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Sample records for layer growth kinetics

  1. Intermetallic compound layer growth kinetics in non-lead bearing solders

    SciTech Connect

    Vianco, P.T.; Kilgo, A.C.; Grant, R.

    1995-04-01

    The introduction of alternative, non-lead bearing solders into electronic assemblies requires a thorough investigation of product manufacturability and reliability. Both of these attributes can be impacted by the excessive growth of intermetallic compound (IMC) layers at the solder/substrate interface. An extensive study has documented the stoichiometry and solid state growth kinetics of IMC layers formed between copper and the lead-free solders: 96.5Sn-3.5Ag (wt.%), 95Sn-5Sb, 100Sn, and 58Bi-42Sn. Aging temperatures were 70--205 C for the Sn-based solders and 55--120 C for the Bi-rich solder. Time periods were 1--400 days for all of the alloys. The Sn/Cu, Sn-Ag/Cu, and Sn-Sb/Cu IMC layers exhibited sub-layers of Cu{sub 6}Sn{sub 5} and Cu{sub 3}Sn; the latter composition was present only following prolonged aging times or higher temperatures. The total layer growth exhibited a time exponent of n = 0.5 at low temperatures and a value of n = 0.42 at higher temperatures in each of the solder/Cu systems. Similar growth kinetics were observed with the low temperature 58Bi-42Sn solder; however, a considerably more complex sub-layer structure was observed. The kinetic data will be discussed with respect to predicting IMC layer growth based upon solder composition.

  2. The kinetic boundary layer around an absorbing sphere and the growth of small droplets

    SciTech Connect

    Widder, M.E.; Titulaer, U.M. )

    1989-06-01

    Deviations from the classical Smoluchowski expression for the growth rate of a droplet in a supersaturated vapor can be expected when the droplet radius is not large compared to the mean free path of a vapor molecule. The growth rate then depends significantly on the structure of the kinetic boundary layer around a sphere. The authors consider this kinetic boundary layer for a dilute system of Brownian particles. For this system a large class of boundary layer problems for a planar wall have been solved. They show how the spherical boundary layer can be treated by a perturbation expansion in the reciprocal droplet radius. In each order one has to solve a finite number of planar boundary layer problems. The first two corrections to the planar problem are calculated explicitly. For radii down to about two velocity persistence lengths (the analog of the mean free path for a Brownian particle) the successive approximations for the growth rate agree to within a few percent. A reasonable estimate of the growth rate for all radii can be obtained by extrapolating toward the exactly known value at zero radius. Kinetic boundary layer effects increase the time needed for growth from 0 to 10 (or 2{1/2}) velocity persistence lengths by roughly 35% (or 175%).

  3. The Powder-Pack Nitriding Process: Growth Kinetics of Nitride Layers on Pure Iron

    NASA Astrophysics Data System (ADS)

    Campos-Silva, I.; Ortiz-Dominguez, M.; Elias-Espinosa, M.; Vega-Morón, R. C.; Bravo-Bárcenas, D.; Figueroa-López, U.

    2015-09-01

    In this study, the growth kinetics of nitride layers that develop during the powder-pack nitriding process on the surface of ARMCO pure iron was estimated. The powder-pack nitriding of pure iron was performed according to the Pulnieren© (H.E.F. Durferrit) method using a "Pulnier" powder and an activator, at 798-848 K with different exposure times (2-12 h) for each temperature. In addition, for the entire set of nitriding conditions, three different activator/"Pulnier" powder ratios (0.20, 0.25, and 0.35) were used to evaluate the activation level during the growth of nitride layers. The kinetics of the nitride layers over the surface of ARMCO pure iron were estimated by two mathematical approaches, that consider the mass balance equations at the growth interphases. The resulting expressions for the effective diffusion coefficients in the nitride layers were evaluated as a function of nitriding temperatures and activator/"Pulnier" powder ratio. Finally, based on the experimental parameters ascribed to the powder-pack nitriding process, two expressions were proposed to estimate the nitride layer thicknesses at 798 and 823 K after 9 h of exposure for each temperature, to validate the diffusion models used in this work.

  4. From atoms to layers: in situ gold cluster growth kinetics during sputter deposition

    NASA Astrophysics Data System (ADS)

    Schwartzkopf, Matthias; Buffet, Adeline; Körstgens, Volker; Metwalli, Ezzeldin; Schlage, Kai; Benecke, Gunthard; Perlich, Jan; Rawolle, Monika; Rothkirch, André; Heidmann, Berit; Herzog, Gerd; Müller-Buschbaum, Peter; Röhlsberger, Ralf; Gehrke, Rainer; Stribeck, Norbert; Roth, Stephan V.

    2013-05-01

    The adjustment of size-dependent catalytic, electrical and optical properties of gold cluster assemblies is a very significant issue in modern applied nanotechnology. We present a real-time investigation of the growth kinetics of gold nanostructures from small nuclei to a complete gold layer during magnetron sputter deposition with high time resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (μGISAXS). We specify the four-stage growth including their thresholds with sub-monolayer resolution and identify phase transitions monitored in Yoneda intensity as a material-specific characteristic. An innovative and flexible geometrical model enables the extraction of morphological real space parameters, such as cluster size and shape, correlation distance, layer porosity and surface coverage, directly from reciprocal space scattering data. This approach enables a large variety of future investigations of the influence of different process parameters on the thin metal film morphology. Furthermore, our study allows for deducing the wetting behavior of gold cluster films on solid substrates and provides a better understanding of the growth kinetics in general, which is essential for optimization of manufacturing parameters, saving energy and resources.The adjustment of size-dependent catalytic, electrical and optical properties of gold cluster assemblies is a very significant issue in modern applied nanotechnology. We present a real-time investigation of the growth kinetics of gold nanostructures from small nuclei to a complete gold layer during magnetron sputter deposition with high time resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (μGISAXS). We specify the four-stage growth including their thresholds with sub-monolayer resolution and identify phase transitions monitored in Yoneda intensity as a material-specific characteristic. An innovative and flexible geometrical model enables the extraction

  5. Layer-growth kinetics on gaseous nitriding of pure iron: Evaluation of diffusion coefficients for nitrogen in iron nitrides

    NASA Astrophysics Data System (ADS)

    Somers, Marcel A. J.; Mittemeijer, Eric J.

    1995-01-01

    Models were derived for monolayer and bilayer growth into a substrate in which diffusion of the solute governs the growth kinetics, as in gas-solid reactions, for example. In the models, the composition dependence of the solute diffusivity in the phases constituting the layers was accounted for by appropriate definition of an effective diffusion coefficient for a (sub)layer. This effective diffusion coefficient is the intrinsic diffusion coefficient weighted over the composition range of the (sub)layer. The models were applied for analyzing the growth kinetics of a γ'-Fe4N1-x monolayer on an α-Fe substrate and the growth kinetics of an ɛ-Fe2N1-z/γ'-Fe4N1-x bilayer on an α-Fe substrate, as observed by gaseous nitriding in an NH3/H2-gas mixture at 843 K. The kinetics of layer development and the evolution of the microstructure were investigated by means of thermogravimetry, layer-thickness measurements, light microscopy, and electron probe X-ray microanalysis (EPMA). The effective and self-diffusion coefficients were determined for each of the nitride layers. The composition dependence of the intrinsic (and effective) diffusion coefficients was established. Re-evaluating literature data for diffusion in γ'-Fe4N1-x on the basis of the present model, it followed that the previous and present data are consistent. The activation energy for diffusion of nitrogen in γ'-Fe4N1-x was determined from the temperature dependence of the self-diffusion coefficient. The self-diffusion coefficient for nitrogen in ɛ-Fe2N1-z was significantly larger than that for γ'-Fe4N1-x. This was explained qualitatively, considering the possible mechanisms for interstitial diffusion of nitrogen atoms in the close-packed iron lattices of the ɛ and γ' iron nitrides.

  6. Effect of GaAs substrate orientation on the growth kinetic of GaN layer grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Laifi, J.; Chaaben, N.; Bouazizi, H.; Fourati, N.; Zerrouki, C.; El Gmili, Y.; Bchetnia, A.; Salvestrini, J. P.; El Jani, B.

    2016-06-01

    We have investigated the kinetic growth of low temperature GaN nucleation layers (LT-GaN) grown on GaAs substrates with different crystalline orientations. GaN nucleation layers were grown by metal organic vapor phase epitaxy (MOVPE) in a temperature range of 500-600 °C on oriented (001), (113), (112) and (111) GaAs substrates. The growth was in-situ monitored by laser reflectometry (LR). Using an optical model, including time-dependent surface roughness and growth rate profiles, simulations were performed to best approach the experimental reflectivity curves. Results are discussed and correlated with ex-situ analyses, such as atomic force microscopy (AFM) and UV-visible reflectance (SR). We show that the GaN nucleation layers growth results the formation of GaN islands whose density and size vary greatly with both growth temperature and substrate orientation. Arrhenius plots of the growth rate for each substrate give values of activation energy varying from 0.20 eV for the (001) orientation to 0.35 eV for the (113) orientation. Using cathodoluminescence (CL), we also show that high temperature (800-900 °C) GaN layers grown on top of the low temperature (550 °C) GaN nucleation layers, grown themselves on the GaAs substrates with different orientations, exhibit cubic or hexagonal phase depending on both growth temperature and substrate orientation.

  7. An identification algorithm of model kinetic parameters of the interfacial layer growth in fiber composites

    NASA Astrophysics Data System (ADS)

    Zubov, V.; Lurie, S.; Solyaev, Y.

    2016-04-01

    This paper considers the identification algorithm of parameters included in a parabolic law that is often used to predict the time dependence of the thickness of the interfacial layers in the structure of composite materials based on a metal matrix. The incubation period of the process and the speed of reaction and pressure are taken into account. The proposed algorithm of identification is based on the introduction of a minimized objective function of a special kind. The problem of identification of unknown parameters in the parabolic law is formulated in a variational form. The authors of the paper have determined the desired parameters, under which the objective function has a minimum value. It is shown that on the basis of four known experimental values of the interfacial layer thickness, corresponding to different values of temperature, pressure and the time of the interfacial layer growth, it is possible to identified four model parameters. They are the activation energy, a pre-exponential parameter, the delay time of the start of the interfacial layer formation, and the parameter determining the pressure effect on the rate of interfacial layer growth. The stability of the proposed identification algorithm is also studied.

  8. Kinetics modeling and growth of Si layers by Liquid Phase Epitaxy Driven by Solvent Evaporation (LPESE)

    NASA Astrophysics Data System (ADS)

    Giraud, S.; Duffar, T.; Pihan, E.; Fave, A.

    2015-12-01

    Crystalline Si thin films on low-cost substrates are expected to be an alternative to bulk Si for PV applications. Liquid Phase Epitaxy (LPE) is one of the most suitable techniques for the growth of high quality Si layers since LPE is performed under almost equilibrium conditions. We investigated a growth technology which allows growing Si epitaxial thin films in steady temperature conditions through the control of solvent evaporation from a metallic solution saturated with silicon: Liquid Phase Epitaxy by Solvent Evaporation (LPESE). An analytical model aiming to predict solvent evaporation and Si crystallization rate is described and discussed for three solvents (Sn, In and Cu). Growth experiments are implemented in order to check the validity of the model. Experimental set up and growth procedure are presented. Si thin films were grown from Sn-Si and In-Si solution at temperatures between 900 and 1200 °C under high vacuum. The predicted solvent evaporation rate and Si growth rate are in agreement with the experimental measurements.

  9. High temperature materials synthesis without heat: Oxide layer growth on electronic materials using high-kinetic-energy atomic oxygen

    SciTech Connect

    Hoffbauer, M.A.; Cross, J.B.; Archuleta, F.A.

    1996-04-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The authors examined thin-film materials-synthesis processes in which chemical reactions are initiated using high-kinetic-energy neutral atomic species instead of high temperatures. The research is aimed at producing device-quality insulating oxide layers on semiconductor materials. Thick, uniform, and fully oxidized insulating layers of unprecedented quality are formed on gallium arsenide by exposure of wafer substrates to a high kinetic-energy ({approximately}3eV) neutral atomic-oxygen beam. The nonthermal oxidation process does not disrupt the crystalline order of the substrate and no detectable elemental arsenic is produced at the oxide/gallium arsenide interface.

  10. High In-content InGaN layers synthesized by plasma-assisted molecular-beam epitaxy: Growth conditions, strain relaxation, and In incorporation kinetics

    NASA Astrophysics Data System (ADS)

    Valdueza-Felip, S.; Bellet-Amalric, E.; Núñez-Cascajero, A.; Wang, Y.; Chauvat, M.-P.; Ruterana, P.; Pouget, S.; Lorenz, K.; Alves, E.; Monroy, E.

    2014-12-01

    We report the interplay between In incorporation and strain relaxation kinetics in high-In-content InxGa1-xN (x = 0.3) layers grown by plasma-assisted molecular-beam epitaxy. For In mole fractions x = 0.13-0.48, best structural and morphological qualities are obtained under In excess conditions, at In accumulation limit, and at a growth temperature where InGaN decomposition is active. Under such conditions, in situ and ex situ analyses of the evolution of the crystalline structure with the layer thickness point to an onset of misfit relaxation after the growth of 40 nm, and a gradual relaxation during more than 200 nm, which results in an inhomogeneous strain distribution along the growth axis. This process is associated with a compositional pulling effect, i.e., indium incorporation is partially inhibited in presence of compressive strain, resulting in a compositional gradient with increasing In mole fraction towards the surface.

  11. High In-content InGaN layers synthesized by plasma-assisted molecular-beam epitaxy: Growth conditions, strain relaxation, and In incorporation kinetics

    SciTech Connect

    Valdueza-Felip, S. Bellet-Amalric, E.; Pouget, S.; Monroy, E.; Wang, Y.; Chauvat, M.-P.; Ruterana, P.; Lorenz, K.; Alves, E.

    2014-12-21

    We report the interplay between In incorporation and strain relaxation kinetics in high-In-content In{sub x}Ga{sub 1-x}N (x = 0.3) layers grown by plasma-assisted molecular-beam epitaxy. For In mole fractions x = 0.13–0.48, best structural and morphological qualities are obtained under In excess conditions, at In accumulation limit, and at a growth temperature where InGaN decomposition is active. Under such conditions, in situ and ex situ analyses of the evolution of the crystalline structure with the layer thickness point to an onset of misfit relaxation after the growth of 40 nm, and a gradual relaxation during more than 200 nm, which results in an inhomogeneous strain distribution along the growth axis. This process is associated with a compositional pulling effect, i.e., indium incorporation is partially inhibited in presence of compressive strain, resulting in a compositional gradient with increasing In mole fraction towards the surface.

  12. Nucleation and growth transformation kinetics

    NASA Astrophysics Data System (ADS)

    Erukhimovitch, V.; Baram, J.

    1995-03-01

    As a result of the reassessment of the Kolmogorov-Johnson-Mehl-Avrami (KJMA) theory for the kinetics of nucleation and growth transformations, an integral-equation formulation has been developed instead of the well-known and widely used Avrami equation. The presented formulation considers interfacial and diffusional growths, in one, two, and three dimensions, with both time-dependent and time-invariant nucleation and growth rates. The integral-equation model corrects reported inadequacies of the KJMA theory when applied in numerous experiments and various solid-state transformations. It is shown that in the example cases examined in this paper, crystallization from the amorphous state in melt-spun ribbons, isothermal aging of CuAlZn, pearlitic transition in an eutectoid steel, and crystallization in a PEKK polymer, the thermodynamic and kinetic interpretation and parameters extracted from best fits of the Avrami equations to the experimental data are erroneous. The KJMA formulation is a simplification of the real physical conditions. The main limitation of the new model is that almost all the integral equations representing the kinetics of solid-state transformations have no analytical solutions.

  13. Domain Growth Kinetics in Stratifying Foam Films

    NASA Astrophysics Data System (ADS)

    Zhang, Yiran; Sharma, Vivek

    2015-03-01

    Baking bread, brewing cappuccino, pouring beer, washing dishes, shaving, shampooing, whipping eggs and blowing bubbles all involve creation of aqueous foam films. Typical foam films consist of two surfactant-laden surfaces that are μ 5 nm - 10 micron apart. Sandwiched between these interfacial layers is a fluid that drains primarily under the influence of viscous and interfacial forces, including disjoining pressure. Interestingly, for certain low molecular weight surfactants, a layered ordering of micelles inside the foam films (thickness <100 nm) leads to a stepwise thinning phenomena called stratification. We experimentally elucidate the influence of these different driving forces, and confinement on drainage kinetics of horizontal stratifying foam films. Thinner, darker domains spontaneously grow within foam films. Quantitative characterization of domain growth visualized in a using Scheludko-type thin film cell and a theoretical model based on lubrication analysis, provide critical insights into hydrodynamics of thin foam films, and the strength and nature of surface forces, including supramolecular oscillatory structural forces.

  14. Bridging in grafted layers : Statics and kinetics

    NASA Astrophysics Data System (ADS)

    Johner, A.

    We discuss bridging between a grafted layer and an opposing plate which adsorbs the polymer. The case of end adsorption is considered, as well as the case where all monomers adsorb. We predict that with increasing adsorption an exclusion zone grows in the vicinity of the adsorbing plate, this slows down the kinetics. For end adsorption we study the kinetics and argue that two main processes are involved: the exploration of the brush by a free end and its adsorption through the exclusion zone.

  15. A Simple Kinetic Model for the Growth of Fe2B Layers on AISI 1026 Steel During the Powder-pack Boriding

    NASA Astrophysics Data System (ADS)

    Flores-Rentería, M. A.; Ortiz-Domínguez, M.; Keddam, M.; Damián-Mejía, O.; Elias-Espinosa, M.; Flores-González, M. A.; Medina-Moreno, S. A.; Cruz-Avilés, A.; Villanueva-Ibañez, M.

    2015-02-01

    This work focused on the determination of boron diffusion coefficient through the Fe2B layers on AISI 1026 steel using a mathematical model. The suggested model solves the mass balance equation at the (Fe2B/substrate) interface. This thermochemical treatment was carried out in the temperature range of 1123-1273 K for a treatment time ranging from 2 to 8 h. The generated boride layers were characterized by different experimental techniques such as light optical microscopy, scanning electron microscopy, XRD analysis and the Daimler-Benz Rockwell-C indentation technique. As a result, the boron activation energy for AISI 1026 steel was estimated as 178.4 kJ/mol. Furthermore, this kinetic model was validated by comparing the experimental Fe2B layer thickness with the predicted one at a temperature of 1253 K for 5 h of treatment. A contour diagram relating the layer thickness to the boriding parameters was proposed to be used in practical applications.

  16. Controlled positions and kinetic analysis of spontaneous tin whisker growth

    NASA Astrophysics Data System (ADS)

    Su, Chien-Hao; Chen, Hao; Lee, Hsin-Yi; Wu, Albert T.

    2011-09-01

    This study achieved controlling the positions of spontaneous growth of tin whiskers. We surmounted the unpredictable growing nature of such whiskers and performed accurately quantitative analyses of the growth kinetics and yielded precise measurement of the growth rate. Furthermore, using synchrotron radiation x-ray, this study determined the stress variations in conjunction with whisker growth that fitted appropriately to the model. Accordingly, the results could address the debate held for decades and prove that forming a surface oxide layer is one of the required and necessary conditions for controlling the positions of spontaneous growth of tin whiskers.

  17. Domain growth kinetics in stratifying foam films

    NASA Astrophysics Data System (ADS)

    Zhang, Yiran; Sharma, Vivek

    2015-11-01

    Baking bread, brewing cappuccino, pouring beer, washing dishes, shaving, shampooing, whipping eggs and blowing bubbles all involve creation of aqueous foam films. Typical foam films consist of two surfactant-laden surfaces that are ~ 5 nm - 10 micron apart. Sandwiched between these interfacial layers is a fluid that drains primarily under the influence of viscous and interfacial forces, including disjoining pressure. Interestingly, a layered ordering of micelles inside the foam films (thickness <100 nm) leads to a stepwise thinning phenomena called stratification, which results in a thickness-dependent variation in reflected light intensity, visualized as progressively darker shades of gray. Thinner, darker domains spontaneously grow within foam films. We show that the domain expansion dynamics exhibit two distinct growth regimes with characteristic scaling laws. Though several studies have focused on the expansion dynamics of isolated domains that exhibit a diffusion-like scaling, the change in expansion kinetics observed after domains contact with the Plateau border has not been reported and analyzed before.

  18. Growth kinetics and morphology of polymer crystals

    NASA Astrophysics Data System (ADS)

    Toda, Akihiko

    2007-03-01

    Originating from the nature of chain folding, polymer single crystals are quite unique in the growth kinetics and morphology. The developments of the understanding in the past 50 years are discussed and the unsolved important issues will be suggested. Polymer single crystals are thin lamellae with the thickness in the order of 10nm determined by the period of chain folding, which keeps a constant value for the isothermal crystallization. The growth of polymer single crystals is modeled by the kinetics of creation and annihilation of growth steps on a rectangular substrate with the pre-determined thickness. The growth face is therefore regarded as a one-dimensional substrate and the kinks and anti-kinks on the substrate correspond to the growth steps propagating in the opposite directions. The kinetic equations of those kinks proposed by Seto and Frank well describe the transition of growth regime as a crossover from single nucleation to multi-nucleation on the basis of the standard model of chain-folded polymer crystallization with surface nucleation proposed by Lauritzen and Hoffman. However, the analysis of the growth kinetics and morphology of single crystals having curved growth front suggests an unusual behavior of the step propagation velocity. The anomaly can be accounted for by a self-poisoning of the growth step interrupted by polymer chains with folding shorter than required. An entropic barrier of pinning proposed by Sadler and Gilmer is a possible candidate of the self-poisoning and is in accordance with recent computer simulation results suggesting the kinetics on a rugged free energy landscape having a resemblance to protein folding. Therefore, the quantitative evaluation of the kinetic barriers of surface nucleation and pinning has been an important issue. In addition, examination of the kinetics of melting will have valuable information because melting of a crystal must be free from nucleation but can still be limited by the entropic barrier.

  19. Growth kinetics and structural perfection of (InN)1/(GaN)1-20 short-period superlattices on +c-GaN template in dynamic atomic layer epitaxy

    NASA Astrophysics Data System (ADS)

    Kusakabe, Kazuhide; Hashimoto, Naoki; Itoi, Takaomi; Wang, Ke; Imai, Daichi; Yoshikawa, Akihiko

    2016-04-01

    The growth kinetics and structural perfection of (InN)1/(GaN)1-20 short-period superlattices (SPSs) were investigated with their application to ordered alloys in mind. The SPSs were grown on +c-GaN template at 650 °C by dynamic atomic layer epitaxy in conventional plasma-assisted molecular beam epitaxy. It was found that coherent structured InN/GaN SPSs could be fabricated when the thickness of the GaN barrier was 4 ML or above. Below 3 ML, the formation of SPSs was quite difficult owing to the increased strain in the SPS structure caused by the use of GaN as a template. The effective or average In composition of the (InN)1/(GaN)4 SPSs was around 10%, and the corresponding InN coverage in the ˜1 ML-thick InN wells was 50%. It was found that the effective InN coverage in ˜1 ML-thick InN wells could be varied with the growth conditions. In fact, the effective In composition could be increased up to 13.5%, i.e., the corresponding effective InN coverage was about 68%, by improving the capping/freezing speed by increasing the growth rate of the GaN barrier layer.

  20. Transport and Growth Kinetics in Microgravity Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Otalora, F.; Garcia-Ruiz, J. M.; Carotenuto, L.; Castagnolo, D.; Novella, M. L.; Chernov, A. A.

    2002-01-01

    The dynamic coupling between mass transport and incorporation of growth units into the surface of a crystal growing from solution in microgravity is used to derive quantitative information on the crystal growth kinetics. To this end, new procedures for experiment preparation, interferometric data processing and model fitting have been developed. The use of experimental data from the bulk diffusive maw transport together with a model for steady state stagnant crystal growth allows the detailed quantitative understanding of the kinetics of both the concentration depletion zone around the crystal and the growth of the crystal interface. The protein crystal used in the experiment is shown to be growing in the mixed kinetic regime (0.2 x 10(exp -6) centimeters per second less than beta R/D less than 0.9 x 10(exp -6) centimeters per second).

  1. Microscopic kinetic model for polymer crystal growth

    NASA Astrophysics Data System (ADS)

    Hu, Wenbing

    2011-03-01

    Linear crystal growth rates characterize the net result of competition between growth and melting at the liquid-solid interfaces. The rate equation for polymer crystal growth can be derived with a barrier term for crystal growth and with a driving force term of excess lamellar thickness, provided that growth and melting share the same rate-determining steps at the growth front. Such an ansatz can be verified by the kinetic symmetry between growth and melting around the melting point of lamellar crystals, as made in our recent dynamic Monte Carlo simulations. The profile of the growth/melting front appears as wedge-shaped, with the free energy barrier for intramolecular secondary crystal nucleation at its top, and with the driving force gained via instant thickening at its bottom. Such a scenario explains unique phenomena on polymer crystal growth, such as chain folding, regime transitions, molecular segregation of polydisperse polymers, self-poisoning with integer-number chain-folding of short chains, and colligative growth rates of binary mixtures of two chain lengths. Financial support from NNSFC No. 20825415 and NBRPC No. 2011CB606100 is acknowledged.

  2. Protein crystal growth - Growth kinetics for tetragonal lysozyme crystals

    NASA Technical Reports Server (NTRS)

    Pusey, M. L.; Snyder, R. S.; Naumann, R.

    1986-01-01

    Results are reported from theoretical and experimental studies of the growth rate of lysozyme as a function of diffusion in earth-gravity conditions. The investigations were carried out to form a comparison database for future studies of protein crystal growth in the microgravity environment of space. A diffusion-convection model is presented for predicting crystal growth rates in the presence of solutal concentration gradients. Techniques used to grow and monitor the growth of hen egg white lysozyme are detailed. The model calculations and experiment data are employed to discuss the effects of transport and interfacial kinetics in the growth of the crystals, which gradually diminished the free energy in the growth solution. Density gradient-driven convection, caused by presence of the gravity field, was a limiting factor in the growth rate.

  3. Growth kinetics of Bacillus stearothermophilus BR219

    SciTech Connect

    Worden, R.M.; Subramanian, R.; Bly, M.J.; Winter, S.; Aronson, C.L.

    1991-12-31

    Bacillus stearothermophilus BR219, a phenol-resistant thermophile, can convert phenol to the specialty chemical catechol. The growth kinetics of this organism were studied in batch, continuous, and immobilized-cell culture. Batch growth was insensitive to pH between 6.0 and 8.0, but little growth occurred at 5.5. In continuous culture on a dilute medium supplemented with 10 mM phenol, several steady states were achieved between dilution rates of 0.25 and 1.3 h{sup -1}. Phenol degradation was found to be uncoupled from growth. Immobilized cells grew rapidly in a rich medium, but cell viability plummeted following a switch to a dilute medium supplemented with 5 mM phenol.

  4. Morphological stability and kinetics in crystal growth from vapors

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz

    1990-01-01

    The following topics are discussed: (1) microscopy image storage and processing system; (2) growth kinetics and morphology study with carbon tetrabromide; (3) photothermal deflection vapor growth setup; (4) bridgman growth of iodine single crystals; (5) vapor concentration distribution measurement during growth; and (6) Monte Carlo modeling of anisotropic growth kinetics and morphology. A collection of presentations and publications of these results are presented.

  5. Droplet Growth Kinetics in Various Environments

    NASA Astrophysics Data System (ADS)

    Raatikainen, T. E.; Lathem, T. L.; Moore, R.; Lin, J. J.; Cerully, K. M.; Padro, L.; Lance, S.; Cozic, J.; Anderson, B. E.; Nenes, A.

    2012-12-01

    The largest uncertainties in the effects of atmospherics aerosols on the global radiation budget are related to their indirect effects on cloud properties (IPCC, the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007). Cloud formation is a kinetic process where the resulting cloud properties depend on aerosol properties and meteorological parameters such as updraft velocity (e.g. McFiggans et al., Atmos. Chem. Phys., 6, 2593-2649, 2006). Droplet growth rates are limited by the water vapor diffusion, but additional kinetic limitations, e.g., due to organic surface films, slow solute dissociation or highly viscous or glassy aerosol states have been hypothesized. Significant additional kinetic limitations can lead to increased cloud droplet number concentration, thus the effect is similar to those of increased aerosol number concentration or changes in vertical velocity (e.g. Nenes et al., Geophys. Res. Lett., 29, 1848, 2002). There are a few studies where slow droplet growth has been observed (e.g. Ruehl et al., Geophys. Res. Lett., 36, L15814, 2009), however, little is currently known about their global occurrence and magnitude. Cloud micro-physics models often describe kinetic limitations by an effective water vapor uptake coefficient or similar parameter. Typically, determining aerosol water vapor uptake coefficients requires experimental observations of droplet growth which are interpreted by a numerical droplet growth model where the uptake coefficient is an adjustable parameter (e.g. Kolb et al., Atmos. Chem. Phys., 10, 10561-10605, 2010). Such methods have not been practical for high time-resolution or long term field measurements, until a model was recently developed for analyzing Droplet Measurement Technologies (DMT) cloud condensation nuclei (CCN) counter data (Raatikainen et al., Atmos. Chem. Phys., 12, 4227-4243, 2012). Model verification experiments showed that the calibration aerosol droplet size can be predicted accurately

  6. Volume Diffusion Growth Kinetics and Step Geometry in Crystal Growth

    NASA Technical Reports Server (NTRS)

    Mazuruk, Konstantin; Ramachandran, Narayanan

    1998-01-01

    The role of step geometry in two-dimensional stationary volume diff4sion process used in crystal growth kinetics models is investigated. Three different interface shapes: a) a planar interface, b) an equidistant hemispherical bumps train tAx interface, and c) a train of right angled steps, are used in this comparative study. The ratio of the super-saturation to the diffusive flux at the step position is used as a control parameter. The value of this parameter can vary as much as 50% for different geometries. An approximate analytical formula is derived for the right angled steps geometry. In addition to the kinetic models, this formula can be utilized in macrostep growth models. Finally, numerical modeling of the diffusive and convective transport for equidistant steps is conducted. In particular, the role of fluid flow resulting from the advancement of steps and its contribution to the transport of species to the steps is investigated.

  7. Amyloid growth: combining experiment and kinetic theory

    NASA Astrophysics Data System (ADS)

    Knowles, Tuomas; Cohen, Samuel; Vendruscolo, Michele; Dobson, Christopher

    2012-02-01

    The conversion of proteins from their soluble forms into fibrillar amyloid nanostructures is a general type of behaviour encountered for many different proteins in the context of disease as well as for the generation of a select class of functional materials in nature. This talk focuses on the problem of defining the rates of the individual molecular level processes involved in the overall conversion reaction. A master equation approach is discussedootnotetextCohen et al, J Chem Phys 2011, 135, 065106 ootnotetextKnowles et al, Science, 2009, 326, 1533-1537 and used in combination with kinetic measurements to yield mechanistic insights into the amyloid growth phenomenon.

  8. Structure of kinetic/non-kinetic scale velocity shear layers and associated Kelvin-Helmholtz vortices: particle simulations

    NASA Astrophysics Data System (ADS)

    Nakamura, T.; Hasegawa, H.; Shinohara, I.

    2009-12-01

    (thinner) as V0/Vthi increases, where Vthi is the ion thermal speed. This is because gyro-radii of ions which cross the boundary become larger (smaller) by the outward (inward) convection electric field in the dawn (dusk) case. Next, we investigated the evolution process of the KHI arising from kinetic and non-kinetic scale velocity shear layers. We first found that the linear growth rates of KHI are not affected by kinetic effects even when D0<ρi. This is because before the KHI onset, the velocity shear layer reaches the true kinetic equilibrium and is flattened to 2ρi. We next found that the ion rotation speed of the KH vortex flow in the dawn (dusk) case is larger (smaller) than the electron rotation speed. This result can be explained by the centrifugal drift for ions; since the directions of the centrifugal force in both cases are outward from the vortex centers, the directions of the centrifugal drift are different according to the rotation directions of vortices. In the dawn (dusk) case, the ion centrifugal drift strengthens (weakens) the ion rotation speed. Note that this centrifugal drift effect becomes larger as the vortex size becomes smaller. In our presentation, we will discuss the application of these results to the Earth's and Mercury's magnetopause.

  9. Growth kinetics of Si and Ge nanowires

    NASA Astrophysics Data System (ADS)

    Kodambaka, S.; Tersoff, J.; Reuter, M. C.; Ross, F. M.

    2009-02-01

    Si and Ge nanowires have potential applications in a wide variety of areas including thermoelectrics, optoelectronics, and sensors. Nanowires are most commonly grown via the vapor-liquid-solid (VLS) process. In this method, a vapor phase containing the material of interest preferentially dissociates at a liquid catalyst and is incorporated as a solid at the solid-liquid interface. However, despite 40 years of research in this area, several aspects of nanowire growth remain unclear, even for relatively simple elemental Si and Ge wires. Here, we will review our in situ transmission electron microscopy (TEM) investigations of Si and Ge nanowire growth kinetics. The observations are carried out in an ultra-high vacuum TEM (the IBM UHV-TEM) equipped with facilities for deposition during observation. Using Au as the catalyst, we study the VLS growth of Si and Ge nanowires as a function of disilane or digermane pressure and substrate temperature. We find surprisingly different growth mechanisms for the two materials. The insights gained from in situ results may help devise methods for large-scale fabrication of wires with controlled architecture.

  10. Layer-by-layer growth of porphyrin supramolecular thin films

    SciTech Connect

    Nishiyama, Fumitaka; Yokoyama, Takashi; Kamikado, Toshiya; Yokoyama, Shiyoshi; Mashiko, Shinro

    2006-06-19

    Multilayer thin film growth of carboxyphenyl-substituted porphyrin on Au(111) was investigated by means of low-temperature scanning tunneling microscopy. The carboxyphenyl-substituted porphyrins are assembled into supramolecular wires on Au(111) by sequential hydrogen bonding between carboxyphenyl groups, and the dense aggregation of the supramolecular wires results in the formation of the first monolayer film. By further molecular deposition, the layer-by-layer growth of the supramolecular wires has been observed, leading to the supramolecular thin film growth.

  11. Epitaxial growth of silicon for layer transfer

    SciTech Connect

    Teplin, Charles; Branz, Howard M

    2015-03-24

    Methods of preparing a thin crystalline silicon film for transfer and devices utilizing a transferred crystalline silicon film are disclosed. The methods include preparing a silicon growth substrate which has an interface defining substance associated with an exterior surface. The methods further include depositing an epitaxial layer of silicon on the silicon growth substrate at the surface and separating the epitaxial layer from the substrate substantially along the plane or other surface defined by the interface defining substance. The epitaxial layer may be utilized as a thin film of crystalline silicon in any type of semiconductor device which requires a crystalline silicon layer. In use, the epitaxial transfer layer may be associated with a secondary substrate.

  12. Temperature dependence of protein solubility-determination, application to crystallization, and growth kinetics studies

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz

    1993-01-01

    A scintillation method was developed for determinations of the temperature dependence of the solubility, and of nucleation induction times of proteins, in 50-100 mu(l) volumes of solution. Solubility data for lysozyme and horse serum albumin were obtained for various combinations of pH and precipitant concentrations. These data and the nucleation induction information were used for dynamic crystallization control, that is, for the controlled separation of nucleation and growth stages. Individual lysozyme and horse serum albumin crystals were grown in 15-20 mu(l) solution volumes contained in x-ray capillaries. The morphology and kinetics of the growth and dissolution of lysozyme in aqueous solutions with 2.5 percent NaCl and at pH = 4.5 was studied in situ with a depth resolution of 300 A (4 unit cells) by high resolution optical microscopy and digital image processing. The bulk super- or under saturation, sigma, of the solution inside a closed growth cell was controlled by temperature. The growth habit was bound by (110) and (101) faces that grew through layer spreading, although with different growth rate dependencies on supersaturation/temperature. At sigma less than 10 (obtained at higher temperatures) growth was purely kinetic ally controlled, with impurity effects (macrostep formation and kinetic hindrance) becoming significant for sigma less than 2. At sigma greater than 10 (lower temperatures), anisotropies in the interfacial kinetics were more pronounced, with interfacial kinetics and bulk transport becoming equally important to the growth morphology. Growth rates were growth history dependent. The formation of striations (layers of irregularly incorporated solution) was unambiguously correlated with growth temperature variations. Etching exposed dislocations and various high-index faces whose growth morphologies were studied during return to the steady state growth form. Growth steps were observed to originate from two-dimensional nuclei or from outcrops

  13. Modeling the growth of an altered layer in mineral weathering

    NASA Astrophysics Data System (ADS)

    Reis, Fábio D. A. Aarão

    2015-10-01

    A stochastic reaction-diffusion model on a lattice is introduced to describe the growth kinetics of an altered layer in the weathering of a mineral. Particles R represent H2O that permanently fills the outer surface and diffuse on M (mineral) and A (altered) sites with coefficients DM and DA , respectively. The transformation M + R → A occurs with rate r, representing the irreversible formation of the altered material in a region of molecular size, viz. the lattice site of size a. These assumptions agree with predictions of the interfacial dissolution-reprecipitation mechanism, although the model does not describe the chemistry of dissolution reactions or precipitation processes. Scaling concepts are used to distinguish kinetic regimes and their crossovers, and are supported by simulation results. In the short time reactive regime, the thickness of the altered layer increases linearly in time and filling of that layer by particles R is high. In the long time diffusive regime, the altered layer thickness grows as (DA t) 1 / 2 . Modeling of single crystals require very small values of DM , which produces atomically narrow interfaces between the altered material and the mineral and absence of R in the latter, in agreement with recent experimental results. If r growth velocity of the altered layer by a factor lAM / a , but no fluid in the bulk mineral. Estimates of the order of magnitude of transformation rates and of diffusion coefficients are obtained by application of the model to some recently studied systems: calcite dissolution, labradorite weathering, and silicate glass weathering. Effects of dissolution of the altered layer are analyzed. Significant differences between the model and leached layer theories are discussed.

