Science.gov

Sample records for molecularly thin alkane

  1. Thermally driven smoothening of molecular thin films: Structural transitions in n-alkane layers studied in real-time

    NASA Astrophysics Data System (ADS)

    Pithan, Linus; Meister, Eduard; Jin, Chenyu; Weber, Christopher; Zykov, Anton; Sauer, Katrein; Brütting, Wolfgang; Riegler, Hans; Opitz, Andreas; Kowarik, Stefan

    2015-10-01

    We use thermal annealing to improve smoothness and to increase the lateral size of crystalline islands of n-tetratetracontane (TTC, C44H90) films. With in situ x-ray diffraction, we find an optimum temperature range leading to improved texture and crystallinity while avoiding an irreversible phase transition that reduces crystallinity again. We employ real-time optical phase contrast microscopy with sub-nm height resolution to track the diffusion of TTC across monomolecular step edges which causes the unusual smoothing of a molecular thin film during annealing. We show that the lateral island sizes increase by more than one order of magnitude from 0.5 μm to 10 μm. This desirable behavior of 2d-Ostwald ripening and smoothing is in contrast to many other organic molecular films where annealing leads to dewetting, roughening, and a pronounced 3d morphology. We rationalize the smoothing behavior with the highly anisotropic attachment energies and low surface energies for TTC. The results are technically relevant for the use of TTC as passivation layer and as gate dielectric in organic field effect transistors.

  2. Thermally driven smoothening of molecular thin films: Structural transitions in n-alkane layers studied in real-time.

    PubMed

    Pithan, Linus; Meister, Eduard; Jin, Chenyu; Weber, Christopher; Zykov, Anton; Sauer, Katrein; Brütting, Wolfgang; Riegler, Hans; Opitz, Andreas; Kowarik, Stefan

    2015-10-28

    We use thermal annealing to improve smoothness and to increase the lateral size of crystalline islands of n-tetratetracontane (TTC, C44H90) films. With in situ x-ray diffraction, we find an optimum temperature range leading to improved texture and crystallinity while avoiding an irreversible phase transition that reduces crystallinity again. We employ real-time optical phase contrast microscopy with sub-nm height resolution to track the diffusion of TTC across monomolecular step edges which causes the unusual smoothing of a molecular thin film during annealing. We show that the lateral island sizes increase by more than one order of magnitude from 0.5 μm to 10 μm. This desirable behavior of 2d-Ostwald ripening and smoothing is in contrast to many other organic molecular films where annealing leads to dewetting, roughening, and a pronounced 3d morphology. We rationalize the smoothing behavior with the highly anisotropic attachment energies and low surface energies for TTC. The results are technically relevant for the use of TTC as passivation layer and as gate dielectric in organic field effect transistors. PMID:26520543

  3. Thermally driven smoothening of molecular thin films: Structural transitions in n-alkane layers studied in real-time

    SciTech Connect

    Pithan, Linus; Weber, Christopher; Zykov, Anton; Sauer, Katrein; Opitz, Andreas; Kowarik, Stefan; Meister, Eduard; Brütting, Wolfgang; Jin, Chenyu; Riegler, Hans

    2015-10-28

    We use thermal annealing to improve smoothness and to increase the lateral size of crystalline islands of n-tetratetracontane (TTC, C{sub 44}H{sub 90}) films. With in situ x-ray diffraction, we find an optimum temperature range leading to improved texture and crystallinity while avoiding an irreversible phase transition that reduces crystallinity again. We employ real-time optical phase contrast microscopy with sub-nm height resolution to track the diffusion of TTC across monomolecular step edges which causes the unusual smoothing of a molecular thin film during annealing. We show that the lateral island sizes increase by more than one order of magnitude from 0.5 μm to 10 μm. This desirable behavior of 2d-Ostwald ripening and smoothing is in contrast to many other organic molecular films where annealing leads to dewetting, roughening, and a pronounced 3d morphology. We rationalize the smoothing behavior with the highly anisotropic attachment energies and low surface energies for TTC. The results are technically relevant for the use of TTC as passivation layer and as gate dielectric in organic field effect transistors.

  4. A nonequilibrium molecular dynamics study of the rheology of alkanes

    SciTech Connect

    Gupta, S.A.; Cui, S.T.; Cummings, P.T.; Cochran, H.D. |

    1996-05-01

    We examine the rheological properties of four different alkanes: n-decane, n-hexadecane, n-tetracosane, and squalane. Simulations of Couette flow are performed for a range of shear rates with 100 molecules in each case using a replicated data version of our code. Number of interaction sites ranges from 1000 to 3000. We have performed extremely long simulations required to obtain acceptable statistics at low shear rates. The alkanes show a transition from non-Newtonian to Newtonian behavior as the shear rate decreases to low values. 1 tab, 1 fig, 17 refs.

  5. Modeling the influence of alkane molecular structure on secondary organic aerosol formation.

    PubMed

    Aumont, Bernard; Camredon, Marie; Mouchel-Vallon, Camille; La, Stéphanie; Ouzebidour, Farida; Valorso, Richard; Lee-Taylor, Julia; Madronich, Sasha

    2013-01-01

    Secondary Organic Aerosols (SOA) production and ageing is a multigenerational oxidation process involving the formation of successive organic compounds with higher oxidation degree and lower vapor pressure. Intermediate Volatility Organic Compounds (IVOC) emitted to the atmosphere are expected to be a substantial source of SOA. These emitted IVOC constitute a complex mixture including linear, branched and cyclic alkanes. The explicit gas-phase oxidation mechanisms are here generated for various linear and branched C10-C22 alkanes using the GECKO-A (Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere) and SOA formation is investigated for various homologous series. Simulation results show that both the size and the branching of the carbon skeleton are dominant factors driving the SOA yield. However, branching appears to be of secondary importance for the particle oxidation state and composition. The effect of alkane molecular structure on SOA yields appears to be consistent with recent laboratory observations. The simulated SOA composition shows, however, an unexpected major contribution from multifunctional organic nitrates. Most SOA contributors simulated for the oxidation of the various homologous series are far too reduced to be categorized as highly oxygenated organic aerosols (OOA). On a carbon basis, the OOA yields never exceeded 10% regardless of carbon chain length, molecular structure or ageing time. This version of the model appears clearly unable to explain a large production of OOA from alkane precursors. PMID:24600999

  6. Molecular dynamics of adsorption and segregation from an Alkane mixture

    SciTech Connect

    Xia, T.K.; Landman, U. )

    1993-09-03

    Adsorption and segregation of n-hexadecane molecules from an equal by weight mixture of n-hexadecane and n-hexane to an Au(001) surface at 315 kelvin are studied with the use of molecular dynamics simulations. Preferential adsorption of n-hexadecane at the solid-to-liquid interface together with subsequent layer-by-layer growth of an ordered, wetting interface were observed. The long chains penetrate and adsorb at the interfacial layer by means of a sequential segmental mechanism involving end-segment anchoring and displacive desorption of preadsorbed n-hexane molecules.

  7. Liquid-vapor equilibria and interfacial properties of n-alkanes and perfluoroalkanes by molecular simulation.

    PubMed

    Amat, Miguel A; Rutledge, Gregory C

    2010-03-21

    A molecular dynamics study is presented to assess the performance of a united-atom model in the prediction of liquid-vapor interfacial properties for short-chain perfluoroalkanes and their alkane counterparts. In particular, the ability of this model to discriminate between the surface-energy values of these two types of compounds was investigated over a wide temperature range corresponding to the liquid-vapor region. Comparisons with available experimental data and surface-tension predictions given by other force-field parameterizations, including those based on the more computationally demanding all-atom method, were performed to gauge the viability of this model. It was found that the model used in this study captures qualitatively the expected behavior of surface energy between alkanes and perfluoroalkanes and yields values that are in excellent agreement with experimental data, especially in the high-temperature limit as the critical temperature is approached. PMID:20331313

  8. Liquid-vapor equilibria and interfacial properties of n-alkanes and perfluoroalkanes by molecular simulation

    NASA Astrophysics Data System (ADS)

    Amat, Miguel A.; Rutledge, Gregory C.

    2010-03-01

    A molecular dynamics study is presented to assess the performance of a united-atom model in the prediction of liquid-vapor interfacial properties for short-chain perfluoroalkanes and their alkane counterparts. In particular, the ability of this model to discriminate between the surface-energy values of these two types of compounds was investigated over a wide temperature range corresponding to the liquid-vapor region. Comparisons with available experimental data and surface-tension predictions given by other force-field parameterizations, including those based on the more computationally demanding all-atom method, were performed to gauge the viability of this model. It was found that the model used in this study captures qualitatively the expected behavior of surface energy between alkanes and perfluoroalkanes and yields values that are in excellent agreement with experimental data, especially in the high-temperature limit as the critical temperature is approached.

  9. Anomalous tunneling in carbon/alkane/TiO(2)/gold molecular electronic junctions: energy level alignment at the metal/semiconductor interface.

    PubMed

    Yan, Haijun; McCreery, Richard L

    2009-02-01

    Carbon/TiO(2)/gold electronic junctions show slightly asymmetric electronic behavior, with higher current observed in current density (J)/voltage (V) curves when carbon is biased negative with respect to the gold top contact. When a approximately 1-nm-thick alkane film is deposited between the carbon and TiO(2), resulting in a carbon/alkane/TiO(2)/gold junction, the current increases significantly for negative bias and decreases for positive bias, thus creating a much less symmetric J/V response. Similar results were obtained when SiO(2) was substituted for the alkane layer, but Al(2)O(3) did not produce the effect. The observation that, by the addition of an insulating material between carbon and TiO(2), the junction becomes more conductive is unexpected and counterintuitive. Kelvin probe measurements revealed that while the apparent work function of the pyrolyzed photoresist film electrode is modulated by surface dipoles of different surface-bound molecular layers, the anomalous effect is independent of the direction of the surface dipole. We propose that by using a nanometer-thick film with a low dielectric constant as an insertion layer, most of the applied potential is dropped across this thin film, thus permitting alignment between the carbon Fermi level and the TiO(2) conduction band. Provided that the alkane layer is sufficiently thin, electrons can directly tunnel from carbon to the TiO(2) conduction band. Therefore, the electron injection barrier at the carbon/TiO(2) interface is effectively reduced by this energy-level alignment, resulting in an increased current when carbon is biased negative. The modulation of injection barriers by a low-kappa molecular layer should be generally applicable to a variety of materials used in micro- and nanoelectronic fabrication. PMID:20353235

  10. Molecular dynamics insight to phase transition in n-alkanes with carbon nanofillers

    NASA Astrophysics Data System (ADS)

    Rastogi, Monisha; Vaish, Rahul

    2015-05-01

    The present work aims to investigate the phase transition, dispersion and diffusion behavior of nanocomposites of carbon nanotube (CNT) and straight chain alkanes. These materials are potential candidates for organic phase change materials(PCMs) and have attracted flurry of research recently. Accurate experimental evaluation of the mass, thermal and transport properties of such composites is both difficult as well as economically taxing. Additionally it is crucial to understand the factors that results in modification or enhancement of their characteristic at atomic or molecular level. Classical molecular dynamics approach has been extended to elucidate the same. Bulk atomistic models have been generated and subjected to rigorous multistage equilibration. To reaffirm the approach, both canonical and constant-temperature, constant- pressure ensembles were employed to simulate the models under consideration. Explicit determination of kinetic, potential, non-bond and total energy assisted in understanding the enhanced thermal and transport property of the nanocomposites from molecular point of view. Crucial parameters including mean square displacement and simulated self diffusion coefficient precisely define the balance of the thermodynamic and hydrodynamic interactions. Radial distribution function also reflected the density variation, strength and mobility of the nanocomposites. It is expected that CNT functionalization could improve the dispersion within n-alkane matrix. This would further ameliorate the mass and thermal properties of the composite. Additionally, the determined density was in good agreement with experimental data. Thus, molecular dynamics can be utilized as a high throughput technique for theoretical investigation of nanocomposites PCMs.

  11. Molecular dynamics insight to phase transition in n-alkanes with carbon nanofillers

    SciTech Connect

    Rastogi, Monisha; Vaish, Rahul

    2015-05-15

    The present work aims to investigate the phase transition, dispersion and diffusion behavior of nanocomposites of carbon nanotube (CNT) and straight chain alkanes. These materials are potential candidates for organic phase change materials(PCMs) and have attracted flurry of research recently. Accurate experimental evaluation of the mass, thermal and transport properties of such composites is both difficult as well as economically taxing. Additionally it is crucial to understand the factors that results in modification or enhancement of their characteristic at atomic or molecular level. Classical molecular dynamics approach has been extended to elucidate the same. Bulk atomistic models have been generated and subjected to rigorous multistage equilibration. To reaffirm the approach, both canonical and constant-temperature, constant- pressure ensembles were employed to simulate the models under consideration. Explicit determination of kinetic, potential, non-bond and total energy assisted in understanding the enhanced thermal and transport property of the nanocomposites from molecular point of view. Crucial parameters including mean square displacement and simulated self diffusion coefficient precisely define the balance of the thermodynamic and hydrodynamic interactions. Radial distribution function also reflected the density variation, strength and mobility of the nanocomposites. It is expected that CNT functionalization could improve the dispersion within n-alkane matrix. This would further ameliorate the mass and thermal properties of the composite. Additionally, the determined density was in good agreement with experimental data. Thus, molecular dynamics can be utilized as a high throughput technique for theoretical investigation of nanocomposites PCMs.

  12. [Molecular topology study of gas chromatographic retention indices of alkane series].

    PubMed

    Nie, Changming; Dai, Yimin; Wen, Songnian; Li, Zhonghai

    2005-01-01

    The gas chromatographic retention indices can be used to qualify some organic compounds. A new topological index based on distance matrix and branch vertex of the atoms in a molecule is proposed by defining equilibrium electronegativity of atoms in the molecule and coloring atoms in the molecular graph with equilibrium electronegativity, which appears unique to the molecular structures and has excellent structural selectivity. The multivariate linear equations of gas chromatographic retention indices are as follows: I(Squalane) = 23.97842N1 - 3.86562N2 + 0.787379N3 + 42.33061, R = 0.9922, n = 70, S = 13.70405, F = 1396.601; I(SE-30) = 23.83937N1 - 3.5687N2 + 0.939876N3 + 22.11952, R = 0.9919, n = 37, S = 11.96088, F = 668.8781; where the N1, N2 and N3 are a group of topological indices; n, R, S and F are sample number, regression coefficient, residual standard deviation and F-statistic value, respectively. The calculated results by the formulae indicate that the average relative deviations between calculated values and experimental data of gas chromatographic retention indices of alkane series on both squalane (column temperature 50 degrees C) and SE-30 (column temperature 80 degrees C) were all 1.31% and the errors were within experimental deviations. The equations can express well the change rule of the relative gas chromatographic retention indices of alkane series. PMID:15881357

  13. Determination of molecular diffusion coefficient in n-alkane binary mixtures: empirical correlations.

    PubMed

    De Mezquia, D Alonso; Bou-Ali, M Mounir; Larrañaga, M; Madariaga, J A; Santamaría, C

    2012-03-01

    In this work we have measured the molecular diffusion coefficient of the n-alkane binary series nC(i)-nC(6), nC(i)-nC(10), and nC(i)-nC(12) at 298 K and 1 atm and a mass fraction of 0.5 by using the so-called sliding symmetric tubes technique. The results show that the diffusion coefficient at this concentration is proportional to the inverse viscosity of the mixture. In addition, we have also measured the diffusion coefficient of the systems nC(12)-nC(6), nC(12)-nC(7), and nC(12)-nC(8) as a function of concentration. From the data obtained, it is shown that the diffusion coefficient of the n-alkane binary mixtures at any concentration can be calculated from the molecular weight of the components and the dynamic viscosity of the corresponding mixture at 50% mass fraction. PMID:22263833

  14. Controlling Morphology and Molecular Packing of Alkane Substituted Phthalocyanine Blend Bulk Heterojunction Solar Cells†

    PubMed Central

    Jurow, Matthew J.; Hageman, Brian A.; Nam, Chang-Yong; Pabon, Cesar; Black, Charles T.

    2013-01-01

    Systematic changes in the exocyclic substiution of core phthalocyanine platform tune the absorption properties to yield commercially viable dyes that function as the primary light absorbers in organic bulk heterojunction solar cells. Blends of these complementary phthalocyanines absorb a broader portion of the solar spectrum compared to a single dye, thereby increasing solar cell performance. We correlate grazing incidence small angle x-ray scattering structural data with solar cell performance to elucidate the role of nanomorphology of active layers composed of blends of phthalocyanines and a fullerene derivative. A highly reproducible device architecture is used to assure accuracy and is relevant to films for solar windows in urban settings. We demonstrate that the number and structure of the exocyclic motifs dictate phase formation, hierarchical organization, and nanostructure, thus can be employed to tailor active layer morphology to enhance exciton dissociation and charge collection efficiencies in the photovoltaic devices. These studies reveal that disordered films make better solar cells, short alkanes increase the optical density of the active layer, and branched alkanes inhibit unproductive homogeneous molecular alignment. PMID:23589766

  15. Controlling Morphology and Molecular Packing of Alkane Substituted Phthalocyanine Blend Bulk Heterojunction Solar Cells.

    PubMed

    Jurow, Matthew J; Hageman, Brian A; Dimasi, Elaine; Nam, Chang-Yong; Pabon, Cesar; Black, Charles T; Drain, Charles Michael

    2013-02-01

    Systematic changes in the exocyclic substiution of core phthalocyanine platform tune the absorption properties to yield commercially viable dyes that function as the primary light absorbers in organic bulk heterojunction solar cells. Blends of these complementary phthalocyanines absorb a broader portion of the solar spectrum compared to a single dye, thereby increasing solar cell performance. We correlate grazing incidence small angle x-ray scattering structural data with solar cell performance to elucidate the role of nanomorphology of active layers composed of blends of phthalocyanines and a fullerene derivative. A highly reproducible device architecture is used to assure accuracy and is relevant to films for solar windows in urban settings. We demonstrate that the number and structure of the exocyclic motifs dictate phase formation, hierarchical organization, and nanostructure, thus can be employed to tailor active layer morphology to enhance exciton dissociation and charge collection efficiencies in the photovoltaic devices. These studies reveal that disordered films make better solar cells, short alkanes increase the optical density of the active layer, and branched alkanes inhibit unproductive homogeneous molecular alignment. PMID:23589766

  16. Semifluorinated Alkanes at the Air-Water Interface: Tailoring Structure and Rheology at the Molecular Scale.

    PubMed

    Theodoratou, Antigoni; Jonas, Ulrich; Loppinet, Benoit; Geue, Thomas; Stangenberg, Rene; Keller, Rabea; Li, Dan; Berger, Rüdiger; Vermant, Jan; Vlassopoulos, Dimitris

    2016-04-01

    Semifluorinated alkanes form monolayers with interesting properties at the air-water interface due to their pronounced amphi-solvophobic nature and the stiffness of the fluorocarbons. In the present work, using a combination of structural and dynamic probes, we investigated how small molecular changes can be used to control the properties of such an interface, in particular its organization, rheology, and reversibility during compression-expansion cycles. Starting from a reference system perfluor(dodecyl)dodecane, we first retained the linear structure but changed the linkage groups between the alkyl chains and the fluorocarbons, by introducing either a phenyl group or two oxygens. Next, the molecular structure was changed from linear to branched, with four side chains (two fluorocarbons and two hydrocarbons) connected to extended aromatic cores. Neutron reflectivity at the air-water interface and scanning force microscopy on deposited films show how the changes in the molecular structure affect molecular arrangement relative to the interface. Rheological and compression-expansion measurements demonstrate the significant consequences of these changes in molecular structure and interactions on the interfacial properties. Remarkably, even with these simple molecules, a wide range of surface rheological behaviors can be engineered, from viscous over viscoelastic to brittle solids, for very similar values of the surface pressure. PMID:26978461

  17. Molecular evaporation and condensation of liquid [ital n]-alkane films

    SciTech Connect

    Xia, T.K.; Landman, U. )

    1994-08-01

    Energetic, structural, and dynamical properties of solid-to-liquid and liquid-to-vapor interfaces and molecular evaporation and condensation processes from high-temperature liquid [ital n]-C[sub 6]H[sub 14] and [ital n]-C[sub 16]H[sub 34] films were investigated with molecular dynamics simulations. For hexadecane all evaporation events occurred via monomers while for hexane, evaporation of monomers as well as dimers were observed. For both alkane liquids the molecular evaporation mechanism is found to be sequential in nature, starting with an end segment of a molecule leaving the surface and subsequently the evaporation of the molecule occurs via sequential dragging'' of the rest of the molecule. The condensation coefficients of vapor molecules onto the liquid surface are estimated as [similar to]0.9 for hexane and [similar to]1 for hexadecane. Evaporation is accompanied by significant molecular conformational changes. In hot liquid [ital n]-C[sub 16]H[sub 34] the [ital trans] ([ital t]) and [ital gauch] ([ital g][sub +] and [ital g][sub [minus

  18. Molecular screening for alkane hydroxylase genes in Gram-negative and Gram-positive strains.

    PubMed

    Smits, T H; Röthlisberger, M; Witholt, B; van Beilen, J B

    1999-08-01

    We have developed highly degenerate oligonucleotides for polymerase chain reaction (PCR) amplification of genes related to the Pseudomonas oleovorans GPo1 and Acinetobacter sp. ADP1 alkane hydroxylases, based on a number of highly conserved sequence motifs. In all Gram-negative and in two out of three Gram-positive strains able to grow on medium- (C6-C11) or long-chain n-alkanes (C12-C16), PCR products of the expected size were obtained. The PCR fragments were cloned and sequenced and found to encode peptides with 43.2-93.8% sequence identity to the corresponding fragment of the P. oleovorans GPo1 alkane hydroxylase. Strains that were unable to grow on n-alkanes did not yield PCR products with homology to alkane hydroxylase genes. The alkane hydroxylase genes of Acinetobacter calcoaceticus EB104 and Pseudomonas putida P1 were cloned using the PCR products as probes. The two genes allow an alkane hydroxylase-negative mutant of Acinetobacter sp. ADP1 and an Escherichia coli recombinant containing all P. oleovorans alk genes except alkB, respectively, to grow on n-alkanes, showing that the cloned genes do indeed encode alkane hydroxylases. PMID:11207749

  19. Quantitative vapor-phase IR intensities and DFT computations to predict absolute IR spectra based on molecular structure: I. Alkanes

    NASA Astrophysics Data System (ADS)

    Williams, Stephen D.; Johnson, Timothy J.; Sharpe, Steven W.; Yavelak, Veronica; Oates, R. P.; Brauer, Carolyn S.

    2013-11-01

    Recently recorded quantitative IR spectra of a variety of gas-phase alkanes are shown to have integrated intensities in both the C3H stretching and C3H bending regions that depend linearly on the molecular size, i.e. the number of C3H bonds. This result is well predicted from CH4 to C15H32 by density functional theory (DFT) computations of IR spectra using Becke's three parameter functional (B3LYP/6-31+G(d,p)). Using the experimental data, a simple model predicting the absolute IR band intensities of alkanes based only on structural formula is proposed: For the C3H stretching band envelope centered near 2930 cm-1 this is given by (km/mol) CH_str=(34±1)×CH-(41±23) where CH is number of C3H bonds in the alkane. The linearity is explained in terms of coordinated motion of methylene groups rather than the summed intensities of autonomous -CH2-units. The effect of alkyl chain length on the intensity of a C3H bending mode is explored and interpreted in terms of conformer distribution. The relative intensity contribution of a methyl mode compared to the total C3H stretch intensity is shown to be linear in the number of methyl groups in the alkane, and can be used to predict quantitative spectra a priori based on structure alone.

