Sample records for nanotube growth kinetics

  1. Growth kinetics and growth mechanism of ultrahigh mass density carbon nanotube forests on conductive Ti/Cu supports.

    PubMed

    Sugime, Hisashi; Esconjauregui, Santiago; D'Arsié, Lorenzo; Yang, Junwei; Makaryan, Taron; Robertson, John

    2014-09-10

    We evaluate the growth kinetics and growth mechanism of ultrahigh mass density carbon nanotube forests. They are synthesized by chemical vapor deposition at 450 °C using a conductive Ti/Cu support and Co-Mo catalyst system. We find that Mo stabilizes Co particles preventing lift off during the initial growth stage, thus promoting the growth of ultrahigh mass density nanotube forests by the base growth mechanism. The morphology of the forest gradually changes with growth time, mostly because of a structural change of the catalyst particles. After 100 min growth, toward the bottom of the forest, the area density decreases from ∼ 3-6 × 10(11) cm(-2) to ∼ 5 × 10(10) cm(-2) and the mass density decreases from 1.6 to 0.38 g cm(-3). We also observe part of catalyst particles detached and embedded within nanotubes. The progressive detachment of catalyst particles results in the depletion of the catalyst metals on the substrate surfaces. This is one of the crucial reasons for growth termination and may apply to other catalyst systems where the same features are observed. Using the packed forest morphology, we demonstrate patterned forest growth with a pitch of ∼ 300 nm and a line width of ∼ 150 nm. This is one of the smallest patterning of the carbon nanotube forests to date.

  2. Growth kinetics of vertically aligned carbon nanotube arrays in clean oxygen-free conditions.

    PubMed

    In, Jung Bin; Grigoropoulos, Costas P; Chernov, Alexander A; Noy, Aleksandr

    2011-12-27

    Vertically aligned carbon nanotubes (CNTs) are an important technological system, as well as a fascinating system for studying basic principles of nanomaterials synthesis; yet despite continuing efforts for the past decade many important questions about this process remain largely unexplained. We present a series of parametric ethylene chemical vapor deposition growth studies in a "hot-wall" reactor using ultrapure process gases that reveal the fundamental kinetics of the CNT growth. Our data show that the growth rate is proportional to the concentration of the carbon feedstock and monotonically decreases with the concentration of hydrogen gas and that the most important parameter determining the rate of the CNT growth is the production rate of active carbon precursor in the gas phase reaction. The growth termination times obtained with the purified gas mixtures were strikingly insensitive to variations in both hydrogen and ethylene pressures ruling out the carbon encapsulation of the catalyst as the main process termination cause.

  3. Integrating carbon nanotube forests into polysilicon MEMS: Growth kinetics, mechanisms, and adhesion

    DOE PAGES

    Ubnoske, Stephen M.; Radauscher, Erich J.; Meshot, Eric R.; ...

    2016-11-19

    The growth of carbon nanotubes (CNTs) on polycrystalline silicon substrates was studied to improve the design of CNT field emission sources for microelectromechanical systems (MEMS) applications and vacuum microelectronic devices (VMDs). Microwave plasma-enhanced chemical vapor deposition (PECVD) was used for CNT growth, resulting in CNTs that incorporate the catalyst particle at their base. The kinetics of CNT growth on polysilicon were compared to growth on Si (100) using the model of Deal and Grove, finding activation energies of 1.61 and 1.54 eV for the nucleation phase of growth and 1.90 and 3.69 eV for the diffusion-limited phase on Si (100)more » and polysilicon, respectively. Diffusivity values for growth on polysilicon were notably lower than the corresponding values on Si (100) and the growth process became diffusion-limited earlier. Evidence favors a surface diffusion growth mechanism involving diffusion of carbon precursor species along the length of the CNT forest to the catalyst at the base. Explanations for the differences in activation energies and diffusivities were elucidated by SEM analysis of the catalyst nanoparticle arrays and through wide-angle X-ray scattering (WAXS) of CNT forests. As a result, methods are presented to improve adhesion of CNT films during operation as field emitters, resulting in a 2.5× improvement.« less

  4. Integrating carbon nanotube forests into polysilicon MEMS: Growth kinetics, mechanisms, and adhesion

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ubnoske, Stephen M.; Radauscher, Erich J.; Meshot, Eric R.

    The growth of carbon nanotubes (CNTs) on polycrystalline silicon substrates was studied to improve the design of CNT field emission sources for microelectromechanical systems (MEMS) applications and vacuum microelectronic devices (VMDs). Microwave plasma-enhanced chemical vapor deposition (PECVD) was used for CNT growth, resulting in CNTs that incorporate the catalyst particle at their base. The kinetics of CNT growth on polysilicon were compared to growth on Si (100) using the model of Deal and Grove, finding activation energies of 1.61 and 1.54 eV for the nucleation phase of growth and 1.90 and 3.69 eV for the diffusion-limited phase on Si (100)more » and polysilicon, respectively. Diffusivity values for growth on polysilicon were notably lower than the corresponding values on Si (100) and the growth process became diffusion-limited earlier. Evidence favors a surface diffusion growth mechanism involving diffusion of carbon precursor species along the length of the CNT forest to the catalyst at the base. Explanations for the differences in activation energies and diffusivities were elucidated by SEM analysis of the catalyst nanoparticle arrays and through wide-angle X-ray scattering (WAXS) of CNT forests. As a result, methods are presented to improve adhesion of CNT films during operation as field emitters, resulting in a 2.5× improvement.« less

  5. Formation and growth mechanisms of single-walled metal oxide nanotubes

    NASA Astrophysics Data System (ADS)

    Yucelen, Gulfem Ipek

    shapes, allowing assembly into nanotubes whose diameters relate directly to the curvatures of shaped precursors. Having obtained considerable insight into aluminosilicate nanotube formation, in Chapter 4 the complex aqueous chemistry of nanotube-forming aluminogermanate solutions are examined. The aluminogermanate system is particularly interesting since it forms ultra-short nanotubes of lengths as small as ˜20 nm. Insights into the underlying important mechanistic differences between aluminogermanate and aluminosilicate nanotube growth as well as structural differences in the final nanotube dimensions are provided. Furthermore, an experimental example of control over nanotube length is shown, using the understanding of the mechanistic differences, along with further suggestions for possible ways of controlling nanotube lengths. In Chapter 5, a generalized kinetic model is formulated to describe the reactions leading to formation and growth of single-walled metal oxide nanotubes. This model is capable of explaining and predicting the evolution of nanotube populations as a function of kinetic parameters. It also allows considerable insight into meso/microscale nanotube growth processes. For example, it shows that two different mechanisms operate during nanotube growth: (1) growth by precursor addition, and (2) by oriented attachment of nanotubes to each other. In Chapter 6, a study of the structure of the nanotube walls is presented. A detailed investigation of the defect structures in aluminosilicate single-walled nanotubes via multiple advanced solid-state NMR techniques is reported. A combination of 1H-29Si and 1H- 27Al FSLG-HETCOR, 1H CRAMPS, and 1H- 29Si CP/MAS NMR experiments were employed to evaluate the proton environments around Al and Si atoms during nanotube synthesis and in the final structure. The HETCOR experiments allowed to track the evolving Si and Al environments during the formation of the nanotubes from precursor species, and relate them to the Si and

  6. The kinetics of chirality assignment in catalytic single-walled carbon nanotube growth and the routes towards selective growth.

    PubMed

    Xu, Ziwei; Qiu, Lu; Ding, Feng

    2018-03-21

    Depending on its specific structure, or so-called chirality, a single-walled carbon nanotube (SWCNT) can be either a conductor or a semiconductor. This feature ensures great potential for building ∼1 nm sized electronics if chirality-selected SWCNTs could be achieved. However, due to the limited understanding of the growth mechanism of SWCNTs, reliable methods for chirality-selected SWCNTs are still pending. Here we present a theoretical model on the chirality assignment and control of SWCNTs during the catalytic growth. This study reveals that the chirality of a SWCNT is determined by the kinetic incorporation of pentagons, especially the last (6 th ) one, during the nucleation stage. Our analysis showed that the chirality of a SWCNT is randomly assigned on a liquid or liquid-like catalyst surface, and two routes of synthesizing chirality-selected SWCNTs, which are verified by recent experimental achievements, are demonstrated. They are (i) by using high melting point crystalline catalysts, such as Ta, W, Re, Os, or their alloys, and (ii) by frequently changing the chirality of SWCNTs during their growth. This study paves the way for achieving chirality-selective SWCNT growth for high performance SWCNT based electronics.

  7. Parametric Investigation of the Kinetics of Growth of Carbon-Nanotube Arrays on Iron Nanoparticles in the Process of Chemical Vapor Deposition of Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Futko, S. I.; Shulitski, B. G.; Labunov, V. A.; Ermolaevaa, E. M.

    2015-03-01

    On the basis of the kinetic model of synthesis of carbon nanotubes on iron nanoparticles in the process of chemical vapor deposition of hydrocarbons, the parametric dependences of characteristics of arrays of vertically oriented nanotubes on the temperature of their synthesis, the concentration of acetylene in a reactor, and the diameter of the catalyst nanoparticles were investigated. It is shown that the maximum on the temperature dependence of the rate of growth of carbon nanotubes, detected in experiments at a temperature of ~700oC is due to the competing processes of increasing the catalytic activity of iron nanoparticles and decreasing the acetylene concentration because of the signifi cant gas-phase decomposition of acetylene in the reactor before it enters the substrate with the catalyst. Our calculations have shown that the indicated maximum arises near the transition point separating the low-temperature region where multiwall nanotubes are predominantly synthesized from the higher-temperature region of generation of single-wall nanotubes in the process of chemical vapor deposition of hydrocarbons.

  8. Investigation of growth dynamics of carbon nanotubes

    PubMed Central

    2017-01-01

    The synthesis of single-walled carbon nanotubes (SWCNTs) with defined properties is required for both fundamental investigations and practical applications. The revealing and thorough understanding of the growth mechanism of SWCNTs is the key to the synthesis of nanotubes with required properties. This paper reviews the current status of the research on the investigation of growth dynamics of carbon nanotubes. The review starts with the consideration of the peculiarities of the growth mechanism of carbon nanotubes. The physical and chemical states of the catalyst during the nanotube growth are discussed. The chirality selective growth of nanotubes is described. The main part of the review is dedicated to the analysis and systematization of the reported results on the investigation of growth dynamics of nanotubes. The studies on the revealing of the dependence of the growth rate of nanotubes on the synthesis parameters are reviewed. The correlation between the lifetime of catalyst and growth rate of nanotubes is discussed. The reports on the calculation of the activation energy of the nanotube growth are summarized. Finally, the growth properties of inner tubes inside SWCNTs are considered. PMID:28503394

  9. Enhanced electron transfer kinetics through hybrid graphene-carbon nanotube films.

    PubMed

    Henry, Philémon A; Raut, Akshay S; Ubnoske, Stephen M; Parker, Charles B; Glass, Jeffrey T

    2014-11-01

    We report the first study of the electrochemical reactivity of a graphenated carbon nanotube (g-CNT) film. The electron transfer kinetics of the ferri-ferrocyanide couple were examined for a g-CNT film and compared to the kinetics to standard carbon nanotubes (CNTs). The g-CNT film exhibited much higher catalytic activity, with a heterogeneous electron-transfer rate constant, k 0 , approximately two orders of magnitude higher than for standard CNTs. Scanning electron microscopy and Raman spectroscopy were used to correlate the higher electron transfer kinetics with the higher edge-density of the g-CNT film.

  10. Chirality-Controlled Growth of Single-Wall Carbon Nanotubes Using Vapor Phase Epitaxy: Mechanistic Understanding and Scalable Production

    DTIC Science & Technology

    2016-09-15

    controlled synthesis of single-wall carbon nanotubes. Firstly, we have successfully demonstrated a vapor-phase-epitaxy-analogous general strategy for...preselected chirality. Moreover, we carried out systematic investigations of the chirality-dependent growth kinetics and termination mechanism for the... generally believed that the diameters of the nanotubes are determined by the size of the catalytic metal particles. Unfortunately, attempts to control

  11. Measurement of the Dewetting, Nucleation, and Deactivation Kinetics of Carbon Nanotube Population Growth by Environmental Transmission Electron Microscopy

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bedewy, Mostafa; Viswanath, B.; Meshot, Eric R.

    In order to understand the collective growth of carbon nanotube (CNT) populations tailoring their properties for many applications is key. During the initial stages of CNT growth by chemical vapor deposition, catalyst nanoparticle formation by thin-film dewetting and the subsequent CNT nucleation processes dictate the CNT diameter distribution, areal density, and alignment. We use in situ environmental transmission electron microscopy (E-TEM) to observe the catalyst annealing, growth, and deactivation stages for a population of CNTs grown from a thin-film catalyst. Complementary in situ electron diffraction and TEM imaging show that, during the annealing step in hydrogen, reduction of the ironmore » oxide catalyst is concomitant with changes in the thin-film morphology; complete dewetting and the formation of a population of nanoparticles is only achieved upon the introduction of the carbon source, acetylene. The dewetting kinetics, i.e., the appearance of distinct nanoparticles, exhibits a sigmoidal (autocatalytic) curve with 95% of all nanoparticles appearing within 6 s. After nanoparticles form, they either nucleate CNTs or remain inactive, with incubation times measured to be as small as 3.5 s. Via E-TEM we also directly observe the crowding and self-alignment of CNTs after dewetting and nucleation. Additionally, in situ electron energy loss spectroscopy reveals that the collective rate of carbon accumulation decays exponentially. We conclude that the kinetics of catalyst formation and CNT nucleation must both be addressed in order to achieve uniform and high CNT density, and their transient behavior may be a primary cause of the well-known nonuniform density of CNT forests.« less

  12. Measurement of the Dewetting, Nucleation, and Deactivation Kinetics of Carbon Nanotube Population Growth by Environmental Transmission Electron Microscopy

    DOE PAGES

    Bedewy, Mostafa; Viswanath, B.; Meshot, Eric R.; ...

    2016-05-23

    In order to understand the collective growth of carbon nanotube (CNT) populations tailoring their properties for many applications is key. During the initial stages of CNT growth by chemical vapor deposition, catalyst nanoparticle formation by thin-film dewetting and the subsequent CNT nucleation processes dictate the CNT diameter distribution, areal density, and alignment. We use in situ environmental transmission electron microscopy (E-TEM) to observe the catalyst annealing, growth, and deactivation stages for a population of CNTs grown from a thin-film catalyst. Complementary in situ electron diffraction and TEM imaging show that, during the annealing step in hydrogen, reduction of the ironmore » oxide catalyst is concomitant with changes in the thin-film morphology; complete dewetting and the formation of a population of nanoparticles is only achieved upon the introduction of the carbon source, acetylene. The dewetting kinetics, i.e., the appearance of distinct nanoparticles, exhibits a sigmoidal (autocatalytic) curve with 95% of all nanoparticles appearing within 6 s. After nanoparticles form, they either nucleate CNTs or remain inactive, with incubation times measured to be as small as 3.5 s. Via E-TEM we also directly observe the crowding and self-alignment of CNTs after dewetting and nucleation. Additionally, in situ electron energy loss spectroscopy reveals that the collective rate of carbon accumulation decays exponentially. We conclude that the kinetics of catalyst formation and CNT nucleation must both be addressed in order to achieve uniform and high CNT density, and their transient behavior may be a primary cause of the well-known nonuniform density of CNT forests.« less

  13. Chemical vapour deposition growth of carbon nanotube forests: kinetics, morphology, composition, and their mechanisms

    NASA Astrophysics Data System (ADS)

    Vinten, Phillip

    This thesis analyzes the chemical vapour deposition (CVD) growth of vertically aligned carbon nanotube (CNT) forests in order to understand how CNT forests grow, why they stop growing, and how to control the properties of the synthesized CNTs. in situ kinetics data of the growth of CNT forests are gathered by in situ optical microscopy. The overall morphology of the forests and the characteristics of the individual CNTs in the forests are investigated using scanning electron microscopy and Raman spectroscopy. The in situ data show that forest growth and termination are activated processes (with activation energies on the order of 1 eV), suggesting a possible chemical origin. The activation energy changes at a critical temperature for ethanol CVD (approximately 870°C). These activation energies and critical temperature are also seen in the temperature dependence of several important characteristics of the CNTs, including the defect density as determined by Raman spectroscopy. This observation is seen across several CVD processes and suggests a mechanism of defect healing. The CNT diameter also depends on the growth temperature. In this thesis, a thermodynamic model is proposed. This model predicts a temperature and pressure dependence of the CNT diameter from the thermodynamics of the synthesis reaction and the effect of strain on the enthalpy of formation of CNTs. The forest morphology suggests significant interaction between the constituent CNTs. These interactions may play a role in termination. The morphology, in particular a microscale rippling feature that is capable of diffracting light, suggest a non-uniform growth rate across the forest. A gas phase diffusion model predicts a non-uniform distribution of the source gas. This gas phase diffusion is suggested as a possible explanation for the non-uniform growth rate. The gas phase diffusion is important because growth by acetylene CVD is found to be very efficient (approximately 30% of the acetylene is

  14. Hybrid C-nanotubes/Si 3D nanostructures by one-step growth in a dual-plasma reactor

    NASA Astrophysics Data System (ADS)

    Toschi, Francesco; Orlanducci, Silvia; Guglielmotti, Valeria; Cianchetta, Ilaria; Magni, Corrado; Terranova, Maria Letizia; Pasquali, Matteo; Tamburri, Emanuela; Matassa, Roberto; Rossi, Marco

    2012-06-01

    Hybrid nanostructures consisting of Si polycrystalline nanocones, with an anemone-like termination coated with C-nanotubes bundles, have been generated on a (1 0 0) Si substrate in a dual mode microwave/radio-frequency plasma reactor. The substrate is both heated and bombarded by energetic H ions during the synthesis process. The nanocones growth is explained considering pull of the growing Si nanocrystalline phase along the lines of the electrical field, likely via a molten/recrystallization mechanism. The one-step building of the achieved complex 3D architectures is described in terms of dynamic competition between Si and C nanotubes growth under the peculiar conditions of kinetically driven processes.

  15. Modeling plasma-assisted growth of graphene-carbon nanotube hybrid

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tewari, Aarti

    2016-08-15

    A theoretical model describing the growth of graphene-CNT hybrid in a plasma medium is presented. Using the model, the growth of carbon nanotube (CNT) on a catalyst particle and thereafter the growth of the graphene on the CNT is studied under the purview of plasma sheath and number density kinetics of different plasma species. It is found that the plasma parameter such as ion density; gas ratios and process parameter such as source power affect the CNT and graphene dimensions. The variation in growth rates of graphene and CNT under different plasma power, gas ratios, and ion densities is analyzed.more » Based on the results obtained, it can be concluded that higher hydrocarbon ion densities and gas ratios of hydrocarbon to hydrogen favor the growth of taller CNTs and graphene, respectively. In addition, the CNT tip radius reduces with hydrogen ion density and higher plasma power favors graphene with lesser thickness. The present study can help in better understanding of the graphene-CNT hybrid growth in a plasma medium.« less

  16. Modeling of the HiPco process for carbon nanotube production. I. Chemical kinetics

    NASA Technical Reports Server (NTRS)

    Dateo, Christopher E.; Gokcen, Tahir; Meyyappan, M.

    2002-01-01

    A chemical kinetic model is developed to help understand and optimize the production of single-walled carbon nanotubes via the high-pressure carbon monoxide (HiPco) process, which employs iron pentacarbonyl as the catalyst precursor and carbon monoxide as the carbon feedstock. The model separates the HiPco process into three steps, precursor decomposition, catalyst growth and evaporation, and carbon nanotube production resulting from the catalyst-enhanced disproportionation of carbon monoxide, known as the Boudouard reaction: 2 CO(g)-->C(s) + CO2(g). The resulting detailed model contains 971 species and 1948 chemical reactions. A second model with a reduced reaction set containing 14 species and 22 chemical reactions is developed on the basis of the detailed model and reproduces the chemistry of the major species. Results showing the parametric dependence of temperature, total pressure, and initial precursor partial pressures are presented, with comparison between the two models. The reduced model is more amenable to coupled reacting flow-field simulations, presented in the following article.

  17. Gallium-mediated growth of multiwall carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Pan, Zheng Wei; Dai, Sheng; Beach, David B.; Evans, Neal D.; Lowndes, Douglas H.

    2003-03-01

    Liquid gallium was used as a viable and effective solvent and template for high-yield growth of multiwall carbon nanotubes. The gallium-mediated nanotubes thus obtained differ morphologically from nanotubes obtained by using transition metals as catalysts. The nanotubes have a pin-like morphology, generally composed of an oval-shaped tip filled with liquid gallium and a tapered hollow body. The inner diameter of the tube is so large that the inner/outer diameter ratio is usually larger than 0.9. The tubes are naturally opened at both ends. These gallium-filled nanotubes may be used as a nanothermometer in the temperature range of 30 to 550 °C. This study opens an interesting route for carbon nanotube synthesis.

  18. PECVD Growth of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    McAninch, Ian; Arnold, James O. (Technical Monitor)

    2001-01-01

    Plasma enhanced chemical vapor deposition (PECVD), using inductively coupled plasma, has been used to grow carbon nanotubes (CNTs) and graphitic carbon fibers (GCF) on substrates sputtered with aluminum and iron catalyst. The capacitive plasma's power has been shown to cause a transition from nanotubes to nanofibers, depending on the strength of the plasma. The temperature, placement, and other factors have been shown to affect the height and density of the tube and fiber growth.

  19. Carbon Nanotubes Growth on Graphite Fibers

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, Ching-Hua; Lehoczky, S. L.; Muntele, I.; Ila, D.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Carbon nanotubes (CNT) were synthesized on graphite fibers by thermal Chemical Vapor Deposition (CVD). On the fiber surface, iron nanoparticles are coated and act as catalysts for CNT growth. The growth temperature ranges from 550 to 1000 C at an ambient pressure. Methane and hydrogen gases with methane contents of 10% to 100% are used for the CNT synthesis. At high growth temperatures (greater than 800 C), the rapid inter-diffusion of the transition metal iron on the graphite surface results in a rough fiber surface with no CNT grown on the surface. When the growth temperature is relatively low (650 - 800 C), CNT are fabricated on the graphite surface with catalytic particles on the nanotube top ends. Using micro Raman spectroscopy in the breath mode region, single-walled or multi-walled CNT can be determined, depending on methane concentrations.

  20. Modeling of the HiPco process for carbon nanotube production. II. Reactor-scale analysis

    NASA Technical Reports Server (NTRS)

    Gokcen, Tahir; Dateo, Christopher E.; Meyyappan, M.

    2002-01-01

    The high-pressure carbon monoxide (HiPco) process, developed at Rice University, has been reported to produce single-walled carbon nanotubes from gas-phase reactions of iron carbonyl in carbon monoxide at high pressures (10-100 atm). Computational modeling is used here to develop an understanding of the HiPco process. A detailed kinetic model of the HiPco process that includes of the precursor, decomposition metal cluster formation and growth, and carbon nanotube growth was developed in the previous article (Part I). Decomposition of precursor molecules is necessary to initiate metal cluster formation. The metal clusters serve as catalysts for carbon nanotube growth. The diameter of metal clusters and number of atoms in these clusters are some of the essential information for predicting carbon nanotube formation and growth, which is then modeled by the Boudouard reaction with metal catalysts. Based on the detailed model simulations, a reduced kinetic model was also developed in Part I for use in reactor-scale flowfield calculations. Here this reduced kinetic model is integrated with a two-dimensional axisymmetric reactor flow model to predict reactor performance. Carbon nanotube growth is examined with respect to several process variables (peripheral jet temperature, reactor pressure, and Fe(CO)5 concentration) with the use of the axisymmetric model, and the computed results are compared with existing experimental data. The model yields most of the qualitative trends observed in the experiments and helps to understanding the fundamental processes in HiPco carbon nanotube production.

  1. Carbon nanotube growth density control

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance D. (Inventor); Schipper, John F. (Inventor)

    2010-01-01

    Method and system for combined coarse scale control and fine scale control of growth density of a carbon nanotube (CNT) array on a substrate, using a selected electrical field adjacent to a substrate surface for coarse scale density control (by one or more orders of magnitude) and a selected CNT growth temperature range for fine scale density control (by multiplicative factors of less than an order of magnitude) of CNT growth density. Two spaced apart regions on a substrate may have different CNT growth densities and/or may use different feed gases for CNT growth.

  2. Catalyst-induced growth of carbon nanotubes on tips of cantilevers and nanowires

    DOEpatents

    Lee, James Weifu; Lowndes, Douglas H.; Merkulov, Vladimir I.; Eres, Gyula; Wei, Yayi; Greenbaum, Elias; Lee, Ida

    2004-06-29

    A method is described for catalyst-induced growth of carbon nanotubes, nanofibers, and other nanostructures on the tips of nanowires, cantilevers, conductive micro/nanometer structures, wafers and the like. The method can be used for production of carbon nanotube-anchored cantilevers that can significantly improve the performance of scaning probe microscopy (AFM, EFM etc). The invention can also be used in many other processes of micro and/or nanofabrication with carbon nanotubes/fibers. Key elements of this invention include: (1) Proper selection of a metal catalyst and programmable pulsed electrolytic deposition of the desired specific catalyst precisely at the tip of a substrate, (2) Catalyst-induced growth of carbon nanotubes/fibers at the catalyst-deposited tips, (3) Control of carbon nanotube/fiber growth pattern by manipulation of tip shape and growth conditions, and (4) Automation for mass production.

  3. Effect of different carrier gases and their flow rates on the growth of carbon nanotubes

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tewari, Aarti; Sharma, Suresh C.

    2015-04-15

    The present paper examines the effect of different carrier gases and their flow rates on the growth of carbon nanotubes (CNTs). A theoretical model is developed incorporating the charging rate of the carbon nanotube, kinetics of all the plasma species, and the growth rate of the CNTs because of diffusion and accretion of ions on the catalyst nanoparticle. The three different carrier gases, i.e., argon (Ar), ammonia, and nitrogen, are considered in the present investigation, and flow rates of all the three carrier gases are varied individually (keeping the flow rates of hydrocarbon and hydrogen gas constant) to investigate themore » variations in the number densities of hydrocarbon and hydrogen ions in the plasma and their consequent effects on the height and radius of CNT. Based on the results obtained, it is concluded that Ar favors the formation of CNTs with larger height and radius whereas ammonia contributes to better height of CNT but decreases the radius of CNT, and nitrogen impedes both the height and radius of CNT. The present work can serve to the better understanding of process parameters during growth of CNTs by a plasma enhanced chemical vapor deposition process.« less

  4. Indium telluride nanotubes: Solvothermal synthesis, growth mechanism, and properties

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhou, Liyan; Yan, Shancheng, E-mail: yansc@njupt.edu.cn; School of Geography and Biological Information, Nanjing University of Posts and Telecommunications, Nanjing 210046

    2014-03-15

    A convenient solvothermal approach was applied for the first time to synthesize In{sub 2}Te{sub 3} nanotubes. The morphology of the resultant nanotubes was studied by scanning electron microscopy and transmission electron microscopy. Nanotubes with a relatively uniform diameter of around 500 nm, tube wall thickness of 50–100 nm, and average length of tens of microns were obtained. X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy were used to study the crystal structures, composition, and optical properties of the products. To understand the growth mechanism of the In{sub 2}Te{sub 3} nanotubes, we studied the influences of temperature, reaction time, and polyvinylpyrrolidonemore » (PVP) and ethylene diamine (EDA) dosages on the final products. Based on the experimental results, a possible growth mechanism of In{sub 2}Te{sub 3} nanotubes was proposed. In this mechanism, TeO{sub 3}{sup −2} is first reduced to allow nucleation. Circumferential edges of these nucleated molecules attract further deposition, and nanotubes finally grow rapidly along the c-axis and relatively slowly along the circumferential direction. The surface area of the products was determined by BET and found to be 137.85 m{sup 2} g{sup −1}. This large surface area indicates that the nanotubes may be suitable for gas sensing and hydrogen storage applications. The nanotubes also showed broad light detection ranging from 300 nm to 1100 nm, which covers the UV–visible–NIR regions. Such excellent optical properties indicate that In{sub 2}Te{sub 3} nanotubes may enable significant advancements in new photodetection and photosensing applications. -- Graphical abstract: A convenient solvothermal approach was applied to synthesize In{sub 2}Te{sub 3} nanotubes, which has not been reported in the literature for our knowledge. Surface area of this material is 137.85 m{sup 2} g{sup −1} from the BET testing, and such a high value makes it probably suitable for gas sensing

  5. In situ evidence for chirality-dependent growth rates of individual carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Rao, Rahul; Liptak, David; Cherukuri, Tonya; Yakobson, Boris I.; Maruyama, Benji

    2012-03-01

    Chiral-selective growth of single-walled carbon nanotubes (SWNTs) remains a great challenge that hinders their use in applications such as electronics and medicine. Recent experimental and theoretical reports have begun to address this problem by suggesting that selectivity may be achieved during nucleation by changing the catalyst composition or structure. Nevertheless, to establish a rational basis for chiral-selective synthesis, the underlying mechanisms governing nucleation, growth, and termination of SWNTs must be better understood. To this end, we report the first measurements of growth rates of individual SWNTs through in situ Raman spectroscopy and correlate them with their chiral angles. Our results show that the growth rates are directly proportional to the chiral angles, in agreement with recent theoretical predictions. Importantly, the evidence singles out the growth stage as responsible for the chiral distribution—distinct from nucleation and termination which might also affect the final product distribution. Our results suggest a route to chiral-selective synthesis of SWNTs through rational synthetic design strategies based on kinetic control.

  6. CVD Growth of Carbon Nanotubes: Structure, Catalyst, and Growth

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance

    2003-01-01

    Carbon nanotubes (CNTs) exhibit extraordinary mechanical and unique electronic properties and hence have been receiving much attention in recent years for their potential in nanoelectronics, field emission devices, scanning probes, high strength composites and many more applications. Catalytic decomposition of hydrocarbon feedstock with the aid of supported transition metal catalysts - also known as chemical vapor deposition (CVD) - has become popular to produce single-walled and multi-walled nanotubes (SWNTs, MWNTs) and multiwalled nanofibers (MWNFs). The ability to grow CNTs on patterned substrates and in vertically aligned arrays, and the simplicity of the process, has made CVD growth of CNTs an attractive approach.

  7. Patterned growth of carbon nanotubes obtained by high density plasma chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Mousinho, A. P.; Mansano, R. D.

    2015-03-01

    Patterned growth of carbon nanotubes by chemical vapor deposition represents an assembly approach to place and orient nanotubes at a stage as early as when they are synthesized. In this work, the carbon nanotubes were obtained at room temperature by High Density Plasmas Chemical Vapor Deposition (HDPCVD) system. This CVD system uses a new concept of plasma generation, where a planar coil coupled to an RF system for plasma generation was used with an electrostatic shield for plasma densification. In this mode, high density plasmas are obtained. We also report the patterned growth of carbon nanotubes on full 4-in Si wafers, using pure methane plasmas and iron as precursor material (seed). Photolithography processes were used to pattern the regions on the silicon wafers. The carbon nanotubes were characterized by micro-Raman spectroscopy, the spectra showed very single-walled carbon nanotubes axial vibration modes around 1590 cm-1 and radial breathing modes (RBM) around 120-400 cm-1, confirming that high quality of the carbon nanotubes obtained in this work. The carbon nanotubes were analyzed by atomic force microscopy and scanning electron microscopy too. The results showed that is possible obtain high-aligned carbon nanotubes with patterned growth on a silicon wafer with high reproducibility and control.

  8. Plasma Enhanced Growth of Carbon Nanotubes For Ultrasensitive Biosensors

    NASA Technical Reports Server (NTRS)

    Cassell, Alan M.; Meyyappan, M.

    2004-01-01

    The multitude of considerations facing nanostructure growth and integration lends itself to combinatorial optimization approaches. Rapid optimization becomes even more important with wafer-scale growth and integration processes. Here we discuss methodology for developing plasma enhanced CVD growth techniques for achieving individual, vertically aligned carbon nanostructures that show excellent properties as ultrasensitive electrodes for nucleic acid detection. We utilize high throughput strategies for optimizing the upstream and downstream processing and integration of carbon nanotube electrodes as functional elements in various device types. An overview of ultrasensitive carbon nanotube based sensor arrays for electrochemical bio-sensing applications and the high throughput methodology utilized to combine novel electrode technology with conventional MEMS processing will be presented.

  9. Plasma Enhanced Growth of Carbon Nanotubes For Ultrasensitive Biosensors

    NASA Technical Reports Server (NTRS)

    Cassell, Alan M.; Li, J.; Ye, Q.; Koehne, J.; Chen, H.; Meyyappan, M.

    2004-01-01

    The multitude of considerations facing nanostructure growth and integration lends itself to combinatorial optimization approaches. Rapid optimization becomes even more important with wafer-scale growth and integration processes. Here we discuss methodology for developing plasma enhanced CVD growth techniques for achieving individual, vertically aligned carbon nanostructures that show excellent properties as ultrasensitive electrodes for nucleic acid detection. We utilize high throughput strategies for optimizing the upstream and downstream processing and integration of carbon nanotube electrodes as functional elements in various device types. An overview of ultrasensitive carbon nanotube based sensor arrays for electrochemical biosensing applications and the high throughput methodology utilized to combine novel electrode technology with conventional MEMS processing will be presented.

  10. Epitaxial Growth of Aligned and Continuous Carbon Nanofibers from Carbon Nanotubes.

    PubMed

    Lin, Xiaoyang; Zhao, Wei; Zhou, Wenbin; Liu, Peng; Luo, Shu; Wei, Haoming; Yang, Guangzhi; Yang, Junhe; Cui, Jie; Yu, Richeng; Zhang, Lina; Wang, Jiaping; Li, Qunqing; Zhou, Weiya; Zhao, Weisheng; Fan, Shoushan; Jiang, Kaili

    2017-02-28

    Exploiting the superior properties of nanomaterials at macroscopic scale is a key issue of nanoscience. Different from the integration strategy, "additive synthesis" of macroscopic structures from nanomaterial templates may be a promising choice. In this paper, we report the epitaxial growth of aligned, continuous, and catalyst-free carbon nanofiber thin films from carbon nanotube films. The fabrication process includes thickening of continuous carbon nanotube films by gas-phase pyrolytic carbon deposition and further graphitization of the carbon layer by high-temperature treatment. As-fabricated nanofibers in the film have an "annual ring" cross-section, with a carbon nanotube core and a graphitic periphery, indicating the templated growth mechanism. The absence of a distinct interface between the carbon nanotube template and the graphitic periphery further implies the epitaxial growth mechanism of the fiber. The mechanically robust thin film with tunable fiber diameters from tens of nanometers to several micrometers possesses low density, high electrical conductivity, and high thermal conductivity. Further extension of this fabrication method to enhance carbon nanotube yarns is also demonstrated, resulting in yarns with ∼4-fold increased tensile strength and ∼10-fold increased Young's modulus. The aligned and continuous features of the films together with their outstanding physical and chemical properties would certainly promote the large-scale applications of carbon nanofibers.

  11. Deployment of titanium thermal barrier for low-temperature carbon nanotube growth

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chen, G.Y.; Poa, C.H.P.; Henley, S.J.

    2005-12-19

    Chemical vapor-synthesized carbon nanotubes are typically grown at temperatures around 600 deg. C. We report on the deployment of a titanium layer to help elevate the constraints on the substrate temperature during plasma-assisted growth. The growth is possible through the lowering of the hydrocarbon content used in the deposition, with the only source of heat provided by the plasma. The nanotubes synthesized have a small diameter distribution, which deviates from the usual trend that the diameter is determined by the thickness of the catalyst film. Simple thermodynamic simulations also show that the quantity of heat, that can be distributed, ismore » determined by the thickness of the titanium layer. Despite the lower synthesis temperature, it is shown that this technique allows for high growth rates as well as better quality nanotubes.« less

  12. In situ study of single-walled carbon nanotube growth in an environmental scanning electron microscope.

    PubMed

    Mehedi, H-A; Ravaux, J; Tahir, S; Podor, R; Jourdain, V

    2016-12-16

    Monitoring individual single-walled carbon nanotubes (SWCNTs) during their growth is a highly sought-after goal in view of understanding the processes involved in the nucleation, elongation and termination which ultimately control the diameter and chiral selectivity. Here, we report on the first truly in situ observations of SWCNT growth in an environmental scanning electron microscope (ESEM). The CNT growth from lithographically patterned catalysts was investigated as a function of the catalyst type (Fe, Co or Ni), temperature, type of precursor (ethanol or acetylene), gas phase composition and pressure, and pretreatment conditions, and we report on the most appropriate conditions for SWCNT growth in ESEM conditions. We show that this approach allows the observation at the submicron scale of the different steps of the nanotube synthesis including the catalyst reduction, the growth and percolation of the nanotube network, and the deposition of individual nanotubes grown in the gas phase on the substrate. Despite these obvious advantages, we identified a few limitations which will need to be tackled for fully taking advantage of the approach, for instance for monitoring the growth of individual SWCNTs by ESEM, including the short lifetime of the catalyst nanoparticles, the preference for kite growth (by opposition to surface growth) and the influence of the electron beam on the nanotube growth.

  13. Thermodynamics versus Kinetics Dichotomy in the Linear Self-Assembly of Mixed Nanoblocks.

    PubMed

    Ruiz, L; Keten, S

    2014-06-05

    We report classical and replica exchange molecular dynamics simulations that establish the mechanisms underpinning the growth kinetics of a binary mix of nanorings that form striped nanotubes via self-assembly. A step-growth coalescence model captures the growth process of the nanotubes, which suggests that high aspect ratio nanostructures can grow by obeying the universal laws of self-similar coarsening, contrary to systems that grow through nucleation and elongation. Notably, striped patterns do not depend on specific growth mechanisms, but are governed by tempering conditions that control the likelihood of depropagation and fragmentation.

  14. Optical Plasma Control During ARC Carbon Nanotube Growth

    NASA Technical Reports Server (NTRS)

    Hinkov, I.; Farhat, S.; DeLaChapelle, M. Lamy; Fan, S. S.; Han, H. X.; Li, G. H.; Scott, C. D.

    2001-01-01

    To improve nanotube production, we developed a novel optical control technique, based on the shape of the visible plasma zone created between the anode and the cathode in the direct current (DC) arc process. For a given inert gas, we adjust the anode to cathode distance (ACD) in order to obtain strong visible vortices around the cathode. This enhance anode vaporization, which improve nanotubes formation. In light of our experimental results, we focus our discussion on the relationship between plasma parameters and nanotube growth. Plasma temperature control during arc process is achieved using argon, helium, and their mixtures as a buffer gases. The variation of the gas mixture from pure argon to pure helium changes plasma temperature. As a consequence, the microscopic characteristics of nanotubes as diameter distribution is changed moving from smaller values for argon to higher diameters for helium. We also observe a dependence of the macroscopic characteristics of the final products as Brunauer-Emmett-Teller (BET) surface area.

  15. Graphene as an atomically thin interface for growth of vertically aligned carbon nanotubes.

    PubMed

    Rao, Rahul; Chen, Gugang; Arava, Leela Mohana Reddy; Kalaga, Kaushik; Ishigami, Masahiro; Heinz, Tony F; Ajayan, Pulickel M; Harutyunyan, Avetik R

    2013-01-01

    Growth of vertically aligned carbon nanotube (CNT) forests is highly sensitive to the nature of the substrate. This constraint narrows the range of available materials to just a few oxide-based dielectrics and presents a major obstacle for applications. Using a suspended monolayer, we show here that graphene is an excellent conductive substrate for CNT forest growth. Furthermore, graphene is shown to intermediate growth on key substrates, such as Cu, Pt, and diamond, which had not previously been compatible with nanotube forest growth. We find that growth depends on the degree of crystallinity of graphene and is best on mono- or few-layer graphene. The synergistic effects of graphene are revealed by its endurance after CNT growth and low contact resistances between the nanotubes and Cu. Our results establish graphene as a unique interface that extends the class of substrate materials for CNT growth and opens up important new prospects for applications.

  16. Graphene as an atomically thin interface for growth of vertically aligned carbon nanotubes

    PubMed Central

    Rao, Rahul; Chen, Gugang; Arava, Leela Mohana Reddy; Kalaga, Kaushik; Ishigami, Masahiro; Heinz, Tony F.; Ajayan, Pulickel M.; Harutyunyan, Avetik R.

    2013-01-01

    Growth of vertically aligned carbon nanotube (CNT) forests is highly sensitive to the nature of the substrate. This constraint narrows the range of available materials to just a few oxide-based dielectrics and presents a major obstacle for applications. Using a suspended monolayer, we show here that graphene is an excellent conductive substrate for CNT forest growth. Furthermore, graphene is shown to intermediate growth on key substrates, such as Cu, Pt, and diamond, which had not previously been compatible with nanotube forest growth. We find that growth depends on the degree of crystallinity of graphene and is best on mono- or few-layer graphene. The synergistic effects of graphene are revealed by its endurance after CNT growth and low contact resistances between the nanotubes and Cu. Our results establish graphene as a unique interface that extends the class of substrate materials for CNT growth and opens up important new prospects for applications. PMID:23712556

  17. Study of the growth of CeO2 nanoparticles onto titanate nanotubes

    NASA Astrophysics Data System (ADS)

    Marques, Thalles M. F.; Ferreira, Odair P.; da Costa, Jose A. P.; Fujisawa, Kazunori; Terrones, Mauricio; Viana, Bartolomeu C.

    2015-12-01

    We report the study of the growth of CeO2 nanoparticles on the external walls and Ce4+ intercalation within the titanate nanotubes. The materials were fully characterized by multiple techniques, such as: Raman spectroscopy, infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The ion exchange processes in the titanate nanotubes were carried out using different concentrations of Ce4+ in aqueous solution. Our results indicate that the growth of CeO2 nanoparticles grown mediated by the hydrolysis in the colloidal species of Ce and the attachment onto the titanate nanotubes happened and get it strongly anchored to the titanate nanotube surface by a simple electrostatic interaction between the nanoparticles and titanate nanotubes, which can explain the small size and even distribution of nanoparticles on titanate supports. It was demonstrated that it is possible to control the amount and size of CeO2 nanoparticles onto the nanotube surface, the species of the Ce ions intercalated between the layers of titanate nanotubes, and the materials could be tuned for using in specific catalysis in according with the amount of CeO2 nanoparticles, their oxygen vacancies/defects and the types of Ce species (Ce4+ or Ce3+) present into the nanotubes.

  18. Controlled Patterning and Growth of Single Wall and Multi-wall Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance D. (Inventor)

    2005-01-01

    Method and system for producing a selected pattern or array of at least one of a single wall nanotube and/or a multi-wall nanotube containing primarily carbon. A substrate is coated with a first layer (optional) of a first selected metal (e.g., Al and/or Ir) and with a second layer of a catalyst (e.g., Fe, Co, Ni and/or Mo), having selected first and second layer thicknesses provided by ion sputtering, arc discharge, laser ablation, evaporation or CVD. The first layer and/or the second layer may be formed in a desired non-uniform pattern, using a mask with suitable aperture(s), to promote growth of carbon nanotubes in a corresponding pattern. A selected heated feed gas (primarily CH4 or C2Hn with n=2 and/or 4) is passed over the coated substrate and forms primarily single wall nanotubes or multiple wall nanotubes, depending upon the selected feed gas and its temperature. Nanofibers, as well as single wall and multi-wall nanotubes, are produced using plasma-aided growth from the second (catalyst) layer. An overcoating of a selected metal or alloy can be deposited, over the second layer, to provide a coating for the carbon nanotubes grown in this manner.

  19. Kinetic Model of Growth of Arthropoda Populations

    NASA Astrophysics Data System (ADS)

    Ershov, Yu. A.; Kuznetsov, M. A.

    2018-05-01

    Kinetic equations were derived for calculating the growth of crustacean populations ( Crustacea) based on the biological growth model suggested earlier using shrimp ( Caridea) populations as an example. The development cycle of successive stages for populations can be represented in the form of quasi-chemical equations. The kinetic equations that describe the development cycle of crustaceans allow quantitative prediction of the development of populations depending on conditions. In contrast to extrapolation-simulation models, in the developed kinetic model of biological growth the kinetic parameters are the experimental characteristics of population growth. Verification and parametric identification of the developed model on the basis of the experimental data showed agreement with experiment within the error of the measurement technique.

  20. Continuous growth of single-wall carbon nanotubes using chemical vapor deposition

    DOEpatents

    Grigorian, Leonid [Raymond, OH; Hornyak, Louis [Evergreen, CO; Dillon, Anne C [Boulder, CO; Heben, Michael J [Denver, CO

    2008-10-07

    The invention relates to a chemical vapor deposition process for the continuous growth of a carbon single-wall nanotube where a carbon-containing gas composition is contacted with a porous membrane and decomposed in the presence of a catalyst to grow single-wall carbon nanotube material. A pressure differential exists across the porous membrane such that the pressure on one side of the membrane is less than that on the other side of the membrane. The single-wall carbon nanotube growth may occur predominately on the low-pressure side of the membrane or, in a different embodiment of the invention, may occur predominately in between the catalyst and the membrane. The invention also relates to an apparatus used with the carbon vapor deposition process.

  1. Continuous growth of single-wall carbon nanotubes using chemical vapor deposition

    DOEpatents

    Grigorian, Leonid; Hornyak, Louis; Dillon, Anne C; Heben, Michael J

    2014-09-23

    The invention relates to a chemical vapor deposition process for the continuous growth of a carbon single-wall nanotube where a carbon-containing gas composition is contacted with a porous membrane and decomposed in the presence of a catalyst to grow single-wall carbon nanotube material. A pressure differential exists across the porous membrane such that the pressure on one side of the membrane is less than that on the other side of the membrane. The single-wall carbon nanotube growth may occur predominately on the low-pressure side of the membrane or, in a different embodiment of the invention, may occur predominately in between the catalyst and the membrane. The invention also relates to an apparatus used with the carbon vapor deposition process.

  2. A Novel Catalyst Deposition Technique for the Growth of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance; Cassell, A.; Stevens, R.; Nguyen, C.; Meyyappan, M.; DeVincenzi, Donald L. (Technical Monitor)

    2001-01-01

    This viewgraph presentation provides information on the development of a technique at NASA's Ames Research Center by which carbon nanotubes (NT) can be grown. The project had several goals which included: 1) scaleability, 2) ability to control single wall nanotube (SWNT) and multiwall nanotube (MWNT) formation, 3) ability to control the density of nanotubes as they grow, 4) ability to apply standard masking techniques for NT patterning. Information regarding the growth technique includes its use of a catalyst deposition process. SWNTs of varying thicknesses can be grown by changing the catalyst composition. Demonstrations are given of various methods of masking including the use of transmission electron microscopic (TEM) grids.

  3. Combinatorial Optimization of Heterogeneous Catalysts Used in the Growth of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Cassell, Alan M.; Verma, Sunita; Delzeit, Lance; Meyyappan, M.; Han, Jie

    2000-01-01

    Libraries of liquid-phase catalyst precursor solutions were printed onto iridium-coated silicon substrates and evaluated for their effectiveness in catalyzing the growth of multi-walled carbon nanotubes (MWNTs) by chemical vapor deposition (CVD). The catalyst precursor solutions were composed of inorganic salts and a removable tri-block copolymer (EO)20(PO)70(EO)20 (EO = ethylene oxide, PO = propylene oxide) structure-directing agent (SDA), dissolved in ethanol/methanol mixtures. Sample libraries were quickly assayed using scanning electron microscopy after CVD growth to identify active catalysts and CVD conditions. Composition libraries and focus libraries were then constructed around the active spots identified in the discovery libraries to understand how catalyst precursor composition affects the yield, density, and quality of the nanotubes. Successful implementation of combinatorial optimization methods in the development of highly active, carbon nanotube catalysts is demonstrated, as well as the identification of catalyst formulations that lead to varying densities and shapes of aligned nanotube towers.

  4. Controlled growth-reversal of catalytic carbon nanotubes under electron-beam irradiation.

    PubMed

    Stolojan, Vlad; Tison, Yann; Chen, Guan Yow; Silva, Ravi

    2006-09-01

    The growth of carbon nanotubes from Ni catalysts is reversed and observed in real time in a transmission electron microscope, at room temperature. The Ni catalyst is found to be Ni3C and remains attached to the nanotube throughout the irradiation sequence, indicating that C most likely diffuses on the surface of the catalyst to form nanotubes. We calculate the energy barrier for saturating the Ni3C (2-13) surface with C to be 0.14 eV, thus providing a low-energy surface for the formation of graphene planes.

  5. Carbon Nanotubes Growth by CVD on Graphite Fibers

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, Ching-Hua; Cochrane, J. C.; Lehoczky, S. L.; Muntele, I.; Ila, D.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Due to the superior electrical and mechanical properties of carbon nanotubes (CNT), synthesizing CNT on various substances for electronics devices and reinforced composites have been engaged in many efforts for applications. This presentation will illustrate CNT synthesized on graphite fibers by thermal CVD. On the fiber surface, iron nanoparticles as catalysts for CNT growth are coated. The growth temperature ranges from 600 to 1000 C and the pressure ranges from 100 Torr to one atmosphere. Methane and hydrogen gases with methane content of 10% to 100% are used for the CNT synthesis. At high growth temperatures (greater than or equal to 900 C), the rapid inter-diffusion of the transition metal iron on the graphite surface results in the rough fiber surface without any CNT grown on it. When the growth temperature is relative low (650-800 C), CNT with catalytic particles on the nanotube top ends are fabricated on the graphite surface. (Methane and hydrogen gases with methane content of 10% to 100% are used for the CNT synthesis.) (By measuring the samples) Using micro Raman spectroscopy in the breath mode region, single-walled or multi-walled CNT (MWCNT), depending on growth concentrations, are found. Morphology, length and diameter of these MWCNT are determined by scanning electron microscopy and Raman spectroscopy. The detailed results of syntheses and characterizations will be discussed in the presentation.

  6. Templated Growth of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Siochik Emilie J. (Inventor)

    2007-01-01

    A method of growing carbon nanotubes uses a synthesized mesoporous si lica template with approximately cylindrical pores being formed there in. The surfaces of the pores are coated with a carbon nanotube precu rsor, and the template with the surfaces of the pores so-coated is th en heated until the carbon nanotube precursor in each pore is convert ed to a carbon nanotube.

  7. Growth behavior of carbon nanotubes on multilayered metal catalyst film (Al/Fe/Mo) in chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Cui, H.; Eres, G.; Howe, J. Y.; Puretzky, A.; Varela, M.; Geohegan, D. B.; Lowndes, D. H.

    2003-03-01

    The temperature- and time- dependences of carbon nanotube (CNT) growth by chemical vapor deposition are studied using a multilayered Al/Fe/Mo catalyst on silicon substrates. Within the 600 - 1100 ^oC temperature range in these studies, narrower temperature ranges were determined for the growth of aligned multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs). Aligned MWCNT growth is favored at lower temperatures ( ˜700 ^oC). At 900 ^oC, in contrast to earlier work, double-walled carbon nanotubes (DWCNTs) are found more abundant than SWCNTs. At further elevated temperature, highly defective carbon structures are produced. Defects also are found to accumulate faster than the ordered graphitic structure if the growth of CNTs is extended to long growth durations. Atomic force microscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy, and Raman spectroscopy are used to characterize the catalyst and various types of CNTs.

  8. Engineering catalytic activity via ion beam bombardment of catalyst supports for vertically aligned carbon nanotube growth

    NASA Astrophysics Data System (ADS)

    Islam, A. E.; Nikolaev, P.; Amama, P. B.; Zakharov, D.; Sargent, G.; Saber, S.; Huffman, D.; Erford, M.; Semiatin, S. L.; Stach, E. A.; Maruyama, B.

    2015-09-01

    Carbon nanotube growth depends on the catalytic activity of metal nanoparticles on alumina or silica supports. The control on catalytic activity is generally achieved by variations in water concentration, carbon feed, and sample placement on a few types of alumina or silica catalyst supports obtained via thin film deposition. We have recently expanded the choice of catalyst supports by engineering inactive substrates like c-cut sapphire via ion beam bombardment. The deterministic control on the structure and chemistry of catalyst supports obtained by tuning the degree of beam-induced damage have enabled better regulation of the activity of Fe catalysts only in the ion beam bombarded areas and hence enabled controllable super growth of carbon nanotubes. A wide range of surface characterization techniques were used to monitor the catalytically active surface engineered via ion beam bombardment. The proposed method offers a versatile way to control carbon nanotube growth in patterned areas and also enhances the current understanding of the growth process. With the right choice of water concentration, carbon feed and sample placement, engineered catalyst supports may extend the carbon nanotube growth yield to a level that is even higher than the ones reported here, and thus offers promising applications of carbon nanotubes in electronics, heat exchanger, and energy storage.

  9. Mechanical coupling limits the density and quality of self-organized carbon nanotube growth

    NASA Astrophysics Data System (ADS)

    Bedewy, Mostafa; Hart, A. John

    2013-03-01

    Aligned carbon nanotube (CNT) structures are promising for many applications; however, as-grown CNT "forests" synthesized by chemical vapor deposition (CVD) are typically low-density and mostly comprise tortuous defective CNTs. Here, we present evidence that the density and alignment of self-organized CNT growth is limited by mechanical coupling among CNTs in contact, in combination with their diameter-dependent growth rates. This study is enabled by comprehensive X-ray characterization of the spatially and temporally-varying internal morphology of CNT forests. Based on this data, we model the time evolution and diameter-dependent scaling of the ensuing mechanical forces on catalyst nanoparticles during CNT growth, which arise from the mismatch between the collective lengthening rate of the forest and the diameter-dependent growth rates of individual CNTs. In addition to enabling self-organization of CNTs into forests, time-varying forces between CNTs in contact dictate the hierarchical tortuous morphology of CNT forests, and may be sufficient to influence the structural quality of CNTs. These forces reach a maximum that is coincident with the maximum density observed in our growth process, and are proportional to CNT diameter. Therefore, we propose that improved manufacturing strategies for self-organized CNTs should consider both chemical and mechanical effects. This may be especially necessary to achieve high density CNT forests with low defect density, such as for improved thermal interfaces and high-permeability membranes.Aligned carbon nanotube (CNT) structures are promising for many applications; however, as-grown CNT "forests" synthesized by chemical vapor deposition (CVD) are typically low-density and mostly comprise tortuous defective CNTs. Here, we present evidence that the density and alignment of self-organized CNT growth is limited by mechanical coupling among CNTs in contact, in combination with their diameter-dependent growth rates. This study is

  10. Water-Assisted Highly Efficient Synthesis of Impurity-Free Single-Walled Carbon Nanotubes-``Super-Growth''

    NASA Astrophysics Data System (ADS)

    Hata, Kenji

    2005-03-01

    We demonstrate an extremely efficient chemical vapour deposition synthesis of single-walled carbon nanotubes where the activity and lifetime of the catalysts are enhanced by water [1]. Water-stimulated enhanced catalytic activity results in massive growth of super-dense and vertically-aligned nanotube forests with heights up to 2.5 millimeters that can be easily separated from the catalysts, providing nanotube material with carbon purity above 99.98%. Moreover, patterned highly organized intrinsic nanotube structures were successfully fabricated. The water-assisted synthesis method addresses many critical problems that currently plague carbon nanotube synthesis. [1] K. Hata, et al., Science, 306, 1362 (2004).

  11. The effects of functional magnetic nanotubes with incorporated nerve growth factor in neuronal differentiation of PC12 cells

    NASA Astrophysics Data System (ADS)

    Xie, Jining; Chen, Linfeng; Varadan, Vijay K.; Yancey, Justin; Srivatsan, Malathi

    2008-03-01

    In this in vitro study the efficiency of magnetic nanotubes to bind with nerve growth factor (NGF) and the ability of NGF-incorporated magnetic nanotubes to release the bound NGF are investigated using rat pheochromocytoma cells (PC12 cells). It is found that functional magnetic nanotubes with NGF incorporation enabled the differentiation of PC12 cells into neurons exhibiting growth cones and neurite outgrowth. Microscope observations show that filopodia extending from neuron growth cones were in close proximity to the NGF-incorporated magnetic nanotubes, at times appearing to extend towards or into them. These results show that magnetic nanotubes can be used as a delivery vehicle for NGF and thus may be exploited in attempts to treat neurodegenerative disorders such as Parkinson's disease with neurotrophins. Further neurite outgrowth can be controlled by manipulating magnetic nanotubes with external magnetic fields, thus helping in directed regeneration.

  12. Directed Growth of Carbon Nanotubes Across Gaps

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance; Meyyapan, Meyya

    2008-01-01

    An experiment has shown that when single-walled carbon nanotubes (SWNTs) are grown by chemical vapor deposition in the presence of an electric field of suitable strength, the nanotubes become aligned along the electric field. In an important class of contemplated applications, one would exploit this finding in fabricating nanotube transistors; one would grow SWNTs across gaps between electrodes that would serve, subsequently, as source and drain contacts during operation of the transistors. In preparation for the experiment, a multilayer catalyst comprising a 20-nmthick underlayer of iridium (platinum group), a 1-nm-thick middle layer of iron, and a 0.2-nm-thick outer layer of molybdenum was ion-beam sputtered onto a quartz substrate. A 25 micrometers-diameter iron wire was used as a shadow mask during the sputtering to create a 25 micrometers gap in the catalyst. Then electrical leads were connected to the catalyst areas separated by the gap so that these catalyst areas would also serve as electrodes. The substrate as thus prepared was placed in a growth chamber that consisted of a quartz tube of 1-in. (2.54-cm) diameter enclosed in a furnace. SWNTs of acceptably high quantity and quality were grown in 10 minutes with methane at atmospheric pressure flowing through the chamber at a rate of 1,000 standard cubic centimeters per minute at a temperature of 900 C. To prevent oxidation of the SWNTs, the chamber was purged with 99.999-percent pure argon before and after growth, and the chamber was cooled to less than 300 C before opening it to the atmosphere after growth. When no voltage was applied across the gap, the SWNTs grew in random directions extending out from the edges of the catalyst at the gap. When a potential of 10 V was applied between the catalyst/electrode areas to create an electric field across the gap, the SWNTs grew across the gap, as shown in the figure.

  13. High yield growth of patterned vertically aligned carbon nanotubes using inkjet-printed catalyst.

    PubMed

    Beard, James D; Stringer, Jonathan; Ghita, Oana R; Smith, Patrick J

    2013-10-09

    This study reports on the fabrication of vertically aligned carbon nanotubes localized at specific sites on a growth substrate by deposition of a nanoparticle suspension using inkjet printing. Carbon nanotubes were grown with high yield as vertically aligned forests to a length of approximately 400 μm. The use of inkjet printing for catalyst fabrication considerably improves the production rate of vertically aligned patterned nanotube forests compared with conventional patterning techniques, for example, electron beam lithography or photolithography.

  14. Crystal growth kinetics of triblock Janus colloids

    NASA Astrophysics Data System (ADS)

    Reinhart, Wesley F.; Panagiotopoulos, Athanassios Z.

    2018-03-01

    We measure the kinetics of crystal growth from a melt of triblock Janus colloids using non-equilibrium molecular dynamics simulations. We assess the impact of interaction anisotropy by systematically varying the size of the attractive patches from 40% to 100% coverage, finding substantially different growth behaviors in the two limits. With isotropic particles, the interface velocity is directly proportional to the subcooling, in agreement with previous studies. With highly anisotropic particles, the growth curves are well approximated by using a power law with exponent and prefactor that depend strongly on the particular surface geometry and patch fraction. This nonlinear growth appears correlated to the roughness of the solid-liquid interface, with the strongest growth inhibition occurring for the smoothest crystal faces. We conclude that crystal growth for patchy particles does not conform to the typical collision-limited mechanism, but is instead an activated process in which the rate-limiting step is the collective rotation of particles into the proper orientation. Finally, we show how differences in the growth kinetics could be leveraged to achieve kinetic control over polymorph growth, either enhancing or suppressing metastable phases near solid-solid coexistence lines.

  15. Engineering catalytic activity via ion beam bombardment of catalyst supports for vertically aligned carbon nanotube growth

    DOE PAGES

    Islam, A. E.; Zakharov, D.; Stach, E. A.; ...

    2015-09-16

    Carbon nanotube growth depends on the catalytic activity of metal nanoparticles on alumina or silica supports. The control on catalytic activity is generally achieved by variations in water concentration, carbon feed, and sample placement on a few types of alumina or silica catalyst supports obtained via thin film deposition. We have recently expanded the choice of catalyst supports by engineering inactive substrates like c-cut sapphire via ion beam bombardment. The deterministic control on the structure and chemistry of catalyst supports obtained by tuning the degree of beam-induced damage have enabled better regulation of the activity of Fe catalysts only inmore » the ion beam bombarded areas and hence enabled controllable super growth of carbon nanotubes. A wide range of surface characterization techniques were used to monitor the catalytically active surface engineered via ion beam bombardment. The proposed method offers a versatile way to control carbon nanotube growth in patterned areas and also enhances the current understanding of the growth process. As a result, with the right choice of water concentration, carbon feed and sample placement, engineered catalyst supports may extend the carbon nanotube growth yield to a level that is even higher than the ones reported here, and thus offers promising applications of carbon nanotubes in electronics, heat exchanger, and energy storage.« less

  16. Adsorption of crystal violet onto functionalised multi-walled carbon nanotubes: Equilibrium and kinetic studies.

    PubMed

    Sabna, V; Thampi, Santosh G; Chandrakaran, S

    2016-12-01

    Synthetic dyes present in effluent from textile, paper and paint industries contain crystal violet (CV), a known carcinogenic agent. This study investigates the modification of multiwalled carbon nanotubes by acid reflux method and equilibrium and kinetic behaviour of adsorption of CV onto functionalized multi-walled carbon nanotubes (fMWNTs) in batch system. High stability of the fMWNTs suspension in water indicates the hydrophilicity of fMWNTs induced due to the formation of functional groups that make hydrogen bonds with water molecules. fMWNTs were characterized by Fourier Transform Infra Red (FTIR) spectroscopy and the functional groups present on the fMWNTs were confirmed. Characteristic variation was observed in the FTIR spectra of fMWNTs after adsorption of crystal violet onto it. Adsorption characteristics were evaluated as a function of system variables such as contact time, dosage of fMWNTs and initial concentration and pH of the crystal violet solution. Adsorption capacity of fMWNTs and percentage removal of the dye increased with increase in contact time, adsorbent dosage and pH but declined with increase in initial concentration of the dye. fMWNTs showed higher adsorption capacity compared to that of pristine MWNTs. Data showed good fit with the Langmuir and Freundlich isotherm models and the pseudo-second order kinetic model; the maximum adsorption capacity was 90.52mg/g. Kinetic parameters such as rate constants, equilibrium adsorption capacities and regression coefficients were estimated. Results indicate that fMWNTs are an effective adsorbent for the removal of crystal violet from aqueous solution. Copyright © 2015 Elsevier Inc. All rights reserved.

  17. Concentration-dependent effects of carbon nanotubes on growth and biphenyl degradation of Dyella ginsengisoli LA-4.

    PubMed

    Qu, Yuanyuan; Wang, Jingwei; Zhou, Hao; Ma, Qiao; Zhang, Zhaojing; Li, Duanxing; Shen, Wenli; Zhou, Jiti

    2016-02-01

    To enrich the understanding on interactions between carbon nanotubes (CNTs) and microbes, the responses of a biphenyl-degrading bacterium to single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and carboxyl single-walled carbon nanotubes (SWCNT-COOHs) were investigated. Electron microscopy, viability test, cellular membrane integrity, and oxidative stress analyses indicated that CNT toxicity was mainly caused by physical piercing. Apart from antibacterial activities, the experimental results showed that CNTs enhanced cell growth and biphenyl degradation at certain concentrations (1.0-1.5 mg/L). The CNTs aggregated and adsorbed cells and biphenyl to form a CNTs-cells-biphenyl coexisting system, thus it created a suitable microenvironment for cell attachment and proliferation where the cells could utilize biphenyl easier for their growth. To the best of our knowledge, this is the first report about CNTs' impact on biodegradation efficacy and growth of aromatic-degrading bacterium.

  18. 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.

  19. Arrays of horizontal carbon nanotubes of controlled chirality grown using designed catalysts

    NASA Astrophysics Data System (ADS)

    Zhang, Shuchen; Kang, Lixing; Wang, Xiao; Tong, Lianming; Yang, Liangwei; Wang, Zequn; Qi, Kuo; Deng, Shibin; Li, Qingwen; Bai, Xuedong; Ding, Feng; Zhang, Jin

    2017-02-01

    The semiconductor industry is increasingly of the view that Moore’s law—which predicts the biennial doubling of the number of transistors per microprocessor chip—is nearing its end. Consequently, the pursuit of alternative semiconducting materials for nanoelectronic devices, including single-walled carbon nanotubes (SWNTs), continues. Arrays of horizontal nanotubes are particularly appealing for technological applications because they optimize current output. However, the direct growth of horizontal SWNT arrays with controlled chirality, that would enable the arrays to be adapted for a wider range of applications and ensure the uniformity of the fabricated devices, has not yet been achieved. Here we show that horizontal SWNT arrays with predicted chirality can be grown from the surfaces of solid carbide catalysts by controlling the symmetries of the active catalyst surface. We obtained horizontally aligned metallic SWNT arrays with an average density of more than 20 tubes per micrometre in which 90 per cent of the tubes had chiral indices of (12, 6), and semiconducting SWNT arrays with an average density of more than 10 tubes per micrometre in which 80 per cent of the nanotubes had chiral indices of (8, 4). The nanotubes were grown using uniform size Mo2C and WC solid catalysts. Thermodynamically, the SWNT was selectively nucleated by matching its structural symmetry and diameter with those of the catalyst. We grew nanotubes with chiral indices of (2m, m) (where m is a positive integer), the yield of which could be increased by raising the concentration of carbon to maximize the kinetic growth rate in the chemical vapour deposition process. Compared to previously reported methods, such as cloning, seeding and specific-structure-matching growth, our strategy of controlling the thermodynamics and kinetics offers more degrees of freedom, enabling the chirality of as-grown SWNTs in an array to be tuned, and can also be used to predict the growth conditions

  20. Efficiency of Nanotube Surface-Treated Dental Implants Loaded with Doxycycline on Growth Reduction of Porphyromonas gingivalis.

    PubMed

    Ferreira, Cimara Fortes; Babu, Jegdish; Hamlekhan, Azhang; Patel, Sweetu; Shokuhfar, Tolou

    The prevalence of peri-implant infection in patients with dental implants has been shown to range from 28% to 56%. A nanotube-modified implant surface can deliver antibiotics locally and suppress periodontal pathogenic bacterial growth. The aim of this study was to evaluate the deliverability of antibiotics via a nanotube-modified implant. Dental implants with a nanotube surface were fabricated and loaded with doxycycline. Afterward, each dental implant with a nanotube surface was placed into 2-mL tubes, removed from solution, and placed in a fresh solution daily for 28 days. Experimental samples from 1, 2, 4, 16, 24, and 28 days were used for this evaluation. The concentration of doxycycline was measured using spectrophotometric analysis at 273-nm absorbance. The antibacterial effect of doxycycline was evaluated by supplementing Porphyromonas gingivalis (P gingivalis) growth media with the solution collected from the dental implants at the aforementioned time intervals for a period of 48 hours under anaerobic conditions. A bacterial viability assay was used to evaluate P gingivalis growth at 550-nm absorbance. Doxycycline concentration varied from 0.33 to 1.22 μg/mL from day 1 to day 28, respectively. A bacterial viability assay showed the highest P gingivalis growth at day 1 (2 nm) and the lowest at day 4 (0.17 nm), with a gradual reduction from day 1 to day 4 of approximately 87.5%. The subsequent growth pattern was maintained and slightly increased from baseline in approximately 48.3% from day 1 to day 24. The final P gingivalis growth measured at day 28 was 29.4% less than the baseline growth. P gingivalis growth was suppressed in media supplemented with solution collected from dental implants with a nanotube surface loaded with doxycycline during a 28-day time interval.

  1. Carbon nanotubes on a substrate

    DOEpatents

    Gao, Yufei [Kennewick, WA; Liu, Jun [West Richland, WA

    2002-03-26

    The present invention includes carbon nanotubes whose hollow cores are 100% filled with conductive filler. The carbon nanotubes are in uniform arrays on a conductive substrate and are well-aligned and can be densely packed. The uniformity of the carbon nanotube arrays is indicated by the uniform length and diameter of the carbon nanotubes, both which vary from nanotube to nanotube on a given array by no more than about 5%. The alignment of the carbon nanotubes is indicated by the perpendicular growth of the nanotubes from the substrates which is achieved in part by the simultaneous growth of the conductive filler within the hollow core of the nanotube and the densely packed growth of the nanotubes. The present invention provides a densely packed carbon nanotube growth where each nanotube is in contact with at least one nearest-neighbor nanotube. The substrate is a conductive substrate coated with a growth catalyst, and the conductive filler can be single crystals of carbide formed by a solid state reaction between the substrate material and the growth catalyst. The present invention further provides a method for making the filled carbon nanotubes on the conductive substrates. The method includes the steps of depositing a growth catalyst onto the conductive substrate as a prepared substrate, creating a vacuum within a vessel which contains the prepared substrate, flowing H2/inert (e.g. Ar) gas within the vessel to increase and maintain the pressure within the vessel, increasing the temperature of the prepared substrate, and changing the H2/Ar gas to ethylene gas such that the ethylene gas flows within the vessel. Additionally, varying the density and separation of the catalyst particles on the conductive substrate can be used to control the diameter of the nanotubes.

  2. Anodic aluminium oxide membranes used for the growth of carbon nanotubes.

    PubMed

    López, Vicente; Morant, Carmen; Márquez, Francisco; Zamora, Félix; Elizalde, Eduardo

    2009-11-01

    The suitability of anodic aluminum oxide (AAO) membranes as template supported on Si substrates for obtaining organized iron catalyst for carbon nanotube (CNT) growth has been investigated. The iron catalyst was confined in the holes of the AAO membrane. CVD synthesis with ethylene as carbon source led to a variety of carbon structures (nanotubes, helices, bamboo-like, etc). In absence of AAO membrane the catalyst was homogeneously distributed on the Si surface producing a high density of micron-length CNTs.

  3. Nucleation and Growth Kinetics from LaMer Burst Data.

    PubMed

    Chu, Daniel B K; Owen, Jonathan S; Peters, Baron

    2017-10-12

    In LaMer burst nucleation, the individual nucleation events happen en masse, quasi-simultaneously, and at nearly identical homogeneous conditions. These properties make LaMer burst nucleation important for applications that require monodispersed particles and also for theoretical analyses. Sugimoto and co-workers predicted that the number of nuclei generated during a LaMer burst depends only on the solute supply rate and the growth rate, independent of the nucleation kinetics. Some experiments confirm that solute supply kinetics control the number of nuclei, but flaws in the original theoretical analysis raise questions about the predicted roles of growth and nucleation kinetics. We provide a rigorous analysis of the coupled equations that govern concentrations of nuclei and solutes. Our analysis confirms that the number of nuclei is largely determined by the solute supply and growth rates, but our predicted relationship differs from that of Sugimoto et al. Moreover, we find that additional nucleus size dependent corrections should emerge in systems with slow growth kinetics. Finally, we show how the nucleation kinetics determine the particle size distribution. We suggest that measured particle size distributions might therefore provide ways to test theoretical models of homogeneous nucleation kinetics.

