WorldWideScience

Sample records for monolayer crystalline phase

  1. Decoupling of crystalline and conformational degrees of freedom in lipid monolayers

    DEFF Research Database (Denmark)

    Ipsen, John Hjorth; Mouritsen, Ole G.; Zuckermann, Martin J.

    1989-01-01

    by a liquid-conformationally ordered phase. This prediction is consistent with synchrotron x-ray experiments which show that the chain-ordering transition and the crystallization process need not take place at the same lateral pressure. A characterization is provided of the nonequilibrium effects and pattern-formation...... of the experimentally observed isotherms of lipid monolayer phase behavior. It is pointed out that cholesterol, which promotes lipid-chain conformational order, has a unique capacity of acting as a `crystal breaker' in the solid monolayer phases and therefore provides a molecular mechanism for decoupling crystalline...... and conformational order in lipid monolayers containing cholesterol. The phase diagram of mixed cholesterol–lipid monolayers is derived and discussed in relation to monolayer experiments. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....

  2. Magnetic and Structural Phases of Monolayer 02 on Graphite

    DEFF Research Database (Denmark)

    McTague, J. P.; Nielsen, Mourits

    1976-01-01

    Neutron diffraction studies of O2 thin films physisorbed on the basal plane of graphite show three distinct two-dimensional crystalline phases, all incommensurate with the substrate lattice. The low-temperature monolayer phase has a distorted triangular structure analogous to the closest-packed p......Neutron diffraction studies of O2 thin films physisorbed on the basal plane of graphite show three distinct two-dimensional crystalline phases, all incommensurate with the substrate lattice. The low-temperature monolayer phase has a distorted triangular structure analogous to the closest...

  3. The crystalline structures of carboxylic acid monolayers adsorbed on graphite.

    Science.gov (United States)

    Bickerstaffe, A K; Cheah, N P; Clarke, S M; Parker, J E; Perdigon, A; Messe, L; Inaba, A

    2006-03-23

    X-ray and neutron diffraction have been used to investigate the formation of solid crystalline monolayers of all of the linear carboxylic acids from C(6) to C(14) at submonolayer coverage and from C(8) to C(14) at multilayer coverages, and to characterize their structures. X-rays and neutrons highlight different aspects of the monolayer structures, and their combination is therefore important in structural determination. For all of the acids with an odd number of carbon atoms, the unit cell is rectangular of plane group pgg containing four molecules. The members of the homologous series with an even number of carbon atoms have an oblique unit cell with two molecules per unit cell and plane group p2. This odd-even variation in crystal structure provides an explanation for the odd-even variation observed in monolayer melting points and mixing behavior. In all cases, the molecules are arranged in strongly hydrogen-bonded dimers with their extended axes parallel to the surface and the plane of the carbon skeleton essentially parallel to the graphite surface. The monolayer crystal structures have unit cell dimensions similar to certain close-packed planes of the bulk crystals, but the molecular arrangements are different. There is a 1-3% compression on increasing the coverage over a monolayer.

  4. Grains and grain boundaries in highly crystalline monolayer molybdenum disulphide.

    Science.gov (United States)

    van der Zande, Arend M; Huang, Pinshane Y; Chenet, Daniel A; Berkelbach, Timothy C; You, YuMeng; Lee, Gwan-Hyoung; Heinz, Tony F; Reichman, David R; Muller, David A; Hone, James C

    2013-06-01

    Recent progress in large-area synthesis of monolayer molybdenum disulphide, a new two-dimensional direct-bandgap semiconductor, is paving the way for applications in atomically thin electronics. Little is known, however, about the microstructure of this material. Here we have refined chemical vapour deposition synthesis to grow highly crystalline islands of monolayer molybdenum disulphide up to 120 μm in size with optical and electrical properties comparable or superior to exfoliated samples. Using transmission electron microscopy, we correlate lattice orientation, edge morphology and crystallinity with island shape to demonstrate that triangular islands are single crystals. The crystals merge to form faceted tilt and mirror twin boundaries that are stitched together by lines of 8- and 4-membered rings. Density functional theory reveals localized mid-gap states arising from these 8-4 defects. We find that mirror twin boundaries cause strong photoluminescence quenching whereas tilt boundaries cause strong enhancement. Meanwhile, mirror twin boundaries slightly increase the measured in-plane electrical conductivity, whereas tilt boundaries slightly decrease the conductivity.

  5. Nanostructures having crystalline and amorphous phases

    Science.gov (United States)

    Mao, Samuel S; Chen, Xiaobo

    2015-04-28

    The present invention includes a nanostructure, a method of making thereof, and a method of photocatalysis. In one embodiment, the nanostructure includes a crystalline phase and an amorphous phase in contact with the crystalline phase. Each of the crystalline and amorphous phases has at least one dimension on a nanometer scale. In another embodiment, the nanostructure includes a nanoparticle comprising a crystalline phase and an amorphous phase. The amorphous phase is in a selected amount. In another embodiment, the nanostructure includes crystalline titanium dioxide and amorphous titanium dioxide in contact with the crystalline titanium dioxide. Each of the crystalline and amorphous titanium dioxide has at least one dimension on a nanometer scale.

  6. Stiffness of lipid monolayers with phase coexistence.

    Science.gov (United States)

    Caruso, Benjamín; Mangiarotti, Agustín; Wilke, Natalia

    2013-08-27

    The surface dilational modulus--or compressibility modulus--has been previously studied for monolayers composed of pure materials, where a jump in this modulus was related with the onset of percolation as a result of the establishment of a connected structure at the molecular level. In this work, we focused on monolayers composed of two components of low lateral miscibility. Our aim was to investigate the compressibility of mixed monolayers at pressures and compositions in the two-phase region of the phase diagram, in order to analyze the effect of the mechanical properties of each phase on the stiffness of the composite. In nine different systems with distinct molecular dipoles and charges, the stiffness of each phase and the texture at the plane of the monolayer were studied. In this way, we were able to analyze the general compressibility of two-phase lipid monolayers, regardless of the properties of their constituent parts. The results are discussed in the light of the following two hypotheses: first, the stiffness of the composite could be dominated by the stiffness of each phase as a weighted sum according to the percentage of each phase area, regardless of the distribution of the phases in the plane of the monolayer. Alternatively, the stiffness of the composite could be dominated by the mechanical properties of the continuous phase. Our results were better explained by this latter proposal, as in all the analyzed mixtures it was found that the mechanical properties of the percolating phase were the determining factors. The value of the compression modulus was closer to the value of the connected phase than to that of the dispersed phase, indicating that the bidimensional composites displayed mechanical properties that were related to the properties of each phases in a rather complex manner.

  7. Non-rotator phases in phospholipid monolayers?

    DEFF Research Database (Denmark)

    Kenn, R.M.; Kjær, K.; Möhwald, H.

    1996-01-01

    Monolayers of diacylphosphatidylethanolamines at the air/water interface are studied by grazing incidence X-ray diffraction. The results prove the existence of phases which show analogies with the rotator phases of single-chain surfactants: hexagonal tail lattice with no tilt; rectangular lattice...

  8. Phase diagrams of binary crystalline-crystalline polymer blends.

    Science.gov (United States)

    Matkar, Rushikesh A; Kyu, Thein

    2006-08-17

    A thermodynamically self-consistent theory has been developed to establish binary phase diagrams for two-crystalline polymer blends by taking into consideration all interactions including amorphous-amorphous, crystal-amorphous, amorphous-crystal, and crystal-crystal interactions. The present theory basically involves combination of the Flory-Huggins free energy for amorphous-amorphous isotropic mixing and the Landau free energy of polymer solidification (e.g., crystallization) of the crystalline constituents. The self-consistent solution via minimization of the free energy of the mixture affords determination of eutectic, peritectic, and azeotrope phase diagrams involving various coexistence regions such as liquid-liquid, liquid-solid, and solid-solid coexistence regions bound by liquidus and solidus lines. To validate the present theory, the predicted eutectic phase diagrams have been compared with the reported experimental binary phase diagrams of blends such as polyethylene fractions as well as polycaprolactone/trioxane mixtures.

  9. Improvements in the characterization of the crystalline structure of acid-terminated alkanethiol self-assembled monolayers on Au(111).

    Science.gov (United States)

    Mendoza, Sandra M; Arfaoui, Imad; Zanarini, Simone; Paolucci, Francesco; Rudolf, Petra

    2007-01-16

    We report a study of acid-terminated self-assembled monolayers of alkanethiols of different length, 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHDA), on Au(111). Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and contact angle techniques were used for characterization, and the results were compared with those obtained from n-alkanethiols of similar chain length, providing a detailed description of the two-dimensional crystalline structure. Molecular resolution STM images show that 11-MUA forms a dense-packed monolayer arranged in a (square root 3 x square root 3)R30 degrees structure with a c(2 x 4) superlattice, where the simple hexagonal phase, the c(2 x 4) superlattice, and nonordered areas coexist. 16-MHDA assembles in a uniform monolayer with similar morphology to that of 11-MUA, but molecular resolution could not be reached in STM due to both the hydrophilicity of the acid groups and the poor conductivity of the thick monolayer. Nevertheless, the monolayer thicknesses estimated by XPS and electrochemistry and the highly blocking character of the film observed by electrochemistry as well as the low water contact angle are consistent with 16-MHDA molecules forming a compact monolayer on the Au(111) substrate with fully extended alkyl chains and acid groups pointing away from the surface. The results obtained for 16-MHDA were reproducible under different preparation conditions such as the addition or omission of acetic acid to the ethanolic solution. Contrary to other reports, we demonstrate that ordered acid-terminated self-assembled monolayers are obtained with the same preparation conditions as those of the methyl-terminated ones, without any additional treatment.

  10. Structural phase transitions in monolayer molybdenum dichalcogenides

    Science.gov (United States)

    Choe, Duk-Hyun; Sung, Ha June; Chang, Kee Joo

    2015-03-01

    The recent discovery of two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs) has provided opportunities to develop ultimate thin channel devices. In contrast to graphene, the existence of moderate band gap and strong spin-orbit coupling gives rise to exotic electronic properties which vary with layer thickness, lattice structure, and symmetry. TMDs commonly appear in two structures with distinct symmetries, trigonal prismatic 2H and octahedral 1T phases which are semiconducting and metallic, respectively. In this work, we investigate the structural and electronic properties of monolayer molybdenum dichalcogenides (MoX2, where X = S, Se, Te) through first-principles density functional calculations. We find a tendency that the semiconducting 2H phase is more stable than the metallic 1T phase. We show that a spontaneous symmetry breaking of 1T phase leads to various distorted octahedral (1T') phases, thus inducing a metal-to-semiconductor transition. We discuss the effects of carrier doping on the structural stability and the modification of the electronic structure. This work was supported by the National Research Foundation of Korea (NRF) under Grant No. NRF-2005-0093845 and Samsung Science and Technology Foundation under Grant No. SSTFBA1401-08.

  11. Monolithic aerogels with nanoporous crystalline phases

    Science.gov (United States)

    Daniel, Christophe; Guerra, Gaetano

    2015-05-01

    High porosity monolithic aerogels with nanoporous crystalline phases can be obtained from syndiotactic polystyrene and poly(2,6-dimethyl-1,4-phenylene)oxide thermoreversible gels by removing the solvent with supercritical CO2. The presence of crystalline nanopores in the aerogels based on these polymers allows a high uptake associated with a high selectivity of volatile organic compounds from vapor phase or aqueous solutions even at very low activities. The sorption and the fast kinetics make these materials particularly suitable as sorption medium to remove traces of pollutants from water and moist air.

  12. Phase diagram for ortho-para-hydrogen monolayers

    CERN Document Server

    Sullivan, N S

    2003-01-01

    The phase diagram for orientational ordering of hydrogen monolayers on graphite and boron nitride is revised in view of current theory and experimental observations from nuclear magnetic resonance (NMR) studies recently reported for ortho-H sub 2 concentrations 0.35 <= c <= 0.92 and temperatures 0.14 <= T <= 1.80 K. The characteristic interaction coupling GAMMA sub 0 = 0.50 +- 0.03 K and the crystalline field amplitude V sub 0 = 0.70 +- 0.10 K are derived from experimental data, and distinct types of the local orientationally ordered structures are analysed using a proposed model for site-diluted uniaxial quadrupoles on a triangular plane lattice of hexagonal symmetry. The long-range periodic pinwheel structure and the short-range quadrupolar glass (QG) phase are stable above the 2D site-percolation limit, c sub p = 0.72, and for 0.48 < c < c sub p , respectively, where quadrupolar-order effects dominate. At very low T, the QG phase shows instability with respect to local dipole-like polariz...

  13. Crystalline self-assembly into monolayers of folded oligomers at the air-water interface

    DEFF Research Database (Denmark)

    Lederer, K.; Godt, A.; Howes, P.B.;

    2000-01-01

    of the folding unit almost perpendicular to the water surface, as determined by synchrotron grazing-incidence X-ray diffraction. Three distinct molecular shapes, of the types U, inverted U, and M, were obtained in the two-dimensional crystalline state, depending upon the number of spacer units, and the number......Insertion of the 115-bis(ethynylene)benzene unit as a rigid spacer into a linear alkyl chain, thus separating the two resulting stems by 9 Angstrom, induces chain folding at the air-water interface. These folded molecules self-assemble into crystalline monolayers at this interface, with the plane...... and position of the hydrophilic groups in the molecule. The molecules form ribbons with a higher crystal coherence in the direction of stacking between the molecular ribbons, and a lower coherence along the ribbon direction. A similar molecule, but with a spacer unit that imposes a 5 Angstrom separation...

  14. Electrical transport in crystalline phase change materials

    Energy Technology Data Exchange (ETDEWEB)

    Woda, Michael

    2012-01-06

    In this thesis, the electrical transport properties of crystalline phase change materials are discussed. Phase change materials (PCM) are a special class of semiconducting and metallic thin film alloys, typically with a high amount of the group five element antimony or the group six element tellurium, such as Ge{sub 2}Sb{sub 2}Te{sub 5}. The unique property portfolio of this material class makes it suitable for memory applications. PCMs reveal fast switching between two stable room-temperature phases (amorphous and crystalline) realized by optical laser or electrical current pulses in memory devices. Additionally, a pronounced property contrast in form of optical reflectivity and electrical conductivity between the amorphous and crystalline phase is the characteristic fingerprint of PCMs. The emerging electrical solid state memory PCRAM is a very promising candidate to replace Flash memory in the near future or to even become a universal memory, which is non-volatile and shows the speed and cyclability of DRAM. One of the main technological challenges is the switching process into the amorphous state, which is the most power demanding step. In order to reduce the switching power, the crystalline resistivity needs to be increased at a given voltage. Thus understanding and tayloring of this property is mandatory. In this work, first the technological relevance, i.e. optical and electrical memory concepts based on PCMs are introduced. Subsequently a description of the physical properties of PCMs in four categories is given. Namely, structure, kinetics, optical properties and electrical properties are discussed. Then important recent developments such as the identification of resonant bonding in crystalline PCMs and a property predicting coordination scheme are briefly reviewed. The following chapter deals with the theoretical background of electrical transport, while the next chapter introduces the experimental techniques: Sputtering, XRR, XRD, DSC, thermal annealing

  15. Phase equilibria in model surfactants forming Langmuir monolayers.

    Science.gov (United States)

    Ramírez, E; Santana, A; Cruz, A; López, G E

    2007-12-14

    The study of Langmuir monolayers has generated the attention of researchers because of their unique properties and their not well understood phase equilibrium. These monolayers exhibit interesting phase diagrams where the unusual liquid-liquid equilibrium can be observed for a single component monolayer. Monte Carlo computer simulations in the virtual Gibbs ensemble were used to obtain the phase diagram of Langmuir monolayers. The liquid-vapor and liquid-liquid phase equilibria were considered by constructing the Cailletet-Mathias phase diagrams. By using the Ising model and the rectilinear approximations the identification of the critical properties for both equilibria was determined. These critical parameters were calculated as a function of the strength of the interaction between the surfactant molecules and the aqueous subphase. As a result, we have identified the coexistence between a liquid expanded state (LES)-vapor and the liquid condensed state-LES, in agreement with experimental and theoretical evidence in the literature. We obtained a clear separation of phases and a strong dependence on the strength of the solvent used. Namely, as the interaction between the solvent and the head of the surfactant increases, the critical properties also increase. Equilibrium states were characterized by computing thermodynamic quantities as a function of temperature and solvent strength.

  16. Crystalline structures of alkylamide monolayers adsorbed on the surface of graphite.

    Science.gov (United States)

    Bhinde, Tej; Clarke, Stuart M; Phillips, Tamsin K; Arnold, Thomas; Parker, Julia E

    2010-06-01

    Synchrotron X-ray and neutron diffraction have been used to determine the two-dimensional crystalline structures of alkylamides adsorbed on graphite at submonolayer coverage. The calculated structures show that the plane of the carbon backbone of the amide molecules is parallel to the graphite substrate. The molecules form hydrogen-bonded dimers, and adjacent dimers form additional hydrogen bonds yielding extended chains. By presenting data from a number of members of the homologous series, we have identified that these chains pack in different arrangements depending on the number of carbons in the amide molecule. The amide monolayers are found to be very stable relative to other closely related alkyl species, a feature which is attributed to the extensive hydrogen bonding present in these systems. The characteristics of the hydrogen bonds have been determined and are found to be in close agreement with those present in the bulk materials.

  17. Isostructural solid-solid phase transition in monolayers of soft core-shell particles at fluid interfaces: structure and mechanics.

    Science.gov (United States)

    Rey, Marcel; Fernández-Rodríguez, Miguel Ángel; Steinacher, Mathias; Scheidegger, Laura; Geisel, Karen; Richtering, Walter; Squires, Todd M; Isa, Lucio

    2016-04-21

    We have studied the complete two-dimensional phase diagram of a core-shell microgel-laden fluid interface by synchronizing its compression with the deposition of the interfacial monolayer. Applying a new protocol, different positions on the substrate correspond to different values of the monolayer surface pressure and specific area. Analyzing the microstructure of the deposited monolayers, we discovered an isostructural solid-solid phase transition between two crystalline phases with the same hexagonal symmetry, but with two different lattice constants. The two phases corresponded to shell-shell and core-core inter-particle contacts, respectively; with increasing surface pressure the former mechanically failed enabling the particle cores to come into contact. In the phase-transition region, clusters of particles in core-core contacts nucleate, melting the surrounding shell-shell crystal, until the whole monolayer moves into the second phase. We furthermore measured the interfacial rheology of the monolayers as a function of the surface pressure using an interfacial microdisk rheometer. The interfaces always showed a strong elastic response, with a dip in the shear elastic modulus in correspondence with the melting of the shell-shell phase, followed by a steep increase upon the formation of a percolating network of the core-core contacts. These results demonstrate that the core-shell nature of the particles leads to a rich mechanical and structural behavior that can be externally tuned by compressing the interface, indicating new routes for applications, e.g. in surface patterning or emulsion stabilization.

  18. A new crystalline phase in magnetar crusts

    CERN Document Server

    Bedaque, Paulo F; Ng, Nathan; Sen, Srimoyee

    2013-01-01

    We show that ions at the low densities and high magnetic fields relevant to the outer crust of magnetars form a novel crystalline phase where ions are strongly coupled along the magnetic field and loosely coupled in the transverse direction. The underlying cause is the anisotropic screening of the Coulomb force by electrons in the presence of a strongly quantizing magnetic field which leads to Friedel oscillations in the ion-ion potential. In particular, the Friedel oscillations are much longer-ranged in the direction of the magnetic field than is the case in the absence of magnetic fields, a factor that has been neglected in previous studies. These "Friedel crystals" have very anisotropic elastic moduli, with potentially interesting implications for the Quasi-periodic Oscillations seen in the X-ray flux of magnetars during their giant flares. We find the minimum energy configuration of ions taking into account these anisotropic effects and find that, depending on the density, temperature and magnetic field s...

  19. Intermolecular band dispersion of quasi-single crystalline organic semiconductor monolayer measured by angle-resolved photoemission spectroscopy

    Science.gov (United States)

    Ohtomo, Manabu; Shimada, Toshihiro; Hasegawa, Tetsuya

    2010-03-01

    Band structure of organic semiconductors is important knowledge to improve the molecular design. Angle-Resolved Photoemission Spectroscopy (ARPES) studies using highly conductive single domain samples grown in-situ is the most direct technique. In this study, we developed a novel method to grow quasi-single crystalline monolayer on conductive substrate and electronic structure was investigated. As a template for orientation control, we used a step-bunched Si(111) substrate with dangling bond termination. In case of pentacene, it was confirmed that the crystal is quasi-single crystal with 2.2^o rotated twins. The band dispersion was identical to that of thin-film phase. The effective mass and transfer integrals are evaluated using two-dimensional tight binding fit and compared with band calculations [1]. We also report the growth of 2,7-Dipheny[1]benzothieno[3,2-b]benzothiophene (DPh-BTBT) [2] on Bi-Si substrate and compare discuss its band structure. [4pt] [1] M.Ohtomo et al., APL 95, 123308 (2009).[0pt] [2] K.Takimiya, JACS 128, 3044 (2006).

  20. Heterogeneous nanotribological response of polymorphic self-assembled monolayers arising from domain and phase dependent friction.

    Science.gov (United States)

    Paradinas, Markos; Munuera, Carmen; Silien, Christophe; Buck, Manfred; Ocal, Carmen

    2013-01-28

    Micro-/nanoelectromechanical systems demand robust ultrathin films for lubrication. As they can drastically modify the frictional properties of surfaces, few nanometers thick self-assembled monolayers (SAMs) constitute accepted candidates as boundary lubricants. Their high stability and easy preparation make them attractive also for low cost applications. Given their high order, organosulfur SAMs have been archetypal systems for structural investigations, but few efforts have been devoted to analyze the influence of lateral inhomogeneities on their surface properties. The impact on the frictional response of the surface due to the existence of crystalline domains with lateral dimension in the sub-micrometer range is considered here. To this end, two polymorphic structures of self-assembled monolayers of ω-(4'-methylbiphenyl-4-yl) butane-1-thiol coexisting on Au(111) are investigated by scanning tunneling and force microscopy. Described by rectangular 5√5 × 3 (α-phase) and oblique 6√3 × 2√3 (β-phase) unit cells, they exhibit pronouncedly different frictional responses. The lateral nano-tribological heterogeneity of the surface is further influenced by the azimuthal orientation dependence of friction for each phase. In particular, this phenomenon is exploited in the less densely packed β-phase for which the separate analysis of forward and backward lateral force scans is used to differentiate domains rotated 180°. The results demonstrate the level of structural control required in the design of SAMs for nano-tribology applications.

  1. Polymorphic phases of galactocerebrosides: spectroscopic evidence of lamellar crystalline structures.

    Science.gov (United States)

    Bou Khalil, M; Carrier, D; Wong, P T; Tanphaichitr, N

    2001-06-06

    Fourier transform infrared spectroscopy was applied to study the structural and thermal properties of bovine brain galactocerebroside (GalCer) containing amide linked non-hydroxylated or alpha-hydroxy fatty acids (NFA- and HFA-GalCer, respectively). Over the temperature range 0-90 degrees C, both GalCer displayed complex thermal transitions, characteristic of polymorphic phase behavior. Upon heating, aqueous dispersions of NFA- and HFA-GalCer exhibited high order-disorder transition temperatures near 80 and 72 degrees C, respectively. En route to the chain melting transition, the patterns of the amide I band of NFA-GalCer were indicative of two different lamellar crystalline phases, whereas those of HFA-GalCer were suggestive of lamellar gel and crystalline bilayers. Cooling from the liquid-crystalline phase resulted in the formation of another crystalline phase of NFA-GalCer and a gel phase of HFA-GalCer, with a phase transition near 62 and 66 degrees C, respectively. Prolonged incubation of GalCer bilayers at 38 degrees C revealed conversions among lamellar crystalline phases (NFA-GalCer) or between lamellar gel and crystalline bilayer structures (HFA-GalCer). Spectral changes indicated that the temperature and/or time induced formation of the lamellar crystalline structures of NFA- and HFA-GalCer was accompanied by partial dehydration and by rearrangements of the hydrogen bonding network and bilayer packing mode of GalCer.

  2. Naturally occurring crystalline phases: analogues for radioactive waste forms

    Energy Technology Data Exchange (ETDEWEB)

    Haaker, R.F.; Ewing, R.C.

    1981-01-01

    Naturally occurring mineral analogues to crystalline phases that are constituents of crystalline radioactive waste forms provide a basis for comparison by which the long-term stability of these phases may be estimated. The crystal structures and the crystal chemistry of the following natural analogues are presented: baddeleyite, hematite, nepheline; pollucite, scheelite;sodalite, spinel, apatite, monazite, uraninite, hollandite-priderite, perovskite, and zirconolite. For each phase in geochemistry, occurrence, alteration and radiation effects are described. A selected bibliography for each phase is included.

  3. Electrospinning of PVDF nanofibrous membranes with controllable crystalline phases

    Science.gov (United States)

    Lei, Tingping; Zhu, Ping; Cai, Xiaomei; Yang, Le; Yang, Fan

    2015-07-01

    Effectively controlling crystalline phases of electrospun polyvinylidene fluoride (PVDF) nanofibers is crucial to produce membranes with special properties for specific applications. Here, the heating treatment during or after electrospinning has been investigated to determine an effective way to control crystalline phase of PVDF nanofibers. By simultaneously controlling the collector temperature and the flow rate during the fiber deposition, a comparatively lower temperature (≤70 °C) is required for obtaining α-, β-, or γ-phase-dominant nanofibrous membranes, whereas a much higher temperature (≥150 °C) is necessary for post-heating of already-deposited fibers. On the other hand, through finely tuning the heating during or after electrospinning, crosslinked nanofibrous membranes can be also obtained, which undoubtedly enhance mechanical performance of the membranes. Therefore, it is hopeful to fabricate high-performance electrospun PVDF nanofibrous membranes with synchronous control of crystalline phases and morphologies, which will further broaden the applications of PVDF materials.

  4. Entropy calculations for a supercooled liquid crystalline blue phase

    Energy Technology Data Exchange (ETDEWEB)

    Singh, U [Physics Department, University of the West Indies, PO Box 64, Bridgetown (Barbados)

    2007-01-15

    We observed, using polarized light microscopy, the supercooling of the blue phase (BPI) of cholesteryl proprionate and measured the corresponding liquid crystalline phase transition temperatures. From these temperatures and additional published data we have provided, for the benefit of undergraduate physics students, a nontraditional example involving entropy calculations for an irreversible transition.

  5. Phases and phase transition in insoluble and adsorbed monolayers of amide amphiphiles: Specific characteristics of the condensed phases.

    Science.gov (United States)

    Vollhardt, D

    2015-08-01

    For understanding the role of amide containing amphiphiles in inherently complex biological processes, monolayers at the air-water interface are used as simple biomimetic model systems. The specific characteristics of the condensed phases and phase transition in insoluble and adsorbed monolayers of amide amphiphiles are surveyed to highlight the effect of the chemical structure of the amide amphiphiles on the interfacial interactions in model monolayers. The mesoscopic topography and/or two-dimensional lattice structures of selected amino acid amphiphiles, amphiphilic N-alkylaldonamide, amide amphiphiles with specific tailored headgroups, such as amide amphiphiles based on derivatized ethanolamine, e.g. acylethanolamines (NAEs) and N-,O-diacylethanolamines (DAEs) are presented. Special attention is devoted the dominance of N,O-diacylated ethanolamine in mixed amphiphilic acid amide monolayers. The evidence that a first order phase transition can occur in adsorption layers and that condensed phase domains of mesoscopic scale can be formed in adsorption layers was first obtained on the basis of the experimental characteristics of a tailored amide amphiphile. New thermodynamic and kinetic concepts for the theoretical description of the characteristics of amide amphiphile's monolayers were developed. In particular, the equation of state for Langmuir monolayers generalized for the case that one, two or more phase transitions occur, and the new theory for phase transition in adsorbed monolayers are experimentally confirmed at first by amide amphiphile monolayers. Despite the significant progress made towards the understanding the model systems, these model studies are still limited to transfer the gained knowledge to biological systems where the fundamental physical principles are operative in the same way. The study of biomimetic systems, as described in this review, is only a first step in this direction.

  6. Local Crystalline Structure in an Amorphous Protein Dense Phase.

    Science.gov (United States)

    Greene, Daniel G; Modla, Shannon; Wagner, Norman J; Sandler, Stanley I; Lenhoff, Abraham M

    2015-10-20

    Proteins exhibit a variety of dense phases ranging from gels, aggregates, and precipitates to crystalline phases and dense liquids. Although the structure of the crystalline phase is known in atomistic detail, little attention has been paid to noncrystalline protein dense phases, and in many cases the structures of these phases are assumed to be fully amorphous. In this work, we used small-angle neutron scattering, electron microscopy, and electron tomography to measure the structure of ovalbumin precipitate particles salted out with ammonium sulfate. We found that the ovalbumin phase-separates into core-shell particles with a core radius of ∼2 μm and shell thickness of ∼0.5 μm. Within this shell region, nanostructures comprised of crystallites of ovalbumin self-assemble into a well-defined bicontinuous network with branches ∼12 nm thick. These results demonstrate that the protein gel is comprised in part of nanocrystalline protein.

  7. Si-C Linked Organic Monolayers on Crystalline Silicon Surfaces as Alternative Gate Insulators

    NARCIS (Netherlands)

    Faber, Erik J.; Smet, de Louis C.P.M.; Olthuis, Wouter; Zuilhof, Han; Sudhölter, Ernst J.R.; Bergveld, Piet; Berg, van den Albert

    2005-01-01

    Herein, the influence of silicon surface modification via Si-CnH2n+1 (n=10,12,16,22) monolayer-based devices on p-type (100) and n-type (100) silicon is studied by forming MIS (metal–insulator–semiconductor) diodes using a mercury probe. From current density–voltage (J–V) and capacitance–voltage (C–

  8. pH sensitivity of Si-C linked organic monolayers on crystalline silicon surfaces

    NARCIS (Netherlands)

    Faber, Erik Jouwert; Sparreboom, Wouter; Groeneveld, Wilrike; de Smet, Louis C.P.M.; Bomer, Johan G.; Olthuis, Wouter; Zuilhof, Han; Sudholter, Ernst; Sudhölter, Ernst J.R.; Bergveld, Piet; van den Berg, Albert

    2007-01-01

    The electrochemical behaviour of Si-C linked organic monolayers is studied in electrolyte-insulator-Si devices, under conditions normally encountered in potentiomeric biosensors, to gain fundamental knowledge on the behaviour of such Si electrodes under practical conditions. This is done via

  9. Crystalline-crystalline phase transformation in two-dimensional In2Se3 thin layers.

    Science.gov (United States)

    Tao, Xin; Gu, Yi

    2013-08-14

    We report, for the first time, the fabrication of single-crystal In2Se3 thin layers using mechanical exfoliation and studies of crystalline-crystalline (α → β) phase transformations as well as the corresponding changes of the electrical properties in these thin layers. Particularly, using electron microscopy and correlative in situ micro-Raman and electrical measurements, we show that, in contrast to bulk single crystals, the β phase can persist in single-crystal thin layers at room temperature (RT). The single-crystal nature of the layers before and after the phase transition allows for unambiguous determination of changes in the electrical resistivity. Specifically, the β phase has an electrical resistivity about 1-2 orders of magnitude lower than the α phase. Furthermore, we find that the temperature of the α → β phase transformation increases by as much as 130 K with the layer thickness decreasing from ~87 nm to ~4 nm. These single-crystal thin layers are ideal for studying the scaling behavior of the phase transformations and associated changes of the electrical properties. For these In2Se3 thin layers, the accessibility of the β phase at RT, with distinct electrical properties than the α phase, provides the basis for multilevel phase-change memories in a single material system.

  10. Si-C linked organic monolayers on crystalline silicon surfaces as alternative gate insulators

    NARCIS (Netherlands)

    Faber, E.J.; Smet, de L.C.P.M.; Olthuis, W.; Zuilhof, H.; Sudhölter, E.J.R.; Bergveld, P.; Berg, van den A.

    2005-01-01

    Herein, the influence of silicon surface modification via SiCnH2n+1 (n=10,12,16,22) monolayer-based devices on p-type 100 and n-type 100 silicon is studied by forming MIS (metal-insulator-semiconductor) diodes using a mercury probe. From current density-voltage (J-V) and capacitance-voltage (C-V) me

  11. Si-C linked organic monolayers on crystalline silicon surfaces as alternative gate insulators

    NARCIS (Netherlands)

    Faber, E.J.; Smet, de L.C.P.M.; Olthuis, W.; Zuilhof, H.; Sudhölter, E.J.R.; Bergveld, P.; Berg, van den A.

    2005-01-01

    Herein, the influence of silicon surface modification via SiCnH2n+1 (n=10,12,16,22) monolayer-based devices on p-type 100 and n-type 100 silicon is studied by forming MIS (metal-insulator-semiconductor) diodes using a mercury probe. From current density-voltage (J-V) and capacitance-voltage (C-V)

  12. Casimir Force Contrast Between Amorphous and Crystalline Phases of AIST

    NARCIS (Netherlands)

    Torrichelli, G.; Zwol, van P.J.; Shpak, O.; Palasantzas, G.; Svetovoy, V.B.; Binns, C.; Kooi, B.J.; Jost, P.; Wittig, M.

    2012-01-01

    Phase change materials (PCMs) can be rapidly and reversibly switched between the amorphous and crystalline state. The structural transformation is accompanied by a signifi cant change of optical and electronic properties rendering PCMs suitable for rewritable optical data storage and nonvolatile ele

  13. Topological Phase Diagrams of Bulk and Monolayer TiS2−xTex

    KAUST Repository

    Zhu, Zhiyong

    2013-02-12

    With the use of ab initio calculations, the topological phase diagrams of bulk and monolayer TiS2−xTex are established. Whereas bulk TiS2−xTex shows two strong topological phases [1;(000)] and [1;(001)] for 0.44monolayer is topologically nontrivial for 0.48monolayer, TiS2−xTex is a unique system for studying topological phases in three and two dimensions simultaneously.

  14. Topological phase diagrams of bulk and monolayer TiS2-x Tex.

    Science.gov (United States)

    Zhu, Zhiyong; Cheng, Yingchun; Schwingenschlögl, Udo

    2013-02-15

    With the use of ab initio calculations, the topological phase diagrams of bulk and monolayer TiS(2-x) Te(x) are established. Whereas bulk TiS(2-x) Te(x) shows two strong topological phases [1;(000)] and [1;(001)] for 0.44monolayer is topologically nontrivial for 0.48monolayer, TiS(2-x) Te(x) is a unique system for studying topological phases in three and two dimensions simultaneously.

  15. Oriented crystalline monolayers and bilayers of 2 x 2 silver(1) grid architectures at the air-solution interface: Their assembly and crystal structure elucidation

    DEFF Research Database (Denmark)

    Weissbuch, J.; Baxter, P.N.W.; Kuzmenko, I.;

    2000-01-01

    Oriented crystalline monolayers, similar to 14 Angstrom thick, of a 2 x 2 Ag+ grid complex, self-assembled at the air-solution interface starting from an water-insoluble ligand 3,6-bis[2-(6-phenylpyridine)]pyridazine spread on silver-ion-containing solutions,were examined by grazing-incidence X-r...

  16. Microscopic characterization of crystalline phases in waste forms

    Energy Technology Data Exchange (ETDEWEB)

    Buck, E.C.; Dietz, N.L.; Wronkiewicz, D.J.; Bates, J.K. [Argonne National Lab., IL (United States); Millar, A. [Purdue Univ., West Lafayette, IN (United States)

    1995-07-01

    Transmission electron microscopy (TEM) has been used to determine the microstructure of crystalline phases present in zirconium- and titanium-bearing glass crystalline composite (GCC) waste forms. The GCC materials were found to contain spinels (maghemite), zirconolites, perovskites (CaTiO{sub 3}) and plagiociase feldspar (anorthite) mineral phases. The structure of the uranium and cerium-bearing monoclinic zirconolite was characterized by medium resolution TEM imaging and electron and X-ray diffraction (XRD). The phase was found to contain high levels of iron in comparison to Synroc-type zirconolites. Excess zirconium in zirconolite has resulted in martensitic baddeleyite (ZrO{sub 2}) formation. Anorthite (CaAl{sub 2}Si{sub 2}O{sub 8}) was present as elongated crystallites within a calcium-rich aluminosilicate glass. Lead and iron-bearing anorthite lying along distinct precipitates were occasionally observed within the an crystallographic planes.

  17. Viscous friction between crystalline and amorphous phase of dragline silk.

    Directory of Open Access Journals (Sweden)

    Sandeep P Patil

    Full Text Available The hierarchical structure of spider dragline silk is composed of two major constituents, the amorphous phase and crystalline units, and its mechanical response has been attributed to these prime constituents. Silk mechanics, however, might also be influenced by the resistance against sliding of these two phases relative to each other under load. We here used atomistic molecular dynamics (MD simulations to obtain friction forces for the relative sliding of the amorphous phase and crystalline units of Araneus diadematus spider silk. We computed the coefficient of viscosity of this interface to be in the order of 10(2 Ns/m(2 by extrapolating our simulation data to the viscous limit. Interestingly, this value is two orders of magnitude smaller than the coefficient of viscosity within the amorphous phase. This suggests that sliding along a planar and homogeneous surface of straight polyalanine chains is much less hindered than within entangled disordered chains. Finally, in a simple finite element model, which is based on parameters determined from MD simulations including the newly deduced coefficient of viscosity, we assessed the frictional behavior between these two components for the experimental range of relative pulling velocities. We found that a perfectly relative horizontal motion has no significant resistance against sliding, however, slightly inclined loading causes measurable resistance. Our analysis paves the way towards a finite element model of silk fibers in which crystalline units can slide, move and rearrange themselves in the fiber during loading.

  18. Inter-domain dipolar repulsion in lipid monolayers with phase coexistence

    CERN Document Server

    Fiori, Elena Rufeil; Banchio, Adolfo J

    2015-01-01

    A great variety of biologically relevant monolayers present phase coexistence characterized by domains formed by lipids in a long-range ordered phase state dispersed in a continuous, disordered phase. Because of the difference in surface densities the domains possess an excess dipolar density with respect to the surrounding liquid phase. In this work we propose an alternative method to measure the dipolar repulsion for neutral lipid monolayers. The procedure is based on the comparison of the radial distribution function, g(r), from experiments and Brownian dynamic (BD) simulations. The domains were modeled as disks with surface dipolar density, whose strength was varied to best describe the experimentally determined monolayer structure. For comparison, the point dipole approximation was also studied. As an example, we applied the method for mixed monolayers with different proportions of distearoylphosphatidylcholine (DSPC) and dimyristoylphosphatidylcholine (DMPC) and obtained the excess dipolar density, whic...

  19. Electron microscopic observation of LE/LC phase transition in dipalmitoyl phosphatidylcholine monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Neuman, R.D.; Fereshtehkhou, S.; Ovalle, R.

    1984-10-01

    The monolayer structure of L-..cap alpha..-dipalmitoyl phosphatidylcholine (DPPC) at the air/water interface was examined using improved electron microscopic techniques. The DPPC monolayer is homogeneous in both the liquid-expanded (LE) and liquid-condensed (LC) states. In the intermediate LE/LC region, however, the monolayer is nonhomogeneous and biphasic. The results of two coexisting phases are consistent with the interpretation of a first-order phase transition occurring between the LE and LC states in monomolecular films. 20 references, 2 figures.

  20. Structure and Phase Transitions of Monolayers of Intermediate-length n-alkanes on Graphite Studied by Neutron Diffraction and Molecular Dynamics Simulation

    Energy Technology Data Exchange (ETDEWEB)

    Taub, H. [University of Missouri, Columbia; Hansen, F.Y. [Technical University of Denmark; Diama, Amand [National University of the Ivory Coast; Matthies, Blake [Goodyear Tire and Rubber Company, The; Criswell, Leah [University of Missouri, Columbia; Mo, Haiding [Advanced Optowave Corporation; Bai, M [University of Missouri, Columbia; Herwig, Kenneth W [ORNL

    2009-01-01

    We present evidence from neutron diffraction measurements and molecular dynamics (MD) simulations of three different monolayer phases of the intermediate-length alkanes tetracosane (n-C(24)H(50) denoted as C24) and dotriacontane (n-C(32)H(66) denoted as C32) adsorbed on a graphite basal-plane surface. Our measurements indicate that the two monolayer films differ principally in the transition temperatures between phases. At the lowest temperatures, both C24 and C32 form a crystalline monolayer phase with a rectangular-centered (RC) structure. The two sublattices of the RC structure each consists of parallel rows of molecules in their all-trans conformation aligned with their long axis parallel to the surface and forming so-called lamellas of width approximately equal to the all-trans length of the molecule. The RC structure is uniaxially commensurate with the graphite surface in its [110] direction such that the distance between molecular rows in a lamella is 4.26 A=sqrt[3a(g)], where a(g)=2.46 A is the lattice constant of the graphite basal plane. Molecules in adjacent rows of a lamella alternate in orientation between the carbon skeletal plane being parallel and perpendicular to the graphite surface. Upon heating, the crystalline monolayers transform to a 'smectic' phase in which the inter-row spacing within a lamella expands by approximately 10% and the molecules are predominantly oriented with the carbon skeletal plane parallel to the graphite surface. In the smectic phase, the MD simulations show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously.

  1. Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation.

    Science.gov (United States)

    Diama, A; Matthies, B; Herwig, K W; Hansen, F Y; Criswell, L; Mo, H; Bai, M; Taub, H

    2009-08-28

    We present evidence from neutron diffraction measurements and molecular dynamics (MD) simulations of three different monolayer phases of the intermediate-length alkanes tetracosane (n-C(24)H(50) denoted as C24) and dotriacontane (n-C(32)H(66) denoted as C32) adsorbed on a graphite basal-plane surface. Our measurements indicate that the two monolayer films differ principally in the transition temperatures between phases. At the lowest temperatures, both C24 and C32 form a crystalline monolayer phase with a rectangular-centered (RC) structure. The two sublattices of the RC structure each consists of parallel rows of molecules in their all-trans conformation aligned with their long axis parallel to the surface and forming so-called lamellas of width approximately equal to the all-trans length of the molecule. The RC structure is uniaxially commensurate with the graphite surface in its [110] direction such that the distance between molecular rows in a lamella is 4.26 A=sqrt[3a(g)], where a(g)=2.46 A is the lattice constant of the graphite basal plane. Molecules in adjacent rows of a lamella alternate in orientation between the carbon skeletal plane being parallel and perpendicular to the graphite surface. Upon heating, the crystalline monolayers transform to a "smectic" phase in which the inter-row spacing within a lamella expands by approximately 10% and the molecules are predominantly oriented with the carbon skeletal plane parallel to the graphite surface. In the smectic phase, the MD simulations show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously.

  2. Phase separated anionic domains in ternary mixed lipid monolayers at the air-water interface.

    Science.gov (United States)

    Maloney, K M; Grainger, D W

    1993-04-01

    A series of ternary mixed monolayers containing varying amounts of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and equimolar additions of 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (LYSO-PC) and palmitic acid (PA) were studied at the air-water interface. These mixed monolayers were used to model phospholipid biomembrane interfaces resulting from phospholipase A2 (PLA2) hydrolysis. Recent work [D.W. Grainger A. Reichert, H. Ringsdorf and C. Salesse (1989) Biochim. Biophys. Acta. 1023, 365-379] has shown that PLA2 hydrolysis of pure phospholipid monolayers results in formation of large PLA2 domains at the air-water interface. These domains are proposed to result from PLA2 adsorption to phase separated regions in the hydrolyzed monolayer. To elucidate the phase behaviour in these monolayer systems, surface pressure-area isotherms were measured for the ternary mixtures on pure water and buffered subphases. Fluorescence microscopy at the air-water interface was used to image fluorescent probe-doped monolayer mixtures during isothermal compressions. A water-soluble cationic carbocyanine dye was used to probe the interfacial properties of the mixed monolayers. Isotherm data do not provide unambiguous evidence for either phase separation or ideal mixing of monolayer components. Fluorescence microscopy is more revealing, showing that lateral phase separation of microstructures containing palmitic acid occurred only when monolayer subphases contained Ca2+ ions at alkaline pH. At either low pH or on Ca(2+)-free subphases, phase separation was not observed.

  3. Surface Shear Viscosity and Phase Transitions of Monolayers at the Air-Water Interface

    Science.gov (United States)

    Relini, A.; Ciuchi, F.; Rolandi, R.

    1995-08-01

    The canal method has been employed to measure the in-plane steady shear viscosity of monolayers of bolaform lipids extracted from the membrane of the thermophilic microorganism Sulfolobus solfataricus. Monolayers were formed with the polar lipid extract (PLE), which is a mixture of several bolaform lipids, each one endowed with two nonequivalent polar headgroups. Viscosities were obtained from the measured flows by using the equation introduced by Joly; this equation contains a semiempirical parameter A, which takes into account the monolayer-subphase mechanical coupling. Measuring the flows for two different substances (PLE and oleic acid) and channel widths, the monolayer viscosities and the parameter A were determined at the same time. The analysis of the viscosity data according to the free area model shows evidences of the molecular conformational changes matching monolayer phase transitions.

  4. Perhydroazulene-based liquid-crystalline materials with smectic phases.

    Science.gov (United States)

    Hussain, Zakir; Hopf, Henning; Eichhorn, S Holger

    2012-01-01

    New liquid-crystalline materials with a perhydroazulene core were synthesized and the stereochemistry of these compounds was investigated. The mesomorphic properties of the new LC compounds were investigated by differential scanning colorimetry, polarizing optical microscopy and X-ray diffraction. We report here on the LC properties of nonchiral materials, which predominantly exhibit smectic phases and display nematic phases only within narrow temperature ranges. The dependence of the mesogenic behavior of the new materials on the stereochemistry of the core system was also investigated. All newly synthesized compounds were fully characterized by the usual spectroscopic and analytical methods.

  5. Perhydroazulene-based liquid-crystalline materials with smectic phases

    Directory of Open Access Journals (Sweden)

    Zakir Hussain

    2012-03-01

    Full Text Available New liquid-crystalline materials with a perhydroazulene core were synthesized and the stereochemistry of these compounds was investigated. The mesomorphic properties of the new LC compounds were investigated by differential scanning colorimetry, polarizing optical microscopy and X-ray diffraction. We report here on the LC properties of nonchiral materials, which predominantly exhibit smectic phases and display nematic phases only within narrow temperature ranges. The dependence of the mesogenic behavior of the new materials on the stereochemistry of the core system was also investigated. All newly synthesized compounds were fully characterized by the usual spectroscopic and analytical methods.

  6. Phase transition of lipid-like monolayer characterized by second harmonic generation

    Institute of Scientific and Technical Information of China (English)

    于安池; 常青; 赵新生; 周晴中; 李东; 黄岩谊; 程天蓉; 黄春辉

    1999-01-01

    Phase transition of a lipid-like hemicyanine compound characterized by second harmonic generation is studied carefully. The phase transition is assigned as the first order transition between solid state and liquid state. The transition temperature increases with an increase in the surface molecular concentration. A monolayer structure parameter a which is very sensitive to the phase transition is introduced.

  7. Removal of phase transfer agent leads to restricted dynamics of alkyl chains in monolayer protected clusters

    Indian Academy of Sciences (India)

    V R Rajeev Kumar; R Mukhopadhyay; T Pradeep

    2008-11-01

    The effect of phase transfer agent in the dynamics of monolayer protected gold nanoparticles has been investigated by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies. The experiments were performed with octadecane thiol and dodecane thiol protected gold nanoparticles. The materials prepared were characterized by UV-Visible spectroscopy, transmission electron microscopy and IR spectroscopy. Repeated purification of the monolayer protected gold clusters made the alkyl chains defect-free. Such effects are reflected in the infrared spectra. Interdigitation of the monolayers that followed the purification leads to alkyl chains with limited mobility. This was reflected in 13C and 1H NMR linewidths. The NMR measurements indicate that the removal of phase transfer agent affects the dynamics of isolated clusters and those with interdigitated monolayers in different ways.

  8. Nucleation and growth studies of crystalline carbon phases at nanoscale

    Science.gov (United States)

    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

  9. Line tension between coexisting phases in monolayers and bilayers of amphiphilic molecules

    Science.gov (United States)

    Sriram, Indira; Schwartz, Daniel K.

    2012-06-01

    Phase coexistence is frequently observed in molecular monolayers and bilayers. The free energy per unit length of phase boundaries in these quasi-two-dimensional (2D) systems is known as line tension, and is directly analogous to surface tension in three dimensions. The existence of line tension implies the possibility of 2D capillary phenomena, a fundamentally intriguing possibility. Moreover, line tension has important implications with respect to the formation and stability of nm-scale features in thin films, ranging from lithographically-prepared molecular features in devices (e.g. sensor nanoarrays or molecular electronics) to signaling domains in biological membranes (i.e. lipid rafts). It has been proposed that such nm-scale domains may have important ramifications for budding and/or fusion in bilayer membranes. Various methods have been developed to measure line tension, including observations of domain boundary fluctuations, relaxation dynamics, nucleation rates, and others. The competition between line tension and long-range forces (e.g. electrostatic repulsion or curvature elasticity) can lead to a preferred equilibrium domain size, domain shape instabilities, or even unusual domain morphologies (e.g. stripe phases) near critical points. Since liquid crystalline mesophases are ubiquitous in 2D, it is not unusual for the line tension to be anisotropic; this can lead to non-circular domains exhibiting kinks and/or chirality. Recent efforts have been aimed at controlling line tension by the addition of line-active compounds that are analogous to surfactants potentially leading to the observation of new 2D “capillary” phenomena.

  10. Phase diagrams and kinetics of solid-liquid phase transitions in crystalline polymer blends

    Science.gov (United States)

    Matkar, Rushikesh A.

    A free energy functional has been formulated based on an order parameter approach to describe the competition between liquid-liquid phase separation and solid-liquid phase separation. In the free energy description, the assumption of complete solvent rejection from the crystalline phase that is inherent in the Flory diluent theory was removed as solvent has been found to reside in the crystalline phase in the form of intercalates. Using this approach, we have calculated various phase diagrams in binary blends of crystalline and amorphous polymers that show upper or lower critical solution temperature. Also, the discrepancy in the chi values obtained from different experimental methods reported in the literature for the polymer blend of poly(vinylidenefluoride) and poly(methylmethacrylate) has been discussed in the context of the present model. Experimental phase diagram for the polymer blend of poly(caprolactone) and polystyrene has also been calculated. Of particular importance is that the crystalline phase concentration as a function of temperature has been calculated using free energy minimization methods instead of assuming it to be pure. In the limit of complete immiscibility of the solvent in the crystalline phase, the Flory diluent theory is recovered. The model is extended to binary crystalline blends and the formation of eutectic, peritectic and azeotrope phase diagrams has been explained on the basis of departure from ideal solid solution behavior. Experimental eutectic phase diagram from literature of a binary blend of crystalline polymer poly(caprolactone) and trioxane were recalculated using the aforementioned approach. Furthermore, simulations on the spatio temporal dynamics of crystallization in blends of crystalline and amorphous polymers were carried out using the Ginzburg-Landau approach. These simulations have provided insight into the distribution of the amorphous polymer in the blends during the crystallization process. The simulated results

  11. Formation of nano quasicrystalline and crystalline phases by mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Shamah, A.M.; Ibrahim, S. [Faculty of Petroleum and Mining Engineering, Suez Canal University, Suez (Egypt); Hanna, F.F., E-mail: fariedhanna@yahoo.com [Faculty of Petroleum and Mining Engineering, Suez Canal University, Suez (Egypt)

    2011-02-03

    Research highlights: > Mechanical alloying (MA) is an important method to investigate the formation of nano sized quasicrystalline phases in Al{sub 86}Cr{sub 14}, Al{sub 84}Fe{sub 16} and Al{sub 62.5}Cu{sub 25}Fe{sub 12.5} compounds. The second part of the present work is an attempt to examine the possibility of formation of the i-phase of the Al{sub 62.5}Cu{sub 25}Fe{sub 12.5}, which lies in the region of the perfect i-phase in the ternary phase diagram, by rapid solidification method. To perform the obtained quasi phase mechanical alloying and heat treatment at the rapid solidified sample were done. - Abstract: In the present work, the formation of nano quasicrystalline icosahedral phase in Al{sub 86}Cr{sub 14}, Al{sub 84}Fe{sub 16} and Al{sub 62.5}Cu{sub 25}Fe{sub 12.5} alloys has been investigated by mechanical alloying. Mixtures of quasicrystalline and related crystalline phases have been observed under various milling conditions. The X-ray diffraction, differential thermal analysis and electrical resistivity techniques have been used for characterization and physical property measurements. The particle size was calculated by X-ray profile using Williamson-Hall plot method and it was found to be 25-50 nm size.

  12. Electronic phases of substances. Phase transitions with change of electron and crystalline structure

    Directory of Open Access Journals (Sweden)

    Nadykto Boris

    2015-01-01

    Full Text Available There is plenty of experimental data on high-pressure phase transformations in various materials. Variations in materials characteristics (for example, equilibrium density and bulk modulus, while the crystalline structure remains unchanged, are indicative of energy variations in outer-shell electrons of solid atoms. In experiments with crystalline structure variations, the dependence of pressure on density in some cases can be described by the same curve, the parameters of which are independent of the crystalline structure. Examples of such transformations in some materials at static compression and in shock-wave experiments are given.

  13. Topological Crystalline Insulator in a New Bi Semiconducting Phase

    Science.gov (United States)

    Munoz, F.; Vergniory, M. G.; Rauch, T.; Henk, J.; Chulkov, E. V.; Mertig, I.; Botti, S.; Marques, M. A. L.; Romero, A. H.

    2016-02-01

    Topological crystalline insulators are a type of topological insulators whose topological surface states are protected by a crystal symmetry, thus the surface gap can be tuned by applying strain or an electric field. In this paper we predict by means of ab initio calculations a new phase of Bi which is a topological crystalline insulator characterized by a mirror Chern number nM = -2, but not a strong topological insulator. This system presents an exceptional property: at the (001) surface its Dirac cones are pinned at the surface high-symmetry points. As a consequence they are also protected by time-reversal symmetry and can survive against weak disorder even if in-plane mirror symmetry is broken at the surface. Taking advantage of this dual protection, we present a strategy to tune the band-gap based on a topological phase transition unique to this system. Since the spin-texture of these topological surface states reduces the back-scattering in carrier transport, this effective band-engineering is expected to be suitable for electronic and optoelectronic devices with reduced dissipation.

  14. Volume phase transitions of cholesteric liquid crystalline gels

    Energy Technology Data Exchange (ETDEWEB)

    Matsuyama, Akihiko, E-mail: matuyama@bio.kyutech.ac.jp [Department of Bioscience and Bioinformatics, Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Kawazu 680-4, Iizuka, Fukuoka 820-8502 (Japan)

    2015-05-07

    We present a mean field theory to describe anisotropic deformations of a cholesteric elastomer without solvent molecules and a cholesteric liquid crystalline gel immersed in isotropic solvents at a thermal equilibrium state. Based on the neoclassical rubber theory of nematic elastomers, we derive an elastic energy and a twist distortion energy, which are important to determine the shape of a cholesteric elastomer (or gel). We demonstrate that when the elastic energy dominates in the free energy, the cholesteric elastomer causes a spontaneous compression in the pitch axis and elongates along the director on the plane perpendicular to the pitch axis. Our theory can qualitatively describe the experimental results of a cholesteric elastomer. We also predict the first-order volume phase transitions and anisotropic deformations of a gel at the cholesteric-isotropic phase transition temperature. Depending on a chirality of a gel, we find a prolate or oblate shape of cholesteric gels.

  15. Phase engineering of monolayer transition-metal dichalcogenide through coupled electron doping and lattice deformation

    Energy Technology Data Exchange (ETDEWEB)

    Ouyang, Bin; Lan, Guoqiang; Song, Jun, E-mail: jun.song2@mcgill.ca [Department of Mining and Materials Engineering, McGill University, Montreal, Quebec H3A 0C5 (Canada); Guo, Yinsheng [Department of Chemistry, Columbia University, New York, New York 10027 (United States); Mi, Zetian [Department of Electrical and Computer Engineering, McGill University, Montreal, Quebec H3A 0E9 (Canada)

    2015-11-09

    First-principles calculations were performed to investigate the phase stability and transition within four monolayer transition-metal dichalcogenide (TMD) systems, i.e., MX{sub 2} (M = Mo or W and X = S or Se) under coupled electron doping and lattice deformation. With the lattice distortion and electron doping density treated as state variables, the energy surfaces of different phases were computed, and the diagrams of energetically preferred phases were constructed. These diagrams assess the competition between different phases and predict conditions of phase transitions for the TMDs considered. The interplay between lattice deformation and electron doping was identified as originating from the deformation induced band shifting and band bending. Based on our findings, a potential design strategy combining an efficient electrolytic gating and a lattice straining to achieve controllable phase engineering in TMD monolayers was demonstrated.

  16. Evidence for the propagation of 2D pressure pulses in lipid monolayers near the phase transition

    CERN Document Server

    Griesbauer, J; Wixforth, A; Schneider, M F

    2012-01-01

    The existence and propagation of acoustic pressure pulses on lipid monolayers at the air/water-interfaces are directly observed by simple mechanical detection. The pulses are excited by small amounts of solvents added to the monolayer from the air phase. Employing a deliberate control of the lipid interface compressibility k, we can show that the pulses propagate at velocities, which are precisely reflecting the nonlinear behavior of the interface. This is manifested by a pronounced minimum of the sound velocity in the monolayer phase transition regime, while ranging up to 1.5 m/s at high lateral pressures. Motivated by the ubiquitous presence of lipid interfaces in biology, we propose the demonstrated sound propagation as an efficient and fast way of communication and protein modulation along nerves, between cells and biological units being controlled by the physical state of the interfaces.

  17. Thermal desorption characteristics of CO, O2 and CO2 on non-porous water, crystalline water and silicate surfaces at sub-monolayer and multilayer coverages

    CERN Document Server

    Noble, J A; Dulieu, F; Fraser, H J

    2011-01-01

    The desorption characteristics of molecules on interstellar dust grains are important for modelling the behaviour of molecules in icy mantles and, critically, in describing the solid-gas interface. In this study, a series of laboratory experiments exploring the desorption of three small molecules from three astrophysically relevant surfaces are presented. The desorption of CO, O2 and CO2 at both sub-monolayer and multilayer coverages was investigated from non-porous water, crystalline water and silicate surfaces. Experimental data was modelled using the Polanyi-Wigner equation to produce a mathematical description of the desorption of each molecular species from each type of surface, uniquely describing both the monolayer and multilayer desorption in a single combined model. The implications of desorption behaviour over astrophysically relevant timescales are discussed.

  18. Review of crystalline structures of some selected homologous series of rod-like molecules capable of forming liquid crystalline phases.

    Science.gov (United States)

    Zugenmaier, Peter

    2011-01-01

    The crystal structures of four homologous series of rod-like molecules are reviewed, two of which form hydrogen bonds and two with a symmetric chemical constitution. Many of the compounds investigated turn into liquid crystalline phases upon temperature increase. It is of valuable interest to know possible conformations and possible packing arrangements as prerequisites to model liquid crystalline structures. The hydrogen bonds of homologous series of pure 4-(ω-hydroxyalkyloxy)-4'-hydroxybiphenyl (HnHBP, n the alkyloxy tail length) are realized through head to tail arrangements of the hydroxyl groups and crystallize except one compound in chiral space groups without the molecules containing any asymmetric carbon. The hydrogen bonds of the homologous series of 4-substituted benzoic acids with various lengths of the tail provide dimers through strong polar bonding of adjacent carboxyl groups and thus provide the stiff part of a mesogenic unit prerequisite for liquid crystalline phases. The homologous series of dialkanoyloxybiphenyls (BP-n, n = 1, 19), of which nine compounds could be crystallized, show liquid crystalline behavior for longer alkane chain lengths, despite the high mobility of the alkane chain ends already detectable in the crystal phase. A single molecule, half a molecule or two half molecules form the asymmetric unit in a centrosymmetric space group. The homologous series of 1,4-terephthalidene-bis-N-(4'-n-alkylaniline) (TBAA-n) exhibit a large variety of packing arrangements in the crystalline state, with or without relying on the symmetry center within the molecules.

  19. Structural Properties and Phase Transition of Na Adsorption on Monolayer MoS2.

    Science.gov (United States)

    He, Hai; Lu, Pengfei; Wu, Liyuan; Zhang, Chunfang; Song, Yuxin; Guan, Pengfei; Wang, Shumin

    2016-12-01

    First-principles calculations are performed to investigate the structural stability of Na adsorption on 1H and 1T phases of monolayer MoS2. Our results demonstrate that it is likely to make the stability of distorted 1T phase of MoS2 over the 1H phase through adsorption of Na atoms. The type of distortion depends on the concentration of adsorbed Na atoms and changes from zigzag-like to diamond-like with the increasing of adsorbed Na atom concentrations. Our calculations show that the phase transition from 1H-MoS2 to 1T-MoS2 can be obtained by Na adsorption. We also calculate the electrochemical properties of Na adsorption on MoS2 monolayer. These results indicate that MoS2 is one of potential negative electrodes for Na-ion batteries.

  20. Evidence of a new crystalline phase in U–Gd–O phase diagram

    Energy Technology Data Exchange (ETDEWEB)

    Pieck, Darío [CEA, DEN, DEC, SESC – Laboratoire des Lois de Comportement des Combustibles (France); Desgranges, Lionel, E-mail: lionel.desgranges@cea.fr [CEA, DEN, DEC, SESC – Laboratoire des Lois de Comportement des Combustibles (France); Matheron, Pierre [CEA, DEN, DEC, SPUA – Laboratoire Combustibles Uranium (France); Palancher, Hervé [CEA, DEN, DEC, SESC – Laboratoire des Lois de Comportement des Combustibles (France)

    2015-06-15

    The U–Gd–O phase diagram was investigated in its high Gd content part. Several samples with the general (U{sub 1−y}, Gd{sub y})O{sub 2±x} composition were prepared by sintering under Ar H{sub 2} 5% atmosphere. The samples were characterized by SEM–EDS and X-ray diffraction. A new cubic crystalline phase was evidenced at high a Gd content that was not expected from previous literature. Rietveld refinements showed that its crystalline structure is related to C-Gd{sub 2}O{sub 3} phase. The existence of this compound has to be taken into account in the sintering of (U,Gd)O{sub 2} nuclear fuel.

  1. Quasiparticle specific heats for the crystalline color superconducting phase of QCD

    CERN Document Server

    Casalbuoni, R; Mannarelli, M; Nardulli, G; Ruggieri, M; Stramaglia, S; 10.1016/j.physletb.2003.09.071

    2003-01-01

    We calculate the specific heats of quasiparticles of two-flavor QCD in its crystalline phases for low temperature. We show that for the different crystalline structures considered here there are gapless modes contributing linearly in temperature to the specific heat. We evaluate also the phonon contributions which are cubic in temperature. These features might be relevant for compact stars with an inner shell in a color superconducting crystalline phase. (21 refs).

  2. Quasi-particle Specific Heats for the Crystalline Color Superconducting Phase of QCD

    CERN Document Server

    Casalbuoni, Roberto; Mannarelli, M; Nardulli, Giuseppe; Ruggieri, Marco; Stramaglia, S

    2003-01-01

    We calculate the specific heats of quasi-particles of two-flavor QCD in its crystalline phases for low temperature. We show that for the different crystalline structures considered here there are gapless modes contributing linearly in temperature to the specific heat. We evaluate also the phonon contributions which are cubic in temperature. These features might be relevant for compact stars with an inner shell in a color superconducting crystalline phase.

  3. Quasi-particle specific heats for the crystalline color superconducting phase of QCD

    Energy Technology Data Exchange (ETDEWEB)

    Casalbuoni, R.; Gatto, R.; Mannarelli, M.; Nardulli, G.; Ruggieri, M.; Stramaglia, S

    2003-11-27

    We calculate the specific heats of quasi-particles of two-flavor QCD in its crystalline phases for low temperature. We show that for the different crystalline structures considered here there are gapless modes contributing linearly in temperature to the specific heat. We evaluate also the phonon contributions which are cubic in temperature. These features might be relevant for compact stars with an inner shell in a color superconducting crystalline phase.

  4. The additional phase transition of DPPC monolayers at high surface pressure confirmed by GIXD study

    DEFF Research Database (Denmark)

    Shen, Chen; Serna, Jorge B. de la; Struth, Bernd

    Pulmonary surfactant forms the alveolar monolayer at the air/aqueous interface within the lung. During the breathing process, the surface pressure periodically varies from ~40mN/m up to ~70mN/m. The film is mechanically stable during this rapid and reversible expansion. The monolayer consists...... of ~90% of lipid with 10% integrated proteins. Among its lipid compounds, di- palmitoyl-phosphatidylcholine (DPPC) dominates (~45wt%). No other lipid but DPPC was so far reported to be compressible to very high surface pressure (~70mN/m) before its monolayer collapsed. Its liquid......-expanded/liquid-condensed (LE/LC) phase transition at ~10mN/m is well known. Here we present results from Langmuir isotherm measurements that evidence a so far not documented second phase transition at elevated surface pressure Π (~50mN/m). The varying lateral structures of the monolayer at 8mN/m, 20mN/m, 30mN/m, 40mN/m, 50m...

  5. Improved aging performance of vapor phase deposited hydrophobic self-assembled monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Gnanappa, Arun Kumar, E-mail: arun@imel.demokritos.gr [Tyndall National Institute, Lee Maltings, Prospect Row, Cork (Ireland); Institute of Microelectronics, NCSR Demokritos, Athens (Greece); O' Murchu, Cian; Slattery, Orla; Peters, Frank [Tyndall National Institute, Lee Maltings, Prospect Row, Cork (Ireland); O' Hara, Tony [Memsstar Technology (registered) , Starlaw Park, Starlaw Road, Livingston (United Kingdom); Aszalos-Kiss, Balazs; Tofail, Syed A.M. [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland)

    2011-02-15

    A hydrophobic self-assembled monolayer (SAM) of fluoro-octyl-trichloro-silane (FOTS) was deposited on silicon using a vapor phase technique. The aging of the hydrophobic layer was examined using water contact angle measurements. It has been found that while such monolayer films suffer from a loss of hydrophobicity with time, pre-immersion nitrogen annealing can significantly improve the aging characteristics of these monolayers. The effect of nitrogen annealing on the improved aging properties of SAM coatings has been investigated by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The hydrolytic stability and the effect of nitrogen annealing were studied by morphological evolution during immersion. A spontaneous formation of silane mounds on the surface of the monolayers was found by AFM. These mounds have been irreversibly transformed from initially uniform hydrophobic surface layers. It is highly probable that the compliance of these mounds can reasonably allow hydrophilic sites to be located around the mounds. Interestingly, the density of these mounds formation is very less on the annealed samples. XPS reveals a higher level of coverage by the N{sub 2}-annealed film due to agglomeration. A relative abundance of CF{sub 3} and CF{sub 2} moieties in the annealed film may explain the enhancement of the hydrophobicity as revealed by higher level of water contact angle. This hydrophobicity was found to be significantly stable in water. This novel finding explains the improved hydrophobic stability of FOTS monolayers as primarily a morpho-chemical effect that originates from the densification of the monolayers upon annealing.

  6. Theoretical and experimental study of the vibrational excitations in ethane monolayers adsorbed on graphite (0001) surfaces

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Taub, H.

    1987-01-01

    The collective vibrational excitations of two different crystalline monolayer phases of ethane (C2H6) adsorbed on the graphite (0001) surface have been investigated theoretically and experimentally. The monolayer phases studied are the commensurate 7/8 ×4 structure in which the ethane molecules lie...

  7. Nanopatterns by phase separation of patterned mixed polymer monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Huber, Dale L; Frischknecht, Amalie

    2014-02-18

    Micron-size and sub-micron-size patterns on a substrate can direct the self-assembly of surface-bonded mixed polymer brushes to create nanoscale patterns in the phase-separated mixed polymer brush. The larger scale features, or patterns, can be defined by a variety of lithographic techniques, as well as other physical and chemical processes including but not limited to etching, grinding, and polishing. The polymer brushes preferably comprise vinyl polymers, such as polystyrene and poly(methyl methacrylate).

  8. Influence of head group methylation on the phase behavior of lipid monolayers

    DEFF Research Database (Denmark)

    Brezesinski, G.; Bringezu, F.; Weidemann, G.

    1998-01-01

    per three tails exceeds that per head, an influence of the head group methylation on the monolayer structure is observed. The tilt angles at lower lateral pressures and the transition pressure to a hexagonal packing of upright oriented chains increase with increasing methylation degree. The transition...... from the NN tilted rectangular to this hexagonal phase is connected with a pressure region where the in-plane components Q(xy) of the two peaks coincide while the out-of-plane components Q(z) differ. This indicates an undistorted hexagonal in-plane lattice even for tilted chains. The area-pressure...... and X-ray measurements below 10 mN/m, can be explained by the formation of holes in the monolayer. Possibly the tilting of the triple-chain molecules leads to an orientational ordering of the head group dipoles and therefore to an electrostatic repulsion between condensed phase domains. (C) 1998...

  9. The influence of glass composition on crystalline phase stability in glass-ceramic wasteforms

    Energy Technology Data Exchange (ETDEWEB)

    Maddrell, Ewan, E-mail: ewan.r.maddrell@nnl.co.uk [National Nuclear Laboratory, Sellafield, Seascale, Cumbria CA20 1PG (United Kingdom); Thornber, Stephanie; Hyatt, Neil C. [Department of Materials Science and Engineering, The University of Sheffield, Mappin Street, Sheffield S1 3JD (United Kingdom)

    2015-01-15

    Highlights: • Crystalline phase formation shown to depend on glass matrix composition. • Zirconolite forms as the sole crystalline phase only for most aluminous glasses. • Thermodynamics indicate that low silica activity glasses stabilise zirconolite. - Abstract: Zirconolite glass-ceramic wasteforms were prepared using a suite of Na{sub 2}O–Al{sub 2}O{sub 3}–B{sub 2}O{sub 3}–SiO{sub 2} glass matrices with variable Al:B ratios. Zirconolite was the dominant crystalline phase only for the most alumina rich glass compositions. As the Al:B ratio decreased zirconolite was replaced by sphene, zircon and rutile. Thermodynamic data were used to calculate a silica activity in the glass melt below which zirconolite is the favoured crystalline phase. The concept of the crystalline reference state of glass melts is then utilised to provide a physical basis for why silica activity varies with the Al:B ratio.