  14. Large-scale epitaxial growth kinetics of graphene: A kinetic Monte Carlo study

    SciTech Connect

    Jiang, Huijun; Hou, Zhonghuai

    2015-08-28

    Epitaxial growth via chemical vapor deposition is considered to be the most promising way towards synthesizing large area graphene with high quality. However, it remains a big theoretical challenge to reveal growth kinetics with atomically energetic and large-scale spatial information included. Here, we propose a minimal kinetic Monte Carlo model to address such an issue on an active catalyst surface with graphene/substrate lattice mismatch, which facilitates us to perform large scale simulations of the growth kinetics over two dimensional surface with growth fronts of complex shapes. A geometry-determined large-scale growth mechanism is revealed, where the rate-dominating event is found to be C{sub 1}-attachment for concave growth-front segments and C{sub 5}-attachment for others. This growth mechanism leads to an interesting time-resolved growth behavior which is well consistent with that observed in a recent scanning tunneling microscopy experiment.

  15. Influence of deformation on dolomite rim growth kinetics

    NASA Astrophysics Data System (ADS)

    Helpa, Vanessa; Rybacki, Erik; Grafulha Morales, Luiz Fernando; Dresen, Georg

    2015-04-01

    Using a gas-deformation apparatus stacks of oriented calcite (CaCO3) and magnesite (MgCO3) single crystals were deformed at T = 750° C and P = 400 MPa to examine the influence of stress and strain on magnesio-calcite and dolomite (CaMg[CO3]2) growth kinetics. Triaxial compression and torsion tests performed at constant stresses between 7 and 38 MPa and test durations between 4 and 171 hours resulted in bulk strains of 0.03-0.2 and maximum shear strains of 0.8-5.6, respectively. The reaction rims consist of fine-grained (2-7 μm) dolomite with palisade-shaped grains growing into magnesite reactants and equiaxed granular dolomite grains next to calcite. In between dolomite and pure calcite, magnesio-calcite grains evolved with an average grain size of 20-40 μm. Grain boundaries tend to be straighter at high bulk strains and equilibrium angles at grain triple junctions are common within the magnesio-calcite layer. Transmission electron microscopy shows almost dislocation free palisades and increasing dislocation density within granular dolomite towards the magnesio-calcite boundary. Within magnesio-calcite grains, dislocations are concentrated at grain boundaries. Variation of time at fixed stress (˜17 MPa) yields a parabolic time dependence of dolomite rim width, indicating diffusion-controlled growth, similar to isostatic rim growth behavior. In contrast, the magnesio-calcite layer growth is enhanced compared to isostatic conditions. Triaxial compression at given time shows no significant change of dolomite rim thickness (11±2 μm) and width of magnesio-calcite layers (33±5 μm) with increasing stress. In torsion experiments, reaction layer thickness and grain size decrease from the center (low stress/strain) to the edge (high strain/stress) of samples. Chemical analysis shows nearly stoichiometric composition of dolomite palisades, but enhanced Ca content within granular grains, indicating local disequilibrium with magnesio-calcite, in particular for twisted

  16. Diamagnetic boundary layers - A kinetic theory. [for collisionless magnetized plasmas

    NASA Technical Reports Server (NTRS)

    Lemaire, J.; Burlaga, L. F.

    1976-01-01

    A kinetic theory is presented for boundary layers associated with MHD tangential 'discontinuities' in a collisionless magnetized plasma, such as those observed in the solar wind. The theory consists of finding self-consistent solutions of Vlasov's equation and Maxwell's equation for stationary one-dimensional boundary layers separating two Maxwellian plasma states. Layers in which the current is carried by electrons are found to have a thickness of the order of a few electron gyroradii, but the drift speed of the current-carrying electrons is found to exceed the Alfven speed, and accordingly such layers are not stable. Several types of layers in which the current is carried by protons are discussed; in particular, cases are considered in which the magnetic-field intensity, direction, or both, changed across the layer. In every case, the thickness was of the order of a few proton gyroradii, and the field changed smoothly, although the characteristics depended somewhat on the boundary conditions. The drift speed was always less than the Alfven speed, consistent with stability of such structures. These results are consistent with observations of boundary layers in the solar wind near 1 AU.

  17. Growth kinetics of Al–Fe intermetallic compounds during annealing treatment of friction stir lap welds

    SciTech Connect

    Movahedi, M.; Kokabi, A.H.; Seyed Reihani, S.M.; Najafi, H.; Farzadfar, S.A.; Cheng, W.J.; Wang, C.J.

    2014-04-01

    In this study, we explored the growth kinetics of the Al–Fe intermetallic (IM) layer at the joint interface of the St-12/Al-5083 friction stir lap welds during post-weld annealing treatment at 350, 400 and 450 °C for 30 to 180 min. Optical microscope (OM), field emission gun scanning electron microscope (FEG-SEM) and transmission electron microscope (TEM) were employed to investigate the structure of the weld zone. The thickness and composition of the IM layers were evaluated using image analysis system and electron back-scatter diffraction (EBSD), respectively. Moreover, kernel average misorientation (KAM) analysis was performed to evaluate the level of stored energy in the as-welded state. The results showed that the growth kinetics of the IM layer was not governed by a parabolic diffusion law. Presence of the IM compounds as well as high stored energy near the joint interface of the as-welded sample was recognized to be the origin of the observed deviation from the parabolic diffusion law. - Highlights: • This work provided a new insight into growth kinetics of Al–Fe IM thickness. • The growth kinetics of IM layer was not governed by a parabolic diffusion law. • IM near the joint interface was the origin of deviation from the parabolic law. • High stored energy at joint interface was origin of deviation from parabolic law.

  18. Determining crystal growth kinetic parameters using optical fibre sensors

    NASA Astrophysics Data System (ADS)

    Boerkamp, M.; Lamb, D. W.; Lye, P. G.

    2012-12-01

    The capability of an 'intrinsic exposed core optical fibre sensor' (IECOFS) as a monitoring device of scale formation has been evaluated. The IECOFS has been used to measure kinetics parameters of calcium carbonate heterogeneous crystal growth such as the activation energy, the crystal growth rate and the induction time. The IECOFS was able to evaluate crystal growth inhibition through the use of chemical inhibitors.

  19. Growth Kinetics of Suspended Microbial Cells: From Single-Substrate-Controlled Growth to Mixed-Substrate Kinetics

    PubMed Central

    Kovárová-Kovar, Karin; Egli, Thomas

    1998-01-01

    Growth kinetics, i.e., the relationship between specific growth rate and the concentration of a substrate, is one of the basic tools in microbiology. However, despite more than half a century of research, many fundamental questions about the validity and application of growth kinetics as observed in the laboratory to environmental growth conditions are still unanswered. For pure cultures growing with single substrates, enormous inconsistencies exist in the growth kinetic data reported. The low quality of experimental data has so far hampered the comparison and validation of the different growth models proposed, and only recently have data collected from nutrient-controlled chemostat cultures allowed us to compare different kinetic models on a statistical basis. The problems are mainly due to (i) the analytical difficulty in measuring substrates at growth-controlling concentrations and (ii) the fact that during a kinetic experiment, particularly in batch systems, microorganisms alter their kinetic properties because of adaptation to the changing environment. For example, for Escherichia coli growing with glucose, a physiological long-term adaptation results in a change in KS for glucose from some 5 mg liter−1 to ca. 30 μg liter−1. The data suggest that a dilemma exists, namely, that either “intrinsic” KS (under substrate-controlled conditions in chemostat culture) or μmax (under substrate-excess conditions in batch culture) can be measured but both cannot be determined at the same time. The above-described conventional growth kinetics derived from single-substrate-controlled laboratory experiments have invariably been used for describing both growth and substrate utilization in ecosystems. However, in nature, microbial cells are exposed to a wide spectrum of potential substrates, many of which they utilize simultaneously (in particular carbon sources). The kinetic data available to date for growth of pure cultures in carbon-controlled continuous culture

  20. Growth of mushy layers with temperature modulations

    NASA Astrophysics Data System (ADS)

    Ding, Guang-Yu; Wu, Chao; Zhong, Jin-Qiang

    2014-11-01

    Directional solidification of aqueous solutions produces a solid-melt coexisting zone whose growth rate can be predicted by the mushy-layer theory. We present measurements of mushy-layer growth when solidifying aqueous ammonium chloride with the cooling temperature modulated periodically TB (t) =T0 + Acos (ωt) . The mush-liquid interface h (t) evolves as the square root of time for a constant TB, but exhibits periodical humps in the present of modulations. The growth rate ḣ (t) is best approximate to ḣ (t) =ḣ0e - γωt / 2 π cos (ωt + π + ϕ (t)) , with a decay rate γ = 0 . 82 +/- 0 . 05 independent on the modulation amplitude A and frequency ω, and a phase-shift ϕ (t) increasingly lag behind TB as a function of time. We discuss a mushy-layer growth model based on the Neumann solution of the Stefan problem with periodical boundary conditions, and show that the numerical results are in agreement with the experimental observations. Supported by NSFC Grant 11202151.

  1. Cancer Progression and Tumor Growth Kinetics

    NASA Astrophysics Data System (ADS)

    Blagoev, Krastan; Kalpathy-Cramer, Jayashree; Wilkerson, Julia; Sprinkhuizen, Sara; Song, Yi-Qiao; Bates, Susan; Rosen, Bruce; Fojo, Tito

    2013-03-01

    We present and analyze tumor growth data from prostate and brain cancer. Scaling the data from different patients shows that early stage prostate tumors show non-exponential growth while advanced prostate and brain tumors enter a stage of exponential growth. The scaling analysis points to the existence of cancer stem cells and/or massive apoptosis in early stage prostate cancer and that late stage cancer growth is not dominated by cancer stem cells. Statistical models of these two growth modes are discussed. Work supported by the National Science Foundation and the National Institutes of Health

  2. Modeling of kinetically limited growth rate for solution-synthesized germanium nanocrystals

    NASA Astrophysics Data System (ADS)

    Shoop, Nicholas; Tribby, Louis J.; Han, Sang M.

    2015-08-01

    Solution synthesis is a common method for preparing semiconductor nanocrystals (NCs). For such solution synthesis, many investigations have considered diffusion-limited growth, in which the diffusion of reactants through the boundary layer (BL) limits the NC growth rate. These studies often model the growth rate with a diffusion BL thickness much larger than the NC size and with unphysically low diffusion constants on the order of 10-12 cm2 s-1. In this work, we have examined the growth of Ge NCs synthesized by injecting Ge amide precursors into a solution of 1-octadecene, oleylamine, and hexadecylamine. We have previously established this low-temperature, low-pressure synthesis route. The resulting Ge growth rate compares well with our model, in which we consider both BL diffusion and surface kinetics of Ge precursors and organic ligand adsorbates. Our modeling results suggest that the NC growth is limited not by diffusion, but by the surface adsorption and desorption kinetics. The BL thickness in the stirred reaction vessel is calculated to be on the same order of magnitude as the crystal radius; therefore, the surface kinetics cannot be ignored. Furthermore, the synthesis temperature is near 300 °C, where the Ge monomer diffusion coefficient within the growth solution is substantially increased and estimated to be on the order of 10-5 cm2 s-1. These considerations agree well with our experimentally measured growth rate and strongly suggest that the NC size evolution is controlled primarily by the surface kinetics.

  3. Model for computing kinetics of the graphene edge epitaxial growth on copper

    NASA Astrophysics Data System (ADS)

    Khenner, Mikhail

    2016-06-01

    A basic kinetic model that incorporates a coupled dynamics of the carbon atoms and dimers on a copper surface is used to compute growth of a single-layer graphene island. The speed of the island's edge advancement on Cu[111] and Cu[100] surfaces is computed as a function of the growth temperature and pressure. Spatially resolved concentration profiles of the atoms and dimers are determined, and the contributions provided by these species to the growth speed are discussed. Island growth under the conditions of a thermal cycling is studied.

  4. Free convection and surface kinetics in crystal growth from solution

    NASA Astrophysics Data System (ADS)

    Baird, James K.; Guo, Lihong

    1998-08-01

    As a crystal grows from solution, there is ordinarily a boundary layer depleted in solute, which forms at the crystal-solution interface. When the normal to the growing crystal surface is oriented in any direction other than parallel to gravity, the boundary layer is set into motion by the force of buoyancy. Using a similarity transformation and a boundary layer approximation, we have solved the Navier-Stokes equation and the equation for convective diffusion for a crystal in the form of a flat plate growing with normal perpendicular to gravity. Parameters in the theory include solute concentration, c0, and diffusion coefficient, D; solution shear viscosity, μ, mass density, ρ, and logarithmic density derivative with respect to concentration, α; crystal solubility, cs, height, h, and linear growth rate, kG; the specific rate, k (sticking coefficient), of the reaction which transfers molecules from the solution to the crystal and the kinetic order, n, of this reaction; and the acceleration due to gravity, g. We find these parameters to be related by the equation log[1-Sh/a (Sc) 1/4(Gr) 1/4φ s1/4]=(1/n) log[a(5/4) n(D/hkc 0n-1)(Sc)1/4(Gr) 1/4]+[(5/4-n)/n]log φs, where a=0.9, Sh=kGh/D, Sc=μ/ρD, Gr=gαh3ρ2/4μ2, and φs=(c0-cs)/c0. Given a knowledge of the solution physical properties, if Sh is measured as a function of φs and the results plotted in accord with the above equation, both n and k can be determined.

  5. Growth of Listeria monocytogenes in Salmon Roe - a kinetic analysis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The objective of this study was to investigate the growth kinetics of Listeria monocytogenes in unsalted and salted (3%) salmon roe. Growth curves, developed using inoculated samples incubated at constant temperatures between 5 and 30 degrees C, were analyzed by curve-fitting to the Huang and Baran...

  6. Crystal Growth Kinetics and Viscous Behavior in Ge2Sb2Se5 Undercooled Melt.

    PubMed

    Barták, Jaroslav; Koštál, Petr; Podzemná, Veronika; Shánělová, Jana; Málek, Jiří

    2016-08-18

    Crystal growth, viscosity, and melting were studied in Ge2Sb2Se5 bulk samples. The crystals formed a compact layer on the surface of the sample and then continued to grow from the surface to the central part of the sample. The formed crystalline layer grew linearly with time, which suggests that the crystal growth is controlled by liquid-crystal interface kinetics. Combining the growth data with the measured viscosities and melting data, crystal growth could be described on the basis of standard crystal growth models. The screw dislocation growth model seems to be operative in describing the temperature dependence of the crystal growth rate in the studied material in a wide temperature range. A detailed discussion on the relation between the kinetic coefficient of crystal growth and viscosity (ukin ∝ η(-ξ)) is presented. The activation energy of crystal growth was found to be higher than the activation energy of crystallization obtained from differential scanning calorimetry, which covers the whole nucleation-growth process. This difference is considered and explained under the experimental conditions. PMID:27441575

  7. Pattern Formation and Growth Kinetics in Eutectic Systems

    SciTech Connect

    Teng, Jing

    2007-01-01

    Growth patterns during liquid/solid phase transformation are governed by simultaneous effects of heat and mass transfer mechanisms, creation of new interfaces, jump of the crystallization units from liquid to solid and their rearrangement in the solid matrix. To examine how the above processes influence the scale of microstructure, two eutectic systems are chosen for the study: a polymeric system polyethylene glycol-p-dibromobenzene (PEG-DBBZ) and a simple molecular system succinonitrile (SCN)-camphor. The scaling law for SCN-camphor system is found to follow the classical Jackson-Hunt model of circular rod eutectic, where the diffusion in the liquid and the interface energy are the main physics governing the two-phase pattern. In contrast, a significantly different scaling law is observed for the polymer system. The interface kinetics of PEG phase and its solute concentration dependence thus have been critically investigated for the first time by directional solidification technique. A model is then proposed that shows that the two-phase pattern in polymers is governed by the interface diffusion and the interface kinetics. In SCN-camphor system, a new branch of eutectic, elliptical shape rodl, is found in thin samples where only one layer of camphor rods is present. It is found that the orientation of the ellipse can change from the major axis in the direction of the thickness to the direction of the width as the velocity and/or the sample thickness is decreased. A theoretical model is developed that predicts the spacing and orientation of the elliptical rods in a thin sample. The single phase growth patterns of SCN-camphor system were also examined with emphasis on the three-dimensional single cell and cell/dendrite transition. For the 3D single cell in a capillary tube, the entire cell shape ahead of the eutectic front can be described by the Saffmann-Taylor finger only at extremely low growth rate. A 3D directional solidification model is developed to

  8. Nonlinear Transient Growth and Boundary Layer Transition

    NASA Technical Reports Server (NTRS)

    Paredes, Pedro; Choudhari, Meelan M.; Li, Fei

    2016-01-01

    Parabolized stability equations (PSE) are used in a variational approach to study the optimal, non-modal disturbance growth in a Mach 3 at plate boundary layer and a Mach 6 circular cone boundary layer. As noted in previous works, the optimal initial disturbances correspond to steady counter-rotating streamwise vortices, which subsequently lead to the formation of streamwise-elongated structures, i.e., streaks, via a lift-up effect. The nonlinear evolution of the linearly optimal stationary perturbations is computed using the nonlinear plane-marching PSE for stationary perturbations. A fully implicit marching technique is used to facilitate the computation of nonlinear streaks with large amplitudes. To assess the effect of the finite-amplitude streaks on transition, the linear form of plane- marching PSE is used to investigate the instability of the boundary layer flow modified by spanwise periodic streaks. The onset of bypass transition is estimated by using an N- factor criterion based on the amplification of the streak instabilities. Results show that, for both flow configurations of interest, streaks of sufficiently large amplitude can lead to significantly earlier onset of transition than that in an unperturbed boundary layer without any streaks.

  9. Multiple substrate growth kinetics of Leptothrix discophora SP-6.

    PubMed

    Yurt, Nurdan; Sears, John; Lewandowski, Zbigniew

    2002-01-01

    The growth parameters of Leptothrix discophora SP-6 were quantified on the basis of the steady-state concentrations and utilization rates of pyruvate, dissolved oxygen, and concentration of microorganisms in a chemostat operated at 25 degrees C, pH 7.2, and an agitation rate of 350 rpm. The results showed that the microbial growth was limited by both pyruvate and dissolved oxygen. A combined growth kinetics model using Monod growth kinetics for pyruvate and Tessier growth kinetics for oxygen showed the best correlation with the experimental data when analyzed using an interactive multiple substrate model. The growth kinetics parameters and the respective confidence limits, estimated using the Monte Carlo simulation, were mu(max) = 0.576 +/- 0.021 h(-1), K(sMp) = 38.81 +/- 4.24 mg L(-1), K(sTo) = 0.39 +/- 0.04 mg L(-1), Y(X/p) = 0.150 (mg microorganism mg(-1) pyruvate), Y(X/o) = 1.24 (mg microorganism mg(-1) oxygen), the maintenance factors for pyruvate and oxygen were m(p) = 0.129 (mg pyruvate consumed mg(-1) microorganism h(-1)) and m(o) = 0.076 (mg oxygen consumed mg(-1) microorganism h(-1)), respectively. PMID:12363350

  10. The role of layer structure in tin oxidation kinetics

    NASA Astrophysics Data System (ADS)

    Duhalde, S.; Arcondo, B.; Sirkin, H.

    1991-11-01

    Tin exhibits different oxidation kinetics which are composition dependent, when it forms intermetallic compounds with the chalcogenides S and Se. This phenomenon is related to the layer compounds SnS2 and SnSe2 crystalline structure. These minerals have anisotropic bonding characteristics, due to Van der Waals bonds presence between chalcogenides adjoining planes. The mentioned weak bonds allow the oxygen diffusion to the bulk, favouring the reaction with the inner tin atoms. In this work we study samples of Sn-S alloy with different thermal treatment by XRD and Mössbauer spectroscopy. Results are discussed and compared with those obtained for Sn-Se alloy in an early work [1].

  11. Graphene CVD growth on copper and nickel: role of hydrogen in kinetics and structure.

    PubMed

    Losurdo, Maria; Giangregorio, Maria Michela; Capezzuto, Pio; Bruno, Giovanni

    2011-12-14

    Understanding the chemical vapor deposition (CVD) kinetics of graphene growth is important for advancing graphene processing and achieving better control of graphene thickness and properties. In the perspective of improving large area graphene quality, we have investigated in real-time the CVD kinetics using CH(4)-H(2) precursors on both polycrystalline copper and nickel. We highlighted the role of hydrogen in differentiating the growth kinetics and thickness of graphene on copper and nickel. Specifically, the growth kinetics and mechanism is framed in the competitive dissociative chemisorption of H(2) and dehydrogenating chemisorption of CH(4), and in the competition of the in-diffusion of carbon and hydrogen, being hydrogen in-diffusion faster in copper than nickel, while carbon diffusion is faster in nickel than copper. It is shown that hydrogen acts as an inhibitor for the CH(4) dehydrogenation on copper, contributing to suppress deposition onto the copper substrate, and degrades quality of graphene. Additionally, the evidence of the role of hydrogen in forming C-H out of plane defects in CVD graphene on Cu is also provided. Conversely, resurfacing recombination of hydrogen aids CH(4) decomposition in the case of Ni. Understanding better and providing other elements to the kinetics of graphene growth is helpful to define the optimal CH(4)/H(2) ratio, which ultimately can contribute to improve graphene layer thickness uniformity even on polycrystalline substrates. PMID:22006173

  12. Growth and Nitrogen Uptake Kinetics in Cultured Prorocentrum donghaiense

    PubMed Central

    Hu, Zhangxi; Duan, Shunshan; Xu, Ning; Mulholland, Margaret R.

    2014-01-01

    We compared growth kinetics of Prorocentrum donghaiense cultures on different nitrogen (N) compounds including nitrate (NO3−), ammonium (NH4+), urea, glutamic acid (glu), dialanine (diala) and cyanate. P. donghaiense exhibited standard Monod-type growth kinetics over a range of N concentraions (0.5–500 μmol N L−1 for NO3− and NH4+, 0.5–50 μmol N L−1 for urea, 0.5–100 μmol N L−1 for glu and cyanate, and 0.5–200 μmol N L−1 for diala) for all of the N compounds tested. Cultures grown on glu and urea had the highest maximum growth rates (μm, 1.51±0.06 d−1 and 1.50±0.05 d−1, respectively). However, cultures grown on cyanate, NO3−, and NH4+ had lower half saturation constants (Kμ, 0.28–0.51 μmol N L−1). N uptake kinetics were measured in NO3−-deplete and -replete batch cultures of P. donghaiense. In NO3−-deplete batch cultures, P. donghaiense exhibited Michaelis-Menten type uptake kinetics for NO3−, NH4+, urea and algal amino acids; uptake was saturated at or below 50 μmol N L−1. In NO3−-replete batch cultures, NH4+, urea, and algal amino acid uptake kinetics were similar to those measured in NO3−-deplete batch cultures. Together, our results demonstrate that P. donghaiense can grow well on a variety of N sources, and exhibits similar uptake kinetics under both nutrient replete and deplete conditions. This may be an important factor facilitating their growth during bloom initiation and development in N-enriched estuaries where many algae compete for bioavailable N and the nutrient environment changes as a result of algal growth. PMID:24710151

  13. Kinetic model of particle-inhibited grain growth

    NASA Astrophysics Data System (ADS)

    Thompson, Gary Scott

    The effects of second phase particles on matrix grain growth kinetics were investigated using Al2O3-SiC as a model system. In particular, the validity of the conclusion drawn from a previous kinetic analysis that the kinetics of particle-inhibited grain growth in Al2 O3-SiC samples with an intermediate volume fraction of second phase could be well quantified by a modified-Zener model was investigated. A critical analysis of assumptions made during the previous kinetic analysis revealed oversimplifications which affect the validity of the conclusion. Specifically, the degree of interaction between particles and grain boundaries was assumed to be independent of the mean second phase particle size and size distribution. In contrast, current measurements indicate that the degree of interaction in Al2O3-SiC is dependent on these parameters. An improved kinetic model for particle-inhibited grain growth in Al 2O3-SiC was developed using a modified-Zener approach. The comparison of model predictions with experimental grain growth data indicated that significant discrepancies (as much as 4--5 orders of magnitude) existed. Based on this, it was concluded that particles had a much more significant effect on grain growth kinetics than that caused by a simple reduction of the boundary driving force due to the removal of boundary area. Consequently, it was also concluded that the conclusion drawn from the earlier kinetic analysis regarding the validity of a modified-Zener model was incorrect. Discrepancies between model and experiment were found to be the result of a significant decrease in experimental growth rate constant not predicted by the model. Possible physical mechanisms for such a decrease were investigated. The investigation of a small amount of SiO2 on grain growth in Al2O3 indicated that the decrease was not the result of a decrease in grain boundary mobility due to impurity contamination by particles. By process of elimination and based on previous observations

  14. Metastable Solution Thermodynamic Properties and Crystal Growth Kinetics

    NASA Technical Reports Server (NTRS)

    Kim, Soojin; Myerson, Allan S.

    1996-01-01

    The crystal growth rates of NH4H2PO4, KH2PO4, (NH4)2SO4, KAl(SO4)2 central dot 12H2O, NaCl, and glycine and the nucleation rates of KBr, KCl, NaBr central dot 2H2O, (NH4)2Cl, and (NH4)2SO4 were expressed in terms of the fundamental driving force of crystallization calculated from the activity of supersaturated solutions. The kinetic parameters were compared with those from the commonly used kinetic expression based on the concentration difference. From the viewpoint of thermodynamics, rate expressions based on the chemical potential difference provide accurate kinetic representation over a broad range of supersaturation. The rates estimated using the expression based on the concentration difference coincide with the true rates of crystallization only in the concentration range of low supersaturation and deviate from the true kinetics as the supersaturation increases.

  15. Kinetics of laser-assisted carbon nanotube growth.

    PubMed

    van de Burgt, Y; Bellouard, Y; Mandamparambil, R

    2014-03-21

    Laser-assisted chemical vapour deposition (CVD) growth is an attractive mask-less process for growing locally aligned carbon nanotubes (CNTs) in selected places on temperature sensitive substrates. The nature of the localized process results in fast carbon nanotube growth with high experimental throughput. Here, we report on the detailed investigation of growth kinetics related to physical and chemical process characteristics. Specifically, the growth kinetics is investigated by monitoring the dynamical changes in reflected laser beam intensity during growth. Benefiting from the fast growth and high experimental throughput, we investigate a wide range of experimental conditions and propose several growth regimes. Rate-limiting steps are determined using rate equations linked to the proposed growth regimes, which are further characterized by Raman spectroscopy and Scanning Electron Microscopy (SEM), therefore directly linking growth regimes to the structural quality of the CNTs. Activation energies for the different regimes are found to be in the range of 0.3-0.8 eV. PMID:24481313

  16. Grain boundary curvature and grain growth kinetics with particle pinning

    NASA Astrophysics Data System (ADS)

    Shahandeh, Sina; Militzer, Matthias

    2013-08-01

    Second-phase particles are used extensively in design of polycrystalline materials to control the grain size. According to Zener's theory, a distribution of particles creates a pinning pressure on a moving grain boundary. As a result, a limiting grain size is observed, but the effect of pinning on the detail of grain growth kinetics is less known. The influence of the particles on the microstructure occurs in multiple length scales, established by particle radius and the grain size. In this article, we use a meso-scale phase-field model that simulates grain growth in the presence of a uniform pinning pressure. The curvature of the grain boundary network is measured to determine the driving pressure of grain growth in 2D and 3D systems. It was observed that the grain growth continues, even under conditions where the average driving pressure is smaller than the pinning pressure. The limiting grain size is reached when the maximum of driving pressure distribution in the structure is equal to the pinning pressure. This results in a limiting grain size, larger than the one predicted by conventional models, and further analysis shows consistency with experimental observations. A physical model is proposed for the kinetics of grain growth using parameters based on the curvature analysis of the grain boundaries. This model can describe the simulated grain growth kinetics.

  17. Kinetics of bacterial growth on chlorinated aliphatic compounds

    SciTech Connect

    Wijngaard, A.J. van den; Wind, R.E.; Janssen, D.B. )

    1993-07-01

    Halogenated aliphatic compounds are frequent constituents of industrial waste gases. Because of the environmental and biological toxic effects of these compounds, there is a growing interest in technologies for their removal. Biological waste gas purification is an option if specialized bacterial strains that use halogenated aliphatics as sole carbon and energy sources can be used. Elimination efficiency of the compounds depends not only on the process technology but on the degradation properties of the bacterial strains. Important aspects of bacterial growth are the Monod half-saturation constant and the maximum growth rate. In this study the kinetic properties of the organisms (Ancylobacter aquaticus AD20 and AD25, Xanthobacter autotrophicus GJ10, Pseudomonas sp. strain AD1) weree measured during growth in continuous cultures and wer compared with the kinetic properties of the first catabolic enzyme involved in the degradation of the growth substrate. The results indicate that the growth of the strains examined followed Monod kinetics. Stains AD20 and GJ10 showed growth rates on DCE somewhat higher than predicted from the amount of haloalkane dehalogenase present in the cells, while strain AD25 was much lower. 33 refs., 3 figs., 4 tabs.

  18. Subdiffusion kinetics of nanoprecipitate growth and destruction in solid solutions

    NASA Astrophysics Data System (ADS)

    Sibatov, R. T.; Svetukhin, V. V.

    2015-06-01

    Based on fractional differential generalizations of the Ham and Aaron-Kotler precipitation models, we study the kinetics of subdiffusion-limited growth and dissolution of new-phase precipitates. We obtain the time dependence of the number of impurities and dimensions of new-phase precipitates. The solutions agree with the Monte Carlo simulation results.

  19. Growth Kinetics and Modeling of ZnO Nanoparticles

    ERIC Educational Resources Information Center

    Hale, Penny S.; Maddox, Leone M.; Shapter, Joe G.; Voelcker, Nico H.; Ford, Michael J.; Waclawik, Eric R.

    2005-01-01

    The technique for producing quantum-sized zinc oxide (ZnO) particles is much safer than a technique that used hydrogen sulfide gas to produce cadmium sulfide and zinc sulfide nanoparticles. A further advantage of this method is the ability to sample the solution over time and hence determine the growth kinetics.

  20. Growth kinetics of sulfur nanoparticles in aqueous surfactant solutions.

    PubMed

    Chaudhuri, Rajib Ghosh; Paria, Santanu

    2011-02-15

    Sulfur is an important element has many practical applications when present as nanoparticles. Despite the practicable applications, limited studies are available in the literature related to synthesis of sulfur nanoparticles. Growth kinetics of colloidal sulfur particles synthesized from aqueous solutions using different surfactants have been studied here. The effects of different parameters such as reactant concentration, temperature, sonication, types of acids, types of surfactants, and even surfactant concentration are studied on the growth kinetics. Since the reaction rate is fast, particle growth depends on the parameters which affect diffusion of sulfur molecules. There is a linear relationship found among the reactant concentration and the particle coarsening rate constant. The growth kinetics was studied in the presence of different surfactants such as nonionic (poly(oxyethylene) p-tert-octylphenyl ether, TX-100), anionic (sodium dodecylbenzene sulfonate, SDBS), cationic (cetyltrimethyammonium bromide, CTAB) and results show the coarsening constant changes according to the following order: water>TX-100>SDBS>CTAB. The particle growth rate also depends on the surfactant concentration, coarsening rate constant decreases with the increase in surfactant concentration and become constant close to the critical micellar concentration (CMC). The coarsening rate constant also highly depends on the types of acid used as catalyst. PMID:21147482

  1. Implications of a concentration-dependent growth rate on the boundary layer crystal-melt model

    NASA Astrophysics Data System (ADS)

    Lasaga, Antonio C.

    1981-12-01

    The influence of a melt boundary layer on crystal growth is analyzed. The treatment extends the results of Burton, Prim and Slichter (1953) and incorporates composition-dependent growth rates. It is shown that in these general cases the growth rate cannot be arbitrarily fixed but must satisfy a self-consistent equation. Self-consistency problems arise because the growth rate determines the composition profile in the melt and, in turn, the composition profile determines the growth rate. The self-consistent growth rate is shown to vary markedly with the ratio δ/D, where δ is the thickness of the boundary layer and D is the appropriate diffusion coefficient in the melt. This self-consistency can be very important in the analysis of both field and laboratory growth rates as well as in trace element partition kinetic models.

  2. Kinetics of phase growth in Nb3Sn formation for heat treatment optimization

    SciTech Connect

    Emanuela Barzi; Sara Mattafirri

    2002-10-25

    The kinetics of growth and superconducting properties of Nb{sub 3}Sn are investigated as a function of the heat treatment (HT) duration and temperature for Internal Tin and Powder-in-Tube strands at 650, 700 and 750 C. For all times and temperatures, the Nb{sub 3}Sn layer thickness is measured, the critical current at 4.2 K is tested as a function of magnetic field, and the upper critical field is evaluated. Results of the layer critical current density are also shown as a function of HT duration and temperature.

  3. Growth kinetics of Staphylococcus aureus on Brie and Camembert cheeses.

    PubMed

    Lee, Heeyoung; Kim, Kyungmi; Lee, Soomin; Han, Minkyung; Yoon, Yohan

    2014-05-01

    In this study, we developed mathematical models to describe the growth kinetics of Staphylococcus aureus on natural cheeses. A five-strain mixture of Staph. aureus was inoculated onto 15 g of Brie and Camembert cheeses at 4 log CFU/g. The samples were then stored at 4, 10, 15, 25, and 30 °C for 2-60 d, with a different storage time being used for each temperature. Total bacterial and Staph. aureus cells were enumerated on tryptic soy agar and mannitol salt agar, respectively. The Baranyi model was fitted to the growth data of Staph. aureus to calculate kinetic parameters such as the maximum growth rate in log CFU units (r max; log CFU/g/h) and the lag phase duration (λ; h). The effects of temperature on the square root of r max and on the natural logarithm of λ were modelled in the second stage (secondary model). Independent experimental data (observed data) were compared with prediction and the respective root mean square error compared with the RMSE of the fit on the original data, as a measure of model performance. The total growth of bacteria was observed at 10, 15, 25, and 30 °C on both cheeses. The r max values increased with storage temperature (P<0·05), but a significant effect of storage temperature on λ values was only observed between 4 and 15 °C (P<0·05). The square root model and linear equation were found to be appropriate for description of the effect of storage temperature on growth kinetics (R 2=0·894-0·983). Our results indicate that the models developed in this study should be useful for describing the growth kinetics of Staph. aureus on Brie and Camembert cheeses. PMID:24731395

  4. Kinetic effects on the Kelvin–Helmholtz instability in ion-to-magnetohydrodynamic scale transverse velocity shear layers: Particle simulations

    PubMed Central

    Nakamura, T. K. M.; Hasegawa, H.; Shinohara, I.