  4. Atomistic Simulations of Graphene Growth: From Kinetics to Mechanism.

    PubMed

    Qiu, Zongyang; Li, Pai; Li, Zhenyu; Yang, Jinlong

    2018-03-20

    Epitaxial growth is a promising strategy to produce high-quality graphene samples. At the same time, this method has great flexibility for industrial scale-up. To optimize growth protocols, it is essential to understand the underlying growth mechanisms. This is, however, very challenging, as the growth process is complicated and involves many elementary steps. Experimentally, atomic-scale in situ characterization methods are generally not feasible at the high temperature of graphene growth. Therefore, kinetics is the main experimental information to study growth mechanisms. Theoretically, first-principles calculations routinely provide atomic structures and energetics but have a stringent limit on the accessible spatial and time scales. Such gap between experiment and theory can be bridged by atomistic simulations using first-principles atomic details as input and providing the overall growth kinetics, which can be directly compared with experiment, as output. Typically, system-specific approximations should be applied to make such simulations computationally feasible. By feeding kinetic Monte Carlo (kMC) simulations with first-principles parameters, we can directly simulate the graphene growth process and thus understand the growth mechanisms. Our simulations suggest that the carbon dimer is the dominant feeding species in the epitaxial growth of graphene on both Cu(111) and Cu(100) surfaces, which enables us to understand why the reaction is diffusion limited on Cu(111) but attachment limited on Cu(100). When hydrogen is explicitly considered in the simulation, the central role hydrogen plays in graphene growth is revealed, which solves the long-standing puzzle into why H 2 should be fed in the chemical vapor deposition of graphene. The simulation results can be directly compared with the experimental kinetic data, if available. Our kMC simulations reproduce the experimentally observed quintic-like behavior of graphene growth on Ir(111). By checking the

  5. Metal Nanoparticle Catalysts for Carbon Nanotube Growth

    NASA Technical Reports Server (NTRS)

    Pierce, Benjamin F.

    2003-01-01

    Work this summer involved and new and unique process for producing the metal nanoparticle catalysts needed for carbon nanotube (CNT) growth. There are many applications attributed to CNT's, and their properties have deemed them to be a hot spot in research today. Many groups have demonstrated the versatility in CNT's by exploring a wide spectrum of roles that these nanotubes are able to fill. A short list of such promising applications are: nanoscaled electronic circuitry, storage media, chemical sensors, microscope enhancement, and coating reinforcement. Different methods have been used to grow these CNT's. Some examples are laser ablation, flame synthesis, or furnace synthesis. Every single approach requires the presence of a metal catalyst (Fe, Co, and Ni are among the best) that is small enough to produce a CNT. Herein lies the uniqueness of this work. Microemulsions (containing inverse micelles) were used to generate these metal particles for subsequent CNT growth. The goal of this summer work was basically to accomplish as much preliminary work as possible. I strived to pinpoint which variable (experimental process, metal product, substrate, method of application, CVD conditions, etc.) was the determining factor in the results. The resulting SEM images were sufficient for the appropriate comparisons to be made. The future work of this project consists of the optimization of the more promising experimental procedures and further exploration onto what exactly dictated the results.

  6. Direct observation of morphological evolution of a catalyst during carbon nanotube forest growth: new insights into growth and growth termination

    NASA Astrophysics Data System (ADS)

    Jeong, Seojeong; Lee, Jaegeun; Kim, Hwan-Chul; Hwang, Jun Yeon; Ku, Bon-Cheol; Zakharov, Dmitri N.; Maruyama, Benji; Stach, Eric A.; Kim, Seung Min

    2016-01-01

    In this study, we develop a new methodology for transmission electron microscopy (TEM) analysis that enables us to directly investigate the interface between carbon nanotube (CNT) arrays and the catalyst and support layers for CNT forest growth without any damage induced by a post-growth TEM sample preparation. Using this methodology, we perform in situ and ex situ TEM investigations on the evolution of the morphology of the catalyst particles and observe the catalyst particles to climb up through CNT arrays during CNT forest growth. We speculate that the lifted catalysts significantly affect the growth and growth termination of CNT forests along with Ostwald ripening and sub-surface diffusion. Thus, we propose a modified growth termination model which better explains various phenomena related to the growth and growth termination of CNT forests.In this study, we develop a new methodology for transmission electron microscopy (TEM) analysis that enables us to directly investigate the interface between carbon nanotube (CNT) arrays and the catalyst and support layers for CNT forest growth without any damage induced by a post-growth TEM sample preparation. Using this methodology, we perform in situ and ex situ TEM investigations on the evolution of the morphology of the catalyst particles and observe the catalyst particles to climb up through CNT arrays during CNT forest growth. We speculate that the lifted catalysts significantly affect the growth and growth termination of CNT forests along with Ostwald ripening and sub-surface diffusion. Thus, we propose a modified growth termination model which better explains various phenomena related to the growth and growth termination of CNT forests. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05547d

  7. Tunneling effects in the kinetics of helium and hydrogen isotopes desorption from single-walled carbon nanotube bundles

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Danilchenko, B. A., E-mail: danil@iop.kiev.ua; Yaskovets, I. I.; Uvarova, I. Y.

    2014-04-28

    The kinetics of desorption both helium isotopes and molecules of hydrogen and deuterium from open-ended or γ-irradiated single-walled carbon nanotube bundles was investigated in temperature range of 10–300 K. The gases desorption rates obey the Arrhenius law at high temperatures, deviate from it with temperature reduction and become constant at low temperatures. These results indicate the quantum nature of gas outflow from carbon nanotube bundles. We had deduced the crossover temperature below which the quantum corrections to the effective activation energy of desorption become significant. This temperature follows linear dependence against the inverse mass of gas molecule and is consistent withmore » theoretical prediction.« less

  8. Chemical vapour deposition growth and Raman characterization of graphene layers and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Lai, Y.-C.; Rafailov, P. M.; Vlaikova, E.; Marinova, V.; Lin, S. H.; Yu, P.; Yu, S.-C.; Chi, G. C.; Dimitrov, D.; Sveshtarov, P.; Mehandjiev, V.; Gospodinov, M. M.

    2016-02-01

    Single-layer graphene films were grown by chemical vapour deposition (CVD) on Cu foil. The CVD process was complemented by plasma enhancement to grow also vertically aligned multiwalled carbon nanotubes using Ni nanoparticles as catalyst. The obtained samples were characterized by Raman spectroscopy analysis. Nature of defects in the samples and optimal growth conditions leading to achieve high quality of graphene and carbon nanotubes are discussed.

  9. Increased Alignment in Carbon Nanotube Growth

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance D. (Inventor)

    2007-01-01

    Method and system for fabricating an array of two or more carbon nanotube (CNT) structures on a coated substrate surface, the structures having substantially the same orientation with respect to a substrate surface. A single electrode, having an associated voltage source with a selected voltage, is connected to a substrate surface after the substrate is coated and before growth of the CNT structures, for a selected voltage application time interval. The CNT structures are then grown on a coated substrate surface with the desired orientation. Optionally, the electrode can be disconnected before the CNT structures are grown.

  10. Design and Development of an Acoustic Levitation System for Use in CVD Growth of Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Qasem, Amal ali

    The most widely used methods for growth of carbon nanotubes (CNTs) arc discharge, laser ablation, and chemical vapor deposition (CVD). Some of these methods have difficulties, such as controlling the quality and straightness of the nanotube in the synthesis of CNTs from substrates. Also, the enhanced plasma chemical vapor deposition method with the catalyst on a substrate produces straighter, larger diameter nanotubes by the tip growth method, but they are short. The difficulty in the floating catalyst method is that the nanotubes stay in the growth furnace for short times limiting growth to about one mm length; this method also leaves many catalyst impurities. One factor that limits CNT growth in these methods is the difficulty of getting enough carbon atoms to the growth catalyst to grow long nanotubes. The motivation of this work is that longer, higher quality nanotubes could be grown by increasing growth time and by increasing carbon atom movement to catalyst. The goal of this project is to use acoustic levitation to assist chemical vapor deposition growth by trapping and vibrating the growing CNTs for better properties. Our levitation system consists of a piezoelectric transducer attached to an aluminum horn and quartz rod extending into the growth furnace. The most important elements of our methods to achieve the acoustic levitation are as follows. 1. Using COMSOL Multi-physic Simulation software to determine the length of quartz rod needed to excite standing waves for levitation in the tube furnace. 2. Determining the resonance frequency of different transducers and horns. 3. Using ultrasound measurement to determine the time of flight, velocity of sound and sound wavelength of different horns. 4. Making Aluminum horns with the appropriate lengths. 5. Using ultrasound measurement to determine the changing of quartz rod velocity of sound and length in the furnace. 6. Mounting the transducer to booster horn and aluminum cylindrical horn above a reflector to

  11. The synergistic effect in the Fe-Co bimetallic catalyst system for the growth of carbon nanotube forests

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hardeman, D.; Esconjauregui, S., E-mail: cse28@cam.ac.uk; Cartwright, R.

    2015-01-28

    We report the growth of multi-walled carbon nanotube forests employing an active-active bimetallic Fe-Co catalyst. Using this catalyst system, we observe a synergistic effect by which—in comparison to pure Fe or Co—the height of the forests increases significantly. The homogeneity in the as-grown nanotubes is also improved. By both energy dispersive spectroscopy and in-situ x-ray photoelectron spectroscopy, we show that the catalyst particles consist of Fe and Co, and this dramatically increases the growth rate of the tubes. Bimetallic catalysts are thus potentially useful for synthesising nanotube forests more efficiently.

  12. 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

  13. Growth mechanisms in chemical vapour deposited carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Vinciguerra, Vincenzo; Buonocore, Francesco; Panzera, Giuseppe; Occhipinti, Luigi

    2003-06-01

    We present a model for the process of the growth of carbon nanotubes (CNTs) obtained by chemical vapour deposition in the presence of transition metal nanoparticles (Me-NPs) which act as a catalyst. We have deduced that the growth of a CNT occurs in the presence of two forces: (i) a viscous force, due to the surrounding hot gas, which opposes and slows down the growth of the CNT, and (ii) an extrusive force that causes the growth and that in the steady-state stage of the growth is completely balanced by the viscous force. We believe that it is the great decrease in free energy in the assembling reaction that occurs at the interface of the Me-NP catalyst that causes the extrusive force for the growth of a CNT. Moreover, the process of chemisorption of a C2 fragment, through the interaction of the C2-pi system with the 3d metal orbitals, has been considered as well as the coordination action of the Fe, Ni and Co metal surfaces. The structural properties of the Fe, Co and Ni surfaces show that the (1, - 1, 0) planes of Fe and the (1, 1, 1) planes of Co and Ni exhibit the symmetry and distances required to overlap with the lattice of a graphene sheet. This gives us information about the coordination mechanism responsible for assembling the CNTs. In fact, we show that it is possible to cleave an Me-NP in such a way as to match the correct symmetry and dimension of the armchair structure of a single-walled nanotube. The mechanism of C2 addition at the edge of the growing CNT has also been considered in relation to the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) symmetry. We demonstrate that the action of d orbitals of the metal atoms forming the Me-NP makes possible the thermally forbidden reaction, which involves the C2-pi system.

  14. Kinetic and isotherm modeling of Cd (II) adsorption by L-cysteine functionalized multi-walled carbon nanotubes as adsorbent.

    PubMed

    Taghavi, Mahmoud; Zazouli, Mohammad Ali; Yousefi, Zabihollah; Akbari-adergani, Behrouz

    2015-11-01

    In this study, multi-walled carbon nanotubes were functionalized by L-cysteine to show the kinetic and isotherm modeling of Cd (II) ions onto L-cysteine functionalized multi-walled carbon nanotubes. The adsorption behavior of Cd (II) ion was studied by varying parameters including dose of L-MWCNTs, contact time, and cadmium concentration. Equilibrium adsorption isotherms and kinetics were also investigated based on Cd (II) adsorption tests. The results showed that an increase in contact time and adsorbent dosage resulted in increase of the adsorption rate. The optimum condition of the Cd (II) removal process was found at pH=7.0, 15 mg/L L-MWCNTs dosage, 6 mg/L cadmium concentration, and contact time of 60 min. The removal percent was equal to 89.56 at optimum condition. Langmuir and Freundlich models were employed to analyze the experimental data. The data showed well fitting with the Langmuir model (R2=0.994) with q max of 43.47 mg/g. Analyzing the kinetic data by the pseudo-first-order and pseudo-second-order equations revealed that the adsorption of cadmium using L-MWSNTs following the pseudo-second-order kinetic model with correlation coefficients (R2) equals to 0.998, 0.992, and 0.998 for 3, 6, and 9 mg/L Cd (II) concentrations, respectively. The experimental data fitted very well with the pseudo-second-order. Overall, treatment of polluted solution to Cd (II) by adsorption process using L-MWCNT can be considered as an effective technology.

  15. Adsorption of cadmium and lead onto oxidized nitrogen-doped multiwall carbon nanotubes in aqueous solution: equilibrium and kinetics

    NASA Astrophysics Data System (ADS)

    Perez-Aguilar, Nancy Veronica; Muñoz-Sandoval, Emilio; Diaz-Flores, Paola Elizabeth; Rangel-Mendez, Jose Rene

    2010-02-01

    Nitrogen-doped multiwall carbon nanotubes (CNx) were chemically oxidized and tested to adsorb cadmium and lead from aqueous solution. Physicochemical characterization of carbon nanotubes included morphological analysis, textural properties, and chemical composition. In addition, the cadmium adsorption capacity of oxidized-CNx was compared with commercially available activated carbon and single wall carbon nanotubes. Carboxylic and nitro groups on the surface of oxidized CNx shifted the point of zero charge from 6.6 to 3.1, enhancing their adsorption capacity for cadmium and lead to 0.083 and 0.139 mmol/g, respectively, at pH 5 and 25 °C. Moreover, oxidized-CNx had higher selectivity for lead when both metal ions were in solution. Kinetic experiments for adsorption of cadmium showed that the equilibrium was reached at about 4 min. Finally, the small size, geometry, and surface chemical composition of oxidized-CNx are the key factors for their higher adsorption capacity than activated carbon.

  16. VQS (vapor-quasiliquid-solid, vapor-quasisolid-solid) mechanism presents a unified foundation for the syntheses of nanotubes, primarily carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Mohammad, S. Noor

    2017-09-01

    Nanotubes are synthesized almost entirely by metal-catalyst-free and metal-catalyst-mediated non-eutectic mechanism(s). An investigation has been carried out to understand the basics of this mechanism. Various possible chemical and physical processes involved in nanotube synthesis have been researched. Various components and attributes of nanotube synthesis have been evaluated. Phase transitions, alloy formation, porosity, carrier transport and the fundamentals underlying them have been examined. Nanoparticle surfaces conducive to nanotube synthesis have been examined. The role of surface treatment, which includes oxidation, oxygenation, acid treatment, plasma treatment, water treatment, sputtering, etc in creating such surfaces, has been investigated. The role of surface treatment and phase transitions as functions of temperature, pressure, ambient, contaminants, surface amorphicity, etc in creating diffusion paths for the diffusion of growth species for supersaturation and nucleation has been explored. Interdiffusion of catalyst and source materials, and hence exchange of materials, on the nanoparticle surface, have been elucidated. This exchange of materials on catalyst surface appears to add a new dimension to the synthesis kinetics. Integrated together, they reveal a general mechanism for probably all metal-catalyst-free and metal-catalyst-mediated non-eutectic nanotube synthesis. Available experiments strongly support the proposed mechanism; they suggest that this mechanism has a broad appeal.

  17. Growth and dissolution kinetics of tetragonal lysozyme

    NASA Technical Reports Server (NTRS)

    Monaco, L. A.; Rosenberger, F.

    1993-01-01

    The growth and dissolution kinetics of lysozyme in a 25 ml solution bridge inside a closed growth cell was investigated. It was found that, under all growth conditions, the growth habit forming (110) and (101) faces grew through layer spreading with different growth rate dependence on supersaturation/temperature. On the other hand, (100) faces which formed only at low temperatures underwent a thermal roughening transition around 12 C.

  18. Bulk nucleation and growth of inorganic nanowires and nanotubes

    NASA Astrophysics Data System (ADS)

    Sharma, Shashank

    The nanometer scale materials such as nanowires and nanotubes will be of particular interest as building blocks for designing novel sensors, catalysts, electronic, optical, and optoelectronic devices. However, in order to realize these applications, bulk amounts of nanowires and nanotubes need to be synthesized with precise control over the nanostructure characteristics. In addition, the structure-property relationships for one-dimensional structures are expected to be different than their bulk when their diameters are less than a characteristic Bohr exciton radius. This fundamental curiosity also necessitates bulk synthesis of nanostructures. The current bulk nanowire synthesis methods utilize either nanometer scale porous molds or nanometer scale transition metal clusters to template one-dimensional growth. All these techniques have inherent limitations in terms of control over the nanowire diameter distribution, composition, the growth direction, and the ability to generate abrupt interfaces within individual nanowires. In this dissertation, a new concept for bulk nucleation and growth of one-dimensional nanostructures is proposed and demonstrated for a variety of inorganic material systems. In this technique, multiple nanowires nucleate and grow from pools of low-melting metal melts when exposed to an activated gas phase containing the necessary precursors. This concept, hereby termed Low Melting Metals and Activated Gas phase (LMAG) mediated method, is specifically demonstrated for the synthesis of, (a) silicon nanowires grown using molten gallium and silane precursors; (b) silicon compound nanowires using solution of molten gallium and appropriate gas phase precursors, and (c) metal-oxide nanostructures grown using direct reaction of the respective metal melts and oxygen precursors. Nanowires resulted from the same molten gallium pool at high densities (>1011/cm2) and with narrow diameter distribution. The silicon nanowires synthesized using the LMAG

  19. Double-sided anodic titania nanotube arrays: a lopsided growth process.

    PubMed

    Sun, Lidong; Zhang, Sam; Sun, Xiao Wei; Wang, Xiaoyan; Cai, Yanli

    2010-12-07

    In the past decade, the pore diameter of anodic titania nanotubes was reported to be influenced by a number of factors in organic electrolyte, for example, applied potential, working distance, water content, and temperature. All these were closely related to potential drop in the organic electrolyte. In this work, the essential role of electric field originating from the potential drop was directly revealed for the first time using a simple two-electrode anodizing method. Anodic titania nanotube arrays were grown simultaneously at both sides of a titanium foil, with tube length being longer at the front side than that at the back side. This lopsided growth was attributed to the higher ionic flux induced by electric field at the front side. Accordingly, the nanotube length was further tailored to be comparable at both sides by modulating the electric field. These results are promising to be used in parallel configuration dye-sensitized solar cells, water splitting, and gas sensors, as a result of high surface area produced by the double-sided architecture.

  20. Carbon Nanotubes and Carbon Nanotube Fiber Sensors: Growth, Processing and Characterization

    NASA Astrophysics Data System (ADS)

    Zhao, Haibo

    With multiple outstanding properties, such as high Young's modulus, high strength, good thermal conductivity and electrical conductivity, carbon nanotube (CNT) has been considered as a new generation of material that has many potential applications in many fields. One obstacle that stands in the way of applying CNTs in the real world is the limited growth length. Catalyst instability is one of the many factors that cause the stops of CNT growth. In this research, intermetalic Fe-Zr catalyst was used to grow millimeter long CNT arrays. The Fe-Zr particles enabled the growth of 1.7 millimeter long carbon nanotube arrays in 45 minutes. A comparison with pure Fe catalyst indicated that adding Zr to iron can stabilize the Fe catalyst at the CNT growth temperature and moderate its reactivity. In future, when CNTs are largely used in industrial, mass production of CNTs at a low cost is vital for market competition. In many current CNT growth methods, a process of depositing a thin catalyst film on top of Al 2O3 film on a piece of silicon wafer is required. Thus the size of CNT samples is limited by the size of the largest silicon wafer currently available, which is 8 inch in diameter. In this study, FeCl2 powders were used as the catalyst to grow CNT arrays not only on traditional silicon substrates but also on quartz substrates and carbon sheets. This unique method does not require the thin film deposition step, which shortens the time used for each batch of CNT growth. The simplicity of this method allows an easy scale-up for mass production of CNTs with a low cost. In order to improve this method, HCl was used to assist the CNT growth. HCl was added via flowing a small amount of C2H2 thorough a bubbuler where HCl solution was contained. With the assistance of HCl, CNT growth could be extended to 1 hour. 3 mm tall non-spinnable arrays and 2 mm tall spinnable arrays were produced using this method. With the increasing use of composite materials, real time health

  1. On the Nonequilibrium Interface Kinetics of Rapid Coupled Eutectic Growth

    NASA Astrophysics Data System (ADS)

    Dong, H.; Chen, Y. Z.; Shan, G. B.; Zhang, Z. R.; Liu, F.

    2017-08-01

    Nonequilibrium interface kinetics (NEIK) is expected to play an important role in coupled growth of eutectic alloys, when solidification velocity is high and intermetallic compound or topologically complex phases form in the crystallized product. In order to quantitatively evaluate the effect of NEIK on the rapid coupled eutectic growth, in this work, two nonequilibrium interface kinetic effects, i.e., atom attachment and solute trapping at the solid-liquid interface, were incorporated into the analyses of the coupled eutectic growth under the rapid solidification condition. First, a coupled growth model incorporating the preceding two nonequilibrium kinetic effects was derived. On this basis, an expression of kinetic undercooling (Δ T k), which is used to characterize the NEIK, was defined. The calculations based on the as-derived couple growth model show good agreement with the reported experimental results achieved in rapidly solidified eutectic Al-Sm alloys consisting of a solid solution phase ( α-Al) and an intermetallic compound phase (Al11Sm3). In terms of the definition of Δ T k defined in this work, the role of NEIK in the coupled growth of the Al-Sm eutectic system was analyzed. The results show that with increasing the coupled growth velocity, Δ T k increases continuously, and its ratio to the total undercooling reaches 0.32 at the maximum growth velocity for coupled eutectic growth. Parametric analyses on two key alloy parameters that influence Δ T k, i.e., interface kinetic parameter ( μ i ) and solute distribution coefficient ( k e ), indicate that both μ i and k e influence the NEIK significantly and the decrease of either these two parameters enhances the NEIK effect.

  2. Simulation of the dc Plasma in Carbon Nanotube Growth

    NASA Technical Reports Server (NTRS)

    Hash, David; Bose, Deepak; Govindan, T. R.; Meyyappan, M.; Biegel, Bryan (Technical Monitor)

    2003-01-01

    A model for the dc plasma used in carbon nanotube growth is presented, and one-dimensional simulations of an acetylene/ammonia/argon system are performed. The effect of dc bias is illustrated by examining electron temperature, electron and ion densities, and neutral densities. Introducing a tungsten filament in the dc plasma, as in hot filament chemical vapor deposition with plasma assistance, shows negligible influence on the system characteristics.

  3. Fabrication of titanium dioxide nanotube arrays using organic electrolytes

    NASA Astrophysics Data System (ADS)

    Yoriya, Sorachon

    to ~2 microm. In comparison to DMSO electrolyte, the electrochemical anodization rates are relatively slower in DEG electrolyte; as a result, the nanotube length is typically less than 10 microm. Pore size of nanotubes grown in DEG has been extended from 150 nm up to approximately 400 nm. The approach to pore widening could be achieved by using a specific condition of low HF concentration and prolonged anodization time. The study of evolution of nanotubes grown in DEG electrolytes showed that a fibrous layer was formed in the early growth stages and then was chemically and gradually removed after a long duration, leaving behind the nanotubes with large pore size. In DEG electrolyte, the closer spacing between Ti and Pt electrodes resulted in the larger nanotube morphological parameters due to the enhanced electrode kinetics facilitating the electrode reactions. Furthermore, this dissertation showed possibilities to crystallize the titania nanotube array films at room temperature via anodization in either DMSO or DEG electrolytes. The partially crystallized films could be achieved specifically in the optimum slow growth process conditions. Due to partial crystallization of the as-anodized samples, the high temperature annealing study revealed that the temperatures of phase transformation are 260 ºC and 430°C for respectively amorphous to anatase and anatase to rutile, which are accounted as the lowest phase transformation temperatures reported to date (2010). Finally, the photoelectrochemical properties of the DMSO fabricated nanotubes were investigated. The maximum photocurrent density of ~ 11 mA cm--2 was achieved by using the 46-microm long nanotube array sample with completely open pores, and photoconversion efficiencies of 5.425 % (+/- 0.087) (under UV light) and 0.197 % (+/- 0.001) (under solar spectrum AM 1.5) have been demonstrated. Biomedical applications of the DEG fabricated nanotube arrays films such as blood clotting, hemocompatibility, and drug

  4. Growth of carbon nanotubes in arc plasma treated graphite disc: microstructural characterization and electrical conductivity study

    NASA Astrophysics Data System (ADS)

    Nayak, B. B.; Sahu, R. K.; Dash, T.; Pradhan, S.

    2018-03-01

    Circular graphite discs were treated in arc plasma by varying arcing time. Analysis of the plasma treated discs by field emission scanning electron microscope revealed globular grain morphologies on the surfaces, but when the same were observed at higher magnification and higher resolution under transmission electron microscope, growth of multiwall carbon nanotubes of around 2 nm diameter was clearly seen. In situ growth of carbon nanotube bundles/bunches consisting of around 0.7 nm tube diameter was marked in the case of 6 min treated disc surface. Both the untreated and the plasma treated graphite discs were characterized by X-ray diffraction, energy dispersive spectra of X-ray, X-ray photoelectron spectroscopy, transmission electron microscopy, micro Raman spectroscopy and BET surface area measurement. From Raman spectra, BET surface area and microstructure observed in transmission electron microscope, growth of several layers of graphene was identified. Four-point probe measurements for electrical resistivity/conductivity of the graphite discs treated under different plasma conditions showed significant increase in conductivity values over that of untreated graphite conductivity value and the best result, i.e., around eightfold increase in conductivity, was observed in the case of 6 min plasma treated sample exhibiting carbon nanotube bundles/bunches grown on disc surface. By comparing the microstructures of the untreated and plasma treated graphite discs, the electrical conductivity increase in graphite disc is attributed to carbon nanotubes (including bundles/bunches) growth on disc surface by plasma treatment.

  5. Nanotubes in Nanoelectronics: Transport, Growth and Modeling

    NASA Technical Reports Server (NTRS)

    Anantram, M.; Delzeit, Lance; Cassell, Alan; Han, Jie; Meyyappan, M.; Arnold, Jim (Technical Monitor)

    2001-01-01

    Carbon nanotube (CNT) baud nanotechnology appears to be promising for future Theoretical analysis and results for the ballistic current carrying capacity of nanotube wires am presented. Aspects of metal-nanotube coupling are examined. Results am also presented for chemical vapor deposition of CNT from hydrocarbon feedstock.

  6. Magnetic nanotubes for drug delivery

    NASA Astrophysics Data System (ADS)

    Ramasamy, Mouli; Kumar, Prashanth S.; Varadan, Vijay K.

    2017-04-01

    Magnetic nanotubes hold the potential for neuroscience applications because of their capability to deliver chemicals or biomolecules and the feasibility of controlling the orientation or movement of these magnetic nanotubes by an external magnetic field thus facilitating directed growth of neurites. Therefore, we sought to investigate the effects of laminin treated magnetic nanotubes and external alternating magnetic fields on the growth of dorsal root ganglion (DRG) neurons in cell culture. Magnetic nanotubes were synthesized by a hydrothermal method and characterized to confirm their hollow structure, the hematite and maghemite phases, and the magnetic properties. DRG neurons were cultured in the presence of magnetic nanotubes under alternating magnetic fields. Electron microscopy showed a close interaction between magnetic nanotubes and the growing neurites Phase contrast microscopy revealed live growing neurons suggesting that the combination of the presence of magnetic nanotubes and the alternating magnetic field were tolerated by DRG neurons. The synergistic effect, from both laminin treated magnetic nanotubes and the applied magnetic fields on survival, growth and electrical activity of the DRG neurons are currently being investigated.

  7. CVD-grown horizontally aligned single-walled carbon nanotubes: synthesis routes and growth mechanisms.

    PubMed

    Ibrahim, Imad; Bachmatiuk, Alicja; Warner, Jamie H; Büchner, Bernd; Cuniberti, Gianaurelio; Rümmeli, Mark H

    2012-07-09

    Single-walled carbon nanotubes (SWCNTs) have attractive electrical and physical properties, which make them very promising for use in various applications. For some applications however, in particular those involving electronics, SWCNTs need to be synthesized with a high degree of control with respect to yield, length, alignment, diameter, and chirality. With this in mind, a great deal of effort is being directed to the precision control of vertically and horizontally aligned nanotubes. In this review the focus is on the latter, horizontally aligned tubes grown by chemical vapor deposition (CVD). The reader is provided with an in-depth review of the established vapor deposition orientation techniques. Detailed discussions on the characterization routes, growth parameters, and growth mechanisms are also provided. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Theoretical studies on lattice-oriented growth of single-walled carbon nanotubes on sapphire

    NASA Astrophysics Data System (ADS)

    Li, Zhengwei; Meng, Xianhong; Xiao, Jianliang

    2017-09-01

    Due to their excellent mechanical and electrical properties, single-walled carbon nanotubes (SWNTs) can find broad applications in many areas, such as field-effect transistors, logic circuits, sensors and flexible electronics. High-density, horizontally aligned arrays of SWNTs are essential for high performance electronics. Many experimental studies have demonstrated that chemical vapor deposition growth of nanotubes on crystalline substrates such as sapphire offers a promising route to achieve such dense, perfectly aligned arrays. In this work, a theoretical study is performed to quantitatively understand the van der Waals interactions between SWNTs and sapphire substrates. The energetically preferred alignment directions of SWNTs on A-, R- and M-planes and the random alignment on the C-plane predicted by this study are all in good agreement with experiments. It is also shown that smaller SWNTs have better alignment than larger SWNTs due to their stronger interaction with sapphire substrate. The strong vdW interactions along preferred alignment directions can be intuitively explained by the nanoscale ‘grooves’ formed by atomic lattice structures on the surface of sapphire. This study provides important insights to the controlled growth of nanotubes and potentially other nanomaterials.

  9. Method of making carbon nanotubes on a substrate

    DOEpatents

    Gao, Yufei; Liu, Jun

    2006-03-14

    The present invention includes carbon nanotubes whose hollow cores are 100% filled with conductive filler. The carbon nanotubes are in uniform arrays on a conductive substrate and are well-aligned and can be densely packed. The uniformity of the carbon nanotube arrays is indicated by the uniform length and diameter of the carbon nanotubes, both which vary from nanotube to nanotube on a given array by no more than about 5%. The alignment of the carbon nanotubes is indicated by the perpendicular growth of the nanotubes from the substrates which is achieved in part by the simultaneous growth of the conductive filler within the hollow core of the nanotube and the densely packed growth of the nanotubes. The present invention provides a densely packed carbon nanotube growth where each nanotube is in contact with at least one nearest-neighbor nanotube. The substrate is a conductive substrate coated with a growth catalyst, and the conductive filler can be single crystals of carbide formed by a solid state reaction between the substrate material and the growth catalyst. The present invention further provides a method for making the filled carbon nanotubes on the conductive substrates. The method includes the steps of depositing a growth catalyst onto the conductive substrate as a prepared substrate, creating a vacuum within a vessel which contains the prepared substrate, flowing H2/inert (e.g. Ar) gas within the vessel to increase and maintain the pressure within the vessel, increasing the temperature of the prepared substrate, and changing the H2/Ar gas to ethylene gas such that the ethylene gas flows within the vessel. Additionally, varying the density and separation of the catalyst particles on the conductive substrate can be used to control the diameter of the nanotubes.

  10. Growth Kinetics and Size Distribution Dynamics of Viscous Secondary Organic Aerosol

    DOE PAGES

    Zaveri, Rahul A.; Shilling, John E.; Zelenyuk, Alla; ...

    2017-12-15

    Low bulk diffusivity inside viscous semisolid atmospheric secondary organic aerosol (SOA) can prolong equilibration time scale, but its broader impacts on aerosol growth and size distribution dynamics are poorly understood. In this article, we present quantitative insights into the effects of bulk diffusivity on the growth and evaporation kinetics of SOA formed under dry conditions from photooxidation of isoprene in the presence of a bimodal aerosol consisting of Aitken (ammonium sulfate) and accumulation (isoprene or α-pinene SOA) mode particles. Aerosol composition measurements and evaporation kinetics indicate that isoprene SOA is composed of several semivolatile organic compounds (SVOCs), with some reversiblymore » reacting to form oligomers. Model analysis shows that liquid-like bulk diffusivities can be used to fit the observed evaporation kinetics of accumulation mode particles but fail to explain the growth kinetics of bimodal aerosol by significantly under-predicting the evolution of the Aitken mode. In contrast, the semisolid scenario successfully reproduces both evaporation and growth kinetics, with the interpretation that hindered partitioning of SVOCs into large viscous particles effectively promotes the growth of smaller particles that have shorter diffusion time scales. This effect has important implications for the growth of atmospheric ultrafine particles to climatically active sizes.« less

  11. Growth Kinetics and Size Distribution Dynamics of Viscous Secondary Organic Aerosol

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zaveri, Rahul A.; Shilling, John E.; Zelenyuk, Alla

    Low bulk diffusivity inside viscous semisolid atmospheric secondary organic aerosol (SOA) can prolong equilibration time scale, but its broader impacts on aerosol growth and size distribution dynamics are poorly understood. In this article, we present quantitative insights into the effects of bulk diffusivity on the growth and evaporation kinetics of SOA formed under dry conditions from photooxidation of isoprene in the presence of a bimodal aerosol consisting of Aitken (ammonium sulfate) and accumulation (isoprene or α-pinene SOA) mode particles. Aerosol composition measurements and evaporation kinetics indicate that isoprene SOA is composed of several semivolatile organic compounds (SVOCs), with some reversiblymore » reacting to form oligomers. Model analysis shows that liquid-like bulk diffusivities can be used to fit the observed evaporation kinetics of accumulation mode particles but fail to explain the growth kinetics of bimodal aerosol by significantly under-predicting the evolution of the Aitken mode. In contrast, the semisolid scenario successfully reproduces both evaporation and growth kinetics, with the interpretation that hindered partitioning of SVOCs into large viscous particles effectively promotes the growth of smaller particles that have shorter diffusion time scales. This effect has important implications for the growth of atmospheric ultrafine particles to climatically active sizes.« less

  12. Comparative study on the process behavior and reaction kinetics in sonocatalytic degradation of organic dyes by powder and nanotubes TiO2.

    PubMed

    Pang, Yean Ling; Abdullah, Ahmad Zuhairi

    2012-05-01

    Sonocatalytic degradation of various organic dyes (Congo Red, Reactive Blue 4, Methyl Orange, Rhodamine B and Methylene Blue) catalyzed by powder and nanotubes TiO(2) was studied. Both catalysts were characterized using transmission electron microscope (TEM), surface analyzer, Raman spectroscope and thermal gravimetric analyzer (TGA). Sonocatalytic activity of powder and nanotubes TiO(2) was elucidated based on the degradation of various organic dyes. The former catalyst was favorable for treatment of anionic dyes, while the latter was more beneficial for cationic dyes. Sonocatalytic activity of TiO(2) nanotubes could be up to four times as compared to TiO(2) powder under an ultrasonic power of 100 W and a frequency of 42 kHz. This was associated with the higher surface area and the electrostatic attraction between dye molecules and TiO(2) nanotubes. Fourier transform-infrared spectrometer (FT-IR) was used to identify changes that occurred on the functional group in Rhodamine B molecules and TiO(2) nanotubes after the reaction. Sonocatalytic degradation of Rhodamine B by TiO(2) nanotubes apparently followed the Langmuir-Hinshelwood adsorption kinetic model with surface reaction rate of 1.75 mg/L min. TiO(2) nanotubes were proven for their high potential to be applied in sonocatalytic degradation of organic dyes. Copyright © 2011 Elsevier B.V. All rights reserved.

  13. Research of influence of the underlayer material on the growth rate of carbon nanotube arrays for manufacturing non-volatile memory elements with high speed

    NASA Astrophysics Data System (ADS)

    Klimin, V. S.; Il'ina, M. V.; Il'in, O. I.; Rudyk, N. N.; Ageev, O. A.

    2017-11-01

    This experimental work is devoted to the regimes of obtaining arrays of carbon nanotubes. Arrays of perpendicular nanotubes perpendicular to the surface were obtained by the method of Plasma-enhanced chemical vapor deposition. In this paper, geometric and electronic parameters of carbon nanotubes were investigated depending on the material of the sublayer. The rates of growth of carbon nanotubes on various structures were also determined. In the experiments for growth, structures such as Ni-Al-Si, Ni-V-Si, Ni-Ti-Si, Ni-Cr-Si were used. The growth rates for the intensive section were for the Ni-Cr-Si structure, the growth rate is about 1 μm / min, for the Ni-V-Si structure it is 0.55 μm / min. The growth rates for the saturation region for the Ni-Cr-Si structure, the growth rate is about 0.2 μm / min, for the Ni-V-Si structure 0.16 μm / min. The results obtained in this paper can be used to optimize the growth regimes perpendicularly oriented to the substrate carbon nanotubes, which are used as various elements in modern nanoelectronics.

  14. Effect of nanostructured titanium on anodization growth of self-organized TiO2 nanotubes

    NASA Astrophysics Data System (ADS)

    Zhang, Lan; Han, Yong

    2010-02-01

    To understand the effect of substrate microstructure on the formation of TiO2 nanotubes, anodic oxidizations of commercially pure titanium subjected to surface mechanical attrition treatment (SMATed-Ti) and unSMATed-Ti in a glycol solution containing NH4F and small amounts of water were investigated. The SMATed-Ti exhibit a nanocrystallized surface layer containing a high density of grain boundaries compared with unSMATed-Ti. The anodization results show that the formed TiO2 nanotube layer on the SMATed-Ti is much thicker than that on the unSMATed-Ti. It is indicated that nanocrystallized Ti is propitious to the growth of TiO2 nanotubes; grain boundaries and dislocations play the leading role in accelerating the reaction rate and ion diffusion coefficient during anodization. In addition, nanocrystallization of Ti does not change surface morphologies and phase components of the TiO2 nanotubes.

  15. Templated Synthesis of Single-Walled Carbon Nanotubes with Specific Structure.

    PubMed

    Yang, Feng; Wang, Xiao; Li, Meihui; Liu, Xiyan; Zhao, Xiulan; Zhang, Daqi; Zhang, Yan; Yang, Juan; Li, Yan

    2016-04-19

    show that the selective growth of (12,6) tubes is due to a good structural match between the carbon atom arrangement around the nanotube circumference and the metal atom arrangement of (0 0 12) planes in the catalyst. Similarly, (16,0) SWNTs exhibit a good structural match to the (116) planes of the W6Co7 catalyst. By optimization of the chemical vapor deposition (CVD) conditions, zigzag (16,0) SWNTs, which are generally known as a kinetically unfavorable species in CVD growth, were obtained with a purity of ∼80%. Generally speaking, the chirality-specific growth of SWNTs is realized by the cooperation of two factors: the structural match between SWNTs and the catalysts makes the growth of SWNTs with specific chirality thermodynamically favorable, and further manipulation of the CVD conditions results in optimized growth kinetics for SWNTs with this designed chirality. We expect that this advanced epitaxial growth strategy will pave the way for the ultimate goal of chirality-specified growth of SWNTs and will also be applicable in the controlled preparation of other nanomaterials.

  16. The effect of growth temperature variation on partially bismuth filled carbon nanotubes synthesis using a soft semi-metallic template.

    PubMed

    Sahoo, R K; Jacob, C

    2014-06-01

    The dewetting of a low melting point metal thin film deposited on silicon substrates was studied. The experimental results suggest that the change in the growth temperature affects the nanostructures that form. Based on the experimental results, the temperature which yielded the smallest features for the growth of nanotubes is determined. The mechanism by which these nano-templates become an efficient seeds for the growth of the carbon nanotubes is discussed. The partial bismuth filling inside the CNTs was optimized. Based on the results, a schematic growth model for better understanding of the process parameters has also been proposed.

  17. Modeling of scale-dependent bacterial growth by chemical kinetics approach.

    PubMed

    Martínez, Haydee; Sánchez, Joaquín; Cruz, José-Manuel; Ayala, Guadalupe; Rivera, Marco; Buhse, Thomas

    2014-01-01

    We applied the so-called chemical kinetics approach to complex bacterial growth patterns that were dependent on the liquid-surface-area-to-volume ratio (SA/V) of the bacterial cultures. The kinetic modeling was based on current experimental knowledge in terms of autocatalytic bacterial growth, its inhibition by the metabolite CO2, and the relief of inhibition through the physical escape of the inhibitor. The model quantitatively reproduces kinetic data of SA/V-dependent bacterial growth and can discriminate between differences in the growth dynamics of enteropathogenic E. coli, E. coli JM83, and Salmonella typhimurium on one hand and Vibrio cholerae on the other hand. Furthermore, the data fitting procedures allowed predictions about the velocities of the involved key processes and the potential behavior in an open-flow bacterial chemostat, revealing an oscillatory approach to the stationary states.

  18. Ivestigation of the Interface Kinetic Effects on Dendritic Growth in a Pure Undercooled Melt

    NASA Astrophysics Data System (ADS)

    Lee, Youngyih; Rappel, Wouter-Jan; Karma, Alain

    1997-03-01

    The non-equilibrium kinetics of the solid-liquid interface is known to strongly influence the growth rate and morphology of dendrites in undercooled melts. In metallic systems, kinetic effects are usually considered relevant only at high undercooling, while in some transparent organic materials, like pivalic acid (PVA), kinetic effects already seem to influence dendritic growth at low undercooling. We investigate quantitatively the effect of isotropic and anisotropic kinetics on dendritic growth in a pure undercooled melt in two and three dimensions using a standard boundary integral approach. Our numerical results are interpreted with the help of a simple dimensional criterion which predicts the critical undercooling at which the transition from surface energy dominated growth to interface kinetics dominated growth takes place. Finally, our calculations are used to estimate the kinetic coefficient of pure Nickel and PVA using a fit to the experimentally observed growth rates.

  19. Localized growth of carbon nanotubes via lithographic fabrication of metallic deposits

    PubMed Central

    Tu, Fan; Drost, Martin; Szenti, Imre; Kiss, Janos; Kónya, Zoltan

    2017-01-01

    We report on the fabrication of carbon nanotubes (CNTs) at predefined positions and controlled morphology, for example, as individual nanotubes or as CNT forests. Electron beam induced deposition (EBID) with subsequent autocatalytic growth (AG) was applied to lithographically produce catalytically active seeds for the localized growth of CNTs via chemical vapor deposition (CVD). With the precursor Fe(CO)5 we were able to fabricate clean iron deposits via EBID and AG. After the proof-of-principle that these Fe deposits indeed act as seeds for the growth of CNTs, the influence of significant EBID/AG parameters on the deposit shape and finally the yield and morphology of the grown CNTs was investigated in detail. Based on these results, the parameters could be optimized such that EBID point matrixes (6 × 6) were fabricated on a silica surface whereby at each predefined site only one CNT was produced. Furthermore, the localized fabrication of CNT forests was targeted and successfully achieved on an Al2O3 layer on a silicon sample. A peculiar lift-up of the Fe seed structures as “flakes” was observed and the mechanism was discussed. Finally, a proof-of-principle was presented showing that EBID deposits from the precursor Co(CO)3NO are also very effective catalysts for the CNT growth. Even though the metal content (Co) of the latter is reduced in comparison to the Fe deposits, effective CNT growth was observed for the Co-containing deposits at lower CVD temperatures than for the corresponding Fe deposits. PMID:29259874

  20. Carbon nanotube-based sensor and method for detection of crack growth in a structure

    NASA Technical Reports Server (NTRS)

    Smits, Jan M. (Inventor); Moore, Thomas C. (Inventor); Kite, Marlen T. (Inventor); Wincheski, Russell A. (Inventor); Ingram, JoAnne L. (Inventor); Watkins, Anthony N. (Inventor); Williams, Phillip A. (Inventor)

    2007-01-01

    A sensor has a plurality of carbon nanotube (CNT)-based conductors operatively positioned on a substrate. The conductors are arranged side-by-side, such as in a substantially parallel relationship to one another. At least one pair of spaced-apart electrodes is coupled to opposing ends of the conductors. A portion of each of the conductors spanning between each pair of electrodes comprises a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis. Because a direct correlation exists between the resistance of a carbon nanotube and its strain, changes experienced by the portion of the structure to which the sensor is coupled induce a corresponding change in the electrical properties of the conductors, thereby enabling detection of crack growth in the structure.

  1. Synthesis of Patterned Vertically Aligned Carbon Nanotubes by PECVD Using Different Growth Techniques: A Review.

    PubMed

    Gangele, Aparna; Sharma, Chandra Shekhar; Pandey, Ashok Kumar

    2017-04-01

    Immense development has been taken place not only to increase the bulk production, repeatability and yield of carbon nanotubes (CNTs) in last 25 years but preference is also given to acknowledge the basic concepts of nucleation and growth methods. Vertically aligned carbon nanotubes (VAC-NTs) are forest of CNTs accommodated perpendicular on a substrate. Their exceptional chemical and physical properties along with sequential arrangement and dense structure make them suitable in various fields. The effect of different type of selected substrate, carbon precursor, catalyst and their physical and chemical status, reaction conditions and many other key parameters have been thoroughly studied and analysed. The aim of this paper is to specify the trend and summarize the effect of key parameters instead of only presenting all the experiments reported till date. The identified trends will be compared with the recent observations on the growth of different types of patterned VACNTs. In this review article, we have presented a comprehensive analysis of different techniques to precisely determine the role of different parameters responsible for the growth of patterned vertical aligned carbon nanotubes. We have covered various techniques proposed in the span of more than two decades to fabricate the different structures and configurations of carbon nanotubes on different types of substrates. Apart from a detailed discussion of each technique along with their specific process and implementation, we have also provided a critical analysis of the associated constraints, benefits and shortcomings. To sum it all for easy reference for researchers, we have tabulated all the techniques based on certain main key factors. This review article comprises of an exhaustive discussion and a handy reference for researchers who are new in the field of synthesis of CNTs or who wants to get abreast with the techniques of determining the growth of VACNTs arrays.

  2. Rapid and Controlled In Situ Growth of Noble Metal Nanostructures within Halloysite Clay Nanotubes.

    PubMed

    Rostamzadeh, Taha; Islam Khan, Md Shahidul; Riche', Kyle; Lvov, Yuri M; Stavitskaya, Anna V; Wiley, John B

    2017-11-14

    A rapid (≤2 min) and high-yield low-temperature synthesis has been developed for the in situ growth of gold nanoparticles (NPs) with controlled sizes in the interior of halloysite nanotubes (HNTs). A combination of HAuCl 4 in ethanol/toluene, oleic acid, and oleylamine surfactants and ascorbic acid reducing agent with mild heating (55 °C) readily lead to the growth of targeted nanostructures. The sizes of Au NPs are tuned mainly by adjusting nucleation and growth rates. Further modification of the process, through an increase in ascorbic acid, allows for the formation of nanorods (NRs)/nanowires within the HNTs. This approach is not limited to gold-a modified version of this synthetic strategy can also be applied to the formation of Ag NPs and NRs within the clay nanotubes. The ability to readily grow such core-shell nanosystems is important to their further development as nanoreactors and active catalysts. NPs within the tube interior can further be manipulated by the electron beam. Growth of Au and Ag could be achieved under a converged electron beam suggesting that both Au@HNT and Ag@HNT systems can be used for the fundamental studies of NP growth/attachment.

  3. Water-assisted growth of graphene-carbon nanotube hybrids in plasma

    NASA Astrophysics Data System (ADS)

    Tewari, Aarti; Ghosh, Santanu; Srivastava, Pankaj

    2018-04-01

    The enhanced growth of graphene-carbon nanotube (CNT) hybrids in a hydrocarbon and hydrogen plasma assisted by water is numerically formulated. The catalyst activity and agglomeration of catalyst particles are the rate determining factors in the growth of hybrids and their constituents, i.e., the CNT and graphene. The water vapor concentration is varied to investigate its effect on the growth process. The enhanced catalyst activity on account of oxidation by hydroxyl ions of water to impede the agglomeration of catalyst particles and the removal of amorphous carbon through etching by hydrogen ions of water are seen to be the main driving forces behind the many fold increase in the dimensions of constituent nanostructures and the hybrids with water vapor concentration. Importantly, beyond a certain specific water vapor concentration, the growth rates dropped due to active oxidation of the catalyst particle.

  4. New observations and insights into the morphology and growth kinetics of hydrate films.

    PubMed

    Li, Sheng-Li; Sun, Chang-Yu; Liu, Bei; Li, Zhi-Yun; Chen, Guang-Jin; Sum, Amadeu K

    2014-02-19

    The kinetics of film growth of hydrates of methane, ethane, and methane-ethane mixtures were studied by exposing a single gas bubble to water. The morphologies, lateral growth rates, and thicknesses of the hydrate films were measured for various gas compositions and degrees of subcooling. A variety of hydrate film textures was revealed. The kinetics of two-dimensional film growth was inferred from the lateral growth rate and initial thickness of the hydrate film. A clear relationship between the morphology and film growth kinetics was observed. The shape of the hydrate crystals was found to favour heat or mass transfer and favour further growth of the hydrate film. The quantitative results on the kinetics of film growth showed that for a given degree of subcooling, the initial film thicknesses of the double hydrates were larger than that of pure methane or ethane hydrate, whereas the thickest hydrate film and the lowest lateral growth rate occurred when the methane mole fraction was approximately 0.6.

  5. New Observations and Insights into the Morphology and Growth Kinetics of Hydrate Films

    PubMed Central

    Li, Sheng-Li; Sun, Chang-Yu; Liu, Bei; Li, Zhi-Yun; Chen, Guang-Jin; Sum, Amadeu K.

    2014-01-01

    The kinetics of film growth of hydrates of methane, ethane, and methane-ethane mixtures were studied by exposing a single gas bubble to water. The morphologies, lateral growth rates, and thicknesses of the hydrate films were measured for various gas compositions and degrees of subcooling. A variety of hydrate film textures was revealed. The kinetics of two-dimensional film growth was inferred from the lateral growth rate and initial thickness of the hydrate film. A clear relationship between the morphology and film growth kinetics was observed. The shape of the hydrate crystals was found to favour heat or mass transfer and favour further growth of the hydrate film. The quantitative results on the kinetics of film growth showed that for a given degree of subcooling, the initial film thicknesses of the double hydrates were larger than that of pure methane or ethane hydrate, whereas the thickest hydrate film and the lowest lateral growth rate occurred when the methane mole fraction was approximately 0.6. PMID:24549241

  6. High-yield growth of vertically aligned carbon nanotubes on a continuously moving substrate.

    PubMed

    Guzmán de Villoria, R; Figueredo, S L; Hart, A J; Steiner, S A; Slocum, A H; Wardle, B L

    2009-10-07

    Vertically aligned carbon nanotube (CNT) arrays are grown on a moving substrate, demonstrating continuous growth of nanoscale materials with long-range order. A cold-wall chamber with an oscillating moving platform is used to locally heat a silicon growth substrate coated with an Fe/Al2O3 catalyst film for CNT growth via chemical vapor deposition. The reactant gases are introduced over the substrate through a directed nozzle to attain high-yield CNT growth. Aligned multi-wall carbon nanotube arrays (or 'forests') with heights of approximately 1 mm are achieved at substrate speeds up to 2.4 mm s(-1). Arrays grown on moving substrates at different velocities are studied in order to identify potential physical limitations of repeatable and fast growth on a continuous basis. No significant differences are noted between static and moving growth as characterized by scanning electron microscopy and Raman spectroscopy, although overall growth height is marginally reduced at the highest substrate velocity. CNT arrays produced on moving substrates are also found to be comparable to those produced through well-characterized batch processes consistent with a base-growth mechanism. Growth parameters required for the moving furnace are found to differ only slightly from those used in a comparable batch process; thermal uniformity appears to be the critical parameter for achieving large-area uniform array growth. If the continuous-growth technology is combined with a reaction zone isolation scheme common in other types of processing (e.g., in the manufacture of carbon fibers), large-scale dense and aligned CNT arrays may be efficiently grown and harvested for numerous applications including providing interlayers for advanced composite reinforcement and improved electrical and thermal transport.

  7. Growth of nanotubes and chemical sensor applications

    NASA Astrophysics Data System (ADS)

    Hone, James; Kim, Philip; Huang, X. M. H.; Chandra, B.; Caldwell, R.; Small, J.; Hong, B. H.; Someya, T.; Huang, L.; O'Brien, S.; Nuckolls, Colin P.

    2004-12-01

    We have used a number of methods to grow long aligned single-walled carbon nanotubes. Geometries include individual long tubes, dense parallel arrays, and long freely suspended nanotubes. We have fabricated a variety of devices for applications such as multiprobe resistance measurement and high-current field effect transistors. In addition, we have measured conductance of single-walled semiconducting carbon nanotubes in field-effect transistor geometry and investigated the device response to water and alcoholic vapors. We observe significant changes in FET drain current when the device is exposed to various kinds of different solvent. These responses are reversible and reproducible over many cycles of vapor exposure. Our experiments demonstrate that carbon nanotube FETs are sensitive to a wide range of solvent vapors at concentrations in the ppm range.

  8. 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.

  9. The role of the substrate surface morphology and water in growth of vertically aligned single-walled carbon nanotubes.

    PubMed

    Pint, Cary; Pheasant, Sean; Nicholas, Nolan; Horton, Charles; Hauge, Robert

    2008-11-01

    Growth of high quality, vertically aligned single-walled carbon nanotubes (carpets) is achieved using a rapid insertion hot filament chemical vapor deposition (HF-CVD) technique. The effect of the substrate morphology on growth is explored by comparing carpets grown on epitaxially polished MgO substrates to those grown on "as-cut", macroscopically rough MgO substrates. Depending on the substrate morphology, we observe differences in both the overall carpet morphology as well as the diameter distribution of nanotubes grown in the carpet based on optical measurements. In addition, we explore the role of water in the growth of carpets on MgO and the conventional Al2O3 coated Si substrates. We find that the addition of a small amount of water is beneficial to the growth rates of the SWNT carpets, enhancing the growth rates by up to eight times.

  10. Growth mechanism and internal structure of vertically aligned single-walled carbon nanotubes.

    PubMed

    Einarsson, Erik; Kadowaki, Masayuki; Ogura, Kazuaki; Okawa, Jun; Xiang, Rong; Zhang, Zhengyi; Yamamoto, Takahisa; Ikuhara, Yuichi; Maruyama, Shigeo

    2008-11-01

    An in situ optical absorbance technique was used to monitor the growth of vertically aligned single-walled carbon nanotubes (VA-SWNTs) at various temperatures and pressures. The effects of the growth temperature and ethanol pressure on the initial growth rate and catalyst lifetime were investigated. It was found that the ideal pressure for VA-SWNT synthesis changes with the growth temperature, shifting toward higher pressure as the growth temperature increases. It was also found that the growth reaction is first-order below this ideal pressure. Additionally, the internal structure of the VA-SWNT film was observed at different depths into the film by transmission electron microscopy. The absence of large bundles was confirmed, and little change in the structure was observed to a depth of approximately 1 microm.

  11. Adsorption Behavior of Ferromagnetic Carbon Nanotubes for Methyl Orange from Aqueous Solution.

    PubMed

    Wang, Liping; Zhang, Mingyu; Zhao, Chenxi; Yang, Shan

    2016-03-01

    The ferromagnetic carbon nanotubes which can be easily separated from aqueous solution were prepared and characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Batch experiments were carried out to investigate the adsorption behavior of ferromagnetic carbon nanotubes for removing methyl orange (MO). The results showed that these ferromagnetic carbon nanotubes were richer in surface function groups than the carbon nanotubes did, furthermore, both γ-Fe2O3 and Fe with ferromagnetism were found on the surface of carbon nanotubes. The results also demonstrated that ferromagnetic carbon nanotubes possessed stronger adsorption ability for MO than carbon nanotubes did. The adsorption isotherms followed Langmuir isotherm equation and the adsorption kinetics could be well described with the pseudo second-order kinetic model. The adsorption process involved an intraparticle diffusion, while it was not the only rate-controlling step. The values of AG were negative and the value of ΔH is -12.37 kJ/mol, proving that the adsorption of MO onto ferromagnetic carbon nanotubes was a spontaneous and exothermic process.

  12. Correcting speleothem oxygen isotopic variations for growth-rate controlled kinetic fractionation effects

    NASA Astrophysics Data System (ADS)

    Stoll, Heather; Moreno, Ana; Cacho, Isabel; Mendez Vicence, Ana; Gonzalez Lemos, Saul; Pirla Casasayas, Gemma; Cheng, Hai; Wang, Xianfeng; Edwards, R. Lawrence

    2015-04-01

    The oxygen isotopic signature may be the most widely used climate indicator in stalagmites, but recent experimental and theoretical studies indicate the potential for kinetic fractionation effects which may be significant, especially in situations where the primary signal from rainfall isotopic composition and cave temperature is limited to a few permil. Here we use a natural set of stalagmites to illustrate the magnitude of such effects and the potential for deconvolving kinetic signals from the primary temperature and rainfall signals. We compare isotopic records from 6 coeval stalagmites covering the interval 140 to 70 ka, from two proximal caves in NW Spain which experienced the same primary variations in temperature and rainfall d18O, but exhibit a large range in growth rates and temporal trends in growth rate. Stalagmites growing at faster rates near 50 microns/year have oxygen isotopic ratios more than 1 permil more negative than coeval stalagmites with very slow (5 micron/year) growth rates. Because growth rate variations also occur over time within any given stalagmite, the measured oxygen isotopic time series for a given stalagmite includes both climatic and kinetic components. Removal of the kinetic component of variation in each stalagmite, based on the dependence of the kinetic component on growth rate, is effective at distilling a common temporal evolution among the oxygen isotopic records of the multiple stalagmites. However, this approach is limited by the quality of the age model. For time periods characterized by very slow growth and long durations between dates, the presence of crypto-hiatus may result in average growth rates which underestimate the instantaneous speleothem deposition rates and which therefore underestimate the magnitude of kinetic effects. We compare the composite corrected oxygen isotopic record with other records of the timing of glacial inception in the North Atlantic realm.

  13. Mechanisms of single-walled carbon nanotube nucleation, growth, and healing determined using QM/MD methods.

    PubMed

    Page, Alister J; Ohta, Yasuhito; Irle, Stephan; Morokuma, Keiji

    2010-10-19

    Since their discovery in the early 1990s, single-walled carbon nanotubes (SWNTs) have spawned previously unimaginable commercial and industrial technologies. Their versatility stems from their unique electronic, physical/chemical, and mechanical properties, which set them apart from traditional materials. Many researchers have investigated SWNT growth mechanisms in the years since their discovery. The most prevalent of these is the vapor-liquid-solid (VLS) mechanism, which is based on experimental observations. Within the VLS mechanism, researchers assume that the formation of a SWNT starts with co-condensation of carbon and metal atoms from vapor to form liquid metal carbide. Once the liquid reaches supersaturation, the solid phase nanotubes begin to grow. The growth process is partitioned into three distinct stages: nucleation of a carbon "cap-precursor," "cap-to-tube" transformation, and continued SWNT growth. In recent years, molecular dynamics (MD) simulations have come to the fore with respect to SWNT growth. MD simulations lead to spatial and temporal resolutions of these processes that are superior to those possible using current experimental techniques, and so provide valuable information regarding the growth process that researchers cannot obtain experimentally. In this Account, we review our own recent efforts to simulate SWNT nucleation, growth, and healing phenomena on transition-metal catalysts using quantum mechanical molecular dynamics (QM/MD) methods. In particular, we have validated each stage of the SWNT condensation mechanism using a self-consistent-charge density-functional tight-binding (SCC-DFTB) methodology. With respect to the nucleation of a SWNT cap-precursor (stage 1), we have shown that the presence of a transition-metal carbide particle is not a necessary prerequisite for SWNT nucleation, contrary to conventional experimental presumptions. The formation and coalescence of polyyne chains on the metal surface occur first, followed by the

  14. Functionalization of multiwalled carbon nanotubes by microwave irradiation for lysozyme attachment: comparison of covalent and adsorption methods by kinetics of thermal inactivation

    NASA Astrophysics Data System (ADS)

    Puentes-Camacho, Daniel; Velázquez, Enrique F.; Rodríguez-Félix, Dora E.; Castillo-Ortega, Mónica; Sotelo-Mundo, Rogerio R.; del Castillo-Castro, Teresa

    2017-12-01

    Proteins suffer changes in their tertiary structure when they are immobilized, and enzymatic activity is affected due to the low biocompatibility of some supporting materials. In this work immobilization of lysozyme on carbon nanotubes previously functionalized by microwave irradiation was studied. The effectiveness of the microwave-assisted acid treatment of carbon nanotubes was evaluated by XPS, TEM, Raman and FTIR spectroscopy. The carboxylic modification of nanotube surfaces by this fast, simple and feasible method allowed the physical adsorption and covalent linking of active lysozyme onto the carbonaceous material. Thermal inactivation kinetics, thermodynamic parameters and storage stability were studied for adsorbed and covalent enzyme complexes. A major stability was found for lysozyme immobilized by the covalent method, the activation energy for inactivation of the enzyme was higher for the covalent method and it was stable after 50 d of storage at 4 °C. The current study highlights the effect of protein immobilization method on the biotechnological potential of nanostructured biocatalysts.

  15. Glass fabrics self-cracking catalytic growth of boron nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Wang, Jilin; Peng, Daijang; Long, Fei; Wang, Weimin; Gu, Yunle; Mo, Shuyi; Zou, Zhengguang; Fu, Zhengyi

    2017-02-01

    Glass fabrics were used to fabricate boron nitride nanotubes (BNNTs) with a broad diameter range through a combined chemical vapor deposition and self-propagation high-temperature synthesis (CVD-SHS) method at different holding times (0min, 30min, 90min, 180min and 360min). SEM characterization has been employed to investigate the macro and micro structure/morphology changes of the glass fabrics and BNNTs in detail. SEM image analysis has provided direct experimental evidences for the rationality of the optimized self-cracking catalyst VLS growth mechanism, including the transformation situations of the glass fabrics and the BNNTs growth processes respectively. This paper was the further research and compensation for the theory and experiment deficiencies in the new preparation method of BNNTs reported in our previous work. In addition, it is likely that the distinctive self-cracking catalyst VLS growth mechanism could provide a new idea to preparation of other inorganic functional nano-materials using similar one-dimensional raw materials as growth templates and catalysts.

  16. Template-Growth of Highly Ordered Carbon Nanotube Arrays on Silicon POSTPRINT

    DTIC Science & Technology

    2006-09-01

    packed uni- form CNTs that are spatially isolated from each other is to use a growth template. Highly ordered anodic aluminum oxide ( AAO ) template can...process for evaporating thick aluminum of high quality and good adhesion. 15. SUBJECT TERMS Anodic Aluminum Oxide Template, Carbon Nanotubes (CNTs...within the highly ordered nanopores of an alumina oxide template, which is in turn formed on silicon through anodization of aluminum of unprecedented

  17. Iron-Doped Carbon Aerogels: Novel Porous Substrates for Direct Growth of Carbon Nanotubes

    DOE R&D Accomplishments Database

    Steiner, S. A.; Baumann, T. F.; Kong, J.; Satcher, J. H.; Dresselhaus, M. S.

    2007-02-20

    We present the synthesis and characterization of Fe-doped carbon aerogels (CAs) and demonstrate the ability to grow carbon nanotubes directly on monoliths of these materials to afford novel carbon aerogel-carbon nanotube composites. Preparation of the Fe-doped CAs begins with the sol-gel polymerization of the potassium salt of 2,4-dihydroxybenzoic acid with formaldehyde, affording K{sup +}-doped gels that can then be converted to Fe{sup 2+}- or Fe{sup 3+}-doped gels through an ion exchange process, dried with supercritical CO{sub 2} and subsequently carbonized under an inert atmosphere. Analysis of the Fe-doped CAs by TEM, XRD and XPS revealed that the doped iron species are reduced during carbonization to form metallic iron and iron carbide nanoparticles. The sizes and chemical composition of the reduced Fe species were related to pyrolysis temperature as well as the type of iron salt used in the ion exchange process. Raman spectroscopy and XRD analysis further reveal that, despite the presence of the Fe species, the CA framework is not significantly graphitized during pyrolysis. The Fe-doped CAs were subsequently placed in a thermal CVD reactor and exposed to a mixture of CH{sub 4} (1000 sccm), H{sub 2} (500 sccm), and C{sub 2}H{sub 4} (20 sccm) at temperatures ranging from 600 to 800 C for 10 minutes, resulting in direct growth of carbon nanotubes on the aerogel monoliths. Carbon nanotubes grown by this method appear to be multiwalled ({approx}25 nm in diameter and up to 4 mm long) and grow through a tip-growth mechanism that pushes catalytic iron particles out of the aerogel framework. The highest yield of CNTs were grown on Fe-doped CAs pyrolyzed at 800 C treated at CVD temperatures of 700 C.

  18. Analysis of Effluent Gases During the CCVD Growth of Multi Wall Carbon Nanotubes from Acetylene

    NASA Technical Reports Server (NTRS)

    Schmitt, T. C.; Biris, A. S.; Miller, D. W.; Biris, A. R.; Lupu, D.; Trigwell, S.; Rahman, Z. U.

    2005-01-01

    Catalytic chemical vapor deposition was used to grow multi-walled carbon nanotubes on a Fe:Co:CaCO3 catalyst from acetylene. The influent and effluent gases were analyzed by gas chromatography and mass spectrometry at different time intervals during the nanotubes growth process in order to better understand and optimize the overall reaction. A large number of byproducts were identified and it was found that the number and the level for some of the carbon byproducts significantly increased over time. The CaCO3 catalytic support thermally decomposed into CaO and CO2 resulting in a mixture of two catalysts for growing the nanotubes, which were found to have outer diameters belonging to two main groups 8 to 35 nm and 40 to 60 nm, respectively.

  19. Effect of Enhanced Thermal Stability of Alumina Support Layer on Growth of Vertically Aligned Single-Walled Carbon Nanotubes and Their Application in Nanofiltration Membranes

    NASA Astrophysics Data System (ADS)

    In, Jung Bin; Cho, Kang Rae; Tran, Tung Xuan; Kim, Seok-Min; Wang, Yinmin; Grigoropoulos, Costas P.; Noy, Aleksandr; Fornasiero, Francesco

    2018-06-01

    We investigate the thermal stability of alumina supporting layers sputtered at different conditions and its effect on the growth of aligned single-walled carbon nanotube arrays. Radio frequency magnetron sputtering of alumina under oxygen-argon atmosphere produces a Si-rich alumina alloy film on a silicon substrate. Atomic force microscopy on the annealed catalysts reveals that Si-rich alumina films are more stable than alumina layers with low Si content at the elevated temperatures at which the growth of single-walled carbon nanotubes is initiated. The enhanced thermal stability of the Si-rich alumina layer results in a narrower (< 2.2 nm) diameter distribution of the single-walled carbon nanotubes. Thanks to the smaller diameters of their nanotube pores, membranes fabricated with vertically aligned nanotubes grown on the stable layers display improved ion selectivity.

  20. Plasma CVD of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance; Cruden, B.; Hash, D.; Meyyappan, M.; DeVincenzi, Donald L. (Technical Monitor)

    2001-01-01

    Carbon nanotubes(CNT) exhibit remarkable mechanical and unique electronic properties and thus have created excitement in the research community about their potential in electronics, computing, sensor and structural applications. Realization of these applications critically depends on the ability to control the properties(such as diameter, chirality) as well purity. We have investigated CNT growth using an inductively coupled plasma(ICP) process using hydrocarbon feedstock. The catalyst required for nanotube growth consists of thin sputtered layers of aluminum and iron(10 nm each) and aligned carbon nanotubes have been obtained. Optical emission diagnostics as well as a plasma modeling effort have been undertaken to understand growth mechanisms. This presentation will discuss growth characteristics under various pressure, power and feedgas compositions and our understanding from modeling and diagnostics.

  1. Patterned growth of carbon nanotubes on Si substrates without predeposition of metal catalysts

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Yu, J.

    2005-07-01

    Aligned carbon nanotubes (CNTs) can be readily synthesized on quartz or silicon-oxide-coated Si substrates using a chemical vapor deposition method, but it is difficult to grow them on pure Si substrates without predeposition of metal catalysts. We report that aligned CNTs were grown by pyrolysis of iron phthalocyanine at 1000°C on the templates created on Si substrates with simple mechanical scratching. Scanning electron microscopy and x-ray energy spectroscopy analysis revealed that the trenches and patterns created on the surface of Si substrates were preferred nucleation sites for nanotube growth due to a high surface energy, metastable surface structure, and possible capillarity effect. A two-step pyrolysis process maintained Fe as an active catalyst.

  2. In situ monitoring of laser-assisted hydrothermal growth of ZnO nanowires: thermally deactivating growth kinetics.

    PubMed

    In, Jung Bin; Kwon, Hyuk-Jun; Lee, Daeho; Ko, Seung Hwan; Grigoropoulos, Costas P

    2014-02-26

    The laser-assisted hydrothermal growth kinetics of a cluster of ZnO nanowires are studied based on optical in situ growth monitoring. The growth yields are orders of magnitude higher than those of conventional hydrothermal methods that use bulk heating. This remarkable improvement is attributed to suppression of precursor depletion occurring by homogeneous growth reactions, as well as to enhanced mass transport. The obtained in situ data show gradually decaying growth kinetics even with negligible precursor consumption. It is revealed that the growth deceleration is caused by thermal deactivation resulting from heat dissipation through the growing nanowires. Finally, it is demonstrated that the tailored temporal modulation of the input power enables sustained growth to extended dimensions. These results provide a key to highly efficient use of growth precursors that has been pursued for industrial use of this functional metal oxide semiconductor. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Developments in Analytical Chemistry: Acoustically Levitated Drop Reactors for Enzyme Reaction Kinetics and Single-Walled Carbon Nanotube-Based Sensors for Detection of Toxic Organic Phosphonates

    ERIC Educational Resources Information Center

    Field, Christopher Ryan

    2009-01-01

    Developments in analytical chemistry were made using acoustically levitated small volumes of liquid to study enzyme reaction kinetics and by detecting volatile organic compounds in the gas phase using single-walled carbon nanotubes. Experience gained in engineering, electronics, automation, and software development from the design and…

  4. 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.

  5. 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.

  6. Nanoscale plasma chemistry enables fast, size-selective nanotube nucleation.

    PubMed

    Ostrikov, Kostya Ken; Mehdipour, Hamid

    2012-03-07

    The possibility of fast, narrow-size/chirality nucleation of thin single-walled carbon nanotubes (SWCNTs) at low, device-tolerant process temperatures in a plasma-enhanced chemical vapor deposition (CVD) is demonstrated using multiphase, multiscale numerical experiments. These effects are due to the unique nanoscale reactive plasma chemistry (NRPC) on the surfaces and within Au catalyst nanoparticles. The computed three-dimensional process parameter maps link the nanotube incubation times and the relative differences between the incubation times of SWCNTs of different sizes/chiralities to the main plasma- and precursor gas-specific parameters and explain recent experimental observations. It is shown that the unique NRPC leads not only to much faster nucleation of thin nanotubes at much lower process temperatures, but also to better selectivity between the incubation times of SWCNTs with different sizes and chiralities, compared to thermal CVD. These results are used to propose a time-programmed kinetic approach based on fast-responding plasmas which control the size-selective, narrow-chirality nucleation and growth of thin SWCNTs. This approach is generic and can be used for other nanostructure and materials systems. © 2012 American Chemical Society

  7. Effect of Enhanced Thermal Stability of Alumina Support Layer on Growth of Vertically Aligned Single-Walled Carbon Nanotubes and Their Application in Nanofiltration Membranes.