  10. Photopatterning of stable, low-density, self-assembled monolayers on gold.

    Science.gov (United States)

    Safazadeh, Leila; Berron, Brad J

    2015-03-10

    Photoinitiated thiol-yne chemistry is utilized as a click reaction for grafting of acid-terminated alkynes to thiol-terminated monolayers on a gold substrate to create stable, low-density monolayers. The resulting monolayers are compared with a well-packed 11-mercaptoundecanoic acid monolayer and the analogous low-density monolayers prepared through a solution phase synthetic approach. The overall structuring of the monolayer prepared by solid-phase grafting is characterized by contact angle goniometry and Fourier transform infrared spectroscopy. The results show that the product monolayer has an intermediate surface energy and a more disordered chemical structuring compared to a traditional well-packed self-assembled monolayer, showing a low-packing density of the chains at the monolayer surface. The monolayer's structure and electrochemical stability were studied by reductive desorption of the thiolates. The prepared low-density monolayers have a higher electrochemical stability than traditional well-packed monolayers, which results from the crystalline structure at the gold interface. This technique allows for simple, fast preparation of low-density monolayers of higher stability than well-packed monolayers. The use of a photomask to restrict light access to the substrate yielded these low-density monolayers in patterned regions defined by light exposure. This general thiol-yne approach is adaptable to a variety of analogous low-density monolayers with diverse chemical functionalities.

  11. Photon Driven Transformation of Cesium Lead Halide Perovskites from Few-Monolayer Nanoplatelets to Bulk Phase.

    Science.gov (United States)

    Wang, Yue; Li, Xiaoming; Sreejith, Sivaramapanicker; Cao, Fei; Wang, Zeng; Stuparu, Mihaiela Corina; Zeng, Haibo; Sun, Handong

    2016-12-01

    Influence of light exposure on cesium lead halide nanostructures has been explored. A discovery of photon driven transformation (PDT) in 2D CsPbBr3 nanoplatelets is reported, in which the quantum-confined few-monolayer nanoplatelets will convert to bulk phase under very low irradiation intensity (≈20 mW cm(-2) ). Benefiting from the remarkable emission color change during PDT, the multicolor luminescence photopatterns and facile information photo-encoding are established.

  12. Phosphatidylcholine Monolayer Formation at a Liquid:Liquid Interface as Monitored by the Dynamic Surface Tension

    Science.gov (United States)

    2007-11-02

    concentration, while liquid crystalline vesicles form tightly packed monolayers at bulk PC concentrations above 2 ^Molar. Resolving this paradigm ...regardless of lipid bilayer phase. Initially, vesicle rupture probably represents an entropically driven process. The system will become increasingly

  13. Gold Nanoparticle Monolayers from Sequential Interfacial Ligand Exchange and Migration in a Three-Phase System

    Science.gov (United States)

    Yang, Guang; Hallinan, Daniel T.

    2016-10-01

    Using a three-phase system, centimeter-scale monolayer gold nanoparticle (Au NP) films have been prepared that have long-range order and hydrophobic ligands. The system contains an interface between an aqueous phase containing Au NPs and an oil phase containing one of various types of amine ligands, and a water/air interface. As the Au NPs diffuse to the water/oil interface, ligand exchange takes place which temporarily traps them at the water/oil interface. The ligand-exchanged particles then spontaneously migrate to the air/water interface, where they self-assemble, forming a monolayer under certain conditions. The spontaneous formation of the NP film at the air/water interface was due to the minimization of the system Helmholtz free energy. However, the extent of surface functionalization was dictated by kinetics. This decouples interfacial ligand exchange from interfacial self-assembly, while maintaining the simplicity of a single system. The interparticle center-to-center distance was dictated by the amine ligand length. The Au NP monolayers exhibit tunable surface plasma resonance and excellent spatial homogeneity, which is useful for surface-enhanced Raman scattering. The “air/water/oil” self-assembly method developed here not only benefits the fundamental understanding of NP ligand conformations, but is also applicable to the manufacture of plasmonic nanoparticle devices with precisely designed optical properties.

  14. Gold Nanoparticle Monolayers from Sequential Interfacial Ligand Exchange and Migration in a Three-Phase System

    Science.gov (United States)

    Yang, Guang; Hallinan, Daniel T.

    2016-01-01

    Using a three-phase system, centimeter-scale monolayer gold nanoparticle (Au NP) films have been prepared that have long-range order and hydrophobic ligands. The system contains an interface between an aqueous phase containing Au NPs and an oil phase containing one of various types of amine ligands, and a water/air interface. As the Au NPs diffuse to the water/oil interface, ligand exchange takes place which temporarily traps them at the water/oil interface. The ligand-exchanged particles then spontaneously migrate to the air/water interface, where they self-assemble, forming a monolayer under certain conditions. The spontaneous formation of the NP film at the air/water interface was due to the minimization of the system Helmholtz free energy. However, the extent of surface functionalization was dictated by kinetics. This decouples interfacial ligand exchange from interfacial self-assembly, while maintaining the simplicity of a single system. The interparticle center-to-center distance was dictated by the amine ligand length. The Au NP monolayers exhibit tunable surface plasma resonance and excellent spatial homogeneity, which is useful for surface-enhanced Raman scattering. The “air/water/oil” self-assembly method developed here not only benefits the fundamental understanding of NP ligand conformations, but is also applicable to the manufacture of plasmonic nanoparticle devices with precisely designed optical properties. PMID:27762394

  15. Review of Crystalline Structures of Some Selected Homologous Series of Rod-Like Molecules Capable of Forming Liquid Crystalline Phases

    Directory of Open Access Journals (Sweden)

    Peter Zugenmaier

    2011-10-01

    Full Text Available The crystal structures of four homologous series of rod-like molecules are reviewed, two of which form hydrogen bonds and two with a symmetric chemical constitution. Many of the compounds investigated turn into liquid crystalline phases upon temperature increase. It is of valuable interest to know possible conformations and possible packing arrangements as prerequisites to model liquid crystalline structures. The hydrogen bonds of homologous series of pure 4-(ω-hydroxyalkyloxy-4′-hydroxybiphenyl (HnHBP, n the alkyloxy tail length are realized through head to tail arrangements of the hydroxyl groups and crystallize except one compound in chiral space groups without the molecules containing any asymmetric carbon. The hydrogen bonds of the homologous series of 4-substituted benzoic acids with various lengths of the tail provide dimers through strong polar bonding of adjacent carboxyl groups and thus provide the stiff part of a mesogenic unit prerequisite for liquid crystalline phases. The homologous series of dialkanoyloxybiphenyls (BP-n, n = 1, 19, of which nine compounds could be crystallized, show liquid crystalline behavior for longer alkane chain lengths, despite the high mobility of the alkane chain ends already detectable in the crystal phase. A single molecule, half a molecule or two half molecules form the asymmetric unit in a centrosymmetric space group. The homologous series of 1,4-terephthalidene-bis-N-(4′-n-alkylaniline (TBAA-n exhibit a large variety of packing arrangements in the crystalline state, with or without relying on the symmetry center within the molecules.

  16. Improvements in the characterization of the crystalline structure of acid-terminated alkanethiol self-assembled monolayers on Au(111)

    NARCIS (Netherlands)

    Mendoza, Sandra M.; Arfaoui, Imad; Zanarini, Simone; Paolucci, Francesco; Rudolf, Petra

    2007-01-01

    We report a study of acid-terminated self-assembled monolayers of alkanethiols of different length, 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHDA), on Au(111). Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electr

  17. Improvements in the characterization of the crystalline structure of acid-terminated alkanethiol self-assembled monolayers on Au(111)

    NARCIS (Netherlands)

    Mendoza, Sandra M.; Arfaoui, Imad; Zanarini, Simone; Paolucci, Francesco; Rudolf, Petra

    2007-01-01

    We report a study of acid-terminated self-assembled monolayers of alkanethiols of different length, 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHDA), on Au(111). Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electr

  18. Structure of cholesterol/ceramide monolayer mixtures

    DEFF Research Database (Denmark)

    Scheffer, L.; Solomonov, I.; Weygand, M.J.

    2005-01-01

    The structure of monolayers of cholesterol/ ceramide mixtures was investigated using grazing incidence x-ray diffraction, immunofluorescence, and atomic force microscopy techniques. Grazing incidence x-ray diffraction measurements showed the existence of a crystalline mixed phase of the two...

  19. Controlled vapor phase growth of single crystalline, two-dimensional GaSe crystals with high photoresponse.

    Science.gov (United States)

    Li, Xufan; Lin, Ming-Wei; Puretzky, Alexander A; Idrobo, Juan C; Ma, Cheng; Chi, Miaofang; Yoon, Mina; Rouleau, Christopher M; Kravchenko, Ivan I; Geohegan, David B; Xiao, Kai

    2014-06-30

    Compared with their bulk counterparts, atomically thin two-dimensional (2D) crystals exhibit new physical properties, and have the potential to enable next-generation electronic and optoelectronic devices. However, controlled synthesis of large uniform monolayer and multi-layer 2D crystals is still challenging. Here, we report the controlled synthesis of 2D GaSe crystals on SiO2/Si substrates using a vapor phase deposition method. For the first time, uniform, large (up to ~60 μm in lateral size), single-crystalline, triangular monolayer GaSe crystals were obtained and their structure and orientation were characterized from atomic scale to micrometer scale. The size, density, shape, thickness, and uniformity of the 2D GaSe crystals were shown to be controllable by growth duration, growth region, growth temperature, and argon carrier gas flow rate. The theoretical modeling of the electronic structure and Raman spectroscopy demonstrate a direct-to-indirect bandgap transition and progressive confinement-induced bandgap shifts for 2D GaSe crystals. The 2D GaSe crystals show p-type semiconductor characteristics and high photoresponsivity (~1.7 A/W under white light illumination) comparable to exfoliated GaSe nanosheets. These 2D GaSe crystals are potentially useful for next-generation electronic and optoelectronic devices such as photodetectors and field-effect transistors.

  20. Etching of Crystalline ZnO Surfaces upon Phosphonic Acid Adsorption: Guidelines for the Realization of Well-Engineered Functional Self-Assembled Monolayers.

    Science.gov (United States)

    Ostapenko, Alexandra; Klöffel, Tobias; Eußner, Jens; Harms, Klaus; Dehnen, Stefanie; Meyer, Bernd; Witte, Gregor

    2016-06-01

    Functionalization of metal oxides by means of covalently bound self-assembled monolayers (SAMs) offers a tailoring of surface electronic properties such as their work function and, in combination with its large charge carrier mobility, renders ZnO a promising conductive oxide for use as transparent electrode material in optoelectronic devices. In this study, we show that the formation of phosphonic acid-anchored SAMs on ZnO competes with an unwanted chemical side reaction, leading to the formation of surface precipitates and severe surface damage at prolonged immersion times of several days. Combining atomic force microscopy (AFM), X-ray diffraction (XRD), and thermal desorption spectroscopy (TDS), the stability and structure of the aggregates formed upon immersion of ZnO single crystal surfaces of different orientations [(0001̅), (0001), and (101̅0)] in phenylphosphonic acid (PPA) solution were studied. By intentionally increasing the immersion time to more than 1 week, large crystalline precipitates are formed, which are identified as zinc phosphonate. Moreover, the energetics and the reaction pathway of this transformation have been evaluated using density functional theory (DFT), showing that zinc phosphonate is thermodynamically more favorable than phosphonic acid SAMs on ZnO. Precipitation is also found for phosphonic acids with fluorinated aromatic backbones, while less precipitation occurs upon formation of SAMs with phenylphosphinic anchoring units. By contrast, no precipitates are formed when PPA monolayer films are prepared by sublimation under vacuum conditions, yielding smooth surfaces without noticeable etching.

  1. Atomic force microscopy reveals two phases in single stranded DNA self-assembled monolayers

    Science.gov (United States)

    Kosaka, Priscila M.; González, Sheila; Domínguez, Carmen M.; Cebollada, Alfonso; San Paulo, Alvaro; Calleja, Montserrat; Tamayo, Javier

    2013-07-01

    We have investigated the structure of single-stranded (ss) DNA self-assembled monolayers (SAMs) on gold by combining peak force tapping, Kelvin probe and phase contrast atomic force microscopy (AFM) techniques. The adhesion, surface potential and phase shift signals show heterogeneities in the DNA film structure at two levels: microscale and nanoscale; which cannot be clearly discerned in the topography. Firstly, there is multilayer aggregation covering less than 5% of the surface. The DNA multilayers seem to be ordered phases and their existence suggests that DNA end-to-end interaction can play a role in the self-assembly process. Secondly, we find the formation of two phases in the DNA monolayer, which differ both in surface energy and surface potential. We relate the two domains to differences in the packing density and in the ssDNA conformation. The discovered heterogeneities in ssDNA SAMs provide a new scenario in our vision of these relevant films that have direct consequences on their biological, chemical and physical properties.

  2. First-Principles Investigation of Phase Stability, Electronic Structure and Optical Properties of MgZnO Monolayer

    Directory of Open Access Journals (Sweden)

    Changlong Tan

    2016-10-01

    Full Text Available MgZnO bulk has attracted much attention as candidates for application in optoelectronic devices in the blue and ultraviolet region. However, there has been no reported study regarding two-dimensional MgZnO monolayer in spite of its unique properties due to quantum confinement effect. Here, using density functional theory calculations, we investigated the phase stability, electronic structure and optical properties of MgxZn1−xO monolayer with Mg concentration x range from 0 to 1. Our calculations show that MgZnO monolayer remains the graphene-like structure with various Mg concentrations. The phase segregation occurring in bulk systems has not been observed in the monolayer due to size effect, which is advantageous for application. Moreover, MgZnO monolayer exhibits interesting tuning of electronic structure and optical properties with Mg concentration. The band gap increases with increasing Mg concentration. More interestingly, a direct to indirect band gap transition is observed for MgZnO monolayer when Mg concentration is higher than 75 at %. We also predict that Mg doping leads to a blue shift of the optical absorption peaks. Our results may provide guidance for designing the growth process and potential application of MgZnO monolayer.

  3. Guided mode extraction in monolayer colloidal crystals based on the phase variation of reflection and transmission coefficients

    Science.gov (United States)

    Nekuee, Seyed Amir Hossein; Akbari, Mahmood; Khavasi, Amin

    2016-04-01

    An accurate and fast method for guided modes extraction in monolayer colloidal crystals and their inverse replicas is presented. These three-dimensional structures are composed of a monolayer of spherical particles that can easily and simply be prepared by self-assembly method in close packed hexagonal lattices. In this work, we describe how the guided modes, even or odd modes and light cone boundary can be easily determined using phase variations of reflection and transmission coefficients. These coefficients are quickly calculated by Fourier modal method. The band structures are obtained for a monolayer of polystyrene particles and two-dimensional TiO2 inverse opal by this proposed method.

  4. Sensitivity of micromechanical actuation on amorphous to crystalline phase transformations under the influence of Casimir forces

    NARCIS (Netherlands)

    Sedighi Ghozotkhar, Mehdi; Broer, W. H.; Palasantzas, G.; Kooi, B. J.

    2013-01-01

    Amorphous to crystalline phase transitions in phase change materials (PCM) can have strong influence on the actuation of microelectromechanical systems under the influence of Casimir forces. Indeed, the bifurcation curves of the stationary equilibrium points and the corresponding phase portraits of

  5. Low-density phases of 3He monolayers adsorbed on graphite

    Science.gov (United States)

    Ruggeri, Michele; Vitali, Ettore; Galli, Davide Emilio; Boninsegni, Massimo; Moroni, Saverio

    2016-03-01

    Quantum Monte Carlo simulations at zero temperature of a 3He monolayer adsorbed on graphite, either clean or preplated with 4He, unexpectedly point to a gas-liquid phase transition at a very low areal density of the order of 0.01 Å-2 . This result stems from an essentially unbiased calculation of the ground-state energy for an infinite, defect-free substrate, which interacts with He atoms via a realistic potential, whereas the interaction between two He atoms includes two- and three-body terms. The sensitivity of the gas-liquid coexistence region on the model Hamiltonian employed is discussed.

  6. Frustrated smectic liquid crystalline phases in lactic acid derivatives

    Science.gov (United States)

    Glogarová, M.; Novotná, V.

    2016-08-01

    We have prepared and studied a series of compounds with different types of molecular core and lactate unit in the chiral terminal chain. We draw a survey and comparison of their mesomorphic properties with respect to the occurrence of twist grain boundary (TGB) phases. The materials exhibit extremely wide TGBA phase more than 60K broad, unique TGBA-TGBC-SmC*-SmCA* phase sequence and unique re-entrant TGBA phase below the SmA phase. TGB phases have been induced in binary mixtures of molecules with different molecular shape and chirality (chiral lactic acid derivative and non-chiral hockey-stick mesogen). Unique effect is observed for compounds with TGBA phase, where the applied electric field transforms the planar texture into the homeotropic one, homogeneously dark in crossed polarizers. The process is analogy of the Frederiks transition so far known only for nematics. This effect, changing the bright state to the dark one, is promising for applications.

  7. Spontaneous phase separation during self-assembly in bi-dispersed spherical iron oxide nanoparticle monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Stanley, Jacob; Boucheron, Leandra; Shpyrko, Oleg, E-mail: lin@cars.uchicago.edu, E-mail: oshpyrko@physics.ucsd.edu [Department of Physics, University of California, San Diego, La Jolla, California 92093 (United States); Lin, Binhua, E-mail: lin@cars.uchicago.edu, E-mail: oshpyrko@physics.ucsd.edu; Meron, Mati [Center for Advanced Radiation Sources (CARS), University of Chicago, Chicago, Illinois 60637 (United States)

    2015-04-20

    Recent developments in the synthesis of iron oxide nanoparticles have resulted in the ability to fabricate roughly spherical particles with extremely high size uniformity (low polydispersity). These particles can form self-assembled monolayer films at an air-water interface. When the polydispersity of the particles is low, these monolayers can be well-ordered over a length scale dozens of times the particle size. The van der Waals force between the particles is what drives this self-assembly. Through the use of Grazing Incidence X-Ray Diffraction we demonstrate that, when these films are formed at the liquid surface from bi-dispersed solutions containing 10 and 20 nm spherical particles suspended in chloroform, the particles phase separate into well-ordered patches during the self-assembly process. Furthermore, the domain sizes of these phase separated regions are at most 2–3 times smaller than that of a film comprising only mono-dispersed particles and their degree of disorder is comparable. This is shown for multiple solutions with differing ratios of 10 and 20 nm particles.

  8. Structural phase study in un-patterned and patterned PVDF semi-crystalline films

    Energy Technology Data Exchange (ETDEWEB)

    Pramod, K., E-mail: rameshg.phy@pondiuni.edu.in; Gangineni, Ramesh Babu, E-mail: rameshg.phy@pondiuni.edu.in [Department of Physics, Pondicherry University, R. V. Nagar, Kalapet, Puducherry - 605014 (India)

    2014-04-24

    This work explores the structural phase studies of organic polymer- polyvinylidene fluoride (PVDF) thin films in semi-crystallized phase and nano-patterned PVDF thin films. The nanopatterns are transferred with the CD layer as a master using soft lithography technique. The semi-crystalline PVDF films were prepared by a still and hot (SH) method, using a homemade spin coater that has the proficiency of substrate heating by a halogen lamp. Using this set up, smooth PVDF thin films in semi-crystalline α-phase were prepared using 2-Butanone as solvent. XRD, AFM and confocal Raman microscope have been utilized to study the structural phase, crystallinity and quality of the films.

  9. Effect of heat and film thickness on a photoinduced phase transition in azobenzene liquid crystalline polyesters

    DEFF Research Database (Denmark)

    Sanchez, C; Alcala, R; Hvilsted, Søren

    2003-01-01

    The liquid crystal to isotropic phase transition induced with 488 nm light in films of liquid crystalline azobenzene polyesters has been studied as a function of temperature, light intensity, and film thickness. That phase transition is associated with the photoinduced trans-cis-trans isomerizati...

  10. STUDY ON THE PHASE TRANSITION KINETICS OF THERMOTROPIC LIQUID CRYSTALLINE AROMATIC-ALIPHATIC COPOLYESTER

    Institute of Scientific and Technical Information of China (English)

    LI Minhui; WANG Xiaogong; LIU Deshan; ZHOU Qixiang

    1991-01-01

    The phase transition kinetics of thermotropic liquid crystalline aromatic-aliphatic regular copolyester:(X) were studied by DSC. By means of Kissinger's method the kinetic equation and parameters including activation energy, rate order and preexponential factor for phase transition from nematic to isotropic were obtained. The activation energy from crystal to nematic was also presented.

  11. On the formation of crystalline microstructures of monolayers seen in terms of qualitative diffusion-type models at mesoscale

    Science.gov (United States)

    Gadomski, A.

    2008-09-01

    It is well known (see, e.g., K. A. Beklemishev and D. B. Berg, Pis’ma Zh. Tekh. Fiz. 33 (19), 40 (2007) [Tech. Phys. Lett. 33, 825 (2007)]) that many diffusion-type growth models allow qualitative features of growing microstructures to be obtained without employing any special information on the molecules constituting the microstructural domains. It has also been noted that the time needed to obtain a polycrystalline structure must be carefully estimated by engaging statistical-mechanical ensemble-averaging methods. The latter seems to be, in general, a difficult task because the problem is left as non-ergodic. The former, in turn, is supposed to be remedied while realizing that the qualitative estimates can become quantitative when offered at the mesoscopic level and when appropriately supported by a suitable construction of the diffusion function. In addition to comprising the Gibbs (non-negative) entropy production framework as a firm basis deeply rooted in the first law of thermodynamics for open thermodynamic systems, this construction can be seen as good as the frequently used Avrami-Kolmogorov phenomenology. This type of proposal cannot be easily postponed in the modeling of phospholipid monolayers or other two-dimensional amphiphilic, soft-matter-type systems.

  12. Nonionic diethanolamide amphiphiles with isoprenoid-type hydrocarbon chains: thermotropic and lyotropic liquid crystalline phase behaviour

    Energy Technology Data Exchange (ETDEWEB)

    Sagnella, Sharon M.; Conn, Charlotte E.; Krodkiewska, Irena; Drummond, Calum J. (CSIRO/MSE)

    2014-09-24

    The thermotropic and lyotropic liquid crystalline phase behaviour of a series of diethanolamide amphiphiles with isoprenoid-type hydrocarbon chains (geranoyl, H-farnesoyl, and phytanoyl) has been investigated. When neat, both H-farnesoyl and phytanoyl diethanolamide form a smectic liquid crystalline structure at sub-zero temperatures. In addition, all three diethanolamides exhibit a glass transition temperature at around -73 C. Geranoyl diethanolamide forms a lamellar crystalline phase with a lattice parameter of 17.4 {angstrom} following long term storage accompanied by the loss of the glass transition. In the presence of water, H-farnesoyl and phytanoyl diethanolamide form lyotropic liquid crystalline phases, whilst geranoyl diethanolamide forms an L{sub 2} phase. H-farnesoyl diethanolamide forms a fluid lamellar phase (L{sub {alpha}}) at room temperature and up to {approx} 40 C. Phytanoyl diethanolamide displays a rich mesomorphism forming the inverse diamond (Q{sub II}{sup D}) and gyroid (Q{sub II}{sup G}) bicontinuous cubic phases in addition to an L{sub {alpha}} phase.

  13. Improvement of multilayer graphene crystallinity by solid-phase precipitation with current stress application during annealing

    Science.gov (United States)

    Sahab Uddin, Md.; Ichikawa, Hiroyasu; Sano, Shota; Ueno, Kazuyoshi

    2016-06-01

    To improve the crystallinity of multilayer graphene (MLG) films by solid-phase precipitation, a new method by which current stress is introduced during annealing of a carbon-doped cobalt (Co-C) layer using cobalt (Co) as the catalyst has been investigated. The effects of current stress on the formation and crystallinity of MLG films were investigated by comparing the characteristics of the films annealed at the same temperature with and without current by taking into account the temperature rise due to Joule heating. The characteristics obtained by Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) measurements revealed that the MLG films produced were crystalline in nature and their crystallinity increased with applied current stress at the same temperature. From SEM observations, beside Joule heating, enhancement of Co grain size by agglomeration induced by current stress may be the potential reason for the improvement of the crystallinity of MLG films. We have also improved the uniformity of MLG films by depositing an additional copper (Cu) capping layer over the Co-C layer. Current stress application can lead to low-temperature fabrication of MLG with higher crystallinity by solid-phase precipitation.

  14. 77 FR 35425 - Crystalline Silicon Photovoltaic Cells and Modules From China; Scheduling of the Final Phase of...

    Science.gov (United States)

    2012-06-13

    ... silicon photovoltaic cells, and modules, laminates, and panels, consisting of crystalline silicon... COMMISSION Crystalline Silicon Photovoltaic Cells and Modules From China; Scheduling of the Final Phase of... crystalline silicon photovoltaic cells and modules, provided for in subheadings 8501.31.80, 8501.61.00,...

  15. Electrostriction and Crystalline Phase Transformations in a Vinylidene Flouride Terpolymer

    Science.gov (United States)

    Roland, C. M.; Garrett, J. T.; Qadri, S. B.

    Substantial electrostrictive strains can be obtained from terpolymers of vinylidene fluoride, trifluoroethylene, and chlorotrifluoroethylene. The mechanism of the electromechanical response was investigated using x-ray diffraction and infrared absorption measurements on the polymer under an electric field. While application of the field is found to induce changes in the crystal phase structure, the phase transition that can effect dimensional changes is too small to account for the magnitude of the electrostriction. Thus, the origin of the exceptional electromechanical properties of this material remains to be fully elucidated.

  16. Amorphous and crystalline phase interaction during the Brill transition in nylon 66

    Directory of Open Access Journals (Sweden)

    2009-07-01

    Full Text Available A prominent α' process in specifically treated nylon 66 and microcomposite samples is identified by dynamic mechanical analysis and proposed to be an amorphous phase counterpart of the Brill transition identified by synchrotron wide-angle X-ray diffraction (WAXD. It is suggested that this α' process, which marks a critical free volume change and an onset of segmental chain movement in the amorphous phase, precedes and prompts the Brill transition in the crystalline phase.

  17. Tuning the phase diagrams: the miscibility studies of multilactate liquid crystalline compounds

    Science.gov (United States)

    Bubnov, Alexej; Tykarska, Marzena; Hamplová, Věra; Kurp, Katarzyna

    2016-09-01

    Design of binary and multicomponent liquid crystalline mixtures is a very powerful tool to reach the desired self-assembling properties. Beyond many advantages, this method has a distinct negativity - it is very material-consuming. While working with unique chiral materials in the research laboratory, this problem can be solved by applying miscibility study by the contact preparation method. In this work, the miscibility studies of lactic acid derivatives and non-chiral/chiral liquid crystalline molecules of different structure have been done in order to establish the phase diagrams. Special attention is focused on the ferro(antiferro)electric smectic phases.

  18. Growth of crystalline Al2O3 via thermal atomic layer deposition: Nanomaterial phase stabilization

    Directory of Open Access Journals (Sweden)

    S. M. Prokes

    2014-03-01

    Full Text Available We report the growth of crystalline Al2O3 thin films deposited by thermal Atomic Layer Deposition (ALD at 200 °C, which up to now has always resulted in the amorphous phase. The 5 nm thick films were deposited on Ga2O3, ZnO, and Si nanowire substrates 100 nm or less in diameter. The crystalline nature of the Al2O3 thin film coating was confirmed using Transmission Electron Microscopy (TEM, including high-resolution TEM lattice imaging, selected area diffraction, and energy filtered TEM. Al2O3 coatings on nanowires with diameters of 10 nm or less formed a fully crystalline phase, while those with diameters in the 20–25 nm range resulted in a partially crystalline coating, and those with diameters in excess of 50 nm were fully amorphous. We suggest that the amorphous Al2O3 phase becomes metastable with respect to a crystalline alumina polymorph, due to the nanometer size scale of the film/substrate combination. Since ALD Al2O3 films are widely used as protective barriers, dielectric layers, as well as potential coatings in energy materials, these findings may have important implications.

  19. Low-pressure phase diagram of crystalline benzene from quantum Monte Carlo

    Science.gov (United States)

    Azadi, Sam; Cohen, R. E.

    2016-08-01

    We studied the low-pressure (0-10 GPa) phase diagram of crystalline benzene using quantum Monte Carlo and density functional theory (DFT) methods. We performed diffusion quantum Monte Carlo (DMC) calculations to obtain accurate static phase diagrams as benchmarks for modern van der Waals density functionals. Using density functional perturbation theory, we computed the phonon contributions to the free energies. Our DFT enthalpy-pressure phase diagrams indicate that the Pbca and P21/c structures are the most stable phases within the studied pressure range. The DMC Gibbs free-energy calculations predict that the room temperature Pbca to P21/c phase transition occurs at 2.1(1) GPa. This prediction is consistent with available experimental results at room temperature. Our DMC calculations give 50.6 ± 0.5 kJ/mol for crystalline benzene lattice energy.

  20. Phase transitions in diglyceride monolayers studied by computer simulations, pressure-area isotherms and x-ray diffraction

    DEFF Research Database (Denmark)

    Peters, Günther H.J.; Toxværd, S.; Larsen, N.B.

    1994-01-01

    1,2-sn-diglyceride monolayers exhibit unique and complex phase transitions as a function of surface pressure. The dynamical response of the layer on expanding the film has been investigated by computer simulations, (π-A) isotherms and grazing-incidence X-ray diffraction. Good agreement is found b...

  1. Chemical composition of glass and crystalline phases in coarse coal gasification ash

    Energy Technology Data Exchange (ETDEWEB)

    R.H. Matjie; Zhongsheng Li; Colin R. Ward; David French [Sasol Technology (Pty) Ltd., Sasolburg (South Africa)

    2008-05-15

    A procedure has been developed for determining the chemical composition and relative abundance of the amorphous or glassy material, as well as crystalline phases, present in coarse coal gasification ash, in order to assist in predicting the behaviour of the material in cement/brick/concrete applications. The procedure is based on a combination of quantitative X-ray diffraction (XRD), chemical analysis and electron microprobe studies. XRD analysis indicates that the clinker samples contain a number of crystalline high temperature phases, including anorthite, mullite, cristobalite, quartz and diopside. Quantitative evaluation using Rietveld-based techniques has been used to determine the percentages of both the individual crystalline phases and the glass component. These data were then combined with the chemistry of the crystalline phases and the overall chemical composition of the ash to estimate the chemical composition of the glass phase, which is typically the most abundant component present in the different materials. Although there is some degree of scatter, comparison between the inferred glass composition from XRD and bulk chemistry and actual data on the glass composition using electron microprobe techniques suggest that the two approaches are broadly consistent. The microprobe further indicates that a range of compositions are present in the glassy and crystalline components of the ashes, including Si-Al-rich glass, metakaolin and Fe-Ca-Mg-Ti phases, as well as quartz, anorthite and an aluminophosphate material. Electron microprobe and XRD studies also show that pyrrhotite (FeS), representing a high temperature transformation product of pyrite, is present in some clinker and partially burnt carbonaceous shale samples. 27 refs., 5 figs., 7 tabs.

  2. Shadow wave-function variational calculations of crystalline and liquid phases of 4He

    Science.gov (United States)

    Vitiello, S. A.; Runge, K. J.; Chester, G. V.; Kalos, M. H.

    1990-07-01

    A new class of variational wave functions for boson systems, shadow wave functions, is used to investigate the properties of solid and liquid 4He. The wave function is translationally invariant and symmetric under particle interchange. In principle, the calculations for the crystalline phase do not require the use of any auxiliary lattice. Using the Metropolis Monte Carlo algorithm, we show that the additional variational degrees of freedom in the wave function lower the energy significantly. This wave function also allows the crystalization of an equilibrated liquid phase when a crystalline seed is used. The pair correlation function and structure factor S(k) are determined in the liquid phase. The condensate fraction is calculated as well. Results are given for the single-particle distribution function around the lattice positions in the solid phase.

  3. Quantitative Phase Development of crystalline, nano-crystalline and amorphous phases during hydration of OPC blended with siliceous fly ash

    OpenAIRE

    Dittrich, Sebastian

    2015-01-01

    Ambitious efforts driven by political and environmental considerations to reduce carbon dioxide emission are currently present, amongst other branches in the construction material industry as well. One possible solution concentrates on the replacement of cement by supplementary cementitious materials like fly ash or granulated blast furnace slag. Due to its high amorphous phase content and the related reactivity potential fly ash seems well suited for being used in cement or concrete. Unfortu...

  4. Water-binding phospholipid nanodomains and phase-separated diacylglycerol nanodomains regulate enzyme reactions in lipid monolayers.

    Science.gov (United States)

    Nagashima, Teruyoshi; Uematsu, Shogo

    2015-02-03

    Phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) nanodomains covered with bound water as well as diacylglycerol 1-palmitoyl-2-oleoyl-sn-glycerol (POG) nanodomains separated from a lipid membrane were studied, using monolayer surfaces of POPC hydrolyzed by phospholipase C (PLC). The investigation was based on the analysis of compression isotherms and on atomic force microscope (AFM) observations of Langmuir-Blodgett (LB) films and Langmuir-Schaefer (LS) films. The results included reaction rate constants obtained by kinetic analysis of phosphocholine at surface pressures from 0.1 to 31 mN/m and determined by a luminol-enhanced chemiluminescence method. Monolayer elastic modulus values and fluorescence microscopic images confirmed that hydrolysis by PLC progressed in the intermediate monolayer between a liquid-expanded (L1) film and a liquid-condensed (L2) film at 2-17 mN/m. Furthermore, the intermediate film was confirmed to consist of L1 film and the POPC nanodomains in the L2 state are covered with bound water, conclusions based on the following AFM results: (1) nanodomains in POPC LS films were catalyzed by PLC, (2) POG nanodomains extended out from LB films of mixed POPC/POG 9/1 (mol/mol) monolayers, and (3) POPC LS films were covered with bound water, as indicated by cross-sectional analysis. At the optimal surface pressure of 10 mN/m, when POPC nanodomains (L2), with internal diameters of ∼75 nm, were hydrolyzed by PLC, they shrank down into pockets of the same size as those that appeared with POG. The resulting pocket sizes on LS films were in agreement with POG nanodomain sizes on LB films. This study demonstrated that PLC reacted with POPC nanodomains (L2) dispersed in L1/L2 mixed phase monolayers selectively and that POG nanodomains were phase-separated from the monolayer as hydrolysis proceeded.

  5. Distinct Topological Crystalline Phases in Models for the Strongly Correlated Topological Insulator SmB_{6}.

    Science.gov (United States)

    Baruselli, Pier Paolo; Vojta, Matthias

    2015-10-09

    SmB_{6} was recently proposed to be both a strong topological insulator and a topological crystalline insulator. For this and related cubic topological Kondo insulators, we prove the existence of four different topological phases, distinguished by the sign of mirror Chern numbers. We characterize these phases in terms of simple observables, and we provide concrete tight-binding models for each phase. Based on theoretical and experimental results for SmB_{6} we conclude that it realizes the phase with C_{k_{z}=0}^{+}=+2, C_{k_{z}=π}^{+}=+1, C_{k_{x}=k_{y}}^{+}=-1, and we propose a corresponding minimal model.

  6. The structure and dynamics of amorphous and crystalline phases of ice

    Energy Technology Data Exchange (ETDEWEB)

    Klug, D. D.; Tse, J. S.; Tulk, C. A.; Svensson, E. C.; Swainson, I.; Loong, C.-K.

    2000-07-14

    The structures of the high and low-density amorphous phases of ice are studied using several techniques. The diffraction patterns of high and low density amorphous ice are analyzed using reverse Monte Carlo methods and compared with molecular dynamics simulations of these phases. The spectra of crystalline and amorphous phases of ice obtained by Raman and incoherent inelastic neutron scattering are analyzed to yield structural features for comparison with the results of molecular dynamics and Reverse Monte Carlo analysis. The structural details obtained indicate that there are significant differences between the structure of liquid water and the amorphous phases of ice.

  7. High-Quality Single Crystalline Ge(111) Growth on Si(111) Substrates by Solid Phase Epitaxy

    Institute of Scientific and Technical Information of China (English)

    SUN Bing; CHANG Hu-Dong; LU Li; LIU Hong-Gang; WU De-Xin

    2012-01-01

    Heterogeneous integration of crystalline Ge layers on cleaned and H-terminated Si(111) substrates are demonstrated by employing a combination of e-beam evaporation and solid phase epitaxy techniques. High-quality single crystalline Ge(111) layers on Si(111) substrates with a smooth Ge surface and an abrupt interface between Ge and Si are obtained.An XRD rocking curve scan of the Ge(111) diffraction peak shovs a FWHM of only 260 arcsec for a 50-nm-thick Ge layer annealed at 600℃ with a ramp-up rate of 20℃/s and a holding time of 1 min. The AFM images exhibit that the rms surface roughness of all the crystalline Ge layers are less than 2.1 nm.

  8. Toward an anisotropic atom-atom model for the crystalline phases of the molecular S8 compound

    OpenAIRE

    Pastorino, C.; Gamba, Z.

    2000-01-01

    We analize two anisotropic atom-atom models used to describe the crystalline alpha,beta and gamma phases of S8 crystals, the most stable compound of elemental sulfur in solid phases, at ambient pressure and T

  9. Spectral descriptors for bulk metallic glasses based on the thermodynamics of competing crystalline phases

    CERN Document Server

    Perim, Eric; Liu, Yanhui; Toher, Cormac; Gong, Pan; Li, Yanglin; Simmons, W Neal; Levy, Ohad; Vlassak, Joost J; Schroers, Jan; Curtarolo, Stefano

    2016-01-01

    Metallic glasses have attracted considerable interest in recent years due to their unique combination of superb properties and processability. Predicting bulk metallic glass formers from known parameters remains a challenge and the search for new systems is still performed by trial and error. It has been speculated that some sort of "confusion" during crystallization of the crystalline phases competing with glass formation could play a key role. Here, we propose a heuristic descriptor quantifying confusion and demonstrate its validity by detailed experiments on two well-known glass forming alloy systems. With the insight provided by these results, we develop a robust model for predicting glass formation ability based on the spectral decomposition of geometrical and energetic features of crystalline phases calculated ab-initio in the AFLOW high throughput framework. Our findings indicate that the formation of metallic glass phases could be a much more common phenomenon than currently estimated, with more than ...

  10. Monolayers of CF4 Adsorbed on Graphite, Studied by Synchrotron X-Ray Diffraction

    DEFF Research Database (Denmark)

    Kjær, Kristian; Nielsen, Mourits; Bohr, Jakob;

    1982-01-01

    With synchrotron x-ray diffraction we have measured the phase diagram of CF4 monolayers adsorbed on the graphite substrate UCAR-ZYX. We have found four two-dimensional crystalline phases including the 2×2 commensurate structure. Between this and the denser incommensurate hexagonal phase we find...

  11. Change in the crystalline structure during the phase transition of the palladium-hydrogen system.

    Science.gov (United States)

    Kawasaki, Akio; Itoh, Satoshi; Shima, Kunihiro; Kato, Kenichi; Ohashi, Haruhiko; Ishikawa, Tetsuya; Yamazaki, Toshimitsu

    2015-10-14

    We performed an X-ray diffraction experiment while a palladium bulk absorbed and desorbed hydrogen to investigate the behavior of the crystalline lattice during the phase transition between the α phase and the β phase. Fast growth of the β phase was observed at around x = 0.1 and x = 0.45 of PdHx, and the phase transition rate has an exponential behavior in between. In addition, slight compression of the lattice at a high hydrogen concentration, an increase in the lattice constant, and broadening of the line width of the α phase after a cycle of absorption and desorption of hydrogen were observed. These behaviors correlated with the change in the sample length, which may infer that the change in shape was related to the phase transition.

  12. High-quality single crystalline NiO with twin phases grown on sapphire substrate by metalorganic vapor phase epitaxy

    Directory of Open Access Journals (Sweden)

    Kazuo Uchida

    2012-12-01

    Full Text Available High-quality single crystalline twin phase NiO grown on sapphire substrates by metalorganic vapor phase epitaxy is reported. X-ray rocking curve analysis of NiO films grown at different temperatures indicates a minimum full width at half maximum of the cubic (111 diffraction peak of 0.107° for NiO film grown at as low as 550 °C. Detailed microstructural analysis by Φ scan X-ray diffraction and transmission electron microscopy reveal that the NiO film consists of large single crystalline domains with two different crystallographic orientations which are rotated relative to each other along the [111] axis by 60°. These single crystal domains are divided by the twin phase boundaries.

  13. Investigations on the liquid crystalline phases of cation-induced condensed DNA

    Indian Academy of Sciences (India)

    C K S Pillai; Neethu Sundaresan; M Radhakrishnan Pillai; T Thomas; T J Thomas

    2005-10-01

    Viral and nonviral condensing agents are used in gene therapy to compact oligonucleotides and plasmid DNA into nanostructures for their efficient transport through the cell membranes. Whereas viral vectors are best by the toxic effects on the immune system, most of the nonviral delivery vehicles are not effective for use in clinical system. Recent investigations indicate that the supramolecular organization of DNA in the condensed state is liquid crystalline. The present level of understanding of the liquid crystalline phase of DNA is inadequate and a thorough investigation is required to understand the nature, stability, texture and the influence of various environmental conditions on the structure of the phase. The present study is mainly concerned with the physicochemical investigations on the liquid crystalline transitions during compaction of DNA by cationic species such as polyamines and metallic cations. As a preliminary to the above investigation, studies were conducted on the evolution of mesophase transitions of DNA with various cationic counterion species using polarized light microscopy. These studies indicated significant variations in the phase behaviour of DNA in the presence of Li and other ions. Apart from the neutralization of the charges on the DNA molecule, these ions are found to influence selectively the hydration sphere of DNA that in turn influences the induction and stabilization of the LC phases. The higher stability observed with the liquid crystalline phases of Li-DNA system could be useful in the production of nanostructured DNA. In the case of the polyamine, a structural specificity effect depending on the nature, charge and structure of the polyamine used has been found to be favoured in the crystallization of DNA.

  14. Investigations on the liquid crystalline phases of cation-induced condensed DNA

    Science.gov (United States)

    Pillai, C. K. S.; Sundaresan, Neethu; Radhakrishnan Pillai, M.; Thomas, T.; Thomas, T. J.

    2005-10-01

    Viral and nonviral condensing agents are used in gene therapy to compact oligonucleotides and plasmid DNA into nanostructures for their efficient transport through the cell membranes. Whereas viral vectors are best by the toxic effects on the immune system, most of the nonviral delivery vehicles are not effective for use in clinical system. Recent investigations indicate that the supramolecular organization of DNA in the condensed state is liquid crystalline. The present level of understanding of the liquid crystalline phase of DNA is inadequate and a thorough investigation is required to understand the nature, stability, texture and the influence of various environmental conditions on the structure of the phase. The present study is mainly concerned with the physico-chemical investigations on the liquid crystalline transitions during compaction of DNA by cationic species such as polyamines and metallic cations. As a preliminary to the above investigation, studies were conducted on the evolution of mesophase transitions of DNA with various cationic counterion species using polarized light microscopy. These studies indicated significant variations in the phase behaviour of DNA in the presence of Li and other ions. Apart from the neutralization of the charges on the DNA molecule, these ions are found to influence selectively the hydration sphere of DNA that in turn influences the induction and stabilization of the LC phases. The higher stability observed with the liquid crystalline phases of Li--DNA system could be useful in the production of nanostructured DNA. In the case of the polyamine, a structural specificity effect depending on the nature, charge and structure of the polyamine used has been found to be favoured in the crystallization of DNA.

  15. Formation of liquid crystalline phases in aqueous suspensions of platelet-like tripalmitin nanoparticles

    Science.gov (United States)

    Schmiele, Martin; Gehrer, Simone; Westermann, Martin; Steiniger, Frank; Unruh, Tobias

    2014-06-01

    Suspensions of platelet-like shaped tripalmitin nanocrystals stabilized by the pure lecithin DLPC and the lecithin blend S100, respectively, have been studied by small-angle x-ray scattering (SAXS) and optical observation of their birefringence at different tripalmitin (PPP) concentrations φPPP. It could be demonstrated that the platelets of these potential drug delivery systems start to form a liquid crystalline phase already at pharmaceutically relevant concentrations φPPP of less than 10 wt. %. The details of this liquid crystalline phase are described here for the first time. As in a previous study [A. Illing et al., Pharm. Res. 21, 592 (2004)] some platelets are found to self-assemble into lamellar stacks above a critical tripalmitin concentration \\varphi _{PPP}^{st} of 4 wt. %. In this study another critical concentration \\varphi _{PPP}^{lc}≈ 7 wt. % for DLPC and \\varphi _{PPP}^{lc}≈ 9 wt. % for S100 stabilized dispersions, respectively, has been observed. \\varphi _{PPP}^{lc} describes the transition from a phase of randomly oriented stacked lamellae and remaining non-assembled individual platelets to a phase in which the stacks and non-assembled platelets exhibit an overall preferred orientation. A careful analysis of the experimental data indicates that for concentrations above \\varphi _{PPP}^{lc} the stacked lamellae start to coalesce to rather small liquid crystalline domains of nematically ordered stacks. These liquid crystalline domains can be individually very differently oriented but possess an overall preferred orientation over macroscopic length scales which becomes successively more expressed when further increasing φPPP. The lower critical concentration for the formation of liquid crystalline domains of the DLPC-stabilized suspension compared to \\varphi _{PPP}^{lc} of the S100-stabilized suspension can be explained by a larger aspect ratio of the corresponding tripalmitin platelets. A geometrical model based on the excluded volumes of

  16. Low-pressure phase diagram of crystalline benzene from quantum Monte Carlo

    CERN Document Server

    Azadi, Sam

    2016-01-01

    We study the low-pressure (0 to 10 GPa) phase diagram of crystalline benzene using quantum Monte Carlo (QMC) and density functional theory (DFT) methods. We consider the $Pbca$, $P4_32_12$, and $P2_1/c$ structures as the best candidates for phase I and phase II. We perform diffusion quantum Monte Carlo (DMC) calculations to obtain accurate static phase diagrams as benchmarks for modern van der Waals density functionals. We use density functional perturbation theory to compute phonon contribution in the free-energy calculations. Our DFT enthalpy-pressure phase diagram indicates that the $Pbca$ and $P2_1/c$ structures are the most stable phases within the studied pressure range. The DMC Gibbs free-energy calculations predict that the room temperature $Pbca$ to $P2_1/c$ phase transition occurs at 2.1(1) GPa. This prediction is consistent with available experimental results at room temperature. Our DMC calculations show an estimate of 50.6$\\pm$0.5 kJ/mol for crystalline benzene lattice energy.

  17. Selective Sequence for the Peptide-Triggered Phase Transition of Lyotropic Liquid-Crystalline Structures.

    Science.gov (United States)

    Liu, Qingtao; Dong, Yao-Da; Boyd, Ben J

    2016-05-24

    A novel concept of using mixed lipids to construct selective peptide-sequence-sensing lyotropic liquid-crystalline (LLC) dispersion systems was investigated. The LLC systems were constructed using a mixture of phytantriol, a lipid that forms lyotropic liquid-crystalline phases, and a novel synthesized peptide-lipid (peplipid) for sensing a target peptide with the RARAR sequence. The internal structure of the dispersed LLC particles was converted from the lamellar structure (liposomes) to the inverse bicontinuous cubic phase (cubosomes) in the presence of the target peptide. The addition of common human proteins did not induce any structural change, indicating a high selectivity of interaction with the target peptide. The concept has potential for the design of targeted controlled release drug delivery agents.

  18. Transitions between imperfectly ordered crystalline structures: A phase switch Monte Carlo study

    OpenAIRE

    Wilms, Dorothea; Wilding, Nigel B.; Binder, Kurt

    2012-01-01

    A model for two-dimensional colloids confined laterally by "structured boundaries" (i.e., ones that impose a periodicity along the slit) is studied by Monte Carlo simulations. When the distance D between the confining walls is reduced at constant particle number from an initial value D_0, for which a crystalline structure commensurate with the imposed periodicity fits, to smaller values, a succession of phase transitions to imperfectly ordered structures occur. These structures have a reduced...

  19. Electric-field triggered controlled release of bioactive volatiles from imine-based liquid crystalline phases.

    Science.gov (United States)

    Herrmann, Andreas; Giuseppone, Nicolas; Lehn, Jean-Marie

    2009-01-01

    Application of an electric field to liquid crystalline film forming imines with negative dielectric anisotropy, such as N-(4-methoxybenzylidene)-4-butylaniline (MBBA, 1), results in the expulsion of compounds that do not participate in the formation of the liquid crystalline phase. Furthermore, amines and aromatic aldehydes undergo component exchange with the imine by generating constitutional dynamic libraries. The strength of the electric field and the duration of its application to the liquid crystalline film influence the release rate of the expelled compounds and, at the same time, modulate the equilibration of the dynamic libraries. The controlled release of volatile organic molecules with different chemical functionalities from the film was quantified by dynamic headspace analysis. In all cases, higher headspace concentrations were detected in the presence of an electric field. These results point to the possibility of using imine-based liquid crystalline films to build devices for the controlled release of a broad variety of bioactive volatiles as a direct response to an external electric signal.

  20. Crystalline behaviors and phase transition during the manufacture of fine denier PA6 fibers

    Institute of Scientific and Technical Information of China (English)

    ZHANG ChengFeng; LIU YuHai; LIU ShaoXuan; LI HuiZhen; HUANG Kun; PAN QingHua; HUA XiaoHui; HAO ChaoWei; MA QingFang; LV ChangYou; LI WeiHong; YANG ZhanLan; ZHAO Ying; WANG DuJin; LAI GuoQiao; JIANG JianXiong; XU YiZhuang; WU JinGuang

    2009-01-01

    Recently we have successfully produced fine denier PA6 fibers by using additives containing lanthanide compounds.Meanwhile,crystallization and phase transition of PA6 fibers during spinning and drawing processes were investigated.During the spinning process,β phase crystal could be obtained In as-spun PA6 fibers which were produced with relatively high melt draw ratio,while γ phase crystal predominated when the melt draw ratio was relatively low.β phase crystal,whose behaviors ere similar with those of γ phase by FT-IR and XRD characterization,could be transformed to α form easily when PA6 fibers are immersed in boiling water.However,γ phase crystal of PA6 remains unchanged in boiling water.Thus,β and γ phase crystals of PA6 can be differentiated by the crystalline behaviors of PA6 fibers after treatment in boiling water.Further experiments demonstrate that the β phase can also be produced during a drawing process where a phase transformation from γ to α occurs.In other words,βphase may act as an intermediate state during the phase transformation.

  1. Nature of phase transitions in crystalline and amorphous GeTe-Sb2Te3 phase change materials.

    Science.gov (United States)

    Kalkan, B; Sen, S; Clark, S M

    2011-09-28

    The thermodynamic nature of phase stabilities and transformations are investigated in crystalline and amorphous Ge(1)Sb(2)Te(4) (GST124) phase change materials as a function of pressure and temperature using high-resolution synchrotron x-ray diffraction in a diamond anvil cell. The phase transformation sequences upon compression, for cubic and hexagonal GST124 phases are found to be: cubic → amorphous → orthorhombic → bcc and hexagonal → orthorhombic → bcc. The Clapeyron slopes for melting of the hexagonal and bcc phases are negative and positive, respectively, resulting in a pressure dependent minimum in the liquidus. When taken together, the phase equilibria relations are consistent with the presence of polyamorphism in this system with the as-deposited amorphous GST phase being the low entropy low-density amorphous phase and the laser melt-quenched and high-pressure amorphized GST being the high entropy high-density amorphous phase. The metastable phase boundary between these two polyamorphic phases is expected to have a negative Clapeyron slope. © 2011 American Institute of Physics

  2. Collagen films with stabilized liquid crystalline phases and concerns on osteoblast behaviors

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Minjian; Ding, Shan; Min, Xiang; Jiao, Yanpeng, E-mail: tjiaoyp@jnu.edu.cn; Li, Lihua; Li, Hong; Zhou, Changren, E-mail: tcrz9@jnu.edu.cn

    2016-01-01

    To duplicate collagen's in vivo liquid crystalline (LC) phase and investigate the relationship between the morphology of LC collagen and osteoblast behavior, a self-assembly method was introduced for preparing collagen films with a stabilized LC phase. The LC texture and topological structure of the films before and after stabilization were observed with polarizing optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The relationship between the collagen films and osteoblast behavior was studied with the 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromide method, proliferation index detection, alkaline phosphatase measurements, osteocalcin assay, inverted microscopy, SEM observation, AFM observation, and cytoskeleton fluorescence staining. The results showed that the LC collagen film had continuously twisting orientations in the cholesteric phase with a typical series of arced patterns. The collagen fibers assembled in a well-organized orientation in the LC film. Compared to the non-LC film, the LC collagen film can promote cell proliferation, and increase ALP and osteocalcin expression, revealing a contact guide effect on osteoblasts. - Highlights: • Collagen film with liquid crystalline (LC) phase was observed by POM, SEM and AFM. • The effect of LC collagen film on osteoblasts behaviors was studied in detail. • LC collagen film promoted osteoblast proliferation and osteogenesis activity.

  3. Liquid crystalline phase transitions in virus and virus/polymer suspensions

    Science.gov (United States)

    Dogic, Zvonimir

    Using experimental, theoretical, and simulation methods, we investigate the relationship between the intermolecular interactions of rod-like colloids and the resulting liquid crystalline phase diagrams. As a model system of rod-like particles we use bacteriophage fd, which is a charge stabilized colloid. We are able to engineer complex attractive and repulsive intermolecular interactions by changing the ionic strengths of the suspensions, attaching covalently bound polymers and adding nonadsorbing polymers. Using standard molecular cloning techniques it is also shown that the aspect ratio of the rod-like particle can be manipulated. In the limit of high ionic strength the fd virus quantitatively agrees with the Onsager theory for the isotropic-nematic (I-N) phase transition in hard rods. The role of attractive interaction on the nature of the I-N phase transition is investigated. As the strength of the attraction is increased we observe isotropic-smectic (I-S) phase transitions. Using an optical microscope we follow the kinetics of the I-S phase transition and observe a wide range of novel structures of unexpected complexity. We also investigate the influence of adding hard spheres, or polymers on the nematic-smectic phase transition. We conclude that adding small spheres stabilizes the smectic phase and destabilizes the nematic phase.

  4. Morphology and crystalline-phase-dependent electrical insulating properties in tailored polypropylene for HVDC cables

    Science.gov (United States)

    Zha, Jun-Wei; Yan, Hong-Da; Li, Wei-Kang; Dang, Zhi-Min

    2016-11-01

    Polypropylene (PP) has become one promising material to potentially replace the cross-link polyethylene used for high voltage direct current cables. Besides the isotactic polypropylene, the block polypropylene (b-PP) and random polypropylene (r-PP) can be synthesized through the copolymerization of ethylene and propylene molecules. In this letter, the effect of morphology and crystalline phases on the insulating electrical properties of PP was investigated. It was found that the introduction of polyethylene monomer resulted in the formation of β and γ phases in b-PP and r-PP. The results from the characteristic trap energy levels indicated that the β and γ phases could induce deep electron traps which enable to capture the carriers. And the space charge accumulation was obviously suppressed. Besides, the decreased electrical conductivity was observed in b-PP and r-PP. It is attributed to the existence of deep traps which can effectively reduce the carrier mobility and density in materials.

  5. Two-dimensional topological crystalline insulator phase in quantum wells of trivial insulators

    Science.gov (United States)

    Niu, Chengwang; Buhl, Patrick M.; Bihlmayer, Gustav; Wortmann, Daniel; Blügel, Stefan; Mokrousov, Yuriy

    2016-06-01

    The realization of two-dimensional (2D) topological insulators (TIs) in HgTe/CdTe quantum wells (QWs) has generated an explosion of research on TIs and novel topologically nontrivial phases. Here we predict, based on first-principles calculations, that the newly discovered 2D topological crystalline insulators (TCIs) phase exists even in the QWs of trivial insulators, e.g. (Sn/Pb)Te and Na(Cl/Br), with mirror Chern number {n}{{M}}=-2. Tunable nontrivial energy gaps ranging from 4 to 238 meV are obtained, guaranteeing further room-temperature observations and applications. The combined effect of strain and electrostatic interaction that can be engineered by the cladding layers leads to a band inversion, resulting in the phase transition from trivial insulator to 2D TCIs. Our work provides a new strategy for engineering topological states in 2D materials.

  6. Sensitivity of micromechanical actuation on amorphous to crystalline phase transformations under the influence of Casimir forces

    Science.gov (United States)

    Sedighi, M.; Broer, W. H.; Palasantzas, G.; Kooi, B. J.

    2013-10-01

    Amorphous to crystalline phase transitions in phase change materials (PCM) can have strong influence on the actuation of microelectromechanical systems under the influence of Casimir forces. Indeed, the bifurcation curves of the stationary equilibrium points and the corresponding phase portraits of the actuation dynamics between gold and AIST (Ag5In5Sb60Te30) PCM, where an increase of the Casimir force of up ˜25% has been measured upon crystallization, show strong sensitivity to changes of the Casimir force as the stiffness of the actuating component decreases and/or the effective interaction area of the Casimir force increases, which can also lead to stiction. However, introduction of intrinsic energy dissipation (associated with a finite quality factor of the actuating system) can prevent stiction by driving the system to attenuated motion towards stable equilibrium depending on the PCM state and the system quality factor.

  7. Multiple phase transitions in single-crystalline Na_{1-delta}FeAs.

    Science.gov (United States)

    Chen, G F; Hu, W Z; Luo, J L; Wang, N L

    2009-06-01

    Specific heat, resistivity, susceptibility, and Hall coefficient measurements were performed on high-quality single-crystalline Na_{1-delta}FeAs. This compound is found to undergo three successive phase transitions at around 52, 41, and 23 K, which correspond to structural, magnetic, and superconducting transitions, respectively. The Hall effect result indicates the development of energy gap at low temperature due to the occurrence of spin-density-wave instability. Our results provide direct experimental evidence of the magnetic ordering in the nearly stoichiometric NaFeAs.

  8. Phase behaviour in binary mixed Langmuir-Blodgett monolayers of triglycerides

    NARCIS (Netherlands)

    Zdravkova, A.N.; van der Eerden, J.P.J.M.

    2007-01-01

    Binary mixed monolayers of the triglycerides (TAGs)-tripalmitin (PPP), tristearin (SSS) and triarachidin (AAA) at the air–water interface are investigated with the Langmuir method. Langmuir–Blodgett (LB) layers obtained by deposition on mica are investigated by Atomic Force Microscopy. Combining

  9. Binary phase diagram of monolayers of simple 1,2-diol derivatives

    DEFF Research Database (Denmark)

    Wolf, C. De; Bringezu, F.; Brezesinski, G.;

    1998-01-01

    The miscibility properties of monolayers of two 1,2-diol derivatives, 1-palmitoylglycerol (1) and 1-hexadecylglycerol (2), have been studied at the air-water interface using grazing incidence X-ray diffraction (GIXD). While, at all pressures investigated, compound (I) exhibits only a NN...

  10. Dynamic characterization of crystalline and glass phases of deuterated 1,1,2,2 tetrachloroethane

    Energy Technology Data Exchange (ETDEWEB)

    Pérez, Silvina C., E-mail: clyde@famaf.unc.edu.ar; Zuriaga, Mariano, E-mail: zuriaga@famaf.unc.edu.ar; Serra, Pablo, E-mail: serra@famaf.unc.edu.ar; Wolfenson, Alberto, E-mail: wolf@famaf.unc.edu.ar [Facultad de Matemática, Astronomía y Física, Universidad Nacional de Córdoba and IFEG-CONICET, Ciudad Universitaria, X5016LAE Córdoba (Argentina); Negrier, Philippe, E-mail: philippe.negrier@u-bordeaux.fr [Université Bordeaux, LOMA, UMR 5798, F-33400 Talence, France and LOMA, UMR 5798, F-33400 Talence (France); Tamarit, Josep Lluis, E-mail: josep.lluis.tamarit@upc.edu [Grup de Caracterització de Materials, Departament de Física i Enginyeria Nuclear, ETSEIB, Diagonal 647, Universitat Politècnica de Catalunya, 08028 Barcelona, Catalonia (Spain)

    2015-10-07

    A thorough characterization of the γ, β, and glass phases of deuterated 1,1,2,2 tetrachloroethane (C{sub 2}D{sub 2}Cl{sub 4}) via nuclear quadrupole resonance and Molecular Dynamic Simulations (MDSs) is reported. The presence of molecular reorientations was experimentally observed in the glass phase and in the β phase. In the β phase, and from MDS, these reorientations are attributed to two possible movements, i.e., a 180°  reorientation around the C{sub 2} molecular symmetry axis and a reorientation of the molecule between two non-equivalent positions. In the glass phase, the spin-lattice relaxation time T{sub 1} is of the order of 16 times lower than in the crystalline phase and varies as T{sup −1} below 100 K in good agreement with the strong quadrupolar relaxation observed in amorphous materials and in the glassy state of molecular organic systems. The activation energy of molecular reorientations in the glass phase (19 kJ/mol) is comparable to that observed in the glassy crystal of a “molecular cousin” compound, Freon 112 (C{sub 2}F{sub 2}Cl{sub 4}), for the secondary β-relaxation. Moreover, the on-site orientational motion of tetrachloroethane molecules offers a new indirect evidence of the prominent role of such orientational disorder in glassy dynamics.

  11. Dynamic characterization of crystalline and glass phases of deuterated 1,1,2,2 Tetrachloroethane

    CERN Document Server

    Perez, Silvina; Serra, Pablo; Wolfenson, Alberto; Negrier, Philippe; Tamarit, Josep

    2015-01-01

    A thorough characterization of the {\\gamma}, {\\beta} and glass phases of deuterated 1,1,2,2 Tetrachloroethane (C2D2Cl4) via Nuclear Quadrupole Resonance and Molecular Dynamic Simulations (MDS) is reported. The presence of molecular reorientations was experimentally observed in the glass phase and in the {\\beta} phase. In the {\\beta} phase, and from MDS, these reorientations are attributed to two possible movements, i.e. a $180^o$ reorientation around the C2 molecular symmetry axis and a reorientation of the molecule between non-equivalent positions. In the glass phase, the spin-lattice relaxation time T1 is of the order of 16 times lower that T1 in the crystalline phase and varies as $T^{-1}$ below 100 K in good agreement with the strong quadrupolar relaxation observed in amorphous materials and in the glassy state of molecular organic systems. The activation energy of molecular reorientations in the glass phase (19 kJ/mol) is comparable to that observed in the glassy crystal of a "molecular cousin" compound,...

  12. Local order and orientational correlations in liquid and crystalline phases of carbon tetrabromide from neutron powder diffraction measurements

    CERN Document Server

    Temleitner, László

    2010-01-01

    The liquid, plastic crystalline and ordered crystalline phases of CBr$_4$ were studied using neutron powder diffraction. The measured total scattering differential cross-sections were modelled by Reverse Monte Carlo simulation techniques (RMC++ and RMCPOW). Following successful simulations, the single crystal diffraction pattern of the plastic phase, as well as partial radial distribution functions and orientational correlations for all the three phases have been calculated from the atomic coordinates ('particle configurations'). The single crystal pattern, calculated from a configuration that had been obtained from modelling the powder pattern, shows identical behavior to the recent single crystal data of Folmer et al. (Phys. Rev. {\\bf B77}, 144205 (2008)). The BrBr partial radial distribution functions of the liquid and plastic crystalline phases are almost the same, while CC correlations clearly display long range ordering in the latter phase. Orientational correlations also suggest strong similarities bet...

  13. Gasification slag rheology and crystalline phase formation in titanium-calcium-alumina-silica-rich glass

    Energy Technology Data Exchange (ETDEWEB)

    Brooker, D.D. [Texaco, Inc., Beacon, NY (United States); Oh, M.S. [Hongik Univ., Seoul (Korea, Republic of)

    1996-10-01

    The Texaco Gasification Process employs a high temperature and pressure slagging gasifier, in which the viscosity of the slag plays a key role in determining operating conditions. The empirical models available in the literature as well as laboratory testing have concentrated on low titanium feeds. During the gasification of waste material, titanium oxide will become an important element in controlling the ash and slag behavior. Slag viscosity was measured at temperatures in the range of 1150-1500{degrees}C under reducing atmosphere with 0-30% titanium in combination with calcium-alumina-silica rich feeds to gain a better understanding of the slag theology. The slag viscosities with most titanium-rich slags showed the behavior of a crystalline slag with T{sub cv} of 1250{degrees}C. Crystalline phase analyses of the slag samples revealed that titanium oxide crystal will nucleate, but the glass phase is dominated by calcium-titanium-silicate and calcium-alumina-silicate glasses which have low melting points.

  14. Evidences of the existence of SiTe2 crystalline phase and a proposed new Si-Te phase diagram

    Science.gov (United States)

    Mishra, R.; Mishra, P. K.; Phapale, S.; Babu, P. D.; Sastry, P. U.; Ravikumar, G.; Yadav, A. K.

    2016-05-01

    The existence of two distinct crystalline phases viz., Si2Te3 and SiTe2, in the Si-Te system is established from differential thermal analysis (DTA) studies. Thermo-gravimetric (TG) data on SiTe2 indicate that the compound decomposes to Si in multiple steps via intermediate Si2Te3 phase. X-ray diffraction (XRD) reveals that SiTe2 crystallizes in P 3 ̅m1 space group with CdI2 trigonal structure, whereas Si2Te3 crystallizes in trigonal structure with space group P 3 ̅1c with varying occupation of octahedral voids. Single Si atoms fill only 1/2 of the octahedral voids in SiTe2 structure whereas in Si2Te3, Si atoms are arranged in pairs occupying 2/3 of the octahedral voids in alternating planes along c-axis. Further, X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) confirm the distinctness of the chemical environment in the two crystalline structures confirming the uniqueness of both the phases. DTA results on the two compounds indicate the presence of one crystallographic phase-transition in each of the compound with transition temperatures at 441 °C for Si2Te3 and 392 °C for SiTe2. At the same time both Si2Te3 and SiTe2 undergo peritectic decomposition at 683 °C and 432 °C forming [Si(s)+Te(liq)] and [α-Si2Te3(s)+Te(liq)], respectively. The system revealed eutectic reaction between β-SiTe2 and Te at 398 °C [L=Te+SiTe2]. Consequently, the phase diagram in the Si-Te system has been delineated.

  15. Phase transitions in polymer monolayers: Application of the Clapeyron equation to PEO in PPO-PEO Langmuir films.

    Science.gov (United States)

    Deschênes, Louise; Lyklema, Johannes; Danis, Claude; Saint-Germain, François

    2015-08-01

    In this paper we investigate the application of the two-dimensional Clapeyron law to polymer monolayers. This is a largely unexplored area of research. The main problems are (1) establishing if equilibrium is reached and (2) if so, identifying and defining phases as functions of the temperature. Once this is validated, the Clapeyron law allows us to obtain the entropy and enthalpy differences between two coexisting phases. In turn, this information can be used to obtain insight into the conformational properties of the films and changes therein. This approach has a wide potential for obtaining additional information on polymer adsorption at interfaces and the structure of their monolayer films. The 2D Clapeyron law was applied emphasizing polyethylene oxide (PEO) in polypropylene oxide (PPO)-PEO block copolymers, based on new well-defined data for their Langmuir films. Values for enthalpy per monomer of 0.12 and 0.23 kT were obtained for the phase transition of two different PEO chains (Neo of 2295 and 409, respectively). This enthalpy was estimated to correspond to 1.2±0.4 kT per EO monomer present in train conformation at the air/water interface.

  16. Molecular dynamics simulation of calcium fluoride——Crystalline, superionic, molten and quenched-amorphous phases

    Institute of Scientific and Technical Information of China (English)

    程兆年; 郏正明; 张静; 陈念贻

    1995-01-01

    The results from the molecular dynamics simulations on crystalline, superionic, molten and quenched-amorphous states of calcium fluoride system are reported. The Ca++ and F- sublattices are studied by using the method of bond order parameters. The result shows that both Ca++ and F- sublattices can be described with the bond-orientation normal distribution model. In the superionic phase the Ca++ cations keep their original stable fcc frame, but in the F- case random distortion generates from their original simple cubic (sc) structure. The simulation on the molten phase gives three radial distribution functions that are difficult to separate from the experimental X-ray diffraction data. The simulation of quenched-amorphous state shows that a dense random packing of equivalent spheres centered by Ca++ cations occurs in the system simulated. However, the system quenched is not stable enough because the Ca++ cation and F- anions around it do not form themselves into a certain configuration.

  17. Improving the performance of polymer solar cells by adjusting the crystallinity and nanoscale phase separation

    Institute of Scientific and Technical Information of China (English)

    Chen Wei-Bing; Xu Zong-Xiang; Li Kai; Chui Stephen Sin-Yin; Roy V.A.L.; Lai Pui-To; Che Chi-Ming

    2012-01-01

    In this paper,we report a high-performance P3HT/PCBM bulk-heterojunction solar cell with a power conversion efficiency of 4.85% fabricated by adjusting the polymer crystallinity and nanoscale phase separation using an ultrasonic irradiation mixing approach for the polymer.The grazing incidence X-ray diffraction,UV/Vis spectroscopic,and atomic force microscopic measurement results for the P3HT/PCBM blend films reveal that the P3HT/PCBM film fabricated by ultrasonic irradiation mixing of the P3HT and PCBM solutions for 10 min has a higher degree of cryetallinity,a higher absorption efficiency,and better phase separation,which together account for the higher charge transport properties and photovoltaic cell performance.

  18. Shifting Phases for Patchy Particles - Effect of mutagenesis and chemical modification on the phase diagram of human gamma D crystallin

    Science.gov (United States)

    McManus, Jennifer J.; James, Susan; McNamara, Ruth; Quinn, Michelle

    2014-03-01

    Single mutations in human gamma D crystallin (HGD), a protein found in the eye lens are associated with several childhood cataracts. Phase diagrams for several of these protein mutants have been measured and reveal that phase boundaries are shifted compared with the native protein, leading to condensation of protein in a physiologically relevant regime. Using HGD as a model protein, we have constructed phase diagrams for double mutants of the protein, incorporating two single amino acid substitutions for which phase diagrams are already known. In doing so, the characteristics of each of the single mutations are maintained but both are now present in the same protein particle. While these proteins are not of interest physiologically, this strategy allows the controlled synthesis of nano-scale patchy particles in which features associated with a known phase behavior can be included. It can also provide a strategy for the controlled crystallisation of proteins. Phase boundaries also change after the chemical modification of the protein, through the covalent attachment of fluorescent labels, for example, and this will also be discussed. The authors acknowledge Science Foundation Ireland Stokes Lectureship and Grant 11/RFP.1/PHY/3165. The authors also acknowledge the Irish Research Council and the John and Pat Hume Scholarship.

  19. Lupane-type pentacyclic triterpenes in Langmuir monolayers: a synchrotron radiation scattering study.

    Science.gov (United States)

    Broniatowski, Marcin; Flasiński, Michał; Wydro, Paweł

    2012-03-20

    Lupane-type pentacyclic triterpenes (lupeol, betulin, and betulinic acid) are natural products isolated from various plant sources. The terpenes exhibit a vast spectrum of biological activity and are applied in therapies for different diseases, among which the anticancer, anti-HIV, antihypercholesteremic, and antiinflammatory are the most promising. These chemicals possess amphiphilic structure and were proved to interact strongly with biomembranes, which can be the key stage in their mechanism of action. In our studies, we applied Langmuir monolayers as versatile models of biomembranes. It turned out that the three investigated terpenes are capable of stable monolayer formation; however, these monolayers differ profoundly regarding their physicochemical characteristics. In our research, we applied the Langmuir technique (surface pressure-mean molecular area (π-A) isotherm registration) coupled with Brewster angle microscopy (BAM), but the main focus was on the synchrotron radiation scattering method, grazing incidence X-ray diffraction (GIXD), which provides information on the amphiphilic molecule ordering in the angström scale. It was proved that all the investigated terpenes form crystalline phases in their monolayers. In the case of lupeol, only the closely packed upright phase was observed, whereas for betulin and betulinic acid, the phase situation was more complex. Betulinic acid molecules can be organized in an upright phase, which is crystalline, and in a tilted phase, which is amorphous. The betulin film is a conglomerate of an upright crystalline monolayer phase, tilted amorphous monolayer phase, and a crystalline tilted bilayer. In our paper, we discuss the factors leading to the formation of the observed phases and the implications of our results to the therapeutic applications of the native lupane-type triterpenes.