    2010-01-01

    Ion-to-magnetohydrodynamic scale physics of the transverse velocity shear layer and associated Kelvin–Helmholtz instability (KHI) in a homogeneous, collisionless plasma are investigated by means of full particle simulations. The shear layer is broadened to reach a kinetic equilibrium when its initial thickness is close to the gyrodiameter of ions crossing the layer, namely, of ion-kinetic scale. The broadened thickness is larger in B⋅Ω<0 case than in B⋅Ω>0 case, where Ω is the vorticity at the layer. This is because the convective electric field, which points out of (into) the layer for B⋅Ω<0 (B⋅Ω>0), extends (reduces) the gyrodiameters. Since the kinetic equilibrium is established before the KHI onset, the KHI growth rate depends on the broadened thickness. In the saturation phase of the KHI, the ion vortex flow is strengthened (weakened) for B⋅Ω<0 (B⋅Ω>0), due to ion centrifugal drift along the rotational plasma flow. In ion inertial scale vortices, this drift effect is crucial in altering the ion vortex size. These results indicate that the KHI at Mercury-like ion-scale magnetospheric boundaries could show clear dawn-dusk asymmetries in both its linear and nonlinear growth. PMID:20838425

  5. Growth Morphologies of Wax in the Presence Kinetic Inhibitors

    NASA Astrophysics Data System (ADS)

    Tetervak, Alexander; Hutter, Jeffrey

    2004-03-01

    Kinetic inhibitors are molecules that alter crystal growth rates and morphologies by adsorbing to growth faces. Such species are used in many commercial processes to control microsctructure, and in other cases to prevent crystallization altogether. Despite their importance, the details of their mechanisms are largely unverified. We are studying the effects of such inhibitors on the crystallization of normal alkanes from solution. We find that inhibitors drastically alter the crystal morphology. As in similar systems, we see ``burst growth,'' in which newly formed solid is able to grow faster due to lower inhibitor coverage. Our experiments show several growth morphologies as a function of conditions: a tree-like structure that in some cases forms bands, and spherulites with characteristics very similar to those seen in polymers. Here, we characterize the front morphology as a function of these conditions and compare the results to numerical models that capture the essential growth behavior.

  6. Kinetic Roughening Transition and Energetics of Tetragonal Lysozyme Crystal Growth

    NASA Technical Reports Server (NTRS)

    Gorti, Sridhar; Forsythe, Elizabeth L.; Pusey, Marc L.

    2004-01-01

    Interpretation of lysozyme crystal growth rates using well-established physical theories enabled the discovery of a phenomenon possibly indicative of kinetic roughening. For example, lysozyme crystals grown above a critical supersaturation sigma, (where supersaturation sigma = ln c/c(sub eq), c = the protein concentration and c(sub eq) = the solubility concentration) exhibit microscopically rough surfaces due to the continuous addition of growth units anywhere on the surface of a crystal. The rate of crystal growth, V(sub c), for the continuous growth process is determined by the continuous flux of macromolecules onto a unit area of the crystal surface, a, from a distance, xi, per unit time due to diffusion, and a probability of attachment onto the crystal surface, expressed. Based upon models applied, the energetics of lysozyme crystal growth was determined. The magnitudes of the energy barriers of crystal growth for both the (110) and (101) faces of tetragonal lysozyme crystals are compared. Finally, evidence supportive of the kinetic roughening hypothesis is presented.

  7. The Kelvin-Helmholtz instability of boundary-layer plasmas in the kinetic regime

    NASA Astrophysics Data System (ADS)

    Steinbusch, Benedikt; Gibbon, Paul; Sydora, Richard D.

    2016-05-01

    The dynamics of the Kelvin-Helmholtz instability are investigated in the kinetic, high-frequency regime with a novel, two-dimensional, mesh-free tree code. In contrast to earlier studies which focused on specially prepared equilibrium configurations in order to compare with fluid theory, a more naturally occurring plasma-vacuum boundary layer is considered here with relevance to both space plasma and linear plasma devices. Quantitative comparisons of the linear phase are made between the fluid and kinetic models. After establishing the validity of this technique via comparison to linear theory and conventional particle-in-cell simulation for classical benchmark problems, a quantitative analysis of the more complex magnetized plasma-vacuum layer is presented and discussed. It is found that in this scenario, the finite Larmor orbits of the ions result in significant departures from the effective shear velocity and width underlying the instability growth, leading to generally slower development and stronger nonlinear coupling between fast growing short-wavelength modes and longer wavelengths.

  8. Coalescence kinetics under the action of alternative grain growth mechanisms

    SciTech Connect

    Gubanov, P. Yu. Maksimov, I. L.

    2008-01-15

    The coalescence process is considered for the case where the prevailing grain growth mechanism is block-to-block diffusion, during which the motion of atoms in a solution occurs in the form of diffusion flux along the block boundaries. Numerical and analytical investigation of the coalescence kinetics in a homogeneous supersaturated solution is performed with allowance for the finite maximum grain size, and the time evolution of the size distribution function of new-phase grains is theoretically described. Possible transition regimes arising during coalescence at a change in the dominant grain growth mechanism are considered.

  9. Residual layer effects on the modeling of convective boundary layer growth rates with a slab model using FIFE data

    NASA Astrophysics Data System (ADS)

    Freire, Livia S.; Dias, Nelson L.

    2013-12-01

    The ability of slab models for the growth of the convective boundary layer (CBL) to work in the presence of residual layers above is analyzed in detail with a large data set from the First International Satellite Land Surface Climatology Project Field Experiment (FIFE)-87 and FIFE-89 experiments. We confirm that the critical element that allows the models to predict the growth as the CBL coalesces with the residual layer is the adoption of a variable lapse rate above the growing CBL. This is not a new finding per se, as several previous studies in the literature have adopted this strategy. Different parameterizations of a slab model, based on the turbulence kinetic energy budget at the top of the CBL, were tested, and the inclusion of the storage and dissipation terms did not improve the model. Among the alternatives for choosing the lapse rate as the CBL grows, fair results are obtained with a simple choice of two values, with absolute mean errors of the order of 270 m for cases with and without a residual layer. Both lapse rates, representative of the residual layer and the free atmosphere, are obtained from the first morning sounding. Finally, an alternative model for the CBL growth into a residual layer that assumes a zero-lapse rate above the CBL did not perform well with the FIFE data.

  10. Insitu Measurements and Modeling of Carbon Nanotube Array Growth Kinetics during Chemical Vapor Deposition

    SciTech Connect

    Puretzky, Alexander A; Geohegan, David B; Jesse, Stephen; Ivanov, Ilia N; Eres, Gyula

    2005-01-01

    Direct measurements of carbon nanotube growth kinetics are described based upon time-resolved reflectivity (TRR) of a HeNe laser beam from vertically aligned nanotube arrays (VANTAs) as they grow during chemical vapor deposition (CVD). Growth rates and terminal lengths were measured in situ for VANTAs growing during CVD between 535 C and 900 C on Si substrates with evaporated Al/Fe/Mo multi-layered catalysts and acetylene feedstock at different feedstock partial pressures. Methods of analysis of the TRR signals are presented to interpret catalyst particle formation and oxidation, as well as the porosity of the VANTAs. A rate-equation model is developed to describe the measured kinetics in terms of activation energies and rate constants for surface carbon formation and diffusion on the catalyst nanoparticle, nanotube growth, and catalyst over-coating. Taken together with the TRR data, this model enables basic understanding and optimization of growth conditions for any catalyst/feedstock combination. The model lends insight into the main processes responsible for the growth of VANTAs, the measured number of walls in the nanotubes at different temperatures, conditions for growth of single-wall carbon nanotube arrays, and likely catalyst poisoning mechanisms responsible for the sharp decline in growth rates observed at high temperatures.

  11. Growth morphologies of wax in the presence of kinetic inhibitors

    NASA Astrophysics Data System (ADS)

    Tetervak, Alexander A.

    Driven by the need to prevent crystallization of normal alkanes from diesel fuels in cold climates, the petroleum industry has developed additives to slow the growth of these crystals and alter their morphologies. Although the utility of these kinetic inhibitors has been well demonstrated in the field, few studies have directly monitored their effect at microscopic morphology, and the mechanisms by which they act remain poorly understood. Here we present a study of the effects of such additives on the crystallization of long-chain n-alkanes from solution. The additives change the growth morphology from plate-like crystals to a microcrystalline mesh. When we impose a front velocity by moving the sample through a temperature gradient, the mesh growth may form a macroscopic banded pattern and also exhibit a burst-crystallization behavior. In this study, we characterize these crystallization phenomena and also two growth models: a continuum model that demonstrates the essential behavior of the banded crystallization, and a simple qualitative cellular automata model that captures basics of the burst-crystallization process. Keywords: solidification; mesh crystallization; kinetic inhibitor; burst growth.

  12. Role of Transport and Kinetics in Growth of Renal Stones

    NASA Technical Reports Server (NTRS)

    Kassemi, Mohammad; Iskovitz, Ilana

    2012-01-01

    Renal stone disease is not only a concern on earth but could conceivably pose as a serious risk to the astronauts health and safety in Space. In this paper, a combined transport-kinetics model for growth of calcium oxalate crystals is presented. The model is used to parametrically investigate the growth of renal calculi in urine with a focus on the coupled effects of transport and surface reaction on the ionic concentrations at the surface of the crystal and their impact on the resulting growth rates. It is shown that under nominal conditions of low solution supersaturation and low Damkohler number that typically exist on Earth, the surface concentrations of calcium and oxalate approach their bulk solution values in the urine and the growth rate is most likely limited by the surface reaction kinetics. But for higher solution supersaturations and larger Damkohler numbers that may be prevalent in the microgravity environment of Space, the calcium and oxalate surface concentrations tend to shift more towards their equilibrium or saturation values and thus the growth process may be limited by the transport through the medium. Furthermore, parametric numerical studies suggest that changes to the renal biochemistry of astronauts due in space may promote development of renal calculi during long duration space expeditions.

  13. Computer Simulation of Grain Growth Kinetics with Solute Drag

    SciTech Connect

    Chen, L.; Chen, S.P.; Fan, D.

    1998-12-23

    The effects of solute dragon grain growth kinetics were studied in two dimensional (2-D) computer simulations by using a diffuse-interface field model. It is shown that, in the low velocity / low driving force regime, the velocity of a grain boundary motion departs from a linear relation with driving force (curvature) with solute drag. The nonlinear relation of migration velocity and driving force comes from the dependence of grain boundary energy and width on the curvature. The growth exponent m of power growth law for a polycrystalline system is affected by the segregation of solutes to grain boundaries. With the solute drag, the growth exponent m can take any value between 2 and 3 depending on the ratio of lattice diffusion to grain boundary mobility. The grain size and topological distributions are unaffected by solute drag, which are the same as those in a pure system.

  14. Morphology and Growth Kinetics of Straight and Kinked Tin Whiskers

    NASA Astrophysics Data System (ADS)

    Susan, Donald; Michael, Joseph; Grant, Richard P.; McKenzie, Bonnie; Yelton, W. Graham

    2013-03-01

    Time-lapse SEM studies of Sn whiskers were conducted to estimate growth kinetics and document whisker morphologies. For straight whiskers, growth rates of 3 to 4 microns per day were measured at room temperature. Two types of kinked whiskers were observed. For Type A kinks, the original growth segment spatial orientation remains unchanged, there are no other changes in morphology or diameter, and growth continues. For Type B kinks, the spatial orientation of the original segment changes and it appears that the whisker bends over. Whiskers with Type B kinks show changes in morphology and diameter at the base, indicating grain boundary motion in the film, which eliminates the conditions suitable for long-term whisker growth. To estimate the errors in the whisker growth measurements, a technique is presented to correct for SEM projection effects. With this technique, the actual growth angles and lengths of a large number of whiskers were collected. It was found that most whiskers grow at moderate or shallow angles with respect to the surface; few straight whiskers grow nearly normal to the surface. In addition, there is no simple correlation between growth angles and lengths for whiskers observed over an approximate 2-year period.

  15. Calcite growth kinetics: Modeling the effect of solution stoichiometry

    NASA Astrophysics Data System (ADS)

    Wolthers, Mariëtte; Nehrke, Gernot; Gustafsson, Jon Petter; Van Cappellen, Philippe

    2012-01-01

    Until recently the influence of solution stoichiometry on calcite crystal growth kinetics has attracted little attention, despite the fact that in most aqueous environments calcite precipitates from non-stoichiometric solution. In order to account for the dependence of the calcite crystal growth rate on the cation to anion ratio in solution, we extend the growth model for binary symmetrical electrolyte crystals of Zhang and Nancollas (1998) by combining it with the surface complexation model for the chemical structure of the calcite-aqueous solution interface of Wolthers et al. (2008). To maintain crystal stoichiometry, the rate of attachment of calcium ions to step edges is assumed to equal the rate of attachment of carbonate plus bicarbonate ions. The model parameters are optimized by fitting the model to the step velocities obtained previously by atomic force microscopy (AFM, Teng et al., 2000; Stack and Grantham, 2010). A variable surface roughness factor is introduced in order to reconcile the new process-based growth model with bulk precipitation rates measured in seeded calcite growth experiments. For practical applications, we further present empirical parabolic rate equations fitted to bulk growth rates of calcite in common background electrolytes and in artificial seawater-type solutions. Both the process-based and empirical growth rate equations agree with measured calcite growth rates over broad ranges of ionic strength, pH, solution stoichiometry and degree of supersaturation.

  16. Analysis of Network Topologies Underlying Ethylene Growth Response Kinetics.

    PubMed

    Prescott, Aaron M; McCollough, Forest W; Eldreth, Bryan L; Binder, Brad M; Abel, Steven M

    2016-01-01

    Most models for ethylene signaling involve a linear pathway. However, measurements of seedling growth kinetics when ethylene is applied and removed have resulted in more complex network models that include coherent feedforward, negative feedback, and positive feedback motifs. The dynamical responses of the proposed networks have not been explored in a quantitative manner. Here, we explore (i) whether any of the proposed models are capable of producing growth-response behaviors consistent with experimental observations and (ii) what mechanistic roles various parts of the network topologies play in ethylene signaling. To address this, we used computational methods to explore two general network topologies: The first contains a coherent feedforward loop that inhibits growth and a negative feedback from growth onto itself (CFF/NFB). In the second, ethylene promotes the cleavage of EIN2, with the product of the cleavage inhibiting growth and promoting the production of EIN2 through a positive feedback loop (PFB). Since few network parameters for ethylene signaling are known in detail, we used an evolutionary algorithm to explore sets of parameters that produce behaviors similar to experimental growth response kinetics of both wildtype and mutant seedlings. We generated a library of parameter sets by independently running the evolutionary algorithm many times. Both network topologies produce behavior consistent with experimental observations, and analysis of the parameter sets allows us to identify important network interactions and parameter constraints. We additionally screened these parameter sets for growth recovery in the presence of sub-saturating ethylene doses, which is an experimentally-observed property that emerges in some of the evolved parameter sets. Finally, we probed simplified networks maintaining key features of the CFF/NFB and PFB topologies. From this, we verified observations drawn from the larger networks about mechanisms underlying ethylene

  17. Analysis of Network Topologies Underlying Ethylene Growth Response Kinetics

    PubMed Central

    Prescott, Aaron M.; McCollough, Forest W.; Eldreth, Bryan L.; Binder, Brad M.; Abel, Steven M.

    2016-01-01

    Most models for ethylene signaling involve a linear pathway. However, measurements of seedling growth kinetics when ethylene is applied and removed have resulted in more complex network models that include coherent feedforward, negative feedback, and positive feedback motifs. The dynamical responses of the proposed networks have not been explored in a quantitative manner. Here, we explore (i) whether any of the proposed models are capable of producing growth-response behaviors consistent with experimental observations and (ii) what mechanistic roles various parts of the network topologies play in ethylene signaling. To address this, we used computational methods to explore two general network topologies: The first contains a coherent feedforward loop that inhibits growth and a negative feedback from growth onto itself (CFF/NFB). In the second, ethylene promotes the cleavage of EIN2, with the product of the cleavage inhibiting growth and promoting the production of EIN2 through a positive feedback loop (PFB). Since few network parameters for ethylene signaling are known in detail, we used an evolutionary algorithm to explore sets of parameters that produce behaviors similar to experimental growth response kinetics of both wildtype and mutant seedlings. We generated a library of parameter sets by independently running the evolutionary algorithm many times. Both network topologies produce behavior consistent with experimental observations, and analysis of the parameter sets allows us to identify important network interactions and parameter constraints. We additionally screened these parameter sets for growth recovery in the presence of sub-saturating ethylene doses, which is an experimentally-observed property that emerges in some of the evolved parameter sets. Finally, we probed simplified networks maintaining key features of the CFF/NFB and PFB topologies. From this, we verified observations drawn from the larger networks about mechanisms underlying ethylene

  18. Phosphate-limited growth of the marine diatom Thalassiosira weissflogii (Bacillariophyceae): evidence of non-monod growth kinetics(1).

    PubMed

    Laws, Edward A; Pei, Shaofeng; Bienfang, Paul

    2013-04-01

    The marine diatom Thalassiosira weissflogii (Grunow) G. A. Fryxell & Hasle was grown in a chemostat over a series of phosphate-limited growth rates. Ambient substrate concentrations were determined from bioassays involving picomolar spikes of (33) P-labeled phosphate, and maximum uptake rates were determined from analogous bioassays that included the addition of micromolar concentrations of unlabeled phosphate and tracer concentrations of (33) P. The relationship between cell phosphorus quotas and growth rates was well described by the Droop equation. Maximum uptake rates of phosphate spikes were several orders of magnitude higher than steady state uptake rates. Despite the large size of the T. weissflogii cells, diffusion of phosphate through the boundary layer around the cells had little effect on growth kinetics, in part because the cellular N:P ratios exceeded the Redfield ratio at all growth rates. Fitting the Monod equation to the experimental data produced an estimate of the nutrient-saturated growth rate that was ~50% greater than the maximum growth rate observed in batch culture. A modified hyperbolic equation with a curvature that is a maximum in magnitude at positive growth rates gave a better fit to the data and an estimate of the maximum growth rate that was consistent with observations. The failure of the Monod equation to describe the data may reflect a transition from substrate to co-substrate limitation and/or the presence of an inducible uptake system. PMID:27008513

  19. Spherulitic growth of wax in the presence of kinetic inhibitors

    NASA Astrophysics Data System (ADS)

    Hutter, Jeffrey L.; Smith, Chris; Khmaladze, Alexander

    2001-03-01

    The petroleum industry has developed polymeric additives to prevent the precipitation of wax from diesel fuels in cold climates. These additives affect the crystallization kinetics of wax growth without affecting the thermodynamics. Some additives apparently operate by adsorbing to crystalline surfaces and blocking step flow, though direct evidence is lacking. We have used optical microscopy to study this process in model n-alkane systems with inhibitors added as a 1 wt% impurity. We find that the presence of the polymer dramatically alters the growth morphology of the wax --- rather than the usual plate-like growth, we see forms with all of the attributes of spherulites typical of bulk polymer growth, including radially oriented lamellae and banding. Since models for spherulitic growth postulate lamellar alignment by entropic pressure due to dangling polymer chains, the surface-adsorbed polymers are likely responsible for the similar alignment in wax spherulites. The banding seen in this case, however, results from periodic growth, rather than from the lamellar twisting seen in traditional polymer spherulites. We have modeled this effect as a coupling between the polymer adsorption rate and the growth rate of wax crystals.

  20. Solution growth kinetics and mechanism: Prismatic face of ADP

    NASA Astrophysics Data System (ADS)

    Chernov, A. A.; Rashkovich, L. N.; Mkrtchan, A. A.

    1986-01-01

    Laser Michelson interferometry has been applied to in situ study the (001) ADP growth kinetics in aqueous solution in the kinetic regime. The technique allows one to simultaneously measure the slope p of a growth hillock and normal growth rate R provided by this hillock. From these data, the average step growth rate v=R/p has been determined as a function of relative supersaturation σ. The dependencev(σ) is found to be linear, demonstrating the unimportance of surface and bulk diffusion. The direct incorporation at steps is characterized by the step kinetic coefficient βl=(5.1-6.4)X10-3 cm/s. The specific step free energy αl=(1.2-1.9) X10-6 erg/cm was determined from the measured linear dependence of the hillock slope on supersaturation for the hillock around presumably single elementary dislocation. For complex dislocation sources with large total Burgers vectors, the tendency to saturationin the hillock slope-supersaturation curves has been found. The curve perfectly fits the BCF expression which takes into account the perimeter 2L of the region occupied by the points in which the dislocation of the complex step source cross the growing face. For two dislocation sources,L=0.92 μm andL=0.31 μm and total Burgers vectors ⋍12h and 6h (h=7.53Å) have been found. The supersaturation dependence of activities for various complex dislocation sources have been directly demonstrated.

  1. A dynamic void growth model governed by dislocation kinetics

    NASA Astrophysics Data System (ADS)

    Wilkerson, J. W.; Ramesh, K. T.

    2014-10-01

    Here we examine the role of dislocation kinetics and substructure evolution on the dynamic growth of voids under very high strain rates, and develop a methodology for accounting for these effects in a computationally efficient manner. In particular, we account for the combined effects of relativistic dislocation drag and an evolving mobile dislocation density on the dynamics of void growth. We compare these effects to the constraints imposed by micro-inertia and discuss the conditions under which each mechanism governs the rate of void growth. The consequences of these constraints may be seen in a number of experimental observations associated with dynamic tensile failure, including the extreme rate-sensitivity of spall strength observed in laser shock experiments, an apparent anomalous temperate dependence of spall strength, and some particular features of void size distributions on spall surfaces.

  2. Kinetics of growth and aniline degradation by Stenotrophomonas maltophilia

    SciTech Connect

    Zissi, U.S.; Lyberatos, G.C.

    1999-01-01

    A pure bacterial culture of Stenotrophomonas maltophilia, capable of using aniline as a sole carbon source, was isolated. Kinetic experiments were conducted to develop a mathematical model that describes accurately the growth and utilization rates of the microorganism on the aniline and an alternate carbon source (glucose) individually and on their mixture. The growth of microorganisms and substrate utilization could be well described by using Monod expressions for limiting substrates. The presence of glucose in the culture medium did not repress aniline catabolism but simultaneous utilization was observed. When both substrates were present, the utilization of one substrate had a considerable effect on the utilization of the other. These effects were shown to be predicted by a mathematical model based on a modified Monod expression. The proposed model was found capable of describing accurately cellular growth as well as aniline and glucose biodegradation.

  3. Energetics and kinetics unveiled on helium cluster growth in tungsten

    NASA Astrophysics Data System (ADS)

    Wang, Jinlong; Niu, Liang-Liang; Shu, Xiaolin; Zhang, Ying

    2015-09-01

    The energetics and kinetics regarding helium (He) cluster growth in bcc tungsten (W) are unveiled using combined techniques of molecular statics and molecular dynamics. The principal mechanisms accounting for the decrease of system potential energy are identified to be trap mutation, < 100>   →  1/2< 111> cluster transformation, loop punching, coalescence between 1/2[1 1-1] and 1/2[1-1-1] loops, and loop capturing. The kinetic barriers associated with these key atomistic events are estimated. This work provides new insights into the complex yet intriguing atomistic evolution sequence of the He cluster and interstitial loop in W-based nuclear fusion materials under irradiation.

  4. Kinetic limitation of chemical ordering in Bi2Te3-x Se x layers grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Schreyeck, S.; Brunner, K.; Kirchner, A.; Bass, U.; Grauer, S.; Schumacher, C.; Gould, C.; Karczewski, G.; Geurts, J.; Molenkamp, L. W.

    2016-04-01

    We study the chemical ordering in Bi2Te3-x Se x grown by molecular beam epitaxy on Si substrates. We produce films in the full composition range from x  =  0 to 3, and determine their material properties using energy dispersive x-ray spectroscopy, x-ray diffraction and Raman spectroscopy. By fitting the parameters of a kinetic growth model to these results, we obtain a consistent description of growth at a microscopic level. Our main finding is that despite the incorporation of Se in the central layer being much more probable than that of Te, the formation of a fully ordered Te-Bi-Se-Bi-Te layer is prevented by kinetic of the growth process. Indeed, the Se concentration in the central layer of Bi2Te2Se1 reaches a maximum of only  ≈75% even under ideal growth conditions. A second finding of our work is that the intensity ratio of the 0 0 12 and 0 0 6 x-ray reflections serves as an experimentally accessible quantitative measure of the degree of ordering in these films.

  5. Kinetic limitation of chemical ordering in Bi2Te3-x Se x layers grown by molecular beam epitaxy.

    PubMed

    Schreyeck, S; Brunner, K; Kirchner, A; Bass, U; Grauer, S; Schumacher, C; Gould, C; Karczewski, G; Geurts, J; Molenkamp, L W

    2016-04-13

    We study the chemical ordering in Bi2Te3-x Se x grown by molecular beam epitaxy on Si substrates. We produce films in the full composition range from x  =  0 to 3, and determine their material properties using energy dispersive x-ray spectroscopy, x-ray diffraction and Raman spectroscopy. By fitting the parameters of a kinetic growth model to these results, we obtain a consistent description of growth at a microscopic level. Our main finding is that despite the incorporation of Se in the central layer being much more probable than that of Te, the formation of a fully ordered Te-Bi-Se-Bi-Te layer is prevented by kinetic of the growth process. Indeed, the Se concentration in the central layer of Bi2Te2Se1 reaches a maximum of only  ≈75% even under ideal growth conditions. A second finding of our work is that the intensity ratio of the 0 0 12 and 0 0 6 x-ray reflections serves as an experimentally accessible quantitative measure of the degree of ordering in these films. PMID:26962934

  6. Conductive layer for biaxially oriented semiconductor film growth

    DOEpatents

    Findikoglu, Alp T.; Matias, Vladimir

    2007-10-30

    A conductive layer for biaxially oriented semiconductor film growth and a thin film semiconductor structure such as, for example, a photodetector, a photovoltaic cell, or a light emitting diode (LED) that includes a crystallographically oriented semiconducting film disposed on the conductive layer. The thin film semiconductor structure includes: a substrate; a first electrode deposited on the substrate; and a semiconducting layer epitaxially deposited on the first electrode. The first electrode includes a template layer deposited on the substrate and a buffer layer epitaxially deposited on the template layer. The template layer includes a first metal nitride that is electrically conductive and has a rock salt crystal structure, and the buffer layer includes a second metal nitride that is electrically conductive. The semiconducting layer is epitaxially deposited on the buffer layer. A method of making such a thin film semiconductor structure is also described.

  7. Nucleation and growth of polytypic-layered crystals from the network liquid zinc chloride

    NASA Astrophysics Data System (ADS)

    Wilson, Mark

    2003-06-01

    The liquid to solid crystallization for zinc (II) chloride is studied by molecular dynamics computer simulation. The transition is unusual in that it involves a change from a three-dimensional network liquid structure to a pseudo-two-dimensional layered crystal. The crystallization events are observed from four distinct liquid starting configurations and are identified by reference to the time evolution of the system energetics and Bragg peaks associated with the cation layering. Order parameters and molecular graphics are applied to understand the transitions at an atomistic length scale. Mechanisms are presented for the initial layer growth, the coherent joining of the layered crystallites, and the destruction of high-energy grain boundaries. The growth kinetics are analyzed by defining times for catastrophic and critical nucleation. The final crystal structures are shown to have essentially random anion close-packed stacking sequences consistent with the large number of experimentally observed polytypic structures. The formation of grain boundary stacking faults is also observed.

  8. Kinetic model of impurity poisoning during growth of calcite

    SciTech Connect

    DeYoreo, J; Wasylenki, L; Dove, P; Wilson, D; Han, N

    2004-05-18

    The central role of the organic component in biologically controlled mineralization is widely recognized. These proteins are characterized by a high proportion of acidic amino acid residues, especially aspartate, Asp. At the same time, biomineralization takes place in the presence of a number of naturally-occurring, inorganic impurities, particularly Mg and Sr. In an attempt to decipher the controls on calcite growth imposed by both classes of modifiers, we have used in situ AFM to investigate the dependence of growth morphology and step kinetics on calcite in the presence of Sr{sup 2+}, as well as a wide suite of Aspartic acid-bearing polypeptides. In each case, we observe a distinct and step-specific modification. Most importantly, we find that the step speed exhibits a characteristic dependence on impurity concentration not predicted by existing crystal growth models. While all of the impurities clearly induce appearance of a 'dead zone,' neither the width of that dead zone nor the dependence of step speed on activity or impurity content can be explained by invoking the Gibbs-Thomson effect, which is the basis for the Cabrera-Vermilyea model of impurity poisoning. Common kink-blocking models also fail to explain the observed dependencies. Here we propose a kinetic model of inhibition based on a 'cooperative' effect of impurity adsorption at adjacent kink sites. The model is in qualitative agreement with the experimental results in that it predicts a non-linear dependence of dead zone width on impurity concentration, as well as a sharp drop in step speed above a certain impurity content. However, a detailed model of impurity adsorption kinetics that give quantitative agreement with the data has yet to be developed.

  9. Investigation of the kinetics of surface-limited thin film growth of SiGe alloys

    SciTech Connect

    Sharp, J.W. . Dept. of Physics and Astronomy); Eres, G. )

    1992-11-01

    The kinetics of surface-limited thin film growth of SiGe alloys was investigated by time-resolved surface differential reflectometry. The source gas, mixtures of disilane and digermane in ratios from 1:1 to 6:1 in helium carrier gas, was delivered to a heated substrate by a fast-acting pulsed molecular jet valve. The adsorption and desorption kinetics were determined from the surface differential reflectance signal obtained using a polarized, high-stability HeNe probe laser. Thin film growth was studied in the temperature range of 400--600[degrees]C on Si(001) substrates. Preferential incorporation of digermane into the film produces an alloy composition that depends upon but does not mirror the gas composition. For all gas mixtures, there is a strong temperature dependence of the rate at which the adsorption layer decomposes into film plus by-product. The kinetic data and the alloy compositions provide a basis for deducing some of the characteristics of the reaction sequence that leads to SiGe alloy thin film growth.

  10. Investigation of the kinetics of surface-limited thin film growth of SiGe alloys

    SciTech Connect

    Sharp, J.W.; Eres, G.

    1992-11-01

    The kinetics of surface-limited thin film growth of SiGe alloys was investigated by time-resolved surface differential reflectometry. The source gas, mixtures of disilane and digermane in ratios from 1:1 to 6:1 in helium carrier gas, was delivered to a heated substrate by a fast-acting pulsed molecular jet valve. The adsorption and desorption kinetics were determined from the surface differential reflectance signal obtained using a polarized, high-stability HeNe probe laser. Thin film growth was studied in the temperature range of 400--600{degrees}C on Si(001) substrates. Preferential incorporation of digermane into the film produces an alloy composition that depends upon but does not mirror the gas composition. For all gas mixtures, there is a strong temperature dependence of the rate at which the adsorption layer decomposes into film plus by-product. The kinetic data and the alloy compositions provide a basis for deducing some of the characteristics of the reaction sequence that leads to SiGe alloy thin film growth.

  11. Glass susceptibility: Growth kinetics and saturation under shear

    NASA Astrophysics Data System (ADS)

    Nandi, Saroj Kumar; Ramaswamy, Sriram

    2016-07-01

    We study the growth kinetics of glassy correlations in a structural glass by monitoring the evolution, within mode-coupling theory, of a suitably defined three-point function χC(t ,tw) with time t and waiting time tw. From the complete wave-vector-dependent equations of motion for domain growth, we pass to a schematic limit to obtain a numerically tractable form. We find that the peak value χCP of χC(t ,tw) , which can be viewed as a correlation volume, grows as tw0.5, and the relaxation time as tw0.8, following a quench to a point deep in the glassy state. These results constitute a theoretical explanation of the simulation findings of Parisi [J. Phys. Chem. B 103, 4128 (1999), 10.1021/jp983967m] and Kob and Barrat [Phys. Rev. Lett. 78, 4581 (1997), 10.1103/PhysRevLett.78.4581], and they are also in qualitative agreement with Parsaeian and Castillo [Phys. Rev. E 78, 060105(R) (2008), 10.1103/PhysRevE.78.060105]. On the other hand, if the quench is to a point on the liquid side, the correlation volume grows to saturation. We present a similar calculation for the growth kinetics in a p -spin spin glass mean-field model where we find a slower growth, χCP˜tw0.13 . Further, we show that a shear rate γ ˙ cuts off the growth of glassy correlations when tw˜1 /γ ˙ for quench in the glassy regime and tw=min(tr,1 /γ ˙) in the liquid, where tr is the relaxation time of the unsheared liquid. The relaxation time of the steady-state fluid in this case is ∝γ˙-0.8 .

  12. Growth of Ni2Si by rapid thermal annealing: Kinetics and moving species

    NASA Astrophysics Data System (ADS)

    Ma, E.; Lim, B. S.; Nicolet, M.-A.; Natan, M.

    1987-10-01

    The growth kinetics is characterized and the moving species is identified for the formation of Ni2Si by Rapid Thermal Annealing (RTA) of sequentially deposited Si and Ni films on a <100> Si substrate. The interfacial Ni2Si layer grows as the square root of time, indicating that the suicide growth process is diffusion-limited. The activation energy is 1.25±0.2 eV in the RTA temperature range of 350 450° C. The results extend those of conventional steady-state furnace annealing quite fittingly, and a common activation energy of 1.3±0.2 eV is deduced from 225° to 450° C. The marker experiment shows that Ni is the dominant moving species during Ni2Si formation by RTA, as is the case for furnace annealing. It is concluded that the two annealing techniques induce the same growth mechanisms in Ni2Si formation.

  13. Kinetic Analysis of Spontaneous Whisker Growth on Pre-treated Surfaces with Weak Oxide

    NASA Astrophysics Data System (ADS)

    Su, Chien-Hao; Chen, Hao; Lee, Hsin-Yi; Liu, Cheng Yi; Ku, Ching-Shun; Wu, Albert T.

    2014-09-01

    This study sought to clarify the relationship between cracks in surface oxide layers and the growth behavior of tin whiskers. The number, length, and total volume of extrusions were precisely calculated and residual stress was measured using synchrotron radiation x-ray diffractometry. The aim was to elucidate the influence of stress on the driving force and flux involved in atomic diffusion. The distance between weak spots was shown to be the most significant factor involved in the growth of whiskers. The results could explain why increasing the density of the surface weak spots could reduce the number of long whiskers. Measuring the dimensions of whiskers yielded a precise kinetic model capable of describing the migration of atoms to the root of whiskers, resulting in their spontaneous growth.

  14. Leuconostoc mesenteroides growth kinetics with application to bacterial profile modification

    SciTech Connect

    Lappan, R.E.; Fogler, H.S. . Dept. of Chemical Engineering)

    1994-04-15

    Bacterial profile modification (BPM) is being developed as an oil recovery technique that uses bacteria to selectively plug oil depleted zones within a reservoir to divert displacing fluids into oil-rich zones. Leuconostoc mesenteroides, which produces dextran when supplied with sucrose, is a bacterium that is technically feasible for use in profile modification. However, the technique requires controlled bacterial growth to produce selective plugging. A kinetic model for the production of cells and polysaccharides has been developed for L. mesenteroides bacteria. This model, based on data from batch growth experiments, predicts saccharide utilization, cell generation, and dextran production. The underlying mechanism is the extracellular breakdown of sucrose into glucose and fructose and the subsequent production of polysaccharide. The monosaccharides are then available for growth. Accompanying sucrose consumption is the utilization of yeast extract. The cell requires a complex media that is provided by yeast extract as a source of vitamins and amino acids. Varying the concentration ratio of yeast extract to sucrose in the growth media provides a means of controlling the amount of polymer produced per cell. Consequently, in situ bacteria growth can be controlled by the manipulation of nutrient media composition, thereby providing the ability to create an overall strategy for the use of L. mesenteroides bacteria for profile modification.

  15. Quantitative Models of CAI Rim Layer Growth

    NASA Astrophysics Data System (ADS)

    Ruzicka, A.; Boynton, W. V.