    PubMed

    In, Jung Bin; Cho, Kang Rae; Tran, Tung Xuan; Kim, Seok-Min; Wang, Yinmin; Grigoropoulos, Costas P; Noy, Aleksandr; Fornasiero, Francesco

    2018-06-07

    We investigate the thermal stability of alumina supporting layers sputtered at different conditions and its effect on the growth of aligned single-walled carbon nanotube arrays. Radio frequency magnetron sputtering of alumina under oxygen-argon atmosphere produces a Si-rich alumina alloy film on a silicon substrate. Atomic force microscopy on the annealed catalysts reveals that Si-rich alumina films are more stable than alumina layers with low Si content at the elevated temperatures at which the growth of single-walled carbon nanotubes is initiated. The enhanced thermal stability of the Si-rich alumina layer results in a narrower (< 2.2 nm) diameter distribution of the single-walled carbon nanotubes. Thanks to the smaller diameters of their nanotube pores, membranes fabricated with vertically aligned nanotubes grown on the stable layers display improved ion selectivity.

  8. Structure, growth kinetics, and ledge flow during vapor-solid-solid growth of copper-catalyzed silicon nanowires.

    PubMed

    Wen, C-Y; Reuter, M C; Tersoff, J; Stach, E A; Ross, F M

    2010-02-10

    We use real-time observations of the growth of copper-catalyzed silicon nanowires to determine the nanowire growth mechanism directly and to quantify the growth kinetics of individual wires. Nanowires were grown in a transmission electron microscope using chemical vapor deposition on a copper-coated Si substrate. We show that the initial reaction is the formation of a silicide, eta'-Cu(3)Si, and that this solid silicide remains on the wire tips during growth so that growth is by the vapor-solid-solid mechanism. Individual wire directions and growth rates are related to the details of orientation relation and catalyst shape, leading to a rich morphology compared to vapor-liquid-solid grown nanowires. Furthermore, growth occurs by ledge propagation at the silicide/silicon interface, and the ledge propagation kinetics suggest that the solubility of precursor atoms in the catalyst is small, which is relevant to the fabrication of abrupt heterojunctions in nanowires.

  9. 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

  10. Growth kinetics of indium metal atoms on Si(1 1 2) surface

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Raj, Vidur; Chauhan, Amit Kumar Singh; Gupta, Govind, E-mail: govind@nplindia.org

    Graphical abstract: Controlled growth of indium atoms on Si(1 1 2) surface has been carried out systematically and the influence of substrate temperature on the kinetics is analysed under various growth conditions. Temperature induced anomalous layer-to-clusters transformation during thermal desorption has also been reported. - Highlights: • Controlled growth of indium atoms on Si(1 1 2) surface & their thermal stability. • Influence of substrate temperature on the kinetics under various growth conditions. • Temperature induced layer-to-clusters transformation during thermal desorption. - Abstract: The growth kinetics and desorption behavior of indium (In) atoms grown on high index Si(1 1 2)more » surface at different substrate temperatures has been studied. Auger electron spectroscopy analysis revealed that In growth at room temperature (RT) and high substrate temperature (HT) ∼250 °C follows Frank–van der Merve growth mode whereas at temperatures ≥450 °C, In growth evolves through Volmer–Weber growth mode. Thermal desorption studies of RT and 250 °C grown In/Si(1 1 2) systems show temperature induced rearrangement of In atoms over Si(1 1 2) surface leading to clusters to layer transformation. The monolayer and bilayer desorption energies for RT grown In/Si(1 1 2) system are calculated to be 2.5 eV and 1.52 eV, while for HT-250 °C the values are found to be 1.6 eV and 1.3 eV, respectively. This study demonstrates the effect of temperature on growth kinetics as well as on the multilayer/monolayer desorption pathway of In on Si(1 1 2) surface.« less

  11. Gas-phase kinetics during diamond growth: CH4 as-growth species

    NASA Astrophysics Data System (ADS)

    Harris, Stephen J.

    1989-04-01

    We have used a one-dimensional kinetic analysis to model the gas-phase chemistry that occurred during the diamond growth experiments of Chauhan, Angus, and Gardner [J. Appl. Phys. 47, 4746 (1976)]. In those experiments the weight of diamond seed crystals heated by lamps in a CH4/H2 environment was monitored by a microbalance. No filament or electric discharge was present. Our analysis shows that diamond growth occurred in this system by direct reaction of CH4 on the diamond surface. C2H2 and CH3, which have been proposed as diamond growth species, played no significant role there, although our results do not address their possible contributions in other systems such as filament- or plasma-assisted diamond growth.

  12. Growth kinetics of Bacillus stearothermophilus BR219

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Worden, R.M.; Subramanian, R.; Bly, M.J.

    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 withmore » 5 mM phenol.« less

  13. Optimal bioprocess design through a gene regulatory network - growth kinetic hybrid model: Towards Replacing Monod kinetics.

    PubMed

    Tsipa, Argyro; Koutinas, Michalis; Usaku, Chonlatep; Mantalaris, Athanasios

    2018-05-02

    Currently, design and optimisation of biotechnological bioprocesses is performed either through exhaustive experimentation and/or with the use of empirical, unstructured growth kinetics models. Whereas, elaborate systems biology approaches have been recently explored, mixed-substrate utilisation is predominantly ignored despite its significance in enhancing bioprocess performance. Herein, bioprocess optimisation for an industrially-relevant bioremediation process involving a mixture of highly toxic substrates, m-xylene and toluene, was achieved through application of a novel experimental-modelling gene regulatory network - growth kinetic (GRN-GK) hybrid framework. The GRN model described the TOL and ortho-cleavage pathways in Pseudomonas putida mt-2 and captured the transcriptional kinetics expression patterns of the promoters. The GRN model informed the formulation of the growth kinetics model replacing the empirical and unstructured Monod kinetics. The GRN-GK framework's predictive capability and potential as a systematic optimal bioprocess design tool, was demonstrated by effectively predicting bioprocess performance, which was in agreement with experimental values, when compared to four commonly used models that deviated significantly from the experimental values. Significantly, a fed-batch biodegradation process was designed and optimised through the model-based control of TOL Pr promoter expression resulting in 61% and 60% enhanced pollutant removal and biomass formation, respectively, compared to the batch process. This provides strong evidence of model-based bioprocess optimisation at the gene level, rendering the GRN-GK framework as a novel and applicable approach to optimal bioprocess design. Finally, model analysis using global sensitivity analysis (GSA) suggests an alternative, systematic approach for model-driven strain modification for synthetic biology and metabolic engineering applications. Copyright © 2018. Published by Elsevier Inc.

  14. Growth kinetics of disk-shaped copper islands in electrochemical deposition.

    PubMed

    Guo, Lian; Zhang, Shouliang; Searson, Peter

    2009-05-01

    The ability to independently dictate the shape and crystal orientation of islands in electrocrystallization remains a significant challenge. The main reason for this is that the complex interplay between the substrate, nucleation, and surface chemistry is not fully understood. Here we report on the kinetics of island growth for copper on ruthenium oxide. The small nucleation overpotential leads to enhanced lateral growth and the formation of hexagonal disk-shaped islands. The amorphous substrate allows the nuclei to achieve the thermodynamically favorable orientation, i.e., a 111 surface normal. Island growth follows power law kinetics in both lateral and vertical directions. At shorter times, the two growth exponents are equal to 1/2 whereas at longer times lateral growth slows down while vertical growth speeds up. We propose a growth mechanism, wherein the lateral growth of disk-shaped islands is initiated by attachment of Cu adatoms on the ruthenium oxide surface onto the island periphery while vertical growth is initiated by two-dimensional nucleation on the top terrace and followed by lateral step propagation. These results indicate three criteria for enhanced lateral growth in electrodeposition: (i) a substrate that leads to a small nucleation overpotential, (ii) fast adatom surface diffusion on substrate to promote lateral growth, and (iii) preferential anion adsorption to stabilize the basal plane.

  15. Effect of growth pressure on the synthesis of vertically aligned carbon nanotubes and their growth termination.

    PubMed

    Park, Sangeun; Song, Wooseok; Kim, Yooseok; Song, Inkyung; Kim, Sung Hwan; Lee, Su Il; Jang, Sung Won; Parkl, Chong-Yun

    2014-07-01

    When vertically aligned carbon nanotubes (VACNTs) are synthesized by thermal chemical vapor deposition (TCVD), their structural features such as height and density can be determined by TCVD growth conditions. In this study we investigated the effect of growth pressure on the structural features of VACNTs. Changes in growth pressure significantly affected the height, density, and crystalinity of synthesized VACNTs. In addition, we suggest that the growth termination of VACNTs could be due to the lack of carbon feedstock supply to the center of the VACNT film induced by the pressure-dependent adsorption of amorphous carbon at the edge of the VACNT film. In addition, the field emission characteristics of the VACNT film were carried out. The turn-on voltage of the VACNT film was 1.62 V/microm and the field enhancement factor (beta) was 2478. These results provide useful information for practical applications of VACNTs, such as field emission display and X-ray source.

  16. Surface modification of TiO2 nanotubes with osteogenic growth peptide to enhance osteoblast differentiation.

    PubMed

    Lai, Min; Jin, Ziyang; Su, Zhiguo

    2017-04-01

    To investigate the influence of surface-biofunctionalized substrates on osteoblast behavior, a layer of aligned TiO 2 nanotubes with a diameter of around 70nm was fabricated on titanium surface by anodization, and then osteogenic growth peptide (OGP) was conjugated onto TiO 2 nanotubes through the intermediate layer of polydopamine. The morphology, composition and wettability of different surfaces were characterized by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements, respectively. The effects of OGP-modified TiO 2 nanotube substrates on the morphology, proliferation and differentiation of osteoblasts were examined in vitro. Immunofluorescence staining revealed that the OGP-functionalized TiO 2 nanotubes were favorable for cell spreading. However, there was no significant difference in cell proliferation observed among the different groups. Cells grown onto OGP-functionalized TiO 2 nanotubes showed significantly higher (p<0.05 or p<0.01) levels of alkaline phosphatase (ALP) and mineralization after 4, 7 and 14days of culture, respectively. Cells grown on OGP-functionalized TiO 2 nanotubes had significantly higher (p<0.05 or p<0.01) expression of osteogenic-related genes including runt related transcription factor 2 (Runx2), ALP, collagen type I (Col I), osteopontin (OPN) and osteocalcin (OC) after 14days of culture. These data suggest that surface functionalization of TiO 2 nanotubes with OGP was beneficial for cell spreading and differentiation. This study provides a novel platform for the development and fabrication of titanium-based implants that enhance the propensity for osseointegration between the native tissue and implant interface. Copyright © 2016 Elsevier B.V. All rights reserved.

  17. Kinetic Model of the Initial Stage of the Nanowire Growth

    NASA Astrophysics Data System (ADS)

    Filimonov, S. N.; Hervieu, Yu. Yu.

    2018-03-01

    A kinetic model of the formation of pyramid-like bulges (pedestals) at the bases of vertical nanowires is proposed. The formation of the pedestals at the early stage of the nanowire growth is assumed to be induced by a higher nucleation rate of two-dimensional islands under the catalyst droplet, as compared to the nucleation rate at the non-activated surface areas. Kinetics of the nucleation and propagation of the steps in the pyramid is described with a model of the multilayer growth, taking into account that the catalyst droplet at the nanowire top is a strong sink for adatoms. It is shown that the transition from the growth of the pyramid to the axial growth of the nanowire is possible if the appearance of a nucleus of the new layer under the catalyst droplet results in a partial dissolution of the underlying layer. In this case a segment of the nanowire sidewall is formed, preventing the lateral growth of the layers generated by the droplet.

  18. Patterned Growth of Carbon Nanotubes or Nanofibers

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance D.

    2004-01-01

    A method and apparatus for the growth of carbon nanotubes or nanofibers in a desired pattern has been invented. The essence of the method is to grow the nanotubes or nanofibers by chemical vapor deposition (CVD) onto a patterned catalyst supported by a substrate. The figure schematically depicts salient aspects of the method and apparatus in a typical application. A substrate is placed in a chamber that contains both ion-beam sputtering and CVD equipment. The substrate can be made of any of a variety of materials that include several forms of silicon or carbon, and selected polymers, metals, ceramics, and even some natural minerals and similar materials. Optionally, the substrate is first coated with a noncatalytic metal layer (which could be a single layer or could comprise multiple different sublayers) by ion-beam sputtering. The choice of metal(s) and thickness(es) of the first layer (if any) and its sublayers (if any) depends on the chemical and electrical properties required for subsequent deposition of the catalyst and the subsequent CVD of the carbon nanotubes. A typical first-sublayer metal is Pt, Pd, Cr, Mo, Ti, W, or an alloy of two or more of these elements. A typical metal for the second sublayer or for an undivided first layer is Al at a thickness .1 nm or Ir at a thickness .5 nm. Proper choice of the metal for a second sublayer of a first layer makes it possible to use a catalyst that is chemically incompatible with the substrate. In the next step, a mask having holes in the desired pattern is placed over the coated substrate. The catalyst is then deposited on the coated substrate by ion-beam sputtering through the mask. Optionally, the catalyst could be deposited by a technique other than sputtering and/or patterned by use of photolithography, electron- beam lithography, or another suitable technique. The catalytic metal can be Fe, Co, Ni, or an alloy of two or more of these elements, deposited to a typical thickness in the range from 0.1 to 20 nm.

  19. Real-time imaging of self-organization and mechanical competition in carbon nanotube forest growth [Real-time environmental TEM investigation of self-organization and mechanical competition in carbon nanotube forest growth

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Balakrishnan, Viswanath; Bedewy, Mostafa; Meshot, Eric R.

    Here, the properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates.more » Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT–CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. As a result, our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.« less

  20. Real-time imaging of self-organization and mechanical competition in carbon nanotube forest growth [Real-time environmental TEM investigation of self-organization and mechanical competition in carbon nanotube forest growth

    DOE PAGES

    Balakrishnan, Viswanath; Bedewy, Mostafa; Meshot, Eric R.; ...

    2016-11-23

    Here, the properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates.more » Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT–CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. As a result, our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.« less

  1. Heteroepitaxial Growth of Single-Walled Carbon Nanotubes from Boron Nitride

    PubMed Central

    Tang, Dai-Ming; Zhang, Li-Li; Liu, Chang; Yin, Li-Chang; Hou, Peng-Xiang; Jiang, Hua; Zhu, Zhen; Li, Feng; Liu, Bilu; Kauppinen, Esko I.; Cheng, Hui-Ming

    2012-01-01

    The growth of single-walled carbon nanotubes (SWCNTs) with predefined structure is of great importance for both fundamental research and their practical applications. Traditionally, SWCNTs are grown from a metal catalyst with a vapor-liquid-solid mechanism, where the catalyst is in liquid state with fluctuating structures, and it is intrinsically unfavorable for the structure control of SWCNTs. Here we report the heteroepitaxial growth of SWCNTs from a platelet boron nitride nanofiber (BNNF), which is composed of stacked (002) planes and is stable at high temperatures. SWCNTs are found to grow epitaxially from the open (002) edges of the BNNFs, and the diameters of the SWCNTs are multiples of the BN (002) interplanar distance. In situ transmission electron microscopy observations coupled with first principles calculations reveal that the growth of SWCNTs from the BNNFs follows a vapor-solid-solid mechanism. Our work opens opportunities for the control over the structure of SWCNTs by hetero-crystallographic epitaxy. PMID:23240076

  2. Investigating the Catalytic Growth of Carbon Nanotubes with In Situ Raman Monitoring

    DTIC Science & Technology

    2015-06-01

    single-walled carbon nanotube growth using cobalt deposited on Si/SiO2 as a model system. In situ Raman studies revealed that thin catalyst layers... cobalt thickness were studied. Surface analyses showed that during the catalyst preparation, catalyst atoms at the interface with silica form small...nanostructures. However, highly-reducing conditions are required to reduce the small silicate domains into small cobalt particles able to grow single-walled

  3. Kinetic Monte Carlo simulations of nucleation and growth in electrodeposition.

    PubMed

    Guo, Lian; Radisic, Aleksandar; Searson, Peter C

    2005-12-22

    Nucleation and growth during bulk electrodeposition is studied using kinetic Monte Carlo (KMC) simulations. Ion transport in solution is modeled using Brownian dynamics, and the kinetics of nucleation and growth are dependent on the probabilities of metal-on-substrate and metal-on-metal deposition. Using this approach, we make no assumptions about the nucleation rate, island density, or island distribution. The influence of the attachment probabilities and concentration on the time-dependent island density and current transients is reported. Various models have been assessed by recovering the nucleation rate and island density from the current-time transients.

  4. Nanotube Production and Applications at Johnson Space Center

    NASA Technical Reports Server (NTRS)

    Nikolaev, Pavel; Files, Bradley; Arepalli, Sivaram; Scott, Carl; Holmes, William; Nicholson, Leonard S. (Technical Monitor)

    2000-01-01

    Promise of applications of carbon nanotubes has led to an intense effort at NASA/JSC, especially in the area of nanotube composites. Using the extraordinary mechanical strength of nanotubes, NASA hopes to design this revolutionary lightweight material for use in aerospace applications. Current research focuses on structural polymeric materials to attempt to lower the weight of spacecraft necessary for interplanetary missions. Other applications of nanotubes are also of interest for energy storage, gas storage, nanoelectronics, field emission, and biomedical applications. In pursuit of these goals, we have set up both laser and arc production processes for nanotubes. An in-depth diagnostic study of the plasma plume in front of the laser target has been studied to try to determine nanotube growth mechanisms. Complementary studies of characterization of nanotube product have added to knowledge of growth conditions. Results of our preliminary experiments in incorporating nanotubes into composites will be presented. Morphology and mechanical properties of the nanotubes composites will be discussed.

  5. Real-Time Imaging of Self-Organization and Mechanical Competition in Carbon Nanotube Forest Growth.

    PubMed

    Balakrishnan, Viswanath; Bedewy, Mostafa; Meshot, Eric R; Pattinson, Sebastian W; Polsen, Erik S; Laye, Fabrice; Zakharov, Dmitri N; Stach, Eric A; Hart, A John

    2016-12-27

    The properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates. Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT-CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. Our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.

  6. 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.

  7. Kinetic aspects of chain growth in Fischer-Tropsch synthesis.

    PubMed

    Filot, Ivo A W; Zijlstra, Bart; Broos, Robin J P; Chen, Wei; Pestman, Robert; Hensen, Emiel J M

    2017-04-28

    Microkinetics simulations are used to investigate the elementary reaction steps that control chain growth in the Fischer-Tropsch reaction. Chain growth in the FT reaction on stepped Ru surfaces proceeds via coupling of CH and CR surface intermediates. Essential to the growth mechanism are C-H dehydrogenation and C hydrogenation steps, whose kinetic consequences have been examined by formulating two novel kinetic concepts, the degree of chain-growth probability control and the thermodynamic degree of chain-growth probability control. For Ru the CO conversion rate is controlled by the removal of O atoms from the catalytic surface. The temperature of maximum CO conversion rate is higher than the temperature to obtain maximum chain-growth probability. Both maxima are determined by Sabatier behavior, but the steps that control chain-growth probability are different from those that control the overall rate. Below the optimum for obtaining long hydrocarbon chains, the reaction is limited by the high total surface coverage: in the absence of sufficient vacancies the CHCHR → CCHR + H reaction is slowed down. Beyond the optimum in chain-growth probability, CHCR + H → CHCHR and OH + H → H 2 O limit the chain-growth process. The thermodynamic degree of chain-growth probability control emphasizes the critical role of the H and free-site coverage and shows that at high temperature, chain depolymerization contributes to the decreased chain-growth probability. That is to say, during the FT reaction chain growth is much faster than chain depolymerization, which ensures high chain-growth probability. The chain-growth rate is also fast compared to chain-growth termination and the steps that control the overall CO conversion rate, which are O removal steps for Ru.

  8. 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.

  9. Heterodoped nanotubes: theory, synthesis, and characterization of phosphorus-nitrogen doped multiwalled carbon nanotubes.

    PubMed

    Cruz-Silva, Eduardo; Cullen, David A; Gu, Lin; Romo-Herrera, Jose Manuel; Muñoz-Sandoval, Emilio; López-Urías, Florentino; Sumpter, Bobby G; Meunier, Vincent; Charlier, Jean-Christophe; Smith, David J; Terrones, Humberto; Terrones, Mauricio

    2008-03-01

    Arrays of multiwalled carbon nanotubes doped with phosphorus (P) and nitrogen (N) are synthesized using a solution of ferrocene, triphenyl-phosphine, and benzylamine in conjunction with spray pyrolysis. We demonstrate that iron phosphide (Fe(3)P) nanoparticles act as catalysts during nanotube growth, leading to the formation of novel PN-doped multiwalled carbon nanotubes. The samples were examined by high resolution electron microscopy and microanalysis techniques, and their chemical stability was explored by means of thermogravimetric analysis in the presence of oxygen. The PN-doped structures reveal important morphology and chemical changes when compared to N-doped nanotubes. These types of heterodoped nanotubes are predicted to offer many new opportunities in the fabrication of fast-response chemical sensors.

  10. Controlled growth of well-aligned carbon nanotubes with large diameters

    NASA Astrophysics Data System (ADS)

    Wang, Xianbao; Liu, Yunqi; Zhu, Daoben

    2001-06-01

    Well-aligned carbon nanotubes (CNTs) with large diameters (25-200 nm) were synthesized by pyrolysis of iron(II) phthalocyanine. The outer diameter up to 218.5 nm and the length of the well-aligned CNTs can be systematically controlled by varying the growth time. A tube-in-tube nano-structure with large and small diameters of 176 and 16.7 nm, respectively, was found. The grain sizes of the iron catalyst play an important role in controlling the CNT diameters. These results are of great importance to design new aligned CNT-based electron field emitters in the potential application of panel displays.

  11. 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

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

    PubMed

    Cabrales, Luis E Bergues; Nava, Juan J Godina; Aguilera, Andrés Ramírez; Joa, Javier A González; Ciria, Héctor M Camué; González, Maraelys Morales; Salas, Miriam Fariñas; Jarque, Manuel Verdecia; González, Tamara Rubio; Mateus, Miguel A O'Farril; Brooks, Soraida C Acosta; Palencia, Fabiola Suárez; Zamora, Lisset Ortiz; Quevedo, María C Céspedes; Seringe, Sarah Edward; Cuitié, Vladimir Crombet; Cabrales, Idelisa Bergues; González, Gustavo Sierra

    2010-10-28

    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. 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. 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. 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.

  13. Preferential growth of short aligned, metallic-rich single-walled carbon nanotubes from perpendicular layered double hydroxide film.

    PubMed

    Zhao, Meng-Qiang; Tian, Gui-Li; Zhang, Qiang; Huang, Jia-Qi; Nie, Jing-Qi; Wei, Fei

    2012-04-07

    Direct bulk growth of single-walled carbon nanotubes (SWCNTs) with required properties, such as diameter, length, and chirality, is the first step to realize their advanced applications in electrical and optical devices, transparent conductive films, and high-performance field-effect transistors. Preferential growth of short aligned, metallic-rich SWCNTs is a great challenge to the carbon nanotube community. We report the bulk preferential growth of short aligned SWCNTs from perpendicular Mo-containing FeMgAl layered double hydroxide (LDH) film by a facile thermal chemical vapor deposition with CH(4) as carbon source. The growth of the short aligned SWCNTs showed a decreased growth velocity with an initial value of 1.9 nm s(-1). Such a low growth velocity made it possible to get aligned SWCNTs shorter than 1 μm with a growth duration less than 15 min. Raman spectra with different excitation wavelengths indicated that the as-grown short aligned SWCNTs showed high selectivity of metallic SWCNTs. Various kinds of materials, such as mica, quartz, Cu foil, and carbon fiber, can serve as the substrates for the growth of perpendicular FeMoMgAl LDH films and also the growth of the short aligned SWCNTs subsequently. These findings highlight the easy route for bulk preferential growth of aligned metallic-rich SWCNTs with well defined length for further bulk characterization and applications. This journal is © The Royal Society of Chemistry 2012

  14. Effects of single-walled carbon nanotubes on lysozyme gelation.

    PubMed

    Tardani, Franco; La Mesa, Camillo

    2014-09-01

    The possibility to disperse carbon nanotubes in biocompatible matrices has got substantial interest from the scientific community. Along this research line, the inclusion of single walled carbon nanotubes in lysozyme-based hydrogels was investigated. Experiments were performed at different nanotube/lysozyme weight ratios. Carbon nanotubes were dispersed in protein solutions, in conditions suitable for thermal gelation. The state of the dispersions was determined before and after thermal treatment. Rheology, dynamic light scattering and different microscopies investigated the effect that carbon nanotubes exert on gelation. The gelation kinetics and changes in gelation temperature were determined. The effect of carbon and lysozyme content on the gel properties was, therefore, determined. At fixed lysozyme content, moderate amounts of carbon nanotubes do not disturb the properties of hydrogel composites. At moderately high volume fractions in carbon nanotubes, the gels become continuous in both lysozyme and nanotubes. This is because percolating networks are presumably formed. Support to the above statements comes by rheology. Copyright © 2014 Elsevier B.V. All rights reserved.

  15. Growth of vertically aligned carbon nanotubes on silicon and quartz substrate by spray pyrolysis of a natural precursor: Turpentine oil

    NASA Astrophysics Data System (ADS)

    Afre, Rakesh A.; Soga, T.; Jimbo, T.; Kumar, Mukul; Ando, Y.; Sharon, M.

    2005-10-01

    Vertically aligned carbon nanotubes (VACNTs) were grown by spray pyrolysis of turpentine oil and ferrocene mixture at 700 °C. Using this simple method, we report the successful growth of vertically aligned nanotubes of 300 μm length and diameter in the range of 50-100 nm on Si(1 0 0) substrate. The ferrocene act as an in situ Fe catalyst precursor and forming the nanosize iron particles for formation of VACNTs on Si and quartz substrates. Morphological differences between aligned carbon nanotubes grown on different substrates are studied and discussed by SEM, TEM and Raman spectroscopy characterizations.

  16. Chemically Functionalized Carbon Nanotubes as Substrates for Neuronal Growth

    PubMed Central

    Hu, Hui; Ni, Yingchun; Montana, Vedrana; Haddon, Robert C.; Parpura, Vladimir

    2009-01-01

    We report the use of chemically modified carbon nanotubes as a substrate for cultured neurons. The morphological features of neurons that directly reflect their potential capability in synaptic transmission are characterized. The chemical properties of carbon nanotubes are systematically varied by attaching different functional groups that confer known characteristics to the substrate. By manipulating the charge carried by functionalized carbon nanotubes we are able to control the outgrowth and branching pattern of neuronal processes. PMID:21394241

  17. Carbon nanotube diameter selection by pretreatment of metal catalysts on surfaces

    DOEpatents

    Hauge, Robert H [Houston, TX; Xu, Ya-Qiong [Houston, TX; Shan, Hongwei [Houston, TX; Nicholas, Nolan Walker [South Charleston, WV; Kim, Myung Jong [Houston, TX; Schmidt, Howard K [Cypress, TX; Kittrell, W Carter [Houston, TX

    2012-02-28

    A new and useful nanotube growth substrate conditioning processes is herein disclosed that allows the growth of vertical arrays of carbon nanotubes where the average diameter of the nanotubes can be selected and/or controlled as compared to the prior art.

  18. Growth behavior of carbon nanotubes on multilayered metal catalyst film in chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Cui, H.; Eres, G.; Howe, J. Y.; Puretkzy, A.; Varela, M.; Geohegan, D. B.; Lowndes, D. H.

    2003-06-01

    The temperature and time dependences of carbon nanotube (CNT) growth by chemical vapor deposition are studied using a multilayered Al/Fe/Mo catalyst on silicon substrates. Within the 600-1100 °C temperature range of these studies, narrower temperature ranges were determined for the growth of distinct types of aligned multi-walled CNTs and single-walled CNTs by using high-resolution transmission electron microscopy and Raman spectroscopy. At 900 °C, in contrast to earlier work, double-walled CNTs are found more abundant than single-walled CNTs. Defects also are found to accumulate faster than the ordered graphitic structure if the growth of CNTs is extended to long durations.

  19. Beneficial role of carbon nanotubes on mustard plant growth: an agricultural prospect

    NASA Astrophysics Data System (ADS)

    Mondal, Anindita; Basu, Ruma; Das, Sukhen; Nandy, Papiya

    2011-10-01

    Nowadays an increasing application of nanotechnology in different fields has arisen an extensive debate about the effect of the engineered nanoparticles on environment . Phytotoxicity of nanoparticles has come into limelight in the last few years. However, very few studies have been done so far on the beneficial aspects of nanoparticles on plants. In this article, we report the beneficial effect of multi-walled carbon nanotubes (MWCNTs) having diameter of 30 nm on Brassica juncea (mustard) seeds. Measurements of germination rate, T 50 (time taken for 50% germination), shoot and root growth have shown encouraging results using low concentration of oxidized MWCNT (OMWCNT) treated seeds as compared to non-oxidized as well as high concentration OMWCNT treated seeds. For toxicity study we measured the germination index and relative root elongation, while conductivity test and infra-red spectra were also performed to study the overall effect of oxidized and non-oxidized nanotubes on mustard seeds and seedlings.

  20. Observation of Charge Generation and Transfer during CVD Growth of Carbon Nanotubes.

    PubMed

    Wang, Jiangtao; Liu, Peng; Xia, Bingyu; Wei, Haoming; Wei, Yang; Wu, Yang; Liu, Kai; Zhang, Lina; Wang, Jiaping; Li, Qunqing; Fan, Shoushan; Jiang, Kaili

    2016-07-13

    Carbon nanotube (CNT) is believed to be the most promising material for next generation IC industries with the prerequisite of chirality specific growth. For various approaches to controlling the chiral indices of CNTs, the key is to deepen the understanding of the catalytic growth mechanism in chemical vapor deposition (CVD). Here we show our discovery that the as-grown CNTs are all negatively charged after Fe-catalyzed CVD process. The extra electrons come from the charge generation and transfer during the growth of CNTs, which indicates that an electrochemical process happens in the surface reaction step. We then designed an in situ measurement equipment, verifying that the CVD growth of CNTs can be regarded as a primary battery system. Furthermore, we found that the variation of the Fermi level in Fe catalysts have a significant impact on the chirality of CNTs when different external electric fields are applied. These findings not only provide a new perspective on the growth of CNTs but also open up new possibilities for controlling the growth of CNTs by electrochemical methods.

  1. Endosomal receptor kinetics determine the stability of intracellular growth factor signalling complexes

    PubMed Central

    Tzafriri, A. Rami; Edelman, Elazer R.

    2006-01-01

    There is an emerging paradigm that growth factor signalling continues in the endosome and that cell response to a growth factor is defined by the integration of cell surface and endosomal events. As activated receptors in the endosome are exposed to a different set of binding partners, they probably elicit differential signals compared with when they are at the cell surface. As such, complete appreciation of growth factor signalling requires understanding of growth factor–receptor binding and trafficking kinetics both at the cell surface and in endosomes. Growth factor binding to surface receptors is well characterized, and endosomal binding is assumed to follow surface kinetics if one accounts for changes in pH. Yet, specific binding kinetics within the endosome has not been examined in detail. To parse the factors governing the binding state of endosomal receptors we analysed a whole-cell mathematical model of epidermal growth factor receptor trafficking and binding. We discovered that the stability of growth factor–receptor complexes within endosomes is governed by three primary independent factors: the endosomal dissociation constant, total endosomal volume and the number of endosomal receptors. These factors were combined into a single dimensionless parameter that determines the endosomal binding state of the growth factor–receptor complex and can distinguish different growth factors from each other and different cell states. Our findings indicate that growth factor binding within endosomal compartments cannot be appreciated solely on the basis of the pH-dependence of the dissociation constant and that the concentration of receptors in the endosomal compartment must also be considered. PMID:17117924

  2. Effects of reaction-kinetic parameters on modeling reaction pathways in GaN MOVPE growth

    NASA Astrophysics Data System (ADS)

    Zhang, Hong; Zuo, Ran; Zhang, Guoyi

    2017-11-01

    In the modeling of the reaction-transport process in GaN MOVPE growth, the selections of kinetic parameters (activation energy Ea and pre-exponential factor A) for gas reactions are quite uncertain, which cause uncertainties in both gas reaction path and growth rate. In this study, numerical modeling of the reaction-transport process for GaN MOVPE growth in a vertical rotating disk reactor is conducted with varying kinetic parameters for main reaction paths. By comparisons of the molar concentrations of major Ga-containing species and the growth rates, the effects of kinetic parameters on gas reaction paths are determined. The results show that, depending on the values of the kinetic parameters, the gas reaction path may be dominated either by adduct/amide formation path, or by TMG pyrolysis path, or by both. Although the reaction path varies with different kinetic parameters, the predicted growth rates change only slightly because the total transport rate of Ga-containing species to the substrate changes slightly with reaction paths. This explains why previous authors using different chemical models predicted growth rates close to the experiment values. By varying the pre-exponential factor for the amide trimerization, it is found that the more trimers are formed, the lower the growth rates are than the experimental value, which indicates that trimers are poor growth precursors, because of thermal diffusion effect caused by high temperature gradient. The effective order for the contribution of major species to growth rate is found as: pyrolysis species > amides > trimers. The study also shows that radical reactions have little effect on gas reaction path because of the generation and depletion of H radicals in the chain reactions when NH2 is considered as the end species.

  3. Thermal degradation of TiO2 nanotubes on titanium

    NASA Astrophysics Data System (ADS)

    Shivaram, Anish; Bose, Susmita; Bandyopadhyay, Amit

    2014-10-01

    The objective of this research was to study thermal degradation behavior of TiO2 nanotubes on titanium (Ti). TiO2 nanotubes were grown via anodization method on commercially pure Ti (Cp-Ti) discs using two different electrolytes, 1 vol. % HF in deionized (DI) water and 1 vol. % HF + 0.5 wt. % NH4F + 10 vol. % DI water in ethylene glycol, to obtain nanotubes with two different lengths, 300 nm and 950 nm keeping the nanotube diameter constant at 100 ± 20 nm. As grown TiO2 nanotubes were subjected to heat treatment to understand thermal degradation as a function of both temperature and hold time. The signs of degradation were observed mainly when amorphous nanotubes started to crystallize, however the crystallization temperature varied based on TiO2 nanotubes length and anodizing condition. Overall, 300 nm nanotubes were thermally stable at least up to 400 °C for 12 h, while the 950 nm long nanotubes show signs of degradation from 400 °C for 6 h only. Clearly, length of nanotubes, heat treatment temperature as well as hold times show influence toward degradation kinetics of TiO2 nanotubes on titanium.

  4. Silicon Carbide Nanotube Oxidation at High Temperatures

    NASA Technical Reports Server (NTRS)

    Ahlborg, Nadia; Zhu, Dongming

    2012-01-01

    Silicon Carbide Nanotubes (SiCNTs) have high mechanical strength and also have many potential functional applications. In this study, SiCNTs were investigated for use in strengthening high temperature silicate and oxide materials for high performance ceramic nanocomposites and environmental barrier coating bond coats. The high · temperature oxidation behavior of the nanotubes was of particular interest. The SiCNTs were synthesized by a direct reactive conversion process of multiwall carbon nanotubes and silicon at high temperature. Thermogravimetric analysis (TGA) was used to study the oxidation kinetics of SiCNTs at temperatures ranging from 800degC to1300degC. The specific oxidation mechanisms were also investigated.

  5. Electrochemical preparation of vertically aligned, hollow CdSe nanotubes and their p-n junction hybrids with electrodeposited Cu2O

    NASA Astrophysics Data System (ADS)

    Debgupta, Joyashish; Devarapalli, Ramireddy; Rahman, Shakeelur; Shelke, Manjusha V.; Pillai, Vijayamohanan K.

    2014-07-01

    Vertically aligned, hollow nanotubes of CdSe are grown on fluorine doped tin oxide (FTO) coated glass substrates by ZnO nanowire template-assisted electrodeposition technique, followed by selective removal of the ZnO core using NH4OH. A detailed mechanism of nucleation and anisotropic growth kinetics of nanotubes have been studied by a combination of characterization tools such as chronoamperometry, SEM and TEM. Interestingly, ``as grown'' CdSe nanotubes (CdSe NTs) on FTO coated glass plates behave as n-type semiconductors exhibiting an excellent photo-response (with a generated photocurrent density value of ~470 μA cm-2) while in contact with p-type Cu2O (p-type semiconductor, grown separately on FTO plates) because of the formation of a n-p heterojunction (type II). The observed photoresponse is 3 times higher than that of a similar device prepared with electrodeposited CdSe films (not nanotubes) and Cu2O on FTO. This has been attributed to the hollow 1-D nature of CdSe NTs, which provides enhanced inner and outer surface areas for better absorption of light and also assists faster transport of photogenerated charge carriers.Vertically aligned, hollow nanotubes of CdSe are grown on fluorine doped tin oxide (FTO) coated glass substrates by ZnO nanowire template-assisted electrodeposition technique, followed by selective removal of the ZnO core using NH4OH. A detailed mechanism of nucleation and anisotropic growth kinetics of nanotubes have been studied by a combination of characterization tools such as chronoamperometry, SEM and TEM. Interestingly, ``as grown'' CdSe nanotubes (CdSe NTs) on FTO coated glass plates behave as n-type semiconductors exhibiting an excellent photo-response (with a generated photocurrent density value of ~470 μA cm-2) while in contact with p-type Cu2O (p-type semiconductor, grown separately on FTO plates) because of the formation of a n-p heterojunction (type II). The observed photoresponse is 3 times higher than that of a similar

  6. Kinetics of Bacterial Growth on Chlorinated Aliphatic Compounds

    PubMed Central

    van den Wijngaard, Arjan J.; Wind, Richèle D.; Janssen, Dick B.

    1993-01-01

    With the pure bacterial cultures Ancylobacter aquaticus AD20 and AD25, Xanthobacter autotrophicus GJ10, and Pseudomonas sp. strain AD1, Monod kinetics was observed during growth in chemostat cultures on 1,2-dichloroethane (AD20, AD25, and GJ10), 2-chloroethanol (AD20 and GJ10), and 1,3-dichloro-2-propanol (AD1). Both the Michaelis-Menten constants (Km) of the first catabolic (dehalogenating) enzyme and the Monod half-saturation constants (Ks) followed the order 2-chloroethanol, 1,3-dichloro-2-propanol, epichlorohydrin, and 1,2-dichloroethane. The Ks values of strains GJ10, AD20, and AD25 for 1,2-dichloroethane were 260, 222, and 24 μM, respectively. The low Ks value of strain AD25 was correlated with a higher haloalkane dehalogenase content of this bacterium. The growth rates of strains AD20 and GJ10 in continuous cultures on 1,2-dichloroethane were higher than the rates predicted from the kinetics of the haloalkane dehalogenase and the concentration of the enzyme in the cells. The results indicate that the efficiency of chlorinated compound removal is indeed influenced by the kinetic properties and cellular content of the first catabolic enzyme. The cell envelope did not seem to act as a barrier for permeation of 1,2-dichloroethane. PMID:16348981

  7. A jellium model of a catalyst particle in carbon nanotube growth

    NASA Astrophysics Data System (ADS)

    Artyukhov, Vasilii I.; Liu, Mingjie; Penev, Evgeni S.; Yakobson, Boris I.

    2017-06-01

    We show how a jellium model can represent a catalyst particle within the density-functional theory based approaches to the growth mechanism of carbon nanotubes (CNTs). The advantage of jellium is an abridged, less computationally taxing description of the multi-atom metal particle, while at the same time in avoiding the uncertainty of selecting a particular atomic geometry of either a solid or ever-changing liquid catalyst particle. A careful choice of jellium sphere size and its electron density as a descriptive parameter allows one to calculate the CNT-metal interface energies close to explicit full atomistic models. Further, we show that using jellium permits computing and comparing the formation of topological defects (sole pentagons or heptagons, the culprits of growth termination) as well as pentagon-heptagon pairs 5|7 (known as chirality-switching dislocation).

  8. 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.

  9. Thermodynamics and kinetics of DNA nanotube polymerization from single-filament measurements† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c3sc53331j Click here for additional data file. Click here for additional data file. Click here for additional data file. Click here for additional data file. Click here for additional data file.

    PubMed Central

    Hariadi, Rizal F.; Yurke, Bernard

    2015-01-01

    DNA nanotubes provide a programmable architecture for molecular self-assembly and can serve as model systems for one-dimensional biomolecular assemblies. While a variety of DNA nanotubes have been synthesized and employed as models for natural biopolymers, an extensive investigation of DNA nanotube kinetics and thermodynamics has been lacking. Using total internal reflection microscopy, DNA nanotube polymerization was monitored in real time at the single filament level over a wide range of free monomer concentrations and temperatures. The measured polymerization rates were subjected to a global nonlinear fit based on polymerization theory in order to simultaneously extract kinetic and thermodynamic parameters. For the DNA nanotubes used in this study, the association rate constant is (5.99 ± 0.15) × 105 M–1 s–1, the enthalpy is 87.9 ± 2.0 kcal mol–1, and the entropy is 0.252 ± 0.006 kcal mol–1 K–1. The qualitative and quantitative similarities between the kinetics of DNA nanotubes, actin filaments, and microtubules polymerization highlight the prospect of building complex dynamic systems from DNA molecules inspired by biological architecture. PMID:29308139

  10. Controlled Growth and Modification of Vertically-Aligned Carbon Nanotubes for Multifunctional Applications

    DTIC Science & Technology

    2010-01-01

    mechanical properties, high electrical conductivity at the metallic state, and high thermal conductivity/stability [1–6]. These interesting properties make...the catalytic particle is lifted up with the growing nanotube, two growth mechanisms , namely ‘‘tip-growth’’ and ‘‘base-growth’’, have been proposed...diameters ranging from 10 to 15 nmwith a tube length of about 150 mmand a tube density of1010–1011 cm2 (Fig. 4B and C). A book of 1480 gwas held

  11. Impact of Silicon Nanocrystal Oxidation on the Nonmetallic Growth of Carbon Nanotubes.

    PubMed

    Rocks, Conor; Mitra, Somak; Macias-Montero, Manuel; Maguire, Paul; Svrcek, Vladimir; Levchenko, Igor; Ostrikov, Kostya; Mariotti, Davide

    2016-07-27

    Carbon nanotube (CNT) growth has been demonstrated recently using a number of nonmetallic semiconducting and metal oxide nanoparticles, opening up pathways for direct CNT synthesis from a number of more desirable templates without the need for metallic catalysts. However, CNT growth mechanisms using these nonconventional catalysts has been shown to largely differ and reamins a challenging synthesis route. In this contribution we show CNT growth from partially oxidized silicon nanocrystals (Si NCs) that exhibit quantum confinement effects using a microwave plasma enhanced chemical vapor deposition (PECVD) method. On the basis of solvent and a postsynthesis frgamentation process, we show that oxidation of our Si NCs can be easily controlled. We determine experimentally and explain with theoretical simulations that the Si NCs morphology together with a necessary shell oxide of ∼1 nm is vital to allow for the nonmetallic growth of CNTs. On the basis of chemical analysis post-CNT-growth, we give insight into possible mechanisms for CNT nucleation and growth from our partially oxidized Si NCs. This contribution is of significant importance to the improvement of nonmetallic catalysts for CNT growth and the development of Si NC/CNT interfaces.

  12. 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.

  13. Is cancer a pure growth curve or does it follow a kinetics of dynamical structural transformation?

    PubMed

    González, Maraelys Morales; Joa, Javier Antonio González; Cabrales, Luis Enrique Bergues; Pupo, Ana Elisa Bergues; Schneider, Baruch; Kondakci, Suleyman; Ciria, Héctor Manuel Camué; Reyes, Juan Bory; Jarque, Manuel Verdecia; Mateus, Miguel Angel O'Farril; González, Tamara Rubio; Brooks, Soraida Candida Acosta; Cáceres, José Luis Hernández; González, Gustavo Victoriano Sierra

    2017-03-07

    Unperturbed tumor growth kinetics is one of the more studied cancer topics; however, it is poorly understood. Mathematical modeling is a useful tool to elucidate new mechanisms involved in tumor growth kinetics, which can be relevant to understand cancer genesis and select the most suitable treatment. The classical Kolmogorov-Johnson-Mehl-Avrami as well as the modified Kolmogorov-Johnson-Mehl-Avrami models to describe unperturbed fibrosarcoma Sa-37 tumor growth are used and compared with the Gompertz modified and Logistic models. Viable tumor cells (1×10 5 ) are inoculated to 28 BALB/c male mice. Modified Gompertz, Logistic, Kolmogorov-Johnson-Mehl-Avrami classical and modified Kolmogorov-Johnson-Mehl-Avrami models fit well to the experimental data and agree with one another. A jump in the time behaviors of the instantaneous slopes of classical and modified Kolmogorov-Johnson-Mehl-Avrami models and high values of these instantaneous slopes at very early stages of tumor growth kinetics are observed. The modified Kolmogorov-Johnson-Mehl-Avrami equation can be used to describe unperturbed fibrosarcoma Sa-37 tumor growth. It reveals that diffusion-controlled nucleation/growth and impingement mechanisms are involved in tumor growth kinetics. On the other hand, tumor development kinetics reveals dynamical structural transformations rather than a pure growth curve. Tumor fractal property prevails during entire TGK.

  14. Net growth rate of continuum heterogeneous biofilms with inhibition kinetics.

    PubMed

    Gonzo, Elio Emilio; Wuertz, Stefan; Rajal, Veronica B

    2018-01-01

    Biofilm systems can be modeled using a variety of analytical and numerical approaches, usually by making simplifying assumptions regarding biofilm heterogeneity and activity as well as effective diffusivity. Inhibition kinetics, albeit common in experimental systems, are rarely considered and analytical approaches are either lacking or consider effective diffusivity of the substrate and the biofilm density to remain constant. To address this obvious knowledge gap an analytical procedure to estimate the effectiveness factor (dimensionless substrate mass flux at the biofilm-fluid interface) was developed for a continuum heterogeneous biofilm with multiple limiting-substrate Monod kinetics to different types of inhibition kinetics. The simple perturbation technique, previously validated to quantify biofilm activity, was applied to systems where either the substrate or the inhibitor is the limiting component, and cases where the inhibitor is a reaction product or the substrate also acts as the inhibitor. Explicit analytical equations are presented for the effectiveness factor estimation and, therefore, the calculation of biomass growth rate or limiting substrate/inhibitor consumption rate, for a given biofilm thickness. The robustness of the new biofilm model was tested using kinetic parameters experimentally determined for the growth of Pseudomonas putida CCRC 14365 on phenol. Several additional cases have been analyzed, including examples where the effectiveness factor can reach values greater than unity, characteristic of systems with inhibition kinetics. Criteria to establish when the effectiveness factor can reach values greater than unity in each of the cases studied are also presented.

  15. Direct Synthesis of Polymer Nanotubes by Aqueous Dispersion Polymerization of a Cyclodextrin/Styrene Complex.

    PubMed

    Chen, Xi; Liu, Lei; Huo, Meng; Zeng, Min; Peng, Liao; Feng, Anchao; Wang, Xiaosong; Yuan, Jinying

    2017-12-22

    A one-step synthesis of nanotubes by RAFT dispersion polymerization of cyclodextrin/styrene (CD/St) complexes directly in water is presented. The resulted amphiphilic PEG-b-PS diblock copolymers self-assemble in situ into nanoparticles with various morphologies. Spheres, worms, lamellae, and nanotubes were controllably obtained. Because of the complexation, the swelling degree of polystyrene (PS) blocks by free St is limited, resulting in limited mobility of PS chains. Consequently, kinetically trapped lamellae and nanotubes were obtained instead of spherical vesicles. During the formation of nanotubes, small vesicles first formed at the ends of the tape-like lamellae, then grew and fused into nanotubes with a limited chain rearrangement. The introduction of a host-guest interaction based on CDs enables the aqueous dispersion polymerization of water-immiscible monomers, and produces kinetically trapped nanostructures, which could be a powerful technique for nanomaterials synthesis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Efficient suppression of nanograss during porous anodic TiO2 nanotubes growth

    NASA Astrophysics Data System (ADS)

    Gui, Qunfang; Yu, Dongliang; Li, Dongdong; Song, Ye; Zhu, Xufei; Cao, Liu; Zhang, Shaoyu; Ma, Weihua; You, Shiyu

    2014-09-01

    When Ti foil was anodized in fluoride-containing electrolyte for a long time, undesired etching-induced "nanograss" would inevitably generate on the top of porous anodic TiO2 nanotubes (PATNTs). The nanograss will hinder the ions transport and in turn yield depressed (photo) electrochemical performance. In order to obtain nanograss-free nanotubes, a modified three-step anodization and two-layer nanostructure of PATNTs were designed to avoid the nanograss. The first layer (L1) nanotubes were obtained by the conventional two-step anodization. After washing and drying processes, the third-step anodization was carried out with the presence of L1 nanotubes. The L1 nanotubes, serving as a sacrificed layer, was etched and transformed into nanograss, while the ultralong nanotubes (L2) were maintained underneath the L1. The bi-layer nanostructure of the nanograss/nanotubes (L1/L2) was then ultrasonically rinsed in deionized water to remove the nanograss (L1 layer). Then much longer nanotubes (L2 layer) with intact nanotube mouths could be obtained. Using this novel approach, the ultralong nanotubes without nanograss can be rationally controlled by adjusting the anodizing times of two layers.

  17. Pyrolytic Carbon Coatings on Aligned Carbon Nanotube Assemblies and Fabrication of Advanced Carbon Nanotube/Carbon Composites

    NASA Astrophysics Data System (ADS)

    Faraji, Shaghayegh

    Chemical vapor deposition (CVD) is a technique used to create a pyrolytic carbon (PyC) matrix around fibrous preforms in carbon/carbon (C/C) composites. Due to difficulties in producing three-dimensional carbon nanotube (CNT) assemblies, use of nanotubes in CVD fabricated CNT/C composites is limited. This dissertation describes efforts to: 1) Study the microstructure of PyC deposited on CNTs in order to understand the effect of microstructure and morphology of carbon coatings on graphitization behavior of CNT/PyC composites. This understanding helped to suggest a new approach for controlled radial growth of CNTs. 2) Evaluate the properties of CNT/PyC structures as a novel form of CNT assemblies with resilient, anisotropic and tunable properties. PyC was deposited on aligned sheets of nanotubes, drawn from spinnable CNT arras, using CVD of acetylene gas. At longer deposition times, the microstructure of PyC changed from laminar turbostratic carbon to a disordered carbon. For samples with short PyC deposition times (up to 30 minutes), deposited carbon layer rearranged during graphitization treatment and resulted in a crystalline structure where the coating and original tube walls could not be easily differentiated. In contrast, in samples with longer carbon deposition durations, carbon layers close to the surface of the coating remained disordered even after graphitization thermal treatment. Understanding the effect of PyC microstructure transition on graphitization behavior of CNT/PyC composites was used to develop a new method for controlled radial growth of CNTs. Carbon coated aligned CNT sheets were graphitized after each short (20 minutes) carbon deposition cycle. This prevented development of disorder carbon during subsequent PyC deposition cycles. Using cyclic-graphitization method, thick PyC coating layers were successfully graphitized into a crystalline structure that could not be differentiated from the original nanotube walls. This resulted into radial

  18. Chitin and carbon nanotube composites as biocompatible scaffolds for neuron growth

    NASA Astrophysics Data System (ADS)

    Singh, Nandita; Chen, Jinhu; Koziol, Krzysztof K.; Hallam, Keith R.; Janas, Dawid; Patil, Avinash J.; Strachan, Ally; G. Hanley, Jonathan; Rahatekar, Sameer S.

    2016-04-01

    The design of biocompatible implants for neuron repair/regeneration ideally requires high cell adhesion as well as good electrical conductivity. Here, we have shown that plasma-treated chitin carbon nanotube composite scaffolds show very good neuron adhesion as well as support of synaptic function of neurons. The addition of carbon nanotubes to a chitin biopolymer improved the electrical conductivity and the assisted oxygen plasma treatment introduced more oxygen species onto the chitin nanotube scaffold surface. Neuron viability experiments showed excellent neuron attachment onto plasma-treated chitin nanotube composite scaffolds. The support of synaptic function was evident on chitin/nanotube composites, as confirmed by PSD-95 staining. The biocompatible and electrically-conducting chitin nanotube composite scaffold prepared in this study can be used for in vitro tissue engineering of neurons and, potentially, as an implantable electrode for stimulation and repair of neurons.

  19. Chitin and carbon nanotube composites as biocompatible scaffolds for neuron growth.

    PubMed

    Singh, Nandita; Chen, Jinhu; Koziol, Krzysztof K; Hallam, Keith R; Janas, Dawid; Patil, Avinash J; Strachan, Ally; G Hanley, Jonathan; Rahatekar, Sameer S

    2016-04-21

    The design of biocompatible implants for neuron repair/regeneration ideally requires high cell adhesion as well as good electrical conductivity. Here, we have shown that plasma-treated chitin carbon nanotube composite scaffolds show very good neuron adhesion as well as support of synaptic function of neurons. The addition of carbon nanotubes to a chitin biopolymer improved the electrical conductivity and the assisted oxygen plasma treatment introduced more oxygen species onto the chitin nanotube scaffold surface. Neuron viability experiments showed excellent neuron attachment onto plasma-treated chitin nanotube composite scaffolds. The support of synaptic function was evident on chitin/nanotube composites, as confirmed by PSD-95 staining. The biocompatible and electrically-conducting chitin nanotube composite scaffold prepared in this study can be used for in vitro tissue engineering of neurons and, potentially, as an implantable electrode for stimulation and repair of neurons.

  20. 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.

  1. Carbon Nanotubes for Space Applications

    NASA Technical Reports Server (NTRS)

    Meyyappan, Meyya

    2000-01-01

    The potential of nanotube technology for NASA missions is significant and is properly recognized by NASA management. Ames has done much pioneering research in the last five years on carbon nanotube growth, characterization, atomic force microscopy, sensor development and computational nanotechnology. NASA Johnson Space Center has focused on laser ablation production of nanotubes and composites development. These in-house efforts, along with strategic collaboration with academia and industry, are geared towards meeting the agency's mission requirements. This viewgraph presentation (including an explanation for each slide) outlines the research focus for Ames nanotechnology, including details on carbon nanotubes' properties, applications, and synthesis.

  2. Study of gas adsorption on as-produced and modified carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Rawat, Dinesh Singh

    Volumetric adsorption isotherm measurements were used to study the adsorption characteristics of Ethane (C2H6) and Butane (C 4H10) on as-produced single-walled carbon nanotubes. The binding energy of the adsorbed alkane molecule was found to increase with increasing carbon chain length. Two adsorption substeps were obtained for each alkane molecule. However, the size of the high pressure substep was found to be gradually smearing with the increase in size of the adsorbed molecule. This phenomenon is interpreted as size entropy effect for linear molecules. This interpretation was also verified by determining the specific surface area of the substrate using linear molecules of different sizes. Kinetics measurements of alkane adsorption on SWNTs were also conducted and their dependence on the molecular length was determined. Similar adsorption measurements were performed for Argon (Ar) on as-produced single-walled carbon nanotubes and nanotubes that were structurally modified using acid treatment. Enhancement of the sorptive capacity and the presence of two distinct kinetics of gas adsorption verified partial opening of single walled carbon nanotubes as a result of chemical treatment. Mutiwalled carbon nanotubes were exposed to oxygen plasma treatment for varying time periods. Afterwards, adsorption measurements of Methane (CH 4) were conducted on untreated and oxygen plasma treated tubes. The presence of an additional substep, after exposing multiwalled carbon nanotubes to oxygen plasma for varying time periods, suggested progressive cleaning of nanotube surface.

  3. 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.

  4. [Sorption mechanism of ofloxacin by carbon nanotubes].

    PubMed

    Zhao, Xing-Xing; Yu, Shui-Li; Wang, Zhe

    2014-02-01

    Sorption of ofloxacin (OFL) by carbon nanotubes is an effective method to control its fate in aquatic environment. The sorption process of OFL by mixed acid-treated and non-treated multi-walled carbon nanotubes was discussed. Sorption kinetics, sorption isotherm, desorption, sorption thermodynamics and effect of pH were investigated. The results indicated that the sorption kinetics followed the pseudo-second order kinetics model. The equilibrium sorption capacity of OFL on MWCNTs-O was higher. The sorption isotherm could be fitted by both the Langmuir and Freundlich models. The equilibrium sorption capacity dropped when the pH of aqueous solution was in the range of 6.0 to 10.0. Obvious desorption hysteresis was observed during the desorption experiments, especially on MWCNTs-O. Sorption thermodynamics analysis showed that the interactions between the OFL and sorbents were mainly between molecules. More oxygen-containing functional groups introduced on MWCNTs provided OFL molecules with more sorptive sites, which facilitated the generation of hydrogen bonds, a relatively strong interaction. The hydrogen bonds dominated the sorption process of OFL by MWCNTs/MWCNTs-O, explaining the experimental phenomena.

  5. Study of the Reactivity of Ni Nanotubes in Media with Different pH

    NASA Astrophysics Data System (ADS)

    Kalkabay, G.; Kozlovskiy, A. L.; Ibragimova, M. A.; Shlimas, D. I.; Zdorovets, M. V.; Borgekov, D. B.; Tikhonov, A. V.

    2018-01-01

    Nickel nanotubes have been synthesized by electrochemical deposition, and their reactivity in aggressive media has been investigated. Kinetic curves of the variation in the atomic ratio between Ni and O in the nanotube crystal structure as a function of the medium acidity are built.

  6. Charge transfer and adsorption-desorption kinetics in carbon nanotube and graphene gas sensing

    NASA Astrophysics Data System (ADS)

    Liang, Sang-Zi; Chen, Gugang; Harutyunyan, Avetik; Cole, Milton; Sofo, Jorge

    2014-03-01

    Detection of molecules in the gas phase by carbon nanotube and graphene has great application potentials due to the high sensitivity and surface-to-volume ratio. In chemiresistor, the conductance of the materials has been proposed to change as a result of charge transfer from the adsorbed molecules. Due to self-interaction errors, calculations using LDA or GGA density functionals have an innate disadvantage in dealing with charge transfer situations. A model which takes into consideration the dielectric interaction between the graphene surface and the molecule is employed to estimate the distance where charge transfer becomes favorable. Adsorption-desorption kinetics is studied with a modified Langmuir model, including sites from which the molecules do not desorb within the experimental time. Assuming a constant mobility, the model reproduces existing experimental conductance data. Its parameters provide information about the microscopic process during the detection and varying them allows optimization of aspects of sensor performance, including sensitivity, detection limit and response time. This work is supported by Honda Research Institute USA, Inc.

  7. Dendritic growth shapes in kinetic Monte Carlo models

    NASA Astrophysics Data System (ADS)

    Krumwiede, Tim R.; Schulze, Tim P.

    2017-02-01

    For the most part, the study of dendritic crystal growth has focused on continuum models featuring surface energies that yield six pointed dendrites. In such models, the growth shape is a function of the surface energy anisotropy, and recent work has shown that considering a broader class of anisotropies yields a correspondingly richer set of growth morphologies. Motivated by this work, we generalize nanoscale models of dendritic growth based on kinetic Monte Carlo simulation. In particular, we examine the effects of extending the truncation radius for atomic interactions in a bond-counting model. This is done by calculating the model’s corresponding surface energy and equilibrium shape, as well as by running KMC simulations to obtain nanodendritic growth shapes. Additionally, we compare the effects of extending the interaction radius in bond-counting models to that of extending the number of terms retained in the cubic harmonic expansion of surface energy anisotropy in the context of continuum models.

  8. Austenite grain growth kinetics in Al-killed plain carbon steels

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Militzer, M.; Giumelli, A.; Hawbolt, E.B.

    1996-11-01

    Austenite grain growth kinetics have been investigated in three Al-killed plain carbon steels. Experimental results have been validated using the statistical grain growth model by Abbruzzese and Luecke, which takes pinning by second-phase particles into account. It is shown that the pinning force is a function of the pre-heat-treatment schedule. Extrapolation to the conditions of a hot-strip mill indicates that grain growth occurs without pinning during conventional processing. Analytical relations are proposed to simulate austenite grain growth for Al-killed plain carbon steels for any thermal path in a hot-strip mill.

  9. The rapid growth of vertically aligned carbon nanotubes using laser heating.

    PubMed

    Park, J B; Jeong, S H; Jeong, M S; Lim, S C; Lee, I H; Lee, Y H

    2009-05-06

    Growth of densely packed vertically aligned carbon nanotubes (VA-CNTs) using laser-induced chemical vapor deposition with visible laser (lambda = 532 nm) irradiation at room temperature is reported. Using a multiple-catalyst layer (Fe/Al/Cr) on quartz as the substrate and an acetylene-hydrogen mixture as the precursor gas, VA-CNT pillars with 60 microm height and 4 microm diameter were grown at a high rate of around 1 microm s(-1) with good reproducibility. It is demonstrated that the fabrication of uniform pillar arrays of VA-CNTs can be achieved with a single irradiation for each pillar using LCVD with no annealing or preprocessing of the substrate. Here, laser fast heating is considered the primary mechanism facilitating the growth of VA-CNT pillars. Field emission characteristics of an array of VA-CNT pillars were then examined to investigate their potential application in vacuum electronic devices.

  10. Efficient removal of cadmium using magnetic multiwalled carbon nanotube nanoadsorbents: equilibrium, kinetic, and thermodynamic study

    NASA Astrophysics Data System (ADS)

    Pashai Gatabi, Maliheh; Milani Moghaddam, Hossain; Ghorbani, Mohsen

    2016-07-01

    Adsorptive potential of maghemite decorated multiwalled carbon nanotubes (MWCNTs) for the removal of cadmium ions from aqueous solution was investigated. The magnetic nanoadsorbent was synthesized using a versatile and cost effective chemical route. Structural, magnetic and surface charge properties of the adsorbent were characterized using FTIR, XRD, TEM, VSM analysis and pHPZC determination. Batch adsorption experiments were performed under varied system parameters such as pH, contact time, initial cadmium concentration and temperature. Highest cadmium adsorption was obtained at pH 8.0 and contact time of 30 min. Adsorption behavior was kinetically studied using pseudo first-order, pseudo second-order, and Weber-Morris intra particle diffusion models among which data were mostly correlated to pseudo second-order model. Adsorbate-adsorbent interactions as a function of temperature was assessed by Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin isotherm models from which Freundlich model had the highest consistency with the data. The adsorption capacity increased with increasing temperature and maximum Langmuir's adsorption capacity was found to be 78.81 mg g-1 at 298 K. Thermodynamic parameters and activation energy value suggest that the process of cadmium removal was spontaneous and physical in nature, which lead to fast kinetics and high regeneration capability of the nanoadsorbent. Results of this work are of great significance for environmental applications of magnetic MWCNTs as promising adsorbent for heavy metals removal from aqueous solutions.

  11. Modeling to predict growth/no growth boundaries and kinetic behavior of Salmonella on cutting board surfaces.

    PubMed

    Yoon, Hyunjoo; Lee, Joo-Yeon; Suk, Hee-Jin; Lee, Sunah; Lee, Heeyoung; Lee, Soomin; Yoon, Yohan

    2012-12-01

    This study developed models to predict the growth probabilities and kinetic behavior of Salmonella enterica strains on cutting boards. Polyethylene coupons (3 by 5 cm) were rubbed with pork belly, and pork purge was then sprayed on the coupon surface, followed by inoculation of a five-strain Salmonella mixture onto the surface of the coupons. These coupons were stored at 13 to 35°C for 12 h, and total bacterial and Salmonella cell counts were enumerated on tryptic soy agar and xylose lysine deoxycholate (XLD) agar, respectively, every 2 h, which produced 56 combinations. The combinations that had growth of ≥0.5 log CFU/cm(2) of Salmonella bacteria recovered on XLD agar were given the value 1 (growth), and the combinations that had growth of <0.5 log CFU/cm(2) were assigned the value 0 (no growth). These growth response data from XLD agar were analyzed by logistic regression for producing growth/no growth interfaces of Salmonella bacteria. In addition, a linear model was fitted to the Salmonella cell counts to calculate the growth rate (log CFU per square centimeter per hour) and initial cell count (log CFU per square centimeter), following secondary modeling with the square root model. All of the models developed were validated with observed data, which were not used for model development. Growth of total bacteria and Salmonella cells was observed at 28, 30, 33, and 35°C, but there was no growth detected below 20°C within the time frame investigated. Moreover, various indices indicated that the performance of the developed models was acceptable. The results suggest that the models developed in this study may be useful in predicting the growth/no growth interface and kinetic behavior of Salmonella bacteria on polyethylene cutting boards.

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Yulan; Hu, Shenyang Y.; Sun, Xin

    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 bubblemore » 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

  13. Digital Isotope Coding to Trace the Growth Process of Individual Single-Walled Carbon Nanotubes.

    PubMed

    Otsuka, Keigo; Yamamoto, Shun; Inoue, Taiki; Koyano, Bunsho; Ukai, Hiroyuki; Yoshikawa, Ryo; Xiang, Rong; Chiashi, Shohei; Maruyama, Shigeo

    2018-04-24

    Single-walled carbon nanotubes (SWCNTs) are attracting increasing attention as an ideal material for high-performance electronics through the preparation of arrays of purely semiconducting SWCNTs. Despite significant progress in the controlled synthesis of SWCNTs, their growth mechanism remains unclear due to difficulties in analyzing the time-resolved growth of individual SWCNTs under practical growth conditions. Here we present a method for tracing the diverse growth profiles of individual SWCNTs by embedding digitally coded isotope labels. Raman mapping showed that, after various incubation times, SWCNTs elongated monotonically until their abrupt termination. Ex situ analysis offered an opportunity to capture rare chirality changes along the SWCNTs, which resulted in sudden acceleration/deceleration of the growth rate. Dependence on growth parameters, such as temperature and carbon concentration, was also traced along individual SWCNTs, which could provide clues to chirality control. Systematic growth studies with a variety of catalysts and conditions, which combine the presented method with other characterization techniques, will lead to further understanding and control of chirality, length, and density of SWCNTs.

  14. Non-classical nuclei and growth kinetics of Cr precipitates in FeCr alloys during ageing

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Yulan; Hu, Shenyang Y.; Zhang, Lei

    2014-01-10

    In this manuscript, we quantitatively calculated the thermodynamic properties of critical nuclei of Cr precipitates in FeCr alloys. The concentration profiles of the critical nuclei and nucleation energy barriers were predicted by the constrained shrinking dimer dynamics (CSDD) method. It is found that Cr concentration distribution in the critical nuclei strongly depend on the overall Cr concentration as well as temperature. The critical nuclei are non-classical because the concentration in the nuclei is smaller than the thermodynamic equilibrium value. These results are in agreement with atomic probe observation. The growth kinetics of both classical and non-classical nuclei was investigated bymore » the phase field approach. The simulations of critical nucleus evolution showed a number of interesting phenomena: 1) a critical classical nucleus first shrinks toward its non-classical nucleus and then grows; 2) a non-classical nucleus has much slower growth kinetics at its earlier growth stage compared to the diffusion-controlled growth kinetics. 3) a critical classical nucleus grows faster at the earlier growth stage than the non-classical nucleus. All of these results demonstrate that it is critical to introduce the correct critical nuclei in order to correctly capture the kinetics of precipitation.« less

  15. Iron-carbide cluster thermal dynamics for catalyzed carbon nanotube growth

    NASA Astrophysics Data System (ADS)

    Ding, Feng; Bolton, Kim; Rosén, Arne

    2004-07-01

    Molecular dynamics simulations have been used to study the thermal behavior of FeN-mCm clusters where N, the total number of atoms, extends up to 2400. Comparison of the computed results with experimental data shows that the simulations yield the correct trends for the liquid-solid region of the iron-carbide phase diagram as well as the correct dependence of cluster melting point as a function of cluster size. The calculation indicates that, when carbon nanotubes (CNTs) are grown on large (>3-4 nm) catalyst particles at low temperatures (<1200 K), the catalyst particles are not completely molten. It is argued that the mechanism of CNT growth under these conditions may be governed by the surface melting of the cluster. .

  16. Study of Composite Interface Strength and Crack Growth Monitoring Using Carbon Nanotubes

    DTIC Science & Technology

    2009-09-01

    Carbon Nanotube Additives,” Applied Physiscs Letters, 91(2007). 14Tsu-Wei Chou and Erik T. Thosetenson. “Carbon Nanotube/Vinyl Ester Nanocomposites...Carbon Nanotube Additives. Applied Physiscs Letters 91. 79 INITIAL DISTRIBUTION LIST 1. Defense Technical Information Center Ft. Belvoir, Virginia

  17. Growth of vertically aligned single-walled carbon nanotubes with metallic chirality through faceted FePt-Au catalysts

    NASA Astrophysics Data System (ADS)

    Ohashi, Toshiyuki; Iwama, Hiroki; Shima, Toshiyuki

    2016-02-01

    Direct synthesis of vertically aligned metallic single-walled carbon nanotubes (m-SWCNT forests) is a difficult challenge. We have successfully synthesized m-SWCNT forests using faceted iron platinum-gold catalysts epitaxially grown on a single crystalline magnesium oxide substrate. The metallic content of the forests estimated by Raman spectroscopy reaches 90%. From the standpoint of growth rate of the forests, the growth mechanism is probably based on the catalyst of solid state. It is suggested that preferential growth of m-SWCNTs is achieved when both factors are satisfied, namely, {111} dominant octahedral facet and ideal size (fine particles) of FePt particles.

  18. Crystal growth kinetics in undercooled melts of pure Ge, Si and Ge-Si alloys

    NASA Astrophysics Data System (ADS)

    Herlach, Dieter M.; Simons, Daniel; Pichon, Pierre-Yves

    2018-01-01

    We report on measurements of crystal growth dynamics in semiconducting pure Ge and pure Si melts and in Ge100-xSix (x = 25, 50, 75) alloy melts as a function of undercooling. Electromagnetic levitation techniques are applied to undercool the samples in a containerless way. The growth velocity is measured by the utilization of a high-speed camera technique over an extended range of undercooling. Solidified samples are examined with respect to their microstructure by scanning electron microscopic investigations. We analyse the experimental results of crystal growth kinetics as a function of undercooling within the sharp interface theory developed by Peter Galenko. Transitions of the atomic attachment kinetics are found at large undercoolings, from faceted growth to dendrite growth. This article is part of the theme issue `From atomistic interfaces to dendritic patterns'.