  20. pH Sensitivity of Si-C Linked Organic Monolayers on Crystalline Silicon Surfaces: Titration Experiments, Mott Schottky Analysis and Site-Binding Modeling

    NARCIS (Netherlands)

    Faber, E.J.; Sparreboom, W.; Groeneveld, W.; Smet, de L.C.P.M.; Bomer, J.; Olthuis, W.; Zuilhof, H.; Sudhölter, E.J.R.; Bergveld, P.; Berg, van den A.

    2007-01-01

    The electrochemical behavior of SiC linked organic monolayers is studied in electrolyte-insulator-Si devices, under conditions normally encountered in potentiometric biosensors, to gain fundamental knowledge on the behavior of such Si electrodes under practical conditions. This is done via titration

  1. Relaxation process and phase transition of lanthanide liquid crystalline complexes by photoacoustic spectroscopy

    Institute of Scientific and Technical Information of China (English)

    LI Junjia; YANG Yuetao; LIU Xiaojun; ZHANG Shuyi; ZHANG Zhongning

    2008-01-01

    Lanthanide-containing liquid crystals exhibiting smectic A phase close to room temperature were obtained. Photoacoustic (PA) spectroscopy was used to study the spectral properties and phase transitions of liquid crystalline metal complexes. It was found that PA intensity of the ligand had a relationship with the probability of nonradiative transitions, which increased in the order of Eu(tta)3L2Phase transitions of europium(III) and erbium(III) complexes, in the temperature range of 383-358 K, could be clearly monitored by both PA amplitude and PA phase signals. As the temperature crossed the transition point, PA amplitude showed a minimum and PA phase a maximum. The results indicated that PA technique could serve as a new tool for investigating the physicochemical properties of liquid crystals containing metal ions.

  2. Gradient measurement technique to identify phase transitions in nano-dispersed liquid crystalline compounds

    Science.gov (United States)

    Pardhasaradhi, P.; Madhav, B. T. P.; Venugopala Rao, M.; Manepalli, R. K. N. R.; Pisipati, V. G. K. M.

    2016-09-01

    Characterization and phase transitions in pure and 0.5% BaTiO3 nano-dispersed liquid crystalline (LC) N-(p-n-heptyloxybenzylidene)-p-n-nonyloxy aniline, 7O.O9, com-pounds are carried out using a polarizing microscope attached with hot stage and camera. We observed that when any of these images are distorted, different local structures suffer from various degradations in a gradient magnitude. So, we examined the pixel-wise gradient magnitude similarity between the reference and distorted images combined with a novel pooling strategy - the standard deviation of the GMS map - to determine the overall phase transition variations. In this regard, MATLAB software is used for gradient measurement technique to identify the phase transitions and transition temperature of the pure and nano-dispersed LC compounds. The image analysis of this method proposed is in good agreement with the standard methods like polarizing microscope (POM) and differential scanning calorimeter (DSC). 0.5% BaTiO3 nano-dispersed 7O.O9 compound induces cholesteric phase quenching the nematic phase, which the pure compound exhibits.

  3. Monodisperse nonionic isoprenoid-type hexahydrofarnesyl ethylene oxide surfactants: high throughput lyotropic liquid crystalline phase determination.

    Science.gov (United States)

    Fong, Celesta; Weerawardena, Asoka; Sagnella, Sharon M; Mulet, Xavier; Krodkiewska, Irena; Chong, Josephine; Drummond, Calum J

    2011-03-15

    The neat and lyotropic phase behavior of eight new ethylene oxide amphiphiles (EO = 1-8) with a hexahydrofarnesyl chain (3,7,11-trimethyldodecyl) and narrow polydispersity (>98.5% purity) is reported. Below five EO units the behavior of the neat surfactants show only a glass transition, Tg ∼ -90 °C. Above four EO units, crystallization (Tcrys) and crystal-isotropic liquid (Tm) transitions are also observed that increase with degree of ethoxylation of the surfactant headgroup. The lyotropic liquid crystalline phase behavior spans a complex spectrum of surfactant-water interfacial curvatures. Specifically, inverse phases are present below ambient temperatures for EO ethoxylation, with the crossover to normal phases occurring at HFarn(EO)(7-8) which exhibits normal hexagonal (H(I)) and cubic (Q(I)) phases at ambient temperatures. The toxicity of colloidal dispersions of these EO amphiphiles was assayed against normal breast epithelial (HMEpiC) and breast cancer (MCF7) cell lines. The IC50 of the EO amphiphiles was similar in both cell lines with moderate toxicity ranging from ca. <5 to 140 μM in an in vitro cell viability assay. Observations are qualitatively rationalized in terms of the molecular geometry of the surfactant. The physicochemical behavior of the HFarnesyl ethylene oxide amphiphiles is compared to other ethylene oxide surfactants.

  4. Solvation Dynamics in Different Phases of the Lyotropic Liquid Crystalline System.

    Science.gov (United States)

    Roy, Bibhisan; Satpathi, Sagar; Gavvala, Krishna; Koninti, Raj Kumar; Hazra, Partha

    2015-09-03

    Reverse hexagonal (HII) liquid crystalline material based on glycerol monooleate (GMO) is considered as a potential carrier for drugs and other important biomolecules due to its thermotropic phase change and excellent morphology. In this work, the dynamics of encapsulated water, which plays important role in stabilization and formation of reverse hexagonal mesophase, has been investigated by time dependent Stokes shift method using Coumarin-343 as a solvation probe. The formation of the reverse hexagonal mesophase (HII) and transformation to the L2 phase have been monitored using small-angle X-ray scattering and polarized light microscopy experiments. REES studies suggest the existence of different polar regions in both HII and L2 systems. The solvation dynamics study inside the reverse hexagonal (HII) phase reveals the existence of two different types of water molecules exhibiting dynamics on a 120-900 ps time scale. The estimated diffusion coefficients of both types of water molecules obtained from the observed dynamics are in good agreement with the measured diffusion coefficient collected from the NMR study. The calculated activation energy is found to be 2.05 kcal/mol, which is associated with coupled rotational-translational water relaxation dynamics upon the transition from "bound" to "quasi-free" state. The observed ∼2 ns faster dynamics of the L2 phase compared to the HII phase may be associated with both the phase transformation as well as thermotropic effect on the relaxation process. Microviscosities calculated from time-resolved anisotropy studies infer that the interface is almost ∼22 times higher viscous than the central part of the cylinder. Overall, our results reveal the unique dynamical features of water inside the cylinder of reverse hexagonal and inverse micellar phases.

  5. Preparation and crystalline phase of a TiO2 porous film by anodic oxidation

    Institute of Scientific and Technical Information of China (English)

    WANG Wei; TAO Jie; ZHANG Weiwei; TAO Haijun; WANG Ling

    2005-01-01

    Anatase titanium dioxide is an active photocatalyst, but it is difficult to immobilize on the substrate. A crystalline TiO2 porous film was prepared directly on the surface of pure titanium by anodic oxidation in this work. Constant voltage and constant current anodic oxidation were adopted with sulphuric acid used as the electrolyte, pure titanium as the anode and copper as the cathode. The morphology and structure of the porous film on the substrate were analyzed with the aid of Field Emission Scanning Electron Microscopy (FESEM) and X-ray Diffraction (XRD). The effects of the parameters of anodic oxidation (such as voltage, the concentration of sulphuric acid, anodization time and current density) on the aperture and the crystalline phase of the TiO2 porous film were systematically investigated. The results indicate that the increase of current density facilitates the augment of the aperture and the generation of anatase and rutile. In addition, the forming mechanism of anatase and rutile TiO2 porous films was discussed.

  6. Durability of crystalline phase in concrete microstructure modified by the mineral powders: evaluation by nanoindentation tests

    Directory of Open Access Journals (Sweden)

    Rajczakowska Magdalena

    2016-03-01

    Full Text Available This paper presents the nanoindentation investigation of the evolution of concrete microstructure modified by the Internal Crystallization Technology mineral powders. The samples under study were retrieved from a fragment of a circular concrete lining of the vertical mine shaft at a depth of approximately 1,000 m. Due to the aggressive environment and exposure to contaminated water, the internal surface of the structure was deteriorated, decreasing its strength significantly. The mineral powders were applied directly on the surface lining. The specimens were investigated one month, three months and one year after the application of the aforementioned substance in order to verify the time dependence of the strengthening processes and durability of the crystalline phase. The microstructural changes of concrete were assessed with the use of nanoindentation technique. The testing procedure involved including the previously cut specimens in the epoxy resin and grinding and polishing in order to reduce the surface roughness. As a result of the nanoindentation tests the hardness as well as Young’s modulus of the material were evaluated. The results were then compared and statistically analyzed. As a consequence, the disintegration time of the crystalline network in the pores of concrete was identified.

  7. MORPHOLOGICAL AND KINETIC STUDIES OF PHASE TRANSITIONS OF A SIDE-CHAIN LIQUID CRYSTALLINE POLYMER

    Institute of Scientific and Technical Information of China (English)

    Chi-bing Tan; Shu-fan Zhang; Mao Xu

    1999-01-01

    The morphological changes of a side-chain liquid-crystalline polymethacrylate during isotropization and liquid-crystallization transitions were studied by means of polarizing microscopy. These transitions were found to be composed of the initiation of a new phase at local places of the old phase matrix and the growth of the new phase domains. The kinetics of the liquid-crystallization of the polymer from an isotropic melt to a smectic mesophase was also investigated. The isothermal process of the transition can be described by the Avrami equation. The values of the Avrami exponent were found to be around 2.6. which is lower than the value usually obtained for crystallization transition of polymers, but larger than that reported for liquid-crystallization transition of main-chain polymers. These results may indicate the difference in growth geometry of new phase during transition between crystallization and liquid-crystallization in general and between liquid-crystallization of main-chain and side-chain polymers. It was found that the liquidcrystallization of the used side-chain polymethacrylate may occur at small undercoolings with high transformation rate similar to that of main-chain polymers and small-molecule liquid crystals, while the crystallization of polymers can only proceed at large undercoolings. These phenomena can be explained by the idea that the surface free energy of nucleus during liquid-crystallization transition is less than that for crystallization, and evidence was obtained from analysis of the temperature dependence of the transformation rate.

  8. Mechanochemical spinodal decomposition: a phenomenological theory of phase transformations in multi-component, crystalline solids

    Science.gov (United States)

    Rudraraju, Shiva; van der Ven, Anton; Garikipati, Krishna

    2016-06-01

    We present a phenomenological treatment of diffusion-driven martensitic phase transformations in multi-component crystalline solids that arise from non-convex free energies in mechanical and chemical variables. The treatment describes diffusional phase transformations that are accompanied by symmetry-breaking structural changes of the crystal unit cell and reveals the importance of a mechanochemical spinodal, defined as the region in strain-composition space, where the free-energy density function is non-convex. The approach is relevant to phase transformations wherein the structural order parameters can be expressed as linear combinations of strains relative to a high-symmetry reference crystal. The governing equations describing mechanochemical spinodal decomposition are variationally derived from a free-energy density function that accounts for interfacial energy via gradients of the rapidly varying strain and composition fields. A robust computational framework for treating the coupled, higher-order diffusion and nonlinear strain gradient elasticity problems is presented. Because the local strains in an inhomogeneous, transforming microstructure can be finite, the elasticity problem must account for geometric nonlinearity. An evaluation of available experimental phase diagrams and first-principles free energies suggests that mechanochemical spinodal decomposition should occur in metal hydrides such as ZrH2-2c. The rich physics that ensues is explored in several numerical examples in two and three dimensions, and the relevance of the mechanism is discussed in the context of important electrode materials for Li-ion batteries and high-temperature ceramics.

  9. Phase field modeling of grain structure evolution during directional solidification of multi-crystalline silicon sheet

    Science.gov (United States)

    Lin, H. K.; Lan, C. W.

    2017-10-01

    Evolution of grain structures and grain boundaries (GBs), especially the coincident site lattice GBs, during directional solidification of multi-crystalline silicon sheet are simulated by using a phase field model for the first time. Since the coincident site lattice GBs having lower mobility, tend to follow their own crystallographic directions despite thermal gradients, the anisotropic energy and mobility of GBs are considered in the model. Three basic interactions of GBs during solidification are examined and they are consistent with experiments. The twinning process for new grain formation is further added in the simulation by considering twin nucleation. The effect of initial distribution of GB types and grain orientations is also investigated for the twinning frequency and the evolution of grain size and GB types.

  10. Tuning Eu{sup 3+} emission in europium sesquioxide films by changing the crystalline phase

    Energy Technology Data Exchange (ETDEWEB)

    Mariscal, A., E-mail: antonio.mariscal@csic.es [Laser Processing Group, Instituto de Óptica, CSIC, C/ Serrano 121, 28006 Madrid (Spain); Quesada, A. [Ceramics for Smart Systems Group, Instituto de Cerámica y Vidrio, C/ Kelsen 5, 28049 Madrid (Spain); Camps, I. [Laser Processing Group, Instituto de Óptica, CSIC, C/ Serrano 121, 28006 Madrid (Spain); Palomares, F.J. [Instituto de Ciencia de Materiales de Madrid, C/ Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain); Fernández, J.F. [Ceramics for Smart Systems Group, Instituto de Cerámica y Vidrio, C/ Kelsen 5, 28049 Madrid (Spain); Serna, R. [Laser Processing Group, Instituto de Óptica, CSIC, C/ Serrano 121, 28006 Madrid (Spain)

    2016-06-30

    Highlights: • PLD production of high quality europium sesquioxide (Eu{sub 2}O{sub 3}) films. • The deposition of Al{sub 2}O{sub 3} capping and/or buffer layers modifies the crystallization for Eu{sub 2}O{sub 3} films upon annealing. • The formation of cubic or monoclinic phases can be favored. • Eu{sup 3+} emission tuning is achieved as a consequence of crystal field effects. - Abstract: We report the growth of europium sesquioxide (Eu{sub 2}O{sub 3}) thin films by pulsed laser deposition (PLD) in vacuum at room temperature from a pure Eu{sub 2}O{sub 3} ceramic bulk target. The films were deposited in different configurations formed by adding capping and/or buffer layers of amorphous aluminum oxide (a-Al{sub 2}O{sub 3}). The optical properties, refractive index and extinction coefficient of the as deposited Eu{sub 2}O{sub 3} layers were obtained. X-ray photoelectron spectroscopy (XPS) measurements were done to assess its chemical composition. Post-deposition annealing was performed at 500 °C and 850 °C in air in order to achieve the formation of crystalline films and to accomplish photoluminescence emission. According to the analysis of X-ray diffraction (XRD) spectra, cubic and monoclinic phases were formed. It is found that the relative amount of the phases is related to the different film configurations, showing that the control over the crystallization phase can be realized by adequately designing the structures. All the films showed photoluminescence emission peaks (under excitation at 355 nm) that are attributed to the intra 4f-transitions of Eu{sup 3+} ions. The emission spectral shape depends on the crystalline phase of the Eu{sub 2}O{sub 3} layer. Specifically, changes in the hypersensitive {sup 5}D{sub 0} → {sup 7}F{sub 2} emission confirm the strong influence of the crystal field effect on the Eu{sup 3+} energy levels.

  11. A theoretical study of the electrical contact between metallic and semiconducting phases in monolayer MoS2

    Science.gov (United States)

    Paz, Wendel S.; Palacios, J. J.

    2017-03-01

    We present a theoretical study of the electrical contact between the two most common crystallographic phases of MoS2 monolayer crystals: the stable semiconducting 2H phase and the metastable metallic 1T phase. A density functional theory (DFT) study of the electronic structure of interface between the two phases shows a higher Schottky barrier for electrons than for holes for the undoped 2H phase. Charge transfer from the 1T to the 2H phase occurs, but, as expected for a one-dimensional contact, the generated dipole potential decays away from the interface and the naive Schottky-Mott band-alignment picture is recovered away from the interface. The decay length of the dipole potential turns out to be larger for the zigzag interface than for the armchair interface due to the different penetration of the edge states into the bulk. Tight-binding quantum transport calculations aided by the DFT results generically confirm a low contact resistance in the range of ≈200-400 Ωμm, as experimentally reported. Furthermore, the contact resistance is predicted to be smaller at the armchair interface for electron injection and, on the contrary, smaller for hole injection at the zigzag interface.

  12. The devitrification of artificial fibers: a multimethodic approach to quantify the temperature-time onset of cancerogenic crystalline phases.

    Science.gov (United States)

    Comodi, Paola; Cera, Fabio; Gatta, Giacomo Diego; Rotiroti, Nicola; Garofani, Patrizia

    2010-11-01

    A variety of artificial fibers extensively employed as lining in high-temperature apparatus may undergo a devitrification process that leads to significant changes in the chemical-physical properties of the materials. Among them, the crystallization of carcinogenic minerals, such as cristobalite, has already been documented for alumino-silicate ceramic fibers. Five fibrous samples with different compositions were treated over a wide range of temperatures (20-1500°C) and times (24-336 h) to investigate the rate and the crystalline phases that are formed as well their onset temperatures. The new phases were characterized by using a multimethodic approach: phase transformations were monitored together with thermal analysis and the new phases were investigated by using X-ray powder diffraction analysis. The crystalline:amorphous ratio was monitored by Rietveld refinement of X-ray diffraction data. Scanning electron microscopy was used to study the effect of heat treatments on the morphology of fibers, and the nanostructures were investigated by transmission electron microscopy (TEM). The results show that the main crystalline phases are cristobalite, diopside, mullite, and zirconia. The onset of cristobalite was observed at temperature lower than that thermodynamically expected. The TEM analysis showed that protostructures were present in the material vitrified from sol-gel-derived products, which can act as crystallization nuclei. The study shows that the devitrification leads to health hazard due to the formation of inhalable powder of cancerogenic crystalline phases.

  13. Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation

    DEFF Research Database (Denmark)

    Diama, A.; Matthies, B.; Herwig, K. W.;

    2009-01-01

    We present evidence from neutron diffraction measurements and molecular dynamics (MD) simulations of three different monolayer phases of the intermediate-length alkanes tetracosane (n-C24H50 denoted as C24) and dotriacontane (n-C32H66 denoted as C32) adsorbed on a graphite basal-plane surface. Our...... show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously...

  14. Transitions between imperfectly ordered crystalline structures: a phase switch Monte Carlo study.

    Science.gov (United States)

    Wilms, Dorothea; Wilding, Nigel B; Binder, Kurt

    2012-05-01

    A model for two-dimensional colloids confined laterally by "structured boundaries" (i.e., ones that impose a periodicity along the slit) is studied by Monte Carlo simulations. When the distance D between the confining walls is reduced at constant particle number from an initial value D(0), for which a crystalline structure commensurate with the imposed periodicity fits, to smaller values, a succession of phase transitions to imperfectly ordered structures occur. These structures have a reduced number of rows parallel to the boundaries (from n to n-1 to n-2, etc.) and are accompanied by an almost periodic strain pattern, due to "soliton staircases" along the boundaries. Since standard simulation studies of such transitions are hampered by huge hysteresis effects, we apply the phase switch Monte Carlo method to estimate the free energy difference between the structures as a function of the misfit between D and D(0), thereby locating where the transitions occur in equilibrium. For comparison, we also obtain this free energy difference from a thermodynamic integration method: The results agree, but the effort required to obtain the same accuracy as provided by phase switch Monte Carlo would be at least three orders of magnitude larger. We also show for a situation where several "candidate structures" exist for a phase, that phase switch Monte Carlo can clearly distinguish the metastable structures from the stable one. Finally, applying the method in the conjugate statistical ensemble (where the normal pressure conjugate to D is taken as an independent control variable), we show that the standard equivalence between the conjugate ensembles of statistical mechanics is violated.

  15. Phase behavior and crystalline structures of cholesteryl ester mixtures: a C-13 MASNMR study.

    Science.gov (United States)

    Guo, W; Hamilton, J A

    1995-06-01

    Cholesteryl esters are a transport and storage form of cholesterol in normal physiology but also a significant lipid in atherosclerotic plaques. To understand better the molecular properties of cholesteryl esters in tissues and plaques, we have studied the polymorphic and mesomorphic features of pure and mixed cholesteryl esters by solid state C-13 NMR with magic angle sample spinning (MASNMR). The temperature-dependent properties of two single components (cholesteryl linoleate (CL, C18:2) and cholesteryl linolenate (CLL, C18:3)), four binary systems (cholesteryl palmitate (CP, C16:0) with CL, CLL or cholesteryl oleate (CO, C18:1), and CO/CL), one ternary system (CO/CP/CL), and one quaternary system (CO/CP/CL/CLL) were studied. The mixing ratios were based on the composition of an atherosclerosis plaque dissected from a cholesterol-fed New Zealand white rabbit. C-13 MASNMR determined the phase transition temperatures, identified the phases present in all systems, and provided novel information about molecular structures. For example, solid CL exhibited a disordered structure with multiple molecular conformations, whereas pure CLL had a crystalline structure different from the three most commonly characterized forms (MLII, MLI, BL). In binary mixtures, the crystalline structure of each cholesteryl ester species was identified by its own characteristic resonances. It was found that CP always existed in its native BL form, but CL and CO were influenced by the composition of the mixture. CL was induced to form MLII crystals by the coexisting CP (55 wt%). When CO was cooled from the isotropic phase, it existed as a mixture of MLII and an amorphous form. The presence of CP significantly accelerated the conversion of the amorphous form to the MLII form. For the ternary mixture co-dried from chloroform, CL cocrystallized with CO in the MLII form and CP existed in BL form. Addition of a small amount of CLL slightly increased the heterogeneity of the solid mixture, but had

  16. Multi-technique Approach for the Evaluation of the Crystalline Phase of Ultrathin High-k Gate Oxide Films

    Science.gov (United States)

    Bersch, E.; LaRose, J. D.; Wells, I.; Consiglio, S.; Clark, R. D.; Leusink, G. J.; Matyi, R. J.; Diebold, A. C.

    2011-11-01

    In order to continue scaling metal oxide semiconductor field effect transistors (MOSFETs) with HfO2 gate oxides, efforts are being made to further improve the deposited high-k film properties. Recently, a process whereby an HfO2 film is deposited through a series of depositions and anneals (so-called DADA process) has been shown to result in films that give rise to MOS capacitors (MOSCAPs) which are electrically scaled compared to MOSCAPs with HfO2 films that only received post deposition anneals (PDA) or no anneals. We have measured as-deposited, DADA and PDA HfO2 films using four measurement techniques, all of which are non-destructive and capable of being used for in-line processing, to evaluate their crystallinity and crystalline phases. Grazing incidence in-plane X-ray diffraction was used to determine the crystalline phases of the HfO2 films. We observed the crystalline phases of these films to be process dependent. Additionally, X-ray and UV photoelectron spectroscopy were used to show the presence of crystallinity in the films. As a fourth technique, spectroscopic ellipsometry was used to determine if the crystalline phases were monoclinic. The combination of techniques was useful in that XPS and UPS were able to confirm the amorphous nature of a 30 cycle DADA film, as measured by GIIXRD, and GIIXRD was able to help us interpret the SE data as being an indication of the monoclinic phase of HfO2.

  17. MRI investigation of water-oil two phase flow in straight capillary, bifurcate channel and monolayered glass bead pack.

    Science.gov (United States)

    Liu, Yu; Jiang, Lanlan; Zhu, Ningjun; Zhao, Yuechao; Zhang, Yi; Wang, Dayong; Yang, Mingjun; Zhao, Jiafei; Song, Yongchen

    2015-09-01

    The study of immiscible fluid displacement between aqueous-phase liquids and non-aqueous-phase liquids in porous media is of great importance to oil recovery, groundwater contamination, and underground pollutant migration. Moreover, the attendant viscous, capillary, and gravitational forces are essential to describing the two-phase flows. In this study, magnetic resonance imaging was used to experimentally examine the detailed effects of the viscous, capillary, and gravitational forces on water-oil flows through a vertical straight capillary, bifurcate channel, and monolayered glass-bead pack. Water flooding experiments were performed at atmospheric pressure and 37.8°C, and the evolution of the distribution and saturation of the oil as well as the characteristics of the two-phase flow were investigated and analyzed. The results showed that the flow paths, i.e., the fingers of the displacing phase, during the immiscible displacement in the porous medium were determined by the viscous, capillary, and gravitational forces as well as the sizes of the pores and throats. The experimental results afford a fundamental understanding of immiscible fluid displacement in a porous medium.

  18. Emergence of topological and topological crystalline phases in TlBiS2 and TlSbS2

    KAUST Repository

    Zhang, Qingyun

    2015-02-11

    Using first-principles calculations, we investigate the band structure evolution and topological phase transitions in TlBiS2 and TlSbS2 under hydrostatic pressure as well as uniaxial and biaxial strain. The phase transitions are identified by parity analysis and by calculating the surface states. Zero, one, and four Dirac cones are found for the (111) surfaces of both TlBiS2 and TlSbS2 when the pressure grows, which confirms trivial-nontrivial-trivial phase transitions. The Dirac cones at the (M) over bar points are anisotropic with large out-of-plane component. TlBiS2 shows normal, topological, and topological crystalline insulator phases under hydrostatic pressure, thus being the first compound to exhibit a phase transition from a topological to a topological crystalline insulator.

  19. Suppression of phase separation in $(AlAs)_{2ML} (InAs)_{2ML}$ superlattices using $Al_{0.48}In_{0.52}$ As monolayer insertions

    CERN Document Server

    Lee, S R; Follstaedt, D M

    2001-01-01

    Al/sub 0.48/In/sub 0.52/As monolayers (ML) are inserted at the binary-compound interfaces of (AlAs)/sub 2/ /sub ML/(InAs)/sub 2/ /sub ML/ short-period superlattices (SPSs) during growth on (001) In P. The insertion of Al/sub 0.48/In/sub 0.52/As interlayers greater than 2 ML thick tends to suppress the phase separation that normally occurs during molecular beam epitaxy of the SPS. The degree of suppression is a sensitive function of both the monolayer-scale thickness, and the intraperiod growth sequence, of the interlayers in the SPS. Given this sensitivity to monolayer-scale variations in the surface-region composition, we propose that cyclical phase transition of the reconstructed surface initiates SPS decomposition. (21 refs).

  20. Control of crystalline phases in magnetic Fe nanoparticles inserted inside a matrix of porous carbon

    Energy Technology Data Exchange (ETDEWEB)

    Fernandez, M.P., E-mail: fernandezpaz.uo@uniovi.e [Dpto. de Fisica, Universidad de Oviedo, Calvo Sotelo, s/n, 33007 Oviedo (Spain); Schmool, D.S. [IN-IFIMUP, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal); Dpto. de Fisica, Universidade do Porto, Rua do Campo Alegre 687, 4440-661 Porto (Portugal); Silva, A.S. [Dpto. de Fisica, Universidade do Porto, Rua do Campo Alegre 687, 4440-661 Porto (Portugal); Sevilla, M.; Fuertes, A.B. [Instituto Nacional del Carbon (CSIC), Apartado 73, 33080 Oviedo (Spain); Gorria, P.; Blanco, J.A. [Dpto. de Fisica, Universidad de Oviedo, Calvo Sotelo, s/n, 33007 Oviedo (Spain)

    2010-05-15

    Two magnetic composites made up of Fe nanoparticles (Fe-NPs) embedded in a porous amorphous carbon matrix are presented. One of the samples, Fe-S-AC, was obtained with the aid of sucrose and the other, Fe-AC, in the absence of this substance. The XRD patterns show Bragg diffraction peaks associated with alpha-Fe and gamma-Fe crystalline phases in the Fe-AC sample, while only peaks corresponding to the alpha-Fe phase are observed for Fe-S-AC powders. The Fe-NPs exhibit broad particle-size distributions for both samples, 5-50 nm for Fe-AC, whereas two populations (2-8 and 10-70 nm) for the Fe-S-AC composite are found. This fact gives rise to poorly defined blocking temperatures, as it can be deduced from the broad maxima observed in M{sub ZFC}(T) variations. In addition, M(H) curves for both Fe-AC and Fe-S-AC samples reveal the existence of exchange-bias effect for T<60 K, probably due to a magnetic coupling within a core/shell structure of the Fe-NPs, although this effect was observed to be less significant for Fe-S-AC.

  1. Liquid crystalline phase as a probe for crystal engineering of lactose: carrier for pulmonary drug delivery.

    Science.gov (United States)

    Patil, Sharvil S; Mahadik, Kakasaheb R; Paradkar, Anant R

    2015-02-20

    The current work was undertaken to assess suitability of liquid crystalline phase for engineering of lactose crystals and their utility as a carrier in dry powder inhalation formulations. Saturated lactose solution was poured in molten glyceryl monooleate which subsequently transformed into gel. The gel microstructure was analyzed by PPL microscopy and SAXS. Lactose particles recovered from gels after 48 h were analyzed for polymorphism using techniques such as FTIR, XRD, DSC and TGA. Particle size, morphology and aerosolisation properties of prepared lactose were analyzed using Anderson cascade impactor. In situ seeding followed by growth of lactose crystals took place in gels with cubic microstructure as revealed by PPL microscopy and SAXS. Elongated (size ∼ 71 μm) lactose particles with smooth surface containing mixture of α and β-lactose was recovered from gel, however percentage of α-lactose was more as compared to β-lactose. The aerosolisation parameters such as RD, ED, %FPF and % recovery of lactose recovered from gel (LPL) were found to be comparable to Respitose® ML001. Thus LC phase (cubic) can be used for engineering of lactose crystals so as to obtain particles with smooth surface, high elongation ratio and further they can be used as carrier in DPI formulations.

  2. New Features on the Phase Transitions of Behenic Acid Monolayers as Unveiled by 2D-Compressibility Coefficient

    Institute of Scientific and Technical Information of China (English)

    GAO Wen-Ying; YU Zhi-Wu

    2008-01-01

    Phase behavior of Langmuir monolayers of behenic acid (BeA) has been examined by two-dimensional compressibility.It was found that phase transitions of BeA could be classified into two distinct categories,named Type-I and Type-II in this work.The former is typified by a positive peak on the compressibility-pressure (β-π)curve,indicating the transition can occur itself in a way of collapse from the initial structure.The latter is characterized by a dropping step on the β-π curve,implying that it cannot happen itself and the driven force is continuous compression.For BeA molecules,compressibility coefficients at the initial and final state are the same,βi=βf,for Type-I phase transition from L2 to L2' state,whilst βi>βf for Type-II phase transition from L.2' state to S state.

  3. Triblock polyphiles through click chemistry: self-assembled thermotropic cubic phases formed by micellar and monolayer vesicular aggregates.

    Science.gov (United States)

    Tan, Xiaoping; Kong, Leiyang; Dai, Heng; Cheng, Xiaohong; Liu, Feng; Tschierske, Carsten

    2013-11-25

    Three series of triblock polyphiles consisting of a rigid 4-phenyl-1,2,3-triazole or 1,4-diphenyl-1,2,3-triazole core with three lipophilic and flexible alkoxyl chains at one end and a polar glycerol group at the opposite end were synthesized by copper-catalyzed azide-alkyne click reactions. Their mesophase behavior was studied by polarizing optical microscopy, differential scanning calorimetry, and XRD. Depending on alkyl chain length and core length, a transition from hexagonal columnar to Pm3n-type cubic phases was observed. In the cubic phases, the molecules are organized as spherical objects. Remarkably, compounds with a longer core unit have a higher tendency to form these cubic phases, and their stability is strongly enhanced over those of the compounds with a shorter core, despite longer cores having a smaller cone angle and therefore being expected to disfavor the formation of spherical objects. There is a large difference in the number of molecules involved in the spherical aggregates formed by compounds with long and short cores. Whereas the aggregates in the cubic phases of the compounds with short rod units are small and could be regarded as micellar, the long-core compounds form much larger aggregates which are regarded as a kind of monolayer vesicular aggregate.

  4. Substrate Biasing during Plasma-Assisted ALD for Crystalline Phase-Control of TiO(2) Thin Films

    NARCIS (Netherlands)

    Profijt, H. B.; M. C. M. van de Sanden,; Kessels, W. M. M.

    2012-01-01

    Substrate biasing has been implemented in a remote plasma atomic layer deposition (ALD) reactor, enabling control of the ion energy up to 260 eV. For TiO(2) films deposited from Ti(Cp(Me))(NMe(2))(3) and O(2) plasma it is demonstrated that the crystalline phase can be tailored by tuning the ion ener

  5. Appearance of large crystalline domains in VO{sub 2} films grown on sapphire (001) and their phase transition characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Azhan, Nurul Hanis; Su, Kui; Okimura, Kunio, E-mail: okifn@keyaki.cc.u-tokai.ac.jp [Graduate School of Science and Technology, Tokai University, Hiratsuka 259-1292 (Japan); Zaghrioui, Mustapha; Sakai, Joe [GREMAN, UMR 7347 CNRS, Université François Rabelais de Tours, Parc de Grandmont 37200 Tours (France)

    2015-06-28

    We report the first observation of large crystalline domains of several μm-size in VO{sub 2} films deposited on Al{sub 2}O{sub 3} (001) substrates by rf-biased reactive sputtering technique. The large crystalline domains, dominated with random in-plane oriented growth of (011){sub M1}-orientation, appear only under adequate substrate biasing, such as 10 W, while most biasing conditions result in conventional nanosized grains of highly oriented (010){sub M1}-orientation. Two temperature-controlled analyses, x-ray diffraction and micro-Raman spectroscopy, have revealed that some parts of large crystalline domains undergo intermediate monoclinic (M2) phase during the thermally-induced structural phase transition from monoclinic (M1) to rutile-tetragonal (R) phase. As an effect of the appearance of large crystalline domains, the film showed in-plane tensile stress, resulting in high T{sub IMT} of 69 °C due to the elongation of the V-V distance in its low-temperature monoclinic phase.

  6. Light-Driven Liquid Crystalline Materials: From Photo-Induced Phase Transitions and Property Modulations to Applications.

    Science.gov (United States)

    Bisoyi, Hari Krishna; Li, Quan

    2016-12-28

    Light-driven phenomena both in living systems and nonliving materials have enabled truly fascinating and incredible dynamic architectures with terrific forms and functions. Recently, liquid crystalline materials endowed with photoresponsive capability have emerged as enticing systems. In this Review, we focus on the developments of light-driven liquid crystalline materials containing photochromic components over the past decade. Design and synthesis of photochromic liquid crystals (LCs), photoinduced phase transitions in LC, and photoalignment and photoorientation of LCs have been covered. Photomodulation of pitch, polarization, lattice constant and handedness inversion of chiral LCs is discussed. Light-driven phenomena and properties of liquid crystalline polymers, elastomers, and networks have also been analyzed. The applications of photoinduced phase transitions, photoalignment, photomodulation of chiral LCs, and photomobile polymers have been highlighted wherever appropriate. The combination of photochromism, liquid crystallinity, and fabrication techniques has enabled some fascinating functional materials which can be driven by ultraviolet, visible, and infrared light irradiation. Nanoscale particles have been incorporated to widen and diversify the scope of the light-driven liquid crystalline materials. The developed materials possess huge potential for applications in optics, photonics, adaptive materials, nanotechnology, etc. The challenges and opportunities in this area are discussed at the end of the Review.

  7. Use of X-ray tomography to map crystalline and amorphous phases in frozen biomaterials.

    Science.gov (United States)

    Bischof, J C; Mahr, B; Choi, J H; Behling, M; Mewes, D

    2007-02-01

    The outcome of both cryopreservation and cryosurgical freezing applications is influenced by the concentration and type of the cryoprotective agent (CPA) or the cryodestructive agent (i.e., the chemical adjuvants referred to here as CDA) added prior to freezing. It also depends on the amount and type of crystalline, amorphous and/or eutectic phases formed during freezing which can differentially affect viability. This work describes the use of X-ray computer tomography (CT) for non-invasive, indirect determination of the phase, solute concentration and temperature within biomaterials (CPA, CDA loaded solutions and tissues) by X-ray attenuation before and after freezing. Specifically, this work focuses on establishing the feasibility of CT (100-420 kV acceleration voltage) to accurately measure the concentration of glycerol or salt as model CPA and CDAs in unfrozen solutions and tissues at 20 degrees C, or the phase in frozen solutions and tissue systems at -78.5 and -196 degrees C. The solutions are composed of water with physiological concentrations of NaCl (0.88% wt/wt) and DMEM (Dulbecco's Modified Eagle's Medium) with added glycerol (0-8 M). The tissue system is chosen as 3 mm thick porcine liver slices as well as 2 cm diameter cores which were either imaged fresh (3-4 h cold ischemia) or after loading with DMEM based glycerol solutions (0-8 M) for times ranging from hours to 7 days at 4 degrees C. The X-ray attenuation is reported in Hounsfield units (HU), a clinical measurement which normalizes X-ray attenuation values by the difference between those of water and air. NaCl solutions from 0 to 23.3% wt/wt (i.e. water to eutectic concentration) were found to linearly correspond to HU in a range from 0 to 155. At -196 degrees C the variation was from -80 to 95 HU while at -78.5 degrees C all readings were roughly 10 HU lower. At 20 degrees C NaCl and DMEM solutions with 0-8 M glycerol loading show a linear variation from 0 to 145 HU. After freezing to -78

  8. Solid-state NMR analysis of a complex crystalline phase of ronacaleret hydrochloride.

    Science.gov (United States)

    Vogt, Frederick G; Williams, Glenn R; Strohmeier, Mark; Johnson, Matthew N; Copley, Royston C B

    2014-08-28

    A crystalline phase of the pharmaceutical compound ronacaleret hydrochloride is studied by solid-state nuclear magnetic resonance (SSNMR) spectroscopy and single-crystal X-ray diffraction. The crystal structure is determined to contain two independent cationic molecules and chloride anions in the asymmetric unit, which combine with the covalent structure of the molecule to yield complex SSNMR spectra. Experimental approaches based on dipolar correlation, chemical shift tensor analysis, and quadrupolar interaction analysis are employed to obtain detailed information about this phase. Density functional theory (DFT) calculations are used to predict chemical shielding and electric field gradient (EFG) parameters for comparison with experiment. (1)H SSNMR experiments performed at 16.4 T using magic-angle spinning (MAS) and homonuclear dipolar decoupling provide information about hydrogen bonding and molecular connectivity that can be related to the crystal structure. (19)F and (13)C assignments for the Z' = 2 structure are obtained using DFT calculations, (19)F homonuclear dipolar correlation, and (13)C-(19)F heteronuclear dipolar correlation experiments. (35)Cl MAS experiments at 16.4 T observe two chlorine sites that are assigned using calculated chemical shielding and EFG parameters. SSNMR dipolar correlation experiments are used to extract (1)H-(13)C, (1)H-(15)N, (1)H-(19)F, (13)C-(19)F, and (1)H-(35)Cl through-space connectivity information for many positions of interest. The results allow for the evaluation of the performance of a suite of SSNMR experiments and computational approaches as applied to a complex but typical pharmaceutical solid phase.

  9. Molecular packing density of a self-assembled monolayer formed from N-(2-aminoethyl)-3-aminopropyltriethoxysilane by a vapor phase process.

    Science.gov (United States)

    Sugimura, Hiroyuki; Moriguchi, Takahiro; Kanda, Masao; Sonobayashi, Yutaka; Nishimura, Hirohito M; Ichii, Takashi; Murase, Kuniaki; Kazama, Shingo

    2011-08-21

    The molecular density of an aminosilane self-assembled monolayer formed from N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAPS) by a vapor phase method has been estimated to be about 3 AEAPS molecules per nm(2) based on chemical labeling, optical absorption spectroscopy and X-ray photoelectron spectroscopy.

  10. Molecular packing density of a self-assembled monolayer formed from N-(2-aminoethyl)-3-aminopropyltriethoxysilane by a vapor phase process.

    OpenAIRE

    2011-01-01

    The molecular density of an aminosilane self-assembled monolayer formed from N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAPS) by a vapor phase method has been estimated to be about 3 AEAPS molecules per nm(2) based on chemical labeling, optical absorption spectroscopy and X-ray photoelectron spectroscopy.

  11. Crystalline-to-plastic phase transitions in molecularly thin n-dotriacontane films adsorbed on solid surfaces

    DEFF Research Database (Denmark)

    Cisternas, Edgardo; Corrales, T. P.; del Campo, V.;

    2009-01-01

    Crystalline-to-rotator phase transitions have been widely studied in bulk hydrocarbons, in particular in normal alkanes. But few studies of these transitions deal with molecularly thin films of pure n-alkanes on solid substrates. In this work, we were able to grow dotriacontane (n-C32H66) films...... identify with a solid-solid phase transition. At higher coverages, we observed additional steps in the ellipsometric signal that we identify with a solid-solid phase transition in multilayer islands (similar to 333 K) and with the transition to the rotator phase in bulk crystallites (similar to 337 K...

  12. Formation of a 1,8-octanedithiol self-assembled monolayer on Au(111) prepared in a lyotropic liquid-crystalline medium.

    Science.gov (United States)

    García Raya, Daniel; Madueño, Rafael; Blázquez, Manuel; Pineda, Teresa

    2010-07-20

    A characterization of the 1,8-octanedithiol (ODT) self-assembled monolayer (SAM) formed from a Triton X-100 lyotropic medium has been conducted by electrochemical techniques. It is found that an ODT layer of standing-up molecules is obtained at short modification time without removing oxygen from the medium. The electrochemical study shows that the ODT layer formed after 15 min of modification time has similar electron-transfer blocking properties to the layers formed from organic solvents at much longer modification times. On the basis of XPS data, it is demonstrated that the inability to bind gold nanoparticles (AuNPs) is due to the presence of extra ODT molecules either interdigited or on top of the layer. Treatment consisting of an acid washing step following the formation of the ODT-Au(111) SAM produces a layer that is able to attach AuNPs as demonstrated by electrochemical techniques and atomic force microscopy (AFM) images.

  13. Scanning tunneling microscopic and spectroscopic studies on a crystalline silica monolayer epitaxially formed on hexagonal SiC(0001¯) surfaces

    Science.gov (United States)

    Tochihara, Hiroshi; Shirasawa, Tetsuroh; Suzuki, Takayuki; Miyamachi, Toshio; Kajiwara, Takashi; Yagyu, Kazuma; Yoshizawa, Shunsuke; Takahashi, Toshio; Tanaka, Satoru; Komori, Fumio

    2014-02-01

    An epitaxial silicon-oxide monolayer of chemical composition of Si2O3 (the Si2O3 layer) formed on hexagonal SiC(0001¯) surfaces has been observed by scanning tunneling microscopy (STM). Filled- and empty-state STM images with atomic resolution support the previously reported model. Typical structural defects in the Si2O3 layer are found to be missing SiOn (n = 1, 2, 3) molecules. The band gap of the Si2O3 layer obtained by point tunneling spectroscopy is 5.5±0.5 eV, exhibiting considerable narrowing from that of bulk SiO2, 8.9 eV. It is proposed that the Si2O3 layer is suitable as a relevant interface material for formation of SiC-based metal-oxide-semiconductor devices.

  14. Phase behaviour of self-assembled monolayers controlled by tuning physisorbed and chemisorbed states: A lattice-model view.

    Science.gov (United States)

    Fortuna, Sara; Cheung, David L; Johnston, Karen

    2016-04-07

    The self-assembly of molecules on surfaces into 2D structures is important for the bottom-up fabrication of functional nanomaterials, and the self-assembled structure depends on the interplay between molecule-molecule interactions and molecule-surface interactions. Halogenated benzene derivatives on platinum have been shown to have two distinct adsorption states: a physisorbed state and a chemisorbed state, and the interplay between the two can be expected to have a profound effect on the self-assembly and phase behaviour of these systems. We developed a lattice model that explicitly includes both adsorption states, with representative interactions parameterised using density functional theory calculations. This model was used in Monte Carlo simulations to investigate pattern formation of hexahalogenated benzene molecules on the platinum surface. Molecules that prefer the physisorbed state were found to self-assemble with ease, depending on the interactions between physisorbed molecules. In contrast, molecules that preferentially chemisorb tend to get arrested in disordered phases. However, changing the interactions between chemisorbed and physisorbed molecules affects the phase behaviour. We propose functionalising molecules in order to tune their adsorption states, as an innovative way to control monolayer structure, leading to a promising avenue for directed assembly of novel 2D structures.

  15. Patterning of self-assembled monolayers by phase-shifting mask and its applications in large-scale assembly of nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Fan; Zhang, Dakuan; Wang, Jianyu; Sheng, Yun; Wang, Xinran; Chen, Kunji; Zhou, Minmin [Key Laboratory of Advanced Photonic and Electronic Materials and School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China); Yan, Shancheng [Key Laboratory of Advanced Photonic and Electronic Materials and School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China); School of Geography and Biological Information, Nanjing University of Posts and Telecommunications, Nanjing 210046 (China); Shen, Jiancang; Pan, Lijia; Shi, Yi, E-mail: yshi@nju.edu.cn [Key Laboratory of Advanced Photonic and Electronic Materials and School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China); Collaborative Innovation Center of Advanced Micro-structures, Nanjing University, Nanjing 210093 (China)

    2015-01-26

    A nonselective micropatterning method of self-assembled monolayers (SAMs) based on laser and phase-shifting mask (PSM) is demonstrated. Laser beam is spatially modulated by a PSM, and periodic SAM patterns are generated sequentially through thermal desorption. Patterned wettability is achieved with alternating hydrophilic/hydrophobic stripes on octadecyltrichlorosilane monolayers. The substrate is then used to assemble CdS semiconductor nanowires (NWs) from a solution, obtaining well-aligned NWs in one step. Our results show valuably the application potential of this technique in engineering SAMs for integration of functional devices.

  16. A novel technique for production of nano-crystalline mono tungsten carbide single phase via mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Razavi, Mansour, E-mail: m-razavi@merc.ac.ir [Materials and Energy Research Center (MERC), P.O. Box 14155-4777, Tehran (Iran, Islamic Republic of); Rahimipour, Mohammad Reza; Yazdani-Rad, Rahim [Materials and Energy Research Center (MERC), P.O. Box 14155-4777, Tehran (Iran, Islamic Republic of)

    2011-06-09

    Highlights: > By adding WC to mixture of tungsten and carbon black unlike the system which does not contain any additive, it can lead to synthesized mono carbide tungsten. > However, the synthesize time has been reduced significantly. > Crystalline size of two systems were in nano-meter scale, this amount in system contain primary WC which was smaller than system without WC. - Abstract: Due to simultaneous synthesis of WC and W{sub 2}C phases in most of the synthesis processes and lower mechanical properties of W{sub 2}C than WC, in this work the possibility of production of nano-crystalline WC single phase as a useful refractory ceramic by means of mechanical alloying has been investigated. The raw materials containing W and C with WC were milled in a planetary ball mill. The sampling has been done in different times. As it was expected, XRD studies showed that after 75 h of milling the WC with W{sub 2}C were produced. By adding WC to the raw materials in the beginning of the process it led to the fact that after 50 h of milling WC was synthesized only without any other phases which remained stable at the higher times while milling. During broadening of XRD peaks, the size of synthesized crystalline WC was estimated in the order of nano-meter. Crystalline size and mean strain of synthesized WC in the system without additive were higher and lower than the system containing WC, respectively.

  17. Coarse-grained electrostatic interactions of coronene: Towards the crystalline phase

    Energy Technology Data Exchange (ETDEWEB)

    Heinemann, Thomas, E-mail: thomas.heinemann@tu-berlin.de; Klapp, Sabine H. L., E-mail: klapp@physik.tu-berlin.de [Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin (Germany); Palczynski, Karol, E-mail: karol.palczynski@helmholtz-berlin.de; Dzubiella, Joachim, E-mail: joachim.dzubiella@helmholtz-berlin.de [Institut für Physik, Humboldt Universität zu Berlin, Newtonstraße 15, 12489 Berlin (Germany); Institut für Weiche Materie und Funktionale Materialen, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner Platz 1, 14109 Berlin (Germany)

    2015-11-07

    In this article, we present and compare two different, coarse-grained approaches to model electrostatic interactions of disc-shaped aromatic molecules, specifically coronene. Our study builds on our previous work [T. Heinemann et al., J. Chem. Phys. 141, 214110 (2014)], where we proposed, based on a systematic coarse-graining procedure starting from the atomistic level, an anisotropic effective (Gay-Berne-like) potential capable of describing van der Waals contributions to the interaction energy. To take into account electrostatics, we introduce, first, a linear quadrupole moment along the symmetry axis of the coronene disc. The second approach takes into account the fact that the partial charges within the molecules are distributed in a ring-like fashion. We then reparametrize the effective Gay-Berne-like potential such that it matches, at short distances, the ring-ring potential. To investigate the validity of these two approaches, we perform many-particle molecular dynamics simulations, focusing on the crystalline phase (karpatite) where electrostatic interaction effects are expected to be particularly relevant for the formation of tilted stacked columns. Specifically, we investigate various structural parameters as well as the melting transition. We find that the second approach yields consistent results with those from experiments despite the fact that the underlying potential decays with the wrong distance dependence at large molecule separations. Our strategy can be transferred to a broader class of molecules, such as benzene or hexabenzocoronene.

  18. Coarse-grained electrostatic interactions of coronene: Towards the crystalline phase.

    Science.gov (United States)

    Heinemann, Thomas; Palczynski, Karol; Dzubiella, Joachim; Klapp, Sabine H L

    2015-11-07

    In this article, we present and compare two different, coarse-grained approaches to model electrostatic interactions of disc-shaped aromatic molecules, specifically coronene. Our study builds on our previous work [T. Heinemann et al., J. Chem. Phys. 141, 214110 (2014)], where we proposed, based on a systematic coarse-graining procedure starting from the atomistic level, an anisotropic effective (Gay-Berne-like) potential capable of describing van der Waals contributions to the interaction energy. To take into account electrostatics, we introduce, first, a linear quadrupole moment along the symmetry axis of the coronene disc. The second approach takes into account the fact that the partial charges within the molecules are distributed in a ring-like fashion. We then reparametrize the effective Gay-Berne-like potential such that it matches, at short distances, the ring-ring potential. To investigate the validity of these two approaches, we perform many-particle molecular dynamics simulations, focusing on the crystalline phase (karpatite) where electrostatic interaction effects are expected to be particularly relevant for the formation of tilted stacked columns. Specifically, we investigate various structural parameters as well as the melting transition. We find that the second approach yields consistent results with those from experiments despite the fact that the underlying potential decays with the wrong distance dependence at large molecule separations. Our strategy can be transferred to a broader class of molecules, such as benzene or hexabenzocoronene.

  19. Germanium ion implantation to Improve Crystallinity during Solid Phase Epitaxy and the effect of AMU Contamination

    Science.gov (United States)

    Lee, K. S.; Yoo, D. H.; Son, G. H.; Lee, C. H.; Noh, J. H.; Han, J. J.; Yu, Y. S.; Hyung, Y. W.; Yang, J. K.; Song, D. G.; Lim, T. J.; Kim, Y. K.; Lee, S. C.; Lee, H. D.; Moon, J. T.

    2006-11-01

    Germanium ion implantation was investigated for crystallinity enhancement during solid phase epitaxial regrowth (SPE) using high current implantation equipment. Electron back-scatter diffraction(EBSD) measurement showed numerical increase of 19 percent of signal, which might be due to pre-amorphization effect on silicon layer deposited by LPCVD process with germanium ion implantation. On the other hand, electrical property such as off-leakage current of NMOS transistor degraded in specific regions of wafers, which implied non-uniform distribution of donor-type impurities into channel area. It was confirmed that arsenic atoms were incorporated into silicon layer during germanium ion implantation. Since the equipment for germanium pre-amorphization implantation(PAI) was using several source gases such as BF3 and AsH3, atomic mass unit(AMU) contamination during PAI of germanium with AMU 74 caused the incorporation of arsenic with AMU 75 which resided in arc-chamber and other parts of the equipment. It was effective to use germanium isotope of AMU 72 to suppress AMU contamination, however it led serious reduction of productivity because of decrease in beam current by 30 percent as known to be difference in isotope abundance. It was effective to use enriched germanium source gas with AMU 72 in order to improve productivity. Spatial distribution of arsenic impurities in wafers was closely related to hardware configuration of ion implantation equipment.

  20. Effect of Alkali Ions on the Amorphous to Crystalline Phase Transition of Silica

    Science.gov (United States)

    Venezia, A. M.; La Parola, V.; Longo, A.; Martorana, A.

    2001-11-01

    The effect of the addition of alkali ions to commercial amorphous silica, generally used as support for heterogeneous catalysts, has been investigated from the point of view of morphological and structural changes. Samples of alkali-doped silica were prepared by impregnation and subsequent calcination at various temperatures. The structural effect of Li, Na, K, and Cs was determined by use of techniques such as wide-angle (WAXS) and small-angle X-ray scattering (SAXS). The WAXS diffractograms, analyzed with the Rietveld method using the GSAS program, allowed qualitative and quantitative identification of the fraction of the different silica polymorphs like quartz, tridymite, and cristobalite. SAXS measurements, using the classical method based on Porod's law, yielded the total surface area of the systems. The calculated areas were compared with the surface areas determined by the nitrogen adsorption technique using the analytical method of Brunauer-Emmett-Teller. The results are explained in terms of sizes of the alkali ions and cell volume of the different crystalline phases.

  1. Second amorphous-to-crystalline phase transformation in Cu60Ti20Zr20 bulk metallic glass

    DEFF Research Database (Denmark)

    Cao, Q.P.; Li, J.F.; Zhang, P.N.

    2007-01-01

    is estimated to be about 2.46 kJ mol(-1) at 753 K, much smaller than the 61 kJ mol(-1) obtained assuming that it is a polymorphic transformation. It was revealed that the phase transformation occurs through a eutectic crystallization of Cu51Zr14 and Cu2TiZr14 having an effective activation energy of the order......The second amorphous-to-crystalline phase transformation in Cu60Ti20Zr20 bulk metallic glass was investigated by differential scanning calorimetry and x-ray diffractometry. The difference of the Gibbs free energies between the amorphous phase and the crystalline products during the transformation...

  2. Analysis of coal tar polycyclic aromatic hydrocarbon LC-fractions by capillary SFC on a liquid crystalline stationary phase

    Energy Technology Data Exchange (ETDEWEB)

    Kithinji, J.P.; Raynor, M.W.; Egia, B.; Davies, I.L.; Bartle, K.D.; Clifford, A.A. (University of Leeds, Leeds (UK). School of Chemistry)

    1990-01-01

    Supercritical fluid chromatography (SFC) on a capillary column coated with a smectic mesomorphic crystalline phase is shown to exhibit a typical turnover effect (retention versus column temperature) for polycyclic aromatic hydrocarbons (PAHs) at lower temperatures than are found on a methylpolysiloxane phase. Liquid chromatography is used to separate various fractions from a coal tar, which are analyzed by high resolution capillary SFC. Different density and temperature programs were investigated to optimize the separations. Simultaneous density and temperature programs gave the best results, and this is thought to be due to increased solute diffusion coefficients which yield highly efficient separations for the high molecular weight polycyclic aromatic hydrocarbons. The separation mechanism is based on the shape of the liquid crystalline phase, solubility, volatility, and molecular geometry of the PAHs.

  3. First-principles computation of mantle materials in crystalline and amorphous phases

    Science.gov (United States)

    Karki, Bijaya B.

    2015-03-01

    First-principles methods based on density functional theory are used extensively in the investigation of the behavior and properties of mantle materials over broad ranges of pressure, temperature, and composition that are relevant. A review of computational results reported during the last couple of decades shows that essentially all properties including structure, phase transition, equation of state, thermodynamics, elasticity, alloying, conductivity, defects, interfaces, diffusivity, viscosity, and melting have been calculated from first principles. Using MgO, the second most abundant oxide of Earth's mantle, as a primary example and considering many other mantle materials in their crystalline and amorphous phases, we have found that most properties are strongly pressure dependent, sometimes varying non-monotonically and anomalously, with the effects of temperature being systematically suppressed with compression. The overall agreement with the available experimental data is excellent; it is remarkable that the early-calculated results such as shear wave velocities of two key phases, MgO and MgSiO3 perovskite, were subsequently reproduced by experimentation covering almost the entire mantle pressure regime. As covered in some detail, the defect formation and migration enthalpies of key mantle materials increase with pressure. The predicted trend is that partial MgO Schottky defects are energetically most favorable in Mg-silicates but their formation enthalpies are high. So, the diffusion in the mantle is likely to be in the extrinsic regime. Preliminary results on MgO and forsterite hint that the grain boundaries can accommodate point defects (including impurities) and enhance diffusion rates at all pressures. The structures are highly distorted in the close vicinity of the defects and at the interface with excess space. Recent simulations of MgO-SiO2 binary and other silicate melts have found that the melt self-diffusion and viscosity vary by several orders of

  4. Characterization of single crystalline ZnTe and ZnSe grown by vapor phase transport

    Energy Technology Data Exchange (ETDEWEB)

    Trigubo, A B; Di Stefano, M C [FRBA-UTN, (1179) Buenos Aires (Argentina); Aguirre, M H [Dpto de Quim Inorg, Fac de Cs Quim, Univ Complutense, (28040) Madrid (Spain); Martinez, A M; D' Elia, R; Canepa, H; Heredia, E, E-mail: atrigubo@citefa.gov.a [CINSO-CITEFA: (1603) Villa Martelli, Pcia de Buenos Aires (Argentina)

    2009-05-01

    Tubular furnaces were designed and built to obtain single crystalline ZnTe and ZnSe ingots using respectively physical and chemical transport methods. Different temperature profiles and growth rates were analyzed in order to optimize the necessary crystalline quality for device development. Optical and scanning electron micrographs of the corrosion figures produced by chemical etching were used to obtain the dislocation density and the misorientation between adjacent subgrains in ZnTe and ZnSe wafers. Structural quality of the single crystalline material was determined by transmission electronic microscopy. Optical transmittance was measured by infrared transmission spectrometry and the resulting values were compared to commercial samples.

  5. Scanning tunneling microscopic and spectroscopic studies on a crystalline silica monolayer epitaxially formed on hexagonal SiC(0001{sup ¯}) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Tochihara, Hiroshi, E-mail: tochihara@fukuoka-u.ac.jp, E-mail: tochihara.hiroshi.146@m.kyushu-u.ac.jp; Suzuki, Takayuki; Yagyu, Kazuma [Department of Electronics Engineering and Computer Science, Fukuoka University, Fukuoka 814-0180 (Japan); Shirasawa, Tetsuroh; Takahashi, Toshio [Laser and Synchrotron Research Center, Institute for Solid State Physics, University of Tokyo, Chiba 277-8581 (Japan); Miyamachi, Toshio; Yoshizawa, Shunsuke; Komori, Fumio [Nanoscale Science Division, Institute for Solid State Physics, University of Tokyo, Chiba 277-8581 (Japan); Kajiwara, Takashi; Tanaka, Satoru [Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka 819-0395 (Japan)

    2014-02-03

    An epitaxial silicon-oxide monolayer of chemical composition of Si{sub 2}O{sub 3} (the Si{sub 2}O{sub 3} layer) formed on hexagonal SiC(0001{sup ¯}) surfaces has been observed by scanning tunneling microscopy (STM). Filled- and empty-state STM images with atomic resolution support the previously reported model. Typical structural defects in the Si{sub 2}O{sub 3} layer are found to be missing SiO{sub n} (n = 1, 2, 3) molecules. The band gap of the Si{sub 2}O{sub 3} layer obtained by point tunneling spectroscopy is 5.5±0.5 eV, exhibiting considerable narrowing from that of bulk SiO{sub 2}, 8.9 eV. It is proposed that the Si{sub 2}O{sub 3} layer is suitable as a relevant interface material for formation of SiC-based metal-oxide-semiconductor devices.

  6. Ultrasonic study of the shear mechanical impedance of butyloxybenzylidene octylaniline near the crystalline-B-smectic-A phase transition

    OpenAIRE

    Thiriet, Y.; Martinoty, P.

    1982-01-01

    We report a detailed study of the shear mechanical impedance near the crystalline-B-smectic-A transition in butyloxybenzylidene octylaniline (40.8). The measurements were performed at various frequencies from 5 to 85 MHz for shear waves propagating along the normal to the layers. In both phases the material response presents strong relaxation effects. The structure change at the transition is indicated by an increase in the real part of the shear impedance. The results at 85 MHz are those exp...

  7. The surface quasiliquid melt acceleration and the role of thermodynamic phase in the thermal decomposition of crystalline organic explosives

    Energy Technology Data Exchange (ETDEWEB)

    Henson, Bryan F [Los Alamos National Laboratory

    2010-01-01

    We show that melt acceleration in the thermal decomposition of crystalline organic solids is a manifestation of the surface quasiliquid phase. We derive a single universal rate law for melt acceleration that is a simple function of the metastable liquid activity below the melting point, and has a zero order term proportional to the quasiliquid thickness. We argue that the underlying mechanisms of this model will provide a molecular definition for the stability of the class of secondary explosives.

  8. Predicting primary crystalline phase and liquidus temperature above or below 1050{degrees}C as functions of glass composition

    Energy Technology Data Exchange (ETDEWEB)

    Redgate, P.E.; Piepel, G.F.

    1996-02-01

    This report presents the results of applying statistical empirical modeling techniques to primary crystalline phase at the liquidus temperature (T{sub L}) and (ii) whether liquidus temperature is above or below 1050{degree}C (1OO{degree}C below a melting temperature of 1150{degree}C). Data used in modeling primary crystalline phase and liquidus temperate are from the Composition Variability Study (CVS) of Hanford waste glass compositions and properties. The majority of the 123 CVS glasses are categorized into one of 13 primary crystalline phases (at the liquidus temperature). They are also classified as to having T{sub L} Above or Below 1050{degree}C. Two common statistical methods used to model such categorical data are the multinomial logit and classification tree models. The classification tree models provided an overall better modeling approach than did the multinomial logit models. The performance of models in this report should be compared to the performance of the revised ``Development of Models and Software for Liquidus Temperature of Glasses of HWVP Products`` models from Ecole Polytechnique. If the Ecole Polytechnique models perform better than the models discussed in this report, no additional effort on these models would be needed. However, if the converse is true, it may be worthwhile to invest additional effort on statistical empirical modeling methods.

  9. Selecting polymers for two-phase partitioning bioreactors (TPPBs): Consideration of thermodynamic affinity, crystallinity, and glass transition temperature.

    Science.gov (United States)

    Bacon, Stuart L; Peterson, Eric C; Daugulis, Andrew J; Parent, J Scott

    2015-01-01

    Two-phase partitioning bioreactor technology involves the use of a secondary immiscible phase to lower the concentration of cytotoxic solutes in the fermentation broth to subinhibitory levels. Although polymeric absorbents have attracted recent interest due to their low cost and biocompatibility, material selection requires the consideration of properties beyond those of small molecule absorbents (i.e., immiscible organic solvents). These include a polymer's (1) thermodynamic affinity for the target compound, (2) degree of crystallinity (wc ), and (3) glass transition temperature (Tg ). We have examined the capability of three thermodynamic models to predict the partition coefficient (PC) for n-butyric acid, a fermentation product, in 15 polymers. Whereas PC predictions for amorphous materials had an average absolute deviation (AAD) of ≥16%, predictions for semicrystalline polymers were less accurate (AAD ≥ 30%). Prediction errors were associated with uncertainties in determining the degree of crystallinity within a polymer and the effect of absorbed water on n-butyric acid partitioning. Further complications were found to arise for semicrystalline polymers, wherein strongly interacting solutes increased the polymer's absorptive capacity by actually dissolving the crystalline fraction. Finally, we determined that diffusion limitations may occur for polymers operating near their Tg , and that the Tg can be reduced by plasticization by water and/or solute. This study has demonstrated the impact of basic material properties that affects the performance of polymers as sequestering phases in TPPBs, and reflects the additional complexity of polymers that must be taken into account in material selection.

  10. Morphology of self assembled monolayers using liquid phase reaction on silica and their effect on the morphology of adsorbed insulin

    Science.gov (United States)

    Sharma, Indu; Pattanayek, Sudip K.; Aggarwal, Varsha; Ghosh, Subhasis

    2017-05-01

    The effect of roughness of two different categories of self-assembled monolayers (SAMs) with propyl amine and propyl groups respectively on the morphology of adsorbed insulin is observed. SAMs are obtained by liquid phase reaction of silica with organo silane coupling agents (SCA). The influence of the morphology and physical characteristics of the SAMs on the reaction time and concentration of the modifiers are explored. We have tested three SCA containing propyl amine with varying groups linked to Si present on it. In addition, we have used a silane coupling agent to prepare SAM of methyl head group. The approach of these molecules towards the surface depends on the head group and the groups linked to Si of the SCA. The morphology of the surfaces is analysed using power spectral density distribution (PSD), skewness, ellipsometry thickness and surface energy. Both chemical nature and physical morphology of the adsorbent influence the morphology of the adsorbed insulin. In general, a low number of aggregates of big size are formed on the surfaces obtained from low concentration of SAMs, while a higher number but of smaller size of aggregates are formed over surfaces obtained from 1% concentration of SAMs modifiers. The peak to valley ratio of the aggregates of insulin is strongly influenced by the size of grains of SCA over the adsorbent.

  11. Effect of trans-cis photoisomerization on phase equilibria and phase transition of liquid-crystalline azobenzene chromophore and its blends with reactive mesogenic diacrylate.

    Science.gov (United States)

    Kim, Namil; Li, Quan; Kyu, Thein

    2011-03-01

    Photoisomerization-induced phase transition of neat liquid-crystalline azobenzene chromophore (LCAC) and its effect on phase diagrams of its mixtures with reactive mesogenic diacrylate monomer (RM257) have been investigated experimentally and theoretically. Upon irradiation with ultraviolet light, the nematic phase of LCAC transformed to isotropic, while the crystal phase showed corrugated textures on the surface (i.e., ripples). The phase-transition temperatures and corresponding morphologies of the blends have been investigated by means of differential scanning calorimetry and optical microscopy. A theoretical phase diagram of a binary nematic and crystalline system was constructed by self-consistently solving the combined free energies of Flory-Huggins, Maier-Saupe, and phase-field theory. The calculation revealed various coexistence regions such as nematic + liquid (N₁ + L₂), crystal + liquid (Cr₁ + L₂), crystal + nematic (Cr₁ + N₂), and crystal + crystal (Cr₁ + Cr₂) over a broad range of compositions including the single-phase nematic (N₁, N₂) of the corresponding constituents. The calculated liquidus lines were in good accord with the depressed mesophase-isotropic transition points. The present paper demonstrates the effect of trans-cis photoisomerization on the mesophase transitions of neat LCAC and the phase diagram of LCAC-RM257 as well as on the ripple formation (i.e., periodic undulation) on the azobenzene crystals.

  12. Short-Range Order of Mesomorphic Phase of a Semi-crystalline Polymer by Solid-State NMR: Isotactic Polypropylene

    Science.gov (United States)

    Yuan, Shichen; Miyoshi, Toshikazu

    2015-03-01

    Mesophase is intermediate phase between crystalline and melt state. Characterization of short-range structures of disordered mesomorphic phase without long-range order is challenging issue in polymer characterization. The short range order was considered same as α or β i PP, or neither. In this work, a new strategy using 13C-13C through space interactions as well as molecular dynamics based on chemical shift anisotropy (CSA) re-orientation is proposed for evaluating short-range order of mesophase of isotactic-polypropylene (iPP). 13C-13C double quantum (DQ) build up curves of 13C 15 percent CH3 selectively labeled iPP and spin dynamics simulations elucidate that local packing structures in mesophase is very close to that in β phase. Moreover, exchange NMR proves that the crystalline chains perform large amplitude motions in all α, β, and mesophase. The correlation time of overall dynamics of stems in mesophase follows the same Arrhenius line with that of β phase but is largely deviated from the Arrhenius line of the α phase. Through the obtained results, it is concluded that short-range order in mesophase is exceedingly close or same to those in β phase. This work was financially supported by the National Science Foundation (Grant No. DMR-1105829) and by UA startup funds.

  13. Crystalline phase transition information induced by high temperature susceptibility transformations in bulk PMP-YBCO superconductor growth in-situ

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, C.P., E-mail: zhangcp6813@126.com [SMRC, Northwest Institute for Non-ferrous Metal Research, Xi’an (China); Physics Department, Université Joseph Fourier, Grenoble (France); State Key Lab of Solidification Processing, Northwest Polytechnical University, Xi’an (China); Chaud, X. [CRETA/CNRS, 25 avenue des martyrs, 38042 Grenoble Cedex 9 (France); Beaugnon, E. [Physics Department, Université Joseph Fourier, Grenoble (France); CRETA/CNRS, 25 avenue des martyrs, 38042 Grenoble Cedex 9 (France); Zhou, L. [SMRC, Northwest Institute for Non-ferrous Metal Research, Xi’an (China); State Key Lab of Solidification Processing, Northwest Polytechnical University, Xi’an (China)

    2015-01-15

    Highlights: • It was the first time we measured the susceptibility of bulk YBCO in powder-melting-process at high temperature up to 1060 °C. • It revealed that the crystalline phase transition of bulk PMP-YBCO growth in process. • A new discovery of Y123 phase pre-formed then melted in heating stage has been found. • It discovered that Y123 crystal solidification started at 1004 °C in cooling stage in PMP route. - Abstract: The dynamic susceptibility transformations of bulk HTSC PMP-YBCO growth have been investigated from 200 °C up to 1060 °C by the Faraday Balance in-situ. It revealed that the crystalline phase transitions of bulk PMP-YBCO growth in process. A new discovery of Y123 phase pre-formed then melted in heating stage has been found. It also discovered that Y123 crystal solidification started at 1004 °C in cooling stage. Before Y123 solidification the liquid phase CuO change to Cu{sub 2}O reciprocally as well as the copper ion valence changed between divalent Cu{sup 2+} and trivalent Cu{sup 1+} each other. It was essential to keep quantities of CuO phase instead of the Cu{sub 2}O for Y123 crystal solidification.

  14. Formation Mechanism and Control of Perovskite Films from Solution to Crystalline Phase Studied by in Situ Synchrotron Scattering.