    1995-09-01

    Many hypotheses have been proposed to account for the ~50 micrometer-thick layer sequences (Wark-Lovering rims) that typically surround coarse-grained Ca,Al-rich inclusions (CAIs), but to date no consensus has emerged on how these rims formed. A two-step process-- flash heating of CAIs to produce a refractory residue on the margins of CAIs [1,2,3], followed by reaction and diffusion between CAIs or the refractory residue and an external medium rich in Mg, Si and other ferromagnesian and volatile elements to form the layers [3,4,5]-- may have formed the rims. We have tested the second step of this process quantitatively, and show that many, but not all, of the layering characteristics of CAI rims in the Vigarano, Leoville, and Efremovka CV3 chondrites can be explained by steady-state reaction and diffusion between CAIs and an external medium rich in Mg and Si. Moreover, observed variations in the details of the layering from one CAI to another can be explained primarily by differences in the identity and composition of the external medium, which appears to have included vapor alone, vapor + olivine, and olivine +/- clinopyroxene +/- vapor. An idealized layer sequence for CAI rims in Vigarano, Leoville, and Efremovka can be represented as MSF|S|AM|D|O, where MSF = melilite (M) + spinel (S) + fassaite (F) in the interior of CAIs; S = spinel-rich layer; AM = a layer consisting either of anorthite (A) alone, or M alone, or both A and M; D = a clinopyroxene layer consisting mainly of aluminous diopside (D) that is zoned to fassaite towards the CAI; and O = olivine-rich layer, composed mainly of individually zoned olivine grains that apparently pre-existed layer formation [3]. A or M are absent between the S and D layers in roughly half of the rims. The O layer varies considerably in thickness (0-60 micrometers thick) and in porosity from rim to rim, with olivine grains either tightly intergrown to form a compact layer or arranged loosely on the outer surfaces of the CAIs

  16. Radiochemical study of the kinetics of crystal growth in gels

    NASA Astrophysics Data System (ADS)

    Cecal, Alexandru; Palamaru, Mircea; Juverdeanu, Anca; Giosan, Marcel

    1996-01-01

    A kinetic study was performed on nucleation and growth of crystals containing radioactive ions in gelatin and agar gels. The investigated crystals were: 60CoHPO 4, 60CoS, 60Co(OH) 2, 60Co(SCN) 2, 204Tl(OH) 3, and 204Tl[(C 2H 5) 2NCS 2] 3. The study shows that the crystal growth rate depends on the cation size and charge, the nature of anion as well as on the colloidal medium. The crystallisation process in the gel has two distinctive steps: diffusion of reactant ions in the gel followed by a chemical reaction which leads to nucleation of the crystal. Both steps are described quantitatively.

  17. Kinetically controlled growth of gallium on stepped Si (553) surface

    NASA Astrophysics Data System (ADS)

    Kumar, Mukesh; Pasha, Syed Khalid; Govind

    2013-10-01

    Kinetically controlled growth of gallium (Ga) metal has been reported on high index stepped Si (553) surface and its thermal stability with various novel superstructural phases has been analyzed. Auger electron spectroscopy studies revealed that the adsorption of Ga at room temperature (RT) follows Frank-van der Merwe (FM) growth mode while for higher substrate temperature, Ga adsorption remains within the submonolayer range. Thermal desorption and low energy electron diffraction studies investigated the formation of thermally stable Ga-islands and the various Ga induced superstructural phase on Si (553). During room temperature adsorption, (1 1 1)7 × 7 facet of Si (553) reconstructed into (1 1 1)6 × 6 facet while during desorption process, stable (1 1 1)6 × 6 and (1 1 1)√3 × √3-R30° surface reconstructions has been observed.

  18. Selective growth of graphene in layer-by-layer via chemical vapor deposition.

    PubMed

    Park, Jaehyun; An, Hyosub; Choi, Dong-Chul; Hussain, Sajjad; Song, Wooseok; An, Ki-Seok; Lee, Won-Jun; Lee, Naesung; Lee, Wan-Gyu; Jung, Jongwan

    2016-08-14

    Selective and precise control of the layer number of graphene remains a critical issue for the practical applications of graphene. First, it is highly challenging to grow a continuous and uniform few-layer graphene since once the monolayer graphene fully covers a copper (Cu) surface, the growth of the second layer stops, resulting in mostly nonhomogeneous films. Second, from the selective adlayer growth point of view, there is no clear pathway for achieving this. We have developed the selective growth of a graphene adlayer in layer-by-layer via chemical vapor deposition (CVD) which makes it possible to stack graphene on a specific position. The key idea is to deposit a thin Cu layer (∼40 nm thick) on pre-grown monolayer graphene and to apply additional growth. The thin Cu atop the graphene/Cu substrate acts as a catalyst to decompose methane (CH4) gas during the additional growth. The adlayer is grown selectively on the pre-grown graphene, and the thin Cu is removed through evaporation during CVD, eventually forming large-area and uniform double layer graphene. With this technology, highly uniform graphene films with precise thicknesses of 1 to 5 layers and graphene check patterns with 1 to 3 layers were successfully demonstrated. This method provides precise LBL growth for a uniform graphene film and a technique for the design of new graphene devices. PMID:27436358

  19. Growth of oxide exchange bias layers

    DOEpatents

    Chaiken, Alison; Michel, Richard P.

    1998-01-01

    An oxide (NiO, CoO, NiCoO) antiferromagnetic exchange bias layer produced by ion beam sputtering of an oxide target in pure argon (Ar) sputtering gas, with no oxygen gas introduced into the system. Antiferromagnetic oxide layers are used, for example, in magnetoresistive readback heads to shift the hysteresis loops of ferromagnetic films away from the zero field axis. For example, NiO exchange bia layers have been fabricated using ion beam sputtering of an NiO target using Ar ions, with the substrate temperature at 200.degree. C., the ion beam voltage at 1000V and the beam current at 20 mA, with a deposition rate of about 0.2 .ANG./sec. The resulting NiO film was amorphous.

  20. Growth of oxide exchange bias layers

    DOEpatents

    Chaiken, A.; Michel, R.P.

    1998-07-21

    An oxide (NiO, CoO, NiCoO) antiferromagnetic exchange bias layer produced by ion beam sputtering of an oxide target in pure argon (Ar) sputtering gas, with no oxygen gas introduced into the system. Antiferromagnetic oxide layers are used, for example, in magnetoresistive readback heads to shift the hysteresis loops of ferromagnetic films away from the zero field axis. For example, NiO exchange bias layers have been fabricated using ion beam sputtering of an NiO target using Ar ions, with the substrate temperature at 200 C, the ion beam voltage at 1000V and the beam current at 20 mA, with a deposition rate of about 0.2 {angstrom}/sec. The resulting NiO film was amorphous. 4 figs.

  1. Continuous growth kinetics of Candida utilis in pineapple cannery effluent

    SciTech Connect

    Prior, B.A.

    1984-01-01

    Candida utilis was grown on a pineapple cannery effluent as the sole carbon and energy source in a chemostat at dilution rates between 0.10 and 0.62 h/sup -1/ to determine the growth kinetics. The principal sugars in the effluent were sucrose, glucose, and fructose. The cell yield coefficient on carbohydrate varied with dilution rate and a maximum value of 0.63 was observed at a dilution rate of 0.33 h/sup -1/. The steady-state concentrations of carbohydrate, reducing sugar, and chemical oxygen demand (COD) appeared to follow Monod saturation kinetics with increasing dilution rate, although none of the measured parameters represented a pure substrate. The maximum specific growth rate and reducing sugar saturation constant were 0.64 h/sup -1/ and 0.060 g/L, respectively. A maximum cell mass productivity of 2.3 g/L h was observed at a dilution rate of 0.51 h/sup -1/. At this dilution rate, only 68% of the COD was removed. A 95% COD removal was attained at a dilution rate of 0.10 h/sup -1/. Optimal yeast productivity and COD reduction occurred at a dilution rate of 0.33 h/sup -1/.

  2. Thermodynamic-kinetic simulation of constrained dendrite growth in steels

    SciTech Connect

    Miettinen, J.

    2000-04-01

    A model of constrained dendritic growth for steels, based on thermodynamic and kinetic theory, is presented. The model links thermodynamic chemical potential-equality equations to an existing, approximate treatment of constrained dendritic growth in multicomponent steels, taking into account the deviation from the local thermodynamic equilibrium of the phase interface caused by interface friction, capillarity, and solute trapping. Due to the thermodynamic approach, with a thermodynamic model and recently assessed data, the present treatment yields a more accurate determination of phase stabilities than the earlier methods. Depending on the steel composition and the growth conditions (growth rate and temperature gradient), the model determines the dendrite tip undercooling, the primary solid phase (ferrite or austenite), the stability of that phase, certain dimensions of the microstructure, and the solute accumulation ahead of the dendrite tip. A special optional calculations is that of the equally probable formation of ferrite and austenite in stainless steels. Calculations for testing the model and for validation it with experimental data are presented.

  3. Glass susceptibility: Growth kinetics and saturation under shear.

    PubMed

    Nandi, Saroj Kumar; Ramaswamy, Sriram

    2016-07-01

    We study the growth kinetics of glassy correlations in a structural glass by monitoring the evolution, within mode-coupling theory, of a suitably defined three-point function χ_{C}(t,t_{w}) with time t and waiting time t_{w}. From the complete wave-vector-dependent equations of motion for domain growth, we pass to a schematic limit to obtain a numerically tractable form. We find that the peak value χ_{C}^{P} of χ_{C}(t,t_{w}), which can be viewed as a correlation volume, grows as t_{w}^{0.5}, and the relaxation time as t_{w}^{0.8}, following a quench to a point deep in the glassy state. These results constitute a theoretical explanation of the simulation findings of Parisi [J. Phys. Chem. B 103, 4128 (1999)JPCBFK1520-610610.1021/jp983967m] and Kob and Barrat [Phys. Rev. Lett. 78, 4581 (1997)PRLTAO0031-900710.1103/PhysRevLett.78.4581], and they are also in qualitative agreement with Parsaeian and Castillo [Phys. Rev. E 78, 060105(R) (2008)PLEEE81539-375510.1103/PhysRevE.78.060105]. On the other hand, if the quench is to a point on the liquid side, the correlation volume grows to saturation. We present a similar calculation for the growth kinetics in a p-spin spin glass mean-field model where we find a slower growth, χ_{C}^{P}∼t_{w}^{0.13}. Further, we show that a shear rate γ[over ̇] cuts off the growth of glassy correlations when t_{w}∼1/γ[over ̇] for quench in the glassy regime and t_{w}=min(t_{r},1/γ[over ̇]) in the liquid, where t_{r} is the relaxation time of the unsheared liquid. The relaxation time of the steady-state fluid in this case is ∝γ[over ̇]^{-0.8}. PMID:27575179

  4. Buffer layer effect on ZnO nanorods growth alignment

    NASA Astrophysics Data System (ADS)

    Zhao, Dongxu; Andreazza, Caroline; Andreazza, Pascal; Ma, Jiangang; Liu, Yichun; Shen, Dezhen

    2005-06-01

    Vertical aligned ZnO nanorods array was fabricated on Si with introducing a ZnO thin film as a buffer layer. Two different nucleation mechanisms were found in growth process. With using Au catalyst, Zn vapor could diffuse into Au nanoclusters with forming a solid solution. Then the ZnO nucleation site is mainly on the catalyst by oxidation of Au/Zn alloy. Without catalyst, nucleation could occur directly on the surface of buffer layer by homoepitaxy. The density and the size of ZnO nanorods could be governed by morphological character of catalyst and buffer layer. The nanorods growth is followed by vapor-solid mechanism.

  5. Arabidopsis thaliana root growth kinetics and lunisolar tidal acceleration.

    PubMed

    Fisahn, Joachim; Yazdanbakhsh, Nima; Klingele, Emile; Barlow, Peter

    2012-07-01

    • All living organisms on Earth are continually exposed to diurnal variations in the gravitational tidal force due to the Sun and Moon. • Elongation of primary roots of Arabidopsis thaliana seedlings maintained at a constant temperature was monitored for periods of up to 14 d using high temporal- and spatial-resolution video imaging. The time-course of the half-hourly elongation rates exhibited an oscillation which was maintained when the roots were placed in the free-running condition of continuous illumination. • Correlation between the root growth kinetics collected from seedlings initially raised under several light protocols but whose roots were subsequently in the free-running condition and the lunisolar tidal profiles enabled us to identify that the latter is the probable exogenous determinant of the rhythmic variation in root elongation rate. Similar observations and correlations using roots of Arabidopsis starch mutants suggest a central function of starch metabolism in the response to the lunisolar tide. The periodicity of the lunisolar tidal signal and the concomitant adjustments in root growth rate indicate that an exogenous timer exists for the modulation of root growth and development. • We propose that, in addition to the sensitivity to Earthly 1G gravity, which is inherent to all animals and plants, there is another type of responsiveness which is attuned to the natural diurnal variations of the lunisolar tidal force. PMID:22583121

  6. Growth kinetics in a phase field model with continuous symmetry

    NASA Astrophysics Data System (ADS)

    Marini Bettolo Marconi, Umberto; Crisanti, Andrea

    1996-07-01

    We discuss the static and kinetic properties of a Ginzburg-Landau spherically symmetric O(N) model recently introduced [U. Marini Bettolo Marconi and A. Crisanti, Phys. Rev. Lett. 75, 2168 (1995)] in order to generalize the so-called phase field model of Langer [Rev. Mod. Phys. 52, 1 (1980); Science 243, 1150 (1989)]. The Hamiltonian contains two O(N) invariant fields φ and U bilinearly coupled. The order parameter field φ evolves according to a nonconserved dynamics, whereas the diffusive field U follows a conserved dynamics. In the limit N-->∞ we obtain an exact solution, which displays an interesting kinetic behavior characterized by three different growth regimes. In the early regime the system displays normal scaling and the average domain size grows as t1/2; in the intermediate regime one observes a finite wave-vector instability, which is related to the Mullins-Sekerka instability; finally, in the late stage the structure function has a multiscaling behavior, while the domain size grows as t1/4.

  7. Oxidation kinetics and chemostat growth kinetics of Thiobacillus ferrooxidans on tetrathionate and thiosulfate.

    PubMed

    Eccleston, M; Kelly, D P

    1978-06-01

    Growth of Thiobacillus ferrooxidans in batch culture on 10 mM potassium tetrathionate was optimal at pH 2.5 (specific growth rate, 0.092 h-1). Oxygen electrode studies on resting cell suspensions showed that the apparent Km for tetrathionate oxidation (0.13 to 8.33 mM) was pH dependent, suggesting higher substrate affinity at higher pH. Conversely, oxidation rates were greatest at low pH. High substrate concentrations (7.7 to 77 mM) did not affect maximum oxidation rates at pH 3.0, but produced substrate inhibition at other pH values. Tetrathionate-grown cell suspensions also oxidized thiosulfate at pH 2.0 to 4.0. Apparent Km values (1.2 to 25 mM) were of the same order as for tetrathionate, but kinetics were complex. Continuous culture on growth-limiting tetrathionate at pH 2.5, followed by continuous culture on growth-limiting thiosulfate at pH 2.5, indicated true growth yield values (grams [dry weight] per gram-molecule of substrate) of 12.2 and 7.5, and maintenance coefficient values (millimoles of substrate per gram [dry weight) of organisms per hour) of 1.01 and 0.97 for tetrathionate and thiosulfate, respectively. Yield was increased on both media at low dilution rates by increase in CO2 supply. The apparent maintenance coefficient was lowered without affecting YG, suggesting better energy coupling in CO2-rich environments. Prolonged continuous cultivation on tetrathionate or thiosulfate did not affect the ability of the organism to grow subsequently in ferrous iron medium. PMID:26665

  8. Kinetic and Fluid Ballooning Stability with Anisotropic Energetic Electron Layers

    SciTech Connect

    Cooper, W. A.

    2006-11-30

    A kinetic ballooning mode theory is developed from the gyrokinetic equation in the frequency range for which the ions are fluid, the thermal electron response is adiabatic and the hot electrons are non-interacting due to their large drift velocity. Trapped particle effects are ignored, The application of the quasineutrality condition together with the parallel and binomial components of Ampere's Law reduces the gyrokinetic equation to a second order ordinary differential equation along the equilibrium magnetic field lines. The instability dynamics are dominated by the pressure gradients of the thermal species in the fluid magnetohydrodynamic limit. The resulting equation combines features of both the Kruskal-Oberman energy principle and the rigid hot particle energy principle proposed by Johnson et al. to model the Astron device.

  9. Nanoshells made easy: improving Au layer growth on nanoparticle surfaces.

    PubMed

    Brinson, Bruce E; Lassiter, J Britt; Levin, Carly S; Bardhan, Rizia; Mirin, Nikolay; Halas, Naomi J

    2008-12-16

    The growth of a continuous, uniform Au layer on a dielectric nanoparticle is the critical step in the synthesis of nanoparticles such as nanoshells or nanorice, giving rise to their unique geometry-dependent plasmon resonant properties. Here, we report a novel, streamlined method for Au layer metallization on prepared nanoparticle surfaces using carbon monoxide as the reducing agent. This approach consistently yields plasmonic nanoparticles with highly regular shell layers and is immune to variations in precursor or reagent preparation. Single particle spectroscopy combined with scanning electron microscopy reveal that thinner, more uniform shell layers with correspondingly red-shifted optical resonances are achievable with this approach. PMID:19360963

  10. Lidar observations of mixed layer dynamics - Tests of parameterized entrainment models of mixed layer growth rate

    NASA Technical Reports Server (NTRS)

    Boers, R.; Eloranta, E. W.; Coulter, R. L.

    1984-01-01

    Ground based lidar measurements of the atmospheric mixed layer depth, the entrainment zone depth and the wind speed and wind direction were used to test various parameterized entrainment models of mixed layer growth rate. Six case studies under clear air convective conditions over flat terrain in central Illinois are presented. It is shown that surface heating alone accounts for a major portion of the rise of the mixed layer on all days. A new set of entrainment model constants was determined which optimized height predictions for the dataset. Under convective conditions, the shape of the mixed layer height prediction curves closely resembled the observed shapes. Under conditions when significant wind shear was present, the shape of the height prediction curve departed from the data suggesting deficiencies in the parameterization of shear production. Development of small cumulus clouds on top of the layer is shown to affect mixed layer depths in the afternoon growth phase.

  11. LIDAR OBSERVATIONS OF MIXED LAYER DYNAMICS: TESTS OF PARAMETERIZED ENTRAINMENT MODELS OF MIXED LAYER GROWTH RATE

    EPA Science Inventory

    Lidar measurements of the atmospheric boundary layer height, the entrainment zone, wind speed and direction, ancillary temperature profiles and surface flux data were used to test current parameterized entrainment models of mixed layer growth rate. Six case studies under clear ai...

  12. Selective growth of graphene in layer-by-layer via chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Park, Jaehyun; An, Hyosub; Choi, Dong-Chul; Hussain, Sajjad; Song, Wooseok; An, Ki-Seok; Lee, Won-Jun; Lee, Naesung; Lee, Wan-Gyu; Jung, Jongwan

    2016-07-01

    Selective and precise control of the layer number of graphene remains a critical issue for the practical applications of graphene. First, it is highly challenging to grow a continuous and uniform few-layer graphene since once the monolayer graphene fully covers a copper (Cu) surface, the growth of the second layer stops, resulting in mostly nonhomogeneous films. Second, from the selective adlayer growth point of view, there is no clear pathway for achieving this. We have developed the selective growth of a graphene adlayer in layer-by-layer via chemical vapor deposition (CVD) which makes it possible to stack graphene on a specific position. The key idea is to deposit a thin Cu layer (~40 nm thick) on pre-grown monolayer graphene and to apply additional growth. The thin Cu atop the graphene/Cu substrate acts as a catalyst to decompose methane (CH4) gas during the additional growth. The adlayer is grown selectively on the pre-grown graphene, and the thin Cu is removed through evaporation during CVD, eventually forming large-area and uniform double layer graphene. With this technology, highly uniform graphene films with precise thicknesses of 1 to 5 layers and graphene check patterns with 1 to 3 layers were successfully demonstrated. This method provides precise LBL growth for a uniform graphene film and a technique for the design of new graphene devices.Selective and precise control of the layer number of graphene remains a critical issue for the practical applications of graphene. First, it is highly challenging to grow a continuous and uniform few-layer graphene since once the monolayer graphene fully covers a copper (Cu) surface, the growth of the second layer stops, resulting in mostly nonhomogeneous films. Second, from the selective adlayer growth point of view, there is no clear pathway for achieving this. We have developed the selective growth of a graphene adlayer in layer-by-layer via chemical vapor deposition (CVD) which makes it possible to stack graphene

  13. Correlation between growth kinetics and nanoscale resistive switching properties of SrTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Muenstermann, Ruth; Menke, Tobias; Dittmann, Regina; Mi, Shaobo; Jia, Chun-Lin; Park, Daesung; Mayer, Joachim

    2010-12-01

    We deliberately fabricated SrTiO3 thin films deviating from ideal stoichiometry and from two-dimensional layer-by-layer growth mode, in order to study the impact of well pronounced defect arrangements on the nanoscale electrical properties. By combining transmission electron microscopy with conductive-tip atomic force microscopy we succeeded to elucidate the microstructure of thin films grown by pulsed laser deposition under kinetically limited growth conditions and to correlate it with the local electrical properties. SrTiO3 thin films, grown in a layer-by-layer growth mode, exhibit a defect structure and conductivity pattern close to single crystals, containing irregularly distributed, resistive switching spots. In contrast to this, Ti-rich films exhibit short-range-ordered, well-conducting resistive switching units. For Ti-rich films grown in a kinetically more restricted island growth mode, we succeeded to identify defective island boundaries with the location of tip-induced resistive switching. The observed nanoscale switching behavior is consistent with a voltage driven oxygen vacancy movement that induces a local redox-based metal-to-insulator transition. Switching occurs preferentially in defect-rich regions, that exhibit a high concentration of oxygen vacancies and might act as easy-diffusion-channels.

  14. Kinetics and mechanisms of crystal growth inhibition of indomethacin by model precipitation inhibitors

    NASA Astrophysics Data System (ADS)

    Patel, Dhaval

    Supersaturating Drug Delivery Systems (SDDS) could enhance oral bioavailability of poorly water soluble drugs (PWSD). Precipitation inhibitors (PIs) in SDDS could maintain supersaturation by inhibiting nucleation, crystal growth, or both. The mechanisms by which these effects are realized are generally unknown. The goal of this dissertation was to explore the mechanisms underpinning the effects of model PIs including hydroxypropyl beta-cyclodextrins (HP-beta-CD), hydroxypropyl methylcellulose (HPMC), and polyvinylpyrrolidone (PVP) on the crystal growth of indomethacin, a model PWSD. At high degrees of supersaturation (S), the crystal growth kinetics of indomethacin was bulk diffusion-controlled, which was attributed to a high energy form deposited on the seed crystals. At lower S, indomethacin growth kinetics was surface integration-controlled. The effect of HP-beta-CD at high S was successfully modeled using the reactive diffusion layer theory. The superior effects of PVP and HPMC as compared to HP-beta-CD at high S were attributed to a change in the rate limiting step from bulk diffusion to surface integration largely due to prevention of the high energy form formation. The effects of PIs at low S were attributed to significant retardation of the surface integration rate, a phenomenon that may reflect the adsorption of PIs onto the growing surface. PVP was selected to further understand the relationship between adsorption and crystal growth inhibition. The Langmuir adsorption isotherm model fit the adsorption isotherms of PVP and N-vinylpyrrolidone well. The affinity and extent of adsorption of PVP were significantly higher than those of N-vinylpyrrolidone, which was attributed to cooperative interactions between PVP and indomethacin. The extent of PVP adsorption on a weight-basis was greater for higher molecular weight PVP but less on a molar-basis indicating an increased percentage of loops and tails for higher molecular weight PVPs. PVP significantly inhibited

  15. Direct Observation of Aggregative Nanoparticle Growth: Kinetic Modeling of the Size Distribution and Growth Rate

    SciTech Connect

    Woehl, Taylor J.; Park, Chiwoo; Evans, James E.; Arslan, Ilke; Ristenpart, William D.; Browning, Nigel D.

    2014-01-08

    Direct observations of solution-phase nanoparticle growth using in situ liquid transmission electron microscopy (TEM) have demonstrated the importance of “non-classical” growth mechanisms, such as aggregation and coalescence, on the growth and final morphology of nanocrystals at the atomic and single nanoparticle scales. To date, groups have quantitatively interpreted the mean growth rate of nanoparticles in terms of the Lifshitz-Slyozov-Wagner (LSW) model for Ostwald ripening, but less attention has been paid to modeling the corresponding particle size distribution. Here we use in situ fluid stage scanning TEM to demonstrate that silver nanoparticles grow by a length-scale dependent mechanism, where individual nanoparticles grow by monomer attachment but ensemble-scale growth is dominated by aggregation. Although our observed mean nanoparticle growth rate is consistent with the LSW model, we show that the corresponding particle size distribution is broader and more symmetric than predicted by LSW. Following direct observations of aggregation, we interpret the ensemble-scale growth using Smoluchowski kinetics and demonstrate that the Smoluchowski model quantitatively captures the mean growth rate and particle size distribution.

  16. Physiologic growth hormone replacement improves fasting lipid kinetics in patients with HIV lipodystrophy syndrome

    Technology Transfer Automated Retrieval System (TEKTRAN)

    HIV lipodystrophy syndrome (HLS) is characterized by accelerated lipolysis, inadequate fat oxidation, increased hepatic reesterification, and a high frequency of growth hormone deficiency (GHD). The effect of growth hormone (GH) replacement on these lipid kinetic abnormalities is unknown. We aimed ...

  17. Double-diffusive layers adjacent to cold chimney flows during transient mushy-layer growth

    NASA Astrophysics Data System (ADS)

    Zhong, Jin-Qiang; Xue, Qiwei; Wettlaufer, John

    2013-03-01

    We examine the cooling effect of chimney flows in the liquid region during transient upward growth of a mushy layer in solidifying aqueous ammonium chloride. Through drainage channels in a mushy layer, cold, relatively fresh fluid is carried into the warm, salt-stratified liquid region. Double-diffusive cells form due to the cooling effect of the chimney flows and evolve into a series of downwelling horizontal layers. Using shadowgraph methods and dyed fluids we demonstrate the vigorous flow circulations and compositional mixing within each layer. Vertical concentration and temperature profiles reveal the double-diffusive staircase structure across the layers. The downward velocity of the layers decreases as they approach to the mush-liquid interface, which is interpreted by a filling-box model representing the momentum and compositional transport of turbulent continuous plumes in a confined region. The present experiment provides insight to evaluate the solute fluxes from growing mushy layers.

  18. Growth kinetics of forsterite reaction rims at high-pressure

    NASA Astrophysics Data System (ADS)

    Nishihara, Yu; Maruyama, Genta; Nishi, Masayuki

    2016-08-01

    Growth kinetics of forsterite (Fo) reaction rims between periclase (Per) and enstatite (En) were studied experimentally at pressure (P) and temperature (T) conditions of 3.0-11.1 GPa and 1473-1873 K, respectively. Pt markers originally placed at the Per-En interface were always observed at the Per-Fo interface, which indicates that Mg and O are the diffusing species in Fo rim growth (Mg-O coupled diffusion). The presence of some En inclusions in Fo grains and the growth rate of the Fo rim suggests that grain boundary diffusion is dominant rather than lattice diffusion. Considering the very fast grain boundary diffusion of O in olivine, the Mg-O coupled grain boundary diffusion in Fo is deduced to be rate-limited by the diffusivity of Mg. Based on an analysis of data collected under dry conditions, the product of the Mg grain boundary diffusion coefficient (Dgb) and the effective grain boundary width (δ) was determined to be δDgb = δDgb,0exp[-(E∗ + PV∗)/RT] with δDgb,0 = 10-9.68 ± 1.51 m3/s, E∗ = 379 ± 44 kJ/mol and V∗ = -1.9 ± 1.4 cm3/mol. Our results, combined with previously reported data on Mg lattice diffusion in Fo, suggest that for Mg, the significance of grain boundary diffusion increases with depth in the Earth's upper mantle, although lattice diffusion is still dominant for typical mantle grain sizes of 1-10 mm.

  19. Determination of kinetic parameters of crystal growth rate of borax in aqueous solution by using the rotating disc technique

    NASA Astrophysics Data System (ADS)

    Sahin, Omer; Aslan, Fevzi; Ozdemir, Mustafa; Durgun, Mustafa

    2004-10-01

    Growth rate of polycrystalline disc of borax compressed at different pressure and rotated at various speed has been measured in a rotating disc crystallizer under well-defined conditions of supersaturation. It was found that the mass transfer coefficient, K, increased while overall growth rate constant, Kg, and surface reaction constant, kr, decreased with increasing smoothness of the disc. It was also determined that kinetic parameters (kr , r , K , g) of crystal growth rate of borax decreased with increasing rotating speed of the polycrystalline disc. The effectiveness factor was calculated from the growth rate data to evaluate the relative magnitude of the steps in series bulk diffusion through the mass transfer boundary layer and the surface integration. At low rotating speed of disc, the crystal growth rate of borax is mainly controlled by integration. However, both diffusion and integration steps affect the growth rate of borax at higher rotating speed of polycrystalline disc.

  20. End-growth/evaporation living polymerization kinetics revisited

    NASA Astrophysics Data System (ADS)

    Semenov, A. N.; Nyrkova, I. A.

    2011-03-01

    End-growth/evaporation kinetics in living polymer systems with "association-ready" free unimers (no initiator) is considered theoretically. The study is focused on the systems with long chains (typical aggregation number N ≫ 1) at long times. A closed system of continuous equations is derived and is applied to study the kinetics of the chain length distribution (CLD) following a jump of a parameter (T-jump) inducing a change of the equilibrium mean chain length from N0 to N. The continuous approach is asymptotically exact for t ≫ t1, where t1 is the dimer dissociation time. It yields a number of essentially new analytical results concerning the CLD kinetics in some representative regimes. In particular, we obtained the asymptotically exact CLD response (for N ≫ 1) to a weak T-jump (ɛ = N0/N - 1 ≪ 1). For arbitrary T-jumps we found that the longest relaxation time tmax = 1/γ is always quadratic in N (γ is the relaxation rate of the slowest normal mode). More precisely tmax ∝4N2 for N0 < 2N and tmax ∝NN0/(1 - N/N0) for N0 > 2N. The mean chain length Nn is shown to change significantly during the intermediate slow relaxation stage t1 ≪ t ≪ tmax . We predict that N_n(t)-N_n(0)∝ √{t} in the intermediate regime for weak (or moderate) T-jumps. For a deep T-quench inducing strong increase of the equilibrium Nn (N ≫ N0 ≫ 1), the mean chain length follows a similar law, N_n(t)∝ √{t}, while an opposite T-jump (inducing chain shortening, N0 ≫ N ≫ 1) leads to a power-law decrease of Nn: Nn(t)∝t-1/3. It is also shown that a living polymer system gets strongly polydisperse in the latter regime, the maximum polydispersity index r = Nw/Nn being r* ≈ 0.77N0/N ≫ 1. The concentration of free unimers relaxes mainly during the fast process with the characteristic time tf ˜ t1N0/N2. A nonexponential CLD dominated by short chains develops as a result of the fast stage in the case of N0 = 1 and N ≫ 1. The obtained analytical results are supported

  1. Release Kinetics of Paclitaxel and Cisplatin from Two and Three Layered Gold Nanoparticles

    PubMed Central

    England, Christopher G.; Miller, M. Clarke; Kuttan, Ashani; Trent, John O.; Frieboes, Hermann B.

    2015-01-01

    Gold nanoparticles functionalized with biologically-compatible layers may achieve stable drug release while avoiding adverse effects in cancer treatment. We study cisplatin and paclitaxel release from gold cores functionalized with hexadecanethiol (TL) and phosphatidylcholine (PC) to form two-layer nanoparticles, or TL, PC, and high density lipoprotein (HDL) to form three-layer nanoparticles. Drug release was monitored for 14 days to assess long term effects of the core surface modifications on release kinetics. Release profiles were fitted to previously developed kinetic models to differentiate possible release mechanisms. The hydrophilic drug (cisplatin) showed an initial (5-hr.) burst, followed by a steady release over 14 days. The hydrophobic drug (paclitaxel) showed a steady release over the same time period. Two layer nanoparticles released 64.0 ± 2.5% of cisplatin and 22.3 ± 1.5% of paclitaxel, while three layer nanoparticles released the entire encapsulated drug. The Korsmeyer-Peppas model best described each release scenario, while the simplified Higuchi model also adequately described paclitaxel release from the two layer formulation. We conclude that functionalization of gold nanoparticles with a combination of TL and PC may help to modulate both hydrophilic and hydrophobic drug release kinetics, while the addition of HDL may enhance long term release of hydrophobic drug. PMID:25753197

  2. On the growth of turbulent regions in laminar boundary layers

    NASA Technical Reports Server (NTRS)

    Gad-El-hak, M.; Riley, J. J.; Blackwelder, R. F.

    1981-01-01

    Turbulent spots evolving in a laminar boundary layer on a nominally zero pressure gradient flat plate are investigated. The plate is towed through an 18 m water channel, using a carriage that rides on a continuously replenished oil film giving a vibrationless tow. Turbulent spots are initiated using a solenoid valve that ejects a small amount of fluid through a minute hole on the working surface. A novel visualization technique that utilizes fluorescent dye excited by a sheet of laser light is employed. Some new aspects of the growth and entrainment of turbulent spots, especially with regard to lateral growth, are inferred from the present experiments. To supplement the information on lateral spreading, a turbulent wedge created by placing a roughness element in the laminar boundary layer is also studied both visually and with probe measurements. The present results show that, in addition to entrainment, another mechanism is needed to explain the lateral growth characteristics of a turbulent region in a laminar boundary layer. This mechanism, termed growth by destabilization, appears to be a result of the turbulence destabilizing the unstable laminar boundary layer in its vicinity. To further understand the growth mechanisms, the turbulence in the spot is modulated using drag-reducing additives and salinity stratification.

  3. The kinetics of dolomite reaction rim growth under isostatic and non-isostatic pressure conditions

    NASA Astrophysics Data System (ADS)

    Helpa, V.; Rybacki, E.; Morales, L. G.; Abart, R.; Dresen, G. H.

    2013-12-01

    During burial and exhumation, rocks are simultaneously exposed to metamorphic reactions and tectonic stresses. Therefore, the reaction rate of newly formed minerals may depend on chemical and mechanical driving forces. Here, we investigate the reaction kinetics of dolomite (CaMg[CO3]2) rim growth by solid-state reactions experiments on oriented calcite (CaCO3) and magnesite (MgCO3) single crystals under isostatic and non-isostatic pressure conditions. Cylindrical samples of 3-5 mm length and 7 mm diameter were drilled and polished perpendicular to the rhombohedral cleavage planes of natural clear crystals. The tests were performed using a Paterson-type deformation apparatus at P = 400 MPa confining pressure, temperatures, T, between 750 and 850°C, and reaction durations, t, of 2 - 146 h to calculate the kinetic parameters of dolomite rim growth under isostatic stress conditions. For non-isostatic reaction experiments we applied in addition differential stresses, σ, up to 40 MPa perpendicular to the contact interface at T = 750°C for 4 - 171 h duration, initiating minor inelastic deformation of calcite. The thickness of the resulting dolomite reaction rims increases linearly with the square root of time, indicating a diffusion-controlled reaction. The rims consist of two different textural domains. Granular dolomite grains (≈ 2 -5 μm grain size) form next to calcite and elongated palisade-shaped grains (1-6 μm diameter) grow perpendicular to the magnesite interface. Texture measurements with the electron backscatter diffraction technique indicate that the orientations of dolomite grains are mainly influenced by the orientation of the calcite educt crystal, in particular in the granular rim. To some extent, the texture of dolomite palisades is also influenced by the orientation of magnesite. The thickness of the two individual layers increases with temperature. At 400 MPa isostatic pressure, T = 750°C and t = 29 hours, a 5 μm thick granular dolomite layer

  4. Cell and tissue kinetics of the subependymal layer in mouse brain following heavy charged particle irradiation

    SciTech Connect

    Manley, N.B.; Fabrikant, J.I.; Alpen, E.L.

    1988-12-01

    The following studies investigate the cellular response and cell population kinetics of the subependymal layer in the mouse brain exposed to heavy charged particle irradiation. Partial brain irradiation with helium and neon ions was confined to one cortex of the brain. Both the irradiated and the unirradiated contralateral cortex showed similar disturbances of the cell and tissue kinetics in the subependymal layers. The irradiated hemisphere exhibited histological damage, whereas the unirradiated side appeared normal histologically. This study concerns the cell population and cell cycle kinetics of the subependymal layer in the mouse brain, and the effects of charged particle irradiations on this cell population. Quantitative high resolution autoradiography was used to study the kinetic parameters in this cell layer. This study should help in understanding the effects of these high-energy heavy ions on normal mammalian brain tissue. The response of the mammalian brain exposure to charged particle ionizing radiation may be extremely variable. It varies from minimal physiological changes to overt tissue necrosis depending on a number of factors such as: the administered dose, dose-rate, the volume of the irradiated tissue, and the biological end-point being examined.

  5. Nonextensive treatment of nucleation and growth in a thin layer

    NASA Astrophysics Data System (ADS)

    Cetinel, Hakan; Kayacan, Ozhan

    2007-01-01

    In this study, a generalized method based upon nonextensive statistics is presented for nucleation and growth processes in a thin layer between two interfaces. It is shown that the presented mathematical model, which uses an index called the entropic index that measures the nonextensivity of the physical system, successfully deals with the nucleation and growth processes, and works better than Johnson-Mehl-Avrami-Kolmogorov model. The presented model also contains Austin-Rickett model as a special case.