  19. Theoretical studies of growth processes and electronic properties of nanostructures on surfaces

    NASA Astrophysics Data System (ADS)

    Mo, Yina

    Low dimensional nanostructures have been of particular interest because of their potential applications in both theoretical studies and industrial use. Although great efforts have been put into obtaining better understanding of the formation and properties of these materials, many questions still remain unanswered. This thesis work has focused on theoretical studies of (1) the growth processes of magnetic nanowires on transition-metal surfaces, (2) the dynamics of pentacene thin-film growth and island structures on inert surfaces, and (3) our proposal of a new type of semiconducting nanotube. In the first study, we elucidated a novel and intriguing kinetic pathway for the formation of Fe nanowires on the upper edge of a monatomic-layer-high step on Cu(111) using first-principles calculations. The identification of a hidden fundamental Fe basal line within the Cu steps prior to the formation of the apparent upper step edge Fe wire produces a totally different view of step-decorating wire structures and offers new possibilities for the study of the properties of these wires. Subsequent experiments with scanning tunneling microscopy unambiguously established the essential role of embedded Fe atoms as precursors to monatomic wire growth. A more general study of adatom behavior near transition-metal step edges illustrated a systematic trend in the adatom energetics and kinetics, resulted from the electronic interactions between the adatom and the surfaces. This work opens the possibility of controlled manufacturing of one-dimensional nanowires. In the second study, we investigated pentacene thin-films on H-diamond, H-silica and OH-silica surfaces via force field molecular dynamics simulations. Pentacene island structures on these surfaces were identified and found to have a 90-degree rotation relative to the structure proposed by some experimental groups. Our work may facilitate the design and control of experimental pentacene thin-film growth, and thus the development

  20. Linking genes to microbial growth kinetics: an integrated biochemical systems engineering approach.

    PubMed

    Koutinas, Michalis; Kiparissides, Alexandros; Silva-Rocha, Rafael; Lam, Ming-Chi; Martins Dos Santos, Vitor A P; de Lorenzo, Victor; Pistikopoulos, Efstratios N; Mantalaris, Athanasios

    2011-07-01

    The majority of models describing the kinetic properties of a microorganism for a given substrate are unstructured and empirical. They are formulated in this manner so that the complex mechanism of cell growth is simplified. Herein, a novel approach for modelling microbial growth kinetics is proposed, linking biomass growth and substrate consumption rates to the gene regulatory programmes that control these processes. A dynamic model of the TOL (pWW0) plasmid of Pseudomonas putida mt-2 has been developed, describing the molecular interactions that lead to the transcription of the upper and meta operons, known to produce the enzymes for the oxidative catabolism of m-xylene. The genetic circuit model was combined with a growth kinetic model decoupling biomass growth and substrate consumption rates, which are expressed as independent functions of the rate-limiting enzymes produced by the operons. Estimation of model parameters and validation of the model's predictive capability were successfully performed in batch cultures of mt-2 fed with different concentrations of m-xylene, as confirmed by relative mRNA concentration measurements of the promoters encoded in TOL. The growth formation and substrate utilisation patterns could not be accurately described by traditional Monod-type models for a wide range of conditions, demonstrating the critical importance of gene regulation for the development of advanced models closely predicting complex bioprocesses. In contrast, the proposed strategy, which utilises quantitative information pertaining to upstream molecular events that control the production of rate-limiting enzymes, predicts the catabolism of a substrate and biomass formation and could be of central importance for the design of optimal bioprocesses. Copyright © 2011 Elsevier Inc. All rights reserved.

  1. Recrystallization and Grain Growth Kinetics in Binary Alpha Titanium-Aluminum Alloys

    NASA Astrophysics Data System (ADS)

    Trump, Anna Marie

    Titanium alloys are used in a variety of important naval and aerospace applications and often undergo thermomechanical processing which leads to recrystallization and grain growth. Both of these processes have a significant impact on the mechanical properties of the material. Therefore, understanding the kinetics of these processes is crucial to being able to predict the final properties. Three alloys are studied with varying concentrations of aluminum which allows for the direct quantification of the effect of aluminum content on the kinetics of recrystallization and grain growth. Aluminum is the most common alpha stabilizing alloying element used in titanium alloys, however the effect of aluminum on these processes has not been previously studied. This work is also part of a larger Integrated Computational Materials Engineering (ICME) effort whose goal is to combine both computational and experimental efforts to develop computationally efficient models that predict materials microstructure and properties based on processing history. The static recrystallization kinetics are measured using an electron backscatter diffraction (EBSD) technique and a significant retardation in the kinetics is observed with increasing aluminum concentration. An analytical model is then used to capture these results and is able to successfully predict the effect of solute concentration on the time to 50% recrystallization. The model reveals that this solute effect is due to a combination of a decrease in grain boundary mobility and a decrease in driving force with increasing aluminum concentration. The effect of microstructural inhomogeneities is also experimentally quantified and the results are validated with a phase field model for recrystallization. These microstructural inhomogeneities explain the experimentally measured Avrami exponent, which is lower than the theoretical value calculated by the JMAK model. Similar to the effect seen in recrystallization, the addition of aluminum

  2. Properties, synthesis, and growth mechanisms of carbon nanotubes with special focus on thermal chemical vapor deposition.

    PubMed

    Nessim, Gilbert D

    2010-08-01

    Carbon nanotubes (CNTs) have been extensively investigated in the last decade because their superior properties could benefit many applications. However, CNTs have not yet made a major leap into industry, especially for electronic devices, because of fabrication challenges. This review provides an overview of state-of-the-art of CNT synthesis techniques and illustrates their major technical difficulties. It also charts possible in situ analyses and new reactor designs that might enable commercialization. After a brief description of the CNT properties and of the various techniques used to synthesize substrate-free CNTs, the bulk of this review analyzes chemical vapor deposition (CVD). This technique receives special attention since it allows CNTs to be grown in predefined locations, provides a certain degree of control of the types of CNTs grown, and may have the highest chance to succeed commercially. Understanding the primary growth mechanisms at play during CVD is critical for controlling the properties of the CNTs grown and remains the major hurdle to overcome. Various factors that influence CNT growth receive a special focus: choice of catalyst and substrate materials, source gases, and process parameters. This review illustrates important considerations for in situ characterization and new reactor designs that may enable researchers to better understand the physical growth mechanisms and to optimize the synthesis of CNTs, thus contributing to make carbon nanotubes a manufacturing reality.

  3. Nucleation and growth kinetics during metal-induced layer exchange crystallization of Ge thin films at low temperatures

    NASA Astrophysics Data System (ADS)

    Hu, Shu; McIntyre, Paul C.

    2012-02-01

    The kinetics of Al-catalyzed layer exchange crystallization of amorphous germanium (Ge) thin films at low temperatures is reported. Observation of Ge mass transport from an underlying amorphous Ge layer to the Al film surface through an interposed sub-nanometer GeOx interfacial layer allows independent measurement of the areal density and average area of crystalline Ge islands formed on the film surface. We show that bias-voltage stressing of the interfacial layer can be used to control the areal density of nucleated Ge islands. Based on experimental observations, the Johnson-Mehl-Avrami-Kolmogorov phase transformation theory is used to model nanoscale nucleation and growth of Ge islands in two dimensions. Ge island nucleation kinetics follows an exponentially decaying nucleation rate with time. Ge island growth kinetics switches from linear growth at a constant growth velocity to diffusion-limited growth as the growth front advances. The transition point between these two regimes depends on the Ge nucleation site density and the annealing temperature. Knowledge of the kinetics of low-temperature crystallization is important in achieving textured polycrystalline Ge thin films with large grains for applications in large-area electronics and solar energy conversion.

  4. Nonlinear Response of Layer Growth Dynamics in the Mixed Kinetics-Bulk-Transport Regime

    NASA Technical Reports Server (NTRS)

    Vekilov, Peter G.; Alexander, J. Iwan D.; Rosenberger, Franz

    1996-01-01

    In situ high-resolution interferometry on horizontal facets of the protein lysozyme reveal that the local growth rate R, vicinal slope p, and tangential (step) velocity v fluctuate by up to 80% of their average values. The time scale of these fluctuations, which occur under steady bulk transport conditions through the formation and decay of step bunches (macrosteps), is of the order of 10 min. The fluctuation amplitude of R increases with growth rate (supersaturation) and crystal size, while the amplitude of the v and p fluctuations changes relatively little. Based on a stability analysis for equidistant step trains in the mixed transport-interface-kinetics regime, we argue that the fluctuations originate from the coupling of bulk transport with nonlinear interface kinetics. Furthermore, step bunches moving across the interface in the direction of or opposite to the buoyancy-driven convective flow increase or decrease in height, respectively. This is in agreement with analytical treatments of the interaction of moving steps with solution flow. Major excursions in growth rate are associated with the formation of lattice defects (striations). We show that, in general, the system-dependent kinetic Peclet number, Pe(sub k) , i.e., the relative weight of bulk transport and interface kinetics in the control of the growth process, governs the step bunching dynamics. Since Pe(sub k) can be modified by either forced solution flow or suppression of buoyancy-driven convection under reduced gravity, this model provides a rationale for the choice of specific transport conditions to minimize the formation of compositional inhomogeneities under steady bulk nutrient crystallization conditions.

  5. A global resource allocation strategy governs growth transition kinetics of Escherichia coli

    PubMed Central

    Erickson, David W; Schink, Severin J.; Patsalo, Vadim; Williamson, James R.; Gerland, Ulrich; Hwa, Terence

    2018-01-01

    A grand challenge of systems biology is to predict the kinetic responses of living systems to perturbations starting from the underlying molecular interactions. Changes in the nutrient environment have long been used to study regulation and adaptation phenomena in microorganisms1–3 and they remain a topic of active investigation4–11. Although much is known about the molecular interactions that govern the regulation of key metabolic processes in response to applied perturbations12–17, they are insufficiently quantified for predictive bottom-up modelling. Here we develop a top-down approach, expanding the recently established coarse-grained proteome allocation models15,18–20 from steady-state growth into the kinetic regime. Using only qualitative knowledge of the underlying regulatory processes and imposing the condition of flux balance, we derive a quantitative model of bacterial growth transitions that is independent of inaccessible kinetic parameters. The resulting flux-controlled regulation model accurately predicts the time course of gene expression and biomass accumulation in response to carbon upshifts and downshifts (for example, diauxic shifts) without adjustable parameters. As predicted by the model and validated by quantitative proteomics, cells exhibit suboptimal recovery kinetics in response to nutrient shifts owing to a rigid strategy of protein synthesis allocation, which is not directed towards alleviating specific metabolic bottlenecks. Our approach does not rely on kinetic parameters, and therefore points to a theoretical framework for describing a broad range of such kinetic processes without detailed knowledge of the underlying biochemical reactions. PMID:29072300

  6. Crystal growth kinetics in undercooled melts of pure Ge, Si and Ge-Si alloys.

    PubMed

    Herlach, Dieter M; Simons, Daniel; Pichon, Pierre-Yves

    2018-02-28

    We report on measurements of crystal growth dynamics in semiconducting pure Ge and pure Si melts and in Ge 100- x Si x ( x  = 25, 50, 75) alloy melts as a function of undercooling. Electromagnetic levitation techniques are applied to undercool the samples in a containerless way. The growth velocity is measured by the utilization of a high-speed camera technique over an extended range of undercooling. Solidified samples are examined with respect to their microstructure by scanning electron microscopic investigations. We analyse the experimental results of crystal growth kinetics as a function of undercooling within the sharp interface theory developed by Peter Galenko. Transitions of the atomic attachment kinetics are found at large undercoolings, from faceted growth to dendrite growth.This article is part of the theme issue 'From atomistic interfaces to dendritic patterns'. © 2018 The Author(s).

  7. Growth Kinetics and Morphology of Barite Crystals Derived from Face-Specific Growth Rates

    DOE PAGES

    Godinho, Jose R. A.; Stack, Andrew G.

    2015-03-30

    Here we investigate the growth kinetics and morphology of barite (BaSO 4) crystals by measuring the growth rates of the (001), (210), (010), and (100) surfaces using vertical scanning interferometry. Solutions with saturation indices 1.1, 2.1, and 3.0 without additional electrolyte, in 0.7 M NaCl, or in 1.3 mM SrCl2 are investigated. Face-specific growth rates are inhibited in the SrCl 2 solution relative to a solution without electrolyte, except for (100). Contrarily, growth of all faces is promoted in the NaCl solution. The variation of face-specific rates is solution-specific, which leads to a. change of the crystal morphology and overallmore » growth rate of crystals. The measured face-specific growth rates are used to model the growth of single crystals. Modeled crystals have a morphology and size similar to those grown from solution. Based on the model the time dependence of surface area and growth rates is analyzed. Growth rates change with time due to surface area normalization for small crystals and large growth intervals. By extrapolating rates to crystals with large surfaces areas, time-independent growth rates are 0.783, 2.96, and 0.513 mmol∙m -2∙h -1, for saturation index 2.1 solutions without additional electrolyte, NaCl, and SrCl 2, respectively.« less

  8. Growth Kinetics and Morphology of Barite Crystals Derived from Face-Specific Growth Rates

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Godinho, Jose R. A.; Stack, Andrew G.

    Here we investigate the growth kinetics and morphology of barite (BaSO 4) crystals by measuring the growth rates of the (001), (210), (010), and (100) surfaces using vertical scanning interferometry. Solutions with saturation indices 1.1, 2.1, and 3.0 without additional electrolyte, in 0.7 M NaCl, or in 1.3 mM SrCl2 are investigated. Face-specific growth rates are inhibited in the SrCl 2 solution relative to a solution without electrolyte, except for (100). Contrarily, growth of all faces is promoted in the NaCl solution. The variation of face-specific rates is solution-specific, which leads to a. change of the crystal morphology and overallmore » growth rate of crystals. The measured face-specific growth rates are used to model the growth of single crystals. Modeled crystals have a morphology and size similar to those grown from solution. Based on the model the time dependence of surface area and growth rates is analyzed. Growth rates change with time due to surface area normalization for small crystals and large growth intervals. By extrapolating rates to crystals with large surfaces areas, time-independent growth rates are 0.783, 2.96, and 0.513 mmol∙m -2∙h -1, for saturation index 2.1 solutions without additional electrolyte, NaCl, and SrCl 2, respectively.« less

  9. 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

  10. Multiwalled carbon nanotubes enter broccoli cells enhancing growth and water uptake of plants exposed to salinity.

    PubMed

    Martínez-Ballesta, M Carmen; Zapata, Lavinia; Chalbi, Najla; Carvajal, Micaela

    2016-06-08

    Carbon nanotubes have been shown to improve the germination and growth of some plant species, extending the applicability of the emerging nano-biotechnology field to crop science. In this work, exploitation of commercial multiwalled carbon nanotubes (MWCNTs) in control and 100 mM NaCl-treated broccoli was performed. Transmission electron microscopy demonstrated that MWCNTs can enter the cells in adult plants with higher accumulation under salt stress. Positive effect of MWCNTs on growth in NaCl-treated plants was consequence of increased water uptake, promoted by more-favourable energetic forces driving this process, and enhanced net assimilation of CO2. MWCNTs induced changes in the lipid composition, rigidity and permeability of the root plasma membranes relative to salt-stressed plants. Also, enhanced aquaporin transduction occurred, which improved water uptake and transport, alleviating the negative effects of salt stress. Our work provides new evidences about the effect of MWCNTs on plasma membrane properties of the plant cell. The positive response to MWCNTs in broccoli plants opens novel perspectives for their technological uses in new agricultural practices, especially when 1plants are exposed to saline environments.

  11. Electrochemical preparation of vertically aligned, hollow CdSe nanotubes and their p-n junction hybrids with electrodeposited Cu2O.

    PubMed

    Debgupta, Joyashish; Devarapalli, Ramireddy; Rahman, Shakeelur; Shelke, Manjusha V; Pillai, Vijayamohanan K

    2014-08-07

    Vertically aligned, hollow nanotubes of CdSe are grown on fluorine doped tin oxide (FTO) coated glass substrates by ZnO nanowire template-assisted electrodeposition technique, followed by selective removal of the ZnO core using NH4OH. A detailed mechanism of nucleation and anisotropic growth kinetics of nanotubes have been studied by a combination of characterization tools such as chronoamperometry, SEM and TEM. Interestingly, "as grown" CdSe nanotubes (CdSe NTs) on FTO coated glass plates behave as n-type semiconductors exhibiting an excellent photo-response (with a generated photocurrent density value of ∼ 470 μA cm(-2)) while in contact with p-type Cu2O (p-type semiconductor, grown separately on FTO plates) because of the formation of a n-p heterojunction (type II). The observed photoresponse is 3 times higher than that of a similar device prepared with electrodeposited CdSe films (not nanotubes) and Cu2O on FTO. This has been attributed to the hollow 1-D nature of CdSe NTs, which provides enhanced inner and outer surface areas for better absorption of light and also assists faster transport of photogenerated charge carriers.

  12. The rapid growth of 3 µm long titania nanotubes by anodization of titanium in a neutral electrochemical bath

    NASA Astrophysics Data System (ADS)

    Lockman, Zainovia; Ismail, Syahriza; Sreekantan, Srimala; Schmidt-Mende, L.; MacManus-Driscoll, J. L.

    2010-02-01

    The length of titania nanotubes formed by anodization of 0.1 mm thick titanium foil was found to be a strong function of the pH of the electrolyte. The longest nanotubes were formed by using an electrolyte consisting of 1 M Na2SO4 plus 5 wt% NH4F with pH 7. At this pH, after 30 min of anodization, 3 µm length nanotubular titania arrays with top diameters of ~50 nm and bottom diameters of 100 nm were produced. No acid was added to this electrolyte. The formation of titania nanotubes in neutral pH systems was therefore successful due to the excess NH4F in the electrolyte which increases the chemical dissolution process at the metal/oxide interface. Since the pH of the electrolyte at the top part of the nanotubes is kept very high, the dissolution of the nanotubes at the surface is minimal. However, the amount is adequate to remove the initial barrier layer, forming a rather well-defined nanoporous structure. All anodized foils were weakly crystalline and the transformation to anatase phase was achieved by heat treatment at temperatures from 200 to 500 °C for 1 h in air. Annealing at temperatures above 500 °C induce rutile phase formation and annealing at higher temperatures accelerates the diffusion of Ti4+ leading to excessive growth and the nanotubular structure diminishes.

  13. Single-crystal gallium nitride nanotubes.

    PubMed

    Goldberger, Joshua; He, Rongrui; Zhang, Yanfeng; Lee, Sangkwon; Yan, Haoquan; Choi, Heon-Jin; Yang, Peidong

    2003-04-10

    Since the discovery of carbon nanotubes in 1991 (ref. 1), there have been significant research efforts to synthesize nanometre-scale tubular forms of various solids. The formation of tubular nanostructure generally requires a layered or anisotropic crystal structure. There are reports of nanotubes made from silica, alumina, silicon and metals that do not have a layered crystal structure; they are synthesized by using carbon nanotubes and porous membranes as templates, or by thin-film rolling. These nanotubes, however, are either amorphous, polycrystalline or exist only in ultrahigh vacuum. The growth of single-crystal semiconductor hollow nanotubes would be advantageous in potential nanoscale electronics, optoelectronics and biochemical-sensing applications. Here we report an 'epitaxial casting' approach for the synthesis of single-crystal GaN nanotubes with inner diameters of 30-200 nm and wall thicknesses of 5-50 nm. Hexagonal ZnO nanowires were used as templates for the epitaxial overgrowth of thin GaN layers in a chemical vapour deposition system. The ZnO nanowire templates were subsequently removed by thermal reduction and evaporation, resulting in ordered arrays of GaN nanotubes on the substrates. This templating process should be applicable to many other semiconductor systems.

  14. Maintenance of supersaturation I: indomethacin crystal growth kinetic modeling using an online second-derivative ultraviolet spectroscopic method.

    PubMed

    Patel, Dhaval D; Joguparthi, Vijay; Wang, Zeren; Anderson, Bradley D

    2011-07-01

    Formulations that produce supersaturated solutions after their oral administration have received increased attention as a means to improve bioavailability of poorly water-soluble drugs. Although it is widely recognized that excipients can prolong supersaturation, the mechanisms by which these beneficial effects are realized are generally unknown. Difficulties in separately measuring the kinetics of nucleation and crystal growth have limited progress in understanding the mechanisms by which excipients contribute to the supersaturation maintenance. This paper describes the crystal growth kinetic modeling of indomethacin, a poorly water-soluble drug, from supersaturated aqueous suspensions using a newly developed, online second-derivative ultraviolet spectroscopic method. The apparent indomethacin equilibrium solubility after crystal growth at a high degree of supersaturation (S=6) was approximately 55% higher than the indomethacin equilibrium solubility determined prior to growth, which was attributed to the deposition of a higher energy indomethacin form on the seed crystals. The indomethacin crystal growth kinetics (S=6) was of first order. By comparing the mass transfer coefficients from indomethacin dissolution and crystal growth, it was shown that the indomethacin crystal growth kinetics at S=6 was bulk diffusion controlled. The change in indomethacin seed crystal size distribution before and after crystal growth was determined and modeled using a mass-balance relationship. Copyright © 2011 Wiley-Liss, Inc. and the American Pharmacists Association

  15. Tuning the Slide-Roll Motion Mode of Carbon Nanotubes via Hydroxyl Groups

    NASA Astrophysics Data System (ADS)

    Li, Rui; Wang, Shiwei; Peng, Qing

    2018-05-01

    Controlling the motion of carbon nanotubes is critical in manipulating nanodevices, including nanorobots. Herein, we investigate the motion behavior of SWCNT (10,10) on Si substrate utilizing molecular dynamics simulations. We show that hydroxyl groups have sensitive effect on the carbon nanotube's motion mode. When the hydroxyl groups' ratio on carbon nanotube and silicon substrate surfaces is larger than 10 and 20%, respectively, the motion of carbon nanotube transforms from sliding to rolling. When the hydroxyl groups' ratio is smaller, the slide or roll mode can be controlled by the speed of carbon nanotube, which is ultimately determined by the competition between the interface potential energy and kinetic energy. The change of motion mode holds true for different carbon nanotubes with hydroxyl groups. The chirality has little effect on the motion behavior, as opposed to the diameter, attributed to the hydroxyl groups' ratio. Our study suggests a new route to control the motion behavior of carbon nanotube via hydroxyl groups.

  16. Tuning the Slide-Roll Motion Mode of Carbon Nanotubes via Hydroxyl Groups.

    PubMed

    Li, Rui; Wang, Shiwei; Peng, Qing

    2018-05-08

    Controlling the motion of carbon nanotubes is critical in manipulating nanodevices, including nanorobots. Herein, we investigate the motion behavior of SWCNT (10,10) on Si substrate utilizing molecular dynamics simulations. We show that hydroxyl groups have sensitive effect on the carbon nanotube's motion mode. When the hydroxyl groups' ratio on carbon nanotube and silicon substrate surfaces is larger than 10 and 20%, respectively, the motion of carbon nanotube transforms from sliding to rolling. When the hydroxyl groups' ratio is smaller, the slide or roll mode can be controlled by the speed of carbon nanotube, which is ultimately determined by the competition between the interface potential energy and kinetic energy. The change of motion mode holds true for different carbon nanotubes with hydroxyl groups. The chirality has little effect on the motion behavior, as opposed to the diameter, attributed to the hydroxyl groups' ratio. Our study suggests a new route to control the motion behavior of carbon nanotube via hydroxyl groups.

  17. Perspectives on the Growth of High Edge Density Carbon Nanostructures: Transitions from Vertically Oriented Graphene Nanosheets to Graphenated Carbon Nanotubes

    PubMed Central

    2015-01-01

    Insights into the growth of high edge density carbon nanostructures were achieved by a systematic parametric study of plasma-enhanced chemical vapor deposition (PECVD). Such structures are important for electrode performance in a variety of applications such as supercapacitors, neural stimulation, and electrocatalysis. A morphological trend was observed as a function of temperature whereby graphenated carbon nanotubes (g-CNTs) emerged as an intermediate structure between carbon nanotubes (CNTs) at lower temperatures and vertically oriented carbon nanosheets (CNS), composed of few-layered graphene, at higher temperatures. This is the first time that three distinct morphologies and dimensionalities of carbon nanostructures (i.e., 1D CNTs, 2D CNSs, and 3D g-CNTs) have been synthesized in the same reaction chamber by varying only a single parameter (temperature). A design of experiments (DOE) approach was utilized to understand the range of growth permitted in a microwave PECVD reactor, with a focus on identifying graphenated carbon nanotube growth within the process space. Factors studied in the experimental design included temperature, gas ratio, catalyst thickness, pretreatment time, and deposition time. This procedure facilitates predicting and modeling high edge density carbon nanostructure characteristics under a complete range of growth conditions that yields various morphologies of nanoscale carbon. Aside from the morphological trends influenced by temperature, a relationship between deposition temperature and specific capacitance emerged from the DOE study. Transmission electron microscopy was also used to understand the morphology and microstructure of the various high edge density structures. From these results, a new graphene foliate formation mechanism is proposed for synthesis of g-CNTs in a single deposition process. PMID:25089165

  18. Growth kinetics of gamma-prime precipitates in a directionally solidified eutectic, gamma/gamma-prime-delta

    NASA Technical Reports Server (NTRS)

    Tewari, S. N.

    1976-01-01

    A directionally solidified eutectic alloy (DSEA), of those viewed as potential candidates for the next generation of aircraft gas turbine blade materials, is studied for the gamma-prime growth kinetics, in the system Ni-Nb-Cr-Al, specifically: Ni-20 w/o Nb-6 w/o Cr-2.5 w/o Al gamma/gamma-prime-delta DSEA. Heat treatment, polishing and etching, and preparation for electron micrography are described, and the size distribution of gamma-prime phase following various anneals is plotted, along with gamma-prime growth kinetics in this specific DSEA, and the cube of gamma-prime particle size vs anneal time. Activation energies and coarsening kinetics are studied.

  19. Compositional-Spread Discovery of Catalysts for the Growth of Long-Length Dense Forests of Vertically Aligned Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Christen, Hans M.; Puretzky, Alex A.; Cui, Hongtao; Lowndes, Douglas H.; Belay, Kalayu; Geohegan, David B.

    2004-03-01

    The growth of dense forests of vertically aligned arrays of multi-walled carbon nanotubes (VAA-MWNTs) by chemical vapor deposition [CVD] from a single metallic catalyst layer typically self-terminates after only a few hundred microns of tube length. In order to obtain maximal growth to long lengths, a systematic simultaneous study of catalyst composition and thickness is needed performed here by a compositional-spread approach. Using Pulsed-Laser Deposition (PLD), metallic layers with a wedge-shaped thickness profile are deposited onto Al-coated silicon substrates. High temperature annealing of the metal catalyst films in flowing Ar/H2 gas followed by the one-hour growth of VA-MWNTs by CVD using acetylene gas yields VAA-MWNTs. Tube height (and thus the catalytic activity) is determined as function of position and can be analyzed as a function of catalyst thickness and composition. A dependence of tube height as function of catalyst composition (Mo/Fe ratio) demonstrates that a specific catalyst composition exhibits a local maximum in catalytic activity, permitting the extension of nanotube array growth up to 4 millimeters in height. Other combinations of catalysts and the growth of single-walled tubes will be discussed. This research was sponsored by the U.S. Department of Energy under contract DE-AC05-00OR22725 with the Oak Ridge National Laboratory, managed by UT-Battelle, LLC, and the Laboratory-Directed Research and Development Program at ORNL.

  20. Carbon nanotubes filled partially or completely with nickel

    NASA Astrophysics Data System (ADS)

    Liang, C. H.; Meng, G. W.; Zhang, L. D.; Shen, N. F.; Zhang, X. Y.

    2000-09-01

    We report the catalytic synthesis of carbon nanotubes filled with Ni by chemical vapor deposition over the Raney-Ni catalyst. Straight and two types of bamboo-shaped carbon nanotubes have been discovered under TEM. Further investigation with TEM shows that an obvious tendency exists, i.e. the straight nanotube encapsulating Ni completely; as for the compartments of bamboo-shaped nanotube, either every one filled with a small Ni particle or only the end is capped with a needle-shaped Ni, which suggests different growth mechanism.

  1. The kinetics of chirality assignment in catalytic single-walled carbon nanotube growth and the routes towards selective growth† †Electronic supplementary information (ESI) available: Details of density functional theory (DFT) calculations, definition of interfacial formation energy (IFE), cap formation energy and fitting equation, Fig. S1–S4 and Table S1. See DOI: 10.1039/c7sc04714b

    PubMed Central

    Xu, Ziwei; Qiu, Lu

    2018-01-01

    Depending on its specific structure, or so-called chirality, a single-walled carbon nanotube (SWCNT) can be either a conductor or a semiconductor. This feature ensures great potential for building ∼1 nm sized electronics if chirality-selected SWCNTs could be achieved. However, due to the limited understanding of the growth mechanism of SWCNTs, reliable methods for chirality-selected SWCNTs are still pending. Here we present a theoretical model on the chirality assignment and control of SWCNTs during the catalytic growth. This study reveals that the chirality of a SWCNT is determined by the kinetic incorporation of pentagons, especially the last (6th) one, during the nucleation stage. Our analysis showed that the chirality of a SWCNT is randomly assigned on a liquid or liquid-like catalyst surface, and two routes of synthesizing chirality-selected SWCNTs, which are verified by recent experimental achievements, are demonstrated. They are (i) by using high melting point crystalline catalysts, such as Ta, W, Re, Os, or their alloys, and (ii) by frequently changing the chirality of SWCNTs during their growth. This study paves the way for achieving chirality-selective SWCNT growth for high performance SWCNT based electronics. PMID:29732090

  2. Characterization of drug-release kinetics in trabecular bone from titania nanotube implants

    PubMed Central

    Aw, Moom Sinn; Khalid, Kamarul A; Gulati, Karan; Atkins, Gerald J; Pivonka, Peter; Findlay, David M; Losic, Dusan

    2012-01-01

    Purpose The aim of this study was to investigate the application of the three-dimensional bone bioreactor for studying drug-release kinetics and distribution of drugs in the ex vivo cancellous bone environment, and to demonstrate the application of nanoengineered titanium (Ti) wires generated with titania nanotube (TNT) arrays as drug-releasing implants for local drug delivery Methods Nanoengineered Ti wires covered with a layer of TNT arrays implanted in bone were used as a drug-releasing implant. Viable bovine trabecular bone was used as the ex vivo bone substrate embedded with the implants and placed in the bone reactor. A hydrophilic fluorescent dye (rhodamine B) was used as the model drug, loaded inside the TNT–Ti implants, to monitor drug release and transport in trabecular bone. The distribution of released model drug in the bone was monitored throughout the bone structure, and concentration profiles at different vertical (0–5 mm) and horizontal (0–10 mm) distances from the implant surface were obtained at a range of release times from 1 hour to 5 days. Results Scanning electron microscopy confirmed that well-ordered, vertically aligned nanotube arrays were formed on the surface of prepared TNT–Ti wires. Thermogravimetric analysis proved loading of the model drug and fluorescence spectroscopy was used to show drug-release characteristics in-vitro. The drug release from implants inserted into bone ex vivo showed a consistent gradual release of model drug from the TNT–Ti implants, with a characteristic three-dimensional distribution into the surrounding bone, over a period of 5 days. The parameters including the flow rate of bone culture medium, differences in trabecular microarchitecture between bone samples, and mechanical loading were found to have the most significant influence on drug distribution in the bone. Conclusion These results demonstrate the utility of the Zetos™ system for ex vivo drug-release studies in bone, which can be applied to

  3. Characterization of drug-release kinetics in trabecular bone from titania nanotube implants.

    PubMed

    Aw, Moom Sinn; Khalid, Kamarul A; Gulati, Karan; Atkins, Gerald J; Pivonka, Peter; Findlay, David M; Losic, Dusan

    2012-01-01

    The aim of this study was to investigate the application of the three-dimensional bone bioreactor for studying drug-release kinetics and distribution of drugs in the ex vivo cancellous bone environment, and to demonstrate the application of nanoengineered titanium (Ti) wires generated with titania nanotube (TNT) arrays as drug-releasing implants for local drug delivery Nanoengineered Ti wires covered with a layer of TNT arrays implanted in bone were used as a drug-releasing implant. Viable bovine trabecular bone was used as the ex vivo bone substrate embedded with the implants and placed in the bone reactor. A hydrophilic fluorescent dye (rhodamine B) was used as the model drug, loaded inside the TNT-Ti implants, to monitor drug release and transport in trabecular bone. The distribution of released model drug in the bone was monitored throughout the bone structure, and concentration profiles at different vertical (0-5 mm) and horizontal (0-10 mm) distances from the implant surface were obtained at a range of release times from 1 hour to 5 days. Scanning electron microscopy confirmed that well-ordered, vertically aligned nanotube arrays were formed on the surface of prepared TNT-Ti wires. Thermogravimetric analysis proved loading of the model drug and fluorescence spectroscopy was used to show drug-release characteristics in-vitro. The drug release from implants inserted into bone ex vivo showed a consistent gradual release of model drug from the TNT-Ti implants, with a characteristic three-dimensional distribution into the surrounding bone, over a period of 5 days. The parameters including the flow rate of bone culture medium, differences in trabecular microarchitecture between bone samples, and mechanical loading were found to have the most significant influence on drug distribution in the bone. These results demonstrate the utility of the Zetos™ system for ex vivo drug-release studies in bone, which can be applied to optimize the delivery of specific therapies

  4. Carbon nanotubes on nanoporous alumina: from surface mats to conformal pore filling

    PubMed Central

    2014-01-01

    Control over nucleation and growth of multi-walled carbon nanotubes in the nanochannels of porous alumina membranes by several combinations of posttreatments, namely exposing the membrane top surface to atmospheric plasma jet and application of standard S1813 photoresist as an additional carbon precursor, is demonstrated. The nanotubes grown after plasma treatment nucleated inside the channels and did not form fibrous mats on the surface. Thus, the nanotube growth mode can be controlled by surface treatment and application of additional precursor, and complex nanotube-based structures can be produced for various applications. A plausible mechanism of nanotube nucleation and growth in the channels is proposed, based on the estimated depth of ion flux penetration into the channels. PACS 63.22.Np Layered systems; 68. Surfaces and interfaces; Thin films and nanosystems (structure and non-electronic properties); 81.07.-b Nanoscale materials and structures: fabrication and characterization PMID:25177216

  5. Controlled growth of gold nanocrystals on biogenic As-S nanotubes by galvanic displacement

    NASA Astrophysics Data System (ADS)

    Liu, Fang; Chen, Wilfred; Myung, Nosang V.

    2018-02-01

    Traditional methods for fabricating nanoscale arrays are usually based on lithographic techniques while alternative new approaches rely on the use of nanoscale templates made of synthetic or biological materials. Here, gold (Au) nanocrystals were grown on the surface of the microbiologically formed As-S nanotubes through the process of galvanic displacement. The size and organization of the synthesized Au nanocrystals were affected by the pH dependent speciation of HAuCl4 precursors as well as the initial ratio of As-S/HAuCl4. We found that as pH increased, the Au nanocrystals grown on As-S nanotubes had smaller sizes but were more likely to assemble in one-dimension along the nanotubes. At a proper initial ratio of As-S/HAuCl4, Au nanotubes were formed at pH 6.0. The mechanism of Au nanostructures formation and the synthesis process at different pHs were proposed. The resulting Au nanoparticle/As-S nanotube and Au nanotube/As-S nanotube hetero-structures may provide important properties to be used for novel nano-electronic devices.

  6. Mechanism of the coupling of diazonium to single-walled carbon nanotubes and its consequences.

    PubMed

    Schmidt, Grégory; Gallon, Salomé; Esnouf, Stéphane; Bourgoin, Jean-Philippe; Chenevier, Pascale

    2009-01-01

    On the tube: The coupling of diazonium ions onto single-walled carbon nanotubes is shown to proceed through a radical chain reaction by kinetic analysis of the absorption peak drop (see picture). Radical species are also revealed by ESR. Metallic (m) nanotubes play a special catalytic role in the functionalization of semiconducting (sc) nanotubes.Due to its simplicity and versatility, diazonium coupling is the most widely used method for carbon nanotube (CNT) functionalization to increase CNT processability and add new functionalities. Yet, its mechanism is so far mostly unknown. Herein, we use kinetic analysis to shed light on this complex mechanism. A free-radical chain reaction is revealed by absorption spectroscopy and ESR. Metallic CNTs are shown to play an unexpected catalytic role. The step determining the selectivity towards metallic CNTs is identified by a Hammett correlation. A mechanistic model is proposed that predicts reactivity and selectivity as a function of diazonium electrophilicity and metallic-to-semiconducting CNT ratio, thus opening perspectives of controlled high-yield functionalization and purification.

  7. Low temperature growth of ultra-high mass density carbon nanotube forests on conductive supports

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sugime, Hisashi; Esconjauregui, Santiago; Yang, Junwei

    2013-08-12

    We grow ultra-high mass density carbon nanotube forests at 450 °C on Ti-coated Cu supports using Co-Mo co-catalyst. X-ray photoelectron spectroscopy shows Mo strongly interacts with Ti and Co, suppressing both aggregation and lifting off of Co particles and, thus, promoting the root growth mechanism. The forests average a height of 0.38 μm and a mass density of 1.6 g cm{sup −3}. This mass density is the highest reported so far, even at higher temperatures or on insulators. The forests and Cu supports show ohmic conductivity (lowest resistance ∼22 kΩ), suggesting Co-Mo is useful for applications requiring forest growth onmore » conductors.« less

  8. Cure Kinetics of Epoxy Nanocomposites Affected by MWCNTs Functionalization: A Review

    PubMed Central

    Saeb, Mohammad Reza; Bakhshandeh, Ehsan; Khonakdar, Hossein Ali; Mäder, Edith; Scheffler, Christina; Heinrich, Gert

    2013-01-01

    The current paper provides an overview to emphasize the role of functionalization of multiwalled carbon nanotubes (MWCNTs) in manipulating cure kinetics of epoxy nanocomposites, which itself determines ultimate properties of the resulting compound. In this regard, the most commonly used functionalization schemes, that is, carboxylation and amidation, are thoroughly surveyed to highlight the role of functionalized nanotubes in controlling the rate of autocatalytic and vitrification kinetics. The current literature elucidates that the mechanism of curing in epoxy/MWCNTs nanocomposites remains almost unaffected by the functionalization of carbon nanotubes. On the other hand, early stage facilitation of autocatalytic reactions in the presence of MWCNTs bearing amine groups has been addressed by several researchers. When carboxylated nanotubes were used to modify MWCNTs, the rate of such reactions diminished as a consequence of heterogeneous dispersion within the epoxy matrix. At later stages of curing, however, the prolonged vitrification was seen to be dominant. Thus, the type of functional groups covalently located on the surface of MWCNTs directly affects the degree of polymer-nanotube interaction followed by enhancement of curing reaction. Our survey demonstrated that most widespread efforts ever made to represent multifarious surface-treated MWCNTs have not been directed towards preparation of epoxy nanocomposites, but they could result in property synergism. PMID:24348181

  9. From Bench Top to Market: Growth of Multi-Walled Carbon Nanotubes by Injection CVD Using Fe Organometallics - Production of a Commercial Reactor

    NASA Technical Reports Server (NTRS)

    Rowsell, J.; Hepp, A. F.; Harris, J. D.; Raffaelle, R. P.; Cowen, J. C.; Scheiman, D. A.; Flood, D. M.; Flood, D. J.

    2009-01-01

    Preferential oriented multiwalled carbon nanotubes were prepared by the injection chemical vapor deposition (CVD) method using either cyclopentadienyliron dicarbonyl dimer or cyclooctatetraene iron tricarbonyl as the iron catalyst source. The catalyst precursors were dissolved in toluene as the carrier solvent for the injections. The concentration of the catalyst was found to influence both the growth (i.e., MWNT orientation) of the nanotubes, as well as the amount of iron in the deposited material. As deposited, the multiwalled carbon nanotubes contained as little as 2.8% iron by weight. The material was deposited onto tantalum foil and fused silica substrates. The nanotubes were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and thermogravimetric analysis. This synthetic route provides a simple and scalable method to deposit MWNTs with a low defect density, low metal content and a preferred orientation. Subsequently, a small start-up was founded to commercialize the deposition equipment. The contrast between the research and entrepreneurial environments will be discussed.

  10. Vertically aligned multiwalled carbon nanotubes as electronic interconnects

    NASA Astrophysics Data System (ADS)

    Gopee, Vimal Chandra

    The drive for miniaturisation of electronic circuits provides new materials challenges for the electronics industry. Indeed, the continued downscaling of transistor dimensions, described by Moore’s Law, has led to a race to find suitable replacements for current interconnect materials to replace copper. Carbon nanotubes have been studied as a suitable replacement for copper due to its superior electrical, thermal and mechanical properties. One of the advantages of using carbon nanotubes is their high current carrying capacity which has been demonstrated to be three orders of magnitude greater than that of copper. Most approaches in the implementation of carbon nanotubes have so far focused on the growth in vias which limits their application. In this work, a process is described for the transfer of carbon nanotubes to substrates allowing their use for more varied applications. Arrays of vertically aligned multiwalled carbon nanotubes were synthesised by photo-thermal chemical vapour deposition with high growth rates. Raman spectroscopy was used to show that the synthesised carbon nanotubes were of high quality. The carbon nanotubes were exposed to an oxygen plasma and the nature of the functional groups present was determined using X-ray photoelectron spectroscopy. Functional groups, such as carboxyl, carbonyl and hydroxyl groups, were found to be present on the surface of the multiwalled carbon nanotubes after the functionalisation process. The multiwalled carbon nanotubes were metallised after the functionalisation process using magnetron sputtering. Two materials, solder and sintered silver, were chosen to bind carbon nanotubes to substrates so as to enable their transfer and also to make electrical contact. The wettability of solder to carbon nanotubes was investigated and it was demonstrated that both functionalisation and metallisation were required in order for solder to bond with the carbon nanotubes. Similarly, functionalisation followed by metallisation

  11. Exponential growth kinetics for Polyporus versicolor and Pleurotus ostreatus in submerged culture

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Carroad, P.A.; Wilke, C.R.

    1977-04-01

    Simple mathematical models for a batch culture of pellet-forming fungi in submerged culture were tested on growth data for Polyporus versicolor (ATCC 12679) and Pleurotus ostreatus (ATCC 9415). A kinetic model based on a growth rate proportional to the two-thirds power of the cell mass was shown to be satisfactory. A model based on a growth rate directly proportional to the cell mass fitted the data equally well, however, and may be preferable because of mathematical simplicity.

  12. 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.

  13. Bimetallic-catalyst-mediated syntheses of nanomaterials (nanowires, nanotubes, nanofibers, nanodots, etc) by the VQS (vapor-quasiliquid-solid, vapor- quasisolid-solid) growth mechanism

    NASA Astrophysics Data System (ADS)

    Mohammad, S. N.

    2016-12-01

    The enhanced synergistic, catalytic effect of bimetallic nanoparticles (BNPs), as compared to monometallic nanoparticles (NPs), on the nanomaterials (nanowires, nanotubes, nanodots, nanofibers, etc) synthesed by chemical vapor deposition has been investigated. A theoretical model for this catalytic effect and hence for nanomaterial growth, has been developed. The key element of the model is the diffusion of the nanomaterial source species through the nanopores of quasiliquid (quasisolid) BNP, rather than through the liquid or solid BNP, for nanomaterial growth. The role of growth parameters such as temperature, pressure and of the BNP material characteristics such as element mole fraction of BNP, has been studied. The cause of enhanced catalytic activity of BNPs as compared to NPs as a function of temperature has been explored. The dependence of growth rate on the nanomaterial diameter has also been examined. The calculated results have been extensively compared with available experiments. Experimental supports for the growth mechanism have been presented as well. Close correspondence between the calculated and experimental results attests to the validity of the proposed model. The wide applicability of the proposed model to nanowires, nanotubes, nanofibers, nanodots, etc suggests that it is general and has broad appeal.

  14. Mapping the transition from catalyst-pool to bamboo-like growth-mechanism in vertically-aligned free-standing films of carbon nanotubes filled with Fe3C: The key role of water

    NASA Astrophysics Data System (ADS)

    Boi, Filippo S.; Wang, Shanling; He, Yi

    2016-08-01

    The control of carbon nanotube growth has challenged researchers for more than a decade due to the complex parameters-control necessary in the commonly used CVD approaches. Here we show that a direct transition from the catalyst-pool growth mechanism characterized by graphene-caps in the direction of growth to a bamboo-shaped mechanism characterized by the repetition of periodic elongated graphitic compartments is present when controlled quantities of water are added to ferrocene/dichlorobenzene. Our results suggest that water-addition allows enhancing the level of stress accumulated under the graphitic nanotubes-cap.

  15. Controlled growth of aligned carbon nanotube using pulsed glow barrier discharge

    NASA Astrophysics Data System (ADS)

    Nozaki, Tomohiro; Kimura, Yoshihito; Okazaki, Ken

    2002-10-01

    We first achieved a catalytic growth of aligned carbon nanotube (CNT) using atmospheric pressure pulsed glow barrier discharge combined with DC bias (1000 V). Aligned CNT can grow with the directional electric field, and this is a big challenge in barrier discharges since dielectric barrier does not allow DC bias and forces to use AC voltage to maintain stable plasma conditions. To overcome this, we developed a power source generating Gaussian-shape pulses at 20 kpps with 4% duty, and DC bias was applied to the GND electrode where Ni-, Fe-coated substrate existed. With positive pulse, i.e. substrate was the cathode, random growth of CNT was observed at about 10^9 cm-2. Growth rate significantly reduced when applied negative pulse; Negative glow formation near substrate is essential for sufficient supply of radical species to the catalyst. If -DC was biased, aligned CNT with 20 nm was synthesized because negative bias enhanced negative glow formation. Interestingly, 2 to 3 CNTs stuck each other with +DC bias, resulting in 50-70 nm and non-aligned CNT. Atmospheric pressure glow barrier discharges can be highly controlled and be a potential alternative to vacuum plasmas for CVD, micro-scale, nano-scale fabrication.

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

    USDA-ARS?s Scientific Manuscript database

    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...

  17. Kinetic model for microbial growth and desulphurisation with Enterobacter sp.

    PubMed

    Liu, Long; Guo, Zhiguo; Lu, Jianjiang; Xu, Xiaolin

    2015-02-01

    Biodesulphurisation was investigated by using Enterobacter sp. D4, which can selectively desulphurise and convert dibenzothiophene into 2-hydroxybiphenyl (2-HBP). The experimental values of growth, substrate consumption and product generation were obtained at 95 % confidence level of the fitted values using three models: Hinshelwood equation, Luedeking-Piret and Luedeking-Piret-like equations. The average error values between experimental values and fitted values were less than 10 %. These kinetic models describe all the experimental data with good statistical parameters. The production of 2-HBP in Enterobacter sp. was by "coupled growth".

  18. Human Growth Hormone Adsorption Kinetics and Conformation on Self-Assembled Monolayers

    PubMed Central

    Buijs, Jos; Britt, David W.; Hlady, Vladimir

    2012-01-01

    The adsorption process of the recombinant human growth hormone on organic films, created by self-assembly of octadecyltrichlorosilane, arachidic acid, and dipalmitoylphosphatidylcholine, is investigated and compared to adsorption on silica and methylated silica substrates. Information on the adsorption process of human growth hormone (hGH) is obtained by using total internal reflection fluorescence (TIRF). The intensity, spectra, and quenching of the intrinsic fluorescence emitted by the growth hormone’s single tryptophan are monitored and related to adsorption kinetics and protein conformation. For the various alkylated hydrophobic surfaces with differences in surface density and conformational freedom it is observed that the adsorbed amount of growth hormone is relatively large if the alkyl chains are in an ordered structure while the amounts adsorbed are considerably lower for adsorption onto less ordered alkyl chains of fatty acid and phospholipid layers. Adsorption on methylated surfaces results in a relatively large conformational change in the growth hormone’s structure, as displayed by a 7 nm blue shift in emission wavelength and a large increase in the effectiveness of fluorescence quenching. Conformational changes are less evident for hGH adsorption onto the fatty acid and phospholipid alkyl chains. Adsorption kinetics on the hydrophilic head groups of the self-assembled monolayers are similar to those on solid hydrophilic surfaces. The relatively small conformational changes in the hGH structure observed for adsorption on silica are even further reduced for adsorption on fatty acid head groups. PMID:25125795

  19. Synthesis of carbon-coated TiO 2 nanotubes for high-power lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Park, Sang-Jun; Kim, Young-Jun; Lee, Hyukjae

    Carbon-coated TiO 2 nanotubes are prepared by a simple one-step hydrothermal method with an addition of glucose in the starting powder, and are characterized by morphological analysis and electrochemical measurement. A thin carbon coating on the nanotube surface effectively suppresses severe agglomeration of TiO 2 nanotubes during hydrothermal reaction and post calcination. This action results in better ionic and electronic kinetics when applied to lithium-ion batteries. Consequently, carbon-coated TiO 2 nanotubes deliver a remarkable lithium-ion intercalation/deintercalation performance, such as reversible capacities of 286 and 150 mAh g -1 at 250 and 7500 mA g -1, respectively.

  20. Kinetic 15N-isotope effects on algal growth

    NASA Astrophysics Data System (ADS)

    Andriukonis, Eivydas; Gorokhova, Elena

    2017-03-01

    Stable isotope labeling is a standard technique for tracing material transfer in molecular, ecological and biogeochemical studies. The main assumption in this approach is that the enrichment with a heavy isotope has no effect on the organism metabolism and growth, which is not consistent with current theoretical and empirical knowledge on kinetic isotope effects. Here, we demonstrate profound changes in growth dynamics of the green alga Raphidocelis subcapitata grown in 15N-enriched media. With increasing 15N concentration (0.37 to 50 at%), the lag phase increased, whereas maximal growth rate and total yield decreased; moreover, there was a negative relationship between the growth and the lag phase across the treatments. The latter suggests that a trade-off between growth rate and the ability to adapt to the high 15N environment may exist. Remarkably, the lag-phase response at 3.5 at% 15N was the shortest and deviated from the overall trend, thus providing partial support to the recently proposed Isotopic Resonance hypothesis, which predicts that certain isotopic composition is particularly favorable for living organisms. These findings confirm the occurrence of KIE in isotopically enriched algae and underline the importance of considering these effects when using stable isotope labeling in field and experimental studies.

  1. XRD and spectral dataset of the UV-A stable nanotubes of 3,5-bis(trifluoromethyl)benzylamine derivative of tyrosine.

    PubMed

    Govindhan, R; Karthikeyan, B

    2017-10-01

    The data presented in this article are related to the research entitled of UV-A stable nanotubes. The nanotubes have been prepared from 3,5-bis(trifluoromethyl)benzylamine derivative of tyrosine (BTTP). XRD data reveals the size of the nanotubes. As-synthesized nanotubes (BTTPNTs) are characterized by UV-vis optical absorption studies [1] and photo physical degradation kinetics. The resulted dataset is made available to enable critical or extended analyzes of the BTTPNTs as an excellent light resistive materials.

  2. Rational growth of Bi2S3 nanotubes from quasi-two-dimensional precursors.

    PubMed

    Ye, Changhui; Meng, Guowen; Jiang, Zhi; Wang, Yinhai; Wang, Guozhong; Zhang, Lide

    2002-12-25

    Synthesis of Bi2S3 nanotubes from rolling of the quasi-two-dimensional (2-D) layered precursor represents new progress in the synthetic approach and adds new members to the present inorganic fullerene family. These nanotubes display multiwalled structures that resemble that of a multiwalled carbon nanotube. The successful synthesis of Bi2S3 nanotubes highlights the feasibility of inorganic fullerene-like structures from other chemicals that possess layered crystalline structures, not only the well-known 2-D family, but possibly also those quasi-2-D members.

  3. Altered cellular kinetics in growth plate according to alterations in weight bearing.

    PubMed

    Park, Hoon; Kong, Sun Young; Kim, Hyun Woo; Yang, Ick Hwan

    2012-05-01

    To examine the effects of change in weight bearing on the growth plate metabolism, a simulated animal model of weightlessness was introduced and the chondrocytes' cellular kinetics was evaluated. Unloading condition on the hind-limb of Sprague-Dawley rats was created by fixing a tail and lifting the hind-limb. Six rats aged 6 weeks old were assigned to each group of unloading, reloading, and control groups of unloading or reloading. Unloading was maintained for three weeks, and then reloading was applied for another one week thereafter. Histomorphometry for the assessment of vertical length of the growth plate, 5-bromo-2'-deoxyuridin immunohistochemistry for cellular kinetics, and biotin nick end labeling transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) assay for chondrocytes apoptosis in the growth plate were performed. The vertical length of the growth plate and the proliferative potential of chondrocytes were decreased in the unloading group compared to those of control groups. Inter-group differences were more significant in the proliferative and hypertrophic zones. Reloading increased the length of growth plate and proliferative potential of chondrocytes. However, apoptotic changes in the growth plate were not affected by the alterations of weight bearing. Alterations in the weight bearing induced changes in the chondrocytic proliferative potential of the growth plate, however, had no effects on the apoptosis. This may explain why non-weight bearing in various clinical situations hampers normal longitudinal bone growth. Further studies on the factors for reversibility of chondrocytic proliferation upon variable mechanical stresses are needed.

  4. Effect of MoO3 on the synthesis of boron nitride nanotubes over Fe and Ni catalysts.

    PubMed

    Nithya, Jeghan Shrine Maria; Pandurangan, Arumugam

    2012-05-01

    Synthesis of boron nitride nanotubes at reduced temperature is important for industrial manufactures. In this study boron nitride nanotubes were synthesized by thermal evaporation method using B/Fe2O3/MoO3 and B/Ni2O3/MoO3 mixtures separately with ammonia as the nitrogen source. The growth of boron nitride nanotubes occurred at 1100 degrees C, which was relatively lower than other metal oxides assisted growth processes requiring higher than 1200 degrees C. MoO3 promoted formation of B2O2 and aided boron nitride nanotubes growth at a reduced temperature. The boron nitride nanotubes with bamboo shaped, nested cone structured and straight tubes like forms were evident from the high resolution transmission electron microscopy. Metallic Fe and Ni, formed during the process, were the catalysts for the growth of boron nitride nanotubes. Their formation was established by X-ray diffraction. FT Raman showed a peak due to B-N vibration of BNNTs close to 1370 cm(-1). Hence MoO3 assisted growth of boron nitride nanotubes is advantageous, as it significantly reduced the synthesis temperature.

  5. Improved Method of Purifying Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance D.

    2004-01-01

    An improved method of removing the residues of fabrication from carbon nanotubes has been invented. These residues comprise amorphous carbon and metal particles that are produced during the growth process. Prior methods of removing the residues include a variety of processes that involved the use of halogens, oxygen, or air in both thermal and plasma processes. Each of the prior methods entails one or more disadvantages, including non-selectivity (removal or damage of nanotubes in addition to removal of the residues), the need to dispose of toxic wastes, and/or processing times as long as 24 hours or more. In contrast, the process described here does not include the use of toxic chemicals, the generation of toxic wastes, causes little or no damage to the carbon nanotubes, and involves processing times of less than 1 hour. In the improved method, purification is accomplished by flowing water vapor through the reaction chamber at elevated temperatures and ambient pressures. The impurities are converted to gaseous waste products by the selective hydrogenation and hydroxylation by the water in a reaction chamber. This process could be performed either immediately after growth or in a post-growth purification process. The water used needs to be substantially free of oxygen and can be obtained by a repeated freeze-pump-thaw process. The presence of oxygen will non-selectively attach the carbon nanotubes in addition to the amorphous carbon.

  6. Carbon Nanotube Material Quality Assessment

    NASA Technical Reports Server (NTRS)

    Yowell, Leonard; Arepalli, Sivaram; Sosa, Edward; Niolaev, Pavel; Gorelik, Olga

    2006-01-01

    The nanomaterial activities at NASA Johnson Space Center focus on carbon nanotube production, characterization and their applications for aerospace systems. Single wall carbon nanotubes are produced by arc and laser methods. Characterization of the nanotube material is performed using the NASA JSC protocol developed by combining analytical techniques of SEM, TEM, UV-VIS-NIR absorption, Raman, and TGA. A possible addition of other techniques such as XPS, and ICP to the existing protocol will be discussed. Changes in the quality of the material collected in different regions of the arc and laser production chambers is assessed using the original JSC protocol. The observed variations indicate different growth conditions in different regions of the production chambers.

  7. Synthesis, characterisation and applications of coiled carbon nanotubes.

    PubMed

    Hanus, Monica J; Harris, Andrew T

    2010-04-01

    Coiled carbon nanotubes are helical carbon structures formed when heptagonal and pentagonal rings are inserted into the hexagonal backbone of a 'straight' nanotube. Coiled carbon nanotubes have been reported with both regular and irregular helical structures. In this work the structure, growth mechanism(s), synthesis, properties and potential applications of coiled carbon nanotubes are reviewed. Published data suggests that coiled carbon nanotube synthesis occurs due to nonuniform extrusion of carbon from a catalyst surface. To date, coiled carbon nanotubes have been synthesised using catalyst modification techniques including: (i) the addition of S or P containing compounds during synthesis; (ii) the use of binary or ternary metal catalysts; (iii) the use of microwaves to create a local temperature gradient around individual catalyst particles and; (iv) the use of pH control during catalyst preparation. In most instances coiled carbon nanotubes are produced as a by-product; high yield and/or large-scale synthesis of coiled carbon nanotubes remains problematic. The qualitative analysis of coiled carbon nanotubes is currently hindered by the absence of specific characterisation data in the literature, e.g., oxidation profiles measured by thermogravimetric analysis and Raman spectra of pure coiled carbon nanotube samples.

  8. Particle growth kinetics over the Amazon rainforest

    NASA Astrophysics Data System (ADS)

    Pinterich, T.; Andreae, M. O.; Artaxo, P.; Kuang, C.; Longo, K.; Machado, L.; Manzi, A. O.; Martin, S. T.; Mei, F.; Pöhlker, C.; Pöhlker, M. L.; Poeschl, U.; Shilling, J. E.; Shiraiwa, M.; Tomlinson, J. M.; Zaveri, R. A.; Wang, J.

    2016-12-01

    Aerosol particles larger than 100 nm play a key role in global climate by acting as cloud condensation nuclei (CCN). Most of these particles, originated from new particle formation or directly emitted into the atmospheric, are initially too small to serve as CCN. These small particles grow to CCN size mainly through condensation of secondary species. In one extreme, the growth is dictated by kinetic condensation of very low-volatility compounds, favoring the growth of the smallest particles; in the other extreme, the process is driven by Raoult's law-based equilibrium partitioning of semi-volatile organic compound, favoring the growth of larger particles. These two mechanisms can lead to very different production rates of CCN. The growth of particles depends on a number of parameters, including the volatility of condensing species, particle phase, and diffusivity inside the particles, and this process is not well understood in part due to lack of ambient data. Here we examine atmospheric particle growth using high-resolution size distributions measured onboard the DOE G-1 aircraft during GoAmazon campaign, which took place from January 2014 to December 2015 near Manaus, Brazil, a city surrounded by natural forest for over 1000 km in every direction. City plumes are clearly identified by the strong enhancement of nucleation and Aitken mode particle concentrations over the clean background. As the plume traveled downwind, particle growth was observed, and is attributed to condensation of secondary species and coagulation (Fig.1). Observed aerosol growth is modeled using MOSAIC (Model for Simulating Aerosol Interactions and Chemistry), which dynamically partitions multiple compounds to all particle size bins by taking into account compound volatility, gas-phase diffusion, interfacial mass accommodation, particle-phase diffusion, and particle-phase reaction. The results from both wet and dry seasons will be discussed.

  9. A comparative study of ethylene growth response kinetics in eudicots and monocots reveals a role for gibberellin in growth inhibition and recovery.

    PubMed

    Kim, Joonyup; Wilson, Rebecca L; Case, J Brett; Binder, Brad M

    2012-11-01

    Time-lapse imaging of dark-grown Arabidopsis (Arabidopsis thaliana) hypocotyls has revealed new aspects about ethylene signaling. This study expands upon these results by examining ethylene growth response kinetics of seedlings of several plant species. Although the response kinetics varied between the eudicots studied, all had prolonged growth inhibition for as long as ethylene was present. In contrast, with continued application of ethylene, white millet (Panicum miliaceum) seedlings had a rapid and transient growth inhibition response, rice (Oryza sativa 'Nipponbare') seedlings had a slow onset of growth stimulation, and barley (Hordeum vulgare) had a transient growth inhibition response followed, after a delay, by a prolonged inhibition response. Growth stimulation in rice correlated with a decrease in the levels of rice ETHYLENE INSENSTIVE3-LIKE2 (OsEIL2) and an increase in rice F-BOX DOMAIN AND LRR CONTAINING PROTEIN7 transcripts. The gibberellin (GA) biosynthesis inhibitor paclobutrazol caused millet seedlings to have a prolonged growth inhibition response when ethylene was applied. A transient ethylene growth inhibition response has previously been reported for Arabidopsis ethylene insensitive3-1 (ein3-1) eil1-1 double mutants. Paclobutrazol caused these mutants to have a prolonged response to ethylene, whereas constitutive GA signaling in this background eliminated ethylene responses. Sensitivity to paclobutrazol inversely correlated with the levels of EIN3 in Arabidopsis. Wild-type Arabidopsis seedlings treated with paclobutrazol and mutants deficient in GA levels or signaling had a delayed growth recovery after ethylene removal. It is interesting to note that ethylene caused alterations in gene expression that are predicted to increase GA levels in the ein3-1 eil1-1 seedlings. These results indicate that ethylene affects GA levels leading to modulation of ethylene growth inhibition kinetics.

  10. Effect of Morphology and Size of Halloysite Nanotubes on Functional Pectin Bionanocomposites for Food Packaging Applications.

    PubMed

    Makaremi, Maziyar; Pasbakhsh, Pooria; Cavallaro, Giuseppe; Lazzara, Giuseppe; Aw, Yoong Kit; Lee, Sui Mae; Milioto, Stefana

    2017-05-24

    Pectin bionanocomposite films filled with various concentrations of two different types of halloysite nanotubes were prepared and characterized in this study as potential films for food packaging applications. The two types of halloysite nanotubes were long and thin (patch) (200-30 000 nm length) and short and stubby (Matauri Bay) (50-3000 nm length) with different morphological, physical, and dispersibility properties. Both matrix (pectin) and reinforcer (halloysite nanotubes) used in this study are considered as biocompatible, natural, and low-cost materials. Various characterization tests including Fourier transform infrared spectroscopy, field emission scanning electron microscopy, release kinetics, contact angle, and dynamic mechanical analysis were performed to evaluate the performance of the pectin films. Exceptional thermal, tensile, and contact angle properties have been achieved for films reinforced by patch halloysite nanotubes due to the patchy and lengthy nature of these tubes, which form a bird nest structure in the pectin matrix. Matauri Bay halloysite nanotubes were dispersed uniformly and individually in the matrix in low and even high halloysite nanotube concentrations. Furthermore, salicylic acid as a biocidal agent was encapsulated in the halloysite nanotubes lumen to control its release kinetics. On this basis, halloysite nanotubes/salicylic acid hybrids were dispersed into the pectin matrix to develop functional biofilms with antimicrobial properties that can be extended over time. Results revealed that shorter nanotubes (Matauri Bay) had better ability for the encapsulation of salicylic acid into their lumen, while patchy structure and longer tubes of patch halloysite nanotubes made the encapsulation process more difficult, as they might need more time and energy to be fully loaded by salicylic acid. Moreover, antimicrobial activity of the films against four different strains of Gram-positive and Gram-negative bacteria indicated the

  11. Self-assembling DNA nanotubes to connect molecular landmarks

    NASA Astrophysics Data System (ADS)

    Mohammed, Abdul M.; Šulc, Petr; Zenk, John; Schulman, Rebecca

    2017-05-01

    Within cells, nanostructures are often organized using local assembly rules that produce long-range order. Because these rules can take into account the cell's current structure and state, they can enable complexes, organelles or cytoskeletal structures to assemble around existing cellular components to form architectures. Although many methods for self-assembling biomolecular nanostructures have been developed, few can be programmed to assemble structures whose form depends on the identity and organization of structures already present in the environment. Here, we demonstrate that DNA nanotubes can grow to connect pairs of molecular landmarks with different separation distances and relative orientations. DNA tile nanotubes nucleate at these landmarks and grow while their free ends diffuse. The nanotubes can then join end to end to form stable connections, with unconnected nanotubes selectively melted away. Connections form between landmark pairs separated by 1-10 µm in more than 75% of cases and can span a surface or three dimensions. This point-to-point assembly process illustrates how self-assembly kinetics can be designed to produce structures with a desired physical property rather than a specific shape.

  12. Toxicity and Radioprotective Effects of DF-1 and Carbon Nanotubes in Human Lung and Liver Cell Lines

    NASA Technical Reports Server (NTRS)

    Burgoyne, Madeline; Holtorf, Heidi; Huff, Janice; Moore, Valerie; Jeevarajan, Antony

    2007-01-01

    The DF-1 compound, a sixty carbon fullerene derivative, has been shown to have antioxidant effects and is thought to possibly help mediate the effects of radiation on cells. While this is potentially useful, it is important to first understand the effect that the DF-1 has on the cells and the growth rate of the cells to determine if the material itself has any innate toxicity. A growth curve was established for both HF-19 cells, human fibroblasts, and HepG2 cells, liver tissue cells in the presence of two different concentrations of DF-1 and for untreated controls. The cells were plated in triplicate in 60mm dishes and were lifted and counted with a hemocytometer daily for one week. The growth curve data for the HF-19 cells show that while the low concentration of DF-1 had no apparent effect on the growth rate, the high concentration of DF-1 appeared to severely inhibit the growth of the HF-19 cells. The growth curve data for the HepG2 cells shows that the DF-1 compound had no significant effect on the rate at which the cells grew. A second growth curve study was performed plain carbon nanotubes, but with only 24 hour exposure to a high and low concentration of material. The carbon nanotubes are another carbon compound similar to DF-1, but in the shape of a tube, rather than a ball. We hypothesize that nanotubes may also mediate the effect of radiation on cells. This time, nanotubes did not showed any significant effect on the growth rate HF-19 or HepG2 cells. A third growth curve study is underway to further determine the effect of DF-1, nanotubes, and a derivatized nanotube (BHT-nanotubes). This derivatized nanotube has been modified with a compound that is known to be very effective at neutralizing free radicals. We expect that the high concentration of DF-1 and possibly the nanotubes and BHT-nanotubes may inhibit the growth of the HF-19 cells while the low concentration will resemble the growth of the control. We also hypothesize that there will be no

  13. Synthesis of Carbon Nanotubes Using Sol Gel Route

    NASA Astrophysics Data System (ADS)

    Abdel-Fattah, Tarek

    2002-12-01

    Since 1990, carbon nanotubes were discovered and they have been the object of intense scientific study ever since. A carbon nanotube is a honeycomb lattice rolled into a cylinder. The diameter of a carbon nanotube is of nanometer size and the length is in the range of micrometer. Many of the extraordinary properties attributed to nanotubes, such as tensile strength and thermal stability, have inspired predictions of microscopic robots, dent-resistant car bodies and earthquake-resistant buildings. The first products to use nanotubes were electrical. Some General Motors cars already include plastic parts to which nanotubes were added; such plastic can be electrified during painting so that the paint will stick more readily. Two nanotube-based lighting and display products are well on their way to market. In the long term, perhaps the most valuable applications will take further advantage of nanotubes' unique electronic properties. Carbon nanotubes can in principle play the same role as silicon does in electronic circuits, but at a molecular scale where silicon and other standard semiconductors cease to work. There are several routes to synthesize carbon nanotubes; laser vaporization, carbon arc and vapor growth. We have applied a different route using sol gel chemistry to obtain carbon nanotubes. This work is patent-pending.

  14. Kinetic models of controllable pore growth of anodic aluminum oxide membrane

    NASA Astrophysics Data System (ADS)

    Huang, Yan; Zeng, Hong-yan; Zhao, Ce; Qu, Ye-qing; Zhang, Pin

    2012-06-01

    An anodized Al2O3 (AAO) membrane with apertures about 72 nm in diameter was prepared by two-step anodic oxidation. The appearance and pore arrangement of the AAO membrane were characterized by energy dispersive x-ray spectroscopy and scanning electron microscopy. It was confirmed that the pores with high pore aspect ratio were parallel, well-ordered, and uniform. The kinetics of pores growth in the AAO membrane was derived, and the kinetic models showed that pores stopped developing when the pressure ( σ) trended to equal the surface tension at the end of anodic oxidation. During pore expansion, the effects of the oxalic acid concentration and expansion time on the pore size were investigated, and the kinetic behaviors were explained with two kinetic models derived in this study. They showed that the pore size increased with extended time ( r= G· t+ G'), but decreased with increased concentration ( r = - K·ln c- K') through the derived mathematic formula. Also, the values of G, G', K, and K' were derived from our experimental data.

  15. Enantiomers of Single-Wall Carbon Nanotubes Show Distinct Coating Displacement Kinetics.

    PubMed

    Zheng, Yu; Bachilo, Sergei M; Weisman, R Bruce

    2018-06-27

    It is known that specific oligomers of single-stranded DNA (ssDNA) can show remarkable selectivity when coating different structural species of single-wall carbon nanotubes (SWCNTs). We report that (ATT) 4 ssDNA coatings strongly distinguish between the two optical isomers of (7,5) SWCNTs. This causes resolvable shifts in their fluorescence spectra and differences of 2 orders of magnitude in the room temperature rates of coating displacement, as monitored through changes in nanotube fluorescence wavelength and intensity on exposure to sodium deoxycholate. During coating displacement, the enantiomer with high affinity for the ssDNA oligomer is deduced to form an intermediate hybrid that is not observed for the low affinity enantiomer. These results reveal that enantiomeric differences in SWCNTs complexed with ssDNA are more diverse and dramatic than previously recognized.

  16. Scaling laws and size effects for amorphous crystallization kinetics: Constraints imposed by nucleation and growth specificities.

    PubMed

    Descamps, Marc; Willart, Jean-François

    2018-05-05

    In the present paper we review different aspects of the crystallization of amorphous compounds in relation to specificities of the nucleation and growth rates. Its main purpose is: i) to underline the interest of a scaling analysis of recrystallization kinetics to identify similarities or disparities of experimental kinetic regimes. ii) to highlight the intrinsic link between the nucleation rate and growth rate with a temperature dependent characteristic transformation time τ(T), and a characteristic size ξ(T). The consequences on the influence of the sample size on kinetics of crystallization is considered. The significance of size effect and confinement for amorphous stabilization in the pharmaceutical sciences is discussed. Copyright © 2018. Published by Elsevier B.V.

  17. Electrical and Raman spectroscopic studies of vertically aligned multi-walled carbon nanotubes.

    PubMed

    Mathur, Ashish; Tweedie, Mark; Roy, Susanta Sinha; Maguire, P D; McLaughlin, James A

    2009-07-01

    Microwave plasma enhanced chemical vapour deposition (MPECVD) was used for the production of carbon nanotubes. Vertically aligned multi-walled carbon nanotubes (MWCNTs) were grown on silicon substrates coated with cobalt thin films of thickness ranging from 0.5 nm to 3 nm. Prior to the nanotube growth the catalyst were treated with N2 plasma for 5-10 minutes that break the films into small nanoparticles which favour the growth of nanotubes. The CNTs were grown at a substrate temperature of 700 degrees C for 5, 10 and 15 minutes. The height of the CNT films ranging from 10 microm-30 microm indicating that the initial growth rate of the CNTs are very high at a rate of approximately 100 nm/sec. Electrical resistivity of the above samples was evaluated from I-V measurements. The activation energy (E(a)) was also calculated from the temperature dependent studies and it was found that the E(a) lies in the range of 15-35 meV. Raman spectroscopy was used to identify the quality of the nanotubes.

  18. Barrierless growth of precursor-free, ultrafast laser-fragmented noble metal nanoparticles by colloidal atom clusters - A kinetic in situ study.

    PubMed

    Jendrzej, Sandra; Gökce, Bilal; Amendola, Vincenzo; Barcikowski, Stephan

    2016-02-01

    Unintended post-synthesis growth of noble metal colloids caused by excess amounts of reactants or highly reactive atom clusters represents a fundamental problem in colloidal chemistry, affecting product stability or purity. Hence, quantified kinetics could allow defining nanoparticle size determination in dependence of the time. Here, we investigate in situ the growth kinetics of ps pulsed laser-fragmented platinum nanoparticles in presence of naked atom clusters in water without any influence of reducing agents or surfactants. The nanoparticle growth is investigated for platinum covering a time scale of minutes to 50days after nanoparticle generation, it is also supplemented by results obtained from gold and palladium. Since a minimum atom cluster concentration is exceeded, a significant growth is determined by time resolved UV/Vis spectroscopy, analytical disc centrifugation, zeta potential measurement and transmission electron microscopy. We suggest a decrease of atom cluster concentration over time, since nanoparticles grow at the expense of atom clusters. The growth mechanism during early phase (<1day) of laser-synthesized colloid is kinetically modeled by rapid barrierless coalescence. The prolonged slow nanoparticle growth is kinetically modeled by a combination of coalescence and Lifshitz-Slyozov-Wagner kinetic for Ostwald ripening, validated experimentally by the temperature dependence of Pt nanoparticle size and growth quenching by Iodide anions. Copyright © 2015. Published by Elsevier Inc.