    Science.gov (United States)

    Chang, Chun-Yu; Huang, Yu-Ching; Tsao, Cheng-Si; Su, Wei-Fang

    2016-10-12

    Controlling the crystallization and morphology of perovskite films is crucial for the fabrication of high-efficiency perovskite solar cells. For the first time, we investigate the formation mechanism of the drop-cast perovskite film from its precursor solution, PbCl2 and CH3NH3I in N,N-dimethylformamide, to a crystalline CH3NH3PbI3-xClx film at different substrate temperatures from 70 to 180 °C in ambient air and humidity. We employed an in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) technique for this study. When the substrate temperature is at or below 100 °C, the perovskite film is formed in three stages: the initial solution stage, transition-to-solid film stage, and transformation stage from intermediates into a crystalline perovskite film. In each stage, the multiple routes for phase transformations are preceded concurrently. However, when the substrate temperature is increased from 100 to 180 °C, the formation mechanism of the perovskite film is changed from the "multistage formation mechanism" to the "direct formation mechanism". The proposed mechanism has been applied to understand the formation of a perovskite film containing an additive. The result of this study provides a fundamental understanding of the functions of the solvent and additive in the solution and transition states to the crystalline film. It provides useful knowledge to design and fabricate crystalline perovskite films for high-efficiency solar cells.

  15. Patterning silver nanocubes in monolayers using phase separated lipids as templates

    Energy Technology Data Exchange (ETDEWEB)

    Ahamad, Nur; Prezgot, Daniel; Ianoul, Anatoli, E-mail: anatoli_ianoul@carleton.ca [Carleton University, Department of Chemistry (Canada)

    2012-02-15

    Strategies for assembling silver nanocubes (NCs) into distinct 2D patterns on Langmuir-Blodgett (LB) films are demonstrated using two different lipid mixtures as vehicles: (1) raft mixtures containing 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), sphingomyelin (SPM), and cholesterol in different mole ratios (2:2:1 and 1:1:1) and (2) 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) at a 1:3 mol ratio. Atomic force microscopy was employed to unveil the mechanisms of such pattern formation in the LB film. The results demonstrate that aggregation of NCs into round-like pattern is governed by preferential localization of NCs within the liquid condensed (LC) domains of DOPC/SPM/Cholesterol mixture. Cholesterol was found to govern the size and shape of the rounded islands. On the other hand, incorporation of NCs within the liquid expanded (LE) phase of DPPC/DLPC mixture produced linear-branched chains, oriented normal to the Langmuir film transfer direction. The as engineered patterns of silver NCs exhibited characteristic plasmonic signatures. Our results reveal the potential in assembling plasmonic metal nanoparticles into diverse patterns on solid substrates by exploiting their preferential localization either in LC or LE phase of appropriate lipid mixture in Langmuir film.

  16. The structural properties of uncompressed crystalline monolayers of alcohols CnH2n+1OH(n=13-31) on water and their role as ice nucleators

    DEFF Research Database (Denmark)

    Majewski, J.; Popovitz-Biro, R.; Bouwman, W.G.;

    1995-01-01

    to 13. The relative amount of two dimensional (2-D crystalline material formed fell drastically; shorter crystalline coherence lengths were also observed. For n = 31-18 the molecules are arranged in a rectangular cell (a approximate to 5 Angstrom, b increases from ca. 7.4 to ca. 8.2 Angstrom) with plane...... symmetry p1g1. For n vertical in the b direction; the tilt angle...... length, lattice dimensions, chain orientation, and molecular motion, may be correlated with the ice-nucleating efficiency of these alcohol monolayers as a function of n....

  17. The influence of dipalmitoyl phosphatidylserine on phase behaviour of and cellular response to lyotropic liquid crystalline dispersions.

    Science.gov (United States)

    Shen, Hsin-Hui; Crowston, Jonathan G; Huber, Florian; Saubern, Simon; McLean, Keith M; Hartley, Patrick G

    2010-12-01

    Lyotropic liquid crystalline nanoparticles (cubosomes) have the potential to act as amphiphilic scaffolds for the presentation of lipids and subsequent application in, for example, bioseparations and therapeutic delivery. In this work we have formulated lyotropic liquid crystalline systems based on the synthetic amphiphile 1,2,3-trihydroxy-3,7,11,15-tetramethylhexadecane (phytantriol) and containing the lipid dipalmitoyl phosphatidylserine (DPPS). We have prepared a range of DPPS-containing phytantriol cubosome formulations and characterized them using Small Angle X-ray Scattering and Cryo-transmission electron microscopy. These techniques show that increased DPPS content induces marked changes in lyotropic liquid crystalline phase behaviour, characterized by changes in crystallographic dimensions and increases in vesicle content. Furthermore, in vitro cell culture studies indicate that these changes correlate with lipid/surfactant cellular uptake and cytotoxicity. A model cell membrane based on a surface supported phospholipid bilayer was used to gain insights into cubosome-bilayer interactions using Quartz Crystal Microgravimetry. The data show that mass uptake at the supported bilayer increased with DPPS content. We propose that the cytotoxicity of the DPPS-containing dispersions results from changes in lipid/surfactant phase behaviour and the preferential attachment and fusion of vesicles at the cell membrane.

  18. Influence of growth parameters on the surface morphology and crystallinity of InSb epilayers grown by liquid phase epitaxy

    Indian Academy of Sciences (India)

    N K Udayashankar; H L Bhat

    2003-12-01

    Unintentionally doped homoepitaxial InSb films have been grown by liquid phase epitaxy employing ramp cooling and step cooling growth modes. The effect of growth temperature, degree of supercooling and growth duration on the surface morphology and crystallinity were investigated. The major surface features of the grown film like terracing, inclusions, meniscus lines, etc are presented step-by-step and a variety of methods devised to overcome such undesirable features are described in sufficient detail. The optimization of growth parameters have led to the growth of smooth and continuous films. From the detailed morphological, X-ray diffraction, scanning electron microscopic and Raman studies, a correlation between the surface morphology and crystallinity has been established.

  19. A method for the quantitative determination of crystalline phases by X-ray

    Science.gov (United States)

    Petzenhauser, I.; Jaeger, P.

    1988-01-01

    A mineral analysis method is described for rapid quantitative determination of crystalline substances in those cases in which the sample is present in pure form or in a mixture of known composition. With this method there is no need for prior chemical analysis.

  20. Crystalline phase transition information induced by high temperature susceptibility transformations in bulk PMP-YBCO superconductor growth in-situ

    Science.gov (United States)

    Zhang, C. P.; Chaud, X.; Beaugnon, E.; Zhou, L.

    2015-01-01

    The dynamic susceptibility transformations of bulk HTSC PMP-YBCO growth have been investigated from 200 °C up to 1060 °C by the Faraday Balance in-situ. It revealed that the crystalline phase transitions of bulk PMP-YBCO growth in process. A new discovery of Y123 phase pre-formed then melted in heating stage has been found. It also discovered that Y123 crystal solidification started at 1004 °C in cooling stage. Before Y123 solidification the liquid phase CuO change to Cu2O reciprocally as well as the copper ion valence changed between divalent Cu2+ and trivalent Cu1+ each other. It was essential to keep quantities of CuO phase instead of the Cu2O for Y123 crystal solidification.

  1. The fabrication of quantum wires in silicon utilising the characteristics of solid phase epitaxial regrowth of crystalline silicon

    Energy Technology Data Exchange (ETDEWEB)

    Liu, A.C.Y.; McCallum, J.C. [Melbourne Univ. Parkville, VIC (Australia). School of Physics, Microanalytical Research Centre

    1998-06-01

    The process of solid phase epitaxy (SPE) in semiconductor materials is one which has been intensively researched due to possible applications in the semiconductor industry. SPE is a solid phase transformation, in which an amorphous layer can be recrystallized either through heating or a combination of heating and ion bombardment. The transformation is believed to occur exclusively at the interface between the amorphous and crystalline layers, with individual atoms from the amorphous phase being incorporated into the crystalline phase by some point defect mechanism. The process has been observed to follow an Arrhenius temperature dependence. A wafer silicon was subjected to a multi-energy silicon implant through a fine nickel grid to amorphise region to a depth of 5{mu}m creating an array of amorphous wells. Metal impurity atoms were then implanted in this region at energy of 500 keV. Samples were examined using an optical microscope and the Alphastep profiler at RMIT. It was confirmed that burgeoning wells were about 2 {mu}m wide and rose about 0.01 {mu}m above the silicon substrate. Extended abstract. 4 refs., 3 figs.

  2. Amorphous and crystalline aerosol particles interacting with water vapor – Part 1: Microstructure, phase transitions, hygroscopic growth and kinetic limitations

    Directory of Open Access Journals (Sweden)

    T. Koop

    2009-03-01

    Full Text Available Interactions with water are crucial for the properties, transformation and climate effects of atmospheric aerosols. Here we outline characteristic features and differences in the interaction of amorphous and crystalline aerosol particles with water vapor. Using a hygroscopicity tandem differential mobility analyzer (H-TDMA, we performed hydration, dehydration and cyclic hydration&dehydration experiments with aerosol particles composed of levoglucosan, oxalic acid and ammonium sulfate (diameters ~100–200 nm, relative uncertainties <0.4%, relative humidities <5% to 95% at 298 K. The measurements and accompanying Köhler model calculations provide new insights into particle microstructure, surface adsorption, bulk absorption, phase transitions and hygroscopic growth. The results of these and related investigations lead to the following main conclusions: 1. Many organic substances (including carboxylic acids, carbohydrates and proteins tend to form amorphous rather than crystalline phases upon drying of aqueous solution droplets. Depending on viscosity and microstructure, the amorphous phases can be classified as glasses, rubbers, gels or viscous liquids. 2. Amorphous organic substances tend to absorb water vapor and undergo gradual deliquescence and hygroscopic growth at much lower relative humidity than their crystalline counterparts. 3. In the course of hydration and dehydration, certain organic substances can form rubber- or gel-like structures (supra-molecular networks and undergo stepwise transitions between swollen and collapsed network structures. 4. Organic gels or (semi-solid amorphous shells (glassy, rubbery, ultra-viscous with low molecular diffusivity can kinetically limit the uptake and release of water by submicron aerosol particles on (multi-second time scales, which may influence the hygroscopic growth and activation of aerosol particles as cloud condensation nuclei (CCN and ice nuclei (IN. 5. The shape and porosity of amorphous

  3. Phase behaviour of macromolecular liquid crystalline materials. Computational studies at the molecular level

    CERN Document Server

    Stimson, L M

    2003-01-01

    Molecular simulations provide an increasingly useful insight into the static and dynamic characteristics of materials. In this thesis molecular simulations of macro-molecular liquid crystalline materials are reported. The first liquid crystalline material that has been investigated is a side chain liquid crystal polymer (SCLCP). In this study semi-atomistic molecular dynamics simulations have been conducted at a range of temperatures and an aligning potential has been applied to mimic the effect of a magnetic field. In cooling the SCLCP from an isotropic melt, microphase separation was observed yielding a domain structure. The application of a magnetic field to this structure aligns the domains producing a stable smectic mesophase. This is the first study in which mesophases have been observed using an off-lattice model of a SCLCP. The second material that has been investigated is a dendrimer with terminal mesogenic functionalization. Here, a multi-scale approach has been taken with Monte Carlo studies of a s...

  4. Rheology of the lamellar liquid-crystalline phase in polyethoxylated alcohol/water/heptane systems.

    Directory of Open Access Journals (Sweden)

    Gallegos, C.

    2005-06-01

    Full Text Available Linear viscoelastic tests as well as transient and steady flow experiments were carried out on lamellar liquid crystalline samples of poly (oxyethylene alcohol/water/heptane systems. The effect of surfactant and heptane concentrations on the rheological properties of the lamellar mesophase was investigated. The mechanical spectrum inside the linear viscoelastic regime shows, in all cases, a well-developed plateau region in the whole frequency range studied. The values of the dynamic functions were higher for intermediate surfactant or heptane concentrations indicative of a major development of the elastic network in the midrange of existence of the lamellar phase. Transient and steady flow experiments point out a shear-induced evolution of the lamellar microstructure. Different power law regions with different values of the flow index were detected in the viscosity versus shear rate plots. These shear-induced structural modifications were confirmed by using polarizing microscopy in an optical shearing cell. Structural modifications appear to be highly influenced by shear rate. In general, applying relatively high constant shear rates, the alignment of the bilayers followed by the appearance of the “oily streaks” structure was observed. Appearance of shear-induced vesicles occurs at high heptane content, as indicates the texture of close-packed monodisperse spherulites detected by polarizing microscopy.n este trabajo se han estudiado las propiedades reológicas de una fase líquido-cristalina laminar contenida en un sistema alcohol polietoxilado/agua/heptano, mediante ensayos viscoelásticos lineales, estacionarios y transitorios. El efecto de distintas variables como la composición de tensioactivo y heptano sobre dichas propiedades reológicas ha sido analizado. El espectro mecánico obtenido de la fase laminar muestra en todos los casos una región “plateau” en el intervalo de frecuencias estudiado así como mayores valores

  5. Growth, stabilization and conversion of semi-metallic and semiconducting phases of MoTe2 monolayer by molecular-beam epitaxy

    OpenAIRE

    2016-01-01

    Monolayer (ML) transition-metal dichalcogenides exist in different phases, such as the hexagonal (2H) and distorted octahedral or monoclinic (1T') phases. The different structures show vastly different properties. For example, the 2H MoTe2 ML is a direct-gap semiconductor while 1T' MoTe2 is a semi-metal. It has been suggested that the formation energies between 2H and 1T' MoTe2 differ very little, so there is a high chance to tune the structures of MoTe2 and thereby to bring in new applicatio...

  6. Phase behavior of mixed Ar-Kr, Ar-Xe and Kr-Xe monolayer films on graphite: a Monte Carlo study.

    Science.gov (United States)

    Patrykiejew, A

    2013-01-01

    Using Monte Carlo simulation methods in the grand canonical ensemble we have studied the behavior of mixed Ar-Kr, Ar-Xe and Kr-Xe monolayer films on the graphite basal plane. We have considered the adsorption of the lighter component, either argon or krypton, under the condition of a fixed chemical potential of the heavier component (krypton or xenon), as well as on the graphite surface with preadsorbed small amounts of a heavier noble gas. In both types of simulation the composition of the adsorbed layer is not conserved. We discuss the phase behavior of mixed films emerging from both types of 'computer experiment'. We also demonstrate that Monte Carlo simulation allows us to estimate the effects of preadsorbed xenon on the commensurate-incommensurate transition in the krypton monolayer film and gives the results that are in good quantitative agreement with experimental data.

  7. Effect of 3-Aminopropyltriethoxysilane Monolayer Self-Assembled Quartz Substrate on the Quality of Vapor Phase-Polymerized Poly(3,4-ethylenedioxythiophene) Nanofilm.

    Science.gov (United States)

    Choi, Byoungbok; Choi, Sangil; Sohn, Honglae; Kim, Sungsoo

    2015-11-01

    Polymer thin film coated on the delay line section of a surface acoustic wave (SAW) sensor has been a main focus in sensor industry to improve its sensitivity. In this study, for an effort to build a highly sensitive SAW sensor, a versatile conducting polymer, Poly(3,4-ethylenedioxythiophene) (PEDOT), has been vapor phase polymerized on 3-aminopropyltriethoxysilane (APS) monolayer self-assembled quartz substrate, which is a representative piezoelectric materials for SAW sensor. And then, the quality and electrical properties of the thin film were evaluated by several thin film analyzing tools such as contact angle analyzer, FE-SEM, optical microscope, adhesion test and 4 point probe. From the evaluation, it was discovered that PEDOT nanofilm is highly smooth and dense, and it is strongly adhered to the substrate particularly when the quartz surface was coated with APS monolayer. Such good quality PEDOT thin film could be a potential candidate for a base platform of highly sensitive SAW sensor devices.

  8. Thiol-yne adsorbates for stable, low-density, self-assembled monolayers on gold.

    Science.gov (United States)

    Stevens, Christopher A; Safazadeh, Leila; Berron, Brad J

    2014-03-04

    We present a novel approach toward carboxylate-terminated, low-density monolayers on gold, which provides exceptional adsorbate stability and conformational freedom of interfacial functional groups. Adsorbates are synthesized through the thiol-yne addition of two thiol-containing head groups to an alkyne-containing tail group. The resulting monolayers have two distinct phases: a highly crystalline head phase adjacent to the gold substrate, and a reduced density tail phase, which is in contact with the environment. The ellipsometric thickness of 27 Å is consistent with the proposed structure, where a densely packed decanedithiol monolayer is capped with an 11 carbon long, second layer at 50% lateral chain density. The Fourier transform infrared peak at 1710 cm(-1) supports the presence of the carbonyl group. Further, the peaks associated with asymmetric and symmetric methylene stretching are shifted toward higher wavenumbers compared to those of well-packed self-assembled monolayers (SAMs), which shows a lower average crystallinity of the thiol-yne monolayers compared to a typical monolayer. Contact angle measurements indicate an intermediate surface energy for the thiol-yne monolayer surface, owing to the contribution of exposed methylene functionality at the surface in addition to the carbonyl terminal group. The conformational freedom at the surface was demonstrated through remodeling the thiol-yne surface under an applied potential. Changes in the receding contact angle in response to an external potential support the capacity for reorientation of the surface presenting groups. Despite the low packing at the solution interface, thiol-yne monolayers are resistant to water and ion transport (R(f) ~ 10(5)), supporting the presence of a densely structured layer at the gold surface. Further, the electrochemical stability of the thiol-yne adsorbates exceeded that of well-packed SAMs, requiring a more reductive potential to desorb the thiol-yne monolayers from the

  9. Mechano-chemical spinodal decomposition: A phenomenological theory of phase transformations in multi-component, crystalline solids

    CERN Document Server

    Rudraraju, Shiva; Garikipati, Krishna

    2015-01-01

    We present a new phenomenological treatment of phase transformations in multi-component crystalline solids driven by free energy density functions that are non-convex in mechanical and chemical variables. We identify the mechano-chemical spinodal as the region in strain-composition space where the free energy density function is non-convex. Our treatment describes diffusional phase transformations that are accompanied by symmetry breaking structural changes of the crystal unit cell due to mechanical instabilities in the mechano-chemical spinodal. This approach is relevant to phase transformations wherein the structural order parameters can be expressed as linear combinations of strains relative to a high-symmetry reference crystal. Because the local strains in an inhomogeneous, transforming microstructure can be finite, the elasticity problem must account for geometric nonlinearity. Furthermore, for physical consistency and mathematical well-posedness, we regularize the free energy density functions by interf...

  10. Gibbs free-energy difference between the glass and crystalline phases of a Ni-Zr alloy

    Science.gov (United States)

    Ohsaka, K.; Trinh, E. H.; Holzer, J. C.; Johnson, W. L.

    1993-01-01

    The heats of eutectic melting and devitrification, and the specific heats of the crystalline, glass, and liquid phases have been measured for a Ni24Zr76 alloy. The data are used to calculate the Gibbs free-energy difference, Delta G(AC), between the real glass and the crystal on an assumption that the liquid-glass transition is second order. The result shows that Delta G(AC) continuously increases as the temperature decreases in contrast to the ideal glass case where Delta G(AC) is assumed to be independent of temperature.

  11. Highly efficient molecular simulation methods for evaluation of thermodynamic properties of crystalline phases

    Science.gov (United States)

    Moustafa, Sabry Gad Al-Hak Mohammad

    Molecular simulation (MS) methods (e.g. Monte Carlo (MC) and molecular dynamics (MD)) provide a reliable tool (especially at extreme conditions) to measure solid properties. However, measuring them accurately and efficiently (smallest uncertainty for a given time) using MS can be a big challenge especially with ab initio-type models. In addition, comparing with experimental results through extrapolating properties from finite size to the thermodynamic limit can be a critical obstacle. We first estimate the free energy (FE) of crystalline system of simple discontinuous potential, hard-spheres (HS), at its melting condition. Several approaches are explored to determine the most efficient route. The comparison study shows a considerable improvement in efficiency over the standard MS methods that are known for solid phases. In addition, we were able to accurately extrapolate to the thermodynamic limit using relatively small system sizes. Although the method is applied to HS model, it is readily extended to more complex hard-body potentials, such as hard tetrahedra. The harmonic approximation of the potential energy surface is usually an accurate model (especially at low temperature and large density) to describe many realistic solid phases. In addition, since the analysis is done numerically the method is relatively cheap. Here, we apply lattice dynamics (LD) techniques to get the FE of clathrate hydrates structures. Rigid-bonds model is assumed to describe water molecules; this, however, requires additional orientation degree-of-freedom in order to specify each molecule. However, we were able to efficiently avoid using those degrees of freedom through a mathematical transformation that only uses the atomic coordinates of water molecules. In addition, the proton-disorder nature of hydrate water networks adds extra complexity to the problem, especially when extrapolating to the thermodynamic limit is needed. The finite-size effects of the proton disorder contribution is

  12. Nanoscale characteristics of triacylglycerol oils: phase separation and binding energies of two-component oils to crystalline nanoplatelets.

    Science.gov (United States)

    MacDougall, Colin J; Razul, M Shajahan; Papp-Szabo, Erzsebet; Peyronel, Fernanda; Hanna, Charles B; Marangoni, Alejandro G; Pink, David A

    2012-01-01

    Fats are elastoplastic materials with a defined yield stress and flow behavior and the plasticity of a fat is central to its functionality. This plasticity is given by a complex tribological interplay between a crystalline phase structured as crystalline nanoplatelets (CNPs) and nanoplatelet aggregates and the liquid oil phase. Oil can be trapped within microscopic pores within the fat crystal network by capillary action, but it is believed that a significant amount of oil can be trapped by adsorption onto crystalline surfaces. This, however, remains to be proven. Further, the structural basis for the solid-liquid interaction remains a mystery. In this work, we demonstrate that the triglyceride liquid structure plays a key role in oil binding and that this binding could potentially be modulated by judicious engineering of liquid triglyceride structure. The enhancement of oil binding is central to many current developments in this area since an improvement in the health characteristics of fat and fat-structured food products entails a reduction in the amount of crystalline triacylglycerols (TAGs) and a relative increase in the amount of liquid TAGs. Excessive amounts of unbound, free oil, will lead to losses in functionality of this important food component. Engineering fats for enhanced oil binding capacity is thus central to the design of more healthy food products. To begin to address this, we modelled the interaction of triacylglycerol oils, triolein (OOO), 1,2-olein elaidin (OOE) and 1,2-elaidin olein (EEO) with a model crystalline nanoplatelet composed of tristearin in an undefined polymorphic form. The surface of the CNP in contact with the oil was assumed to be planar. We considered pure OOO and mixtures of OOO + OOE and OOO + EEO with 80% OOO. The last two cases were taken as approximations to high oleic sunflower oil (HOSO). The intent was to investigate whether phase separation on a nanoscale took place. We defined an "oil binding capacity" parameter, B

  13. Identifying the crystallinity, phase, and arsenic uptake of the nanomineral schwertmannite using analytical high resolution transmission electron microscopy

    Science.gov (United States)

    French, R. A.; Kim, B.; Murayama, M.; Hochella, M. F.

    2010-12-01

    Schwertmannite, an iron oxyhydroxide sulfate nanomineral, plays a significant role in the geochemistry of acid mine drainage (AMD) as a metastable phase with respect to goethite and by retaining toxic metals, e.g. arsenic [1]. Schwertmannite’s characteristic morphology is needles 100-300 nm long and only 5-10 nm in diameter extending from a dense aggregate. The poorly-and nano-crystalline nature of this mineral requires using high resolution electron microscopy (HRTEM) to be fully characterized. We used HRTEM to identify the polyphasic nature of natural samples of schwertmannite collected from the Iberian Pyrite Belt in Spain. In order to analyze the dense core, samples were prepared in thin section using an ultramicrotome. Data on a sample identified as pure schwertmannite through powder XRD shows the presence of 5-10 nm goethite nanocrystals making up a significant portion of one of the nanoneedle tips (Figure 1). These nanocrystals exhibit lattice fringes and faceted surfaces, both of which match that expected for goethite. The great majority of the nanoneedles are poorly-crystalline (no lattice fringes) with atomically rough surfaces which may be highly active in the uptake of As. The presence of a range of phases and crystallinities in this sample demonstrate incipient stages of the mechanism that results in transformation of schwertmannite to goethite. Further analytical TEM analyses will help us track sorption/desorption, as well as the specific locations of As within these materials upon initial formation, as well as during transformation. [1] Acero et al. (2006) GCA 70, 4130-4139. Figure 1. HRTEM image of 'schwertmannite' nanoneedle with FFT data (inset).

  14. Vapor-phase hydrothermal transformation of HTiOF3 intermediates into {001} faceted anatase single-crystalline nanosheets.

    Science.gov (United States)

    Liu, Porun; Wang, Yun; Zhang, Haimin; An, Taicheng; Yang, Huagui; Tang, Zhiyong; Cai, Weiping; Zhao, Huijun

    2012-12-07

    For the first time, a facile, one-pot hydrofluoric acid vapor-phase hydrothermal (HF-VPH) method is demonstrated to directly grow single-crystalline anatase TiO(2) nanosheets with 98.2% of exposed {001} faceted surfaces on the Ti substrate via a distinctive two-stage formation mechanism. The first stage produces a new intermediate crystal (orthorhombic HTiOF(3) ) that is transformed into anatase TiO(2) nanosheets during the second stage. The findings reveal that the HF-VPH reaction environment is unique and differs remarkably from that of liquid-phase hydrothermal processes. The uniqueness of the HF-VPH conditions can be readily used to effectively control the nanostructure growth.

  15. Combined toxicity of two crystalline phases (anatase and rutile) of Titania nanoparticles towards freshwater microalgae: Chlorella sp

    Energy Technology Data Exchange (ETDEWEB)

    Iswarya, V.; Bhuvaneshwari, M.; Alex, Sruthi Ann; Iyer, Siddharth; Chaudhuri, Gouri [Centre for Nanobiotechnology, VIT University, Vellore (India); Chandrasekaran, Prathna Thanjavur [Department of Materials Engineering, Indian Institute of Science, Bangalore (India); Bhalerao, Gopalkrishna M.; Chakravarty, Sujoy [UGC-DAE CSR, Kalpakkam Node, Kokilamedu (India); Raichur, Ashok M. [Department of Materials Engineering, Indian Institute of Science, Bangalore (India); Chandrasekaran, N. [Centre for Nanobiotechnology, VIT University, Vellore (India); Mukherjee, Amitava, E-mail: amit.mookerjea@gmail.com [Centre for Nanobiotechnology, VIT University, Vellore (India)

    2015-04-15

    Highlights: • Toxicity of two crystalline phases of titania NPs on freshwater microalgae studied. • (Anatase, Rutile) mixture showed additive and antagonistic effect on microalgae. • Rutile had more colloidal stability than anatase and binary mixtures. • ROS generation varied with the crystallinity of the NPs. • Ultrastructural damages observed in TEM images. - Abstract: In view of the increasing usage of anatase and rutile crystalline phases of titania NPs in the consumer products, their entry into the aquatic environment may pose a serious risk to the ecosystem. In the present study, the possible toxic impact of anatase and rutile nanoparticles (individually and in binary mixture) was investigated using freshwater microalgae, Chlorella sp. at low exposure concentrations (0.25, 0.5 and 1 mg/L) in freshwater medium under UV irradiation. Reduction of cell viability as well as a reduction in chlorophyll content were observed due to the presence of NPs. An antagonistic effect was noted at certain concentrations of binary mixture such as (0.25, 0.25), (0.25, 0.5), and (0.5, 0.5) mg/L, and an additive effect for the other combinations, (0.25, 1), (0.5, 0.25), (0.5, 1), (1, 0.25), (1, 0.5), and (1, 1) mg/L. The hydrodynamic size analyses in the test medium revealed that rutile NPs were more stable in lake water than the anatase and binary mixtures [at 6 h, the sizes of anatase (1 mg/L), rutile NPs (1 mg/L), and binary mixture (1, 1 mg/L) were 948.83 ± 35.01 nm, 555.74 ± 19.93 nm, and 1620.24 ± 237.87 nm, respectively]. The generation of oxidative stress was found to be strongly dependent on the crystallinity of the nanoparticles. The transmission electron microscopic images revealed damages in the nucleus and cell membrane of algal cells due to the interaction of anatase NPs, whereas rutile NPs were found to cause chloroplast and internal organelle damages. Mis-shaped chloroplasts, lack of nucleus, and starch-pyrenoid complex were noted in binary

  16. Molecular structure of the discotic liquid crystalline phase of hexa-peri-hexabenzocoronene/oligothiophene hybrid and their charge transport properties

    Energy Technology Data Exchange (ETDEWEB)

    Bag, Saientan; Maingi, Vishal; Maiti, Prabal K., E-mail: maiti@physics.iisc.ernet.in [Department of Physics, Center for Condensed Matter Theory, Indian Institute of Science, Bangalore 560012 (India); Yelk, Joe; Glaser, Matthew A.; Clark, Noel A. [Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States); Walba, David M. [Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309 (United States)

    2015-10-14

    Using atomistic molecular dynamics simulation, we study the discotic columnar liquid crystalline (LC) phases formed by a new organic compound having hexa-peri-Hexabenzocoronene (HBC) core with six pendant oligothiophene units recently synthesized by Nan Hu et al. [Adv. Mater. 26, 2066 (2014)]. This HBC core based LC phase was shown to have electric field responsive behavior and has important applications in organic electronics. Our simulation results confirm the hexagonal arrangement of columnar LC phase with a lattice spacing consistent with that obtained from small angle X-ray diffraction data. We have also calculated various positional and orientational correlation functions to characterize the ordering of the molecules in the columnar arrangement. The molecules in a column are arranged with an average twist of 25° having an average inter-molecular separation of ∼5 Å. Interestingly, we find an overall tilt angle of 43° between the columnar axis and HBC core. We also simulate the charge transport through this columnar phase and report the numerical value of charge carrier mobility for this liquid crystal phase. The charge carrier mobility is strongly influenced by the twist angle and average spacing of the molecules in the column.

  17. Suppressed Release of Clarithromycin from Tablets by Crystalline Phase Transition of Metastable Polymorph Form I.

    Science.gov (United States)

    Fujiki, Sadahiro; Watanabe, Narumi; Iwao, Yasunori; Noguchi, Shuji; Mizoguchi, Midori; Iwamura, Takeru; Itai, Shigeru

    2015-08-01

    The pharmaceutical properties of clarithromycin (CAM) tablets containing the metastable form I of crystalline CAM were investigated. Although the dissolution rate of form I was higher than that of stable form II, the release of CAM from form I tablet was delayed. Disintegration test and liquid penetration test showed that the disintegration of the tablet delayed because of the slow penetration of an external solution into form I tablet. Investigation by scanning electron microscopy revealed that the surface of form I tablet was covered with fine needle-shaped crystals following an exposure to the external solution. These crystals were identified as form IV crystals by powder X-ray diffraction. The phenomenon that CAM releases from tablet was inhibited by fine crystals spontaneously formed on the tablet surface could be applied to the design of sustained-release formulation systems with high CAM contents by minimizing the amount of functional excipients. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

  18. Stereodynamic control of star-epoxy/anhydride crosslinking actuated by liquid-crystalline phase transitions.

    Science.gov (United States)

    Pin, Jean-Mathieu; Mija, Alice; Sbirrazzuoli, Nicolas

    2017-02-07

    The epoxy/anhydride copolymerization kinetics of an original star-epoxy monomer (TriaEP) was explored in dynamic heating mode using a series of isoconversional methods. Negative values of the apparent activation energy (Eα) related to an anti-Arrhenius behavior were observed. The transition from Arrhenius to anti-Arrhenius behavior and vice versa depending on the Eα of polymerization was correlated with the dynamics of mesophasic fall-in/fall-out events, physically induced transition (PIT) and chemically induced transition (CIT). This self-assembly phenomenon induces the generation of an anisotropic crosslinked architecture exhibiting both nematic discotic (ND) and nematic columnar (NC) organization. Particular emphasis was placed on evaluating the juxtaposition/contribution of the liquid-crystalline transitions to crosslinking, considering both the reaction dynamics and the macromolecular vision.

  19. Structural mechanisms of the Ih–II and II → Ic transitions between the crystalline phases of aqueous ice

    Energy Technology Data Exchange (ETDEWEB)

    Zheligovskaya, E. A., E-mail: lmm@phyche.ac.ru [Russian Academy of Sciences, Frumkin Institute of Physical Chemistry and Electrochemistry (Russian Federation)

    2015-09-15

    Structural mechanisms are proposed for experimentally observed phase transitions between crystalline modifications of aqueous ice, Ih and II, as well as II and Ic. It is known that the Ih–II transition occurs with the conservation of large structural units (hexagonal channels) common for these ices. It is shown that the Ih → II transition may occur with the conservation of 5/6 of all hydrogen bonds in crystal, including all hydrogen bonds in the retained channels (3/4 of the total number of bonds in crystal) and 1/3 of the bonds between these channels (1/12 of the total number). The transformation of other hydrogen bonds between the retained channels leads to the occurrence of proton order in ice II. A structural mechanism is proposed to explain the transformation of single crystals of ice Ih either into single crystals of ice II or into crystalline twins of ice II with c axes rotated by 180° with respect to each other, which is often observed at the Ih → II transition. It is established that up to 7/12 of all hydrogen bonds are retained at the irreversible cooperative II → Ic transition.

  20. Effect of fabrication technique on the crystalline phase and electrical properties of PVDF films

    Directory of Open Access Journals (Sweden)

    Mahato P. K.

    2015-03-01

    Full Text Available The effect of different fabrication techniques on the formation of electroactive β-phase polyvinylidene fluoride (PVDF has been investigated. Films with varying concentration of PVDF and solvent - dimethyl formamide (DMF were synthesized by tape casting and solvent casting techniques. The piezoelectric β-phase as well as non polar β-phase were observed for both the tape cast and solvent cast films from X-ray diffraction (XRD micrographs and Fourier transform infra-red spectroscopy (FT-IR spectra. A maximum percentage (80 % of β-phase was obtained from FT-IR analysis for a solvent cast PVDF film. The surface morphology of the PVDF films was analyzed by FESEM imaging. The dielectric properties as a function of temperature and frequency and the ferroelectric hysteresis loop as a function of voltage were measured. An enhancement in the value of the dielectric constant and polarization was obtained in solvent cast films.

  1. Atomic-level simulations of nanoindentation-induced phase transformation in mono-crystalline silicon

    Science.gov (United States)

    Lin, Yen-Hung; Chen, Tei-Chen; Yang, Ping-Feng; Jian, Sheng-Rui; Lai, Yi-Shao

    2007-12-01

    Molecular dynamics (MD) simulations of nanoindentation are carried out to investigate the phase transformations in Si with a spherical indenter. Since the phase transformation induced by deformation in micro-scale is closely related to the carrier mobility of the material, it has become a key issue to be investigated for the chips especially with smaller feature size. Up to now, however, it is not possible to carry out the nanoindentation experimentally in such a small feature. Consequently, molecular dynamic simulation on nanoindentation is resorted to and becomes a powerful tool to understand the detailed mechanisms of stress-induced phase transformation in nano-scale. In this study, the inter-atomic interaction of Si atoms is modeled by Tersoff's potential, while the interaction between Si atoms and diamond indenter atoms is modeled by Morse potential. It is found that the diamond cubic structure of Si in the indentation zone transforms into a phase with body-centred tetragonal structure (β-Si) just underneath the indenter during loading stage and then changes to amorphous after unloading. By using the technique of coordinate number the results reveal that indentation on the (0 0 1) surface exhibits significant phase transformation along the direction. In addition, indentation on the (1 1 0) surface shows more significant internal slipping and spreading of phase transformation than on the (0 0 1) surface. Furthermore, during the indentation process phase transformations of Si are somewhat reversible. Parts of transformed phases that are distributed over the region of elastic deformation can be gradually recovered to original mono-crystal structure after unloading.

  2. Integrating superconducting phase and topological crystalline quantum spin Hall effect in hafnium intercalated gallium film

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Jian, E-mail: jzhou2@vcu.edu, E-mail: pjena@vcu.edu; Jena, Puru, E-mail: jzhou2@vcu.edu, E-mail: pjena@vcu.edu [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284 (United States); Zhang, Shunhong [Center for Applied Physics and Technology, College of Engineering, Peking University, Beijing 100871 (China); Wang, Qian [Center for Applied Physics and Technology, College of Engineering, Peking University, Beijing 100871 (China); Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284 (United States)

    2016-06-20

    Motivated by the growth of superconducting atomic hexagonal Ga layers on GaN surface we have calculated the electronic properties of Hf intercalated honeycomb Ga layers using first-principles theory. In contrast to the hexagonal Ga layers where substrate is necessary for their stability, we find the above structure to be dynamically stable in its freestanding form with small formation energy. In particular, six Dirac cones composed of Hf-d{sub xy}/d{sub x2-y2} orbitals are observed in the first Brillouin zone, slightly below the Fermi energy. Spin-orbit coupling opens a large band gap of 177 meV on these Dirac cones. By calculating its mirror Chern number, we demonstrate that this band gap is topologically nontrivial and protected by mirror symmetry. Such mirror symmetry protected band gaps are rare in hexagonal lattice. A large topological crystalline quantum spin Hall conductance σ{sub SH} ∼ −4 e{sup 2}/h is also revealed. Moreover, electron-phonon coupling calculations reveal that this material is superconducting with a transition temperature T{sub c} = 2.4 K, mainly contributed by Ga out-of-plane vibrations. Our results provide a route toward manipulating quantum spin Hall and superconducting behaviors in a single material which helps to realize Majorana fermions and topological superconductors.

  3. Form-stable crystalline polymer pellets for thermal energy storage. Phase 1

    Energy Technology Data Exchange (ETDEWEB)

    Botham, R.A.; Jenkins, G.H.; Ball, G.L. III; Salyer, I.O.

    1977-07-01

    The objective of this project was to develop a form-stable, crystalline polymer pellet TES bed material, useful in the 120 to 140/sup 0/C temperature range suitable for solar absorption air conditioning applications. This objective was achieved with a Si-O-Si crosslinked HDPE pellet material, demonstrated to have a high heat of fusion value (46 cal/g, approximately 98% of the HDPE's heat of fusion value prior to crosslinking). Further, on melt/freeze cycling of these TES pellets through 400 cycles in ethylene glycol, they retained nearly 100% of their initial heat of fusion value, and had excellent form-stability characteristics, with little or no inter-particle adhesion. Appropriate testing of this TES pellet material, from analytical (DSC) to a one gallon lab-scale TES unit, and finally to a 60 gallon prototype TES demonstration unit, consistently verified these results. C-C crosslinked PE products, which were slightly inferior to the Si-O-Si crosslinked PE in terms of good heat of fusion and form-stability properties, were also developed and are potential alternatives to the prime PE TES product.

  4. A 4F2-cross-point phase change memory using nano-crystalline doped GeSbTe material

    Science.gov (United States)

    Takaura, Norikatsu; Kinoshita, Masaharu; Tai, Mitsuharu; Ohyanagi, Takasumi; Akita, Kenichi; Morikawa, Takahiro

    2015-04-01

    This paper reports on the use of nano-crystalline doped GeSbTe, or nano-GST, to fabricate a cross-point phase change memory with 4F2 cell size and test results obtained for it. We show the characteristics of a poly-Si diode select device with a high on-off ratio and data writing in a 4F2 memory cell array. The advantages of nano-GST over conventional GeSbTe are presented in terms of neighboring disturbance and 4F2 cross-point array formation. The memory cells’ high drivability, low power, and selective write and read performances are demonstrated. The scalability of the diode current density is also presented.

  5. Sitting Phase Monolayers of Polymerizable Phospholipids Create Dimensional, Molecular-Scale Wetting Control for Scalable Solution-Based Patterning of Layered Materials.

    Science.gov (United States)

    Choong, Shi Wah; Russell, Shane R; Bang, Jae Jin; Patterson, Justin K; Claridge, Shelley A

    2017-06-07

    The use of dimensionally ordered ligands on layered materials to direct local electronic structure and interactions with the environment promises to streamline integration into nanostructured electronic, optoelectronic, sensing, and nanofluidic interfaces. Substantial progress has been made in using ligands to control substrate electronic structure. Conversely, using the exposed face of the ligand layer to structure wetting and binding interactions, particularly with scalable solution- or spray-processed materials, remains a significant challenge. However, nature routinely utilizes wetting control at scales from nanometer to micrometer to build interfaces of striking geometric precision and functional complexity, suggesting the possibility of leveraging similar control in synthetic materials. Here, we assemble striped "sitting" phases of polymerizable phospholipids on highly oriented pyrolytic graphite, producing a surface consisting of 1 nm wide hydrophilic stripes alternating with 5 nm wide hydrophobic stripes. Protruding, strongly wetting headgroup chemistries in these monolayers enable formation of rodlike wetted patterns with widths as little as ∼6 nm and lengths up to 100 nm from high-surface-tension liquids (aqueous solutions of glycerol) commonly utilized to assess interfacial wetting properties at larger length scales. In contrast, commonly used lying-down phases of diynoic acids with in-plane headgroups do not promote droplet sticking or directional spreading. These results point to a broadly applicable strategy for achieving high-resolution solution-based patterning on layered materials, utilizing nanometer-wide patterns of protruding, charged functional groups in a noncovalent monolayer to define pattern edges.

  6. An advanced regime of the anomalous acousto-optical interaction with tangential phase matching in crystalline materials

    Science.gov (United States)

    Shcherbakov, Alexandre S.; Arellanes, Adan O.

    2016-09-01

    Regime of effective non-collinear acousto-optical interaction with tangential phase matching had been identified and previously observed only in two limiting cases: in tellurium dioxide (TeO2) at low acoustic frequencies ( 60 MHz) and in rutile (TiO2) at ultra-high frequencies ( 5 GHz). Both these limits are motivated by optical properties of the chosen materials. Low frequencies in TeO2 admit designing a wide-aperture acousto-optical cell, but limit the frequency bandwidth. While an acousto-optical cell made of TiO2 has very small aperture and exhibits low spectral resolution due to the effect of linear acoustic attenuation. Instead of those limits, we propose an advanced regime of the anomalous acousto-optical interaction with tangential phase matching, which allows us varying the frequency range and optimizing all the performances (for instance, the spectral resolution) of a wide-aperture acousto-optical cell made of the chosen crystal, as the case requires. Recently, we had suggested and successfully tested experimentally the revealed additional degree of freedom, i.e. the action of the tilt angle within the refractive indices ellipsoids to manipulate by the performances of crystalline acousto-optical cells. Now, we consider an opportunity of refining this additional degree of freedom within those ellipsoids of crystalline acousto-optical cell through some declination of the acoustic beam. For our investigations, the lithium niobate (LiNbO3) and rutile (TiO2) crystals of about 5 cm length, operating with the slow-shear acoustic mode along the acoustic axes had been selected. The needed theoretical analysis, numerical estimations, and 3D-vector diagrams have been developed to reveal potential benefits of the proposed technique.

  7. Positional order in Langmuir monolayers

    DEFF Research Database (Denmark)

    Kaganer, V.M.; Brezesinski, G.; Möhwald, H.;

    1998-01-01

    We find that a structural solid-solid phase transition in a two-dimensional Langmuir film is accompanied by strong positional disorder. Specifically, we find by a grazing-incidence x-ray diffraction experiment that in monolayers of octadecanol both the hexagonal phase LS and the centered rectangu......We find that a structural solid-solid phase transition in a two-dimensional Langmuir film is accompanied by strong positional disorder. Specifically, we find by a grazing-incidence x-ray diffraction experiment that in monolayers of octadecanol both the hexagonal phase LS and the centered...

  8. Study of crystalline morphology and phase structure in poly(styrene-b-ethylene oxide-b-styrene) triblock copolymers bu solid state RMN spin diffusion

    Energy Technology Data Exchange (ETDEWEB)

    Mantovani, Gerson L., E-mail: gerson.mantovani@ufabc.edu.b [Universidade Federal do ABC (UFABC), Santo Andre, SP (Brazil). Centro de Engenharia, Modelagem e Ciencias Sociais Aplicadas; Bonk, Fabio A. [Universidade Estadual de Campinas (IQ/UNICAMP) SP (Brazil). Inst. de Quimica; Caldarelli, Stefano Caldarelli [Aix-Marseille Universite ISm2, Site de Saint Jerome, Marseille (France); Phan, Trang; Bertin, Denis [Universite de Provence, Site de Saint Jerome, Marseille (France); Azevedo, Eduardo R. de; Bonagamba, Tito J. [Universidade de Sao Paulo (IF/USP), Sao Carlos, SP (Brazil). Inst. de Fisica

    2009-07-01

    The phase structure and crystalline morphology of a series of polystyrene-b-polyethylene oxide-b-polystyrene (PS-b- PEO-b-PS) triblock copolymers, with different compositions and molecular weights, has been studied by solid-state NMR. WAXS and DSC measurements were used to detect the presence of crystalline domains of polyethylene oxide (PEO) blocks at room temperature as a function of the copolymer composition. {sup 1}H NMR spin diffusion analyses provided an estimation of the size of the dispersed phases of the nano structured copolymers. (author)

  9. Phenomenological Modeling for Langmuir Monolayers

    Science.gov (United States)

    Baptiste, Dimitri; Kelly, David; Safford, Twymun; Prayaga, Chandra; Varney, Christopher N.; Wade, Aaron

    Experimentally, Langmuir monolayers have applications in molecular optical, electronic, and sensor devices. Traditionally, Langmuir monolayers are described by a rigid rod model where the rods interact via a Leonard-Jones potential. Here, we propose effective phenomenological models and utilize Monte Carlo simulations to analyze the phase behavior and compare with experimental isotherms. Research reported in this abstract was supported by UWF NIH MARC U-STAR 1T34GM110517-01.

  10. Collective stringlike motion of semiflexible filamentous particles in columnar liquid crystalline phases

    NARCIS (Netherlands)

    Naderi, S.; van der Schoot, P. P. A. M.

    2013-01-01

    We study, by means of Brownian dynamics simulations, heterogeneous dynamics in a dense columnar phase of monodisperse hard filamentous particles, and find that in a background of barely moving particles, some particles occasionally engage in a fast coherent string-type motion similar to what is

  11. Polymorphism: characterization and study of the properties of a crystalline phase

    Directory of Open Access Journals (Sweden)

    Gilson da Silva

    2010-09-01

    Full Text Available Despite the same chemical composition, the physicochemical properties of polymorphs can be totally different, such as leading or not electricity. The legality of recognize them as completely new products is discussed, in front of the characteristics that a polymorph may have over another. The fact is that the differential solubility and stability and formation of active sites in different phases of a substance engage the interest of many active sectors of the economy. There are no few polymorphic energetic materials, or their precursors, which also have therapeutic applications. Therefore, some of the techniques developed by the lucrative pharmaceutical industry to study the polymorphism can be tailored to the needs of the war industry. This paper presents energetic and pharmacological materials recognized for their polymorphism and discuss properties, characterization techniques and the study of phase transition in these materials.

  12. Cooperative effect of electrospinning and nanoclay on formation of polar crystalline phases in poly(vinylidene fluoride).

    Science.gov (United States)

    Liu, Yi-Liao; Li, Ying; Xu, Jun-Ting; Fan, Zhi-Qiang

    2010-06-01

    Poly(vinylidene difluoride)/organically modified montmorillonite (PVDF/OMMT) composite nanofibers were prepared by electrospinning the solution of PVDF/OMMT precursor in DMF. Wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) show that in the bulk of the PVDF/OMMT precursor OMMT platelets are homogeneously dispersed in PVDF and can be both intercalated and exfoliated. It is found that the diameter of the PVDF/OMMT composite nanofibers is smaller than that of the neat PVDF fibers because the lower viscosity of PVDF/OMMT solution, which is attributed to the possible adsorption of PVDF chains on OMMT layers and thus reduction in number of entanglement. The crystal structure of the composite nanofibers was investigated using WAXD and Fourier transform infrared (FT-IR) and compared with that of thin film samples. The results show that the nonpolar alpha phase is completely absent in the electrospun PVDF/OMMT composite nanofibers, whereas it is still present in the neat PVDF electrospun fibers and in the thin films of PVDF/OMMT nanocomposites. The cooperative effect between electrospinning and nanoclay on formation of polar beta and gamma crystalline phases in PVDF is discussed. The IR result reveals that electrospinning induces formation of long trans conformation, whereas OMMT platelets can retard relaxation of PVDF chains and stabilize such conformation due to the possible interaction between the PVDF chains and OMMT layers. This cooperative effect leads to extinction of nonpolar alpha phase and enhances the polar beta and gamma phases in the electrospun PVDF/OMMT composite nanofibers.

  13. Mechanisms of zinc incorporation in aluminosilicate crystalline structures and the leaching behaviour of product phases.

    Science.gov (United States)

    Tang, Yuanyuan; Shih, Kaimin

    2015-01-01

    This study quantitatively evaluates a waste-to-resource strategy of blending zinc-laden sludge and clay material for low-cost ceramic products. Using ZnO as the simulated zinc-laden sludge to sinter with kaolinite, both zinc aluminate spinel (ZnAl₂O₄) and willemite (Zn₂SiO₄) phases were formed during the sintering process. To analyse the details of zinc incorporation reactions, γ-Al₂O₃and quartz were further used as precursors to observe ZnAl₂O₄and Zn₂SiO₄formations. By firing the ZnO mixtures and their corresponding precursors at 750-1350°C for 3 h, the efficiency of zinc transformation was determined through Rietveld refinement analyses of X-ray diffraction data. The results also show different incorporation behaviour for kaolinite and mullite precursors during the formation of ZnAl2O₄and Zn2SiO₄in the system. In addition, with a competitive formation between ZnAl₂O₄and Zn₂SiO₄, the ZnAl₂O₄spinel phase is predominant at temperatures higher than 1050°C. This study used a prolonged leaching test modified from the US Environmental Protection Agency's toxicity characteristic leaching procedure to evaluate ZnO, ZnAl₂O₄, and Zn₂SiO₄product phases. The zinc concentrations in ZnO and Zn₂SiO₄leachates were about two orders of magnitude higher than that of ZnAl₂O₄ leachate at the end of the experiment, indicating that ZnAl₂O₄formation is the preferred stabilization mechanism for incorporating zinc in ceramic products.

  14. Phospholipid barrier to fibrinolysis: role for the anionic polar head charge and the gel phase crystalline structure.

    Science.gov (United States)

    Váradi, Balázs; Kolev, Krasimir; Tenekedjiev, Kiril; Mészáros, Gyöngyi; Kovalszky, Ilona; Longstaff, Colin; Machovich, Raymund

    2004-09-17

    The massive presence of phospholipids is demonstrated in frozen sections of human arterial thrombi. Purified platelet phospholipids and synthetic phospholipids retard in vitro tissue-type plasminogen activator (tPA)-induced fibrinolysis through effects on plasminogen activation and plasmin function. The inhibition of plasminogen activation on the surface of fibrin correlates with the fraction of anionic phospholipid. The phospholipids decrease the amount of tPA penetrating into the clot by 75% and the depth of the reactive surface layer occupied by the activator by up to 30%, whereas for plasmin both of these parameters decrease by approximately 50%. The phospholipids are not only a diffusion barrier, they also bind the components of the fibrinolytic system. Isothermal titration calorimetry shows binding characterized with dissociation constants in the range 0.35-7.64 microm for plasmin and tPA (lower values with more negative phospholipids). The interactions are endothermic and thermodynamically driven by an increase in entropy, probably caused by the rearrangements in the ordered gel structure of the phospholipids (in line with the stronger inhibition at gel phase temperatures compared with liquid crystalline phase temperatures). These findings show a phospholipid barrier, which should be overcome during lysis of arterial thrombi.

  15. Detachment of CVD-grown graphene from single crystalline Ni films by a pure gas phase reaction

    Science.gov (United States)

    Zeller, Patrick; Henß, Ann-Kathrin; Weinl, Michael; Diehl, Leo; Keefer, Daniel; Lippmann, Judith; Schulz, Anne; Kraus, Jürgen; Schreck, Matthias; Wintterlin, Joost

    2016-11-01

    Despite great previous efforts there is still a high need for a simple, clean, and upscalable method for detaching epitaxial graphene from the metal support on which it was grown. We present a method based on a pure gas phase reaction that is free of solvents and polymer supports and avoids mechanical transfer steps. The graphene was grown on 150 nm thick, single crystalline Ni(111) films on Si(111) wafers with YSZ buffer layers. Its quality was monitored by using low energy electron diffraction and scanning tunneling microscopy. The gas phase etching uses a chemical transport reaction, the so-called Mond process, based on the formation of gaseous nickel tetracarbonyl in ~ 1 bar of CO at ~ 75 °C and by adding small amounts of sulfide catalysts. X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy were used to characterize the detached graphene. It was found that the method successfully removes the nickel from underneath the graphene layer, so that the graphene lies on the insulating oxide buffer layer. Small residual particles of nickel sulfide and cracks in the obtained graphene layer were identified. The defect concentrations were comparable to graphene samples obtained by wet chemical etching and by the bubbling transfer.

  16. A Phase Field Technique for Modeling and Predicting Flow Induced Crystallization Morphology of Semi-Crystalline Polymers

    Directory of Open Access Journals (Sweden)

    Xiaodong Wang

    2016-06-01

    Full Text Available Flow induced crystallization of semi-crystalline polymers is an important issue in polymer science and engineering because the changes in morphology strongly affect the properties of polymer materials. In this study, a phase field technique considering polymer characteristics was established for modeling and predicting the resulting morphologies. The considered crystallization process can be divided into two stages, which are nucleation upon the flow induced structures and subsequent crystal growth after the cessation of flow. Accordingly, the proposed technique consists of two parts which are a flow induced nucleation model based on the calculated information of molecular orientation and stretch, and a phase field crystal growth model upon the oriented nuclei. Two-dimensional simulations are carried out to predict the crystallization morphology of isotactic polystyrene under an injection molding process. The results of these simulations demonstrate that flow affects crystallization morphology mainly by producing oriented nuclei. Specifically, the typical skin-core structures along the thickness direction can be successfully predicted. More importantly, the results reveal that flow plays a dominant part in generating oriented crystal morphologies compared to other parameters, such as anisotropy strength, crystallization temperature, and physical noise.

  17. Chiral Cyclobutane β-Amino Acid-Based Amphiphiles: Influence of Cis/Trans Stereochemistry on Condensed Phase and Monolayer Structure.

    Science.gov (United States)

    Sorrenti, Alessandro; Illa, Ona; Ortuño, Rosa M; Pons, Ramon

    2016-07-12

    New diastereomeric nonionic amphiphiles, cis- and trans-1, based on an optically pure cyclobutane β-amino ester moiety have been investigated to gain insight into the influence exerted by cis/trans stereochemistry and stereochemical constraints on the physicochemical behavior, molecular organization, and morphology of their Langmuir monolayers and dry solid states. All these features are relevant to the rational design of functional materials. trans-1 showed a higher thermal stability than cis-1. For the latter, a higher fluidity of its monolayers was observed when compared with the films formed by trans-1 whose BAM images revealed the formation of condensed phase domains with a dendritic shape, which are chiral, and all of them feature the same chiral sign. Although the formation of LC phase domains was not observed by BAM for cis-1, compact dendritic crystals floating on a fluid subphase were observed beyond the collapse, which are attributable to multilayered 3D structures. These differences can be explained by the formation of hydrogen bonds between the amide groups of consecutive molecules allowing the formation of extended chains for trans-1 giving ordered arrangements. However, for cis-1, this alignment coexists with another one that allows the simultaneous formation of two hydrogen bonds between the amide and the ester groups of adjacent molecules. In addition, the propensity to form intramolecular hydrogen bonds must be considered to justify the formation of different patterns of hydrogen bonding and, consequently, the formation of less ordered phases. Those characteristics are congruent also with the results obtained from SAXS-WAXS experiments which suggest a more bent configuration for cis-1 than for trans-1.

  18. Investigation of the deposition and thermal behavior of striped phases of unsymmetric disulfide self-assembled monolayers on Au(111): The case of 11-hydroxyundecyl decyl disulfide

    Energy Technology Data Exchange (ETDEWEB)

    Albayrak, Erol [Department of Materials and Metallurgical Engineering, Ahi Evran University, Kırşehir 40000 (Turkey); Karabuga, Semistan [Department of Chemistry, Kahramanmaraş Sütçü İmam University, Kahramanmaraş 46030 (Turkey); Bracco, Gianangelo [CNR-IMEM and Department of Physics, University of Genoa, via Dodecaneso 33, Genoa 16146 (Italy); Danışman, M. Fatih, E-mail: danisman@metu.edu.tr [Department of Chemistry, Middle East Technical University, Ankara 06800 (Turkey)

    2015-01-07

    Self-assembled monolayers (SAMs) of unsymmetric disulfides on Au(111) are used to form mixed SAMs that can be utilized in many applications. Here, we have studied 11-hydroxyundecyl decyl disulfide (CH{sub 3}–(CH{sub 2}){sub 9}–S–S–(CH{sub 2}){sub 11}–OH, HDD) SAMs produced by supersonic molecular beam deposition and characterized by He diffraction. The film growth was monitored at different temperatures up to a coverage which corresponds to a full lying down phase and the diffraction analysis shows that below 250 K the phase is different from the phase measured above 300 K. During the annealing of the film, two phase transitions were observed, at 250 K and 350 K. The overall data suggest that the former is related to an irreversible phase separation of HDD above 250 K to decanethiolate (–S–(CH{sub 2}){sub 9}–CH{sub 3}, DTT) and hydroxyundecylthiolate (–S–(CH{sub 2}){sub 11}–OH, MUDT), while the latter to a reversible melting of the film. Above 450 K, the specular intensity shows an increase related to film desorption and different chemisorbed states were observed with energies in the same range as observed for decanethiol (H–S–(CH{sub 2}){sub 9}–CH{sub 3}, DT) and mercaptoundecanol (H–S–(CH{sub 2}){sub 11}–OH, MUD) SAMs.

  19. Synthesis of TiO2 visible light catalysts with controllable crystalline phase and morphology from Ti-bearing electric arc furnace molten slag.

    Science.gov (United States)

    Li, Yang; Liu, Lulu; Guo, Min; Zhang, Mei

    2016-09-01

    TiO2 visible light catalysts with different crystalline phases and morphologies were synthesized from titanium-bearing electric arc furnace molten slag (Ti-bearing EAF slag) by using a simple acidolysis process. The effects of the pH of the HCl solution, liquid to solid ratio (RL/S, HCl solution to the residue ratio, mL/g) and acidolysis time on the micro-morphology and crystalline phase of as-prepared TiO2 photocatalysts were systematically investigated. The results indicated that with decreasing pH in the HCl solution and increasing RL/S, the crystalline phase and micro-morphology of the obtained TiO2 nanostructures tended to transform from anatase type TiO2 with spherical nanoparticle structures to rutile type TiO2 with needle-like nanorod structures. The acidolysis time had little influence on the crystalline phase but great impact on the size of the obtained TiO2. The growth mechanism of TiO2 from Ti-bearing EAF slag during the acidolysis process was also discussed. In addition, the influence of RL/S on the photocatalytic properties of the synthesized nanostructured TiO2 was studied. The results showed that the photodegradation efficiency for Rhodamine B solution could reach 91.00% in 120min when the RL/S was controlled at 50:1.

  20. Reversible amorphous-crystalline phase changes in a wide range of Se1-xTex alloys studied using ultrafast differential scanning calorimetry

    NARCIS (Netherlands)

    Vermeulen, Paul. A.; Momand, Jamo; Kooi, Bart J.

    2014-01-01

    The reversible amorphous-crystalline phase change in a chalcogenide material, specifically the Se1-xTex alloy, has been investigated for the first time using ultrafast differential scanning calorimetry. Heating rates and cooling rates up to 5000 K/s were used. Repeated reversible amorphous-crystalli

  1. Reversible electrical resistance switching in GeSbTe thin films : An electrolytic approach without amorphous-crystalline phase-change

    NARCIS (Netherlands)

    Pandian, Ramanathaswamy; Kooi, Bart J.; Palasantzas, George; De Hosson, Jeff Th. M.; Wouters, DJ; Hong, S; Soss, S; Auciello, O

    2008-01-01

    Besides the well-known resistance switching originating from the amorphous-crystalline phase-change in GeSbTe thin films, we demonstrate another switching mechanism named 'polarity-dependent resistance (PDR) switching'. 'Me electrical resistance of the film switches between a low- and high-state whe

  2. The magnetic and crystalline structure of the Laves phase superconductor CeRu{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Huxley, A.; Boucherle, J.X.; Bonnet, M.; Bourdarot, F.; Schustler, I.; Caplan, D. [CEA, Departement de Recherche Fondamental sur la Matiere Condensee, SPSMS, Grenoble 38054 (France); Lelievre, E.; Bernhoeft, N. [Institut Laue - Langevin, Grenoble (France); Lejay, P. [Centre de Recherche sur les Tres Basses Temperatures, CNRS, Grenoble (France); Gillon, B. [CEA, Laboratoire Leon Brillouin, Saclay (France)

    1997-05-19

    We report measurements of the field-induced magnetization density in CeRu{sub 2}. The main results of the study are that the magnetic density is located equally at the Ce and Ru sites, and that the distribution of the induced magnetization about the Ce site extends to larger distances than predicted for Ce{sup 3+} ions with well localized f electrons. Our measurements also cover the superconducting state, where we do not observe any suppression of the spin susceptibility. In an accompanying structural study (in zero field) of our single crystal we detect a small deviation from the ideal Laves phase structure. These results are discussed in relation to the unusual electronic and magnetic properties of this compound. (author)

  3. Interaction of fibrinogen and albumin with titanium dioxide nanoparticles of different crystalline phases

    Science.gov (United States)

    Marucco, Arianna; Fenoglio, Ivana; Turci, Francesco; Fubini, Bice

    2013-04-01

    TiO2 nanoparticles (NPs) are contained in different kinds of industrial products including paints, self-cleaning glasses, sunscreens. TiO2 is also employed in photocatalysis and it has been proposed for waste water treatment. Micrometric TiO2 is generally considered a safe material, while there is concern on the possible health effects of nanometric titania. Due to their small size NPs may migrate within the human body possibly entering in the blood stream. Therefore studies on the interaction of NPs with plasma proteins are needed. In fact, the interaction with proteins is believed to ultimately influences the NPs biological fate. Fibrinogen and albumin are two of the most abundant plasma proteins. They are involved in several important physiological functions. Furthermore, fibrinogen is known to trigger platelet adhesion and inflammation. For these reasons the study of the interaction between these protein and nanoparticles is an important step toward the understanding of the behavior of NPs in the body. In this study we investigated the interaction of albumin and fibrinogen with TiO2 nanoparticles of different crystal phases (rutile and anatase) using an integrated set of techniques. The amount of adsorbed fibrinogen and albumin for each TiO2 surface was investigated by using the bicinchoninic acid assay (BCA). The variation of the surface charge of the NP-protein conjugates respect to the naked NPs was used to indirectly estimate both surface coverage and reversibility of the adsorption upon dilution. Surface charge was monitored by measuring the ζ potential with a conventional electrophoretic light scattering (ELS) system. The extent of protein deformation was evaluated by Raman Spectroscopy. We found that both proteins adsorb irreversibly against electrostatic repulsion, likely undergoing conformational changes or selective orientation upon adsorption. The size of primary particles and the particles aggregation rather than the crystal phase modulate the

  4. Crystalline Confinement

    CERN Document Server

    Banerjee, D; Jiang, F -J; Wiese, U -J

    2013-01-01

    We show that exotic phases arise in generalized lattice gauge theories known as quantum link models in which classical gauge fields are replaced by quantum operators. While these quantum models with discrete variables have a finite-dimensional Hilbert space per link, the continuous gauge symmetry is still exact. An efficient cluster algorithm is used to study these exotic phases. The $(2+1)$-d system is confining at zero temperature with a spontaneously broken translation symmetry. A crystalline phase exhibits confinement via multi-stranded strings between charge-anti-charge pairs. A phase transition between two distinct confined phases is weakly first order and has an emergent spontaneously broken approximate $SO(2)$ global symmetry. The low-energy physics is described by a $(2+1)$-d $\\mathbb{R}P(1)$ effective field theory, perturbed by a dangerously irrelevant $SO(2)$ breaking operator, which prevents the interpretation of the emergent pseudo-Goldstone boson as a dual photon. This model is an ideal candidat...

  5. Phase Structure and Properties of a Biodegradable Block Copolymer Coalesced from It's Crystalline Inclusion Compound Formed with alpha-Cyclodextrin

    Science.gov (United States)

    Shuai, Xintao; Wei, Min; Probeni, Francis; Bullions, Todd A.; Shin, I. Daniel; Tonelli, Alan E.

    2002-03-01

    A well-defined biodegradable block copolymer of poly(epsilon caprolactone) (PCL) and poly(L-lactic acid) (PLLA) was synthesized and characterized and then included as a guest in an inclusion compound (IC) formed with the host alpha-cyclodextrin (CD). The PCL-b-PLLA block copolymer was subsequently coalesced from it's CD-IC crystals by either treatment with hot water (50 C) or an aqueous amylase solution at 25 C. The coalesced PCL-b-PLLA was examined by FTIR, DSC, TGA, and WAXD and was found to be much more homogeneosly organized, with much less segregation and crystallinity of the PCL and PLLA microphases. The morpholgy, crystallization kinetics, thermal behavior, and biodegradability of the coalesced PCL-b-PLLA block copolymer was studied by comparison to similar observations made on as-synthesized PCL-b-PLLA, PCL and PLLA homopolymers, and their solution-cast blend. The PCL and PLLA blocks are found to be more intimately mixed, with less phase segregation, in the coalesced diblock copolymer, and this leads to homogeneous bulk crystallization, which is not observed for the as-synthesized diblock copolymer. The coalesced PCL-b-PLLA was also found to be more quickly biodegraded (lipase from Rhizopus arrhizus)than the as-synthesized PCL-b-PLLA or the physical blend of PCL and PLLA homopolymers. Overall, the coalescence of the inherently phase segregated diblock copolymer PCL-b-PLLA results in a small amount of compact, chain-extended PCL and PLLA crystals embedded in an amorphous phase, largely consisting of well-mixed PCL and PLLA blocks. Thus, we have demonstrated that it is possible to control the morpholgy of a biodegradable diblock copolymer, thereby significantly modifying it's properties, by coalescence from it's CD-IC crystals.

  6. Liquid crystalline phases in suspensions of pigments in non-polar solvents

    Science.gov (United States)

    Klein, Susanne; Richardson, Robert M.; Eremin, Alexey

    We will discuss colloid suspensions of pigments and compare their electro-optic properties with those of traditional dyed low molecular weight liquid crystal systems. There are several potential advantages of colloidal suspensions over low molecular weight liquid crystal systems: a very high contrast because of the high orientational order parameter of suspensions of rod shaped nano-particles, the excellent light fastness of pigments as compared to dyes and high colour saturations resulting from the high loading of the colour stuff. Although a weak `single-particle' electro-optic response can be observed in dilute suspensions, the response is very much enhanced when the concentration of the particles is sufficient to lead to a nematic phase. Excellent stability of suspensions is beneficial for experimental observation and reproducibility, but it is a fundamental necessity for display applications. We therefore discuss a method to achieve long term stability of dispersed pigments and the reasons for its success. Small angle X-ray scattering was used to determine the orientational order parameter of the suspensions as a function of concentration and the dynamic response to an applied electric field. Optical properties were investigated for a wide range of pigment concentrations. Electro-optical phenomena, such as field-induced birefringence and switching, were characterised. In addition, mixtures of pigment suspensions with small amounts of ferrofluids show promise as future magneto-optical materials.

  7. Fast Atomic-Scale Chemical Imaging of Crystalline Materials and Dynamic Phase Transformations.

    Science.gov (United States)

    Lu, Ping; Yuan, Ren Liang; Ihlefeld, Jon F; Spoerke, Erik David; Pan, Wei; Zuo, Jian Min

    2016-04-13

    Atomic-scale phenomena fundamentally influence materials form and function that makes the ability to locally probe and study these processes critical to advancing our understanding and development of materials. Atomic-scale chemical imaging by scanning transmission electron microscopy (STEM) using energy-dispersive X-ray spectroscopy (EDS) is a powerful approach to investigate solid crystal structures. Inefficient X-ray emission and collection, however, require long acquisition times (typically hundreds of seconds), making the technique incompatible with electron-beam sensitive materials and study of dynamic material phenomena. Here we describe an atomic-scale STEM-EDS chemical imaging technique that decreases the acquisition time to as little as one second, a reduction of more than 100 times. We demonstrate this new approach using LaAlO3 single crystal and study dynamic phase transformation in beam-sensitive Li[Li0.2Ni0.2Mn0.6]O2 (LNMO) lithium ion battery cathode material. By capturing a series of time-lapsed chemical maps, we show for the first time clear atomic-scale evidence of preferred Ni-mobility in LNMO transformation, revealing new kinetic mechanisms. These examples highlight the potential of this approach toward temporal, atomic-scale mapping of crystal structure and chemistry for investigating dynamic material phenomena.

  8. Structural phase analysis of a sol-gel nano-crystalline lithium-mica glass-ceramic through different compositions

    Energy Technology Data Exchange (ETDEWEB)

    Tohidifar, M.R., E-mail: tohidifar@znu.ac.ir [Faculty of Engineering, University of Zanjan, P.O. Box 45371-38791, Zanjan (Iran, Islamic Republic of); Alizadeh, P. [Department of Materials Science and Engineering, Tarbiat Modares University, P.O. Box 14115-143, Tehran (Iran, Islamic Republic of)

    2016-08-15

    The current paper attempts to study the influence of chemical composition on the phase development of nano-crystalline lithium-mica glass-ceramic. For this purpose, aqueous sol-gel technique was employed to prepare the glass-ceramics. The synthesis process was accomplished using two chemical compositions of Li{sub (1+x)}Mg{sub 3}AlSi{sub 3(1+x)}O{sub 10+6.5x}F{sub 2} and LiMg{sub 3}AlSi{sub 3(1+x)}O{sub 10+6x}F{sub 2} at different x values along with various mass% of MgF{sub 2} inclusion. It was found that considering an optimized amount of MgF{sub 2}, the specimens synthesized through a new formulation of LiMg{sub 3}AlSi{sub 3(1+x)}O{sub 10+6x}F{sub 2} composition are more appropriate for the sol-gel synthesis method, especially because of intensifying the lithium-mica precipitation and also omission of the secondary phase (i.e. lithium aluminum silicate). The results also indicated that any deviation from the optimized amount of MgF{sub 2} (8%) would cause degradation in the intensity of the precipitated lithium-mica, following the nucleation treatment. - Highlights: • Higher intensity of mica phase obtains through LiMg{sub 3}AlSi{sub 3(1+x)}O{sub 10+6x}F{sub 2} composition. • LiMg{sub 3}AlSi{sub 3(1+x)}O{sub 10+6x}F{sub 2} composition offers mica phase without applying excess MgF{sub 2}. • Applying LiMg{sub 3}AlSi{sub 3(1+x)}O{sub 10+6x}F{sub 2} composition leads to omission of minor phases. • Li{sub (1+x)}Mg{sub 3}AlSi{sub 3(1+x)}O{sub 10+6.5x}F{sub 2} formula cannot be useful in mica nucleation process. • Optimum amount of MgF{sub 2} was obtained as 8% following the nucleation process.

