysis of AFM cantilever dynamics close to sample surface

    NASA Astrophysics Data System (ADS)

    Habibnejad Korayem, A.; Habibnejad Korayem, Moharam; Ghaderi, Reza

    2013-07-01

    For imaging and manipulation of biological specimens application of atomic force microscopy (AFM) in liquid is necessary. In this paper, tapping-mode AFM cantilever dynamics in liquid close to sample surface is modeled and simulated by well defining the contact forces. The effect of cantilever tilting angle has been accounted carefully. Contact forces have some differences in liquid in comparison to air or vacuum in magnitude or formulation. Hydrodynamic forces are also applied on the cantilever due to the motion in liquid. A continuous beam model is used with its first mode and forward-time simulation method for simulation of its hybrid dynamics and the frequency response and amplitude versus separation diagrams are extracted. The simulation results show a good agreement with experimental results. The resonance frequency in liquid is so small in comparison to air due to additional mass and also additional damping due to the viscosity of the liquid around. The results show that the effect of separation on free vibration amplitude is great. Its effect on resonance frequency is considerable too.

  10. Pathogen identification using peptide nanotube biosensors and impedance AFM

    NASA Astrophysics Data System (ADS)

    Maccuspie, Robert I.

    Pathogen identification at highly sensitive levels is crucial to meet urgent needs in fighting the spread of disease or detecting bioterrorism events. Toward that end, a new method for biosensing utilizing fluorescent antibody nanotubes is proposed. Fundamental studies on the self-assembly of these peptide nanotubes are performed, as are applications of aligning these nanotubes on surfaces. As biosensors, these nanotubes incorporate recognition units with antibodies at their ends and fluorescent signaling units at their sidewalls. When viral pathogens were mixed with these antibody nanotubes in solution, the nanotubes rapidly aggregated around the viruses. The size of the aggregates increased as the concentration of viruses increased, as detected by flow cytometry on the order of attomolar concentrations by changes in fluorescence and light scattering intensities. This enabled determination of the concentrations of viruses at trace levels (102 to 106 pfu/mL) within 30 minutes from the receipt of samples to the final quantitative data analysis, as demonstrated on Adenovirus, Herpes Simplex Virus, Influenza, and Vaccinia virus. As another separate approach, impedance AFM is used to study the electrical properties of individual viruses and nanoparticles used as model systems. The design, development, and implementation of the impedance AFM for an Asylum Research platform is described, as well as its application towards studying the impedance of individual nanoparticles as a model system for understanding the fundamental science of how the life cycle of a virus affects its electrical properties. In combination, these approaches fill a pressing need to quantify viruses both rapidly and sensitively.

  11. Does colloid shape affect detachment of colloids by a moving air-water interface?

    PubMed

    Aramrak, Surachet; Flury, Markus; Harsh, James B; Zollars, Richard L; Davis, Howard P

    2013-05-14

    Air-water interfaces interact strongly with colloidal particles by capillary forces. The magnitude of the interaction force depends on, among other things, the particle shape. Here, we investigate the effects of particle shape on colloid detachment by a moving air-water interface. We used hydrophilic polystyrene colloids with four different shapes (spheres, barrels, rods, and oblong disks), but otherwise identical surface properties. The nonspherical shapes were created by stretching spherical microspheres on a film of polyvinyl alcohol (PVA). The colloids were then deposited onto the inner surface of a glass channel. An air bubble was introduced into the channel and passed through, thereby generating a receding followed by an advancing air-water interface. The detachment of colloids by the air-water interfaces was visualized with a confocal microscope, quantified by image analysis, and analyzed statistically to determine significant differences. For all colloid shapes, the advancing air-water interface caused pronounced colloid detachment (>63%), whereas the receding interface was ineffective in colloid detachment (<1.5%). Among the different colloid shapes, the barrels were most readily removed (94%) by the advancing interface, followed by the spheres and oblong disks (80%) and the rods (63%). Colloid detachment was significantly affected by colloid shape. The presence of an edge, as it occurs in a barrel-shaped colloid, promoted colloid detachment because the air-water interface is being pinned at the edge of the colloid. This suggests that the magnitude of colloid mobilization and transport in porous media is underestimated for edged particles and overestimated for rodlike particles when a sphere is used as a model colloid.

  12. Dynamic Colloidal Stabilization by Nanoparticle Halos

    NASA Astrophysics Data System (ADS)

    Karanikas, S.; Louis, A. A.

    2004-12-01

    We explore the conditions under which colloids can be stabilized by the addition of smaller particles. The largest repulsive barriers between colloids occur when the added particles repel each other with soft interactions, leading to an accumulation near the colloid surfaces. At lower densities these layers of mobile particles (nanoparticle halos) result in stabilization, but when too many are added, the interactions become attractive again. We systematically study these effects—accumulation repulsion, reentrant attraction, and bridging—by accurate integral equation techniques.

  13. Binodal Colloidal Aggregation Test - 4: Polydispersion

    NASA Technical Reports Server (NTRS)

    Chaikin, Paul M.

    2008-01-01

    Binodal Colloidal Aggregation Test - 4: Polydispersion (BCAT-4-Poly) will use model hard-spheres to explore seeded colloidal crystal nucleation and the effects of polydispersity, providing insight into how nature brings order out of disorder. Crewmembers photograph samples of polymer and colloidal particles (tiny nanoscale spheres suspended in liquid) that model liquid/gas phase changes. Results will help scientists develop fundamental physics concepts previously cloaked by the effects of gravity.

  14. Binary Colloidal Alloy Test Conducted on Mir

    NASA Technical Reports Server (NTRS)

    Hoffmann, Monica I.; Ansari, Rafat R.

    1999-01-01

    Colloids are tiny (submicron) particles suspended in fluid. Paint, ink, and milk are examples of colloids found in everyday life. The Binary Colloidal Alloy Test (BCAT) is part of an extensive series of experiments planned to investigate the fundamental properties of colloids so that scientists can make colloids more useful for technological applications. Some of the colloids studied in BCAT are made of two different sized particles (binary colloidal alloys) that are very tiny, uniform plastic spheres. Under the proper conditions, these colloids can arrange themselves in a pattern to form crystals. These crystals may form the basis of new classes of light switches, displays, and optical devices. Windows made of liquid crystals are already in the marketplace. These windows change their appearance from transparent to opaque when a weak electric current is applied. In the future, if the colloidal crystals can be made to control the passage of light through them, such products could be made much more cheaply. These experiments require the microgravity environment of space because good quality crystals are difficult to produce on Earth because of sedimentation and convection in the fluid. The BCAT experiment hardware included two separate modules for two different experiments. The "Slow Growth" hardware consisted of a 35-mm camera with a 250- exposure photo film cartridge. The camera was aimed toward the sample module, which contained 10 separate colloid samples. A rack of small lights provided backlighting for the photographs. The BCAT hardware was launched on the shuttle and was operated aboard the Russian space station Mir by American astronauts John Blaha and David Wolf (launched September 1996 and returned January 1997; reflown September 1997 and returned January 1998). To begin the experiment, one of these astronauts would mix the samples to disperse the colloidal particles and break up any crystals that might have already formed. Once the samples were mixed and

  15. PLGA-chitosan/PLGA-alginate Nanoparticle Blends as Biodegradable Colloidal Gels for Seeding Human Umbilical Cord Mesenchymal Stem Cells

    PubMed Central

    Wang, Qun; Jamal, Syed; Detamore, Michael S.; Berkland, Cory

    2010-01-01

    The natural polymers chitosan and alginate represent an attractive material choice for biodegradable inplants. These were used as coating materials to make positively and negatively charged PLGA nanoparticles, respectively. After blending at total solids concentration >10% wt/vol, these oppositely charged nanoparticles yielded a cohesive colloidal gel. Electrostatic forces between oppositely charged nanoparticles produced a stable 3-D porous network that may be extruded or molded to the desired shape. This high concentration colloidal system demonstrated shear-thinning behavior due to the disruption of interparticle interactions. Once the external force was removed, the cohesive property of the colloidal gel was recovered. Scanning electron micrographs of dried colloidal networks revealed an organized, 3-D microporous structure. Rheological studies were employed to probe the differences in plasticity and shear sensitivity of colloidal gels. Viability tests of hUCMSCs seeded on the colloidal gels also demonstrated the negligible cytotoxicity of the materials. All the results indicated the potential application of the biodegradable colloidal gels as an injectable scaffold in tissue engineering and drug release. PMID:21254383

  16. Collective motion in populations of colloidal bots

    NASA Astrophysics Data System (ADS)

    Bartolo, Denis

    One of the origins of active matter physics was the idea that flocks, herds, swarms and shoals could be quantitatively described as emergent ordered phases in self-driven materials. From a somehow dual perspective, I will show how to engineer active materials our of colloidal flocks. I will show how to motorize colloidal particles capable of sensing the orientation of their neighbors and how to handle them in microfluidic chips. These populations of colloidal bots display a non-equilibrium transition toward collective motion. A special attention will be paid to the robustness of the resulting colloidal flocks with respect to geometrical frustration and to quenched disorder.

  17. Colloid Coalescence with Focused X Rays

    SciTech Connect

    Weon, B. M.; Kim, J. T.; Je, J. H.; Yi, J. M.; Wang, S.; Lee, W.-K.

    2011-07-01

    We show direct evidence that focused x rays enable us to merge polymer colloidal particles at room temperature. This phenomenon is ascribed to the photochemical scission of colloids with x rays, reducing the molecular weight, glass transition temperature, surface tension, and viscosity of colloids. The observation of the neck bridge growth with time shows that the x-ray-induced colloid coalescence is analogous to viscoelastic coalescence. This finding suggests a feasible protocol of photonic nanofabrication by sintering or welding of polymers, without thermal damage, using x-ray photonics.

  18. Aggregation kinetics in a model colloidal suspension

    SciTech Connect

    Bastea, S

    2005-08-08

    The authors present molecular dynamics simulations of aggregation kinetics in a colloidal suspension modeled as a highly asymmetric binary mixture. Starting from a configuration with largely uncorrelated colloidal particles the system relaxes by coagulation-fragmentation dynamics to a structured state of low-dimensionality clusters with an exponential size distribution. The results show that short range repulsive interactions alone can give rise to so-called cluster phases. For the present model and probably other, more common colloids, the observed clusters appear to be equilibrium phase fluctuations induced by the entropic inter-colloidal attractions.

  19. Colloid Titration--A Rapid Method for the Determination of Charged Colloid.

    ERIC Educational Resources Information Center

    Ueno, Keihei; Kina, Ken'yu

    1985-01-01

    "Colloid titration" is a volumetric method for determining charged polyelectrolytes in aqueous solutions. The principle of colloid titration, reagents used in the procedure, methods of endpoint detection, preparation of reagent solutions, general procedure used, results obtained, and pH profile of colloid titration are considered. (JN)

  20. In situ probing the interior of single bacterial cells at nanometer scale

    NASA Astrophysics Data System (ADS)

    Liu, Boyin; Hemayet Uddin, Md; Ng, Tuck Wah; Paterson, David L.; Velkov, Tony; Li, Jian; Fu, Jing

    2014-10-01

    We report a novel approach to probe the interior of single bacterial cells at nanometre resolution by combining focused ion beam (FIB) and atomic force microscopy (AFM). After removing layers of pre-defined thickness in the order of 100 nm on the target bacterial cells with FIB milling, AFM of different modes can be employed to probe the cellular interior under both ambient and aqueous environments. Our initial investigations focused on the surface topology induced by FIB milling and the hydration effects on AFM measurements, followed by assessment of the sample protocols. With fine-tuning of the process parameters, in situ AFM probing beneath the bacterial cell wall was achieved for the first time. We further demonstrate the proposed method by performing a spatial mapping of intracellular elasticity and chemistry of the multi-drug resistant strain Klebsiella pneumoniae cells prior to and after it was exposed to the ‘last-line’ antibiotic polymyxin B. Our results revealed increased stiffness occurring in both surface and interior regions of the treated cells, suggesting loss of integrity of the outer membrane from polymyxin treatments. In addition, the hydrophobicity measurement using a functionalized AFM tip was able to highlight the evident hydrophobic portion of the cell such as the regions containing cell membrane. We expect that the proposed FIB-AFM platform will help in gaining deeper insights of bacteria-drug interactions to develop potential strategies for combating multi-drug resistance.

  1. Individual particle motion in colloids: Microviscosity, microdiffusivity, and normal stresses

    NASA Astrophysics Data System (ADS)

    Zia, Roseanna N.