  20. Alkane-Metal Interfacial Structure and Elastic Properties by Molecular Dynamics Simulation.

    PubMed

    Sebeck, Katherine; Shao, Chen; Kieffer, John

    2016-07-01

    The structure of amorphous materials near the interface with an ordered substrate can be affected by various characteristics of the adjoining phases, such as the lattice spacing of the adherent surface, polymer chain length, and adhesive strength. To discern the influence of each of these factors, four FCC metal lattices are examined for three chain lengths of n-alkane and van der Waals interfacial interactions are controlled by adjusting the Lennard-Jones 12-6 potential parameters. The role of interaction strength is investigated for a single chain length and substrate combination. Four nanoconfined systems are also analyzed in terms of their mechanical strength. A strong layering effect is observed near the interface for all systems. The distinctiveness of polymer layering, i.e., the maximum density and spatial extent, exhibits a logarithmic dependence on the interaction strength between polymer and substrate. Congruency with the substrate lattice parameter further enhances this effect. Moreover, the elastic modulus of the alkane phase as a function of layer thickness indicates that the effects of ordering within the structure extend beyond the immediately obvious interfacial region. PMID:27282363

  1. Added Alkane Allows Thermal Thinning of Supramolecular Columns by Forming Superlattice-An X-ray and Neutron Study.

    PubMed

    Yen, Ming-Huei; Chaiprapa, Jitrin; Zeng, Xiangbing; Liu, Yongsong; Cseh, Liliana; Mehl, Georg H; Ungar, Goran

    2016-05-11

    We report a columnar superlattice formed by blends of dendron-like Li 3,4,5-tris(n-alkoxy)benzoates with n-alkanes. Without the alkane, the wedge-shaped molecules form liquid crystal columns with 3 dendrons in a supramolecular disk. The same structure exists in the blend, but on heating one dendron is expelled from the disks in every third column and is replaced by the alkane. This superlattice of unequal columns is confirmed by complementary X-ray and neutron diffraction studies. Lateral thermal expansion of dendrons normally leads to the expulsion of excess molecules from the column, reducing the column diameter. However, in the already narrow columns of pure Li salt, expulsion of one of only three dendrons in a disk is not viable. The added alkane facilitates the expulsion, as it replaces the missing dendron. Replacing the alkane with a functional compound can potentially lead to active nanoarrays with relatively large periodicity by using only small molecules. PMID:27101731

  2. QSPR models based on molecular mechanics and quantum chemical calculations. 1. Construction of Boltzmann-averaged descriptors for alkanes, alcohols, diols, ethers and cyclic compounds.

    PubMed

    Dyekjaer, Jane; Rasmussen, Kjeld; Jónsdóttir, Svava

    2002-09-01

    Values for nine descriptors for QSPR (quantitative structure-property relationships) modeling of physical properties of 96 alkanes, alcohols, ethers, diols, triols and cyclic alkanes and alcohols in conjunction with the program Codessa are presented. The descriptors are Boltzmann-averaged by selection of the most relevant conformers out of a set of possible molecular conformers generated by a systematic scheme presented in this paper. Six of these descriptors are calculated with molecular mechanics and three with quantum chemical methods. Especially interesting descriptors are the relative van der Waals energies and the molecular polarizabilities, which correlate very well with boiling points. Five more simple descriptors that only depend on the molecular constitutional formula are also discussed briefly. PMID:12415333

  3. Characterization of sorbent properties of soil organic matter and carbonaceous geosorbents using n-alkanes and cycloalkanes as molecular probes

    SciTech Connect

    Satoshi Endo; Peter Grathwohl; Stefan B. Haderlein; Torsten C. Schmidt

    2009-01-15

    Nonspecific interactions and modes (i.e., adsorption vs absorption) of sorption by noncondensed, amorphous organic phases (here termed organic matter; OM) in soils and by rigid, aromatic, and condensed phases (termed carbonaceous geosorbents; CGs) were investigated using n-alkanes and cycloalkanes as molecular probes. Sorption isotherms of and cyclooctane from water for seven CGs (charcoal, lignite coke, activated carbon, graphite, partially oxidized graphite, diesel soot, bituminous coal), four sorbents with a predominance of OM (lignite, peat, two sapric soils), and two soils containing OM and high amounts of CGs were measured in batch systems. The peat and the sapric soils showed extensively linear sorption, while the CGs exhibited highly nonlinear and strong (K{sub oc} values being up to 105 times those for the OM-rich materials at low concentrations) sorption for the alkanes studied, showing that enhanced sorption by CGs can occur to completely apolar sorbates that do not undergo any specific interaction. The n-octane-to-cyclooctane sorption coefficient ratios for adsorption to CGs were {ge}1, being distinctly different from those for absorption to the OM-rich materials. The measured sorption isotherms and the CG compositions in the soils determined by quantitative petrography analysis suggest, however, that CGs occurring in soils may be far less effective sorbents than the reference CGs used in the sorption experiments at least for nonspecifically interacting sorbates, probably because of competitive sorption and/or pore blocking by natural OM. The presented approaches and results offer a basis for interpreting sorption data for other organic compounds, as nonspecific interactions and sorption modes are relevant for any compound. 47 refs., 4 figs., 2 tabs.

  4. A molecular dynamics study of the effect of thermal boundary conductance on thermal transport of ideal crystal of n-alkanes with different number of carbon atoms

    NASA Astrophysics Data System (ADS)

    Rastgarkafshgarkolaei, Rouzbeh; Zeng, Yi; Khodadadi, J. M.

    2016-05-01

    Phase change materials such as n-alkanes that exhibit desirable characteristics such as high latent heat, chemical stability, and negligible supercooling are widely used in thermal energy storage applications. However, n-alkanes have the drawback of low thermal conductivity values. The low thermal conductivity of n-alkanes is linked to formation of randomly oriented nano-domains of molecules in their solid structure that is responsible for excessive phonon scattering at the grain boundaries. Thus, understanding the thermal boundary conductance at the grain boundaries can be crucial for improving the effectiveness of thermal storage systems. The concept of the ideal crystal is proposed in this paper, which describes a simplified model such that all the nano-domains of long-chain n-alkanes are artificially aligned perfectly in one direction. In order to study thermal transport of the ideal crystal of long-chain n-alkanes, four (4) systems (C20H42, C24H50, C26H54, and C30H62) are investigated by the molecular dynamics simulations. Thermal boundary conductance between the layers of ideal crystals is determined using both non-equilibrium molecular dynamics (NEMD) and equilibrium molecular dynamics (EMD) simulations. Both NEMD and EMD simulations exhibit no significant change in thermal conductance with the molecular length. However, the values obtained from the EMD simulations are less than the values from NEMD simulations with the ratio being nearly three (3) in most cases. This difference is due to the nature of EMD simulations where all the phonons are assumed to be in equilibrium at the interface. Thermal conductivity of the n-alkanes in three structures including liquid, solid, and ideal crystal is investigated utilizing NEMD simulations. Our results exhibit a very slight rise in thermal conductivity values as the number of carbon atoms of the chain increases. The key understanding is that thermal transport can be significantly altered by how the molecules and the

  5. Molecular theory of liquid crystal thin films

    NASA Astrophysics Data System (ADS)

    Meng, Shihong

    A molecular theory has been developed to describe the isotropic-nematic transitoon of model nematogens in bulk and in thin films. The surfaces of thin films can be hard surfaces or coated with surfactant monolayers. The theory only includes hard body interactions between all molecule species: solvent, nematogens and surfactants. We have studied the influence of the separation between confining walls, concentration of nematogens, as well as the surface anchoring and areal density of surfactant at the interface upon the phases of nematogens. We have explained the possible existence of planar degenerate phase through entropic pictures and have confirmed close to the bulk isotropic-nematic transition point, the order of the phases of nematogens from isotropic to nematic then back to isotropic when varying the areal density of surfactant monolayers at interfaces. From the results obtained, we believe that we have captured the main competing interactions between surfactants and nematogens and our molecular level theory is capable of describing these two interactions of different natures. Our results can provide a guideline for molecular design of biosensors. We have modeled the molecular systems with as much simplification as possible while retaining the main features. The thesis is arranged into introduction, results on bulk, thin films confined between hard walls and between surfactant monolayers.

  6. Molecular simulations of the n -alkane liquid-vapor interface: interfacial properties and their long range corrections.

    PubMed

    Ibergay, C; Ghoufi, A; Goujon, F; Ungerer, P; Boutin, A; Rousseau, B; Malfreyt, P

    2007-05-01

    Monte Carlo simulations have been performed to study the interfacial properties of the liquid-vapor interface of alkanes. We highlight the chemical equilibrium of the liquid-vapor interface by calculating a local chemical potential including the appropriate long-range corrections profiles. We extend the "test-area" (TA) technique developed by Gloor [J. Chem. Phys. 123, 134703 (2005)] on Lennard-Jones and square-well fluids to molecular systems. We establish both operational expressions of the TA approach for the calculation of the surface tension profile and the corresponding long-range corrections by underlining the approximations used. We compare the results between the different operational expressions of the surface tension and focus on the truncation procedures to explain the difference between the different techniques using either the potential or force equations. We make the results of surface tension identical between the different methods by using consistent potential and force equations. In the case of a relatively small cutoff, we propose to show that the Irving-Kirkwood definition and TA methods lead to the same value of the surface tension under condition that appropriate long-range corrections be included in the calculation. We end this paper by calculation of the entropy change profile and a comparison with experiments. PMID:17677073

  7. Detailed molecular dynamics simulation of the self-diffusion of n-alkane and cis-1,4 polyisoprene oligomer melts

    NASA Astrophysics Data System (ADS)

    Harmandaris, V. A.; Doxastakis, M.; Mavrantzas, V. G.; Theodorou, D. N.

    2002-01-01

    Results are presented for the self-diffusion properties of monodisperse n-alkanes and cis-1,4 polyisoprene (PI) oligomer melts, as obtained through detailed atomistic molecular dynamics (MD) simulations. The simulations have been conducted in the NVT statistical ensemble on model systems thoroughly pre-equilibrated through an efficient Monte Carlo (MC) algorithm. Results for the self-diffusion coefficient D as a function of molecular weight M support a scaling law of the form D˜Mb, with b strongly depending on temperature T, for both the n-alkanes and the cis-1,4 PI melts. The simulation results have been fitted to an expression for D involving elements of Rouse dynamics and Cohen-Turnbull-Bueche chain-end (excess free volume) effects, proposed recently by von Meerwall et al. [J. Chem. Phys. 108, 4299 (1998)]. Using a geometric analysis involving tessellation of space in Delaunay tetrahedra developed by Greenfield and Theodorou [Macromolecules 26, 5461 (1993)], we have also calculated the excess chain-end free volume of the alkane and cis-1,4 PI melts. Calculated self-diffusivities and apparent activation energies for the two different polymers as a function of their molecular weight M are in excellent agreement with the experimental measurements of von Meerwall et al. (1998).

  8. Examination of surface nucleation during the growth of long alkane crystals by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Bourque, Alexander; Rutledge, Gregory

    2015-03-01

    Crystal growth from the melt of n-pentacontane (C50) was studied by molecular dynamics simulation using a validated united atom model. By quenching below the melting temperature of C50 (370 K), propagation of the crystal growth front into the C50 melt from a crystalline polyethylene surface was observed. By tracking the location of the midpoint in the orientational order parameter profile between the crystal and melt, crystal growth rates between 0.015-0.040 m/s were observed, for quench depths of 10 to 70 K below the melting point. In this work, surface nucleation is identified with the formation of 2D clusters of crystalline sites within layers parallel to the propagating growth front, by analogy to the formation of 3D clusters in primary, homogeneous nucleation. These surface nucleation events were tracked over several layers and numerous simulations, and a mean first passage time analysis was employed to estimate critical nucleus sizes, induction times and rates for surface nucleation. Based on new insights provided by the detailed molecular trajectories obtained from simulation, the classical theory proposed by Lauritzen and Hoffman is re-examined.

  9. Preface: Thin films of molecular organic materials

    NASA Astrophysics Data System (ADS)

    Fraxedas, J.

    2008-03-01

    This special issue is devoted to thin films of molecular organic materials and its aim is to assemble numerous different aspects of this topic in order to reach a wide scientific audience. Under the term 'thin films', structures with thicknesses spanning from one monolayer or less up to several micrometers are included. In order to narrow down this relaxed definition (how thin is thin?) I suggest joining the stream that makes a distinction according to the length scale involved, separating nanometer-thick films from micrometer-thick films. While the physical properties of micrometer-thick films tend to mimic those of bulk materials, in the low nanometer regime new structures (e.g., crystallographic and substrate-induced phases) and properties are found. However, one has to bear in mind that some properties of micrometer-thick films are really confined to the film/substrate interface (e.g. charge injection), and are thus of nanometer nature. Supported in this dimensionality framework, this issue covers the most ideal and model 0D case, a single molecule on a surface, through to the more application-oriented 3D case, placing special emphasis on the fascinating 2D domain that is monolayer assembly. Thus, many aspects will be reviewed, such as single molecules, self-organization, monolayer regime, chirality, growth, physical properties and applications. This issue has been intentionally restricted to small molecules, thus leaving out polymers and biomolecules, because for small molecules it is easier to establish structure--property relationships. Traditionally, the preparation of thin films of molecular organic materials has been considered as a secondary, lower-ranked part of the more general field of this class of materials. The coating of diverse surfaces such as silicon, inorganic and organic single crystals, chemically modified substrates, polymers, etc., with interesting molecules was driven by the potential applications of such molecular materials

  10. Optical Properties of Thin Film Molecular Mixtures

    NASA Technical Reports Server (NTRS)

    Jaworske, Donald A.; Shumway, Dean A.; Lyons, Valerie (Technical Monitor)

    2002-01-01

    Thin films composed of molecular mixtures of metal and dielectric are being considered for use as solar selective coatings for a variety of space power applications. By controlling the degree of molecular mixing, the solar selective coatings can be tailored to have the combined properties of high solar absorptance, alpha, and low infrared emittance, epsilon. On orbit, these combined properties would simultaneously maximize the amount of solar energy captured by the coating and minimize the amount of thermal energy radiated. Mini-satellites equipped with solar collectors coated with these cermet coatings may utilize the captured heat energy to power a heat engine to generate electricity, or to power a thermal bus that directs heat to remote regions of the spacecraft. Early work in this area identified the theoretical boundary conditions needed to operate a Carnot cycle in space, including the need for a solar concentrator, a solar selective coating at the heat inlet of the engine, and a radiator. A solar concentrator that can concentrate sunlight by a factor of 100 is ideal. At lower values, the temperature of the solar absorbing surface becomes too low for efficient heat engine operation, and at higher values, cavity type heat receivers become attractive. In designing the solar selective coating, the wavelength region yielding high solar absorptance must be separated from the wavelength region yielding low infrared emittance by establishing a sharp transition in optical properties. In particular, a sharp transition in reflectance is desired in the infrared to achieve the desired optical performance. For a heat engine operating at 450C, a sharp transition at 1.8 micrometers is desired. The radiator completes the heat flow through the Carnot cycle. Additional work has been done supporting the use of molecular mixtures for terrestrial applications. Sputter deposition provides a means to apply coatings to the tubes that carry a working fluid at the focus of trough

  11. Porous Organic Cage Thin Films and Molecular-Sieving Membranes.

    PubMed

    Song, Qilei; Jiang, Shan; Hasell, Tom; Liu, Ming; Sun, Shijing; Cheetham, Anthony K; Sivaniah, Easan; Cooper, Andrew I

    2016-04-01

    Porous organic cage molecules are fabricated into thin films and molecular-sieving membranes. Cage molecules are solution cast on various substrates to form amorphous thin films, with the structures tuned by tailoring the cage chemistry and processing conditions. For the first time, uniform and pinhole-free microporous cage thin films are formed and demonstrated as molecular-sieving membranes for selective gas separation. PMID:26800019

  12. Molecular simulation of adsorption and separation of mixtures of short linear alkanes in pillared layered materials at ambient temperature.

    PubMed

    Li, Wen-Zhuo; Liu, Zi-Yang; Che, Yu-Liang; Zhang, Dan

    2007-08-15

    Grand canonical Monte Carlo and configurational-bias Monte Carlo techniques are carried out to simulate the adsorption of ternary and quaternary mixtures of short linear alkanes, involving methane, ethane, propane, and n-butane, in pillared layered materials at ambient temperature, T=300 K. In the simulation, a pillared layered pore is modeled by a uniform distribution of pillars between two layered walls built by making two separate talc lamellas parallel each other with a given size of interlayer distance. The interaction between fluid molecules and two layered walls is measured by storing potentials calculated in advance at a series of grid points. The interaction between fluid molecules and pillars is also calculated by a site-to-site method. The potential model proposed in this work is proved to be effective because of the simulation result being good agreement with the experimental data for the adsorption of nitrogen at 77 K. Then, the adsorption isotherms of mixtures of short linear alkanes in pillared layered pores with three different porosities psi=0.98, 0.93 and 0.85, and three pore widths H=1.02, 1.70 and 2.38 nm at 300 K are obtained by taking advantage of the model. The simulation results tell us that the longer chain component is preferentially adsorbed at low pressures, and its adsorption increases and then decreases as the pressure increases while the shorter chain component is still adsorbed at high pressures. Moreover, the sorption selectivity of pillared layered materials for the longest chain component in alkane mixtures increases as the mole fraction of methane in the gas phase increases. The selectivity of pillared layered materials for the longest chain component in alkane mixtures also increases as the pore width decreases and the porosity increases. PMID:17482203

  13. Optical Properties of Thin Film Molecular Mixtures

    NASA Technical Reports Server (NTRS)

    Jaworske, Donald A.; Shumway, Dean A.

    2003-01-01

    Thin films composed of molecular mixtures of metal and dielectric are being considered for use as solar selective coatings for a variety of space power applications. By controlling the degree of molecular mixing, the solar selective coatings can be tailored to have the combined properties of high solar absorptance, , and low infrared emittance, . On orbit, these combined properties would simultaneously maximize the amount of solar energy captured by the coating and minimize the amount of thermal energy radiated. Mini-satellites equipped with solar collectors coated with these cermet coatings may utilize the captured heat energy to power a heat engine to generate electricity, or to power a thermal bus that directs heat to remote regions of the spacecraft. Early work in this area identified the theoretical boundary conditions needed to operate a Carnot cycle in space, including the need for a solar concentrator, a solar selective coating at the heat inlet of the engine, and a radiator.1 A solar concentrator that can concentrate sunlight by a factor of 100 is ideal. At lower values, the temperature of the solar absorbing surface becomes too low for efficient heat engine operation, and at higher values, cavity type heat receivers become attractive. In designing the solar selective coating, the wavelength region yielding high solar absorptance must be separated from the wavelength region yielding low infrared emittance by establishing a sharp transition in optical properties. In particular, a sharp transition in reflectance is desired in the infrared to achieve the desired optical performance. For a heat engine operating at 450 C, a sharp transition at 1.8 micrometers is desired.2 The radiator completes the heat flow through the Carnot cycle.

  14. Analysis of the orientational order effect on n-alkanes: Evidences on experimental response functions and description using Monte Carlo molecular simulation.

    PubMed

    Bessières, D; Piñeiro, M M; De Ferron, G; Plantier, F

    2010-08-21

    Short-range correlations of the molecular orientations in liquid n-alkanes have been extensively studied from depolarized Rayleigh scattering and thermodynamic measurements. These correlations between segments induce structural anisotropy in the fluid bulk. This phenomenon, which is characteristic of linear chain molecules when the constituting segments are nor freely jointed, but interact through a given angular potential, is then present in the linear n-Cn series, increasing its magnitude with chain length, and it is therefore less relevant or even completely absent in branched alkanes. This intermolecular effect is clearly revealed in second-order excess magnitudes such as heat capacities when the linear molecule is mixed with one whose structure approaches sphericity. The mixing process of different aspect ratio chain molecules is thought to modify the original pure fluid structure, by producing a diminution of the orientational order previously existing between pure n-alkane chains. However, second-order thermodynamics quantities of pure liquids C(P), ( partial differentialv/ partial differentialT)(P), and ( partial differentialv/ partial differentialP)(P) are known to be very sensitive to the specific interactions occurring at the microscopic level. In other words, the behavior of these derived properties versus temperature and pressure can be regarded as response functions of the complexity of the microscopic interactions. Thus, the purpose of the present work is to rationalize the orientational order evolution with both temperature and molecular chain length from the analysis of pure fluid properties. To this aim, we focused on two linear alkanes, n-octane (n-C(8)) and n-hexadecane (n-C(16)), and two of their branched isomers, i.e., 2,2,4-trimethylpentane (br-C(8)) and 2,2,4,4,6,8,8-heptamethylnonane (br-C(16)). For each compound, we propose a combined study from direct experimental determination of second-order derivative properties and Monte Carlo

  15. Molecular dynamics study of solubilization of immiscible solutes by a micelle: Free energy of transfer of alkanes from water to the micelle core by thermodynamic integration method.

    PubMed

    Fujimoto, K; Yoshii, N; Okazaki, S

    2010-08-21

    Free energy of transfer, DeltaG(w-->m), from water phase to a sodium dodecyl sulfate (SDS) micelle core has been calculated for a series of hydrophobic solutes originally immiscible with water by thermodynamic integration method combined with molecular dynamics calculations. The calculated free energy of transfer is in good correspondence to the experiment as well as the theoretical free energy of transfer. The calculated DeltaG(w-->m)'s are all negative, implying that the alkane molecules are more stable in the micelle than in the water phase. It decreases almost linearly as a function of the number of carbon atoms of the alkanes longer than methane with a decrement of 3.3 kJ mol(-1) per one methylene group. The calculated free energy of transfer indicates that, for example, at the micelle concentration of 50 CMC (critical micelle concentration), about only 1 of 6 micelles or 1 of 32 000 micelles does not contain a solute methane or n-octane molecule, respectively. PMID:20726656

  16. Molecular dynamics study of solubilization of immiscible solutes by a micelle: Free energy of transfer of alkanes from water to the micelle core by thermodynamic integration method

    NASA Astrophysics Data System (ADS)

    Fujimoto, K.; Yoshii, N.; Okazaki, S.

    2010-08-01

    Free energy of transfer, ΔGw→m, from water phase to a sodium dodecyl sulfate (SDS) micelle core has been calculated for a series of hydrophobic solutes originally immiscible with water by thermodynamic integration method combined with molecular dynamics calculations. The calculated free energy of transfer is in good correspondence to the experiment as well as the theoretical free energy of transfer. The calculated ΔGw→m's are all negative, implying that the alkane molecules are more stable in the micelle than in the water phase. It decreases almost linearly as a function of the number of carbon atoms of the alkanes longer than methane with a decrement of 3.3 kJ mol-1 per one methylene group. The calculated free energy of transfer indicates that, for example, at the micelle concentration of 50 CMC (critical micelle concentration), about only 1 of 6 micelles or 1 of 32 000 micelles does not contain a solute methane or n-octane molecule, respectively.

  17. Comparing the accuracy of high-dimensional neural network potentials and the systematic molecular fragmentation method: A benchmark study for all-trans alkanes

    NASA Astrophysics Data System (ADS)

    Gastegger, Michael; Kauffmann, Clemens; Behler, Jörg; Marquetand, Philipp

    2016-05-01

    Many approaches, which have been developed to express the potential energy of large systems, exploit the locality of the atomic interactions. A prominent example is the fragmentation methods in which the quantum chemical calculations are carried out for overlapping small fragments of a given molecule that are then combined in a second step to yield the system's total energy. Here we compare the accuracy of the systematic molecular fragmentation approach with the performance of high-dimensional neural network (HDNN) potentials introduced by Behler and Parrinello. HDNN potentials are similar in spirit to the fragmentation approach in that the total energy is constructed as a sum of environment-dependent atomic energies, which are derived indirectly from electronic structure calculations. As a benchmark set, we use all-trans alkanes containing up to eleven carbon atoms at the coupled cluster level of theory. These molecules have been chosen because they allow to extrapolate reliable reference energies for very long chains, enabling an assessment of the energies obtained by both methods for alkanes including up to 10 000 carbon atoms. We find that both methods predict high-quality energies with the HDNN potentials yielding smaller errors with respect to the coupled cluster reference.

  18. Comparing the accuracy of high-dimensional neural network potentials and the systematic molecular fragmentation method: A benchmark study for all-trans alkanes.