  6. The boundary layer growth in an urban area.

    PubMed

    Pino, D; Vilà-Guerau de Arellano, J; Comerón, A; Rocadenbosch, F

    2004-12-01

    The development and maintenance of the atmospheric boundary layer (ABL) plays a key role in the distribution of atmospheric constituents, especially in a polluted urban area. In particular, the ABL has a direct impact on the concentration and transformation of pollutants. In this work, in order to analyze the different mechanisms which control the boundary layer growth, we have simulated by means of the non-hydrostatic model MM5 several boundary layer observed in the city of Barcelona (Spain). Sensitivity analysis of the modelled ABL is carried out by using various descriptions of the planetary boundary layer (PBL). Direct and continuous measurements of the boundary layer depth taken by a lidar are used to evaluate the results obtained by the model. PMID:15504507

  7. Sensitivity of the two-dimensional shearless mixing layer to the initial turbulent kinetic energy and integral length scale

    NASA Astrophysics Data System (ADS)

    Fathali, M.; Deshiri, M. Khoshnami

    2016-04-01

    The shearless mixing layer is generated from the interaction of two homogeneous isotropic turbulence (HIT) fields with different integral scales ℓ1 and ℓ2 and different turbulent kinetic energies E1 and E2. In this study, the sensitivity of temporal evolutions of two-dimensional, incompressible shearless mixing layers to the parametric variations of ℓ1/ℓ2 and E1/E2 is investigated. The sensitivity methodology is based on the nonintrusive approach; using direct numerical simulation and generalized polynomial chaos expansion. The analysis is carried out at Reℓ 1=90 for the high-energy HIT region and different integral length scale ratios 1 /4 ≤ℓ1/ℓ2≤4 and turbulent kinetic energy ratios 1 ≤E1/E2≤30 . It is found that the most influential parameter on the variability of the mixing layer evolution is the turbulent kinetic energy while variations of the integral length scale show a negligible influence on the flow field variability. A significant level of anisotropy and intermittency is observed in both large and small scales. In particular, it is found that large scales have higher levels of intermittency and sensitivity to the variations of ℓ1/ℓ2 and E1/E2 compared to the small scales. Reconstructed response surfaces of the flow field intermittency and the turbulent penetration depth show monotonic dependence on ℓ1/ℓ2 and E1/E2 . The mixing layer growth rate and the mixing efficiency both show sensitive dependence on the initial condition parameters. However, the probability density function of these quantities shows relatively small solution variations in response to the variations of the initial condition parameters.

  8. Ion beam generation at the plasma sheet boundary layer by kinetic Alfven waves

    NASA Technical Reports Server (NTRS)

    Moghaddam-Taaheri, E.; Goertz, C. K.; Smith, R. A.

    1989-01-01

    A two-dimensional quasi-linear numerical code was developed for studying ion beam generation at the plasma sheet boundary layer by kinetic Alfven waves. The model assumes that the central plasma sheet is the particle source, and that the last magnetic field lines on which kinetic Alfven waves exist and diffusion occurs can be either open or closed. As the possible source for the excitement of the kinetic Alfven waves responsible for ion diffusion, the resonant mode conversion of the surface waves to kinetic Alfven waves is considered. It is shown that, depending on the topology of the magnetic field at the lobe side of the simulation system, i.e., on whether field lines are open or closed, the ion distribution function may or may not reach a steady state.

  9. Buoyant production and consumption of turbulence kinetic energy in cloud-topped mixed layers

    NASA Technical Reports Server (NTRS)

    Randall, D. A.

    1984-01-01

    It is pointed out that studies of the entraining planetary boundary layer (PBL) have generally emphasized the role of buoyancy fluxes in driving entrainment. The buoyancy flux is proportional to the rate of conversion of the potential energy of the mean flow into the kinetic energy of the turbulence. It is not unusual for conversion to proceed in both directions simultaneously. This occurs, for instance, in both clear and cloudy convective mixed layers which are capped by inversions. A partitioning of the net conversion into positive parts, generating turbulence kinetic energy (TKE), and negative parts (TKE-consuming), would make it possible to include the positive part in the gross production rate, and closure would be achieved. Three different approaches to partitioning have been proposed. The present investigation is concerned with a comparison of the three partitioning theories. Particular attention is given to the cloud-topped mixed layer because in this case the differences between two partitioning approaches are most apparent.

  10. Kinetic equilibrium for an asymmetric tangential layer with rotation of the magnetic fiel

    NASA Astrophysics Data System (ADS)

    Dorville, N.; Belmont, G.; Aunai, N.; Rezeau, L.

    2014-12-01

    Finding kinetic equilibria for tangential current layers is a key issue for the modeling of plasma phenomena such as magnetic reconnection, for which theoretical and numerical studies usually aim in starting from steady state current layers. The famous Harris equilibrium is known to be limited to symmetric layers surrounded by vacuum, with constant temperature, and constant ion and electron flow velocities, and with a current variation depending only on the density variation. It is clearly not suited for the modeling of ``magnetopause-like'' layers, which separate two plasmas of different densities and temperatures. In order to understand this kind of boundaries, Belmont et al (2012) presented a new asymmetric equilibrium which was validated in a hybrid simulation by Aunai et al (2013), and more recently in a fully kinetic simulation as well. For this equilibrium to be computed, the magnetic field had to stay coplanar inside the layer. We present here an important generalization, where the magnetic field rotates inside the layer (restricted to a 180° rotation hitherto). The tangential layers so obtained are thus closer to those encountered at the magnetopause. This will be necessary, in the future, for comparing directly the theoretical profiles with the experimental ones for the various physical parameters. As it was done previously, the equilibrium is tested with a hybrid simulation.

  11. Nucleation and Early Stages of Layer-by-Layer Growth of Metal Organic Frameworks on Surfaces

    PubMed Central

    2015-01-01

    High resolution atomic force microscopy (AFM) is used to resolve the evolution of crystallites of a metal organic framework (HKUST-1) grown on Au(111) using a liquid-phase layer-by-layer methodology. The nucleation and faceting of individual crystallites is followed by repeatedly imaging the same submicron region after each cycle of growth and we find that the growing surface is terminated by {111} facets leading to the formation of pyramidal nanostructures for [100] oriented crystallites, and triangular [111] islands with typical lateral dimensions of tens of nanometres. AFM images reveal that crystallites can grow by 5–10 layers in each cycle. The growth rate depends on crystallographic orientation and the morphology of the gold substrate, and we demonstrate that under these conditions the growth is nanocrystalline with a morphology determined by the minimum energy surface. PMID:26709359

  12. Growth mode evolution of hafnium oxide by atomic layer deposition

    SciTech Connect

    Nie, Xianglong; Ma, Fei; Ma, Dayan; Xu, Kewei

    2014-01-15

    HfO{sub 2} thin films were deposited using tetrakis-ethylmethylamido hafnium and H{sub 2}O as precursors on silicon by atomic layer deposition (ALD). The morphology and microstructures at different ALD cycles were characterized by atomic force microscopy and high-resolution transmission electron microscopy. Based on the height–height correlation function and power spectral density function, quantitative analysis of surface morphologies was performed. Three characteristic dimensions (ξ{sub 1}, ξ{sub 2}, and ξ{sub 3}) corresponding to three surface structures, islands, local and global fluctuations, were identified. The evolution of ALD growth mode at range of the three critical scales was investigated, respectively. It suggests the transformation of growth mode from quasi two-dimensional layer-by-layer to three-dimensional island for global fluctuations.

  13. Kinetics and mechanisms of creep crack growth in a creep-resisting steel

    SciTech Connect

    Vainshtok, V.A.; Baumshtein, M.V.; Makovetskaya, I.A.; Man'ko, V.D.

    1986-02-01

    This paper discusses the nature of kinetic diagrams of growth of fatigue cracks in the temperature range typical of operation of important components of power equipment and examines the proportion of the incubation period of crack growth in the total life. The relationship of the kinetic diagrams of crack growth with the fracture mechanisms are examined and the effect of running life on creep crack propagation is reviewed.

  14. Isothermal Ice Crystallization Kinetics in the Gas-Diffusion Layer of a Proton-Exchange-Membrane Fuel Cell

    SciTech Connect

    Dursch, Thomas J.; Ciontea, Monica A.; Radke, Clayton J.; Weber, Adam Z.

    2011-12-01

    Nucleation and growth of ice in the fibrous gas-diffusion layer (GDL) of a proton-exchange membrane fuel cell (PEMFC) are studied using isothermal differential scanning calorimetry (DSC). Isothermal crystallization rates and pseudo-steady-state nucleation rates are obtained as a function of subcooling from heat-flow and induction-time measurements. Kinetics of ice nucleation and growth are studied at two polytetrafluoroethylene (PTFE) loadings (0 and 10 wt %) in a commercial GDL for temperatures between 240 and 273 K. A nonlinear ice-crystallization rate expression is developed using Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory, in which the heat-transfer-limited growth rate is determined from the moving-boundary Stefan problem. Induction times follow a Poisson distribution and increase upon addition of PTFE, indicating that nucleation occurs more slowly on a hydrophobic fiber than on a hydrophilic fiber. The determined nucleation rates and induction times follow expected trends from classical nucleation theory. Finally, a validated rate expression is now available for predicting ice-crystallization kinetics in GDLs.

  15. Direct atomic-scale observation of layer-by-layer oxide growth during magnesium oxidation

    SciTech Connect

    Zheng, He; Wu, Shujing; Sheng, Huaping; Liu, Chun; Liu, Yu; Cao, Fan; Zhou, Zhichao; Zhao, Dongshan E-mail: dszhao@whu.edu.cn; Wang, Jianbo E-mail: dszhao@whu.edu.cn; Zhao, Xingzhong

    2014-04-07

    The atomic-scale oxide growth dynamics are directly revealed by in situ high resolution transmission electron microscopy during the oxidation of Mg surface. The oxidation process is characterized by the layer-by-layer growth of magnesium oxide (MgO) nanocrystal via the adatom process. Consistently, the nucleated MgO crystals exhibit faceted surface morphology as enclosed by (200) lattice planes. It is believed that the relatively lower surface energies of (200) lattice planes should play important roles, governing the growth mechanism. These results facilitate the understanding of the nanoscale oxide growth mechanism that will have an important impact on the development of magnesium or magnesium alloys with improved resistance to oxidation.

  16. Exploring growth kinetics of carbon nanotube arrays by in situ optical diagnostics and modeling

    SciTech Connect

    Puretzky, Alexander A; Geohegan, David B; Pannala, Sreekanth; Rouleau, Christopher

    2014-01-01

    Simple kinetic models of carbon nanotube growth have been able to successfully link together many experimental parameters involved in the growth of carbon nanotubes for practical applications including the prediction of growth rates, terminal lengths, number of walls, activation energies, and their dependences on the growth environment. The implications of recent experiments utilizing in situ monitoring of carbon nanotube growth on our past kinetic model are first reviewed. Then, sub-second pulsed feedstock gas introduction is discussed to explore the nucleation and initial growth of carbon nanotubes in the context of the kinetic model. Moreover, kinetic effects in "pulsed CVD" - using repeated pulsed gas introduction to stop and restart nanotube growth - are explored to understand renucleation, the origin of alignment in nanotube arrays, and incremental growth. Time-resolved reflectivity of the surface is used to remotely understand the kinetics of nucleation and the coordinated growth of arrays. This approach demonstrates that continuous vertically aligned single wall carbon nanotubes can be grown incrementally by pulsed CVD, and that the first exposure of fresh catalyst to feedstock gas is critical to nanotubes site density required for coordinated growth. Aligned nanotube arrays (as short as 60 nm) are shown to nucleate and grow within single, sub-second gas pulses. The multiple-pulse growth experiments (> 100 pulses) show that a high fraction of nanotubes renucleate on subsequent gas pulses.

  17. Notes on Interface Growth Kinetics 50 Years after Burton, Cabrera and Frank

    NASA Technical Reports Server (NTRS)

    Chernov, A. A.

    2004-01-01

    This overview is devoted to some unresolved basic problems in crystal growth kinetics. The density wave approach to propagation of a spatially diffuse interface between a growing crystal and its simple (e.g., metallic) melt is discussed is Section 2. This approach allows for the calculation of kinetic coefficients and is an alternative to the localized interface concept in which each atom belongs to either a solid or a liquid. Sections 3 and 4 deals mainly with layer growth from solution. Mutual retardation of the growth steps via their bulk and d a c e diffusion fields is the major subject. The influence of solution flow on step bunching (Section 4) suggests the essential influence of bulk diffusion on the surface morphology. The flow within the solution boundary layer enhances step-step interaction, influences the step bunching process and the resulting step pattern morphology on the growing surface. Recent experiments on the rates at which strongly polygonized steps on protein and small molecule crystals propagate during growth from solution are analyzed in Section 5 . We have shown that the step segments may be "singular" and that "one-dimensional nucleation" may be the rate limiting stage for the segments that are shorter or comparable in length to the thermodynamically equilibrium interlink distance. In this case, the reciprocal dependence of the segment propagation rate on the segment length that follow from the Gibbs-Thompson law, should be replaced by an abrupt switch from zero to a finite constant velocity. Until recently, the Kossel crystal remained the only model used in crystal growth theory. In such Kossel Gibbs-Thomson law, should be replaced by an abrupt switch &om zero to a finite constant velocity. crystals, all kinks at the steps are identical and the kink rate is a linear function of the supersaturation. In the non-Kossel crystals, there may be several kink configurations characterized by different geometries and energies. These configurations

  18. Layer-by-layer assembly of epidermal growth factors on polyurethane films for wound closure.

    PubMed

    Kulkarni, Abhilash; Diehl-Jones, William; Ghanbar, Sadegh; Liu, Song

    2014-02-13

    To facilitate the healing of chronic wounds, growth factors such as epidermal growth factor need to be safely encapsulated for their sustained and effective delivery to the wound bed. Using a layer-by-layer assembly technique, epidermal growth factor is successfully encapsulated on the surface of poly(acrylic acid)-modified polyurethane film. The amount of encapsulated epidermal growth factor is controlled by adjusting the number of chitosan/epidermal growth factor bilayers. A controlled release of epidermal growth factor from the surface of polyurethane film for a period of five days is achieved with well-retained bioactivity (over 90%) as evidenced by a cell proliferation assay. In an in vitro cellular wounding assay, the cell gap covered with the epidermal growth factor-loaded polyurethane film closes at a rate more than twice as fast as that covered with a control polyurethane film. Fluorescent staining of F-actin reveals that the released epidermal growth factor induces differences in cytoskeletal organization, suggesting that stimulated cell migration also contributes to the close of the cell gap. PMID:24525716

  19. Methods for improved growth of group III nitride buffer layers

    DOEpatents

    Melnik, Yurity; Chen, Lu; Kojiri, Hidehiro

    2014-07-15

    Methods are disclosed for growing high crystal quality group III-nitride epitaxial layers with advanced multiple buffer layer techniques. In an embodiment, a method includes forming group III-nitride buffer layers that contain aluminum on suitable substrate in a processing chamber of a hydride vapor phase epitaxy processing system. A hydrogen halide or halogen gas is flowing into the growth zone during deposition of buffer layers to suppress homogeneous particle formation. Some combinations of low temperature buffers that contain aluminum (e.g., AlN, AlGaN) and high temperature buffers that contain aluminum (e.g., AlN, AlGaN) may be used to improve crystal quality and morphology of subsequently grown group III-nitride epitaxial layers. The buffer may be deposited on the substrate, or on the surface of another buffer. The additional buffer layers may be added as interlayers in group III-nitride layers (e.g., GaN, AlGaN, AlN).

  20. Underpotential deposition-mediated layer-by-layer growth of thin films

    SciTech Connect

    Wang, Jia Xu; Adzic, Radoslav R.

    2015-05-19

    A method of depositing contiguous, conformal submonolayer-to-multilayer thin films with atomic-level control is described. The process involves the use of underpotential deposition of a first element to mediate the growth of a second material by overpotential deposition. Deposition occurs between a potential positive to the bulk deposition potential for the mediating element where a full monolayer of mediating element forms, and a potential which is less than, or only slightly greater than, the bulk deposition potential of the material to be deposited. By cycling the applied voltage between the bulk deposition potential for the mediating element and the material to be deposited, repeated desorption/adsorption of the mediating element during each potential cycle can be used to precisely control film growth on a layer-by-layer basis. This process is especially suitable for the formation of a catalytically active layer on core-shell particles for use in energy conversion devices such as fuel cells.

  1. Phase-field Model for Interstitial Loop Growth Kinetics and Thermodynamic and Kinetic Models of Irradiated Fe-Cr Alloys

    SciTech Connect

    Li, Yulan; Hu, Shenyang Y.; Sun, Xin; Khaleel, Mohammad A.

    2011-06-15

    Microstructure evolution kinetics in irradiated materials has strongly spatial correlation. For example, void and second phases prefer to nucleate and grow at pre-existing defects such as dislocations, grain boundaries, and cracks. Inhomogeneous microstructure evolution results in inhomogeneity of microstructure and thermo-mechanical properties. Therefore, the simulation capability for predicting three dimensional (3-D) microstructure evolution kinetics and its subsequent impact on material properties and performance is crucial for scientific design of advanced nuclear materials and optimal operation conditions in order to reduce uncertainty in operational and safety margins. Very recently the meso-scale phase-field (PF) method has been used to predict gas bubble evolution, void swelling, void lattice formation and void migration in irradiated materials,. Although most results of phase-field simulations are qualitative due to the lake of accurate thermodynamic and kinetic properties of defects, possible missing of important kinetic properties and processes, and the capability of current codes and computers for large time and length scale modeling, the simulations demonstrate that PF method is a promising simulation tool for predicting 3-D heterogeneous microstructure and property evolution, and providing microstructure evolution kinetics for higher scale level simulations of microstructure and property evolution such as mean field methods. This report consists of two parts. In part I, we will present a new phase-field model for predicting interstitial loop growth kinetics in irradiated materials. The effect of defect (vacancy/interstitial) generation, diffusion and recombination, sink strength, long-range elastic interaction, inhomogeneous and anisotropic mobility on microstructure evolution kinetics is taken into account in the model. The model is used to study the effect of elastic interaction on interstitial loop growth kinetics, the interstitial flux, and sink

  2. Adsorption of cobalt ferrite nanoparticles within layer-by-layer films: a kinetic study carried out using quartz crystal microbalance.

    PubMed

    Alcantara, Gustavo B; Paterno, Leonardo G; Afonso, André S; Faria, Ronaldo C; Pereira-da-Silva, Marcelo A; Morais, Paulo C; Soler, Maria A G

    2011-12-28

    The paper reports on the successful use of the quartz crystal microbalance technique to assess accurate kinetics and equilibrium parameters regarding the investigation of in situ adsorption of nanosized cobalt ferrite particles (CoFe(2)O(4)--10.5 nm-diameter) onto two different surfaces. Firstly, a single layer of nanoparticles was deposited onto the surface provided by the gold-coated quartz resonator functionalized with sodium 3-mercapto propanesulfonate (3-MPS). Secondly, the layer-by-layer (LbL) technique was used to build multilayers in which the CoFe(2)O(4) nanoparticle-based layer alternates with the sodium sulfonated polystyrene (PSS) layer. The adsorption experiments were conducted by modulating the number of adsorbed CoFe(2)O(4)/PSS bilayers (n) and/or by changing the CoFe(2)O(4) nanoparticle concentration while suspended as a stable colloidal dispersion. Adsorption of CoFe(2)O(4) nanoparticles onto the 3-MPS-functionalized surface follows perfectly a first order kinetic process in a wide range (two orders of magnitude) of nanoparticle concentrations. These data were used to assess the equilibrium constant and the adsorption free energy. Alternatively, the Langmuir adsorption constant was obtained while analyzing the isotherm data at the equilibrium. Adsorption of CoFe(2)O(4) nanoparticles while growing multilayers of CoFe(2)O(4)/PSS was conducted using colloidal suspensions with CoFe(2)O(4) concentration in the range of 10(-8) to 10(-6) (moles of cobalt ferrite per litre) and for different numbers of cycles n = 1, 3, 5, and 10. We found the adsorption of CoFe(2)O(4) nanoparticles within the CoFe(2)O(4)/PSS bilayers perfectly following a first order kinetic process, with the characteristic rate constant growing with the increase of CoFe(2)O(4) nanoparticle concentration and decreasing with the rise of the number of LbL cycles (n). Additionally, atomic force microscopy was employed for assessing the LbL film roughness and thickness. We found the film

  3. Structure and Growth of the Marine Boundary Layer

    NASA Technical Reports Server (NTRS)

    Mccumber, M.

    1984-01-01

    LANDSAT visible imagery and a one-dimensional Lagrangian boundary layer model were used to hypothesize the nature and the development of the marine boundary layer during a winter episode of strong seaward cold air advection. Over-water heating and moistening of the cold, dry continental air is estimable from linear relations involving horizontal gradients of the near-surface air temperature and humidity. A line of enhanced convection paralleling the Atlantic U.S. coast from south of New York Bay to the vicinity of Virginia Beach, VA was attributed to stronger convergence at low levels. This feature was characterized as a mesoscale front. With the assistance of a three-dimensional mesoscale boundary layer model, initialized with data obtained from the MASEX, the marine boundary layer can be mapped over the entire Atlantic coastal domain and the evolution of the boundary layer can be studied as a function of different characteristics of important surface level forcings. The effects on boundary layer growth due to the magnitude and pattern of sea surface temperature, to the shape of the coastline, and to atmospheric conditions, such as the orientation of the prevailing wind are examined.

  4. Arbitrary amplitude double layers in warm dust kinetic Alfven wave plasmas

    SciTech Connect

    Gogoi, Runmoni; Devi, Nirupama

    2008-07-15

    Large amplitude electrostatic structures associated with low-frequency dust kinetic Alfvenic waves are investigated under the pressure (temperature) gradient indicative of dust dynamics. The set of equations governing the dust dynamics, Boltzmann electrons, ions and Maxwell's equation have been reduced to a single equation known as the Sagdeev potential equation. Parameter ranges for the existence of arbitrary amplitude double layers are observed. Exact analytical expressions for the energy integral is obtained and computed numerically through which sub-Alfvenic arbitrary amplitude rarefactive double layers are found to exist.

  5. Kinetics of protein adsorption/desorption mediated by pH-responsive polymer layer

    NASA Astrophysics Data System (ADS)

    Su, Xiao-Hang; Lei, Qun-Li; Ren, Chun-Lai

    2015-11-01

    We propose a new way of regulating protein adsorption by using a pH-responsive polymer. According to the theoretical results obtained from the molecular theory and kinetic approaches, both thermodynamics and kinetics of protein adsorption are verified to be well controlled by the solution pH. The kinetics and the amount of adsorbed proteins at equilibrium are greatly increased when the solution environment changes from acid to neutral. The reason is that the increased pH promotes the dissociation of the weak polyelectrolyte, resulting in more charged monomers and more stretched chains. Thus the steric repulsion within the polymer layer is weakened, which effectively lowers the barrier felt by the protein during the process of adsorption. Interestingly, we also find that the kinetics of protein desorption is almost unchanged with the variation of pH. It is because although the barrier formed by the polymer layer changes along with the change of pH, the potential at contact with the surface varies equally. Our results may provide useful insights into controllable protein adsorption/desorption in practical applications. Project supported by the National Natural Science Foundation of China (Grant Nos. 21274062, 11474155, and 91027040).

  6. Carbon nanotube forests growth using catalysts from atomic layer deposition

    SciTech Connect

    Chen, Bingan; Zhang, Can; Esconjauregui, Santiago; Xie, Rongsi; Zhong, Guofang; Robertson, John; Bhardwaj, Sunil; Cepek, Cinzia

    2014-04-14

    We have grown carbon nanotubes using Fe and Ni catalyst films deposited by atomic layer deposition. Both metals lead to catalytically active nanoparticles for growing vertically aligned nanotube forests or carbon fibres, depending on the growth conditions and whether the substrate is alumina or silica. The resulting nanotubes have narrow diameter and wall number distributions that are as narrow as those grown from sputtered catalysts. The state of the catalyst is studied by in-situ and ex-situ X-ray photoemission spectroscopy. We demonstrate multi-directional nanotube growth on a porous alumina foam coated with Fe prepared by atomic layer deposition. This deposition technique can be useful for nanotube applications in microelectronics, filter technology, and energy storage.

  7. Model-based predictions of solid state intermetallic compound layer growth in hybrid microelectronic circuits

    SciTech Connect

    Vianco, P.T.; Erickson, K.L.; Hopkins, P.L.

    1997-12-31

    A mathematical model was developed to quantitatively describe the intermetallic compound (IMC) layer growth that takes place between a Sn-based solder and a noble metal thick film conductor material used in hybrid microcircuit (HMC) assemblies. The model combined the reaction kinetics of the solder/substrate interaction, as determined from ancillary isothermal aging experiments, with a 2-D finite element mesh that took account of the porous morphology of the thick film coating. The effect of the porous morphology on the IMC layer growth when compared to the traditional 1-D computations was significant. The previous 1-D calculations under-predicted the nominal IMC layer thickness relative to the 2-D case. The 2-D model showed greater substrate consumption by IMC growth and lesser solder consumption that was determined with the 1-D computation. The new 2-D model allows the design engineer to better predict circuit aging and hence, the reliability of HMC hardware that is placed in the field.

  8. Study of oxide and α-Zr(O) growth kinetics from high temperature steam oxidation of Zircaloy-4 cladding

    NASA Astrophysics Data System (ADS)

    Sawarn, Tapan K.; Banerjee, Suparna; Samanta, Akanksha; Rath, B. N.; Kumar, Sunil

    2015-12-01

    Oxidation kinetics of Zircaloy-4 cladding of fuel pins of Indian pressurized heavy water reactors (IPHWRs) under a simulated loss of coolant accident (LOCA) condition was investigated. The kinetic rate constants for the oxide and oxygen stabilized α-Zr phase growth were established from the isothermal metal-steam reaction at high temperatures (900-1200 °C) with soaking periods in the range of 60-900 s. Oxide and α-Zr(O) layer thickness were measured to derive the respective growth rates. The observed rates obeyed a parabolic law and Arrhenius expressions of rate constants were established. Percentage equivalent clad reacted (%ECR) was calculated using Baker-Just equation. Hydrogen estimation was carried out on the oxidized samples using inert gas fusion technique. The hydrogen pick up was found to be in the range 10-30 ppm. The measured values of oxide and α-Zr(O) layer thickness were compared with the results obtained using OXYCON, an indigenously developed model. The model predicts the oxide growth reasonably well but under predicts the α-Zr(O) growth significantly at thickness values higher than 80 μm.

  9. Synthesis of layer-tunable graphene: A combined kinetic implantation and thermal ejection approach

    SciTech Connect

    Wang, Gang; Zhang, Miao; Liu, Su; Xie, Xiaoming; Ding, Guqiao; Wang, Yongqiang; Chu, Paul K.; Gao, Heng; Ren, Wei; Yuan, Qinghong; Zhang, Peihong; Wang, Xi; Di, Zengfeng

    2015-05-04

    Layer-tunable graphene has attracted broad interest for its potentials in nanoelectronics applications. However, synthesis of layer-tunable graphene by using traditional chemical vapor deposition (CVD) method still remains a great challenge due to the complex experimental parameters and the carbon precipitation process. Herein, by performing ion implantation into a Ni/Cu bilayer substrate, the number of graphene layers, especially single or double layer, can be controlled precisely by adjusting the carbon ion implant fluence. The growth mechanism of the layer-tunable graphene is revealed by monitoring the growth process is observed that the entire implanted carbon atoms can be expelled towards the substrate surface and thus graphene with designed layer number can be obtained. Such a growth mechanism is further confirmed by theoretical calculations. The proposed approach for the synthesis of layer-tunable graphene offers more flexibility in the experimental conditions. Being a core technology in microelectronics processing, ion implantation can be readily implemented in production lines and is expected to expedite the application of graphene to nanoelectronics.

  10. Synthesis of layer-tunable graphene: A combined kinetic implantation and thermal ejection approach

    DOE PAGESBeta

    Wang, Gang; Zhang, Miao; Liu, Su; Xie, Xiaoming; Ding, Guqiao; Wang, Yongqiang; Chu, Paul K.; Gao, Heng; Ren, Wei; Yuan, Qinghong; et al

    2015-05-04

    Layer-tunable graphene has attracted broad interest for its potentials in nanoelectronics applications. However, synthesis of layer-tunable graphene by using traditional chemical vapor deposition (CVD) method still remains a great challenge due to the complex experimental parameters and the carbon precipitation process. Herein, by performing ion implantation into a Ni/Cu bilayer substrate, the number of graphene layers, especially single or double layer, can be controlled precisely by adjusting the carbon ion implant fluence. The growth mechanism of the layer-tunable graphene is revealed by monitoring the growth process is observed that the entire implanted carbon atoms can be expelled towards the substratemore » surface and thus graphene with designed layer number can be obtained. Such a growth mechanism is further confirmed by theoretical calculations. The proposed approach for the synthesis of layer-tunable graphene offers more flexibility in the experimental conditions. Being a core technology in microelectronics processing, ion implantation can be readily implemented in production lines and is expected to expedite the application of graphene to nanoelectronics.« less

  11. The effect of growth temperature of seed layer on the structural and optical properties of ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Gautam, Khyati; Singh, Inderpreet; Bhatnagar, P. K.; Peta, Koteswara Rao

    2016-05-01

    The structural and optical properties of ZnO nanorods are investigated as a function of growth temperature of the seed layer. The seed layer comprising of ZnO nanocrystallites is grown on ITO substrates at five different temperatures (150-550 °C) and the nanorods are grown on the seed layer by the facile hydrothermal method. The seed layer grown at 350 °C is observed to be uniformly textured with c-axis orientation leading to the synthesis of vertically aligned nanorods with smaller diameter. The HR-TEM analysis and the intense peak along (002) direction in the XRD spectra of this sample implied that the nanorods possess c-axis orientation. An enhanced UV emission is also observed in the photoluminescence spectra of this sample. The diversity in the morphology and orientation of the seeds at different temperatures has been explained by the growth kinetics of the ZnO nanocrystallites.

  12. Layer growth in Au-Pb/In solder joints

    SciTech Connect

    Yost, F.G.; Ganyard, F.P.; Karnowsky, M.M.

    1986-01-01

    The solid state reaction between a Pb-In solder alloy and thin film Au has been investigated at ten aging temperatures ranging from 70 to 170/sup 0/C. Also, bulk Au-solder samples were aged at 150/sup 0/C for metallographic analysis. No significant difference was found between the aging behavior of thin and bulk Au specimens. A thin single phase layer of Au/sub 9/In/sub 4/ was found adjacent to Au while a thick two-phase layer of AuIn/sub 2/ and Pb was found between Au/sub 9/In/sub 4/ and solder. The Pb phase was shown to have considerable mobility and able to ripen at room temperature. Peculiar planar interface instabilities and voids in the Au-Au/sub 9/In/sub 4/ interface were found. The total layer thickness was found to vary linearly with aging time, indicating an interface-controlled reaction. An activation energy of 14,000 calories per mole was found by regression analysis of the kinetic data.

  13. Kinetic Alfven wave in the presence of kappa distribution function in plasma sheet boundary layer

    SciTech Connect

    Shrivastava, G. Ahirwar, G.; Shrivastava, J.

    2015-07-31

    The particle aspect approach is adopted to investigate the trajectories of charged particles in the electromagnetic field of kinetic Alfven wave. Expressions are found for the dispersion relation, damping/growth rate and associated currents in the presence of kappa distribution function. Kinetic effect of electrons and ions are included to study kinetic Alfven wave because both are important in the transition region. It is found that the ratio β of electron thermal energy density to magnetic field energy density and the ratio of ion to electron thermal temperature (T{sub i}/T{sub e}), and kappa distribution function affect the dispersion relation, damping/growth rate and associated currents in both cases(warm and cold electron limit).The treatment of kinetic Alfven wave instability is based on assumption that the plasma consist of resonant and non resonant particles. The resonant particles participate in an energy exchange process, whereas the non resonant particles support the oscillatory motion of the wave.

  14. Modified energetics and growth kinetics on H-terminated GaAs (110)

    SciTech Connect

    Galiana, B.; Benedicto, M.; Díez-Merino, L.; Tejedor, P.; Lorbek, S.; Hlawacek, G.; Teichert, C.

    2013-10-28

    Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As{sub 4}, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å{sup 2} measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As{sub 4} molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

  15. Modified energetics and growth kinetics on H-terminated GaAs (110)

    NASA Astrophysics Data System (ADS)

    Galiana, B.; Benedicto, M.; Díez-Merino, L.; Lorbek, S.; Hlawacek, G.; Teichert, C.; Tejedor, P.

    2013-10-01

    Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As4, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å2 measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

  16. Computing the reconnection rate in turbulent kinetic layers by using electron mixing to identify topology

    SciTech Connect

    Daughton, W.; Nakamura, T. K. M.; Karimabadi, H.; Roytershteyn, V.; Loring, B.

    2014-05-15

    Three-dimensional kinetic simulations of magnetic reconnection for parameter regimes relevant to the magnetopause current layer feature the development of turbulence, driven by the magnetic and velocity shear, and dominated by coherent structures including flux ropes, current sheets, and flow vortices. Here, we propose a new approach for computing the global reconnection rate in the presence of this complexity. The mixing of electrons originating from separate sides of the magnetopause layer is used as a proxy to rapidly identify the magnetic topology and track the evolution of magnetic flux. The details of this method are illustrated for an asymmetric current layer relevant to the subsolar magnetopause and for a flow shear dominated layer relevant to the lower latitude magnetopause. While the three-dimensional reconnection rates show a number of interesting differences relative to the corresponding two-dimensional simulations, the time scale for the energy conversion remains very similar. These results suggest that the mixing of field lines between topologies is more easily influenced by kinetic turbulence than the physics responsible for the energy conversion.

  17. Computer Simulations of Interstitial Loop Growth Kinetics in irradiated bcc Fe

    SciTech Connect

    Li, Yulan; Hu, Shenyang Y.; Henager, Charles H.; Deng, Huiqiu; Gao, Fei; Sun, Xin; Khaleel, Mohammad A.

    2012-08-01

    The growth kinetics of (001) [001] interstitial loops in bcc Fe is studied by phase-field modeling. The effect of defect (vacancy/interstitial) concentration, generation, recombination, sink strength, and elastic interaction on the growth kinetics of interstitial loops is systematically simulated. Results show that the elastic interaction between the defects and interstitial loops speeds up the growth kinetics and affects the morphology of the interstitial loops. Linear growth rate, i.e., the loop average radius is linear to time, under both aging and irradiation are predicted, which is in agreement with experimental observation. The results also show that the interstitial loop growth rate, which is directly related to the sink strength of the interstitial loop for interstitials, increases linearly with the initial interstitial concentration during aging while changing logarithmically with the interstitial generation rate under irradiation.