    We study the evolution of stress and microstructure in a colloidal dispersion by tracking transient probe motion during start-up and cessation of a strong flow. For large Pe, steady state is reached when a boundary layer (in which advection balances diffusion) forms at particle contact on the timescale of the flow, a/U , where a is the probe size and U its speed. On the other hand, relaxation following cessation occurs over several timescales corresponding to distinct physical processes. For very short times, the timescale for relaxation is set by the diffusion over the boundary-layer thickness. Nearly all stress relaxation occurs during this process, owing to the dependence of the bath-particle drag on the contact value of the microstructure. At longer times the collective diffusion of the bath particles acts to close the wake. In this long-time limit as structural isotropy is restored, the majority of the microstructural relaxation occurs with very little change in suspension stress. Theoretical results are presented and compared with Brownian dynamics simulation. Two regimes of probe motion are studied: an externally applied constant force and an imposed constant velocity. The microstructural evolution is qualitatively different for the two regimes, with a longer transient phase and a thinner boundary layer and longer wake at steady state in the latter case. The work is also compared to analogous results for sheared suspensions undergoing start-up and cessation. The study moves next to investigations of dual-probe microrheology. Motivated by the phenomenon of equilibrium depletion interactions, we study the interaction between a pair of probe particles translating with equal velocity through a dispersion with their line of centers transverse to the external forcing. The character of the microstructure surrounding the probes is determined both by the distance R by which the two probes are separated and by the strength of the external forcing, Pe = U a/Db , where

  2. Gamma radiation synthesis of colloidal AgNPs for its potential application in antimicrobial fabrics

    NASA Astrophysics Data System (ADS)

    Bera, Anuradha; Garai, Purabi; Singh, Rita; Prakash Gupta, P.; Malav, Shatrughan; Singh, Durgeshwer; Kumar, Devendra; Tiwari, B. L.; Vaijapurkar, S. G.

    2015-10-01

    Highly stable colloidal solution of silver nanoparticles in a water-isopropanol-polyvinyl alcohol system was prepared through 60Co-gamma radiation at total dose of 35 kGy at dose rate of 5.67 kGy/h under nitrogen atmosphere. Ultraviolet-visible (UV-vis), X-ray diffraction (XRD), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) of the obtained colloidal solution indicated the formation of spherical shaped well mono dispersed silver nanoparticles with average diameter about 30 nm having very narrow size distribution. The radiolytically obtained nanosilver colloid was coated onto cotton fabrics by a simple industrial screen printing method and its adhesion with the fabric was found out by leaching studies using Atomic Absorption Spectrophotometry (AAS). Good adhesion was achieved by the adopted method wherein 89.5% of the coated nanosilver was retained in the fabric even after keeping the fabrics soaked in water for more than 60 h. Antimicrobial efficacy tests of the nanosilver coated cotton fabric showed that nanosilver coating is effective in killing both bacterial and fungal strains even at very low nanosilver loading (21.81 μgm/cm2). Nanosilver coating on the cotton fabric did not allow microbes (Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli and Candida albicans) to adhere and proliferate on fabric surface. Staphylococci (Staphylococcus aureus) and Yeast (Candida albicans) showed inhibition zones in presence of these nanosilver coated fabrics while no inhibition zone was observed with the uncoated control fabric.

  3. AFM CHARACTERIZATION OF RAMAN LASER INDUCED DAMAGE ON CDZNTECRYSTAL SURFACES

    SciTech Connect

    Teague, L.; Duff, M.

    2008-10-07

    High quality CdZnTe (or CZT) crystals have the potential for use in room temperature gamma-ray and X-ray spectrometers. Over the last decade, the methods for growing high quality CZT have improved the quality of the produced crystals however there are material features that can influence the performance of these materials as radiation detectors. The presence of structural heterogeneities within the crystals, such as twinning, pipes, grain boundaries (polycrystallinity), and secondary phases (SPs) can have an impact on the detector performance. There is considerable need for reliable and reproducible characterization methods for the measurement of crystal quality. With improvements in material characterization and synthesis, these crystals may become suitable for widespread use in gamma radiation detection. Characterization techniques currently utilized to test for quality and/or to predict performance of the crystal as a gamma-ray detector include infrared (IR) transmission imaging, synchrotron X-ray topography, photoluminescence spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and Raman spectroscopy. In some cases, damage caused by characterization methods can have deleterious effects on the crystal performance. The availability of non-destructive analysis techniques is essential to validate a crystal's quality and its ability to be used for either qualitative or quantitative gamma-ray or X-ray detection. The work presented herein discusses the damage that occurs during characterization of the CZT surface by a laser during Raman spectroscopy, even at minimal laser powers. Previous Raman studies have shown that the localized annealing from tightly focused, low powered lasers results in areas of higher Te concentration on the CZT surface. This type of laser damage on the surface resulted in decreased detector performance which was most likely due to increased leakage current caused by areas of higher Te concentration. In this study

  4. Effect of tip mass on frequency response and sensitivity of AFM cantilever in liquid.

    PubMed

    Farokh Payam, Amir; Fathipour, Morteza

    2015-03-01

    The effect of tip mass on the frequency response and sensitivity of atomic force microscope (AFM) cantilever in the liquid environment is investigated. For this purpose, using Euler-Bernoulli beam theory and considering tip mass and hydrodynamic functions in a liquid environment, an expression for the resonance frequencies of AFM cantilever in liquid is derived. Then, based on this expression, the effect of the surface contact stiffness on the flexural mode of a rectangular AFM cantilever in fluid is investigated and compared with the case where the AFM cantilever operates in the air. The results show that in contrast with an air environment, the tip mass has no significant impact on the resonance frequency and sensitivity of the AFM cantilever in the liquid. Hence, analysis of AFM behaviour in liquid environment by neglecting the tip mass is logical. PMID:25562584

  5. Colloid transport in dual-permeability media.

    PubMed

    Leij, Feike J; Bradford, Scott A

    2013-07-01

    It has been widely reported that colloids can travel faster and over longer distances in natural structured porous media than in uniform structureless media used in laboratory studies. The presence of preferential pathways for colloids in the subsurface environment is of concern because of the increased risks for disease caused by microorganisms and colloid-associated contaminants. This study presents a model for colloid transport in dual-permeability media that includes reversible and irreversible retention of colloids and first-order exchange between the aqueous phases of the two regions. The model may also be used to describe transport of other reactive solutes in dual-permeability media. Analytical solutions for colloid concentrations in aqueous and solid phases were obtained using Laplace transformation and matrix decomposition. The solutions proved convenient to assess the effect of model parameters on the colloid distribution. The analytical model was used to describe effluent concentrations for a bromide tracer and 3.2- or 1-μm-colloids that were observed after transport through a composite 10-cm long porous medium made up of a cylindrical lens or core of sand and a surrounding matrix with sand of a different grain size. The tracer data were described very well and realistic estimates were obtained for the pore-water velocity in the two flow domains. An accurate description was also achieved for most colloid breakthrough curves. Dispersivity and retention parameters were typically greater for the larger 3.2-μm-colloids while both reversible and irreversible retention rates tended to be higher for the finer sands than the coarser sand. The relatively small sample size and the complex flow pattern in the composite medium made it difficult to reach definitive conclusions regarding transport parameters for colloid transport.

  6. Colloid transport in dual-permeability media

    NASA Astrophysics Data System (ADS)

    Leij, Feike J.; Bradford, Scott A.

    2013-07-01

    It has been widely reported that colloids can travel faster and over longer distances in natural structured porous media than in uniform structureless media used in laboratory studies. The presence of preferential pathways for colloids in the subsurface environment is of concern because of the increased risks for disease caused by microorganisms and colloid-associated contaminants. This study presents a model for colloid transport in dual-permeability media that includes reversible and irreversible retention of colloids and first-order exchange between the aqueous phases of the two regions. The model may also be used to describe transport of other reactive solutes in dual-permeability media. Analytical solutions for colloid concentrations in aqueous and solid phases were obtained using Laplace transformation and matrix decomposition. The solutions proved convenient to assess the effect of model parameters on the colloid distribution. The analytical model was used to describe effluent concentrations for a bromide tracer and 3.2- or 1-μm-colloids that were observed after transport through a composite 10-cm long porous medium made up of a cylindrical lens or core of sand and a surrounding matrix with sand of a different grain size. The tracer data were described very well and realistic estimates were obtained for the pore-water velocity in the two flow domains. An accurate description was also achieved for most colloid breakthrough curves. Dispersivity and retention parameters were typically greater for the larger 3.2-μm-colloids while both reversible and irreversible retention rates tended to be higher for the finer sands than the coarser sand. The relatively small sample size and the complex flow pattern in the composite medium made it difficult to reach definitive conclusions regarding transport parameters for colloid transport.

  7. Ultrasmall mixed ferrite colloids as multidimensional magnetic resonance imaging, cell labeling, and cell sorting agents.

    PubMed

    Groman, Ernest V; Bouchard, Jacqueline C; Reinhardt, Christopher P; Vaccaro, Dennis E

    2007-01-01

    One area that has been overlooked in the evolution of magnetic nanoparticle technology is the possibility of introducing informational atoms into the iron oxide core of the coated colloid. Introduction of suitable atoms into the iron oxide core offers an opportunity to produce a quantifiable probe, thereby adding one or more dimensions to the magnetic colloid's informational status. Lanthanide-doped iron oxide nanoparticles have been synthesized to introduce informational atoms through the formation of colloidal mixed ferrites. These colloids are designated ultrasmall mixed ferrite iron oxides (USMIOs). USMIOs containing 5 mol % europium exhibit superparamagnetic behavior with an induced magnetization of 56 emu/g Fe at 1.5 T, a powder X-ray diffraction pattern congruent with magnetite, and R1 and R2 relaxivity values of 15.4 (mM s) (-1) and 33.9 (mM s) (-1), respectively, in aqueous solution at 37 degrees C and 0.47 T. USMIO can be detected by five physical methods, combining the magnetic resonance imaging (MRI) qualities of iron with the sensitive and quantitative detection of lanthanide metals by neutron activation analysis (NA), time-resolved fluorescence (TRF), X-ray fluorescence, along with detection by electron microscopy (EM). In addition to quantitative detection using neutron activation analysis, the presence of lanthanides in the iron oxide matrix confers attractive optical properties for long-term multilabeling studies with europium and terbium. These USMIOs offer high photostability, a narrow emission band, and a broad absorption band combining the high sensitivity of time-resolved fluorescence with the high spatial resolution of MRI. USMIO nanoparticles are prepared through modifications of traditional magnetite-based iron oxide colloid synthetic methods. A 5 mol % substitution of ferric iron with trivalent europium yielded a colloid with nearly identical magnetic, physical, and chemical characteristics to its magnetite colloid parent.

  8. Combined quantitative ultrasonic and time-resolved interaction force AFM imaging

    SciTech Connect

    Parlak, Z.; Degertekin, F. L.

    2011-01-15

    The authors describe a method where quantitative ultrasonic atomic force microscopy (UAFM) is achieved during time-resolved interaction force (TRIF) imaging in intermittent contact mode. The method uses a calibration procedure for quantitative UAFM. It improves elasticity measurements of stiff regions of surfaces while retaining the capabilities of the TRIF mode for topography, adhesion, dissipation, and elasticity measurements on soft regions of sample surfaces. This combination is especially advantageous when measuring and imaging samples with broad stiffness range in a nondestructive manner. The experiments utilize an active AFM probe with high bandwidth and the UAFM calibration is performed by measuring the magnitude of the time-resolved UAFM signal at a judiciously chosen frequency for different contact stiffness values during individual taps. Improved sensitivity to stiff surface elasticity is demonstrated on a special sample. The results show that combining UAFM with TRIF provides 2.5 GPa (5%) standard deviation on the silicon surface reduced Young's modulus, representing 5x improvement over using only TRIF mode imaging.