  9. Effect of long range order on sheared liquid crystalline materials: flow regimes, transitions, and rheological phase diagrams

    Science.gov (United States)

    Tsuji; Rey

    2000-12-01

    A generalized theory that includes short-range elasticity, long-range elasticity, and flow effects is used to simulate and characterize the shear flow of liquid crystalline materials as a function of the Deborah (De) and Ericksen (Er) numbers in the presence of fixed planar director boundary conditions; the results are also interpreted as a function of the ratio R between short-range and long-range elasticity. The results are effectively summarized into rheological phase diagrams spanned by De and Er, and also by R and Er, where the stability region of four distinct flow regimes are indicated. The four regimes for planar (two-dimensional orientation) shear flow are (1) the elastic-driven steady state, (2) the composite tumbling-wagging periodic state, (3) the wagging periodic state, and (4) the viscous-driven steady state. The coexistence of the four regimes at a quacritical point is shown to be due to the emergence of a defect structure. The origin, the significant steady and dynamical features, and the transitions between these regimes are thoroughly characterized and analyzed. Quantitative and qualitative comparisons between the present complete model predictions and those obtained from the classical theories of nematodynamics (Leslie-Ericksen and Doi theories) are presented and the main physical mechanisms that drive the observed deviations between the predictions of these models are identified. The presented results fill the previously existing gap between the classical Leslie-Ericksen theory and the Doi theory, and present a unified description of nematodynamics.

  10. Fabrication of tensile-strained single-crystalline GeSn on transparent substrate by nucleation-controlled liquid-phase crystallization

    Science.gov (United States)

    Oka, Hiroshi; Amamoto, Takashi; Koyama, Masahiro; Imai, Yasuhiko; Kimura, Shigeru; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2017-01-01

    We developed a method of forming single-crystalline germanium-tin (GeSn) alloy on transparent substrates that is based on liquid-phase crystallization. By controlling and designing nucleation during the melting growth process, a highly tensile-strained single-crystalline GeSn layer was grown on a quartz substrate without using any crystal-seeds or catalysts. The peak field-effect hole mobility of 423 cm2/V s was obtained for a top-gate single-crystalline GeSn MOSFET on a quartz substrate with a Sn content of 2.6%, indicating excellent crystal quality and mobility enhancement due to Sn incorporation and tensile strain.

  11. Semiconductor monolayer assemblies with oriented crystal faces

    KAUST Repository

    Ma, Guijun

    2012-01-01

    Fabrication of two-dimensional monolayers of crystalline oxide and oxynitride particles was attempted on glass plate substrates. X-Ray diffraction patterns of the assemblies show only specific crystal facets, indicative of the uniform orientation of the particles on the substrate. The selectivity afforded by this immobilization technique enables the organization of randomly distributed polycrystalline powders in a controlled manner.

  12. Combined toxicity of two crystalline phases (anatase and rutile) of Titania nanoparticles towards freshwater microalgae: Chlorella sp.

    Science.gov (United States)

    Iswarya, V; Bhuvaneshwari, M; Alex, Sruthi Ann; Iyer, Siddharth; Chaudhuri, Gouri; Chandrasekaran, Prathna Thanjavur; Bhalerao, Gopalkrishna M; Chakravarty, Sujoy; Raichur, Ashok M; Chandrasekaran, N; Mukherjee, Amitava

    2015-04-01

    In view of the increasing usage of anatase and rutile crystalline phases of titania NPs in the consumer products, their entry into the aquatic environment may pose a serious risk to the ecosystem. In the present study, the possible toxic impact of anatase and rutile nanoparticles (individually and in binary mixture) was investigated using freshwater microalgae, Chlorella sp. at low exposure concentrations (0.25, 0.5 and 1mg/L) in freshwater medium under UV irradiation. Reduction of cell viability as well as a reduction in chlorophyll content were observed due to the presence of NPs. An antagonistic effect was noted at certain concentrations of binary mixture such as (0.25, 0.25), (0.25, 0.5), and (0.5, 0.5) mg/L, and an additive effect for the other combinations, (0.25, 1), (0.5, 0.25), (0.5, 1), (1, 0.25), (1, 0.5), and (1, 1) mg/L. The hydrodynamic size analyses in the test medium revealed that rutile NPs were more stable in lake water than the anatase and binary mixtures [at 6h, the sizes of anatase (1mg/L), rutile NPs (1mg/L), and binary mixture (1, 1mg/L) were 948.83±35.01nm, 555.74±19.93nm, and 1620.24±237.87nm, respectively]. The generation of oxidative stress was found to be strongly dependent on the crystallinity of the nanoparticles. The transmission electron microscopic images revealed damages in the nucleus and cell membrane of algal cells due to the interaction of anatase NPs, whereas rutile NPs were found to cause chloroplast and internal organelle damages. Mis-shaped chloroplasts, lack of nucleus, and starch-pyrenoid complex were noted in binary-treated cells. The findings from the current study may facilitate the environmental risk assessment of titania NPs in an aquatic ecosystem.

  13. The effects of sulfate content on crystalline phase, microstructure, and chemical durability of zirconolite−barium borosilicate glass-ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Lang, E-mail: lang.wu@163.com [State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology, Mianyang 621010 (China); Wang, Xin; Li, Huidong; Teng, Yuancheng [State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology, Mianyang 621010 (China); Peng, Long [Sichuan Province Key Laboratory of Information Materials and Devices Application, Chengdu University of Information Technology, Chengdu 610225 (China)

    2016-09-15

    The effects of sulfate content on structure and chemical durability of barium borosilicate glass-ceramics were studied. The results show that the glass-ceramics with 0–1.10 mol% SO{sub 3} possess mainly CaZrTi{sub 2}O{sub 7}-2M phase along with a small amount of CaZrTi{sub 2}O{sub 7}-3T and ZrO{sub 2} phases. The hexagonal CaZrTi{sub 2}O{sub 7}-3T crystals crystallize on the surface of glass-ceramics. For the samples with 1.24–1.55 mol% SO{sub 3}, the main crystalline phases are CaTiSiO{sub 5} and CaZrTi{sub 2}O{sub 7}-2M in the bulk, while a separate sulfate layer containing Na{sub 2}SO{sub 4} and BaSO{sub 4} is observed on the surface. X-ray fluorescence analysis indicates that about 2/3 of the SO{sub 3} originally added has been lost by volatility. The normalized mass loss (NL{sub i}) for Na, B, Ca elements remains almost unchanged (∼10{sup −2} g/m{sup 2}) after 7 days for the samples with 0–1.10 mol% SO{sub 3}. The NL{sub i} for both Na and B increases gradually after 7 days when the SO{sub 3} content is 1.24 mol%. - Highlights: • Strip-shaped CaZrTi{sub 2}O{sub 7}-2M and plate-like CaTiSiO{sub 5} crystals crystallize in the bulk. • CaZrTi{sub 2}O{sub 7}-3T crystals crystallize on the surface for samples with 0–1.10 mol% SO{sub 3}. • A separate sulfate layer crystallizes on the surface when SO{sub 3} exceeds solubility.

  14. First-leaflet phase effect on properties of phospholipid bilayer formed through vesicle adsorption on LB monolayer.

    Science.gov (United States)

    Park, Jin-Won

    2010-10-01

    Phospholipid bilayers were formed on mica using the Langmuir-Blodgett technique and liposome fusion, as a model system for biomembranes. Nanometer-scale surface physical properties of the bilayers were quantitatively characterized upon the different phases of the first leaflets. Lower hydration/steric forces on the bilayers were observed at the liquid phase of the first leaflet than at the solid phase. The forces appear to be related to the low mechanical stability of the lipid bilayer, which was affected by the first leaflet phase. The first leaflet phase also influenced the long-range repulsive forces over the second leaflet. Surface forces, measured using a modified probe with an atomic force microscope, showed that lower long-range repulsive forces were also found at the liquid phase of the first leaflet. Force measurements were performed at 300 mM sodium chloride solution so that the effect of the phase on the long-range repulsive forces could be investigated by reducing the effect of the repulsion between the second-leaflet lipid headgroups on the long-range repulsive forces. Forces were analyzed using the Derjaguin-Landau-Verwey-Overbeek theory so that the surface potential and surface charge density of the lipid bilayers were quantitatively acquired for each phase of the first leaflet.

  15. On the relationship between crystalline structure and amorphous phase dynamics during isothermal crystallization of bacterial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymers.

    Science.gov (United States)

    Sics, I; Ezquerra, T A; Nogales, A; Baltá-Calleja, F J; Kalniņs, M; Tupureina, V

    2001-01-01

    The isothermal crystallization process of a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer, P(HB-co-HV) with a HB/HV ratio 78/22 was investigated by simultaneous small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and dielectric spectroscopy (DS). By use of this experimental setup (SWD), we have obtained simultaneous information about changes occurring in both the crystalline and the amorphous phases during crystallization. By using the Havriliak-Negami formalism to analyze the dielectric relaxation data, a strong dependence of the relaxation curve shape with the development of the crystalline phase was found. However, in this particular copolymer, the developing crystalline domains do not affect significantly the average segmental mobility in the amorphous phase. This effect is discussed in the light of the enrichment of amorphous phase by HV comonomer units during primary crystallization, hindering the secondary crystallization processes. Results support the hypothesis that the decrease of the physical-aging-like behavior, observed in P(HB-co-HV) copolymers as the amount of HV increases, can be attributed to the progressive inhibition of secondary crystallization mechanisms.

  16. Efficient and Stable Ternary Organic Solar Cells Based on Two Planar Nonfullerene Acceptors with Tunable Crystallinity and Phase Miscibility.

    Science.gov (United States)

    Wang, Jialin; Peng, Jiajun; Liu, Xiaoyu; Liang, Ziqi

    2017-06-21

    Planar perylene diimides (PDIs), when used as nonfullerene acceptors for organic photovoltaics, are constrained by their large π-aggregation in solid state. To tackle this issue, another planar nonfullerene acceptor 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC) with weak crystallinity and near-infrared light absorption is introduced into the PTB7-Th:PDI binary blend to fabricate efficient and stable ternary solar cells. We have finely tuned the PDI/ITIC weight ratio to investigate the influences of individual ITIC and PDI on the optical, electronic, and morphological properties of the PTB7-Th:ITIC:PDI ternary blend. Compared to the binary blend, complementary optical absorption is achieved in all ternary blends. More importantly, it is found that ITIC plays a critical role on largely suppressing the PDI aggregates in the PTB7-Th:PDI blend, while PDI aids to form an interpenetrating network morphology to facilitate charge transport in the PTB7-Th:ITIC blend. Consequently, when the PDI/ITIC ratio is 3:7 (w/w), the PTB7-Th:ITIC:PDI based inverted solar cells exhibit the highest power conversion efficiency of 8.64% due to their favorable out-of-plane π-π stacking, finest phase-separation morphology, and highest charge mobility. Remarkably, the optimal cells that are solution-processed in air show the promising efficiency of 7.09%, suggesting good ambient stability of such ternary solar cells.

  17. Filling the gap in Ca input-output budgets in base-poor forest ecosystems: The contribution of non-crystalline phases evidenced by stable isotopic dilution

    Science.gov (United States)

    van der Heijden, Gregory; Legout, Arnaud; Mareschal, Louis; Ranger, Jacques; Dambrine, Etienne

    2017-07-01

    In terrestrial ecosystems, plant-available pools of magnesium and calcium are assumed to be stored in the soil as exchangeable cations adsorbed on the surface of mineral and/or organic particles. The pools of exchangeable magnesium and calcium are measured by ion-exchange soil extractions. These pools are sustained in the long term by the weathering of primary minerals in the soil and atmospheric inputs. This conceptual model is the base of input-output budgets from which soil acidification and the sustainability of soil chemical fertility is inferred. However, this model has been questioned by data from long-term forest ecosystem monitoring sites, particularly for calcium. Quantifying the contribution of atmospheric inputs, ion exchange and weathering of both primary, secondary and non-crystalline phases to tree nutrition in the short term is challenging. In this study, we developed and applied a novel isotopic dilution technique using the stable isotopes of magnesium and calcium to study the contribution of the different soil phases to soil solution chemistry in a very acidic soil. The labile pools of Mg and Ca in the soil (pools in equilibrium with the soil solution) were isotopically labeled by spraying a solution enriched in 26Mg and 44Ca on the soil. Labeled soil columns were then percolated with a dilute acid solution during a 3-month period and the isotopic dilution of the tracers was monitored in the leaching solution, in the exchangeable (2 sequential 1 mol L-1 ammonium acetate extractions) and non-crystalline (2 sequential soil digestions: oxalic acid followed by nitric acid) phases. Significant amounts of Mg and Ca isotope tracer were recovered in the non-crystalline soil phases. These phases represented from 5% to 25% and from 24% to 50%, respectively, of the Mg and Ca labile pools during the experiment. Our results show that non-crystalline phases act as both a source and a sink of calcium and magnesium in the soil, and contribute directly to soil

  18. Colloidal-crystal-assisted patterning of crystalline materials.

    Science.gov (United States)

    Li, Cheng; Qi, Limin

    2010-04-06

    Colloidal crystals have shown great potential as versatile templates for the fabrication of patterned micro- and nanostructures with complex architectures and novel properties. The patterning of functional crystalline materials in two and three dimensions is essential to the realization of their applications in many technologically important fields. This article highlights some recent progress in the fabrication of 2D and 3D patterned crystalline materials with the assistance of colloidal crystals. By combining a bioinspired synthetic strategy based on a transient amorphous phase with a colloidal-crystal templating method, unique 3D ordered macroporous (3DOM) calcite single crystals can be created. Moreover, patterned arrays of regular ZnO nanopillars with controlled size, shape, and orientation can be fabricated via a facile wet chemical approach by using masks derived from monolayer colloidal crystals (MCC).

  19. Achieving balanced intermixed and pure crystalline phases in PDI-based non-fullerene organic solar cells via selective solvent additives.

    Science.gov (United States)

    Li, Mingguang; Liu, Jiangang; Cao, Xinxiu; Zhou, Ke; Zhao, Qiaoqiao; Yu, Xinhong; Xing, Rubo; Han, Yanchun

    2014-12-28

    Herein, balanced intermixed and pure crystalline phases in N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI)-based non-fullerene organic solar cells (OSCs) were achieved via selective solvent additives (SAs). Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl

  20. Liquid-crystalline rigid-core semiconductor oligothiophenes: influence of molecular structure on phase behaviour and thin-film properties.

    Science.gov (United States)

    Melucci, Manuela; Favaretto, Laura; Bettini, Christian; Gazzano, Massimo; Camaioni, Nadia; Maccagnani, Piera; Ostoja, Paolo; Monari, Magda; Barbarella, Giovanna

    2007-01-01

    The design, synthesis and properties of liquid-crystalline semiconducting oligothiophenes containing dithienothiophene (DTT), benzothiadiazole (BTZ) and carbazole (CBZ) rigid cores are described. The effect of molecular structure (shape, size and substitution) on their thermal behaviour and electrical properties has been investigated. Polarised optical microscopy (POM) and differential scanning calorimetry (DSC) analyses have revealed highly ordered smectic mesophases for most of the newly synthesised compounds. X-ray diffraction (XRD) studies performed at various temperatures have shown that the smectic order is retained in the crystalline state upon cooling across the transition temperature, affording cast films with a more favourable morphology for FET applications.

  1. The evolution of strength and crystalline phases for alkali-activated ground blast furnace slag and fly ash-based geopolymers

    KAUST Repository

    Oh, Jae Eun

    2010-02-01

    The increase in strength and evolution of crystalline phases in inorganic polymer cement, made by the alkali activation of slag, Class C and Class F fly ashes, was followed using compressive strength test and synchrotron X-ray diffraction. In order to increase the crystallinity of the product the reactions were carried out at 80 °C. We found that hydrotalcite formed in both the alkali-activated slag cements and the fly ash-based geopolymers. Hydroxycancrinite, one member of the ABC-6 family of zeolites, was found only in the fly ash geopolymers. Assuming that the predominantly amorphous geopolymer formed under ambient conditions relates to the crystalline phases found when the mixture is cured at high temperature, we propose that the structure of this zeolitic precursor formed in Na-based high alkaline environment can be regarded as a disordered form of the basic building unit of the ABC-6 group of zeolites which includes poly-types such as hydroxycancrinite, hydroxysodalite and chabazite-Na. © 2009 Elsevier Ltd.

  2. The potential for the fabrication of wires embedded in the crystalline silicon substrate using the solid phase segregation of gold in crystallising amorphous volumes

    Energy Technology Data Exchange (ETDEWEB)

    Liu, A.C.Y.; McCallum, J.C

    2004-05-15

    The refinement of gold in crystallising amorphous silicon volumes was tested as a means of creating a conducting element embedded in the crystalline matrix. Amorphous silicon volumes were created by self-ion-implantation through a mask. Five hundred kiloelectronvolt Au{sup +} was then implanted into the volumes. The amorphous volumes were crystallised on a hot stage in air, and the crystallisation was characterised using cross sectional transmission electron microscopy. It was found that the amorphous silicon volumes crystallised via solid phase epitaxy at all the lateral and vertical interfaces. The interplay of the effects of the gold and also the hydrogen that infilitrated from the surface oxide resulted in a plug of amorphous material at the surface. Further annealing at this temperature demonstrated that the gold, once it had reached a certain critical concentration nucleated poly-crystalline growth instead of solid phase epitaxy. Time resolved reflectivity and Rutherford backscattering and channeling measurements were performed on large area samples that had been subject to the same implantation regime to investigate this system further. It was discovered that the crystallisation dynamics and zone refinement of the gold were complicated functions of both gold concentration and temperature. These findings do not encourage the use of this method to obtain conducting elements embedded in the crystalline silicon substrate.

  3. The structure and functional properties of Ti2 NiCu alloy rapidly quenched ribbons with different fractions of crystalline phase

    Science.gov (United States)

    Belyaev, S. P.; Istomin-Kastrovskiy, V. V.; Koledov, V. V.; Kuchin, D. S.; Resnina, N. N.; Shavrov, V. G.; Shelyakov, A. V.; Ivanov, S. E.

    The samples of Ti2NiCu rapidly quenched alloy with different fractions of crystalline phase have been prepared by electric pulse technique from as spun amorphous ribbons. The structure and thermomechanical properties of these samples have been studied. The mixture of amorphous and nanocrystalline structures with mean grains size less than 10 nm has been observed by HRTEM. The remarkable thermomechanical properties of the samples with the ratio of crystalline fraction in the range of r = 0.4 - 0.6 (determined by electrical resistivity measurements) have been found. The two-way shape memory effect with the reverse deformation Δε = 0.31 % has been induced in the sample with r = 0.46 by single deformation at cooling below the temperature of martensite transformation. The prototype of microtweezers based on amorphous-nanocrystalline Ti2NiCu melt-spun ribbon alloy with two-way shape memory effect has been designed and tested.

  4. New tellurite glasses and crystalline phases in the Bi{sub 2}O{sub 3}-CaO-TeO{sub 2} system: Synthesis and characterization

    Energy Technology Data Exchange (ETDEWEB)

    Chagraoui, Abdeslam; Tairi, Abdelmjid; Ajebli, Kaltoum; Bensaid, Hanane; Moussaoui, Abdenajib [Laboratoire de Chimie Analytique et Physico-chimie des Materiaux, Departement de Chimie, Faculte des Sciences Ben M' sik, Universite HassanII-Mohammedia Casablanca (Morocco)

    2010-04-09

    Tellurite glasses containing calcium and bismuth oxides have been prepared at 800 {sup o}C and investigated by X-ray diffraction, DSC, IR and Raman spectroscopy. The crystalline phases of glasses in TeO{sub 2}-CaO revealed {gamma}TeO{sub 2} phase which transforms into the stable {alpha}TeO{sub 2} phase up to 500 {sup o}C. IR and Raman studies show the transition of TeO{sub 4}, TeO{sub 3+1} and TeO{sub 3} units with increasing CaO content. The value of refractive index and density of glasses have been measured. The investigation in the system using XRD reveals new phases.

  5. Hierarchical architectures TiO2: pollen-inducted synthesis, remarkable crystalline-phase stability, tunable size, and reused photo-catalysis.

    Science.gov (United States)

    Dou, Lingling; Gao, Lishuang; Yang, Xiaohui; Song, Xiuqin

    2012-02-15

    TiO(2) with hierarchical architectures, tunable crystalline phase and thermal stability is successfully fabricated on a large scale through a facile hydrolysis process of TiCl(4) combining with inducing of pollen. The structure of the as-prepared TiO(2) is characterized by X-ray diffraction, Raman spectroscopy, infrared spectra, and scanning electron microscopy. The experimental results indicate that different phases (anatase, rutile or mixed crystallite) of TiO(2) can be synthesized by controlling the experimental conditions. The pure phase of rutile or anatase can be obtained at 100°C, while the pure phase of anatase can be retained after being annealed at 900°C. The hierarchical structures TiO(2) are constitute through self-assembly of nanoparticles or nanorods TiO(2), which exhibit high and reused photo-catalytic properties for degradation of methylene blue.

  6. Enhanced Crystalline Phase Purity of CH3NH3PbI3-xClx Film for High-Efficiency Hysteresis-Free Perovskite Solar Cells.

    Science.gov (United States)

    Yang, Yingguo; Feng, Shanglei; Xu, Weidong; Li, Meng; Li, Li; Zhang, Xingmin; Ji, Gengwu; Zhang, Xiaonan; Wang, Zhaokui; Xiong, Yimin; Cao, Liang; Sun, Baoquan; Gao, Xingyu

    2017-07-12

    Despite rapid successful developments toward promising perovskite solar cells (PSCs) efficiency, they often suffer significant hysteresis effects. Using synchrotron-based grazing incidence X-ray diffraction (GIXRD) with different probing depths by varying the incident angle, we found that the perovskite films consist of dual phases with a parent phase dominant in the interior and a child phase with a smaller (110) interplanar space (d(110)) after rapid thermal annealing (RTA), which is a widely used post treatment to improve the crystallization of solution-processed perovskite films for high-performance planar PSCs. In particular, the child phase composition gradually increases with decreasing depth till it becomes the majority on the surface, which might be one of the key factors related to hysteresis in fabricated PSCs. We further improve the crystalline phase purity of the solution-processed CH3NH3PbI3-xClx perovskite film (referred as g-perovskite) by using a facile gradient thermal annealing (GTA), which shows a uniformly distributed phase structure in pinhole-free morphology with less undercoordinated Pb and I ions determined by synchrotron-based GIXRD, grazing incidence small-angle X-ray scattering, scanning electron microscopy, and X-ray photoelectron spectroscopy. Regardless of device structures (conventional and inverted types), the planar heterojunction PSCs employing CH3NH3PbI3-xClx g-perovskite films exhibit negligible hysteresis with a champion power conversion efficiency of 17.04% for TiO2-based conventional planar PSCs and 14.83% for poly(3,4-ethylenedioxythiophene:poly(styrenesulfonate) (PEDOT:PSS)-based inverted planar PSCs. Our results indicate that the crystalline phase purity in CH3NH3PbI3-xClx perovskite film, especially in the surface region, plays a crucial role in determining the hysteresis effect and device performance.

  7. Detection of a minor amorphous phase in crystalline etoricoxib by dynamic mechanical analysis: comparison with Raman spectroscopy and modulated differential scanning calorimetry.

    Science.gov (United States)

    Clas, Sophie-Dorothee; Lalonde, Karine; Khougaz, Karine; Dalton, Chad R; Bilbeisi, Rana

    2012-02-01

    Detection and quantification of the amorphous phase of etoricoxib bulk drug substances, a selective cycloogenase-2 inhibitor used for the treatment of osteoarthritis, rheumatoid arthritis, and dental pain, was carried out using modulated differential scanning calorimetry (MDSC), dynamic mechanical analysis (DMA), and Raman spectroscopy. Detection of amorphous content in pharmaceutical powders by DMA is a special application of dynamic mechanical spectroscopy. DMA was found to be a sensitive technique, able to detect the presence of an amorphous phase in a crystalline phase at concentrations as low as 0.5%. The limit of detection (LOD) determined for DMA was 2.5%. In comparison, Raman spectroscopy and MDSC had LOD values of 2% and 5% amorphous, respectively.

  8. Cubic-to-monoclinic phase transition during the epitaxial growth of crystalline Gd2O3 films on Ge(001) substrates

    Science.gov (United States)

    Molle, Alessandro; Wiemer, Claudia; Bhuiyan, Md. Nurul Kabir; Tallarida, Grazia; Fanciulli, Marco; Pavia, Giuseppe

    2007-05-01

    Thin crystalline films of Gd2O3 are grown on an atomically flat Ge(001) surface by molecular beam epitaxy and are characterized in situ by reflection high energy electron diffraction and x-ray photoelectron spectroscopy, and ex situ by x-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy. The first stage of the growth corresponds to a cubic (110) structure, with two equiprobable, 90° rotated, in-plane domains. Increasing the thickness of the films, a phase transition from cubic (110) to monoclinic (100) oriented crystallites is observed which keeps the in-plane domain rotation, as evidenced by XRD and AFM.

  9. Drug induced `softening' in phospholipid monolayers

    Science.gov (United States)

    Basak, Uttam Kumar; Datta, Alokmay; Bhattacharya, Dhananjay

    2015-06-01

    Compressibility measurements on Langmuir monolayers of the phospholipid Dimystoryl Phospatidylcholine (DMPC) in pristine form and in the presence of the Non-steroidal Anti-inflammatory Drug (NSAID) Piroxicam at 0.025 drug/lipid (D/L) molecular ratio at different temperatures, show that the monolayer exhibits large increase (and subsequent decrease) in compressibility due to the drug in the vicinity of the Liquid Expanded - Liquid Condensed (LE-LC) phase transition. Molecular dynamics simulations of the lipid monolayer in presence of drug molecules show a disordering of the tail tilt, which is consistent with the above result.

  10. Monolayer coverage and channel length set the mobility in self-assembled monolayer field-effect transistors

    Science.gov (United States)

    Mathijssen, Simon G. J.; Smits, Edsger C. P.; van Hal, Paul A.; Wondergem, Harry J.; Ponomarenko, Sergei A.; Moser, Armin; Resel, Roland; Bobbert, Peter A.; Kemerink, Martijn; Janssen, René A. J.; de Leeuw, Dago M.

    2009-11-01

    The mobility of self-assembled monolayer field-effect transistors (SAMFETs) traditionally decreases dramatically with increasing channel length. Recently, however, SAMFETs using liquid-crystalline molecules have been shown to have bulk-like mobilities that are virtually independent of channel length. Here, we reconcile these scaling relations by showing that the mobility in liquid crystalline SAMFETs depends exponentially on the channel length only when the monolayer is incomplete. We explain this dependence both numerically and analytically, and show that charge transport is not affected by carrier injection, grain boundaries or conducting island size. At partial coverage, that is when the monolayer is incomplete, liquid-crystalline SAMFETs thus form a unique model system to study size-dependent conductance originating from charge percolation in two dimensions.

  11. Thermal and structural studies of imidazolium-based ionic liquids with and without liquid-crystalline phases: the origin of nanostructure.

    Science.gov (United States)

    Nemoto, Fumiya; Kofu, Maiko; Yamamuro, Osamu

    2015-04-16

    To clarify the origin of the nanostructure of ionic liquids (ILs), we have investigated two series of ILs 1-alkyl-3-methylimidazolium hexafluorophosphate (CnmimPF6, n = 4-16, n is an alkyl-carbon number) and 1-alkyl-3-methylimidazolium chloride (CnmimCl, n = 4-14) using differential scanning calorimetry and X-ray diffraction techniques. The PF6 samples with n > 13 and the Cl samples with n > 10 exhibited the liquid-crystalline (LC) to liquid (L) phase transitions, as reported before. We found that both samples with smaller n also exhibited the LC to L transitions under supercooled states as far as the ionic motions were not frozen-in at the glass transition temperatures Tg. The Tg of the LC phase was close to that of the L phase, indicating that the characteristic length of the glass transition is shorter than that of the nanostructure. A low-Q peak due to the nanostructure in the L phase and a diffraction peak due to the layer structure in the LC phase appeared at almost the same Q positions in both samples. On the basis of the above results and some thermodynamic analysis, we argue that the nanostructures of ILs are essentially the same as the layer structures in the LC phases.

  12. Primordial hexagonal phase formation during the bcc dezincification of the {beta} Cu-Zn single crystalline surface: Matrix instabilization and transformation path

    Energy Technology Data Exchange (ETDEWEB)

    Baruj, A. [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica (CNEA), (8400) San Carlos de Bariloche, Rio Negro (Argentina); CONICET (Argentina)], E-mail: baruj@cab.cnea.gov.ar; Granada, M.; Arneodo Larochette, P. [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica (CNEA), (8400) San Carlos de Bariloche, Rio Negro (Argentina); CONICET (Argentina); Sommadossi, S. [F. Ingenieria, U. N. Comahue, Buenos Aires 1400, (8300) Neuquen (Argentina); CONICET (Argentina); Troiani, H.E. [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica (CNEA), (8400) San Carlos de Bariloche, Rio Negro (Argentina); CONICET (Argentina)

    2009-07-29

    Subjecting Cu-Zn samples to annealing under dynamical vacuum produces the evaporation of Zn, a process known as dezincification. Here, we study the phase transitions related to dezincification of Cu-48 at.% Zn (bcc, Beta phase) single crystalline surfaces with residual stresses due to mechanical polishing. In order to identify different steps in the dezincification process of these deformed samples we apply a combination of in situ optical microscopy and transmission electron microscopy (TEM) observations. The former allows us to control and stop the dezincification process at a specific stage of evolution while the latter allows relating surface features with structure and composition changes. Due to dezincification, the formation of an on average 4H hexagonal phase and the fcc equilibrium phase take place. TEM observations show that the bcc to 4H phase transformation occurs by a mechanism of nucleation and growth. In particular, we show evidence of the mechanism of embryo formation for the first time. During the subsequent growth process, the coalescence of transformed zones defines regions in the micron range which after subsequent prolonged dezincification transform to the final fcc equilibrium structure. These experiments provide an insight on the reason for the formation of the non-equilibrium hexagonal phase during the dezincification of electropolished (non-deformed) samples. The new experimental results evidence the heterogeneous character of the dezincification.

  13. Synchrotron X-Ray Study of Novel Crystalline-B Phases in Heptyloxybenzylidene-Heptylaniline (70.7)

    DEFF Research Database (Denmark)

    Collet, J.; Sorensen, L. B.; Pershan, P. S.;

    1982-01-01

    This paper reports an x-ray diffraction study of structures and restacking transitions within the B phases of heptyloxybenzylidene-heptylaniline. The system evolves from a hexagonal close-packed structure, through intermediate orthorhombic and monoclinic phases, to a simple hexagonal structure. T....... The monoclinic phase has a temperature-dependent shear which transforms the system from orthorhombic to hexagonal. The latter three phases exhibit a single-q⃗ sinusoidal modulation of the molecular layers....

  14. In-plane X-ray diffraction from monolayers of perfluorinated fatty acids: evidence for azimuthal ordering in the condensed phase

    OpenAIRE

    Goldmann, M; Nassoy, Pierre; Rondelez, Francis; Renault, Anne; Shin, Seokmin; Rice, Stuart

    1994-01-01

    We report the results of new grazing incidence X-ray diffraction studies of Langmuir monolayers of F(CF2)11COOH and F(CF2)10CH2COOH supported on water ; in each case the locations and intensities of the first three diffraction peaks ((1, 0), (1, 1) and (2, 0)) have been measured. These new data are consistent with earlier ones in that both monolayers have simple hexagonal packing of molecules with their long axes nearly perpendicular to the water surface at maximum surface densities. By compa...

  15. Formation of single-crystalline aragonite tablets/films via an amorphous precursor.

    Science.gov (United States)

    Amos, Fairland F; Sharbaugh, Denise M; Talham, Daniel R; Gower, Laurie B; Fricke, Marc; Volkmer, Dirk

    2007-02-13

    Thin tablets and films of calcium carbonate have been grown at the air-water interface via an amorphous precursor route using soluble process-directing agents and a Langmuir monolayer based on resorcarene. By using appropriate concentrations of poly(acrylic acid-sodium salt) in combination with Mg2+ ion, an initially amorphous film is deposited on the monolayer template, which subsequently crystallizes into a mosaic film composed of a mixture of single-crystalline and spherulitic patches of calcite and aragonite. Of particular importance is the synthesis of single-crystalline "tablets" of aragonite (approximately 600 nm thick), because this phase generally forms needle-like polycrystalline aggregates when grown in vitro. To our knowledge, a tabular single-crystalline morphology of aragonite has only been observed in the nacreous layer of mollusk shells. Therefore, this in vitro system may serve as a useful model for examining mechanistic issues pertinent to biomineralization, such as the influence of organic templates on nucleation from an amorphous phase.

  16. Liquid crystalline dihydroazulene photoswitches

    DEFF Research Database (Denmark)

    Petersen, Anne Ugleholdt; Jevric, Martyn; Mandle, Richard J.

    2015-01-01

    A large selection of photochromic dihydroazulene (DHA) molecules incorporating various substituents at position 2 of the DHA core was prepared and investigated for their ability to form liquid crystalline phases. Incorporation of an octyloxy-substituted biphenyl substituent resulted in nematic...

  17. Thermal ripples in model molybdenum disulfide monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Remsing, Richard C.; Klein, Michael L. [Institute for Computational Molecular Science, Center for the Computational, Design of Functional Layered Materials, and Department of Chemistry, Temple University, 1925 N. 12th St., 19122, Philadelphia, PA (United States); Waghmare, Umesh V. [Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, 560 064, Jakkur, Bangalore (India)

    2017-01-15

    Molybdenum disulfide (MoS{sub 2}) monolayers have the potential to revolutionize nanotechnology. To reach this potential, it will be necessary to understand the behavior of this two-dimensional (2D) material on large length scales and under thermal conditions. Herein, we use molecular dynamics (MD) simulations to investigate the nature of the rippling induced by thermal fluctuations in monolayers of the 2H and 1T phases of MoS{sub 2}. The 1T phase is found to be more rigid than the 2H phase. Both monolayer phases are predicted to follow long wavelength scaling behavior typical of systems with anharmonic coupling between vibrational modes as predicted by classic theories of membrane-like systems. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Formation of liquid-crystalline structures in the bile salt-chitosan system and triggered release from lamellar phase bile salt-chitosan capsules.

    Science.gov (United States)

    Tangso, Kristian J; Lindberg, Seth; Hartley, Patrick G; Knott, Robert; Spicer, Patrick; Boyd, Ben J

    2014-08-13

    Nanostructured capsules comprised of the anionic bile salt, sodium taurodeoxycholate (STDC), and the biocompatible cationic polymer, chitosan, were prepared to assess their potential as novel tailored release nanomaterials. For comparison, a previously studied system, sodium dodecyl sulfate (SDS), and polydiallyldimethylammonium chloride (polyDADMAC) was also investigated. Crossed-polarizing light microscopy (CPLM) and small-angle X-ray scattering (SAXS) identified the presence of lamellar and hexagonal phase at the surfactant-polymer interface of the respective systems. The hydrophobic and electrostatic interactions between the oppositely charged components were studied by varying temperature and salt concentration, respectively, and were found to influence the liquid-crystalline nanostructure formed. The hexagonal phase persisted at high temperatures, however the lamellar phase structure was lost above ca. 45 °C. Both mesophases were found to dissociate upon addition of 4% NaCl solution. The rate of release of the model hydrophilic drug, Rhodamine B (RhB), from the lamellar phase significantly increased in response to changes in the solution conditions studied, suggesting that modulating the drug release from these bile salt-chitosan capsules is readily achieved. In contrast, release from the hexagonal phase capsules had no appreciable response to the stimuli applied. These findings provide a platform for these oppositely charged surfactant and polymer systems to function as stimuli-responsive or sustained-release drug delivery systems.

  19. Synthesis, characterization and structural control of nano crystalline molybdenum oxide MoO{sub 3} single phase by low cost technique

    Energy Technology Data Exchange (ETDEWEB)

    Afify, H.H.; Hassan, S.A. [Solid State Department, Physics Division, National Research Centre, 33 El Bohouthst. (fromer El Tahrirst.), Dokki, P.O. 12622, Giza (Egypt); Abouelsayed, A., E-mail: as.abouelsayed@gmail.com [Spectroscopy Department, Physics Division, National Research Centre, 33 El Bohouthst. (fromer El Tahrirst.), Dokki, P.O. 12622, Giza (Egypt); Demian, S.E. [Solid State Department, Physics Division, National Research Centre, 33 El Bohouthst. (fromer El Tahrirst.), Dokki, P.O. 12622, Giza (Egypt); Zayed, H.A. [Physics Department, Faculty of Girls for Art, Sciences and Education, Ain Shams University (Egypt)

    2016-06-15

    Thermodynamically stable α- MoO{sub 3} thin film is prepared without any other phases of the molybdenum oxides. Simple and low coast spray pyrolysis technique is used. Growth conditions are optimized to produce pure α- MoO{sub 3} with controlled crystallite size and surface morphology. Small angle (GAXRD) diffractometer is used to elucidate the structure. Profile shape function (PSF) model is made for the experimental data. WinFit software is going first to fit (PSF) to use the refined profile parameters for determination of crystallite size and internal residual strain. The (GAXRD) patterns prove the existence of α- MoO{sub 3} only with layered structure, indicated by the appearance of only (0k0). The calculated crystallite sizes and the strain are found to range from 10 to 28 nm and 0.28%–0.05% respectively. Ultraviolet and Visible transmission measurements were performed over a wavelength range 190–2500 nm on the MoO{sub 3} thin films synthesized by spray pyrolysis technique at different substrate temperature. The two sub-bands corresponds to the electronic transition between the molybdenum oxidation states Mo{sup 4+}, Mo{sup 5+} and Mo{sup 6+} are observed. Quantitative information on the temperature-induced blue shift of the sub-bands was obtained by fitting the spectra with Lorentz functions. The transition from Mo{sup 5+} to Mo{sup 6+} oxidation states show a blue shift up to Tc = 325 °C. Above Tc, the transition Mo{sup 5+} to Mo{sup 6+} increases more drastically, resulting in an anomaly in the temperature-induced shift at Tc. The anomaly can be attributed to the amorphous-to-crystalline phase transition at 325 °C. In addition, both refractive index and extinction coefficient are calculated as a function of substrate temperature. - Highlights: • Single phase α-MoO{sub 3} nano crystalline MoO{sub 3} thin films have been synthesized. • Amorphous-to-crystalline phase transition occurs at 325 °C for MoO{sub 3} thin films. • A clear

  20. Thermodynamics of Crystalline States

    CERN Document Server

    Fujimoto, Minoru

    2010-01-01

    Thermodynamics is a well-established discipline of physics for properties of matter in thermal equilibrium surroundings. Applying to crystals, however, the laws encounter undefined properties of crystal lattices, which therefore need to be determined for a clear and well-defined description of crystalline states. Thermodynamics of Crystalline States explores the roles played by order variables and dynamic lattices in crystals in a wholly new way. This book is divided into three parts. The book begins by clarifying basic concepts for stable crystals. Next, binary phase transitions are discussed to study collective motion of order variables, as described mostly as classical phenomena. In the third part, the multi-electron system is discussed theoretically, as a quantum-mechanical example, for the superconducting state in metallic crystals. Throughout the book, the role played by the lattice is emphasized and examined in-depth. Thermodynamics of Crystalline States is an introductory treatise and textbook on meso...

  1. Field-Induced Crystalline-to-Amorphous Phase Transformation on the Si Nano-Apex and the Achieving of Highly Reliable Si Nano-Cathodes

    Science.gov (United States)

    Huang, Yifeng; Deng, Zexiang; Wang, Weiliang; Liang, Chaolun; She, Juncong; Deng, Shaozhi; Xu, Ningsheng

    2015-05-01

    Nano-scale vacuum channel transistors possess merits of higher cutoff frequency and greater gain power as compared with the conventional solid-state transistors. The improvement in cathode reliability is one of the major challenges to obtain high performance vacuum channel transistors. We report the experimental findings and the physical insight into the field induced crystalline-to-amorphous phase transformation on the surface of the Si nano-cathode. The crystalline Si tip apex deformed to amorphous structure at a low macroscopic field (0.6~1.65 V/nm) with an ultra-low emission current (1~10 pA). First-principle calculation suggests that the strong electrostatic force exerting on the electrons in the surface lattices would take the account for the field-induced atomic migration that result in an amorphization. The arsenic-dopant in the Si surface lattice would increase the inner stress as well as the electron density, leading to a lower amorphization field. Highly reliable Si nano-cathodes were obtained by employing diamond like carbon coating to enhance the electron emission and thus decrease the surface charge accumulation. The findings are crucial for developing highly reliable Si-based nano-scale vacuum channel transistors and have the significance for future Si nano-electronic devices with narrow separation.

  2. Pressure-induced lattice collapse in the tetragonal phase of single-crystalline Fe(1.05)Te

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Chao [Beijing National Laboratory for Condensed Matter Physics/Chinese Academy of Scie; Yi, Wei [Beijing National Laboratory for Condensed Matter Physics/Chinese Academy of Scie; Sun, Liling [Beijing National Laboratory for Condensed Matter Physics/Chinese Academy of Scie; Chen, Xiao-Jia [Carnegie Institution of Washington; Hemley, Russell [Carnegie Institution of Washington; Mao, Ho-Kwang [Carnegie Institution of Washington; Lu, Wei [Beijing National Laboratory for Condensed Matter Physics/Chinese Academy of Scie; Dong, Xiaoli [Beijing National Laboratory for Condensed Matter Physics/Chinese Academy of Scie; Ligang, Bai [Institute of High Energy Physics, Chinese Academy of Sciences, China; Jing, Liu [Institute of High Energy Physics, Chinese Academy of Sciences, China; Moreira Dos Santos, Antonio F [ORNL; Molaison, Jamie J [ORNL; Tulk, Christopher A [ORNL; Chen, Genfu [Beijing National Laboratory for Condensed Matter Physics/Chinese Academy of Scie; Wang, Nanlin [The Institute of Physics, Chinese Academy of Sciences; Zhao, Zhongxian [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics

    2009-01-01

    Pressure-induced lattice collapse was discovered in tetragonal T phase of single crystal Fe{sub 1.05}Te at room temperature through x-ray and neutron-diffraction measurements. A remarkable compression along the c axis {approx}5% was observed upon increasing pressure from the ambient condition to 4 GPa. Indexed results demonstrate that the crystallographic structure remains unchanged after the collapse, revealing that the collapse does not break symmetry of crystal structure. The Fe-spin state change was proposed to account for the lattice collapse. The equations of state for the T phase and pressure-induced collapsed T phase were determined from the diffraction measurements.

  3. Magnetic and magnetothermal properties and the magnetic phase diagram of high purity single crystalline terbium along the easy magnetization direction.

    Science.gov (United States)

    Zverev, V I; Tishin, A M; Chernyshov, A S; Mudryk, Ya; Gschneidner, K A; Pecharsky, V K

    2014-02-12

    The magnetic and magnetothermal properties of a high purity terbium single crystal have been re-investigated from 1.5 to 350 K in magnetic fields ranging from 0 to 75 kOe using magnetization, ac magnetic susceptibility and heat capacity measurements. The magnetic phase diagram has been refined by establishing a region of the fan-like phase broader than reported in the past, by locating a tricritical point at 226 K, and by a more accurate definition of the critical fields and temperatures associated with the magnetic phases observed in Tb.

  4. Determination of Crystallinity and Crystal Structure of Hylamer™ Polyethylene after in vivo Wear

    OpenAIRE

    Visentin, M; Stea, S.; De Clerico, M.; Reggiani, M.; Fagnano, C.; Squarzoni, S.; De Toni, A

    2006-01-01

    Abstract Hylamer? polyethylene is a crystalline form of polyethylene of 70% crystallinity whereas conventional polyethylene (PE) has 50% crystallinity. Crystallinity is the percentage by weight of the crystalline phase present in the whole polymer, which comprises both amorphous and crystalline phases. Clinical experience has shown that Hylamer? components used in joint prostheses, if sterilized ...

  5. Determination of Crystallinity and Crystal Structure of Hylamer™ Polyethylene after in vivo Wear

    OpenAIRE

    Visentin, M; Stea, S.; Clerico, M; Reggiani, M.; Fagnano, C.; Squarzoni, S.; Toni, A.

    2006-01-01

    Abstract Hylamer? polyethylene is a crystalline form of polyethylene of 70% crystallinity whereas conventional polyethylene (PE) has 50% crystallinity. Crystallinity is the percentage by weight of the crystalline phase present in the whole polymer, which comprises both amorphous and crystalline phases. Clinical experience has shown that Hylamer? components used in joint prostheses, if sterilized ...

  6. Hexagonal Close-Packed ^4{He} as Crystalline Multilayered Polytype: An Alternative for `Supersolid' or `Glassy-Like' Phase

    Science.gov (United States)

    Chishko, K. A.; Antsygina, T. N.; Poltavskaya, M. I.

    2017-01-01

    We apply the model of a crystalline polytype built of close-packed 2D monoatomic basal planes with triangular lattice to interpret the anomalous thermodynamical and mechanical properties of solid hexagonal close-packed (HCP) ^4{He} . The polytype is a 3D stack of the basal planes, and its structure can be built from the simplest periodic packing (HCP, FCC, 4H, 5H, 6R, ldots etc.) up to random stacking fault system (RSFS) totally aperiodic in only c-direction perpendicular to the basal planes. RSFS is a crystal without microscopic translation symmetry along c-axis, i.e., entirely disordered in only one spatial direction. Despite of packing disorder, c-direction remains the crystallographic axis of third order at arbitrary sequence of the 2D plates in the whole stack. In a long-wave limit the HCP polytype can be treated as 3D anisotropic continuum, as a result its phonon spectrum and Helmholtz free energy have been calculated. The temperature dependence of the phonon pressure is calculated theoretically and compared with experimental data. A quantitative agreement between the theory and the experiment is achieved. Mechanical properties of ^4{He} crystals in the framework of the polytype model are briefly discussed.

  7. Atomic-scale study of the amorphous-to-crystalline phase transition mechanism in GeTe thin films

    CERN Document Server

    Mantovan, R.; Mokhles Gerami, A.; Mølholt, T. E.; Wiemer, C.; Longo, M.; Gunnlaugsson, H. P.; Johnston, K.; Masenda, H.; Naidoo, D.; Ncube, M.; Bharuth-Ram, K.; Fanciulli, M.; Gislason, H. P.; Langouche, G.; Ólafsson, S.; Weyer, G.

    The underlying mechanism driving the structural amorphous-to-crystalline transition in Group VI chalcogenides is still a matter of debate even in the simplest GeTe system. We exploit the extreme sensitivity of 57Fe emission Mössbauer spectroscopy, following dilute implantation of 57Mn (T½ = 1.5 min) at ISOLDE/CERN, to study the electronic charge distribution in the immediate vicinity  of the 57Fe probe substituting Ge (FeGe), and to interrogate the local environment of FeGe over the amorphous-crystalline phase transition in GeTe thin films. Our results show that the local structure  of as-sputtered amorphous GeTe is a combination of tetrahedral and defect-octahedral sites. The main effect of the crystallization is the conversion from tetrahedral to defect-free octahedral sites.  We discover that only the tetrahedral fraction in amorphous GeTe participates to the change of the FeGe-Te chemical bond...

  8. Distinct molecular structures and hydrogen bond patterns of α,α-diethyl-substituted cyclic imide, lactam, and acetamide derivatives in the crystalline phase

    Science.gov (United States)

    Krivoshein, Arcadius V.; Ordonez, Carlos; Khrustalev, Victor N.; Timofeeva, Tatiana V.

    2016-10-01

    α,α-Dialkyl- and α-alkyl-α-aryl-substituted cyclic imides, lactams, and acetamides show promising anticonvulsant, anxiolytic, and anesthetic activities. While a number of crystal structures of various α-substituted cyclic imides, lactams, and acetamides were reported, no in-depth comparison of crystal structures and solid-state properties of structurally matched compounds have been carried out so far. In this paper, we report molecular structure and intermolecular interactions of three α,α-diethyl-substituted compounds - 3,3-diethylpyrrolidine-2,5-dione, 3,3-diethylpyrrolidin-2-one, and 2,2-diethylacetamide - in the crystalline phase, as studied using single-crystal X-ray diffraction and IR spectroscopy. We found considerable differences in the patterns of H-bonding and packing of the molecules in crystals. These differences correlate with the compounds' melting points and are of significance to physical pharmacy and formulation development of neuroactive drugs.

  9. Understanding the Crystallinity Indices Behavior of Burned Bones and Teeth by ATR-IR and XRD in the Presence of Bioapatite Mixed with Other Phosphate and Carbonate Phases

    Directory of Open Access Journals (Sweden)

    Giampaolo Piga

    2016-01-01

    Full Text Available We have critically investigated the ATR-IR spectroscopy data behavior of burned human teeth as opposed to the generally observed behavior in human bones that were subjected to heat treatment, whether deliberate or accidental. It is shown that the deterioration of the crystallinity index (CI behavior sometimes observed in bones subjected to high temperature appears to be of higher frequency in the case of bioapatite from teeth. This occurs because the formation of the β-tricalcium phosphate (β-TCP phase, otherwise known as whitlockite, clearly ascertained by the X-ray diffraction (XRD patterns collected on the same powdered specimens investigated by ATR-IR. These results point to the need of combining more than one physicochemical technique even if apparently well suitable, in order to verify whether the assumed conditions assessed by spectroscopy are fully maintained in the specimens after temperature and/or mechanical processing.

  10. Crystalline phases during the melting of Bi sub 2 Sr sub 2 CaCu sub 2 O sub x

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Ming; Polonka, J.; Goldman, A.I.; Finnemore, D.K.; Li, Qiang; Laabs, F.C.

    1991-01-01

    The melting of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} material has been studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) in order to study the phases that formed in the high temperature regions. Two distinct phases of (Sr{sub 1-x}Ca{sub x})CuO{sub 2} and (Sr{sub 1-x}Ca{sub x}){sub 2}CuO{sub 3} have been observed in the Bi-rich matrix depending upon quenching temperatures. Crystallization from the melt by fast cooling usually produce the co-existence of Bi (2201) and these Sr-Ca-Cu-O phases. 12 refs., 2 figs.

  11. Role of sintering time, crystalline phases and symmetry in the piezoelectric properties of lead-free KNN-modified ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Rubio-Marcos, F., E-mail: frmarcos@icv.csic.es [Electroceramic Department, Instituto de Ceramica y Vidrio, CSIC, Kelsen 5, 28049 Madrid (Spain); Marchet, P.; Merle-Mejean, T. [SPCTS, UMR 6638 CNRS, Universite de Limoges, 123, Av. A. Thomas, 87060 Limoges (France); Fernandez, J.F. [Electroceramic Department, Instituto de Ceramica y Vidrio, CSIC, Kelsen 5, 28049 Madrid (Spain)

    2010-09-01

    Lead-free KNN-modified piezoceramics of the system (Li,Na,K)(Nb,Ta,Sb)O{sub 3} were prepared by conventional solid-state sintering. The X-ray diffraction patterns revealed a perovskite phase, together with some minor secondary phase, which was assigned to K{sub 3}LiNb{sub 6}O{sub 17}, tetragonal tungsten-bronze (TTB). A structural evolution toward a pure tetragonal structure with the increasing sintering time was observed, associated with the decrease of TTB phase. A correlation between higher tetragonality and higher piezoelectric response was clearly evidenced. Contrary to the case of the LiTaO{sub 3} modified KNN, very large abnormal grains with TTB structure were not detected. As a consequence, the simultaneous modification by tantalum and antimony seems to induce during sintering a different behaviour from the one of LiTaO{sub 3} modified KNN.

  12. Protecting the properties of monolayer MoS2 on silicon based substrates with an atomically thin buffer

    Science.gov (United States)

    Man, Michael K. L.; Deckoff-Jones, Skylar; Winchester, Andrew; Shi, Guangsha; Gupta, Gautam; Mohite, Aditya D.; Kar, Swastik; Kioupakis, Emmanouil; Talapatra, Saikat; Dani, Keshav M.

    2016-02-01

    Semiconducting 2D materials, like transition metal dichalcogenides (TMDs), have gained much attention for their potential in opto-electronic devices, valleytronic schemes, and semi-conducting to metallic phase engineering. However, like graphene and other atomically thin materials, they lose key properties when placed on a substrate like silicon, including quenching of photoluminescence, distorted crystalline structure, and rough surface morphology. The ability to protect these properties of monolayer TMDs, such as molybdenum disulfide (MoS2), on standard Si-based substrates, will enable their use in opto-electronic devices and scientific investigations. Here we show that an atomically thin buffer layer of hexagonal-boron nitride (hBN) protects the range of key opto-electronic, structural, and morphological properties of monolayer MoS2 on Si-based substrates. The hBN buffer restores sharp diffraction patterns, improves monolayer flatness by nearly two-orders of magnitude, and causes over an order of magnitude enhancement in photoluminescence, compared to bare Si and SiO2 substrates. Our demonstration provides a way of integrating MoS2 and other 2D monolayers onto standard Si-substrates, thus furthering their technological applications and scientific investigations.

  13. Sub-THz Characterisation of Monolayer Graphene

    Directory of Open Access Journals (Sweden)

    Ehsan Dadrasnia

    2014-01-01

    Full Text Available We explore the optical and electrical characteristics of monolayer graphene by using pulsed optoelectronic terahertz time-domain spectroscopy in the frequency range of 325–500 GHz based on fast direct measurements of phase and amplitude. We also show that these parameters can, however, be measured with higher resolution using a free space continuous wave measurement technique associated with a vector network analyzer that offers a good dynamic range. All the scattering parameters (both magnitude and phase are measured simultaneously. The Nicholson-Ross-Weir method is implemented to extract the monolayer graphene parameters at the aforementioned frequency range.

  14. Control of Crystalline Forms and Morphologies for CaCO3 Crystals on 3-Mercaptopropionic Acid Self-assembled Monolayers%3-巯基丙酸自组装单层控制碳酸钙晶型及形貌的研究

    Institute of Scientific and Technical Information of China (English)

    张素; 王海水

    2013-01-01

    In the present study, the crystals of CaCO3 were obtained by the slow diffusion of NH3 and CO2 into the CaCl2 solutions. Experimental results showed that both 3-mercaptopropionic acid self-assembled monolayers (SAMs) and solution temperature have significant influence on the crystalline forms and morphologies of calcium carbonates crystals. The precipitations of calcium carbonate were easily obtained from solutions at 25℃ but with polymorphism including calcite, vaterite and aragonite, while on the self-assembled monolayers there exist calcite crystals only. The morphologies of calcite crystals can be mediated by temperature. For example, the calcite precipitated at 25℃ has smooth surface while that precipitated at 60℃ has porous structure even though they were obtained on the same SAMs. XRD analysis showed that the growth of calcite on SAMs were along (104) and (006) planes.%采用碳酸铵分解产生的NH3和CO2扩散并溶入氯化钙溶液中,得到了碳酸钙晶体.研究结果表明,3-巯基丙酸自组装单层和溶液温度对碳酸钙晶体的晶型和形貌具有重要影响.25℃条件下,纯溶液中得到了方解石,文石和球霰石三种晶型的混合沉淀物,而在自组装单层存在条件下只得到了表面光滑的菱面体方解石.改变温度,自组装单层调控得到的方解石晶体具有不同的形貌.在60℃得到了多孔方解石,与25℃时典型菱面体方解石有重要区别.XRD分析表明自组装膜上所得碳酸钙晶体为沿着(104)和(006)晶面取向生长的方解石.

  15. Electrical induction and optical erasure of birefringence in the isotropic liquid phase of a dichiral azobenzene liquid-crystalline compound (Presentation Recording)

    Science.gov (United States)

    Yamamoto, Takahiro; Nishiyama, Isa

    2015-10-01

    Liquid crystal is a representative soft matter, which has physical properties between those of conventional liquid and those of crystal in a temperature range above a melting point. A liquid-crystal display (LCD) employs the response of the liquid-crystal alignment to the electric field and is a key device of an information display. For common LCDs, the precise control of the initial alignment of LC molecules is needed so that a good dark state, thus a high contrast ratio, can be obtained. If the birefringence can be induced in the liquid phase by the application of electric field, it is of great use as a material for the LCD application. In this study, we will report a unique property of dichiral azobenzene liquid crystals: an electric induction of birefringence in a liquid phase of an antiferroelectric dichiral azobenzene liquid crystal. The optically isotropic texture changes into the homogenous birefringent texture by the application of the in-plane electric field above the clearing temperature of the liquid crystal. We find that one of the possible reasons of the induction of the birefringence in the isotropic phase is the electrically-induced increase of the phase transition temperature between the antiferroelectric liquid-crystalline and "liquid" phases, i.e., increase in the clearing temperature. The resulting birefringence can be disappeared by the irradiation of UV light, due to the photoinduced isomerization of the azobenzene compound, thus dual control of the birefringent structure, by the irradiation of light and/or by the application of the electric field, is achieved.

  16. Bietti's Crystalline Dystrophy

    Science.gov (United States)

    ... Dystrophy > Facts About Bietti's Crystalline Dystrophy Facts About Bietti's Crystalline Dystrophy This information was developed by the ... is the best person to answer specific questions. Bietti’s Crystalline Dystrophy Defined What is Bietti’s Crystalline Dystrophy? ...

  17. Crystalline systems. [Book chapter

    Energy Technology Data Exchange (ETDEWEB)

    Kispert, L.D.

    The use of two double resonance methods, electron-nuclear double resonance (ENDOR) and electron-electron double resonance (ELDOR) in the study of free radicals in solids is reviewed. Included are descriptions of how crystalline-phase ENDOR is used to determine small hyperfine splittings, quadrupoly couplings, and reaction mechanisms or radical formation and how crystalline phase ELDOR is used to determine large hyperfine splittings, to identify radicals with large quadrupole moments and to study spin exchange processes. The complementary role played by the ENDOR and ELDOR spectroscopy in the separation of overlapping EPR spectra, in the study of proton-deuterium exchange, in the study of methyl groups undergoing tunneling rotation, and in the determination of the rates of intermolecular motion are dealt with. 13 figures, 1 table. (DP)

  18. Thermodynamics of Crystalline States

    CERN Document Server

    Fujimoto, Minoru

    2013-01-01

    Thermodynamics is a well-established discipline of physics for properties of matter in thermal equilibrium with the surroundings. Applying to crystals, however, the laws encounter undefined properties of crystal lattice, which therefore need to be determined for a clear and well-defined description of crystalline states. Thermodynamics of Crystalline States explores the roles played by order variables and dynamic lattices in crystals in a wholly new way. The book begins by clarifying basic concepts for stable crystals. Next, binary phase transitions are discussed to study collective motion of order variables, as described mostly as classical phenomena. New to this edition is the examination of magnetic crystals, where magnetic symmetry is essential for magnetic phase transitions. The multi-electron system is also discussed  theoretically, as a quantum-mechanical example, for superconductivity in metallic crystals. Throughout the book, the role played by the lattice is emphasized and studied in-depth. Thermod...

  19. Theoretical study of phase behaviour of DLVO model for lysozyme and γ-crystalline aqueous electrolyte solutions

    Directory of Open Access Journals (Sweden)

    R. Melnyk

    2015-03-01

    Full Text Available Mean spherical approximation (MSA, second-order Barker-Henderson (BH perturbation theory and thermodynamic perturbation theory (TPT for associating fluids in combination with BH perturbation theory are applied to the study of the structural properties and phase behaviour of the Derjaguin-Landau-Verwey-Overbeek (DLVO model of lysozyme and γ-cristalline aqueous electrolyte solutions. Predictions of the MSA for the structure factors are in good agreement with the corresponding computer simulation predictions. The agreement between theoretical results for the liquid-gas phase diagram and the corresponding results of the experiment and computer simulation is less satisfactory, with predictions of the combined BH-TPT approach being the most accurate.

  20. Crystalline phase of Y2O3:Eu particles generated in a substrate-free flame process

    Institute of Scientific and Technical Information of China (English)

    Bing Guo; Hoon Yim; Wonjoong Hwang; Matt Nowell; Zhiping Luo

    2011-01-01

    In this study, factors affecting the crystal structure of flame-synthesized Y2O3:Eu particles were investigated, especially the particle size effect and its interaction with Eu doping concentration. Polydisperse Y2O3:Eu (size range 200nm to 3 μm) powder samples with Eu doping concentrations from 2.5 mol% to 25 mol% were generated in either H2/air or H2/O2 substrate-free flames. The crystal structure of the powder samples was determined by powder X-ray diffraction (XRD),which was complemented by photoluminescence (PL) measurements. Single particle crystal structure was determined by single particle selected area electron diffraction (SAED),and for the first time,by electron backscatter diffraction (EBSD).H2/air flames resulted in cubic phase Y2O3:Eu particles with hollow morphology and irregular shapes.Particles from H2/O2 flames had dense and spherical morphology; samples with lower Eu doping concentrations had mixed cubic/monoclinic phases: samples with the highest Eu doping concentrations were phase-pure monoclinic. For samples generated from H2/O2 flames,a particle size effect and its interaction with Eu doping concentration were found: particles smaller than a critical diameter had the monoclinic phase,and this critical diameter increased with increasing Eu doping concentration. These findings suggest that the formation of monoclinic Y2O3:Eu is inevitable when extremely hot substrate-free flames are used,because typical flame-synthesized Y2O3:Eu particle sizes are well below the critical diameter.However,it may be possible to generate particles with dense,spherical morphology and the desired cubic structure by using a moderately high flame temperature that enables fast sintering without melting the particles.

  1. Quasicritical behavior of the low-frequency dielectric permittivity in the isotropic phase of liquid crystalline materials.

    Science.gov (United States)

    Drozd-Rzoska, A; Rzoska, S J; Zioło, J; Jadzyn, J

    2001-05-01

    Results presented give evidence of the existence of quasicritical, fluidlike behavior in the isotropic phase of 4-cyano-4-pentyl-biphenyl (5CB) for frequencies ranging from the static to the ionic-dominated [low-frequency (LF)] region. Despite the boost of dielectric permittivity on lowering the frequency below 1 kHz, values of the isotropic-nematic transition discontinuity (approximately 1.1 K) and the critical exponent alpha (approximately 0.5) remain constant. It is shown that the contribution from residual ionic impurities is a linear function of temperature in the critical, prenematic fluctuation-dominated region. The validity of the fluidlike and critical behavior for LF dielectric permittivity confirmed results of a derivative analysis of the experimental data: d(epsilon)/dT proportional to (T-T*)(-alpha), originally proposed for critical mixtures. Results of a preliminary test in the isotropic phase of 4-decyl-4'-isothiocyanatobiphenyl (10BT), on approaching the smectic-E phase, may indicate a general validity of results obtained.

  2. Effect of Ce2O3 on Structure, Viscosity, and Crystalline Phase of CaO-Al2O3-Li2O-Ce2O3 Slags

    Science.gov (United States)

    Qi, Jie; Liu, Chengjun; Zhang, Chi; Jiang, Maofa

    2017-02-01

    Aiming at devising new mold flux for Ce-bearing stainless steel, a fundamental investigation on the effect of Ce2O3 on properties of the CaO-Al2O3-Li2O-Ce2O3 slag was provided by the present work. The results show that adding Ce2O3 could decrease the viscosity of the slag due to its effects on decreasing the polymerization of the slag. The crystalline process was restrained by increasing the content of Ce2O3, and the crystalline phases also can be influenced by the slag structure. The crystalline phases were transferred from LiAlO2 and CaO to LiAlO2 and CaCeAlO4 with the addition of Ce2O3 to the slag, which could be well confirmed by the structure of the unit cell of the crystals.

  3. 宽温域蓝相液晶材料%Wide Temperature Range Blue Phase Liquid Crystalline Materials

    Institute of Scientific and Technical Information of China (English)

    何万里; 王玲; 王乐; 崔晓鹏; 谢谟文; 杨槐

    2012-01-01

    Blue phases (BPs) are mesophases usually exhibited by highly chiral materials and commonly occur in a narrow temperature range below the isotropic phase. They are optically active and non-birefringent, while exhibit Bragg diffraction of light in the visible wavelength. Recently, BPs have attracted growing attention in the field of optoelectronics and photonics. This paper reviews the recent research advances in BPs liquid crystals, also with a brief introduction of the history of the blue phase studies, and some special properties, especially the frustration in the double twist molecular alignment. Finally, the current challenges for applications of BPs materials are highlighted, and the focus of future research and development are proposed%蓝相常在高手性液晶体系的清亮点附近温度区间出现,由于具有优异的光学特性如无双折射现象和选择性反射可见光等,近年来蓝相在光电和光子领域越来越受到人们的关注。本文综述了蓝相的发现、分子排列和光学特性等,详细介绍了宽温域蓝相液晶材料在国内外的研究进展和应用现状。最后分析了蓝相液晶用于平板显示领域在技术方面存在的主要问题和未来发展方向。

  4. On the Evolution of Quasicrystalline and Crystalline Phases in Rapidly Quenched Al-Co-Cu-Ni Alloy

    OpenAIRE

    Yadav, T. P.; Mukhopadhyay, N. K.; Tiwari, R. S.; O. N. Srivastava

    2006-01-01

    The occurrence of stable decagonal quasicrystalline phase in Al-Co-Ni and Al-Cu-Co alloys through conventional solidification is well established. Earlier, we have studied the effect of Cu substitution in place of Co in the Al70 Co15Ni15 alloy. Here we report the structural/micro-structural changes with substitution of Cu for Ni in rapidly solidified Al-Co-Ni alloys. The melt-spun ribbons have been characterized using X-ray diffractometry (XRD), Scanning and transmission electron microscopy (...

  5. Fabrication of pure and Ag-doped TiO2 nanorods and study of the lattice strain and the activation energy of the crystalline phases

    Science.gov (United States)

    Riazian, Mehran; Rad, Shima Daliri; Azinabadi, Reza Ramezani

    2013-02-01

    TiO2 nanorods can be used as dye-sensitized solar cells and as various sensors and photocatalysts. These nanorods are synthesized by using a thermal corrosion process in a NaOH solution at 200 °C with TiO2 powder as a source material. In the present work, the synthesis of TiO2 nanorods in anatase, rutile and Ti8O15 phases and the synthesis of TiO2 nanorods by using the sol-gel method and alkaline corrosion to incorporate silver and silver-oxide dopants are reported. The morphologies and the crystalline structures of the TiO2 nanorods are characterized using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), tunneling electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The obtained results show an aggregation structure at high calcining temperatures with spherical particles and with Ti-O-Ti, Ti-O and Ag-O bonds. The effects of the chemical composition and the calcining temperature on the surface topography, lattice strain and phase crystallization are studied. The activation energy (E) of nanoparticle formation in a pure state during thermal treatment is calculated.

  6. Nanocrystalline calcitic lens arrays fabricated by self-assembly followed by amorphous-to-crystalline phase transformation.

    Science.gov (United States)

    Schmidt, Ingo; Lee, Kyubock; Zolotoyabko, Emil; Werner, Peter; Shim, Tae Soup; Oh, You-Kwan; Fratzl, Peter; Wagermaier, Wolfgang

    2014-09-23

    Natural calcium carbonate-based nanocomposites often have superior physical properties and provide a comprehensive source for bioinspired synthetic materials. Here we present thermodynamically stable, transparent CaCO3 microlens arrays (MLA) produced by transforming an amorphous CaCO3 phase into nanocrystalline calcite. We analyze the structure and properties of crystallized MLA by X-ray scattering, transmitted and polarized light microscopy, and electron microscopy and find that MLA are crystallized in spherulite-like patterns without changing the shape of the microlens. The key finding is that nanocrystallinity of the calcite formed diminishes structural anisotropy on the wavelength scale and results in greatly reduced birefringent effects. The remnant preferred orientation of the optical axes of calcite crystals in the plane of the microlens arrays leads to some directionality of optical properties, which may be beneficial for technical applications.

  7. A fresh look at dense hydrogen under pressure. IV. Two structural models on the road from paired to monatomic hydrogen, via a possible non-crystalline phase.

    Science.gov (United States)

    Labet, Vanessa; Hoffmann, Roald; Ashcroft, N W

    2012-02-21

    In this paper, we examine the transition from a molecular to monatomic solid in hydrogen over a wide pressure range. This is achieved by setting up two models in which a single parameter δ allows the evolution from a molecular structure to a monatomic one of high coordination. Both models are based on a cubic Bravais lattice with eight atoms in the unit cell; one belongs to space group Pa3, the other to space group R3m. In Pa3 one moves from effective 1-coordination, a molecule, to a simple cubic 6-coordinated structure but through a very special point (the golden mean is involved) of 7-coordination. In R3m, the evolution is from 1 to 4 and then to 3 to 6-coordinate. If one studies the enthalpy as a function of pressure as these two structures evolve (δ increases), one sees the expected stabilization of minima with increased coordination (moving from 1 to 6 to 7 in the Pa3 structure, for instance). Interestingly, at some specific pressures, there are in both structures relatively large regions of phase space where the enthalpy remains roughly the same. Although the structures studied are always higher in enthalpy than the computationally best structures for solid hydrogen - those emerging from the Pickard and Needs or McMahon and Ceperley numerical laboratories - this result is suggestive of the possibility of a microscopically non-crystalline or "soft" phase of hydrogen at elevated pressures, one in which there is a substantial range of roughly equi-enthalpic geometries available to the system. A scaling argument for potential dynamic stabilization of such a phase is presented.

  8. Positronium diffusion in crystalline polyethylene

    Energy Technology Data Exchange (ETDEWEB)

    Serna, J. (Dept. de Fisica de Materiales, Univ. Complutense, Madrid (Spain))

    1990-12-16

    The analysis in four components of the positron lifetime spectra of nine different and structurally well characterised lamellar polyethylene samples has allowed to associate the two longest-lived components to positronium annihilation in the crystalline and amorphous phases. Further assumption on positronium tunneling through the interface between both phases, and a simple geometrical model, led to a value for the positronium diffusion coefficient in the crystalline phase of the order of 10{sup -4} cm{sup 2}/s. Interfaces have thicknesses around 1.5 nm and are shallow traps for positronium. (orig.).

  9. The effect of heating power on impurity formation and transport during the holding phase in a Bridgman furnace for directional solidification of multi-crystalline silicon

    Science.gov (United States)

    Ellingsen, Kjerstin; Lindholm, Dag; M`Hamdi, Mohammed

    2016-06-01

    Oxygen and carbon are the most common impurities in multi-crystalline silicon. The general mechanism for formation and transport of O and C in the solidification furnace is as follows: oxygen from the silica crucible comes into the melt and combines with a silicon atom and evaporates at the gas/melt interface in the form of silicon oxide (SiO). Argon inert gas, injected into the furnace chamber, carries the SiO to the hot graphite fixtures, where it reacts with carbon to form carbon monoxide (CO) and silicon carbide (SiC). CO is carried by the gas to the melt free surface, where it dissociates into carbon and oxygen. Finally, during solidification oxygen and carbon are incorporated into the crystal. A global furnace model accounting for heat transfer, melt flow, gas flow and impurity transport has been applied to investigate the oxygen and carbon formation and transport in a vertical Bridgman furnace during the holding phase when the furnace is at its hottest. A case study is performed to investigate the effect of the applied heating power on the carbon and oxygen concentrations in the melt prior to solidification.