  18. Lateral epitaxial growth of two-dimensional layered semiconductor heterojunctions.

    PubMed

    Duan, Xidong; Wang, Chen; Shaw, Jonathan C; Cheng, Rui; Chen, Yu; Li, Honglai; Wu, Xueping; Tang, Ying; Zhang, Qinling; Pan, Anlian; Jiang, Jianhui; Yu, Ruqing; Huang, Yu; Duan, Xiangfeng

    2014-12-01

    Two-dimensional layered semiconductors such as MoS₂ and WSe₂ have attracted considerable interest in recent times. Exploring the full potential of these layered materials requires precise spatial modulation of their chemical composition and electronic properties to create well-defined heterostructures. Here, we report the growth of compositionally modulated MoS₂-MoSe₂ and WS₂-WSe₂ lateral heterostructures by in situ modulation of the vapour-phase reactants during growth of these two-dimensional crystals. Raman and photoluminescence mapping studies demonstrate that the resulting heterostructure nanosheets exhibit clear structural and optical modulation. Transmission electron microscopy and elemental mapping studies reveal a single crystalline structure with opposite modulation of sulphur and selenium distributions across the heterostructure interface. Electrical transport studies demonstrate that the WSe₂-WS₂ heterojunctions form lateral p-n diodes and photodiodes, and can be used to create complementary inverters with high voltage gain. Our study is an important advance in the development of layered semiconductor heterostructures, an essential step towards achieving functional electronics and optoelectronics. PMID:25262331

  19. Layer-by-layer polysaccharide-coated liposomes for sustained delivery of epidermal growth factor.

    PubMed

    Kaminski, Gabriel A T; Sierakowski, Maria Rita; Pontarolo, Roberto; Santos, Larissa Antoniacomi Dos; de Freitas, Rilton Alves

    2016-04-20

    A three-dimensional layer-by-layer (LbL) structure composed by xanthan and galactomannan biopolymers over dioctadecyldimethylammonium bromide (DODAB) liposome template was proposed and characterized for protein drug delivery. The polymers and the surfactant interaction were sufficiently strong to create a LbL structure up to 8 layers, evaluated using quartz crystal microbalance (QCM) and zeta potential analysis. The polymer-liposome binding enthalpy was determined by isothermal titration calorimetry (ITC). The bilayer of biopolymer-coated liposomes with diameters of 165 (±15)nm, measured by dynamic light scattering (DLS), and ζ-potential of -4 (±13)mV. These bilayer-coated nanoparticles increased up to 5 times the sustained release of epidermal growth factor (EGF) at a first order rate of 0.005min(-1). This system could be useful for improving the release profile of low-stability drugs like EGF. PMID:26876836

  20. Kinetics of Ion Transport in Perovskite Active Layers and Its Implications for Active Layer Stability.

    PubMed

    Bag, Monojit; Renna, Lawrence A; Adhikari, Ramesh Y; Karak, Supravat; Liu, Feng; Lahti, Paul M; Russell, Thomas P; Tuominen, Mark T; Venkataraman, D

    2015-10-14

    Solar cells fabricated using alkyl ammonium metal halides as light absorbers have the right combination of high power conversion efficiency and ease of fabrication to realize inexpensive but efficient thin film solar cells. However, they degrade under prolonged exposure to sunlight. Herein, we show that this degradation is quasi-reversible, and that it can be greatly lessened by simple modifications of the solar cell operating conditions. We studied perovskite devices using electrochemical impedance spectroscopy (EIS) with methylammonium (MA)-, formamidinium (FA)-, and MA(x)FA(1-x) lead triiodide as active layers. From variable temperature EIS studies, we found that the diffusion coefficient using MA ions was greater than when using FA ions. Structural studies using powder X-ray diffraction (PXRD) show that for MAPbI3 a structural change and lattice expansion occurs at device operating temperatures. On the basis of EIS and PXRD studies, we postulate that in MAPbI3 the predominant mechanism of accelerated device degradation under sunlight involves thermally activated fast ion transport coupled with a lattice-expanding phase transition, both of which are facilitated by absorption of the infrared component of the solar spectrum. Using these findings, we show that the devices show greatly improved operation lifetimes and stability under white-light emitting diodes, or under a solar simulator with an infrared cutoff filter or with cooling. PMID:26414066

  1. Kinetics of nickel silicide growth in silicon nanowires: From linear to square root growth

    NASA Astrophysics Data System (ADS)

    Yaish, Y. E.; Katsman, A.; Cohen, G. M.; Beregovsky, M.

    2011-05-01

    The common practice for nickel silicide formation in silicon nanowires (SiNWs) relies on axial growth of silicide along the wire that is initiated from nickel reservoirs at the source and drain contacts. In the present work the silicide intrusions were studied for various parameters including wire diameter (25-50 nm), annealing time (15-120 s), annealing temperature (300-440∘C), and the quality of the initial Ni/Si interface. The silicide formation was investigated by high-resolution scanning electron microscopy, high-resolution transmission electron microscopy (TEM), and atomic force microscopy. The main part of the intrusion formed at 420∘C consists of monosilicide NiSi, as was confirmed by energy dispersive spectroscopy STEM, selected area diffraction TEM, and electrical resistance measurements of fully silicided SiNWs. The kinetics of nickel silicide axial growth in the SiNWs was analyzed in the framework of a diffusion model through constrictions. The model calculates the time dependence of the intrusion length, L, and predicts crossover from linear to square root time dependency for different wire parameters, as confirmed by the experimental data.

  2. Large area growth of layered WSe2 films

    NASA Astrophysics Data System (ADS)

    Browning, Robert; Kuperman, Neal; Solanki, Raj; Kanzyuba, Vasily; Rouvimov, Sergei

    2016-09-01

    Growth of smooth and continuous films of WSe2 has been demonstrated by employing atomic layer deposition (ALD) on 5 cm × 5 cm substrates. The substrates consisted of silicon wafers with a layer of SiO2. The ALD precursors were WCl5 and H2Se. The film properties characterized using Raman spectroscopy and x-ray photoelectron spectroscopy are comparable to those reported for WSe2 films produced by chemical vapor deposition and exfoliation. Carrier mobilities were determined with back-gated transistors. With Pd contacts, median electron and hole mobilities of 531 cm2 V‑1 s‑1 and 354 cm2 V‑1 s‑1, respectively, were measured.

  3. Zinc oxide nanoparticle suspensions and layer-by-layer coatings inhibit staphylococcal growth.

    PubMed

    McGuffie, Matthew J; Hong, Jin; Bahng, Joong Hwan; Glynos, Emmanouil; Green, Peter F; Kotov, Nicholas A; Younger, John G; VanEpps, J Scott

    2016-01-01

    Despite a decade of engineering and process improvements, bacterial infection remains the primary threat to implanted medical devices. Zinc oxide nanoparticles (ZnO-NPs) have demonstrated antimicrobial properties. Their microbial selectivity, stability, ease of production, and low cost make them attractive alternatives to silver NPs or antimicrobial peptides. Here we sought to (1) determine the relative efficacy of ZnO-NPs on planktonic growth of medically relevant pathogens; (2) establish the role of bacterial surface chemistry on ZnO-NP effectiveness; (3) evaluate NP shape as a factor in the dose-response; and (4) evaluate layer-by-layer (LBL) ZnO-NP surface coatings on biofilm growth. ZnO-NPs inhibited bacterial growth in a shape-dependent manner not previously seen or predicted. Pyramid shaped particles were the most effective and contrary to previous work, larger particles were more effective than smaller particles. Differential susceptibility of pathogens may be related to their surface hydrophobicity. LBL ZnO-NO coatings reduced staphylococcal biofilm burden by >95%. From the Clinical Editor: The use of medical implants is widespread. However, bacterial colonization remains a major concern. In this article, the authors investigated the use of zinc oxide nanoparticles (ZnO-NPs) to prevent bacterial infection. They showed in their experiments that ZnO-NPs significantly inhibited bacterial growth. This work may present a new alternative in using ZnO-NPs in medical devices. PMID:26515755

  4. Modeling of Interaction Layer Growth Between U-Mo Particles and an Al Matrix

    SciTech Connect

    Yeon Soo Kim; G. L. Hofman; Ho Jin Ryu; Jong Man Park; A. B. Robinson; D. M. Wachs

    2013-12-01

    Interaction layer growth between U-Mo alloy fuel particles and Al in a dispersion fuel is a concern due to the volume expansion and other unfavorable irradiation behavior of the interaction product. To reduce interaction layer (IL) growth, a small amount of Si is added to the Al. As a result, IL growth is affected by the Si content in the Al matrix. In order to predict IL growth during fabrication and irradiation, empirical models were developed. For IL growth prediction during fabrication and any follow-on heating process before irradiation, out-of-pile heating test data were used to develop kinetic correlations. Two out-of-pile correlations, one for the pure Al matrix and the other for the Al matrix with Si addition, respectively, were developed, which are Arrhenius equations that include temperature and time. For IL growth predictions during irradiation, the out-of-pile correlations were modified to include a fission-rate term to consider fission enhanced diffusion, and multiplication factors to incorporate the Si addition effect and the effect of the Mo content. The in-pile correlation is applicable for a pure Al matrix and an Al matrix with the Si content up to 8 wt%, for fuel temperatures up to 200 degrees C, and for Mo content in the range of 6 – 10wt%. In order to cover these ranges, in-pile data were included in modeling from various tests, such as the US RERTR-4, -5, -6, -7 and -9 tests and Korea’s KOMO-4 test, that were designed to systematically examine the effects of the fission rate, temperature, Si content in Al matrix, and Mo content in U-Mo particles. A model converting the IL thickness to the IL volume fraction in the meat was also developed.

  5. COMPARATIVE KINETIC STUDIES OF NITRATE-LIMITED GROWTH AND NITRATE UPTAKE IN PHYTOPLANKTON IN CONTINUOUS CULTURE

    EPA Science Inventory

    A comparative kinetic study of nitrate-limited growth and nitrate uptake was carried out in chemostat cultures of Ankistrodesmus falcatus, Asterionella formosa, Fragilaria crotonensis. In each species growth rate (microgram) was related to total cell nitrogen or cell quota (q) by...

  6. Domain growth and ordering kinetics in dense quark matter

    SciTech Connect

    Singh, A.; Puri, S.; Mishra, H.

    2012-06-15

    The kinetics of chiral transitions in quark matter is studied in a two-flavor Nambu-Jona-Lasinio model. We focus on the phase-ordering dynamics subsequent to a temperature quench from the massless quark phase to the massive quark phase. We study the dynamics by considering a phenomenological model (Ginzburg-Landau free-energy functional). The morphology of the ordering system is characterized by the scaling of the order-parameter correlation function.

  7. Determining the Kinetic Parameters Characteristic of Microalgal Growth.

    ERIC Educational Resources Information Center

    Martinez Sancho, Maria Eugenie; And Others

    1991-01-01

    An activity in which students obtain a growth curve for algae, identify the exponential and linear growth phases, and calculate the parameters which characterize both phases is described. The procedure, a list of required materials, experimental conditions, analytical technique, and a discussion of the interpretations of individual results are…

  8. Nanowire growth kinetics in aberration corrected environmental transmission electron microscopy.

    PubMed

    Chou, Yi-Chia; Panciera, Federico; Reuter, Mark C; Stach, Eric A; Ross, Frances M

    2016-04-14

    We visualize atomic level dynamics during Si nanowire growth using aberration corrected environmental transmission electron microscopy, and compare with lower pressure results from ultra-high vacuum microscopy. We discuss the importance of higher pressure observations for understanding growth mechanisms and describe protocols to minimize effects of the higher pressure background gas. PMID:27041654

  9. Kinetics of monolayer graphene growth by segregation on Pd(111)

    SciTech Connect

    Mok, H. S.; Murata, Y.; Kodambaka, S.; Ebnonnasir, A.; Ciobanu, C. V.; Nie, S.; McCarty, K. F.

    2014-03-10

    Using in situ low-energy electron microscopy and density functional theory calculations, we follow the growth of monolayer graphene on Pd(111) via surface segregation of bulk-dissolved carbon. Upon lowering the substrate temperature, nucleation of graphene begins on graphene-free Pd surface and continues to occur during graphene growth. Measurements of graphene growth rates and Pd surface work functions establish that this continued nucleation is due to increasing C adatom concentration on the Pd surface with time. We attribute this anomalous phenomenon to a large barrier for attachment of C adatoms to graphene coupled with a strong binding of the non-graphitic C to the Pd surface.

  10. Monoculture parameters successfully predict coculture growth kinetics of Bacteroides thetaiotaomicron and two Bifidobacterium strains.

    PubMed

    Van Wey, A S; Cookson, A L; Roy, N C; McNabb, W C; Soboleva, T K; Shorten, P R

    2014-11-17

    Microorganisms rarely live in isolation but are most often found in a consortium. This provides the potential for cross-feeding and nutrient competition among the microbial species, which make it challenging to predict the growth kinetics in coculture. In this paper we developed a mathematical model to describe substrate consumption and subsequent microbial growth and metabolite production for bacteria grown in monoculture. The model characterized substrate utilization kinetics of 18 Bifidobacterium strains. Some bifidobacterial strains demonstrated preferential degradation of oligofructose in that sugars with low degree of polymerization (DP) (DP≤3 or 4) were metabolized before sugars of higher DP, or vice versa. Thus, we expanded the model to describe the preferential degradation of oligofructose. In addition, we adapted the model to describe the competition between human colonic bacteria Bacteroides thetaiotaomicron LMG 11262 and Bifidobacterium longum LMG 11047 or Bifidobacterium breve Yakult for inulin as well as cross-feeding of breakdown products from the extracellular hydrolysis of inulin by B. thetaiotaomicron LMG 11262. We found that the coculture growth kinetics could be predicted based on the respective monoculture growth kinetics. Using growth kinetics from monoculture experiments to predict coculture dynamics will reduce the number of in vitro experiments required to parameterize multi-culture models. PMID:25282609

  11. Kinetic model for an auroral double layer that spans many gravitational scale heights

    SciTech Connect

    Robertson, Scott

    2014-12-15

    The electrostatic potential profile and the particle densities of a simplified auroral double layer are found using a relaxation method to solve Poisson's equation in one dimension. The electron and ion distribution functions for the ionosphere and magnetosphere are specified at the boundaries, and the particle densities are found from a collisionless kinetic model. The ion distribution function includes the gravitational potential energy; hence, the unperturbed ionospheric plasma has a density gradient. The plasma potential at the upper boundary is given a large negative value to accelerate electrons downward. The solutions for a wide range of dimensionless parameters show that the double layer forms just above a critical altitude that occurs approximately where the ionospheric density has fallen to the magnetospheric density. Below this altitude, the ionospheric ions are gravitationally confined and have the expected scale height for quasineutral plasma in gravity.

  12. Kinetic constants of abnormal grain growth in nanocrystalline nickel

    NASA Astrophysics Data System (ADS)

    Aleshin, A. N.

    2016-02-01

    The grain growth in nanocrystalline nickel with a purity of 99.5 at % during non-isothermal annealing was experimentally investigated using differential scanning calorimetry and transmission electron microscopy. Nanocrystalline nickel was prepared by electrodeposition and had an average grain size of approximately 20 nm. It was shown that, at a temperature corresponding to the calorimetric signal peak, abnormal grain growth occurs with the formation of a bimodal grain microstructure. Calorimeters signals were processed within the Johnson-Mehl-Avrami formalism. This made it possible to determine the exponent of the corresponding equation, the frequency factor, and the activation energy of the grain growth, which was found to be equal to the activation energy of the vacancy migration. The reasons for the abnormal grain growth in nanocrystalline nickel were discussed.

  13. Direct growth of ultrafast transparent single-layer graphene defoggers.

    PubMed

    Tan, Lifang; Zeng, Mengqi; Wu, Qiong; Chen, Linfeng; Wang, Jiao; Zhang, Tao; Eckert, Jürgen; Rümmeli, Mark H; Fu, Lei

    2015-04-17

    The idea flat surface, superb thermal conductivity and excellent optical transmittance of single-layer graphene promise tremendous potential for graphene as a material for transparent defoggers. However, the resistance of defoggers made from conventional transferred graphene increases sharply once both sides of the film are covered by water molecules which, in turn, leads to a temperature drop that is inefficient for fog removal. Here, the direct growth of large-area and continuous graphene films on quartz is reported, and the first practical single-layer graphene defogger is fabricated. The advantages of this single-layer graphene defogger lie in its ultrafast defogging time for relatively low input voltages and excellent defogging robustness. It can completely remove fog within 6 s when supplied a safe voltage of 32 V. No visible changes in the full defogging time after 50 defogging cycles are observed. This outstanding performance is attributed to the strong interaction forces between the graphene films and the substrates, which prevents the permeation of water molecules. These directly grown transparent graphene defoggers are expected to have excellent prospects in various applications such as anti-fog glasses, auto window and mirror defogging. PMID:25510608

  14. Growth kinetics and H-shaped crystals of SAPO-40

    NASA Astrophysics Data System (ADS)

    Di Renzo, F.; Dumont, Nathalie; Trens, P.; Gabelica, Zelimir

    2003-11-01

    Crystal morphologies with well-defined macroscopic cavities are very rare occurrences. Tabular crystals of SAPO-40 with a symmetrical notch at each end have been obtained by selective inhibition of the growth of the large-pore faces. Crystal growth has continued on the small-pores (0 1 0) faces, circumvented the inhibited sphenoidal faces formed a protruding tab at the corners of the crystals.

  15. Growth Kinetics and Mechanics of Hydrate Films by Interfacial Rheology.

    PubMed

    Leopércio, Bruna C; de Souza Mendes, Paulo R; Fuller, Gerald G

    2016-05-01

    A new approach to study and understand the kinetics and mechanical properties of hydrates by interfacial rheology is presented. This is made possible using a "double wall ring" interfacial rheology cell that has been designed to provide the necessary temperature control. Cyclopentane and water are used to form hydrates, and this model system forms these structures at ambient pressures. Different temperature and water/hydrocarbon contact protocols are explored. Of particular interest is the importance of first contacting the hydrocarbon against ice crystals in order to initiate hydrate formation. Indeed, this is found to be the case, even though the hydrates may be created at temperatures above the melting point of ice. Once hydrates completely populate the hydrocarbon/water interface, strain sweeps of the interfacial elastic and viscous moduli are conducted to interrogate the mechanical response and fragility of the hydrate films. The dependence on temperature, Tf, by the kinetics of formation and the mechanical properties is reported, and the cyclopentane hydrate dissociation temperature was found to be between 6 and 7 °C. The formation time (measured from the moment when cyclopentane first contacts ice crystals) as well as the elastic modulus and the yield strain increase as Tf increases. PMID:27076092

  16. Comparing kinetic and fluid simulations of scrape-off layer physics

    NASA Astrophysics Data System (ADS)

    Churchill, R. M.; Canik, J. M.; Chang, C. S.; Hager, R.; Leonard, A. W.; Maingi, R.; Nazikian, R.; Stotler, D. P.

    2015-11-01

    Simulations using the fully kinetic code XGCa were undertaken to explore the impact of kinetic effects on scrape-off layer (SOL) physics in DIII-D H-mode plasmas. XGCa is a total-f, gyrokinetic code which self-consistently calculates the axisymmetric electrostatic potential and plasma dynamics, and includes modules for neutral Monte Carlo transport. Fluid simulations are usually used to simulate the SOL, due to its high collisionality. However, a number of discrepancies have been observed between experiment and leading SOL fluid codes (e.g. SOLPS), including underestimating outer target temperatures, radial electric field in the SOL, parallel ion SOL flows at the low field side, and impurity radiation. Many of these discrepancies may be linked to the fluid treatment, and could be resolved by including kinetic effects in SOL simulations. Status of benchmarking efforts to compare XGCa with the fluid code SOLPS and traditional two-point models will be presented in the sheath-limited and medium-recycling regimes, including future plans to compare results in the high-recycling and detached regimes. This work supported by U.S. DoE contracts DE- AC02-09CH11466 and DE-FG02-06ER5484.

  17. Kinetic-structural analysis of neuronal growth cone veil motility.

    PubMed

    Mongiu, Anne K; Weitzke, Elizabeth L; Chaga, Oleg Y; Borisy, Gary G

    2007-03-15

    Neuronal growth cone advance was investigated by correlative light and electron microscopy carried out on chick dorsal root ganglion cells. Advance was analyzed in terms of the two principal organelles responsible for protrusive motility in the growth cone - namely, veils and filopodia. Veils alternated between rapid phases of protrusion and retraction. Electron microscopy revealed characteristic structural differences between the phases. Our results provide a significant advance in three respects: first, protruding veils are comprised of a densely branched network of actin filaments that is lamellipodial in appearance and includes the Arp2/3 complex. On the basis of this structural and biomarker evidence, we infer that the dendritic nucleation and/or array-treadmilling mechanism of protrusive motility is conserved in veil protrusion of growth cones as in the motility of fibroblasts; second, retracting veils lack dendritic organization but contain a sparse network of long filaments; and third, growth cone filopodia have the capacity to nucleate dendritic networks along their length, a property consistent with veil formation seen at the light microscopic level but not previously understood in supramolecular terms. These elements of veil and filopodial organization, when taken together, provide a conceptual framework for understanding the structural basis of growth cone advance. PMID:17327278

  18. Two types of quasi-liquid layers on ice crystals are formed kinetically.

    PubMed

    Asakawa, Harutoshi; Sazaki, Gen; Nagashima, Ken; Nakatsubo, Shunichi; Furukawa, Yoshinori

    2016-02-16

    Surfaces of ice are covered with thin liquid water layers, called quasi-liquid layers (QLLs), even below their melting point (0 °C), which govern a wide variety of phenomena in nature. We recently found that two types of QLL phases appear that exhibit different morphologies (droplets and thin layers) [Sazaki G. et al. (2012) Proc Natl Acad Sci USA 109(4):1052-1055]. However, revealing the thermodynamic stabilities of QLLs remains a longstanding elusive problem. Here we show that both types of QLLs are metastable phases that appear only if the water vapor pressure is higher than a certain critical supersaturation. We directly visualized the QLLs on ice crystal surfaces by advanced optical microscopy, which can detect 0.37-nm-thick elementary steps on ice crystal surfaces. At a certain fixed temperature, as the water vapor pressure decreased, thin-layer QLLs first disappeared, and then droplet QLLs vanished next, although elementary steps of ice crystals were still growing. These results clearly demonstrate that both types of QLLs are kinetically formed, not by the melting of ice surfaces, but by the deposition of supersaturated water vapor on ice surfaces. To our knowledge, this is the first experimental evidence that supersaturation of water vapor plays a crucially important role in the formation of QLLs. PMID:26831089

  19. Two types of quasi-liquid layers on ice crystals are formed kinetically

    PubMed Central

    Asakawa, Harutoshi; Sazaki, Gen; Nagashima, Ken; Nakatsubo, Shunichi; Furukawa, Yoshinori

    2016-01-01

    Surfaces of ice are covered with thin liquid water layers, called quasi-liquid layers (QLLs), even below their melting point (0 °C), which govern a wide variety of phenomena in nature. We recently found that two types of QLL phases appear that exhibit different morphologies (droplets and thin layers) [Sazaki G. et al. (2012) Proc Natl Acad Sci USA 109(4):1052−1055]. However, revealing the thermodynamic stabilities of QLLs remains a longstanding elusive problem. Here we show that both types of QLLs are metastable phases that appear only if the water vapor pressure is higher than a certain critical supersaturation. We directly visualized the QLLs on ice crystal surfaces by advanced optical microscopy, which can detect 0.37-nm-thick elementary steps on ice crystal surfaces. At a certain fixed temperature, as the water vapor pressure decreased, thin-layer QLLs first disappeared, and then droplet QLLs vanished next, although elementary steps of ice crystals were still growing. These results clearly demonstrate that both types of QLLs are kinetically formed, not by the melting of ice surfaces, but by the deposition of supersaturated water vapor on ice surfaces. To our knowledge, this is the first experimental evidence that supersaturation of water vapor plays a crucially important role in the formation of QLLs. PMID:26831089

  20. Desorption isotherms and mathematical modeling of thin layer drying kinetics of tomato

    NASA Astrophysics Data System (ADS)

    Belghith, Amira; Azzouz, Soufien; ElCafsi, Afif

    2016-03-01

    In recent years, there is an increased demand on the international market of dried fruits and vegetables with significant added value. Due to its important production, consumption and nutrient intake, drying of tomato has become a subject of extended and varied research works. The present work is focused on the drying behavior of thin-layer tomato and its mathematical modeling in order to optimize the drying processes. The moisture desorption isotherms of raw tomato were determined at four temperature levels namely 45, 50, 60 and 65 °C using the static gravimetric method. The experimental data obtained were modeled by five equations and the (GAB) model was found to be the best-describing these isotherms. The drying kinetics were experimentally investigated at 45, 55 and 65 °C and performed at air velocities of 0.5 and 2 m/s. In order to investigate the effect of the exchange surface on drying time, samples were dried into two different shapes: tomato halves and tomato quarters. The impact of various drying parameters was also studied (temperature, air velocity and air humidity). The drying curves showed only the preheating period and the falling drying rate period. In this study, attention was paid to the modeling of experimental thin-layer drying kinetics. The experimental results were fitted with four different models.

  1. Turbulence Kinetic Energy Budgets and Dissipation Rates in Disturbed Stable Boundary Layers

    SciTech Connect

    Lundquist, J K; Piper, M; Kosovic, B

    2004-06-18

    An important parameter in the numerical simulation of atmospheric boundary layers is the dissipation length scale, l{sub {var_epsilon}}. It is especially important in weakly to moderately stable conditions, in which a tenuous balance between shear production of turbulence, buoyant destruction of turbulence, and turbulent dissipation is maintained. In large-scale models, the dissipation rate is often parameterized using a diagnostic equation based on the production of turbulent kinetic energy (TKE) and an estimate of the dissipation length scale. Proper parameterization of the dissipation length scale from experimental data requires accurate estimation of the rate of dissipation of TKE from experimental data. Using data from the MICROFRONTS and CASES-99 field programs, we evaluate turbulent kinetic energy (TKE), TKE dissipation rate {var_epsilon}, and dissipation length l{sub {var_epsilon}} over a range of stability regimes represented by a stable boundary layer (SBL), a destabilizing intrusion (by first a cold front and second a density current) and recovery. These data may be utilized to test recent parameterizations of dissipation rate {var_epsilon} and l{sub {var_epsilon}} in order to determine the suitability of these models for inclusion in mesoscale models for numerical weather prediction or pollution dispersion prediction.

  2. Kinetics of Ni2Si growth from pure Ni and Ni(V) films on (111) and (100) Si

    NASA Astrophysics Data System (ADS)

    Harith, M. A.; Zhang, J. P.; Campisano, S. U.; Klaar, H.-J.

    1987-01-01

    The kinetics of Ni2Si growth from pure Ni and from Ni0.93V0.07 films on (111) and (100) silicon has been studied by the combination of He+ backscattering, x-ray diffraction, Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) techniques. The activation energies are 1.5 and 1.0 eV for pure Ni and Ni(V) films, respectively while the pre-exponential factors in Ni(V) are 4 5 orders of magnitude smaller than in the pure Ni case. The variations in the measured rates are related to the different grain size of the growing suicide layers. The vanadium is rejected from the silicide layer and piles up at the metalsilicide interface.

  3. Comprehensive kinetic analysis of the plasma-wall transition layer in a strongly tilted magnetic field

    SciTech Connect

    Tskhakaya, D. D.; Kos, L.

    2014-10-15

    The magnetized plasma-wall transition (MPWT) layer at the presence of the obliquity of the magnetic field to the wall consists of three sub-layers: the Debye sheath (DS), the magnetic pre-sheath (MPS), and the collisional pre-sheath (CPS) with characteristic lengths λ{sub D} (electron Debye length), ρ{sub i} (ion gyro-radius), and ℓ (the smallest relevant collision length), respectively. Tokamak plasmas are usually assumed to have the ordering λ{sub D}≪ρ{sub i}≪ℓ, when the above-mentioned sub-layers can be distinctly distinguished. In the limits of ε{sub Dm}(λ{sub D}/ρ{sub i})→0 and ε{sub mc}(ρ{sub i}/ℓ)→0 (“asymptotic three-scale (A3S) limits”), these sub-layers are precisely defined. Using the smallness of the tilting angle of the magnetic field to the wall, the ion distribution functions are found for three sub-regions in the analytic form. The equations and characteristic length-scales governing the transition (intermediate) regions between the neighboring sub-layers (CPS – MPS and MPS – DS) are derived, allowing to avoid the singularities arising from the ε{sub Dm}→0 and ε{sub mc}→0 approximations. The MPS entrance and the related kinetic form of the Bohm–Chodura condition are successfully defined for the first time. At the DS entrance, the Bohm condition maintains its usual form. The results encourage further study and understanding of physics of the MPWT layers in the modern plasma facilities.

  4. Kinetic Monte Carlo Simulation of Epitaxial Thin Film Growth: Formation of Submonolayer Islands and Multilayer Mounds

    SciTech Connect

    Evans, J. W.; Thiel, P. A.; Li, Maozhi

    2007-06-14

    We consider homoepitaxy (or low-misfit heteroepitaxy) via vapor deposition or MBE under UHV conditions. Thin film growth is initiated by nucleation and growth of 2D islands in the submonolayer regime. For atoms subsequently deposited on top of islands, a step edge barrier often inhibits downward transport and produces kinetic roughening during multilayer growth. Such unstable growth is characterized by the formation of 3D mounds (multilayer stacks of 2D islands). Kinetic Monte Carlo (KMC) simulation of suitable atomistic lattice-gas models can address fundamental or general issues related to both submonolayer and multilayer film evolution, and can also provide a predictive tool for morphological evolution in specific systems. Examples of the successes of KMC modeling are provided for metal homoepitaxial film growth, specifically for contrasting behavior in the classic Ag/Ag(100) and Ag/Ag(111) systems.

  5. Natural History, Growth Kinetics and Outcomes of Untreated Clinically Localized Renal Tumors Under Active Surveillance

    PubMed Central

    Crispen, Paul L.; Viterbo, Rosalia; Boorjian, Stephen A.; Greenberg, Richard E.; Chen, David Y.T.; Uzzo, Robert G.

    2010-01-01

    Background The growth kinetics of untreated solid organ malignancies are not defined. Radiographic active surveillance (AS) of renal tumors in patient unfit or unwilling to undergo intervention provides an opportunity to quantitate the natural history of untreated localized tumors. Here we report the radiographic growth kinetics of renal neoplasms during a period of surveillance. Methods We identified patients with enhancing renal masses who were radiographically observed for at least 12 months. Clinical and pathological records were reviewed to determine tumor growth kinetics and clinical outcomes. Tumor growth kinetics were expressed in terms of absolute and relative linear and volumetric growth. Results We identified 172 renal tumors in 154 patients under AS. Median tumor diameter and volume on presentation was 2.0 cm (mean 2.5, range 0.4 - 12.0) and 4.18 cm3 (mean 20.0, range 0.0033 – 904). Median duration of follow-up was 24 months (mean 31, range 12 – 156). A significant association between presenting tumor size and proportional growth was noted, with smaller tumors growing faster than larger tumors. 39% (68/173) of tumors underwent delayed intervention and 84% (57/68) were pathologically malignant. Progression to metastatic disease was noted in 1.3% (2/154) of patients. Conclusions We demonstrate the association between a tumor’s volume and subsequent growth with smaller tumors exhibiting significantly faster volumetric growth than larger tumors, consistent with Gompertzian kinetics. Surveillance of localized renal tumors is associated with a low rate of disease progression in the intermediate term and suggests potential over-treatment biases in select patients. PMID:19402168

  6. Role of plasma activation in the kinetics of CNT growth in PECVD process

    NASA Astrophysics Data System (ADS)

    Lebedeva, Irina; Gavrikov, Alexey; Baranov, Alexey; Belov, Maxim; Knizhnik, Andrey; Potapkin, Boris; Sommerer, Timothy

    2009-10-01

    The work presents kinetic modeling of the effect of acceleration for the growth kinetics of carbon nanotubes by hydrocarbon gas mixture modification with plasma discharge. The plasma activation creates active species in hydrocarbon gas mixture, which can easily adsorb and dissociate on the catalyst surface. So plasma treatment of the gas mixture in the CVD process allows to increase the carbon supply rate by a few orders of magnitude compared to that in thermal CVD process. On the other hand, plasma can also provide etching of carbon species from the catalyst surface. To correctly reproduce both of these effects of plasma, the kinetic model of growth of carbon nanotubes is developed based on first-principles analysis of heterogeneous processes on the catalyst surface and detailed kinetics of gas phase chemistry. The model is used to compare the growth rates of carbon nanotubes in thermal and plasma-enhanced CVD processes and to determine critical gas pressures, at which CNT growth kinetics switches from the adsorption limitation to the limitation by reaction and diffusion on the catalyst.

  7. Epitaxial growth of tungsten layers on MgO(001)

    SciTech Connect

    Zheng, Pengyuan; Ozsdolay, Brian D.; Gall, Daniel

    2015-11-15

    Smooth single crystal W(001) layers were grown on MgO(001) substrates by magnetron sputtering at 900 °C. X-ray diffraction ω–2θ scans, ω-rocking curves, pole figures, and reciprocal space maps indicate a 45°-rotated epitaxial relationship: (001){sub W}‖(001){sub MgO} and [010]{sub W}‖[110]{sub MgO}, and a relaxed lattice constant of 3.167 ± 0.001 nm. A residual in-plane biaxial compressive strain is primarily attributed to differential thermal contraction after growth and decreases from −0.012 ± 0.001 to −0.001 ± 0.001 with increasing layer thickness d = 4.8–390 nm, suggesting relaxation during cooling by misfit dislocation growth through threading dislocation glide. The in-plane x-ray coherence length increases from 3.4 to 33.6 nm for d = 4.8–390 nm, while the out-of-plane x-ray coherence length is identical to the layer thickness for d ≤ 20 nm, but is smaller than d for d ≥ 49.7 nm, indicating local strain variations along the film growth direction. X-ray reflectivity analyses indicate that the root-mean-square surface roughness increases from 0.50 ± 0.05 to 0.95 ± 0.05 nm for d = 4.8–19.9 nm, suggesting a roughness exponent of 0.38, but remains relatively constant for d > 20 nm with a roughness of 1.00 ± 0.05 nm at d = 47.9 nm.

  8. Crystallization of pumpkin seed globulin: growth and dissolution kinetics

    NASA Astrophysics Data System (ADS)

    Malkin, Alexander J.; McPherson, Alexander

    1993-10-01

    Quasi-elastic light scattering was used to investigate the nucleation and crystallization of pumpkin ( Cucurbita) seed globulin. The diameter of the pumpkin globulin monomer was measured to be ≈ 5-6 nm. The supersaturation dependence of critical nucleus size was obtained, and this allowed an estimate of the interfacial free energy to be α ≈ 6.1 x 10 -2 erg/cm 2. The crystallization and dissolution kinetics were investigated for 4.9-16 mg/ml protein solutions containing 1-7% NaCl. The solubility data as a function of precipitant concentration and temperature were obtained and these will be utilized for optimization of the crystallization conditions for the pumpkin globulin.

  9. Self-consistent ion-by-ion growth model for kinetic isotopic fractionation during calcite precipitation

    NASA Astrophysics Data System (ADS)

    Nielsen, Laura C.; DePaolo, Donald J.; De Yoreo, James J.

    2012-06-01

    Microscopic mechanisms operating at the mineral-aqueous interface control rates of growth and dissolution, isotope fractionation and trace element partitioning during crystal growth. Despite the importance of characterizing surface kinetic controls on isotopic partitioning, no self-consistent microscopic theory has yet been presented which can simultaneously model both mineral growth rate and isotopic composition. Using a kinetic theory for AB or di-ionic crystal growth, we derive a model to predict precipitation rate and isotope fractionation as a function of growth solution oversaturation and solution stoichiometry and apply the theory to calcium isotope fractionation during calcite precipitation. Our model assimilates the current understanding of surface controlled isotope fractionation with kinetic theories of ion-by-ion mineral growth to predict isotopic partitioning during the growth of ionic crystals. This approach accounts for the effect of solution composition on microscopic mineral surface structure and composition, providing numerous testable hypotheses for growth of sparingly soluble AB crystals such as calcite, namely: Both oversaturation and solution stoichiometry control growth rate and partitioning of isotopes during precipitation; for growth driven primarily by step propagation, distinct expressions describe dislocation- and 2D nucleation-driven growth rates, while the expression for isotope fractionation is the same for both mechanisms; mineral precipitation occurring via the formation of an amorphous precursor will generate isotope effects that are not compatible with ion-by-ion growth theory and may therefore be excluded from comparison; and, the absolute kinetic limit of isotope fractionation may not be accessible at high oversaturation due to the formation of amorphous precursors. Using calcite as a model system, we derive expressions for growth rate and isotopic fractionation as a function of oversaturation and Ca:CO32- in solution

  10. An Estimation of Turbulent Kinetic Energy and Energy Dissipation Rate Based on Atmospheric Boundary Layer Similarity Theory

    NASA Technical Reports Server (NTRS)

    Han, Jongil; Arya, S. Pal; Shaohua, Shen; Lin, Yuh-Lang; Proctor, Fred H. (Technical Monitor)

    2000-01-01

    Algorithms are developed to extract atmospheric boundary layer profiles for turbulence kinetic energy (TKE) and energy dissipation rate (EDR), with data from a meteorological tower as input. The profiles are based on similarity theory and scalings for the atmospheric boundary layer. The calculated profiles of EDR and TKE are required to match the observed values at 5 and 40 m. The algorithms are coded for operational use and yield plausible profiles over the diurnal variation of the atmospheric boundary layer.

  11. The kinetics of parasitic growth in GaAs MOVPE

    NASA Astrophysics Data System (ADS)

    Clayton, A. J.; Irvine, S. J. C.