    PubMed

    Gastegger, Michael; Kauffmann, Clemens; Behler, Jörg; Marquetand, Philipp

    2016-05-21

    Many approaches, which have been developed to express the potential energy of large systems, exploit the locality of the atomic interactions. A prominent example is the fragmentation methods in which the quantum chemical calculations are carried out for overlapping small fragments of a given molecule that are then combined in a second step to yield the system's total energy. Here we compare the accuracy of the systematic molecular fragmentation approach with the performance of high-dimensional neural network (HDNN) potentials introduced by Behler and Parrinello. HDNN potentials are similar in spirit to the fragmentation approach in that the total energy is constructed as a sum of environment-dependent atomic energies, which are derived indirectly from electronic structure calculations. As a benchmark set, we use all-trans alkanes containing up to eleven carbon atoms at the coupled cluster level of theory. These molecules have been chosen because they allow to extrapolate reliable reference energies for very long chains, enabling an assessment of the energies obtained by both methods for alkanes including up to 10 000 carbon atoms. We find that both methods predict high-quality energies with the HDNN potentials yielding smaller errors with respect to the coupled cluster reference. PMID:27208939

  19. Patterns and conformations in molecularly thin films

    NASA Astrophysics Data System (ADS)

    Basnet, Prem B.

    Molecularly thin films have been a subject of great interest for the last several years because of their large variety of industrial applications ranging from micro-electronics to bio-medicine. Additionally, molecularly thin films can be used as good models for biomembrane and other systems where surfaces are critical. Many different kinds of molecules can make stable films. My research has considered three such molecules: a polymerizable phospholipid, a bent-core molecules, and a polymer. One common theme of these three molecules is chirality. The phospolipid molecules studied here are strongly chiral, which can be due to intrinsically chiral centers on the molecules and also due to chiral conformations. We find that these molecules give rise to chiral patterns. Bent-core molecules are not intrinsically chiral, but individual molecules and groups of molecules can show chiral structures, which can be changed by surface interactions. One major, unconfirmed hypothesis for the polymer conformation at surface is that it forms helices, which would be chiral. Most experiments were carried out at the air/water interface, in what are called Langmuir films. Our major tools for studying these films are Brewster Angle Microscopy (BAM) coupled with the thermodynamic information that can be deduced from surface pressure isotherms. Phospholipids are one of the important constituents of liposomes -- a spherical vesicle com-posed of a bilayer membrane, typically composed of a phospholipid and cholesterol bilayer. The application of liposomes in drug delivery is well-known. Crumpling of vesicles of polymerizable phospholipids has been observed. With BAM, on Langmuir films of such phospholipids, we see novel spiral/target patterns during compression. We have found that both the patterns and the critical pressure at which they formed depend on temperature (below the transition to a i¬‘uid layer). Bent-core liquid crystals, sometimes knows as banana liquid crystals, have drawn

  20. Liquid-liquid interfaces of semifluorinated alkane diblock copolymers with water, alkanes, and perfluorinated alkanes.

    SciTech Connect

    Perahia, Dvora, Dr.; Pierce, Flint; Tsige, Mesfin; Grest, Gary Stephen, Dr.

    2008-08-01

    The liquid-liquid interface between semifluorinated alkane diblock copolymers of the form F3C(CF2)n-1-(CH2)m-1CH3 and water, protonated alkanes, and perfluorinated alkanes are studied by fully atomistic molecular dynamics simulations. A modified version of the OPLS-AA (Optimized Parameter for Liquid Simulation All-Atom) force field of Jorgensen et al. has been used to study the interfacial behavior of semifluorinated diblocks. Aqueous interfaces are found to be sharp, with correspondingly large values of the interfacial tension. Due to the reduced hydrophobicity of the protonated block compared to the fluorinated block, hydrogen enhancement is observed at the interface. Water dipoles in the interfacial region are found to be oriented nearly parallel to the liquid-liquid interface. A number of protonated alkanes and perfluorinated alkanes are found to be mutually miscible with the semifluorinated diblocks. For these liquids, interdiffusion follows the expected Fickian behavior, and concentration-dependent diffusivities are determined.

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

    SciTech Connect

    Taub, H.; Hansen, F.Y.; Diama, Amand; Matthies, Blake; Criswell, Leah; Mo, Haiding; Bai, M; Herwig, Kenneth 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-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. Structural insights into diversity and n-alkane biodegradation mechanisms of alkane hydroxylases

    PubMed Central

    Ji, Yurui; Mao, Guannan; Wang, Yingying; Bartlam, Mark

    2013-01-01

    Environmental microbes utilize four degradation pathways for the oxidation of n-alkanes. Although the enzymes degrading n-alkanes in different microbes may vary, enzymes functioning in the first step in the aerobic degradation of alkanes all belong to the alkane hydroxylases. Alkane hydroxylases are a class of enzymes that insert oxygen atoms derived from molecular oxygen into different sites of the alkane terminus (or termini) depending on the type of enzymes. In this review, we summarize the different types of alkane hydroxylases, their degrading steps, and compare typical enzymes from various classes with regard to their three-dimensional structures, in order to provide insights into how the enzymes mediate their different roles in the degradation of n-alkanes and what determines their different substrate ranges. Through the above analyzes, the degrading mechanisms of enzymes can be elucidated and molecular biological methods can be utilized to expand their catalytic roles in the petrochemical industry or in bioremediation of oil-contaminated environments. PMID:23519435

  3. Products of Chemistry: Alkanes: Abundant, Pervasive, Important, and Essential.

    ERIC Educational Resources Information Center

    Seymour, Raymond B.

    1989-01-01

    Discusses the history and commercialization of alkanes. Examines the nomenclature and uses of alkanes. Studies polymerization and several types of polyethylenes: low-density, high-density, low-molecular-weight, cross-linked, linear low-density, and ultrahigh-molecular-weight. Includes a glossary of hydrocarbon terms. (MVL)

  4. Catalytic conversion of light alkanes

    SciTech Connect

    Lyons, J.E.

    1992-06-30

    The second Quarterly Report of 1992 on the Catalytic Conversion of Light Alkanes reviews the work done between April 1, 1992 and June 31, 1992 on the Cooperative Agreement. The mission of this work is to devise a new catalyst which can be used in a simple economic process to convert the light alkanes in natural gas to oxygenate products that can either be used as clean-burning, high octane liquid fuels, as fuel components or as precursors to liquid hydrocarbon uwspomdon fuel. During the past quarter we have continued to design, prepare, characterize and test novel catalysts for the mild selective reaction of light hydrocarbons with air or oxygen to produce alcohols directly. These catalysts are designed to form active metal oxo (MO) species and to be uniquely active for the homolytic cleavage of the carbon-hydrogen bonds in light alkanes producing intermediates which can form alcohols. We continue to investigate three molecular environments for the active catalytic species that we are trying to generate: electron-deficient macrocycles (PHASE I), polyoxometallates (PHASE II), and regular oxidic lattices including zeolites and related structures as well as other molecular surface structures having metal oxo groups (PHASE I).

  5. Molecular dynamics simulation of C-C bond scission in polyethylene and linear alkanes: effects of the condensed phase.

    PubMed

    Popov, Konstantin V; Knyazev, Vadim D

    2014-03-27

    The reaction of C-C bond scission in polyethylene chains of various lengths was studied using molecular dynamics under the conditions of vacuum and condensed phase (polymer melt). A method of assigning meaningful rate constant values to condensed-phase bond scission reactions based on a kinetic mechanism accounting for dissociation, reverse recombination, and diffusional separation of fragments was developed. The developed method accounts for such condensed-phase phenomena as cage effects and diffusion of the decay products away from the reaction site. The results of C-C scission simulations indicate that per-bond rate constants decrease by an order of magnitude as the density of the system increases from vacuum to the normal density of a polyethylene melt. Additional calculations were performed to study the dependence of the rate constant on the length of the polymer chain under the conditions of the condensed phase. The calculations demonstrate that the rate constant is independent of the degree of polymerization if polyethylene samples of different lengths are kept at the same pressure. However, if instead molecular systems of different polyethylene chain lengths decompose under the conditions of the same density, shorter chains result in higher pressures and lower rate constants. The observed effect is attributed to a higher degree of molecular crowding (lower fraction of free intermolecular space available for molecular motion) in the case of shorter molecules. PMID:24571517

  6. Bubble bursting as an aerosol generation mechanism during an oil spill in the deep-sea environment: molecular dynamics simulations of oil alkanes and dispersants in atmospheric air/salt water interfaces.

    PubMed

    Liyana-Arachchi, Thilanga P; Zhang, Zenghui; Ehrenhauser, Franz S; Avij, Paria; Valsaraj, Kalliat T; Hung, Francisco R

    2014-01-01

    Potential of mean force (PMF) calculations and molecular dynamics (MD) simulations were performed to investigate the properties of oil n-alkanes [i.e., n-pentadecane (C15), n-icosane (C20) and n-triacontane (C30)], as well as several surfactant species [i.e., the standard anionic surfactant sodium dodecyl sulfate (SDS), and three model dispersants similar to the Tween and Span species present in Corexit 9500A] at air/salt water interfaces. This study was motivated by the 2010 Deepwater Horizon (DWH) oil spill, and our simulation results show that, from the thermodynamic point of view, the n-alkanes and the model dispersants have a strong preference to remain at the air/salt water interface, as indicated by the presence of deep free energy minima at these interfaces. The free energy minimum of these n-alkanes becomes deeper as their chain length increases, and as the concentration of surfactant species at the interface increases. The n-alkanes tend to adopt a flat orientation and form aggregates at the bare air/salt water interface. When this interface is coated with surfactants, the n-alkanes tend to adopt more tilted orientations with respect to the vector normal to the interface. These simulation results are consistent with the experimental findings reported in the accompanying paper [Ehrenhauser et al., Environ. Sci.: Processes Impacts 2013, in press, (DOI: 10.1039/c3em00390f)]. The fact that these long-chain n-alkanes show a strong thermodynamic preference to remain at the air/salt water interfaces, especially if these interfaces are coated with surfactants, makes these species very likely to adsorb at the surface of bubbles or droplets and be ejected to the atmosphere by sea surface processes such as whitecaps (breaking waves) and bubble bursting. Finally, the experimental finding that more oil hydrocarbons are ejected when Corexit 9500A is present in the system is consistent with the deeper free energy minima observed for the n-alkanes at the air/salt water

  7. SAFT-γ force field for the simulation of molecular fluids: 2. Coarse-grained models of greenhouse gases, refrigerants, and long alkanes.

    PubMed

    Avendaño, Carlos; Lafitte, Thomas; Adjiman, Claire S; Galindo, Amparo; Müller, Erich A; Jackson, George

    2013-03-01

    In the first paper of this series [C. Avendaño, T. Lafitte, A. Galindo, C. S. Adjiman, G. Jackson, and E. A. Müller, J. Phys. Chem. B2011, 115, 11154] we introduced the SAFT-γ force field for molecular simulation of fluids. In our approach, a molecular-based equation of state (EoS) is used to obtain coarse-grained (CG) intermolecular potentials that can then be employed in molecular simulation over a wide range of thermodynamic conditions of the fluid. The macroscopic experimental data for the vapor-liquid equilibria (saturated liquid density and vapor pressure) of a given system are represented with the SAFT-VR Mie EoS and used to estimate effective intermolecular parameters that provide a good description of the thermodynamic properties by exploring a wide parameter space for models based on the Mie (generalized Lennard-Jones) potential. This methodology was first used to develop a simple single-segment CG Mie model of carbon dioxide (CO2) which allows for a reliable representation of the fluid-phase equilibria (for which the model was parametrized), as well as an accurate prediction of other properties such as the enthalpy of vaporization, interfacial tension, supercritical density, and second-derivative thermodynamic properties (thermal expansivity, isothermal compressibility, heat capacity, Joule-Thomson coefficient, and speed of sound). In our current paper, the methodology is further applied and extended to develop effective SAFT-γ CG Mie force fields for some important greenhouse gases including carbon tetrafluoride (CF4) and sulfur hexafluoride (SF6), modeled as simple spherical molecules, and for long linear alkanes including n-decane (n-C10H22) and n-eicosane (n-C20H42), modeled as homonuclear chains of spherical Mie segments. We also apply the SAFT-γ methodology to obtain a CG homonuclear two-segment Mie intermolecular potential for the more challenging polar and asymmetric compound 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), a novel replacement

  8. Growth and physical properties of molecular organic thin films

    NASA Astrophysics Data System (ADS)

    Fraxedas, J.

    2004-04-01

    Highly-oriented polycrystalline thin films of molecular organic materials consisting of small molecules can be easily obtained by physical and chemical vapour deposition methods. The crystallographic phase, orientation and morphology of the films critically depend on the interface and on the kinetics of growth and can be controlled, to a certain extent, by a judicious selection of the substrates and of the growth parameters. This article shortly explores the formation of organic-inorganic heterostructures as a function of coverage: from the most fundamental case, a single molecule on a surface, to thick films (thickness ˜ 1 μ m). The case of high-quality thick TTF-TCNQ films exemplifies the fact that the derived physical properties are essentially identical to those obtained from single crystals. Key words. Molecular organic materials thin films interfaces.

  9. Abundance and diversity of n-alkane-degrading bacteria in a forest soil co-contaminated with hydrocarbons and metals: a molecular study on alkB homologous genes.

    PubMed

    Pérez-de-Mora, Alfredo; Engel, Marion; Schloter, Michael

    2011-11-01

    Unraveling functional genes related to biodegradation of organic compounds has profoundly improved our understanding of biological remediation processes, yet the ecology of such genes is only poorly understood. We used a culture-independent approach to assess the abundance and diversity of bacteria catalyzing the degradation of n-alkanes with a chain length between C(5) and C(16) at a forest site co-contaminated with mineral oil hydrocarbons and metals for nearly 60 years. The alkB gene coding for a rubredoxin-dependent alkane monooxygenase enzyme involved in the initial activation step of aerobic aliphatic hydrocarbon metabolism was used as biomarker. Within the area of study, four different zones were evaluated: one highly contaminated, two intermediately contaminated, and a noncontaminated zone. Contaminant concentrations, hydrocarbon profiles, and soil microbial respiration and biomass were studied. Abundance of n-alkane-degrading bacteria was quantified via real-time PCR of alkB, whereas genetic diversity was examined using molecular fingerprints (T-RFLP) and clone libraries. Along the contamination plume, hydrocarbon profiles and increased respiration rates suggested on-going natural attenuation at the site. Gene copy numbers of alkB were similar in contaminated and control areas. However, T-RFLP-based fingerprints suggested lower diversity and evenness of the n-alkane-degrading bacterial community in the highly contaminated zone compared to the other areas; both diversity and evenness were negatively correlated with metal and hydrocarbon concentrations. Phylogenetic analysis of alkB denoted a shift of the hydrocarbon-degrading bacterial community from Gram-positive bacteria in the control zone (most similar to Mycobacterium and Nocardia types) to Gram-negative genotypes in the contaminated zones (Acinetobacter and alkB sequences with little similarity to those of known bacteria). Our results underscore a qualitative rather than a quantitative response of

  10. Chloroaluminum phthalocyanine thin films: chemical reaction and molecular orientation.

    PubMed

    Latteyer, Florian; Peisert, Heiko; Uihlein, Johannes; Basova, Tamara; Nagel, Peter; Merz, Michael; Schuppler, Stefan; Chassé, Thomas

    2013-05-01

    The chemical transformation of the polar chloroaluminum phthalocyanine, AlClPc, to μ-(oxo)bis(phthalocyaninato)aluminum(III), (PcAl)2O, in thin films on indium tin oxide is studied and its influence on the molecular orientation is discussed. The studies were conducted using complementary spectroscopic techniques: Raman spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In addition, density functional theory calculations were performed in order to identify specific vibrations and to monitor the product formation. The thin films of AlClPc were annealed in controlled environmental conditions to obtain (PcAl)2O. It is shown that the chemical transformation in the thin films can proceed only in the presence of water. The influence of the reaction and the annealing on the molecular orientation was studied with Raman spectroscopy and NEXAFS spectroscopy in total electron yield and partial electron yield modes. The comparison of the results obtained from these techniques allows the determination of the molecular orientation of the film as a function of the probing depth. PMID:23494276

  11. Molecular dynamics simulations of cholesterol-rich membranes using a coarse-grained force field for cyclic alkanes

    NASA Astrophysics Data System (ADS)

    MacDermaid, Christopher M.; Kashyap, Hemant K.; DeVane, Russell H.; Shinoda, Wataru; Klauda, Jeffery B.; Klein, Michael L.; Fiorin, Giacomo

    2015-12-01

    The architecture of a biological membrane hinges upon the fundamental fact that its properties are determined by more than the sum of its individual components. Studies on model membranes have shown the need to characterize in molecular detail how properties such as thickness, fluidity, and macroscopic bending rigidity are regulated by the interactions between individual molecules in a non-trivial fashion. Simulation-based approaches are invaluable to this purpose but are typically limited to short sampling times and model systems that are often smaller than the required properties. To alleviate both limitations, the use of coarse-grained (CG) models is nowadays an established computational strategy. We here present a new CG force field for cholesterol, which was developed by using measured properties of small molecules, and can be used in combination with our previously developed force field for phospholipids. The new model performs with precision comparable to atomistic force fields in predicting the properties of cholesterol-rich phospholipid bilayers, including area per lipid, bilayer thickness, tail order parameter, increase in bending rigidity, and propensity to form liquid-ordered domains in ternary mixtures. We suggest the use of this model to quantify the impact of cholesterol on macroscopic properties and on microscopic phenomena involving localization and trafficking of lipids and proteins on cellular membranes.

  12. Molecular dynamics simulations of cholesterol-rich membranes using a coarse-grained force field for cyclic alkanes

    SciTech Connect

    MacDermaid, Christopher M. Klein, Michael L.; Fiorin, Giacomo; Kashyap, Hemant K.; DeVane, Russell H.; Shinoda, Wataru; Klauda, Jeffery B.

    2015-12-28

    The architecture of a biological membrane hinges upon the fundamental fact that its properties are determined by more than the sum of its individual components. Studies on model membranes have shown the need to characterize in molecular detail how properties such as thickness, fluidity, and macroscopic bending rigidity are regulated by the interactions between individual molecules in a non-trivial fashion. Simulation-based approaches are invaluable to this purpose but are typically limited to short sampling times and model systems that are often smaller than the required properties. To alleviate both limitations, the use of coarse-grained (CG) models is nowadays an established computational strategy. We here present a new CG force field for cholesterol, which was developed by using measured properties of small molecules, and can be used in combination with our previously developed force field for phospholipids. The new model performs with precision comparable to atomistic force fields in predicting the properties of cholesterol-rich phospholipid bilayers, including area per lipid, bilayer thickness, tail order parameter, increase in bending rigidity, and propensity to form liquid-ordered domains in ternary mixtures. We suggest the use of this model to quantify the impact of cholesterol on macroscopic properties and on microscopic phenomena involving localization and trafficking of lipids and proteins on cellular membranes.

  13. Control of wettability of molecularly thin liquid films by nanostructures.

    PubMed

    Fukuzawa, Kenji; Deguchi, Takanori; Yamawaki, Yasuhiro; Itoh, Shintaro; Muramatsu, Takuro; Zhang, Hedong

    2008-03-18

    The patterning of liquid thin films on solid surfaces is very important in various fields of science and engineering related to surfaces and interfaces. A method of nanometer-scale patterning of a molecularly thin liquid film on a silicon substrate using the lyophobicity of the oxide nanostructures has recently been reported (Fukuzawa, K.; Deguchi, T.; Kawamura, J.; Mitsuya, Y.; Muramatsu, T.; Zhang, H. Appl. Phys. Lett. 2005, 87, 203108). However, the origin of the lyophobicity of the nanostructure with a height of around 1 nm, which was fabricated by probe oxidation, has not yet been clarified. In the present study, the change in thickness of the liquid film on mesa-shaped nanostructures and the wettability for the various combinations of the thickness of the liquid films and the height of ridge-shaped nanostructures were investigated. These revealed that lyophobicity is caused by a lowering of the intermolecular interaction between the liquid and silicon surfaces by the nanostructure and enables the patterning of a liquid film along it. The tendency of the wettability for a given liquid film and nanostructure size can be predicted by estimating the contributions of the intermolecular interaction and capillary pressure. In this method, the height of the nanostructure can control the wettability. These results can provide a novel method of nanoscale patterning of liquid thin films, which will be very useful in creating new functional surfaces. PMID:18237215

  14. Molecular tailoring of interfaces for thin film on substrate systems

    NASA Astrophysics Data System (ADS)

    Grady, Martha Elizabeth

    Thin film on substrate systems appear most prevalently within the microelectronics industry, which demands that devices operate in smaller and smaller packages with greater reliability. The reliability of these multilayer film systems is strongly influenced by the adhesion of each of the bimaterial interfaces. During use, microelectronic components undergo thermo-mechanical cycling, which induces interfacial delaminations leading to failure of the overall device. The ability to tailor interfacial properties at the molecular level provides a mechanism to improve thin film adhesion, reliability and performance. This dissertation presents the investigation of molecular level control of interface properties in three thin film-substrate systems: photodefinable polyimide films on passivated silicon substrates, self-assembled monolayers at the interface of Au films and dielectric substrates, and mechanochemically active materials on rigid substrates. For all three materials systems, the effect of interfacial modifications on adhesion is assessed using a laser-spallation technique. Laser-induced stress waves are chosen because they dynamically load the thin film interface in a precise, noncontacting manner at high strain rates and are suitable for both weak and strong interfaces. Photodefinable polyimide films are used as dielectrics in flip chip integrated circuit packages to reduce the stress between silicon passivation layers and mold compound. The influence of processing parameters on adhesion is examined for photodefinable polyimide films on silicon (Si) substrates with three different passivation layers: silicon nitride (SiNx), silicon oxynitride (SiOxNy), and the native silicon oxide (SiO2). Interfacial strength increases when films are processed with an exposure step as well as a longer cure cycle. Additionally, the interfacial fracture energy is assessed using a dynamic delamination protocol. The high toughness of this interface (ca. 100 J/m2) makes it difficult

  15. Preparation of Robust, Thin Zeolite Membrane Sheet for Molecular Separation

    SciTech Connect

    Liu, Wei; Zhang, Jian; Canfield, Nathan L.; Saraf, Laxmikant V.

    2011-10-19

    This paper reports a feasibility study on the preparation of zeolite membrane films on a thin, porous metal support sheet (50-{micro}m thick). Zeolite sodium A (NaA) and silicalite zeolite frameworks are chosen to represent synthesis of respective hydrophilic-type and hydrophobic-type zeolite membranes on this new support. It is found that a dense, continuous inter-grown zeolite crystal layer at a thickness less than 2 {micro}m can be directly deposited on such a support by using direct and secondary growth techniques. The resulting membrane shows excellent adhesion on the metal sheet. Molecular-sieving functions of the prepared membranes are characterized with ethanol/water separation, CO2 separation, and air dehumidification. The results show great potential to make flexible metal-foil-like zeolite membranes for a range of energy conversion and environmental applications.

  16. Alkane metathesis by tandem alkane-dehydrogenation-olefin-metathesis catalysis and related chemistry.

    PubMed

    Haibach, Michael C; Kundu, Sabuj; Brookhart, Maurice; Goldman, Alan S

    2012-06-19

    stable solid metal oxides as the olefin-metathesis catalysts. Both the pincer complexes and the alkylidene complexes have been supported on alumina via adsorption through basic para-substituents. This process does not significantly affect catalyst activity, and in some cases it increases both the catalyst lifetime and the compatibility of the co-catalysts. These molecular catalysts are the first systems that effect alkane metathesis with molecular-weight selectivity, particularly for the conversion of C(n)n-alkanes to C(2n-2)n-alkanes plus ethane. This molecular-weight selectivity offers a critical advantage over the few previously reported alkane metathesis systems. We have studied the factors that determine molecular-weight selectivity in depth, including the isomerization of the olefinic intermediates and the regioselectivity of the pincer-iridium catalyst for dehydrogenation at the terminal position of the n-alkane. Our continuing work centers on the development of co-catalysts with improved interoperability, particularly olefin-metathesis catalysts that are more robust at high temperature and dehydrogenation catalysts that are more active at low temperature. We are also designing dehydrogenation catalysts based on metals other than iridium. Our ongoing mechanistic studies are focused on the apparently complex combination of factors that determine molecular-weight selectivity. PMID:22584036

  17. Reflectance spectroscopy of organic compounds: 1. Alkanes

    USGS Publications Warehouse

    Clark, R.N.; Curchin, J.M.; Hoefen, T.M.; Swayze, G.A.