  9. Experimental evidence of ultrathin polymer film stratification by AFM force spectroscopy.

    PubMed

    Delorme, Nicolas; Chebil, Mohamed Souheib; Vignaud, Guillaume; Le Houerou, Vincent; Bardeau, Jean-François; Busselez, Rémi; Gibaud, Alain; Grohens, Yves

    2015-06-01

    By performing Atomic Force Microscopy measurements of pull-off force as a function of the temperature, we were able to probe the dynamic of supported thin polystyrene (PS) films. Thermal transitions induce modifications in the surface energy, roughness and surface modulus that are clearly detected by AFM and related to PS chain relaxation mechanisms. We demonstrated the existence of three transition temperatures that can be associated to the relaxation of polymer chains located at different depth regions within the polymer film. Independently of the film thickness, we have confirmed the presence of a region of high mobility for the polymer chains at the free interface. The thickness of this region is estimated to be above 7nm. The detection of a transition only present for film thicker than the gyration radius Rg is linked to the dynamics of polymer chains in a bulk conformation (i.e. not in contact with the free interface). We claim here that our results demonstrate, in agreement with other techniques, the stratification of thin polymer film depth profile in terms of relaxation behavior. PMID:26087914

  10. Interactions and collective behavior of attractive colloidal rods and microspheres grafted with filamentous bacteriophage

    NASA Astrophysics Data System (ADS)

    Huang, Fei

    Interactions and collective behavior are investigated for two systems of attractive colloidal rods and colloidal stars. Attractive colloidal rods are constructed by grafting the temperature-sensitive polymer poly(N-isopropylacrylamide) (PNIPAM) to the surface of the semi-flexible filamentous fd virus. The phase diagram of fd-PNIPAM system becomes independent of ionic strength at high salt concentration and low temperature, i.e., the rods are sterically stabilized by the polymer. However, the network of rods undergoes a sol-gel transition as the temperature is raised. The viscoelastic moduli of fd and fd-PNIPAM suspensions are compared as a function of temperature, and the effect of ionic strength on the gelling behavior of fd-PNIPAM solution is measured. For all fluidlike and solidlike samples, the frequency-dependant linear viscoelastic moduli can be scaled onto universal master curves. Colloidal stars are constructed by grafting to 1 mum polystyrene beads a dense brush of 1 mum long and 10 nm wide semi-flexible filamentous viruses. The pair interaction potentials of colloidal stars are measured using an experimental implementation of umbrella sampling, a technique originally developed in computer simulations in order to probe rare events. The influence of ionic strength and grafting density on the interaction is measured. Good agreements are found between the measured interactions and theoretical predictions based upon the osmotic pressure of counterions.

  11. Tip Based Nanofabrication Using Multi-mode Scanning Probe Microscopy

    NASA Astrophysics Data System (ADS)

    Hu, Weihua

    Scanning probe microscopy (SPM) based nanotechnology is a promising technology in nano-device fabrication. It is able to both manipulate nanostructures and characterize the created nanopatterns using the nano-tip of the scanning probe on a mechanical basis or electrical basis. With the tip and device on similar scales, nano-tip based fabrication permits accurate control over the device geometry through tip manipulation with nanometer (or better) accuracy. However, SPM based nanofabrication is a slow process because the scanning velocity of the microscopy is low. Large, multi-tip arrays offer the possibility for parallel device fabrication, allowing mass fabrication with nanometer control. The goal of Tip-directed Field-emission Assisted Nanofabrication (TFAN) project was to realize parallel fabrication using our probe arrays. We started by fabricating nanodevice using one single probe. In this work, we investigated the study of fabricating single electron transistor (SET) using one single SPM probe. There were four stages we went through toward fabricating a SET. The first stage was to accomplish atomic-precision lithography in TFAN system. Atomic level lithography was achieved by desorbing hydrogen atoms, which were previously adsorbed to the Si(100)-2 × 1 surface, in ultrahigh vacuum scanning tunneling microscopy (UHV-STM). The second stage was to develop method for fabricating SET. SPM based local oxidation was chosen as the method to fabricate a SET on a thin titanium (Ti) film. A multi-mode SPM oxidation method was developed, in which both scanning tunneling microscopy (STM) mode and atomic microscopy (AFM) mode local oxidation were used to fabricated Ti-TiOx-Ti structures with the same conductive AFM probe. This multi-mode method enabled significantly fine feature size control by STM mode, working on insulating SiO2 substrates needed to isolate the device by AFM mode and in situ electrical characterization with conductive AFM mode. After developing the multi

  12. Mechanical properties study of SW480 cells based on AFM.

    PubMed

    Liu, Xiaogang; Song, Zhengxun; Qu, Yingmin; Wang, Guoliang; Wang, Zuobin

    2015-08-01

    Since the invention of the atomic force microscope (AFM), it has been widely applied in biomedicine. One of the most important applications is used as an indenter tool to do the indentation experiment in order to get the mechanical properties of cells. In this paper, SW480 cells were used as the test subjects. Through the analysis of the contact and indentation, Young's modulus (E), which is an important parameter of cancer cells, has been estimated. Experimental results show that different mechanical models should be chosen to calculate the E in different indentation depths. Here, the E of SW480 cells was (2.5 ± 0.8) KPa at the indentation depth of 99 nm.

  13. BOREAS AFM-04 Twin Otter Aircraft Sounding Data

    NASA Technical Reports Server (NTRS)

    MacPherson, J. Ian; Desjardins, Raymond L.; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-4 team used the National Research Council, Canada (NRC) Twin Otter aircraft to make sounding measurements through the boundary layer. These measurements included concentrations of carbon dioxide and ozone, atmospheric pressure, dry bulb temperature, potential temperature, dewpoint temperature, calculated mixing ratio, and wind speed and direction. Aircraft position, heading, and altitude were also recorded. Data were collected at both the Northern Study Area (NSA) and the Southern Study Area (SSA) in 1994 and 1996. These data are stored in tabular ASCII files. The Twin Otter aircraft sounding data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files also are available on a CD-ROM (see document number 20010000884).

  14. Visualization of internal structure of banana starch granule through AFM.

    PubMed

    Peroni-Okita, Fernanda H G; Gunning, A Patrick; Kirby, Andrew; Simão, Renata A; Soares, Claudinéia A; Cordenunsi, Beatriz R

    2015-09-01

    Atomic force microscopy (AFM) is a high resolution technique for studying the external and internal structures of starch granules. For this purpose granules were isolated from bananas and embedded in a non-penetrating resin. To achieve image contrast of the ultrastructure, the face of the cut blocks were wetted in steam and force modulation mode imaging was used. Images of starch from green bananas showed large variation of height across the granule due to a locational specific absorption of water and swelling of amorphous regions; the data reveal that the center of the granules are structurally different and have different viscoelastic properties. Images of starches from ripe bananas showed an even greater different level of organization: absence of growth rings around the hilum; the central region of the granule is richer in amylose; very porous surface with round shaped dark structures; the size of blocklets are larger than the green fruits. PMID:26005137

  15. Mechanical Characterization of Photo-crosslinkable Hydrogels with AFM

    NASA Astrophysics Data System (ADS)

    McKenna, Alyssa; Byun, Myunghwan; Hayward, Ryan; Aidala, Katherine

    2012-02-01

    Stimuli-responsive hydrogel films formed from photo-crosslinkable polymers are versatile materials for controlled drug delivery devices, three-dimensional micro-assemblies, and components in microfluidic systems. For such applications, it is important to understand both the mechanical properties and the dynamics responses of these materials. We describe the use of atomic force microscope (AFM) based indentation experiments to characterize the properties of poly(N-isopropylacrylamide) copolymer films, crosslinked by activation of pendent benzophenone units using ultraviolet light. In particular, we study how the elastic modulus of the material, determined using the Johnson, Kendall, and Roberts model, depends on UV dose, and simultaneously investigate stress relaxation in these materials in the context of viscoelastic and poroelastic relaxation models.

  16. AFM of self-assembled lambda DNA-histone networks.

    PubMed

    Liu, YuYing; Guthold, Martin; Snyder, Matthew J; Lu, HongFeng

    2015-10-01

    Atomic force microscopy (AFM) was used to investigate the self-assembly behavior of λ-DNA and histones at varying histone:DNA ratios. Without histones and at the lowest histone:DNA ratio (less than one histone per 1000 base pairs of DNA), the DNA appeared as individual (uncomplexed), double-stranded DNA molecules. At increasing histone concentrations (one histone per 500, 250 and 167 base pairs of DNA), the DNA molecules started to form extensive polygonal networks of mostly pentagons and hexagons. The observed networks might be one of the naturally occurring, stable DNA-histone structures. The condensing effects of the divalent cations Mg(2+) and Ca(2+) on the DNA-histone complexes were also investigated. The networks persisted at high Mg(2+) concentration (20mM) and the highest histone concentration. At high Ca(2+) concentration and the highest histone concentration, the polygonal network disappeared and, instead, individual, tightly condensed aggregates were formed. PMID:26141439

  17. Modeling AFM Induced Mechanical Deformation of Living Cells

    SciTech Connect

    Rudd, R E; McElfresh, M; Balhorn, R; Allen, M J; Belak, J

    2002-11-15

    Finite element modeling has been applied to study deformation of living cells in Atomic Force Microscopy (AFM) and particularly Recognition Force Microscopy (RFM). The abstract mechanical problem of interest is the response to RFM point loads of an incompressible medium enclosed in a fluid membrane. Cells are soft systems, susceptible to large deformations in the course of an RFM measurement. Often the local properties such as receptor anchoring forces, the reason for the measurement, are obscured by the response of the cell as a whole. Modeling can deconvolute these effects. This facilitates experimental efforts to have reproducible measurements of mechanical and chemical properties at specific kinds of receptor sites on the membrane of a living cell. In this article we briefly review the RFM technique for cells and the problems it poses, and then report on recent progress in modeling the deformation of cells by a point load.

  18. Structural color from colloidal glasses

    NASA Astrophysics Data System (ADS)

    Magkiriadou, Sofia

    When a material has inhomogeneities at a lengthscale comparable to the wavelength of light, interference can give rise to structural colors: colors that originate from the interaction of the material's microstructure with light and do not require absorbing dyes. In this thesis we study a class of these materials, called photonic glasses, where the inhomogeneities form a dense and random arrangement. Photonic glasses have angle-independent structural colors that look like those of conventional dyes. However, when this work started, there was only a handful of colors accessible with photonic glasses, mostly hues of blue. We use various types of colloidal particles to make photonic glasses, and we study, both theoretically and experimentally, how the optical properties of these glasses relate to their structure and constituent particles. Based on our observations from glasses of conventional particles, we construct a theoretical model that explains the scarcity of yellow, orange, and red photonic glasses. Guided by this model, we develop novel colloidal systems that allow a higher degree of control over structural color. We assemble glasses of soft, core-shell particles with scattering cores and transparent shells, where the resonant wavelength can be tuned independently of the reflectivity. We then encapsulate glasses of these core-shell particles into emulsion droplets of tunable size; in this system, we observe, for the first time, angle-independent structural colors that cover the entire visible spectrum. To enhance color saturation, we begin experimenting with inverse glasses, where the refractive index of the particles is lower than the refractive index of the medium, with promising results. Finally, based on our theoretical model for scattering from colloidal glasses, we begin an exploration of the color gamut that could be achieved with this technique, and we find that photonic glasses are a promising approach to a new type of long-lasting, non-toxic, and

  19. Highly uniform polyhedral colloids formed by colloidal crystal templating

    NASA Astrophysics Data System (ADS)

    Wang, Yifan; McGinley, James; Crocker, John; Crocker Research Group Team

    2015-03-01

    We seek to create polyhedral solid particles by trapping oil droplets in a colloidal crystal, and polymerizing them in situ, resulting in polyhedral particles containing spherical dimples in an ordered arrangement. Specifically, highly monodisperse, micron-sized droplets of 3-methacryloxypropyl trimethoxysilane (TPM) were first prepared through a poly condensation reaction, following well established methods. The droplets were mixed with an excess of polystyrene(PS) particles (diameter in 2.58 μm), which formed close packed (FCC or HCP) colloidal crystals by natural sedimentation and compression under partial drying to an extent, with TPM oil droplets trapped into their tetrahedral and octahedral interstitial sites and wet PS particles. Depending on the initial particle volume fraction and extent of drying, a high yield of dimpled particles having different shapes including tetrahedra and cubes were obtained after oil initiated polymerization and dissolution of the host PS particles, as seen under SEM. The effects of TPM to PS particles size ratio, drying time, and other factors in relation to the yield of tetrahedral and cubic dimpled particles will be presented. Finally, fractionation techniques were used to obtain suspensions of uniform polyhedral particles of high purity.

  20. Phase-Imaging with a Sharpened Multi-Walled Carbon Nanotube AFM Tip: Investigation of Low-k Dielectric Polymer Hybrids

    NASA Technical Reports Server (NTRS)

    Nguyen, Cattien V.; Stevens, Ramsey M.; Meyyappan, M.; Volksen, Willi; Miller, Robert D.