    2007-03-01

    Gallium arsenide (GaAs) deposition was carried out in a horizontal quartz reactor tube with trimethylgallium (TMGa) and arsine (AsH 3) as precursors, using a hydrogen (H 2) carrier gas. Temperatures were in the range 400-500 °C, where surface reactions limit deposition rate. Nucleation time and deposition rate were monitored using laser interferometry, optimum reflectance was gained by aligning a quartz wafer to back reflect the incident beam. The 980 nm infrared laser beam was sufficiently long in wavelength to be able to penetrate the wall deposit. Results showing the effect of temperature and V/III ratio on the nucleation time and deposition rate are presented, where with temperature the nucleation delay was observed to reduce and the growth rate to increase. The nucleation delay is consistent with a thermally activated surface nucleation for the parasitic GaAs. A theoretical growth rate model, based on a restricted set of reaction steps was used to compare with the experimental growth rates. Without any free parameters, the growth rates from theoretical calculation and experiment agreed within a factor of two and showed the same trends with V/III ratio and temperature. The non-linearity of the theoretical growth rates on an Arrhenius plot indicates that there is more than one dominant reaction step over the temperature range investigated. The range of experimental activation energies, calculated from Arrhenius plots, was 17.56-23.59 kJ mol -1. A comparison of these activation energies and minimum deposition temperature with the literature indicates that the wall temperature measurement on an Aixtron reactor is over 100 °C higher than previously reported.

  12. Graphene Layer Growth Chemistry: Five-Six-Ring Flip Reaction

    SciTech Connect

    Whitesides, R.; Domin, D.; Salomon-Ferrer, R.; Lester Jr., W.A.; Frenklach, M.

    2007-12-01

    Reaction pathways are presented for hydrogen-mediated isomerization of a five and six member carbon ring complex on the zigzag edge of a graphene layer. A new reaction sequence that reverses orientation of the ring complex, or 'flips' it, was identified. Competition between the flip reaction and 'ring separation' was examined. Ring separation is the reverse of the five and six member ring complex formation reaction, previously reported as 'ring collision'. The elementary steps of the pathways were analyzed using density-functional theory (DFT). Rate coefficients were obtained by solution of the energy master equation and classical transition state theory utilizing the DFT energies, frequencies, and geometries. The results indicate that the flip reaction pathway dominates the separation reaction and should be competitive with other pathways important to the graphene zigzag edge growth in high temperature environments.

  13. Biopolymer immobilization during the crystalline growth of layered double hydroxide

    NASA Astrophysics Data System (ADS)

    Leroux, Fabrice; Gachon, Julien; Besse, Jean-Pierre

    2004-01-01

    Alginic acid, a biopolymer produced by brown seaweed, is incorporated between the sheets of a layered double hydroxide (LDH) via direct coprecipitation. The growth of the inorganic crystalline seeds over the polymer gives rise to a lamellar structure. The obtained nanocomposite presents a basal spacing in agreement with the ideal picture of the polymer lying perpendicularly to the inorganic sheets. A study using FTIR and 13C CP-MAS spectroscopies suggests that the interaction between the organic guest and the inorganic framework is weak. However, the polymer has a stabilizing effect in temperature, since ZnO is observed at 350°C, whereas it appears at 200°C for the chloride LDH pristine material.

  14. Growth of transition metals on cerium tungstate model catalyst layers.

    PubMed

    Skála, T; Tsud, N; Stetsovych, V; Mysliveček, J; Matolín, V

    2016-10-01

    Two model catalytic metal/oxide systems were investigated by photoelectron spectroscopy and scanning tunneling microscopy. The mixed-oxide support was a cerium tungstate epitaxial thin layer grown in situ on the W(1 1 0) single crystal. Active particles consisted of palladium and platinum 3D islands deposited on the tungstate surface at 300 K. Both metals were found to interact weakly with the oxide support and the original chemical state of both support and metals was mostly preserved. Electronic and morphological changes are discussed during the metal growth and after post-annealing at temperatures up to 700 K. Partial transition-metal coalescence and self-cleaning from the CO and carbon impurities were observed. PMID:27494195

  15. Kinetic surface roughening and wafer bow control in heteroepitaxial growth of 3C-SiC on Si(111) substrates.

    PubMed

    Wang, Li; Walker, Glenn; Chai, Jessica; Iacopi, Alan; Fernandes, Alanna; Dimitrijev, Sima

    2015-01-01

    A thin, chemically inert 3C-SiC layer between GaN and Si helps not only to avoid the "melt-back" effect, but also to inhibit the crack generation in the grown GaN layers. The quality of GaN layer is heavily dependent on the unique properties of the available 3C-SiC/Si templates. In this paper, the parameters influencing the roughness, crystalline quality, and wafer bow are investigated and engineered to obtain high quality, low roughness 3C-SiC/Si templates suitable for subsequent GaN growth and device processing. Kinetic surface roughening and SiC growth mechanisms, which depend on both deposition temperature and off-cut angle, are reported for heteroepitaxial growth of 3C-SiC on Si substrates. The narrower terrace width on 4° off-axis Si enhances the step-flow growth at 1200 °C, with the roughness of 3C-SiC remaining constant with increasing thickness, corresponding to a scaling exponent of zero. Crack-free 3C-SiC grown on 150-mm Si substrate with a wafer bow of less than 20 μm was achieved. Both concave and convex wafer bow can be obtained by in situ tuning of the deposited SiC layer thicknesses. The 3C-SiC grown on off-axis Si, compared to that grown on on-axis Si, has lower surface roughness, better crystallinity, and smaller bow magnitude. PMID:26487465

  16. Kinetic surface roughening and wafer bow control in heteroepitaxial growth of 3C-SiC on Si(111) substrates

    PubMed Central

    Wang, Li; Walker, Glenn; Chai, Jessica; Iacopi, Alan; Fernandes, Alanna; Dimitrijev, Sima

    2015-01-01

    A thin, chemically inert 3C-SiC layer between GaN and Si helps not only to avoid the “melt-back” effect, but also to inhibit the crack generation in the grown GaN layers. The quality of GaN layer is heavily dependent on the unique properties of the available 3C-SiC/Si templates. In this paper, the parameters influencing the roughness, crystalline quality, and wafer bow are investigated and engineered to obtain high quality, low roughness 3C-SiC/Si templates suitable for subsequent GaN growth and device processing. Kinetic surface roughening and SiC growth mechanisms, which depend on both deposition temperature and off-cut angle, are reported for heteroepitaxial growth of 3C-SiC on Si substrates. The narrower terrace width on 4° off-axis Si enhances the step-flow growth at 1200 °C, with the roughness of 3C-SiC remaining constant with increasing thickness, corresponding to a scaling exponent of zero. Crack-free 3C-SiC grown on 150-mm Si substrate with a wafer bow of less than 20 μm was achieved. Both concave and convex wafer bow can be obtained by in situ tuning of the deposited SiC layer thicknesses. The 3C-SiC grown on off-axis Si, compared to that grown on on-axis Si, has lower surface roughness, better crystallinity, and smaller bow magnitude. PMID:26487465

  17. When is one layer complete? Using simultaneous in-situ RHEED and x-ray reflectivity to map layer-by-layer thin-film oxide growth

    NASA Astrophysics Data System (ADS)

    Sullivan, M. C.; Ward, M. J.; Joress, H.; Gutierrez-Llorente, A.; White, A. E.; Woll, A.; Brock, J. D.

    2014-03-01

    The most popular tool for characterizing in situ layer-by-layer growth is Reflection High-Energy Electron Diffraction (RHEED). X-ray reflectivity can also be used to study layer-by-layer growth, as long as the incident angle of the x-rays is far from a Bragg peak. During layer-by-layer homoepitaxial growth, both the RHEED intensity and the reflected x-ray intensity will oscillate, and each complete oscillation indicates the addition of one layer of material. However, it is well documented, but not well understood, that the maxima in the RHEED intensity oscillations do not necessarily occur at the completion of a layer. In contrast, the maxima in the x-ray intensity oscillations do occur at the completion of a layer, thus the RHEED and x-ray oscillations are rarely in phase. We present our results on simultaneous in situ x-ray reflectivity and RHEED during layer-by-layer growth of SrTiO3 and discuss how to determine the completion of a layer for RHEED oscillations independent of the phase of the RHEED oscillation. Supported by DOE Office of Basic Energy Sciences Award DE-SC0001086, CHESS is supported by the NSF & NIH/NIGMS via NSF award DMR-0936384.

  18. The first layer of water on Rh(111): Microscopic structure and desorption kinetics

    SciTech Connect

    Beniya, Atsushi; Yamamoto, Susumu; Mukai, Kozo; Yamashita, Yoshiyuki; Yoshinobu, Jun

    2006-08-07

    The adsorption states and growth process of the first water (D{sub 2}O) layer on Rh(111) were investigated using infrared reflection absorption spectroscopy, temperature programed desorption, and spot-profile-analysis low energy electron diffraction. Water molecules wet the Rh(111) surface intact. At the early stage of first layer growth, a ({radical}3x{radical}3)R30 deg. commensurate water layer grows where 'up' and 'down' species coexist; the up and down species represent water molecules which have free OD, pointing to a vacuum and the substrate, respectively. The up domain was a flatter structure than an icelike bilayer. Water desorption from Rh(111) was a half-order process. The activation energy and the preexponential factor of desorption are estimated to be 60 kJ/mol and 4.8x10{sup 16} ML{sup 1/}2/s at submonolayer coverage, respectively. With an increase in water coverage, the flat up domain becomes a zigzag layer, like an ice bilayer. At the saturation coverage, the amount of down species is 1.3 times larger than that of the up species. In addition, the activation energy and the preexponential factor of desorption decrease to 51 kJ/mol and 1.3x10{sup 14} ML{sup 1/2}/s, respectively.

  19. Modified Gompertz equation for electrotherapy murine tumor growth kinetics: predictions and new hypotheses

    PubMed Central

    2010-01-01

    Background Electrotherapy effectiveness at different doses has been demonstrated in preclinical and clinical studies; however, several aspects that occur in the tumor growth kinetics before and after treatment have not yet been revealed. Mathematical modeling is a useful instrument that can reveal some of these aspects. The aim of this paper is to describe the complete growth kinetics of unperturbed and perturbed tumors through use of the modified Gompertz equation in order to generate useful insight into the mechanisms that underpin this devastating disease. Methods The complete tumor growth kinetics for control and treated groups are obtained by interpolation and extrapolation methods with different time steps, using experimental data of fibrosarcoma Sa-37. In the modified Gompertz equation, a delay time is introduced to describe the tumor's natural history before treatment. Different graphical strategies are used in order to reveal new information in the complete kinetics of this tumor type. Results The first stage of complete tumor growth kinetics is highly non linear. The model, at this stage, shows different aspects that agree with those reported theoretically and experimentally. Tumor reversibility and the proportionality between regions before and after electrotherapy are demonstrated. In tumors that reach partial remission, two antagonistic post-treatment processes are induced, whereas in complete remission, two unknown antitumor mechanisms are induced. Conclusion The modified Gompertz equation is likely to lead to insights within cancer research. Such insights hold promise for increasing our understanding of tumors as self-organizing systems and, the possible existence of phase transitions in tumor growth kinetics, which, in turn, may have significant impacts both on cancer research and on clinical practice. PMID:21029411

  20. Kinetics of Ge-Se-In Film Growth

    SciTech Connect

    Stoilova, A.; Petkov, P.; Nedeva, Y.; Monchev, B.

    2010-01-21

    The processes of vacuum evaporation and condensation in the Ge-Se-In system were investigated. Thin amorphous films were deposited by modified thermal evaporation from previously synthesized non-crystalline (GeSe{sub y}){sub 1-x}In{sub x} ingots, where x = 0, 5, 10, 15, 20 and y = 4, 5 and 6. The specific evaporation rate was determined by measuring of the mass of evaporator before evaporation and the mass of empty evaporator after evaporation in temperature range of evaporation (500-800) K. The substrate temperature was varied in the range (300-430) K to study the condensation process and specific condensation rate was determined by measuring of the substrate mass before and after condensation. The condensation energy of the (GeSe{sub y}){sub 1-x}In{sub x} layers steady increases at indium addition.The thin films studied by transmission electron microscopy (TEM) and electron microdiffraction (EMD) reveal homogeneous and amorphous structure. The layer composition determined by Auger electron spectroscopy is close to that of the corresponded bulk samples.

  1. Kinetics of endothelialization of the multilayer flow modulator and single-layer arterial stents.

    PubMed

    Sultan, Sherif; Kavanagh, Edel P; Bonneau, Michel; Kang, Chantal; Alves, Antoine; Hynes, Niamh M

    2016-02-01

    The multilayer flow modulator (MFM; Cardiatis, Isnes, Belgium) is a self-expandable mesh of braided cobalt alloy wires, used for treatment of aortic and peripheral aneurysms. To further improve our understanding of this novel technology, the endothelialization kinetics of the MFM was investigated and compared with those of two marketed single-layer stents. Five porcine animal models were used in which a total of 19 stents were implanted in the iliac and carotid arteries between one and five weeks before sacrifice. All 19 stents were successfully delivered. For all devices, nonsignificant signs of inflammation or thrombosis were noted, and there was no evidence of local intolerance. The MFM developed a thin layer of endothelial cells earlier and was associated with less neointimal development than the two single-layer stents. A differing phenomenon of integration was also revealed and hypothesized as endothelialization from adhesion of circulating endothelial progenitor cells, as well as adhesion from the arterial wall, and also by the differences in trauma exposed to the arterial wall. PMID:25957343

  2. Nanoporous anodic titanium dioxide layers as potential drug delivery systems: Drug release kinetics and mechanism.

    PubMed

    Jarosz, Magdalena; Pawlik, Anna; Szuwarzyński, Michał; Jaskuła, Marian; Sulka, Grzegorz D

    2016-07-01

    Nanoporous anodic titanium dioxide (ATO) layers on Ti foil were prepared via a three step anodization process in an electrolyte based on an ethylene glycol solution with fluoride ions. Some of the ATO samples were heat-treated in order to achieve two different crystallographic structures - anatase (400°C) and a mixture of anatase and rutile (600°C). The structural and morphological characterizations of ATO layers were performed using a field emission scanning electron microscope (SEM). The hydrophilicity of ATO layers was determined with contact angle measurements using distilled water. Ibuprofen and gentamicin were loaded effectively inside the ATO nanopores. Afterwards, an in vitro drug release was conducted for 24h under a static and dynamic flow conditions in a phosphate buffer solution at 37°C. The drug concentrations were determined using UV-Vis spectrophotometry. The absorbance of ibuprofen was measured directly at 222nm, whether gentamicin was determined as a complex with silver nanoparticles (Ag NPs) at 394nm. Both compounds exhibited long term release profiles, despite the ATO structure. A new release model, based on the desorption of the drug from the ATO top surface followed by the desorption and diffusion of the drug from the nanopores, was derived. The proposed release model was fitted to the experimental drug release profiles, and kinetic parameters were calculated. PMID:27037782

  3. The logistic growth of duckweed (Lemna minor) and kinetics of ammonium uptake.

    PubMed

    Zhang, Kun; Chen, You-Peng; Zhang, Ting-Ting; Zhao, Yun; Shen, Yu; Huang, Lei; Gao, Xu; Guo, Jin-Song

    2014-01-01

    Mathematical models have been developed to describe nitrogen uptake and duckweed growth experimentally to study the kinetics of ammonium uptake under various concentrations. The kinetics of duckweed ammonium uptake was investigated using the modified depletion method after plants were grown for two weeks at different ammonium concentrations (0.5-14 mg/L) in the culture medium. The maximum uptake rate and Michaelis-Menten constant for ammonium were estimated as 0.082 mg/(g fresh weight x h) and 1.877 mg/L, respectively. Duckweed growth was assessed when supplied at different total nitrogen (TN) concentrations (1-5 mg/L) in the culture medium. The results showed that the intrinsic growth rate was from 0.22 to 0.26 d(-1), and TN concentrations had no significant influence on the duckweed growth rate. PMID:24645435

  4. Nonlinear estimation of Monod growth kinetic parameters from a single substrate depletion curve.

    PubMed Central

    Robinson, J A; Tiedje, J M

    1983-01-01

    Monod growth kinetic parameters were estimated by fitting sigmoidal substrate depletion data to the integrated Monod equation, using nonlinear least-squares analysis. When the initial substrate concentration was in the mixed-order region, nonlinear estimation of simulated data sets containing known measurement errors provided accurate estimates of the mu max, Ks, and Y values used to create these data. Nonlinear regression analysis of sigmoidal substrate depletion data was also evaluated for H2-limited batch growth of Desulfovibrio sp. strain G11. The integrated Monod equation can be more convenient for the estimation of growth kinetic parameters, particularly for gaseous substrates, but it must be recognized that the estimates of mu max, Ks, and Y obtained may be influenced by the growth rate history of the inoculum. PMID:6870238

  5. Kinetic analysis of MgB2 layer formation in advanced internal magnesium infiltration (AIMI) processed MgB2 wires

    PubMed Central

    Li, G. Z.; Sumption, M. D.; Collings, E. W.

    2015-01-01

    Significantly enhanced critical current density (Jc) for MgB2 superconducting wires can be obtained following the advanced internal Mg infiltration (AIMI) route. But unless suitable precautions are taken, the AIMI-processed MgB2 wires will exhibit incomplete MgB2 layer formation, i.e. reduced superconductor core size and hence suppressed current-carrying capability. Microstructural characterization of AIMI MgB2 wires before and after the heat treatment reveals that the reaction mechanism changes from a “Mg infiltration-reaction” at the beginning of the heat treatment to a “Mg diffusion-reaction” once a dense MgB2 layer is formed. A drastic drop in the Mg transport rate from infiltration to diffusion causes the termination of the MgB2 core growth. To quantify this process, a two-stage kinetic model is built to describe the MgB2 layer formation and growth. The derived kinetic model and the associated experimental observations indicate that fully reacted AIMI-processed MgB2 wires can be achieved following the optimization of B particle size, B powder packing density, MgB2 reaction activation energy and its response to the additions of dopants. PMID:26973431

  6. Kinetic Roughening and Energetics of Tetragonal Lysozyme Crystal Growth: A Preliminary Atomic Force Microscopy Investigation

    NASA Technical Reports Server (NTRS)

    Gorti, Sridhar; Forsythe, Elizabeth L.; Pusey, Marc L.

    2004-01-01

    We examined particulars of crystal growth from measurements obtained at both microscopic and molecular levels. The crystal growth measurements performed at the microscopic level are well characterized by a model that balances the flux of macromolecules towards the crystal surface with the flux of the crystal surface. Numerical evaluation of model with measurements of crystal growth, in time, provided accurate estimates for the average growth velocities. Growth velocities thus obtained were also interpreted using well-established phenomenological theories. Moreover, we find that microscopic measurements of growth velocity measurements obtained as a function of temperature best characterizes changes in crystal growth modes, when present. We also examined the possibility of detecting a change in crystal growth modes at the molecular level using atomic force microscopy, AFM. From preliminary AFM measurements performed at various supersaturations, we find that magnitude of surface height fluctuations, h(x), increases with supersaturation. Further examination of surface height fluctuations using methods established for fluctuation spectroscopy also enabled the discovery of the existence of a characteristic length, c, which may possibly determine the mode of crystal growth. Although the results are preliminary, we establish the non- critical divergence of 5 and the root-mean-square (rms) magnitude of height-height fluctuations as the kinetic roughening transition temperatures are approached. Moreover, we also examine approximate models for interpreting the non-critical behavior of both 6 and rms magnitude of height-height fluctuations, as the solution supersaturation is increased towards the kinetic roughening supersaturation.

  7. COMPARATIVE KINETIC STUDIES OF PHOSPHATE-LIMITED GROWTH AND PHOSPHATE UPTAKE IN PHYTOPLANKTON IN CONTINUOUS CULTURE

    EPA Science Inventory

    A comparative kinetic study of phosphate-limited growth and phosphate uptake was carried out in chemostat cultures of Anabaena flos-aquae Lyng. Breb., Ankistrodesmus falcatus (Corda) Ralfs, Asterionella formosa Hass., Fragilaria crotonensis Kitt., and Microcystis sp. Lemm. For ea...

  8. Growth Kinetics of Intracellular RNA/Protein Droplets: Signature of a Liquid-Liquid Phase Transition?

    NASA Astrophysics Data System (ADS)

    Berry, Joel; Weber, Stephanie C.; Vaidya, Nilesh; Zhu, Lian; Haataja, Mikko; Brangwynne, Clifford P.

    2015-03-01

    Nonmembrane-bound organelles are functional, dynamic assemblies of RNA and/or protein that can self-assemble and disassemble within the cytoplasm or nucleoplasm. The possibility that underlying intracellular phase transitions may drive and mediate the morphological evolution of some membrane-less organelles has been supported by several recent studies. In this talk, results from a collaborative experimental-theoretical study of the growth and dissolution kinetics of nucleoli and extranucleolar droplets (ENDs) in C. elegans embryos will be presented. We have employed Flory-Huggins solution theory, reaction-diffusion kinetics, and quantitative statistical dynamic scaling analysis to characterize the specific growth mechanisms at work. Our findings indicate that both in vivo and in vitro droplet scaling and growth kinetics are consistent with those resulting from an equilibrium liquid-liquid phase transition mediated by passive nonequilibrium growth mechanisms - simultaneous Brownian coalescence and Ostwald ripening. This supports a view in which cells can employ phase transitions to drive structural organization, while utilizing active processes, such as local transcriptional activity, to fine tune the kinetics of these phase transitions in response to given conditions.

  9. Mathematical modeling and growth kinetics of Clostridium sporogenes in cooked beef

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Clostridium sporogenes PA 3679 is a common surrogate for proteolytic Clostridium botulinum for thermal process development and validation. However, little information is available concerning the growth kinetics of C. sporogenes in food. Therefore, the objective of this study was to investigate the...

  10. Effect of blanching on thin layer drying kinetics of aonla (Emblica officinalis) shreds.

    PubMed

    Gupta, R K; Sharma, Alka; Kumar, Pradeep; Vishwakarma, R K; Patil, R T

    2014-07-01

    The effect of hot water blanching treatment on thin layer drying kinetics of aonla shreds was studied at drying air temperatures of 50, 55 and 60 °C with the air velocity of 1.2 m/s. The drying time decreased with the increase in air temperature and blanching. The drying process was observed in falling rate. Drying after blanching reduced the vitamin C content of aonla shreds by 69.36% whereas it decreased by 27.78% in unblanched shreds. Eight commonly used mathematical models were evaluated to predict the drying behavior of aonla shreds. The Midilli model described the drying behaviour of unblanched aonla shreds at all temperatures better than other models whereas two-term model described the drying kinetics of blanched aonla shreds satisfactorily. The effective diffusivities of the unblanched and blanched aonla shreds were determined using Fick's law of diffusion. The activation energy was found to be 47.21 kJ/mol for unblanched and 43.98 kJ/mol for blanched aonla shreds. PMID:24966422

  11. Crystalline Grain Interior Configuration Affects Lithium Migration Kinetics in Li-Rich Layered Oxide.

    PubMed

    Yu, Haijun; So, Yeong-Gi; Kuwabara, Akihide; Tochigi, Eita; Shibata, Naoya; Kudo, Tetsuichi; Zhou, Haoshen; Ikuhara, Yuichi

    2016-05-11

    The electrode kinetics of Li-ion batteries, which are important for battery utilization in electric vehicles, are affected by the grain size, crystal orientation, and surface structure of electrode materials. However, the kinetic influences of the grain interior structure and element segregation are poorly understood, especially for Li-rich layered oxides with complex crystalline structures and unclear electrochemical phenomena. In this work, cross-sectional thin transmission electron microscopy specimens are "anatomized" from pristine Li1.2Mn0.567Ni0.167Co0.067O2 powders using a new argon ion slicer technique. Utilizing advanced microscopy techniques, the interior configuration of a single grain, multiple monocrystal-like domains, and nickel-segregated domain boundaries are clearly revealed; furthermore, a randomly distributed atomic-resolution Li2MnO3-like with an intergrown LiTMO2 (TM = transitional metals) "twin domain" is demonstrated to exist in each domain. Further theoretical calculations based on the Li2MnO3-like crystal domain boundary model reveal that Li(+) migration in the Li2MnO3-like structure with domain boundaries is sluggish, especially when the nickel is segregated in domain boundaries. Our work uncovers the complex configuration of the crystalline grain interior and provides a conceptual advance in our understanding of the electrochemical performance of several compounds for Li-ion batteries. PMID:27088669

  12. Mechanism And Kinetics Of Silylation Of Resist Layers From The Gas Phase

    NASA Astrophysics Data System (ADS)

    Visser, Robert-Jan; Schellekens, Jack P.; Reuhman-Huisken, Marian E.; Van Ijzendoorn, Leo J.

    1987-08-01

    The silylation from the gas phase of photoresists based on diazoquinone and novolac or polyvinylphenol, which can be used in dry developable systems has been investigated. It is shown that the phenolic hydroxyl groups are almost completely silylated. The kinetics of the reaction have been followed by gravimetry, IR spectroscopy and Rutherford backscattering spectrometry. During the reaction a completely silylated, swollen layer is formed with a sharp front separating it from the unreacted resin. The rate controlling processes are the relaxation of the polymer and the diffusion of the reagent. When the relaxation is slow with respect to diffusion, linear reaction kinetics as in Case II diffusion are observed. When the relaxation is fast the reaction proceeds with the square root of time. The increase of the reaction rate with UV exposure of the resist is attributed to an increase in the relaxation rate of the resist. A model explains the higher photoselectivity of the reaction at elevated temperatures. Results with a number of model resists indicate that some diazoquinones can act as physical crosslinks between polymer chains via the formation of hydrogen bonds whereas the corresponding indenecarboxylic acids cannot. Due to the high content of silicon after the treatment these resists become highly etch-resistant towards oxygen plasmas.

  13. Mechanism And Kinetics Of Silylation Of Resist Layers From The Gas Phase

    NASA Astrophysics Data System (ADS)

    Visser, Robert-Jan; Schellekens, Jack P. W.; Reuhman-Huisken, Marian E.

    1987-09-01

    The silylation from the gas phase of photoresists based on diazoquinone and novolac or polyvinylphenol, which can be used in dry developable systems has been investigated. It is shown that the phenolic hydroxyl groups are almost completely silylated. The kinetics of the reaction have been followed by gravimetry, IR spectroscopy and Rutherford backscattering spectrometry. During the reaction a completely silylated, swollen layer is formed with a sharp front separating it from the unreacted resin. The rate control-ling processes are the relaxation of the polymer and the diffusion of the reagent. When the relaxation is slow with respect to diffusion, linear reaction kinetics as in Case II diffusion are observed. When the relaxation is fast the reaction proceeds with the square root of time. The increase of the reaction rate with UV exposure of the resist is attributed to an increase in the relaxation rate of the resist. A model explains the higher photoselectivity of the reaction at elevated temperatures. Results with a number of model resists indicate that some diazoquinones can act as physical crosslinks between polymer chains via the formation of hydrogen bonds whereas the corresponding in-denecarboxylic acids cannot. Due to the high content of silicon after the treatment these resists become highly etch-resistant towards oxygen plasmas.

  14. Atomistic kinetic Monte Carlo study of atomic layer deposition derived from density functional theory.

    PubMed

    Shirazi, Mahdi; Elliott, Simon D

    2014-01-30

    To describe the atomic layer deposition (ALD) reactions of HfO2 from Hf(N(CH3)2)4 and H2O, a three-dimensional on-lattice kinetic Monte-Carlo model is developed. In this model, all atomistic reaction pathways in density functional theory (DFT) are implemented as reaction events on the lattice. This contains all steps, from the early stage of adsorption of each ALD precursor, kinetics of the surface protons, interaction between the remaining precursors (steric effect), influence of remaining fragments on adsorption sites (blocking), densification of each ALD precursor, migration of each ALD precursors, and cooperation between the remaining precursors to adsorb H2O (cooperative effect). The essential chemistry of the ALD reactions depends on the local environment at the surface. The coordination number and a neighbor list are used to implement the dependencies. The validity and necessity of the proposed reaction pathways are statistically established at the mesoscale. The formation of one monolayer of precursor fragments is shown at the end of the metal pulse. Adsorption and dissociation of the H2O precursor onto that layer is described, leading to the delivery of oxygen and protons to the surface during the H2O pulse. Through these processes, the remaining precursor fragments desorb from the surface, leaving the surface with bulk-like and OH-terminated HfO2, ready for the next cycle. The migration of the low coordinated remaining precursor fragments is also proposed. This process introduces a slow reordering motion (crawling) at the mesoscale, leading to the smooth and conformal thin film that is characteristic of ALD. PMID:24249148

  15. Grain growth kinetics during ion beam irradiation of chemical vapor deposited amorphous silicon

    SciTech Connect

    Spinella, C.; Lombardo, S. ); Campisano, S.U. )

    1990-08-06

    The amorphous to polycrystal transition during Kr ion beam irradiation of chemical vapor deposited silicon layers has been studied in the temperature range 320--480 {degree}C. At each irradiation temperature the average grain diameter increases linearly with the Kr dose, while the grain density remains constant within the experimental accuracy. The growth rate follows a complex behavior which can be described by dynamic defect generation and annihilation. The absolute value of the grain growth rate is equal to that of the ion-assisted epitaxial layer by layer crystallization in the silicon (111) orientation. This result can be related to the crystal grain structure and morphology.

  16. Growth kinetics of three species of Tetrahymena on solid agar

    SciTech Connect

    Dobra, K.W.; McArdle, E.W.; Ehret, C.F.

    1980-01-01

    A nutrient-agar method without liquid overlay has been developed for cultivation of ciliates. Three species of Tetrahymena-T. pyriformis strain W, T. rostrata strain UNI, and T. vorax strain V/sub 2/S, representing the 3 main groups of Tetrahymena species, were used; however the method should apply to other ciliates. Growth on the surface of the agar was facilitated by an optimal surface-to-volume ratio yielding a high density of ciliates and short generation times. At the highest density achieved, the cells became irregularly hexagonal and formed a monolayer tissue on the agar. Ciliates grown on agar were like those in liquid culture, typical oral ciliature, food-vacuole formation, and typical cortical patterns being retained. Advantages of this method include high cell density, easy recovery, and optimal O/sub 2/ supply. The organisms can also be cultivated on the surface of sterile cellulose-nitrate filters, facilitating in situ fixation and staining as well as transfer into different media by transfer of filters with cells, without prior centrifugation and resuspension.

  17. Growth of high quality GaN layer on carbon nanotube-graphene network structure as intermediate layer

    NASA Astrophysics Data System (ADS)

    Seo, Taeo Hoon; Park, Ah Hyun; Park, Sungchan; Kim, Myung Jong; Suh, Eun-Kyung

    2015-03-01

    In general, high-quality GaN layers are synthesized on low-temperature (LT) GaN buffer layer on a single crystal sapphire substrate. However, large differences in fundamental properties such as lattice constants and thermal expansion coefficients between GaN layer and sapphire substrate generate high density of threading dislocation (TD) that leads to deterioration of optical and structural properties. Graphene has been attracting much attention due to its excellent physical properties However, direct epitaxial growth of GaN film onto graphene layer on substrates is not easily accessible due to the lack of chemical reactivity on graphene which consisted of C-C bond of sp2 hexagonally arranged carbon atoms with no dangling bonds. In this work, an intermediate layer for the GaN growth on sapphire substrate was constructed by inserting carbon nanotubes and graphene hybrid structure (CGH) Optical and structural properties of GaN layer grown on CGH were compared with those of GaN layer directly grown on sapphire CNTs act as nucleation sites and play a crucial role in the growth of single crystal high-quality GaN on graphene layer. Also, graphene film acts as a mask for epitaxial lateral overgrowth of GaN layer, which can effectively reduce TD density. A grant from the Korea Institute of Science and Technology (KIST) institutional program.

  18. Critical-layer nonlinearity in the resonance growth of three-dimensional waves in boundary layers

    NASA Technical Reports Server (NTRS)

    Mankbadi, Reda R.

    1990-01-01

    The nonlinear interactions of a triad of initially linear stability waves are addressed. The triad consisted of a single two-dimensional mode at a given frequency and two oblique modes with equal and opposite spanwise wave numbers. The oblique waves were at half the frequency and streamwise wave number of the two-dimensional mode. Attention was focused on the boundary-layer transition at low frequencies and high Reynolds numbers. A five-zoned structure and low-frequency scaling were used to derive the nonlinear-interaction equations. The initial nonlinear development of the waves was analyzed; the results indicated that the two-dimensional wave behaves according to linear theory. Nonlinear interactions caused exponential-of-an-exponential growth of the oblique modes. This resonant amplification of the subharmonic depended on the initial amplitude of the two-dimensional wave and on the initial phase angle between the two-dimensional wave and the oblique waves. The resonant growth of the oblique modes was more pronounced at lower frequencies than at higher frequencies. The results are in good agreement with experimental results and offer explanations of the observed process.

  19. Kinetics of growth of thin-films of Co2Si, Ni2Si, WSi2 and VSi2 during a reactive diffusion process

    NASA Astrophysics Data System (ADS)

    Akintunde, S. O.; Selyshchev, P. A.

    A theoretical approach is developed which describes the growth kinetics of thin films of near noble metal silicide (especially of cobalt silicide (Co2Si) and nickel silicide (Ni2Si)) and refractory metal silicide (particularly of tungsten disilicide (WSi2) and vanadium disilicide (VSi2)) at the interfaces of metal-silicon system. In this approach, metal species are presented as A-atoms, silicon as B-atoms, and silicide as AB-compound. The AB-compound is formed as a result of chemical transformation between A- and B-atoms at the reaction interfaces A/AB and AB/B. The growth of AB-compound at the interfaces occurs in two stages. The first growth stage is reaction controlled stage which takes place at the interface with excess A or B-atoms and the second stage is diffusion limited stage which occurs at both interfaces. The critical thickness of AB-compound and the corresponding time is determined at the transition point between the two growth stages. The result that follows from this approach shows that the growth kinetics of any growing silicides depends on the number of kinds of dominant diffusing species in the silicide layer and also on their number densities at the reaction interface. This result shows a linear-parabolic growth kinetics for WSi2, VSi2, Co2Si, and Ni2Si and it is in good agreement with experiment.

  20. Diameter-Independent Kinetics in the Vapor-Liquid-Solid Growth of Si Nanowires

    NASA Astrophysics Data System (ADS)

    Kodambaka, S.; Tersoff, J.; Reuter, M. C.; Ross, F. M.

    2006-03-01

    We examine individual Si nanowires grown by the vapor-liquid-solid mechanism, using real-time in situ ultra high vacuum transmission electron microscopy. By directly observing Au-catalyzed growth of Si wires from disilane, we show that the growth rate is independent of wire diameter, contrary to the expected behavior. Our measurements show that the unique rate-limiting step here is the irreversible, kinetically limited, dissociative adsorption of disilane directly on the catalyst surface. We also identify a novel dependence of growth rate on wire taper.

  1. Diameter-independent kinetics in the vapor-liquid-solid growth of Si nanowires.

    PubMed

    Kodambaka, S; Tersoff, J; Reuter, M C; Ross, F M

    2006-03-10

    We examine individual Si nanowires grown by the vapor-liquid-solid mechanism, using real-time in situ ultra high vacuum transmission electron microscopy. By directly observing Au-catalyzed growth of Si wires from disilane, we show that the growth rate is independent of wire diameter, contrary to the expected behavior. Our measurements show that the unique rate-limiting step here is the irreversible, kinetically limited, dissociative adsorption of disilane directly on the catalyst surface. We also identify a novel dependence of growth rate on wire taper. PMID:16606284

  2. Kinetic Simulation of Gold Nanorod Growth in Solution Based on Optical Spectra

    NASA Astrophysics Data System (ADS)

    Wang, Ying-ying; Li, Bo-xuan; Vdovic, Silvije; Wang, Xue-fei; Xia, An-dong

    2012-04-01

    By monitoring the time evolution of the optical absorption spectrum corresponding to dynamic information of aspect ratio (AR) and volume, we succeeded in following the growth kinetics of gold nanorods. The results indicate that the rods growth consists of two stages: seeds develop into rods with a fast AR increase and the rods grow big with constant AR. Here, a charge transfer model, involving positive charge transfer from Au(I) to seed and neutralization by electron from ascorbic acid, has been introduced to explain the autocatalysis mechanism of rod growth. The good agreement between the numerical simulation based on this model and experimental results supports the proposed mechanism.