  10. Ge Implantation to Improve Crystallinity and Productivity for Solid Phase Epitaxy Prepared by Atomic Mass Unit Cross Contamination-Free Technique

    Science.gov (United States)

    Lee, Kong-Soo; Yoo, Dae-Han; Han, Jae-Jong; Son, Gil-Hwan; Lee, Chang-Hun; Noh, Ju-Hee; Kim, Seok-Jae; Kim, Yong-Kwon; You, Young-Sub; Hyung, Yong-Woo; Lee, Hyeon-Deok

    2006-11-01

    Germanium (Ge) ion implantation was investigated for crystallinity enhancement during solid phase epitaxial (SPE) regrowth. Electron back-scatter diffraction (EBSD) measurement showed numerical increase of 19% of (100) signal, which might be due to the effect of pre-amorphization implantation (PAI) on silicon layer. On the other hand, electrical property such as off-leakage current of n-channel metal oxide semiconductor (NMOS) transistor degraded in specific regions of wafers. It was confirmed that arsenic (As) atoms were incorporated into channel area during Ge ion implantation. Since the equipment for Ge PAI was using several source gases such as BF3 and AsH3, atomic mass unit (AMU) contamination during PAI of Ge with AMU 74 caused the incorporation of As with AMU 75 which resided in arc-chamber and other parts of the equipment. It was effective to use Ge isotope of AMU 72 to suppress AMU contamination. It was effective to use enriched Ge source gas with AMU 72 in order to improve productivity.

  11. Pure, single phase, high crystalline, chamfered-edge zeolite 4A synthesized from coal fly ash for use as a builder in detergents.

    Science.gov (United States)

    Hui, K S; Chao, C Y H

    2006-09-01

    Single phase chamfered-edge zeolite 4A samples in pure form with a high crystallinity were synthesized by applying step-change of synthesis temperature during hydrothermal treatment of coal fly ash. The calcium binding capacity of these zeolite 4A samples (prepared from coal fly ash) and the commercial detergent grade zeolite 4A were tested for usage as a detergent builder. The results show that these zeolite 4A samples behaved similarly as the commercial one in removing calcium ions during the washing cycle. Moreover, from the leaching tests (evaluation of toxicological safety), the results show that these zeolite 4A samples leached the same elements (Sb, As, Se and Tl) as the commercial one with the concentrations in the same order of magnitude. This shows that the toxicological effect of the coal fly ash converted zeolite 4A was not worse than that of the commercial sample. Finally, economic and environmental aspects of converting coal fly ash to useful products were discussed.

  12. Terahertz and direct current losses and the origin of non-Drude terahertz conductivity in the crystalline states of phase change materials

    Science.gov (United States)

    Shimakawa, Koichi; Wagner, Tomas; Frumar, Miloslav; Kadlec, Filip; Kadlec, Christelle; Kasap, Safa

    2013-12-01

    THz and DC losses in crystalline states of GeSbTe and AgInSbTe phase-change material systems are re-examined and discussed. Although a simple free carrier transport has been assumed so far in the GeSbTe (GST) system, it is shown through recent experimental results that a series sequence of intragrain and intergrain (tunneling) transport, as recently formulated in Shimakawa et al., "The origin of non-Drude terahertz conductivity in nanomaterials," Appl. Phys. Lett. 100, 132102 (2012) may dominate the electronic transport in the commercially utilized GST system, producing a non-Drude THz conductivity. The extracted physical parameters such as the free-carrier density and mobility are significantly different from those obtained from the Drude law. These physical parameters are consistent with those obtained from the DC loss data, and provide further support for the model. Negative temperature coefficient of resistivity is found even in the metallic state, similar to amorphous metals, when the mean free path is short. It is shown that the concept of minimum metallic conductivity, often used in the metal-insulator transition, cannot be applied to electronic transport in these materials.

  13. Terahertz and direct current losses and the origin of non-Drude terahertz conductivity in the crystalline states of phase change materials

    Energy Technology Data Exchange (ETDEWEB)

    Shimakawa, Koichi [Department of General and Inorganic Chemistry, University of Pardubice, Pardubice (Czech Republic); Department of Electrical Engineering, Gifu University (Japan); Wagner, Tomas; Frumar, Miloslav [Department of General and Inorganic Chemistry, University of Pardubice, Pardubice (Czech Republic); Kadlec, Filip; Kadlec, Christelle [Institute of Physics, Academy of Sciences of the Czech Republic, Prague (Czech Republic); Kasap, Safa [Department of Electrical Engineering, University of Saskatchewan, Saskatoon SK S7N 5A9 (Canada)

    2013-12-21

    THz and DC losses in crystalline states of GeSbTe and AgInSbTe phase-change material systems are re-examined and discussed. Although a simple free carrier transport has been assumed so far in the GeSbTe (GST) system, it is shown through recent experimental results that a series sequence of intragrain and intergrain (tunneling) transport, as recently formulated in Shimakawa et al., “The origin of non-Drude terahertz conductivity in nanomaterials,” Appl. Phys. Lett. 100, 132102 (2012) may dominate the electronic transport in the commercially utilized GST system, producing a non-Drude THz conductivity. The extracted physical parameters such as the free-carrier density and mobility are significantly different from those obtained from the Drude law. These physical parameters are consistent with those obtained from the DC loss data, and provide further support for the model. Negative temperature coefficient of resistivity is found even in the metallic state, similar to amorphous metals, when the mean free path is short. It is shown that the concept of minimum metallic conductivity, often used in the metal-insulator transition, cannot be applied to electronic transport in these materials.

  14. Activated kinetics of the Crystalline to Nematic (K-N) and Nematic to Isotropic (N-I) phase transitions of Pentylcyanobiphenyl (5CB) liquid crystal

    Science.gov (United States)

    Sharma, Dipti

    2011-04-01

    Activated kinetics of the crystalline to Nematic (K-N) and the Nematic to Isotropic (N-I) phase transitions of the Pentylcyanobiphenyl (5CB) liquid crystal are discussed here. A kinetic comparison of the same types of transitions of other family member with higher number of carbon atoms i.e. Octylcyanobiphenyl (8CB) are also made to see the difference between the kinetic behavior of the above two transitions of the liquid crystals. Experiments were performed using high resolution calorimetric technique for heating and cooling runs. Two different scans i.e. Temperature scans and Rate scans were performed for 5CB and 8CB from 280 to 333 K at various rates to get the detailed behavior of the transitions. As a result, Double activation was observed for 5CB for two heating rate regimes whereas 8CB indicated single activation only. The 5CB has smaller enthalpy and entropy of the transitions and needs larger activation than 8CB. This kinetic change can be explained in terms of the length scale and mobility of the liquid crystal molecules.

  15. Fullerene monolayer formation by spray coating.

    Science.gov (United States)

    Cervenka, J; Flipse, C F J

    2010-02-10

    Many large molecular complexes are limited in thin film applications by their insufficient thermal stability, which excludes deposition via commonly used vapour phase deposition methods. Here we demonstrate an alternative way of monolayer formation of large molecules by a simple spray coating method under ambient conditions. This technique has been successfully applied on C(60) dissolved in toluene and carbon disulfide. Monolayer thick C(60) films have been formed on graphite and gold surfaces at particular deposition parameters, as confirmed by atomic force and scanning tunnelling microscopies. Structural and electronic properties of spray coated C(60) films on Au(111) have been found comparable to thermally evaporated C(60). We attribute the monolayer formation in spray coating to a crystallization process mediated by an ultrathin solution film on a sample surface.

  16. Molecular tilt on monolayer-protected nanoparticles

    KAUST Repository

    Giomi, L.

    2012-02-01

    The structure of the tilted phase of monolayer-protected nanoparticles is investigated by means of a simple Ginzburg-Landau model. The theory contains two dimensionless parameters representing the preferential tilt angle and the ratio ε between the energy cost due to spatial variations in the tilt of the coating molecules and that of the van der Waals interactions which favors the preferential tilt. We analyze the model for both spherical and octahedral particles. On spherical particles, we find a transition from a tilted phase, at small ε, to a phase where the molecules spontaneously align along the surface normal and tilt disappears. Octahedral particles have an additional phase at small ε characterized by the presence of six topological defects. These defective configurations provide preferred sites for the chemical functionalization of monolayer-protected nanoparticles via place-exchange reactions and their consequent linking to form molecules and bulk materials. Copyright © EPLA, 2012.

  17. Preliminary treatment of chlorinated streams containing fission products: mechanisms leading to crystalline phases in molten chloride media; Pretraitement pyrochimique de flux charges en produits de fission: mecanismes conduisant a l'obtention de phases cristallines en milieux chlorures fondus

    Energy Technology Data Exchange (ETDEWEB)

    Hudry, D

    2008-10-15

    The world of the nuclear power gets ready for profound modifications so that 'the atom' can aspire in conformance with long-lasting energy: it is what we call the development of generation IV nuclear systems. So, the new pyrochemical separation processes for the spent fuel reprocessing are currently being investigated. Techniques in molten chloride media generate an ultimate flow (with high chlorine content) which cannot be incorporated in conventional glass matrices. This flow is entirely water-soluble and must be conditioned in a chemical form which is compatible with a long-term disposal. This work of thesis consists in studying new ways for the management of the chlorinated streams loaded with fission products (FP). To do it, a strategy of selective FP extraction via the in situ formation of crystalline phases was retained. The possibility of extracting rare earths in the eutectic LiCl-KCl was demonstrated via the development of a new way of synthesis of rare earth phosphates (TRPO{sub 4}). As regards alkaline earths, the conversion of strontium and barium chlorides to the corresponding tungstates or molybdates was studied in different solvents. Mechanisms leading to the crystalline phases in molten chloride media were studied via the coupling of NMR and XRD techniques. First of all, it has been shown that these mechanisms are dependent on the stability of the used precursors. So in the case of the formation of rare earth phosphates the solvent is chemically active. On the other hand, in the case of the formation of alkaline earth tungstates it would seem that the solvent plays the role of structuring agent which can control the ability to react of chlorides. (author)

  18. 单层二硫化钼多相性质及相变的第一性原理研究∗%First-principles study on multiphase prop erty and phase transition of monolayer MoS2

    Institute of Scientific and Technical Information of China (English)

    张理勇; 方粮; 彭向阳

    2016-01-01

    Using first principles calculations within density functional theory, we investigate multiphase property and phase transition of monolayer MoS2. All the quantities are calculated using the Vienna ab initio simulation package. Calcula-tions are performed within the generalized gradient approximation with van der Waals corrections (optimized Perdew-Burke-Ernzerhof-vdW). The cutoff energy of plane-wave is set to be 400 eV. The atomic plane and its neighboring image are separated by a 15 Å vacuum layer. The k-meshes for the structure relaxation and post analysis are 11 × 11 × 1 and 19 × 19 × 1 respectively. Firstly, we obtain the geometry configurations of 2H-MoS2, 1T-MoS2 and ZT-MoS2 phases through structure re-laxing. The lattice constants of 2H-MoS2 are a=3.190 Å and b=5.524 Å, and total energy is−39.83 eV which means that it is the most stable phase. The lattice constants of 1T-MoS2 are a=3.191 Å and b=5.528 Å, and total energy is−38.21 eV, which means that it is the most unstable phase. Both 2H-MoS2 and 1T-MoS2 have a three-layer structure with two S layers sandwiching one Mo layer. The difference of 1T-MoS2 from the 2H-MoS2 is the upper S layer shifting. The ZT-MoS2 derives from 1T-MoS2 through lattice distortion. The lattice constants of ZT-MoS2 are a = 3.185 Å and b = 5.725 Å, and total energy is −38.80 eV. The total energy determines the following stability order of three phases: 2H-MoS2>ZT-MoS2>1T-MoS2. Our computed results agree well with the other computed and experimental results. Band structure and density of states confirm that 1T-MoS2 is metallic and ZT-MoS2 is semiconducting. But the bandgap of ZT-MoS2 phase is only 0.01 eV. Then we compute the intrinsic carrier mobility values of 2H-MoS2 and ZT-MoS2 at 300 K with the deformation potential theory. The carrier mobility of 2H-MoS2 is between 100 cm2·V−1·s−1 and 400 cm2·V−1·s−1. Owing to ZT-MoS2 carrier effective mass decreasing obviously, the carrier mobility of ZT phase

  19. Amorphous-crystalline dual-layer structures resulting from metastable liquid phase separation in (Fe50Co25B15Si10)8oCu20 melt-spun ribbons

    Institute of Scientific and Technical Information of China (English)

    Cao Chong-De; Gong Su-Lian; Guo Jin-Bo; Song Rui-Bo; Sun Zhan-Bo; Yang Sen; Wang Wei-Min

    2012-01-01

    (Fe50Co25B15Si10)80Cu20 ribbons are prepared by using the single-roller melt-spinning method.A dual-layer structure consisting of a (Fe,Co)-rich amorphous phase and a Cu-rich crystalline phase forms due to metastable liquid phase separation before solidification.The magnetic hysteresis loops of the as-quenched and annealed samples are measured at room temperature.It is indicated that the coercivity of the ribbon is almost zero in the as-quenched state.The crystallization leads to the increase of coercivity and decrease of saturation magnetization.

  20. Liquid-expanded-liquid-condensed phase transition in amphiphilic monolayers: A renormalization-group approach to chiral-symmetry breaking of hydrocarbon-chain defects

    Science.gov (United States)

    Legré, J.-P.; Albinet, G.; Firpo, J.-L.; Tremblay, A.-M. S.

    1984-11-01

    This paper is concerned with the liquid-expanded (LE) -liquid-condensed (LC) transition in monolayers of amphiphilic molecules at the air-water interface. A model, which can be mapped into the Blume-Emery-Griffiths Hamiltonian, has been considered before within the (mean-field) Bragg-Williams approximation and it gave results which could be successfully compared with experiment. The LE-LC transition has been associated with a chiral-symmetry breaking of the hydrocarbon-chain defects. This model is treated here with a Migdal-Kadanoff approximate position-space renormalization group. Renormalization-group flows are consistent with those obtained by previous authors. The connection between experimental and Hamiltonian parameters is easiest for a particular choice of ensemble, which turns out to be rather subtle for this problem. As in the work of Lavis, Southern, and Bell, isotherms in the surface-pressure-molecular-area plane do not show a signature of the LE-LC transition. The better agreement between experiments (showing a compressibility jump at the LE-LC transition) and mean-field theory suggests that in these cases long-range forces depending on the nature of the polar head and on the water substrate pH are responsible for the jump.

  1. Substrate effect on the growth of monolayer dendritic MoS2 on LaAlO3 (100) and its electrocatalytic applications

    Science.gov (United States)

    Li, Cong; Zhang, Yu; Ji, Qingqing; Shi, Jianping; Chen, Zhaolong; Zhou, Xiebo; Fang, Qiyi; Zhang, Yanfeng

    2016-09-01

    In accommodating the rapid development of two-dimensional (2D) nanomaterials, chemical vapor deposition (CVD) has become a powerful tool for their batch production with desirable characteristics, such as high crystal quality, large domain size, and tunable domain shape. The crystallinity and morphology of the growth substrates usually play a crucial role in the CVD synthesis of high-quality monolayer MoS2, a kind of 2D layered material which has ignited huge interest in nanoelectronics, optoelectronics and energy harvesting, etc. Herein, by utilizing a low-pressure chemical vapor deposition (LPCVD) system, we demonstrate a regioselective synthesis of monolayer MoS2 on the corrugated single-crystal LaAlO3 (100) with twin crystal domains induced by the second-order phase transition. Unique dendritic morphologies with tunable nucleation densities were obtained in different regions of the undulated substrate, presenting a strong substrate modulation effect. Interestingly, the exposure of abundant active edge sites along with the rather high nucleation density makes the monolayer dendritic MoS2 a good electrocatalyst for hydrogen evolution reaction (HER), particularly featured by a rather high exchange current density (70.4 μA cm-2). Furthermore, uniform monolayer MoS2 films can also be obtained and transferred to arbitrary substrates. We believe that this work provides a new growth system for the controllable synthesis of 2D layered materials with unique dendritic morphologies, as well as its great application potential in energy conversion and harvesting.

  2. Coulomb excitations of monolayer germanene

    Science.gov (United States)

    Shih, Po-Hsin; Chiu, Yu-Huang; Wu, Jhao-Ying; Shyu, Feng-Lin; Lin, Ming-Fa

    2017-01-01

    The feature-rich electronic excitations of monolayer germanene lie in the significant spin-orbit coupling and the buckled structure. The collective and single-particle excitations are diversified by the magnitude and direction of transferred momentum, the Fermi energy and the gate voltage. There are four kinds of plasmon modes, according to the unique frequency- and momentum-dependent phase diagrams. They behave as two-dimensional acoustic modes at long wavelength. However, for the larger momenta, they might change into another kind of undamped plasmons, become the seriously suppressed modes in the heavy intraband e–h excitations, keep the same undamped plasmons, or decline and then vanish in the strong interband e–h excitations. Germanene, silicene and graphene are quite different from one another in the main features of the diverse plasmon modes. PMID:28091555

  3. Monolayer arrangement of fatty hydroxystearic acids on graphite: Influence of hydroxyl groups

    Energy Technology Data Exchange (ETDEWEB)

    Medina, S. [Laboratorio de Rayos-X, Centro de Investigación Tecnología e Innovación, de la Universidad de Sevilla (CITIUS), Universidad de Sevilla, Avenida Reina Mercedes, 4B. 41012, Sevilla (Spain); Benítez, J.J.; Castro, M.A. [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain); Cerrillos, C. [Servicio de Microscopía, Centro de Investigación Tecnología e Innovación, de la Universidad de Sevilla (CITIUS), Universidad de Sevilla, Avenida Reina Mercedes, 4B. 41012, Sevilla (Spain); Millán, C. [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain); Alba, M.D., E-mail: alba@icmse.csic.es [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain)

    2013-07-31

    Previous studies have indicated that long-chain linear carboxylic acids form commensurate packed crystalline monolayers on graphite even at temperatures above their melting point. This study examines the effect on the monolayer formation and structure of adding one or more secondary hydroxyl, functional groups to the stearic acid skeleton (namely, 12-hydroxystearic and 9,10-dihydroxystearic acid). Moreover, a comparative study of the monolayer formation on recompressed and monocrystalline graphite has been performed through X-ray diffraction (XRD) and Scanning Tunneling Microscopy (STM), respectively. The Differential Scanning Calorimetry (DSC) and XRD data were used to confirm the formation of solid monolayers and XRD data have provided a detailed structural analysis of the monolayers in good correspondence with obtained STM images. DSC and XRD have demonstrated that, in stearic acid and 12-hydroxystearic acid adsorbed onto graphite, the monolayer melted at a higher temperature than the bulk form of the carboxylic acid. However, no difference was observed between the melting point of the monolayer and the bulk form for 9,10-dihydroxystearic acid adsorbed onto graphite. STM results indicated that all acids on the surface have a rectangular p2 monolayer structure, whose lattice parameters were uniaxially commensurate on the a-axis. This structure does not correlate with the initial structure of the pure compounds after dissolving, but it is conditioned to favor a) hydrogen bond formation between the carboxylic groups and b) formation of hydrogen bonds between secondary hydroxyl groups, if spatially permissible. Therefore, the presence of hydroxyl functional groups affects the secondary structure and behavior of stearic acid in the monolayer. - Highlights: • Hydroxyl functional groups affect structure and behavior of acids in the monolayer. • Acids on the surface have a rectangular p2 monolayer structure. • Lattice parameters of acids are uniaxially

  4. PHASE STRUCTURE AND THERMAL BEHAVIOR OF LIQUID CRYSTALLINE MULTI-BLOCK COPOLYMERS,POLY[1,6-BIS(4-OXYBENZOYL-OXY)HEXANE TEREPHTHALATE]-b-BISPHENOL A POLYCARBONATE

    Institute of Scientific and Technical Information of China (English)

    Hui-qing Zhang; Xiong-yan Zhao; De-shan Liu; Qi-xiang Zhou

    1999-01-01

    Liquid crystalline multi-block copolymers poly[1,6-bis(4-oxybenzoyl-oxy)hexane terephthalate]-b-bisphenol A polycarbonate (PHTH-6-b-PC) with different segments of polycarbonate (PC) and thermotropic polyester PHTH-6 were synthesized in tetrachloroethane at 144~146℃. The influence of segment length on the resulting phase structure and thermal behavior of block copolymers was also discussed. It is demonstrated by TEM and DMA that the resulting block copolymers show a considerable microphase separation. The degree of phase separation and the thermal behavior of the block copolymers are strongly dependent on the molecular weight of the segments incorporated.

  5. Manipulating interface states in monolayer-bilayer graphene planar junctions

    Science.gov (United States)

    Zhao, Fang; Xu, Lei; Zhang, Jun

    2016-05-01

    We report on transport properties of monolayer-bilayer graphene planar junctions in a magnetic field. Due to its unique geometry, the edge and interface states can be independently manipulated by either interlayer potential or Zeeman field, and the conductance exhibits interesting quantized behaviors. In the hybrid graphene junction, the quantum Hall (QH) conductance is no longer antisymmetric with respect to the charge neutrality point. When the Zeeman field is considered, a quantum spin Hall (QSH) phase is found in the monolayer region while the weak-QSH phase stays in the bilayer region. In the presence of both interlayer potential and Zeeman field, the bilayer region hosts a QSH phase, whereas the monolayer region is still in a QH phase, leading to a spin-polarized current in the interface. In particular, the QSH phase remains robust against the disorder.

  6. A global sensitivity analysis of two-phase flow between fractured crystalline rock and bentonite with application to spent nuclear fuel disposal

    Science.gov (United States)

    Dessirier, Benoît; Frampton, Andrew; Jarsjö, Jerker

    2015-11-01

    Geological disposal of spent nuclear fuel in deep crystalline rock is investigated as a possible long term solution in Sweden and Finland. The fuel rods would be cased in copper canisters and deposited in vertical holes in the floor of deep underground tunnels, embedded within an engineered bentonite buffer. Recent experiments at the Äspö Hard Rock Laboratory (Sweden) showed that the high suction of unsaturated bentonite causes a de-saturation of the adjacent rock at the time of installation, which was also independently predicted in model experiments. Remaining air can affect the flow patterns and alter bio-geochemical conditions, influencing for instance the transport of radionuclides in the case of canister failure. However, thus far, observations and model realizations are limited in number and do not capture the conceivable range and combination of parameter values and boundary conditions that are relevant for the thousands of deposition holes envisioned in an operational final repository. In order to decrease this knowledge gap, we introduce here a formalized, systematic and fully integrated approach to study the combined impact of multiple factors on air saturation and dissolution predictions, investigating the impact of variability in parameter values, geometry and boundary conditions on bentonite buffer saturation times and on occurrences of rock de-saturation. Results showed that four parameters consistently appear in the top six influential factors for all considered output (target) variables: the position of the fracture intersecting the deposition hole, the background rock permeability, the suction representing the relative humidity in the open tunnel and the far field pressure value. The combined influence of these compared to the other parameters increases as one targets a larger fraction of the buffer reaching near-saturation. Strong interaction effects were found, which means that some parameter combinations yielded results (e.g., time to

  7. A global sensitivity analysis of two-phase flow between fractured crystalline rock and bentonite with application to spent nuclear fuel disposal.

    Science.gov (United States)

    Dessirier, Benoît; Frampton, Andrew; Jarsjö, Jerker

    2015-11-01

    Geological disposal of spent nuclear fuel in deep crystalline rock is investigated as a possible long term solution in Sweden and Finland. The fuel rods would be cased in copper canisters and deposited in vertical holes in the floor of deep underground tunnels, embedded within an engineered bentonite buffer. Recent experiments at the Äspö Hard Rock Laboratory (Sweden) showed that the high suction of unsaturated bentonite causes a de-saturation of the adjacent rock at the time of installation, which was also independently predicted in model experiments. Remaining air can affect the flow patterns and alter bio-geochemical conditions, influencing for instance the transport of radionuclides in the case of canister failure. However, thus far, observations and model realizations are limited in number and do not capture the conceivable range and combination of parameter values and boundary conditions that are relevant for the thousands of deposition holes envisioned in an operational final repository. In order to decrease this knowledge gap, we introduce here a formalized, systematic and fully integrated approach to study the combined impact of multiple factors on air saturation and dissolution predictions, investigating the impact of variability in parameter values, geometry and boundary conditions on bentonite buffer saturation times and on occurrences of rock de-saturation. Results showed that four parameters consistently appear in the top six influential factors for all considered output (target) variables: the position of the fracture intersecting the deposition hole, the background rock permeability, the suction representing the relative humidity in the open tunnel and the far field pressure value. The combined influence of these compared to the other parameters increases as one targets a larger fraction of the buffer reaching near-saturation. Strong interaction effects were found, which means that some parameter combinations yielded results (e.g., time to

  8. Crystalline and Crystalline International Disposal Activities

    Energy Technology Data Exchange (ETDEWEB)

    Viswanathan, Hari S. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Chu, Shaoping [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Reimus, Paul William [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Makedonska, Nataliia [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hyman, Jeffrey De' Haven [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Karra, Satish [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Dittrich, Timothy M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-12-21

    This report presents the results of work conducted between September 2014 and July 2015 at Los Alamos National Laboratory in the crystalline disposal and crystalline international disposal work packages of the Used Fuel Disposition Campaign (UFDC) for DOE-NE’s Fuel Cycle Research and Development program.

  9. Facile preparation of surface-exchangeable core@shell iron oxide@gold nanoparticles for magnetic solid-phase extraction: use of gold shell as the intermediate platform for versatile adsorbents with varying self-assembled monolayers.

    Science.gov (United States)

    Li, Yaping; Qi, Li; Shen, Ying; Ma, Huimin

    2014-02-06

    The core@shell Fe3O4@Au nanoparticles (NPs) functionalized with exchangeable self-assembled monolayers have been developed for mode switching magnetic solid-phase extraction (MSPE) using high performance liquid chromatography with ultraviolet detection. The adsorbents were synthesized by chemical coprecipitation to prepare magnetic cores followed by sonolysis to produce gold shells. Functionalization of Fe3O4@Au NPs surface was realized through self-assembly of commercially available low molecular weight thiol-containing ligands using gold shells as intermediate platform and the dynamic nature of Au-S chemistry allowed substituent of one thiol-containing ligand with another simply by thiol exchange process. The resultant adsorbents were characterized by transmission electronic microscopy, Fourier transform infrared spectroscopy, elemental analysis, contact angle measurement, and vibrating sample magnetometry. To evaluate the versatile performance of the developed MSPE adsorbents, they were applied for normal-phase SPE followed by reversed-phase SPE. A few kinds of diphenols and polycyclic aromatic hydrocarbons (PAHs) were employed as model analytes, respectively. The predominant parameters affecting extraction efficiency were investigated and optimized. Under the optimum experimental conditions, wide dynamic linear range (6.25-1600 μg L(-1) for diphenols and 1.56-100 μg L(-1) for PAHs) with good linearity (r(2)≥0.989) and low detection limits (0.34-16.67 μg L(-1) for diphenols and 0.26-0.52 μg L(-1) for PAHs) were achieved. The advantage of the developed method is that the Fe3O4@Au NPs could be reutilized for preconcentrating diverse target analytes in different SPE modes sequentially simply through treatment with desired thiol-containing ligands.

  10. Crystalline 'Genes' in Metallic Liquids

    CERN Document Server

    Sun, Yang; Ye, Zhuo; Fang, Xiaowei; Ding, Zejun; Wang, Cai-Zhuang; Mendelev, Mikhail I; Ott, Ryan T; Kramer, M J; Ho, Kai-Ming

    2014-01-01

    The underlying structural order that transcends the liquid, glass and crystalline states is identified using an efficient genetic algorithm (GA). GA identifies the most common energetically favorable packing motif in crystalline structures close to the alloy's Al-10 at.% Sm composition. These motifs are in turn compared to the observed packing motifs in the actual liquid structures using a cluster-alignment method which reveals the average topology. Conventional descriptions of the short-range order, such as Voronoi tessellation, are too rigid in their analysis of the configurational poly-types when describing the chemical and topological ordering during transition from undercooled metallic liquids to crystalline phases or glass. Our approach here brings new insight into describing mesoscopic order-disorder transitions in condensed matter physics.

  11. Site-Targeted Interfacial Solid-Phase Chemistry: Surface Functionalization of Organic Monolayers via Chemical Transformations Locally Induced at the Boundary between Two Solids.

    Science.gov (United States)

    Maoz, Rivka; Burshtain, Doron; Cohen, Hagai; Nelson, Peter; Berson, Jonathan; Yoffe, Alexander; Sagiv, Jacob

    2016-09-26

    Effective control of chemistry at interfaces is of fundamental importance for the advancement of methods of surface functionalization and patterning that are at the basis of many scientific and technological applications. A conceptually new type of interfacial chemical transformations has been discovered, confined to the contact surface between two solid materials, which may be induced by exposure to X-rays, electrons or UV light, or by the application of electrical bias. One of the reacting solids is a removable thin film coating that acts as a reagent/catalyst in the chemical modification of the solid surface on which it is applied. Given the diversity of thin film coatings that may be used as solid reagents/catalysts and the lateral confinement options provided by the use of irradiation masks, conductive AFM probes or stamps, and electron beams in such solid-phase reactions, this approach is suitable for precise targeting of different desired chemical modifications to predefined surface sites spanning the macro- to nanoscale.

  12. Ion-irradiation-assisted phase selection in single crystalline Fe7Pd3 ferromagnetic shape memory alloy thin films: from fcc to bcc along the Nishiyama-Wassermann path.

    Science.gov (United States)

    Arabi-Hashemi, A; Mayr, S G

    2012-11-09

    When processing Fe-Pd ferromagnetic shape memory thin films, selection of the desired phases and their transformation temperatures constitutes one of the largest challenges from an application point of view. In the present contribution we demonstrate that irradiation with 1.8 MeV Kr(+) ions is the method of choice to achieve this goal: Single crystalline Fe(7)Pd(3) thin films that are grown with molecular beam epitaxy on MgO (001) substrates and subsequently irradiated with ions reveal a phase transformation along the whole phase transformation path ranging from fcc austenite to bcc martensite. While for 10(14) ions/cm(2) a fcc-fct phase transformation is observed, increasing the fluence to 5 × 10(14) ions/cm(2) and 5 × 10(15) ions/cm(2) leads to a phase transformation to the bcc phase. Pole figure measurements reveal an orientation relationship for the fcc-bcc phase transformation according to Nishiyama and Wassermann.

  13. Electrochemical Properties of Organosilane Self Assembled Monolayers on Aluminum 2024

    Science.gov (United States)

    Hintze, Paul E.; Calle, Luz Marina

    2004-01-01

    Self assembled monolayers are commonly used to modify surfaces. Within the last 15 years, self assembled monolayers have been investigated as a way to protect from corrosion[1,2] or biofouling.[3] In this study, self assembled monolayers of decitriethoxysilane (C10H21Si(OC2H5)3) and octadecyltriethoxysilane (C18H37Si(OC2H5)3) were formed on aluminum 2024-T3. The modified surfaces and bare Al 2024 were characterized by dynamic water contact angle measurements, x-ray photoelectron spectroscopy (XIPS) and infrared spectroscopy. Electrochemical impedance spectroscopy (EIS) in 0.5 M NaCl was used to characterize the monolayers and evaluate their corrosion protection properties. The advancing water contact angle and infrared measurements show that the mono layers form a surface where the hydrocarbon chains are packed and oriented away from the surface, consistent with what is found in similar systems. The contact angle hysteresis measured in these systems is relatively large, perhaps indicating that the hydrocarbon chains are not as well packed as monolayers formed on other substrates. The results of the EIS measurements were modeled using a Randle's circuit modified by changing the capacitor to a constant phase element. The constant phase element values were found to characterize the monolayer. The capacitance of the monolayer modified surface starts lower than the bare Al 2024, but approaches values similar to the bare Al 2024 within 24 hours as the monolayer is degraded. The n values found for bare Al 2024 quickly approach the value of a true capacitor and are greater than 0.9 within hours after the start of exposure. For the monolayer modified structure, n can stay lower than 0.9 for a longer period of time. In fact, n for the monolayer modified surfaces is different from the bare surface even after the capacitance values have converged. This indicates that the deviation from ideal capacitance is the most sensitive indicator of the presence of the monolayer.

  14. Photocontrollable liquid-crystalline actuators

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Haifeng [Top Runner Incubation Center for Academia-Industry Fusion and Department of Materials and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka 940-2188 (Japan); Ikeda, Tomiki [Chemical Resources Laboratory, Tokyo Institute of Technology, R1-11, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)

    2011-05-17

    Coupling photochromic molecules with liquid crystalline (LC) materials enables one to reversibly photocontrol unique LC features such as phase transition, photoalignment, and molecular cooperative motion. LC elastomers show photomechanical and photomobile properties, directly converting light energy into mechanical energy. In well-defined LC block copolymers, regular patternings of nanostructures in macroscopic scales are fabricated by photo-manipulation of LC actuators. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Liquid Crystalline Esters of Dibenzophenazines

    Directory of Open Access Journals (Sweden)

    Kevin John Anthony Bozek

    2015-01-01

    Full Text Available A series of esters of 2,3,6,7-tetrakis(hexyloxydibenzo[a,c]phenazine-11-carboxylic acid was prepared in order to probe the effects of the ester groups on the liquid crystalline behavior. These compounds exhibit columnar hexagonal phases over broad temperature ranges. Variations in chain length, branching, terminal groups, and the presence of cyclic groups were found to modify transition temperatures without substantially destabilizing the mesophase range.

  16. Heavy ion irradiation of crystalline water ice

    CERN Document Server

    Dartois, E; Boduch, P; Brunetto, R; Chabot, M; Domaracka, A; Ding, J J; Kamalou, O; Lv, X Y; Rothard, H; da Silveira, E F; Thomas, J C

    2015-01-01

    Under cosmic irradiation, the interstellar water ice mantles evolve towards a compact amorphous state. Crystalline ice amorphisation was previously monitored mainly in the keV to hundreds of keV ion energies. We experimentally investigate heavy ion irradiation amorphisation of crystalline ice, at high energies closer to true cosmic rays, and explore the water-ice sputtering yield. We irradiated thin crystalline ice films with MeV to GeV swift ion beams, produced at the GANIL accelerator. The ice infrared spectral evolution as a function of fluence is monitored with in-situ infrared spectroscopy (induced amorphisation of the initial crystalline state into a compact amorphous phase). The crystalline ice amorphisation cross-section is measured in the high electronic stopping-power range for different temperatures. At large fluence, the ice sputtering is measured on the infrared spectra, and the fitted sputtering-yield dependence, combined with previous measurements, is quadratic over three decades of electronic ...

  17. A study on the properties of C-doped Ge8Sb2Te11 thin films during an amorphous-to-crystalline phase transition

    Science.gov (United States)

    Park, Cheol-Jin; Kong, Heon; Lee, Hyun-Yong; Yeo, Jong-Bin

    2016-04-01

    In this work, we evaluated the structural, electrical and optical properties of carbon-doped Ge8Sb2Te11 thin films. In a previous work, GeSbTe alloys were doped with different materials in an attempt to improve the thermal stability. Ge8Sb2Te11 and carbon-doped Ge8Sb2Te11 films of 250 nm in thickness were deposited on p-type Si (100) and glass substrates by using a RF magnetron reactive co-sputtering system at room temperature. The fabricated films were annealed in a furnance in the 0 ~ 400°C temperature range. The structural properties were analyzed by using X-ray diffraction (XRD), and the result showed that the carbon-doped Ge8Sb2Te11 had a face-centeredcubic (fcc) crystalline structure and an increased crystallization temperature ( T c ). An increase in the T c leads to thermal stability in the amorphous state. The optical properties were analyzed by using an UV-Vis-IR spectrophotometer, and the result showed an increase in the optical-energy band gap ( E op ) in the crystalline materials and an increase in the E op difference (Δ E op ), which is a good effect for reducing the noise in the memory device. The electrical properties were analyzed by using a 4-point probe, which showed an increase in the sheet resistance ( R s ) in the amorphous state and the crystalline state, which means a reduced programming current in the memory device.

  18. Improved Cross Validation of a Static Ubiquitin Structure Derived from High Precision Residual Dipolar Couplings Measured in a Drug-Based Liquid Crystalline Phase

    OpenAIRE

    2014-01-01

    The antibiotic squalamine forms a lyotropic liquid crystal at very low concentrations in water (0.3-3.5% w/v), which remains stable over a wide range of temperature (1-40 °C) and pH (4-8). Squalamine is positively charged, and comparison of the alignment of ubiquitin relative to 36 previously reported alignment conditions shows that it differs substantially from most of these, but is closest to liquid crystalline cetyl pyridinium bromide. High precision residual dipolar couplings (RDCs) measu...

  19. Monolayer patterning using ketone dipoles.

    Science.gov (United States)

    Kim, Min Kyoung; Xue, Yi; Pašková, Tereza; Zimmt, Matthew B

    2013-08-14

    The self-assembly of multi-component monolayers with designed patterns requires molecular recognition among components. Dipolar interactions have been found to influence morphologies of self-assembled monolayers and can affect molecular recognition functions. Ketone groups have large dipole moments (2.6 D) and are easily incorporated into molecules. The potential of ketone groups for dipolar patterning has been evaluated through synthesis of two 1,5-disubstituted anthracenes bearing mono-ketone side chains, STM characterization of monolayers self-assembled from their single and two component solutions and molecular mechanics simulations to determine their self-assembly energetics. The results reveal that (i) anthracenes bearing self-repulsive mono-ketone side chains assemble in an atypical monolayer morphology that establishes dipolar attraction, instead of repulsion, between ketones in adjacent side chains; (ii) pairs of anthracene molecules whose self-repulsive ketone side chains are dipolar complementary spontaneously assemble compositionally patterned monolayers, in which the two components segregate into neighboring, single component columns, driven by side chain dipolar interactions; (iii) compositionally patterned monolayers also assemble from dipolar complementary anthracene pairs that employ different dipolar groups (ketones or CF2 groups) in their side chains; (iv) the ketone group, with its larger dipole moment and size, provides comparable driving force for patterned monolayer formation to that of the smaller dipole, and smaller size, CF2 group.

  20. Thermoelectric properties of SnSe2 monolayer

    Science.gov (United States)

    Li, Guanpeng; Ding, Guangqian; Gao, Guoying

    2017-01-01

    The 2H (MoS2-type) phase of 2D transition metal dichalcogenides (TMDCs) has been extensively studied and exhibits excellent electronic and optoelectronic properties, but the high phonon thermal conductivity is detrimental to the thermoelectric performances. Here, we use first-principles methods combined with Boltzmann transport theory to calculate the electronic and phononic transport properties of 1T (CdI2-type) SnSe2 monolayer, a recently realized 2D metal dichalcogenide semiconductor. The calculated band gap is 0.85 eV, which is a little larger than the bulk value. Lower phonon thermal conductivity and higher power factor are obtained in 1T-SnSe2 monolayer compared to 2H-TMDCs monolayers. The low phonon thermal conductivity (3.27 W mK-1 at room temperature) is mainly due to the low phonon frequency of acoustic modes and the coupling of acoustic modes with optical modes. We also find that the p-type has better thermoelectric performance than the n-type, and the figure of merit within p-type can reach 0.94 at 600 K for 1T-SnSe2 monolayer, which is higher than those of most 2H-TMDCs monolayers, making 1T-SnSe2 monolayer a promising candidate for thermoelectric applications.

  1. Langmuir monolayers composed of single and double tail sulfobetaine lipids.

    Science.gov (United States)

    Hazell, Gavin; Gee, Anthony P; Arnold, Thomas; Edler, Karen J; Lewis, Simon E

    2016-07-15

    Owing to structural similarities between sulfobetaine lipids and phospholipids it should be possible to form stable Langmuir monolayers from long tail sulfobetaines. By modification of the density of lipid tail group (number of carbon chains) it should also be possible to modulate the two-dimensional phase behaviour of these lipids and thereby compare with that of equivalent phospholipids. Potentially this could enable the use of such lipids for the wide array of applications that currently use phospholipids. The benefit of using sulfobetaine lipids is that they can be synthesised by a one-step reaction from cheap and readily available starting materials and will degrade via different pathways than natural lipids. The molecular architecture of the lipid can be easily modified allowing the design of lipids for specific purposes. In addition the reversal of the charge within the sulfobetaine head group relative to the charge orientation in phospholipids may modify behaviour and thereby allow for novel uses of these surfactants. Stable Langmuir monolayers were formed composed of single and double tailed sulfobetaine lipids. Surface pressure-area isotherm, Brewster Angle Microscopy and X-ray and neutron reflectometry measurements were conducted to measure the two-dimensional phase behaviour and out-of-plane structure of the monolayers as a function of molecular area. Sulfobetaine lipids are able to form stable Langmuir monolayers with two dimensional phase behaviour analogous to that seen for the well-studied phospholipids. Changing the number of carbon tail groups on the lipid from one to two promotes the existence of a liquid condensed phase due to increased Van der Waals interactions between the tail groups. Thus the structure of the monolayers appears to be defined by the relative sizes of the head and tail groups in a predictable way. However, the presence of sub-phase ions has little effect on the monolayer structure, behaviour that is surprisingly different to

  2. Crystalline and Crystalline International Disposal Activities

    Energy Technology Data Exchange (ETDEWEB)

    Viswanathan, Hari S. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Chu, Shaoping [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Dittrich, Timothy M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hyman, Jeffrey De' Haven [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Karra, Satish [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Makedonska, Nataliia [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Reimus, Paul William [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-03-06

    This report presents the results of work conducted between September 2015 and July 2016 at Los Alamos National Laboratory in the crystalline disposal and crystalline international disposal work packages of the Used Fuel Disposition Campaign (UFDC) for DOE-NE’s Fuel Cycle Research and Development program. Los Alamos focused on two main activities during this period: Discrete fracture network (DFN) modeling to describe flow and radionuclide transport in complex fracture networks that are typical of crystalline rock environments, and a comprehensive interpretation of three different colloid-facilitated radionuclide transport experiments conducted in a fractured granodiorite at the Grimsel Test Site in Switzerland between 2002 and 2013. Chapter 1 presents the results of the DFN work and is divided into three main sections: (1) we show results of our recent study on the correlation between fracture size and fracture transmissivity (2) we present an analysis and visualization prototype using the concept of a flow topology graph for characterization of discrete fracture networks, and (3) we describe the Crystalline International work in support of the Swedish Task Force. Chapter 2 presents interpretation of the colloidfacilitated radionuclide transport experiments in the crystalline rock at the Grimsel Test Site.

  3. Pressure-area isotherm of a lipid monolayer from molecular dynamics simulations

    NARCIS (Netherlands)

    Baoukina, Svetlana; Monticelli, Luca; Marrink, Siewert J.; Tieleman, D. Peter

    2007-01-01

    We calculated the pressure-area isotherm of a dipalmitoyl-phosphatidylcholine (DPPC) lipid monolayer from molecular dynamics simulations using a coarse-grained molecular model. We characterized the monolayer structure, geometry, and phases directly from the simulations and compared the calculated

  4. Gold nanoparticle self-assembly in two-component lipid Langmuir monolayers.

    Science.gov (United States)

    Mogilevsky, Alina; Jelinek, Raz

    2011-02-15

    Self-assembly processes are considered to be fundamental factors in supramolecular chemistry. Langmuir monolayers of surfactants or lipids have been shown to constitute effective 2D "templates" for self-assembled nanoparticles and colloids. Here we show that alkyl-coated gold nanoparticles (Au NPs) adopt distinct configurations when incorporated within Langmuir monolayers comprising two lipid components at different mole ratios. Thermodynamic and microscopy analyses reveal that the organization of the Au NP aggregates is governed by both lipid components. In particular, we show that the configurations of the NP assemblies were significantly affected by the extent of molecular interactions between the two lipid components within the monolayer and the monolayer phases formed by each individual lipid. This study demonstrates that multicomponent Langmuir monolayers significantly modulate the self-assembly properties of embedded Au NPs and that parameters such as the monolayer composition, surface pressure, and temperature significantly affect the 2D nanoparticle organization.

  5. Crystalline Silica Primer

    Science.gov (United States)

    ,

    1992-01-01

    Crystalline silica is the scientific name for a group of minerals composed of silicon and oxygen. The term crystalline refers to the fact that the oxygen and silicon atoms are arranged in a threedimensional repeating pattern. This group of minerals has shaped human history since the beginning of civilization. From the sand used for making glass to the piezoelectric quartz crystals used in advanced communication systems, crystalline silica has been a part of our technological development. Crystalline silica's pervasiveness in our technology is matched only by its abundance in nature. It's found in samples from every geologic era and from every location around the globe. Scientists have known for decades that prolonged and excessive exposure to crystalline silica dust in mining environments can cause silicosis, a noncancerous lung disease. During the 1980's, studies were conducted that suggested that crystalline silica also was a carcinogen. As a result of these findings, crystalline silica has been regulated under the Occupational Safety and Health Administration's (OSHA) Hazard Communication Standard (HCS). Under HCS, OSHAregulated businesses that use materials containing 0.1% or more crystalline silica must follow Federal guidelines concerning hazard communication and worker training. Although the HCS does not require that samples be analyzed for crystalline silica, mineral suppliers or OSHAregulated

  6. Monolayer structures of alkyl aldehydes: Odd-membered homologues

    Energy Technology Data Exchange (ETDEWEB)

    Phillips, T.K. [BP Institute, Department of Chemistry, University of Cambridge, Cambridge (United Kingdom); Clarke, S.M., E-mail: stuart@bpi.cam.ac.u [BP Institute, Department of Chemistry, University of Cambridge, Cambridge (United Kingdom); Bhinde, T. [BP Institute, Department of Chemistry, University of Cambridge, Cambridge (United Kingdom); Castro, M.A.; Millan, C. [Instituto Ciencia de los Materiales de Sevilla, Departamento de Quimica Inorganica (CSIC-Universidad de Sevilla) (Spain); Medina, S. [Centro de Investigacion, Tecnologia e Innovacion de la Universidad de Sevilla (CITIUS), Sevilla (Spain)

    2011-03-01

    Crystalline monolayers of three aldehydes with an odd number of carbon atoms in the alkyl chain (C{sub 7}, C{sub 9} and C{sub 11}) at low coverages are observed by a combination of X-ray and neutron diffraction. Analysis of the diffraction data is discussed and possible monolayer crystal structures are proposed; although unique structures could not be ascertained for all molecules. We conclude that the structures are flat on the surface, with the molecules lying in the plane of the layer. The C{sub 11} homologue is determined to have a plane group of either p2, pgb or pgg, and for the C{sub 7} homologue the p2 plane group is preferred.

  7. A generic model for lipid monolayers, bilayers, and membranes

    CERN Document Server

    Schmid, F; Lenz, O; West, B

    2007-01-01

    We describe a simple coarse-grained model which is suited to study lipid layers and their phase transitions. Lipids are modeled by short semiflexible chains of beads with a solvophilic head and a solvophobic tail component. They are forced to self-assemble into bilayers by a computationally cheap `phantom solvent' environment. The model reproduces the most important phases and phase transitions of monolayers and bilayers. Technical issues such as Monte Carlo parallelization schemes are briefly discussed.

  8. Simulated Effects of Odd-Alkane Impurities in a Hexane Monolayer on Graphite

    OpenAIRE

    Pint, Cary L.; Roth, Michael W.

    2005-01-01

    We present the results of molecular dynamics simulations of odd alkane impurities present within the hexane (even alkane) monolayer. We simulate various temperatures at ca. 3%, 5%, 10%, and 15% impurities of propane, pentane, heptane, nonane, and undecane, each having a low-temperature solid phase belonging to a different space group as compared to hexane, to study the effects of impurities on the various phases and phase transitions for hexane monolayers that are well-characterized through p...

  9. Mediated Electron Transfer at Redox Active Monolayers

    Directory of Open Access Journals (Sweden)

    Michael E.G. Lyons

    2001-12-01

    Full Text Available A theoretical model describing the transport and kinetic processes involved in heterogeneous redox catalysis of solution phase reactants at electrode surfaces coated with redox active monolayers is presented. Although the analysis presented has quite general applicability, a specific focus of the paper is concerned with the idea that redox active monolayers can be used to model an ensemble of individual molecular nanoelectrodes. Three possible rate determining steps are considered: heterogeneous electron transfer between immobilized mediator and support electrode ; bimolecular chemical reaction between redox mediator and reactant species in the solution phase, and diffusional mass transport of reactant in solution. A general expression for the steady state reaction flux is derived which is valid for any degree of reversibility of both the heterogeneous electron transfer reaction involving immobilized mediator species and of the bimolecular cross exchange reaction between immobilized mediator and solution phase reactant. The influence of reactant transport in solution is also specifically considered. Simplified analytical expressions for the net reaction flux are derived for experimentally reasonable situations and a kinetic case diagram is constructed outlining the relationships between the various approximate solutions. The theory enables simple diagnostic plots to be constructed which can be used to analyse experimental data.

  10. Predicting Two-Dimensional Silicon Carbide Monolayers.

    Science.gov (United States)

    Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I

    2015-10-27

    Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics.

  11. Preparation of Porous Crystalline Spherical Titania under Atmospheric Liquid Phase Conditions%结晶二氧化钛多孔球的常压液相制备

    Institute of Scientific and Technical Information of China (English)

    申乾宏; 黎胜; 宗建娟; 杨辉

    2009-01-01

    Porous crystalline spherical titania was facilely prepared by treating the organic titanium precursor spheres with boiling water. The spherical titania was characterized by X-ray diffraction, scanning electron mi-croscopy and transmission electron microscopy. The probable mechanism for formation of anatase nanocrystal and the morphology change of precursor spheres was also discussed. The results demonstrate that extending the treating time in boiling water is helpful for the formation of porous structure as well as the crystallization of nanoparticles. With increasing in treating time, the surface of the procursor spheres become rougher and rougher, and the crys-tallinity of anatase titania improves gradually. The forming mechanism of porous structure and anatase nanoerystal is attributed to the complete in-situ hydrolysis and condensation of the organic titanium precursor spheres in boiling water.%利用沸水处理有机钛前驱体球较为便捷地制备出结晶二氧化钛多孔球,采用XRD、SEM和TEM对二氧化钛球进行表征,并探讨了二氧化钛球锐钛矿纳米晶形成以及形貌变化的机理.结果表明:延长沸水处理时间有利于多孔结构的形成和纳米粒子的晶化,随处理时间的增加,前驱体球表面变得越来越粗糙,二氧化钛结晶度也逐渐增强.其形成机理主要归因于沸水处理过程中有机钛前驱体球原位发生的完全水解和聚合.

  12. Crystalline Bioceramic Materials

    Directory of Open Access Journals (Sweden)

    de Aza, P. N.

    2005-06-01

    Full Text Available A strong interest in the use of ceramics for biomedical engineering applications developed in the late 1960´s. Used initially as alternatives to metallic materials in order to increase the biocompatibility of implants, bioceramics have become a diverse class of biomaterials, presently including three basic types: relatively bioinert ceramics; bioactive or surface reactive bioceramics and bioresorbable ceramics. This review will only refer to bioceramics “sensus stricto”, it is to say, those ceramic materials constituted for nonmetallic inorganic compounds, crystallines and consolidated by thermal treatments of powders to high temperatures. Leaving bioglasses, glass-ceramics and biocements apart, since, although all of them are obtained by thermal treatments to high temperatures, the first are amorphous, the second are obtained by desvitrification of a glass and in them vitreous phase normally prevails on the crystalline phases and the third are consolidated by means of a hydraulic or chemical reaction to room temperature. A review of the composition, physiochemical properties and biological behaviour of the principal types of crystalline bioceramics is given, based on the literature data and on the own experience of the authors.

    A finales de los años sesenta se despertó un gran interés por el uso de los materiales cerámicos para aplicaciones biomédicas. Inicialmente utilizados como una alternativa a los materiales metálicos, con el propósito de incrementar la biocompatibilidad de los implantes, las biocerámicas se han convertido en una clase diversa de biomateriales, incluyendo actualmente tres tipos: cerámicas cuasi inertes; cerámicas bioactivas o reactivas superficialmente y cerámicas reabsorbibles o biodegradables. En la presente revisión se hace referencia a las biocerámicas en sentido estricto, es decir, a aquellos materiales constitutitos por compuestos inorgánicos no metálicos, cristalinos y consolidados

  13. On some liquid crystalline phases exhibited by compounds made of bent-core molecules and their mixtures with rod-like molecules

    Indian Academy of Sciences (India)

    R Pratibha; N V Madhusudana; B K Sadashiva

    2003-08-01

    In most homologous series of compounds made of bent-core (BC) molecules, the B2, B1 and B6 phases occur as the chain length decreases. We have studied binary mixtures of the compound 1,3-phenylene bis[4-(3-methylbenzoyloxy)]4'--dodecylbiphenyl 4'-carboxylate (BC12) which exhibits the B2 phase with the compound 4-biphenylyl 4''--undecyloxybenzoate (BO11) made of rod-like (R) molecules. We find the above sequence of occurrence of the B phases with increasing concentration of BO11. In this paper we describe the physical origin for the formation of these phases in both pure compounds and in the mixtures. We have also found the occurrence of the biaxial smectic A phase when the BO11 concentration is increased to 87–95.5 mol%. We also report on another binary system composed of BC12 and 4--octyloxy 4'- cyanobiphenyl (8OCB) made of R molecules. This system exhibits the biaxial smectic A phase down to 30°C. Using polarized infrared spectroscopy we find that the mutual orientation of the R and BC molecules in the SmAdb liquid crystal is such that the arrow axes of the BC molecules are along the layer normal of the partial bilayer smectic structure formed by the rods. We also describe unusual growth patterns obtained when the nematic phase transforms to the SmAdb phase in a mixture with 24 mol% of BC12.

  14. Crystalline boron nitride aerogels

    Science.gov (United States)

    Zettl, Alexander K.; Rousseas, Michael; Goldstein, Anna P.; Mickelson, William; Worsley, Marcus A.; Woo, Leta

    2017-04-04

    This disclosure provides methods and materials related to boron nitride aerogels. In one aspect, a material comprises an aerogel comprising boron nitride. The boron nitride has an ordered crystalline structure. The ordered crystalline structure may include atomic layers of hexagonal boron nitride lying on top of one another, with atoms contained in a first layer being superimposed on atoms contained in a second layer.

  15. Crystalline boron nitride aerogels

    Energy Technology Data Exchange (ETDEWEB)

    Zettl, Alexander K.; Rousseas, Michael; Goldstein, Anna P.; Mickelson, William; Worsley, Marcus A.; Woo, Leta

    2017-04-04

    This disclosure provides methods and materials related to boron nitride aerogels. In one aspect, a material comprises an aerogel comprising boron nitride. The boron nitride has an ordered crystalline structure. The ordered crystalline structure may include atomic layers of hexagonal boron nitride lying on top of one another, with atoms contained in a first layer being superimposed on atoms contained in a second layer.

  16. Influence of deposition temperature and bias voltage on the crystalline phase of Er{sub 2}O{sub 3} thin films deposited by filtered cathodic arc

    Energy Technology Data Exchange (ETDEWEB)

    Adelhelm, Christoph, E-mail: christoph.adelhelm@ipp.mpg.de [Max-Planck-Institut fuer Plasmaphysik, Materials Research, EURATOM Association, Boltzmannstrasse 2, 85748 Garching (Germany); Pickert, Thomas [Max-Planck-Institut fuer Plasmaphysik, Materials Research, EURATOM Association, Boltzmannstrasse 2, 85748 Garching (Germany); Koch, Freimut, E-mail: freimut.koch@ipp.mpg.de [Max-Planck-Institut fuer Plasmaphysik, Materials Research, EURATOM Association, Boltzmannstrasse 2, 85748 Garching (Germany); Balden, Martin; Jahn, Stephan [Max-Planck-Institut fuer Plasmaphysik, Materials Research, EURATOM Association, Boltzmannstrasse 2, 85748 Garching (Germany); Rinke, Monika [Forschungszentrum Karlsruhe, Institute for Materials Research I, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Maier, Hans [Max-Planck-Institut fuer Plasmaphysik, Materials Research, EURATOM Association, Boltzmannstrasse 2, 85748 Garching (Germany)

    2011-10-01

    Er{sub 2}O{sub 3} thin films on Eurofer steel substrates were produced by a filtered cathodic arc device, varying the substrate temperature (RT - 700 deg. C) and sample bias (0 to -450 V). The crystallographic phase was analyzed by X-ray diffraction and Raman spectroscopy. Deposition at {>=}600 deg. C without bias lead to solely formation of the cubic Er{sub 2}O{sub 3} phase. Thin films of the uncommon, monoclinic B-phase were prepared with a negative bias voltage of {>=}100 V at RT, and at temperatures {<=}500 deg. C for -250 V bias. The B-phase films exhibit a strongly textured film structure. Residual stress measurements show high compressive stress for B-phase films deposited at RT.

  17. Influence of the oxygen concentration on the formation of crystalline phases of TiO2 during the low-pressure arc-discharge plasma synthesis

    Science.gov (United States)

    Ushakov, A. V.; Karpov, I. V.; Lepeshev, A. A.

    2016-02-01

    The synthesis of titanium dioxide (TiO2) nanoparticles with different percentage of anatase and rutile phases is investigated. The synthesis is performed by controlling the oxygen percentage in the gas mixture in the plasmachemical evaporation-condensation process employing a low-pressure arc discharge. In all our experiments, the pressure in the plasmachemical reactor and the average size of particles remain constant and are 60 Pa and 6 nm, respectively. The crystal structure of synthesized TiO2 is studied using X-ray diffraction; the morphology of the particles is analyzed employing transmission electron microscopy. Using X-ray phase analysis, it is established that the concentration of the TiO2 anatase phase decreases upon a decrease in the oxygen concentration in the gas mixture. It is shown that the TiO2 anatase phase is more efficient for photocatalytic decomposition of methylene blue than the rutile phase.

  18. Carbon phosphide monolayers with superior carrier mobility

    Science.gov (United States)

    Wang, Gaoxue; Pandey, Ravindra; Karna, Shashi P.

    2016-04-01

    Two dimensional (2D) materials with a finite band gap and high carrier mobility are sought after materials from both fundamental and technological perspectives. In this paper, we present the results based on the particle swarm optimization method and density functional theory which predict three geometrically different phases of the carbon phosphide (CP) monolayer consisting of sp2 hybridized C atoms and sp3 hybridized P atoms in hexagonal networks. Two of the phases, referred to as α-CP and β-CP with puckered or buckled surfaces are semiconducting with highly anisotropic electronic and mechanical properties. More remarkably, they have the lightest electrons and holes among the known 2D semiconductors, yielding superior carrier mobility. The γ-CP has a distorted hexagonal network and exhibits a semi-metallic behavior with Dirac cones. These theoretical findings suggest that the binary CP monolayer is a yet unexplored 2D material holding great promise for applications in high-performance electronics and optoelectronics.Two dimensional (2D) materials with a finite band gap and high carrier mobility are sought after materials from both fundamental and technological perspectives. In this paper, we present the results based on the particle swarm optimization method and density functional theory which predict three geometrically different phases of the carbon phosphide (CP) monolayer consisting of sp2 hybridized C atoms and sp3 hybridized P atoms in hexagonal networks. Two of the phases, referred to as α-CP and β-CP with puckered or buckled surfaces are semiconducting with highly anisotropic electronic and mechanical properties. More remarkably, they have the lightest electrons and holes among the known 2D semiconductors, yielding superior carrier mobility. The γ-CP has a distorted hexagonal network and exhibits a semi-metallic behavior with Dirac cones. These theoretical findings suggest that the binary CP monolayer is a yet unexplored 2D material holding great

  19. Monolayer semiconductor nanocavity lasers with ultralow thresholds

    Science.gov (United States)

    Wu, Sanfeng; Buckley, Sonia; Schaibley, John R.; Feng, Liefeng; Yan, Jiaqiang; Mandrus, David G.; Hatami, Fariba; Yao, Wang; Vučković, Jelena; Majumdar, Arka; Xu, Xiaodong

    2015-04-01

    Engineering the electromagnetic environment of a nanometre-scale light emitter by use of a photonic cavity can significantly enhance its spontaneous emission rate, through cavity quantum electrodynamics in the Purcell regime. This effect can greatly reduce the lasing threshold of the emitter, providing a low-threshold laser system with small footprint, low power consumption and ultrafast modulation. An ultralow-threshold nanoscale laser has been successfully developed by embedding quantum dots into a photonic crystal cavity (PCC). However, several challenges impede the practical application of this architecture, including the random positions and compositional fluctuations of the dots, extreme difficulty in current injection, and lack of compatibility with electronic circuits. Here we report a new lasing strategy: an atomically thin crystalline semiconductor--that is, a tungsten diselenide monolayer--is non-destructively and deterministically introduced as a gain medium at the surface of a pre-fabricated PCC. A continuous-wave nanolaser operating in the visible regime is thereby achieved with an optical pumping threshold as low as 27 nanowatts at 130 kelvin, similar to the value achieved in quantum-dot PCC lasers. The key to the lasing action lies in the monolayer nature of the gain medium, which confines direct-gap excitons to within one nanometre of the PCC surface. The surface-gain geometry gives unprecedented accessibility and hence the ability to tailor gain properties via external controls such as electrostatic gating and current injection, enabling electrically pumped operation. Our scheme is scalable and compatible with integrated photonics for on-chip optical communication technologies.

  20. Chiral and herringbone symmetry breaking in water-surface monolayers

    DEFF Research Database (Denmark)

    Peterson, I.R.; Kenn, R.M.; Goudot, A.

    1996-01-01

    We report the observation from monolayers of eicosanoic acid in the L(2)' phase of three distinct out-of-plane first-order diffraction peaks, indicating molecular tilt in a nonsymmetry direction and hence the absence of mirror symmetry. At lower pressures the molecules tilt in the direction of th...

  1. Ablation behavior of monolayer and multilayer Ir coatings under carburizing and oxidizing oxyacetylene flames

    Science.gov (United States)

    Wu, Wangping; Jiang, Jinjin; Chen, Zhaofeng

    2016-06-01

    Iridium is one of the most promising candidates for protective barrier of refractory materials to endure high service temperature. The multilayer iridium coating was produced by a double glow plasma process on the polished tungsten carbide substrates, compared with monolayer. The ablation behaviors of the monolayer on the unpolished and polished substrates were investigated under carburizing and oxidizing oxyacetylene flames, respectively, at the same time the multilayer coating ablated under oxidizing flames. Multilayer coating was a polycrystalline phase with the preferential (220) orientation. Monolayer on the unpolished substrate had fine coarse grains and some small microcracks were present. Multilayer consisted of columnar grains with some voids between the grains boundaries. The formation of a WIr phase in the as-deposited multilayer was attributed to high deposition temperature. The monolayer could endure high temperature up to 1800 °C in carburizing flame. The substrates could be protected more effectively by multilayer than monolayer at 2000- 2200 °C in oxidizing flame.

  2. Surface viscoelastic properties of spread ferroelectric liquid crystal monolayer on air-water interface

    Science.gov (United States)

    Kaur, Ramneek; Bhullar, Gurpreet Kaur; Raina, K. K.

    2013-06-01

    Ferroelectric Liquid crystal having Smectic C* phase at room temperature was capable of forming Langmuir monolayer due to presence of both hydrophilic and hydrophobic groups in it. Surface viscoelasticity properties of FLC monolayer spread on water surface had been determined by dynamic oscillation method and discussed as a function of surface pressure. Dynamic viscoelastic properties such as G (Elastic modulus), G' (storage (elastic) modulus), G' (Loss (viscous) modulus) and phase change with sinusoidal oscillation had been measured at phase changing surface pressure values. As monolayer was becoming condensed, increasing trend was observed in G' values while G' was decreasing. At higher frequencies, viscous modulus G' had negative values. This relaxation phenomenon was probably caused by conformational rearrangements that acted to fluidize monolayer. Phase change tan θ was positive, response in surface pressure was ahead of the de-formation in area and the monolayer had positive dilatational viscosity. Phase change tan θ was negative, response in surface pressure was hysteretic to the deformation in area, and negative dilatational viscosity had been observed. Studies of monolayer in barrier oscillating mode provided us the surface pressure which was most suitable for Langmuir Blodgett monolayer deposition.

  3. Controlling the texture and crystallinity of evaporated lead phthalocyanine thin films for near-infrared sensitive solar cells.

    Science.gov (United States)

    Vasseur, Karolien; Broch, Katharina; Ayzner, Alexander L; Rand, Barry P; Cheyns, David; Frank, Christian; Schreiber, Frank; Toney, Michael F; Froyen, Ludo; Heremans, Paul

    2013-09-11

    To achieve organic solar cells with a broadened spectral absorption, we aim to promote the growth of the near-infrared (NIR)-active polymorph of lead phthalocyanine (PbPc) on a relevant electrode for solar cell applications. We studied the effect of different substrate modification layers on PbPc thin film structure as a function of thickness and deposition rate (rdep). We characterized crystallinity and orientation by grazing incidence X-ray diffraction (GIXD) and in situ X-ray reflectivity (XRR) and correlated these data to the performance of bilayer solar cells. When deposited onto a self-assembled monolayer (SAM) or a molybdenum oxide (MoO3) buffer layer, the crystallinity of the PbPc films improves with thickness. The transition from a partially crystalline layer close to the substrate to a more crystalline film with a higher content of the NIR-active phase is enhanced at low rdep, thereby leading to solar cells that exhibit a higher maximum in short circuit current density (JSC) for thinner donor layers. The insertion of a CuI layer induces the formation of strongly textured, crystalline PbPc layers with a vertically homogeneous structure. Solar cells based on these templated donor layers show a variation of JSC with thickness that is independent of rdep. Consequently, without decreasing rdep we could achieve JSC=10 mA/cm2, yielding a bilayer solar cell with a peak external quantum efficiency (EQE) of 35% at 900 nm, and an overall power conversion efficiency (PCE) of 2.9%.

  4. Magnetism of Ta dichalcogenide monolayers tuned by strain and hydrogenation

    Energy Technology Data Exchange (ETDEWEB)

    Manchanda, Priyanka; Sellmyer, D. J.; Skomski, Ralph [Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588 (United States); Sharma, Vinit [Department of Materials Science and Engineering and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269 (United States); Yu, Hongbin [School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, Arizona 85287 (United States)

    2015-07-20

    The effects of strain and hydrogenation on the electronic, magnetic, and optical properties of monolayers of Ta based dichalcogenides (TaX{sub 2}; X = S, Se, and Te) are investigated using density-functional theory. We predict a complex scenario of strain-dependent magnetic phase transitions involving paramagnetic, ferromagnetic, and modulated antiferromagnetic states. Covering one of the two chalcogenide surfaces with hydrogen switches the antiferromagnetic/nonmagnetic TaX{sub 2} monolayers to a semiconductor, and the optical behavior strongly depends on strain and hydrogenation. Our research opens pathways towards the manipulation of magnetic as well as optical properties for future spintronics and optoelectronics applications.

  5. Phospholipidic Monolayers on Formamide

    Science.gov (United States)

    Graner, François; Perez-Oyarzun, Santiago; Saint-Jalmes, Arnaud; Flament, Cyrille; Gallet, François

    1995-02-01

    We report the first phase diagram of a Langmuir film at the air-formamide interface. Stable films of phospholipids such as DPPC or DSPC undergo phase transitions observed on isotherms or by fluorescence microscopy. They display bidimensional gas, liquid and solid phases, as well as two mesophases; the latter coexist with liquid on a sharp first-order transition plateau. We compare these observations with known results on films on water. Nous présentons le premier diagramme de phase d'un film de Langmuir à l'interface air-formamide. On observe, sur des isothermes et par microscopie de fluorescence, des transitions de phase dans des films stables de phospholipides comme le DPPC ou le DSPC. Cinq phases bidimensionnelles sont mises en évidence : gaz, liquide, solide, ainsi que deux mésophases ; ces deux dernières coexistent avec le liquide sur un plateau très marqué de transition du premier ordre. Nous comparons ces observations avec les résultats connus pour les films sur l'eau.

  6. Synthesis and crystalline phase of monazite-type Ce{sub 1−x}Gd{sub x}PO{sub 4} solid solutions for immobilization of minor actinide curium

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Hang; Teng, Yuancheng, E-mail: tyc239@163.com; Ren, Xuetan; Wu, Lang; Liu, Haichang; Wang, Shanlin; Xu, Liuyang

    2014-01-15

    Gadolinium (Gd{sup 3+}) was used to simulate trivalent minor actinide curium (Cm{sup 3+}), and monazite-type solid solutions with composition of Ce{sub 1−x}Gd{sub x}PO{sub 4} (x = 0–1) were prepared by the solid state reaction method using Ce{sub 2}(C{sub 2}O{sub 4}){sub 3}·10H{sub 2}O, NH{sub 4}H{sub 2}PO{sub 4}, and Gd{sub 2}O{sub 3} as starting materials. The effects of Gd content on the crystalline phase and microstructure of Ce{sub 1−x}Gd{sub x}PO{sub 4} solid solutions were investigated, and the calcining parameters of Ce{sub 0.9}Gd{sub 0.1}PO{sub 4} solid solution were optimized by means of XRD, TG-DSC and SEM. The results show that pure monazite-type crystalline phase was obtained for the Ce{sub 1−x}Gd{sub x}PO{sub 4} with x = 0–1, and the incorporation of minor actinide curium simulated by gadolinium in monazite was confirmed. The change of Gd content had no significant effect on the microstructure of Ce{sub 1−x}Gd{sub x}PO{sub 4} solid solutions, and the grain size was approximately 0.1–1 μm. Besides, the optimal calcining temperature and holding time of Ce{sub 0.9}Gd{sub 0.1}PO{sub 4} solid solution were 1000 °C and 2 h, respectively.

  7. Controlled electrodeposition of Au monolayer film on ionic liquid

    Science.gov (United States)

    Ma, Qiang; Pang, Liuqing; Li, Man; Zhang, Yunxia; Ren, Xianpei; Liu, Shengzhong Frank

    2016-05-01

    Gold (Au) nanoparticles have been attractive for centuries for their vibrant appearance enhanced by their interaction with sunlight. Nowadays, there have been tremendous research efforts to develop them for high-tech applications including therapeutic agents, sensors, organic photovoltaics, medical applications, electronics and catalysis. However, there remains to be a challenge to fabricate a monolayer Au coating with complete coverage in controlled fashion. Here we present a facile method to deposit a uniform Au monolayer (ML) film on the [BMIM][PF6] ionic liquid substrate using an electrochemical deposition process. It demonstrates that it is feasible to prepare a solid phase coating on the liquid-based substrate. Moreover, the thickness of the monolayer coating can be controlled to a layer-by-layer accuracy.

  8. Thermodynamic and real-space structural evidence of a 2D critical point in phospholipid monolayers

    DEFF Research Database (Denmark)

    Nielsen, Lars K.; Bjørnholm, Thomas; Mouritsen, Ole G.