  19. Intrinsic Chirality Origination in Carbon Nanotubes.

    PubMed

    Pierce, Neal; Chen, Gugang; P Rajukumar, Lakshmy; Chou, Nam Hawn; Koh, Ai Leen; Sinclair, Robert; Maruyama, Shigeo; Terrones, Mauricio; Harutyunyan, Avetik R

    2017-10-24

    Elucidating the origin of carbon nanotube chirality is key for realizing their untapped potential. Currently, prevalent theories suggest that catalyst structure originates chirality via an epitaxial relationship. Here we studied chirality abundances of carbon nanotubes grown on floating liquid Ga droplets, which excludes the influence of catalyst features, and compared them with abundances grown on solid Ru nanoparticles. Results of growth on liquid droplets bolsters the intrinsic preference of carbon nuclei toward certain chiralities. Specifically, the abundance of the (11,1)/χ = 4.31° tube can reach up to 95% relative to (9,4)/χ = 17.48°, although they have exactly the same diameter, (9.156 Å). However, the comparative abundances for the pair, (19,3)/χ = 7.2° and (17,6)/χ = 14.5°, with bigger diameter, (16.405 Å), fluctuate depending on synthesis temperature. The abundances of the same pairs of tubes grown on floating solid polyhedral Ru nanoparticles show completely different trends. Analysis of abundances in relation to nucleation probability, represented by a product of the Zeldovich factor and the deviation interval of a growing nuclei from equilibrium critical size, explain the findings. We suggest that the chirality in the nanotube in general is a result of interplay between intrinsic preference of carbon cluster and induction by catalyst structure. This finding can help to build the comprehensive theory of nanotube growth and offers a prospect for chirality-preferential synthesis of carbon nanotubes by the exploitation of liquid catalyst droplets.

  20. Microstructure development in Kolmogorov, Johnson-Mehl, and Avrami nucleation and growth kinetics

    NASA Astrophysics Data System (ADS)

    Pineda, Eloi; Crespo, Daniel

    1999-08-01

    A statistical model with the ability to evaluate the microstructure developed in nucleation and growth kinetics is built in the framework of the Kolmogorov, Johnson-Mehl, and Avrami theory. A populational approach is used to compute the observed grain-size distribution. The impingement process which delays grain growth is analyzed, and the effective growth rate of each population is estimated considering the previous grain history. The proposed model is integrated for a wide range of nucleation and growth protocols, including constant nucleation, pre-existing nuclei, and intermittent nucleation with interface or diffusion-controlled grain growth. The results are compared with Monte Carlo simulations, giving quantitative agreement even in cases where previous models fail.

  1. Growth and laccase production kinetics of Trametes versicolor in a stirred tank reactor.

    PubMed

    Thiruchelvam, A T; Ramsay, Juliana A

    2007-03-01

    White rot fungi are a promising option to treat recalcitrant organic molecules, such as lignin, polycyclic aromatic hydrocarbons, and textile dyes, because of the lignin-modifying enzymes (LMEs) they secrete. Because knowledge of the kinetic parameters is important to better design and operate bioreactors to cultivate these fungi for degradation and/or to produce LME(s), these parameters were determined using Trametes versicolor ATCC 20869 (ATCC, American Type Culture Collection) in a magnetic stir bar reactor. A complete set of kinetic data has not been previously published for this culture. Higher than previously reported growth rates with high laccase production of up to 1,385 U l(-1) occurred during growth without [Formula: see text] or glucose limitation. The maximum specific growth rate averaged 0.94 +/- 0.23 day(-1), whereas the maximum specific substrate consumption rates for glucose and ammonium were 3.37 +/- 1.16 and 0.15 +/- 0.04 day(-1), respectively. The maximum specific oxygen consumption rate was 1.63 +/- 0.36 day(-1).

  2. 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.

  3. Interplay of bistable kinetics of gene expression during cellular growth

    NASA Astrophysics Data System (ADS)

    Zhdanov, Vladimir P.

    2009-02-01

    In cells, the bistable kinetics of gene expression can be observed on the level of (i) one gene with positive feedback between protein and mRNA production, (ii) two genes with negative mutual feedback between protein and mRNA production, or (iii) in more complex cases. We analyse the interplay of two genes of type (ii) governed by a gene of type (i) during cellular growth. In particular, using kinetic Monte Carlo simulations, we show that in the case where gene 1, operating in the bistable regime, regulates mutually inhibiting genes 2 and 3, also operating in the bistable regime, the latter genes may eventually be trapped either to the state with high transcriptional activity of gene 2 and low activity of gene 3 or to the state with high transcriptional activity of gene 3 and low activity of gene 2. The probability to get to one of these states depends on the values of the model parameters. If genes 2 and 3 are kinetically equivalent, the probability is equal to 0.5. Thus, our model illustrates how different intracellular states can be chosen at random with predetermined probabilities. This type of kinetics of gene expression may be behind complex processes occurring in cells, e.g., behind the choice of the fate by stem cells.

  4. Selective growth of palladium and titanium dioxide nanostructures inside carbon nanotube membranes.

    PubMed

    Hevia, Samuel; Homm, Pía; Cortes, Andrea; Núñez, Verónica; Contreras, Claudia; Vera, Jenniffer; Segura, Rodrigo

    2012-06-25

    Hybrid nanostructured arrays based on carbon nanotubes (CNT) and palladium or titanium dioxide materials have been synthesized using self-supported and silicon-supported anodized aluminum oxide (AAO) as nanoporous template. It is well demonstrated that carbon nanotubes can be grown using these membranes and hydrocarbon precursors that decompose at temperatures closer to 600°C without the use of a metal catalyst. In this process, carbonic fragments condensate to form stacked graphitic sheets, which adopt the shape of the pores, yielding from these moulds' multi-walled carbon nanotubes. After this process, the ends of the tubes remain open and accessible to other substances, whereas the outer walls are protected by the alumina. Taking advantage of this fact, we have performed the synthesis of palladium and titanium dioxide nanostructures selectively inside carbon nanotubes using these CNT-AAO membranes as nanoreactors.

  5. Selective growth of palladium and titanium dioxide nanostructures inside carbon nanotube membranes

    PubMed Central

    2012-01-01

    Hybrid nanostructured arrays based on carbon nanotubes (CNT) and palladium or titanium dioxide materials have been synthesized using self-supported and silicon-supported anodized aluminum oxide (AAO) as nanoporous template. It is well demonstrated that carbon nanotubes can be grown using these membranes and hydrocarbon precursors that decompose at temperatures closer to 600°C without the use of a metal catalyst. In this process, carbonic fragments condensate to form stacked graphitic sheets, which adopt the shape of the pores, yielding from these moulds' multi-walled carbon nanotubes. After this process, the ends of the tubes remain open and accessible to other substances, whereas the outer walls are protected by the alumina. Taking advantage of this fact, we have performed the synthesis of palladium and titanium dioxide nanostructures selectively inside carbon nanotubes using these CNT-AAO membranes as nanoreactors. PMID:22731888

  6. Selective growth of palladium and titanium dioxide nanostructures inside carbon nanotube membranes

    NASA Astrophysics Data System (ADS)

    Hevia, Samuel; Homm, Pía; Cortes, Andrea; Núñez, Verónica; Contreras, Claudia; Vera, Jenniffer; Segura, Rodrigo

    2012-06-01

    Hybrid nanostructured arrays based on carbon nanotubes (CNT) and palladium or titanium dioxide materials have been synthesized using self-supported and silicon-supported anodized aluminum oxide (AAO) as nanoporous template. It is well demonstrated that carbon nanotubes can be grown using these membranes and hydrocarbon precursors that decompose at temperatures closer to 600°C without the use of a metal catalyst. In this process, carbonic fragments condensate to form stacked graphitic sheets, which adopt the shape of the pores, yielding from these moulds' multi-walled carbon nanotubes. After this process, the ends of the tubes remain open and accessible to other substances, whereas the outer walls are protected by the alumina. Taking advantage of this fact, we have performed the synthesis of palladium and titanium dioxide nanostructures selectively inside carbon nanotubes using these CNT-AAO membranes as nanoreactors.

  7. Kinetics of growth and sugar consumption in yeasts.

    PubMed

    van Dijken, J P; Weusthuis, R A; Pronk, J T

    1993-01-01

    An overview is presented of the steady- and transient state kinetics of growth and formation of metabolic byproducts in yeasts. Saccharomyces cerevisiae is strongly inclined to perform alcoholic fermentation. Even under fully aerobic conditions, ethanol is produced by this yeast when sugars are present in excess. This so-called 'Crabtree effect' probably results from a multiplicity of factors, including the mode of sugar transport and the regulation of enzyme activities involved in respiration and alcoholic fermentation. The Crabtree effect in S. cerevisiae is not caused by an intrinsic inability to adjust its respiratory activity to high glycolytic fluxes. Under certain cultivation conditions, for example during growth in the presence of weak organic acids, very high respiration rates can be achieved by this yeast. S. cerevisiae is an exceptional yeast since, in contrast to most other species that are able to perform alcoholic fermentation, it can grow under strictly anaerobic conditions. 'Non-Saccharomyces' yeasts require a growth-limiting supply of oxygen (i.e. oxygen-limited growth conditions) to trigger alcoholic fermentation. However, complete absence of oxygen results in cessation of growth and therefore, ultimately, of alcoholic fermentation. Since it is very difficult to reproducibly achieve the right oxygen dosage in large-scale fermentations, non-Saccharomyces yeasts are therefore not suitable for large-scale alcoholic fermentation of sugar-containing waste streams. In these yeasts, alcoholic fermentation is also dependent on the type of sugar. For example, the facultatively fermentative yeast Candida utilis does not ferment maltose, not even under oxygen-limited growth conditions, although this disaccharide supports rapid oxidative growth.

  8. Simulation of carbon nanotube welding through Ar bombardment.

    PubMed

    Kucukkal, Mustafa U; Stuart, Steven J

    2017-04-01

    Single-walled carbon nanotubes show promise as nanoscale transistors for nanocomputing applications. This use will require appropriate methods for creating electrical connections between distinct nanotubes, analogous to welding of metallic wires at larger length scales, but methods for performing nanoscale chemical welding are not yet sufficiently understood. This study examines the effect of Ar bombardment on the junction of two crossed single-walled carbon nanotubes, to understand the value and limitations of this method for generating connections between nanotubes. A geometric criterion was used to assess the quality of the junctions formed, with the goal of identifying the most productive conditions for experimental ion bombardment. In particular, the effects of nanotube chirality, Ar impact kinetic energy, impact particle flux and fluence, and annealing temperature were considered. The most productive bombardment conditions, leading to the most crosslinking of the tubes with the smallest loss of graphitic (i.e., conductive) character, were found to be at relatively mild impact energies (100 eV), with low flux and high-temperature (3000 K) annealing. Particularly noteworthy for experimental application, a high junction quality is maintained for a relatively broad range of fluences, from 3 × 10 19  m -2 to at least 1 × 10 20  m -2 .

  9. Enhanced cold wall CVD reactor growth of horizontally aligned single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Mu, Wei; Kwak, Eun-Hye; Chen, Bingan; Huang, Shirong; Edwards, Michael; Fu, Yifeng; Jeppson, Kjell; Teo, Kenneth; Jeong, Goo-Hwan; Liu, Johan

    2016-05-01

    HASynthesis of horizontally-aligned single-walled carbon nanotubes (HA-SWCNTs) by chemical vapor deposition (CVD) directly on quartz seems very promising for the fabrication of future nanoelectronic devices. In comparison to hot-wall CVD, synthesis of HA-SWCNTs in a cold-wall CVD chamber not only means shorter heating, cooling and growth periods, but also prevents contamination of the chamber. However, since most synthesis of HA-SWCNTs is performed in hot-wall reactors, adapting this well-established process to a cold-wall chamber becomes extremely crucial. Here, in order to transfer the CVD growth technology from a hot-wall to a cold-wall chamber, a systematic investigation has been conducted to determine the influence of process parameters on the HA-SWCNT's growth. For two reasons, the cold-wall CVD chamber was upgraded with a top heater to complement the bottom substrate heater; the first reason to maintain a more uniform temperature profile during HA-SWCNTs growth, and the second reason to preheat the precursor gas flow before projecting it onto the catalyst. Our results show that the addition of a top heater had a significant effect on the synthesis. Characterization of the CNTs shows that the average density of HA-SWCNTs is around 1 - 2 tubes/ μm with high growth quality as shown by Raman analysis. [Figure not available: see fulltext.

  10. Boron-doped few-walled carbon nanotubes: novel synthesis and properties

    NASA Astrophysics Data System (ADS)

    Preston, Colin; Song, Da; Taillon, Josh; Cumings, John; Hu, Liangbing

    2016-11-01

    Few-walled carbon nanotubes offer a unique marriage of graphitic quality and robustness to ink-processing; however, doping procedures that may alter the band structure of these few-walled nanotubes are still lacking. This report introduces a novel solution-injected chemical vapor deposition growth process to fabricate the first boron-doped few-walled carbon nanotubes (B-FWNTs) reported in literature, which may have extensive applications in battery devices. A comprehensive characterization of the as-grown B-FWNTs confirms successful boron substitution in the graphitic lattice, and reveals varying growth parameters impact the structural properties of B-FWNT yield. An investigation into the optimal growth purification parameters and ink-making procedures was also conducted. This study introduces the first process technique to successfully grow intrinsically p-doped FWNTs, and provides the first investigation into the impact factors of the growth parameters, purification steps, and ink-making processes on the structural properties of the B-FWNTs and the electrical properties of the resulting spray-coated thin-film electrodes.

  11. Synthesis of hematite and maghemite nanotubes and study of their applications in neuroscience and drug delivery

    NASA Astrophysics Data System (ADS)

    Chen, Linfeng; Xie, Jining; Aatre, Kiran R.; Yancey, Justin; Chetan, Sahitya; Srivatsan, Malathi; Varadan, Vijay K.

    2011-04-01

    This report discusses our work on synthesis of hematite and maghemite nanotubes, analysis of their biocompatibility with pheochromocytoma cells (PC12 cells), and study of their applications in the culture of dorsal root ganglion (DRG) neurons and the delivery of ibuprofen sodium salt (ISS) drug model. Two methods, template-assisted thermal decomposition method and hydrothermal method, were used for synthesizing hematite nanotubes, and maghemite nanotubes were obtained from the synthesized hematite nanotubes by thermal treatment. The crystalline, morphology and magnetic properties of the hematite and maghemite nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM), respectively. The biocompatibility of the synthesized hematite nanotubes was confirmed by the survival and differentiation of PC12 cells in the presence of the hematite nanotubes coupled to nerve growth factor (NGF). To study the combined effects of the presence of magnetic nanotubes and external magnetic fields on neurite growth, laminin was coupled to hematite and maghemite nanotubes, and DRG neurons were cultured in the presence of the treated nanotubes with the application of external magnetic fields. It was found that neurons can better tolerate external magnetic fields when magnetic nanotubes were present. Close contacts between nanotubes and filopodia that were observed under SEM showed that the nanotubes and the growing neurites interacted readily. The drug loading and release capabilities of hematite nanotubes synthesized by hydrothermal method were tested by using ibuprofen sodium salt (ISS) as a drug model. Our experimental results indicate that hematite and maghemite nanotubes have good biocompatibility with neurons, could be used in regulating neurite growth, and are promising vehicles for drug delivery.

  12. Dynamic identification of growth and survival kinetic parameters of microorganisms in foods

    USDA-ARS?s Scientific Manuscript database

    Inverse analysis is a mathematical method used in predictive microbiology to determine the kinetic parameters of microbial growth and survival in foods. The traditional approach in inverse analysis relies on isothermal experiments that are time-consuming and labor-intensive, and errors are accumula...

  13. Improved carbon nanotube growth inside an anodic aluminum oxide template using microwave radiation

    NASA Astrophysics Data System (ADS)

    Dadras, Sedigheh; Faraji, Maryam

    2018-05-01

    In this study, we achieved superfast growth of carbon nanotubes (CNTs) in an anodic aluminum oxide (AAO) template by applying microwave (MW) radiation. This is a simple and direct approach for growing CNTs using a MW oven. The CNTs were synthesized using MW radiation at a frequency of 2.45 GHz and power was applied at various levels of 900, 600, and 450 W. We used graphite and ferrocene in equal portions as precursors. The optimum conditions for the growth of CNTs inside a MW oven were a time period of 5 s and power of 450 W. In order to grow uniform CNTs, an AAO template was applied with the CNTs synthesized under optimum conditions. The morphology of the synthesized CNTs was investigated by scanning electron microscopy analysis. The average diameters of the CNTs obtained without the template were 22-27 nm, whereas the diameters of the CNTs prepared inside the AAO template were about 4-6 nm.

  14. In Situ μGISAXS: II. Thaumatin Crystal Growth Kinetic

    PubMed Central

    Gebhardt, Ronald; Pechkova, Eugenia; Riekel, Christian; Nicolini, Claudio

    2010-01-01

    The formation of thaumatin crystals by Langmuir-Blodgett (LB) film nanotemplates was studied by the hanging-drop technique in a flow-through cell by synchrotron radiation micrograzing-incidence small-angle x-ray scattering. The kinetics of crystallization was measured directly on the interface of the LB film crystallization nanotemplate. The evolution of the micrograzing-incidence small-angle x-ray scattering patterns suggests that the increase in intensity in the Yoneda region is due to protein incorporation into the LB film. The intensity variation suggests several steps, which were modeled by system dynamics based on first-order differential equations. The kinetic data can be described by two processes that take place on the LB film, a first, fast, process, attributed to the crystal growth and its detachment from the LB film, and a second, slower process, attributed to an unordered association and conversion of protein on the LB film. PMID:20713011

  15. Investigations of the kinetics of surfactant-assisted growth of cobalt/copper multilayers

    NASA Astrophysics Data System (ADS)

    Peterson, Brennan Lovelace

    Surfactants---a term given to a broad family of surface additives used in thin film growth---provide a potentially useful tool for the deposition engineer. A long history of work on the field has produced a sometimes conflicting view of what surfactants do, and while their efficacy in improving magnetic films is well established, the attendant structural changes remain unclear. Early work on surfactant-assisted growth was generally confined to deposition at near equilibrium conditions: high temperature and very slow deposition rates on very smooth (single crystal) substrates. In the case of low temperature sputter deposition, the kinetic phenomena differ greatly from the near-equilibrium case: high rate, more interlayer diffusive pathways, high grain boundary density, and few well defined atomic steps. There are two major ideas which underlie and explain the use of surfactants. First, they are used to alter growth kinetics of a single material by changing the diffusion barriers on the growing surface. Second, surfactants alter the initial nucleation parameters in heteroepitaxial growth, which is often explained with reference to changes in the surface energy, gamma. Changes to these parameters result, in turn, to variations of the roughness and conformality of thin films grown with the assistance of surfactants. Finally, the roughness and conformality are critical for determining the performance of modern thin film magnetic sensors. As surfactants offer a way to alter the nucleation and growth kinetics, they offer tremendous potential benefits. However, before surfactants are trustworthy deposition tool, a better understanding of their structural effects and underlying surface energy and kinetic changes is necessary. In order to investigate these phenomena, DC magnetron sputtered [Co/Cu] multilayers were deposited on Si/SiO2 substrates using O2 , Ag, Pb, and In as surfactants. Oxygen was introduced during growth at partial pressures ranging from 10-9 to 10-6 Torr

  16. Film growth kinetics and electric field patterning during electrospray deposition of block copolymer thin films

    NASA Astrophysics Data System (ADS)

    Toth, Kristof; Hu, Hanqiong; Choo, Youngwoo; Loewenberg, Michael; Osuji, Chinedum

    The delivery of sub-micron droplets of dilute polymer solutions to a heated substrate by electrospray deposition (ESD) enables precisely controlled and continuous growth of block copolymer (BCP) thin films. Here we explore patterned deposition of BCP films by spatially varying the electric field at the substrate using an underlying charged grid, as well as film growth kinetics. Numerical analysis was performed to examine pattern fidelity by considering the trajectories of charged droplets during flight through imposed periodic field variations in the vicinity of the substrate. Our work uncovered an unexpected modality for improving the resolution of the patterning process via stronger field focusing through the use of a second oppositely charged grid beneath a primary focusing array, with an increase in highly localized droplet deposition on the intersecting nodes of the grid. Substrate coverage kinetics are considered for homopolymer deposition in the context of simple kinetic models incorporating temperature and molecular weight dependence of diffusivity. By contrast, film coverage kinetics for block copolymer depositions are additionally convoluted with preferential wetting and thickness-periodicity commensurability effects. NSF GRFP.

  17. Kinetics of low pressure CVD growth of SiO2 on InP and Si

    NASA Technical Reports Server (NTRS)

    Iyer, R.; Lile, D. L.

    1988-01-01

    The kinetics of low pressure CVD growth of SiO2 from SiH4 and O2 has been investigated for the case of an indirect (remote) plasma process. Homogeneous (gas phase) and heterogeneous operating ranges have been experimentally identified. The process was shown to be consistent within the heterogeneous surface-reaction dominated range of operation. A kinetic rate equation is given for growth at 14 W RF power input and 400 mtorr total pressure on both InP and Si substrates. The process exhibits an activation energy of 8.4 + or - 0.6 kcal/mol.

  18. Effect of catalyst film thickness on carbon nanotube growth by selective area chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wei, Y. Y.; Eres, Gyula; Merkulov, V. I.; Lowndes, D. H.

    2001-03-01

    The correlation between prepatterned catalyst film thickness and carbon nanotube (CNT) growth by selective area chemical vapor deposition (CVD) was studied using Fe and Ni as catalyst. To eliminate sample-to-sample variations and create a growth environment in which the film thickness is the sole variable, samples with continuously changing catalyst film thickness from 0 to 60 nm were fabricated by electron-gun evaporation. Using thermal CVD CNTs preferentially grow as a dense mat on the thin regions of the catalyst film. Moreover, beyond a certain critical film thickness no tubes were observed. The critical film thickness for CNT growth was found to increase with substrate temperature. There appears to be no strong correlation between the film thickness and the diameter of the tubes. In contrast, using plasma enhanced CVD with Ni as catalyst, vertically oriented CNTs grow in the entire range of catalyst film thickness. The diameter of these CNTs shows a strong correlation with the catalyst film thickness. The significance of these experimental trends is discussed within the framework of the diffusion model for CNT growth.

  19. Growth Kinetics of Extremely Halophilic Archaea (Family Halobacteriaceae) as Revealed by Arrhenius Plots

    PubMed Central

    Robinson, Jessie L.; Pyzyna, Brandy; Atrasz, Rachelle G.; Henderson, Christine A.; Morrill, Kira L.; Burd, Anna Mae; DeSoucy, Erik; Fogleman, Rex E.; Naylor, John B.; Steele, Sarah M.; Elliott, Dawn R.; Leyva, Kathryn J.; Shand, Richard F.

    2005-01-01

    Members of the family Halobacteriaceae in the domain Archaea are obligate extreme halophiles. They occupy a variety of hypersaline environments, and their cellular biochemistry functions in a nearly saturated salty milieu. Despite extensive study, a detailed analysis of their growth kinetics is missing. To remedy this, Arrhenius plots for 14 type species of the family were generated. These organisms had maximum growth temperatures ranging from 49 to 58°C. Nine of the organisms exhibited a single temperature optimum, while five grew optimally at more than one temperature. Generation times at these optimal temperatures ranged from 1.5 h (Haloterrigena turkmenica) to 3.0 h (Haloarcula vallismortis and Halorubrum saccharovorum). All shared an inflection point at 31 ± 4°C, and the temperature characteristics for 12 of the 14 type species were nearly parallel. The other two species (Natronomonas pharaonis and Natronorubrum bangense) had significantly different temperature characteristics, suggesting that the physiology of these strains is different. In addition, these data show that the type species for the family Halobacteriaceae share similar growth kinetics and are capable of much faster growth at higher temperatures than those previously reported. PMID:15659670

  20. Contactless Stimulation and Control of Biomimetic Nanotubes by Calcium Ion Gradients.

    PubMed

    Kirejev, Vladimir; Ali Doosti, Baharan; Shaali, Mehrnaz; Jeffries, Gavin D M; Lobovkina, Tatsiana

    2018-04-17

    Membrane tubular structures are important communication pathways between cells and cellular compartments. Studying these structures in their native environment is challenging, due to the complexity of membranes and varying chemical conditions within and outside of the cells. This work demonstrates that a calcium ion gradient, applied to a synthetic lipid nanotube, triggers lipid flow directed toward the application site, resulting in the formation of a bulge aggregate. This bulge can be translated in a contactless manner by moving a calcium ion source along the lipid nanotube. Furthermore, entrapment of polystyrene nanobeads within the bulge does not tamper the bulge movement and allows transporting of the nanoparticle cargo along the lipid nanotube. In addition to the synthetic lipid nanotubes, the response of cell plasma membrane tethers to local calcium ion stimulation is investigated. The directed membrane transport in these tethers is observed, but with slower kinetics in comparison to the synthetic lipid nanotubes. The findings of this work demonstrate a novel and contactless mode of transport in lipid nanotubes, guided by local exposure to calcium ions. The observed lipid nanotube behavior can advance the current understanding of the cell membrane tubular structures, which are constantly reshaped during dynamic cellular processes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Hydrothermal Atomic Force Microscopy Investigation of Barite Growth: Role of Spectator Ions in Elementary Step Edge Growth Kinetics and Hillock Morphology [Supporting Information Only

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jindra, Sarah A.; Bertagni, Angela L.; Bracco, Jacquelyn N.

    Here, to better understand the role of spectator ions in barite growth, the kinetics of step edge growth on barite (001) surfaces were studied under various salt solutions. Hydrothermal atomic force microscopy (HAFM) was used to investigate the effect of background electrolytes (NaCl, NaBr, and NaNO 3) as a function of saturation index and ionic strength ( I) on barite growth sourced at dislocations at 108 °C. Results demonstrate that hillock morphology is affected by I, as well as type of anion, where the prevalence of steps aligned on the [010] direction is highest under Cl –. There is amore » modest increase in kinetic coefficient of 55–130% with a 10-fold increase in I for each salt. In comparing the kinetic coefficients of the salts at low ionic strength (0.01 M), there is a moderate difference, suggesting that the anion may play a role in barium attachment.« less

  2. Spontaneous and controlled-diameter synthesis of single-walled and few-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Inoue, Shuhei; Lojindarat, Supanat; Kawamoto, Takahiro; Matsumura, Yukihiko; Charinpanitkul, Tawatchai

    2018-05-01

    In this study, we explored the spontaneous and controlled-diameter growth of carbon nanotubes. We evaluated the effects of catalyst density, reduction time, and a number of catalyst coating on the substrate (for multi-walled carbon nanotubes) on the diameter of single-walled carbon nanotubes and the number of layers in few-walled carbon nanotubes. Increasing the catalyst density and reduction time increased the diameters of the carbon nanotubes, with the average diameter increasing from 1.05 nm to 1.86 nm for single-walled carbon nanotubes. Finally, we succeeded in synthesizing a significant double-walled carbon nanotube population of 24%.

  3. Carbon Nanotube Microarrays Grown on Nanoflake Substrates

    NASA Technical Reports Server (NTRS)

    Schmidt, Howard K.; Hauge, Robert H.; Pint, Cary; Pheasant, Sean

    2013-01-01

    This innovation consists of a new composition of matter where single-walled carbon nanotubes (SWNTs) are grown in aligned arrays from nanostructured flakes that are coated in Fe catalyst. This method of growth of aligned SWNTs, which can yield well over 400 percent SWNT mass per unit substrate mass, exceeds current yields for entangled SWNT growth. In addition, processing can be performed with minimal wet etching treatments, leaving aligned SWNTs with superior properties over those that exist in entangled mats. The alignment of the nanotubes is similar to that achieved in vertically aligned nanotubes, which are called "carpets. " Because these flakes are grown in a state where they are airborne in a reactor, these flakes, after growing SWNTs, are termed "flying carpets. " These flakes are created in a roll-to-roll evaporator system, where three subsequent evaporations are performed on a 100-ft (approx. =30-m) roll of Mylar. The first layer is composed of a water-soluble "release layer, " which can be a material such as NaCl. After depositing NaCl, the second layer involves 40 nm of supporting layer material . either Al2O3 or MgO. The thickness of the layer can be tuned to synthesize flakes that are larger or smaller than those obtained with a 40-nm deposition. Finally, the third layer consists of a thin Fe catalyst layer with a thickness of 0.5 nm. The thickness of this layer ultimately determines the diameter of SWNT growth, and a layer that is too thick will result in the growth of multiwalled carbon nanotubes instead of single-wall nanotubes. However, between a thickness of 0.5 nm to 1 nm, single-walled carbon nanotubes are known to be the primary constituent. After this three-layer deposition process, the Mylar is rolled through a bath of water, which allows catalyst-coated flakes to detach from the Mylar. The flakes are then collected and dried. The method described here for making such flakes is analogous to that which is used to make birefringent ink that is

  4. Kinetics of Si and Ge nanowires growth through electron beam evaporation

    PubMed Central

    2011-01-01

    Si and Ge have the same crystalline structure, and although Si-Au and Ge-Au binary alloys are thermodynamically similar (same phase diagram, with the eutectic temperature of about 360°C), in this study, it is proved that Si and Ge nanowires (NWs) growth by electron beam evaporation occurs in very different temperature ranges and fluence regimes. In particular, it is demonstrated that Ge growth occurs just above the eutectic temperature, while Si NWs growth occurs at temperature higher than the eutectic temperature, at about 450°C. Moreover, Si NWs growth requires a higher evaporated fluence before the NWs become to be visible. These differences arise in the different kinetics behaviors of these systems. The authors investigate the microscopic growth mechanisms elucidating the contribution of the adatoms diffusion as a function of the evaporated atoms direct impingement, demonstrating that adatoms play a key role in physical vapor deposition (PVD) NWs growth. The concept of incubation fluence, which is necessary for an interpretation of NWs growth in PVD growth conditions, is highlighted. PMID:21711696

  5. Kinetics of Si and Ge nanowires growth through electron beam evaporation.

    PubMed

    Artoni, Pietro; Pecora, Emanuele Francesco; Irrera, Alessia; Priolo, Francesco

    2011-02-21

    Si and Ge have the same crystalline structure, and although Si-Au and Ge-Au binary alloys are thermodynamically similar (same phase diagram, with the eutectic temperature of about 360°C), in this study, it is proved that Si and Ge nanowires (NWs) growth by electron beam evaporation occurs in very different temperature ranges and fluence regimes. In particular, it is demonstrated that Ge growth occurs just above the eutectic temperature, while Si NWs growth occurs at temperature higher than the eutectic temperature, at about 450°C. Moreover, Si NWs growth requires a higher evaporated fluence before the NWs become to be visible. These differences arise in the different kinetics behaviors of these systems. The authors investigate the microscopic growth mechanisms elucidating the contribution of the adatoms diffusion as a function of the evaporated atoms direct impingement, demonstrating that adatoms play a key role in physical vapor deposition (PVD) NWs growth. The concept of incubation fluence, which is necessary for an interpretation of NWs growth in PVD growth conditions, is highlighted.

  6. Nucleation and growth in cluster dynamics: A quantitative test of the classical kinetic approach

    NASA Astrophysics Data System (ADS)

    Gránásy, László; James, Peter F.

    2000-12-01

    Nucleation and size dependent growth of nanometer sized crystalline particles in glassy media have been studied by numerically solving the Turnbull-Fisher master equations that describe the time evolution of cluster population. Time dependencies of the formation rate and number density are determined for large clusters (built of up to 2×105 formula units, containing 1.8×106 atoms). We demonstrate that the formation rate and number density of such clusters are well approximated by Shneidman's asymptotically exact analytical solution. A quantitative test of the kinetic Turnbull-Fisher model has been performed: Evaluating the kinetic coefficients and interfacial parameters from the transient time and steady-state nucleation rates measured on six stoichiometric oxide glass compositions (lithium-disilicate, barium-disilicate, lithium-diborate, wollastonite, 1:2:3 and 2:1:3 soda-lime-silica glass compositions), we calculated the macroscopic growth rates and compared with experiments. For wollastonite, lithium-diborate and the 1:2:3 soda-lime-silica glass, differences of 2 to 4 orders of magnitude have been observed between theory and experiment. This inadequacy of the microscopic kinetic parameters in describing macroscopic growth cannot be explained by either the curvature effect on the interfacial free energy or the self-consistency correction for the cluster free energy. The origin of the discrepancy is discussed.

  7. Analytical solution of Luedeking-Piret equation for a batch fermentation obeying Monod growth kinetics.

    PubMed

    Garnier, Alain; Gaillet, Bruno

    2015-12-01

    Not so many fermentation mathematical models allow analytical solutions of batch process dynamics. The most widely used is the combination of the logistic microbial growth kinetics with Luedeking-Piret bioproduct synthesis relation. However, the logistic equation is principally based on formalistic similarities and only fits a limited range of fermentation types. In this article, we have developed an analytical solution for the combination of Monod growth kinetics with Luedeking-Piret relation, which can be identified by linear regression and used to simulate batch fermentation evolution. Two classical examples are used to show the quality of fit and the simplicity of the method proposed. A solution for the combination of Haldane substrate-limited growth model combined with Luedeking-Piret relation is also provided. These models could prove useful for the analysis of fermentation data in industry as well as academia. © 2015 Wiley Periodicals, Inc.

  8. Ultrafast carrier dynamics of titanic acid nanotubes investigated by transient absorption spectroscopy.

    PubMed

    Wang, Li; Zhao, Hui; Pan, Lin Yun; Weng, Yu Xiang; Nakato, Yoshihiro; Tamai, Naoto

    2010-12-01

    Carrier dynamics of titanic acid nanotubes (phase of H2Ti2O5.H2O) deposited on a quartz plate was examined by visible/near-IR transient absorption spectroscopy with an ultraviolet excitation. The carrier dynamics of titanic acid nanotubes follows the fast trapping process which attributed to the intrinsic tubular structure, the relaxation of shallow trapped carriers and the recombination as a second-order kinetic process. Transient absorption of titanic acid nanotubes was dominated by the absorption of surface-trapped holes in visible region around 500 nm, which was proved by the faster decay dynamics in the presence of polyvinyl alcohol as a hole-scavenger. However, the slow relaxation of free carriers was much more pronounced in the TiO2 single crystals, as compared with the transient absorption spectra of titanic acid nanotubes under the similar excitation.

  9. Blowing Carbon Nanotubes to Carbon Nanobulbs

    NASA Astrophysics Data System (ADS)

    Su, D. S.; Zhu, Z. P.; Lu, Y.; Schlögl, R.; Weinberg, G.; Liu, Z. Y.

    2004-09-01

    We report the blowing of multi-walled carbon nanotubes into carbon nanobulbs. This is realized in a unique tube growth environment generated by explosive decomposition of picric acid mixed with nickel formate. The carbon spherical bulbs are characterized by large dimensions (up to 900 nm), thin walls (around 10 nm), and fully hollow cores. The walls are in graphitic structure of sp2 hybridized carbons. Bulb-tube assemblies are found as intermediate derivatives of blowing. A joint action of the filled high-pressure gases and the structural defects in the carbon nanotubes is responsible to the formation of the carbon nanobulbs. Our finding may indicate the possibility to engineer the carbon nanotubes to the designed nanostructures.

  10. 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.

  11. Water-Assisted Highly Efficient Synthesis of Impurity-Free Single-Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Hata, Kenji; Futaba, Don N.; Mizuno, Kohei; Namai, Tatsunori; Yumura, Motoo; Iijima, Sumio

    2004-11-01

    We demonstrate the efficient chemical vapor deposition synthesis of single-walled carbon nanotubes where the activity and lifetime of the catalysts are enhanced by water. Water-stimulated enhanced catalytic activity results in massive growth of superdense and vertically aligned nanotube forests with heights up to 2.5 millimeters that can be easily separated from the catalysts, providing nanotube material with carbon purity above 99.98%. Moreover, patterned, highly organized intrinsic nanotube structures were successfully fabricated. The water-assisted synthesis method addresses many critical problems that currently plague carbon nanotube synthesis.

  12. Surface Stability and Growth Kinetics of Compound Semiconductors: An Ab Initio-Based Approach

    PubMed Central

    Kangawa, Yoshihiro; Akiyama, Toru; Ito, Tomonori; Shiraishi, Kenji; Nakayama, Takashi

    2013-01-01

    We review the surface stability and growth kinetics of III-V and III-nitride semiconductors. The theoretical approach used in these studies is based on ab initio calculations and includes gas-phase free energy. With this method, we can investigate the influence of growth conditions, such as partial pressure and temperature, on the surface stability and growth kinetics. First, we examine the feasibility of this approach by comparing calculated surface phase diagrams of GaAs(001) with experimental results. In addition, the Ga diffusion length on GaAs(001) during molecular beam epitaxy is discussed. Next, this approach is systematically applied to the reconstruction, adsorption and incorporation on various nitride semiconductor surfaces. The calculated results for nitride semiconductor surface reconstructions with polar, nonpolar, and semipolar orientations suggest that adlayer reconstructions generally appear on the polar and the semipolar surfaces. However, the stable ideal surface without adsorption is found on the nonpolar surfaces because the ideal surface satisfies the electron counting rule. Finally, the stability of hydrogen and the incorporation mechanisms of Mg and C during metalorganic vapor phase epitaxy are discussed. PMID:28811438

  13. Microstructural evolution and grain growth kinetics of GZ31 magnesium alloy

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Roostaei, M., E-mail: miladroustaei68@ut.ac.ir

    2016-08-15

    Grain growth behavior of Mg–3Gd–1Zn (GZ31) magnesium alloy was studied in a wide range of annealing time and temperature to clarify the kinetics of grain growth, microstructural evolution and related metallurgical phenomena. This material exhibited typical normal grain growth mode under annealing conditions with annealing temperature of lower than 300 °C and soaking time of lower than 240 min. However, the abnormality in grain growth was also evident at annealing temperature of 400 °C and 500 °C. The dependence of abnormal grain growth (AGG) at mentioned annealing temperatures upon microstructural features such as dispersed precipitates, which were rich in Znmore » and Gd, was investigated by optical micrographs, X-ray diffraction patterns, scanning electron microscopy images, and energy dispersive X-ray analysis spectra. The bimodality in grain-size distribution histograms also signified the occurrence of AGG. Based on the experimental data on grain growth obtained by annealing treatments, the grain growth exponent and the activation energy were also figured out.« less

  14. Inactivation of Bacillus Anthracis Spores Using Carbon Nanotubes

    DTIC Science & Technology

    2014-10-30

    S1793984412300129 Marquita Lilly, Liju Yang, Kamal Aferchich. Effect of Single-walled Carbon Nanotubes on Bacillus Anthracis Cell Growth, Sporulation ...addition,  SWNTs  treatment  did  not  induce  sporulation  of B. anthracis.  [Aferichich, et al. 2012]. 2)  SWNTs  in  combination with oxidizing agents...8. Kamal Aferchich, Marquita Lilly, Liju Yang*. 2012. Effect of Single‐walled Carbon Nanotubes on  Bacillus Anthracis Cell Growth,  Sporulation , and

  15. Batch growth kinetic studies of locally isolated cyanide-degrading Serratia marcescens strain AQ07.

    PubMed

    Karamba, Kabiru Ibrahim; Ahmad, Siti Aqlima; Zulkharnain, Azham; Yasid, Nur Adeela; Ibrahim, Salihu; Shukor, Mohd Yunus

    2018-01-01

    The evaluation of degradation and growth kinetics of Serratia marcescens strain AQ07 was carried out using three half-order models at all the initial concentrations of cyanide with the values of regression exceeding 0.97. The presence of varying cyanide concentrations reveals that the growth and degradation of bacteria were affected by the increase in cyanide concentration with a total halt at 700 ppm KCN after 72 h incubation. In this study, specific growth and degradation rates were found to trail the substrate inhibition kinetics. These two rates fitted well to the kinetic models of Teissier, Luong, Aiba and Heldane, while the performance of Monod model was found to be unsatisfactory. These models were used to clarify the substrate inhibition on the bacteria growth. The analyses of these models have shown that Luong model has fitted the experimental data with the highest coefficient of determination ( R 2 ) value of 0.9794 and 0.9582 with the lowest root mean square error (RMSE) value of 0.000204 and 0.001, respectively, for the specific rate of degradation and growth. It is the only model that illustrates the maximum substrate concentration ( S m ) of 713.4 and empirical constant ( n ) of 1.516. Tessier and Aiba fitted the experimental data with a R 2 value of 0.8002 and 0.7661 with low RMSE of 0.0006, respectively, for specific biodegradation rate, while having a R 2 value of 0.9 and RMSE of 0.001, respectively, for specific growth rate. Haldane has the lowest R 2 value of 0.67 and 0.78 for specific biodegradation and growth rate with RMSE of 0.0006 and 0.002, respectively. This indicates the level of the bacteria stability in varying concentrations of cyanide and the maximum cyanide concentration it can tolerate within a specific time period. The biokinetic constant predicted from this model demonstrates a good ability of the locally isolated bacteria in cyanide remediation in industrial effluents.

  16. Electrical device fabrication from nanotube formations

    DOEpatents

    Nicholas, Nolan Walker; Kittrell, W. Carter; Kim, Myung Jong; Schmidt, Howard K.

    2013-03-12

    A method for forming nanotube electrical devices, arrays of nanotube electrical devices, and device structures and arrays of device structures formed by the methods. Various methods of the present invention allow creation of semiconducting and/or conducting devices from readily grown SWNT carpets rather than requiring the preparation of a patterned growth channel and takes advantage of the self-controlling nature of these carpet heights to ensure a known and controlled channel length for reliable electronic properties as compared to the prior methods.

  17. Kinetics of substrate utilization and bacterial growth of crude oil degraded by Pseudomonas aeruginosa.

    PubMed

    Talaiekhozani, Amirreza; Jafarzadeh, Nematollah; Fulazzaky, Mohamad Ali; Talaie, Mohammad Reza; Beheshti, Masoud

    2015-01-01

    Pollution associated with crude oil (CO) extraction degrades the quality of waters, threatens drinking water sources and may ham air quality. The systems biology approach aims at learning the kinetics of substrate utilization and bacterial growth for a biological process for which very limited knowledge is available. This study uses the Pseudomonas aeruginosa to degrade CO and determines the kinetic parameters of substrate utilization and bacterial growth modeled from a completely mixed batch reactor. The ability of Pseudomonas aeruginosa can remove 91 % of the total petroleum hydrocarbons and 83 % of the aromatic compounds from oily environment. The value k of 9.31 g of substrate g(-1) of microorganism d(-1) could be far higher than the value k obtained for petrochemical wastewater treatment and that for municipal wastewater treatment. The production of new cells of using CO as the sole carbon and energy source can exceed 2(3) of the existing cells per day. The kinetic parameters are verified to contribute to improving the biological removal of CO from oily environment.

  18. Carbon Nanotubes Filled with Different Ferromagnetic Alloys Affect the Growth and Development of Rice Seedlings by Changing the C:N Ratio and Plant Hormones Concentrations.

    PubMed

    Hao, Yi; Yu, Feifan; Lv, Ruitao; Ma, Chuanxin; Zhang, Zetian; Rui, Yukui; Liu, Liming; Cao, Weidong; Xing, Baoshan

    2016-01-01

    The aim of this study was to investigate the phytotoxicity of thin-walled carbon nanotubes (CNTs) to rice (Oryza sativa L.) seedlings. Three different CNTs, including hollow multi-walled carbon nanotubes (MWCNTs), Fe-filled carbon nanotubes (Fe-CNTs), and Fe-Co-filled carbon nanotubes (FeCo-CNTs), were evaluated. The CNTs significantly inhibited rice growth by decreasing the concentrations of endogenous plant hormones. The carbon to nitrogen ratio (C:N ratio) significantly increased in rice roots after treatments with CNTs, and all three types of CNTs had the same effects on the C:N ratio. Interestingly, the increase in the C:N ratio in roots was largely because of decreased N content, indicating that the CNTs significantly decreased N assimilation. Analyses of the Fe and Co contents in plant tissues, transmission electron microscope (TEM) observations and energy dispersive X-ray spectroscopy (EDS) analysis proved that the CNTs could penetrate the cell wall and the cell membrane, and then enter the root cells. According to the author's knowledge, this is the first time to study the relationship between carbon nanotubes and carbon nitrogen ratio and plant hormones.

  19. Carbon Nanotubes Filled with Different Ferromagnetic Alloys Affect the Growth and Development of Rice Seedlings by Changing the C:N Ratio and Plant Hormones Concentrations

    PubMed Central

    Lv, Ruitao; Ma, Chuanxin; Zhang, Zetian; Rui, Yukui; Liu, Liming; Cao, Weidong; Xing, Baoshan

    2016-01-01

    The aim of this study was to investigate the phytotoxicity of thin-walled carbon nanotubes (CNTs) to rice (Oryza sativa L.) seedlings. Three different CNTs, including hollow multi-walled carbon nanotubes (MWCNTs), Fe-filled carbon nanotubes (Fe-CNTs), and Fe-Co-filled carbon nanotubes (FeCo-CNTs), were evaluated. The CNTs significantly inhibited rice growth by decreasing the concentrations of endogenous plant hormones. The carbon to nitrogen ratio (C:N ratio) significantly increased in rice roots after treatments with CNTs, and all three types of CNTs had the same effects on the C:N ratio. Interestingly, the increase in the C:N ratio in roots was largely because of decreased N content, indicating that the CNTs significantly decreased N assimilation. Analyses of the Fe and Co contents in plant tissues, transmission electron microscope (TEM) observations and energy dispersive X-ray spectroscopy (EDS) analysis proved that the CNTs could penetrate the cell wall and the cell membrane, and then enter the root cells. According to the author's knowledge, this is the first time to study the relationship between carbon nanotubes and carbon nitrogen ratio and plant hormones. PMID:27284692

  20. Surface-restrained growth of vertically aligned carbon nanotube arrays with excellent thermal transport performance.

    PubMed

    Ping, Linquan; Hou, Peng-Xiang; Liu, Chang; Li, Jincheng; Zhao, Yang; Zhang, Feng; Ma, Chaoqun; Tai, Kaiping; Cong, Hongtao; Cheng, Hui-Ming

    2017-06-22

    A vertically aligned carbon nanotube (VACNT) array is a promising candidate for a high-performance thermal interface material in high-power microprocessors due to its excellent thermal transport property. However, its rough and entangled free tips always cause poor interfacial contact, which results in serious contact resistance dominating the total thermal resistance. Here, we employed a thin carbon cover to restrain the disorderly growth of the free tips of a VACNT array. As a result, all the free tips are seamlessly connected by this thin carbon cover and the top surface of the array is smoothed. This unique structure guarantees the participation of all the carbon nanotubes in the array in the heat transport. Consequently the VACNT array grown on a Cu substrate shows a record low thermal resistance of 0.8 mm 2 K W -1 including the two-sided contact resistances, which is 4 times lower than the best result previously reported. Remarkably, the VACNT array can be easily peeled away from the Cu substrate and act as a thermal pad with excellent flexibility, adhesive ability and heat transport capability. As a result the CNT array with a thin carbon cover shows great potential for use as a high-performance flexible thermal interface material.

  1. Electrical properties of 0.4 cm long single walled nanotubes

    NASA Astrophysics Data System (ADS)

    Yu, Zhen

    2005-03-01

    Centimeter scale aligned carbon nanotube arrays are grown from nanoparticle/metal catalyst pads[1]. We find the nanotubes grow both with and ``against the wind.'' A metal underlayer provides in-situ electrical contact to these long nanotubes with no post growth processing needed. Using the electrically contacted nanotubes, we study electrical transport of 0.4 cm long nanotubes[2]. Using this data, we are able to determine the resistance of a nanotube as a function of length quantitatively, since the contact resistance is negligible in these long nanotubes. The source drain I-V curves are quantitatively described by a classical, diffusive model. Our measurements show that the outstanding transport properties of nanotubes can be extended to the cm scale and open the door to large scale integrated nanotube circuits with macroscopic dimensions. These are the longest electrically contacted single walled nanotubes measured to date. [1] Zhen Yu, Shengdong Li, Peter J. Burke, ``Synthesis of Aligned Arrays of Millimeter Long, Straight Single-Walled Carbon Nanotubes,'' Chemistry of Materials, 16(18), 3414-3416 (2004). [2] Shengdong Li, Zhen Yu, Christopher Rutherglen, Peter J. Burke, ``Electrical properties of 0.4 cm long single-walled carbon nanotubes'' Nano Letters, 4(10), 2003-2007 (2004).

  2. Effects of film growth kinetics on grain coarsening and grain shape.

    PubMed

    Reis, F D A Aarão

    2017-04-01

    We study models of grain nucleation and coarsening during the deposition of a thin film using numerical simulations and scaling approaches. The incorporation of new particles in the film is determined by lattice growth models in three different universality classes, with no effect of the grain structure. The first model of grain coarsening is similar to that proposed by Saito and Omura [Phys. Rev. E 84, 021601 (2011)PLEEE81539-375510.1103/PhysRevE.84.021601], in which nucleation occurs only at the substrate, and the grain boundary evolution at the film surface is determined by a probabilistic competition of neighboring grains. The surface grain density has a power-law decay, with an exponent related to the dynamical exponent of the underlying growth kinetics, and the average radius of gyration scales with the film thickness with the same exponent. This model is extended by allowing nucleation of new grains during the deposition, with constant but small rates. The surface grain density crosses over from the initial power law decay to a saturation; at the crossover, the time, grain mass, and surface grain density are estimated as a function of the nucleation rate. The distributions of grain mass, height, and radius of gyration show remarkable power law decays, similar to other systems with coarsening and particle injection, with exponents also related to the dynamical exponent. The scaling of the radius of gyration with the height h relative to the base of the grain show clearly different exponents in growth dominated by surface tension and growth dominated by surface diffusion; thus it may be interesting for investigating the effects of kinetic roughening on grain morphology. In growth dominated by surface diffusion, the increase of grain size with temperature is observed.

  3. Inhibition of DNA nanotube-conjugated mTOR siRNA on the growth of pulmonary arterial smooth muscle cells.

    PubMed

    You, Zaichun; Qian, Hang; Wang, Changzheng; He, Binfeng; Yan, Jiawei; Mao, Chengde; Wang, Guansong

    2015-12-01

    Here we provide raw and processed data and methods behind mTOR siRNA loaded DNA nanotubes (siRNA-DNA-NTs) in the growth of pulmonary arterial smooth muscle cells (PASMCs) under both normoxic and hypoxic condition, and also related to (You et al., Biomaterials, 2015, 67:137-150, [1]). The MTT analysis, Semi-quantitative RT-PCR data presented here were used to probe cytotoxicity of mTOR siRNA-DNA-NT complex in its TAE-Mg(2+) buffer. siRNA-DNA-NTs have a lower cytotoxicity and higher transfection efficiency and can, based on inhibition of mTOR expression, decrease PASMCs growth both hypoxic and normal condition.

  4. Dynamic DNA-controlled "stop-and-go" assembly of well-defined protein domains on RNA-scaffolded TMV-like nanotubes.

    PubMed

    Schneider, Angela; Eber, Fabian J; Wenz, Nana L; Altintoprak, Klara; Jeske, Holger; Eiben, Sabine; Wege, Christina

    2016-12-01

    A DNA-based approach allows external control over the self-assembly process of tobacco mosaic virus (TMV)-like ribonucleoprotein nanotubes: their growth from viral coat protein (CP) subunits on five distinct RNA scaffolds containing the TMV origin of assembly (OAs) could be temporarily blocked by a stopper DNA oligomer hybridized downstream (3') of the OAs. At two upstream (5') sites tested, simple hybridization was not sufficient for stable stalling, which correlates with previous findings on a non-symmetric assembly of TMV. The growth of DNA-arrested particles could be restarted efficiently by displacement of the stopper via its toehold by using a release DNA oligomer, even after storage for twelve days. This novel strategy for growing proteinaceous tubes under tight kinetic and spatial control combines RNA guidance and its site-specific but reversible interruption by DNA blocking elements. As three of the RNA scaffolds contained long heterologous non-TMV sequence portions that included the stopping sites, this method is applicable to all RNAs amenable to TMV CP encapsidation, albeit with variable efficiency most likely depending on the scaffolds' secondary structures. The use of two distinct, selectively addressable CP variants during the serial assembly stages finally enabled an externally configured fabrication of nanotubes with highly defined subdomains. The "stop-and-go" strategy thus might pave the way towards production routines of TMV-like particles with variable aspect ratios from a single RNA scaffold, and of nanotubes with two or even more adjacent protein domains of tightly pre-defined lengths.

  5. 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

  6. Characterizing the Growth Kinetics in Estrogen Responsive ...

    EPA Pesticide Factsheets

    There is a need to develop high-throughput screening (HTS) tests capable of testing thousands of environmental chemicals for endocrine disrupting potential. The estrogen signaling pathway is a known xenobiotic target that has been implicated in a variety of adverse health effects including reproductive deficits and cancer promotion. Using real-time measurements of growth kinetics by electrode impedance, the estrogen-responsive human ductal carcinoma cell line, T47D, was treated with 2000 chemicals of environmental relevance. Cells were treated in concentration response and measurements of cellular impedance were recorded every hour for six days. Exponential impedance, signifying increased proliferation, was observed by prototypical estrogen receptor agonists (17β-estradiol, genestein, bisphenol-A, nonylphenol, 4-tert-octylphenol). Several compounds, including bisphenol-A and genestein, induced cell proliferation at comparable levels to 17β-estradiol, although at much higher concentrations. Progestins, and mineralocortocoids (progesterone, dihydrotestosterone, aldosterone) invoked a biphasic impedance signature. In conclusion, the real-time nature of this assay allows for rapid detection of differential growth characteristics shows potential, in combination with other ToxCast HTS assays, to detect environmental chemicals with potential endocrine activity. [This abstract does not necessarily reflect Agency policy]. Several compounds, including bisphenol-A and

  7. Polymerization initated at sidewalls of carbon nanotubes

    NASA Technical Reports Server (NTRS)

    Tour, James M. (Inventor); Hudson, Jared L. (Inventor); Krishnamoorti, Ramanan (Inventor); Yurekli, Koray (Inventor); Mitchell, Cynthia A. (Inventor)

    2011-01-01

    The present invention is directed to aryl halide (such as aryl bromide) functionalized carbon nanotubes that can be utilized in anionic polymerization processes to form polymer-carbon nanotube materials with improved dispersion ability in polymer matrices. In this process the aryl halide is reacted with an alkyllithium species or is reacted with a metal to replace the aryl-bromine bond with an aryl-lithium or aryl-metal bond, respectively. It has further been discovered that other functionalized carbon nanotubes, after deprotonation with a deprotonation agent, can similarly be utilized in anionic polymerization processes to form polymer-carbon nanotube materials. Additionally or alternatively, a ring opening polymerization process can be performed. The resultant materials can be used by themselves due to their enhanced strength and reinforcement ability when compared to their unbound polymer analogs. Additionally, these materials can also be blended with pre-formed polymers to establish compatibility and enhanced dispersion of nanotubes in otherwise hard to disperse matrices resulting in significantly improved material properties. The resultant polymer-carbon nanotube materials can also be used in drug delivery processes due to their improved dispersion ability and biodegradability, and can also be used for scaffolding to promote cellular growth of tissue.

  8. Silver-decorated orthorhombic nanotubes of lithium vanadium oxide: an impeder of bacterial growth and biofilm.

    PubMed

    Diggikar, Rahul S; Patil, Rajendra H; Kale, Sheetal B; Thombre, Dipalee K; Gade, Wasudeo N; Kulkarni, Milind V; Kale, Bharat B

    2013-09-01

    Reoccurrence of infectious diseases and ability of pathogens to resist antibacterial action has raised enormous challenges which may possibly be confronted by nanotechnology routes. In the present study, uniformly embedded silver nanoparticles in orthorhombic nanotubes of lithium vanadium oxide (LiV2O5/Ag) were explored as an impeder of bacterial growth and biofilm. The LiV2O5/Ag nanocomposites have impeded growth of Gram-positive Bacillus subtilis NCIM 2063 and Gram-negative Escherichia coli NCIM 2931 at 60 to 120 μg/mL. It also impeded the biofilm in Pseudomonas aeruginosa NCIM 2948 at 12.5 to 25 μg/mL. Impedance in the growth and biofilm occurs primarily by direct action of the nanocomposites on the cell surfaces of test organisms as revealed by surface perturbation in scanning electron microscopy. As the metabolic growth and biofilm formation phenomena of pathogens play a central role in progression of pathogenesis, LiV2O5/Ag nanocomposite-based approach is likely to curb the menace of reoccurrence of infectious diseases. Thus, LiV2O5/Ag nanocomposites can be viewed as a promising candidate in biofabrication of biomedical materials.

  9. Thermal chemical vapor deposition (T-CVD) growth of carbon nanotubes on different metallic underlayers

    NASA Astrophysics Data System (ADS)

    Kim, S. M.; Gangloff, L.

    2011-06-01

    The synthesis of carbon nanotubes (CNTs) on various substrates by thermal chemical vapor deposition (T-CVD) (500-800 °C) is described. C 2H 2 (98% purity) is used as the carbon feedstock and the metallic underlayers, i.e., AlCu, Cu, Ag, Ta, and NiV are used. A crucial component is the insertion (or inclusion) of an Al layer between the metal and the catalyst, which then leads to the effective growth of CNTs. The types of CNTs (single or multi walled) could be dependent on the diameter of Al xO y nanoparticles that are formed during the annealing process. In situ mass spectroscopy reveals that the increase in CO 2 and H 2O with temperature, during the growth, could be correlated to the formation of longer CNTs (∼2 μm) on NiV and Ta due to their etching effects (i.e. C+CO 2→2CO and C+H 2O→CO+H 2).

  10. Selective Growth of Metallic and Semiconducting Single Walled Carbon Nanotubes on Textured Silicon.

    PubMed

    Jang, Mira; Lee, Jongtaek; Park, Teahee; Lee, Junyoung; Yang, Jonghee; Yi, Whikun

    2016-03-01

    We fabricated the etched Si substrate having the pyramidal pattern size from 0.5 to 4.2 μm by changing the texturing process parameters, i.e., KOH concentration, etching time, and temperature. Single walled carbon nanotubes (SWNTs) were then synthesized on the etched Si substrates with different pyramidal pattern by chemical vapor deposition. We investigated the optical and electronic properties of SWNT film grown on the etched Si substrates of different morphology by using scanning electron microscopy, Raman spectroscopy and conducting probe atomic force microscopy. We confirmed that the morphology of substrate strongly affected the selective growth of the SWNT film. Semiconducting SWNTs were formed on larger pyramidal sized Si wafer with higher ratio compared with SWNTs on smaller pyramidal sized Si.

  11. Synthesis of 1D-glyconanomaterials by a hybrid noncovalent-covalent functionalization of single wall carbon nanotubes: a study of their selective interactions with lectins and with live cells

    NASA Astrophysics Data System (ADS)

    Pernía Leal, M.; Assali, M.; Cid, J. J.; Valdivia, V.; Franco, J. M.; Fernández, I.; Pozo, D.; Khiar, N.

    2015-11-01

    To take full advantage of the remarkable applications of carbon nanotubes in different fields, there is a need to develop effective methods to improve their water dispersion and biocompatibility while maintaining their physical properties. In this sense, current approaches suffer from serious drawbacks such as loss of electronic structure together with low surface coverage in the case of covalent functionalizations, or instability of the dynamic hybrids obtained by non-covalent functionalizations. In the present work, we examined the molecular basis of an original strategy that combines the advantages of both functionalizations without their main drawbacks. The hierarchical self-assembly of diacetylenic-based neoglycolipids into highly organized and compacted rings around the nanotubes, followed by photopolymerization leads to the formation of nanotubes covered with glyconanorings with a shish kebab-type topology exposing the carbohydrate ligands to the water phase in a multivalent fashion. The glyconanotubes obtained are fully functional, and able to establish specific interactions with their cognate receptors. In fact, by taking advantage of this selective binding, an easy method to sense lectins as a working model of toxin detection was developed based on a simple analysis of TEM images. Remarkably, different experimental settings to assess cell membrane integrity, cell growth kinetics and cell cycle demonstrated the cellular biocompatibility of the sugar-coated carbon nanotubes compared to pristine single-walled carbon nanotubes.To take full advantage of the remarkable applications of carbon nanotubes in different fields, there is a need to develop effective methods to improve their water dispersion and biocompatibility while maintaining their physical properties. In this sense, current approaches suffer from serious drawbacks such as loss of electronic structure together with low surface coverage in the case of covalent functionalizations, or instability of

  12. Sustained Release of Antibacterial Agents from Doped Halloysite Nanotubes

    PubMed Central

    Patel, Shraddha; Jammalamadaka, Uday; Sun, Lin; Tappa, Karthik; Mills, David K.

    2015-01-01

    The use of nanomaterials for improving drug delivery methods has been shown to be advantageous technically and viable economically. This study employed the use of halloysite nanotubes (HNTs) as nanocontainers, as well as enhancers of structural integrity in electrospun poly-e-caprolactone (PCL) scaffolds. HNTs were loaded with amoxicillin, Brilliant Green, chlorhexidine, doxycycline, gentamicin sulfate, iodine, and potassium calvulanate and release profiles assessed. Selected doped halloysite nanotubes (containing either Brilliant Green, amoxicillin and potassium calvulanate) were then mixed with poly-e-caprolactone (PLC) using the electrospinning method and woven into random and oriented-fibered nanocomposite mats. The rate of drug release from HNTs, HNTs/PCL nanocomposites, and their effect on inhibiting bacterial growth was investigated. Release profiles from nanocomposite mats showed a pattern of sustained release for all bacterial agents. Nanocomposites were able to inhibit bacterial growth for up to one-month with only a slight decrease in bacterial growth inhibition. We propose that halloysite doped nanotubes have the potential for use in a variety of medical applications including sutures and surgical dressings, without compromising material properties. PMID:28952563

  13. Selective growth of chirality-enriched semiconducting carbon nanotubes by using bimetallic catalysts from salt precursors.

    PubMed

    Zhao, Xiulan; Yang, Feng; Chen, Junhan; Ding, Li; Liu, Xiyan; Yao, Fengrui; Li, Meihui; Zhang, Daqi; Zhang, Zeyao; Liu, Xu; Yang, Juan; Liu, Kaihui; Li, Yan

    2018-04-19

    Bimetallic catalysts play important roles in the selective growth of single-walled carbon nanotubes (SWNTs). Using the simple salts (NH4)6W7O24·6H2O and Co(CH3COO)2·4H2O as precursors, tungsten-cobalt catalysts were prepared. The catalysts were composed of W6Co7 intermetallic compounds and tungsten-dispersed cobalt. With the increase of the W/Co ratio in the precursors, the content of W6Co7 was increased. Because the W6Co7 intermetallic compound can enable the chirality specified growth of SWNTs, the selectivity of the resulting SWNTs is improved at a higher W/Co ratio. At a W/Co ratio of 6 : 4 and under optimized chemical vapor deposition conditions, we realized the direct growth of semiconducting SWNTs with the purity of ∼96%, in which ∼62% are (14, 4) tubes. Using salts as precursors to prepare tungsten-cobalt bimetallic catalysts is flexible and convenient. This offers an efficient pathway for the large-scale preparation of chirality enriched semiconducting SWNTs.

  14. Process for making polymers comprising derivatized carbon nanotubes and compositions thereof

    NASA Technical Reports Server (NTRS)

    Tour, James M. (Inventor); Bahr, Jeffrey L. (Inventor); Yang, Jiping (Inventor)

    2007-01-01

    The present invention incorporates new processes for blending derivatized carbon nanotubes into polymer matrices to create new polymer/composite materials. When modified with suitable chemical groups using diazonium chemistry, the nanotubes can be made chemically compatible with a polymer matrix, allowing transfer of the properties of the nanotubes (such as mechanical strength) to the properties of the composite material as a whole. To achieve this, the derivatized (modified) carbon nanotubes are physically blended with the polymeric material, and/or, if desired, allowed to react at ambient or elevated temperature. These methods can be utilized to append functionalities to the nanotubes that will further covalently bond to the host polymer matrix, or directly between two tubes themselves. Furthermore, the nanotubes can be used as a generator of polymer growth, wherein the nanotubes are derivatized with a functional group that is an active part of a polymerization process, which would also result in a composite material in which the carbon nanotubes are chemically involved.

  15. Quantifying Variability in Growth and Thermal Inactivation Kinetics of Lactobacillus plantarum.

    PubMed

    Aryani, D C; den Besten, H M W; Zwietering, M H

    2016-08-15

    variability with respect to the growth and thermal inactivation kinetics of Lactobacillus plantarum and to quantify the variability in thermal resistance attributed to growth history. The quantitative knowledge obtained on experimental, reproduction, and strain variabilities can be used to improve experimental designs and to adequately select strains for challenge growth and inactivation tests. Moreover, the integration of strain variability in prediction of microbial growth and inactivation kinetics will result in more realistic predictions of L. plantarum dynamics along the food production chain. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

  16. Production of single-walled carbon nanotube grids

    DOEpatents

    Hauge, Robert H; Xu, Ya-Qiong; Pheasant, Sean

    2013-12-03

    A method of forming a nanotube grid includes placing a plurality of catalyst nanoparticles on a grid framework, contacting the catalyst nanoparticles with a gas mixture that includes hydrogen and a carbon source in a reaction chamber, forming an activated gas from the gas mixture, heating the grid framework and activated gas, and controlling a growth time to generate a single-wall carbon nanotube array radially about the grid framework. A filter membrane may be produced by this method.

  17. A Comparative Study of Ethylene Growth Response Kinetics in Eudicots and Monocots Reveals a Role for Gibberellin in Growth Inhibition and Recovery1[W][OA

    PubMed Central

    Kim, Joonyup; Wilson, Rebecca L.; Case, J. Brett; Binder, Brad M.

    2012-01-01

    Time-lapse imaging of dark-grown Arabidopsis (Arabidopsis thaliana) hypocotyls has revealed new aspects about ethylene signaling. This study expands upon these results by examining ethylene growth response kinetics of seedlings of several plant species. Although the response kinetics varied between the eudicots studied, all had prolonged growth inhibition for as long as ethylene was present. In contrast, with continued application of ethylene, white millet (Panicum miliaceum) seedlings had a rapid and transient growth inhibition response, rice (Oryza sativa ‘Nipponbare’) seedlings had a slow onset of growth stimulation, and barley (Hordeum vulgare) had a transient growth inhibition response followed, after a delay, by a prolonged inhibition response. Growth stimulation in rice correlated with a decrease in the levels of rice ETHYLENE INSENSTIVE3-LIKE2 (OsEIL2) and an increase in rice F-BOX DOMAIN AND LRR CONTAINING PROTEIN7 transcripts. The gibberellin (GA) biosynthesis inhibitor paclobutrazol caused millet seedlings to have a prolonged growth inhibition response when ethylene was applied. A transient ethylene growth inhibition response has previously been reported for Arabidopsis ethylene insensitive3-1 (ein3-1) eil1-1 double mutants. Paclobutrazol caused these mutants to have a prolonged response to ethylene, whereas constitutive GA signaling in this background eliminated ethylene responses. Sensitivity to paclobutrazol inversely correlated with the levels of EIN3 in Arabidopsis. Wild-type Arabidopsis seedlings treated with paclobutrazol and mutants deficient in GA levels or signaling had a delayed growth recovery after ethylene removal. It is interesting to note that ethylene caused alterations in gene expression that are predicted to increase GA levels in the ein3-1 eil1-1 seedlings. These results indicate that ethylene affects GA levels leading to modulation of ethylene growth inhibition kinetics. PMID:22977279

  18. Exploring doxorubicin localization in eluting TiO2 nanotube arrays through fluorescence correlation spectroscopy analysis.

    PubMed

    De Santo, Ilaria; Sanguigno, Luigi; Causa, Filippo; Monetta, Tullio; Netti, Paolo A

    2012-11-07

    Drug elution properties of TiO(2) nanotube arrays have been largely investigated by means of solely macroscopic observations. Controversial elution performances have been reported so far and a clear comprehension of these phenomena is still missing as a consequence of a lack of molecular investigation methods. Here we propose a way to discern drug elution properties of nanotubes through the evaluation of drug localization by Fluorescence Correlation Spectroscopy (FCS) analysis. We verified this method upon doxorubicin elution from differently loaded TiO(2) nanotubes. Diverse elution profiles were obtained from nanotubes filled by soaking and wet vacuum impregnation methods. Impregnated nanotubes controlled drug diffusion up to thirty days, while soaked samples completed elution in seven days. FCS analysis of doxorubicin motion in loaded nanotubes clarified that more than 90% of drugs dwell preferentially in inter-nanotube spaces in soaked samples due to decorrelation in a 2D fashion, while a 97% fraction of molecules showed 1D mobility ascribable to displacements along the nanotube vertical axis of wet vacuum impregnated nanotubes. The diverse drug localizations inferred from FCS measurements, together with distinct drug-surface interaction strengths resulting from diverse drug filling techniques, could explain the variability in elution kinetics.

  19. 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.

  20. Kinetics of solution crystal growth of strengite, FePO4,2H2O

    NASA Astrophysics Data System (ADS)

    Lundager Madsen, Hans E.; Koch, Christian Bender

    2018-01-01

    The iron(III) phosphate strengite, FePO4,2H2O, has been precipitated at 25 °C by mixing solutions of iron alum and ammonium phosphate. The rate of crystallization has been determined by pH recording. Three stages of crystal growth kinetics could be distinguished: (1) mononuclear growth, (2) polynuclear growth and, in a few cases, (3) spiral growth (BCF mechanism). From the first two, the value of edge free energy λ = 87 ± 1 pJ/m was found. The identity of the precipitate was verified by SEM, XRD and Mössbauer spectroscopy.

  1. Future Nanotube Commercialization Opportunities at the NASA Marshall Space Flight Center and the US Army Aviation and Missile Command

    NASA Technical Reports Server (NTRS)

    Watson, Michael; Shah, Sandeep; Kaul, Raj; Zhu, Shen; Vandiver, Terry; Zimmerman, Joe E. (Technical Monitor)

    2001-01-01

    Nanotube technology has broad applicability to programs at both the NASA Marshall Space Flight Center (MSFC) and the US Army Aviation and Missile Command (AMCOM). MSFC has interest in applications of nanotubes as sensors and high strength lightweight materials for propulsion system components, avionic systems, and scientific instruments. MSFC is currently pursuing internal programs to develop nanotube temperature sensors, heat pipes, and metal matrix composites. In support of these application areas MSFC is interested in growth of long nanotubes, growth of nanotubes in the microgravity environment, and nanotubes fabricated from high temperature materials such as Boron Nitride or Silicon Carbide. AMCOM is similarly interested in nanotube applications which take advantage of the nanotube thermal conductance properties, high strength, and lightweight. Applications of interest to AMCOM include rocket motor casing structures, rocket nozzles, and lightweight structure and aeronautic skins.

  2. Kinetic Behavior of Exchange-Driven Growth with Catalyzed-Birth Processes

    NASA Astrophysics Data System (ADS)

    Wang, Hai-Feng; Lin, Zhen-Quan; Kong, Xiang-Mu

    2006-12-01

    Two catalyzed-birth models of n-species (n>=2) aggregates with exchange-driven growth processes are proposed and compared. In the first one, the exchange reaction occurs between any two aggregates Amk and Amj of the same species with the rate kernels Km(k,j) = Kmkj (m = 1,2,...,n, n>=2), and aggregates of An species catalyze a monomer-birth of Al species (l = 1,2,...,n-1) with the catalysis rate kernel Jl(k,j) = Jlkjυ. The kinetic behaviors are investigated by means of the mean-field theory. We find that the evolution behavior of aggregate-size distribution alk(t) of Al species depends crucially on the value of the catalysis rate parameter υ: (i) alk(t) obeys the conventional scaling law in the case of υ<=0, (ii) alk(t) satisfies a modified scaling form in the case of υ>0. In the second model, the mechanism of monomer-birth of An-species catalyzed by Al species is added on the basis of the first model, that is, the aggregates of Al and An species catalyze each other to cause monomer-birth. The kinetic behaviors of Al and An species are found to fall into two categories for the different υ: (i) growth obeying conventional scaling form with υ<=0, (ii) gelling at finite time with υ>0.