    2005-01-01

    Phase shift tapping mode scanning force microscopy (TMSFM) has evolved into a very powerful technique for the nanoscale surface characterization of compositional variations in heterogeneous samples. Phase shift signal measures the difference between the phase angle of the excitation signal and the phase angle of the cantilever response. The signal correlates to the tip-sample inelastic interactions, identifying the different chemical and/or physical property of surfaces. In general, the resolution and quality of scanning probe microscopic images are highly dependent on the size of the scanning probe tip. In improving AFM tip technology, we recently developed a technique for sharpening the tip of a multi-walled carbon nanotube (CNT) AFM tip, reducing the radius of curvature of the CNT tip to less than 5 nm while still maintaining the inherent stability of multi-walled CNT tips. Herein we report the use of sharpened (CNT) AFM tips for phase-imaging of polymer hybrids, a precursor for generating nanoporous low-k dielectrics for on-chip interconnect applications. Using sharpened CNT tips, we obtained phase-contrast images having domains less than 10 nm. In contrast, conventional Si tips and unsharpened CNT tips (radius greater than 15 nm) were not able to resolve the nanoscale domains in the polymer hybrid films. C1early, the size of the CNT tip contributes significantly to the resolution of phase-contrast imaging. In addition, a study on the nonlinear tapping dynamics of the multi-walled CNT tip indicates that the multi-walled CNT tip is immune to conventional imaging instabilities related to the coexistence of attractive and repulsive tapping regimes. This factor may also contribute to the phase-contrast image quality of multi-walled CNT AFM tips. This presentation will also offer data in support of the stability of the CNT tip for phase shift TMSFM.

  1. Binary Colloidal Alloy Test-5: Aspheres

    NASA Technical Reports Server (NTRS)

    Chaikin, Paul M.; Hollingsworth, Andrew D.

    2008-01-01

    The Binary Colloidal Alloy Test - 5: Aspheres (BCAT-5-Aspheres) experiment photographs initially randomized colloidal samples (tiny nanoscale spheres suspended in liquid) in microgravity to determine their resulting structure over time. BCAT-5-Aspheres will study the properties of concentrated systems of small particles when they are identical, but not spherical in microgravity..

  2. Colloid transport in dual-permeability media

    Technology Transfer Automated Retrieval System (TEKTRAN)

    It has been widely reported that colloids can travel faster and over longer distances in natural structured porous media than in uniform structureless media used in laboratory studies. The presence of preferential pathways for colloids in the subsurface environment is of concern because of the incre...

  3. Colloidal Electrolytes and the Critical Micelle Concentration

    ERIC Educational Resources Information Center

    Knowlton, L. G.

    1970-01-01

    Describes methods for determining the Critical Micelle Concentration of Colloidal Electrolytes; methods described are: (1) methods based on Colligative Properties, (2) methods based on the Electrical Conductivity of Colloidal Electrolytic Solutions, (3) Dye Method, (4) Dye Solubilization Method, and (5) Surface Tension Method. (BR)

  4. Characterizing nanoscale scanning probes using electron microscopy: A novel fixture and a practical guide

    NASA Astrophysics Data System (ADS)

    Jacobs, Tevis D. B.; Wabiszewski, Graham E.; Goodman, Alexander J.; Carpick, Robert W.

    2016-01-01

    The nanoscale geometry of probe tips used for atomic force microscopy (AFM) measurements determines the lateral resolution, contributes to the strength of the tip-surface interaction, and can be a significant source of uncertainty in the quantitative analysis of results. While inverse imaging of the probe tip has been used successfully to determine probe tip geometry, direct observation of the tip profile using electron microscopy (EM) confers several advantages: it provides direct (rather than indirect) imaging, requires fewer algorithmic parameters, and does not require bringing the tip into contact with a sample. In the past, EM-based observation of the probe tip has been achieved using ad hoc mounting methods that are constrained by low throughput, the risk of contamination, and repeatability issues. We report on a probe fixture designed for use in a commercial transmission electron microscope that enables repeatable mounting of multiple AFM probes as well as a reference grid for beam alignment. This communication describes the design, fabrication, and advantages of this probe fixture, including full technical drawings for machining. Further, best practices are discussed for repeatable, non-destructive probe imaging. Finally, examples of the fixture's use are described, including characterization of common commercial AFM probes in their out-of-the-box condition.

  5. Optical probe

    DOEpatents

    Hencken, Kenneth; Flower, William L.

    1999-01-01

    A compact optical probe is disclosed particularly useful for analysis of emissions in industrial environments. The instant invention provides a geometry for optically-based measurements that allows all optical components (source, detector, rely optics, etc.) to be located in proximity to one another. The geometry of the probe disclosed herein provides a means for making optical measurements in environments where it is difficult and/or expensive to gain access to the vicinity of a flow stream to be measured. Significantly, the lens geometry of the optical probe allows the analysis location within a flow stream being monitored to be moved while maintaining optical alignment of all components even when the optical probe is focused on a plurality of different analysis points within the flow stream.

  6. Characterization of microscale wear in a ploysilicon-based MEMS device using AFM and PEEM-NEXAFS spectromicroscopy.

    SciTech Connect

    Grierson, D. S.; Konicek, A. R.; Wabiszewski, G. E.; Sumant, A. V.; de Boer, M. P.; Corwin, A. D.; Carpick, R. W.

    2009-12-01

    Mechanisms of microscale wear in silicon-based microelectromechanical systems (MEMS) are elucidated by studying a polysilicon nanotractor, a device specifically designed to conduct friction and wear tests under controlled conditions. Photoelectron emission microscopy (PEEM) was combined with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and atomic force microscopy (AFM) to quantitatively probe chemical changes and structural modification, respectively, in the wear track of the nanotractor. The ability of PEEM-NEXAFS to spatially map chemical variations in the near-surface region of samples at high lateral spatial resolution is unparalleled and therefore ideally suited for this study. The results show that it is possible to detect microscopic chemical changes using PEEM-NEXAFS, specifically, oxidation at the sliding interface of a MEMS device. We observe that wear induces oxidation of the polysilicon at the immediate contact interface, and the spectra are consistent with those from amorphous SiO{sub 2}. The oxidation is correlated with gouging and debris build-up in the wear track, as measured by AFM and scanning electron microscopy (SEM).

  7. Shape-dependent oriented trapping and scaffolding of plasmonic nanoparticles by topological defects for self-assembly of colloidal dimers in liquid crystals.

    PubMed

    Senyuk, Bohdan; Evans, Julian S; Ackerman, Paul J; Lee, Taewoo; Manna, Pramit; Vigderman, Leonid; Zubarev, Eugene R; van de Lagemaat, Jao; Smalyukh, Ivan I

    2012-02-01

    We demonstrate scaffolding of plasmonic nanoparticles by topological defects induced by colloidal microspheres to match their surface boundary conditions with a uniform far-field alignment in a liquid crystal host. Displacing energetically costly liquid crystal regions of reduced order, anisotropic nanoparticles with concave or convex shapes not only stably localize in defects but also self-orient with respect to the microsphere surface. Using laser tweezers, we manipulate the ensuing nanoparticle-microsphere colloidal dimers, probing the strength of elastic binding and demonstrating self-assembly of hierarchical colloidal superstructures such as chains and arrays.

  8. Shape-dependent oriented trapping and scaffolding of plasmonic nanoparticles by topological defects for self-assembly of colloidal dimers in liquid crystals.

    PubMed

    Senyuk, Bohdan; Evans, Julian S; Ackerman, Paul J; Lee, Taewoo; Manna, Pramit; Vigderman, Leonid; Zubarev, Eugene R; van de Lagemaat, Jao; Smalyukh, Ivan I

    2012-02-01

    We demonstrate scaffolding of plasmonic nanoparticles by topological defects induced by colloidal microspheres to match their surface boundary conditions with a uniform far-field alignment in a liquid crystal host. Displacing energetically costly liquid crystal regions of reduced order, anisotropic nanoparticles with concave or convex shapes not only stably localize in defects but also self-orient with respect to the microsphere surface. Using laser tweezers, we manipulate the ensuing nanoparticle-microsphere colloidal dimers, probing the strength of elastic binding and demonstrating self-assembly of hierarchical colloidal superstructures such as chains and arrays. PMID:22233163

  9. Colloid transport in saturated porous media: Elimination of attachment efficiency in a new colloid transport model

    NASA Astrophysics Data System (ADS)

    Landkamer, Lee L.; Harvey, Ronald W.; Scheibe, Timothy D.; Ryan, Joseph N.

    2013-05-01

    A colloid transport model is introduced that is conceptually simple yet captures the essential features of colloid transport and retention in saturated porous media when colloid retention is dominated by the secondary minimum because an electrostatic barrier inhibits substantial deposition in the primary minimum. This model is based on conventional colloid filtration theory (CFT) but eliminates the empirical concept of attachment efficiency. The colloid deposition rate is computed directly from CFT by assuming all predicted interceptions of colloids by collectors result in at least temporary deposition in the secondary minimum. Also, a new paradigm for colloid re-entrainment based on colloid population heterogeneity is introduced. To accomplish this, the initial colloid population is divided into two fractions. One fraction, by virtue of physiochemical characteristics (e.g., size and charge), will always be re-entrained after capture in a secondary minimum. The remaining fraction of colloids, again as a result of physiochemical characteristics, will be retained "irreversibly" when captured by a secondary minimum. Assuming the dispersion coefficient can be estimated from tracer behavior, this model has only two fitting parameters: (1) the fraction of the initial colloid population that will be retained "irreversibly" upon interception by a secondary minimum, and (2) the rate at which reversibly retained colloids leave the secondary minimum. These two parameters were correlated to the depth of the Derjaguin-Landau-Verwey-Overbeek (DLVO) secondary energy minimum and pore-water velocity, two physical forces that influence colloid transport. Given this correlation, the model serves as a heuristic tool for exploring the influence of physical parameters such as surface potential and fluid velocity on colloid transport.

  10. Physics in ordered and disordered colloidal matter composed of poly(N-isopropylacrylamide) microgel particles.

    PubMed

    Yunker, Peter J; Chen, Ke; Gratale, Matthew D; Lohr, Matthew A; Still, Tim; Yodh, A G

    2014-05-01

    This review collects and describes experiments that employ colloidal suspensions to probe physics in ordered and disordered solids and related complex fluids. The unifying feature of this body of work is its clever usage of poly(N-isopropylacrylamide) (PNIPAM) microgel particles. These temperature-sensitive colloidal particles provide experimenters with a 'knob' for in situ control of particle size, particle interaction and particle packing fraction that, in turn, influence the structural and dynamical behavior of the complex fluids and solids. A brief summary of PNIPAM particle synthesis and properties is given, followed by a synopsis of current activity in the field. The latter discussion describes a variety of soft matter investigations including those that explore formation and melting of crystals and clusters, and those that probe structure, rearrangement and rheology of disordered (jammed/glassy) and partially ordered matter. The review, therefore, provides a snapshot of a broad range of physics phenomenology which benefits from the unique properties of responsive microgel particles.

  11. Structural transitions in condensed colloidal virus phases

    NASA Astrophysics Data System (ADS)

    Schmidt, Nathan; Barr, Steve; Udit, Andrew; Gutierrez, Leonardo; Nguyen, Thanh; Finn, M. G.; Luijten, Erik; Wong, Gerard

    2010-03-01

    Analogous to monatomic systems colloidal phase behavior is entirely determined by the interaction potential between particles. This potential can be tuned using solutes such as multivalent salts and polymers with varying affinity for the colloids to create a hierarchy of attractions. Bacteriophage viruses are a naturally occurring type of colloidal particle with characteristics difficult to achieve by laboratory synthesis. They are monodisperse, nanometers in size, and have heterogeneous surface charge distributions. We use the MS2 and Qbeta bacteriophages (diameters 27-28nm) to understand the interplay between different attraction mechanisms on nanometer-sized colloids. Small Angle X-ray Scattering (SAXS) is used to characterize the inter-particle interaction between colloidal viruses using several polymer species and different salt types.

  12. Cocklebur-shaped colloidal dispersions.

    PubMed

    Lestage, David J; Urban, Marek W

    2005-11-01

    Unique cocklebur-shaped colloidal dispersions were prepared using a combination of a nanoextruder applied to the aqueous solution containing methyl methacrylate (MMA) and n-butyl acrylate (n-BA) with azo-bis-isobutyronitrile (AIBN) or potassium persulfate (KPS) initiators and stabilized by a mixture of sodium dioctyl sulfosuccinate (SDOSS) and 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DCPC) phospholipid. Upon extrusion and heating to 75 degrees C, methyl methacrylate/n-butyl acrylate (MMA/nBA) colloidal particles containing tubules pointing outward were obtained as a result of DCPC phospholipids present at the particle surfaces. The same cocklebur-shaped particles were obtained when classical polymerization was used without a nanoextruder under similar compositional and thermal conditions, giving a particle size of 159 nm. However, when Ca(2+) ions are present during polymerization, cocklebur morphologies are disrupted. Because DCPC tubules undergo a transition at 38 degrees C, such cocklebur morphologies may offer numerous opportunities for devices with stimuli-responsive characteristics. PMID:16262269

  13. Kinetically guided colloidal structure formation

    PubMed Central

    Hecht, Fabian M.; Bausch, Andreas R.