    2007-01-01

    The two-dimensional phase diagram of phospholipid monolayers at air-water interfaces has been constructed from Langmuir compression isotherms. The coexistence region between the solid and fluid phases of the monolayer ends at the critical temperature of the transition. The small-scale lateral...... structure of the monolayers has been imaged by atomic force microscopy in the nm to mu m range at distinct points in the phase diagram. The lateral structure is immobilized by transferring the monolayer from an air-water interface to a solid mica support using Langmuir-Blodgett techniques. A transfer...... a critical point. The critical behavior inferred from the thermodynamic as well as the structural data is found to be consistent with the 2D Ising universality class. Additional results are presented demonstrating the presence of striped phases and coexisting domains in binary mixtures....

  9. Low-temperature polymorphic phase transition in a crystalline tripeptide L-Ala-L-Pro-Gly·H2O revealed by adiabatic calorimetry.

    Science.gov (United States)

    Markin, Alexey V; Markhasin, Evgeny; Sologubov, Semen S; Ni, Qing Zhe; Smirnova, Natalia N; Griffin, Robert G

    2015-02-05

    We demonstrate application of precise adiabatic vacuum calorimetry to observation of phase transition in the tripeptide L-alanyl-L-prolyl-glycine monohydrate (APG) from 6 to 320 K and report the standard thermodynamic properties of the tripeptide in the entire range. Thus, the heat capacity of APG was measured by adiabatic vacuum calorimetry in the above temperature range. The tripeptide exhibits a reversible first-order solid-to-solid phase transition characterized by strong thermal hysteresis. We report the standard thermodynamic characteristics of this transition and show that differential scanning calorimetry can reliably characterize the observed phase transition with <5 mg of the sample. Additionally, the standard entropy of formation from the elemental substances and the standard entropy of hypothetical reaction of synthesis from the amino acids at 298.15 K were calculated for the studied tripeptide.

  10. Low-Temperature Polymorphic Phase Transition in a Crystalline Tripeptide l-Ala-l-Pro-Gly·H2O Revealed by Adiabatic Calorimetry

    Science.gov (United States)

    Markin, Alexey V.; Markhasin, Evgeny; Sologubov, Semen S.; Ni, Qing Zhe; Smirnova, Natalia N.; Griffin, Robert G.

    2015-01-01

    We demonstrate application of precise adiabatic vacuun calorimetry to observation of phase transition in the tripeptide l-alanyl-l-prolyl-glycine monohydrate (APG) from 6 to 320 K and report the standard thermodynamic properties of the tripeptide in the entire range. Thus, the heat capacity of APG was measured by adiabatic vacuun calorimetry in the above temperature range. The tripeptide exhibits a reversible first-order solid-to-solid phase transition characterized by strong thermal hysteresis. We report the standard thermodynamic characteristics of this transition and show that differential scanning calorimetry can reliably characterize the observed phase transition with <5 mg of the sample. Additionally, the standard entropy of formation from the elemental substances and the standard entropy of hypothetical reaction of synthesis from the amino acids at 298.15 K were calculated for the studied tripeptide. PMID:25588051

  11. Liquid crystalline thermosetting polyimides. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Hoyt, A.E.; Huang, S.J. [Connecticut Univ., Storrs, CT (United States). Inst. of Materials Science

    1993-07-01

    Phase separation of rodlike reinforcing polymers and flexible coil matrix polymers is a common problem in formulating molecular composites. One way to reduce phase separation might be to employ liquid crystalline thermosets as the matrix material. In this work, functionally terminated polyimide oligomers which exhibit lyotropic liquid crystalline behavior were successfully prepared. Materials based on 2,2{prime}-bis(trifluoromethyl)-4,4{prime}-diaminobiphenyl and 3,3{prime},4,4{prime}-biphenylenetetra-carboxylic dianhydride have been synthesized and characterized.

  12. Improved cross validation of a static ubiquitin structure derived from high precision residual dipolar couplings measured in a drug-based liquid crystalline phase.

    Science.gov (United States)

    Maltsev, Alexander S; Grishaev, Alexander; Roche, Julien; Zasloff, Michael; Bax, Ad

    2014-03-12

    The antibiotic squalamine forms a lyotropic liquid crystal at very low concentrations in water (0.3-3.5% w/v), which remains stable over a wide range of temperature (1-40 °C) and pH (4-8). Squalamine is positively charged, and comparison of the alignment of ubiquitin relative to 36 previously reported alignment conditions shows that it differs substantially from most of these, but is closest to liquid crystalline cetyl pyridinium bromide. High precision residual dipolar couplings (RDCs) measured for the backbone (1)H-(15)N, (15)N-(13)C', (1)H(α)-(13)C(α), and (13)C'-(13)C(α) one-bond interactions in the squalamine medium fit well to the static structural model previously derived from NMR data. Inclusion into the structure refinement procedure of these RDCs, together with (1)H-(15)N and (1)H(α)-(13)C(α) RDCs newly measured in Pf1, results in improved agreement between alignment-induced changes in (13)C' chemical shift, (3)JHNHα values, and (13)C(α)-(13)C(β) RDCs and corresponding values predicted by the structure, thereby validating the high quality of the single-conformer structural model. This result indicates that fitting of a single model to experimental data provides a better description of the average conformation than does averaging over previously reported NMR-derived ensemble representations. The latter can capture dynamic aspects of a protein, thus making the two representations valuable complements to one another.

  13. Study of clay chemical composition in formation of new phases in crystalline materials ceramic; Estudo da composicao quimica de argilas na formacao de novas fases cristalinas em materiais ceramicos

    Energy Technology Data Exchange (ETDEWEB)

    Lima, L.K.S.; Goncalves, W.P.; Silva, V.J.; Dias, G.; Neves, G.A.; Santana, L.N.L., E-mail: lizandralima15@gmail.com, E-mail: lisiane@dema.ufcg.edu.br [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Unidade Academica de Engenharia dos Materiais

    2016-07-01

    The knowledge of the characteristics of raw materials and the behavior of these during the heat treatment is crucial before starting any manufacturing process of clay-based products. The objective of this work was to study phase transformations of clay under different heat treatments using conventional oven. To achieve the same were used two clays coming from the municipality of Cubati - PB and kaolin from an industry in the Northeast. The samples were subjected to beneficiation process, crushing, grinding and sieving and further characterized: chemical analysis, particle size, thermal and mineralogical. For heat treatment temperatures employed were 1000, 1100 and 1200 ° C, heating rate 5 ° C / min and residence time of 60min. After this step, the mineralogical characterization was performed by x-ray diffraction technique. Clays with larger particle size fraction below 2um and greater amount of flux oxides showed higher amount of mullite for the temperatures studied. The results also showed nucleation of mullite phase from 1100 °C, a band 2theta in the range of between 20 and 25°, characteristic of amorphous silica and the temperature rise was observed intensification of crystalline phases. (author)

  14. Evolution of the crystalline structure in (Bi{sub 0}.5Na{sub 0}.5){sub 1}-xBaxTiO{sub 3} thin films around the Morpho tropic Phase Boundary

    Energy Technology Data Exchange (ETDEWEB)

    Perez-Mezcua, D.; Calzada, M. L.; Bretos, I.; Ricote, J.; Chateigner, D.; Escobar-Galindo, R.; Jimenez, R.; Sirera, R.

    2014-02-01

    (Bi{sub 0}.5Na{sub 0}.5){sub 1}-xBa{sub x}TiO{sub 3} (BNBT), which exhibits compositions for the morphotropic phase boundary (MPB) where exist an intimate coexistence of the rhombohedral and tetragonal structures, is being considered as promising lead-free alternative to the well known Pb(Zr{sub x},Ti{sub 1}-x)O{sub 3} (PZT). In this work, BNBT thin films were fabricated by chemical solution deposition (CSD) with a wide range of compositions (x{approx}{approx}0.050-0.150) onto Pt/TiO{sub 2}/SiO{sub 2}/(100)Si substrates. Structural studies by X-ray diffraction ({lambda}Cu{approx}1.5406 A) using a four-circle goniometer were carried out to determine the crystalline structure of the films. Rietveld analysis of the experimental X-ray patterns showed different volume fractions of the rhombohedral and tetragonal phases as a function of the Ba{sup 2}+ content and the coexistence of both phases, characteristic of a MPB region, for x{approx}­0.055-0.080. Finally, Rutherford backscattering experiments (RBS) were performed to determine the compositional profile of the films. This study revealed a homogenous composition of the BNBT films with abrupt film/substrate interfaces. (Author)

  15. Electromelting of Confined Monolayer Ice

    CERN Document Server

    Qiu, Hu

    2013-01-01

    In sharp contrast to the prevailing view that electric fields promote water freezing, here we show by molecular dynamics simulations that monolayer ice confined between two parallel plates can melt into liquid water under perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to field-induced disruption of the water-wall interaction induced well-ordered network of hydrogen bond. This electromelting process should add an important new ingredient to the physics of water.

  16. Diacetylene mixed Langmuir monolayers for interfacial polymerization.

    Science.gov (United States)

    Ariza-Carmona, Luisa; Rubia-Payá, Carlos; García-Espejo, G; Martín-Romero, María T; Giner-Casares, Juan J; Camacho, Luis

    2015-05-19

    Polydiacetylene (PDA) and its derivatives are promising materials for applications in a vast number of fields, from organic electronics to biosensing. PDA is obtained through polymerization of diacetylene (DA) monomers, typically using UV irradiation. DA polymerization is a 1-4 addition reaction with both initiation and growth steps with topochemical control, leading to the "blue" polymer form as primary reaction product in bulk and at interfaces. Herein, the diacetylene monomer 10,12-pentacosadiynoic acid (DA) and the amphiphilic cationic N,N'-dioctadecylthiapentacarbocyanine (OTCC) have been used to build a mixed Langmuir monolayer. The presence of OTCC imposes a monolayer supramolecular structure instead of the typical trilayer of pure DA. Surface pressure, Brewster angle microscopy, and UV-vis reflection spectroscopy measurements, as well as computer simulations, have been used to assess in detail the supramolecular structure of the DA:OTCC Langmuir monolayer. Our experimental results indicate that the DA and OTCC molecules are sequentially arranged, with the two OTCC alkyl chains acting as spacing diacetylene units. Despite this configuration is expected to prevent photopolymerization of DA, the polymerization takes place without phase segregation, thus exclusively leading to the red polydiacetylene form. We propose a simple model for the initial formation of the "blue" or "red" PDA forms as a function of the relative orientation of the DA units. The structural insights and the proposed model concerning the supramolecular structure of the "blue" and "red" forms of the PDA are aimed at the understanding of the relation between the molecular and macroscopical features of PDAs.

  17. Is uracil aromatic? The enthalpies of hydrogenation in the gaseous and crystalline phases, and in aqueous solution, as tools to obtain an answer.

    Science.gov (United States)

    Galvão, Tiago L P; Rocha, Inês M; da Silva, Maria D M C Ribeiro; da Silva, Manuel A V Ribeiro

    2013-07-18

    The enthalpy of hydrogenation of uracil was derived from the experimental enthalpies of formation, in the gaseous phase, of uracil and 5,6-dihydrouracil, in order to analyze its aromaticity. The enthalpy of formation of 5,6-dihydrouracil was obtained from combustion calorimetry, Knudsen effusion technique and Calvet microcalorimetry results. High-level computational methods were tested for the enthalpy of hydrogenation of uracil, but only with G3 was possible to obtain results in agreement with the experimental ones. It was found that uracil possesses 30.0% of aromatic character in the gaseous phase. Using both implicit, explicit, and hybrid solvation methods, it was possible to obtain a reference value for the enthalpy of hydrogenation of uracil in the aqueous solution and the effect of polarity and hydrogen bonds on the aromaticity of uracil was analyzed. The value of the hydrogenation enthalpy of uracil in aqueous solution was compared with the experimental value in the crystal phase, also dominated by polarity and hydrogen bonds, derived from combustion calorimetry results. The supramolecular effects on the crystal lattice were explored by the computational simulation of π-π staking dimers and hydrogen bonded dimers.

  18. Monolayer MoSe 2 Grown by Chemical Vapor Deposition for Fast Photodetection

    KAUST Repository

    Chang, Yung-Huang

    2014-08-26

    Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe 2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs in 2D material-based optoelectronic devices. © 2014 American Chemical Society.

  19. Influence of molecular ordering on electrical and friction properties of omega-(trans-4-stilbene)alkylthiol self-assembled monolayers on Au (111)

    Energy Technology Data Exchange (ETDEWEB)

    Qi, Yabing; Liu, Xiaosong; Hendriksen, B.L.M.; Navarro, V.; Park, Jeong Y.; Ratera, Imma; Klopp, J.M.; Edder, C.; Himpsel, Franz J.; Frechet, J.M.J.; Haller, Eugene E.; Salmeron, Miquel

    2010-04-21

    The electrical and friction properties of omega-(trans-4-stilbene)alkylthiol self-assembled monolayers (SAMs) on Au(111) were investigated using atomic force microscopy (AFM) and near edge x-ray absorption fine structure spectroscopy (NEXAFS). The sample surface was uniformly covered with a molecular film consisting of very small grains. Well-ordered and flat monolayer islands were formed after the sample was heated in nitrogen at 120 oC for 1 h. While lattice resolved AFM images revealed a crystalline phase in the islands, the area between islands showed no order. The islands exhibit substantial reduction (50percent) in friction, supporting the existence of good ordering. NEXAFS measurements revealed an average upright molecular orientation in the film, both before and after heating, with a narrower tilt-angle distribution for the heated fim. Conductance-AFM measurements revealed a two orders of magnitude higher conductivity on the ordered islands than on the disordered phase. We propose that the conductance enhancement is a result of a better pi-pi stacking between the trans-stilbene molecular units as a result of improved ordering in islands.

  20. Synthesis and Phase Behavior of Branched-Arm Liquid Crystalline-Containing Isosorbide with Chiral Core%以手性核为中心的枝臂液晶的合成与相行为

    Institute of Scientific and Technical Information of China (English)

    何晓智; 韩丽; 姚丹姝; 田梅

    2013-01-01

    In this paper, three branched-arm liquid crystalline:bi-10-(4(4-(4-ethoxyl)benzoxy)biphenyl) decylic acid isosorbide ester(MA1) , bi-4-[10-(4(4-(4-ethoxyl)biphenyl)biphenyl)oxycarbonyl capryloxy] benzoic isosorbide ester(MA2), bi-3,4,5-三-[l0-(4(4-(4-ethoxyl)benzoxy)biphenyl)oxycarbonyl capryloxy] benzoic isosorbide ester (MA3), were synthesized. The structures, optical and thermodynamic properties of the liquid crystalline were investigated by FT-IR spectroscopy, 1H-NMR, differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). MA1 ~ MA3 all show the cholesteric phase. MA3 which has six-arms owns more liquid crystalline texture and wide scopes of liquid crystalline phase. MA1 and MA2 have the right-hand rotation, but MA3 owns the left-hand rotation, which is opposite to the rotation of the chiral core. These branched-arm molecules turn out good fluidity and clear characteristic texture.%设计与合成了3种以异山梨醇为手性核中心的枝臂液晶分子——双-10-(4-(4-(4-乙氧基)苯甲酰氧基)联苯)氧羰基癸酸异山梨醇酯(MA1)、双-4-[10-(4-(4-(4-乙氧基)苯甲酰氧基)联苯)氧羰基癸酰氧基]苯甲(酸)异山梨醇酯(MA2)、双-3,4,5-三-[10-(4-(4-(4-乙氧基)苯甲酰氧基)联苯)氧羰基癸酰氧基]苯甲酸异山梨醇酯(MA3).通过红外光谱、核磁共振、偏光显微镜、差示扫描量热和X射线衍射等手段研究了枝臂液晶分子的结构和性能.MA1~MA3均为胆甾相液晶,且具有6个臂的MA3织构较丰富且液晶相范围也较宽.手性分子MA1、MA2为右旋,而MA3为左旋,与手性核的旋光度方向相反,具有很好的流动性及清晰的特征织构.

  1. Characterization of Particulate Matter Transport across the Lung-Surfactant Barrier using Langmuir Monolayers

    Science.gov (United States)

    Eaton, Jeremy; Dennin, Michael; Levine, Alex; George, Steven

    2014-03-01

    We investigate the transport of particulate matter acros the lung using a monolayer of bovine lung surfactant tagged with NBD in conjunction with alveolar lung cells below the air-water interface. The monolaye dynamically compressed and expanded to induce phase transitions as well as buckling and folding. Polystyrene spheres ranging from 20 to 500 nm in diameter were tagged with fluorescent molecules and deposited on the monolayer. We will present results of preliminary studies of the transport of beads from the air-water surface to the lung cells through the monolayer. Characterization of the transfer will focus on differential fluorescence microscopy to distinguish uncoated beads from beads from beads coated with surfactant monolayers. The presence or absence of surfactant associated with the beads provides insight into potential transfer mechanisms and will serve as an input into models of the bead transfer. We gladly acknowledge the support of NSF grant DMR-1309402.

  2. Investigation of the amorphous to crystalline phase transition of chemical solution deposited Pb(Zr30Ti70)O3 thin films by soft x-ray absorption and soft x-ray emission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Schneller, T.; Schneller, T.; Kohlstedt, H.; Petraru, A.; Waser, R.; Guo, J.; Denlinger, J.; Learmonth, T.; Glans, Per-Andres; Smith, K. E.

    2008-08-01

    Chemical solution deposited (CSD) complex oxide thin films attract considerable interest in various emerging fields as for example, fuel cells, ferroelectric random access memories or coated conductors. In the present paper the results of soft-x-ray spectroscopy between 100 eV and 500 eV on the amorphous to crystalline phase transition of ferroelectric PbZr{sub 0.3}Ti{sub 0.7}O{sub 3} (PZT) thin films are presented. Five CSD samples derived from the same wafer coated with a PZT film pyrolyzed at 350 C were heat treated at different temperatures between 400 C and 700 C. At first the sample were morphologically and electrically characterized. Subsequently the soft-x-ray absorption and emission experiments were performed at the undulator beamline 8.0 of the Advanced Light Source of the Lawrence Berkeley National Laboratory. Soft-x-ray absorption spectra were acquired for the Ti L{sub 2,3-}, O K-, and C K-edge thresholds by using simultaneously the total electron yield (TEY) and total fluorescence yield (TFY) detection methods. For two samples, annealed at 400 C and 700 C, respectively, the resonant inelastic soft-x-ray spectroscopy (RIXS) was applied for various excitation energies near the Ti L-, O K-edges. We observed clear evidence of a rutile phase at untypically low temperatures. This rutile phase transforms into the perovskite phase upon increasing annealing temperature. These results are discussed in the framework of current microscopic models of the PZT (111) texture selection.

  3. Crystalline Silicon Dielectrics for Superconducting Qubit Circuits

    Science.gov (United States)

    Hover, David; Peng, Weina; Sendelbach, Steven; Eriksson, Mark; McDermott, Robert

    2009-03-01

    Superconducting qubit energy relaxation times are limited by microwave loss induced by a continuum of two-level state (TLS) defects in the dielectric materials of the circuit. State-of-the-art phase qubit circuits employ a micron-scale Josephson junction shunted by an external capacitor. In this case, the qubit T1 time is directly proportional to the quality factor (Q) of the capacitor dielectric. The amorphous capacitor dielectrics that have been used to date display intrinsic Q of order 10^3 to 10^4. Shunt capacitors with a Q of 10^6 are required to extend qubit T1 times well into the microsecond range. Crystalline dielectric materials are an attractive candidate for qubit capacitor dielectrics, due to the extremely low density of TLS defects. However, the robust integration of crystalline dielectrics with superconducting qubit circuits remains a challenge. Here we describe a novel approach to the realization of high-Q crystalline capacitor dielectrics for superconducting qubit circuits. The capacitor dielectric is a crystalline silicon nanomembrane. We discuss characterization of crystalline silicon capacitors with low-power microwave transport measurements at millikelvin temperatures. In addition, we report progress on integrating the crystalline capacitor process with Josephson qubit fabrication.

  4. Separación de fases y cristalinidad en mezclas epoxy/poli-3-hidroxibutirato Phase separation and crystallinity in epoxy/poly-3-hydroxybutyrate blends

    Directory of Open Access Journals (Sweden)

    Sebastián Tognana

    2013-01-01

    Full Text Available En este trabajo se estudiaron mezclas epoxy/poli-3-hidroxibutirato (PHB en dos proporciones distintas 90/10 y 85/15. Para ello se prepararon muestras sometiéndolas a temperaturas de 80 ºC y 120 ºC, a efectos de producir el curado del epoxy. Se analizó la separación de fases y la cristalización del PHB mediante microscopía óptica y calorimetría diferencial de barrido. Asimismo la estructura lamelar del PHB se caracterizó mediante dispersión de rayos X de bajo ángulo. Se encontraron diferencias significativas entre las dos proporciones estudiadas; mientras que la muestra 90/10 presenta miscibilidad, la muestra 85/15 indica una separación de fases. Asimismo se encontró que, sobre todo para la muestra 90/10, el epoxy afecta considerablemente la estructura lamelar del PHB. Los resultados se analizaron en términos de la competencia entre los procesos de cristalización y separación de fases.In this work, epoxy/poly-3-hydroxybutyrate (PHB blends in two different proportions, 90/10 and 85/15, were studied. For this purpose, the samples were submitted to 80ºC and 120ºC for the curing process of epoxy. The phase separation and the crystallization were analyzed using optical microscopy and differential scanning calorimetry. Likewise, the lamellar structure of PHB was characterized using small angle X-ray scattering. Significant differences between the two proportions studied were found; while the 90/10 sample presents miscibility, the 85/15 sample indicates a phase separation. Besides, the lamellar structure of PHB is affected due to the epoxy, mainly in the 90/10 sample. The results were analyzed on the basis of the competition between crystallization and phase separation processes.

  5. Aqueous-phase exfoliation of graphite in the presence of polyvinylpyrrolidone for the production of water-soluble graphenes

    Science.gov (United States)

    Bourlinos, Athanasios B.; Georgakilas, Vasilios; Zboril, Radek; Steriotis, Theodore A.; Stubos, Athanasios K.; Trapalis, Christos

    2009-12-01

    Treatment of crystalline graphite fine powder with an aqueous solution of the harmless and versatile substance polyvinylpyrrolidone under sonication results in water-soluble, polymer-protected graphene single layers without oxidation or destruction of the sp 2 character of the carbon core. The liquid-phase extraction of graphene monolayers was evidenced by TEM and AFM techniques, while their graphitic character was checked with Raman spectroscopy. Besides PVP, the water-soluble biopolymers albumin and sodic carboxymethylcellulose were also employed successfully in the aqueous-phase exfoliation of graphite, thereby supporting the generic character of the present method using a variety of suitable polymeric extractants.

  6. Dynamics of monolayers adsorbed at the solid-liquid interface

    Energy Technology Data Exchange (ETDEWEB)

    Clarke, Stuart M. [BP Institute, Department of Chemistry, Univ. of Cambridge (United Kingdom); Inaba, Akira [Department of Chemistry, Osaka Univ., Osaka (Japan); Arnold, Thomas [Physical and Theoretical Chemistry Laboratory, Univ. of Oxford (United Kingdom); Thomas, Robert K.; Castro, Miguel A. [Instituto de Ciencia de Materiale de Sevilla, Avda. Americo Vespucio (Spain)

    2001-03-01

    Recently we have demonstrated, using a variety of techniques including calorimetry and neutron diffraction, the existence of translationally ordered two-dimensional phases of short chain n-alkanes (CnH2n+2) on the surface of graphite. Dodecane (n=12) is unusual in that it is found from diffraction experiments to adopt a structure with parallel molecules, similar to that seen for the odd alkanes, and exhibits a monolayer phase transition at 281 K, before the layer melts at 286 K. This additional transition is reminiscent of the rotator phase transitions seen in the longer bulk alkanes. In this work we present elastic incoherent neutron scattering (EISF) data which probe the dynamics of the monolayer and clearly demonstrate that the adsorbed layer is indeed far from static but has a high degree of rotational mobility. (author)

  7. Monolayer curvature stabilizes nanoscale raft domains in mixed lipid bilayers

    CERN Document Server

    Meinhardt, Sebastian; Schmid, Friederike

    2013-01-01

    According to the lipid raft hypothesis, biological lipid membranes are laterally heterogeneous and filled with nanoscale ordered "raft" domains, which are believed to play an important role for the organization of proteins in membranes. However, the mechanisms stabilizing such small rafts are not clear, and even their existence is sometimes questioned. Here we report the observation of raft-like structures in a coarse-grained molecular model for multicomponent lipid bilayers. On small scales, our membranes demix into a liquid ordered (lo) and a liquid disordered (ld) phase. On large scales, phase separation is suppressed and gives way to a microemulsion-type state that contains nanometer size lo domains in a ld environment. Furthermore, we introduce a mechanism that generates rafts of finite size by a coupling between monolayer curvature and local composition. We show that mismatch between the spontaneous curvatures of monolayers in the lo and ld phase induces elastic interactions, which reduce the line tensi...

  8. The human crystallin gene families

    Directory of Open Access Journals (Sweden)

    Wistow Graeme

    2012-12-01

    Full Text Available Abstract Crystallins are the abundant, long-lived proteins of the eye lens. The major human crystallins belong to two different superfamilies: the small heat-shock proteins (α-crystallins and the βγ-crystallins. During evolution, other proteins have sometimes been recruited as crystallins to modify the properties of the lens. In the developing human lens, the enzyme betaine-homocysteine methyltransferase serves such a role. Evolutionary modification has also resulted in loss of expression of some human crystallin genes or of specific splice forms. Crystallin organization is essential for lens transparency and mutations; even minor changes to surface residues can cause cataract and loss of vision.

  9. Synergistic Effects of Sm and C Co-Doped Mixed Phase Crystalline TiO2 for Visible Light Photocatalytic Activity

    Directory of Open Access Journals (Sweden)

    Fuchang Peng

    2017-02-01

    Full Text Available Mixed phase TiO2 nanoparticles with element doping by Sm and C were prepared via a facile sol-gel procedure. The UV-Vis light-diffuse reflectance spectroscopy analysis showed that the absorption region of co-doped TiO2 was shifted to the visible-light region, which was attributed to incorporation of samarium and carbon into the TiO2 lattice during high-temperature reaction. Samarium effectively decreased the anatase-rutile phase transformation. The grain size can be controlled by Sm doping to achieve a large specific surface area useful for the enhancement of photocatalytic activity. The photocatalytic activities under visible light irradiation were evaluated by photocatalytic degradation of methylene blue (MB. The degradation rate of MB over the Sm-C co-doped TiO2 sample was the best. Additionally, first-order apparent rate constants increased by about 4.3 times compared to that of commercial Degusssa P25 under the same experimental conditions. Using different types of scavengers, the results indicated that the electrons, holes, and •OH radicals are the main active species for the MB degradation. The high visible-light photocatalytic activity was attributed to low recombination of the photo-generated electrons and holes which originated from the synergistic effect of the co-doped ions and the heterostructure.

  10. TiO{sub 2} nanoparticles obtained by laser ablation in water: Influence of pulse energy and duration on the crystalline phase

    Energy Technology Data Exchange (ETDEWEB)

    Giorgetti, E., E-mail: emilia.giorgetti@fi.isc.cnr.it [Istituto dei Sistemi Complessi (ISC) CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino (Italy); Muniz Miranda, M.; Caporali, S. [Dipartimento di Chimica “Ugo Schiff”, Università di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino (Italy); Canton, P. [Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari, Via Torino, 30170 Venezia-Mestre (Italy); Marsili, P. [Istituto dei Sistemi Complessi (ISC) CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino (Italy); Dipartimento di Fisica, Università di Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa (Italy); Vergari, C.; Giammanco, F. [Dipartimento di Fisica, Università di Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa (Italy)

    2015-09-15

    Highlights: • Laser ablation of Ti in water at 1064 nm and comparison of ns and ps temporal regimes. • Structural and spectroscopic characterization of the colloids: TiO{sub 2} is the predominant phase. • Determination of an energy window where ps ablation produces more anatase than rutile. • Modelling of the experimental dependence of anatase/rutile yield on pulse length and energy. - Abstract: We fabricated Ti oxide nanoparticles by laser ablation of a Ti target in doubly deionized water with ps or ns pulses at a laser wavelength of 1064 nm. Electron microscopy, Raman, X-ray diffraction and X-ray photoelectron spectroscopy showed that, while with ns pulses the dominant oxide phase is rutile, with ps pulses anatase is the most abundant form in an intermediate energy window centered around 25 mJ per pulse. This experimental behavior can be described by a theoretical model which calculates the pressure and temperature evolution of the ablated material and, from this, the rutile and anatase yield.

  11. Polymorphism of Alprazolam (Xanax): a review of its crystalline phases and identification, crystallographic characterization, and crystal structure of a new polymorph (form III).

    Science.gov (United States)

    de Armas, Héctor Novoa; Peeters, Oswald M; Van den Mooter, Guy; Blaton, Norbert

    2007-05-01

    A new polymorphic form of Alprazolam (Xanax), 8-chloro-1-methyl-6-phenyl-4H-[1,2,4]triazolo-[4,3-alpha][1,4]benzodiazepine, C(17)H(13)ClN(4), has been investigated by means of X-ray powder diffraction (XRPD), single crystal X-ray diffraction, and differential scanning calorimetry (DSC). This polymorphic form (form III) was obtained during DSC experiments after the exothermic recrystallization of the melt of form I. The crystal unit cell dimensions for form III were determined from diffractometer methods. The monoclinic unit cell found for this polymorph using XRPD after indexing the powder diffractogram was confirmed by the cell parameters obtained from single crystal X-ray diffractometry on a crystal isolated from the DSC pans. The single crystal unit cell parameters are: a = 28.929(9), b = 13.844(8), c = 7.361(3) angstroms, beta = 92.82(3) degrees , V = 2944(2) angstroms(3), Z = 8, space group P2(1) (No.4), Dx = 1.393 Mg/m(3). The structure obtained from single crystal X-ray diffraction was used as initial model for Rietveld refinement on the powder diffraction data of form III. The temperature phase transformations of alprazolam were also studied using high temperature XRPD. A review of the different phases available in the Powder Diffraction File (PDF) database for this drug is described bringing some clarification and corrections.

  12. Smeared gap equations in crystalline color superconductivity

    CERN Document Server

    Ruggieri, M

    2006-01-01

    In the framework of HDET, we discuss an averaging procedure of the NJL quark-quark interaction lagrangian, treated in the mean field approximation, for the two flavor LOFF phase of QCD. This procedure gives results which are valid in domains where Ginzburg-Landau results may be questionable. We compute and compare the free energy for different LOFF crystalline structures.

  13. Crystalline damage development during martensitic transformations

    NARCIS (Netherlands)

    Suiker, A.S.J.; Turteltaub, S.R.

    2006-01-01

    A recently developed thermo-mechanical model [1] is presented that can be used to simulate the interactions between martensitic phase transformations and crystalline damage growth at the austenitic grain level. Subgrain information is included in the model via the crystallographic theory of martensi

  14. Anisotropic phase diagram and superconducting fluctuations of single-crystalline SmFeAsO0.85F0.15

    Science.gov (United States)

    Welp, U.; Chaparro, C.; Koshelev, A. E.; Kwok, W. K.; Rydh, A.; Zhigadlo, N. D.; Karpinski, J.; Weyeneth, S.

    2011-03-01

    We report on the specific-heat determination of the anisotropic phase diagram of single crystals of optimally doped SmFeAsO1-xFx. In zero field, we find a clear cusplike anomaly in C/T with ΔC/Tc=24 mJ/mol K2 at Tc=49.5 K. In magnetic fields along the c axis, pronounced superconducting fluctuations induce broadening and suppression of the specific-heat anomaly which can be described using three-dimensional lowest-Landau-level scaling with an upper critical field slope of -3.5 T/K and an anisotropy of Γ =8. The small value of ΔC/Tc yields a Sommerfeld coefficient γ ˜ 8 mJ/mol K2, indicating that SmFeAsO1-xFx is characterized by a modest density of states and strong coupling.

  15. The determination of the phase transition temperatures of a semifluorinated liquid crystalline biphenyl ester by impedance spectroscopy as an alternative method

    Science.gov (United States)

    Yıldız, Alptekin; Canli, Nimet Yilmaz; Karanlık, Gürkan; Ocak, Hale; Okutan, Mustafa; Eran, Belkız Bilgin

    2016-12-01

    Dielectric spectroscopy (DS) is a very powerful and important for better understanding of the molecular dynamics and relaxation phenomena in liquid crystals. The dielectric and impedance characteristics Ethyl 4-(7,7,8,8,9,9,10,10,10-nonafluorodecyloxy)biphenyl-4‧-carboxylate (ENBC) liquid crystal have been analyzed over the frequency range of 100 Hz to MHz in the temperature region from room temperature to 180 °C. The compound ENBC shows enantiotropic a smectic mesophase in a wide temperature range. The phase transition temperatures T (°C) of the liquid crystal ENBC, which were characterized by Differential Scanning Calorimetry (DSC), have been verified by the dielectric measurements and conductivity mechanisms of the ENBC. The activation energies for some selected angular frequencies have also been calculated.

  16. Photodegradation of sugarcane vinasse: evaluation of the effect of vinasse pre-treatment and the crystalline phase of TiO2

    Directory of Open Access Journals (Sweden)

    Renata Padilha de Souza

    2016-04-01

    Full Text Available In this work, photocatalysis was employed in the treatment of vinasse using TiO2 and UV light. The parameters investigated were: TiO2 phases (anatase and rutile and vinasse pre-treatments (coagulation/flocculation and dilution. The TiO2 catalysts employed were: Kronos without thermal treatment (100% anatase, calcined at 1000°C (33.5% anatase and immobilized on glass slides (100% anatase; and P25 Degussa without thermal treatment (86.6% anatase. The results showed that natural coagulant removed about 50, 85 and 97% of COD, color and turbidity, respectively. However, pre-treatment followed by photocatalysis with TiO2 87% anatase removed 67% of COD within 48h of irradiation. Bioassays with Artemia salina confirmed the efficacy of the methodology. The treatments reduced the toxicity of vinasse by up to 10 times.

  17. The determination of the phase transition temperatures of a semifluorinated liquid crystalline biphenyl ester by impedance spectroscopy as an alternative method

    Energy Technology Data Exchange (ETDEWEB)

    Yıldız, Alptekin [Istanbul Technical University, Department of Physics Engineering, Maslak, 34469 Istanbul (Turkey); Yildiz Technical University, Department of Physics, 34220 Istanbul (Turkey); Canli, Nimet Yilmaz, E-mail: niyilmaz@yahoo.com [Yildiz Technical University, Department of Physics, 34220 Istanbul (Turkey); Karanlık, Gürkan; Ocak, Hale [Yildiz Technical University, Department of Chemistry, 34220 Istanbul (Turkey); Okutan, Mustafa [Yildiz Technical University, Department of Physics, 34220 Istanbul (Turkey); Eran, Belkız Bilgin [Yildiz Technical University, Department of Chemistry, 34220 Istanbul (Turkey)

    2016-12-15

    Dielectric spectroscopy (DS) is a very powerful and important for better understanding of the molecular dynamics and relaxation phenomena in liquid crystals. The dielectric and impedance characteristics Ethyl 4-(7,7,8,8,9,9,10,10,10-nonafluorodecyloxy)biphenyl-4′-carboxylate (ENBC) liquid crystal have been analyzed over the frequency range of 100 Hz to MHz in the temperature region from room temperature to 180 °C. The compound ENBC shows enantiotropic a smectic mesophase in a wide temperature range. The phase transition temperatures T (°C) of the liquid crystal ENBC, which were characterized by Differential Scanning Calorimetry (DSC), have been verified by the dielectric measurements and conductivity mechanisms of the ENBC. The activation energies for some selected angular frequencies have also been calculated.

  18. Аnodic formation of nanoporous crystalline niobium oxide

    Directory of Open Access Journals (Sweden)

    LEONID SKATKOV

    2014-05-01

    Full Text Available The research results of anodic deposition of crystalline niobium oxide are presented in this work. The factors that have an impact on crystalline phase nucleation and its primary growth are revealed. Dependence of morphology and properties of nanoporous niobium oxide on modes of its formation is shown.

  19. Chemical Vapor Deposition of Large-Size Monolayer MoSe2 Crystals on Molten Glass.

    Science.gov (United States)

    Chen, Jianyi; Zhao, Xiaoxu; Tan, Sherman J R; Xu, Hai; Wu, Bo; Liu, Bo; Fu, Deyi; Fu, Wei; Geng, Dechao; Liu, Yanpeng; Liu, Wei; Tang, Wei; Li, Linjun; Zhou, Wu; Sum, Tze Chien; Loh, Kian Ping

    2017-01-25

    We report the fast growth of high-quality millimeter-size monolayer MoSe2 crystals on molten glass using an ambient pressure CVD system. We found that the isotropic surface of molten glass suppresses nucleation events and greatly improves the growth of large crystalline domains. Triangular monolayer MoSe2 crystals with sizes reaching ∼2.5 mm, and with a room-temperature carrier mobility up to ∼95 cm(2)/(V·s), can be synthesized in 5 min. The method can also be used to synthesize millimeter-size monolayer MoS2 crystals. Our results demonstrate that "liquid-state" glass is a highly promising substrate for the low-cost growth of high-quality large-size 2D transition metal dichalcogenides (TMDs).

  20. Kinetics of low-pressure, low-temperature graphene growth: toward single-layer, single-crystalline structure.

    Science.gov (United States)

    Mehdipour, Hamid; Ostrikov, Kostya Ken

    2012-11-27

    Graphene grown on metal catalysts with low carbon solubility is a highly competitive alternative to exfoliated and other forms of graphene, yet a single-layer, single-crystal structure remains a challenge because of the large number of randomly oriented nuclei that form grain boundaries when stitched together. A kinetic model of graphene nucleation and growth is developed to elucidate the effective controls of the graphene island density and surface coverage from the onset of nucleation to the full monolayer formation in low-pressure, low-temperature CVD. The model unprecedentedly involves the complete cycle of the elementary gas-phase and surface processes and shows a precise quantitative agreement with the recent low-energy electron diffraction measurements and also explains numerous parameter trends from a host of experimental reports. These agreements are demonstrated for a broad pressure range as well as different combinations of precursor gases and supporting catalysts. The critical role of hydrogen in controlling the graphene nucleation and monolayer formation is revealed and quantified. The model is generic and can be extended to even broader ranges of catalysts and precursor gases/pressures to enable the as yet elusive effective control of the crystalline structure and number of layers of graphene using the minimum amounts of matter and energy.

  1. X-Ray Diffraction Reference Intensity Ratios of Amorphous and Poorly Crystalline Phases: Implications for CheMin on the Mars Science Laboratory

    Science.gov (United States)

    Morris, R. V.; Achilles, C. N.; Chipera, S. J.; Ming, D. W.; Rampe, E. B.

    2013-01-01

    The CheMin instrument on the Mars Science Laboratory (MSL) rover Curiosity is an X-ray diffraction (XRD) and X-ray fluorescence (XRF) instrument capable of providing the mineralogical and chemical compositions of rocks and soils on the surface of Mars. CheMin uses a microfocus X-ray tube with a Co target, transmission geometry, and an energy-discriminating X-ray sensitive CCD to produce simultaneous 2-D XRD patterns and energy-dispersive X-ray histograms from powdered samples. Piezoelectric vibration of the cell is used to randomize the sample to reduce preferred orientation effects. Instrument details are provided in [1, 2, 3]. Analyses of rock and soil samples by the Mars Exploration Rovers (MER) show nanophase ferric oxide (npOx) is a significant component of the Martian global soil [4] and is thought to be one of the major contributing phases that the Curiosity rover will encounter if a soil sample is analyzed in Gale Crater. Because of the nature of this material, npOx will likely contribute to an X-ray amorphous or short-order component of a XRD pattern measured by the CheMin instrument.

  2. A Solid Ag Film Deposited from Solution on Self-assembled Mercaptopropyltrimethoxysilane (MPTS) Monolayer

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Mercaptopropyltrimethoxysilane (MPTS) bearing mercapto groups was used to form self-assembly monolayers (SAMs) on glass substrates by solution extraction. SEM, XRD and rubbing test analysis illustrated that the Ag film on the SAMs-modified glass was more durable than that on the commonly-modified glass and that the crystallinity of Ag film on the SAMs-modified glass was identical with those of the Ag film on the commonly-modified glass and pure Ag.

  3. Nano-titanium dioxide bioreactivity with human alveolar type-I-like epithelial cells: Investigating crystalline phase as a critical determinant.

    Science.gov (United States)

    Sweeney, Sinbad; Berhanu, Deborah; Ruenraroengsak, Pakatip; Thorley, Andrew J; Valsami-Jones, Eugenia; Tetley, Teresa D

    2015-05-01

    There can be significant variability between bioreactivity studies of nanomaterials that are apparently the same, possibly reflecting differences in the models used and differing sources of experimental material. In this study, we have generated two crystal forms of titanium dioxide nanoparticles (nano-TiO2), pure anatase and pure rutile to address the hypothesis that the bioreactivity of these nanoparticles with human alveolar epithelium will depend on their crystal phase. We used a human alveolar type-I-like epithelial cell model (TT1; generated in-house from primary human alveolar epithelial type II cells); these cells cover 95% of the alveolar epithelial surface area and are an important target cell for inhaled nanomaterials. Using literature as a guide, we hypothesised that pure anatase nano-TiO2 would display greater bioreactivity with TT1 cells in comparison to pure rutile nano-TiO2. However, we found the profile and pattern of inflammatory mediator release was similar between these two nano-TiO2 formats, although pure rutile treatment caused a small, but consistently greater, response for IL-6, IL-8 and MCP-1. Interestingly, the temporal induction of oxidative stress (increased reactive oxygen species levels and depleted glutathione) varied markedly between the different nano-TiO2 formats. We have shown that a combination of using nanomaterials synthesised specifically for toxicological study and the use of a highly relevant, reproducible human lung cell model, offers a useful approach to delineating the physicochemical properties of nanomaterials that may be important in their cellular reactivity.

  4. Crystallization of calcium carbonate (CaCO3) in a flowing system: Influence of Cu2+ additives on induction time and crystalline phase transformation

    Science.gov (United States)

    Usmany, Y.; Putranto, W. A.; Bayuseno, A. P.; Muryanto, S.

    2016-04-01

    Scaling of calcium carbonate (CaCO3) is commonly found in piping systems in oil, gas, desalination and other chemical processes. The scale may create technical problems, leading to the reduction of heat transfer, increase of energy consumption and unscheduled equipment shutdown. This paper presents crystallization scaling experiments and evaluation of the effect of Cu2+ additives on the induction time and calcium carbonate transformation. The crystals precursors were prepared using equimolar of CaCl2 and Na2CO3 resulted in concentrations of 3000 ppm Ca2+ in the solution. The Cu2+ in amounts of 0, 1 and 10 ppm was separately added in the solution. The flow rates (20, 35, and 60 mL/min) and elevated temperatures (27, 35 and 45°C) were selected in the study. The induction time for crystallization of CaCO3 was observed by measuring the solution conductivity over time, while the phase transformation of calcium carbonate was examined by XRD method and SEM/EDX. It was found that the conductivity remained steady for a certain period reflecting to the induction time of crystal formation, and then decreased sharply afterwards,. The induction time was increased from 34 and 48 minutes in the presence of Cu additives (1 and 10 ppm), depending on the flow rates and temperature observed. In all the experiments, the Cu2+ addition leads to the reduction of mass of crystals. Apparently, the presence of Cu2+ could inhibit the CaCO3 crystallization. In the absence of Cu2+ and at elevated temperature, the crystals obtained were a mixture of vaterite and calcite. In the presence of Cu2+ and at elevated temperature, the crystals formed were aragonite and calcite. Here, the presence of Cu2+ additives might have controlled the crystal transformation of CaCO3.

  5. Correlation of Effective Dispersive and Polar Surface Energies in Heterogeneous Self-Assembled Monolayer Coatings

    DEFF Research Database (Denmark)

    Zhuang, Yanxin; Hansen, Ole

    2009-01-01

    We show, theoretically, that the measured effective dispersive and polar surface energies of a heterogeneous Surface are correlated; the correlation, however, differs whether a Cassic or an Israelachvili and Gee model is assumed. Fluorocarbon self-assembled monolayers with varying coverage were...... grown oil oxidized (100) silicon Surfaces in a vapor phase process using five different precursors. Experimentally, effective surface energy components of the fluorocarbon self-assembled monolayers were determined from measured contact angles using the Owens-Wendt-Rabel-Kaelble method. We show...... that the correlation between the effective surface energy components of the heterogeneous Surfaces coated with fluorocarbon self-assembled monolayers is in agreement with the Cassie model....

  6. Large-Scale Synthesis and Systematic Photoluminescence Properties of Monolayer MoS2 on Fused Silica.

    Science.gov (United States)

    Wan, Yi; Zhang, Hui; Zhang, Kun; Wang, Yilun; Sheng, Bowen; Wang, Xinqiang; Dai, Lun

    2016-07-20

    Monolayer MoS2, with fascinating mechanical, electrical, and optical properties, has generated enormous scientific curiosity and industrial interest. Controllable and scalable synthesis of monolayer MoS2 on various desired substrates has significant meaning in both basic scientific research and device application. Recent years have witnessed many advances in the direct synthesis of single-crystalline MoS2 flakes or their polycrystalline aggregates on numerous diverse substrates, such as SiO2-Si, mica, sapphire, h-BN, and SrTiO3, etc. In this work, we used the dual-temperature-zone atmospheric-pressure chemical vapor deposition method to directly synthesize large-scale monolayer MoS2 on fused silica, the most ordinary transparent insulating material in daily life. We systematically investigated the photoluminescence (PL) properties of monolayer MoS2 on fused silica and SiO2-Si substrates, which have different thermal conductivity coefficients and thermal expansion coefficients. We found that there exists a stronger strain on monolayer MoS2 grown on fused silica, and the strain becomes more obvious as temperature decreases. Moreover, the monolayer MoS2 grown on fused silica exhibits the unique trait of a fractal shape with tortuous edges and has stronger adsorbability. The monolayer MoS2 grown on fused silica may find application in sensing, energy storage, and transparent optoelectronics, etc.

  7. Interaction of Egg-Sphingomyelin with DOPC in Langmuir Monolayers

    Institute of Scientific and Technical Information of China (English)

    Chang-chun Hao; Run-guang Sun; Jing Zhang

    2012-01-01

    Lipid rafts are a dynamic microdomain structure found in recent years,enriched in sphingolipids,cholesterol and particular proteins.The change of structure and function of lipid rafts could result in many diseases.In this work,the monolayer miscibility behavior of mixed systems of Egg-Sphingomyelin (ESM) with 1,2-dioleoyl-sn-glycero-3-phosphocholine was investigated in terms of mean surface area per molecule and excess molecular area △Aex at certain surface pressure,surface pressure and excess surface pressure △πex at certain mean molecular area.The stability and compressibility of the mixed monolayers was assessed by the parameters of surface excess Gibbs free energy △Gex,excess Helmholtz energy △Hex and elasticity.Thermodynamic analysis indicates △Aex and △πex in the binary systems with positive deviations from the ideal behavior,suggesting repulsive interaction.The maximum of △Gex and △Hex was at the molar fraction of ESM of 0.6,demonstrating the mixed monolayer was more unstable.The repulsive interaction induced phase separation in the monolayer.

  8. Interaction of Egg-Sphingomyelin with DOPC in Langmuir Monolayers

    Science.gov (United States)

    Hao, Chang-chun; Sun, Run-guang; Zhang, Jing

    2012-12-01

    Lipid rafts are a dynamic microdomain structure found in recent years, enriched in sphingolipids, cholesterol and particular proteins. The change of structure and function of lipid rafts could result in many diseases. In this work, the monolayer miscibility behavior of mixed systems of Egg-Sphingomyelin (ESM) 1 with 2-dioleoyl-sn-glycero-3-phosphocholine was investigated in terms of mean surface area per molecule and excess molecular area ΔAex at certain surface pressure, surface pressure and excess surface pressure Δπex at certain mean molecular area. The stability and compressibility of the mixed monolayers was assessed by the parameters of surface excess Gibbs free energy ΔGex, excess Helmholtz energy ΔHex and elasticity. Thermodynamic analysis indicates ΔAex and Δπex in the binary systems with positive deviations from the ideal behavior, suggesting repulsive interaction. The maximum of ΔGex and ΔHex was at the molar fraction of ESM of 0.6, demonstrating the mixed monolayer was more unstable. The repulsive interaction induced phase separation in the monolayer.

  9. Gemini型表面活性剂在离子液体中构筑的溶致液晶%Lyotropic liquid crystalline phases formed by Gemini surfactants in anionic liquid

    Institute of Scientific and Technical Information of China (English)

    宋冰蕾; 陈涛; 田金年; 裴晓梅; 孟丽

    2015-01-01

    通过差示扫描量热仪(DSC)、X 射线衍射仪(XRD)、热台偏光显微镜(POM)和红外光谱仪等手段研究了Gemini表面活性剂在硝酸乙基铵(EAN)中构筑的溶致液晶体系(lyotropic liquid crystal,LLc)的性质.结果表明,在液晶区内,所形成的溶致液晶均为层状介晶A相(SmA),且EAN主要存在于液晶相分子层的极性亚层中;液晶相稳定存在的温度区间随Gemini表面活性剂的浓度、尾链长度的增加而变大,随联接链的增加表现出先增大再减小的趋势;羟基削弱了离子头基与反离子间的相互作用,进而缩小了液晶相稳定存在的温度区间.%The lyotropic liquid crystals formed by Gemini surfactants in ethyl ammonium nitrate (EAN) were investigated by differential scanning calorimetry(DSC),X ray diffractometer(XRD),polarizing microscope(POM) equipped with a hot stage and FTIR. All the surfactants form smectic A phase(SmA) in liquid crystalline region. The EAN molecules mainly exist in the polar sublayers of liquid crystals. The temperature ranges of liquid crystal phase increase with increasing Gemini surfactant alkyl chain length while show maximum with the increase of spacer length. The hydroxyl groups decrease the interactions between the ionic head groups and counterions. The temperature range of liquid crystal state is thus narrowed.

  10. Improved Josephson Qubits incorporating Crystalline Silicon Dielectrics

    Science.gov (United States)

    Gao, Yuanfeng; Maurer, Leon; Hover, David; Patel, Umeshkumar; McDermott, Robert

    2010-03-01

    Josephson junction phase quibts are a leading candidate for scalable quantum computing in the solid state. Their energy relaxation times are currently limited by microwave loss induced by a high density of two-level state (TLS) defects in the amorphous dielectric films of the circuit. It is expected that the integration of crystalline, defect-free dielectrics into the circuits will yield substantial improvements in qubit energy relaxation times. However, the epitaxial growth of a crystalline dielectric on a metal underlayer is a daunting challenge. Here we describe a novel approach in which the crystalline silicon nanomembrane of a Silicon-on-Insulator (SOI) wafer is used to form the junction shunt capacitor. The SOI wafer is thermocompression bonded to the device wafer. The handle and buried oxide layers of the SOI are then etched away, leaving the crystalline silicon layer for subsequent processing. We discuss device fabrication issues and present microwave transport data on lumped-element superconducting resonators incorporating the crystalline silicon.

  11. Site-selective growth of surface-anchored metal-organic frameworks on self-assembled monolayer patterns prepared by AFM nanografting

    Directory of Open Access Journals (Sweden)

    Tatjana Ladnorg

    2013-10-01

    Full Text Available Surface anchored metal-organic frameworks, SURMOFs, are highly porous materials, which can be grown on modified substrates as highly oriented, crystalline coatings by a quasi-epitaxial layer-by-layer method (liquid-phase epitaxy, or LPE. The chemical termination of the supporting substrate is crucial, because the most convenient method for substrate modification is the formation of a suitable self-assembled monolayer. The choice of a particular SAM also allows for control over the orientation of the SURMOF. Here, we demonstrate for the first time the site-selective growth of the SURMOF HKUST-1 on thiol-based self-assembled monolayers patterned by the nanografting technique, with an atomic force microscope as a structuring tool. Two different approaches were applied: The first one is based on 3-mercaptopropionic acid molecules which are grafted in a 1-decanethiolate SAM, which serves as a matrix for this nanolithography. The second approach uses 16-mercaptohexadecanoic acid, which is grafted in a matrix of an 1-octadecanethiolate SAM. In both cases a site-selective growth of the SURMOF is observed. In the latter case the roughness of the HKUST-1 is found to be significantly higher than for the 1-mercaptopropionic acid. The successful grafting process was verified by time-of-flight secondary ion mass spectrometry and atomic force microscopy. The SURMOF structures grown via LPE were investigated and characterized by atomic force microscopy and Fourier-transform infrared microscopy.

  12. Packing of ganglioside-phospholipid monolayers

    DEFF Research Database (Denmark)

    Majewski, J.; Kuhl, T.L.; Kjær, K.

    2001-01-01

    DPPE monolayer and does not distort the hexagonal in-plane unit cell or out-of-plane two-dimensional (2-D) packing compared with a pure DPPE monolayer. The oligosaccharide headgroups were found to extend normally from the monolayer surface, and the incorporation of these glycolipids into DPPE...... monolayers did not affect hydrocarbon tail packing (fluidization or condensation of the hydrocarbon region). This is in contrast to previous investigations of lipopolymer-lipid mixtures, where the packing structure of phospholipid monolayers was greatly altered by the inclusion of lipids bearing hydrophilic...... polymer groups. Indeed, the lack of packing disruptions by the oligosaccharide groups indicates that protein-GM, interactions, including binding, insertion, chain fluidization, and domain formation (lipid rafts), can be studied in 2-D monolayers using scattering techniques....

  13. Modeling Stimuli-Responsive Nanoparticle Monolayer

    Science.gov (United States)

    Yong, Xin

    2015-03-01

    Using dissipative particle dynamics (DPD), we model a monolayer formed at the water-oil interface, which comprises stimuli-responsive nanoparticles. The solid core of the nanoparticle encompasses beads arranged in an fcc lattice structure and its surface is uniformly grafted with stimuli-responsive polymer chains. The surface-active nanoparticles adsorb to the interface from the suspension to minimize total energy of the system and create a monolayer covering the interface. We investigate the monolayer formation by characterizing the detailed adsorption kinetics. We explore the microstructure of the monolayer at different surface coverage, including the particle crowding and ordering, and elucidate the response of monolayer to external stimuli. The collective behavior of the particles within the monolayer is demonstrated quantitatively by vector-vector autocorrelation functions. This study provides a fundamental understanding of the interfacial behavior of stimuli-responsive nanoparticles.

  14. Improving the dielectric properties of ethylene-glycol alkanethiol self-assembled monolayers.

    Science.gov (United States)

    Zaccari, Irene; Catchpole, Benjamin G; Laurenson, Sophie X; Davies, A Giles; Wälti, Christoph

    2014-02-11

    Self-assembled monolayers (SAMs) can be formed at the interface between solids and fluids, and are often used to modify the surface properties of the solid. One of the most widely employed SAM systems is exploiting thiol-gold chemistry, which, together with alkane-chain-based molecules, provides a reliable way of SAM formation to modify the surface properties of electrodes. Oligo ethylene-glycol (OEG) terminated alkanethiol monolayers have shown excellent antifouling properties and have been used extensively for the coating of biosensor electrodes to minimize nonspecific binding. Here, we report the investigation of the dielectric properties of COOH-capped OEG monolayers and demonstrate a strategy to improve the dielectric properties significantly by mixing the OEG SAM with small concentrations of 11-mercaptoundecanol (MUD). The monolayer properties and composition were characterized by means of impedance spectroscopy, water contact angle, ellipsometry and X-ray photoelectron spectroscopy. An equivalent circuit model is proposed to interpret the EIS data and to determine the conductivity of the monolayer. We find that for increasing MUD concentrations up to about 5% the resistivity of the SAM steadily increases, which together with a considerable decrease of the phase of the impedance, demonstrates significantly improved dielectric properties of the monolayer. Such monolayers will find widespread use in applications which depend critically on good dielectric properties such as capacitive biosensor.

  15. Intermolecular forces in spread phospholipid monolayers at oil/water interfaces.

    Science.gov (United States)

    Mingins, James; Pethica, Brian A

    2004-08-31

    The lateral intermolecular forces between phospholipids are of particular relevance to the behavior of biomembranes, and have been approached via studies of monolayer isotherms at aqueous interfaces, mostly restricted to air/water (A/W) systems. For thermodynamic properties, the oil/water (O/W) interface has major advantages but is experimentally more difficult and less studied. A comprehensive reanalysis of the available thermodynamic data on spread monolayers of phosphatidyl cholines (PC) and phosphatidyl ethanolamines (PE) at O/W interfaces is conducted to identify the secure key features that will underpin further development of molecular models. Relevant recourse is made to isotherms of single-chain molecules and of mixed monolayers to identify the contributions of chain-chain interactions and interionic forces. The emphasis is on the properties of the phase transitions for a range of oil phases. Apparent published discrepancies in thermodynamic properties are resolved and substantial agreement emerges on the main features of these phospholipid monolayer systems. In compression to low areas, the forces between the zwitterions of like phospholipids are repulsive. The molecular model for phospholipid headgroup interactions developed by Stigter et al. accounts well for the virial coefficients in expanded phospholipid O/W monolayers. Inclusion of the changes in configuration and orientation of the zwitterion headgroups on compression, which are indicated by the surface potentials in the phase transition region, and inclusion of the energy of chain demixing from the oil phase will be required for molecular modeling of the phase transitions.

  16. Nanoconfinement crystallization of frustrated alkyl groups: crossover of mesophase to crystalline structure.

    Science.gov (United States)

    Shi, Haifeng; Wang, Haixia; Xin, John H; Zhang, Xingxiang; Wang, Dujin

    2011-04-07

    Crossover of mesophase to crystalline structure in the nanoconfinement crystallization process of frustrated side groups elucidates the critical crystal thickness d(c) or the length scale of side groups, which defines the transition process from mesophase (hexagonal and monoclinic phase) to crystalline phase (orthorhombic phase) of confined CH(2) sequences in a given crystal size restriction.

  17. Phosphonate-anchored monolayers for antibody binding to magnetic nanoparticles.

    Science.gov (United States)

    Benbenishty-Shamir, Helly; Gilert, Roni; Gotman, Irena; Gutmanas, Elazar Y; Sukenik, Chaim N

    2011-10-04

    Targeted delivery of magnetic iron oxide nanoparticles (IONPs) to a specific tissue can be achieved by conjugation with particular biological ligands on an appropriately functionalized IONP surface. To take best advantage of the unique magnetic properties of IONPs and to maximize their blood half-life, thin, strongly bonded, functionalized coatings are required. The work reported herein demonstrates the successful application of phosphonate-anchored self-assembled monolayers (SAMs) as ultrathin coatings for such particles. It also describes a new chemical approach to the anchoring of antibodies on the surface of SAM-coated IONPs (using nucleophilic aromatic substitution). This anchoring strategy results in stable, nonhydrolyzable, covalent attachment and allows the reactivity of the particles toward antibody binding to be activated in situ, such that prior to the activation the modified surface is stable for long-term storage. While the SAMs do not have the well-packed crystallinity of other such monolayers, their structure was studied using smooth model substrates based on an iron oxide layer on a double-side polished silicon wafer. In this way, atomic force microscopy, ellipsometry, and contact angle goniometry (tools that could not be applied to the nanoparticles' surfaces) could contribute to the determination of their monomolecular thickness and uniformity. Finally, the successful conjugation of IgG antibodies to the SAM-coated IONPs such that the antibodies retain their biological activity is verified by their complexation to a secondary fluorescent antibody.

  18. Depinning transition and 2D superlubricity in incommensurate colloidal monolayers

    Science.gov (United States)

    Mandelli, Davide; Vanossi, Andrea; Manini, Nicola; Tosatti, Erio

    2014-03-01

    Colloidal monolayers sliding over periodic corrugated potential are highly tunable systems allowing to visualize the dynamics between crystalline surfaces. Based on molecular dynamics, Vanossi and coworkers reproduced the main experimental results and explored the potential impact of colloid sliding in nanotribology. The degree of interface commensurability was found to play a major role in determining the frictional properties, the static friction force Fs becoming vanishingly small in incommensurate geometries for weak corrugation U0.Lead by this result,here we systematically investigate the possibility to observe a 2D Aubry-like transition from a superlubric state to a pinned state for increasing U0. By using a reliable protocol, we generate annealed configurations at different values of U0 for an underdense monolayer. We find Fs to be vanishingly small up to a critical corrugation Uc coinciding with an abrupt structural transition in the ground state configuration. Similarly to what is observed in the Frenkel Kontorova model,this transition is characterized by a significant decrease in the number of particles sampling regions near the maxima of the substrate potential. Research partly sponsored by Sinergia Project CRSII2 136287-1 and ERC 2012ADG320796 MODPHYSFRICT.

  19. Searching for line active molecules on biphasic lipid monolayers.

    Science.gov (United States)

    Bischof, Andrea Alejandra; Mangiarotti, Agustín; Wilke, Natalia

    2015-03-21

    In membranes with phase coexistence, line tension appears as an important parameter for the determination of the amount of domains, as well as their size and their shape, thus defining the membrane texture. Different molecules have been proposed as "linactants" (i.e. molecules that reduce the line tension, thereby modulating the membrane texture). In this work, we explore the efficiency of different molecules as linactants in monolayers with two coexisting phases of different thicknesses. We tested the linactant ability of a molecule with chains of different saturation degrees, another molecule with different chain lengths and a bulky molecule. In this way, we show in the same system the effect of molecules with chains of different rigidities, with an intrinsic thickness mismatch and with a bulky moiety, thereby analyzing different hypotheses of how a molecule may change the line tension in a monolayer system. Both lipids with different hydrocarbon chains did not act as linactants, while only one of the bulky molecules tested decreased the line tension in the monolayer studied. We conclude that there are no universal rules for the structure of a molecule that enable us to predict that it will behave as a linactant and thus, designing linactants appears to be a difficult task and a challenge for future studies. Furthermore, in regard to the membrane texture, there was no direct influence of the line tension in the distribution of domain sizes.

  20. Lipid monolayers and adsorbed polyelectrolytes with different degrees of polymerization.

    Science.gov (United States)

    Ortmann, Thomas; Ahrens, Heiko; Lawrenz, Frank; Gröning, Andreas; Nestler, Peter; Günther, Jens-Uwe; Helm, Christiane A

    2014-06-17

    Polystyrene sulfonate (PSS) of different molecular weight M(w) is adsorbed to oppositely charged DODAB monolayers from dilute solutions (0.01 mmol/L). PSS adsorbs flatly in a lamellar manner, as is shown by X-ray reflectivity and grazing incidence diffraction (exception: PSS with M(w) below 7 kDa adsorbs flatly disordered to the liquid expanded phase). The surface coverage and the separation of the PSS chains are independent of PSS M(w). On monolayer compression, the surface charge density increases by a factor of 2, and the separation of the PSS chains decreases by the same factor. Isotherms show that on increase of PSS M(w) the transition pressure of the LE/LC (liquid expanded/liquid condensed) phase transition decreases. When the contour length exceeds the persistence length (21 nm), the transition pressure is low and constant. For low-M(w) PSS (<7 kDa) the LE/LC transition of the lipids and the disordered/ordered transition of adsorbed PSS occur simultaneously, leading to a maximum in the contour length dependence of the transition enthalpy. These findings show that lipid monolayers at the air/water interface are a suitable model substrate with adjustable surface charge density to study the equilibrium conformation of adsorbed polyelectrolytes as well as their interactions with a model membrane.

  1. A trough for improved SFG spectroscopy of lipid monolayers

    Science.gov (United States)

    Franz, Johannes; van Zadel, Marc-Jan; Weidner, Tobias

    2017-05-01

    Lipid monolayers are indispensable model systems for biological membranes. The main advantage over bilayer model systems is that the surface pressure within the layer can be directly and reliably controlled. The sensitive interplay between surface pressure and temperature determines the molecular order within a model membrane and consequently determines the membrane phase behavior. The lipid phase is of crucial importance for a range of membrane functions such as protein interactions and membrane permeability. A very reliable method to probe the structure of lipid monolayers is sum frequency generation (SFG) vibrational spectroscopy. Not only is SFG extremely surface sensitive but it can also directly access critical parameters such as lipid order and orientation, and it can provide valuable information about protein interactions along with interfacial hydration. However, recent studies have shown that temperature gradients caused by high power laser beams perturb the lipid layers and potentially obscure the spectroscopic results. Here we demonstrate how the local heating problem can be effectively reduced by spatially distributing the laser pulses on the sample surface using a translating Langmuir trough for SFG experiments at lipid monolayers. The efficiency of the trough is illustrated by the detection of enhanced molecular order due to reduced heat load.

  2. Monolayers at air-water interfaces: from origins-of-life to nanotechnology.

    Science.gov (United States)

    Ariga, Katsuhiko; Hill, Jonathan P

    2011-08-01

    The air-water interface presents several interesting features, namely a) a molecularly flat environment, b) a boundary region between two phases with different dielectric constants, c) permits or promotes dynamic interactions within the interface region, and d) a point of interaction between hydrophobic compounds and aqueous molecules. Accordingly, Langmuir monolayers at the air-water interface have several unique characteristics and properties, which require investigation. In this review-type personal account, typical examples of molecular recognition and molecular patterning at air-water interfaces are first introduced, followed by descriptions of specific and unusual properties of monolayers on water. In addition, two examples of our own results concerning Langmuir monolayers are explained. We have selected examples from two apparently unrelated research areas, these being the origin of life and future nanotechnology, in order to emphasize the diverse scientific contribution of research on monolayers at the air-water interface. Copyright © 2011 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

  3. Atomic Defects and Doping of Monolayer NbSe2.

    Science.gov (United States)

    Nguyen, Lan; Komsa, Hannu-Pekka; Khestanova, Ekaterina; Kashtiban, Reza J; Peters, Jonathan J P; Lawlor, Sean; Sanchez, Ana M; Sloan, Jeremy; Gorbachev, Roman V; Grigorieva, Irina V; Krasheninnikov, Arkady V; Haigh, Sarah J

    2017-02-24

    We have investigated the structure of atomic defects within monolayer NbSe2 encapsulated in graphene by combining atomic resolution transmission electron microscope imaging, density functional theory (DFT) calculations, and strain mapping using geometric phase analysis. We demonstrate the presence of stable Nb and Se monovacancies in monolayer material and reveal that Se monovacancies are the most frequently observed defects, consistent with DFT calculations of their formation energy. We reveal that adventitious impurities of C, N, and O can substitute into the NbSe2 lattice stabilizing Se divacancies. We further observe evidence of Pt substitution into both Se and Nb vacancy sites. This knowledge of the character and relative frequency of different atomic defects provides the potential to better understand and control the unusual electronic and magnetic properties of this exciting two-dimensional material.

  4. Dynamics of decanethiol self-assembled monolayers on Au(111) studied by Scanning tunnelling microscopy

    NARCIS (Netherlands)

    Wu, Hairong; Sotthewes, Kai; Kumar, Avijit; Vancso, Gyula J.; Schön, Peter Manfred; Zandvliet, Henricus J.W.

    2013-01-01

    We investigated the dynamics of decanethiol self-assembled monolayers on Au(111) surfaces using time-resolved scanning tunneling microscopy at room temperature. The expected ordered phases (β, δ, χ*, and ) and a disordered phase (ε) were observed. Current–time traces with the feedback loop disabled

  5. Crystalline mesoporous metal oxide

    Institute of Scientific and Technical Information of China (English)

    Wenbo Yue; Wuzong Zhou

    2008-01-01

    Since the discovery of many types of mesoporous silicas, such as SBA-15, KIT-6, FDU-12 and SBA-16, porous crystalline transition metal oxides, such as Cr2O3, Co3O4, In2O3, NiO, CeO2, WO3, Fe2O3 and MnO2, have been synthesized using the mesoporous silicas as hard templates. Several synthetic methods have been developed. These new porous materials have high potential applications in catalysis, Li-ion rechargeable batteries and gas sensors. This article gives a brief review of the research of porous crystals of metal oxides in the last four years.

  6. Lateral pressure profiles in lipid monolayers

    NARCIS (Netherlands)

    Baoukina, Svetlana; Marrink, Siewert J.; Tieleman, D. Peter

    2010-01-01

    We have used molecular dynamics simulations with coarse-grained and atomistic models to study the lateral pressure profiles in lipid monolayers. We first consider simple oil/air and oil/water interfaces, and then proceed to lipid monolayers at air/water and oil/water interfaces. The results are qual

  7. Monte Carlo studies of model Langmuir monolayers.

    Science.gov (United States)

    Opps, S B; Yang, B; Gray, C G; Sullivan, D E

    2001-04-01

    This paper examines some of the basic properties of a model Langmuir monolayer, consisting of surfactant molecules deposited onto a water subphase. The surfactants are modeled as rigid rods composed of a head and tail segment of diameters sigma(hh) and sigma(tt), respectively. The tails consist of n(t) approximately 4-7 effective monomers representing methylene groups. These rigid rods interact via site-site Lennard-Jones potentials with different interaction parameters for the tail-tail, head-tail, and head-head interactions. In a previous paper, we studied the ground-state properties of this system using a Landau approach. In the present paper, Monte Carlo simulations were performed in the canonical ensemble to elucidate the finite-temperature behavior of this system. Simulation techniques, incorporating a system of dynamic filters, allow us to decrease CPU time with negligible statistical error. This paper focuses on several of the key parameters, such as density, head-tail diameter mismatch, and chain length, responsible for driving transitions from uniformly tilted to untilted phases and between different tilt-ordered phases. Upon varying the density of the system, with sigma(hh)=sigma(tt), we observe a transition from a tilted (NNN)-condensed phase to an untilted-liquid phase and, upon comparison with recent experiments with fatty acid-alcohol and fatty acid-ester mixtures [M. C. Shih, M. K. Durbin, A. Malik, P. Zschack, and P. Dutta, J. Chem. Phys. 101, 9132 (1994); E. Teer, C. M. Knobler, C. Lautz, S. Wurlitzer, J. Kildae, and T. M. Fischer, J. Chem. Phys. 106, 1913 (1997)], we identify this as the L'(2)/Ov-L1 phase boundary. By varying the head-tail diameter ratio, we observe a decrease in T(c) with increasing mismatch. However, as the chain length was increased we observed that the transition temperatures increased and differences in T(c) due to head-tail diameter mismatch were diminished. In most of the present research, the water was treated as a hard

  8. Evidence for variable crystallinity in bivalve shells

    Science.gov (United States)

    Jacob, D. E.; Wehrmeister, U.