  3. Si/Ge double-layered nanotube array as a lithium ion battery anode.

    PubMed

    Song, Taeseup; Cheng, Huanyu; Choi, Heechae; Lee, Jin-Hyon; Han, Hyungkyu; Lee, Dong Hyun; Yoo, Dong Su; Kwon, Moon-Seok; Choi, Jae-Man; Doo, Seok Gwang; Chang, Hyuk; Xiao, Jianliang; Huang, Yonggang; Park, Won Il; Chung, Yong-Chae; Kim, Hansu; Rogers, John A; Paik, Ungyu

    2012-01-24

    Problems related to tremendous volume changes associated with cycling and the low electron conductivity and ion diffusivity of Si represent major obstacles to its use in high-capacity anodes for lithium ion batteries. We have developed a group IVA based nanotube heterostructure array, consisting of a high-capacity Si inner layer and a highly conductive Ge outer layer, to yield both favorable mechanics and kinetics in battery applications. This type of Si/Ge double-layered nanotube array electrode exhibits improved electrochemical performances over the analogous homogeneous Si system, including stable capacity retention (85% after 50 cycles) and doubled capacity at a 3C rate. These results stem from reduced maximum hoop strain in the nanotubes, supported by theoretical mechanics modeling, and lowered activation energy barrier for Li diffusion. This electrode technology creates opportunities in the development of group IVA nanotube heterostructures for next generation lithium ion batteries. © 2011 American Chemical Society

  4. Selective synthesis and device applications of semiconducting single-walled carbon nanotubes using isopropyl alcohol as feedstock.

    PubMed

    Che, Yuchi; Wang, Chuan; Liu, Jia; Liu, Bilu; Lin, Xue; Parker, Jason; Beasley, Cara; Wong, H-S Philip; Zhou, Chongwu

    2012-08-28

    The development of guided chemical vapor deposition (CVD) growth of single-walled carbon nanotubes provides a great platform for wafer-scale integration of aligned nanotubes into circuits and functional electronic systems. However, the coexistence of metallic and semiconducting nanotubes is still a major obstacle for the development of carbon-nanotube-based nanoelectronics. To address this problem, we have developed a method to obtain predominantly semiconducting nanotubes from direct CVD growth. By using isopropyl alcohol (IPA) as the carbon feedstock, a semiconducting nanotube purity of above 90% is achieved, which is unambiguously confirmed by both electrical and micro-Raman measurements. Mass spectrometric study was performed to elucidate the underlying chemical mechanism. Furthermore, high performance thin-film transistors with an on/off ratio above 10(4) and mobility up to 116 cm(2)/(V·s) have been achieved using the IPA-synthesized nanotube networks grown on silicon substrate. The method reported in this contribution is easy to operate and the results are highly reproducible. Therefore, such semiconducting predominated single-walled carbon nanotubes could serve as an important building block for future practical and scalable carbon nanotube electronics.

  5. Vertically aligned single-walled carbon nanotubes by chemical assembly--methodology, properties, and applications.

    PubMed

    Diao, Peng; Liu, Zhongfan

    2010-04-06

    Single-walled carbon nanotubes (SWNTs), as one of the most promising one-dimension nanomaterials due to its unique structure, peculiar chemical, mechanical, thermal, and electronic properties, have long been considered as an important building block to construct ordered alignments. Vertically aligned SWNTs (v-SWNTs) have been successfully prepared by using direct growth and chemical assembly strategies. In this review, we focus explicitly on the v-SWNTs fabricated via chemical assembly strategy. We provide the readers with a full and systematic summary covering the advances in all aspects of this area, including various approaches for the preparation of v-SWNTs using chemical assembly techniques, characterization, assembly kinetics, and electrochemical properties of v-SWNTs. We also review the applications of v-SWNTs in electrochemical and bioelectrochemical sensors, photoelectric conversion, and scanning probe microscopy.

  6. Carbon nanotubes in neuroregeneration and repair.

    PubMed

    Fabbro, Alessandra; Prato, Maurizio; Ballerini, Laura

    2013-12-01

    In the last decade, we have experienced an increasing interest and an improved understanding of the application of nanotechnology to the nervous system. The aim of such studies is that of developing future strategies for tissue repair to promote functional recovery after brain damage. In this framework, carbon nanotube based technologies are emerging as particularly innovative tools due to the outstanding physical properties of these nanomaterials together with their recently documented ability to interface neuronal circuits, synapses and membranes. This review will discuss the state of the art in carbon nanotube technology applied to the development of devices able to drive nerve tissue repair; we will highlight the most exciting findings addressing the impact of carbon nanotubes in nerve tissue engineering, focusing in particular on neuronal differentiation, growth and network reconstruction. © 2013.

  7. Chemical Reaction and Flow Modeling in Fullerene and Nanotube Production

    NASA Technical Reports Server (NTRS)

    Scott, Carl D.; Farhat, Samir; Greendyke, Robert B.

    2004-01-01

    The development of processes to produce fullerenes and carbon nanotubes has largely been empirical. Fullerenes were first discovered in the soot produced by laser ablation of graphite [1]and then in the soot of electric arc evaporated carbon. Techniques and conditions for producing larger and larger quantities of fullerenes depended mainly on trial and error empirical variations of these processes, with attempts to scale them up by using larger electrodes and targets and higher power. Various concepts of how fullerenes and carbon nanotubes were formed were put forth, but very little was done based on chemical kinetics of the reactions. This was mainly due to the complex mixture of species and complex nature of conditions in the reactors. Temperatures in the reactors varied from several thousand degrees Kelvin down to near room temperature. There are hundreds of species possible, ranging from atomic carbon to large clusters of carbonaceous soot, and metallic catalyst atoms to metal clusters, to complexes of metals and carbon. Most of the chemical kinetics of the reactions and the thermodynamic properties of clusters and complexes have only been approximated. In addition, flow conditions in the reactors are transient or unsteady, and three dimensional, with steep spatial gradients of temperature and species concentrations. All these factors make computational simulations of reactors very complex and challenging. This article addresses the development of the chemical reaction involved in fullerene production and extends this to production of carbon nanotubes by the laser ablation/oven process and by the electric arc evaporation process. In addition, the high-pressure carbon monoxide (HiPco) process is discussed. The article is in several parts. The first one addresses the thermochemical aspects of modeling; and considers the development of chemical rate equations, estimates of reaction rates, and thermodynamic properties where they are available. The second part

  8. Magnetic nanotubes

    DOEpatents

    Matsui, Hiroshi; Matsunaga, Tadashi

    2010-11-16

    A magnetic nanotube includes bacterial magnetic nanocrystals contacted onto a nanotube which absorbs the nanocrystals. The nanocrystals are contacted on at least one surface of the nanotube. A method of fabricating a magnetic nanotube includes synthesizing the bacterial magnetic nanocrystals, which have an outer layer of proteins. A nanotube provided is capable of absorbing the nanocrystals and contacting the nanotube with the nanocrystals. The nanotube is preferably a peptide bolaamphiphile. A nanotube solution and a nanocrystal solution including a buffer and a concentration of nanocrystals are mixed. The concentration of nanocrystals is optimized, resulting in a nanocrystal to nanotube ratio for which bacterial magnetic nanocrystals are immobilized on at least one surface of the nanotubes. The ratio controls whether the nanocrystals bind only to the interior or to the exterior surfaces of the nanotubes. Uses include cell manipulation and separation, biological assay, enzyme recovery, and biosensors.

  9. Interpretation of orbital scale variability in mid-latitude speleothem δ18O: Significance of growth rate controlled kinetic fractionation effects

    NASA Astrophysics Data System (ADS)

    Stoll, Heather; Mendez-Vicente, Ana; Gonzalez-Lemos, Saul; Moreno, Ana; Cacho, Isabel; Cheng, Hai; Edwards, R. Lawrence

    2015-11-01

    Oxygen isotopes have been the most widely used climate indicator in stalagmites, applied to reconstruct past changes in rainfall δ18O and cave temperature. However, the δ18O signal in speleothems may also be influenced by variable kinetic fractionation effects, here conceived broadly as fractionation effects not arising from temperature variation. The regional reproducibility of speleothem δ18O signals has been proposed as a way to distinguish the δ18O variations arising directly from changes rainfall δ18O and cave temperature, from variations due to kinetic effects which may nonetheless be influenced by climate. Here, we compare isotopic records from 5 coeval stalagmites from two proximal caves in NW Spain covering the interval 140 to 70 ka, which experienced the same primary variations in temperature and rainfall δ18O, but exhibit a large range in growth rates and temporal trends in growth rate. Stalagmites growing at faster rates near 50 μm/yr have oxygen isotopic ratios over 1‰ more negative than coeval stalagmites with very slow (5 μm/yr) growth rates. Because growth rate variations also occur over time within any given stalagmite, the measured oxygen isotopic time series for a given stalagmite includes both climatic and kinetic components. Removal of the kinetic component of variation in each stalagmite, based on the dependence of the kinetic component on growth rate, is effective at distilling a common temporal evolution of among the oxygen isotopic records of the multiple stalagmites. However, this approach is limited by the quality of the age model. For time periods characterized by very slow growth and long durations between dates, the presence of crypto-hiatus may result in average growth rates which underestimate the instantaneous speleothem deposition rates and which therefore underestimate the magnitude of kinetic effects. The stacked growth rate-corrected speleothem δ18O is influenced by orbital scale variation in the cave temperature and

  10. Applications of Carbon Nanotubes in Biotechnology and Biomedicine

    PubMed Central

    Bekyarova, Elena; Ni, Yingchun; Malarkey, Erik B.; Montana, Vedrana; McWilliams, Jared L.; Haddon, Robert C.; Parpura, Vladimir

    2009-01-01

    Due to their electrical, chemical, mechanical and thermal properties, carbon nanotubes are one of the most promising materials for the electronics, computer and aerospace industries. Here, we discuss their properties in the context of future applications in biotechnology and biomedicine. The purification and chemical modification of carbon nanotubes with organic, polymeric and biological molecules are discussed. Additionally we review their uses in biosensors, assembly of structures and devices, scanning probe microscopy and as substrates for neuronal growth. We note that additional toxicity studies of carbon nanotubes are necessary so that exposure guidelines and safety regulations can be established in a timely manner. PMID:19763242

  11. Atomic force microscopy investigation of the kinetic growth mechanisms of sputtered nanostructured Au film on mica: towards a nanoscale morphology control

    PubMed Central

    2011-01-01

    The study of surface morphology of Au deposited on mica is crucial for the fabrication of flat Au films for applications in biological, electronic, and optical devices. The understanding of the growth mechanisms of Au on mica allows to tune the process parameters to obtain ultra-flat film as suitable platform for anchoring self-assembling monolayers, molecules, nanotubes, and nanoparticles. Furthermore, atomically flat Au substrates are ideal for imaging adsorbate layers using scanning probe microscopy techniques. The control of these mechanisms is a prerequisite for control of the film nano- and micro-structure to obtain materials with desired morphological properties. We report on an atomic force microscopy (AFM) study of the morphology evolution of Au film deposited on mica by room-temperature sputtering as a function of subsequent annealing processes. Starting from an Au continuous film on the mica substrate, the AFM technique allowed us to observe nucleation and growth of Au clusters when annealing process is performed in the 573-773 K temperature range and 900-3600 s time range. The evolution of the clusters size was quantified allowing us to evaluate the growth exponent 〈z〉 = 1.88 ± 0.06. Furthermore, we observed that the late stage of cluster growth is accompanied by the formation of circular depletion zones around the largest clusters. From the quantification of the evolution of the size of these zones, the Au surface diffusion coefficient was evaluated in D(T) = [(7.42 × 10−13) ± (5.94 × 10−14) m2/s]exp(−(0.33±0.04) eVkT). These quantitative data and their correlation with existing theoretical models elucidate the kinetic growth mechanisms of the sputtered Au on mica. As a consequence we acquired a methodology to control the morphological characteristics of the Au film simply controlling the annealing temperature and time. PMID:24576328

  12. Intrinsic Kinetics Fluctuations as Cause of Growth Inhomogeneity in Protein Crystals

    NASA Technical Reports Server (NTRS)

    Vekilov, Peter G.; Rosenberger, Franz

    1998-01-01

    Intrinsic kinetics instabilities in the form of growth step bunching during the crystallization of the protein lysozyme from solution were characterized by in situ high-resolution optical interferometry. Compositional variations (striations) in the crystal, which potentially decrease its utility, e.g., for molecular structure studies by diffraction methods, were visualized by polarized light reflection microscopy. A spatiotemporal correlation was established between the sequence of moving step bunches and the striations.

  13. A kinetic Monte Carlo simulation method of van der Waals epitaxy for atomistic nucleation-growth processes of transition metal dichalcogenides.

    PubMed

    Nie, Yifan; Liang, Chaoping; Cha, Pil-Ryung; Colombo, Luigi; Wallace, Robert M; Cho, Kyeongjae

    2017-06-07

    Controlled growth of crystalline solids is critical for device applications, and atomistic modeling methods have been developed for bulk crystalline solids. Kinetic Monte Carlo (KMC) simulation method provides detailed atomic scale processes during a solid growth over realistic time scales, but its application to the growth modeling of van der Waals (vdW) heterostructures has not yet been developed. Specifically, the growth of single-layered transition metal dichalcogenides (TMDs) is currently facing tremendous challenges, and a detailed understanding based on KMC simulations would provide critical guidance to enable controlled growth of vdW heterostructures. In this work, a KMC simulation method is developed for the growth modeling on the vdW epitaxy of TMDs. The KMC method has introduced full material parameters for TMDs in bottom-up synthesis: metal and chalcogen adsorption/desorption/diffusion on substrate and grown TMD surface, TMD stacking sequence, chalcogen/metal ratio, flake edge diffusion and vacancy diffusion. The KMC processes result in multiple kinetic behaviors associated with various growth behaviors observed in experiments. Different phenomena observed during vdW epitaxy process are analysed in terms of complex competitions among multiple kinetic processes. The KMC method is used in the investigation and prediction of growth mechanisms, which provide qualitative suggestions to guide experimental study.

  14. Shape transition of endotaxial islands growth from kinetically constrained to equilibrium regimes

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Zhi-Peng, E-mail: LI.Zhipeng@nims.go.jp; Global Research Center for Environment and Energy based on Nanomaterials Science, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044; Tok, Engsoon

    2013-09-01

    Graphical abstract: - Highlights: • All Fe{sub 13}Ge{sub 8} islands will grow into Ge(0 0 1) substrate at temperatures from 350 to 675 °C. • Shape transition occurred from kinetically constrained to equilibrium regime. • All endotaxial islands can be clarified into two types. • The mechanisms of endotaxial growth and shape transition have been rationalized. - Abstract: A comprehensive study of Fe grown on Ge(0 0 1) substrates has been conducted at elevated temperatures, ranging from 350 to 675 °C. All iron germinide islands, with the same Fe{sub 13}Ge{sub 8} phase, grow into the Ge substrate with the samemore » epitaxial relationship. Shape transition occurs from small square islands (low temperatures), to elongated orthogonal islands or orthogonal nanowires (intermediate temperatures), and then finally to large square orthogonal islands (high temperatures). According to both transmission electron microscopy (TEM) and atomic force microscopy (AFM) investigations, all islands can be defined as either type-I or type-II. Type-I islands usually form at kinetically constrained growth regimes, like truncated pyramids. Type-II islands usually appear at equilibrium growth regimes forming a dome-like shape. Based on a simple semi-quantitative model, type-II islands have a lower total energy per volume than type-I, which is considered as the dominant mechanism for this type of shape transition. Moreover, this study not only elucidates details of endotaxial growth in the Fe–Ge system, but also suggests the possibility of controlled fabrication of temperature-dependent nanostructures, especially in materials with dissimilar crystal structures.« less

  15. Investigation of Chirality Selection Mechanism of Single-Walled Carbon Nanotube

    DTIC Science & Technology

    2015-07-17

    Final 3. DATES COVERED (From - To) 01-June-2014 to 31-May-2015 4. TITLE AND SUBTITLE Investigation of Chirality Selection Mechanism of...of two significant mechanistic aspects of carbon nanotube (CNT) array growth under chemical vapor deposition conditions: chirality selectivity and...affected by the morphological evolution of catalyst particles. 15. SUBJECT TERMS Carbon Nanotubes, Chirality , Processing, Catalysis

  16. Synthesis of 1D-glyconanomaterials by a hybrid noncovalent-covalent functionalization of single wall carbon nanotubes: a study of their selective interactions with lectins and with live cells.

    PubMed

    Pernía Leal, M; Assali, M; Cid, J J; Valdivia, V; Franco, J M; Fernández, I; Pozo, D; Khiar, N

    2015-12-07

    To take full advantage of the remarkable applications of carbon nanotubes in different fields, there is a need to develop effective methods to improve their water dispersion and biocompatibility while maintaining their physical properties. In this sense, current approaches suffer from serious drawbacks such as loss of electronic structure together with low surface coverage in the case of covalent functionalizations, or instability of the dynamic hybrids obtained by non-covalent functionalizations. In the present work, we examined the molecular basis of an original strategy that combines the advantages of both functionalizations without their main drawbacks. The hierarchical self-assembly of diacetylenic-based neoglycolipids into highly organized and compacted rings around the nanotubes, followed by photopolymerization leads to the formation of nanotubes covered with glyconanorings with a shish kebab-type topology exposing the carbohydrate ligands to the water phase in a multivalent fashion. The glyconanotubes obtained are fully functional, and able to establish specific interactions with their cognate receptors. In fact, by taking advantage of this selective binding, an easy method to sense lectins as a working model of toxin detection was developed based on a simple analysis of TEM images. Remarkably, different experimental settings to assess cell membrane integrity, cell growth kinetics and cell cycle demonstrated the cellular biocompatibility of the sugar-coated carbon nanotubes compared to pristine single-walled carbon nanotubes.

  17. Ascorbic-acid-assisted growth of high quality M@ZnO: a growth mechanism and kinetics study.

    PubMed

    Yang, Yun; Han, Shuhua; Zhou, Guangju; Zhang, Lijie; Li, Xingliang; Zou, Chao; Huang, Shaoming

    2013-12-07

    We present a general route for synthesizing M@ZnO nanoparticles (NPs) by using ascorbic acid (AA) to induce deposition of ZnO on various shaped and structured cationic-surfactant-capped NP surfaces (noble, magnetic, semiconductor, rod-like, spherical, cubic, dendrite, alloy, core@shell). The results show that the complexing (AA and Zn(2+)) and cooperative effects (AA and CTAB) play important roles in the formation of polycrystalline ZnO shells. Besides, the growth kinetics of M@ZnO was systematically studied. It was found that the slow growth rate favors the successful formation of uniform core@ZnO NPs with relatively loose shells. An appropriate growth rate allows achieving high quality M@ZnO NPs with dense shells. However, very fast growth causes significant additional nucleation and the formation of pure ZnO NPs. This general method is suitable for preparing M@ZnO using seed NPs prepared in both water and organic phases. It might be an alternative route for functionalizing NPs for bioapplications (ZnO is biocompatible), modulating material properties as designed, or synthesizing template materials for building other nanostructures.

  18. One-pot nucleation, growth, morphogenesis, and passivation of 1.4 nm Au nanoparticles on self-assembled rosette nanotubes.

    PubMed

    Chhabra, Rahul; Moralez, Jesus G; Raez, Jose; Yamazaki, Takeshi; Cho, Jae-Young; Myles, Andrew J; Kovalenko, Andriy; Fenniri, Hicham

    2010-01-13

    A one-pot strategy for the nucleation, growth, morphogenesis, and passivation of 1.4 nm Au nanoparticles (NPs) on self-assembled rosette nanotubes (RNTs) is described. Tapping-mode atomic force microscopy, transmission electron microscopy, energy-dispersive X-ray analysis, and selected-area electron diffraction were used to establish the structure and organization of this hybrid material. Notably, we found that the Au NPs formed were nearly monodisperse clusters of Au(55) (1.4-1.5 nm) nestled in pockets on the RNT surface.

  19. Grain growth kinetics in pyrolite material under lower mantle condition: Implications for the rheology of the lower mantle

    NASA Astrophysics Data System (ADS)

    Imamura, M.; Kubo, T.; Takumi, K.

    2016-12-01

    Rheology of the lower mantle largely depends on the grain-size evolution in constituent minerals. The pioneering work on the grain growth kinetics in MgSiO3 bridgmanite and MgO periclase (Yamazaki et al., 1996) has raised the problem that the grain growth rate is too slow to explain the lower-mantle viscosity. This inconsistency may arise from effects of elastic stress due to the eutectoid transformation (e.g., Solomatov et al., 2002) and it may be difficult to extrapolate the slow kinetics obtained to geological timescales. We conducted grain growth experiments in pyrolitic material at 25-27 GPa, and 1600-1950°C for 30-3000 min using Kawai-type high pressure apparatus at Kyushu University. Four phases of bridgmanite, ferro-priclase, Ca-perovskite and majoritic garnet were present in recovered samples annealed at 25 GPa. To avoid the effects of the eutectoid texture, we took the grain growth data only from the sample exhibiting relatively homogeneous equi-granular texture. That was achieved after annealing for 30 minutes at 1800-1950°C (use these grain sizes as d0), and not achieved even after annealing for 3000 minutes at 1600°C. We preliminarily obtained kinetic parameters of n=4.9 and H* 420 kJ/mol for bridgmanite, and n=4.7 and H* 160 kJ/mol for ferro-pericalse. The ratio of grain sizes of bridgmanite and ferro-periclase is almost constant during the grain growth process. These results indicate faster kinetics compared to the previous study, and can be reasonably interpreted as the grain growth occurred by Ostwald ripening. On the other hand, three phases without majoritic garnet were present at higher pressure of 27 GPa and 1800°C, in which the grain size was slightly larger probably due to the smaller proportion of the secondary phases. When extrapolating the grain growth kinetics obtained in the four phases, the grain size of bridgmanite is roughly estimated to be 4-50 µm at 800-1200°C and 200-600 µm at 1600-2000°C in 108 years. These grain sizes may

  20. Carbon nanotubes might improve neuronal performance by favouring electrical shortcuts.

    PubMed

    Cellot, Giada; Cilia, Emanuele; Cipollone, Sara; Rancic, Vladimir; Sucapane, Antonella; Giordani, Silvia; Gambazzi, Luca; Markram, Henry; Grandolfo, Micaela; Scaini, Denis; Gelain, Fabrizio; Casalis, Loredana; Prato, Maurizio; Giugliano, Michele; Ballerini, Laura

    2009-02-01

    Carbon nanotubes have been applied in several areas of nerve tissue engineering to probe and augment cell behaviour, to label and track subcellular components, and to study the growth and organization of neural networks. Recent reports show that nanotubes can sustain and promote neuronal electrical activity in networks of cultured cells, but the ways in which they affect cellular function are still poorly understood. Here, we show, using single-cell electrophysiology techniques, electron microscopy analysis and theoretical modelling, that nanotubes improve the responsiveness of neurons by forming tight contacts with the cell membranes that might favour electrical shortcuts between the proximal and distal compartments of the neuron. We propose the 'electrotonic hypothesis' to explain the physical interactions between the cell and nanotube, and the mechanisms of how carbon nanotubes might affect the collective electrical activity of cultured neuronal networks. These considerations offer a perspective that would allow us to predict or engineer interactions between neurons and carbon nanotubes.

  1. Adsorption of direct dyes from aqueous solutions by carbon nanotubes: determination of equilibrium, kinetics and thermodynamics parameters.

    PubMed

    Kuo, Chao-Yin; Wu, Chung-Hsin; Wu, Jane-Yii

    2008-11-15

    This study examined the feasibility of removing direct dyes C.I. Direct Yellow 86 (DY86) and C.I. Direct Red 224 (DR224) from aqueous solutions using carbon nanotubes (CNTs). The effects of dye concentration, CNT dosage, ionic strength and temperature on adsorption of direct dyes by CNTs were also evaluated. Pseudo second-order, intraparticle diffusion and Bangham models were adopted to evaluate experimental data and thereby elucidate the kinetic adsorption process. Additionally, this study used the Langmuir, Freundlich, Dubinin and Radushkevich (D-R) and Temkin isotherms to describe equilibrium adsorption. The adsorption percentage of direct dyes increased as CNTs dosage, NaCl addition and temperature increased. Conversely, the adsorption percentage of direct dyes decreased as dye concentration increased. The pseudo second-order model best represented adsorption kinetics. Based on the regressions of intraparticle diffusion and Bangham models, experimental data suggest that the adsorption of direct dyes onto CNTs involved intraparticle diffusion, but that was not the only rate-controlling step. The equilibrium adsorption of DR86 is best fitted in the Freundlich isotherm and that of DR224 was best fitted in the D-R isotherm. The capacity of CNTs to adsorb DY86 and DR224 was 56.2 and 61.3 mg/g, respectively. For DY86, enthalpy (DeltaH(0)) and entropy (DeltaS(0)) were 13.69 kJ/mol and 139.51 J/mol K, respectively, and those for DR224 were 24.29 kJ/mol and 172.06 J/mol K, respectively. The values of DeltaH(0), DeltaG(0) and E all indicate that the adsorption of direct dyes onto CNTs was a physisorption process.

  2. Antibacterial effect of silver nanoparticles and the modeling of bacterial growth kinetics using a modified Gompertz model.

    PubMed

    Chatterjee, Tanaya; Chatterjee, Barun K; Majumdar, Dipanwita; Chakrabarti, Pinak

    2015-02-01

    An alternative to conventional antibiotics is needed to fight against emerging multiple drug resistant pathogenic bacteria. In this endeavor, the effect of silver nanoparticle (Ag-NP) has been studied quantitatively on two common pathogenic bacteria Escherichia coli and Staphylococcus aureus, and the growth curves were modeled. The effect of Ag-NP on bacterial growth kinetics was studied by measuring the optical density, and was fitted by non-linear regression using the Logistic and modified Gompertz models. Scanning Electron Microscopy and fluorescence microscopy were used to study the morphological changes of the bacterial cells. Generation of reactive oxygen species for Ag-NP treated cells were measured by fluorescence emission spectra. The modified Gompertz model, incorporating cell death, fits the observed data better than the Logistic model. With increasing concentration of Ag-NP, the growth kinetics of both bacteria shows a decline in growth rate with simultaneous enhancement of death rate constants. The duration of the lag phase was found to increase with Ag-NP concentration. SEM showed morphological changes, while fluorescence microscopy using DAPI showed compaction of DNA for Ag-NP-treated bacterial cells. E. coli was found to be more susceptible to Ag-NP as compared to S. aureus. The modified Gompertz model, using a death term, was found to be useful in explaining the non-monotonic nature of the growth curve. The modified Gompertz model derived here is of general nature and can be used to study any microbial growth kinetics under the influence of antimicrobial agents. Copyright © 2014 Elsevier B.V. All rights reserved.

  3. A Kinetic Model for GaAs Growth by Hydride Vapor Phase Epitaxy

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Schulte, Kevin L.; Simon, John; Jain, Nikhil

    2016-11-21

    Precise control of the growth of III-V materials by hydride vapor phase epitaxy (HVPE) is complicated by the fact that the growth rate depends on the concentrations of nearly all inputs to the reactor and also the reaction temperature. This behavior is in contrast to metalorganic vapor phase epitaxy (MOVPE), which in common practice operates in a mass transport limited regime where growth rate and alloy composition are controlled almost exclusively by flow of the Group III precursor. In HVPE, the growth rate and alloy compositions are very sensitive to temperature and reactant concentrations, which are strong functions of themore » reactor geometry. HVPE growth, particularly the growth of large area materials and devices, will benefit from the development of a growth model that can eventually be coupled with a computational fluid dynamics (CFD) model of a specific reactor geometry. In this work, we develop a growth rate law using a Langmuir-Hinshelwood (L-H) analysis, fitting unknown parameters to growth rate data from the literature that captures the relevant kinetic and thermodynamic phenomena of the HVPE process. We compare the L-H rate law to growth rate data from our custom HVPE reactor, and develop quantitative insight into reactor performance, demonstrating the utility of the growth model.« less

  4. Soft and flexible poly(ethylene glycol) nanotubes for local drug delivery.

    PubMed

    Newland, B; Taplan, C; Pette, D; Friedrichs, J; Steinhart, M; Wang, W; Voit, B; Seib, F P; Werner, C

    2018-05-10

    Nanotubes are emerging as promising materials for healthcare applications but the selection of clinically relevant starting materials for their synthesis remains largely unexplored. Here we present, for the first time, the synthesis of poly(ethylene glycol) (PEG) based nanotubes via the photopolymerization of poly(ethylene glycol) diacrylate and other diacrylate derivatives within the pores of anodized aluminum oxide templates. Template-assisted synthesis allowed the manufacture of a diverse set of polymeric nanotubes with tunable physical characteristics including diameter (∼200-400 nm) and stiffness (405-902 kPa). PEG nanotubes were subjected to cytotoxicty assessment in cell lines and primary stem cells and showed excellent cytocompatability (IC50 > 120 μg ml-1). Nanotubes were readily drug loaded but released the majority of the drug over 5 days. Direct administration of drug loaded nanotubes to human orthotopic breast tumors substantially reduced tumor growth and metastasis and outperformed i.v. administration at the equivalent dose. Overall, this nanotube templating platform is emerging as a facile route for the manufacture of poly(ethylene glycol) nanotubes.

  5. Kinetic Monte Carlo Simulation of the Growth of Various Nanostructures through Atomic and Cluster Deposition: Application to Gold Nanostructure Growth on Graphite

    NASA Astrophysics Data System (ADS)

    Claassens, C. H.; Hoffman, M. J. H.; Terblans, J. J.; Swart, H. C.

    2006-01-01

    A Kinetic Monte Carlo (KMC) method is presented to describe the growth of metallic nanostructures through atomic and cluster deposition in the mono -and multilayer regime. The model makes provision for homo- and heteroepitaxial systems with small lattice mismatch. The accuracy of the model is tested with simulations of the growth of gold nanostructures on HOPG and comparisons are made with existing experimental data.

  6. Diffusion of One-Dimensional Crystals in Channels of Single-Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Zhigalina, V. G.; Kumskov, A. S.; Falaleev, N. S.; Vasiliev, A. L.; Kiselev, N. A.

    2018-05-01

    The transport of one-dimensional CuI crystals in channels of single-walled carbon nanotubes (SWCNTs) has been studied by high resolution electron microscopy. The diffusion kinetics has been investigated by counting the number of CuI atoms escaping from the nanotube channel. The diffusivity is calculated to be 6.8 × 10-21 m2/s, which corresponds to an activation-barrier height of 1 eV/atom. A comparison with the theoretically estimated height of the energy barrier for molecular transport through a graphene layer is indicative of mass transfer through vacancy defects in graphene.

  7. Direct dynamic kinetic analysis and computer simulation of growth of Clostridium perfringens in cooked turkey during cooling

    USDA-ARS?s Scientific Manuscript database

    This research applied a new one-step methodology to directly construct a tertiary model for describing the growth of C. perfringens in cooked turkey meat under dynamically cooling conditions. The kinetic parameters of the growth models were determined by numerical analysis and optimization using mu...

  8. Carbon Nanotube Electrode Arrays For Enhanced Chemical and Biological Sensing

    NASA Technical Reports Server (NTRS)

    Han, Jie

    2003-01-01

    Applications of carbon nanotubes for ultra-sensitive electrical sensing of chemical and biological species have been a major focus in NASA Ames Center for Nanotechnology. Great progress has been made toward controlled growth and chemical functionalization of vertically aligned carbon nanotube arrays and integration into micro-fabricated chip devices. Carbon nanotube electrode arrays devices have been used for sub-attomole detection of DNA molecules. Interdigitated carbon nanotubes arrays devices have been applied to sub ppb (part per billion) level chemical sensing for many molecules at room temperature. Stability and reliability have also been addressed in our device development. These results show order of magnitude improvement in device performance, size and power consumption as compared to micro devices, promising applications of carbon nanotube electrode arrays for clinical molecular diagnostics, personal medical testing and monitoring, and environmental monitoring.

  9. Chandipura virus growth kinetics in vertebrate cell lines, insect cell lines & embryonated eggs.

    PubMed

    Jadi, R S; Sudeep, A B; Kumar, Satyendra; Arankalle, V A; Mishra, A C

    2010-08-01

    Since not much information on Chandipura virus is available, an attempt was made to study the growth kinetics of the virus in certain vertebrate, invertebrate cell lines and embryonated chicken eggs. Comparative study of Chandipura virus (CHPV) growth kinetics in three vertebrate cell lines [Vero E6, Rhabdo myosarcoma (RD), Porcine stable kidney (PS) cell lines], two insect cell lines [Aedes aegypti (AA) and Phlebotomus papatasi (PP-9) cell lines] and embryonated pathogen free chicken eggs was conducted, by tissue culture infective dose 50 per cent (TCID(50)) and indirect immunofluorescence assay (IFA). All the cell lines and embryonated egg supported the growth of CHPV and yielded high virus titre. The vertebrate cell lines showed distinct cytopathic effect (CPE) within 4-6 h post infection (PI), while no CPE was observed in insect cell lines. PP-9 cell line was the most sensitive system to CHPV as viral antigen could be detected at 1 h PI by IFA. Our results demonstrated that all the systems were susceptible to CHPV and achieved high yield of virus. However, the PP-9 cell line had an edge over the others due to its high sensitivity to the virus which might be useful for detection and isolation of the virus during epidemics.

  10. The effect of heat treatment on microstructure evolution in artificially aged carbon nanotube/Al2024 composites synthesized by mechanical alloying

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Pérez-Bustamante, R.

    Although carbon nanotubes/aluminum (CNT/Al) composites are promising materials in the production of structural components, their mechanical behavior under overaging conditions has not been considered. In this paper the effect of CNTs on the microstructural and mechanical behavior of a 2024 aluminum alloy (Al2024) synthesized by mechanical alloying (MA) and powder metallurgy routes is discussed, as well as the effect of aging heat treatments at different temperatures and aging times. The mechanical behavior of composites was screened by hardness measurements as function of aging time. After 96 h of aging time, composites showed mechanical stability in their hardness performance. Images frommore » transmission electron microscopy showed that the mechanical stability of composites was due to a homogeneous dispersion of CNTs in the aluminum matrix and a subsequent alteration in the kinetics of precipitation is due to their presence in the aluminum matrix. Even though strengthening precipitation took place during aging, this was not the main strengthening mechanism observed in composites. - Highlights: • Dispersion of carbon nanotubes during mechanical alloying • Microstructural evolution observed by HRTEM. • Mechanical performance evaluated through micro-hardness test. • Increased mechanical performance at high working temperatures • Acceleration of kinetics of precipitation due to CNTs, and milling conditions.« less

  11. Growth Kinetics of Magnesio-Aluminate Spinel in Al/Mg Lamellar Composite Interface

    NASA Astrophysics Data System (ADS)

    Fouad, Yasser; Rabeeh, Bakr Mohamed

    The synthesis of Mg-Al2O3 double layered interface is introduced via the application of hot isostatic pressing, HIPing, in Al-Mg foils. Polycrystalline spinel layers are grown experimentally at the interfacial contacts between Al-Mg foils. The growth behavior of the spinel layers along with the kinetic parameters characterizing interface motion and long-range diffusion is established. Low melting depressant (LMD), Zn, and alloying element segregation tends to form micro laminated and/or Nano structure interphase in a lamellar composite solid state processing. Nano composite ceramic interphase materials offer interesting mechanical properties not achievable in other materials, such as superplastic flow and metal-like machinability. Microstructural characterization, mechanical characterization is also established via optical microscopy scanning electron microscopy, energy dispersive X-ray spectroscopy and tensile testing. Chemical and mechanical bonding via inter diffusion processing with alloy segregation are dominant for interphase kinetics. Mechanical characterization with interfacial shear strength is also introduced. HIPing processing is successfully applied on 6082 Al-alloy and AZ31 magnesium alloy for either particulate or micro-laminated interfacial composite processing. The interphase kinetic established through localized micro plasticity, metal flow, alloy segregation and delocalized Al oxide and Mg oxide. The kinetic of interface/interphase induce new nontraditional crack mitigation a long with new bridging and toughening mechanisms.

  12. High-resolution TEM Studies of Carbon Nanotubes and Catalyst Nanoparticles Produced During CVD from Metal Multilayer Films

    NASA Astrophysics Data System (ADS)

    Howe, Jane Y.; Puretzky, Alex A.; Geohegan, David B.; Cui, Hongtao; Eres, Varela; Maria, Alex A.; Lowndes, Douglas H.

    2003-03-01

    The structure of single-wall and multiwall carbon nanotubes and associated metal catalyst nanoparticles produced during chemical vapor deposition from multilayered metal films deposited on Si and Mo substrates were studied by high-resolution TEM and EDS. Electron beam-evaporated metal multilayer films (e.g. Al-Fe-Mo, typically 11-50 nm total thickness) roughen upon heat treatment to form a variety of catalyst particle sizes suitable for carbon nanotube growth by chemical vapor deposition using acetylene, hydrogen, and argon flow gases. This study investigates these nanoparticles, the type of nanotubes grown, their wall, tip, and basal structures, as well as the associated amounts of amorphous carbon deposited on their walls in different temperature and pressure ranges. Mixtures of SWNT and MWNT are found even for low growth temperatures (650-700 C), while rapid growth of vertically-aligned multiwall nanotubes (VA-MWNTs) predominate in a narrow temperature range at a given pressure. Arrested growth experiments were performed to determine the time periods for SWNT vs. MWNT growth. The nature of the catalyst nanoparticles, their support structure, and insights on the mechanisms of growth will be discussed.

  13. Catalytic chemical vapor deposition synthesis and electron microscopy observation of coiled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Xie, Jining; Mukhopadyay, K.; Yadev, J.; Varadan, V. K.

    2003-10-01

    Coiled carbon nanotubes exhibit excellent mechanical and electrical properties because of the combination of coil morphology and properties of nanotubes. They could have potential novel applications in nanocomposites and nano-electronic devices as well as nano-electromechanical systems. In this work, synthesis of regularly coiled carbon nanotubes is presented. It involves pyrolysis of hydrocarbon gas over metal/support catalyst by both thermal filament and microwave catalytic chemical vapor deposition methods. Scanning electron microscopy and transmission electron microscopy were performed to observe the coil morphology and nanostructure of coiled nanotubes. The growth mechanism and structural and electrical properties of coiled carbon nanotubes are also discussed.

  14. In Situ Growth of MnO2 Nanosheets on N-Doped Carbon Nanotubes Derived from Polypyrrole Tubes for Supercapacitors.

    PubMed

    Ou, Xu; Li, Qi; Xu, Dan; Guo, Jiangna; Yan, Feng

    2018-03-02

    Nitrogen-doped porous carbon nanotubes@MnO 2 (N-CNTs@MnO 2 ) nanocomposites are prepared through the in situ growth of MnO 2 nanosheets on N-CNTs derived from polypyrrole nanotubes (PNTs). Benefiting from the synergistic effects between N-CNTs (high conductivity and N doping level) and MnO 2 nanosheets (high theoretical capacity), the as-prepared N-CNTs@MnO 2 -800 nanocomposites show a specific capacitance of 219 F g -1 at a current density of 1.0 A g -1 , which is higher than that of pure MnO 2 nanosheets (128 F g -1 ) and PNTs (42 F g -1 ) in 0.5 m Na 2 SO 4 solution. Meanwhile, the capacitance retention of 86.8 % (after 1000 cycles at 10 A g -1 ) indicates an excellent electrochemical performance of N-CNTs@MnO 2 prepared in this work. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Schematic construction of flanged nanobearings from double-walled carbon nanotubes.

    PubMed

    Shenai, Prathamesh Mahesh; Zhao, Yang

    2010-08-01

    The performance of nanobearings constructed from double walled carbon nanotubes is considered to be crucially dependent on the initial rotational speed. Wearless rotation ceases for a nanobearing operating beyond a certain angular velocity. We propose a new design of nanobearings by manipulation of double walled carbon nanotubes leading to a flanged structure which possesses a built-in hindrance to the intertube oscillation without obstructing rotational motion. Through blocking the possible leakage path for rotational kinetic energy to the intertube oscillatory motion, the flanged bearing lowers its dissipative tendency when set into motion. Using molecular dynamics, it is shown that on account of its distinctive structure, the flanged bearing has superior operating characteristics and a broader working domain.

  16. Forming a Highly Active, Homogeneously Alloyed AuPt Co-catalyst Decoration on TiO2 Nanotubes Directly During Anodic Growth.

    PubMed

    Bian, Haidong; Nguyen, Nhat Truong; Yoo, JeongEun; Hejazi, Seyedsina; Mohajernia, Shiva; Müller, Julian; Spiecker, Erdmann; Tsuchiya, Hiroaki; Tomanec, Ondrej; Sanabria-Arenas, Beatriz E; Zboril, Radek; Li, Yang Yang; Schmuki, Patrik

    2018-05-30

    Au and Pt do not form homogeneous bulk alloys as they are thermodynamically not miscible. However, we show that anodic TiO 2 nanotubes (NTs) can in situ be uniformly decorated with homogeneous AuPt alloy nanoparticles (NPs) during their anodic growth. For this, a metallic Ti substrate containing low amounts of dissolved Au (0.1 atom %) and Pt (0.1 atom %) is used for anodizing. The matrix metal (Ti) is converted to oxide, whereas at the oxide/metal interface direct noble metal particle formation and alloying of Au and Pt takes place; continuously these particles are then picked up by the growing nanotube wall. In our experiments, the AuPt alloy NPs have an average size of 4.2 nm, and at the end of the anodic process, these are regularly dispersed over the TiO 2 nanotubes. These alloyed AuPt particles act as excellent co-catalyst in photocatalytic H 2 generation, with a H 2 production rate of 12.04 μL h -1 under solar light. This represents a strongly enhanced activity as compared to TiO 2 NTs decorated with monometallic particles of Au (7 μL h -1 ) or Pt (9.96 μL h -1 ).

  17. In situ observation of carbon nanotube layer growth on microbolometers with substrates at ambient temperature

    NASA Astrophysics Data System (ADS)

    Svatoš, Vojtěch; Gablech, Imrich; Ilic, B. Robert; Pekárek, Jan; Neužil, Pavel

    2018-03-01

    Carbon nanotubes (CNTs) have near unity infrared (IR) absorption efficiency, making them extremely attractive for IR imaging devices. Since CNT growth occurs at elevated temperatures, the integration of CNTs with IR imaging devices is challenging and has not yet been achieved. Here, we show a strategy for implementing CNTs as IR absorbers using differential heating of thermally isolated microbolometer membranes in a C2H2 environment. During the process, CNTs were catalytically grown on the surface of a locally heated membrane, while the substrate was maintained at an ambient temperature. CNT growth was monitored in situ in real time using optical microscopy. During growth, we measured the intensity of light emission and the reflected light from the heated microbolometer. Our measurements of bolometer performance show that the CNT layer on the surface of the microbolometer membrane increases the IR response by a factor of (2.3 ± 0.1) (mean ± one standard deviation of the least-squares fit parameters). This work opens the door to integrating near unity IR absorption, CNT-based, IR absorbers with hybrid complementary metal-oxide-semiconductor focal plane array architectures.

  18. Multiwalled carbon nanotubes effect on the bioavailability of artemisinin and its cytotoxity to cancerous cells

    NASA Astrophysics Data System (ADS)

    Rezaei, Behzad; Majidi, Najmeh; Noori, Shokoofe; Hassan, Zuhair M.

    2011-12-01

    Artemisinin regarded as one of the most promising anticancer drugs can bind to DNA with a binding constant of 1.04 × 104 M-1. The electrochemical experiments indicated that for longer incubation time periods, the reduction peak current of artemisinin on carbon nanotube modified electrode increases. Therefore, the uptake of drug molecules from a solution into CNTs will be achieved automatically by adsorption of 88.7% of artemisinin onto carbon nanotubes surface without alteration in drug properties. Hence, capability of carbon nanotubes to have synergistic effect on the bioavailability of artemisinin was investigated. Experimental tests on K562 cancer cell lines growth by MTT assay proved that multi-walled carbon nanotubes can enhance the cytotoxity of artemisinin to the targeted cancer cells with unprecedented accuracy and efficiency. The IC50 values were 65 and 35 μM for artemisinin and artemisinin loaded on multi-walled carbon nanotubes, respectively; demonstrating that artemisinin loaded on multi-walled carbon nanotubes is more effective in inhibition of cancer cell lines growth.

  19. Hydroxyl radical induced photo-transformation of single-walled carbon nanotubes in the aquatic environment

    EPA Science Inventory

    Inevitably, the growth in production of carbon nanotubes will translate into their release into our environment, yet existing information about their fate and persistence is limited. We hypothesize that indirect photochemical transformation of unfunctionalized carbon nanotubes is...

  20. Controlled growth of vertically aligned carbon nanotubes on metal substrates

    NASA Astrophysics Data System (ADS)

    Gao, Zhaoli

    Carbon nanotube (CNT) is a fascinating material with extraordinary electrical thermal and mechanical properties. Growing vertically aligned CNT (VACNT) arrays on metal substrates is an important step in bringing CNT into practical applications such as thermal interface materials (TIMs) and microelectrodes. However, the growth process is challenging due to the difficulties in preventing catalyst diffusion and controlling catalyst dewetting on metal substrates with physical surface heterogeneity. In this work, the catalyst diffusion mechanism and catalyst dewetting theory were studied for the controlled growth of VACNTs on metal substrates. The diffusion time of the catalyst, the diffusion coefficients for the catalyst in the substrate materials and the number density of catalyst nanoparticles after dewetting are identified as the key parameters, based on which three strategies are developed. Firstly, a fast-heating catalyst pretreatment strategy was used, aiming at preserving the amount of catalyst prior to CNT growth by reducing the catalyst diffusion time. The catalyst lifetime is extended from half an hour to one hour on a patterned Al thin film and a VACNT height of 106 mum, about twenty fold of that reported in the literature, was attained. Secondly, a diffusion barrier layer strategy is employed for a reduction of catalyst diffusion into the substrate materials. Enhancement of VACNT growth on Cu substrates was achieved by adopting a conformal Al2O 3 diffusion barrier layer fabricated by a specially designed atomic layer deposition (ALD) system. Lastly, a novel catalyst glancing angle deposition (GLAD) strategy is performed to manipulate the morphology of a relatively thick catalyst on metal substrates with physical surface heterogeneity, aiming to obtain uniform and dense catalyst nanoparticles after dewetting in the pretreatment process for enhanced VACNT growth. We are able to control the VACNT growth conditions on metal substrates in terms of their

  1. Abnormal growth kinetics of h-BN epitaxial monolayer on Ru(0001) enhanced by subsurface Ar species

    NASA Astrophysics Data System (ADS)

    Wei, Wei; Meng, Jie; Meng, Caixia; Ning, Yanxiao; Li, Qunxiang; Fu, Qiang; Bao, Xinhe

    2018-04-01

    Growth kinetics of epitaxial films often follows the diffusion-limited aggregation mechanism, which shows a "fractal-to-compact" morphological transition with increasing growth temperature or decreasing deposition flux. Here, we observe an abnormal "compact-to-fractal" morphological transition with increasing growth temperature for hexagonal boron nitride growth on the Ru(0001) surface. The unusual growth process can be explained by a reaction-limited aggregation (RLA) mechanism. Moreover, introduction of the subsurface Ar atoms has enhanced this RLA growth behavior by decreasing both reaction and diffusion barriers. Our work may shed light on the epitaxial growth of two-dimensional atomic crystals and help to control their morphology.

  2. TiO2 Nanotubes: Recent Advances in Synthesis and Gas Sensing Properties

    PubMed Central

    Galstyan, Vardan; Comini, Elisabetta; Faglia, Guido; Sberveglieri, Giorgio

    2013-01-01

    Synthesis—particularly by electrochemical anodization-, growth mechanism and chemical sensing properties of pure, doped and mixed titania tubular arrays are reviewed. The first part deals on how anodization parameters affect the size, shape and morphology of titania nanotubes. In the second part fabrication of sensing devices based on titania nanotubes is presented, together with their most notable gas sensing performances. Doping largely improves conductivity and enhances gas sensing performances of TiO2 nanotubes. PMID:24184919

  3. Electric-Loading Enhanced Kinetics in Oxide Ceramics: Pore Migration, Sintering and Grain Growth: Final Report

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chen, I-Wei

    Solid oxide fuel cells and solid oxide electrolysis cells rely on solid electrolytes in which a large ionic current dominates. This project was initiated to investigate microstructural changes in such devices under electrochemical forces, because nominally insignificant processes may couple to the large ionic current to yield non-equilibrium phenomena that alter the microstructure. Our studies had focused on yttria-stabilized cubic zirconia (YSZ) widely used in these devices. The experiments have revealed enhanced grain growth at higher temperatures, pore and gas bubble migration at all temperatures, and the latter also lead to enhanced sintering of highly porous ceramics into fully densemore » ceramics at unprecedentedly low temperatures. These results have shed light on kinetic processes that fall completely outside the realm of classical ceramic processing. Other fast-oxygen oxide ceramics closely related to, and often used in conjunction with zirconia ceramics, have also be investigated, as are closely related scientific problems in zirconia ceramics. These include crystal structures, defects, diffusion kinetics, oxygen potentials, low temperature sintering, flash sintering, and coarsening theory, and all have resulted in greater clarity in scientific understanding. The knowledge is leveraged to provide new insight to electrode kinetics and near-electrode mixed conductivity and to new materials. In the following areas, our research has resulted in completely new knowledge that defines the state-of-the-art of the field. (a) Electrical current driven non-equilibrium phenomena, (b) Enhanced grain growth under electrochemically reducing conditions, (c) Development of oxygen potential polarization in electrically loaded electrolyte, (d) Low temperature sintering and grain growth, and (e) Structure, defects and cation kinetics of fluorite-structured oxides. Our research has also contributed to synthesis of new energy-relevant electrochemical materials and new

  4. Guided growth of large-scale, horizontally aligned arrays of single-walled carbon nanotubes and their use in thin-film transistors.

    PubMed

    Kocabas, Coskun; Hur, Seung-Hyun; Gaur, Anshu; Meitl, Matthew A; Shim, Moonsub; Rogers, John A

    2005-11-01

    A convenient process for generating large-scale, horizontally aligned arrays of pristine, single-walled carbon nanotubes (SWNTs) is described. The approach uses guided growth, by chemical vapor deposition (CVD), of SWNTs on miscut single-crystal quartz substrates. Studies of the growth reveal important relationships between the density and alignment of the tubes, the CVD conditions, and the morphology of the quartz. Electrodes and dielectrics patterned on top of these arrays yield thin-film transistors that use the SWNTs as effective thin-film semiconductors. The ability to build high-performance devices of this type suggests significant promise for large-scale aligned arrays of SWNTs in electronics, sensors, and other applications.

  5. Observational Constraints on Modeling Growth and Evaporation Kinetics of Isoprene SOA

    NASA Astrophysics Data System (ADS)

    Zaveri, R. A.; Shilling, J. E.; Zelenyuk, A.; Liu, J.; Wilson, J. M.; Laskin, A.; Wang, B.; Fast, J. D.; Easter, R. C.; Wang, J.; Kuang, C.; Thornton, J. A.; Setyan, A.; Zhang, Q.; Onasch, T. B.; Worsnop, D. R.

    2014-12-01

    Isoprene is thought to be a major contributor to the global secondary organic aerosol (SOA) budget, and therefore has the potential to exert a significant influence on earth's climate via aerosol direct and indirect radiative effects. Both aerosol optical and cloud condensation nuclei properties are quite sensitive to aerosol number size distribution, as opposed to the total aerosol mass concentration. Recent studies suggest that SOA particles can be highly viscous, which can affect the kinetics of SOA partitioning and size distribution evolution when the condensing organic vapors are semi-volatile. In this study, we examine the growth kinetics of SOA formed from isoprene photooxidation in the presence of pre-existing Aitken and accumulation mode aerosols in: (a) the ambient atmosphere during the CARES field campaign, and (b) the environmental chamber at PNNL. Each growth episode is analyzed and interpreted with the updated MOSAIC aerosol box model, which performs kinetic gas-particle partitioning of SOA and takes into account diffusion and chemical reaction within the particle phase. The model is initialized with the observed aerosol size distribution and composition at the beginning of the experiment, and the total amount of SOA formed in the model at any given time is constrained by the observed total amount of SOA formed. The variable model parameters include the number of condensing organic species, their gas-phase formation rates, their effective volatilities, and their bulk diffusivities in the Aitken and accumulation modes. The objective of the constrained modeling exercise is then to determine which model configuration is able to best reproduce the observed size distribution evolution, thus providing valuable insights into the possible mechanism of SOA formation. We also examine the evaporation kinetics of size-selected particles formed in the environmental chamber to provide additional constraints on the effective volatility and bulk diffusivity of the

  6. Carbon nanotubes in blends of polycaprolactone/thermoplastic starch.

    PubMed

    Taghizadeh, Ata; Favis, Basil D

    2013-10-15

    Despite the importance of polymer-polymer multiphase systems, very little work has been carried out on the preferred localization of solid inclusions in such multiphase systems. In this work, carbon nanotubes (CNT) are dispersed with polycaprolactone (PCL) and thermoplastic starch (TPS) at several CNT contents via a combined solution/twin-screw extrusion melt mixing method. A PCL/CNT masterbatch was first prepared and then blended with 20 wt% TPS. Transmission and scanning electron microscopy images reveal a CNT localization principally in the TPS phase and partly at the PCL/TPS interface, with no further change by annealing. This indicates a strong driving force for the CNTs toward TPS. Young's model predicts that the nanotubes should be located at the interface. X-ray photoelectron spectroscopy (XPS) of extracted CNTs quantitatively confirms an encapsulation by TPS and reveals a covalent bonding of CNTs with thermoplastic starch. It appears likely that the nanotubes migrate to the interface, react with TPS and then are subsequently drawn into the low viscosity TPS phase. In a low shear rate/low shear stress internal mixer the nanotubes are found both in the PCL phase and at the PCL/TPS interface and have not completed the transit to the TPS phase. This latter result indicates the importance of choosing appropriate processing conditions in order to minimize kinetic effects. The addition of CNTs to PCL results in an increase in the crystallization temperature and a decrease in the percent crystallinity confirming the heterogeneous nucleating effect of the nanotubes. Finally, DMA analysis reveals a dramatic decrease in the starch rich phase transition temperature (~26 °C), for the system with nanotubes located in the TPS phase. Copyright © 2013 Elsevier Ltd. All rights reserved.

  7. Aligned carbon nanotubes patterned photolithographically by silver

    NASA Astrophysics Data System (ADS)

    Huang, Shaoming; Mau, Albert H. W.

    2003-02-01

    Selective growth of aligned carbon nanotubes (CNTs) by pyrolysis of iron (II) phthalocyanine (FePc) on quartz substrate patterned photolithographically by metallic silver has been demonstrated. Micro/nanopattern of aligned CNTs can be achieved by using a photomask with features on a microscale. With convenient use of simple high-contract black and white films as a photomask, aligned nanotubes patterned with 20 μm resolution in large scale can be fabricated. This practical fabrication of aligned CNTs on patterned conducting substrate could be applied to various device applications of CNTs.

  8. A parametric study of single-wall carbon nanotube growth by laser ablation

    NASA Technical Reports Server (NTRS)

    Arepalli, Sivaram; Holmes, William A.; Nikolaev, Pavel; Hadjiev, Victor G.; Scott, Carl D.

    2004-01-01

    Results of a parametric study of carbon nanotube production by the double-pulse laser oven process are presented. The effect of various operating parameters on the production of single-wall carbon nanotubes (SWCNTs) is estimated by characterizing the nanotube material using analytical techniques, including scanning electron microscopy, transmission electron microscopy, thermo gravimetric analysis and Raman spectroscopy. The study included changing the sequence of the laser pulses, laser energy, pulse separation, type of buffer gas used, operating pressure, flow rate, inner tube diameter, as well as its material, and oven temperature. It was found that the material quality and quantity improve with deviation from normal operation parameters such as laser energy density higher than 1.5 J/cm2, pressure lower than 67 kPa, and flow rates higher than 100 sccm. Use of helium produced mainly small diameter tubes and a lower yield. The diameter of SWCNTs decreases with decreasing oven temperature and lower flow rates.

  9. Carbon nanotubes functionalized with fibroblast growth factor accelerate proliferation of bone marrow-derived stromal cells and bone formation

    NASA Astrophysics Data System (ADS)

    Hirata, Eri; Ménard-Moyon, Cécilia; Venturelli, Enrica; Takita, Hiroko; Watari, Fumio; Bianco, Alberto; Yokoyama, Atsuro

    2013-11-01

    Multi-walled carbon nanotubes (MWCNTs) were functionalized with fibroblast growth factor (FGF) and the advantages of their use as scaffolds for bone augmentation were evaluated in vitro and in vivo. The activity of FGF was assessed by measuring the effect on the proliferation of rat bone marrow stromal cells (RBMSCs). The presence of FGF enhanced the proliferation of RBMSCs and the FGF covalently conjugated to the nanotubes (FGF-CNT) showed the same effect as FGF alone. In addition, FGF-CNT coated sponges were implanted between the parietal bone and the periosteum of rats and the formation of new bone was investigated. At day 14 after implantation, a larger amount of newly formed bone was clearly observed in most pores of FGF-CNT coated sponges. These findings indicated that MWCNTs accelerated new bone formation in response to FGF, as well as the integration of particles into new bone during its formation. Scaffolds coated with FGF-CNT could be considered as promising novel substituting materials for bone regeneration in future tissue engineering applications.

  10. Gemcitabine Hydrochloride-Loaded Functionalised Carbon Nanotubes as Potential Carriers for Tumour Targeting

    PubMed Central

    Das, Shilpee; Desai, Jagruti L.; Thakkar, Hetal P.

    2013-01-01

    The objective of the present work was to formulate gemcitabine hydrochloride loaded functionalised carbon nanotubes to achieve tumour targeted drug release and thereby reducing gemcitabine hydrochloride toxicity. Multiwalled carbon nanotubes were functionalised using 1,2-distearoylphosphatidyl ethanolamine-methyl polyethylene glycol conjugate 2000. Optimised ratio 1:2 of carbon nanotubes:1,2-distearoylphosphatidyl ethanolamine-methyl polyethylene glycol conjugate 2000 was taken for loading of gemcitabine hydrochloride. The formulation was evaluated for different parameters. The results showed that maximum drug loading efficiency achieved was 41.59% with an average particle size of 188.7 nm and zeta potential of −10−1 mV. Scanning electron microscopy and transmission electron microscopy images confirmed the tubular structure of the formulation. The carbon nanotubes were able to release gemcitabine hydrochloride faster in acidic pH than at neutral pH indicating its potential for tumour targeting. Gemcitabine hydrochloride release from carbon nanotubes was found to follow Korsmeyer-Peppas kinetic model with non-Fickian diffusion pattern. Cytotoxic activity of formulation on A549 cells was found to be higher in comparison to free gemcitabine hydrochloride. Stability studies indicated that lyophilised samples of the formulation were more stable for 3 months under refrigerated condition than at room temperature. Thus carbon nanotubes can be promising carrier for the anticancer drug gemcitabine hydrochloride. PMID:24591746

  11. Growth kinetics and mass transport mechanisms of GaN columns by selective area metal organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Xue; Hartmann, Jana; Mandl, Martin; Sadat Mohajerani, Matin; Wehmann, Hergo-H.; Strassburg, Martin; Waag, Andreas

    2014-04-01

    Three-dimensional GaN columns recently have attracted a lot of attention as the potential basis for core-shell light emitting diodes for future solid state lighting. In this study, the fundamental insights into growth kinetics and mass transport mechanisms of N-polar GaN columns during selective area metal organic vapor phase epitaxy on patterned SiOx/sapphire templates are systematically investigated using various pitch of apertures, growth time, and silane flow. Species impingement fluxes on the top surface of columns Jtop and on their sidewall Jsw, as well as, the diffusion flux from the substrate Jsub contribute to the growth of the GaN columns. The vertical and lateral growth rates devoted by Jtop, Jsw and Jsub are estimated quantitatively. The diffusion length of species on the SiOx mask surface λsub as well as on the sidewall surfaces of the 3D columns λsw are determined. The influences of silane on the growth kinetics are discussed. A growth model is developed for this selective area metal organic vapor phase epitaxy processing.

  12. Importance of oxygen in the metal-free catalytic growth of single-walled carbon nanotubes from SiO(x) by a vapor-solid-solid mechanism.

    PubMed

    Liu, Bilu; Tang, Dai-Ming; Sun, Chenghua; Liu, Chang; Ren, Wencai; Li, Feng; Yu, Wan-Jing; Yin, Li-Chang; Zhang, Lili; Jiang, Chuanbin; Cheng, Hui-Ming

    2011-01-19

    To understand in-depth the nature of the catalyst and the growth mechanism of single-walled carbon nanotubes (SWCNTs) on a newly developed silica catalyst, we performed this combined experimental and theoretical study. In situ transmission electron microscopy (TEM) observations revealed that the active catalyst for the SWCNT growth is solid and amorphous SiO(x) nanoparticles (NPs), suggesting a vapor-solid-solid growth mechanism. From in situ TEM and chemical vapor deposition growth experiments, we found that oxygen plays a crucial role in SWCNT growth in addition to the well-known catalyst size effect. Density functional theory calculations showed that oxygen atoms can enhance the capture of -CH(x) and consequently facilitate the growth of SWCNTs on oxygen-containing SiO(x) NPs.

  13. Growth of carbon nanotubes on fully processed silicon-on-insulator CMOS substrates.

    PubMed

    Haque, M Samiul; Ali, S Zeeshan; Guha, P K; Oei, S P; Park, J; Maeng, S; Teo, K B K; Udrea, F; Milne, W I

    2008-11-01

    This paper describes the growth of Carbon Nanotubes (CNTs) both aligned and non-aligned on fully processed CMOS substrates containing high temperature tungsten metallization. While the growth method has been demonstrated in fabricating CNT gas sensitive layers for high temperatures SOI CMOS sensors, it can be employed in a variety of applications which require the use of CNTs or other nanomaterials with CMOS electronics. In our experiments we have grown CNTs both on SOI CMOS substrates and SOI CMOS microhotplates (suspended on membranes formed by post-CMOS deep RIE etching). The fully processed SOI substrates contain CMOS devices and circuits and additionally, some wafers contained high current LDMOSFETs and bipolar structures such as Lateral Insulated Gate Bipolar Transistors. All these devices were used as test structures to investigate the effect of additional post-CMOS processing such as CNT growth, membrane formation, high temperature annealing, etc. Electrical characterisation of the devices with CNTs were performed along with SEM and Raman spectroscopy. The CNTs were grown both at low and high temperatures, the former being compatible with Aluminium metallization while the latter being possible through the use of the high temperature CMOS metallization (Tungsten). In both cases we have found that there is no change in the electrical behaviour of the CMOS devices, circuits or the high current devices. A slight degradation of the thermal performance of the CMOS microhotplates was observed due to the extra heat dissipation path created by the CNT layers, but this is expected as CNTs exhibit a high thermal conductance. In addition we also observed that in the case of high temperature CNT growth a slight degradation in the manufacturing yield was observed. This is especially the case where large area membranes with a diameter in excess of 500 microns are used.

  14. Modeling the growth kinetics of Bacillus cereus as a function of temperature, pH, sodium lactate and sodium chloride concentrations.

    PubMed

    Olmez, Hülya Kaptan; Aran, Necla

    2005-02-01

    Mathematical models describing the growth kinetic parameters (lag phase duration and growth rate) of Bacillus cereus as a function of temperature, pH, sodium lactate and sodium chloride concentrations were obtained in this study. In order to get a residual distribution closer to a normal distribution, the natural logarithm of the growth kinetic parameters were used in modeling. For reasons of parsimony, the polynomial models were reduced to contain only the coefficients significant at a level of pgrowth parameters. Predicted data were compared with the predictions from Pathogen Modeling Program (PMP-US Department of Agriculture-Agricultural Research Service) and validated against data extracted from the literature. The mean absolute relative error (MARE) and the median relative error (MRE) of the predicted generation times with the derived model were 25.6% and -16.7%, respectively, showing that the growth rate model accurately and safely predicted the growth kinetics of B. cereus. Results of the modeling study indicated that all of the studied factors had a significant effect on the growth of B. cereus in the experimental range studied.

  15. Highly efficient growth of vertically aligned carbon nanotubes on Fe-Ni based metal alloy foils for supercapacitors

    NASA Astrophysics Data System (ADS)

    Amalina Raja Seman, Raja Noor; Asyadi Azam, Mohd; Ambri Mohamed, Mohd

    2016-12-01

    Supercapacitors are highly promising energy devices with superior charge storage performance and a long lifecycle. Construction of the supercapacitor cell, especially electrode fabrication, is critical to ensure good performance in applications. This work demonstrates direct growth of vertically aligned carbon nanotubes (CNTs) on Fe-Ni based metal alloy foils, namely SUS 310S, Inconel 600 and YEF 50, and their use in symmetric vertically aligned CNT supercapacitor electrodes. Alumina and cobalt thin film catalysts were deposited onto the foils, and then CNT growth was performed using alcohol catalytic chemical vapour deposition. By this method, vertically aligned CNTs were successfully grown and used directly as a binder-free supercapacitor electrode to deliver excellent electrochemical performance. The device showed relatively good specific capacitance, a superior rate capability and excellent cycle stability, maintaining about 96% capacitance up to 1000 cycles.

  16. Growth of carbon nanotubes by Fe-catalyzed chemical vapor processes on silicon-based substrates

    NASA Astrophysics Data System (ADS)

    Angelucci, Renato; Rizzoli, Rita; Vinciguerra, Vincenzo; Fortuna Bevilacqua, Maria; Guerri, Sergio; Corticelli, Franco; Passini, Mara

    2007-03-01

    In this paper, a site-selective catalytic chemical vapor deposition synthesis of carbon nanotubes on silicon-based substrates has been developed in order to get horizontally oriented nanotubes for field effect transistors and other electronic devices. Properly micro-fabricated silicon oxide and polysilicon structures have been used as substrates. Iron nanoparticles have been obtained both from a thin Fe film evaporated by e-gun and from iron nitrate solutions accurately dispersed on the substrates. Single-walled nanotubes with diameters as small as 1 nm, bridging polysilicon and silicon dioxide “pillars”, have been grown. The morphology and structure of CNTs have been characterized by SEM, AFM and Raman spectroscopy.

  17. 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.

  18. 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.

  19. Adhesion to Carbon Nanotube Conductive Scaffolds Forces Action-Potential Appearance in Immature Rat Spinal Neurons

    PubMed Central

    Toma, Francesca Maria; Calura, Enrica; Rizzetto, Lisa; Carrieri, Claudia; Roncaglia, Paola; Martinelli, Valentina; Scaini, Denis; Masten, Lara; Turco, Antonio; Gustincich, Stefano; Prato, Maurizio; Ballerini, Laura

    2013-01-01

    In the last decade, carbon nanotube growth substrates have been used to investigate neurons and neuronal networks formation in vitro when guided by artificial nano-scaled cues. Besides, nanotube-based interfaces are being developed, such as prosthesis for monitoring brain activity. We recently described how carbon nanotube substrates alter the electrophysiological and synaptic responses of hippocampal neurons in culture. This observation highlighted the exceptional ability of this material in interfering with nerve tissue growth. Here we test the hypothesis that carbon nanotube scaffolds promote the development of immature neurons isolated from the neonatal rat spinal cord, and maintained in vitro. To address this issue we performed electrophysiological studies associated to gene expression analysis. Our results indicate that spinal neurons plated on electro-conductive carbon nanotubes show a facilitated development. Spinal neurons anticipate the expression of functional markers of maturation, such as the generation of voltage dependent currents or action potentials. These changes are accompanied by a selective modulation of gene expression, involving neuronal and non-neuronal components. Our microarray experiments suggest that carbon nanotube platforms trigger reparative activities involving microglia, in the absence of reactive gliosis. Hence, future tissue scaffolds blended with conductive nanotubes may be exploited to promote cell differentiation and reparative pathways in neural regeneration strategies. PMID:23951361

  20. Aggregation Kinetics and Transport of Single-Walled CarbonNanotubes at Low Surfactant Concentrations

    EPA Science Inventory

    Little is known about how low levels of surfactants can affect the colloidal stability of single-walled carbon nanotubes (SWNTs) and how surfactant-wrapping of SWNTs can impact ecological exposures in aqueous systems. In this study, SWNTs were suspended in water with sodium ...

  1. Inorganic nanotubes.

    PubMed

    Tenne, Reshef; Rao, C N R

    2004-10-15

    Following the discovery of carbon fullerenes and carbon nanotubes, it was hypothesized that nanoparticles of inorganic compounds with layered (two-dimensional) structure, such as MoS(2), will not be stable against folding and form nanotubes and fullerene-like structures: IF. The synthesis of numerous other inorganic nanotubes has been reported in recent years. Various techniques for the synthesis of inorganic nanotubes, including high-temperature reactions and strategies based on 'chemie douce' (soft chemistry, i.e. low-temperature) processes, are described. First-principle, density functional theory based calculations are able to provide substantial information on the structure and properties of such nanotubes. Various properties of inorganic nanotubes, including mechanical, electronic and optical properties, are described in brief. Some potential applications of the nanotubes in tribology, protection against impact, (photo)catalysis, batteries, etc., are discussed.

  2. Atomistic Modeling of Thermal Conductivity of Epoxy Nanotube Composites

    NASA Astrophysics Data System (ADS)

    Fasanella, Nicholas A.; Sundararaghavan, Veera

    2016-05-01

    The Green-Kubo method was used to investigate the thermal conductivity as a function of temperature for epoxy/single wall carbon nanotube (SWNT) nanocomposites. An epoxy network of DGEBA-DDS was built using the `dendrimer' growth approach, and conductivity was computed by taking into account long-range Coulombic forces via a k-space approach. Thermal conductivity was calculated in the direction perpendicular to, and along the SWNT axis for functionalized and pristine SWNT/epoxy nanocomposites. Inefficient phonon transport at the ends of nanotubes is an important factor in the thermal conductivity of the nanocomposites, and for this reason discontinuous nanotubes were modeled in addition to long nanotubes. The thermal conductivity of the long, pristine SWNT/epoxy system is equivalent to that of an isolated SWNT along its axis, but there was a 27% reduction perpendicular to the nanotube axis. The functionalized, long SWNT/epoxy system had a very large increase in thermal conductivity along the nanotube axis (~700%), as well as the directions perpendicular to the nanotube (64%). The discontinuous nanotubes displayed an increased thermal conductivity along the SWNT axis compared to neat epoxy (103-115% for the pristine SWNT/epoxy, and 91-103% for functionalized SWNT/epoxy system). The functionalized system also showed a 42% improvement perpendicular to the nanotube, while the pristine SWNT/epoxy system had no improvement over epoxy. The thermal conductivity tensor is averaged over all possible orientations to see the effects of randomly orientated nanotubes, and allow for experimental comparison. Excellent agreement is seen for the discontinuous, pristine SWNT/epoxy nanocomposite. These simulations demonstrate there exists a threshold of the SWNT length where the best improvement for a composite system with randomly oriented nanotubes would transition from pristine SWNTs to functionalized SWNTs.