    2009-01-01

    Reflectance spectra of the organic compounds comprising the alkane series are presented from the ultraviolet to midinfrared, 0.35 to 15.5 /??m. Alkanes are hydrocarbon molecules containing only single carbon-carbon bonds, and are found naturally on the Earth and in the atmospheres of the giant planets and Saturn's moon, Titan. This paper presents the spectral properties of the alkanes as the first in a series of papers to build a spectral database of organic compounds for use in remote sensing studies. Applications range from mapping the environment on the Earth, to the search for organic molecules and life in the solar system and throughout the. universe. We show that the spectral reflectance properties of organic compounds are rich, with major diagnostic spectral features throughout the spectral range studied. Little to no spectral change was observed as a function of temperature and only small shifts and changes in the width of absorption bands were observed between liquids and solids, making remote detection of spectral properties throughout the solar system simpler. Some high molecular weight organic compounds contain single-bonded carbon chains and have spectra similar to alkanes even ' when they fall into other families. Small spectral differences are often present allowing discrimination among some compounds, further illustrating the need to catalog spectral properties for accurate remote sensing identification with spectroscopy.

  18. New Molecular Theory for Dense, Thin Polymer Films

    NASA Astrophysics Data System (ADS)

    Freed, Karl

    2015-03-01

    The development of a molecular theory for dense polymer systems ranks among the most challenging problems in the statistical mechanics of complex matter. These difficulties become compounded when considering the influence of molecular details on thermodynamic properties of thin polymer films, properties deviating from those of the bulk phases. A new theory of dense polymer films is developed as a significant generalization of methods used to devise the lattice cluster theory, an extension of Flory-Huggins theory that include details of monomer structure and short range correlations (neglected in FH theory) and that has successfully been applied to a wide range of polymer systems. The new theory incorporates the essential ``transport'' constraints of Helfand and focuses on the strict imposition of excluded volume constraints, appropriate to dense polymer systems, rather than the maintenance of chain connectivity as appropriate for lower densities and implemented in self-consistent theories of polymer adsorption at interfaces. The theory is illustrated by presenting examples of the computed density and chain end profiles for free standing films as a function of bulk density, chain length, temperature, and chain semi-flexibility.

  19. Molecularly Oriented Polymeric Thin Films for Space Applications

    NASA Technical Reports Server (NTRS)

    Fay, Catharine C.; Stoakley, Diane M.; St.Clair, Anne K.

    1997-01-01

    The increased commitment from NASA and private industry to the exploration of outer space and the use of orbital instrumentation to monitor the earth has focused attention on organic polymeric materials for a variety of applications in space. Some polymeric materials have exhibited short-term (3-5 yr) space environmental durability; however, future spacecraft are being designed with lifetimes projected to be 10-30 years. This gives rise to concern that material property change brought about during operation may result in unpredicted spacecraft performance. Because of their inherent toughness and flexibility, low density, thermal stability, radiation resistance and mechanical strength, aromatic polyimides have excellent potential use as advanced materials on large space structures. Also, there exists a need for high temperature (200-300 C) stable, flexible polymeric films that have high optical transparency in the 300-600nm range of the electromagnetic spectrum. Polymers suitable for these space applications were fabricated and characterized. Additionally, these polymers were molecularly oriented to further enhance their dimensional stability, stiffness, elongation and strength. Both unoriented and oriented polymeric thin films were also cryogenically treated to temperatures below -184 C to show their stability in cold environments and determine any changes in material properties.

  20. Molecular dynamics simulation of VN thin films under indentation

    NASA Astrophysics Data System (ADS)

    Fu, Tao; Peng, Xianghe; Huang, Cheng; Yin, Deqiang; Li, Qibin; Wang, Zhongchang

    2015-12-01

    We investigated with molecular dynamics simulation the mechanical responses of VN (0 0 1) thin films subjected to indentation with a diamond columnar indenter. We calculated the generalized stacking-fault energies as a function of the displacement in the rbond2 1 1 0lbond2 directions on the {0 0 1}, {1 1 0}, and {1 1 1} planes, and analyzed systematically the microstructures and their evolution during the indentation with the centro-symmetry parameters and the slices of the VN films. We found the slips on {1 1 0}rbond2 1 1 0lbond2 of the VN film under indentation at the initial stage. With the increase of indentation depth, slips are also activated on {1 1 1}rbond2 1 1 0lbond2 and {1 0 0}rbond2 0 1 1lbond2 systems. We further found that the slip system is determined by the stacking-fault energy rather than the layer spacing. The indentations with other different parameters were also performed, and the results further prove the validity of the conclusion.

  1. Supercritical fluid molecular spray thin films and fine powders

    DOEpatents

    Smith, Richard D.

    1988-01-01

    Solid films are deposited, or fine powders formed, by dissolving a solid material into a supercritical fluid solution at an elevated pressure and then rapidly expanding the solution through a short orifice into a region of relatively low pressure. This produces a molecular spray which is directed against a substrate to deposit a solid thin film thereon, or discharged into a collection chamber to collect a fine powder. The solvent is vaporized and pumped away. Solution pressure is varied to determine, together with flow rate, the rate of deposition and to control in part whether a film or powder is produced and the granularity of each. Solution temperature is varied in relation to formation of a two-phase system during expansion to control porosity of the film or powder. A wide variety of film textures and powder shapes are produced of both organic and inorganic compounds. Films are produced with regular textural feature dimensions of 1.0-2.0 .mu.m down to a range of 0.01 to 0.1 .mu.m. Powders are formed in very narrow size distributions, with average sizes in the range of 0.02 to 5 .mu.m.

  2. Ordered nanocolumn-array organic semiconductor thin films with controllable molecular orientation

    NASA Astrophysics Data System (ADS)

    Yang, Bingchu; Duan, Haichao; Zhou, Conghua; Gao, Yongli; Yang, Junliang

    2013-12-01

    Ordered nanocolumn-array phthalocynine semiconductor thin films with controllable molecular orientation were fabricated by combining molecular template growth (MTG) and glancing angle deposition (GLAD) techniques. The pre-deposited planar perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) molecular template layer induces phthalocynine molecules arrange with a lying-down molecular orientation, in which the π-π stacking is vertical to the substrate improving the charge transport along the vertical direction; While the GLAD technique supports the formation of nanocolumn-array thin films, supplying a much larger exposed surface area than the conventional compact thin films. The ordered nanocolumn-array thin films with controllable molecular orientation fabricated by combining MTG and GLAD techniques show the potentials to fabricate ordered bulk heterojunction for improving the performance in organic photovoltaics.

  3. Molecular solution processing of metal chalcogenide thin film solar cells

    NASA Astrophysics Data System (ADS)

    Yang, Wenbing

    The barrier to utilize solar generated electricity mainly comes from their higher cost relative to fossil fuels. However, innovations with new materials and processing techniques can potentially make cost effective photovoltaics. One such strategy is to develop solution processed photovoltaics which avoid the expensive vacuum processing required by traditional solar cells. The dissertation is mainly focused on two absorber material system for thin film solar cells: chalcopyrite CuIn(S,Se)2 (CISS) and kesterite Cu2ZnSn(S,Se) 4 organized in chronological order. Chalcopyrite CISS is a very promising material. It has been demonstrated to achieve the highest efficiency among thin film solar cells. Scaled-up industry production at present has reached the giga-watt per year level. The process however mainly relies on vacuum systems which account for a significant percentage of the manufacturing cost. In the first section of this dissertation, hydrazine based solution processed CISS has been explored. The focus of the research involves the procedures to fabricate devices from solution. The topics covered in Chapter 2 include: precursor solution synthesis with a focus on understanding the solution chemistry, CISS absorber formation from precursor, properties modification toward favorable device performance, and device structure innovation toward tandem device. For photovoltaics to have a significant impact toward meeting energy demands, the annual production capability needs to be on TW-level. On such a level, raw materials supply of rare elements (indium for CIS or tellurium for CdTe) will be the bottleneck limiting the scalability. Replacing indium with zinc and tin, earth abundant kesterite CZTS exhibits great potential to reach the goal of TW-level with no limitations on raw material availability. Chapter 3 shows pioneering work towards solution processing of CZTS film at low temperature. The solution processed devices show performances which rival vacuum

  4. Molecular dynamics studies of thin film nucleation and substrate modification

    NASA Astrophysics Data System (ADS)

    Hu, Yanhong

    Deposition of energetic particles on solid surfaces has found increasing application in surface science. However, the detailed surface chemistry and relevant atomic mechanisms are not well understood. Molecular dynamics (MD) simulations are an ideal method to study these processes atomistically because they usually occur on short time scales (of the order of a few picoseconds). In this dissertation, MD simulations are performed to investigate thin film formation through organic cluster beam deposition and chemical modification of carbon nanotube/polymer composites via polyatomic ion beam deposition. The interatomic forces are calculated from the reactive empirical bond-order (REBO) potential for carbon-based systems coupled with the Lennard-Jones potentials. The reliability of this approach is examined by comparing its predictions for ethylene-cluster beam deposition with the results of a more accurate order-N nonorthogonal tight-binding method. The results show that the REBO potential captures the general characters of the relevant chemistry. The deposition processes of interest occur at room temperature; hence, appropriate temperature control methods must be employed in the simulations. A comparison study of four temperature control methods during the simulation of cluster deposition finds that the generalized Langevin equation approach is sufficient for dissipation of excess system energy if the deposition occurs on a large enough substrate at a moderate incident energy (<40 eV/cluster-atom). A new temperature control method has been developed for use at higher incident energies. In the simulations of thin film formation through organic cluster beam deposition, the dependence of the results on the intracluster bonding, incident angle and deposition direction is examined. Beams of ethylene clusters, adamantane molecules, and C20 molecules are thus deposited on a diamond surface with varying lateral momenta along two different crystallographic orientations at

  5. Molecular Aspects of Transport in Thin Films of Controlled Architecture

    SciTech Connect

    Paul W. Bohn

    2009-04-16

    Our laboratory focuses on developing spatially localized chemistries which can produce structures of controlled architecture on the supermolecular length scale -- structures which allow us to control the motion of molecular species with high spatial resolution, ultimately on nanometer length scales. Specifically, nanocapillary array membranes (NCAMs) contain an array of nanometer diameter pores connecting vertically separated microfluidic channels. NCAMs can manipulate samples with sub-femtoliter characteristic volumes and attomole sample amounts and are opening the field of chemical analysis of mass-limited samples, because they are capable of digital control of fluid switching down to sub-attoliter volumes; extension of analytical “unit operations” down to sub-femtomole sample sizes; and exerting spatiotemporal control over fluid mixing to enable studies of reaction dynamics. Digital flow switching mediated by nanocapillary array membranes can be controlled by bias, ionic strength, or pore diameter and is being studied by observing the temporal characteristics of transport across a single nanopore in thin PMMA membranes. The control of flow via nanopore surface characteristics, charge density and functional group presentation, is being studied by coupled conductivity and laser-induced fluorescence (LIF) measurements. Reactive mixing experiments previously established low millisecond mixing times for NCAM-mediated fluid transfer, and this has been exploited to demonstrate capture of mass-limited target species by Au colloids. Voltage and thermally-activated polymer switches have been developed for active control of transport in NCAMs. Thermally-switchable and size-selective transport was achieved by grafting poly(N-isopropylacrylamide) brushes onto the exterior surface of a Au-coated polycarbonate track-etched membrane, while the voltage-gated properties of poly(hydroxyethylmethacrylate) were characterized dynamically. Electrophoretic separations have been

  6. Molecular Sieves: Porous Organic Cage Thin Films and Molecular-Sieving Membranes (Adv. Mater. 13/2016).

    PubMed

    Song, Qilei; Jiang, Shan; Hasell, Tom; Liu, Ming; Sun, Shijing; Cheetham, Anthony K; Sivaniah, Easan; Cooper, Andrew I

    2016-04-01

    Porous organic cage molecules are a new class of molecular materials that combine microporosity and solution-processability. On page 2629, E. Sivaniah, A. I. Cooper, and co-workers demonstrate solution processing of cage molecules into thin films with tunable structures. For the first time, cage molecules are fabricated into continuous and pinhole-free microporous molecular-sieving membranes, as confirmed by selective gas transport in terms of high permeance and molecular selectivity. Image credit: Adam Kewley. PMID:27037946

  7. Vibrational studies of molecular organization in evaporated phthalocyanine thin solid films

    SciTech Connect

    Aroca, R.; Thedchanamoorthy, A.

    1995-01-01

    This report presents results on the study of the molecular organization, utilizing transmission and reflection absorption FTIR spectroscopy, of thin films of phthalocyanine complexes and metal free phthalocyanine. The spatial anisotropy was probed.

  8. Enhanced Rates of Photoinduced Molecular Orientation in a Series of Molecular Glassy Thin Films.

    PubMed

    Snell, Kristen E; Hou, Renjie; Ishow, Eléna; Lagugné-Labarthet, François

    2015-07-01

    Photoinduced orientation in a series of molecular glasses made of small push-pull azo derivatives is dynamically investigated for the first time. Birefringence measurements at 632.8 nm are conducted with a temporal resolution of 100 ms to probe the fast rate of the azo orientation induced under polarized light and its temporal stability over several consecutive cycles. To better evaluate the influence of the azo chemical substituents and their electronic properties on the orientation of the whole molecule, a series of push-pull azo derivatives involving a triphenylaminoazo core substituted with distinct electron-withdrawing moieties is studied. All resulting thin films are probed using polarization modulation infrared spectroscopy that yields dynamical linear dichroism measurements during a cycle of orientation followed by relaxation. We show here in particular that the orientation rates of small molecule-based azo materials are systematically increased up to 7-fold compared to those of a reference polymer counterpart. For specific compounds, the percentage of remnant orientation is also higher, which makes these materials of great interest and promising alternatives to azobenzene-containing polymers for a variety of applications requiring a fast response and absolute control over the molecular weight. PMID:26072966

  9. Alkane fluids confined and compressed by two smooth crystalline gold surfaces: Pure liquids and mixtures

    NASA Astrophysics Data System (ADS)

    Alvarez, Lina P. Merchan

    With the use of grand canonical molecular dynamics, we studied the slow compression(0.01m/s) of very thin liquid films made of equimolar mixtures of short and long alkane chains (hexane and hexadecane), and branched and unbranched alkanes (phytane and hexadecane). Besides comparing how these mixtures behave under constant speed compression, we will compare their properties with the behavior and structure of the pure systems undergoing the same type of slow compression. To understand the arrangement of the molecules inside the confinement, we present segmental and molecular density profiles, average length and orientation of the molecules inside well formed gaps. To observe the effects of the compression on the fluids, we present the number of confined molecules, the inlayer orientation, the solvation force and the inlayer diffusion coefficient, versus the thickness of the gap. We observe that pure hexadecane, although liquid at this temperature, starts presenting strong solid-like behavior when it is compressed to thicknesses under 30A, while pure hexane and pure phytane continue to behave liquid-like except at 13A when they show some weak solid-like features. When hexadecane is mixed with the short straight hexane, it remains liquid down to 28A at which point this mixture behaves solid-like with an enhanced alignment of the long molecules not seen in its pure form; but when hexade-cane is mixed with the branched phytane the system does not present the solid-like features seen when hexadecane is compressed pure.

  10. Vibrational modes and changing molecular conformation of perfluororubrene in thin films and solution

    NASA Astrophysics Data System (ADS)

    Anger, F.; Scholz, R.; Gerlach, A.; Schreiber, F.

    2015-06-01

    We investigate the vibrational properties of perfluororubrene (PF-RUB) in thin films on silicon wafers with a native oxide layer as well as on silicon wafers covered with a self-assembled monolayer and in dichloromethane solution. In comparison with computed Raman and IR spectra, we can assign the molecular modes and identify two molecular conformations with twisted and planar tetracene backbones of the molecule. Moreover, we employ Raman imaging techniques to study the morphology and distribution of the molecular conformation in PF-RUB thin films.

  11. High Temperature Chemical Kinetic Combustion Modeling of Lightly Methylated Alkanes

    SciTech Connect

    Sarathy, S M; Westbrook, C K; Pitz, W J; Mehl, M

    2011-03-01

    Conventional petroleum jet and diesel fuels, as well as alternative Fischer-Tropsch (FT) fuels and hydrotreated renewable jet (HRJ) fuels, contain high molecular weight lightly branched alkanes (i.e., methylalkanes) and straight chain alkanes (n-alkanes). Improving the combustion of these fuels in practical applications requires a fundamental understanding of large hydrocarbon combustion chemistry. This research project presents a detailed high temperature chemical kinetic mechanism for n-octane and three lightly branched isomers octane (i.e., 2-methylheptane, 3-methylheptane, and 2,5-dimethylhexane). The model is validated against experimental data from a variety of fundamental combustion devices. This new model is used to show how the location and number of methyl branches affects fuel reactivity including laminar flame speed and species formation.

  12. Dewetting dynamics of nickel thin film on alpha-quartz substrate: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Maekawa, Yuki; Shibuta, Yasushi

    2016-08-01

    Dewetting dynamics of the nickel thin film on the alpha-quartz substrate is closely investigated by molecular dynamics simulation. Morphology after the spontaneous dewetting of thin films changes from multi-droplets, single-droplet and cylindrical structure as the film thickness increases. In the thin cylindrical structure, a neck is induced to break into the droplet due to the Plateau-Rayleigh instability whereas the thick cylindrical structure does not break. Nucleation and subsequent solidification happen only in the large droplet after the dewetting due to the size effect, which is dominated by the kinetic factor of nucleation in the small system.

  13. Adsorption and dissociation kinetics of alkanes on CaO(100)

    NASA Astrophysics Data System (ADS)

    Chakradhar, A.; Liu, Y.; Schmidt, J.; Kadossov, E.; Burghaus, U.

    2011-08-01

    The adsorption kinetics of ethane, butane, pentane, and hexane on CaO(100) have been studied by multi-mass thermal desorption (TDS) spectroscopy. The sample cleanliness was checked by Auger electron spectroscopy. A molecular and dissociative adsorption pathway was evident for the alkanes, except for ethane, which does not undergo bond activation. Two TDS peaks appeared when recording the parent mass, which are assigned to different adsorption sites/configurations of the molecularly adsorbed alkanes. Bond activation leads to desorption of hydrogen and several alkane fragments assigned to methane and ethylene formation. Only one TDS feature is seen in this case. Formation of carbon residuals was absent.

  14. Characterization of cyclic and acyclic alkanes in Forties and Kuwait petroleum crudes

    SciTech Connect

    Jones, D.W. ); Pakdel, H. ); Bartle, K.D. )

    1990-01-01

    Alkane hydrocarbon fractions from Forties (North Sea) and Kuwait petroleum crudes, separated by distillation, solvent extraction and silicagel column chromatography and sub-fractionated by molecular-sieve adsorption, have been examined by gas chromatography (GC), {sup 1}H and {sup 13}C NMR spectroscopy, GC-mass spectrometry (MS) and field desorption (FD)MS. GC indicates that Forties contains rather more acyclic isoprenoids and cyclic alkanes than Kuwait; FDMS of Kuwait shows molecular-weight ranges for mono-, di-, tri-, tetra-, and pentacyclic alkanes. {sup 13}C NMR spectra provide evidence of higher aromatic carbon, C{sub A}, in Forties than Kuwait and longer T{sub 1} relaxation times.

  15. Anomalous scaling behavior and surface roughening in molecular thin-film deposition

    SciTech Connect

    Yim, S.; Jones, T. S.

    2006-04-15

    The thin film growth dynamics of a molecular semiconductor, free-base phthalocyanine (H{sub 2}Pc), deposited by organic molecular beam deposition, has been studied by atomic force microscopy (AFM) and height difference correlation function (HDCF) analysis. The measured dynamic scaling components ({alpha}{sub loc}=0.61{+-}0.12, {beta}=1.02{+-}0.08, and 1/z=0.72{+-}0.13) are consistent with rapid surface roughening and anomalous scaling behavior. A detailed analysis of AFM images and simple growth models suggest that this behavior arises from the pronounced upward growth of crystalline H{sub 2}Pc mounds during the initial stages of thin film growth.

  16. Thin Films of Molecular Metals TTF-TCNQ

    NASA Astrophysics Data System (ADS)

    Fraxedas, J.; Molas, S.; Figueras, A.; Jiménez, I.; Gago, R.; Auban-Senzier, P.; Goffman, M.

    2002-11-01

    We present recent results on the characterization of highly ordered polycrystalline thin films of the charge transfer salt TTF-TCNQ (TTF=tetrathiafulvalene, TCNQ=tetracyanoquinodimethane) prepared by thermal sublimation in high vacuum under different conditions. The increase in orientation and microcrystal size as a function of substrate and annealing temperatures is addressed. A consequence of such an increase is the reduction of the conductivity activation energy, which eventually leads to the observation of the Peierls transition by resistivity measurements. X-ray absorption near edge spectroscopy studies performed with synchrotron radiation reveal directly the influence of charge transfer on unoccupied states near the Fermi level.

  17. Influence of molecular architecture on the dewetting of thin polystyrene films.

    PubMed

    Krishnan, R S; Mackay, M E; Hawker, C J; Van Horn, B

    2005-06-21

    The control of dewetting for thin polymer films is a technical challenge and of significant academic interest. We have used polystyrene nanoparticles to inhibit dewetting of high molecular weight, linear polystyrene, demonstrating that molecular architecture has a unique effect on surface properties. Neutron reflectivity measurements were used to demonstrate that the nanoparticles were uniformly distributed in the thin (ca. 40 nm) film prior to high temperature annealing, yet after annealing, they were found to separate to the solid substrate, a silanized silicon wafer. Dewetting was eliminated when the nanoparticles separated to form a monolayer or above while below this surface coverage the dewetting dynamics was severely retarded. Blending linear polystyrene of similar molecular weight to the polystyrene nanoparticle with the high molecular weight polystyrene did not eliminate dewetting. PMID:15952821

  18. On droplet combustion of biodiesel fuel mixed with diesel/alkanes in microgravity condition

    SciTech Connect

    Pan, Kuo-Long; Li, Je-Wei; Chen, Chien-Pei; Wang, Ching-Hua

    2009-10-15

    The burning characteristics of a biodiesel droplet mixed with diesel or alkanes such as dodecane and hexadecane were experimentally studied in a reduced-gravity environment so as to create a spherically symmetrical flame without the influence of natural convection due to buoyancy. Small droplets on the order of 500 {mu}m in diameter were initially injected via a piezoelectric technique onto the cross point intersected by two thin carbon fibers; these were prepared inside a combustion chamber that was housed in a drag shield, which was freely dropped onto a foam cushion. It was found that, for single component droplets, the tendency to form a rigid soot shell was relatively small for biodiesel fuel as compared to that exhibited by the other tested fuels. The soot created drifted away readily, showing a puffing phenomenon; this could be related to the distinct molecular structure of biodiesel leading to unique soot layers that were more vulnerable to oxidative reactivity as compared to the soot generated by diesel or alkanes. The addition of biodiesel to these more traditional fuels also presented better performance with respect to annihilating the soot shell, particularly for diesel. The burning rate generally follows that of multi-component fuels, by some means in terms of a lever rule, whereas the mixture of biodiesel and dodecane exhibits a somewhat nonlinear relation with the added fraction of dodecane. This might be related to the formation of a soot shell. (author)

  19. Tunneling Nanoelectromechanical Switches Based on Compressible Molecular Thin Films.

    PubMed

    Niroui, Farnaz; Wang, Annie I; Sletten, Ellen M; Song, Yi; Kong, Jing; Yablonovitch, Eli; Swager, Timothy M; Lang, Jeffrey H; Bulović, Vladimir

    2015-08-25

    Abrupt switching behavior and near-zero leakage current of nanoelectromechanical (NEM) switches are advantageous properties through which NEMs can outperform conventional semiconductor electrical switches. To date, however, typical NEMs structures require high actuation voltages and can prematurely fail through permanent adhesion (defined as stiction) of device components. To overcome these challenges, in the present work we propose a NEM switch, termed a "squitch," which is designed to electromechanically modulate the tunneling current through a nanometer-scale gap defined by an organic molecular film sandwiched between two electrodes. When voltage is applied across the electrodes, the generated electrostatic force compresses the sandwiched molecular layer, thereby reducing the tunneling gap and causing an exponential increase in the current through the device. The presence of the molecular layer avoids direct contact of the electrodes during the switching process. Furthermore, as the layer is compressed, the increasing surface adhesion forces are balanced by the elastic restoring force of the deformed molecules which can promote zero net stiction and recoverable switching. Through numerical analysis, we demonstrate the potential of optimizing squitch design to enable large on-off ratios beyond 6 orders of magnitude with operation in the sub-1 V regime and with nanoseconds switching times. Our preliminary experimental results based on metal-molecule-graphene devices suggest the feasibility of the proposed tunneling switching mechanism. With optimization of device design and material engineering, squitches can give rise to a broad range of low-power electronic applications. PMID:26244821

  20. Modeling Ellipsometry Measurements of Molecular Thin-Film Contamination on Genesis Array Samples

    NASA Technical Reports Server (NTRS)

    Calaway, Michael J.; Stansbery, E. K.; McNamara, K. M.