    2012-04-01

    Bivalve shells are used as important palaeoclimate proxy archives and monitor regional climate variations. The shells mostly exist of two crystalline polymorphic phases of calcium carbonate calcite (rombohedric) and aragonite (orthorhombic). Calcite is the most stable polymorph at standard conditions, whereas vaterite (hexagonal) is the least stable and only rarely found in these structures. Shells are characterized by organized structures and several micro architectures of mollusc shell structures have been identified: Nacre shows different types: columnar and bricked forms and consists of composite inorganic- organic at the nano-scale. They are well known to display a "brick and mortar" structure. By AFM and FIB/TEM methods it could be shown, that its nanostructure consists of the structures in the range of 50 - 100 nm [1, 2]. These structures are vesicles, consisting of CaCO3 and are individually coated by a membrane. Most probably, the mantle epithelian cells of the bivalve extrude CaCO3 vesicles. By Raman spectroscopic investigations the crystalline CaCO3 polymorphs calcite, aragonite and vaterite, as well as ACC were determined. For some species (Diplodon chilensis patagonicus, Hyriopsis cumingii) pure ACC (i.e. not intermingled with a crystalline phase) could be identified. The presence of an amorphous phase is generally deduced from the lack of definite lattice modes, whereas a broad Raman band in this region is to observe. In most of the cultured pearls (Pinctada maxima and genus Hyriopsis) the ν1-Raman band of ACC clearly displays an asymmetric shape and splits into two different bands according to a nanocrystalline and an amorphous fraction. The FWHMs of most of the crystalline fractions are too high for well crystallized materials and support the assumption of nanocrystalline calcium carbonate polymorph clusters in ACC. They are primarily composed of amorphous calcium carbonate (ACC) which is later transformed into a crystalline modification [3

  9. Protein-induced surface structuring in myelin membrane monolayers.

    Science.gov (United States)

    Rosetti, Carla M; Maggio, Bruno

    2007-12-15

    Monolayers prepared from myelin conserve all the compositional complexity of the natural membrane when spread at the air-water interface. They show a complex pressure-dependent surface pattern that, on compression, changes from the coexistence of two liquid phases to a viscous fractal phase embedded in a liquid phase. We dissected the role of major myelin protein components, myelin basic protein (MBP), and Folch-Lees proteolipid protein (PLP) as crucial factors determining the structural dynamics of the interface. By analyzing mixtures of a single protein with the myelin lipids we found that MBP and PLP have different surface pressure-dependent behaviors. MBP stabilizes the segregation of two liquid phases at low pressures and becomes excluded from the film under compression, remaining adjacent to the interface. PLP, on the contrary, organizes a fractal-like pattern at all surface pressures when included in a monolayer of the protein-free myelin lipids but it remains mixed in the MBP-induced liquid phase. The resultant surface topography and dynamics is regulated by combined near to equilibrium and out-of-equilibrium effects. PLP appears to act as a surface skeleton for the whole components whereas MBP couples the structuring to surface pressure-dependent extrusion and adsorption processes.

  10. DECOVALEX-THMC Project. Task D. Long-Term Permeability/Porosity Changes in the EDZ and Near Field due to THM and THC Processes in Volcanic and Crystalline-Bentonite Systems. Phase 1 Report

    Energy Technology Data Exchange (ETDEWEB)

    Birkholzer, J.; Rutqvist, J.; Sonnenthal, E. [Lawrence Berkeley National Laboratory, CA (United States); Barr, D. [Office of Repository Development, DOE (United States)

    2007-02-15

    The general goal of this project is to encourage multidisciplinary interactive and cooperative research on modeling coupled processes in geologic formations in support of the performance assessment for underground storage of radioactive waste. Three multi-year project stages of DECOVALEX have been completed in the past decade, mainly focusing on coupled thermal-hydrological-mechanical processes. Currently, a fourth three-year project stage of DECOVALEX is under way, referred to as DECOVALEX-THMC. THMC stands for Thermal, Hydrological, Mechanical, and Chemical processes. The new project stage aims at expanding the traditional geomechanical scope of the previous DECOVALEX project stages by incorporating geochemical processes important for repository performance. The U.S. Department of Energy (DOE) leads Task D of the new DECOVALEX phase, entitled 'Long-term Permeability/Porosity Changes in the EDZ and Near Field due to THC and THM Processes for Volcanic and Crystalline-Bentonite Systems.' In its leadership role for Task D, DOE coordinates and sets the direction for the cooperative research activities of the international research teams engaged in Task D. The research program developed for Task D of DECOVALEX-THMC involves geomechanical and geochemical research areas. THM and THC processes may lead to changes in hydrological properties that are important for performance because the flow processes in the vicinity of emplacement tunnels will be altered from their initial state. Some of these changes can be permanent (irreversible), in which case they persist after the thermal conditions have returned to ambient; i.e., they will affect the entire regulatory compliance period. Geochemical processes also affect the water and gas chemistry close to the waste packages, which are relevant for waste package corrosion, buffer stability, and radionuclide transport. Research teams participating in Task D evaluate long-term THM and THC processes in two generic geologic

  11. An All-Organic Composite System for Resistive Change Memory via the Self-Assembly of Plastic-Crystalline Molecules.

    Science.gov (United States)

    Cha, An-Na; Lee, Sang-A; Bae, Sukang; Lee, Sang Hyun; Lee, Dong Su; Wang, Gunuk; Kim, Tae-Wook

    2017-01-25

    An all-organic composite system was introduced as an active component for organic resistive memory applications. The active layer was prepared by mixing a highly polar plastic-crystalline organic molecule (succinonitrile, SN) into an insulating polymer (poly(methyl methacrylate), PMMA). As increasing concentrations of SN from 0 to 3.0 wt % were added to solutions of different concentrations of PMMA, we observed distinguishable microscopic surface structures on blended films of SN and PMMA at certain concentrations after the spin-casting process. The structures were organic dormant volcanos composed of micron-scale PMMA craters and disk type SN lava. Atomic force microscopy (AFM), cross-sectional transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometer (EDX) analysis showed that these structures were located in the middle of the film. Self-assembly of the plastic-crystalline molecules resulted in the phase separation of the SN:PMMA mixture during solvent evaporation. The organic craters remained at the surface after the spin-casting process, indicative of the formation of an all-organic composite film. Because one organic crater contains one SN disk, our system has a coplanar monolayer disk composite system, indicative of the simplest composite type of organic memory system. Current-voltage (I-V) characteristics of the composite films with organic craters revealed that our all-organic composite system showed unipolar type resistive switching behavior. From logarithmic I-V characteristics, we found that the current flow was governed by space charge limited current (SCLC). From these results, we believe that a plastic-crystalline molecule-polymer composite system is one of the most reliable ways to develop organic composite systems as potential candidates for the active components of organic resistive memory applications.

  12. Crystalline mono- and multilayer self-assemblies of oligothiophenes at the air-water interface

    DEFF Research Database (Denmark)

    Isz, S.; Weissbuch, I.; Kjær, K.;

    1997-01-01

    of aromatic nonamphiphilic molecules, self-aggregated at the air-water interface. As model systems we have examined the deposition of quaterthiophene (S-4), quinquethiophene (S-5). and sexithiophene (S-6) from chloroform solutions on the water surface. The structures of the films were determined by surface...... pressure-area isotherms, by scanning force microscopy (SFM) after transfer of the films onto atomically smooth mica, by cryo-transmission electron microscopy (Cryo-TEM) on vitreous ice, and by grazing incidence synchrotron X-ray diffraction (GID) directly on the water surface. S-4 forms two polymorphic...... surface. S-5 self-ageregates at the water surface to form mixtures of monolayers and bilayers of the beta polymorph; S-6 forms primarily crystalline monolayers of both alpha and beta forms. The crystalline assemblies preserve their integrity during transfer from the water surface onto solid supports...

  13. Liquid crystalline order in polymers

    CERN Document Server

    Blumstein, Alexandre

    1978-01-01

    Liquid Crystalline Order in Polymers examines the topic of liquid crystalline order in systems containing rigid synthetic macromolecular chains. Each chapter of the book provides a review of one important area of the field. Chapter 1 discusses scattering in polymer systems with liquid crystalline order. It also introduces the field of liquid crystals. Chapter 2 treats the origin of liquid crystalline order in macromolecules by describing the in-depth study of conformation of such macromolecules in their unassociated state. The chapters that follow describe successively the liquid crystalli

  14. Influence of the Head Group Size on the Direction of Tilt in Langmuir Monolayers

    CERN Document Server

    Schmid, F

    1996-01-01

    A model of rods with heads of variable size, which are confined to a planar surface, is used to study the influence of the head group size on tilted phases in Langmuir monolayers. Simple free energy considerations as well as exact zero temperature calculations indicate that molecules with small head groups tilt towards next nearest neighbors, and molecules with larger head groups towards nearest neighbors. This provides a possible explanation for recent experimental results, and for details of the generic phase diagram for fatty acid monolayers.

  15. DECOVALEX-THMC Project. Task D. Long-Term Permeability/Porosity Changes in the EDZ and Near Field due to THM and THC Processes in Volcanic and Crystalline-Bentonite Systems. Phase 1 Report

    Energy Technology Data Exchange (ETDEWEB)

    Birkholzer, J.; Rutqvist, J.; Sonnenthal, E. [Lawrence Berkeley National Laboratory, CA (United States); Barr, D. [Office of Repository Development, DOE (United States)

    2007-02-15

    The general goal of this project is to encourage multidisciplinary interactive and cooperative research on modeling coupled processes in geologic formations in support of the performance assessment for underground storage of radioactive waste. Three multi-year project stages of DECOVALEX have been completed in the past decade, mainly focusing on coupled thermal-hydrological-mechanical processes. Currently, a fourth three-year project stage of DECOVALEX is under way, referred to as DECOVALEX-THMC. THMC stands for Thermal, Hydrological, Mechanical, and Chemical processes. The new project stage aims at expanding the traditional geomechanical scope of the previous DECOVALEX project stages by incorporating geochemical processes important for repository performance. The U.S. Department of Energy (DOE) leads Task D of the new DECOVALEX phase, entitled 'Long-term Permeability/Porosity Changes in the EDZ and Near Field due to THC and THM Processes for Volcanic and Crystalline-Bentonite Systems.' In its leadership role for Task D, DOE coordinates and sets the direction for the cooperative research activities of the international research teams engaged in Task D. The research program developed for Task D of DECOVALEX-THMC involves geomechanical and geochemical research areas. THM and THC processes may lead to changes in hydrological properties that are important for performance because the flow processes in the vicinity of emplacement tunnels will be altered from their initial state. Some of these changes can be permanent (irreversible), in which case they persist after the thermal conditions have returned to ambient; i.e., they will affect the entire regulatory compliance period. Geochemical processes also affect the water and gas chemistry close to the waste packages, which are relevant for waste package corrosion, buffer stability, and radionuclide transport. Research teams participating in Task D evaluate long-term THM and THC processes in two generic geologic

  16. Oleic acid disorders stratum corneum lipids in Langmuir monolayers.

    Science.gov (United States)

    Mao, Guangru; VanWyck, Dina; Xiao, Xin; Mack Correa, M Catherine; Gunn, Euen; Flach, Carol R; Mendelsohn, Richard; Walters, Russel M

    2013-04-16

    Oleic acid (OA) is well-known to affect the function of the skin barrier. In this study, the molecular interactions between OA and model stratum corneum (SC) lipids consisting of ceramide, cholesterol, and palmitic acid (PA) were investigated with Langmuir monolayer and associated techniques. Mixtures with different OA/SC lipid compositions were spread at the air/water interface, and the phase behavior was tracked with surface pressure-molecular area (π-A) isotherms. With increasing OA levels in the monolayer, the films became more fluid and more compressible. The thermodynamic parameters derived from π-A isotherms indicated that there are preferential interactions between OA and SC lipids and that films of their mixtures were thermodynamically stable. The domain structure and lipid conformational order of the monolayers were studied through Brewster angle microscopy (BAM) and infrared reflection absorption spectroscopy (IRRAS), respectively. Results indicate that lower concentrations of OA preferentially mix with and disorder the ceramide-enriched domains, followed by perturbation of the PA-enriched domains and disruption of SC lipid domain separation at higher OA levels.

  17. New ice rules for nanoconfined monolayer ice from first principles

    CERN Document Server

    Corsetti, Fabiano; Artacho, Emilio

    2016-01-01

    Understanding the structural tendencies of nanoconfined water is of great interest for nanoscience and biology, where nano/micro-sized objects may be separated by very few layers of water. Here we investigate the properties of ice confined to a quasi-2D monolayer by a featureless, chemically neutral potential, using density-functional theory simulations with a non-local van der Waals density functional. An ab initio random structure search reveals all the energetically competitive monolayer configurations to belong to only two of the previously-identified families, characterized by a square or honeycomb hydrogen-bonding network, respectively. From an in-depth analysis we show that the well-known ice rules for bulk ice need to be revised for the monolayer, with distinct new rules appearing for the two networks. All identified stable phases for both are found to be non-polar (but with a topologically non-trivial texture for the square) and, hence, non-ferroelectric, in contrast to the predictions of empirical f...

  18. Palmitic Acid on Salt Subphases and in Mixed Monolayers of Cerebrosides: Application to Atmospheric Aerosol Chemistry

    Directory of Open Access Journals (Sweden)

    Ellen M. Adams

    2013-10-01

    Full Text Available Palmitic acid (PA has been found to be a major constituent in marine aerosols, and is commonly used to investigate organic containing atmospheric aerosols, and is therefore used here as a proxy system. Surface pressure-area isotherms (π-A, Brewster angle microscopy (BAM, and vibrational sum frequency generation (VSFG were used to observe a PA monolayer during film compression on subphases of ultrapure water, CaCl2 and MgCl2 aqueous solutions, and artificial seawater (ASW. π-A isotherms indicate that salt subphases alter the phase behavior of PA, and BAM further reveals that a condensation of the monolayer occurs when compared to pure water. VSFG spectra and BAM images show that Mg2+ and Ca2+ induce ordering of the PA acyl chains, and it was determined that the interaction of Mg2+ with the monolayer is weaker than Ca2+. π-A isotherms and BAM were also used to monitor mixed monolayers of PA and cerebroside, a simple glycolipid. Results reveal that PA also has a condensing effect on the cerebroside monolayer. Thermodynamic analysis indicates that attractive interactions between the two components exist; this may be due to hydrogen bonding of the galactose and carbonyl headgroups. BAM images of the collapse structures show that mixed monolayers of PA and cerebroside are miscible at all surface pressures. These results suggest that the surface morphology of organic-coated aerosols is influenced by the chemical composition of the aqueous core and the organic film itself.

  19. Electrochemical Deposition Of Thiolate Monolayers On Metals

    Science.gov (United States)

    Porter, Marc D.; Weissharr, Duane E.

    1995-01-01

    Electrochemical method devised for coating metal (usually, gold) surfaces with adherent thiolate monolayers. Affords greater control over location and amount of material deposited and makes it easier to control chemical composition of deposits. One important potential use for this method lies in fabrication of chemically selective thin-film resonators for microwave oscillators used to detect pollutants: monolayer formulated to bind selectively pollutant chemical species of interest, causing increase in mass of monolayer and corresponding decrease in frequency of resonance. Another important potential use lies in selective chemical derivatization for purposes of improving adhesion, lubrication, protection against corrosion, electrocatalysis, and electroanalysis.

  20. Influence of calcium on ceramide-1-phosphate monolayers

    Directory of Open Access Journals (Sweden)

    Joana S. L. Oliveira

    2016-02-01

    Full Text Available Ceramide-1-phosphate (C1P plays an important role in several biological processes, being identified as a key regulator of many protein functions. For instance, it acts as a mediator of inflammatory responses. The mediation of the inflammation process happens due to the interaction of C1P with the C2 domain of cPLA2α, an effector protein that needs the presence of submicromolar concentrations of calcium ions. The aim of this study was to determine the phase behaviour and structural properties of C1P in the presence and absence of millimolar quantities of calcium in a well-defined pH environment. For that purpose, we used monomolecular films of C1P at the soft air/liquid interface with calcium ions in the subphase. The pH was varied to change the protonation degree of the C1P head group. We used surface pressure versus molecular area isotherms coupled with other monolayer techniques as Brewster angle microscopy (BAM, infrared reflection–absorption spectroscopy (IRRAS and grazing incidence X-ray diffraction (GIXD. The isotherms indicate that C1P monolayers are in a condensed state in the presence of calcium ions, regardless of the pH. At higher pH without calcium ions, the monolayer is in a liquid-expanded state due to repulsion between the negatively charged phosphate groups of the C1P molecules. When divalent calcium ions are added, they are able to bridge the highly charged phosphate groups, enhancing the regular arrangement of the head groups. Similar solidification of the monolayer structure can be seen in the presence of a 150 times larger concentration of monovalent sodium ions. Therefore, calcium ions have clearly a strong affinity for the phosphomonoester of C1P.

  1. COLD DRAWING IN CRYSTALLINE POLYMERS

    Science.gov (United States)

    alcohols, phenol) in Nylon 6 produced changes in the crystalline structure as well as plasticizer action; these two effects must therefore be carefully...distinguished. Changes in the crystalline structure were followed by changes in the infrared spectrum. Dynamic mechanical and thermogravimetric analysis

  2. Preferential Incorporation of Azelaic Acid Units into the Crystalline Phase of the Copoly(Alkylene Dicarboxylate Derived from 1,9-Nonanediol and an Equimolar Mixture of Pimelic and Azelaic Acids

    Directory of Open Access Journals (Sweden)

    Angélica Díaz

    2015-09-01

    Full Text Available The crystalline structure of two biodegradable odd-odd polyesters (i.e., poly(nonamethylene pimelate (PES 9,7 and poly(nonamethylene azelate (PES 9,9 was investigated by means of electron and X-ray diffraction of single crystals and oriented fibers, respectively. Truncated rhombic crystals were obtained with an aspect ratio that was strongly depended on the supercooling degree. The crystalline structure of both homopolyesters was defined by an orthorhombic P21ab space group and a large unit cell containing four molecular segments with an all-trans conformation. Nevertheless, the structure in the chain axis projection was equivalent to a simpler cell containing only two segments. Crystalline lamellae were effectively degraded by lipases, starting the enzymatic attack on the lamellar surfaces. The random copolymer constituted by an equimolar amount of pimelate and azelate units (COPES 9,7/9 crystallized according to regular lamellae with a similar molecular arrangement in the chain axis projection. The structure of this copolymer was preferably conditioned by the azelate component as could be deduced from both, diffraction and spectroscopic data. Analysis of small angle X-ray scattering patterns pointed out that less crystalline lamellae with higher amorphous thickness had developed in the copolymer. This feature was interpreted as a consequence of the preferential incorporation of pimelate comonomer units in the folding surface.

  3. Effects of surface pressure on the properties of Langmuir monolayers and interfacial water at the air-water interface.

    Science.gov (United States)

    Lin, Wei; Clark, Anthony J; Paesani, Francesco

    2015-02-24

    The effects of surface pressure on the physical properties of Langmuir monolayers of palmitic acid (PA) and dipalmitoylphosphatidic acid (DPPA) at the air/water interface are investigated through molecular dynamics simulations with atomistic force fields. The structure and dynamics of both monolayers and interfacial water are compared across the range of surface pressures at which stable monolayers can form. For PA monolayers at T = 300 K, the untilted condensed phase with a hexagonal lattice structure is found at high surface pressure, while the uniformly tilted condensed phase with a centered rectangular lattice structure is observed at low surface pressure, in agreement with the available experimental data. A state with uniform chain tilt but no periodic spatial ordering is observed for DPPA monolayers on a Na(+)/water subphase at both high and low surface pressures. The hydrophobic acyl chains of both monolayers pack efficiently at all surface pressures, resulting in a very small number of gauche defects. The analysis of the hydrogen-bonding structure/dynamics at the monolayer/water interface indicates that water molecules hydrogen-bonded to the DPPA head groups reorient more slowly than those hydrogen-bonded to the PA head groups, with the orientational dynamics becoming significantly slower at high surface pressure. Possible implications for physicochemical processes taking place on marine aerosols in the atmosphere are discussed.

  4. Optical properties of structures composed of periodic, quasi-periodic, and aperiodic sequences of particulate monolayers

    Science.gov (United States)

    Loiko, V. A.; Miskevich, A. A.

    2017-01-01

    The spectra of the coherent transmission and reflection coefficients of multilayers consisting of the periodic, Fibonacci (quasi-periodic), and Thue-Morse (aperiodic) sequences of plane-parallel monolayers of monodisperse spherical alumina and silica particles are investigated using the quasi-crystalline approximation (QCA) and the transfer matrix method (TMM). The additional opportunities for the transmission and reflection spectra manipulation in comparison with the periodic sequence of monolayers are demonstrated. Photonic band gaps in the spectra of the particulate structures are shifted to the short-wavelength range in comparison with those for systems of homogeneous layers. The shift is larger for the Thue-Morse sequence. The widths of the photonic band gaps for particulate systems are narrower than the ones for multilayers consisting of homogeneous layers of an equivalent volume of matter. The results can be used to create optical, optoelectronics, and photonics devices—for example, multispectral filters, light emitting diodes, solar cells, displays.

  5. Chiral hierarchical self-assembly in Langmuir monolayers of diacetylenic lipids

    KAUST Repository

    Basnet, Prem B.

    2013-01-01

    When compressed in the intermediate temperature range below the chain-melting transition yet in the low-pressure liquid phase, Langmuir monolayers made of chiral lipid molecules form hierarchical structures. Using Brewster angle microscopy to reveal this structure, we found that as the liquid monolayer is compressed, an optically anisotropic condensed phase nucleates in the form of long, thin claws. These claws pack closely to form stripes. This appears to be a new mechanism for forming stripes in Langmuir monolayers. In the lower temperature range, these stripes arrange into spirals within overall circular domains, while near the chain-melting transition, the stripes arrange into target patterns. We attributed this transition to a change in boundary conditions at the core of the largest-scale circular domains. © 2013 The Royal Society of Chemistry.

  6. Achieving Uniform Monolayer Transition Metal Dichalcogenides Film on Silicon Wafer via Silanization Treatment: A Typical Study on WS2.

    Science.gov (United States)

    Chen, Ying; Gan, Lin; Li, Huiqiao; Ma, Ying; Zhai, Tianyou

    2017-02-01

    A silanization reaction is employed to improve the dispersion of precursors on a silicon wafer for a large-size uniform transition metal dichalcogenide (TMD) film synthesis and to achieve a highly crystalline monolayer WS2 film up to 1 cm(2) . The novel strategy is also verified for the synthesis of WSe2 and MoS2 uniform films, suggesting universality for TMD film fabrication.

  7. Tuning the molecular order of C60-based self-assembled monolayers in field-effect transistors.

    Science.gov (United States)

    Schmaltz, Thomas; Khassanov, Artoem; Steinrück, Hans-Georg; Magerl, Andreas; Hirsch, Andreas; Halik, Marcus

    2014-11-07

    The control of order in organic semiconductor systems is crucial to achieve desired properties in electronic devices. We have studied the order in fullerene functionalized self-assembled monolayers by mixing the active molecules with supporting alkyl phosphonic acids of different chain length. By adjusting the length of the molecules, structural modifications of the alignment of the C60 head groups within the SAM can be tuned in a controlled way. These changes on the sub-nanometre scale were analysed by grazing incidence X-ray diffraction and X-ray reflectivity. To study the electron transport properties across these layers, self-assembled monolayer field-effect transistors (SAMFETs) were fabricated containing only the single fullerene monolayer as semiconductor. Electrical measurements revealed that a high 2D crystalline order is not the only important aspect. If the fullerene head groups are too confined by the supporting alkyl phosphonic acid molecules, defects in the crystalline C60 film, such as grain boundaries, start to strongly limit the charge transport properties. By close interpretation of the results of structural investigations and correlating them to the results of electrical characterization, an optimum chain length of the supporting alkyl phosphonic acids in the range of C10 was determined. With this study we show that minor changes in the order on the sub-nanometre scale, can strongly influence electronic properties of functional self-assembled monolayers.

  8. Method to synthesize metal chalcogenide monolayer nanomaterials

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Sanchez, Bernadette A.; Boyle, Timothy J.

    2016-12-13

    Metal chalcogenide monolayer nanomaterials can be synthesized from metal alkoxide precursors by solution precipitation or solvothermal processing. The synthesis routes are more scalable, less complex and easier to implement than other synthesis routes.

  9. Strain Tuning of the Charge Density Wave in Monolayer and Bilayer 1T-TaS2

    KAUST Repository

    Gan, Liyong

    2015-12-07

    By first-principles calculations, we investigate the strain effects on the charge density wave states of monolayer and bilayer 1T-TaS2. The modified stability of the charge density wave in the monolayer is understood in terms of the strain dependent electron localization, which determines the distortion amplitude. On the other hand, in the bilayer the effect of strain on the interlayer interaction is also crucial. The rich phase diagram under strain opens new venues for applications of 1T-TaS2. We interpret the experimentally observed insulating state of bulk 1T-TaS2 as inherited from the monolayer by effective interlayer decoupling.

  10. Structural study of monolayer cobalt phthalocyanine adsorbed on graphite

    CERN Document Server

    Scheffler, M; Baumann, D; Schlegel, R; Hänke, T; Toader, M; Büchner, B; Hietschold, M; Hess, C

    2014-01-01

    We present microscopic investigations on the two-dimensional arrangement of cobalt phthalocyanine molecules on a graphite (HOPG) substrate in the low coverage regime. The initial growth and ordering of molecular layers is revealed in high resolution scanning tunneling microscopy (STM). On low coverages single molecules orient mostly along one of the substrate lattice directions, while they form chains at slightly higher coverage. Structures with two different unit cells can be found from the first monolayer on. A theoretical model based on potential energy calculations is presented, which relates the two phases to the driving ordering forces.

  11. Structure of adsorbed monolayers. The surface chemical bond

    Energy Technology Data Exchange (ETDEWEB)

    Somorjai, G.A.; Bent, B.E.

    1984-06-01

    This paper attempts to provide a summary of what has been learned about the structure of adsorbed monolayers and about the surface chemical bond from molecular surface science. While the surface chemical bond is less well understood than bonding of molecules in the gas phase or in the solid state, our knowledge of its properties is rapidly accumulating. The information obtained also has great impact on many surface science based technologies, including heterogeneous catalysis and electronic devices. It is hoped that much of the information obtained from studies at solid-gas interfaces can be correlated with molecular behavior at solid-liquid interfaces. 31 references, 42 figures, 1 table.

  12. Fractal growth in impurity-controlled solidification in lipid monolayers

    DEFF Research Database (Denmark)

    Fogedby, Hans C.; Sørensen, Erik Schwartz; Mouritsen, Ole G.

    1987-01-01

    A simple two-dimensional microscopic model is proposed to describe solidifcation processes in systems with impurities which are miscible only in the fluid phase. Computer simulation of the model shows that the resulting solids are fractal over a wide range of impurity concentrations and impurity...... diffusional constants. A fractal-forming mechanism is suggested for impurity-controlled solidification which is consistent with recent experimental observations of fractal growth of solid phospholipid domains in monolayers. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....

  13. Fracture Characteristics of Monolayer CVD-Graphene

    OpenAIRE

    Hwangbo, Yun; Lee, Choong-Kwang; Kim, Sang-Min; Kim, Jae-Hyun; Kim, Kwang-Seop; Jang, Bongkyun; Lee, Hak-Joo; Lee, Seoung-Ki; Kim, Seong-Su; Ahn, Jong-Hyun; Lee, Seung-Mo

    2014-01-01

    We have observed and analyzed the fracture characteristics of the monolayer CVD-graphene using pressure bulge testing setup. The monolayer CVD-graphene has appeared to undergo environmentally assisted subcritical crack growth in room condition, i.e. stress corrosion cracking arising from the adsorption of water vapor on the graphene and the subsequent chemical reactions. The crack propagation in graphene has appeared to be able to be reasonably tamed by adjusting applied humidity and stress. ...

  14. 2D "soap"-assembly of nanoparticles via colloid-induced condensation of mixed Langmuir monolayers of fatty surfactants.

    Science.gov (United States)

    Babenko, Denis I; Ezhov, Alexander A; Turygin, Dmitry S; Ivanov, Vladimir A; Ivanov, Vladimir K; Arslanov, Vladimir V; Kalinina, Maria A

    2012-01-10

    We describe a new type of colloidal 2D gels formed in mixed Langmuir monolayers of stearic acid and octadecylamine on a surface of gold hydrosol. The adsorption of gold nanoparticles on the mixed monolayer led to an increase of interactions between oppositely charged surfactants giving a "soap" of mixed fatty salt. The observed effect is equivalent to a virtual "cooling" of floating monolayer, which undergoes rapid condensation on a surface of aqueous colloid. The consequent shrinking and rearrangement of the monolayer resulted in aggregation of nanoparticles into colloidal 2D "soap"-gels, which represented arrested colloidal phases within nonadsorbing organic medium. When sequentially deposited onto solids by Langmuir-Blodgett technique, the 2D "soap"-gels separated into organic and colloidal phases and gave dendrite-like bilateral organic crystallites coated with gold nanoparticles. The reported colloidal "soap"-assembly can offer a new opportunity to design 2D colloidal systems of widely variable chemistry and structures.

  15. Monolayer spontaneous curvature of raft-forming membrane lipids

    Science.gov (United States)

    Kollmitzer, Benjamin; Heftberger, Peter; Rappolt, Michael; Pabst, Georg

    Monolayer spontaneous curvatures for cholesterol, DOPE, POPE, DOPC, DPPC, DSPC, POPC, SOPC, and egg sphingomyelin were obtained using small-angle X-ray scattering (SAXS) on inverted hexagonal phases (HII). Spontaneous curvatures of bilayer forming lipids were estimated by adding controlled amounts to a HII forming template following previously established protocols. Spontanous curvatures of both phosphatidylethanolamines and cholesterol were found to be at least a factor of two more negative than those of phosphatidylcholines, whose J0 are closer to zero. Interestingly, a significant positive J0 value (+0.1 1/nm) was retrieved for DPPC at 25 {\\deg}C. We further determined the temperature dependence of the spontaneous curvatures J0(T) in the range from 15 to 55 \\degC, resulting in a quite narrow distribution of -1 to -3 * 10^-3 1/nm{\\deg}C for most investigated lipids. The data allowed us to estimate the monolayer spontaneous curvatures of ternary lipid mixtures showing liquid ordered / liquid disordered phase coexistence. We report spontaneous curvature phase diagrams for DSPC/DOPC/Chol, DPPC/DOPC/Chol and SM/POPC/Chol and discuss effects on protein insertion and line tension.

  16. Mass spectrometric analysis of monolayer protected nanoparticles

    Science.gov (United States)

    Zhu, Zhengjiang

    Monolayer protected nanoparticles (NPs) include an inorganic core and a monolayer of organic ligands. The wide variety of core materials and the tunable surface monolayers make NPs promising materials for numerous applications. Concerns related to unforeseen human health and environmental impacts of NPs have also been raised. In this thesis, new analytical methods based on mass spectrometry are developed to understand the fate, transport, and biodistributions of NPs in the complex biological systems. A laser desorption/ionization mass spectrometry (LDI-MS) method has been developed to characterize the monolayers on NP surface. LDI-MS allows multiple NPs taken up by cells to be measured and quantified in a multiplexed fashion. The correlations between surface properties of NPs and cellular uptake have also been explored. LDI-MS is further coupled with inductively coupled plasma mass spectrometry (ICP-MS) to quantitatively measure monolayer stability of gold NPs (AuNPs) and quantum dots (QDs), respectively, in live cells. This label-free approach allows correlating monolayer structure and particle size with NP stability in various cellular environments. Finally, uptake, distribution, accumulation, and excretion of NPs in higher order organisms, such as fish and plants, have been investigated to understand the environmental impact of nanomaterials. The results indicate that surface chemistry is a primary determinant. NPs with hydrophilic surfaces are substantially less toxic and present a lower degree of bioaccumulation, making these nanomaterials attractive for sustainable nanotechnology.

  17. Research on the Mineral Phase and Component of Non-Crystalline and Nano-Crystalline Corrosion Products on Bronzes Unearthed from Shang Tomb in Xingan%新干商墓青铜器非晶与纳米晶锈蚀产物结构的分析研究

    Institute of Scientific and Technical Information of China (English)

    成小林; 潘路

    2012-01-01

    应用微区X射线衍射仪(μXRD)及高分辨透射电镜(HTEM)分析江西新干商墓出土的青铜器粉状锈蚀产物,结果表明锈蚀产物主要为具有锡石结构的SnO2,晶态形式为非晶与晶粒尺寸为4~5.7 nm的纳米晶共混;能谱分析表明样品中除含有大量锡外,还有少量的铜、硅、铅与铁等元素.通过对锈蚀产物的高分辨透射电镜晶格条纹像计算,说明纳米晶SnO2的晶格中并没有其他原子的掺杂;对该锈蚀产物拉曼光谱的分析研究表明,样品不含有表征SnO2的体相拉曼峰,更具有非晶SnO2的特征,而973 cm-1的弱而宽的峰表明样品含有非晶的硅酸盐类的锈蚀物,推测锈蚀产物中的少量铜、硅、铅与铁等元素应以非晶的形式存在.%The patinas on bronzes in Shang Tomb of Xingan were powdery, pale green, which were more like "bronze disease", but the mineral composition of patinas was not paratacamite or atacamite. Micro X-ray diffraction (XRD) and high performance transmission electroscope ( HTEM) showed that the patinas were mainly composed of non-crystalline and nano-crystalline SnO2, and the size of nano-crystalline particle was in the range of 4 ~ 5. 7 nm; Moreover, the energy-dispersive X-ray spectrometry showed that element tin is the primary ingredient of the sample, as well as little copper, silicon, lead and iron were detected. By studying the crystal lattice stripe image of the nanometer SnQ2, it was deduced that the chemical formula of nano-crystalline SnO2 did not include other elements; The Raman spectrum of the sample showed that there were not any characteristic peaks of SnO2, the spectrum was more like non-crystalline SnO2, and the weak and broad peak of 973 cm-1 indicated that the sample may contain silicate grains, It was inferred that little of copper, silicon, lead and iron should exist in the form of non-crystalline silicate particles.

  18. Genetics Home Reference: Bietti crystalline dystrophy

    Science.gov (United States)

    ... Understand Genetics Home Health Conditions Bietti crystalline dystrophy Bietti crystalline dystrophy Enable Javascript to view the expand/ ... boxes. Download PDF Open All Close All Description Bietti crystalline dystrophy is a disorder in which numerous ...

  19. Terahertz Spectroscopy of Crystalline and Non-Crystalline Solids

    DEFF Research Database (Denmark)

    Parrott, Edward P. J.; Fischer, Bernd M.; Gladden, Lynn F.

    2013-01-01

    Terahertz spectroscopy of crystalline and non-crystalline solids is probably one of the most active research fields within the terahertz community. Many potential applications, amongst which spectral recognition is probably one of the most prominent, have significantly stimulated the development...... selected examples, the potential the technique holds for various different applications. A particular focus will be given to data analysis and, in particular, how we may account for effects resulting from non-ideal sample preparation....

  20. Electronic Structure of Single-Crystal Monolayer Graphene on Hydrogen-Terminated Germanium Surface

    Science.gov (United States)

    Ahn, Sung Joon; Lee, Jae-Hyun; Ahn, Joung Real; Whang, Dongmok

    2015-03-01

    Graphene, atomically flat 2-Dimensional layered nano material, has a lot of interesting characteristics from its unusual electronic structure. Almost properties of graphene are influenced by its crystallinity, therefore the uniform growth of single crystal graphene and layer control over the wafer scale areas remains a challenge in the fields of electronic, photonic and other devices based on graphene. Here, we report the method to make wafer scale single crystal monolayer graphene on hydrogen terminated germanium(110) surface and properties and electronic band structure of the graphene by using the tool of scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, electron transport measurement, electron diffraction and angle-resolved photoemission spectroscopy.

  1. Synthesis and Supramolecular Chemistry of Novel Liquid Crystalline Crown Ether-Substituted Phthalocyanines : Toward Molecular Wires and Molecular Ionoelectronics

    NARCIS (Netherlands)

    Nostrum, Cornelus F. van; Picken, Stephen J.; Schouten, Arend-Jan; Nolte, Roeland J.M.

    1995-01-01

    The synthesis of the metal-free and the dihydroxysilicon derivatives of tetrakis[4’,5’-bis(decoxy)benzo-18-crown-6]phthalocyanine is described. The metal-free phthalocyanine is liquid crystalline and exhibits a crystalline phase to mesophase transition at 148 °C. The structures of the crystalline ph

  2. Synthesis and Supramolecular Chemistry of Novel Liquid Crystalline Crown Ether-Substituted Phthalocyanines : Toward Molecular Wires and Molecular Ionoelectronics

    NARCIS (Netherlands)

    Nostrum, Cornelus F. van; Picken, Stephen J.; Schouten, Arend-Jan; Nolte, Roeland J.M.

    1995-01-01

    The synthesis of the metal-free and the dihydroxysilicon derivatives of tetrakis[4’,5’-bis(decoxy)benzo-18-crown-6]phthalocyanine is described. The metal-free phthalocyanine is liquid crystalline and exhibits a crystalline phase to mesophase transition at 148 °C. The structures of the crystalline

  3. Synthesis and Supramolecular Chemistry of Novel Liquid Crystalline Crown Ether-Substituted Phthalocyanines : Toward Molecular Wires and Molecular Ionoelectronics

    NARCIS (Netherlands)

    Nostrum, Cornelus F. van; Picken, Stephen J.; Schouten, Arend-Jan; Nolte, Roeland J.M.

    1995-01-01

    The synthesis of the metal-free and the dihydroxysilicon derivatives of tetrakis[4’,5’-bis(decoxy)benzo-18-crown-6]phthalocyanine is described. The metal-free phthalocyanine is liquid crystalline and exhibits a crystalline phase to mesophase transition at 148 °C. The structures of the crystalline ph

  4. Structure and dynamics of lipid monolayers: Implications for enzyme catalysed lipolysis

    DEFF Research Database (Denmark)

    Peters, Günther H.J.; Toxværd, S.; Larsen, N.B.;

    1995-01-01

    We have investigated the role of the substrate on the interfacial activation of Upases by an interdisciplinary study of the structure and dynamics of 1,2-sn dipalmitoylglycerol monolayers at distinct surface pressures. The diglyceride Langmuir film undergoes two phase transitions occurring at 38....

  5. Fluidization of a dipalmitoyl phosphatidylcholine monolayer by fluorocarbon gases: potential use in lung surfactant therapy.

    Science.gov (United States)

    Gerber, Frédéric; Krafft, Marie Pierre; Vandamme, Thierry F; Goldmann, Michel; Fontaine, Philippe

    2006-05-01

    Fluorocarbon gases (gFCs) were found to inhibit the liquid-expanded (LE)/liquid-condensed (LC) phase transition of dipalmitoyl phosphatidylcholine (DPPC) Langmuir monolayers. The formation of domains of an LC phase, which typically occurs in the LE/LC coexistence region upon compression of DPPC, is prevented when the atmosphere above the DPPC monolayer is saturated with a gFC. When contacted with gFC, the DPPC monolayer remains in the LE phase for surface pressures lower than 38 mN m(-1), as assessed by compression isotherms and fluorescence microscopy (FM). Moreover, gFCs can induce the dissolution of preexisting LC phase domains and facilitate the respreading of the DPPC molecules on the water surface, as shown by FM and grazing incidence x-ray diffraction. gFCs have thus a highly effective fluidizing effect on the DPPC monolayer. This gFC-induced fluidizing effect was compared with the fluidizing effect brought about by a mixture of unsaturated lipids and proteins, namely the two commercially available lung surfactant substitutes, Curosurf and Survanta, which are derived from porcine and bovine lung extracts, respectively. The candidate FCs were chosen among those already investigated for biomedical applications, and in particular for intravascular oxygen transport, i.e., perfluorooctyl bromide, perfluorooctylethane, bis(perfluorobutyl)ethene, perfluorodecalin, and perfluorooctane. The fluidizing effect is most effective with the linear FCs. This study suggests that FCs, whose biocompatibility is well documented, may be useful in lung surfactant substitute compositions.

  6. Using Compression Isotherms of Phospholipid Monolayers to Explore Critical Phenomena: A Biophysical Chemistry Experiment

    Science.gov (United States)

    Gragson, Derek E.; Beaman, Dan; Porter, Rhiannon

    2008-01-01

    Two experiments are described in which students explore phase transitions and critical phenomena by obtaining compression isotherms of phospholipid monolayers using a Langmuir trough. Through relatively simple analysis of their data students gain a better understanding of compression isotherms, the application of the Clapeyron equation, the…

  7. Synthesis of Novel Amphiphilic Azobenzenes and X-ray Scattering Studies of Their Langmuir Monolayers

    DEFF Research Database (Denmark)

    Sørensen, Thomas Just; Kjær, Kristian; Breiby, Dag Werner;

    2008-01-01

    . At the air-water interface, the amphiphilic azobenzenes form noncrystalline but stable Langmuir films that display an unusual reversible monolayer collapse close to 35 mN/m. The structures and phase transitions were studied by X-ray reflectivity (XR) and grazing-incidence X-ray diffraction, both utilizing...

  8. Observing Altshuler--Aronov--Spivak Oscillation in a Hexagonal Antidot Array of Monolayer Graphene

    Science.gov (United States)

    Yagi, Ryuta; Shimomura, Midori; Tahara, Fumiya; Kobara, Hiroaki; Fukada, Seiya

    2012-06-01

    We show that hexagonal antidot lattices of monolayer graphene exhibited the Altshuler--Aronov--Spivak (AAS) effect in low field magnetoresistance. In higher magnetic fields, Aharonov--Bohm-type oscillations were visible. The phase of AAS oscillation indicated that the chirality effect of graphene is suppressed because of inter-valley scattering due to boundary scatterings.

  9. Intramolecular and Lattice Melting in n-Alkane Monolayers: An Analog of Melting in Lipid Bilayers

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Herwig, K.W.; Matthies, B.

    1999-01-01

    to 350 K above which a large thermal expansion and decrease in coherence length occurs. The MD simulations provide evidence that this behavior is due to a phase transition in the monolayer in which intramolecular and translational order are lost simultaneously. This melting transition is qualitatively...

  10. Topology of nonsymmorphic crystalline insulators and superconductors

    Science.gov (United States)

    Shiozaki, Ken; Sato, Masatoshi; Gomi, Kiyonori

    2016-05-01

    Topological classification in our previous paper [K. Shiozaki and M. Sato, Phys. Rev. B 90, 165114 (2014), 10.1103/PhysRevB.90.165114] is extended to nonsymmorphic crystalline insulators and superconductors. Using the twisted equivariant K theory, we complete the classification of topological crystalline insulators and superconductors in the presence of additional order-two nonsymmorphic space-group symmetries. The order-two nonsymmorphic space groups include half-lattice translation with Z2 flip, glide, twofold screw, and their magnetic space groups. We find that the topological periodic table shows modulo-2 periodicity in the number of flipped coordinates under the order-two nonsymmorphic space group. It is pointed out that the nonsymmorphic space groups allow Z2 topological phases even in the absence of time-reversal and/or particle-hole symmetries. Furthermore, the coexistence of the nonsymmorphic space group with time-reversal and/or particle-hole symmetries provides novel Z4 topological phases, which have not been realized in ordinary topological insulators and superconductors. We present model Hamiltonians of these new topological phases and analytic expressions of the Z2 and Z4 topological invariants. The half-lattice translation with Z2 spin flip and glide symmetry are compatible with the existence of boundaries, leading to topological surface gapless modes protected by the order-two nonsymmorphic symmetries. We also discuss unique features of these gapless surface modes.

  11. Intermolecular forces in lipid monolayers. Two-dimensional virial coefficients for pentadecanoic acid from micromanometry on spread monolayers at the air/water interface.

    Science.gov (United States)

    Pallas, Norman R; Pethica, Brian A

    2009-07-07

    The lateral intermolecular forces between surfactant or lipid molecules in monolayers at interfaces are fundamental to understanding the phenomena of surface activity and the interactions of lipids in two-dimensional structures such as smectic phases and biomembranes. The classical approach to these forces is via the two-dimensional virial coefficients, which requires precise micromanometry on monolayer isotherms in the dilute gaseous region. Low pressure isotherms out to high surface areas in the two-dimensional gas range have been measured at 15, 25 and 30 degrees C for insoluble monolayers of n-pentadecanoic acid spread at the interface between water-vapour saturated air and a dilute aqueous solution of HCl. The data allow estimates of virial coefficients up to the third term. The second virial coefficients are compared with those predicted from a statistical mechanical model for monolayers of n-alkylcarboxylic acids treated as side-by-side parallel chains extended at the surface with the carboxyl head groups shielded in the water phase. The two sets coincide at approximately 26 degrees C, but the experimental estimates show a much larger dependence on temperature than the model predicts. Chain conformation effects, head group interactions and surface field polarization are discussed as possible temperature-dependent contributions to the lateral potentials of mean force.

  12. Assembly of organic monolayers on polydicyclopentadiene.

    Science.gov (United States)

    Perring, Mathew; Bowden, Ned B

    2008-09-16

    The first well-defined organic monolayers assembled on polydicyclopentadiene is reported. Commercial grade dicyclopentadiene was polymerized with the Grubbs' second-generation catalyst in a fume hood under ambient conditions at very low monomer to catalyst loadings of 20 000 to 1. This simple method resulted in a polymer that was a hard solid and appeared slightly yellow. Brief exposures of a few seconds of this polymer to Br 2 lead to a surface with approximately half of the olefins brominated as shown by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection-infrared (ATR-IR) spectroscopy. The ATR-IR spectroscopy was carried out with the polymer in contact with a Ge hemisphere housed in a GATR accessory from Harrick. This brominated polydicyclopentadiene was immersed in DMF with 4-(trifluoromethyl)benzylamine to assemble a monolayer. The amines displaced Br on the surface to form a monolayer that exposed a CF 3 group on the surface. The surface was extensively studied by XPS using the method described by Tougaard to find the distribution of F within the surface layer. The ratio for the peak area, Ap, to the background height, B, measured 30 eV below the peak maximum was 109.8 eV. This value clearly indicated that F was found only at the surface and was not found within the polymer. A surface coverage of 1.37 amines per nm (2) was estimated and indicated that the monolayer was 28% as dense as a similar monolayer assembled from thiols on gold. Finally, a simple method to pattern these monolayers using soft lithography is described. This work is critically important because it reports the first monolayers on a relatively new and emerging polymer that has many desirable physical characteristics such as high hardness, chemical stability, and ease of forming different shapes.

  13. MORPHOLOGICAL STUDIES OF A THERMOTROPIC SIDE-CHAIN LIQUID CRYSTALLINE POLYMER DURING MESOPHASE TRANSITIONS

    Institute of Scientific and Technical Information of China (English)

    Chi-bing Tan; Quan-ling Zhang; Shu-fan Zhang; Xia-yu Wang; Mao Xu

    1999-01-01

    The morphological features of a side-chain liquid crystalline polymer during the mesophase transitions were investigated by using the DSC technique. The polymer used was polyacrylate with mesogens of three benzene rings attached to the main chain through a flexible spacer. A special two-phase texture was observed in the transition temperature range. Similar to main-chain liquid crystalline polymers the transition process of the side-chain liquid crystalline polymer was composed of an initiation of the new phase at local places of the old phase matrix and a growth process of the new phase domains.

  14. Influence of Crystal Allomorph and Crystallinity on the Products and Behavior of Cellulose during Fast Pyrolysis

    Energy Technology Data Exchange (ETDEWEB)

    Mukarakate, Calvin; Mittal, Ashutosh; Ciesielski, Peter N.; Budhi, Sridhar; Thompson, Logan; Iisa, Kristiina; Nimlos, Mark R.; Donohoe, Bryon S.

    2016-09-06

    Cellulose is the primary biopolymer responsible for maintaining the structural and mechanical integrity of cell walls and, during the fast pyrolysis of biomass, may be restricting cell wall expansion and inhibiting phase transitions that would otherwise facilitate efficient escape of pyrolysis products. Here, we test whether modifications in two physical properties of cellulose, its crystalline allomorph and degree of crystallinity, alter its performance during fast pyrolysis. We show that both crystal allomorph and relative crystallinity of cellulose impact the slate of primary products produced by fast pyrolysis. For both cellulose-I and cellulose-II, changes in crystallinity dramatically impact the fast pyrolysis product portfolio. In both cases, only the most highly crystalline samples produced vapors dominated by levoglucosan. Cellulose-III, on the other hand, produces largely the same slate of products regardless of its relative crystallinity and produced as much or more levoglucosan at all crystallinity levels compared to cellulose-I or II. In addition to changes in products, the different cellulose allomorphs affected the viscoelastic properties of cellulose during rapid heating. Real-time hot-stage pyrolysis was used to visualize the transition of the solid material through a molten phase and particle shrinkage. SEM analysis of the chars revealed additional differences in viscoelastic properties and molten phase behavior impacted by cellulose crystallinity and allomorph. Regardless of relative crystallinity, the cellulose-III samples displayed the most obvious evidence of having transitioned through a molten phase.

  15. Amorphization of Crystalline Water Ice

    CERN Document Server

    Zheng, Weijun; Kaiser, Ralf I

    2008-01-01

    We conducted a systematic experimental study to investigate the amorphization of crystalline ice by irradiation in the 10-50 K temperature range with 5 keV electrons at a dose of ~140 eV per molecule. We found that crystalline water ice can be converted partially to amorphous ice by electron irradiation. Our experiments showed that some of the 1.65-micrometer band survived the irradiation, to a degree that depends on the temperature, demonstrating that there is a balance between thermal recrystallization and irradiation-induced amorphization, with thermal recrystallizaton dominant at higher temperatures. At 50 K, recrystallization due to thermal effects is strong, and most of the crystalline ice survived. Temperatures of most known objects in the solar system, including Jovian satellites, Saturnian satellites, and Kuiper belt objects, are equal to or above 50 K, this might explain why water ice detected on those objects is mostly crystalline.

  16. Liquid-crystalline lanthanide complexes

    OpenAIRE

    Binnemans, Koen

    1999-01-01

    The paper describes the recent developments in the field of liquid-crystalline lanthanide complexes. The role of trivalent lanthanide ions as the central metal ion in metallomesogens is considered. An outlook for the future is given.

  17. Diffusion in porous crystalline materials

    NARCIS (Netherlands)

    Krishna, R.

    2012-01-01

    The design and development of many separation and catalytic process technologies require a proper quantitative description of diffusion of mixtures of guest molecules within porous crystalline materials. This tutorial review presents a unified, phenomenological description of diffusion inside meso-

  18. Mechanical Properties of Water-Assembled Graphene Oxide Langmuir Monolayers: Guiding Controlled Transfer.

    Science.gov (United States)

    Harrison, Katharine L; Biedermann, Laura B; Zavadil, Kevin R

    2015-09-15

    Liquid-phase transfer of graphene oxide (GO) and reduced graphene oxide (RGO) monolayers is investigated from the perspective of the mechanical properties of these films. Monolayers are assembled in a Langmuir-Blodgett trough, and oscillatory barrier measurements are used to characterize the resulting compressive and shear moduli as a function of surface pressure. GO monolayers are shown to develop a significant shear modulus (10-25 mN/m) at relevant surface pressures while RGO monolayers do not. The existence of a shear modulus indicates that GO is acting as a two-dimensional solid driven by strong interaction between the individual GO sheets. The absence of such behavior in RGO is attributed to the decrease in oxygen moieties on the sheet basal plane, permitting RGO sheets to slide across one another with minimum energy dissipation. Knowledge of this two-dimensional solid behavior is exploited to successfully transfer large-area, continuous GO films to hydrophobic Au substrates. The key to successful transfer is the use of shallow-angle dipping designed to minimize tensile stress present during the insertion or extraction of the substrate. A shallow dip angle on hydrophobic Au does not impart a beneficial effect for RGO monolayers, as these monolayers do not behave as two-dimensional solids and do not remain coherent during the transfer process. We hypothesize that this observed correlation between monolayer mechanical properties and continuous film transfer success is more universally applicable across substrate hydrophobicities and could be exploited to control the transfer of films composed of two-dimensional materials.

  19. Thin-Film Behavior of Poly(methyl methacrylates). 3. Epitaxial Crystallization in Thin Films of Isotactic Poly(methyl methacrylate) Using Crystalline Langmuir-Blodgett Layers

    NARCIS (Netherlands)

    Brinkhuis, R.H.G.; Schouten, A.J.

    1992-01-01

    A procedure is introduced using monolayer crystallized films of isotactic poly(methyl methacrylate) (i-PMMA) to induce crystallization in amorphous films of i-PMMA. Use of the Langmuir-Blodgett films as surface crystallization nuclei permits the preparation of highly crystalline films with thickness

  20. Stability of two-dimensional PN monolayer sheets and their electronic properties.

    Science.gov (United States)

    Ma, ShuangYing; He, Chaoyu; Sun, L Z; Lin, Haiping; Li, Youyong; Zhang, K W

    2015-12-21

    Three two-dimensional phosphorus nitride (PN) monolayer sheets (named as α-, β-, and γ-PN, respectively) with fantastic structures and properties are predicted based on first-principles calculations. The α-PN and γ-PN have a buckled structure, whereas β-PN shows puckered characteristics. Their unique structures endow these atomic PN sheets with high dynamic stabilities and anisotropic mechanical properties. They are all indirect semiconductors and their band gap sensitively depends on the in-plane strain. Moreover, the nanoribbons patterned from these three PN monolayers demonstrate a remarkable quantum size effect. In particular, the zigzag α-PN nanoribbon shows size-dependent ferromagnetism. Their significant properties show potential in nano-electronics. The synthesis of the three phases of the PN monolayer sheet is proposed theoretically, which is deserving of further study in experiments.

  1. Novel Crystalline SiO2 Nanoparticles via Annelids Bioprocessing of Agro-Industrial Wastes

    Science.gov (United States)

    Espíndola-Gonzalez, A.; Martínez-Hernández, A. L.; Angeles-Chávez, C.; Castaño, V. M.; Velasco-Santos, C.

    2010-09-01

    The synthesis of nanoparticles silica oxide from rice husk, sugar cane bagasse and coffee husk, by employing vermicompost with annelids ( Eisenia foetida) is reported. The product ( humus) is calcinated and extracted to recover the crystalline nanoparticles. X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS) show that the biotransformation allows creating specific crystalline phases, since equivalent particles synthesized without biotransformation are bigger and with different crystalline structure.

  2. Alkali Metal-incorporated Mesoporous Smectites:Crystallinity and Textural Properties

    Institute of Scientific and Technical Information of China (English)

    HE Yan-feng; Shinichiro Fujita; Nobuhiro Iwasa; Bhalchandra M. Bhanage; Masahiko Arai

    2003-01-01

    A series of mesoporous smectite-like materials incorporated with alkali metals such as Li, Na, K and Cs has been synthesized with the hydrothermal method. The crystalline and the pore structures of the materials synthesized significantly change with the introduction of alkali metals. The addition of Li gives highly ordered layer phases, while the incorporation of Cs yields much less crystalline structures. Although Na or K has little effect on the crystalline structure, they modify the pore structure.

  3. Influence of Crystalline Nanoprecipitates on Shear-Band Propagation in Cu-Zr Based Metallic Glasses

    OpenAIRE

    Brink, Tobias; Peterlechner, Martin; Rösner, Harald; Albe, Karsten; Wilde, Gerhard

    2015-01-01

    The interaction of shear bands with crystalline nanoprecipitates in Cu-Zr-based metallic glasses is investigated by a combination of high-resolution TEM imaging and molecular-dynamics computer simulations. Our results reveal different interaction mechanisms: Shear bands can dissolve precipitates, can wrap around crystalline obstacles, or can be blocked depending on size and density of the precipitates. If the crystalline phase has a low yield strength, we also observe slip transfer through th...

  4. Novel Crystalline SiO2 Nanoparticles via Annelids Bioprocessing of Agro-Industrial Wastes

    Directory of Open Access Journals (Sweden)

    Angeles-Chávez C

    2010-01-01

    Full Text Available Abstract The synthesis of nanoparticles silica oxide from rice husk, sugar cane bagasse and coffee husk, by employing vermicompost with annelids (Eisenia foetida is reported. The product (humus is calcinated and extracted to recover the crystalline nanoparticles. X-ray diffraction (XRD, transmission electron microscopy (TEM, high-resolution transmission electron microscopy (HRTEM and dynamic light scattering (DLS show that the biotransformation allows creating specific crystalline phases, since equivalent particles synthesized without biotransformation are bigger and with different crystalline structure.

  5. Paramagnetic defect centres in crystalline Alq{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Grecu, M N [National Institute for Materials Physics, POB MG-7, 077125 Magurele-Bucharest (Romania); Mirea, A [Experimental Physics II, Bayreuth University, 95440 Bayreuth (Germany); Ghica, C [National Institute for Materials Physics, POB MG-7, 077125 Magurele-Bucharest (Romania); Coelle, M [Philips Research, Laboratories, NL-5656 AA Eindhoven (Netherlands); Schwoerer, M [Experimental Physics II, Bayreuth University, 95440 Bayreuth (Germany)

    2005-10-05

    X- and Q-band electron paramagnetic resonance (EPR) investigation of different crystalline Alq{sub 3} (tris(8-hydroxyquinoline)aluminium (III)) fractions formed by a train sublimation method are reported. Several paramagnetic defect centres corresponding to 1/2, 1, and 3/2 spin are observed at room temperature. Their intensity is dependent on the temperature, nature of the crystalline phase, and preparation conditions. Spectra simulation and analysis based on the spin Hamiltonian appropriate to a high spin system (S{>=}1) suggest the existence of randomly oriented triplets and quartets in annealed Alq{sub 3} fractions. The crystalline Alq{sub 3} phases responsible for the EPR powder spectra have been identified by transmission electron microscopy measurements performed on these sample fractions.

  6. Electron tunneling through ultrathin boron nitride crystalline barriers.

    Science.gov (United States)

    Britnell, Liam; Gorbachev, Roman V; Jalil, Rashid; Belle, Branson D; Schedin, Fred; Katsnelson, Mikhail I; Eaves, Laurence; Morozov, Sergey V; Mayorov, Alexander S; Peres, Nuno M R; Neto, Antonio H Castro; Leist, Jon; Geim, Andre K; Ponomarenko, Leonid A; Novoselov, Kostya S

    2012-03-14

    We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel.

  7. Continuity of Monolayer-Bilayer Junctions for Localization of Lipid Raft Microdomains in Model Membranes.

    Science.gov (United States)

    Ryu, Yong-Sang; Wittenberg, Nathan J; Suh, Jeng-Hun; Lee, Sang-Wook; Sohn, Youngjoo; Oh, Sang-Hyun; Parikh, Atul N; Lee, Sin-Doo

    2016-05-27

    We show that the selective localization of cholesterol-rich domains and associated ganglioside receptors prefer to occur in the monolayer across continuous monolayer-bilayer junctions (MBJs) in supported lipid membranes. For the MBJs, glass substrates were patterned with poly(dimethylsiloxane) (PDMS) oligomers by thermally-assisted contact printing, leaving behind 3 nm-thick PDMS patterns. The hydrophobicity of the transferred PDMS patterns was precisely tuned by the stamping temperature. Lipid monolayers were formed on the PDMS patterned surface while lipid bilayers were on the bare glass surface. Due to the continuity of the lipid membranes over the MBJs, essentially free diffusion of lipids was allowed between the monolayer on the PDMS surface and the upper leaflet of the bilayer on the glass substrate. The preferential localization of sphingomyelin, ganglioside GM1 and cholesterol in the monolayer region enabled to develop raft microdomains through coarsening of nanorafts. Our methodology provides a simple and effective scheme of non-disruptive manipulation of the chemical landscape associated with lipid phase separations, which leads to more sophisticated applications in biosensors and as cell culture substrates.

  8. Model for large-area monolayer coverage of polystyrene nanospheres by spin coating

    Science.gov (United States)

    Chandramohan, Abhishek; Sibirev, Nikolai V.; Dubrovskii, Vladimir G.; Petty, Michael C.; Gallant, Andrew J.; Zeze, Dagou A.

    2017-01-01

    Nanosphere lithography, an inexpensive and high throughput technique capable of producing nanostructure (below 100 nm feature size) arrays, relies on the formation of a monolayer of self-assembled nanospheres, followed by custom-etching to produce nanometre size features on large-area substrates. A theoretical model underpinning the self-ordering process by centrifugation is proposed to describe the interplay between the spin speed and solution concentration. The model describes the deposition of a dense and uniform monolayer by the implicit contribution of gravity, centrifugal force and surface tension, which can be accounted for using only the spin speed and the solid/liquid volume ratio. We demonstrate that the spin recipe for the monolayer formation can be represented as a pathway on a 2D phase plane. The model accounts for the ratio of polystyrene nanospheres (300 nm), water, methanol and surfactant in the solution, crucial for large area uniform and periodic monolayer deposition. The monolayer is exploited to create arrays of nanoscale features using ‘short’ or ‘extended’ reactive ion etching to produce 30–60 nm (diameter) nanodots or 100–200 nm (diameter) nanoholes over the entire substrate, respectively. The nanostructures were subsequently utilized to create master stamps for nanoimprint lithography.

  9. Model for large-area monolayer coverage of polystyrene nanospheres by spin coating

    Science.gov (United States)

    Chandramohan, Abhishek; Sibirev, Nikolai V.; Dubrovskii, Vladimir G.; Petty, Michael C.; Gallant, Andrew J.; Zeze, Dagou A.

    2017-01-01

    Nanosphere lithography, an inexpensive and high throughput technique capable of producing nanostructure (below 100 nm feature size) arrays, relies on the formation of a monolayer of self-assembled nanospheres, followed by custom-etching to produce nanometre size features on large-area substrates. A theoretical model underpinning the self-ordering process by centrifugation is proposed to describe the interplay between the spin speed and solution concentration. The model describes the deposition of a dense and uniform monolayer by the implicit contribution of gravity, centrifugal force and surface tension, which can be accounted for using only the spin speed and the solid/liquid volume ratio. We demonstrate that the spin recipe for the monolayer formation can be represented as a pathway on a 2D phase plane. The model accounts for the ratio of polystyrene nanospheres (300 nm), water, methanol and surfactant in the solution, crucial for large area uniform and periodic monolayer deposition. The monolayer is exploited to create arrays of nanoscale features using ‘short’ or ‘extended’ reactive ion etching to produce 30–60 nm (diameter) nanodots or 100–200 nm (diameter) nanoholes over the entire substrate, respectively. The nanostructures were subsequently utilized to create master stamps for nanoimprint lithography. PMID:28102358

  10. Thermal transport in monolayer InSe

    Science.gov (United States)

    Nissimagoudar, Arun S.; Ma, Jinlong; Chen, Yani; Li, Wu

    2017-08-01

    Two-dimensional InSe, a recently synthesized semiconductor having a moderate band gap, has gained attention due to its ultra high mobility and high photo-responsivity. In this work, we calculate the lattice thermal conductivity (κ) of monolayer InSe by solving the phonon Boltzmann transport equation (BTE) with first-principles calculated inter atomic force constants. κ of monolayer InSe is isotropic and found to be around 27.6 W m K-1 at room temperature along the in-plane direction. The size dependence of κ shows the size effect can persist up to 20 μm. Further, κ can be reduced to half by tuning the sample size to 300 nm. This low value suggests that κ might be a limiting factor for emerging nanoelectronic applications of monolayer InSe.

  11. Elastic bending modulus of monolayer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Lu Qiang; Huang Rui [Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, TX 78712 (United States); Arroyo, Marino [Department of Applied Mathematics 3, LaCaN, Universitat Politecnica de Catalunya (UPC), Barcelona 08034 (Spain)

    2009-05-21

    An analytic formula is derived for the elastic bending modulus of monolayer graphene based on an empirical potential for solid-state carbon atoms. Two physical origins are identified for the non-vanishing bending stiffness of the atomically thin graphene sheet, one due to the bond-angle effect and the other resulting from the bond-order term associated with the dihedral angles. The analytical prediction compares closely with ab initio energy calculations. Pure bending of graphene monolayers into cylindrical tubes is simulated by a molecular mechanics approach, showing slight nonlinearity and anisotropy in the tangent bending modulus as the bending curvature increases. An intrinsic coupling between bending and in-plane strain is noted for graphene monolayers rolled into carbon nanotubes. (fast track communication)

  12. Magneto photoluminescence measurements of tungsten disulphide monolayers

    Science.gov (United States)

    Kuhnert, Jan; Rahimi-Iman, Arash; Heimbrodt, Wolfram

    2017-03-01

    Layered transition-metal dichalcogenides have attracted great interest in the last few years. Thinned down to the monolayer limit they change from an indirect band structure to a direct band gap in the visible region. Due to the monolayer thickness the inversion symmetry of the crystal is broken and spin and valley are coupled to each other. The degeneracy between the two equivalent valleys, K and K‧, respectively, can be lifted by applying an external magnetic field. Here, we present photoluminescence measurements of CVD-grown tungsten disulphide (WS2) monolayers at temperatures of 2 K. By applying magnetic fields up to 7 T in Faraday geometry, a splitting of the photoluminescence peaks can be observed. The magnetic field dependence of the A-exciton, the trion and three bound exciton states is discussed and the corresponding g-factors are determined.

  13. The structure and dynamics of Nano Particles encapsulated by the SDS monolayer collapse at the water/TCE interface

    Science.gov (United States)

    Shi, Wenxiong

    2016-11-01

    The super-saturated surfactant monolayer collapses with the nanoparticles (NPs) at the water/trichloroethylene (TCE) interface are investigated using molecular dynamics (MD) simulations. The results show that sodium alkyl sulfate (SDS) monolayer collapse is initiated by buckling and followed primarily by budding and the bud encapsulating the NPs and oil molecules. The developed bud detaches from the monolayer into a water phase and forms the swollen micelle emulsion with NPs and oil molecules. We investigate the wavelength of the initial budding and the theoretical description of the budding process. The wavelength of the monolayer increases with bending modulus. The energy barrier of the budding can be easily overcome by thermal fluctuation energy, which indicates that budding process proceeds rapidly.

  14. Workshop on hydrology of crystalline basement rocks

    Energy Technology Data Exchange (ETDEWEB)

    Davis, S.N. (comp.)

    1981-08-01

    This workshop covered the following subjects: measurements in relatively shallow boreholes; measurement and interpretation of data from deep boreholes; hydrologic properties of crystalline rocks as interpreted by geophysics and field geology; rock mechanics related to hydrology of crystalline rocks; the possible contributions of modeling to the understanding of the hydrology of crystalline rocks; and geochemical interpretations of the hydrology of crystalline rocks. (MHR)

  15. Understanding the interfacial properties of nanostructured liquid crystalline materials for surface-specific delivery applications.

    Science.gov (United States)

    Dong, Yao-Da; Larson, Ian; Barnes, Timothy J; Prestidge, Clive A; Allen, Stephanie; Chen, Xinyong; Roberts, Clive J; Boyd, Ben J

    2012-09-18

    Nonlamellar liquid crystalline dispersions such as cubosomes and hexosomes have great potential as novel surface-targeted active delivery systems. In this study, the influence of internal nanostructure, chemical composition, and the presence of Pluronic F127 as a stabilizer, on the surface and interfacial properties of different liquid crystalline particles and surfaces, was investigated. The interfacial properties of the bulk liquid crystalline systems with coexisting excess water were dependent on the internal liquid crystalline nanostructure. In particular, the surfaces of the inverse cubic systems were more hydrophilic than that of the inverse hexagonal phase. The interaction between F127 and the bulk liquid crystalline systems depended on the internal liquid crystalline structure and chemical composition. For example, F127 adsorbed to the surface of the bulk phytantriol cubic phase, while for monoolein cubic phase, F127 was integrated into the liquid crystalline structure. Last, the interfacial adsorption behavior of the dispersed liquid crystalline particles also depended on both the internal nanostructure and the chemical composition, despite the dispersions all being stabilized using F127. The findings highlight the need to understand the specific surface characteristics and the nature of the interaction with colloidal stabilizer for understanding and optimizing the behavior of nonlamellar liquid crystalline systems in surface delivery applications.

  16. Low temperature photoresponse of monolayer tungsten disulphide

    Directory of Open Access Journals (Sweden)

    Bingchen Cao

    2014-11-01

    Full Text Available High photoresponse can be achieved in monolayers of transition metal dichalcogenides. However, the response times are inconveniently limited by defects. Here, we report low temperature photoresponse of monolayer tungsten disulphide prepared by exfoliation and chemical vapour deposition (CVD method. The exfoliated device exhibits n-type behaviour; while the CVD device exhibits intrinsic behaviour. In off state, the CVD device has four times larger ratio of photoresponse for laser on/off and photoresponse decay–rise times are 0.1 s (limited by our setup, while the exfoliated device has few seconds. These findings are discussed in terms of charge trapping and localization.

  17. Nonlinear optical studies of organic monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Y.R.

    1988-02-01

    Second-order nonlinear optical effects are forbidden in a medium with inversion symmetry, but are necessarily allowed at a surface where the inversion summary is broken. They are often sufficiently strong so that a submonolayer perturbation of the surface can be readily detected. They can therefore be used as effective tools to study monolayers adsorbed at various interfaces. We discuss here a number of recent experiments in which optical second harmonic generation (SHG) and sum-frequency generation (SFG) are employed to probe and characterize organic monolayers. 15 refs., 5 figs.

  18. Fluorine-containing triphenylenes. Liquid crystalline properties and surface ordering

    NARCIS (Netherlands)

    Umesh, C.P.; Marcelis, A.T.M.; Zuilhof, H.

    2014-01-01

    The synthesis and liquid crystalline properties of two novel series of triphenylenes with 4 or 5 pentafuoropentyloxy tails and 1 or 2 alkoxy tails of varying length are reported. All compounds form wide-range hexagonal columnar phases. The isotropisation temperatures and the corresponding enthalpy

  19. Interfacial properties in Langmuir monolayers and LB films of DPPC with partially fluorinated alcohol (F8H7OH).

    Science.gov (United States)

    Nakahara, Hiromichi; Hirano, Chikayo; Fujita, Ichiro; Shibata, Osamu

    2013-01-01

    Two-component interactions between (perfluorooctyl) heptanol (F8H7OH) and dipalmitoylphosphatidylcholine (DPPC), which is a major component of pulmonary surfactants in mammals, were systematically elucidated using Langmuir monolayers and Langmuir-Blodgett (LB) films of the compounds. The interactions such as the miscibility of the compounds and their phase behavior were examined from thermodynamic and morphological perspectives. The surface pressure (π)-molecular area (A) and surface potential (ΔV)-A isotherms of the binary monolayers containing F8H7OH in different mole fractions (XF8H7OH) were measured simultaneously. The excess Gibbs free energy of mixing of the two components was calculated from the π-A isotherms. The resulting isotherm data were employed to construct a two-dimensional (2D) phase diagram of the system. The phase diagram revealed that the transition pressure as well as the monolayer collapse pressure change with changes in XF8H7OH. These thermodynamic analyses suggested that the miscibility of the two components and the solidification of DPPC monolayers can be induced by the addition of F8H7OH. The phase behavior upon monolayer compression was observed morphologically in situ using Brewster angle microscopy (BAM) and fluorescence microscopy (FM), as well as ex situ using atomic force microscopy (AFM). Interestingly, the AFM-based analysis revealed the formation of monodispersed 2D micelles consisting of F8H7OH at low surface pressures.

  20. High-Quality Alkyl Monolayers on Silicon Surfaces

    NARCIS (Netherlands)

    Sieval, A.B.; Linke, R.; Zuilhof, H.; Sudh"lter, E.J.R.

    2000-01-01

    Covalent attachment of functionalized monolayers onto silicon surfaces (see Figure for examples) is presented here as a strategy for surface modification. The preparation and structure of both unfunctionalized and functionalized alkyl-based monolayers are described, as are potential applications,