    2016-01-01

    The self-organization of colloidal particles is a promising approach to create novel structures and materials, with applications spanning from smart materials to optoelectronics to quantum computation. However, designing and producing mesoscale-sized structures remains a major challenge because at length scales of 10–100 μm equilibration times already become prohibitively long. Here, we extend the principle of rapid diffusion-limited cluster aggregation (DLCA) to a multicomponent system of spherical colloidal particles to enable the rational design and production of finite-sized anisotropic structures on the mesoscale. In stark contrast to equilibrium self-assembly techniques, kinetic traps are not avoided but exploited to control and guide mesoscopic structure formation. To this end the affinities, size, and stoichiometry of up to five different types of DNA-coated microspheres are adjusted to kinetically control a higher-order hierarchical aggregation process in time. We show that the aggregation process can be fully rationalized by considering an extended analytical DLCA model, allowing us to produce mesoscopic structures of up to 26 µm in diameter. This scale-free approach can easily be extended to any multicomponent system that allows for multiple orthogonal interactions, thus yielding a high potential of facilitating novel materials with tailored plasmonic excitation bands, scattering, biochemical, or mechanical behavior. PMID:27444018

  14. Synthesis of substantially monodispersed colloids

    NASA Technical Reports Server (NTRS)

    Klabunde, Kenneth J. (Inventor); Stoeva, Savka (Inventor); Sorensen, Christopher (Inventor)

    2003-01-01

    A method of forming ligated nanoparticles of the formula Y(Z).sub.x where Y is a nanoparticle selected from the group consisting of elemental metals having atomic numbers ranging from 21-34, 39-52, 57-83 and 89-102, all inclusive, the halides, oxides and sulfides of such metals, and the alkali metal and alkaline earth metal halides, and Z represents ligand moieties such as the alkyl thiols. In the method, a first colloidal dispersion is formed made up of nanoparticles solvated in a molar excess of a first solvent (preferably a ketone such as acetone), a second solvent different than the first solvent (preferably an organic aryl solvent such as toluene) and a quantity of ligand moieties; the first solvent is then removed under vacuum and the ligand moieties ligate to the nanoparticles to give a second colloidal dispersion of the ligated nanoparticles solvated in the second solvent. If substantially monodispersed nanoparticles are desired, the second dispersion is subjected to a digestive ripening process. Upon drying, the ligated nanoparticles may form a three-dimensional superlattice structure.

  15. Colloid-Associated Radionuclide Concentration Limits: ANL

    SciTech Connect

    C. Mertz

    2000-12-21

    The purpose and scope of this report is to describe the analysis of available colloidal data from waste form corrosion tests at Argonne National Laboratory (ANL) to extract characteristics of these colloids that can be used in modeling their contribution to the source term for sparingly soluble radioelements (e.g., Pu). Specifically, the focus is on developing a useful description of the following waste form colloid characteristics: (1) composition, (2) size distribution, and (3) quantification of the rate of waste form colloid generation. The composition and size distribution information are intended to support analysis of the potential transport of the sparingly soluble radionuclides associated with the waste form colloids. The rate of colloid generation is intended to support analysis of the waste form colloid-associated radionuclide concentrations. In addressing the above characteristics, available data are interpreted to address mechanisms controlling colloid formation and stability. This report was developed in accordance with the ''Technical Work Plan for Waste Form Degradation Process Model Report for SR'' (CRWMS M&O 2000). Because the end objective is to support the source term modeling we have organized the conclusions into two categories: (1) data analysis conclusions and (2) recommendations for colloid source term modeling. The second category is included to facilitate use of the conclusions from the data analysis in the abstraction of a colloid source term model. The data analyses and conclusions that are presented in this report are based on small-scale laboratory tests conducted on a limited number of waste glass compositions and spent fuel types.

  16. The physics of pulling polyproteins: a review of single molecule force spectroscopy using the AFM to study protein unfolding

    NASA Astrophysics Data System (ADS)

    Hughes, Megan L.; Dougan, Lorna

    2016-07-01

    One of the most exciting developments in the field of biological physics in recent years is the ability to manipulate single molecules and probe their properties and function. Since its emergence over two decades ago, single molecule force spectroscopy has become a powerful tool to explore the response of biological molecules, including proteins, DNA, RNA and their complexes, to the application of an applied force. The force versus extension response of molecules can provide valuable insight into its mechanical stability, as well as details of the underlying energy landscape. In this review we will introduce the technique of single molecule force spectroscopy using the atomic force microscope (AFM), with particular focus on its application to study proteins. We will review the models which have been developed and employed to extract information from single molecule force spectroscopy experiments. Finally, we will end with a discussion of future directions in this field.

  17. The physics of pulling polyproteins: a review of single molecule force spectroscopy using the AFM to study protein unfolding.

    PubMed

    Hughes, Megan L; Dougan, Lorna

    2016-07-01

    One of the most exciting developments in the field of biological physics in recent years is the ability to manipulate single molecules and probe their properties and function. Since its emergence over two decades ago, single molecule force spectroscopy has become a powerful tool to explore the response of biological molecules, including proteins, DNA, RNA and their complexes, to the application of an applied force. The force versus extension response of molecules can provide valuable insight into its mechanical stability, as well as details of the underlying energy landscape. In this review we will introduce the technique of single molecule force spectroscopy using the atomic force microscope (AFM), with particular focus on its application to study proteins. We will review the models which have been developed and employed to extract information from single molecule force spectroscopy experiments. Finally, we will end with a discussion of future directions in this field.

  18. Plutonium and Cesium Colloid Mediated Transport

    NASA Astrophysics Data System (ADS)

    Boukhalfa, H.; Dittrich, T.; Reimus, P. W.; Ware, D.; Erdmann, B.; Wasserman, N. L.; Abdel-Fattah, A. I.

    2013-12-01

    Plutonium and cesium have been released to the environment at many different locations worldwide and are present in spent fuel at significant levels. Accurate understanding of the mechanisms that control their fate and transport in the environment is important for the management of contaminated sites, for forensic applications, and for the development of robust repositories for the disposal of spent nuclear fuel and nuclear waste. Plutonium, which can be present in the environment in multiple oxidations states and various chemical forms including amorphous oxy(hydr)oxide phases, adsorbs/adheres very strongly to geological materials and is usually immobile in all its chemical forms. However, when associated with natural colloids, it has the potential to migrate significant distances from its point of release. Like plutonium, cesium is not very mobile and tends to remain adhered to geological materials near its release point, although its transport can be enhanced by natural colloids. However, the reactivity of plutonium and cesium are very different, so their colloid-mediated transport might be significantly different in subsurface environments. In this study, we performed controlled experiments in two identically-prepared columns; one dedicated to Pu and natural colloid transport experiments, and the other to Cs and colloid experiments. Multiple flow-through experiments were conducted in each column, with the effluent solutions being collected and re-injected into the same column two times to examine the persistence and scaling behavior of the natural colloids, Pu and Cs. The data show that that a significant fraction of colloids were retained in the first elution through each column, but the eluted colloids collected from the first run transported almost conservatively in subsequent runs. Plutonium transport tracked natural colloids in the first run but deviated from the transport of natural colloids in the second and third runs. Cesium transport tracked natural

  19. Colloid Transport in Saturated Porous Media: Elimination of Attachment Efficiency in a New Colloid Transport Model

    SciTech Connect

    Landkamer, Lee L.; Harvey, Ronald W.; Scheibe, Timothy D.; Ryan, Joseph N.

    2013-05-11

    A new colloid transport model is introduced that is conceptually simple but captures the essential features of complicated attachment and detachment behavior of colloids when conditions of secondary minimum attachment exist. This model eliminates the empirical concept of collision efficiency; the attachment rate is computed directly from colloid filtration theory. Also, a new paradigm for colloid detachment based on colloid population heterogeneity is introduced. Assuming the dispersion coefficient can be estimated from tracer behavior, this model has only two fitting parameters: (1) the fraction of colloids that attach irreversibly and (2) the rate at which reversibly attached colloids leave the surface. These two parameters were correlated to physical parameters that control colloid transport such as the depth of the secondary minimum and pore water velocity. Given this correlation, the model serves as a heuristic tool for exploring the influence of physical parameters such as surface potential and fluid velocity on colloid transport. This model can be extended to heterogeneous systems characterized by both primary and secondary minimum deposition by simply increasing the fraction of colloids that attach irreversibly.

  20. Nonspherical colloidal crystals fabricated by the thermal pressing of colloidal crystal chips.

    PubMed

    Sun, Z Q; Chen, X; Zhang, J H; Chen, Z M; Zhang, K; Yan, X; Wang, Y F; Yu, W Z; Yang, B

    2005-09-27

    Nonspherical colloids and their ordered arrays may be more attractive in applications such as photonic crystals than their spherical counterparts because of their lower symmetries, although such structures are difficult to achieve. In this letter, we describe the fabrication and characterization of colloidal crystals constructed from nonspherical polyhedrons. We fabricated such nonspherical colloidal crystals by pressing spherical polymer colloidal crystal chips at a temperature slightly lower than the glass-transition temperature (T(g)) of these polymer colloids. During this process, the polymer microspheres were distinctively transformed into polyhedrons according to their crystal structures, whereas the long-range order of the 3D lattice was essentially preserved. Because a working temperature lower than T(g) effectively prevented the colloidal crystals from fusing into films, the spherical colloidal crystals were transformed greatly under pressure, which lead to obvious change in the optical properties of colloidal crystals. Besides their special symmetry and optical properties, these nonspherical colloidal crystals can be used as templates for 2D or 3D structures of special symmetry, such as 2D nano-networks. We anticipate that this fabrication technique for nonspherical colloidal crystals can also be extended to nonspherical porous materials.

  1. 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.

  2. Colloid-polymer mixtures in solution with refractive index matched acrylate colloids.

    PubMed

    Kramer, Thomas; Scholz, Stephanie; Maskos, Michael; Huber, Klaus

    2004-11-15

    Colloid-polymer (CP) mixtures extend between two limiting cases, the colloid limit with the polymer coil size small compared to the colloid radius Rcol and the protein limit with the colloidal particles much smaller in size than the radius of gyration of the polymer chains Rg. In the present work, model systems are developed for the protein limit. The colloid-solvent pairs are optimized in terms of their isorefractivity in order to facilitate the characterization of large polystyrene chains in suspensions of small colloids. The degree of isorefractivity of colloidal particles was successfully evaluated in terms of a reduced scattering intensity. Two polystyrene samples with radii of gyration of Rg = 96 nm and Rg = 78 nm, respectively, are used. The radii of the colloidal particles are close to Rcol = 12 nm, leading to size ratios of Rg/Rcol = 8 and Rg/Rcol = 6.5. Four colloid solvent systems were found to be suitable for polymer characterization by light scattering, one based on silica particles and three systems with acrylate particles. The present investigation is focused on the three acrylate systems: poly(methyl methacrylate) in ethyl benzoate (ETB) at 7 degrees C, poly(ethyl methacrylate) in toluene at 7 degrees C and poly(ethyl methacrylate) in ETB at 40 degrees C. Characterization of PS chains is for the first time performed in colloid concentrations up to 2.5% by weight. In all cases, the size and shape of the polymer chains remain unchanged. A slight mismatch of the colloid scattering or a limited colloid solubility prevented investigation of PS chains at higher colloid concentration.

  3. Colloid transport and retention in unsaturated porous media: effect of colloid input concentration.

    PubMed

    Zhang, Wei; Morales, Verónica L; Cakmak, M Ekrem; Salvucci, Anthony E; Geohring, Larry D; Hay, Anthony G; Parlange, Jean-Yves; Steenhuis, Tammo S

    2010-07-01

    Colloids play an important role in facilitating transport of adsorbed contaminants in soils. Recent studies showed that under saturated conditions colloid retention was a function of its concentration. It is unknown if this is the case under unsaturated conditions. In this study, the effect of colloid concentration on colloid retention was investigated in unsaturated columns by increasing concentrations of colloid influents with varying ionic strength. Colloid retention was observed in situ by bright field microscopy and quantified by measuring colloid breakthrough curves. In our unsaturated experiments, greater input concentrations resulted in increased colloid retention at ionic strength above 0.1 mM, but not in deionized water (i.e., 0 mM ionic strength). Bright field microscope images showed that colloid retention mainly occurred at the solid-water interface and wedge-shaped air-water-solid interfaces, whereas the retention at the grain-grain contacts was minor. Some colloids at the air-water-solid interfaces were rotating and oscillating and thus trapped. Computational hydrodynamic simulation confirmed that the wedge-shaped air-water-solid interface could form a "hydrodynamic trap" by retaining colloids in its low velocity vortices. Direct visualization also revealed that colloids once retained acted as new retention sites for other suspended colloids at ionic strength greater than 0.1 mM and thereby could explain the greater retention with increased input concentrations. Derjaguin-Landau-Verwey-Overbeek (DLVO) energy calculations support this concept. Finally, the results of unsaturated experiments were in agreement with limited saturated experiments under otherwise the same conditions.