    2006-01-01

    The discovery of a molecular thin-film contamination on Genesis flown array samples changed the course of preliminary assessment strategies. Analytical techniques developed to measure solar wind elemental abundances must now compensate for a thin-film contamination. Currently, this is done either by experimental cleaning before analyses or by depth-profiling techniques that bypass the surface contamination. Inside Johnson Space Center s Genesis dedicated ISO Class 4 (Class 10) cleanroom laboratory, the selection of collector array fragments allocated for solar wind analyses are based on the documentation of overall surface quality, visible surface particle contamination greater than 1 m, and the amount of thin film contamination measured by spectroscopic ellipsometry. Documenting the exact thickness, surface topography, and chemical composition of these contaminates is also critical for developing accurate cleaning methods. However, the first step in characterization of the molecular film is to develop accurate ellipsometry models that will determine an accurate thickness measurement of the contamination film.

  1. Optical observations of molecular dissociation in thin foils

    SciTech Connect

    Berry, H.G.; Gay, T.J.; Brooks, R.L.

    1981-01-01

    We have measured the intensity and polarizations of light emitted from atomic excited states of dissociated molecular ions. Using HeH/sup +/ projectiles, we have observed factors of 1 to 5 enhancements of the light from n=3, /sup 1/ /sup 3/P,D states of He I and some He II and H I emissions. Observations of Lyman-..cap alpha.. emission after dissociation of H/sub 2//sup +/ and H/sub 3//sup +/ show rapid variations in light yield for small internuclear separations at the foil surface.

  2. [Sources, Migration and Conversion of Dissolved Alkanes, Dissolved Fatty Acids in a Karst Underground River Water, in Chongqing Area].

    PubMed

    Liang, Zuo-bing; Sun, Yu-chuan; Wang, Zun-bo; Shi, Yang; Jiang, Ze-li; Zhang, Mei; Xie, Zheng-Lan; Liao, Yu

    2015-09-01

    Dissolved alkanes and dissolved fatty acids were collected from Qingmuguan underground river in July, October 2013. By gas chromatography-mass spectrometer (GC-MS), alkanes and fatty acids were quantitatively analyzed. The results showed that average contents of alkanes and fatty acids were 1 354 ng.L-1, 24203 ng.L-1 in July, and 667 ng.L-1, 2526 ng.L-1 in October respectively. With the increasing migration distance of dissolved alkanes and dissolved fatty acids in underground river, their contents decreased. Based on the molecular characteristic indices of alkanes, like CPI, OEP, Paq and R, dissolved alkanes were mainly originated from microorganisms in July, and aquatic plants in October. Saturated straight-chain fatty acid had the highest contents in all samples with the dominant peak in C16:0, combined with the characteristics of carbon peak, algae or bacteria might be the dominant source of dissolved fatty acids. PMID:26717680

  3. Molecular-Orientation-Induced Rapid Roughening and Morphology Transition in Organic Semiconductor Thin-Film Growth

    PubMed Central

    Yang, Junliang; Yim, Sanggyu; Jones, Tim S.

    2015-01-01

    We study the roughening process and morphology transition of organic semiconductor thin film induced by molecular orientation in the model of molecular semiconductor copper hexadecafluorophthalocyanine (F16CuPc) using both experiment and simulation. The growth behaviour of F16CuPc thin film with the thickness, D, on SiO2 substrate takes on two processes divided by a critical thickness: (1) D ≤ 40 nm, F16CuPc thin films are composed of uniform caterpillar-like crystals. The kinetic roughening is confirmed during this growth, which is successfully analyzed by Kardar-Parisi-Zhang (KPZ) model with scaling exponents α = 0.71 ± 0.12, β = 0.36 ± 0.03, and 1/z = 0.39 ± 0.12; (2) D > 40 nm, nanobelt crystals are formed gradually on the caterpillar-like crystal surface and the film growth shows anomalous growth behaviour. These new growth behaviours with two processes result from the gradual change of molecular orientation and the formation of grain boundaries, which conversely induce new molecular orientation, rapid roughening process, and the formation of nanobelt crystals. PMID:25801646

  4. Molecular orientation in soft matter thin films studied by resonant soft X-ray reflectivity

    SciTech Connect

    Mezger, Markus; Jerome, Blandine; Kortright, Jeffrey B.; Valvidares, Manuel; Gullikson, Eric; Giglia, Angelo; Mahne, Nicola; Nannarone, Stefano

    2011-01-12

    We present a technique to study depth profiles of molecular orientation in soft matter thin films with nanometer resolution. The method is based on dichroism in resonant soft X-ray reflectivity using linear s- and p-polarization. It combines the chemical sensitivity of Near-Edge X-ray Absorption Fine Structure spectroscopy to specific molecular bonds and their orientation relative to the polarization of the incident beam with the precise depth profiling capability of X-ray reflectivity. We demonstrate these capabilities on side chain liquid crystalline polymer thin films with soft X-ray reflectivity data at the carbon K edge. Optical constants of the anisotropic refractive index ellipsoid were obtained from a quantitative analysis using the Berreman formalism. For films up to 50 nm thickness we find that the degree of orientation of the long axis exhibits no depth variation and isindependent of the film thickness.

  5. Rupture mechanism of liquid crystal thin films realized by large-scale molecular simulations

    SciTech Connect

    Nguyen, Trung D; Carrillo, Jan-Michael Y; Brown, W Michael; Matheson, Michael A

    2014-01-01

    The ability of liquid crystal (LC) molecules to respond to changes in their environment makes them an interesting candidate for thin film applications, particularly in bio-sensing, bio-mimicking devices, and optics. Yet the understanding of the (in)stability of this family of thin films has been limited by the inherent challenges encountered by experiment and continuum models. Using unprecedented largescale molecular dynamics (MD) simulations, we address the rupture origin of LC thin films wetting a solid substrate at length scales similar to those in experiment. Our simulations show the key signatures of spinodal instability in isotropic and nematic films on top of thermal nucleation, and importantly, for the first time, evidence of a common rupture mechanism independent of initial thickness and LC orientational ordering. We further demonstrate that the primary driving force for rupture is closely related to the tendency of the LC mesogens to recover their local environment in the bulk state. Our study not only provides new insights into the rupture mechanism of liquid crystal films, but also sets the stage for future investigations of thin film systems using peta-scale molecular dynamics simulations.

  6. Rupture mechanism of liquid crystal thin films realized by large-scale molecular simulations.

    PubMed

    Nguyen, Trung Dac; Carrillo, Jan-Michael Y; Matheson, Michael A; Brown, W Michael

    2014-03-21

    The ability of liquid crystal (LC) molecules to respond to changes in their environment makes them an interesting candidate for thin film applications, particularly in bio-sensing, bio-mimicking devices, and optics. Yet the understanding of the (in)stability of this family of thin films has been limited by the inherent challenges encountered by experiment and continuum models. Using unprecedented large-scale molecular dynamics (MD) simulations, we address the rupture origin of LC thin films wetting a solid substrate at length scales similar to those in experiment. Our simulations show the key signatures of spinodal instability in isotropic and nematic films on top of thermal nucleation, and importantly, for the first time, evidence of a common rupture mechanism independent of initial thickness and LC orientational ordering. We further demonstrate that the primary driving force for rupture is closely related to the tendency of the LC mesogens to recover their local environment in the bulk state. Our study not only provides new insights into the rupture mechanism of liquid crystal films, but also sets the stage for future investigations of thin film systems using peta-scale molecular dynamics simulations. PMID:24264516

  7. Molecular layer-by-layer assembled thin-film composite membranes for water desalination.

    PubMed

    Gu, Joung-Eun; Lee, Seunghye; Stafford, Christopher M; Lee, Jong Suk; Choi, Wansuk; Kim, Bo-Young; Baek, Kyung-Youl; Chan, Edwin P; Chung, Jun Young; Bang, Joona; Lee, Jung-Hyun

    2013-09-14

    Molecular layer-by-layer (mLbL) assembled thin-film composite membranes fabricated by alternating deposition of reactive monomers on porous supports exhibit both improved salt rejection and enhanced water flux compared to traditional reverse osmosis membranes prepared by interfacial polymerization. Additionally, the well-controlled structures achieved by mLbL deposition further lead to improved antifouling performance. PMID:23847127

  8. MIR and NIR group spectra of n-alkanes and 1-chloroalkanes

    NASA Astrophysics Data System (ADS)

    Kwaśniewicz, Michał; Czarnecki, Mirosław A.

    2015-05-01

    Numerous attempts were undertaken to resolve the absorption originating from different parts of alkanes. The separation of the contributions from the terminal and midchain methylene units was observed only in the spectra of solid alkanes at low temperatures. On the other hand, for liquid alkanes this effect was not reported as yet. In this study, ATR-IR, Raman and NIR spectra of eight n-alkanes and seven 1-chloroalkanes in the liquid phase were measured from 1000 to 12,000 cm-1. The spectra were analyzed by using two-dimensional (2D) correlation approach and chemometrics methods. It was shown that in 2D asynchronous contour plots, constructed from the spectra of n-alkanes and 1-chloroalkanes, the methylene band was resolved into two components. These two components were assigned to the terminal and midchain methylene groups. For the first time, the contributions from these two molecular fragments were resolved in the spectra of liquid n-alkanes and 1-chloroalkanes. MCR-ALS resolved these spectra into two components that were assigned to the ethyl and midchain methylene groups. These components represent the group spectra that can be used for assignment, spectral analysis and prediction of unknown spectra. The spectral prediction based on the group spectra provides very good results for n-alkanes, especially in the first and second overtone regions.

  9. Thickness determination of molecularly thin lubricant films by angle-dependent X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Pang, Chongjun; Bai, Mingwu

    2007-03-01

    An angle-dependent X-ray photoelectron spectroscopy (XPS) method used to measure the thickness of molecularly thin lubricants was developed. The method was built based on an island model of patched overlayer on a flat substrate by using the photoemission signal solely from the lubricant film. Typical molecularly thin Zdol films on the CHx overcoat of unused commercial magnetic disks were measured to verify the metrology. The lubricant thickness determined by the metrology was equal to the recent result by thermostatic high vacuum atomic force microscopy. The measured deduction in the thickness of the molecularly thin lubricant films, successively irradiated by the monochromatic source operated at 14 kV/250 W, was as low as 1 Ǻ during the first irradiation hour. XPS spectra showed that no hydrocarbons, water or oxygen were adsorbed over the Zdol outer surfaces in the tested XPS conditions. The inelastic mean free path (IMFP) of C 1s in Zdol or in CHx was found to be independent of take off angle (TOA) when TOA < 40°. The IMFP of C 1s in Zdol was ˜63.5 Ǻ and the lubricant island thickness was ˜35 Ǻ.

  10. Alkane biohydroxylation: Interests, constraints and future developments.

    PubMed

    Soussan, Laurence; Pen, Nakry; Belleville, Marie-Pierre; Marcano, José Sanchez; Paolucci-Jeanjean, Delphine

    2016-03-20

    Alkanes constitute one of the vastest reserves of raw materials for the production of fine chemicals. This paper focuses on recent advances in alkane biohydroxylation, i.e. the bioactivation of alkanes into their corresponding alcohols. Enzyme and whole-cell biocatalysts have been reviewed. Process considerations to implement such biocatalysts in bioreactors at large scale by coupling the bioconversion with cofactor regeneration and product removal are also discussed. PMID:26853477

  11. Highly-oriented molecular arrangements and enhanced magnetic interactions in thin films of CoTTDPz using PTCDA templates.

    PubMed

    Eguchi, Keitaro; Nanjo, Chihiro; Awaga, Kunio; Tseng, Hsiang-Han; Robaschik, Peter; Heutz, Sandrine

    2016-07-14

    In the present work, the templating effect of thin layers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on the growth of cobalt tetrakis(thiadiazole)porphyrazine (CoTTDPz) thin films was examined. X-ray diffraction and optical absorption spectra indicate that while CoTTDPz forms amorphous thin films on the bare substrates, it forms crystalline thin films on the PTCDA templates, in which the molecular planes of CoTTDPz are considered to be parallel to the substrates. Magnetic measurements reveal a significantly enhanced antiferromagnetic interaction of CoTTDPz in the templated thin films, with values reaching over 13 K. The ability to generate crystalline films and to control their orientation using molecular templates is an important strategy in the fields of organic electronics and spintronics in order to tailor the physical properties of organic thin films to suit their intended application. PMID:27183955

  12. Secondary organic aerosol composition from C12 alkanes.

    PubMed

    Schilling Fahnestock, Katherine A; Yee, Lindsay D; Loza, Christine L; Coggon, Matthew M; Schwantes, Rebecca; Zhang, Xuan; Dalleska, Nathan F; Seinfeld, John H

    2015-05-14

    The effects of structure, NOx conditions, relative humidity, and aerosol acidity on the chemical composition of secondary organic aerosol (SOA) are reported for the photooxidation of three C12 alkanes: n-dodecane, cyclododecane, and hexylcyclohexane. Acidity was modified through seed particle composition: NaCl, (NH4)2SO4, and (NH4)2SO4 + H2SO4. Off-line analysis of SOA was carried out by solvent extraction and gas chromatography-mass spectrometry (GC/MS) and direct analysis in real-time mass spectrometry. We report here 750 individual masses of SOA products identified from these three alkane systems and 324 isomers resolved by GC/MS analysis. The chemical compositions for each alkane system provide compelling evidence of particle-phase chemistry, including reactions leading to oligomer formation. Major oligomeric species for alkane SOA are peroxyhemiacetals, hemiacetals, esters, and aldol condensation products. Furans, dihydrofurans, hydroxycarbonyls, and their corresponding imine analogues are important participants in these oligomer-producing reactions. Imines are formed in the particle phase from the reaction of the ammonium sulfate seed aerosol with carbonyl-bearing compounds present in all the SOA systems. Under high-NO conditions, organonitrate products can lead to an increase of aerosol volume concentration by up to a factor of 5 over that in low-NO conditions. Structure was found to play a key role in determining the degree of functionalization and fragmentation of the parent alkane, influencing the mean molecular weight of the SOA produced and the mean atomic O:C ratio. PMID:24814371

  13. Defect-Controlled Preparation of UiO-66 Metal-Organic Framework Thin Films with Molecular Sieving Capability.

    PubMed

    Zhang, Caiqin; Zhao, Yajing; Li, Yali; Zhang, Xuetong; Chi, Lifeng; Lu, Guang

    2016-01-01

    Metal-organic framework (MOF) UiO-66 thin films are solvothermally grown on conducting substrates. The as-synthesized MOF thin films are subsequently dried by a supercritical process or treated with polydimethylsiloxane (PDMS). The obtained UiO-66 thin films show excellent molecular sieving capability as confirmed by the electrochemical studies for redox-active species with different sizes. PMID:26548455

  14. Adsorption of alkanes on stoichiometric and oxygen-rich RuO2(110).

    PubMed

    Li, Tao; Kim, Minkyu; Rai, Rahul; Liang, Zhu; Asthagiri, Aravind; Weaver, Jason F

    2016-08-10

    We investigated the molecular adsorption of methane, ethane, propane and n-butane on stoichiometric and oxygen-rich RuO2(110) surfaces using temperature-programmed desorption (TPD) and dispersion-corrected density functional theory (DFT-D3) calculations. We find that each alkane adsorbs strongly on the coordinatively-unsaturated Ru (Rucus) atoms of s-RuO2(110), with desorption from this state producing a well-defined TPD peak at low alkane coverage. As the coverage increases, we find that alkanes first form a compressed layer on the Rucus atoms and subsequently adsorb on the bridging O atoms of the surface until the monolayer saturates. DFT-D3 calculations predict that methane preferentially adsorbs on top of a Rucus atom and that the C2 to C4 alkanes preferentially adopt bidentate configurations in which each molecule aligns parallel to the Rucus atom row and datively bonds to neighboring Rucus atoms. DFT-D3 predicts binding energies that agree quantitatively with our experimental estimates for alkane σ-complexes on RuO2(110). We find that oxygen atoms adsorbed on top of Rucus atoms (Oot atoms) stabilize the adsorbed alkane complexes that bind in a given configuration, while also blocking the sites needed for σ-complex formation. This site blocking causes the coverage of the most stable, bidentate alkane complexes to decrease sharply with increasing Oot coverage. Concurrently, we find that a new peak develops in the C2 to C4 alkane TPD spectra with increasing Oot coverage, and that the desorption yield in this TPD feature passes through a maximum at Oot coverages between ∼50% and 60%. We present evidence that the new TPD peak arises from C2 to C4 alkanes that adsorb in upright, monodentate configurations on stranded Rucus sites located within the Oot layer. PMID:27477390

  15. Reaction pathway for alkane dehydrocyclization

    SciTech Connect

    Shi, Buchang; Davis, B.H.

    1996-08-01

    Naphtha reforming to produce high octane gasoline is an important process. Many reaction mechanisms are involved in this process. For example, the study of the fundamentals of this process led to the concept of bi- or poly-functional catalysis. The results of this study provide additional mechanistic information about the dehydrocyclization of an n-alkane to produce aromatics. The reaction coordinate diagram advanced to account for the observation of irreversible adsorption should be modified to account for the present results. 32 refs., 1 fig.

  16. Alkanes in flower surface waxes of Momordica cochinchinensis influence attraction to Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae).

    PubMed

    Mukherjee, A; Sarkar, N; Barik, A

    2013-08-01

    Extraction, thin-layer chromatography, and gas chromatography-mass spectrophotometry analyses revealed 15 alkanes representing 97.14% of the total alkanes in the surface waxes of Momordica cochinchinensis Spreng flowers. Nonacosane was the prevailing alkane followed by hexatriacontane, nonadecane, heptacosane, and hentriacontane, accounting for 39.08%, 24.24%, 13.52%, 6.32%, and 5.12%, respectively. The alkanes from flower surface waxes followed by a synthetic mixture of alkanes mimicking alkanes of flower surface waxes elicited attraction of the female insect, Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) between 2 and 10-μg/mL concentrations in a Y-shaped glass tube olfactometer bioassay under laboratory conditions. Synthetic nonadecane from 178.28-891.37 ng, heptacosane from 118.14-590.72 ng, and nonacosane at 784.73 ng showed attraction of the insect. A synthetic mixture of 534.82 ng nonadecane, 354.43 ng heptacosane, and 2,354.18 ng nonacosane elicited highest attraction of A. foveicollis. PMID:23949856

  17. n-Alkane hydroconversion on Zeogrid and colloidal ZSM-5 assembled from aluminosilicate nanoslabs of MFI framework type.

    PubMed

    Aerts, Alexander; Huybrechts, Ward; Kremer, Sebastien P B; Kirschhock, Christine E A; Theunissen, Elisabeth; Van Isacker, Annabel; Denayer, Joeri F M; Baron, Gino V; Thybaut, Joris W; Marin, Guy B; Jacobs, Pierre A; Martens, Johan A

    2003-08-01

    n-Alkane hydroisomerisation and hydrocracking experiments reveal that ZSM-5 materials synthesized by self-assembly of nanoslabs show different molecular shape selectivity than ZSM-5 synthesized by hydrothermal methods. PMID:12932017

  18. Molecularly thin fluoro-polymeric nanolubricant films: tribology, rheology, morphology, and applications.

    PubMed

    Chung, Pil Seung; Jhon, Myung S; Choi, Hyoung Jin

    2016-03-01

    Molecularly thin perfluoropolyether (PFPE) has been used extensively as a high-performance lubricant in various applications and, more importantly, on carbon overcoats to enhance the reliability and lubrication of micro-/nanoelectro-mechanical systems, where the tribological performance caused by its molecular architecture is a critical issue, as are its physical properties and rheological characteristics. This Highlight addresses recent trends in the development of fluoro-polymeric lubricant films with regard to their tribology, rheology, and physio-chemical properties as they relate to heat-assisted magnetic recording. Nanorheology has been employed to examine the dynamic response of nonfunctional and functional PFPEs, while the viscoelastic properties of nanoscale PFPE films and the relaxation processes as a function of molecular structure and end-group functionality were analyzed experimentally; furthermore, the characteristics of binary blends were reported. PMID:26907953

  19. Production of Liquid Alkanes by Aqueous-Phase Processing of Biomass-Derived Carbohydrates

    NASA Astrophysics Data System (ADS)

    Huber, George W.; Chheda, Juben N.; Barrett, Christopher J.; Dumesic, James A.

    2005-06-01

    Liquid alkanes with the number of carbon atoms ranging from C7 to C15 were selectively produced from biomass-derived carbohydrates by acid-catalyzed dehydration, which was followed by aldol condensation over solid base catalysts to form large organic compounds. These molecules were then converted into alkanes by dehydration/hydrogenation over bifunctional catalysts that contained acid and metal sites in a four-phase reactor, in which the aqueous organic reactant becomes more hydrophobic and a hexadecane alkane stream removes hydrophobic species from the catalyst before they go on further to form coke. These liquid alkanes are of the appropriate molecular weight to be used as transportation fuel components, and they contain 90% of the energy of the carbohydrate and H2 feeds.

  20. Changes in iso- and n-alkane distribution during biodegradation of crude oil under nitrate and sulphate reducing conditions.

    PubMed

    Hasinger, Marion; Scherr, Kerstin E; Lundaa, Tserennyam; Bräuer, Leopold; Zach, Clemens; Loibner, Andreas Paul

    2012-02-20

    Crude oil consists of a large number of hydrocarbons with different susceptibility to microbial degradation. The influence of hydrocarbon structure and molecular weight on hydrocarbon biodegradation under anaerobic conditions is not fully explored. In this study oxygen, nitrate and sulphate served as terminal electron acceptors (TEAs) for the microbial degradation of a paraffin-rich crude oil in a freshly contaminated soil. During 185 days of incubation, alkanes from n-C11 to n-C39, three n- to iso-alkane ratios commonly used as weathering indicators and the unresolved complex mixture (UCM) were quantified and statistically analyzed. The use of different TEAs for hydrocarbon degradation resulted in dissimilar degradative patterns for n- and iso-alkanes. While n-alkane biodegradation followed well-established patterns under aerobic conditions, lower molecular weight alkanes were found to be more recalcitrant than mid- to high-molecular weight alkanes under nitrate-reducing conditions. Biodegradation with sulphate as the TEA was most pronounced for long-chain (n-C32 to n-C39) alkanes. The observation of increasing ratios of n-C17 to pristane and of n-C18 to phytane provides first evidence of the preferential degradation of branched over normal alkanes under sulphate reducing conditions. The formation of distinctly different n- and iso-alkane biodegradation fingerprints under different electron accepting conditions may be used to assess the occurrence of specific degradation processes at a contaminated site. The use of n- to iso-alkane ratios for this purpose may require adjustment if applied for anaerobic sites. PMID:22001845

  1. Synthesis, characterization, and pulsed laser ablation of molecular sieves for thin film applications

    NASA Astrophysics Data System (ADS)

    Munoz, Trinidad, Jr.