  3. Vertically Aligned Carbon Nanotubes at Different Temperatures by Spray Pyrolysis Techniques

    NASA Astrophysics Data System (ADS)

    Afre, Rakesh A.; Soga, T.; Jimbo, T.; Kumar, Mukul; Ando, Y.; Sharon, M.

    Vertically aligned arrays of multi-walled carbon nanotubes (VACNTs) were grown by spray pyrolysis of turpentine oil and ferrocene mixture at temperatures higher than 700°C. Using this simple method, we report the successful growth of vertically aligned nanotubes of ~300μm length and diameter in the range of ?20-80nm on Si(100) substrate. The ferrocene acts as an in situ Fe catalyst precursor, forming the nano-sized metallic iron particles for formation of VACNTs on the Si substrate. The morphological characteristics of VACNTs are confirmed by SEM, TEM and Raman spectroscopy and growth mechanism is discussed in short.

  4. Mild in situ growth of platinum nanoparticles on multiwalled carbon nanotube-poly (vinyl alcohol) hydrogel electrode for glucose electrochemical oxidation

    NASA Astrophysics Data System (ADS)

    Liu, Shumin; Zheng, Yudong; Qiao, Kun; Su, Lei; Sanghera, Amendeep; Song, Wenhui; Yue, Lina; Sun, Yi

    2015-12-01

    This investigation describes an effective strategy to fabricate an electrochemically active hybrid hydrogel made from platinum nanoparticles that are highly dense, uniformly dispersed, and tightly embedded throughout the conducting hydrogel network for the electrochemical oxidation of glucose. A suspension of multiwalled carbon nanotubes and polyvinyl alcohol aqueous was coated on glassy carbon electrode by electrophoretic deposition and then physically crosslinked to form a three-dimensional porous conductive hydrogel network by a process of freezing and thawing. The network offered 3D interconnected mass-transport channels (around 200 nm) and confined nanotemplates for in situ growth of uniform platinum nanoparticles via the moderate reduction agent, ascorbic acid. The resulting hybrid hydrogel electrode membrane demonstrates an effective method for loading platinum nanoparticles on multiwalled carbon nanotubes by the electrostatic adsorption between multiwalled carbon nanotubes and platinum ions within porous hydrogel network. The average diameter of platinum nanoparticles is 37 ± 14 nm, which is less than the particle size by only using the moderate reduction agent. The hybrid hydrogel electrode membrane-coated glassy carbon electrode showed excellent electrocatalytic activity and good long-term stability toward glucose electrochemical oxidation. The glucose oxidation current exhibited a linear relationship with the concentration of glucose in the presence of chloride ions, promising for potential applications of implantable biofuel cells, biosensors, and electronic devices.

  5. Nanotube Dispersions Made With Charged Surfactant

    NASA Technical Reports Server (NTRS)

    Kuper, Cynthia; Kuzma, Mike

    2006-01-01

    Dispersions (including monodispersions) of nanotubes in water at relatively high concentrations have been formulated as prototypes of reagents for use in making fibers, films, and membranes based on single-walled carbon nanotubes (SWNTs). Other than water, the ingredients of a dispersion of this type include one or more charged surfactant(s) and carbon nanotubes derived from the HiPco(TradeMark) (or equivalent) process. Among reagents known to be made from HiPco(TradeMark)(or equivalent) SWNTs, these are the most concentrated and are expected to be usable in processing of bulk structures and materials. Test data indicate that small bundles of SWNTs and single SWNTs at concentrations up to 1.1 weight percent have been present in water plus surfactant. This development is expected to contribute to the growth of an industry based on applied carbon nanotechnology. There are expected to be commercial applications in aerospace, avionics, sporting goods, automotive products, biotechnology, and medicine.

  6. Molecular imprinting at walls of silica nanotubes for TNT recognition.

    PubMed

    Xie, Chenggen; Liu, Bianhua; Wang, Zhenyang; Gao, Daming; Guan, Guijian; Zhang, Zhongping

    2008-01-15

    This paper reports the molecular imprinting at the walls of highly uniform silica nanotubes for the recognition of 2,4,6-trinitrotoluene (TNT). It has been demonstrated that TNT templates were efficiently imprinted into the matrix of silica through the strong acid-base pairing interaction between TNT and 3-aminopropyltriethoxysilane (APTS). TNT-imprinted silica nanotubes were synthesized by the gelation reaction between APTS and tetraethylorthosilicate (TEOS), selectively occurring at the porous walls of APTS-modified alumina membranes. The removal of the original TNT templates leaves the imprinted cavities with covalently anchored amine groups at the cavity walls. A high density of recognition sites with molecular selectivity to the TNT analyte was created at the wall of silica nanotubes. Furthermore, most of these recognition sites are situated at the inside and outside surfaces of tubular walls and in the proximity of the two surfaces due to the ultrathin wall thickness of only 15 nm, providing a better site accessibility and lower mass-transfer resistance. Therefore, greater capacity and faster kinetics of uptaking target species were achieved. The silica nanotube reported herein is an ideal form of material for imprinting various organic or biological molecules toward applications in chemical/biological sensors and bioassay.

  7. Fast growth with crystal splitting of morphology-controllable Bi2S3 flowers on TiO2 nanotube arrays

    NASA Astrophysics Data System (ADS)

    Yang, L. X.; Ding, Y. B.; Luo, S. L.; Luo, Y.; Deng, F.; Li, Y.

    2013-03-01

    Bi2S3 crystals with flower-like morphologies are deposited on TiO2 nanotube arrays (NTs) by applying the cathodic pulse electrodeposition (PED) technique at 120 °C in 20 s. The highly oriented TiO2 NTs/Ti serving as substrate has high surface energy which is favorable for Gibbs free energy decreasing in nucleation process. Numerous boundaries between NTs are nucleation sites for atomic clusters, resulting in a fast nucleation velocity. Effective and fast heterogeneous nucleation initiates a thermodynamic control growth model and finally leads to the fast formation of highly crystallized Bi2S3 with a typical splitting property. Ethylene glycol (EG) was introduced into the electrolytes to inhibit the typical growth along the c axis ([0 0 1] plane) and facilitate the growth along the ab plane, producing Bi2S3 crystals with variable morphologies from sheaves to flowers by increasing EG contents.

  8. Growth dynamics of carbon-metal particles and nanotubes synthesized by CO2 laser vaporization

    NASA Astrophysics Data System (ADS)

    Kokai, F.; Takahashi, K.; Yudasaka, M.; Iijima, S.

    To study the growth of carbon-Co/Ni particles and single-wall carbon nanotubes (SWNTs) by 20 ms CO2 laser-pulse irradiation of a graphite-Co/Ni (1.2 at.%) target in an Ar gas atmosphere (600 Torr), we used emission imaging spectroscopy and shadowgraphy with a temporal resolution of 1.67 ms. Wavelength-selected emission images showed that C2 emission was strong in the region close to the target (within 2 cm), while for the same region the blackbody radiation from the large clusters or particles increased with increasing distance from the target. Shadowgraph images showed that the viscous flow of carbon and metal species formed a mushroom or a turbulent cloud spreading slowly into the Ar atmosphere, indicating that particles and SWNTs continued to grow as the ejected material cooled. In addition, emission imaging spectroscopy at 1200 °C showed that C2 and hot clusters and particles with higher emission intensities were distributed over much wider areas. We discuss the growth dynamics of the particles and SWNTs through the interaction of the ambient Ar with the carbon and metal species released from the target by the laser pulse.

  9. 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

  10. The mathematical properties of the quasi-chemical model for microorganism growth-death kinetics in foods.

    PubMed

    Ross, E W; Taub, I A; Doona, C J; Feeherry, F E; Kustin, K

    2005-03-15

    Knowledge of the mathematical properties of the quasi-chemical model [Taub, Feeherry, Ross, Kustin, Doona, 2003. A quasi-chemical kinetics model for the growth and death of Staphylococcus aureus in intermediate moisture bread. J. Food Sci. 68 (8), 2530-2537], which is used to characterize and predict microbial growth-death kinetics in foods, is important for its applications in predictive microbiology. The model consists of a system of four ordinary differential equations (ODEs), which govern the temporal dependence of the bacterial life cycle (the lag, exponential growth, stationary, and death phases, respectively). The ODE system derives from a hypothetical four-step reaction scheme that postulates the activity of a critical intermediate as an antagonist to growth (perhaps through a quorum sensing biomechanism). The general behavior of the solutions to the ODEs is illustrated by several examples. In instances when explicit mathematical solutions to these ODEs are not obtainable, mathematical approximations are used to find solutions that are helpful in evaluating growth in the early stages and again near the end of the process. Useful solutions for the ODE system are also obtained in the case where the rate of antagonist formation is small. The examples and the approximate solutions provide guidance in the parameter estimation that must be done when fitting the model to data. The general behavior of the solutions is illustrated by examples, and the MATLAB programs with worked examples are included in the appendices for use by predictive microbiologists for data collected independently.

  11. Growth of non-toxigenic Clostridium botulinum mutant LNT01 in cooked beef: One-step kinetic analysis and comparison with C. sporogenes and C. perfringens.

    PubMed

    Huang, Lihan

    2018-05-01

    The objective of this study was to investigate the growth kinetics of Clostridium botulinum LNT01, a non-toxigenic mutant of C. botulinum 62A, in cooked ground beef. The spores of C. botulinum LNT01 were inoculated to ground beef and incubated anaerobically under different temperature conditions to observe growth and develop growth curves. A one-step kinetic analysis method was used to analyze the growth curves simultaneously to minimize the global residual error. The data analysis was performed using the USDA IPMP-Global Fit, with the Huang model as the primary model and the cardinal parameters model as the secondary model. The results of data analysis showed that the minimum, optimum, and maximum growth temperatures of this mutant are 11.5, 36.4, and 44.3 °C, and the estimated optimum specific growth rate is 0.633 ln CFU/g per h, or 0.275 log CFU/g per h. The maximum cell density is 7.84 log CFU/g. The models and kinetic parameters were validated using additional isothermal and dynamic growth curves. The resulting residual errors of validation followed a Laplace distribution, with about 60% of the residual errors within ±0.5 log CFU/g of experimental observations, suggesting that the models could predict the growth of C. botulinum LNT01 in ground beef with reasonable accuracy. Comparing with C. perfringens, C. botulinum LNT01 grows at much slower rates and with much longer lag times. Its growth kinetics is also very similar to C. sporogenes in ground beef. The results of computer simulation using kinetic models showed that, while prolific growth of C. perfringens may occur in ground beef during cooling, no growth of C. botulinum LNT01 or C. sporogenes would occur under the same cooling conditions. The models developed in this study may be used for prediction of the growth and risk assessments of proteolytic C. botulinum in cooked meats. Published by Elsevier Ltd.

  12. Influence of carbon nanotubes on the buckling of microtubule bundles in viscoelastic cytoplasm using nonlocal strain gradient theory

    NASA Astrophysics Data System (ADS)

    Farajpour, A.; Rastgoo, A.

    Carbon nanotubes are a new class of microtubule-stabilizing agents since they interact with protein microtubules in living cells, interfering with cell division and inducing apoptosis. In the present work, a modified beam model is developed to investigate the effect of carbon nanotubes on the buckling of microtubule bundles in living cell. A realistic interaction model is employed using recent experimental data on the carbon nanotube-stabilized microtubules. Small scale and surface effects are taken into account applying the nonlocal strain gradient theory and surface elasticity theory. Pasternak model is used to describe the normal and shearing effects of enclosing filament matrix on the buckling behavior of the system. An exact solution is obtained for the buckling growth rates of the mixed bundle in viscoelastic surrounding cytoplasm. The present results are compared with those reported in the open literature for single microtubules and an excellent agreement is found. Finally, the effects of different parameters such as the size, chirality, position and surface energy of carbon nanotubes on the buckling growth rates of microtubule bundles are studied. It is found that the buckling growth rate may increase or decrease by adding carbon nanotubes, depending on the diameter and chirality of carbon nanotubes.

  13. Nanotube junctions

    DOEpatents

    Crespi, Vincent Henry; Cohen, Marvin Lou; Louie, Steven Gwon; Zettl, Alexander Karlwalte

    2004-12-28

    The present invention comprises a new nanoscale metal-semiconductor, semiconductor-semiconductor, or metal-metal junction, designed by introducing topological or chemical defects in the atomic structure of the nanotube. Nanotubes comprising adjacent sections having differing electrical properties are described. These nanotubes can be constructed from combinations of carbon, boron, nitrogen and other elements. The nanotube can be designed having different indices on either side of a junction point in a continuous tube so that the electrical properties on either side of the junction vary in a useful fashion. For example, the inventive nanotube may be electrically conducting on one side of a junction and semiconducting on the other side. An example of a semiconductor-metal junction is a Schottky barrier. Alternatively, the nanotube may exhibit different semiconductor properties on either side of the junction. Nanotubes containing heterojunctions, Schottky barriers, and metal-metal junctions are useful for microcircuitry.

  14. Nanotube junctions

    DOEpatents

    Crespi, Vincent Henry; Cohen, Marvin Lou; Louie, Steven Gwon Sheng; Zettl, Alexander Karlwalter

    2003-01-01

    The present invention comprises a new nanoscale metal-semiconductor, semiconductor-semiconductor, or metal-metal junction, designed by introducing topological or chemical defects in the atomic structure of the nanotube. Nanotubes comprising adjacent sections having differing electrical properties are described. These nanotubes can be constructed from combinations of carbon, boron, nitrogen and other elements. The nanotube can be designed having different indices on either side of a junction point in a continuous tube so that the electrical properties on either side of the junction vary in a useful fashion. For example, the inventive nanotube may be electrically conducting on one side of a junction and semiconducting on the other side. An example of a semiconductor-metal junction is a Schottky barrier. Alternatively, the nanotube may exhibit different semiconductor properties on either side of the junction. Nanotubes containing heterojunctions, Schottky barriers, and metal-metal junctions are useful for microcircuitry.

  15. Reduction of furnace temperature in ultra long carbon nanotube growth by plasmonic excitation of electron Fermi gas of catalytic nanocluster

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Saeidi, Mohammadreza, E-mail: Saeidi.mr@gmail.com, E-mail: m.saeidi@shahed.ac.ir

    2016-06-15

    In this paper, a novel physical method is presented to reduce the temperature of the furnace and prevent loss of thermal energy in ultra long carbon nanotube (CNT) growth process by catalytic chemical vapor deposition. This method is based on the plasmonic excitation of electron Fermi gas of catalytic nanocluster sitting at tip end of CNT by ultraviolet (UV) irradiation. Physical concepts of the method are explained in detail. The results of applying the presented method consequences to an appropriate tip-growth mechanism of the ultra long CNTs show that, in the presence of plasmonic excitation, the growth rate of themore » CNT is enhanced. Demonstration of temperature reduction and simultaneous increase in CNT length by UV irradiation with the proper frequency are the most important and practical result of the paper. All results are interpreted and discussed.« less

  16. Controlling the Growth of Au on Icosahedral Seeds of Pd by Manipulating the Reduction Kinetics

    DOE PAGES

    Lv, Tian; Yang, Xuan; Zheng, Yiqun; ...

    2016-03-29

    This article reports a systematic study of how Au atoms nucleate and grow on Pd icosahedral seeds with a multiply twinned structure. By manipulating the reduction kinetics, we obtained Pd–Au bimetallic nanocrystals with two distinct shapes and structures. Specifically, Pd@Au core–shell icosahedra were formed when a relatively fast reduction rate was used for the HAuCl 4 precursor. At a slow reduction rate, in contrast, the nucleation and growth of Au atoms were mainly confined to one of the vertices of a Pd icosahedral seed, resulting in the formation of a Au icosahedron by sharing five adjacent faces with the Pdmore » seed. The same growth pattern was observed for Pd icosahedral seeds with both sizes of 32 and 20 nm. Also, we have also investigated the effects of other kinetic parameters, including the concentration of reducing agent and reaction temperature, on the growth pathway undertaken by the Au atoms. In conclusion, we believe that the mechanistic insights obtained from this study can be extended to other systems, including the involvement of different metals and/or seeds with different morphologies.« less

  17. Synthesis of silicon nanotubes with cobalt silicide ends using anodized aluminum oxide template.

    PubMed

    Zhang, Zhang; Liu, Lifeng; Shimizu, Tomohiro; Senz, Stephan; Gösele, Ulrich

    2010-02-05

    Silicon nanotubes (SiNTs) are compatible with Si-based semiconductor technology. In particular, the small diameters and controllable structure of such nanotubes are remaining challenges. Here we describe a method to fabricate SiNTs intrinsically connected with cobalt silicide ends based on highly ordered anodic aluminum oxide (AAO) templates. Size and growth direction of the SiNTs can be well controlled via the templates. The growth of SiNTs is catalyzed by the Co nanoparticles reduced on the pore walls of the AAO after annealing, with a controllable thickness at a given growth temperature and time. Simultaneously, cobalt silicide forms on the bottom side of the SiNTs.

  18. Exact solutions of kinetic equations in an autocatalytic growth model.

    PubMed

    Jędrak, Jakub

    2013-02-01

    Kinetic equations are introduced for the transition-metal nanocluster nucleation and growth mechanism, as proposed by Watzky and Finke [J. Am. Chem. Soc. 119, 10382 (1997)]. Equations of this type take the form of Smoluchowski coagulation equations supplemented with the terms responsible for the chemical reactions. In the absence of coagulation, we find complete analytical solutions of the model equations for the autocatalytic rate constant both proportional to the cluster mass, and the mass-independent one. In the former case, ξ(k)=s(k)(ξ(1))[proportionality]ξ(1)(k)/k was obtained, while in the latter, the functional form of s(k)(ξ(1)) is more complicated. In both cases, ξ(1)(t)=h(μ)(M(μ)(t)) is a function of the moments of the mass distribution. Both functions, s(k)(ξ(1)) and h(μ)(M(μ)), depend on the assumed mechanism of autocatalytic growth and monomer production, and not on other chemical reactions present in a system.

  19. Effect of clofibrate on the growth-kinetics of the murine P 1798(sc) lymphoma.

    PubMed Central

    Ubeira, F. M.; Seoane, R.; Puentes, E.; Faro, J.; Regueiro, B. J.

    1983-01-01

    Clofibrate (CPIB) is a drug applied as an antilipidaemic agent in mammals. In this work we have tested its efficacy in vivo on the growth kinetics of P 1798(sc) lymphoma transplanted to recipient (BALB/c x AKR)F1 mice. Our results show a facilitation of the tumour growth rate in treated recipients. This fact may be related to an effect of the agent on the recipient which produces a decrease in the immune response as was confirmed on testing CPIB on thymus-dependent antigens in haemolytic plaque assays. Images Figure 3 PMID:6351886

  20. Growing Aligned Carbon Nanotubes for Interconnections in ICs

    NASA Technical Reports Server (NTRS)

    Li, Jun; Ye, Qi; Cassell, Alan; Ng, Hou Tee; Stevens, Ramsey; Han, Jie; Meyyappan, M.

    2005-01-01

    electron-beam lithography. These and other nanotubes were found to have lengths ranging from 2 to 10 m and diameters ranging from 30 to 200 nm, the exact values of length depending on growth times and conditions and the exact values of diameter depending on the diameters and thicknesses of the catalyst spots. The bottom part of Figure 2 is an SEM of an embedded array of carbon nanotubes after CMP.

  1. Negative results of growing titania nanotubes on cellulose nanocrystals - Effect of hydrothermal reaction

    NASA Astrophysics Data System (ADS)

    Chamakh, Mariem Mohamed; Ponnamma, Deepalekshmi; Al-Maadeed, Mariam Al Ali

    Titania nanotubes (TiO2 nanotubes or TNT) are grown hydrothermally on cellulose nanocrystals (CNC) synthesized from microcrystalline cellulose. It is observed that the CNC are lost during synthesis due to its low thermal stability. This negative result of metal growth on CNC and its influence on thermal degradation are reported here.

  2. Comprehensive Property Characterization of Nanotube Buckypaper-Reinforced Composite Materials

    DTIC Science & Technology

    2004-04-01

    Kim, S. G., Rinzler, A. G., and Colbert , D. T., "Crystalline Ropes of Metallic Carbon Nanotubes," Science, 1996, Volume 273, No. 5274, pp. 483-487. [7...Nikolaev, P. Bronikowski, M. J., Bradley, R. K., Colbert , D. T., Smith, K. A., and Smalley, R. E., "Gas-phase Catalytic Growth of Single-walled Carbon...Casavant, M. J., Liu, J., Colbert , D. T., Smith, K. A., and Smalley, R. E., "Elastic Strain of Freely Suspended Single-wall Carbon Nanotube Ropes

  3. Carbon nanotubes and methods of forming same at low temperature

    DOEpatents

    Biris, Alexandru S.; Dervishi, Enkeleda

    2017-05-02

    In one aspect of the invention, a method for growth of carbon nanotubes includes providing a graphitic composite, decorating the graphitic composite with metal nanostructures to form graphene-contained powders, and heating the graphene-contained powders at a target temperature to form the carbon nanotubes in an argon/hydrogen environment that is devoid of a hydrocarbon source. In one embodiment, the target temperature can be as low as about 150.degree. C. (.+-.5.degree. C.).

  4. Characterization of a Structural Transformation of Carbon Nanotube Materials by Raman Spectroscopy

    NASA Technical Reports Server (NTRS)

    Cui, Y.; Burger, A.; Zhu, S.; Su, C.-H.; Lehoczky, S. L.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Raman spectra of carbon nanotubes and carbon microstructure materials synthesized on Si substrates by pulsed laser vaporization have been measured in the range of 50/cm to 4500/cm with the excitation of He-Ne laser. It is found that the formation of nanotubes depends strongly on the growth temperatures and high quality multi-wall and single-wall nanotubes were produced at 700 and 990 C, respectively. The Raman spectra of one sample grown at 700 C were found to be dependent on the excitation intensity. The spectra of the sample suggest that the structure is similar to that of multi-wall nanotubes at low excitation intensity (2.5 kW/sq cm) and it converts to the structure of single-wall nanotubes at higher intensity (25 kW/sq cm). Measurements taken while cycling the light intensity indicate a reversible structural transition.

  5. Nanotube Sensors

    NASA Technical Reports Server (NTRS)

    McEuen, Paul L.

    2002-01-01

    Under this project, we explored the feasibility of utilizing carbon nanotubes in sensing applications. The grant primarily supported a graduate student, who worked on a number of aspects of the electrical properties of carbon nanotubes in collaboration with other researchers in my group. The two major research accomplishments are described below. The first accomplishment is the demonstration that solution carbon nanotube transistors functioned well in an electrolyte environment. This was important for two reasons. First, it allowed us to explore the ultimate limits of nanotube electronic performance by using the electrolyte as a highly effective gate, with a dielectric constant of approximately 80 and an effective insulator thickness of approximately 1 nm. Second, it showed that nanotubes function well under biologically relevant conditions (salty water) and therefore offer great promise as biological sensors. The second accomplishment was the demonstration that a voltage pulse applied to an AFM tip could be used to electrically cut carbon nanotubes. We also showed that a carefully applied pulse could also 'nick' a nanotube, creating a tunnel barrier without completely breaking the tube. Nicking was employed to make, for example, a quantum dot within a nanotube.

  6. Modelling the growth kinetics of Kocuria marina DAGII as a function of single and binary substrate during batch production of β-Cryptoxanthin.

    PubMed

    Mitra, Ruchira; Chaudhuri, Surabhi; Dutta, Debjani

    2017-01-01

    In the present investigation, growth kinetics of Kocuria marina DAGII during batch production of β-Cryptoxanthin (β-CRX) was studied by considering the effect of glucose and maltose as a single and binary substrate. The importance of mixed substrate over single substrate has been emphasised in the present study. Different mathematical models namely, the Logistic model for cell growth, the Logistic mass balance equation for substrate consumption and the Luedeking-Piret model for β-CRX production were successfully implemented. Model-based analyses for the single substrate experiments suggested that the concentrations of glucose and maltose higher than 7.5 and 10.0 g/L, respectively, inhibited the growth and β-CRX production by K. marina DAGII. The Han and Levenspiel model and the Luong product inhibition model accurately described the cell growth in glucose and maltose substrate systems with a R 2 value of 0.9989 and 0.9998, respectively. The effect of glucose and maltose as binary substrate was further investigated. The binary substrate kinetics was well described using the sum-kinetics with interaction parameters model. The results of production kinetics revealed that the presence of binary substrate in the cultivation medium increased the biomass and β-CRX yield significantly. This study is a first time detailed investigation on kinetic behaviours of K. marina DAGII during β-CRX production. The parameters obtained in the study might be helpful for developing strategies for commercial production of β-CRX by K. marina DAGII.

  7. Influence of Structural Properties and Kinetic Constraints on Bacillus cereus Growth

    PubMed Central

    Stecchini, Mara Lucia; Del Torre, Manuela; Sarais, Ileana; Saro, Onorio; Messina, Mariella; Maltini, Enrico

    1998-01-01

    The influence of structural properties and kinetic constraints on the behavior of Bacillus cereus was investigated on agar media. Dimensional criteria were used to study the growth in bacterial colonies. The architecture of the agar gel as modified by the agar content was found to influence the colony size, and smaller colonies were observed on media containing 50 to 70 g of agar liter−1. Except at low nutrient levels, colonies responded to nutrient gradients by decreasing in size the farther away they were from the nutrient source, and the decrease in colony size was influenced by the agar content. The diffusivities of glucose and a protein (insulin-like growth factor) were not affected by the gel architecture, suggesting that other factors, such as mechanical factors, could influence microbial growth in the agar systems used. Increasing the viscosity of the liquid phase of the agar media by adding polyvinylpyrrolidone resulted in a reduction in colony size. When the agar concentration was increased, the colony areas were not influenced by the viscosity of the system. PMID:9501447

  8. Grain growth kinetics of ringwoodite and majorite garnet mixtures and implications for the rheology of the transition zone

    NASA Astrophysics Data System (ADS)

    Ezad, I.; Dobson, D. P.; Brodholt, J. P.; Thomson, A.; Hunt, S.

    2017-12-01

    The grain size of the transition zone is a poorly known but important geophysical parameter. Among others, the grain size may control the rheology, seismic attenuation and radiative thermal conductivity of the mantle. However, the grain size of the transition zone minerals ringwoodite (Mg,Fe)2SiO4 and majorite garnet MgSiO3 under appropriate zone conditions is currently unknown and there are very few experiments with which to constrain it. In order to determine the grain size of the transition zone, the grain growth kinetics must be determined for a range of mantle compositions. We have, therefore, experimentally determined the grain growth kinetics of the lowermost transition zone minerals through multi anvil experiments at University College London (UCL). This is achieved through a comprehensive set of time series experiments at pressures of 21 GPa and temperatures relevant to the transition zone. We have also determined the effect of varying water content, oxygen fugacity, iron content and aluminium content also discussed by Dobson and Mariani., (2014). Our initial grain growth experiments conducted at 1200°C and 1400°C at 18 GPa show extremely slow grain growth kinetics; time series experiments extended to 105.8 seconds are unable to produce grains larger than 100 nm. This suggests that fine-grained material at the base of the transition zone will persist on geological timescales. Such small grains size suggests that diffusion creep might be the dominant deformation mechanism in this region. Reference: Dobson, D.P., Mariani, E., 2014. The kinetics of the reaction of majorite plus ferropericlase to ringwoodite: Implications for mantle upwellings crossing the 660 km discontinuity. Earth Planet. Sci. Lett. 408, 110-118. doi:10.1016/j.epsl.2014.10.009

  9. Length Dependent Foam-Like Mechanical Response of Axially Indented Vertically Oriented Carbon Nanotube Arrays

    DTIC Science & Technology

    2011-01-01

    Sands T, Xu X, Fisher T. Dendrimer -assisted controlled growth of carbon nanotubes for enhanced thermal interface conductance. Nanotechnology 2007;18...surfaces. Rev Sci Instrum 2006;77(9):095105-1–3. [11] Allaoui A, Hoa S, Evesque P, Bai J. Electronic transport in carbon nanotube tangles under compression

  10. Electrochemical growth behavior, surface properties, and enhanced in vivo bone response of TiO2 nanotubes on microstructured surfaces of blasted, screw-shaped titanium implants

    PubMed Central

    Sul, Young-Taeg

    2010-01-01

    TiO2 nanotubes are fabricated on TiO2 grit-blasted, screw-shaped rough titanium (ASTM grade 4) implants (3.75 × 7 mm) using potentiostatic anodization at 20 V in 1 M H3PO4 + 0.4 wt.% HF. The growth behavior and surface properties of the nanotubes are investigated as a function of the reaction time. The results show that vertically aligned nanotubes of ≈700 nm in length, with highly ordered structures of ≈40 nm spacing and ≈15 nm wall thickness may be grown independent of reaction time. The geometrical properties of nanotubes increase with reaction time (mean pore size, pore size distribution [PSD], and porosity ≈90 nm, ≈40–127 nm and 45%, respectively for 30 minutes; ≈107 nm, ≈63–140 nm and 56% for one hour; ≈108 nm, ≈58–150 nm and 60% for three hours). It is found that the fluorinated chemistry of the nanotubes of F-TiO2, TiOF2, and F-Ti-O with F ion incorporation of ≈5 at.%, and their amorphous structure is the same regardless of the reaction time, while the average roughness (Sa) gradually decreases and the developed surface area (Sdr) slightly increases with reaction time. The results of studies on animals show that, despite their low roughness values, after six weeks the fluorinated TiO2 nanotube implants in rabbit femurs demonstrate significantly increased osseointegration strengths (41 vs 29 Ncm; P = 0.008) and new bone formation (57.5% vs 65.5%; P = 0.008) (n = 8), and reveal more frequently direct bone/cell contact at the bone–implant interface by high-resolution scanning electron microscope observations as compared with the blasted, moderately rough implants that have hitherto been widely used for clinically favorable performance. The results of the animal studies constitute significant evidence that the presence of the nanotubes and the resulting fluorinated surface chemistry determine the nature of the bone responses to the implants. The present in vivo results point to potential applications of the TiO2 nanotubes in the

  11. Anti-fouling response of gold-carbon nanotubes composite for enhanced ethanol electrooxidation

    NASA Astrophysics Data System (ADS)

    Sai Siddhardha, R. S.; Anupam Kumar, Manne; Lakshminarayanan, V.; Ramamurthy, Sai Sathish

    2014-12-01

    We report the synthesis of gold carbon nanotubes composite through a one-pot surfactant free approach and its utility for ethanol electrooxidation reaction (EOR). The method involves the application of laser ablation for nanoparticle synthesis and simultaneous assembly of these on carbon nanotubes. The catalyst has been characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX) and UV-vis spectroscopic techniques. A systematic study of gold carbon nanotubes modified carbon paste electrode for EOR has been pursued. The kinetic study revealed the excellent stability of the modified electrode even after 200 cycles of EOR and with an Arrhenius energy as low as ∼28 kJ mol-1. Tafel slopes that are the measure of electrode activity have been monitored as a function of temperature of the electrolyte. The results indicate that despite an increase in the reaction rate with temperature, the electrode surface has not been significantly passivated by carbonaceous species produced at high temperatures.

  12. Integrating Carbon Nanotubes For Atomic Force Microscopy Imaging Applications

    NASA Technical Reports Server (NTRS)

    Ye, Qi; Cassell, Alan M.; Liu, Hongbing; Han, Jie; Meyyappan, Meyya

    2004-01-01

    Carbon nanotube (CNT) related nanostructures possess remarkable electrical, mechanical, and thermal properties. To produce these nanostructures for real world applications, a large-scale controlled growth of carbon nanotubes is crucial for the integration and fabrication of nanodevices and nanosensors. We have taken the approach of integrating nanopatterning and nanomaterials synthesis with traditional silicon micro fabrication techniques. This integration requires a catalyst or nanomaterial protection scheme. In this paper, we report our recent work on fabricating wafer-scale carbon nanotube AFM cantilever probe tips. We will address the design and fabrication considerations in detail, and present the preliminary scanning probe test results. This work may serve as an example of rational design, fabrication, and integration of nanomaterials for advanced nanodevice and nanosensor applications.

  13. Nucleation and growth studies of crystalline carbon phases at nanoscale

    NASA Astrophysics Data System (ADS)

    Mani, Radhika C.

    Understanding the nucleation and early stage growth of crystals from the vapor phase is important for realizing large-area single-crystal quality films, controlled synthesis of nanocrystals, and the possible discovery of new phases of materials. Carbon provides the most interesting system because all its known crystalline phases (diamond, graphite and carbon nanotubes) are technologically important materials. Hence, this dissertation is focused on studying the nucleation and growth of carbon phases synthesized from the vapor phase. Nucleation experiments were performed in a microwave plasma chemical vapor deposition (CVD) reactor, and the resulting carbon nanocrystals were analyzed primarily using electron nanodiffraction and Raman spectroscopy. These studies led to the discovery of two new crystalline phases of sp 3 carbon other than diamond: face-centered and body-centered cubic carbon. Nanodiffraction results revealed possible hydrogen substitution into diamond-cubic lattices, indicating that these new phases probably act as intermediates in diamond nucleation. Nucleation experiments also led to the discovery of two new morphologies for sp2 carbon: nanocrystals of graphite and tapered, hollow 1-D structures termed here as "carbon nanopipettes". A Kinetic Monte Carlo (KMC) algorithm was developed to simulate the growth of individual diamond crystals from the vapor phase, starting with small clusters of carbon atoms (or seeds). Specifically, KMC simulations were used to distinguish the kinetic rules that give rise to a star-shaped decahedral morphology compared to decahedral crystals. KMC simulations revealed that slow adsorption on the {111} step-propagation sites compared to kink sites leads to star-decahedral crystals, and higher adsorption leads to decahedral crystals. Since the surfaces of the nanocrystals of graphite and nanopipettes were expected to be composed primarily of edge-plane sites, the electrochemical behavior of both these materials were

  14. 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

  15. Functional materials based on carbon nanotubes: Carbon nanotube actuators and noncovalent carbon nanotube modification

    NASA Astrophysics Data System (ADS)

    Fifield, Leonard S.

    Carbon nanotubes have attractive inherent properties that encourage the development of new functional materials and devices based on them. The use of single wall carbon nanotubes as electromechanical actuators takes advantage of the high mechanical strength, surface area and electrical conductivity intrinsic to these molecules. The work presented here investigates the mechanisms that have been discovered for actuation of carbon nanotube paper: electrostatic, quantum chemical charge injection, pneumatic and viscoelastic. A home-built apparatus for the measurement of actuation strain is developed and utilized in the investigation. An optical fiber switch, the first demonstrated macro-scale device based on the actuation of carbon nanotubes, is described and its performance evaluated. Also presented here is a new general process designed to modify the surface of carbon nanotubes in a non-covalent, non-destructive way. This method can be used to impart new functionalities to carbon nanotube samples for a variety of applications including sensing, solar energy conversion and chemical separation. The process described involves the achievement of large degrees of graphitic surface coverage with polycyclic aromatic hydrocarbons through the use of supercritical fluids. These molecules are bifunctional agents that anchor a desired chemical group to the aromatic surface of the carbon nanotubes without adversely disrupting the conjugated backbone that gives rise the attractive electronic and physical properties of the nanotubes. Both the nanotube functionalization work and the actuator work presented here emphasize how an understanding and control of nanoscale structure and phenomena can be of vital importance in achieving desired performance for active materials. Opportunities for new devices with improved function over current state-of-the-art can be envisioned and anticipated based on this understanding and control.

  16. The role of carbon solubility in Fe-C nano-clusters on the growth of small single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Curtarolo, Stefano; Awasthy, Neha; Setyawan, Wahyu; Mora, Elena; Tokune, Toshio; Bolton, Kim; Harutyunyan, Avetik

    2008-03-01

    Various diameters of alumina-supported Fe catalysts are used to grow single-walled carbon nanotubes (SWCNTs) with chemical vapor decomposition. We find that the reduction of the catalyst size requires an increase of the minimum temperature necessary for the growth. We address this phenomenon in terms of solubility of C in Fe nanoclusters and, by using first principles calculations, we devise a simple model to predict the behavior of the phases competing for stability in Fe-C nanoclusters at low temperature. We show that, as a function particles size, there are three scenarios compatible with steady state-, limited- and no-growth of SWCNTs, corresponding to unaffected, reduced and no solubility of C in the particles. The result raises previously unknown concerns about the growth feasibility of small and very-long SWCNTs within the current Fe CVD technology, and suggests new strategies in the search of better catalysts. Research supported by Honda R.I. and NSF.

  17. Facile kinetics of Li-ion intake causes superior rate capability in multiwalled carbon nanotube@TiO2 nanocomposite battery anodes

    NASA Astrophysics Data System (ADS)

    Acevedo-Peña, Próspero; Haro, Marta; Rincón, Marina E.; Bisquert, Juan; Garcia-Belmonte, Germà

    2014-12-01

    Nanotechnology produces hybrids with superior properties than its individual constituents. Here MWCNT@TiO2 composites have been synthesized by controlled hydrolysis of titanium isopropoxide over MWCNT, to be incorporated into Li-ion battery electrodes. Outstanding rate capability of the coated nanotubes is observed in comparison to pristine TiO2. Specific storage capacity as high as 250 mAh g-1 is achieved for the nanocomposite electrode which doubles that encountered for TiO2-based anodes. The mechanism explaining the enhancement in power performance has been revealed by means of electrochemical impedance methods. Although both pristine TiO2 and MWCNT@TiO2 would potentially exhibit comparable specific capacity, the charge transfer resistance for the latter is reduced by a factor 10, implying a key role of MWCNTs to favor the interfacial Li+ ion intake from the electrolyte. MWCNT efficiently provides electrons to the nanostructure through the Ti-C bond which assists the Li+ ion incorporation. These findings provide access to the detailed lithiation kinetics of a broad class of nanocomposites for battery applications.

  18. Efficient Transfer Doping of Carbon Nanotube Forests by MoO3.

    PubMed

    Esconjauregui, Santiago; D'Arsié, Lorenzo; Guo, Yuzheng; Yang, Junwei; Sugime, Hisashi; Caneva, Sabina; Cepek, Cinzia; Robertson, John

    2015-10-27

    We dope nanotube forests using evaporated MoO3 and observe the forest resistivity to decrease by 2 orders of magnitude, reaching values as low as ∼5 × 10(-5) Ωcm, thus approaching that of copper. Using in situ photoemission spectroscopy, we determine the minimum necessary MoO3 thickness to dope a forest and study the underlying doping mechanism. Homogenous coating and tube compaction emerge as key factors for decreasing the forest resistivity. When all nanotubes are fully coated with MoO3 and packed, conduction channels are created both inside the nanotubes and on the outside oxide layer. This is supported by density functional theory calculations, which show a shift of the Fermi energy of the nanotubes and the conversion of the oxide into a layer of metallic character. MoO3 doping removes the need for chirality control during nanotube growth and represents a step forward toward the use of forests in next-generation electronics and in power cables or conductive polymers.

  19. Simple design for DNA nanotubes from a minimal set of unmodified strands: rapid, room-temperature assembly and readily tunable structure.

    PubMed

    Hamblin, Graham D; Hariri, Amani A; Carneiro, Karina M M; Lau, Kai L; Cosa, Gonzalo; Sleiman, Hanadi F

    2013-04-23

    DNA nanotubes have great potential as nanoscale scaffolds for the organization of materials and the templation of nanowires and as drug delivery vehicles. Current methods for making DNA nanotubes either rely on a tile-based step-growth polymerization mechanism or use a large number of component strands and long annealing times. Step-growth polymerization gives little control over length, is sensitive to stoichiometry, and is slow to generate long products. Here, we present a design strategy for DNA nanotubes that uses an alternative, more controlled growth mechanism, while using just five unmodified component strands and a long enzymatically produced backbone. These tubes form rapidly at room temperature and have numerous, orthogonal sites available for the programmable incorporation of arrays of cargo along their length. As a proof-of-concept, cyanine dyes were organized into two distinct patterns by inclusion into these DNA nanotubes.

  20. Predicting crystal growth via a unified kinetic three-dimensional partition model

    NASA Astrophysics Data System (ADS)

    Anderson, Michael W.; Gebbie-Rayet, James T.; Hill, Adam R.; Farida, Nani; Attfield, Martin P.; Cubillas, Pablo; Blatov, Vladislav A.; Proserpio, Davide M.; Akporiaye, Duncan; Arstad, Bjørnar; Gale, Julian D.

    2017-04-01

    Understanding and predicting crystal growth is fundamental to the control of functionality in modern materials. Despite investigations for more than one hundred years, it is only recently that the molecular intricacies of these processes have been revealed by scanning probe microscopy. To organize and understand this large amount of new information, new rules for crystal growth need to be developed and tested. However, because of the complexity and variety of different crystal systems, attempts to understand crystal growth in detail have so far relied on developing models that are usually applicable to only one system. Such models cannot be used to achieve the wide scope of understanding that is required to create a unified model across crystal types and crystal structures. Here we describe a general approach to understanding and, in theory, predicting the growth of a wide range of crystal types, including the incorporation of defect structures, by simultaneous molecular-scale simulation of crystal habit and surface topology using a unified kinetic three-dimensional partition model. This entails dividing the structure into ‘natural tiles’ or Voronoi polyhedra that are metastable and, consequently, temporally persistent. As such, these units are then suitable for re-construction of the crystal via a Monte Carlo algorithm. We demonstrate our approach by predicting the crystal growth of a diverse set of crystal types, including zeolites, metal-organic frameworks, calcite, urea and L-cystine.

  1. Laser printing of nanoparticle toner enables digital control of micropatterned carbon nanotube growth.

    PubMed

    Polsen, Erik S; Stevens, Adam G; Hart, A John

    2013-05-01

    Commercialization of materials utilizing patterned carbon nanotube (CNT) forests, such as hierarchical composite structures, dry adhesives, and contact probe arrays, will require catalyst patterning techniques that do not rely on cleanroom photolithography. We demonstrate the large scale patterning of CNT growth catalyst via adaptation of a laser-based electrostatic printing process that uses magnetic ink character recognition (MICR) toner. The MICR toner contains iron oxide nanoparticles that serve as the catalyst for CNT growth, which are printed onto a flexible polymer (polyimide) and then transferred to a rigid substrate (silicon or alumina) under heat and mechanical pressure. Then, the substrate is processed for CNT growth under an atmospheric pressure chemical vapor deposition (CVD) recipe. This process enables digital control of patterned CNT growth via the laser intensity, which controls the CNT density; and via the grayscale level, which controls the pixelation of the image into arrays of micropillars. Moreover, virtually any pattern can be designed using standard software (e.g., MS Word, AutoCAD, etc.) and printed on demand. Using a standard office printer, we realize isolated CNT microstructures as small as 140 μm and isolated catalyst ″pixels″ as small as 70 μm (one grayscale dot) and determine that individual toner microparticles result in features of approximately 5-10 μm . We demonstrate that grayscale CNT patterns can function as dry adhesives and that large-area catalyst patterns can be printed directly onto metal foils or transferred to ceramic plates. Laser printing therefore shows promise to enable high-speed micropatterning of nanoparticle-containing thin films under ambient conditions, possibly for a wide variety of nanostructures by engineering of toners containing nanoparticles of desired composition, size, and shape.

  2. Morphology and Kinetics of Growth of CaCO3 Precipitates Formed in Saline Water at 30°C

    NASA Astrophysics Data System (ADS)

    Sui, Xin; Wang, Baohui; Wu, Haiming

    2018-02-01

    The crystallization kinetics and morphology of CaCO3 crystals precipitated from the high salinity oilfield water were studied. The crystallization kinetics measurements show that nucleation and nuclei growth obey the first order reaction kinetics. The induction period of precipitation is extended in the high salinity solutions. Morphological studies show that impurity ions remain mostly in the solution phase instead of filling the CaCO3 crystal lattice. The morphology of CaCO3 precipitates can be changed from a smooth surface (calcite) to rough spheres (vaterite), and spindle rod bundles, or spherical, ellipsoid, flowers, plates and other shapes (aragonite).

  3. Release kinetics of platelet-derived and plasma-derived growth factors from autologous plasma rich in growth factors.

    PubMed

    Anitua, Eduardo; Zalduendo, Mari Mar; Alkhraisat, Mohammad Hamdan; Orive, Gorka

    2013-10-01

    Many studies have evaluated the biological effects of platelet rich plasma reporting the final outcomes on cell and tissues. However, few studies have dealt with the kinetics of growth factor delivery by plasma rich in growth factors. Venous blood was obtained from three healthy volunteers and processed with PRGF-Endoret technology to prepare autologous plasma rich in growth factors. The gel-like fibrin scaffolds were then incubated in triplicate, in a cell culture medium to monitor the release of PDGF-AB, VEGF, HGF and IGF-I during 8 days of incubation. A leukocyte-platelet rich plasma was prepared employing the same technology and the concentrations of growth factors and interleukin-1β were determined after 24h of incubation. After each period, the medium was collected, fibrin clot was destroyed and the supernatants were stored at -80°C until analysis. The growth factor delivery is diffusion controlled with a rapid initial release by 30% of the bioactive content after 1h of incubation and a steady state release when almost 70% of the growth factor content has been delivered. Autologous fibrin matrix retained almost 30% of the amount of the growth factors after 8 days of incubation. The addition of leukocytes to the formula of platelet rich plasma did not increase the concentration of the growth factors, while it drastically increased the presence of pro-inflammatory IL-1β. Further studies employing an in vitro inflammatory model would be interesting to study the difference in growth factors and pro-inflammatory cytokines between leukocyte-free and leukocyte-rich platelet rich plasma. Copyright © 2013 Elsevier GmbH. All rights reserved.

  4. Novel nanofluidic chemical cells based on self-assembled solid-state SiO2 nanotubes.

    PubMed

    Zhu, Hao; Li, Haitao; Robertson, Joseph W F; Balijepalli, Arvind; Krylyuk, Sergiy; Davydov, Albert V; Kasianowicz, John J; Suehle, John S; Li, Qiliang

    2017-10-27

    Novel nanofluidic chemical cells based on self-assembled solid-state SiO 2 nanotubes on silicon-on-insulator (SOI) substrate have been successfully fabricated and characterized. The vertical SiO 2 nanotubes with a smooth cavity are built from Si nanowires which were epitaxially grown on the SOI substrate. The nanotubes have rigid, dry-oxidized SiO 2 walls with precisely controlled nanotube inner diameter, which is very attractive for chemical-/bio-sensing applications. No dispersion/aligning procedures were involved in the nanotube fabrication and integration by using this technology, enabling a clean and smooth chemical cell. Such a robust and well-controlled nanotube is an excellent case of developing functional nanomaterials by leveraging the strength of top-down lithography and the unique advantage of bottom-up growth. These solid, smooth, clean SiO 2 nanotubes and nanofluidic devices are very encouraging and attractive in future bio-medical applications, such as single molecule sensing and DNA sequencing.

  5. Reduction of short wavelength reflectance of multi-wall carbon nanotubes through ultraviolet laser irradiation

    NASA Astrophysics Data System (ADS)

    Stephens, Michelle S.; Simonds, Brian J.; Yung, Christopher S.; Conklin, Davis; Livigni, David J.; Oliva, Alberto Remesal; Lehman, John H.

    2018-05-01

    Multi-wall carbon nanotube coatings are used as broadband, low-reflectance absorbers for bolometric applications and for stray light control. They are also used as high emittance blackbody radiators. Irradiation of single wall carbon nanotubes with ultraviolet (UV) laser light has been shown to remove amorphous carbon debris, but there have been few investigations of the interaction of UV light with the more complex physics of multi-wall carbon nanotubes. We present measurements of reflectance and surface morphology before and after exposure of multi-wall carbon nanotube coatings to 248 nm UV laser light. We show that UV exposure reduces the reflectivity at wavelengths below 600 nm and present modeling of the thermal cycling the UV exposure causes at the surface of the carbon nanotubes. This effect can be used to flatten the spectral shape of the reflectivity curve of carbon nanotube absorber coatings used for broadband applications. Finally, we find that the effect of UV exposure depends on the nanotube growth process.

  6. Novel nanofluidic chemical cells based on self-assembled solid-state SiO2 nanotubes

    NASA Astrophysics Data System (ADS)

    Zhu, Hao; Li, Haitao; Robertson, Joseph W. F.; Balijepalli, Arvind; Krylyuk, Sergiy; Davydov, Albert V.; Kasianowicz, John J.; Suehle, John S.; Li, Qiliang

    2017-10-01

    Novel nanofluidic chemical cells based on self-assembled solid-state SiO2 nanotubes on silicon-on-insulator (SOI) substrate have been successfully fabricated and characterized. The vertical SiO2 nanotubes with a smooth cavity are built from Si nanowires which were epitaxially grown on the SOI substrate. The nanotubes have rigid, dry-oxidized SiO2 walls with precisely controlled nanotube inner diameter, which is very attractive for chemical-/bio-sensing applications. No dispersion/aligning procedures were involved in the nanotube fabrication and integration by using this technology, enabling a clean and smooth chemical cell. Such a robust and well-controlled nanotube is an excellent case of developing functional nanomaterials by leveraging the strength of top-down lithography and the unique advantage of bottom-up growth. These solid, smooth, clean SiO2 nanotubes and nanofluidic devices are very encouraging and attractive in future bio-medical applications, such as single molecule sensing and DNA sequencing.

  7. Modifying the morphology and properties of aligned CNT foams through secondary CNT growth.

    PubMed

    Faraji, Shaghayegh; Stano, Kelly; Akyildiz, Halil; Yildiz, Ozkan; Jur, Jesse S; Bradford, Philip D

    2018-07-20

    In this work, we report for the first time, growth of secondary carbon nanotubes (CNTs) throughout a three-dimensional assembly of CNTs. The assembly of nanotubes was in the form of aligned CNT/carbon (ACNT/C) foams. These low-density CNT foams were conformally coated with an alumina buffer layer using atomic layer deposition. Chemical vapor deposition was further used to grow new CNTs. The CNT foam's extremely high porosity allowed for growth of secondary CNTs inside the bulk of the foams. Due to the heavy growth of new nanotubes, density of the foams increased more than 2.5 times. Secondary nanotubes had the same graphitic quality as the primary CNTs. Microscopy and chemical analysis revealed that the thickness of the buffer layer affected the diameter, nucleation density as well as growth uniformity across the thickness of the foams. The effects of secondary nanotubes on the compressive mechanical properties of the foams was also investigated.

  8. Modifying the morphology and properties of aligned CNT foams through secondary CNT growth

    NASA Astrophysics Data System (ADS)

    Faraji, Shaghayegh; Stano, Kelly; Akyildiz, Halil; Yildiz, Ozkan; Jur, Jesse S.; Bradford, Philip D.

    2018-07-01

    In this work, we report for the first time, growth of secondary carbon nanotubes (CNTs) throughout a three-dimensional assembly of CNTs. The assembly of nanotubes was in the form of aligned CNT/carbon (ACNT/C) foams. These low-density CNT foams were conformally coated with an alumina buffer layer using atomic layer deposition. Chemical vapor deposition was further used to grow new CNTs. The CNT foam’s extremely high porosity allowed for growth of secondary CNTs inside the bulk of the foams. Due to the heavy growth of new nanotubes, density of the foams increased more than 2.5 times. Secondary nanotubes had the same graphitic quality as the primary CNTs. Microscopy and chemical analysis revealed that the thickness of the buffer layer affected the diameter, nucleation density as well as growth uniformity across the thickness of the foams. The effects of secondary nanotubes on the compressive mechanical properties of the foams was also investigated.

  9. Differential stimulation of neurotrophin release by the biocompatible nano-material (carbon nanotube) in primary cultured neurons.

    PubMed

    Kim, Yun Gi; Kim, Jong Wan; Pyeon, Hee Jang; Hyun, Jung Keun; Hwang, Ji-Young; Choi, Seong-Jun; Lee, Ja-Yeon; Deák, Ferenc; Kim, Hae-Won; Lee, Young Il

    2014-01-01

    In order to develop novel, effective therapies for central nervous system regeneration, it is essential to better understand the role of neurotrophic factors and to design, accordingly, better artificial scaffolds to support both neurite outgrowth and synapse formation. Both nerve growth factor and brain-derived neurotrophic factor are major factors in neural survival, development, synaptogenesis, and synaptic connectivity of primary cultured neurons. As a prime candidate coating material for such neural cultures, carbon nanotubes offer unique structural, mechanical, and electrical properties. In this study, carbon nanotubes coated glass-coverslips were used as the matrix of a primary neural culture system used to investigate the effects of carbon nanotubes on neurite outgrowth and nerve growth factor/brain-derived neurotrophic factor release and expression. For these purposes, we performed comparative analyses of primary cultured neurons on carbon nanotubes coated, non-coated, and Matrigel-coated coverslips. The morphological findings showed definite carbon nanotubes effects on the neurite outgrowths and synaptogenic figures in both cortical and hippocampal neurons when compared with the non-coated negative control. Although the carbon nanotubes did not change neurotrophin expression levels, it stimulated brain-derived neurotrophic factor release into the media from both types of neurons. Accordingly, we suggest a different mechanism of action between carbon nanotubes and Matrigel in relation to the specific neurotrophic factors. Since carbon nanotubes supply long-term extracellular molecular cues for the survival and neurite outgrowths of cultured neurons, the results from this study will contribute to an understanding of carbon nanotubes biological effects and provide new insight into their role in the secretion of neurotrophic factors.

  10. Properties of Carbon Nanotubes: Defects, Adsorbates, and Gas Sensing

    NASA Astrophysics Data System (ADS)

    Eastman, Micah C.

    Carbon naotubes and graphene have been a trending research topic in the past decade. These graphitic compounds exhibit numerous advantageous properties (electronic, mechanical, thermal, optical, etc) which industry and researchers alike are excited to take advantage of. Beyond the challenges of yield and controlled growth, there are a number of standing questions which govern some of the more fundamental characteristics of these materials: What role do lattice defects play in the adsorption of gas molecules on the surface of carbon nanotubes? How are the electronic states of the carbon nanotubes influenced by these adsorbed molecules? And how can we develop models to predict useful applications of this knowledge? In order to address these questions, this study combines Raman spectroscopy and electronic measurements carried out in highly controlled environments of carbon nanotube transistors. Assessing these data in conjunction shows that the defect density of a carbon nanotube channel has no correlation with observed threshold voltage shifts, or change in Schottky barrier, due to the presence of ambient oxygen. With these insights in mind, a dynamic adsorption-desorption model is proposed which addresses the oxygen sensitivity of carbon nanotube transistors. Instrumentation and computational developments which facilitated these measurements are also disclosed.

  11. Recent advances in the research of inorganic nanotubes and fullerene-like nanoparticles

    NASA Astrophysics Data System (ADS)

    Tenne, Reshef

    2014-06-01

    This minireview outlines the main scientific directions in the research of inorganic nanotubes (INT) and fullerene-like (IF) nanoparticles from layered compounds, in recent years. In particular, this review describes to some detail the progress in the synthesis of new nanotubes, including those from misfit compounds; core-shell and the successful efforts to scale-up the synthesis of WS2 multiwall nanotubes. The high-temperature catalytic growth of nanotubes, via solar ablation is discussed as well. Furthermore, the doping of the IF-MoS2 nanoparticles and its influence on the physiochemical properties of the nanoparticles, including their interesting tribological properties are briefly discussed. Finally, the numerous applications of these nanoparticles as superior solid lubricants and for reinforcing variety of polymers are discussed in brief.

  12. Growth Kinetics for Microalgae Grown in Palm Oil Mill Effluent (POME) medium at various CO2 Levels

    NASA Astrophysics Data System (ADS)

    Razali, S.; Salihon, J.; Ahmad, M. A.

    2018-05-01

    This paper sought to find the growth kinetic data of maximum specific growth rate (μmax) and substrate saturation constant (KS) for a microalgal reaction system over various dissolved CO2 levels (0.04, 0.1, 0.3, 0.5, 0.8, 1.0, 5.0, 10.0% v/v) at a constant sparging rate of 1.2 vvm, by using logistic model and Monod kinetics. The reaction system consisted of microalgae growing in palm oil mill effluent (POME) medium in 1 L flask with constant light illumination and sparged with the specified CO2 gas mixture. It is found from the experimental works that the values of μmax and KS to be at 0.04958 h-1 and 0.03523% (v/v) respectively. The results also showed that utilizing CO2 levels (v/v) in the sparging gas mixture more than 1% (v/v) would not improve microalgae growth significantly as expressed in the values of specific growth rate µ. These data and information are critically important for bioreactor scaling up purposes, especially bioreactor system dedicated for microalgae products and CO2 sequestration.

  13. Controlled Growth of Carbon Nanotubes on Micropatterned Au/Cr Composite Film and Field Emission from Their Arrays

    NASA Astrophysics Data System (ADS)

    Kamide, Koichi; Araki, Hisashi; Yoshino, Katsumi

    2003-12-01

    Carbon nanotube (CNT) arrays with a controlled density are prepared on a micropatterned Au/Cr composite film formed on a quartz glass plate by pyrolysis of Ni-phthalocyanine at 800°C. It is clarified from characteristic X-ray analyses for those samples that a catalytic Ni nanoparticle is not contained within the base of the whisker-like CNT in contrast to that of the bamboo-like CNT, suggesting that the growth process of the present novel CNT is incompatible with that of the bamboo-like CNT. In the Au/Cr composite film, both the Cr atomic content of approximately 30% and the presence of the Ni catalyst devoid of a particle-like shape are important factors for the growth of CNTs. Field emission from the novel CNT arrays exhibits a lower turn-on voltage and a higher current density compared with that from the bamboo-like arrays formed on a quartz plate.

  14. KINETICS OF GROWTH AND ETHANOL PRODUCTION ON DIFFERENT CARBON SUBSTRATES USING GENETICALLY ENGINEERED XYLOSE-FERMENTING YEAST

    EPA Science Inventory

    Saccharomyces cerevisiae 424A (LNH-ST) strain was used for fermentation of glucose and xylose. Growth kinetics and ethanol productivity were calculated for batch fermentation on media containing different combinations of glucose and xylose to give a final sugar concentra...

  15. Novel Magnetic Zinc Oxide Nanotubes for Phenol Adsorption: Mechanism Modeling

    PubMed Central

    Elkady, Marwa F.; Hassan, Hassan Shokry; Amer, Wael A.; Salama, Eslam; Algarni, Hamed; Shaaban, Essam Ramadan

    2017-01-01

    Considering the great impact of a material’s surface area on adsorption processes, hollow nanotube magnetic zinc oxide with a favorable surface area of 78.39 m2/g was fabricated with the assistance of microwave technology in the presence of poly vinyl alcohol (PVA) as a stabilizing agent followed by sonic precipitation of magnetite nano-particles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) micrographs identified the nanotubes’ morphology in the synthesized material with an average aspect ratio of 3. X-ray diffraction (XRD) analysis verified the combination of magnetite material with the hexagonal wurtzite structure of ZnO in the prepared material. The immobilization of magnetite nanoparticles on to ZnO was confirmed using vibrating sample magnetometry (VSM). The sorption affinity of the synthesized magnetic ZnO nanotube for phenolic compounds from aqueous solutions was examined as a function of various processing factors. The degree of acidity of the phenolic solution has great influence on the phenol sorption process on to magnetic ZnO. The calculated value of ΔH0 designated the endothermic nature of the phenol uptake process on to the magnetic ZnO nanotubes. Mathematical modeling indicated a combination of physical and chemical adsorption mechanisms of phenolic compounds on to the fabricated magnetic ZnO nanotubes. The kinetic process correlated better with the second-order rate model compared to the first-order rate model. This result indicates the predominance of the chemical adsorption process of phenol on to magnetic ZnO nanotubes. PMID:29186853

  16. Fabrication of SrTiO3 nanotubes via an isomorphic conversion strategy

    NASA Astrophysics Data System (ADS)

    Yang, Dong; Zou, Xiaoyan; Tong, Zhenwei; Nan, Yanhu; Ding, Fei; Jiang, Zhongyi

    2018-02-01

    One-dimensional nanotubes have attracted enormous attention due to their specific structure and excellent performance since the carbon nanotube was prepared. In this study, the open-ended SrTiO3 nanotubes (STNTs) have been fabricated for the first time via an isomorphic conversion strategy using the protonated titanate nanotubes (HTNTs) as the precursor and template under the hydrothermal treatment. The as-prepared STNTs consist of uniform and continuous multilayers, having inner and outer diameters about 8.0 and 13 nm. The STNT formation involves the exchange of Sr2+ ions with H+ ions in HTNTs and then in situ growth of cubic SrTiO3 crystals by the templating of HTNT frameworks. It is found that the diffusion process of Sr2+ ions plays a critical role in controlling the nanotube morphology of SrTiO3 crystals. In addition, the SrTiO3 nanotubes exhibit high photocatalytic activity for the Cr(VI) reduction, which can reduce nearly 100% Cr(VI) within 6 h under simulated sunlight irradiation. The current strategy may be broadly applicable for fabricating the nanotubes from raw materials without 2D layered nanostructure. [Figure not available: see fulltext.

  17. Three-dimensional kinetic Monte Carlo simulations of cubic transition metal nitride thin film growth

    NASA Astrophysics Data System (ADS)

    Nita, F.; Mastail, C.; Abadias, G.

    2016-02-01

    A three-dimensional kinetic Monte Carlo (KMC) model has been developed and used to simulate the microstructure and growth morphology of cubic transition metal nitride (TMN) thin films deposited by reactive magnetron sputtering. Results are presented for the case of stoichiometric TiN, chosen as a representative TMN prototype. The model is based on a NaCl-type rigid lattice and includes deposition and diffusion events for both N and Ti species. It is capable of reproducing voids and overhangs, as well as surface faceting. Simulations were carried out assuming a uniform flux of incoming particles approaching the surface at normal incidence. The ballistic deposition model is parametrized with an interaction parameter r0 that mimics the capture distance at which incoming particles may stick on the surface, equivalently to a surface trapping mechanism. Two diffusion models are implemented, based on the different ways to compute the site-dependent activation energy for hopping atoms. The influence of temperature (300-500 K), deposition flux (0.1-100 monolayers/s), and interaction parameter r0 (1.5-6.0 Å) on the obtained growth morphology are presented. Microstructures ranging from highly porous, [001]-oriented straight columns with smooth top surface to rough columns emerging with different crystallographic facets are reproduced, depending on kinetic restrictions, deposited energy (seemingly captured by r0), and shadowing effect. The development of facets is a direct consequence of the diffusion model which includes an intrinsic (minimum energy-based) diffusion anisotropy, although no crystallographic diffusion anisotropy was explicitly taken into account at this stage. The time-dependent morphological evolution is analyzed quantitatively to extract the growth exponent β and roughness exponent α , as indicators of kinetic roughening behavior. For dense TiN films, values of α ≈0.7 and β =0.24 are obtained in good agreement with existing experimental data. At this

  18. Single-molecule electrocatalysis by single-walled carbon nanotubes.

    PubMed

    Xu, Weilin; Shen, Hao; Kim, Yoon Ji; Zhou, Xiaochun; Liu, Guokun; Park, Jiwoong; Chen, Peng

    2009-12-01

    We report a single-molecule fluorescence study of electrocatalysis by single-walled carbon nanotubes (SWNTs) at single-reaction resolution. Applying super-resolution optical imaging, we find that the electrocatalysis occurs at discrete, nanometer-dimension sites on SWNTs. Single-molecule kinetic analysis leads to an electrocatalytic mechanism, allowing quantification of the reactivity and heterogeneity of individual reactive sites. Combined with conductivity measurements, this approach will be powerful to interrogate how the electronic structure of SWNTs affects the electrocatalytic interfacial charge transfer, a process fundamental to photoelectrochemical cells.

  19. Multiscale Modeling of Carbon Nanotube-Epoxy Nanocomposites

    NASA Astrophysics Data System (ADS)

    Fasanella, Nicholas A.

    Epoxy-composites are widely used in the aerospace industry. In order to improve upon stiffness and thermal conductivity; carbon nanotube additives to epoxies are being explored. This dissertation presents multiscale modeling techniques to study the engineering properties of single walled carbon nanotube (SWNT)-epoxy nanocomposites, consisting of pristine and covalently functionalized systems. Using Molecular Dynamics (MD), thermomechanical properties were calculated for a representative polymer unit cell. Finite Element (FE) and orientation distribution function (ODF) based methods were used in a multiscale framework to obtain macroscale properties. An epoxy network was built using the dendrimer growth approach. The epoxy model was verified by matching the experimental glass transition temperature, density, and dilatation. MD, via the constant valence force field (CVFF), was used to explore the mechanical and dilatometric effects of adding pristine and functionalized SWNTs to epoxy. Full stiffness matrices and linear coefficient of thermal expansion vectors were obtained. The Green-Kubo method was used to investigate the thermal conductivity as a function of temperature for the various nanocomposites. Inefficient phonon transport at the ends of nanotubes is an important factor in the thermal conductivity of the nanocomposites, and for this reason discontinuous nanotubes were modeled in addition to long nanotubes. To obtain continuum-scale elastic properties from the MD data, multiscale modeling was considered to give better control over the volume fraction of nanotubes, and investigate the effects of nanotube alignment. Two methods were considered; an FE based method, and an ODF based method. The FE method probabilistically assigned elastic properties of elements from the MD lattice results based on the desired volume fraction and alignment of the nanotubes. For the ODF method, a distribution function was generated based on the desired amount of nanotube alignment

  20. Changes in cell-cycle kinetics responsible for limiting somatic growth in mice

    PubMed Central

    Chang, Maria; Parker, Elizabeth A.; Muller, Tessa J. M.; Haenen, Caroline; Mistry, Maanasi; Finkielstain, Gabriela P.; Murphy-Ryan, Maureen; Barnes, Kevin M.; Sundaram, Rajeshwari; Baron, Jeffrey

    2009-01-01

    In mammals, the rate of somatic growth is rapid in early postnatal life but then slows with age, approaching zero as the animal approaches adult body size. To investigate the underlying changes in cell-cycle kinetics, [methyl-3H]thymidine and 5’-bromo-2’deoxyuridine were used to double-label proliferating cells in 1-, 2-, and 3-week-old mice for four weeks. Proliferation of renal tubular epithelial cells and hepatocytes decreased with age. The average cell-cycle time did not increase in liver and increased only 1.7 fold in kidney. The fraction of cells in S-phase that will divide again declined approximately 10 fold with age. Concurrently, average cell area increased approximately 2 fold. The findings suggest that somatic growth deceleration primarily results not from an increase in cell-cycle time but from a decrease in growth fraction (fraction of cells that continue to proliferate). During the deceleration phase, cells appear to reach a proliferative limit and undergo their final cell divisions, staggered over time. Concomitantly, cells enlarge to a greater volume, perhaps because they are relieved of the size constraint imposed by cell division. In conclusion, a decline in growth fraction with age causes somatic growth deceleration and thus sets a fundamental limit on adult body size. PMID:18535488

  1. Delivery of Cisplatin Anti-Cancer Drug from Carbon, Boron Nitride, and Silicon Carbide Nanotubes Forced by Ag-Nanowire: A Comprehensive Molecular Dynamics Study.

    PubMed

    Mehrjouei, Esmat; Akbarzadeh, Hamed; Shamkhali, Amir Nasser; Abbaspour, Mohsen; Salemi, Sirous; Abdi, Pooya

    2017-07-03

    In this work, liberation of cisplatin molecules from interior of a nanotube due to entrance of an Ag-nanowire inside it was simulated by classical molecular dynamics method. The aim of this simulation was investigation on the effects of diameter, chirality, and composition of the nanotube, as well as the influence of temperature on this process. For this purpose, single walled carbon, boron nitride, and silicon carbide nanotube were considered. In order for a more concise comparison of the results, a new parameter namely efficiency of drug release, was introduced. The results demonstrated that the efficiency of drug release is sensitive to its adsorption on outer surface of the nanotube. Moreover, this efficiency is also sensitive to the nanotube composition and its diameter. For the effect of nanotube composition, the results indicated that silicon carbide nanotube has the least efficiency for drug release, due to its strong drug-nanotube. Also, the most important acting forces on drug delivery are van der Waals interactions. Finally, the kinetic of drug release is fast and is not related to the structural parameters of the nanotube and temperature, significantly.

  2. Sequential and coordinated action of phytochromes A and B during Arabidopsis stem growth revealed by kinetic analysis

    NASA Technical Reports Server (NTRS)

    Parks, B. M.; Spalding, E. P.; Evans, M. L. (Principal Investigator)

    1999-01-01

    Photoreceptor proteins of the phytochrome family mediate light-induced inhibition of stem (hypocotyl) elongation during the development of photoautotrophy in seedlings. Analyses of overt mutant phenotypes have established the importance of phytochromes A and B (phyA and phyB) in this developmental process, but kinetic information that would augment emerging molecular models of phytochrome signal transduction is absent. We have addressed this deficiency by genetically dissecting phytochrome-response kinetics, after having solved the technical issues that previously limited growth studies of small Arabidopsis seedlings. We show here, with resolution on the order of minutes, that phyA initiated hypocotyl growth inhibition upon the onset of continuous red light. This primary contribution of phyA began to decrease after 3 hr of irradiation, the same time at which immunochemically detectable phyA disappeared and an exclusively phyB-dependent phase of inhibition began. The sequential and coordinated actions of phyA and phyB in red light were not observed in far-red light, which inhibited growth persistently through an exclusively phyA-mediated pathway.

  3. Growth kinetics and island evolution during double-pulsed molecular beam epitaxy of InN

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kraus, A.; Hein, C.; Bremers, H.

    The kinetic processes of InN growth using alternating source fluxes with sub-monolayer In pulses in plasma-assisted molecular beam epitaxy have been investigated. Growth at various temperatures reveals the existence of two growth regimes. While growth at low temperatures is solely governed by surface diffusion, a combination of decomposition, desorption, and diffusion becomes decisive at growth temperatures of 470 °C and above. At this critical temperature, the surface morphology changes from a grainy structure to a structure made of huge islands. The formation of those islands is attributed to the development of an indium adlayer, which can be observed via reflection highmore » energy electron diffraction monitoring. Based on the growth experiments conducted at temperatures below T{sub Growth} = 470 °C, an activation energy for diffusion of 0.54 ± 0.02 eV has been determined from the decreasing InN island density. A comparison between growth on metalorganic vapor phase epitaxy GaN templates and pseudo bulk GaN indicates that step edges and dislocations are favorable nucleation sites. Based on the results, we developed a growth model, which describes the main mechanisms of the growth.« less

  4. Binding and condensation of plasmid DNA onto functionalized carbon nanotubes: toward the construction of nanotube-based gene delivery vectors.