  4. Polymer-Induced Depletion Interaction and Its Effect on Colloidal Sedimentation in Colloid-Polymer Mixtures

    NASA Technical Reports Server (NTRS)

    Tong, Penger

    1996-01-01

    In this paper we focus on the polymer-induced depletion attraction and its effect on colloidal sedimentation in colloid-polymer mixtures. We first report a small angle neutron scattering (SANS) study of the depletion effect in a mixture of hard-sphere-like colloid and non-adsorbing polymer. Then we present results of our recent sedimentation measurements in the same colloid-polymer mixture. A key parameter in controlling the sedimentation of heavy colloidal particles is the interparticle potential U(tau), which is the work required to bring two colloidal particles from infinity to a distance tau under a give solvent condition. This potential is known to affect the average settling velocity of the particles and experimentally one needs to have a way to continuously vary U(tau) in order to test the theory. The interaction potential U(tau) can be altered by adding polymer molecules into the colloidal suspension. In a mixture of colloid and non-adsorbing polymer, the potential U(tau) can develop an attractive well because of the depletion effect, in that the polymer chains are expelled from the region between two colloidal particles when their surface separation becomes smaller than the size of the polymer chains. The exclusion of polymer molecules from the space between the colloidal particles leads to an unbalanced osmotic pressure difference pushing the colloidal particles together, which results in an effective attraction between the two colloidal particles. The polymer-induced depletion attraction controls the phase stability of many colloid-polymer mixtures, which are directly of interest to industry.

  5. Design and optimization of a harmonic probe with step cross section in multifrequency atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Cai, Jiandong; Wang, Michael Yu; Zhang, Li

    2015-12-01

    In multifrequency atomic force microscopy (AFM), probe's characteristic of assigning resonance frequencies to integer harmonics results in a remarkable improvement of detection sensitivity at specific harmonic components. The selection criterion of harmonic order is based on its amplitude's sensitivity on material properties, e.g., elasticity. Previous studies on designing harmonic probe are unable to provide a large design capability along with maintaining the structural integrity. Herein, we propose a harmonic probe with step cross section, in which it has variable width in top and bottom steps, while the middle step in cross section is kept constant. Higher order resonance frequencies are tailored to be integer times of fundamental resonance frequency. The probe design is implemented within a structural optimization framework. The optimally designed probe is micromachined using focused ion beam milling technique, and then measured with an AFM. The measurement results agree well with our resonance frequency assignment requirement.

  6. BOREAS AFM-12 1-km AVHRR Seasonal Land Cover Classification

    NASA Technical Reports Server (NTRS)

    Steyaert, Lou; Hall, Forrest G.; Newcomer, Jeffrey A. (Editor); Knapp, David E. (Editor); Loveland, Thomas R.; Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-12 team's efforts focused on regional scale Surface Vegetation and Atmosphere (SVAT) modeling to improve parameterization of the heterogeneous BOREAS landscape for use in larger scale Global Circulation Models (GCMs). This regional land cover data set was developed as part of a multitemporal one-kilometer Advanced Very High Resolution Radiometer (AVHRR) land cover analysis approach that was used as the basis for regional land cover mapping, fire disturbance-regeneration, and multiresolution land cover scaling studies in the boreal forest ecosystem of central Canada. This land cover classification was derived by using regional field observations from ground and low-level aircraft transits to analyze spectral-temporal clusters that were derived from an unsupervised cluster analysis of monthly Normalized Difference Vegetation Index (NDVI) image composites (April-September 1992). This regional data set was developed for use by BOREAS investigators, especially those involved in simulation modeling, remote sensing algorithm development, and aircraft flux studies. Based on regional field data verification, this multitemporal one-kilometer AVHRR land cover mapping approach was effective in characterizing the biome-level land cover structure, embedded spatially heterogeneous landscape patterns, and other types of key land cover information of interest to BOREAS modelers.The land cover mosaics in this classification include: (1) wet conifer mosaic (low, medium, and high tree stand density), (2) mixed coniferous-deciduous forest (80% coniferous, codominant, and 80% deciduous), (3) recent visible bum, vegetation regeneration, or rock outcrops-bare ground-sparsely vegetated slow regeneration bum (four classes), (4) open water and grassland marshes, and (5) general agricultural land use/ grasslands (three classes). This land cover mapping approach did not detect small subpixel-scale landscape

  7. Beyond topography - enhanced imaging of cometary dust with the MIDAS AFM

    NASA Astrophysics Data System (ADS)

    Bentley, M. S.; Torkar, K.; Jeszenszky, H.; Romstedt, J.

    2013-09-01

    The MIDAS atomic force microscope (AFM) onboard the Rosetta spacecraft is primarily designed to return the 3D shape and structure of cometary dust particles collected at comet 67P/Churyumov-Gerasimenko [1]. Commercial AFMs have, however, been further developed to measure many other sample properties. The possibilities to make such measurements with MIDAS are explored here.

  8. Nano-Wilhelmy investigation of dynamic wetting properties of AFM tips through tip-nanobubble interaction

    NASA Astrophysics Data System (ADS)

    Wang, Yuliang; Wang, Huimin; Bi, Shusheng; Guo, Bin

    2016-07-01

    The dynamic wetting properties of atomic force microscopy (AFM) tips are of much concern in many AFM-related measurement, fabrication, and manipulation applications. In this study, the wetting properties of silicon and silicon nitride AFM tips are investigated through dynamic contact angle measurement using a nano-Wilhelmy balance based method. This is done by capillary force measurement during extension and retraction motion of AFM tips relative to interfacial nanobubbles. The working principle of the proposed method and mathematic models for dynamic contact angle measurement are presented. Geometric models of AFM tips were constructed using scanning electronic microscopy (SEM) images taken from different view directions. The detailed process of tip-nanobubble interaction was investigated using force-distance curves of AFM on nanobubbles. Several parameters including nanobubble height, adhesion and capillary force between tip and nanobubbles are extracted. The variation of these parameters was studied over nanobubble surfaces. The dynamic contact angles of the AFM tips were calculated from the capillary force measurements. The proposed method provides direct measurement of dynamic contact angles for AFM tips and can also be taken as a general approach for nanoscale dynamic wetting property investigation.

  9. Nano-Wilhelmy investigation of dynamic wetting properties of AFM tips through tip-nanobubble interaction

    PubMed Central

    Wang, Yuliang; Wang, Huimin; Bi, Shusheng; Guo, Bin

    2016-01-01

    The dynamic wetting properties of atomic force microscopy (AFM) tips are of much concern in many AFM-related measurement, fabrication, and manipulation applications. In this study, the wetting properties of silicon and silicon nitride AFM tips are investigated through dynamic contact angle measurement using a nano-Wilhelmy balance based method. This is done by capillary force measurement during extension and retraction motion of AFM tips relative to interfacial nanobubbles. The working principle of the proposed method and mathematic models for dynamic contact angle measurement are presented. Geometric models of AFM tips were constructed using scanning electronic microscopy (SEM) images taken from different view directions. The detailed process of tip-nanobubble interaction was investigated using force-distance curves of AFM on nanobubbles. Several parameters including nanobubble height, adhesion and capillary force between tip and nanobubbles are extracted. The variation of these parameters was studied over nanobubble surfaces. The dynamic contact angles of the AFM tips were calculated from the capillary force measurements. The proposed method provides direct measurement of dynamic contact angles for AFM tips and can also be taken as a general approach for nanoscale dynamic wetting property investigation. PMID:27452115

  10. 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.

  11. 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.

  12. Ionic colloidal crystals of oppositely charged particles.

    PubMed

    Leunissen, Mirjam E; Christova, Christina G; Hynninen, Antti-Pekka; Royall, C Patrick; Campbell, Andrew I; Imhof, Arnout; Dijkstra, Marjolein; van Roij, René; van Blaaderen, Alfons

    2005-09-01

    Colloidal suspensions are widely used to study processes such as melting, freezing and glass transitions. This is because they display the same phase behaviour as atoms or molecules, with the nano- to micrometre size of the colloidal particles making it possible to observe them directly in real space. Another attractive feature is that different types of colloidal interactions, such as long-range repulsive, short-range attractive, hard-sphere-like and dipolar, can be realized and give rise to equilibrium phases. However, spherically symmetric, long-range attractions (that is, ionic interactions) have so far always resulted in irreversible colloidal aggregation. Here we show that the electrostatic interaction between oppositely charged particles can be tuned such that large ionic colloidal crystals form readily, with our theory and simulations confirming the stability of these structures. We find that in contrast to atomic systems, the stoichiometry of our colloidal crystals is not dictated by charge neutrality; this allows us to obtain a remarkable diversity of new binary structures. An external electric field melts the crystals, confirming that the constituent particles are indeed oppositely charged. Colloidal model systems can thus be used to study the phase behaviour of ionic species. We also expect that our approach to controlling opposite-charge interactions will facilitate the production of binary crystals of micrometre-sized particles, which could find use as advanced materials for photonic applications.

  13. Structural evolution of Colloidal Gels under Flow

    NASA Astrophysics Data System (ADS)

    Boromand, Arman; Maia, Joao; Jamali, Safa

    Colloidal suspensions are ubiquitous in different industrial applications ranging from cosmetic and food industries to soft robotics and aerospace. Owing to the fact that mechanical properties of colloidal gels are controlled by its microstructure and network topology, we trace the particles in the networks formed under different attraction potentials and try to find a universal behavior in yielding of colloidal gels. Many authors have implemented different simulation techniques such as molecular dynamics (MD) and Brownian dynamics (BD) to capture better picture during phase separation and yielding mechanism in colloidal system with short-ranged attractive force. However, BD neglects multi-body hydrodynamic interactions (HI) which are believed to be responsible for the second yielding of colloidal gels. We envision using dissipative particle dynamics (DPD) with modified depletion potential and hydrodynamic interactions, as a coarse-grain model, can provide a robust simulation package to address the gel formation process and yielding in short ranged-attractive colloidal systems. The behavior of colloidal gels with different attraction potentials under flow is examined and structural fingerprints of yielding in these systems will be discussed.

  14. Quantification of hydrophobic interaction affinity of colloids

    NASA Astrophysics Data System (ADS)

    Saini, G.; Nasholm, N.; Wood, B. D.

    2009-12-01

    Colloids play an important role in a wide variety of disciplines, including water and wastewater treatment, subsurface transport of metals and organic contaminants, migration of fines in oil reservoirs, biocolloid (virus and bacteria) transport in subsurface, and are integral to laboratory transport studies. Although the role of hydrophobicity in adhesion and transport of colloids, particularly bacteria, is well known; there is scarcity of literature regarding hydrophobicity measurement of non-bacterial colloids and other micron-sized particles. Here we detail an experimental approach based on differential partitioning of colloids between two liquid phases (hydrocarbon and buffer) as a measure of the hydrophobic interaction affinity of colloids. This assay, known as Microbial adhesion to hydrocarbons or MATH, is frequently used in microbiology and bacteriology for quantifying the hydrophobicity of microbes. Monodispersed colloids and particles, with sizes ranging from 1 micron to 33 micron, were used for the experiments. A range of hydrophobicity values were observed for different particles. The hydrophobicity results are also verified against water contact angle measurements of these particles. This liquid-liquid partitioning assay is quick, easy-to-perform and requires minimal instrumentation. Estimation of the hydrophobic interaction affinity of colloids would lead to a better understanding of their adhesion to different surfaces and subsequent transport in porous media.

  15. Adsorption-induced reversible colloidal aggregation

    NASA Astrophysics Data System (ADS)

    Law, B. M.; Petit, J.-M.; Beysens, D.