    1998-12-01

    Molecular sieves are one class of crystalline low density metal oxides which are made up of one-, two-, and three dimensional pores and/or cages. We have investigated the synthesis and characterization of metal substituted aluminophosphates and all silica molecular sieves for thin film applications. A new copper substituted aluminophosphate, CuAPO-5 has been synthesized and characterized using x-ray powder diffraction, FT-IR spectroscopy and scanning electron microscopy. Electron spin resonance and electron spin echo modulation provided supporting evidence of framework incorporation of Cu(II) ions. Thus, an exciting addition has been added to the family of metal substituted aluminophosphates where substitution of the metal has been demonstrated as framework species. Also presented here is the synthesis and characterization of an iron substituted aluminophosphate, FeAPO-5, and an all silica zeolite, UTD-1 for thin film applications. Pulsed laser ablation has been employed as the technique to generate thin films. Here an excimer laser (KrFsp*, 248 nm) was used to deposit the molecular sieves on a variety of substrates including polished silicon, titanium nitride, and porous stainless steel disks. The crystallinity of the deposited films was enhanced by a post hydrothermal treatment. A vapor phase treatment of the laser deposited FeAPO-5 films has been shown to increase the crystallinity of the film without increasing film thickness. Thin films of the FeAPO-5 molecular sieves were subsequently used as the dielectric phase in capacitive type chemical sensors. The capacitance change of the FeAPO-5 devices to the relative moisture makes them potential humidity sensors. The all silica zeolite UTD-1 thin films were deposited on polished silicon and porous supports. A brief post hydrothermal treatment of the laser deposited films deposited on polished silicon and porous metal supports resulted in oriented film growth lending these films to applications in gas separations

  2. Molecular Orientation of Hydroquinone Adsorbed at a Platinum(111) Thin-Layer Electrode.

    PubMed

    Ren; Hubbard

    1999-01-15

    Reported are new findings regarding the molecular orientation of hydroquinone (HQ) adsorbed on Pt surfaces. The packing density of hydroquinone adsorbed from 1 M HClO4 supporting electrolyte has been measured by use of a Pt(111) thin-layer electrode. The packing-density-vs-concentration profiles for hydroquinone, measured by a differential thin-layer electrode method at an ordered Pt(111) surface and at an electrochemically disordered Pt(111) surface, are identical within an experimental error of about 8%. The profiles from this study are similar to the ones obtained previously at an ordered Pt(111) surface by Auger spectroscopy, but they are significantly different from those reported previously for polycrystalline Pt thin-layer electrodes. A procedure based upon displacement of HQ by thiocyanate has been developed as an alternative method for determining the packing density of adsorbed HQ. Both methods afford information regarding the molecular state of HQ adsorbed at the Pt(111) surface. Copyright 1999 Academic Press. PMID:9885274

  3. The effects of polymer molecular weight on filament thinning and drop breakup in microchannels

    NASA Astrophysics Data System (ADS)

    Arratia, P. E.; Cramer, L.-A.; Gollub, J. P.; Durian, D. J.

    2009-11-01

    We investigate the effects of fluid elasticity on the dynamics of filament thinning and drop breakup processes in a cross-slot microchannel. Elasticity effects are examined using dilute aqueous polymeric solutions of molecular weight (MW) ranging from 1.5×103 to 1.8×107. Results for polymeric fluids are compared to those for a viscous Newtonian fluid. The shearing or continuous phase that induces breakup is mineral oil. All fluids possess similar shear-viscosity (~0.2 Pa s) so that the viscosity ratio between the oil and aqueous phases is close to unity. Measurements of filament thickness as a function of time show different thinning behavior for the different aqueous fluids. For Newtonian fluids, the thinning process shows a single exponential decay of the filament thickness. For low MW fluids (103, 104 and 105), the thinning process also shows a single exponential decay, but with a decay rate that is slower than for the Newtonian fluid. The decay time increases with polymer MW. For high MW (106 and 107) fluids, the initial exponential decay crosses over to a second exponential decay in which elastic stresses are important. We show that the decay rate of the filament thickness in this exponential decay regime can be used to measure the steady extensional viscosity of the fluids. At late times, all fluids cross over to an algebraic decay which is driven mainly by surface tension.

  4. Alkane-Based Urethane Potting Compounds

    NASA Technical Reports Server (NTRS)

    Morris, D. E.

    1986-01-01

    New low viscosity urethanes easily mixed, molded, and outgassed. Alkane-based urethanes resist hydrolysis and oxidation and have excellent dielectric properties. Low-viscosity alkane-based urethane prepolymer prepared by one-step reaction of either isophorone diisocyanate or methyl-bis (4-cyclohexyl isocyanate) with hydrogenated, hydroxy-terminated polybutadiene (HTPBD).

  5. Atomic/molecular layer deposition: a direct gas-phase route to crystalline metal-organic framework thin films.

    PubMed

    Ahvenniemi, E; Karppinen, M

    2016-01-21

    Atomic/molecular layer deposition offers us an elegant way of fabricating crystalline copper(ii)terephthalate metal-organic framework (MOF) thin films on various substrate surfaces. The films are grown from two gaseous precursors with a digital atomic/molecular level control for the film thickness under relatively mild conditions in a simple and fast one-step process. PMID:26612265

  6. Molecular dynamics as observed with probes of different dimensions in thin polymer films

    NASA Astrophysics Data System (ADS)

    Zhao, Jiang; Zhang, Hao; Yang, Jingfa; Wang, Fuyi; Liu, Di

    Rotational motion of individual fluorescence molecules doped in thin films of poly vinylacetate (PVAc) was monitored by single molecule fluorescence de-focus microscopy. Perylendiimide and its derivatives of different dimension were chosen as probes for local dynamics. The results demonstrate that the local vibration mode detected by different molecules probe depends on dimension of the probes - the larger probes the lower frequency. The population of rotating probes is found to increase with temperature elevation, depending on the molecular dimension as well. The comparison of the results with thermo-dynamic measurements helps to shed new light on the physical picture of glass transition. Supported by MoST of China.

  7. Influence of molecular structure and microstructure on device performance of polycrystalline pentacene thin-film transistors

    NASA Astrophysics Data System (ADS)

    Cheng, Horng-Long; Mai, Yu-Shen; Chou, Wei-Yang; Chang, Li-Ren

    2007-04-01

    The authors have fabricated the pentacene thin films on polymethylmethacrylate (PMMA) and on silicon dioxide dielectric surfaces featuring similar surface energy and surface roughness. On both surfaces the pentacene films displayed high crystal quality from x-ray diffraction scans, although the film on PMMA had significantly smaller grain size. The pentacene transistors with PMMA exhibited excellent electrical characteristics, including high mobility of above 1.1cm2/Vs, on/off ratio above 106, and sharp subthreshold slope below 1V/decade. The analysis of molecular microstructure of the pentacene films provided a reasonable explanation for the high performance using resonance micro-Raman spectroscopy.

  8. Ion-beam assisted deposition of thin molybdenum films studied by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Robbemond, Arie; Thijsse, Barend J.

    1997-05-01

    We report results obtained by molecular dynamics simulation of low energy argon-ion assisted growth of thin molybdenum films (≈ 20 Å). The effects of a single ion impact are discussed, but more particularly we consider film growth from a manufacturing viewpoint and examine the properties of the completed films. Results for ion-beam assisted deposition are compared with those for unassisted growth (i.e. physical vapor deposition). Surface orientation, atomic displacements, surface roughness, sputtering, point defects, and the influence of off-normal atom incidence are discussed.

  9. Imaging the condensation and evaporation of molecularly thin ethanol films with surface forces apparatus

    SciTech Connect

    Zhao, Gutian; Tan, Qiyan; Xiang, Li; Zhang, Di; Ni, Zhonghua E-mail: yunfeichen@seu.edu.cn; Yi, Hong; Chen, Yunfei E-mail: yunfeichen@seu.edu.cn

    2014-01-15

    A new method for imaging condensation and evaporation of molecularly thin ethanol films is reported. It is found that the first adsorbed layer of ethanol film on mica surface behaves as solid like structure that cannot flow freely. With the increase of exposure time, more ethanol molecules condense over the mica surface in the saturated ethanol vapor condition. The first layer of adsorbed ethanol film is about 3.8 Å thick measured from the surface forces apparatus, which is believed to be the average diameter of ethanol molecules while they are confined in between two atomically smooth mica surfaces.

  10. Morphological Behavior of Thin Polyhedral Oligomeric Silsesquioxane Films at the Molecular Scale

    SciTech Connect

    G Evmenenko; B Stripe; P Dutta

    2011-12-31

    Synchrotron X-ray reflectivity (XRR) was used to study the structure of thin films of polyhedral oligomeric silsesquioxanes (POSS) with side organic chains of different flexibility and containing terminal epoxy groups. POSS films were deposited from volatile solvents on hydroxylated and hydrogen-passivated silicon surfaces. The XRR data show a variety of structural morphologies, including autophobic molecular monolayers and bilayers as well as uniform films. The role of conformational and energetic factors governing the development of different morphologies in a restricted geometry is discussed.

  11. Oxidation Products of Semi-volatile Alkanes by Hydroxyl Radicals

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Worton, D. R.; Nah, T.; Goldstein, A. H.; Wilson, K. R.

    2013-12-01

    Alkanes are ubiquitous in the atmosphere and are important components that influence atmospheric chemistry. Semi-volatile alkanes are partitioned between the gas- and the particle-phases and can be readily oxidized in both phases. Previous studies have demonstrated that reaction rates and the products of OH oxidation are very different for organic compounds in the gas- and particle phases. In the present study, n-octadecane (C18H38), n-eicosane (C20H42), n-docosane (C22H46), n-tricosane (C24H50), and n-pentadecylcyclohexane (C21H42) were chosen as model compounds for semi-volatile alkanes to examine their OH-initiated oxidation reactions in a flow tube reactor. OH exposure was varied in the experiments, equivalent to oxidation of up to one week in the atmosphere. Oxidation products were collected on filters and analyzed using two-dimensional gas chromatography coupled to a high-resolution time-of-flight electron impact ionization and vacuum ultraviolet photoionization mass spectrometer. Most of the oxygenated higher molecular weight isomers were separated and quantified. Our results suggest that aerosol samples formed in the n-octadecane experiment were more oxidized than the other model compounds (i.e., functionalization products with three oxygen atoms per molecule compared to two oxygen atoms per molecule) at similar OH exposures and aerosol mass loadings. This is likely due to the concentration of n-octadecane in the gas phase where oxidation is more rapid. We find that the first-generation gas-phase oxidation products quickly partition to the particle phase after which higher-generation oxidation likely occurs in the particle phase. Interestingly, functionalized carbonyl isomers for the normal alkanes were only observed on the 4 carbon positions closest to the molecule end in all cases, which is in contrast to structure-reactivity relationship (SRR) predictions for gas-phase reactions. For n-octadecane, the concentrations of first-generation functionalization

  12. Molecular doping for control of gate bias stress in organic thin film transistors

    SciTech Connect

    Hein, Moritz P. Lüssem, Björn; Jankowski, Jens; Tietze, Max L.; Riede, Moritz K.; Zakhidov, Alexander A.; Leo, Karl; Fraunhofer COMEDD, Maria-Reiche-Str. 2, 01109 Dresden

    2014-01-06

    The key active devices of future organic electronic circuits are organic thin film transistors (OTFTs). Reliability of OTFTs remains one of the most challenging obstacles to be overcome for broad commercial applications. In particular, bias stress was identified as the key instability under operation for numerous OTFT devices and interfaces. Despite a multitude of experimental observations, a comprehensive mechanism describing this behavior is still missing. Furthermore, controlled methods to overcome these instabilities are so far lacking. Here, we present the approach to control and significantly alleviate the bias stress effect by using molecular doping at low concentrations. For pentacene and silicon oxide as gate oxide, we are able to reduce the time constant of degradation by three orders of magnitude. The effect of molecular doping on the bias stress behavior is explained in terms of the shift of Fermi Level and, thus, exponentially reduced proton generation at the pentacene/oxide interface.

  13. Coexistence of spinodal instability and thermal nucleation in thin-film rupture: insights from molecular levels.

    PubMed

    Nguyen, Trung Dac; Fuentes-Cabrera, Miguel; Fowlkes, Jason D; Rack, Philip D

    2014-03-01

    Despite extensive investigation using hydrodynamic models and experiments over the past decades, there remain open questions regarding the origin of the initial rupture of thin liquid films. One of the reasons that makes it difficult to identify the rupture origin is the coexistence of two dewetting mechanisms, namely, thermal nucleation and spinodal instability, as observed in many experimental studies. Using a coarse-grained model and large-scale molecular dynamics simulations, we are able to characterize the very early stage of dewetting in nanometer-thick liquid-metal films wetting a solid substrate. We observe the features characteristic of both spinodal instability and thermal nucleation in the spontaneously dewetting films and show that these two macroscopic mechanisms share a common origin at molecular levels. PMID:24730848

  14. Coexistence of spinodal instability and thermal nucleation in thin-film rupture: Insights from molecular levels

    NASA Astrophysics Data System (ADS)

    Nguyen, Trung Dac; Fuentes-Cabrera, Miguel; Fowlkes, Jason D.; Rack, Philip D.

    2014-03-01

    Despite extensive investigation using hydrodynamic models and experiments over the past decades, there remain open questions regarding the origin of the initial rupture of thin liquid films. One of the reasons that makes it difficult to identify the rupture origin is the coexistence of two dewetting mechanisms, namely, thermal nucleation and spinodal instability, as observed in many experimental studies. Using a coarse-grained model and large-scale molecular dynamics simulations, we are able to characterize the very early stage of dewetting in nanometer-thick liquid-metal films wetting a solid substrate. We observe the features characteristic of both spinodal instability and thermal nucleation in the spontaneously dewetting films and show that these two macroscopic mechanisms share a common origin at molecular levels.

  15. Vacuum sublimed α ,ω-dihexylsexithiophene thin films: Correlating electronic structure and molecular orientation

    NASA Astrophysics Data System (ADS)

    Duhm, S.; Salzmann, I.; Koch, N.; Fukagawa, H.; Kataoka, T.; Hosoumi, S.; Nebashi, K.; Kera, S.; Ueno, N.

    2008-08-01

    In order to correlate the molecular orientation of organic thin films with charge injection barriers at organic/metal interfaces, the electronic structure and molecular orientation of vacuum sublimed thin films of α ,ω-dihexylsexithiophene (DH6T) on the substrates Ag(111), highly oriented pyrolytic graphite (HOPG), and tetratetracontane (TTC) precovered Ag(111) were investigated. Results from metastable atom electron spectroscopy, ultraviolet photoelectron spectroscopy, and x-ray diffraction were used to derive growth models (including molecular orientation and conformation) of DH6T on the different substrates. On Ag(111), DH6T exhibits a transition from lying molecules in the monolayer/bilayer range to almost standing upright molecules in multilayers. This is accompanied by a shift of the molecular energy levels to a lower binding energy by 0.65 eV with respect to the vacuum level. The unit cell of standing DH6T on lying DH6T on Ag(111) is estimated to be similar to the DH6T bulk phase. On HOPG, DH6T grows in the bulk phase with lying orientation, starting already from the monolayer coverage. DH6T on TTC precovered Ag(111) grows in an almost lying orientation and a conformation that allows a strong overlap of the hexyl chains of DH6T with the alkyl chains of TTC. In all cases, the electronic structure and, particulary, the ionization energy of DH6T is dependent on the orientation of DH6T, i.e., lying DH6T has higher ionization energy than standing DH6T.

  16. Measuring long chain alkanes in diesel engine exhaust by thermal desorption PTR-MS

    NASA Astrophysics Data System (ADS)

    Erickson, M. H.; Gueneron, M.; Jobson, B. T.

    2014-01-01

    A method using thermal desorption sampling and analysis by proton transfer reaction mass spectrometry (PTR-MS) to measure long chain alkanes (C12-C18) and other larger organics associated with diesel engine exhaust emissions is described. Long chain alkanes undergo dissociative proton transfer reactions forming a series of fragment ions with formula CnH2n+1. The PTR-MS is insensitive to n-alkanes less than C8 but displays an increasing sensitivity for larger alkanes. Fragment ion distribution and sensitivity is a function of drift conditions. At 80 Td the most abundant ion fragments from C10 to C16 n-alkanes were m/z 57, 71 and 85. The mass spectrum of gasoline and diesel fuel at 80 Td displayed ion group patterns that can be related to known fuel constituents, such as alkanes, alkylbenzenes and cycloalkanes, and other compound groups that are inferred from molecular weight distributions such as dihydronapthalenes and naphthenic monoaromatics. It is shown that thermal desorption sampling of gasoline and diesel engine exhausts at 80 Td allows for discrimination against volatile organic compounds, allowing for quantification of long chain alkanes from the abundance of CnH2n+1 fragment ions. The total abundance of long chain alkanes in diesel engine exhaust was measured to be similar to the total abundance of C1-C4 alkylbenzene compounds. The abundance patterns of compounds determined by thermal desorption sampling may allow for emission profiles to be developed to better quantify the relative contributions of diesel and gasoline exhaust emissions on organic compounds concentrations in urban air.

  17. Channel cracks in atomic-layer and molecular-layer deposited multilayer thin film coatings

    SciTech Connect

    Long, Rong; Dunn, Martin L.

    2014-06-21

    Metal oxide thin film coatings produced by atomic layer deposition have been shown to be an effective permeation barrier. The primary failure mode of such coatings under tensile loads is the propagation of channel cracks that penetrate vertically into the coating films. Recently, multi-layer structures that combine the metal oxide material with relatively soft polymeric layers produced by molecular layer deposition have been proposed to create composite thin films with desired properties, including potentially enhanced resistance to fracture. In this paper, we study the effects of layer geometry and material properties on the critical strain for channel crack propagation in the multi-layer composite films. Using finite element simulations and a thin-film fracture mechanics formalism, we show that if the fracture energy of the polymeric layer is lower than that of the metal oxide layer, the channel crack tends to penetrate through the entire composite film, and dividing the metal oxide and polymeric materials into thinner layers leads to a smaller critical strain. However, if the fracture energy of the polymeric material is high so that cracks only run through the metal oxide layers, more layers can result in a larger critical strain. For intermediate fracture energy of the polymer material, we developed a design map that identifies the optimal structure for given fracture energies and thicknesses of the metal oxide and polymeric layers. These results can facilitate the design of mechanically robust permeation barriers, an important component for the development of flexible electronics.

  18. Photoluminescence of localized excitons in ZnCdO thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wu, T. Y.; Huang, Y. S.; Hu, S. Y.; Lee, Y. C.; Tiong, K. K.; Chang, C. C.; Shen, J. L.; Chou, W. C.

    2016-07-01

    We have investigated the luminescence characteristics of Zn1-xCdxO thin films with different Cd contents grown by molecular beam epitaxy system. The temperature-dependent photoluminescence (PL) and excitation power-dependent PL spectra were measured to clarify the luminescence mechanisms of the Zn1-xCdxO thin films. The peak energy of the Zn1-xCdxO thin films with increasing the Cd concentration is observed as redshift and can be fitted by the quadratic function of alloy content. The broadened full-width at half-maximum (FWHM) estimated from the 15 K PL spectra as a function of Cd content shows a larger deviation between the experimental values and theoretical curve, which indicates that experimental FWHM values are affected not only by alloy compositional disorder but also by localized excitons occupying states in the tail of the density of states. The Urbach energy determined from an analysis of the lineshape of the low-energy side of the PL spectrum and the degree of localization effect estimated from the temperature-induced S-shaped PL peak position described an increasing mean exciton-localization effects in ZnCdO films with increasing the Cd content. In addition, the PL intensity and peak position as a function of excitation power are carried out to clarify the types of radiative recombination and the effects of localized exciton in the ZnCdO films with different Cd contents.

  19. Organic and inorganic-organic thin film structures by molecular layer deposition: A review.

    PubMed

    Sundberg, Pia; Karppinen, Maarit

    2014-01-01

    The possibility to deposit purely organic and hybrid inorganic-organic materials in a way parallel to the state-of-the-art gas-phase deposition method of inorganic thin films, i.e., atomic layer deposition (ALD), is currently experiencing a strongly growing interest. Like ALD in case of the inorganics, the emerging molecular layer deposition (MLD) technique for organic constituents can be employed to fabricate high-quality thin films and coatings with thickness and composition control on the molecular scale, even on complex three-dimensional structures. Moreover, by combining the two techniques, ALD and MLD, fundamentally new types of inorganic-organic hybrid materials can be produced. In this review article, we first describe the basic concepts regarding the MLD and ALD/MLD processes, followed by a comprehensive review of the various precursors and precursor pairs so far employed in these processes. Finally, we discuss the first proof-of-concept experiments in which the newly developed MLD and ALD/MLD processes are exploited to fabricate novel multilayer and nanostructure architectures by combining different inorganic, organic and hybrid material layers into on-demand designed mixtures, superlattices and nanolaminates, and employing new innovative nanotemplates or post-deposition treatments to, e.g., selectively decompose parts of the structure. Such layer-engineered and/or nanostructured hybrid materials with exciting combinations of functional properties hold great promise for high-end technological applications. PMID:25161845

  20. Growth of SrVO{sub 3} thin films by hybrid molecular beam epitaxy

    SciTech Connect

    Eaton, Craig; Brahlek, Matthew; Engel-Herbert, Roman; Moyer, Jarrett A.; Alipour, Hamideh M.; Grimley, Everett D.; LeBeau, James M.

    2015-11-15

    The authors report the growth of stoichiometric SrVO{sub 3} thin films on (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (001) substrates using hybrid molecular beam epitaxy. This growth approach employs a conventional effusion cell to supply elemental A-site Sr and the metalorganic precursor vanadium oxytriisopropoxide (VTIP) to supply vanadium. Oxygen is supplied in its molecular form through a gas inlet. An optimal VTIP:Sr flux ratio has been identified using reflection high-energy electron-diffraction, x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy, demonstrating stoichiometric SrVO{sub 3} films with atomically flat surface morphology. Away from the optimal VTIP:Sr flux, characteristic changes in the crystalline structure and surface morphology of the films were found, enabling identification of the type of nonstoichiometry. For optimal VTIP:Sr flux ratios, high quality SrVO{sub 3} thin films were obtained with smallest deviation of the lattice parameter from the ideal value and with atomically smooth surfaces, indicative of the good cation stoichiometry achieved by this growth technique.

  1. Organic and inorganic–organic thin film structures by molecular layer deposition: A review

    PubMed Central

    Sundberg, Pia

    2014-01-01

    Summary The possibility to deposit purely organic and hybrid inorganic–organic materials in a way parallel to the state-of-the-art gas-phase deposition method of inorganic thin films, i.e., atomic layer deposition (ALD), is currently experiencing a strongly growing interest. Like ALD in case of the inorganics, the emerging molecular layer deposition (MLD) technique for organic constituents can be employed to fabricate high-quality thin films and coatings with thickness and composition control on the molecular scale, even on complex three-dimensional structures. Moreover, by combining the two techniques, ALD and MLD, fundamentally new types of inorganic–organic hybrid materials can be produced. In this review article, we first describe the basic concepts regarding the MLD and ALD/MLD processes, followed by a comprehensive review of the various precursors and precursor pairs so far employed in these processes. Finally, we discuss the first proof-of-concept experiments in which the newly developed MLD and ALD/MLD processes are exploited to fabricate novel multilayer and nanostructure architectures by combining different inorganic, organic and hybrid material layers into on-demand designed mixtures, superlattices and nanolaminates, and employing new innovative nanotemplates or post-deposition treatments to, e.g., selectively decompose parts of the structure. Such layer-engineered and/or nanostructured hybrid materials with exciting combinations of functional properties hold great promise for high-end technological applications. PMID:25161845

  2. Molecular orientation dependence of hole-injection barrier in pentacene thin film on the Au surface in organic thin film transistor

    NASA Astrophysics Data System (ADS)

    Ihm, Kyuwook; Kim, Bongsoo; Kang, Tai-Hee; Kim, Ki-Jeong; Joo, Min Ho; Kim, Tae Hyeong; Yoon, Sang Soo; Chung, Sukmin

    2006-07-01

    We have investigated the effects of a buffer layer insertion on the performance of the pentacene based thin film transistor with a bottom contact structure. When the pentacene molecules have a standing up coordination on the Au surface that is modified by the benzenethiol or methanethiol, the transition region in the pentacene thin film is removed along the boundary between the Au and silicon oxide region, and the hole-injection barrier decreases by 0.4eV. Pentacene on various surfaces showed that the highly occupied molecular level is 0.2-0.4eV lower in the standing up coordination than in the lying down coordination.