  3. Bio-layer interferometry for measuring kinetics of protein-protein interactions and allosteric ligand effects.

    PubMed

    Shah, Naman B; Duncan, Thomas M

    2014-01-01

    We describe the use of Bio-layer Interferometry to study inhibitory interactions of subunit ε with the catalytic complex of Escherichia coli ATP synthase. Bacterial F-type ATP synthase is the target of a new, FDA-approved antibiotic to combat drug-resistant tuberculosis. Understanding bacteria-specific auto-inhibition of ATP synthase by the C-terminal domain of subunit ε could provide a new means to target the enzyme for discovery of antibacterial drugs. The C-terminal domain of ε undergoes a dramatic conformational change when the enzyme transitions between the active and inactive states, and catalytic-site ligands can influence which of ε's conformations is predominant. The assay measures kinetics of ε's binding/dissociation with the catalytic complex, and indirectly measures the shift of enzyme-bound ε to and from the apparently nondissociable inhibitory conformation. The Bio-layer Interferometry signal is not overly sensitive to solution composition, so it can also be used to monitor allosteric effects of catalytic-site ligands on ε's conformational changes. PMID:24638157

  4. On role of kinetic fluctuations in laminar-turbulent transition in chemically nonequilibrium boundary layer flows

    NASA Astrophysics Data System (ADS)

    Tumin, Anatoli

    2015-11-01

    Zavol'skii and Reutov (1983), Luchini (2008, 2010), Fedorov (2010, 2012, 2014) explored potential role of kinetic fluctuations (KF) in incompressible and calorically perfect gas boundary layer flows. The results indicate that role of KF is comparable with other disturbance sources in flight experiments and in quiet wind tunnels. The analysis is based on the Landau and Lifshitz (1957) concept of fluctuating hydrodynamics representing the dissipative fluxes as an average and fluctuating parts. We are extending analysis of the receptivity problem to the fluctuating dissipative fluxes in chemically reacting nonequilibrium boundary layer flows of binary mixtures. There are new terms in the energy, and the species equations. The species conservation equation includes the dissipative diffusion flux and the species generation due to dissociation. The momentum equation includes fluctuating stress tensor. The energy equation includes fluctuating heat flux, energy flux due to diffusion of the species, and fluctuating dissipative flux due to viscosity. The effects are compared for the cases stemming from constraints of the HTV project (Klentzman and Tumin, AIAA Paper 2013-2882). Supported by AFOSR.

  5. Lack of a unique kinetic pathway in the growth and decay of Pluronic micelles.

    PubMed

    Arranja, Alexandra; Waton, Gilles; Schosseler, François; Mendes, Eduardo

    2016-01-21

    We report kinetic experiments on dilute brine solutions of P84, P94 and P104 Pluronic copolymer micelles. The growth and the decay of micelles after temperature steps are measured by non-standard time resolved multi-angle photon correlation spectroscopy. Several concurrent mechanisms are at work during the very slow equilibration of solutions, namely insertion/expulsion of unimers, aggregation/dissociation of micellar aggregates, and fusion/budding of micellar aggregates. Their relative rates determine both the kinetic pathways and the morphologies of the micellar assemblies, which depend markedly on modest changes in the copolymer molecular weight. For the typical Pluronic copolymers investigated here, none of these elementary processes can be neglected if the resulting morphology is to be explained. This feature imposes multiple kinetic behaviours where growth and decay of Pluronic micelles become strongly dependent on the thermal history. We point out to some possible shortcomings in the studies of micellar growth kinetics by light scattering techniques. Extensive time-resolved multiangle measurements are a prerequisite for avoiding these pitfalls. PMID:26523415

  6. Kinetic characteristics and modelling of growth and substrate removal by Alcaligenes faecalis strain NR.

    PubMed

    Chen, Jie; Zhao, Bin; An, Qiang; Wang, Xia; Zhang, Yi Xin

    2016-04-01

    Alcaligenes faecalis strain NR has the capability of simultaneous ammonium and organic carbon removal under sole aerobic conditions. The growth and substrate removal characteristics of A. faecalis strain NR were studied and appropriate kinetic models were developed. The maximum substrate removal rate of NH4 (+)-N and TOC were determined as 2.27 mg NH4 (+)-N/L/h and 30.00 mg TOC/L/h, respectively with initial NH4 (+)-N = 80 mg/L and TOC = 800 mg/L. Single-substrate models and double-substrate models based on Monod, Contois, Moser and Teissier were employed to describe the bioprocess kinetic coefficients. As a result, two double-substrate models, Teissier-Contois and Contois-Contois, were considered to be appropriate to model growth kinetics with both NH4 (+)-N and TOC as limiting substrates. The kinetic constants of maximum growth rate (μ max) and half-saturation constant (K S and B S) were obtained by solving multiple equations with regression. This work can be used to further understand and predict the performance of heterotrophic nitrifiers, and thus provides specific guidance of these functional strains in practical wastewater treatment process. PMID:26796583

  7. Kinetics of cesium lead halide perovskite nanoparticle growth; focusing and de-focusing of size distribution

    NASA Astrophysics Data System (ADS)

    Koolyk, Miriam; Amgar, Daniel; Aharon, Sigalit; Etgar, Lioz

    2016-03-01

    In this work we study the kinetics of cesium lead halide perovskite nanoparticle (NP) growth; the focusing and de-focusing of the NP size distribution. Cesium lead halide perovskite NPs are considered to be attractive materials for optoelectronic applications. Understanding the kinetics of the formation of these all-inorganic perovskite NPs is critical for reproducibly and reliably generating large amounts of uniformly sized NPs. Here we investigate different growth durations for CsPbI3 and CsPbBr3 NPs, tracking their growth by high-resolution transmission electron microscopy and size distribution analysis. As a result, we are able to provide a detailed model for the kinetics of their growth. It was observed that the CsPbI3 NPs exhibit focusing of the size distribution in the first 20 seconds of growth, followed by de-focusing over longer growth durations, while the CsPbBr3 NPs show de-focusing of the size distribution starting from the beginning of the growth. The monomer concentration is depleted faster in the case of CsPbBr3 than in the case of CsPbI3, due to faster diffusion of the monomers, which increases the critical radius and results in de-focusing of the population. Accordingly, focusing is not observed within 40 seconds of growth in the case of CsPbBr3. This study provides important knowledge on how to achieve a narrow size distribution of cesium lead halide perovskite NPs when generating large amounts of these promising, highly luminescent NPs.In this work we study the kinetics of cesium lead halide perovskite nanoparticle (NP) growth; the focusing and de-focusing of the NP size distribution. Cesium lead halide perovskite NPs are considered to be attractive materials for optoelectronic applications. Understanding the kinetics of the formation of these all-inorganic perovskite NPs is critical for reproducibly and reliably generating large amounts of uniformly sized NPs. Here we investigate different growth durations for CsPbI3 and CsPbBr3 NPs, tracking

  8. Dynamics of layer-by-layer growth of a polyelectrolyte multilayer studied in situ using attenuated total reflectance infrared spectroscopy.

    PubMed

    Owusu-Nkwantabisah, Silas; Gammana, Madhira; Tripp, Carl P

    2014-10-01

    Attenuated total reflectance infrared spectroscopy (ATR-IR) was used to study the dynamic layer-by-layer (LBL) growth of a sodium polyacrylate (NaPA)/poly(diallydimethylammonium) chloride (PDADMAC) multilayer on TiO2 particles. Molecular weights (Mw) used were 30 and 60 kDa for NaPA and 8.5 and 150 kDa for PDADMAC. IR spectra were recorded in situ as a function of time and were used to obtain the dynamic mass adsorbed and bound fraction of the polymers during each deposition step. For 30 kDa NaPA layers, the dynamics of adsorption show an initial rapid rise in mass followed by a slow increase toward a plateau value upon LBL with 150 kDa PDADMAC. In contrast, the 60 kDa NaPA layers achieve a plateau quickly and do not show a slow increase toward a plateau. In the case of LBL with 150 kDa PDADMAC, the dynamics of the bound fraction of polymer per layer suggest that polymer diffusion and conformational rearrangement occur for the layers of 30 kDa NaPA but not for the 60 kDa NaPA layers. Furthermore, PDADMAC adsorption profiles show that there is no diffusion of the PDADMAC layers and that PDADMAC flattens onto the underlying layer. A linear growth in the mass adsorbed per layer was observed for 150 kDa PDADMAC with both molecular weights of NaPA. In the case of 8.5 kDa PDADMAC, smaller growth increments and the desorption of underlying layers were observed. This work demonstrates the use of ATR-IR in obtaining the dynamics of LBL multilayer formation. Furthermore, it provides an example in which polymer diffusion during LBL film formation does not lead to exponential growth. PMID:25203136

  9. The Kinetic Scale Structure of the Low Latitude Boundary Layer: Initial MMS Results

    NASA Astrophysics Data System (ADS)

    Dorelli, John; Gershman, Dan; Avanov, Levon; Pollock, Craig; Giles, Barbara; Gliese, Ulrik; Barrie, Alexander; Holland, Matthew; Salo, Chad; Dickson, Charles; Coffey, Victoria; Chandler, Michael; Sato, Yoshifumi; Strangeway, Robert; Russell, Christopher; Baumjohann, Wolfgang; Khotyainstev, Yuri; Torbert, Roy; Burch, James

    2016-04-01

    Since its launch in March of 2015, NASA's Magnetospheric Multiscale (MMS) mission has captured thousands of high resolution magnetopause crossings, routinely resolving the sub-Larmor radius structure of the magnetopause boundary layer for the first time. The primary goal of MMS is to understand the microphysics of magnetic reconnection, and it is well on its way to achieving this objective. However, MMS is also making routine measurements of the electron and ion gyroviscous and heat flux tensors with unprecedented resolution and accuracy. This opens up the possibility of directly observing the physical processes that facilitate momentum and energy transport across the magnetopause boundary layer under arbitrary conditions (e.g., magnetic field geometry and flow shear) far from the reconnection X line. Currently, our global magnetosphere fluid models (e.g., resistive or Hall MHD) do not include accurate descriptions of viscosity and heat flow, both of which are known to be critical players at the magnetopause (not just at the reconnection sites), and several groups are attempting to make progress on this difficult fluid closure problem. In this talk, we will address the fluid closure problem in the context of MMS observations of the Low Latitude Boundary Layer (LLBL), focusing on high resolution particle observations by the Fast Plasma Investigation (FPI). FPI electron bulk velocities are accurate enough to compute current density in both the high density magnetosheath and low density magnetosphere and have already revealed that the LLBL has a complex parallel current structure on the proton Larmor radius scale. We discuss the relationship between these parallel currents and the Hall electric field structures predicted by kinetic models. We also present first observations of the ion and electron gyroviscous and heat flux tensors in the LLBL and discuss implications for the fluid closure problem at Earth's magnetopause.

  10. Near-inertial kinetic energy budget of the mixed layer and shear evolution in the transition layer in the Arabian Sea during the monsoons

    NASA Astrophysics Data System (ADS)

    Majumder, Sudip; Tandon, Amit; Rudnick, Daniel L.; Thomas Farrar, J.

    2015-09-01

    We present the horizontal kinetic energy (KE) balance of near-inertial currents in the mixed layer and explain shear evolution in the transition layer using observations from a mooring at 15.26° N in the Arabian Sea during the southwest monsoon. The highly sheared and stratified transition layer at the mixed-layer base varies between 5 m and 35 m and correlates negatively with the wind stress. Results from the mixed layer near-inertial KE (NIKE) balance suggest that wind energy at times can energize the transition layer and at other times is fully utilized within the mixed layer. A simple two layer model is utilized to study the shear evolution in the transition layer and shown to match well with observations. The shear production in this model arises from alignment of wind stress and shear. Although the winds are unidirectional during the monsoon, the shear in the transition layer is predominantly near-inertial. The near-inertial shear bursts in the observations show the same phasing and magnitude at near-inertial frequencies as the wind-shear alignment term.

  11. Thermodynamics and kinetic behaviors of thickness-dependent crystallization in high-k thin films deposited by atomic layer deposition

    SciTech Connect

    Nie, Xianglong; Ma, Fei; Ma, Dayan; Xu, Kewei

    2015-01-15

    Atomic layer deposition is adopted to prepare HfO{sub 2} and Al{sub 2}O{sub 3} high-k thin films. The HfO{sub 2} thin films are amorphous at the initial growth stage, but become crystallized when the film thickness (h) exceeds a critical value (h{sub critical}{sup *}). This phase transition from amorphous to crystalline is enhanced at higher temperatures and is discussed, taking into account the effect of kinetic energy. At lower temperatures, the amorphous state can be maintained even when h>h{sub critical}{sup *} owing to the small number of activated atoms. However, the number of activated atoms increases with the temperature, allowing crystallization to occur even in films with smaller thickness. The Al{sub 2}O{sub 3} thin films, on the other hand, maintain their amorphous state independent of the film thickness and temperature owing to the limited number of activated atoms. A thermodynamic model is proposed to describe the thickness-dependent phase transition.

  12. Multistep Kinetic Behavior of the Thermal Decomposition of Granular Sodium Percarbonate: Hindrance Effect of the Outer Surface Layer.

    PubMed

    Wada, Takeshi; Nakano, Masayoshi; Koga, Nobuyoshi

    2015-09-24

    The kinetics and mechanism of the thermal decomposition of granular sodium percarbonate (SPC), which is used as a household oxygen bleach, were studied by thermoanalytical measurements under systematically changing conditions and morphological observation of the reactant solids at different reaction stages. A physico-geometrical kinetic behavior of the reaction that occurs in a core-shell structure composed of an outer surface layer and internal aggregates of SPC crystalline particles was illustrated through detailed kinetic analyses using the kinetic deconvolution method. Simultaneously, the hazardous nature of SPC as a combustion improver was evaluated on the basis of the kinetic behavior of the thermal decomposition. It was found that the outer surface layers of the SPC granules hinder the diffusional removal of product gases generated by the thermal decomposition of the internal SPC crystalline particles. The reaction rate decelerates because of an increase in the internal gaseous pressure as the reaction advances. However, the reaction rate accelerates once crack formation occurs in the outer surface layer at the midpoint of the reaction. Therefore, the overall reaction was empirically demonstrated to consist of two overlapping reaction steps owing to the changes in the self-generated reaction conditions in the interior of the SPC granules. PMID:26372469

  13. In-situ ellipsometric characterization of the growth of porous anisotropic nanocrystalline ZnO layers

    SciTech Connect

    Laha, P. Terryn, H.; Ustarroz, J.; Nazarkin, M. Y. Gavrilov, S. A.; Volkova, A. V.; Simunin, M. M.

    2015-03-09

    ZnO films have increasingly been in the spotlight due to their largely varied electro-physical and optical properties. For several applications, porous anisotropic nanocrystalline layers are especially interesting. To study the growth kinetics of such films during different fabrication processes, a powerful non-destructive in-situ technique is required. In this work, both ex-situ and in-situ spectroscopic ellipsometry are used along with advanced modelling techniques that are able to take both the anisotropy and the porosity of the films into account. Scanning electron microscopy, along with nitrogen absorption methods for measuring porosity, validated the ellipsometric data and proposed model. The film, grown by chemical bath deposition, was monitored from around 700 to 1800 nm in thickness. This same principle can now be used to monitor any other porous and/or anisotropic structure in an effective in-situ manner, e.g., growth of porous anodic aluminium oxides, nano-porous silica films, etc.

  14. Analysis of layer-by-layer thin-film oxide growth using RHEED and Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Adler, Eli; Sullivan, M. C.; Gutierrez-Llorente, Araceli; Joress, H.; Woll, A.; Brock, J. D.

    2015-03-01

    Reflection high energy electron diffraction (RHEED) is commonly used as an in situ analysis tool for layer-by-layer thin-film growth. Atomic force microscopy is an equally common ex situ tool for analysis of the film surface, providing visual evidence of the surface morphology. During growth, the RHEED intensity oscillates as the film surface changes in roughness. It is often assumed that the maxima of the RHEED oscillations signify a complete layer, however, the oscillations in oxide systems can be misleading. Thus, using only the RHEED maxima is insufficient. X-ray reflectivity can also be used to analyze growth, as the intensity oscillates in phase with the smoothness of the surface. Using x-ray reflectivity to determine the thin film layer deposition, we grew three films where the x-ray and RHEED oscillations were nearly exactly out of phase and halted deposition at different points in the growth. Pre-growth and post-growth AFM images emphasize the fact that the maxima in RHEED are not a justification for determining layer completion. Work conducted at the Cornell High Energy Synchrotron Source (CHESS) supported by NSF Awards DMR-1332208 and DMR-0936384 and the Cornell Center for Materials Research Shared Facilities are supported through DMR-1120296.

  15. AxBAxB… pulsed atomic layer deposition: Numerical growth model and experiments

    NASA Astrophysics Data System (ADS)

    Muneshwar, Triratna; Cadien, Ken

    2016-02-01

    Atomic layer deposition (ALD) is widely used for the fabrication of advanced semiconductor devices and related nanoscale structures. During ALD, large precursor doses (>1000 L per pulse) are often required to achieve surface saturation, of which only a small fraction is utilized in film growth while the rest is pumped from the system. Since the metal precursor constitutes a significant cost of ALD, strategies to enhance precursor utilization are essential for the scaling of ALD processes. In the precursor reaction step, precursor physisorption is restricted by steric hindrance (mA1) from ligands on the precursor molecules. On reaction, some of these ligands are removed as by-products resulting in chemisorbed species with reduced steric hindrance (mA1 → mA2, where mA2 < mA1) and some of the initially hindered surface reaction sites becoming accessible for further precursor physisorption. To utilize these additional reaction sites, we propose a generalized AxBAxB… pulsed deposition where the total precursor dose (ΦA) is introduced as multiple x (x > 1, x ∈ I) short-pulses rather than a single pulse. A numerical first-order surface reaction kinetics growth model is presented and applied to study the effect of AxBAxB… pulsed ALD on the growth per cycle (GPC). The model calculations predict higher GPC for AxBAxB… pulsing than with ABAB… deposition. In agreement with the model predictions, with AxBAxB… pulsed deposition, the GPC was found to increase by ˜46% for ZrN plasma enhanced ALD (PEALD), ˜49% for HfO2 PEALD, and ˜8% for thermal Al2O3 ALD with respect to conventional ABAB… pulsed growth.

  16. Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals

    PubMed Central

    Gokhale, Shreyas; Nagamanasa, K. Hima; Santhosh, V.; Sood, A. K.; Ganapathy, Rajesh

    2012-01-01

    The fabrication of functional materials via grain growth engineering implicitly relies on altering the mobilities of grain boundaries (GBs) by applying external fields. Although computer simulations have alluded to kinetic roughening as a potential mechanism for modifying GB mobilities, its implications for grain growth have remained largely unexplored owing to difficulties in bridging the widely separated length and time scales. Here, by imaging GB particle dynamics as well as grain network evolution under shear, we present direct evidence for kinetic roughening of GBs and unravel its connection to grain growth in driven colloidal polycrystals. The capillary fluctuation method allows us to quantitatively extract shear-dependent effective mobilities. Remarkably, our experiments reveal that for sufficiently large strains, GBs with normals parallel to shear undergo preferential kinetic roughening, resulting in anisotropic enhancement of effective mobilities and hence directional grain growth. Single-particle level analysis shows that the mobility anisotropy emerges from strain-induced directional enhancement of activated particle hops normal to the GB plane. We expect our results to influence materials fabrication strategies for atomic and block copolymeric polycrystals as well. PMID:23169661

  17. Kinetics of growth and caffeine demethylase production of Pseudomonas sp. in bioreactor.

    PubMed

    Gummadi, Sathyanarayana N; Santhosh, Devarai

    2010-09-01

    The effect of various initial caffeine concentrations on growth and caffeine demethylase production by Pseudomonas sp. was studied in bioreactor. At initial concentration of 6.5 g l(-1) caffeine, Pseudomonas sp. showed a maximum specific growth rate of 0.2 h(-1), maximum degradation rate of 1.1 g h(-1), and caffeine demethylase activity of 18,762 U g CDW(-1) (CDW: cell dry weight). Caffeine degradation rate was 25 times higher in bioreactor than in shake flask. For the first time, we show highest degradation of 75 g caffeine (initial concentration 20 g l(-1)) in 120 h, suggesting that the tested strain has potential for successful bioprocess for caffeine degradation. Growth kinetics showed substrate inhibition phenomenon. Various substrate inhibition models were fitted to the kinetic data, amongst which the double-exponential (R(2) = 0.94), Luong (R(2) = 0.92), and Yano and Koga 2 (R(2) = 0.94) models were found to be the best. The Luedeking-Piret model showed that caffeine demethylase production kinetics was growth related. This is the first report on production of high levels of caffeine demethylase in batch bioreactor with faster degradation rate and high tolerance to caffeine, hence clearly suggesting that Pseudomonas sp. used in this study is a potential biocatalyst for industrial decaffeination. PMID:20495941

  18. On the Effect of Atoms in Solid Solution on Grain Growth Kinetics

    NASA Astrophysics Data System (ADS)

    Hersent, Emmanuel; Marthinsen, Knut; Nes, Erik

    2014-10-01

    The discrepancy between the classical grain growth law in high purity metals (grain size ) and experimental measurements has long been a subject of debate. It is generally believed that a time growth exponent less than 1/2 is due to small amounts of impurity atoms in solid solution even in high purity metals. The present authors have recently developed a new approach to solute drag based on solute pinning of grain boundaries, which turns out to be mathematically simpler than the classic theory for solute drag. This new approach has been combined with a simple parametric law for the growth of the mean grain size to simulate the growth kinetics in dilute solid solution metals. Experimental grain growth curves in the cases of aluminum, iron, and lead containing small amounts of impurities have been well accounted for.

  19. Kinetic modeling of Moorella thermoacetica growth on single and dual-substrate systems.

    PubMed

    Schmitt, Elliott; Bura, Renata; Gustafson, Rick; Ehsanipour, Mandana

    2016-10-01

    Acetic acid is an important chemical raw material that can be produced directly from sugars in lignocellulosic biomass. Development of kinetic models that capture the bioconversion dynamics of multiple sugar systems will be critical to optimization and process control in future lignocellulosic biorefinery processes. In this work, a kinetic model was developed for the single- and dual-substrate conversion of xylose and glucose to acetic acid using the acetogen Moorella thermoacetica. Batch fermentations were performed experimentally at 20 g L(-1) total sugar concentration using synthetic glucose, xylose, and a mixture of glucose and xylose at a 1:1 ratio. The product yield, calculated as total product formed divided by total sugars consumed, was 79.2, 69.9, and 69.7 % for conversion of glucose, xylose, and a mixture of glucose and xylose (1:1 ratio), respectively. During dual-substrate fermentation, M. thermoacetica demonstrated diauxic growth where xylose (the preferred substrate) was almost entirely consumed before consumption of glucose began. Kinetic parameters were similar for the single-substrate fermentations, and a strong linear correlation was determined between the maximum specific growth rate μ max and substrate inhibition constant, K s . Parameters estimated for the dual-substrate system demonstrated changes in the specific growth rate of both xylose and glucose consumption. In particular, the maximum growth rate related to glucose tripled compared to the single-substrate system. Kinetic growth is affected when multiple substrates are present in a fermentation system, and models should be developed to reflect these features. PMID:27262717

  20. Tissue Integration of Growth Factor-Eluting Layer-by-Layer Polyelectrolyte Multilayer Coated Implants

    PubMed Central

    Macdonald, Mara L.; Samuel, Raymond E.; Shah, Nisarg J.; Padera, Robert; Beben, Yvette M.; Hammond, Paula T.

    2011-01-01

    Drug eluting coatings that can direct the host tissue response to implanted medical devices have the potential to ameliorate both the medical and financial burden of complications from implantation. However, because many drugs useful in this arena are biologic in nature, a paucity of delivery strategies for biologics, including growth factors, currently limits the control that can be exerted on the implantation environment. Layer-by-Layer (LbL) polyelectrolyte multilayer films are highly attractive as ultrathin biologic reservoirs, due to conformal coating of difficult geometries, aqueous processing likely to preserve fragile protein function, and tenability of incorporation and release profiles. Herein, we describe the first LbL films capable of microgram-scale release of the biologic Bone Morphogenetic Protein 2 (BMP-2), which is capable of directing the host tissue response to create bone from native progenitor cells. Ten micrograms of BMP-2 are released over a period of two weeks in vitro; less than 1% is released in the first 3 hours (compared with commercial collagen matrices which can release up to 60% of BMP-2, too quickly to induce differentiation). BMP-2 released from LbL films retains its ability to induce bone differentiation in MC3T3 E1S4 preosteoblasts, as measured by induction of alkaline phosphatase and stains for calcium (via Alizarin Red) and calcium matrix (via Von Kossa). In vivo, BMP-2 film coated scaffolds were compared with film coated scaffolds lacking BMP-2. BMP-2 coatings implanted intramuscularly were able to initiate host progenitor cells to differentiate into bone, which matured and expanded from four to nine weeks as measured by MicroCT and histology. Such LbL films represent new steps towards controlling and tuning host response to implanted medical devices, which may ultimately increase the success of implanted devices, provide alternative new approaches toward bone wound healing, and lay the foundation for development of a multi

  1. Growth of III-V nitrides and buffer layer investigation by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Huang, Tzu-Fang

    1999-11-01

    III-V nitrides have been investigated intensively due to the enormous interest in optoelectronic device applications in the green, blue, violet, and near-ultraviolet regions. Advances in III-V nitride materials for short wavelength light sources will lead to both a revolution in optical disk storage, as higher densities can be achieved with short wavelengths, and a major impact on imaging and graphic technology as high quality red, green, and blue light-emitting diodes (LED) and lasers become available. High quality GaN films have mostly been prepared by metal-organic vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE) and vapor phase epitaxy (VPE). Compared to these techniques, pulsed laser deposition (PLD) is a relatively new growth technique used widely for the growth of oxide thin films. However, several advantages of PLD make it worthy of study as a method of growing nitrides. The congruent ablation achieved with short UV-laser pulses allows deposition of a multicomponent material by employing a single target and the ability for depositing a wide variety of materials. This advantage makes PLD very suitable for growing multilayer structures sequentially in the same chamber and investigating the effect of buffer layers. Moreover, the strong nonequilibrium growth conditions of PLD may lead to different nucleation and growth processes. In this work, GaN and (Al,Ga)N films have been epitaxially grown on (0001) sapphire substrate by PLD, which has been successfully applied to controlling the lattice constant and band gap of (Al,Ga)N. Room-temperature photoluminescence of PLD-GaN exhibits a strong band edge emission at 3.4eV. The threading dislocations of GaN are predominantly screw dislocations with Burgers vector of <0001> while edge dislocations with Burgers vector of 1/3<11-20> are the dominant ones in GaN grown by MBE, MOCVD and VPE. This variation observed in defect characteristics may come from the difference in nucleation and growth kinetics between PLD

  2. Dissolution and Growth of (10(1) over-bar4) Calcite in Flowing Water: Estimation of Back Reaction Rates via Kinetic Monte Carlo Simulations

    SciTech Connect

    Williford, Rick E.; Baer, Donald R.; Amonette, James E.; Lea, Alan S.

    2004-02-15

    Although calcite is an important mineral for many processes, there have been relatively few simulations of it's growth and dissolution behavior. Such simulations are complicated by the multitude of defect types and by the asymmetry of the crystal. The present work combined a kinetic Monte Carlo (KMC) technique with the Kossel crystal (100) simple cubic concept and the Blasius boundary layer model to simulate the simultaneous growth and dissolution of the (1014)calcite cleavage surface in flowing water. The objective was to determine the activation energies of the back reaction (growth) from those of the forward reaction (dissolution) by obtaining agreement with cleavage-step morphologies and step dissolution velocities previously measured using an atomic force microscope (AFM). Blasius boundary layer conditions for the flowing fluid defined a model that treated the solid, the dissolution/growth interface, and the fluid kinetics. Microscopic reversibility and the laws of large number s gave an expression for the back reaction activation energies in terms of the forward reaction energies and the entropy of mixing, a quantity estimated from the concentration of desorbates in a very small fluid layer adjacent to the interface. The KMC simulations produced cleavage-step morphologies that were in qualitative agreement with observations from AFM. The kinetics were dominated by diffusion events on the solid/fluid interface and in the fluid, as expected. The relative magnitudes of the desorption and adsorption activation energies were consistent with experimental data, entropic arguments, and crystal roughening theories. Qualitative agreement with measured step velocities was best when the boundary layer parameters were given physically reasonable values, indicating that the model is self consistent.

  3. Kinetic Particle-In Simulations of Transport in a Tokamak Scrape-Off Layer.

    NASA Astrophysics Data System (ADS)

    Procassini, Richard Joseph

    1990-01-01

    The focus of this thesis is the application of particle-in-cell (PIC) simulation techniques to the study of particle and energy transport in the scrape-off layer (SOL) of a tokamak fusion device. The PIC computer code that is used in this endeavor provides a fully-kinetic, self-consistent description of plasma transport in one spatial dimension (along the open magnetic field lines in the SOL) and two velocity components (v_ {|} and v_{ |}). The diverted-tokamak SOL system was modeled with various levels of physical complexity. The most rudimentary system studied, a collisionless bounded plasma-sheath region, was used to investigate the dependence of the potential structure on the source distribution function used to inject plasma into the SOL. The results from this study were in reasonable agreement with the predictions of previously developed analytic theories. The next level of complexity included the effects of Coulomb collisions. Plasma transport in the SOL was modeled over the wide range of collisionality encountered in current and near-term devices. The electron heat conduction flux in these simulations was limited to 11-21% of the free-streaming thermal flux. Finally, the atomic physics processes of charge exchange and ionization were included in the collisional model. These interactions between the charged-plasma and recycled-neutral particles can significantly affect energy transport through the SOL. This complete version of the kinetic PIC model was used to simulate SOL transport for various values of neutral particle density between the low-and high-recycling limits. The electron and ion kinetic energy fluxes to the divertor plate exhibit a marked decrease as the level of neutral particle recycling increases. The performance of the direct implicit PIC code has been determined with regard to the size of the time step Delta t and grid spacing Delta z. Each of the physics packages incorporated into the PIC code has been benchmarked against either available

  4. Kinetics and Mechanisms of Cadmium Carbonate Heteroepitaxial Growth at the Calcite (101¯4) Surface

    SciTech Connect

    Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien N.

    2014-06-01

    Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at calcite-water interfaces was investigated by exposing calcite (10-14) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the crystallization of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the calcite substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and calcite shows perfect, dislocation-free epitaxy.

  5. Kinetics and mechanisms of cadmium carbonate heteroepitaxial growth at the calcite (10 1bar 4) surface

    NASA Astrophysics Data System (ADS)

    Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien

    2014-06-01

    Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at calcite-water interfaces was investigated by exposing calcite (10 1bar 4) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the crystallization of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the calcite substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and calcite shows perfect, dislocation-free epitaxy.

  6. Estimation of the growth kinetics for the cooling crystallisation of paracetamol and ethanol solutions

    NASA Astrophysics Data System (ADS)

    Mitchell, Niall A.; Ó'Ciardhá, Clifford T.; Frawley, Patrick J.

    2011-08-01

    This work details the estimation of the growth kinetics of paracetamol in ethanol solutions for cooling crystallisation processes, by means of isothermal seeded batch experiments. The growth kinetics of paracetamol crystals were evaluated in isolation, with the growth rate assumed to be size independent. Prior knowledge of the Metastable Zone Width (MSZW) was required, so that supersaturation ratios of 1.7-1.1 could be induced in solution without the occurrence of nucleation. The technique involved the utilisation of two in-situ Process Analytical Techniques (PATs), with a Focused Beam Reflectance Measurement (FBRM ®) utilised to ensure that negligible nucleation occurred and an Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) probe employed for online monitoring of solute concentration. Initial Particle Size Distributions (PSDs) were used in conjunction with desupersaturation profiles to determine the growth rate as a function of temperature and supersaturation. Furthermore, the effects of seed loading and size on the crystal growth rate were investigated. A numerical model, incorporating the population balance equation and the method of moments, was utilised to describe the crystal growth process. Experimental parameters were compared to the model simulation, with the accuracy of the model validated by means of the final product PSDs and solute concentration.

  7. Kinetic Monte Carlo simulations of thermally activated magnetization reversal in dual-layer Exchange Coupled Composite recording media

    NASA Astrophysics Data System (ADS)

    Plumer, M. L.; Almudallal, A. M.; Mercer, J. I.; Whitehead, J. P.; Fal, T. J.

    The kinetic Monte Carlo (KMC) method developed for thermally activated magnetic reversal processes in single-layer recording media has been extended to study dual-layer Exchange Coupled Composition (ECC) media used in current and next generations of disc drives. The attempt frequency is derived from the Langer formalism with the saddle point determined using a variant of Bellman Ford algorithm. Complication (such as stagnation) arising from coupled grains having metastable states are addressed. MH-hysteresis loops are calculated over a wide range of anisotropy ratios, sweep rates and inter-layer coupling parameter. Results are compared with standard micromagnetics at fast sweep rates and experimental results at slow sweep rates.

  8. Kinetics of gypsum crystal growth from high ionic strength solutions: A case study of Dead Sea - seawater mixtures

    NASA Astrophysics Data System (ADS)

    Reznik, Itay J.; Gavrieli, Ittai; Antler, Gilad; Ganor, Jiwchar

    2011-04-01

    Gypsum precipitation kinetics were examined from a wide range of chemical compositions (11growth theory ( Burton et al., 1951) and other layer-by-layer growth mechanisms ( Goto and Ridge, 1967; Van Rosmalen et al., 1981; Bosbach and Rammensee, 1994). Under further-away-from-equilibrium conditions, the reaction is dominated by an apparent 10th order reaction. A conceptual model for gypsum growth kinetics is presented. The model is based on the 2nd order kinetic coefficients determined in the present study and data from the literature and is valid under a wide range of ionic strengths and Ca/SO42- ratios. According to this model, the integration of SO42- to kinks on the surface of the growing crystals is the rate-limiting step in the precipitation reaction. At ionic strengths above 8.5 m the precipitation rate of gypsum is enhanced, possibly due to the formation of CaSO4° ion pairs and/or a decrease in hydration frequencies.

  9. Nonlinear Growth Kinetics of Breast Cancer Stem Cells: Implications for Cancer Stem Cell Targeted Therapy

    NASA Astrophysics Data System (ADS)

    Liu, Xinfeng; Johnson, Sara; Liu, Shou; Kanojia, Deepak; Yue, Wei; Singn, Udai; Wang, Qian; Wang, Qi; Nie, Qing; Chen, Hexin

    2013-08-01

    Cancer stem cells (CSCs) have been identified in primary breast cancer tissues and cell lines. The CSC population varies widely among cancerous tissues and cell lines, and is often associated with aggressive breast cancers. Despite of intensive research, how the CSC population is regulated within a tumor is still not well understood so far. In this paper, we present a mathematical model to explore the growth kinetics of CSC population both in vitro and in vivo. Our mathematical models and supporting experiments suggest that there exist non-linear growth kinetics of CSCs and negative feedback mechanisms to control the balance between the population of CSCs and that of non-stem cancer cells. The model predictions can help us explain a few long-standing questions in the field of cancer stem cell research, and can be potentially used to predict the efficicacy of anti-cancer therapy.

  10. Growth of lanthanum manganate buffer layers for coated conductors via a metal-organic decomposition process

    NASA Astrophysics Data System (ADS)

    Venkataraman, Kartik

    LaMnO3 (LMO) was identified as a possible buffer material for YBa2Cu3O7-x conductors due to its diffusion barrier properties and close lattice match with YBa2Cu 3O7-x. Growth of LMO films via a metal-organic decomposition (MOD) process on Ni, Ni-5at.%W (Ni-5W), and single crystal SrTiO3 substrates was investigated. Phase-pure LMO was grown via MOD on Ni and SrTiO 3 substrates at temperatures and oxygen pressures within a thermodynamic "process window" wherein LMO, Ni, Ni-5W, and SrTiO3 are all stable components. LMO could not be grown on Ni-5W in the "process window" because tungsten diffused from the substrate into the overlying film, where it reacted to form La and Mn tungstates. The kinetics of tungstate formation and crystallization of phase-pure LMO from the La and Mn acetate precursors are competitive in the temperature range explored (850--1100°C). Temperatures <850°C might mitigate tungsten diffusion from the substrate to the film sufficiently to obviate tungstate formation, but LMO films deposited via MOD require temperatures ≥850°C for nucleation and grain growth. Using a Y2O3 seed layer on Ni-5W to block tungsten from diffusing into the LMO film was explored; however, Y2O3 reacts with tungsten in the "process window" at 850--1100°C. Tungsten diffusion into Y2O3 can be blocked if epitaxial, crack-free NiWO4 and NiO layers are formed at the interface between Ni-5W and Y2O3. NiWO 4 only grows epitaxially if the overlying NiO and buffer layers are thick enough to mechanically suppress (011)-oriented NiWO4 grain growth. This is not the case when a bare 75 nm-thick Y2O3 film on Ni-5W is processed at 850°C. These studies show that the Ni-5W substrate must be at a low temperature to prevent tungsten diffusion, whereas the LMO precursor film must be at elevated temperature to crystallize. An excimer laser-assisted MOD process was used where a Y2O 3-coated Ni-5W substrate was held at 500°C in air and the pulsed laser photo-thermally heated the Y2O3 and LMO