    1998-05-01

    Reversible colloidal aggregation in binary liquid mixtures has been studied for a number of years. As the phase separation temperature of the liquid mixture is approached the thickness of an adsorption layer around the colloidal particles increases. Beysens et al. [Phys. Rev. Lett. 54, 2123 (1985); Ber. Bunsenges. Phys. Chem. 98, 382 (1994)] have demonstrated experimentally that this adsorption layer is intimately connected with the aggregation of the colloidal particles; however, no definitive theory has been available that can explain all of the experimental observations. In a recent work [J.-M. Petit, B. M. Law, and D. Beysens, J. Colloid Interface Sci. (to be published)] we have extended and improved the Derjaguin-Landau-Verwey-Overbeek theory of colloidal aggregation [E. J. W. Verwey and J. Th. G. Overbeek, Theory of the Stability of Lyophobic Colloids (Elsevier, New York, 1948)] by taking into account the presence of an adsorption layer and by more realistically modeling the attractive dispersion interactions using the Dzyaloshinskii-Lifshitz-Pitaevskii theory [Adv. Phys. 10, 165 (1961)]. In the present paper we apply this theory to a lutidine-water mixture containing a small volume fraction of silica colloidal particles. We demonstrate that the theory can quantitatively account for many of the experimentally observed features such as the characteristics of the aggregated state, the general shape of the aggregation line, and the temperature dependence of the second virial coefficient.

  16. Interactions between radioactively labeled colloids and natural particles: Evidence for colloidal pumping

    NASA Astrophysics Data System (ADS)

    Wen, Liang-Saw; Santschi, Peter H.; Tang, Degui

    1997-07-01

    It has been hypothesized that colloidal forms of trace metals can be reactive intermediaries in the scavenging processes leading to the removal of their particulate forms. A series of radiotracer experiments using natural colloidal organic matter from Galveston Bay, USA were carried out in order to test this hypothesis. Suspended particle uptake of originally colloidally bound trace metals occurred in a matter of hours to days in estuarine waters. After ten days, the majority (>50%) of the colloidal trace metals had been transferred into the particulate phase (≥0.45 μm), except for 65Zn. Two distinctively different temporal regions of removal of colloidal trace metals were identified: a faster reaction during the first four hours, followed by a slower reaction after approximately one day. In a separate river water-seawater mixing experiment, the solid/solution partitioning of the radiotracers was investigated in the absence of suspended matter. About 30% of most of the elements, except Ag and Fe (˜60%), were associated with a newly formed particulate phase after eight days. There were two major trends: (1) the particulate fraction of 59Fe and 110Ag increased while the colloidal fraction decreased, suggesting a colloidal pumping mechanism. (2) The particulate fraction of 54Mn, 133Ba, 65Zn, 109Cd, 113Sn, and 60CO increased while the LMW (≤ 1 kDa) fraction decreased, suggesting a direct uptake into the particulate fraction with less involvement of a transitory colloidal phase. The values of the particle-water ( Kd) and colloid-water partitioning ( Kc) coefficients for most trace metals were similar to those observed in Galveston Bay waters, suggesting complementary results to field studies. The results from these experiments suggested two different pathways for colloidal tracer uptake by particles: (1) colloidal pumping of a major component (e.g., biopolymer) of the colloidal pool and (2) coagulation of trace components (e.g., phytochelatins) with varying

  17. Conductivity Probe

    NASA Technical Reports Server (NTRS)

    2008-01-01

    The Thermal and Electrical Conductivity Probe (TECP) for NASA's Phoenix Mars Lander took measurements in Martian soil and in the air.

    The needles on the end of the instrument were inserted into the Martian soil, allowing TECP to measure the propagation of both thermal and electrical energy. TECP also measured the humidity in the surrounding air.

    The needles on the probe are 15 millimeters (0.6 inch) long.

    The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  18. Colloidal Synthesis of Gold Semishells

    PubMed Central

    Rodríguez-Fernández, Denis; Pérez-Juste, Jorge; Pastoriza-Santos, Isabel; Liz-Marzán, Luis M

    2012-01-01

    This work describes a novel and scalable colloid chemistry strategy to fabricate gold semishells based on the selective growth of gold on Janus silica particles (500 nm in diameter) partly functionalized with amino groups. The modulation of the geometry of the Janus silica particles allows us to tune the final morphology of the gold semishells. This method also provides a route to fabricating hollow gold semishells through etching of the silica cores with hydrofluoric acid. The optical properties were characterized by visible near-infrared (vis-NIR) spectroscopy and compared with simulations performed using the boundary element method (BEM). These revealed that the main optical features are located beyond the NIR region because of the large core size. PMID:24551496

  19. Hydrodynamic synchronization of colloidal oscillators

    PubMed Central

    Kotar, Jurij; Leoni, Marco; Bassetti, Bruno; Lagomarsino, Marco Cosentino; Cicuta, Pietro

    2010-01-01

    Two colloidal spheres are maintained in oscillation by switching the position of an optical trap when a sphere reaches a limit position, leading to oscillations that are bounded in amplitude but free in phase and period. The interaction between the oscillators is only through the hydrodynamic flow induced by their motion. We prove that in the absence of stochastic noise the antiphase dynamical state is stable, and we show how the period depends on coupling strength. Both features are observed experimentally. As the natural frequencies of the oscillators are made progressively different, the coordination is quickly lost. These results help one to understand the origin of hydrodynamic synchronization and how the dynamics can be tuned. Cilia and flagella are biological systems coupled hydrodynamically, exhibiting dramatic collective motions. We propose that weakly correlated phase fluctuations, with one of the oscillators typically precessing the other, are characteristic of hydrodynamically coupled systems in the presence of thermal noise. PMID:20385848

  20. Colloids at NAPL-Interfaces

    NASA Astrophysics Data System (ADS)

    Baumann, Thomas; Metz, Christian

    2014-05-01

    Non-aqueous phase liquids in subsurface are relevant in the scope of contaminated sites as well as for enhanced oil recovery. In both cases colloids and engineered nanoparticles are applied to increase the efficiency of NAPL removal. Particle tracking experiments using fluoresecent latex beads and opaque particles have been run in micromodels mimicking the pore structure of subsurface media. The results show that the interface between NAPL and water is highly dynamic, especially in its early stage. There is a distinct circular flow pattern at the interface, effectively increasing the interfacial area. Concentration gradients measured with Raman Microspectrometry at low Peclet numbers suggest that the mass transfer of dissolved contaminants from the NAPL into the water is highly affected by the interface dynamics. On the other hand the interfaces themselves are less accessible, which has implications for the remediation of contaminated sites.

  1. AFM imaging of functionalized double-walled carbon nanotubes.

    PubMed

    Lamprecht, C; Danzberger, J; Lukanov, P; Tîlmaciu, C-M; Galibert, A-M; Soula, B; Flahaut, E; Gruber, H J; Hinterdorfer, P; Ebner, A; Kienberger, F

    2009-07-01

    We present a comparative study of several non-covalent approaches to disperse, debundle and non-covalently functionalize double-walled carbon nanotubes (DWNTs). We investigated the ability of bovine serum albumin (BSA), phospholipids grafted onto amine-terminated polyethylene glycol (PL-PEG(2000)-NH(2)), as well as a combination thereof, to coat purified DWNTs. Topographical imaging with the atomic force microscope (AFM) was used to assess the coating of individual DWNTs and the degree of debundling and dispersion. Topographical images showed that functionalized DWNTs are better separated and less aggregated than pristine DWNTs and that the different coating methods differ in their abilities to successfully debundle and disperse DWNTs. Height profiles indicated an increase in the diameter of DWNTs depending on the functionalization method and revealed adsorption of single molecules onto the nanotubes. Biofunctionalization of the DWNT surface was achieved by coating DWNTs with biotinylated BSA, providing for biospecific binding of streptavidin in a simple incubation step. Finally, biotin-BSA-functionalized DWNTs were immobilized on an avidin layer via the specific avidin-biotin interaction. PMID:19375857

  2. AFM Investigation of Liquid-Filled Polymer Microcapsules Elasticity.

    PubMed

    Sarrazin, Baptiste; Tsapis, Nicolas; Mousnier, Ludivine; Taulier, Nicolas; Urbach, Wladimir; Guenoun, Patrick

    2016-05-10

    Elasticity of polymer microcapsules (MCs) filled with a liquid fluorinated core is studied by atomic force microscopy (AFM). Accurately characterized spherical tips are employed to obtain the Young's moduli of MCs having four different shell thicknesses. We show that those moduli are effective ones because the samples are composites. The strong decrease of the effective MC elasticity (from 3.0 to 0.1 GPa) as the shell thickness decreases (from 200 to 10 nm) is analyzed using a novel numerical approach. This model describes the evolution of the elasticity of a coated half-space according to the contact radius, the thickness of the film, and the elastic moduli of bulk materials. This numerical model is consistent with the experimental data and allows simulating the elastic behavior of MCs at high frequencies (5 MHz). While the quasi-static elasticity of the MCs is found to be very dependent on the shell thickness, the high frequency (5 MHz) elastic behavior of the core leads to a stable behavior of the MCs (from 2.5 to 3 GPa according to the shell thickness). Finally, the effect of thermal annealing on the MCs elasticity is investigated. The Young's modulus is found to decrease because of the reduction of the shell thickness due to the loss of the polymer. PMID:27058449

  3. BOREAS AFM-03-NCAR Electra 1994 Aircraft Sounding Data

    NASA Technical Reports Server (NTRS)

    Lenschow, Donald H.; Oncley, Steven P.; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-3 team used the National Center for Atmospheric Research's (NCAR) Electra aircraft to make sounding measurements to study the planetary boundary layer using in situ and remote-sensing measurements. Measurements were made of wind speed and direction, air pressure and temperature, potential temperature, dewpoint, mixing ratio of H, O, CO, concentration, and ozone concentration. Twenty-five research missions were flown over the Northern Study Area (NSA), Southern Study Area (SSA), and the transect during BOREAS Intensive Field Campaigns (IFCs) 1, 2, and 3 during 1994. All missions had from four to ten soundings through the top of the planetary boundary layer. This sounding data set contains all of the in situ vertical profiles through the boundary layer top that were made (with the exception of 'porpoise' maneuvers). Data were recorded in one-second time intervals. These data are stored in tabular ASCII files. The NCAR Electra 1994 aircraft sounding data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  4. BOREAS AFM-2 Wyoming King Air 1994 Aircraft Sounding Data

    NASA Technical Reports Server (NTRS)

    Kelly, Robert D.; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The BOREAS AFM-2 team used the University of Wyoming King Air aircraft during IFCs 1, 2, and 3 in 1994 to collected pass-by-pass fluxes (and many other statistics) for the large number of level (constant altitude), straight-line passes used in a variety of flight patterns over the SSA and NSA and areas along the transect between these study areas. The data described here form a second set, namely soundings that were incorporated into nearly every research flight by the King Air in 1994. These soundings generally went from near the surface to above the inversion layer. Most were flown immediately after takeoff or immediately after finishing the last flux pattern of that particular day's flights. The parameters that were measured include wind direction, wind speed, west wind component (u), south wind component (v), static pressure, air dry bulb temperature, potential temperature, dewpoint, temperature, water vapor mixing ratio, and CO2 concentration. Data on the aircraft's location, attitude, and altitude during data collection are also provided. These data are stored in tabular ASCH files. The data files are available on a CD-ROM (see document number 20010000884) or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  5. AFM-based force microsensor for a microrobot

    NASA Astrophysics Data System (ADS)

    Fatikow, Sergej; Fahlbusch, Stephan

    2001-10-01

    Microrobots are the result of increasing research activities at the border between microsystem technology and robotics. Today already, robots with dimensions of a few cubic- centimeters can be developed. Like conventional robots, microrobots represent a complex system that usually contains several different types of actuators and sensors. The measurement of gripping forces is the most important sensor application in micromanipulation besides visual servoing to protect the parts from too high surface pressures and thereby damage during the assembly process. Very small forces in the range of 200 (mu) N down to 0.1 (mu) N or even less have to be sensed. Thus, the aim of our current research activities is the development of a high-resolution integrated force microsensor for measuring gripping forces in a microhandling robot. On the one hand, the sensor should be a device for teleoperated manipulation tasks in a flexible microhandling station. On the other hand, typical microhandling operations should to a large extend be automated with the aid of computer-based signal processing of sensor information. The user should be provided with an interface for teleoperated manipulation and an interface for partially automated manipulation of microobjects. In this paper, a concept for the measurement of gripping forces in microrobotics using piezoresistive AFM (atomic force microscope) cantilevers is introduced. Further on, the concept of a microrobot-based SEM station and its applications are presented.

  6. Transport in charged colloids driven by thermoelectricity.

    PubMed

    Würger, Alois

    2008-09-01

    We study the thermal diffusion coefficient D{T} of a charged colloid in a temperature gradient, and find that it is to a large extent determined by the thermoelectric response of the electrolyte solution. The thermally induced salinity gradient leads in general to a strong increase with temperature. The difference of the heat of transport of coions and counterions gives rise to a thermoelectric field that drives the colloid to the cold or to the warm, depending on the sign of its charge. Our results provide an explanation for recent experimental findings on thermophoresis in colloidal suspensions. PMID:18851262

  7. Three-dimensional ultrasonic colloidal crystals

    NASA Astrophysics Data System (ADS)

    Caleap, Mihai; Drinkwater, Bruce W.