    PubMed

    Singh, Ravi; Pantarotto, Davide; McCarthy, David; Chaloin, Olivier; Hoebeke, Johan; Partidos, Charalambos D; Briand, Jean-Paul; Prato, Maurizio; Bianco, Alberto; Kostarelos, Kostas

    2005-03-30

    Carbon nanotubes (CNTs) constitute a class of nanomaterials that possess characteristics suitable for a variety of possible applications. Their compatibility with aqueous environments has been made possible by the chemical functionalization of their surface, allowing for exploration of their interactions with biological components including mammalian cells. Functionalized CNTs (f-CNTs) are being intensively explored in advanced biotechnological applications ranging from molecular biosensors to cellular growth substrates. We have been exploring the potential of f-CNTs as delivery vehicles of biologically active molecules in view of possible biomedical applications, including vaccination and gene delivery. Recently we reported the capability of ammonium-functionalized single-walled CNTs to penetrate human and murine cells and facilitate the delivery of plasmid DNA leading to expression of marker genes. To optimize f-CNTs as gene delivery vehicles, it is essential to characterize their interactions with DNA. In the present report, we study the interactions of three types of f-CNTs, ammonium-functionalized single-walled and multiwalled carbon nanotubes (SWNT-NH3+; MWNT-NH3+), and lysine-functionalized single-walled carbon nanotubes (SWNT-Lys-NH3+), with plasmid DNA. Nanotube-DNA complexes were analyzed by scanning electron microscopy, surface plasmon resonance, PicoGreen dye exclusion, and agarose gel shift assay. The results indicate that all three types of cationic carbon nanotubes are able to condense DNA to varying degrees, indicating that both nanotube surface area and charge density are critical parameters that determine the interaction and electrostatic complex formation between f-CNTs with DNA. All three different f-CNT types in this study exhibited upregulation of marker gene expression over naked DNA using a mammalian (human) cell line. Differences in the levels of gene expression were correlated with the structural and biophysical data obtained for the f

  5. 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

  6. Carbon nanotubes on carbon fibers: Synthesis, structures and properties

    NASA Astrophysics Data System (ADS)

    Zhang, Qiuhong

    The interface between carbon fibers (CFs) and the resin matrix in traditional high performance composites is characterized by a large discontinuity in mechanical, electrical, and thermal properties which can cause inefficient energy transfer. Due to the exceptional properties of carbon nanotubes (CNTs), their growth at the surface of carbon fibers is a promising approach to controlling interfacial interactions and achieving the enhanced bulk properties. However, the reactive conditions used to grow carbon nanotubes also have the potential to introduce defects that can degrade the mechanical properties of the carbon fiber (CF) substrate. In this study, using thermal chemical vapor deposition (CVD) method, high density multi-wall carbon nanotubes have been successfully synthesized directly on PAN-based CF surface without significantly compromising tensile properties. The influence of CVD growth conditions on the single CF tensile properties and carbon nanotube (CNT) morphology was investigated. The experimental results revealed that under high temperature growth conditions, the tensile strength of CF was greatly decreased at the beginning of CNT growth process with the largest decrease observed for sized CFs. However, the tensile strength of unsized CFs with CNT was approximately the same as the initial CF at lower growth temperature. The interfacial shear strength of CNT coated CF (CNT/CF) in epoxy was studied by means of the single-fiber fragmentation test. Results of the test indicate an improvement in interfacial shear strength with the addition of a CNT coating. This improvement can most likely be attributed to an increase in the interphase yield strength as well as an improvement in interfacial adhesion due to the presence of the nanotubes. CNT/CF also offers promise as stress and strain sensors in CF reinforced composite materials. This study investigates fundamental mechanical and electrical properties of CNT/CF using nanoindentation method by designed

  7. Constitutive Modeling of Nanotube/Polymer Composites with Various Nanotube Orientations

    NASA Technical Reports Server (NTRS)

    Odegard, Gregory M.; Gates, Thomas S.

    2002-01-01

    In this study, a technique has been proposed for developing constitutive models for polymer composite systems reinforced with single-walled carbon nanotubes (SWNT) with various orientations with respect to the bulk material coordinates. A nanotube, the local polymer adjacent to the nanotube, and the nanotube/polymer interface have been modeled as an equivalent-continuum fiber by using an equivalent-continuum modeling method. The equivalent-continuum fiber accounts for the local molecular structure and bonding information and serves as a means for incorporating micromechanical analyses for the prediction of bulk mechanical properties of SWNT/polymer composite. As an example, the proposed approach is used for the constitutive modeling of a SWNT/LaRC-SI (with a PmPV interface) composite system, with aligned nanotubes, three-dimensionally randomly oriented nanotubes, and nanotubes oriented with varying degrees of axisymmetry. It is shown that the Young s modulus is highly dependent on the SWNT orientation distribution.

  8. Prognostic markers and tumour growth kinetics in melanoma patients progressing on vemurafenib.

    PubMed

    Seifert, Heike; Fisher, Rosalie; Martin-Liberal, Juan; Edmonds, Kim; Hughes, Peta; Khabra, Komel; Gore, Martin; Larkin, James

    2016-04-01

    The BRAF inhibitor vemurafenib is an effective drug in patients with BRAF mutant metastatic melanoma, but resistance occurs after a median of 6 months. The anti-CTLA4-antibody, ipilimumab, is a standard first-line and second-line treatment option in Europe, with a median time to response of 2-3 months, but some patients show rapid clinical deterioration before that. The aim of this analysis was to identify prognostic markers for survival after failure of vemurafenib treatment to identify patients who have a sufficient life expectancy to respond to new immunotherapy treatments. We retrospectively analysed 101 consecutive unselected patients treated with vemurafenib for metastatic melanoma at a single institution. The association between clinical parameters and death within 3 months after cessation of vemurafenib (n=69) was assessed by binary logistic and Cox regression. Of the patients, 45% died within 3 months of progression on vemurafenib. Elevated baseline serum lactate dehydrogenase, absence of normalization of serum lactate dehydrogenase on vemurafenib therapy, performance status of at least 2 at progression and time from primary tumour to metastatic disease less than 5 years were identified as poor prognostic markers. In an exploratory tumour growth kinetics analysis (n=16), we found that following cessation of vemurafenib, approximately a third each showed a stable, decelerated or accelerated rate of tumour growth. Patients with these poor prognostic markers are unlikely to have sufficient life expectancy to complete ipilimumab treatment after failure with vemurafenib. Consideration needs to be given to the elective use of immunotherapy before patients become resistant to vemurafenib. This requires prospective randomized evaluation. Our tumour growth kinetics analysis requires confirmation; however, it may suggest that intermittent vemurafenib treatment should be investigated in clinical trials.

  9. Assessing Atmospheric CO2 Entrapped in Clay Nanotubes using Residual Gas Analyzer.

    PubMed

    Das, Sankar; Maity, Abhijit; Pradhan, Manik; Jana, Subhra

    2016-02-16

    A residual gas analyzer (RGA) coupled with a high-vacuum chamber has been explored to measure atmospheric CO2 entrapped in aminosilane-modified clay nanotubes. Ambient CO2 uptake efficacy together with stability of these novel adsorbents composed of both primary and/or secondary amine sites has been demonstrated at standard ambient temperature and pressure. The unprecedented sensitivity and accuracy of the RGA-based mass spectrometry technique toward atmospheric CO2 measurement has been substantiated with a laser-based optical cavity-enhanced integrated cavity output spectroscopy. The adsorption kinetics of atmospheric CO2 on amine-functionalized clay nanotubes followed the fractional-order kinetic model compared to that of the pseudo-first-order or pseudo-second-order rate equations. The efficiency along with stability of these novel adsorbents has also been demonstrated by their repetitive use for CO2 capture in the oxidative environment. Our findings thus point to a fundamental study on the atmospheric CO2 adsorption by amine-loaded adsorbents using an easy handling and low-cost benchtop RGA-based mass spectrometer, opening a new strategy for CO2 capture and sequestering study.

  10. Linear increases in carbon nanotube density through multiple transfer technique.

    PubMed

    Shulaker, Max M; Wei, Hai; Patil, Nishant; Provine, J; Chen, Hong-Yu; Wong, H-S P; Mitra, Subhasish

    2011-05-11

    We present a technique to increase carbon nanotube (CNT) density beyond the as-grown CNT density. We perform multiple transfers, whereby we transfer CNTs from several growth wafers onto the same target surface, thereby linearly increasing CNT density on the target substrate. This process, called transfer of nanotubes through multiple sacrificial layers, is highly scalable, and we demonstrate linear CNT density scaling up to 5 transfers. We also demonstrate that this linear CNT density increase results in an ideal linear increase in drain-source currents of carbon nanotube field effect transistors (CNFETs). Experimental results demonstrate that CNT density can be improved from 2 to 8 CNTs/μm, accompanied by an increase in drain-source CNFET current from 4.3 to 17.4 μA/μm.

  11. Mechanism of axial strain effects on friction in carbon nanotube rotating bearings.

    PubMed

    Huang, Jianzhang; Han, Qiang

    2018-08-10

    A systematic study of axial strain effects on friction in carbon nanotube bearings is conducted in this paper. The relationships between friction and axial strains are determined by implementing molecular dynamics simulations. It is found that the dependence of friction on velocity and temperature is altered by axial strains. The mechanism of strain effects is revealed through numerical and theoretical analyses. Based on phonon computations, axial strain effects tune friction by adjusting the distribution of the phonon frequency density, which affects the transfer efficiency of orderly kinetic energy into disorderly thermal energy. The findings in this work advance the understanding of friction in carbon nanotubes and suggest the great potential of axial strain effects on tuning friction in nanodevice applications.

  12. Effect of Functionalised and Non-Functionalised Carbon Nanotubes-Urea Fertilizer on the Growth of Paddy.

    PubMed

    Yatim, Norazlina Mohamad; Shaaban, Azizah; Dimin, Mohd Fairuz; Yusof, Faridah; Razak, Jeefferie Abd

    2018-03-01

    The roles of multi-walled carbon nanotubes (MWNTs) and functionalised multiwalled carbon nanotubes (fMWNTs) in enhancing the efficacy of urea fertilizer (UF) as plant nutrition for local MR219 paddy variety was investigated. The MWNTs and fMWNTs were grafted onto UF to produce UF-MWNTs fertilizer with three different conditions, coded as FMU1 (0.6 wt. % fMWNTs), FMU2 (0.1 wt. % fMWNTs) and MU (0.6 wt. % MWNTs. The batches of MR219 paddy were systematically grown in accordance to the general practice performed by the Malaysian Agricultural Research and Development Institute (MARDI). The procedure was conducted using a pot under exposure to natural light at three different fertilization times; after a certain number of days of sowing (DAS) at 14, 35 and 55 days. Interestingly, it was found that the crop growth of plants treated with FMU1 and FMU2 significantly increased by 22.6% and 38.5% compared to plants with MU addition. Also, paddy treated with FMU1 produced 21.4% higher number of panicles and 35% more grain yield than MU while paddy treated with FMU2 gave 28.6% more number of panicles and 36% higher grain yield than MU, which implies the advantage of fMWNTs over MWNTs to be combined with UF as plant nutrition. The chemical composition and morphology of UF-MWNTs fertilizers which is further characterised by FTiR and FESEM confirmed the successful and homogeneous grafting of UF onto the fMWNTs.

  13. Effect of Functionalised and Non-Functionalised Carbon Nanotubes-Urea Fertilizer on the Growth of Paddy

    PubMed Central

    Yatim, Norazlina Mohamad; Shaaban, Azizah; Dimin, Mohd Fairuz; Yusof, Faridah; Razak, Jeefferie Abd

    2018-01-01

    The roles of multi-walled carbon nanotubes (MWNTs) and functionalised multiwalled carbon nanotubes (fMWNTs) in enhancing the efficacy of urea fertilizer (UF) as plant nutrition for local MR219 paddy variety was investigated. The MWNTs and fMWNTs were grafted onto UF to produce UF-MWNTs fertilizer with three different conditions, coded as FMU1 (0.6 wt. % fMWNTs), FMU2 (0.1 wt. % fMWNTs) and MU (0.6 wt. % MWNTs. The batches of MR219 paddy were systematically grown in accordance to the general practice performed by the Malaysian Agricultural Research and Development Institute (MARDI). The procedure was conducted using a pot under exposure to natural light at three different fertilization times; after a certain number of days of sowing (DAS) at 14, 35 and 55 days. Interestingly, it was found that the crop growth of plants treated with FMU1 and FMU2 significantly increased by 22.6% and 38.5% compared to plants with MU addition. Also, paddy treated with FMU1 produced 21.4% higher number of panicles and 35% more grain yield than MU while paddy treated with FMU2 gave 28.6% more number of panicles and 36% higher grain yield than MU, which implies the advantage of fMWNTs over MWNTs to be combined with UF as plant nutrition. The chemical composition and morphology of UF-MWNTs fertilizers which is further characterised by FTiR and FESEM confirmed the successful and homogeneous grafting of UF onto the fMWNTs. PMID:29644013

  14. Physiological-phased kinetic characteristics of microalgae Chlorella vulgaris growth and lipid synthesis considering synergistic effects of light, carbon and nutrients.

    PubMed

    Liao, Qiang; Chang, Hai-Xing; Fu, Qian; Huang, Yun; Xia, Ao; Zhu, Xun; Zhong, Nianbing

    2018-02-01

    To comprehensively understand kinetic characteristics of microalgae growth and lipid synthesis in different phases, a phase-feeding strategy was proposed to simultaneously regulate light, carbon and nutrients in adaption, growth and stationary phases of microalgae cultivation. Physiological-phased kinetic characteristics of microalgae Chlorella vulgaris growth and lipid synthesis under synergistic effects of light, carbon and nutrients were investigated, and supply-demand relationships of electrons and energy between light and dark reactions of photosynthesis process were discussed. Finally, the optimized cultivation strategy for microalgae in various phases were obtained, under which the lipid productivity was significantly improved from 130.11 mg/L/d to 163.42 mg/L/d. The study provided some important guidance for the large-scale production of biofuels from microalgae. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. A study on carbon nanotube bridge as a electromechanical memory device

    NASA Astrophysics Data System (ADS)

    Kang, Jeong Won; Ha Lee, Jun; Joo Lee, Hoong; Hwang, Ho Jung

    2005-04-01

    A nanoelectromechanical (NEM) nanotube random access memory (NRAM) device based on carbon nanotube (CNT) was investigated using atomistic simulations. For the CNT-based NEM memory, the mechanical properties of the CNT-bridge and van der Waals interactions between the CNT-bridge and substrate were very important. The critical amplitude of the CNT-bridge was 16% of the length of the CNT-bridge. As molecular dynamics time increased, the CNT-bridge went to the steady state under the electrostatic force with the damping of the potential and the kinetic energies of the CNT-bridge. The interatomic interaction between the CNT-bridge and substrate, value of the CNT-bridge slack, and damping rate of the CNT-bridge were very important for the operation of the NEM memory device as a nonvolatile memory.

  16. Multi-wall carbon nanotube@zeolite imidazolate framework composite from a nanoscale zinc oxide precursor

    DOE PAGES

    Yue, Yanfeng; Guo, Bingkun; Qiao, Zhenan; ...

    2014-07-24

    Nanocomposite of multi-walled carbon nanotube@zeolite imidazolate frameworks (MWNT@ZIF) was prepared through a nanotube-facilitated growth based on a nanosized ZnO precursor. The electrically conductive nanocomposite displays a capacity of 380 mAh/g at 0.1 °C in Li–sulfur battery, transforming electrically inactive ZIF into the active one for battery applications.

  17. Structural and surface property characterization of titanium dioxide nanotubes for orthopedic implants

    NASA Astrophysics Data System (ADS)

    Shokuhfar, Tolou

    This research focused on the to modification of the surface structure of titanium implants with nanostructured morphology of TiO2 nanotubes and studied the interaction of nanotubes with osteoblast cells to understand the parameters that affect the cell growth. The electrical, mechanical, and structural properties of TiO2 nanotubes were characterized to establish a better understanding on the properties of such nanoscale morphological structures. To achieve the objectives of this research work I transformed the titanium and its alloys, either in bulk sheet form, bulk machined form, or thin film deposited on another substrate into a surface of titania nanotubes using a low cost and environmentally friendly process. The process requires only a simple electrolyte, low cost electrode, and a DC power supply. With this simple approach of scalable nanofabrication, a typical result is nanotubes that are each approximately 100nm in diameter and have a wall thickness of about 20nm. By changing the fabrication parameters, independent nanotubes can be fabricated with open volume between them. Titanium in this form is termed onedimensional since electron transport is narrowly confined along the length of the nanotube. My Ph.D. accomplishments have successfully shown that osteoblast cells, the cells that are the precursors to bone, have a strong tendency to attach to the inside and outside of the titanium nanotubes onto which they are grown using their filopodia -- cell's foot used for locomotion -- anchored to titanium nanotubes. In fact it was shown that the cell prefers to find many anchoring sites. These sites are critical for cell locomotion during the first several weeks of maturity and upon calcification as a strongly anchored bone cell. In addition I have shown that such a surface has a greater cell density than a smooth titanium surface. My work also developed a process that uses a focused and controllably rastered ion beam as a nano-scalpel to cut away sections of the

  18. The thickness effect of pre-deposited catalyst film on carbon nanotube growth by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wei, Y. Y.; Eres, Gyula; Lowndes, Douglas H.

    2001-03-01

    Chemical vapor deposition (CVD) of multi wall carbon nanotubes (MWCNTs) was realized on a substrate with a layer of iron film used as a catalyst. The catalyst film was pre-deposited in an electron-gun evaporator equipped with a movable shutter which partially blocks the beam during the evaporation process to produce a catalyst film with a continuously changing thickness from 0 to 60 nm. This technique creates a growth environment in which the film thickness is the only variable and eliminates sample-to-sample variations, enabling a systematic study of the thickness effect of the catalyst film on CNT growth. After the deposition of the catalyst film, the sample was immediately transferred into a CVD chamber where CNT growth was performed. Using Acetylene (C_2H_2) as a carbon-source gas, at the substrate temperature of around 700^oC, MWCNTs preferentially grow as a dense mat on the thin regions of the catalyst film. Moreover, beyond a certain critical film thickness no tubes were observed. The critical film thickness for CNT growth was found to increase with substrate temperature from 640^oC to 800^oC. There appears to be no strong correlation between the film thickness and the diameter of the tubes. At the substrate temperature of over 900^oC, the deposited carbon formed graphite sheets surrounding the catalyst particles and no CNTs were observed. A plot of the critical thickness of the catalyst film where CNTs start to grow as a function of the substrate temperature has obtained, which can be served as a reference for selecting the growth parameter in MWCNT growth. The significance of these experimental trends is discussed within the framework of the diffusion model for MWCNT growth.

  19. Fibril growth kinetics link buffer conditions and topology of 3D collagen I networks.

    PubMed

    Kalbitzer, Liv; Pompe, Tilo

    2018-02-01

    Three-dimensional fibrillar networks reconstituted from collagen I are widely used as biomimetic scaffolds for in vitro and in vivo cell studies. Various physicochemical parameters of buffer conditions for in vitro fibril formation are well known, including pH-value, ion concentrations and temperature. However, there is a lack of a detailed understanding of reconstituting well-defined 3D network topologies, which is required to mimic specific properties of the native extracellular matrix. We screened a wide range of relevant physicochemical buffer conditions and characterized the topology of the reconstituted 3D networks in terms of mean pore size and fibril diameter. A congruent analysis of fibril formation kinetics by turbidimetry revealed the adjustment of the lateral growth phase of fibrils by buffer conditions to be key in the determination of pore size and fibril diameter of the networks. Although the kinetics of nucleation and linear growth phase were affected by buffer conditions as well, network topology was independent of those two growth phases. Overall, the results of our study provide necessary insights into how to engineer 3D collagen matrices with an independent control over topology parameters, in order to mimic in vivo tissues in in vitro experiments and tissue engineering applications. The study reports a comprehensive analysis of physicochemical conditions of buffer solutions to reconstitute defined 3D collagen I matrices. By a combined analysis of network topology, i.e., pore size and fibril diameter, and the kinetics of fibril formation we can reveal the dependence of 3D network topology on buffer conditions, such as pH-value, phosphate concentration and sodium chloride content. With those results we are now able to provide engineering strategies to independently tune the topology parameters of widely used 3D collagen scaffolds based on the buffer conditions. By that, we enable the straightforward mimicking of extracellular matrices of in vivo

  20. Rebar graphene from functionalized boron nitride nanotubes.

    PubMed

    Li, Yilun; Peng, Zhiwei; Larios, Eduardo; Wang, Gunuk; Lin, Jian; Yan, Zheng; Ruiz-Zepeda, Francisco; José-Yacamán, Miguel; Tour, James M

    2015-01-27

    The synthesis of rebar graphene on Cu substrates is described using functionalized boron nitride nanotubes (BNNTs) that were annealed or subjected to chemical vapor deposition (CVD) growth of graphene. Characterization shows that the BNNTs partially unzip and form a reinforcing bar (rebar) network within the graphene layer that enhances the mechanical strength through covalent bonds. The rebar graphene is transferrable to other substrates without polymer assistance. The optical transmittance and conductivity of the hybrid rebar graphene film was tested, and a field effect transistor was fabricated to explore its electrical properties. This method of synthesizing 2D hybrid graphene/BN structures should enable the hybridization of various 1D nanotube and 2D layered structures with enhanced mechanical properties.

  1. Carbon nanotube macroelectronics

    NASA Astrophysics Data System (ADS)

    Zhang, Jialu

    In this dissertation, I discuss the application of carbon nanotubes in macroelectronis. Due to the extraordinary electrical properties such as high intrinsic carrier mobility and current-carrying capacity, single wall carbon nanotubes are very desirable for thin-film transistor (TFT) applications such as flat panel display, transparent electronics, as well as flexible and stretchable electronics. Compared with other popular channel material for TFTs, namely amorphous silicon, polycrystalline silicon and organic materials, nanotube thin-films have the advantages of low-temperature processing compatibility, transparency, and flexibility, as well as high device performance. In order to demonstrate scalable, practical carbon nanotube macroelectroncis, I have developed a platform to fabricate high-density, uniform separated nanotube based thin-film transistors. In addition, many other essential analysis as well as technology components, such as nanotube film density control, purity and diameter dependent semiconducting nanotube electrical performance study, air-stable n-type transistor fabrication, and CMOS integration platform have also been demonstrated. On the basis of the above achievement, I have further demonstrated various kinds of applications including AMOLED display electronics, PMOS and CMOS logic circuits, flexible and transparent electronics. The dissertation is structured as follows. First, chapter 1 gives a brief introduction to the electronic properties of carbon nanotubes, which serves as the background knowledge for the following chapters. In chapter 2, I will present our approach of fabricating wafer-scale uniform semiconducting carbon nanotube thin-film transistors and demonstrate their application in display electronics and logic circuits. Following that, more detailed information about carbon nanotube thin-film transistor based active matrix organic light-emitting diode (AMOLED) displays is discussed in chapter 3. And in chapter 4, a technology to

  2. Tolerance and growth kinetics of bacteria isolated from gold and gemstone mining sites in response to heavy metal concentrations.

    PubMed

    Oladipo, Oluwatosin Gbemisola; Ezeokoli, Obinna Tobechukwu; Maboeta, Mark Steve; Bezuidenhout, Jacobus Johannes; Tiedt, Louwrens R; Jordaan, Anine; Bezuidenhout, Cornelius Carlos

    2018-04-15

    Response and growth kinetics of microbes in contaminated medium are useful indices for the screening and selection of tolerant species for eco-friendly bio-augmentative remediation of polluted environments. In this study, the heavy metal (HM) tolerance, bioaccumulation and growth kinetics of seven bacterial strains isolated from mining sites to 10 HMs (Cd, Hg, Ni, Al, Cr, Pb, Cu, Fe, Mn and Zn) at varied concentrations (25-600 mgL -1 ) were investigated. The isolates were phylogenetically (16S rRNA gene) related to Lysinibacillus macroides, Achromobacter spanius, Bacillus kochii, B. cereus, Klebsiella pneumoniae, Pseudomonas mosselii and P. nitroreducens. Metal tolerance, effects on lag phase duration and growth rates were assessed using the 96-well micro-titre method. Furthermore, metal bioaccumulation and quantities within cells were determined by transmission electron microscopy and electron dispersive x-ray analyses. Tolerance to Ni, Pb, Fe and Mn occurred at highest concentrations tested. Growth rates increased with increasing Fe concentrations, but reduced significantly (p < .05) with increasing Zn, Cu, Hg, Cd and Al. Significantly higher (p < .05) growth rates (compared to controls) was found with some isolates in Hg (25 mgL -1 ), Ni (100 mgL -1 ), Cr (150 mgL -1 ), Mn (600 mgL -1 ), Pb (100 mgL -1 ), Fe (600 mgL -1 ) and Al (50 mgL -1 ). Lag phase urations were isolate- and heavy metal-specific, in direct proportion to concentrations. A. spanius accumulated the most Mn and Zn, while B. cereus accumulated the most Cu. Metals accumulated intra-cellularly without cell morphology distortions. The isolates' multi-metal tolerance, intra-cellular metal bioaccumulation and growth kinetics suggest potentials for application in the synergetic biodegradation and bioremediation of polluted environments, especially HM-rich sites. Copyright © 2018 Elsevier Ltd. All rights reserved.

  3. Kinetic characteristics of Cu (II) adsorption on nano(poly)-cumulene

    NASA Astrophysics Data System (ADS)

    Babkin, Alexander; Neskoromnaya, Elena; Burakova, Irina; Kucherova, Ananstasia; Burakov, Alexander; Mkrtchyan, Elina

    2017-11-01

    The present paper considers the possibility of using a new type of nanocarbon materials for sorption - polycumulene modified with "Taunit-M" carbon nanotubes or graphene nanoplatelets. To evaluate the efficiency of these novel nanomodified materials as sorbents, the following studies were carried out: 1) determination of the optimum pH value to perform static batch sorption experiments, 2) identification of the onset of equilibrium for the adsorption of heavy metal ions (on the example of Cu(II) ions), and 3) elucidation of kinetic adsorption mechanisms. As a result of implementation of kinetic models such as external and internal diffusion, as well as pseudo-first- and pseudo-second-order and Elovich (to determine the contribution of chemisorption), rate constants for the Cu(II) adsorption were estimated. It was noted that the absorption process occurs in a mixed-diffusion mode with the influence of the limiting factor - "sorbate-sorbate" chemical interaction. The equilibrium time was found to be 45 min at the sorption capacity values of about 30.71 mg g-1 (in the case of the material containing carbon nanotubes) and about 24.7 mg g-1 (in the case of the material containing graphene nanoplatelets).

  4. Heteroporphyrin nanotubes and composites

    DOEpatents

    Shelnutt, John A.; Medforth, Craig J.; Wang, Zhongchun

    2006-11-07

    Heteroporphyrin nanotubes, metal nanostructures, and metal/porphyrin-nanotube composite nanostructures formed using the nanotubes as photocatalysts and structural templates, and the methods for forming the nanotubes and composites.

  5. Heteroporphyrin nanotubes and composites

    DOEpatents

    Shelnutt, John A [Tijeras, NM; Medforth, Craig J [Winters, CA; Wang, Zhongchun [Albuquerque, NM

    2007-05-29

    Heteroporphyrin nanotubes, metal nanostructures, and metal/porphyrin-nanotube composite nanostructures formed using the nanotubes as photocatalysts and structural templates, and the methods for forming the nanotubes and composites.

  6. Sequential protein unfolding through a carbon nanotube pore

    NASA Astrophysics Data System (ADS)

    Xu, Zhonghe; Zhang, Shuang; Weber, Jeffrey K.; Luan, Binquan; Zhou, Ruhong; Li, Jingyuan

    2016-06-01

    An assortment of biological processes, like protein degradation and the transport of proteins across membranes, depend on protein unfolding events mediated by nanopore interfaces. In this work, we exploit fully atomistic simulations of an artificial, CNT-based nanopore to investigate the nature of ubiquitin unfolding. With one end of the protein subjected to an external force, we observe non-canonical unfolding behaviour as ubiquitin is pulled through the pore opening. Secondary structural elements are sequentially detached from the protein and threaded into the nanotube, interestingly, the remaining part maintains native-like characteristics. The constraints of the nanopore interface thus facilitate the formation of stable ``unfoldon'' motifs above the nanotube aperture that can exist in the absence of specific native contacts with the other secondary structure. Destruction of these unfoldons gives rise to distinct force peaks in our simulations, providing us with a sensitive probe for studying the kinetics of serial unfolding events. Our detailed analysis of nanopore-mediated protein unfolding events not only provides insight into how related processes might proceed in the cell, but also serves to deepen our understanding of structural arrangements which form the basis for protein conformational stability.An assortment of biological processes, like protein degradation and the transport of proteins across membranes, depend on protein unfolding events mediated by nanopore interfaces. In this work, we exploit fully atomistic simulations of an artificial, CNT-based nanopore to investigate the nature of ubiquitin unfolding. With one end of the protein subjected to an external force, we observe non-canonical unfolding behaviour as ubiquitin is pulled through the pore opening. Secondary structural elements are sequentially detached from the protein and threaded into the nanotube, interestingly, the remaining part maintains native-like characteristics. The constraints of

  7. Both Enhanced Biocompatibility and Antibacterial Activity in Ag-Decorated TiO2 Nanotubes

    PubMed Central

    Lan, Ming-Ying; Liu, Chia-Pei; Huang, Her-Hsiung; Lee, Sheng-Wei

    2013-01-01

    In this study, Ag is electron-beam evaporated to modify the topography of anodic TiO2 nanotubes of different diameters to obtain an implant with enhanced antibacterial activity and biocompatibility. We found that highly hydrophilic as-grown TiO2 nanotubes became poorly hydrophilic with Ag incorporation; however they could effectively recover their wettability to some extent under ultraviolet light irradiation. The results obtained from antibacterial tests suggested that the Ag-decorated TiO2 nanotubes could greatly inhibit the growth of Staphylococcus aureus. In vitro biocompatibility evaluation indicated that fibroblast cells exhibited an obvious diameter-dependent behavior on both as-grown and Ag-decorated TiO2 nanotubes. Most importantly, of all samples, the smallest diameter (25-nm-diameter) Ag-decorated nanotubes exhibited the most obvious biological activity in promoting adhesion and proliferation of human fibroblasts, and this activity could be attributed to the highly irregular topography on a nanometric scale of the Ag-decorated nanotube surface. These experimental results demonstrate that by properly controlling the structural parameters of Ag-decorated TiO2 nanotubes, an implant surface can be produced that enhances biocompatibility and simultaneously boosts antibacterial activity. PMID:24124484

  8. NH2+ implantations induced superior hemocompatibility of carbon nanotubes.

    PubMed

    Guo, Meixian; Li, Dejun; Zhao, Mengli; Zhang, Yiteng; Deng, Xiangyun; Geng, Dongsheng; Li, Ruying; Sun, Xueliang; Gu, Hanqing; Wan, Rongxin

    2013-05-01

    NH2+ implantation was performed on multiwalled carbon nanotubes (MWCNTs) prepared by chemical vapor deposition. The hemocompatibility of MWCNTs and NH2+-implanted MWCNTs was evaluated based on in vitro hemolysis, platelet adhesion, and kinetic-clotting tests. Compared with MWCNTs, NH2+-implanted MWCNTs displayed more perfect platelets and red blood cells in morphology, lower platelet adhesion rate, lower hemolytic rate, and longer kinetic blood-clotting time. NH2+-implanted MWCNTs with higher fluency of 1 × 1016 ions/cm2 led to the best thromboresistance, hence desired hemocompatibility. Fourier transfer infrared and X-ray photoelectron spectroscopy analyses showed that NH2+ implantation caused the cleavage of some pendants and the formation of some new N-containing functional groups. These results were responsible for the enhanced hemocompatibility of NH2+-implanted MWCNTs.

  9. Growth and microstructural investigation of multiwall carbon nanotubes fabricated using electrodeposited nickel nanodeposits and chemical vapor deposition method

    NASA Astrophysics Data System (ADS)

    Zanganeh, Navid; Rajabi, Armin; Torabi, Morteza; Allahkarami, Masoud; Moghaddas, Arshak; Sadrnezhaad, S. K.

    2014-09-01

    This study proposes a common approach for growing multiwall carbon nanotubes (MWCNTs) on nickel nanodeposits. MWCNT growth was performed in two separate stages. In the first stage, nickel nanodeposits were electrodeposited on n-Si(1 1 1):H substrate in the presence of sulfuric acid. Based on atomic force microscopy (AFM) observations, the nickel deposits had a fairly polygonal morphology and were distributed on the prepared n-Si(1 1 1):H substrate. In the second stage, acetylene gas was decomposed on the surfaces of the nickel nanodeposits using chemical vapor deposition method at 700 °C. When carbon is saturated in a catalyst, it acts as a primary nucleating element for MWCNT growth. The structure of the MWCNTs was also investigated using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Results showed that the synthesized MWCNTs had a small wall thickness and were formed under the experimental conditions applied to the system.

  10. Nanotube phonon waveguide

    DOEpatents

    Chang, Chih-Wei; Zettl, Alexander K.

    2013-10-29

    Disclosed are methods and devices in which certain types of nanotubes (e.g., carbon nanotubes and boron nitride nanotubes conduct heat with high efficiency and are therefore useful in electronic-type devices.

  11. Production and Characterization of Carbon Nanotubes and Nanotube-Based Composites

    NASA Technical Reports Server (NTRS)

    Nikolaev, Pavel; Arepalli, Sivaram; Holmes, William; Gorelik, Olga; Files, Brad; Scott, Carl; Santos, Beatrice; Mayeaux, Brian; Victor, Joe

    1999-01-01

    The Nobel Prize winning discovery of the Buckuball (C60) in 1985 at Rice University by a group including Dr. Richard Smalley led to the whole new class of carbon allotropes including fullerenes and nanotubes. Especially interesting from many viewpoints are single-walled carbon nanotubes, which structurally are like a single graphitic sheet wrapped around a cylinder and capped at the ends. This cylinders have diameter as small as 0.5 - 2 nm (1/100,000th the diameter of a human hair) and are as long as 0.1 - 1 mm. Nanotubes are really individual molecules and believed to be defect-free, leading to high tensile strength despite their low density. Additionally, these fibers exhibit electrical conductivity as high as copper, thermal conductivity as high as diamond, strength 100 times higher than steel at one-sixth the weight, and high strain to failure. Thus it is believed that developments in the field of nanotechnology will lead to stronger and lighter composite materials for next generation spacecraft. Lack of a bulk method of production is the primary reason nanotubes are not used widely today. Toward this goal JSC nanotube team is exploring three distinct production techniques: laser ablation, arc discharge and chemical vapor deposition (CVD, in collaboration with Rice University). In laser ablation technique high-power laser impinges on the piece of carbon containing small amount of catalyst, and nanotubes self-assemble from the resulting carbon vapor. In arc generator similar vapor is created in arc discharge between carbon electrodes with catalyst. In CVD method nanotubes grow at much lower temperature on small catalyst particles from carbon-containing feedstock gas (methane or carbon monoxide). As of now, laser ablation produces cleanest material, but mass yield is rather small. Arc discharge produces grams of material, but purity is low. CVD technique is still in baby steps, but preliminary results look promising, as well as perspective of scaling the process

  12. Investigation of formaldehyde interaction with carbon nanotubes and quartz sand

    NASA Astrophysics Data System (ADS)

    Georgopoulou, Maria P.; Chrysikopoulos, Constantinos V.

    2017-04-01

    Assessment of the potential impact of synthetic carbon nanotubes on the fate and transport of common chemical contaminants (pesticides, pharmaceuticals, etc.) in groundwater systems is considered to be an increasingly important aspect of environmental research. This study investigates the interaction of formaldehyde with multi-walled carbon nanotubes (MWCNTs) and quartz sand under static and dynamic conditions. Due to polarity, formaldehyde, is expected to develop strong adsorptive interactions with carbon nanotubes. Several batch adsorption experiments were conducted in test tubes, under controlled conditions. Various initial formaldehyde solution concentration (2, 5, 8 ppm), contact times, and temperatures (8, 18, 25 °C) were considered. Supernatant liquid samples were collected at regular intervals, and centrifuged. Subsequently, the formaldehyde concentration in the supernatant was quantified indirectly, by derivatization with Nash reagent and subsequent measurement of the resulting complex using spectrophotometry in the visible spectral range. Experimental results suggested that formaldehyde has a low affinity for quartz sand, but an enhanced potential for adsorption onto carbon nanotubes. Formaldehyde adsorption onto both absorbents (quartz sand and MWCNTs) was more pronounced under dynamic than static conditions, probably, because agitation improves the mixing of the absorbent within the solution. Also, it was shown that the adsorption data were adequately described by the pseudo-second order kinetic model, suggesting that the primary adsorption mechanism was chemisorption, where two or more (sequential or parallel) processes (e.g. surface chemisorption, intraparticle diffusion) were taking place. Therefore, MWCNTs could be promising adsorbent materials for groundwater remediation.

  13. Visible diffraction from quasi-crystalline arrays of carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Butler, Timothy P.; Butt, Haider; Wilkinson, Timothy D.; Amaratunga, Gehan A. J.

    2015-08-01

    Large area arrays of vertically-aligned carbon nanotubes (VACNTs) are patterned in a quasi-crystalline Penrose tile arrangement through electron beam lithography definition of Ni catalyst dots and subsequent nanotube growth by plasma-enhanced chemical vapour deposition. When illuminated with a 532 nm laser beam high-quality and remarkable diffraction patterns are seen. The diffraction is well matched to theoretical calculations which assume apertures to be present at the location of the VACNTs for transmitted light. The results show that VACNTs act as diffractive elements in reflection and can be used as spatially phased arrays for producing tailored diffraction patterns.

  14. The effect of cation:anion ratio in solution on the mechanism of barite growth at constant supersaturation: Role of the desolvation process on the growth kinetics

    NASA Astrophysics Data System (ADS)

    Kowacz, M.; Putnis, C. V.; Putnis, A.

    2007-11-01

    The mechanism of barite growth has been investigated in a fluid cell of an Atomic Force Microscope by passing solutions of constant supersaturation ( Ω) but variable ion activity ratio ( r=a/a) over a barite substrate.The observed dependence of step-spreading velocity on solution stoichiometry can be explained by considering non-equivalent attachment frequency factors for the cation and anion. We show that the potential for two-dimensional nucleation changes under a constant thermodynamic driving force due to the kinetics of barium integration into the surface, and that the growth mode changes from preexisting step advancement to island spreading as the cation/anion activity ratio increases. Scanning electron microscopy studies of crystals grown in bulk solutions support our findings that matching the ion ratio in the fluid to that of the crystal lattice does not result in maximum growth and nucleation rates. Significantly more rapid rates correspond to solution stoichiometries where [Ba 2+] is in excess with respect to [ SO42-]. Experiments performed in dilute aqueous solutions of methanol show that even 0.02 molar fraction of organic cosolvent in the growth solution significantly accelerates step growth velocity and nucleation rates (while keeping Ω the same as in the reference solution in water). Our observations suggest that the effect of methanol on barite growth results first of all from reduction of the barrier that prevents the Ba 2+ from reaching the surface and corroborate the hypothesis that desolvation of the cation and of the surface is the rate limiting kinetic process for two-dimensional nucleation and for crystal growth.

  15. Kinetics of crystal nucleation and growth in Pd(40)Ni(40)P(20) glass

    NASA Technical Reports Server (NTRS)

    Drehman, A. J.; Greer, A. L.

    1984-01-01

    Samples of Pd(40)Ni(40)P(20) glass, produced by cooling the melt at 1 or 800 K/s, are heated in a differential scanning calorimeter to determine the crystallization kinetics. Optical microscopy shows that eutectic crystallization proceeds both by growth from the surface of the samples and by the growth of spherical regions around preexisting nuclei in the interior. A modified Kissinger (1957) analysis is used to obtain the activation energy for crystal growth (3.49 eV). The steady state homogeneous nucleation frequency at 590 K is about 10 million/cu m per sec. This is estimated to be the maximum nucleation frequency: it is too low to account for the observed population of quenched-in nuclei, which are therefore presumed to be heterogeneous. The major practical obstacle to glass formation in this system is heterogeneous nucleation.

  16. Modeling of Fusarium redolens Dzf2 mycelial growth kinetics and optimal fed-batch fermentation for beauvericin production.

    PubMed

    Xu, Li-Jian; Liu, Yuan-Shuai; Zhou, Li-Gang; Wu, Jian-Yong

    2011-09-01

    Beauvericin (BEA) is a cyclic hexadepsipeptide mycotoxin with notable phytotoxic and insecticidal activities. Fusarium redolens Dzf2 is a highly BEA-producing fungus isolated from a medicinal plant. The aim of the current study was to develop a simple and valid kinetic model for F. redolens Dzf2 mycelial growth and the optimal fed-batch operation for efficient BEA production. A modified Monod model with substrate (glucose) and product (BEA) inhibition was constructed based on the culture characteristics of F. redolens Dzf2 mycelia in a liquid medium. Model parameters were derived by simulation of the experimental data from batch culture. The model fitted closely with the experimental data over 20-50 g l(-1) glucose concentration range in batch fermentation. The kinetic model together with the stoichiometric relationships for biomass, substrate and product was applied to predict the optimal feeding scheme for fed-batch fermentation, leading to 54% higher BEA yield (299 mg l(-1)) than in the batch culture (194 mg l(-1)). The modified Monod model incorporating substrate and product inhibition was proven adequate for describing the growth kinetics of F. redolens Dzf2 mycelial culture at suitable but not excessive initial glucose levels in batch and fed-batch cultures.

  17. Influence of synthesis parameters on CCVD growth of vertically aligned carbon nanotubes over aluminum substrate.

    PubMed

    Szabó, Anna; Kecsenovity, Egon; Pápa, Zsuzsanna; Gyulavári, Tamás; Németh, Krisztián; Horvath, Endre; Hernadi, Klara

    2017-08-25

    In the past two decades, important results have been achieved in the field of carbon nanotube (CNT) research, which revealed that carbon nanotubes have extremely good electrical and mechanical properties The range of applications widens more, if CNTs form a forest-like, vertically aligned structure (VACNT) Although, VACNT-conductive substrate structure could be very advantageous for various applications, to produce proper system without barrier films i.e. with good electrical contact is still a challenge. The aim of the current work is to develop a cheap and easy method for growing carbon nanotubes forests on conductive substrate with the CCVD (Catalytic Chemical Vapor Deposition) technique at 640 °C. The applied catalyst contained Fe and Co and was deposited via dip coating onto an aluminum substrate. In order to control the height of CNT forest several parameters were varied during the both catalyst layer fabrication (e.g. ink concentration, ink composition, dipping speed) and the CCVD synthesis (e.g. gas feeds, reaction time). As-prepared CNT forests were investigated with various methods such as scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry. With such an easy process it was possible to tune both the height and the quality of carbon nanotube forests.

  18. Enhancing the efficiency of lithium intercalation in carbon nanotube bundles using surface functional groups.

    PubMed

    Xiao, Shiyan; Zhu, Hong; Wang, Lei; Chen, Liping; Liang, Haojun

    2014-08-14

    The effect of surface functionalization on the ability and kinetics of lithium intercalation in carbon nanotube (CNT) bundles has been studied by comparing the dynamical behaviors of lithium (Li) ions in pristine and -NH2 functionalized CNTs via ab initio molecular dynamics simulations. It was observed that lithium intercalation has been achieved quickly for both the pristine and surface functionalized CNT bundle. Our calculations demonstrated for the first time that CNT functionalization improved the efficiency of lithium intercalation significantly at both low and high Li ion density. Moreover, we found that keeping the nanotubes apart with an appropriate distance and charging the battery at a rational rate were beneficial to achieve a high rate of lithium intercalation. Besides, the calculated adsorption energy curves indicated that the potential wells in the system of -NH2 functionalized CNT were deeper than that of the pristine CNT bundle by 0.74 eV, and a third energy minimum with a value of 2.64 eV existed at the midpoint of the central axis of the nanotube. Thus, it would be more difficult to remove Li ions from the nanotube interior after surface functionalization. The barrier for lithium diffusion in the interior of the nanotube is greatly decreased because of the surface functional groups. Based on these results, we would suggest to "damage" the nanotube by introducing defects at its sidewall in order to improve not only the capacity of surface functionalized CNTs but also the efficiency of lithium intercalation and deintercalation processes. Our results presented here are helpful in understanding the mechanism of lithium intercalation into nanotube bundles, which may potentially be applied in the development of CNT based electrodes.

  19. Effects of growth rate, cell size, motion, and elemental stoichiometry on nutrient transport kinetics

    PubMed Central

    Skibinski, David O. F.

    2018-01-01

    Nutrient acquisition is a critical determinant for the competitive advantage for auto- and osmohetero- trophs alike. Nutrient limited growth is commonly described on a whole cell basis through reference to a maximum growth rate (Gmax) and a half-saturation constant (KG). This empirical application of a Michaelis-Menten like description ignores the multiple underlying feedbacks between physiology contributing to growth, cell size, elemental stoichiometry and cell motion. Here we explore these relationships with reference to the kinetics of the nutrient transporter protein, the transporter rate density at the cell surface (TRD; potential transport rate per unit plasma-membrane area), and diffusion gradients. While the half saturation value for the limiting nutrient increases rapidly with cell size, significant mitigation is afforded by cell motion (swimming or sedimentation), and by decreasing the cellular carbon density. There is thus potential for high vacuolation and high sedimentation rates in diatoms to significantly decrease KG and increase species competitive advantage. Our results also suggest that Gmax for larger non-diatom protists may be constrained by rates of nutrient transport. For a given carbon density, cell size and TRD, the value of Gmax/KG remains constant. This implies that species or strains with a lower Gmax might coincidentally have a competitive advantage under nutrient limited conditions as they also express lower values of KG. The ability of cells to modulate the TRD according to their nutritional status, and hence change the instantaneous maximum transport rate, has a very marked effect upon transport and growth kinetics. Analyses and dynamic models that do not consider such modulation will inevitably fail to properly reflect competitive advantage in nutrient acquisition. This has important implications for the accurate representation and predictive capabilities of model applications, in particular in a changing environment. PMID:29702650

  20. Specific effects of background electrolytes on the kinetics of step propagation during calcite growth

    NASA Astrophysics Data System (ADS)

    Ruiz-Agudo, Encarnación; Putnis, Christine V.; Wang, Lijun; Putnis, Andrew

    2011-07-01

    The mechanisms by which background electrolytes modify the kinetics of non-equivalent step propagation during calcite growth were investigated using Atomic Force Microscopy (AFM), at constant driving force and solution stoichiometry. Our results suggest that the acute step spreading rate is controlled by kink-site nucleation and, ultimately, by the dehydration of surface sites, while the velocity of obtuse step advancement is mainly determined by hydration of calcium ions in solution. According to our results, kink nucleation at acute steps could be promoted by carbonate-assisted calcium attachment. The different sensitivity of obtuse and acute step propagation kinetics to cation and surface hydration could be the origin of the reversed geometries of calcite growth hillocks (i.e., rate of obtuse step spreading < rate of acute step spreading) observed in concentrated (ionic strength, IS = 0.1) KCl and CsCl solutions. At low IS (0.02), ion-specific effects seem to be mainly associated with changes in the solvation environment of calcium ions in solution. With increasing electrolyte concentration, the stabilization of surface water by weakly paired salts appears to become increasingly important in determining step spreading rate. At high ionic strength (IS = 0.1), overall calcite growth rates increased with increasing hydration of calcium in solution (i.e., decreasing ion pairing of background electrolytes for sodium-bearing salts) and with decreasing hydration of the carbonate surface site (i.e., increasing ion pairing for chloride-bearing salts). Changes in growth hillock morphology were observed in the presence of Li +, F - and SO42-, and can be interpreted as the result of the stabilization of polar surfaces due to increased ion hydration. These results increase our ability to predict crystal reactivity in natural fluids which contain significant amounts of solutes.

  1. Growth hormone distribution kinetics are markedly reduced in adults with growth hormone deficiency.

    PubMed

    Catalina, Pablo F; Páramo, Concepción; Andrade, Maria Amalia; Mallo, Federico

    2007-03-01

    Growth hormone (GH) circulating levels are highly dependent not only on GH secretion rate from the pituitary, but also on the hormone distribution in the compartments of the body and elimination phenomena. In adult GH-deficient patients these factors become critical nowadays, especially when recombinant human GH (rhGH) is available for replacement therapy. In the present study, we assess the influence of both distribution and elimination phenomena on GH pharmacokinetics in adult GH-deficient patients. We used a four-step methodology following a compartmental approach after an intravenous bolus of recombinant GH in adult GH-deficient patients. We found that GH kinetics are clearly explained by a bi-exponential, two-compartmental model in GH-deficient patients, similarly than in normal or diabetic subjects, as previously shown. We have also observed a marked delay in the whole GH elimination process in GH-deficient patients compared to normal adult subjects, as revealed by metabolic clearance ratio (MCR), elimination constant from central compartment (k(10)), and mean resident time in the body (MRT). Interestingly, such a delay appear to be caused by deep changes in the distribution phase (Mtt(1)- mean transit time-1; T(1/2alpha)- GH half-life at distribution phase), while the elimination phenomenon remains unaltered. Our results emphasize the relevance of distribution phenomena in GH pharmacokinetics, and indicates that studies avoiding data from the GH distribution phase, such as those carried out in steady-state conditions, or those using noncompartmental models, could easily miss relevant information. Our data should be taken into consideration when establishing the appropriate dosage for GH replacement treatments in GH-deficient patients, and calculations should include GH distribution kinetics.

  2. Chemical models for simulating single-walled nanotube production in arc vaporization and laser ablation processes

    NASA Technical Reports Server (NTRS)

    Scott, Carl D.

    2004-01-01

    Chemical kinetic models for the nucleation and growth of clusters and single-walled carbon nanotube (SWNT) growth are developed for numerical simulations of the production of SWNTs. Two models that involve evaporation and condensation of carbon and metal catalysts, a full model involving all carbon clusters up to C80, and a reduced model are discussed. The full model is based on a fullerene model, but nickel and carbon/nickel cluster reactions are added to form SWNTs from soot and fullerenes. The full model has a large number of species--so large that to incorporate them into a flow field computation for simulating laser ablation and arc processes requires that they be simplified. The model is reduced by defining large clusters that represent many various sized clusters. Comparisons are given between these models for cases that may be applicable to arc and laser ablation production. Solutions to the system of chemical rate equations of these models for a ramped temperature profile show that production of various species, including SWNTs, agree to within about 50% for a fast ramp, and within 10% for a slower temperature decay time.

  3. Helicity-dependent single-walled carbon nanotube alignment on graphite for helical angle and handedness recognition

    PubMed Central

    Chen, Yabin; Shen, Ziyong; Xu, Ziwei; Hu, Yue; Xu, Haitao; Wang, Sheng; Guo, Xiaolei; Zhang, Yanfeng; Peng, Lianmao; Ding, Feng; Liu, Zhongfan; Zhang, Jin

    2013-01-01

    Aligned single-walled carbon nanotube arrays provide a great potential for the carbon-based nanodevices and circuit integration. Aligning single-walled carbon nanotubes with selected helicities and identifying their helical structures remain a daunting issue. The widely used gas-directed and surface-directed growth modes generally suffer the drawbacks of mixed and unknown helicities of the aligned single-walled carbon nanotubes. Here we develop a rational approach to anchor the single-walled carbon nanotubes on graphite surfaces, on which the orientation of each single-walled carbon nanotube sensitively depends on its helical angle and handedness. This approach can be exploited to conveniently measure both the helical angle and handedness of the single-walled carbon nanotube simultaneously at a low cost. In addition, by combining with the resonant Raman spectroscopy, the (n,m) index of anchored single-walled carbon nanotube can be further determined from the (d,θ) plot, and the assigned (n,m) values by this approach are validated by both the electronic transition energy Eii measurement and nanodevice application. PMID:23892334

  4. Enhancing quality of carbon nanotubes through a real-time controlled CVD process with application to next-generation nanosystems

    NASA Astrophysics Data System (ADS)

    Laxminarayana, Karthik; Jalili, Nader

    2004-07-01

    Nanocrystals and nanostructures will be the building blocks for future materials that will exhibit enhanced or entirely new combinations of properties with tremendous opportunity for novel technologies that can have far-reaching impact on our society. It is, however, realized that a major challenge for the near future is the design, synthesis and integration of nanostructures to develop functional nanosystems. In view of this, this exploratory research seeks to facilitate the development of a controlled and deterministic framework for nanomanufacturing of nanotubes as the most suitable choice among nanostructures for a plethora of potential applications in areas such as nanoelectronic devices, biological probes, fuel cell electrodes, supercapacitors and filed emission devices. Specifically, this paper proposes to control and maintain the most common nanotube growth parameters (i.e., reaction temperature and gas flow rate) through both software and hardware modifications. The influence of such growth parameters in a CVD process on some of the most vital and crucial aspects of nanotubes (e.g., length, diameter, yield, growth rate and structure) can be utilized to arrive at some unique and remarkable properties for the nanotubes. The objective here is, therefore, to control the process parameters to pinpoint accuracy, which would enable us to fabricate nanotubes having the desired properties and thereby maximize their ability to function at its fullest potential. To achieve this and in order to provide for experimental validation of the proposed research program, an experimental test-bed using the nanotube processing test chamber and a mechatronics workstation are being constructed.

  5. Rebar Graphene from Functionalized Boron Nitride Nanotubes

    PubMed Central

    2015-01-01

    The synthesis of rebar graphene on Cu substrates is described using functionalized boron nitride nanotubes (BNNTs) that were annealed or subjected to chemical vapor deposition (CVD) growth of graphene. Characterization shows that the BNNTs partially unzip and form a reinforcing bar (rebar) network within the graphene layer that enhances the mechanical strength through covalent bonds. The rebar graphene is transferrable to other substrates without polymer assistance. The optical transmittance and conductivity of the hybrid rebar graphene film was tested, and a field effect transistor was fabricated to explore its electrical properties. This method of synthesizing 2D hybrid graphene/BN structures should enable the hybridization of various 1D nanotube and 2D layered structures with enhanced mechanical properties. PMID:25486451

  6. Carbon nanotubes: their potential and pitfalls for bone tissue regeneration and engineering.

    PubMed

    Newman, Peter; Minett, Andrew; Ellis-Behnke, Rutledge; Zreiqat, Hala

    2013-11-01

    The extracellular environment which supports cell life is composed of a hierarchy of maintenance, force and regulatory systems which integrate from the nano- through to macroscale. For this reason, strategies to recreate cell supporting environments have been investigating the use of nanocomposite biomaterials. Here, we review the use of carbon nanotubes as part of a bottom-up approach for use in bone tissue engineering. We evaluate the properties of carbon nanotubes in the context of synthetic tissue substrates and contrast them with the nanoscale features of the extracellular environment. Key studies are evaluated with an emphasis on understanding the mechanisms through which carbon nanotubes interact with biological systems. This includes an examination of how the different properties of carbon nanotubes affect tissue growth, how these properties and variation to them might be leveraged in regenerative tissue therapies and how impurities or contaminates affect their toxicity and biological interaction. In this comprehensive review, the authors describe the status and potential applications of carbon nanotubes in bone tissue engineering. © 2013.

  7. Inorganic fullerenes and nanotubes: Wealth of materials and morphologies

    NASA Astrophysics Data System (ADS)

    Bar-Sadan, M.; Kaplan-Ashiri, I.; Tenne, R.

    2007-10-01

    It is already well established today that numerous materials form closed-cage structures, of which carbon fullerenes and nanotubes are a special case [1]. Inorganic fullerene-like nanoparticles (designated IF) and inorganic nanotubes (INT) have been produced by different routes and experimental techniques, achieving persistent growth of a variety of materials and structural wealth within them. The research in this area has focused on synthesizing new IF and INT materials and understanding their different properties as well as scaling up the synthetic process in order to make it suitable for industrial applications. In this review, the main synthetic procedures to obtain inorganic fullerene-like nanoparticles and nanotubes will be discussed alongside with the different mechanisms that affect the morphology of the final product. The main differences between the morphologies will be presented. Some general considerations relating the properties of the parent compound with the morphology of the product will be mentioned.

  8. Working Toward Nanotube Composites

    NASA Technical Reports Server (NTRS)

    Arepalli, Sivaram; Nikolaev, Pavel; Gorelik, Olga; Hadjiev, Victor G.; Scott, Carl D.; Files, Bradley S.

    2001-01-01

    One of the most attractive applications of single-wall carbon nanotubes (SWNT) is found in the area of structural materials. Nanotubes have a unique combination of high strength, modulus, and elongation to failure, and therefore have potential to significantly enhance the mechanical properties of today's composites. This is especially attractive for the aerospace industry looking for any chance to save weight. This is why NASA has chosen to tackle this difficult application of SWNT. Nanotube properties differ significantly from that of conventional carbon fibers, and a whole new set of problems, including adhesion and dispersion in the adhesive polymer matrix, must be resolved in order to engineer superior composite materials. From recent work on a variety of applications it is obvious that the wide range of research in nanotubes will lead to advances in physics, chemistry, and engineering. However, the possibility of ultralightweight structures is what causes dreamers to really get excited. One of the important issues in composite engineering is aspect ratio of the fibers, since it affects load transfer in composites. Nanotube length was a gray area for years, since they are formed in bundles, making it impossible to monitor individual nanotube length. Even though bundles are observed to be tens and hundreds of microns long, they can be built of relatively short tubes weakly bound by Van der Waals forces. Nanotube length can be affected by subsequent purification and ultrasound processing, which has been necessary in order to disperse nanotubes and introduce them into a polymer matrix. Some calculations show that nanotubes with 10(exp 5) aspect ratio may be necessary to achieve good load transfer. We show here that nanotubes produced in our laser system are as much as tens of microns long and get cut into lengths of hundreds of nanometers during ultrasound processing. Nanotube length was measured by AFM on pristine nanotube specimens as well, as after sonication

  9. Growth of Carbon Nanostructure Materials Using Laser Vaporization

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, Ching-Hua; Lehozeky, S.

    2000-01-01

    Since the potential applications of carbon nanotubes (CNT) was discovered in many fields, such as non-structure electronics, lightweight composite structure, and drug delivery, CNT has been grown by many techniques in which high yield single wall CNT has been produced by physical processes including arc vaporization and laser vaporization. In this presentation, the growth mechanism of the carbon nanostructure materials by laser vaporization is to be discussed. Carbon nanoparticles and nanotubes have been synthesized using pulsed laser vaporization on Si substrates in various temperatures and pressures. Two kinds of targets were used to grow the nanostructure materials. One was a pure graphite target and the other one contained Ni and Co catalysts. The growth temperatures were 600-1000 C and the pressures varied from several torr to 500 torr. Carbon nanoparticles were observed when a graphite target was used, although catalysts were deposited on substrates before growing carbon films. When the target contains catalysts, carbon nanotubes (CNT) are obtained. The CNT were characterized by scanning electron microscopy, x-ray diffraction, optical absorption and transmission, and Raman spectroscopy. The temperature-and pressure-dependencies of carbon nanotubes' growth rate and size were investigated.

  10. Fully Depleted Ti-Nb-Ta-Zr-O Nanotubes: Interfacial Charge Dynamics and Solar Hydrogen Production.

    PubMed

    Chiu, Yi-Hsuan; Lai, Ting-Hsuan; Chen, Chun-Yi; Hsieh, Ping-Yen; Ozasa, Kazunari; Niinomi, Mitsuo; Okada, Kiyoshi; Chang, Tso-Fu Mark; Matsushita, Nobuhiro; Sone, Masato; Hsu, Yung-Jung

    2018-05-01

    Poor kinetics of hole transportation at the electrode/electrolyte interface is regarded as a primary cause for the mediocre performance of n-type TiO 2 photoelectrodes. By adopting nanotubes as the electrode backbone, light absorption and carrier collection can be spatially decoupled, allowing n-type TiO 2 , with its short hole diffusion length, to maximize the use of the available photoexcited charge carriers during operation in photoelectrochemical (PEC) water splitting. Here, we presented a delicate electrochemical anodization process for the preparation of quaternary Ti-Nb-Ta-Zr-O mixed-oxide (denoted as TNTZO) nanotube arrays and demonstrated their utility in PEC water splitting. The charge-transfer dynamics for the electrodes was investigated using time-resolved photoluminescence, electrochemical impedance spectroscopy, and the decay of open-circuit voltage analysis. Data reveal that the superior photoactivity of TNTZO over pristine TiO 2 originated from the introduction of Nd, Ta, and Zr elements, which enhanced the amount of accessible charge carriers, modified the electronic structure, and improved the hole injection kinetics for expediting water splitting. By modulating the water content of the electrolyte employed in the anodization process, the wall thickness of the grown TNTZO nanotubes can be reduced to a size smaller than that of the depletion layer thickness, realizing a fully depleted state for charge carriers to further advance the PEC performance. Hydrogen evolution tests demonstrate the practical efficacy of TNTZO for realizing solar hydrogen production. Furthermore, with the composition complexity and fully depleted band structure, the present TNTZO nanotube arrays may offer a feasible and universal platform for the loading of other semiconductors to construct a sophisticated heterostructure photoelectrode paradigm, in which the photoexcited charge carriers can be entirely utilized for efficient solar-to-fuel conversion.

  11. Self-assembly of protein-based biomaterials initiated by titania nanotubes.

    PubMed

    Forstater, Jacob H; Kleinhammes, Alfred; Wu, Yue

    2013-12-03

    Protein-based biomaterials are a promising strategy for creating robust highly selective biocatalysts. The assembled biomaterials must sufficiently retain the near-native structure of proteins and provide molecular access to catalytically active sites. These requirements often exclude the use of conventional assembly techniques, which rely on covalent cross-linking of proteins or entrapment within a scaffold. Here we demonstrate that titania nanotubes can initiate and template the self-assembly of enzymes, such as ribonuclease A, while maintaining their catalytic activity. Initially, the enzymes form multilayer thick ellipsoidal aggregates centered on the nanotube surface; subsequently, these nanosized entities assemble into a micrometer-sized enzyme material that has enhanced enzymatic activity and contains as little as 0.1 wt % TiO2 nanotubes. This phenomenon is uniquely associated with the active anatase (001)-like surface of titania nanotubes and does not occur on other anatase nanomaterials, which contain significantly fewer undercoordinated Ti surface sites. These findings present a nanotechnology-enabled mechanism of biomaterial growth and open a new route for creating stable protein-based biomaterials and biocatalysts without the need for chemical modification.

  12. Process Parameters for Successful Synthesis of Carbon Nanotubes by Chemical Vapor Deposition: Implications for Chemical Mechanisms and Life-cycle Assessment

    NASA Astrophysics Data System (ADS)

    Xue, Ke

    CNT precursors by themselves. Acetylene does not show an additional energy demand or thermal conversion in the synthesis, and it could be the direct CNT precursors by itself; or at least, it would be most easily to get access to carbon nanotube growth while minimizing synthesis temperature. In detail, methane employs more energy demand (Tavg=883°C) than ethylene (Tavg=766°C), which in turn demands more energy than acetylene (Tavg=710°C) to successfully synthesize carbon nanotubes. The distinction in energy demand could be the result of kinetic energy requirements by the thermal conversion process of methane and ethylene to form direct CNT precursors, and methane employs the highest activation demand among three hydrocarbons. Thus, these results support the hypothesis that methane and ethylene could be thermally converted to form acetylene before CNT incorporation. In addition, methane and ethylene show the demand for hydrogen in thermal conversion process before CNT incorporation; whereas, hydrogen does not contribute to the synthesis via acetylene before CNT incorporation, except the reduction of catalyst. At relatively low hydrogen concentration, this work suggests that hydrogen prompts growth of carbon nanotubes via methane and ethylene, probably by reducing the catalysts or participating thermal reactions. In addition, "polymerization-like formation mechanism" could be supported by the higher growth rate of CNTs via ethylene than acetylene. There could be an optimum residence time to maintain a relatively higher growth rate. At too low residence time, carbon source could not be accumulated, causing a waste of material; while too high residence time may cause the limitation of carbon source supplement and accumulation of byproducts. At last, high concentration of carbon source and hydrogen could cause more energy consumption, while it helps to achieve a high growth rate, due to the more presence of direct carbon precursor.

  13. Carbon Nanotubes Filled with Ferromagnetic Materials

    PubMed Central

    Weissker, Uhland; Hampel, Silke; Leonhardt, Albrecht; Büchner, Bernd

    2010-01-01

    Carbon nanotubes (CNT) filled with ferromagnetic metals like iron, cobalt or nickel are new and very interesting nanostructured materials with a number of unique properties. In this paper we give an overview about different chemical vapor deposition (CVD) methods for their synthesis and discuss the influence of selected growth parameters. In addition we evaluate possible growth mechanisms involved in their formation. Moreover we show their identified structural and magnetic properties. On the basis of these properties we present different application possibilities. Some selected examples reveal the high potential of these materials in the field of medicine and nanotechnology. PMID:28883334

  14. Synthesis of Carbon Nanotubes and Nanospheres from Coconut Fibre and the Role of Synthesis Temperature on Their Growth

    NASA Astrophysics Data System (ADS)

    Adewumi, Gloria A.; Inambao, Freddie; Eloka-Eboka, Andrew; Revaprasadu, Neerish

    2018-07-01

    Carbon nanotubes (CNT) and carbon nanospheres were successfully synthesized from coconut fibre-activated carbon. The biomass was first carbonized then physically activated, followed by treatment using ethanol vapor at 700°C to 1100°C at 100°C intervals. The effect of synthesis temperature on the formation of the nanomaterials was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectrometry, x-ray diffraction (XRD), Fourier transform infrared microscopy (FTIR) and thermogravimetric analysis. SEM analysis revealed that nanospheres were formed at higher temperatures of 1000°C and 1100°C, while lower temperatures of 800°C and 900°C favored the growth of CNT. At 700°C, however, no tubes or spheres were formed. TEM and FTIR were used to observe spectral features, such as the peak positions, intensity and bandwidth, which are linked to some structural properties of the samples investigated. All these observations provided facts on the nanosphere and nanotube dimensions, vibrational modes and the degree of purity of the obtained samples. The TEM results show spheres of diameter in the range 50 nm to 250 nm while the tubes had diameters between 50 nm to 100 nm. XRD analysis reveals the materials synthesized are amorphous in nature with a hexagonal graphite structure.

  15. Synthesis of Carbon Nanotubes and Nanospheres from Coconut Fibre and the Role of Synthesis Temperature on Their Growth

    NASA Astrophysics Data System (ADS)

    Adewumi, Gloria A.; Inambao, Freddie; Eloka-Eboka, Andrew; Revaprasadu, Neerish

    2018-04-01

    Carbon nanotubes (CNT) and carbon nanospheres were successfully synthesized from coconut fibre-activated carbon. The biomass was first carbonized then physically activated, followed by treatment using ethanol vapor at 700°C to 1100°C at 100°C intervals. The effect of synthesis temperature on the formation of the nanomaterials was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectrometry, x-ray diffraction (XRD), Fourier transform infrared microscopy (FTIR) and thermogravimetric analysis. SEM analysis revealed that nanospheres were formed at higher temperatures of 1000°C and 1100°C, while lower temperatures of 800°C and 900°C favored the growth of CNT. At 700°C, however, no tubes or spheres were formed. TEM and FTIR were used to observe spectral features, such as the peak positions, intensity and bandwidth, which are linked to some structural properties of the samples investigated. All these observations provided facts on the nanosphere and nanotube dimensions, vibrational modes and the degree of purity of the obtained samples. The TEM results show spheres of diameter in the range 50 nm to 250 nm while the tubes had diameters between 50 nm to 100 nm. XRD analysis reveals the materials synthesized are amorphous in nature with a hexagonal graphite structure.

  16. Carbon nanotube nanoelectrode arrays

    DOEpatents

    Ren, Zhifeng; Lin, Yuehe; Yantasee, Wassana; Liu, Guodong; Lu, Fang; Tu, Yi

    2008-11-18

    The present invention relates to microelectode arrays (MEAs), and more particularly to carbon nanotube nanoelectrode arrays (CNT-NEAs) for chemical and biological sensing, and methods of use. A nanoelectrode array includes a carbon nanotube material comprising an array of substantially linear carbon nanotubes each having a proximal end and a distal end, the proximal end of the carbon nanotubes are attached to a catalyst substrate material so as to form the array with a pre-determined site density, wherein the carbon nanotubes are aligned with respect to one another within the array; an electrically insulating layer on the surface of the carbon nanotube material, whereby the distal end of the carbon nanotubes extend beyond the electrically insulating layer; a second adhesive electrically insulating layer on the surface of the electrically insulating layer, whereby the distal end of the carbon nanotubes extend beyond the second adhesive electrically insulating layer; and a metal wire attached to the catalyst substrate material.

  17. Three-dimensional Nitrogen-Doped Reduced Graphene Oxide/Carbon Nanotube Composite Catalysts for Vanadium Flow Batteries

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fu, Shaofang; Zhu, Chengzhou; Song, Junhua

    The development of vanadium redox flow battery is limited by the sluggish kinetics of the reaction, especially the cathodic VO2+/VO2+ redox couples. Therefore, it is vital to develop new electrocatalyst with enhanced activity to improve the battery performance. Herein, we first synthesized the hydrogel precursor by a facile hydrothermal method. After the following carbonization, nitrogen-doped reduced graphene oxide/carbon nanotube composite was obtained. By virtue of the large surface area and good conductivey, which are ensured by the unique hybrid structure, as well as the proper nitrogen doping, the as-prepared composite presents enhanced catalytic performance toward the VO2+/VO2+ redox reaction. Wemore » also demonstrated the composite with carbon nanotube loading of 2 mg/mL exhibits the highest activity and remarkable stability in aqueous solution due to the strong synergy between reduced graphene oxide and carbon nanotubes, indicating that this composite might show promising applications in vanadium redox flow battery.« less

  18. Carbon nanotube-based black coatings

    NASA Astrophysics Data System (ADS)

    Lehman, J.; Yung, C.; Tomlin, N.; Conklin, D.; Stephens, M.

    2018-03-01

    Coatings comprising carbon nanotubes are very black, that is, characterized by uniformly low reflectance over a broad range of wavelengths from the visible to far infrared. Arguably, there is no other material that is comparable. This is attributable to the intrinsic properties of graphitic material as well as the morphology (density, thickness, disorder, and tube size). We briefly describe a history of other coatings such as nickel phosphorous, gold black, and carbon-based paints and the comparable structural morphology that we associate with very black coatings. The need for black coatings is persistent for a variety of applications ranging from baffles and traps to blackbodies and thermal detectors. Applications for space-based instruments are of interest and we present a review of space qualification and the results of outgassing measurements. Questions of nanoparticle safety depend on the nanotube size and aspect ratio as well as the nature and route of exposure. We describe the growth of carbon nanotube forests along with the catalyst requirements and temperature limitations. We also describe coatings derived from carbon nanotubes and applied like paint. Building the measurement apparatus and determining the optical properties of something having negligible reflectance are challenging and we summarize the methods and means for such measurements. There exists information in the literature for effective media approximations to model the dielectric function of vertically aligned arrays. We summarize this along with the refractive index of graphite from the literature that is necessary for modeling the optical properties. In our experience, the scientific questions can be overshadowed by practical matters, so we provide an appendix of recipes for making as-grown and sprayed coatings along with an example of reflectance measurements.

  19. Improved attachment of mesenchymal stem cells on super-hydrophobic TiO2 nanotubes.

    PubMed

    Bauer, Sebastian; Park, Jung; von der Mark, Klaus; Schmuki, Patrik

    2008-09-01

    Self-organized layers of vertically orientated TiO(2) nanotubes providing defined diameters ranging from 15 up to 100nm were grown on titanium by anodic oxidation. These TiO(2) nanotube layers show super-hydrophilic behavior. After coating TiO(2) nanotube layers with a self-assembled monolayer (octadecylphosphonic acid) they showed a diameter-dependent wetting behavior ranging from hydrophobic (108+/-2 degrees ) up to super-hydrophobic (167+/-2 degrees ). Cell adhesion, spreading and growth of mesenchymal stem cells on the unmodified and modified nanotube layers were investigated and compared. We show that cell adhesion and proliferation are strongly affected in the super-hydrophobic range. Adsorption of extracellular matrix proteins as fibronectin, type I collagen and laminin, as well as bovine serum albumin, on the coated and uncoated surfaces showed a strong influence on wetting behavior and dependence on tube diameter.

  20. Flame Synthesis Used to Create Metal-Catalyzed Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    VanderWal, Randy L.

    2001-01-01

    carbon, seen here in cross section. They form a nested series of concentric cylinders, much like the growth rings on a tree. This sample was obtained by the supported catalyst method, whereby the nanoscale catalysts are dispersed on a substrate providing their support. The substrate with catalyst particles was immersed within an acetylene diffusion flame to which nitrogen had been added to eliminate soot formation. Upon removal from the flame, the nanotubes were dispersed on a holder suitable for electron microscopy. Although not seen in the figure, the tube diameter reflects that of the catalyst particle.