  3. Apparatus for producing ultraclean bicrystals by the molecular beam epitaxy growth and ultrahigh vacuum bonding of thin films

    SciTech Connect

    Amiri-Hezaveh, A.; Balluffi, R.W. )

    1993-10-01

    An apparatus has been designed and constructed which is capable of growing single-crystal thin films and then bonding them together face-to-face to produce bicrystals under ultrahigh vacuum (UHV) conditions. The films are grown in molecular beam epitaxy (MBE) system capable of growing well-characterized single-crystal thin films of metals, semiconductors, and high [ital T][sub [ital c

  4. Solar Selective Coatings Prepared From Thin-Film Molecular Mixtures and Evaluated

    NASA Technical Reports Server (NTRS)

    Jaworske, Don A.

    2003-01-01

    Thin films composed of molecular mixtures of metal and dielectric are being considered for use as solar selective coatings for a variety of space power applications. By controlling molecular mixing during ion-beam sputter deposition, researchers can tailor the solar selective coatings to have the combined properties of high solar absorptance and low infrared emittance. On orbit, these combined properties simultaneously maximize the amount of solar energy captured by the coating and minimize the amount of thermal energy radiated. The solar selective coatings are envisioned for use on minisatellites, for applications where solar energy is used to power heat engines or to heat remote regions in the interior of the spacecraft. Such systems may be useful for various missions, particularly those to middle Earth orbit. Sunlight must be concentrated by a factor of 100 or more to achieve the desired heat inlet operating temperature. At lower concentration factors, the temperature of the heat inlet surface of the heat engine is too low for efficient operation, and at high concentration factors, cavity type heat receivers become attractive. The an artist's concept of a heat engine, with the annular heat absorbing surface near the focus of the concentrator coated with a solar selective coating is shown. In this artist's concept, the heat absorbing surface powers a small Stirling convertor. The astronaut's gloved hand is provided for scale. Several thin-film molecular mixtures have been prepared and evaluated to date, including mixtures of aluminum and aluminum oxide, nickel and aluminum oxide, titanium and aluminum oxide, and platinum and aluminum oxide. For example, a 2400- Angstrom thick mixture of titanium and aluminum oxide was found to have a solar absorptance of 0.93 and an infrared emittance of 0.06. On the basis of tests performed under flowing nitrogen at temperatures as high as 680 C, the coating appeared to be durable at elevated temperatures. Additional durability

  5. Supported organoiridium catalysts for alkane dehydrogenation

    DOEpatents

    Baker, R. Thomas; Sattelberger, Alfred P.; Li, Hongbo

    2013-09-03

    Solid supported organoiridium catalysts, a process for preparing such solid supported organoiridium catalysts, and the use of such solid supported organoiridium catalysts in dehydrogenation reactions of alkanes is provided. The catalysts can be easily recovered and recycled.

  6. High-temperature antiferromagnetism in molecular semiconductor thin films and nanostructures

    PubMed Central

    Serri, Michele; Wu, Wei; Fleet, Luke R.; Harrison, Nicholas M.; Hirjibehedin, Cyrus F.; Kay, Christopher W.M.; Fisher, Andrew J.; Aeppli, Gabriel; Heutz, Sandrine

    2014-01-01

    The viability of dilute magnetic semiconductors in applications is linked to the strength of the magnetic couplings, and room temperature operation is still elusive in standard inorganic systems. Molecular semiconductors are emerging as an alternative due to their long spin-relaxation times and ease of processing, but, with the notable exception of vanadium-tetracyanoethylene, magnetic transition temperatures remain well below the boiling point of liquid nitrogen. Here we show that thin films and powders of the molecular semiconductor cobalt phthalocyanine exhibit strong antiferromagnetic coupling, with an exchange energy reaching 100 K. This interaction is up to two orders of magnitude larger than in related phthalocyanines and can be obtained on flexible plastic substrates, under conditions compatible with routine organic electronic device fabrication. Ab initio calculations show that coupling is achieved via superexchange between the singly occupied a1g () orbitals. By reaching the key milestone of magnetic coupling above 77 K, these results establish quantum spin chains as a potentially useable feature of molecular films. PMID:24445992

  7. High-temperature antiferromagnetism in molecular semiconductor thin films and nanostructures.

    PubMed

    Serri, Michele; Wu, Wei; Fleet, Luke R; Harrison, Nicholas M; Hirjibehedin, Cyrus F; Kay, Christopher W M; Fisher, Andrew J; Aeppli, Gabriel; Heutz, Sandrine

    2014-01-01

    The viability of dilute magnetic semiconductors in applications is linked to the strength of the magnetic couplings, and room temperature operation is still elusive in standard inorganic systems. Molecular semiconductors are emerging as an alternative due to their long spin-relaxation times and ease of processing, but, with the notable exception of vanadium-tetracyanoethylene, magnetic transition temperatures remain well below the boiling point of liquid nitrogen. Here we show that thin films and powders of the molecular semiconductor cobalt phthalocyanine exhibit strong antiferromagnetic coupling, with an exchange energy reaching 100 K. This interaction is up to two orders of magnitude larger than in related phthalocyanines and can be obtained on flexible plastic substrates, under conditions compatible with routine organic electronic device fabrication. Ab initio calculations show that coupling is achieved via superexchange between the singly occupied a1g () orbitals. By reaching the key milestone of magnetic coupling above 77 K, these results establish quantum spin chains as a potentially useable feature of molecular films. PMID:24445992

  8. Evaporation characteristics of thin film liquid argon in nano-scale confinement: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Hasan, Mohammad Nasim; Shavik, Sheikh Mohammad; Rabbi, Kazi Fazle; Haque, Mominul

    2016-07-01

    Molecular dynamics simulation has been carried out to explore the evaporation characteristics of thin liquid argon film in nano-scale confinement. The present study has been conducted to realize the nano-scale physics of simultaneous evaporation and condensation inside a confined space for a three phase system with particular emphasis on the effect of surface wetting conditions. The simulation domain consisted of two parallel platinum plates; one at the top and another at the bottom. The fluid comprised of liquid argon film at the bottom plate and vapor argon in between liquid argon and upper plate of the domain. Considering hydrophilic and hydrophobic nature of top and bottom surfaces, two different cases have been investigated: (i) Case A: Both top and bottom surfaces are hydrophilic, (ii) Case B: both top and bottom surfaces are hydrophobic. For all cases, equilibrium molecular dynamics (EMD) was performed to reach equilibrium state at 90 K. Then the lower wall was set to four different temperatures such as 110 K, 120 K, 130 K and 140 K to perform non-equilibrium molecular dynamics (NEMD). The variation of temperature and density as well as the variation of system pressure with respect to time were closely monitored for each case. The heat fluxes normal to top and bottom walls were estimated and discussed to illuminate the effectiveness of heat transfer in both hydrophilic and hydrophobic confinement at various boundary temperatures of the bottom plate.

  9. Solar photothermochemical alkane reverse combustion.

    PubMed

    Chanmanee, Wilaiwan; Islam, Mohammad Fakrul; Dennis, Brian H; MacDonnell, Frederick M

    2016-03-01

    A one-step, gas-phase photothermocatalytic process for the synthesis of hydrocarbons, including liquid alkanes, aromatics, and oxygenates, with carbon numbers (Cn) up to C13, from CO2 and water is demonstrated in a flow photoreactor operating at elevated temperatures (180-200 °C) and pressures (1-6 bar) using a 5% cobalt on TiO2 catalyst and under UV irradiation. A parametric study of temperature, pressure, and partial pressure ratio revealed that temperatures in excess of 160 °C are needed to obtain the higher Cn products in quantity and that the product distribution shifts toward higher Cn products with increasing pressure. In the best run so far, over 13% by mass of the products were C5+ hydrocarbons and some of these, i.e., octane, are drop-in replacements for existing liquid hydrocarbons fuels. Dioxygen was detected in yields ranging between 64% and 150%. In principle, this tandem photochemical-thermochemical process, fitted with a photocatalyst better matched to the solar spectrum, could provide a cheap and direct method to produce liquid hydrocarbons from CO2 and water via a solar process which uses concentrated sunlight for both photochemical excitation to generate high-energy intermediates and heat to drive important thermochemical carbon-chain-forming reactions. PMID:26903631

  10. Solar photothermochemical alkane reverse combustion

    PubMed Central

    Chanmanee, Wilaiwan; Islam, Mohammad Fakrul; Dennis, Brian H.; MacDonnell, Frederick M.

    2016-01-01

    A one-step, gas-phase photothermocatalytic process for the synthesis of hydrocarbons, including liquid alkanes, aromatics, and oxygenates, with carbon numbers (Cn) up to C13, from CO2 and water is demonstrated in a flow photoreactor operating at elevated temperatures (180–200 °C) and pressures (1–6 bar) using a 5% cobalt on TiO2 catalyst and under UV irradiation. A parametric study of temperature, pressure, and partial pressure ratio revealed that temperatures in excess of 160 °C are needed to obtain the higher Cn products in quantity and that the product distribution shifts toward higher Cn products with increasing pressure. In the best run so far, over 13% by mass of the products were C5+ hydrocarbons and some of these, i.e., octane, are drop-in replacements for existing liquid hydrocarbons fuels. Dioxygen was detected in yields ranging between 64% and 150%. In principle, this tandem photochemical–thermochemical process, fitted with a photocatalyst better matched to the solar spectrum, could provide a cheap and direct method to produce liquid hydrocarbons from CO2 and water via a solar process which uses concentrated sunlight for both photochemical excitation to generate high-energy intermediates and heat to drive important thermochemical carbon-chain-forming reactions. PMID:26903631

  11. Metathesis of alkanes and related reactions.

    PubMed

    Basset, Jean-Marie; Copéret, Christophe; Soulivong, Daravong; Taoufik, Mostafa; Cazat, Jean Thivolle

    2010-02-16

    The transformation of alkanes remains a difficult challenge because of the relative inertness of the C-H and C-C bonds. The rewards for asserting synthetic control over unfunctionalized, saturated hydrocarbons are considerable, however, because converting short alkanes into longer chain analogues is usually a value-adding process. Alkane metathesis is a novel catalytic and direct transformation of two molecules of a given alkane into its lower and higher homologues; moreover, the process proceeds at relatively low temperature (ambient conditions or higher). It was discovered through the use of a silica-supported tantalum hydride, ([triple bond]SiO)(2)TaH, a multifunctional catalyst with a single site of action. This reaction completes the story of the metathesis reactions discovered over the past 40 years: olefin metathesis, alkyne metathesis, and ene-yne cyclizations. In this Account, we examine the fundamental mechanistic aspects of alkane metathesis as well as the novel reactions that have been derived from its study. The silica-supported tantalum hydride catalyst was developed as the result of systematic and meticulous studies of the interaction between oxide supports and organometallic complexes, a field of study denoted surface organometallic chemistry (SOMC). A careful examination of this surface-supported tantalum hydride led to the later discovery of alumina-supported tungsten hydride, W(H)(3)/Al(2)O(3), which proved to be an even better catalyst for alkane metathesis. Supported tantalum and tungsten hydrides are highly unsaturated, electron-deficient species that are very reactive toward the C-H and C-C bonds of alkanes. They show a great versatility in various other reactions, such as cross-metathesis between methane and alkanes, cross-metathesis between toluene and ethane, or even methane nonoxidative coupling. Moreover, tungsten hydride exhibits a specific ability in the transformation of isobutane into 2,3-dimethylbutane as well as in the metathesis

  12. Self-Limiting Growth of Metal Fluoride Thin Films by Oxidation Reactions Employing Molecular Precursors

    SciTech Connect

    Qiu, S. R.; Lai, H.-F.; Yarmoff, J. A.

    2000-08-14

    FeF{sub 2} films are grown by the reaction of XeF{sub 2} and SeF{sub 6} with iron foil. The growth initially follows the Mott-Cabrera parabolic rate law, indicating that the process is diffusion limited. At a certain film thickness, however, the growth abruptly stops, with the thickness using XeF{sub 2} being nearly double that with SeF{sub 6} . It is suggested that the shutdown is due to the inability of the molecules to dissociate when too far from the substrate and that SeF{sub 6} must approach more closely than XeF{sub 2} . This work suggests the use of molecular precursors to grow thin films via a self-limiting chemical process. (c) 2000 The American Physical Society.

  13. Improved Stability Of Amorphous Zinc Tin Oxide Thin Film Transistors Using Molecular Passivation

    SciTech Connect

    Rajachidambaram, Meena Suhanya; Pandey, Archana; Vilayur Ganapathy, Subramanian; Nachimuthu, Ponnusamy; Thevuthasan, Suntharampillai; Herman, Gregory S.

    2013-10-21

    The role of back channel surface chemistry on amorphous zinc tin oxide (ZTO) bottom gate thin film transistors (TFT) have been characterized by positive bias-stress measurements and x-ray photoelectron spectroscopy. Positive bias-stress turn-on voltage shifts for ZTO-TFTs were significantly reduced by passivation of back channel surfaces with self-assembled monolayers of n-hexylphosphonic acid (n-HPA) when compared to ZTO-TFTs with no passivation. These results indicate that adsorption of molecular species on exposed back channel of ZTO-TFTs strongly influence observed turn-on voltage shifts, as opposed to charge injection into the dielectric or trapping due to oxygen vacancies.

  14. Epitaxial Cd3As2 Thin Films Synthesized by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Schumann, Timo; Goyal, Manik; Stemmer, Susanne

    Cd3As2 is a three-dimensional (3D) Dirac semimetal, i.e. it possesses Dirac cones in a 3D bulk state where the band dispersion relation is linear near the Fermi energy. Cd3As2 is has raised considerable interest due to its high electron mobilities in bulk crystals and for novel quantum phenomena, such as chiral anomalies. However, few studies have been performed using thin films of Cd3As2. In this presentation, we report on the synthesis of Cd3As2 thin films by molecular beam epitaxy (MBE). Single phase, epitaxial films were grown on undoped GaSb(111)B substrates with the (112) facet of Cd3As2 parallel to the GaSb(111) surface. We report on the structural quality and orientation variants in the films. Electrical transport properties indicate electron mobilities exceeding 6000 cm2V-1s-1. We discuss the impact of the MBE growth parameters and substrate preparation on the structural and electrical properties of the films.

  15. Molecular Layer-seeded Ultra-thin Top-gate Dielectrics for High Transconductance Graphene Transistors

    NASA Astrophysics Data System (ADS)

    Sangwan, Vinod; Jariwala, Deep; Karmel, Hunter; Alaboson, Justice; Lauhon, Lincoln; Marks, Tobin; Hersam, Mark

    2012-02-01

    The potential of graphene in integrated analog and digital circuits can only be fully realized through incorporation of ultra-thin gate dielectrics to enable large-scale small-channel graphene field-effect transistors (GFETs). Atomic-layer deposition (ALD) is a viable technique to fabricate gate-dielectrics, however, it requires a seeding layer on otherwise inert graphene. Here, we demonstrate a single molecule thick perylene-3,4,9,10-tetracarboxylic dianhydride overlayer as an effective seeding layer to grow high-κ Al2O3 on mechanically exfoliated graphene for high-performance GFETs. Using an ultra-thin (< 1nm) seeding layer, in contrast to polymer films (5-10 nm), we demonstrate fabrication of the thinnest ALD-grown gate-dielectric (4 nm) reported to date in top-gated GFETs. This yields high performance GFETs with the intrinsic transconductance parameter approaching 2.4 mS and the field-effect mobility ˜3000 cm^2/Vs. We also demonstrate generalization of this molecular layer seeded-ALD growth method to higher- κ gate dielectrics, yielding further enhanced GFET transconductance for possible application to radio-frequency circuits.

  16. Coherent growth of superconducting TiN thin films by plasma enhanced molecular beam epitaxy

    SciTech Connect

    Krockenberger, Yoshiharu; Karimoto, Shin-ichi; Yamamoto, Hideki; Semba, Kouich

    2012-10-15

    We have investigated the formation of titanium nitride (TiN) thin films on (001) MgO substrates by molecular beam epitaxy and radio frequency acitvated nitrogen plasma. Although cubic TiN is stabile over a wide temperature range, superconducting TiN films are exclusively obtained when the substrate temperature exceeds 710 Degree-Sign C. TiN films grown at 720 Degree-Sign C show a high residual resistivity ratio of approximately 11 and the superconducting transition temperature (T{sub c}) is well above 5 K. Superconductivity has been confirmed also by magnetiztion measurements. In addition, we determined the upper critical magnetic field ({mu}{sub 0}H{sub c2}) as well as the corresponding coherence length ({xi}{sub GL}) by transport measurements under high magnetic fields. High-resolution transmission electron microscopy data revealed full in plane coherency to the substrate as well as a low defect density in the film, in agreement with a mean-free path length Script-Small-L Almost-Equal-To 106 nm, which is estimated from the residual resistivity value. The observations of reflection high energy electron diffraction intensity oscillations during the growth, distinct Laue fringes around the main Bragg peaks, and higher order diffraction spots in the reciprocal space map suggest the full controlability of the thickness of high quality superconducting TiN thin films.

  17. Nanometric thin polymeric films based on molecularly imprinted technology: towards electrochemical sensing applications.

    PubMed

    Ginzburg-Turgeman, Roni; Mandler, Daniel

    2010-09-28

    A new approach for assembling selective electrodes based on molecularly imprinted polymers (MIPs) is presented. The approach is based on the radical polymerization of a mixture of methacrylic acid (MAA) and ethyleneglycol dimethacrylate (EGDMA) in the presence of an initiator, benzoyl peroxide (BPO) and an activator, N,N'-dimethyl-p-toluidine (DMpT) at room temperature and atmospheric pressure. To form nanometric thin polymeric films the polymerization solution was spin-coated in the course of polymerization. The different physical and chemical parameters that affected the properties of the films, such as the spinning rate and the EGDMA:MAA ratio, were studied and optimized. A variety of techniques, e.g., rheoscopy, SEM, AFM, profilometry and electrochemistry, were used to characterize the films and the polymerization process. By optimizing the conditions very thin and reproducible films could be prepared and imprinted. The electrochemical behavior of the films showed that they were permeable to water-soluble electroactive species providing that either polyethylene glycol or template species were added to the polymerization mixture. Finally, we demonstrated that films imprinted with ferrocenylmethyl alcohol (Fc-MeOH) successfully extracted the imprinted species after their removal from MIPs. PMID:20668737

  18. Growth Parameters for Thin Film InBi Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Keen, B.; Makin, R.; Stampe, P. A.; Kennedy, R. J.; Sallis, S.; Piper, L. J.; McCombe, B.; Durbin, S. M.

    2014-04-01

    The alloying of bismuth with III-V semiconductors, in particular GaAs and InAs thin films grown by molecular beam epitaxy (MBE), has attracted considerable interest due to the accompanying changes in band structure and lattice constant. Specifically, bismuth incorporation in these compounds results in both a reduction in band gap (through shifting of the valence band) and an increase in the lattice constant of the alloy. To fully understand the composition of these alloys, a better understanding of the binary endpoints is needed. At present, a limited amount of literature exists on the III-Bi family of materials, most of which is theoretical work based on density functional theory calculations. The only III-Bi material known to exist (in bulk crystal form) is InBi, but its electrical properties have not been sufficiently studied and, to date, the material has not been fabricated as a thin film. We have successfully deposited crystalline InBi on (100) GaAs substrates using MBE. Wetting of the substrate is poor, and regions of varying composition exist across the substrate. To obtain InBi, the growth temperature had to be below 100 °C. It was found that film crystallinity improved with reduced Bi flux, into an In-rich regime. Additionally, attempts were made to grow AlBi and GaBi.

  19. Multiferroic fluoride BaCoF4 Thin Films Grown Via Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Borisov, Pavel; Johnson, Trent; García-Castro, Camilo; Kc, Amit; Schrecongost, Dustin; Cen, Cheng; Romero, Aldo; Lederman, David

    Multiferroic materials exhibit exciting physics related to the simultaneous presence of multiple long-range orders, in many cases consisting of antiferromagnetic (AF) and ferroelectric (FE) orderings. In order to provide a new, promising route for fluoride-based multiferroic material engineering, we grew multiferroic fluoride BaCoF4 in thin film form on Al2O3 (0001) substrates by molecular beam epitaxy. The films grow with the orthorhombic b-axis out-of-plane and with three in-plane structural twin domains along the polar c-axis directions. The FE ordering in thin films was verified by FE remanent hysteresis loops measurements at T = 14 K and by room temperature piezoresponse force microscopy (PFM). An AF behavior was found below Neel temperature TN ~ 80 K, which is in agreement with the bulk properties. At lower temperatures two additional magnetic phase transitions at 19 K and 41 K were found. First-principles calculations demonstrated that the growth strain applied to the bulk BaCoF4 indeed favors two canted spin orders, along the b- and a-axes, respectively, in addition to the main AF spin order along the c-axis. Supported by FAME (Contract 2013-MA-2382), WV Research Challenge Grant (HEPC.dsr.12.29), and DMREF-NSF 1434897.

  20. Highly Ordered Organic Molecular Thin Films on Silicon Studied by STM and LEED

    NASA Astrophysics Data System (ADS)

    Wagner, Sean; Zhang, Pengpeng

    2014-03-01

    Achieving growth of long-range ordered organic molecular thin films on inorganic substrates continues to be a significant challenge for organic electronics applications. Here, we report the growth of highly ordered zinc phthalocyanine (ZnPc) thin films both in-plane and out-of-plane on the deactivated Si(111) surface by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). By adjusting the substrate temperature during deposition, the anisotropic step-flow growth mode can be accessed causing a reduction in the substrate symmetry which allows for the long-range in-plane ordering as well as the decrease of grain boundary density. Additionally, the ZnPc molecules are able to maintain a highly ordered configuration in multi-layers despite a gradual decrease in the molecule-substrate interaction, which is attributed to the strong interlayer π- π interaction. We appreciate the fruitful discussion with Prof. Richard Lunt. This research is funded by the DOE Office of Science Early Career Research Program (Grant number DE-SC0006400) through the Office of Basic Energy Sciences.

  1. Thin film growth of CaFe2As2 by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hatano, T.; Kawaguchi, T.; Fujimoto, R.; Nakamura, I.; Mori, Y.; Harada, S.; Ujihara, T.; Ikuta, H.

    2016-01-01

    Film growth of CaFe2As2 was realized by molecular beam epitaxy on six different substrates that have a wide variation in the lattice mismatch to the target compound. By carefully adjusting the Ca-to-Fe flux ratio, we obtained single-phase thin films for most of the substrates. Interestingly, an expansion of the CaFe2As2 lattice to the out-of-plane direction was observed for all films, even when an opposite strain was expected. A detailed microstructure observation of the thin film grown on MgO by transmission electron microscope revealed that it consists of cube-on-cube and 45°-rotated domains. The latter domains were compressively strained in plane, which caused a stretching along the c-axis direction. Because the domains were well connected across the boundary with no appreciable discontinuity, we think that the out-of-plane expansion in the 45°-rotated domains exerted a tensile stress on the other domains, resulting in the unexpectedly large c-axis lattice parameter, despite the apparently opposite lattice mismatch.