    2016-05-01

    Colloidal assembly represents a powerful method for the fabrication of functional materials. In this article, we describe how acoustic radiation forces can guide the assembly of colloidal particles into structures that serve as microscopic elements in novel acoustic metadevices or act as phononic crystals. Using a simple three-dimensional orthogonal system, we show that a diversity of colloidal structures with orthorhombic symmetry can be assembled with megahertz-frequency (MHz) standing pressure waves. These structures allow rapid tuning of acoustic properties and provide a new platform for dynamic metamaterial applications. xml:lang="fr"

  8. Colloidal CdSe Quantum Rings.

    PubMed

    Fedin, Igor; Talapin, Dmitri V

    2016-08-10

    Semiconductor quantum rings are of great fundamental interest because their non-trivial topology creates novel physical properties. At the same time, toroidal topology is difficult to achieve for colloidal nanocrystals and epitaxially grown semiconductor nanostructures. In this work, we introduce the synthesis of luminescent colloidal CdSe nanorings and nanostructures with double and triple toroidal topology. The nanorings form during controlled etching and rearrangement of two-dimensional nanoplatelets. We discuss a possible mechanism of the transformation of nanoplatelets into nanorings and potential utility of colloidal nanorings for magneto-optical (e.g., Aharonov-Bohm effect) and other applications.

  9. Polarity inversion of ζ-potential in concentrated colloidal dispersions.

    PubMed

    Manzanilla-Granados, Héctor M; Jiménez-Ángeles, Felipe; Lozada-Cassou, Marcelo

    2011-10-27

    A concentrated colloidal dispersion is studied by applying an integral equations theory to the colloidal primitive model fluid. Important effects, attributed to large size and charge and to the finite concentration of colloidal particles, are found. We observe a polarity inversion of ζ-potential for concentrated colloidal dispersions, while it is not present for a single colloidal particle at infinite dilution. An excellent qualitative agreement between our theoretical predictions and our computer simulations is observed.

  10. Colloid-Facilitated Transport of Radionuclides through the Vadose Zone

    SciTech Connect

    Flury, Markus; Harsh, James B.; Zachara, John M.; McCarthy, John F.; Lichtner, Peter C.

    2006-05-31

    This project seeks to improve the basic understanding of the role of colloids in facilitating the transport of contaminants in the vadose zone. We focus on three major thrusts: (1) thermodynamic stability and mobility of colloids formed by reactions of sediments with highly alkaline tank waste solutions, (2) colloid-contaminant interactions, and (3) in-situ colloid mobilization and colloid facilitated contaminant transport occurring in both contaminated and uncontaminated Hanford sediments.

  11. Combined strategies for optimal detection of the contact point in AFM force-indentation curves obtained on thin samples and adherent cells.

    PubMed

    Gavara, Núria

    2016-01-01

    Atomic Force Microscopy (AFM) is a widely used tool to study cell mechanics. Current AFM setups perform high-throughput probing of living cells, generating large amounts of force-indentations curves that are subsequently analysed using a contact-mechanics model. Here we present several algorithms to detect the contact point in force-indentation curves, a crucial step to achieve fully-automated analysis of AFM-generated data. We quantify and rank the performance of our algorithms by analysing a thousand force-indentation curves obtained on thin soft homogeneous hydrogels, which mimic the stiffness and topographical profile of adherent cells. We take advantage of the fact that all the proposed algorithms are based on sequential search strategies, and show that a combination of them yields the most accurate and unbiased results. Finally, we also observe improved performance when force-indentation curves obtained on adherent cells are analysed using our combined strategy, as compared to the classical algorithm used in the majority of previous cell mechanics studies. PMID:26891762

  12. Combined strategies for optimal detection of the contact point in AFM force-indentation curves obtained on thin samples and adherent cells

    NASA Astrophysics Data System (ADS)

    Gavara, Núria

    2016-02-01

    Atomic Force Microscopy (AFM) is a widely used tool to study cell mechanics. Current AFM setups perform high-throughput probing of living cells, generating large amounts of force-indentations curves that are subsequently analysed using a contact-mechanics model. Here we present several algorithms to detect the contact point in force-indentation curves, a crucial step to achieve fully-automated analysis of AFM-generated data. We quantify and rank the performance of our algorithms by analysing a thousand force-indentation curves obtained on thin soft homogeneous hydrogels, which mimic the stiffness and topographical profile of adherent cells. We take advantage of the fact that all the proposed algorithms are based on sequential search strategies, and show that a combination of them yields the most accurate and unbiased results. Finally, we also observe improved performance when force-indentation curves obtained on adherent cells are analysed using our combined strategy, as compared to the classical algorithm used in the majority of previous cell mechanics studies.

  13. Combined strategies for optimal detection of the contact point in AFM force-indentation curves obtained on thin samples and adherent cells

    PubMed Central

    Gavara, Núria

    2016-01-01

    Atomic Force Microscopy (AFM) is a widely used tool to study cell mechanics. Current AFM setups perform high-throughput probing of living cells, generating large amounts of force-indentations curves that are subsequently analysed using a contact-mechanics model. Here we present several algorithms to detect the contact point in force-indentation curves, a crucial step to achieve fully-automated analysis of AFM-generated data. We quantify and rank the performance of our algorithms by analysing a thousand force-indentation curves obtained on thin soft homogeneous hydrogels, which mimic the stiffness and topographical profile of adherent cells. We take advantage of the fact that all the proposed algorithms are based on sequential search strategies, and show that a combination of them yields the most accurate and unbiased results. Finally, we also observe improved performance when force-indentation curves obtained on adherent cells are analysed using our combined strategy, as compared to the classical algorithm used in the majority of previous cell mechanics studies. PMID:26891762

  14. Pollution Probe.

    ERIC Educational Resources Information Center

    Chant, Donald A.

    This book is written as a statement of concern about pollution by members of Pollution Probe, a citizens' anti-pollution group in Canada. Its purpose is to create public awareness and pressure for the eventual solution to pollution problems. The need for effective government policies to control the population explosion, conserve natural resources,…

  15. Fullerene (C60) nano-colloids in nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Visco, Angelo; Sobczak, Kevin; Mahmood, Rizwan

    2015-03-01

    We report high resolution homodyne light scattering studies to probe director fluctuations in bend/splay mode in bulk nematic liquid crystal and as a function of fullerene (C60) nanoparticles concentration. The preliminary analysis shows that the relaxation time of these fluctuations is fairly constant with in the experimental uncertainty despite the constraints imposed on the director fluctuations due to the insertion of nano colloids. The relaxation time extracted from the data found to be in nano seconds range and the diffusion constant (D) found to be, D = 4.29 x 106 cm/sec. The authors acknowledge the financial support from grants office, Dean, college of Health, Environment & Science and the physics department.

  16. Hydrogenated Amorphous Silicon (a-Si:H) Colloids

    SciTech Connect

    Harris, Justin T.; Hueso, Jose L.; Korgel, Brian A.

    2010-12-14

    Colloidal particles of hydrogenated amorphous silicon (a-Si:H) were synthesized by decomposition of trisilane (Si{sub 3}H{sub 8}) in supercritical n-hexane (sc-hexane) at temperatures ranging from 380 to 550 °C. The reaction temperature, pressure and Si{sub 3}H{sub 8} concentration have a significant influence on the average particle size, Si bond order and hydrogen content. The particle diameter could be varied from 170 nm to 1.7 μm, with hydrogen loadings between 10% and 58%. Raman spectroscopy of the particles revealed significant differences in Si bond order that correlated with hydrogen content, with the lowest reaction temperatures yielding particles with the least structural order and most associated hydrogen. Particles synthesized at temperatures higher than 420 °C had sufficient bond order to allow crystallization under the Raman laser probe.

  17. Probing Micromechanical Properties of the Extracellular Matrix of Soft Tissues by Atomic Force Microscopy.

    PubMed

    Jorba, Ignasi; Uriarte, Juan J; Campillo, Noelia; Farré, Ramon; Navajas, Daniel

    2017-01-01

    The extracellular matrix (ECM) determines 3D tissue architecture and provides structural support and chemical and mechanical cues to the cells. Atomic force microscopy (AFM) has unique capabilities to measure ECM mechanics at the scale at which cells probe the mechanical features of their microenvironment. Moreover, AFM measurements can be readily combined with bright field and fluorescence microscopy. Performing reliable mechanical measurements with AFM requires accurate calibration of the device and correct computation of the mechanical parameters. A suitable approach to isolate ECM mechanics from cell contribution is removing the cells by means of an effective decellularization process that preserves the composition, structure and mechanical properties of the ECM. AFM measurement of ECM micromechanics provides important insights into organ biofabrication, cell-matrix mechanical crosstalk and disease-induced tissue stiffness alterations. J. Cell. Physiol. 232: 19-26, 2017. © 2016 Wiley Periodicals, Inc. PMID:27163411

  18. Probing Micromechanical Properties of the Extracellular Matrix of Soft Tissues by Atomic Force Microscopy.

    PubMed

    Jorba, Ignasi; Uriarte, Juan J; Campillo, Noelia; Farré, Ramon; Navajas, Daniel

    2017-01-01

    The extracellular matrix (ECM) determines 3D tissue architecture and provides structural support and chemical and mechanical cues to the cells. Atomic force microscopy (AFM) has unique capabilities to measure ECM mechanics at the scale at which cells probe the mechanical features of their microenvironment. Moreover, AFM measurements can be readily combined with bright field and fluorescence microscopy. Performing reliable mechanical measurements with AFM requires accurate calibration of the device and correct computation of the mechanical parameters. A suitable approach to isolate ECM mechanics from cell contribution is removing the cells by means of an effective decellularization process that preserves the composition, structure and mechanical properties of the ECM. AFM measurement of ECM micromechanics provides important insights into organ biofabrication, cell-matrix mechanical crosstalk and disease-induced tissue stiffness alterations. J. Cell. Physiol. 232: 19-26, 2017. © 2016 Wiley Periodicals, Inc.

  19. Surface Modeling of Nanopatterned Polymer Films Obtained by Colloidal Templated Electropolymerization.

    PubMed

    Cernat, Andreea; Bodoki, Ede; Farcau, Cosmin; Aştilean, Simion; Griveau, Sophie; Bedioui, Fethi; Săndulescu, Robert

    2015-05-01

    Nanostructured polypyrrole surfaces are fabricated by a one step colloidal templating approach, involving simultaneous polystyrene bead deposition with the electropolymerization of the pyrrole monomer. Using response surface modeling, the influence of several experimental parameters was studied, following as response the resulted film's thickness and the nanopattern's surface density. Polystyrene beads of 100 nm were immobilized by the electropolymerization of pyrrole and the spheres were dissolved in tetrahydrofuran at room temperature. The obtained nanostructures were analyzed by atomic force microscopy (AFM) and the results served to build the mathematical model (central composite face centered design, quadratic model) best describing the correlations between variables and responses. The obtained response surface model revealed the specific influence of each of the studied variables over the followed responses and it also allowed the controlled fabrication of nanopatterned surfaces.

  20. Fabrication of a polymer-metal combined atomic force microscopy probe for coarse food surface imaging.

    PubMed

    Kang, Hyen-Wook; Muramatsu, Hiroshi; Kwon, Young-Soo

    2013-05-01

    We fabricated a polymer-metal combined atomic force microscopy (AFM) probe by two steps; a polymeric resin was used at first step, and a metal-ion was used at second step which needs more fabricating time than the resin. At first step, we fabricated a cylindrical base on to a commercial cantilever. At second step, we fabricated a conical probe on to the fabricated cylindrical base. To make the conical probe composed with silver, a 0.2 M aqueous solution of silver nitrate (AgNO3) was used. A 50 microm length polymeric-metallic hybrid tip has been fabricated to observe large bio and food samples. Generally, the AFM images of bio/food samples show cliff-like sharp patters in vertical. However, the AFM image by fabricated long tip shows clear structure of each brown rice flours. As most of commercial tips have three-angular pyramidal, the scanned results should be influenced by the lateral face of the three-angular pyramid, which results in cliff-like images. Because the sample size is large, the side area of the sample was adversely affected by the pyramidal structure during imaging. This problem may be resolved by designing conical structure tips. As the conical structure has no edge, the AFM image becomes clear. The fabricated tip has conical structure, and a clear AFM image was achieved. PMID:23858900