  2. Molecular separations using nanostructured porous thin films fabricated by glancing angle deposition

    NASA Astrophysics Data System (ADS)

    Bezuidenhout, Louis Wentzel

    Biomolecular separation techniques are an enabling technology that indirectly in.uence many aspects of our lives. Advances have led to faster analyses, reduced costs, higher specificity, and new analytical techniques, impacting areas such as health care, environmental monitoring, polymer sciences, agriculture, and nutrition. Further development of separations technology is anticipated to follow the path of computing technology such that miniaturization through the development of microfluidics technology, lab-on-a-chip systems, and other integrative, multi-component systems will further extend our analysis capabilities. Creation of new and improvement of existing separation technologies is an integral part of the pathway to miniaturized systems. the work of this thesis investigates molecular separations using porous nanostructured films fabricated by the thin film process glancing angle deposition (GLAD). Structural architecture, pore size and shape, and film density can be finely controlled to produce high-surface area thin films with engineered morphology. The characteristic size scales and structural control of GLAD films are well-suited to biomolecules and separation techniques, motivating investigation into the utility and performance of GLAD films for biomolecular separations. This project consisted of three phases. First, chromatographic separation of dye molecules on silica GLAD films was demonstrated by thin layer chromatography Direct control of film nanostructure altered the separation characteristics; most strikingly, anisotropic structures provided two-dimensional analyte migration. Second, nanostructures made with GLAD were integrated in PDMS microfluidic channels using a sacrificial etching process; DNA molecules (10/48 kbp and 6/10/20 kbp mixtures) were electrophoretically separated on a microfluidic chip using a porous bed of SiO2 vertical posts. Third, mass spectrometry of proteins and drugs in the mass range of 100-1300 m/z was performed using

  3. Mass effect on the Soret coefficient in n-alkane mixtures.

    PubMed

    Alonso de Mezquia, David; Bou-Ali, M Mounir; Madariaga, J Antonio; Santamaría, Carlos

    2014-02-28

    We have determined the Soret coefficient of different equimolar and non equimolar n-alkane mixtures from measurements of the molecular diffusion and thermal diffusion coefficients. It is shown that equimolar mixtures behave as isotopic-like mixtures in which only the mass effect contributes to the Soret effect. In non equimolar mixtures, a small linear dependence with the molar fraction is observed. Finally, we have obtained a new correlation, which allows the determination of the Soret coefficient of n-alkane mixtures using the data of viscosity, the thermal expansion coefficient of the pure components, and the density of the equimolar mixture. PMID:24588181

  4. Invertebrate muscles: thin and thick filament structure; molecular basis of contraction and its regulation, catch and asynchronous muscle

    PubMed Central

    Hooper, Scott L.; Hobbs, Kevin H.; Thuma, Jeffrey B.

    2008-01-01

    This is the second in a series of canonical reviews on invertebrate muscle. We cover here thin and thick filament structure, the molecular basis of force generation and its regulation, and two special properties of some invertebrate muscle, catch and asynchronous muscle. Invertebrate thin filaments resemble vertebrate thin filaments, although helix structure and tropomyosin arrangement show small differences. Invertebrate thick filaments, alternatively, are very different from vertebrate striated thick filaments and show great variation within invertebrates. Part of this diversity stems from variation in paramyosin content, which is greatly increased in very large diameter invertebrate thick filaments. Other of it arises from relatively small changes in filament backbone structure, which results in filaments with grossly similar myosin head placements (rotating crowns of heads every 14.5 nm) but large changes in detail (distances between heads in azimuthal registration varying from three to thousands of crowns). The lever arm basis of force generation is common to both vetebrates and invertebrates, and in some invertebrates this process is understood on the near atomic level. Invertebrate actomyosin is both thin (tropomyosin:troponin) and thick (primarily via direct Ca++ binding to myosin) filament regulated, and most invertebrate muscles are dually regulated. These mechanisms are well understood on the molecular level, but the behavioral utility of dual regulation is less so. The phosphorylation state of the thick filament associated giant protein, twitchin, has been recently shown to be the molecular basis of catch. The molecular basis of the stretch activation underlying asynchronous muscle activity, however, remains unresolved. PMID:18616971

  5. Molecular beam epitaxy deposition of Gd2O3 thin films on SrTiO3 (100) substrate

    NASA Astrophysics Data System (ADS)

    Wang, Jinxing; Hao, Jinghua; Zhang, Yangyang; Wei, Hongmei; Mu, Juyi

    2016-06-01

    Gd2O3 thin films are grown on the SrTiO3 (100) substrate by molecular beam epitaxy (MBE) deposition. X-ray diffraction (XRD) analysis, conventional transmission electron microscopy (TEM) and aberration-corrected scanning transmission electron microscopy (STEM) are performed to investigate the microstructure of deposited thin films. It is found that the as-deposited thin film possesses a very uniform thickness of ∼40 nm and is composed of single cubic phase Gd2O3 grains. STEM and TEM observations reveal that Gd2O3 thin film grows epitaxially on the SrTiO3 (100) substrate with (001)Gd2O3//(100)STO and [110]Gd2O3//[001]STO orientations. Furthermore, the Gd atoms are found to diffuse into the SrTiO3 substrate for a depth of one unit cell and substitute for the Sr atoms near the interface.

  6. Phases, line tension and pattern formation in molecularly thin films at the air-water interface

    NASA Astrophysics Data System (ADS)

    Mandal, Pritam

    A Langmuir film, which is a molecularly thin insoluble film on a liquid substrate, is one practical realization of a quasi-two dimensional matter. The major advantages of this system for the study of phase separation and phase co-existence are (a) it allows accurate control of the components and molecular area of the film and (b) it can be studied by various methods that require very flat films. Phase separation in molecularly thin films plays an important role in a range of systems from biomembranes to biosensors. For example, phase-separated lipid nano-domains in biomembranes are thought to play crucial roles in membrane function. I use Brewster Angel Microscopy (BAM) coupled with Fluorescence Microscopy (FM) and static Light Scattering Microscopy (LSM) to image phases and patterns within Langmuir films. The three microscopic techniques --- BAM, FM and LSM --- are complimentary to each other, providing distinct sets of information. They allow direct comparison with literature results in lipid systems. I have quantitatively validated the use of detailed hydrodynamic simulations to determine line tension in monolayers. Line tension decreases as temperature rises. This decrease gives us information on the entropy associated with the line, and thus about line structure. I carefully consider the thermodynamics of line energy and entropy to make this connection. In the longer run, LSM will be exploited to give us further information about line structure. I have also extended the technique by testing it on domains within the curved surface of a bilayer vesicle. I also note that in the same way that the presence of surface-active agents, known as surfactants, affects surface energy, the addiction of line active agents alters the inter-phase line energy. Thus my results set to stage to systematically study the influence of line active agents ---'linactants' --- on the inter-phase line energy. Hierarchal self-assembled chiral patterns were observed as a function of

  7. The synergetic effect of starch and alpha amylase on the biodegradation of n-alkanes.

    PubMed

    Karimi, M; Biria, D

    2016-06-01

    The impact of adding soluble starch on biodegradation of n-alkanes (C10-C14) by Bacillus subtilis TB1 was investigated. Gas chromatography was employed to measure the residual hydrocarbons in the system. It was observed that the efficiency of biodegradation improved with the presence of starch and the obtained residual hydrocarbons in the system were 53% less than the samples without starch. The produced bacterial enzymes were studied through electrophoresis and reverse zymography for explaining the observations. The results indicated that the produced amylase by the bacteria can degrade hydrocarbons and the same was obtained by the application of a commercial alpha amylase sample. In addition, in silico docking of alpha-amylase with n-alkanes with different molecular weights was studied by Molegro virtual docker which showed high negative binding energies and further substantiated the experimental observations. Overall, the findings confirmed the catalytic effect of alpha amylase on n-alkanes degradation. PMID:26971168

  8. Catalytic dehydroaromatization of n-alkanes by pincer-ligated iridium complexes

    NASA Astrophysics Data System (ADS)

    Ahuja, Ritu; Punji, Benudhar; Findlater, Michael; Supplee, Carolyn; Schinski, William; Brookhart, Maurice; Goldman, Alan S.

    2011-02-01

    Aromatic hydrocarbons are among the most important building blocks in the chemical industry. Benzene, toluene and xylenes are obtained from the high temperature thermolysis of alkanes. Higher alkylaromatics are generally derived from arene-olefin coupling, which gives branched products—that is, secondary alkyl arenes—with olefins higher than ethylene. The dehydrogenation of acyclic alkanes to give alkylaromatics can be achieved using heterogeneous catalysts at high temperatures, but with low yields and low selectivity. We present here the first catalytic conversion of n-alkanes to alkylaromatics using homogeneous or molecular catalysts—specifically ‘pincer’-ligated iridium complexes—and olefinic hydrogen acceptors. For example, the reaction of n-octane affords up to 86% yield of aromatic product, primarily o-xylene and secondarily ethylbenzene. In the case of n-decane and n-dodecane, the resulting alkylarenes are exclusively unbranched (that is, n-alkyl-substituted), with selectivity for the corresponding o-(n-alkyl)toluene.

  9. Molecular dynamic simulations of surface morphology and pulsed laser deposition growth of lithium niobate thin films on silicon substrate

    NASA Astrophysics Data System (ADS)

    Liu, Yue; Zhu, Hao-Nan; Pei, Zi-Dong; Kong, Yong-Fa; Xu, Jing-Jun

    2015-05-01

    The molecular dynamic simulation of lithium niobate thin films deposited on silicon substrate is carried out by using the dissipative particle dynamics method. The simulation results show that the Si (111) surface is more suitable for the growth of smooth LiNbO3 thin films compared to the Si(100) surface, and the optimal deposition temperature is around 873 K, which is consistent with the atomic force microscope results. In addition, the calculation molecular number is increased to take the electron spins and other molecular details into account. Project supported by the National Basic Research Program of China (Grant No. 2011CB922003), the International S&T Cooperation Program of China (Grant No. 2013DFG52660), the Taishan Scholar Construction Project Special Fund, China, and the Fundamental Research Funds for the Central Universities, China (Grant Nos. 65030091 and 65010961).

  10. The hydrodeoxygenation of bioderived furans into alkanes

    NASA Astrophysics Data System (ADS)

    Sutton, Andrew D.; Waldie, Fraser D.; Wu, Ruilian; Schlaf, Marcel; ‘Pete' Silks, Louis A.; Gordon, John C.

    2013-05-01

    The conversion of biomass into fuels and chemical feedstocks is one part of a drive to reduce the world's dependence on crude oil. For transportation fuels in particular, wholesale replacement of a fuel is logistically problematic, not least because of the infrastructure that is already in place. Here, we describe the catalytic defunctionalization of a series of biomass-derived molecules to provide linear alkanes suitable for use as transportation fuels. These biomass-derived molecules contain a variety of functional groups, including olefins, furan rings and carbonyl groups. We describe the removal of these in either a stepwise process or a one-pot process using common reagents and catalysts under mild reaction conditions to provide n-alkanes in good yields and with high selectivities. Our general synthetic approach is applicable to a range of precursors with different carbon content (chain length). This allows the selective generation of linear alkanes with carbon chain lengths between eight and sixteen carbons.

  11. The hydrodeoxygenation of bioderived furans into alkanes.

    PubMed

    Sutton, Andrew D; Waldie, Fraser D; Wu, Ruilian; Schlaf, Marcel; Silks, Louis A Pete; Gordon, John C

    2013-05-01

    The conversion of biomass into fuels and chemical feedstocks is one part of a drive to reduce the world's dependence on crude oil. For transportation fuels in particular, wholesale replacement of a fuel is logistically problematic, not least because of the infrastructure that is already in place. Here, we describe the catalytic defunctionalization of a series of biomass-derived molecules to provide linear alkanes suitable for use as transportation fuels. These biomass-derived molecules contain a variety of functional groups, including olefins, furan rings and carbonyl groups. We describe the removal of these in either a stepwise process or a one-pot process using common reagents and catalysts under mild reaction conditions to provide n-alkanes in good yields and with high selectivities. Our general synthetic approach is applicable to a range of precursors with different carbon content (chain length). This allows the selective generation of linear alkanes with carbon chain lengths between eight and sixteen carbons. PMID:23609095

  12. Structure and solvation forces in confined films: Linear and branched alkanes

    SciTech Connect

    Gao, J.; Luedtke, W.D.; Landman, U.

    1997-03-01

    Equilibrium structures, solvation forces, and conformational dynamics of thin confined films of n-hexadecane and squalane are investigated using a new grand canonical ensemble molecular dynamics method for simulations of confined liquids. The method combines constant pressure simulations with a computational cell containing solid surfaces and both bulk and confined liquid regions in equilibrium with each other. Layered density oscillations in the confined films are found for various widths of the confining gap. The solvation force oscillations as a function of the gap width for the straight chain n-hexadecane liquid are more pronounced exhibiting attractive and repulsive regions, while for the branched alkane the solvation forces are mostly repulsive, with the development of shallow local attractive regions for small values of the gap width. Furthermore, the nature of the transitions between well-formed layered configurations is different in the two systems. The n-hexadecane film exhibits solid-like characteristics portrayed by step-like variations in the number of confined segments occurring in response to a small decrease in the gap width, starting from well-layered states of the film; the behavior of the squalane film is liquid-like, exhibiting a monotonic continuous decrease in the number of confined segments as the gap width is decreased. These characteristics are correlated with structural properties of the confined films which, for n-hexadecane, exhibit enhanced layered ordering and in-plane ordered molecular arrangements, as well as with the relatively high tendency for interlayer molecular interdigitation in the squalane films. Reduced conformational (trans-guache) transition rates in the confined films, compared to their bulk values, are found, and their oscillatory dependence on the degree of confinement is analyzed, showing smaller transition rates for the well-formed layered states of the films. {copyright} {ital 1997 American Institute of Physics.}

  13. Growth mechanism of CuZnInSe2 thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tseng, Ya Hsin; Yang, Chu Shou; Wu, Chia Hsing; Chiu, Jai Wei; Yang, Min De; Wu, Chih-Hung

    2013-09-01

    CuZnInSe2 (CZIS) has potential application in solar cell for absorption layer, and give an advantage to change the band gap from CuInSe2 (1.02 eV) to ZnSe (2.67 eV). Using molecular beam epitaxy technology, the CZIS thin films were grown via CuInSe (CIS) and ZnSe base. In the case of CIS, thin films were grown on Mo-coated soda lime glass with various zinc flux. CIS was transformed into chalcopyrite and sphalerite coexisting CZIS easily but it is difficult to transform into the pure sphalerite CZIS. Zn/(Zn+In+Cu) ratio has limited to approximate 36 at% and the excess-Zn played a catalyst role. In the case of ZnSe base, which was grown on GaAs (001), various In and Cu flux defined as the TIn series and TCu series, respectively. There are four types of compound in the TIn series and TCu series, including ZnSe, InxSey, ZnIn2Se4 (ZIS) and CZIS. In the TIn series under the lowest In and Cu flux, selenium (Se) were randomly combined with cations to form the CZIS. When TIn is increased in this moment, the CZIS was transformed into ZIS. In the TCu series, CZIS demonstrated via In-rich ZIS (Zn(In, Cu)Se) and InxSey base ((Zn, Cu)InSe). It is chalcopyrite and sphalerite coexisting structure in the medium TCu region. In the high TCu region, it is transformed into the Zn-poor and Cu-rich CZIS.

  14. Enzymes and genes involved in aerobic alkane degradation

    PubMed Central

    Wang, Wanpeng; Shao, Zongze

    2013-01-01

    Alkanes are major constituents of crude oil. They are also present at low concentrations in diverse non-contaminated because many living organisms produce them as chemo-attractants or as protecting agents against water loss. Alkane degradation is a widespread phenomenon in nature. The numerous microorganisms, both prokaryotic and eukaryotic, capable of utilizing alkanes as a carbon and energy source, have been isolated and characterized. This review summarizes the current knowledge of how bacteria metabolize alkanes aerobically, with a particular emphasis on the oxidation of long-chain alkanes, including factors that are responsible for chemotaxis to alkanes, transport across cell membrane of alkanes, the regulation of alkane degradation gene and initial oxidation. PMID:23755043

  15. Improved Alkane Production in Nitrogen-Fixing and Halotolerant Cyanobacteria via Abiotic Stresses and Genetic Manipulation of Alkane Synthetic Genes.

    PubMed

    Kageyama, Hakuto; Waditee-Sirisattha, Rungaroon; Sirisattha, Sophon; Tanaka, Yoshito; Mahakhant, Aparat; Takabe, Teruhiro

    2015-07-01

    Cyanobacteria possess the unique capacity to produce alkane. In this study, effects of nitrogen deficiency and salt stress on biosynthesis of alkanes were investigated in three kinds of cyanobacteria. Intracellular alkane accumulation was increased in nitrogen-fixing cyanobacterium Anabaena sp. PCC7120, but decreased in non-diazotrophic cyanobacterium Synechococcus elongatus PCC7942 and constant in a halotolerant cyanobacterium Aphanothece halophytica under nitrogen-deficient condition. We also found that salt stress increased alkane accumulation in Anabaena sp. PCC7120 and A. halophytica. The expression levels of two alkane synthetic genes were not upregulated significantly under nitrogen deficiency or salt stress in Anabaena sp. PCC7120. The transformant Anabaena sp. PCC7120 cells with additional alkane synthetic gene set from A. halophytica increased intracellular alkane accumulation level compared to control cells. These results provide a prospect to improve bioproduction of alkanes in nitrogen-fixing halotolerant cyanobacteria via abiotic stresses and genetic engineering. PMID:25971893

  16. In situ detection of anaerobic alkane metabolites in subsurface environments

    PubMed Central

    Agrawal, Akhil; Gieg, Lisa M.

    2013-01-01

    Alkanes comprise a substantial fraction of crude oil and refined fuels. As such, they are prevalent within deep subsurface fossil fuel deposits and in shallow subsurface environments such as aquifers that are contaminated with hydrocarbons. These environments are typically anaerobic, and host diverse microbial communities that can potentially use alkanes as substrates. Anaerobic alkane biodegradation has been reported to occur under nitrate-reducing, sulfate-reducing, and methanogenic conditions. Elucidating the pathways of anaerobic alkane metabolism has been of interest in order to understand how microbes can be used to remediate contaminated sites. Alkane activation primarily occurs by addition to fumarate, yielding alkylsuccinates, unique anaerobic metabolites that can be used to indicate in situ anaerobic alkane metabolism. These metabolites have been detected in hydrocarbon-contaminated shallow aquifers, offering strong evidence for intrinsic anaerobic bioremediation. Recently, studies have also revealed that alkylsuccinates are present in oil and coal seam production waters, indicating that anaerobic microbial communities can utilize alkanes in these deeper subsurface environments. In many crude oil reservoirs, the in situ anaerobic metabolism of hydrocarbons such as alkanes may be contributing to modern-day detrimental effects such as oilfield souring, or may lead to more beneficial technologies such as enhanced energy recovery from mature oilfields. In this review, we briefly describe the key metabolic pathways for anaerobic alkane (including n-alkanes, isoalkanes, and cyclic alkanes) metabolism and highlight several field reports wherein alkylsuccinates have provided evidence for anaerobic in situ alkane metabolism in shallow and deep subsurface environments. PMID:23761789

  17. 40 CFR 721.10163 - Chloro fluoro alkane (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Chloro fluoro alkane (generic). 721... Substances § 721.10163 Chloro fluoro alkane (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as chloro fluoro alkane (PMN...

  18. 40 CFR 721.10163 - Chloro fluoro alkane (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Chloro fluoro alkane (generic). 721... Substances § 721.10163 Chloro fluoro alkane (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as chloro fluoro alkane (PMN...

  19. Graphene nanosheet: synthesis, molecular engineering, thin film, hybrids, and energy and analytical applications.

    PubMed

    Guo, Shaojun; Dong, Shaojun

    2011-05-01

    The emergence of graphene nanosheet (GN, 2010 Nobel Prize for Physics) has recently opened up an exciting new field in the science and technology of two-dimensional (2D) nanomaterials with continuously growing academic and technological impetus. GN exhibits unique electronic, optical, magnetic, thermal and mechanical properties arising from its strictly 2D structure and thus has many important technical applications. Actually, GN-based materials have enormous potential to rival or even surpass the performance of carbon nanotube-based counterparts, given that cheap, large-scale production and processing methods for high-quality GN become available. Therefore, the studies on GN in the aspects of chemistry, physical, materials, biology and interdisciplinary science have been in full flow in the past five years. In this critical review, from the viewpoint of chemistry and materials, we will cover recent significant advances in synthesis, molecular engineering, thin film, hybrids, and energy and analytical applications of the "star-material" GN together with discussion on its major challenges and opportunities for future GN research (315 references). PMID:21283849

  20. Adhesion and friction properties of molecularly thin perfluoropolyether liquid films on solid surface.

    PubMed

    Tani, Hiroshi; Tagawa, Norio

    2012-02-28

    The adhesion and friction properties of molecularly thin perfluoropolyether (PFPE) lubricant films dip-coated on a diamond-like carbon (DLC) overcoat of magnetic disks were studied using a pin-on-disk-type micro-tribotester that we developed. The load and friction forces were simultaneously measured on a rotating disk surface under an increasing/decreasing load cycle and slow sliding conditions. Experiments were performed using two types of PFPE lubricants: Fomblin Z-tetraol2000S with functional end-groups and Fomblin Z-03 without any end-group. The curves of the friction force as a function of the applied load agree with the curves estimated using the Johnson-Kendall-Roberts (JKR) model. The friction forces on the Z-03 films having different thicknesses were not found to decrease drastically; however, the friction forces on the Z-tetraol film were found to decrease drastically when the film thickness is more than ~1.2 nm. This drastic change in the case of the Z-tetraol film is estimated to be affected by the coverage of the lubricant film. PMID:22292931

  1. Molecular Ionization-Desorption Analysis Source (MIDAS) for Mass Spectrometry: Thin-Layer Chromatography.

    PubMed

    Winter, Gregory T; Wilhide, Joshua A; LaCourse, William R

    2016-02-01

    Molecular ionization-desorption analysis source (MIDAS), which is a desorption atmospheric pressure chemical ionization (DAPCI) type source, for mass spectrometry has been developed as a multi-functional platform for the direct sampling of surfaces. In this article, its utility for the analysis of thin-layer chromatography (TLC) plates is highlighted. Amino acids, which are difficult to visualize without staining reagents or charring, were detected and identified directly from a TLC plate. To demonstrate the full potential of MIDAS, all active ingredients from an analgesic tablet, separated on a TLC plate, were successfully detected using both positive and negative ion modes. The identity of each of the compounds was confirmed from their mass spectra and compared against standards. Post separation, the chemical signal (blue permanent marker) as reference marks placed at the origin and solvent front were used to calculate retention factor (Rf) values from the resulting ion chromatogram. The quantitative capabilities of the device were exhibited by scanning caffeine spots on a TLC plate of increasing sample amount. A linear curve based on peak are, R2 = 0.994, was generated for seven spots ranging from 50 to 1000 ng of caffeine per spot. PMID:26471042

  2. Atomically-thin molecular layers for electrode modification of organic transistors.

    PubMed

    Gim, Yuseong; Kang, Boseok; Kim, BongSoo; Kim, Sun-Guk; Lee, Joong-Hee; Cho, Kilwon; Ku, Bon-Cheol; Cho, Jeong Ho

    2015-09-01

    Atomically-thin molecular layers of aryl-functionalized graphene oxides (GOs) were used to modify the surface characteristics of source-drain electrodes to improve the performances of organic field-effect transistor (OFET) devices. The GOs were functionalized with various aryl diazonium salts, including 4-nitroaniline, 4-fluoroaniline, or 4-methoxyaniline, to produce several types of GOs with different surface functional groups (NO2-Ph-GO, F-Ph-GO, or CH3O-Ph-GO, respectively). The deposition of aryl-functionalized GOs or their reduced derivatives onto metal electrode surfaces dramatically enhanced the electrical performances of both p-type and n-type OFETs relative to the performances of OFETs prepared without the GO modification layer. Among the functionalized rGOs, CH3O-Ph-rGO yielded the highest hole mobility of 0.55 cm(2) V(-1) s(-1) and electron mobility of 0.17 cm(2) V(-1) s(-1) in p-type and n-type FETs, respectively. Two governing factors: (1) the work function of the modified electrodes and (2) the crystalline microstructures of the benchmark semiconductors grown on the modified electrode surface were systematically investigated to reveal the origin of the performance improvements. Our simple, inexpensive, and scalable electrode modification technique provides a significant step toward optimizing the device performance by engineering the semiconductor-electrode interfaces in OFETs. PMID:26243510

  3. Producing and imaging a thin line of He2 ∗ molecular tracers in helium-4

    NASA Astrophysics Data System (ADS)

    Gao, J.; Marakov, A.; Guo, W.; Pawlowski, B. T.; Van Sciver, S. W.; Ihas, G. G.; McKinsey, D. N.; Vinen, W. F.

    2015-09-01

    Cryogenic helium-4 has long been recognized as a useful material in fluids research. The unique properties of helium-4 in the gaseous phase and the normal liquid phase allow for the generation of turbulent flows with exceptionally high Reynolds and Rayleigh numbers. In the superfluid phase, helium-4 exhibits two-fluid hydrodynamics and possesses fascinating properties due to its quantum nature. However, studying the flows in helium-4 has been very challenging largely due to the lack of effective visualization and velocimetry techniques. In this article, we discuss the development of novel instrumentation for flow-visualization in helium based on the generation and imaging of thin lines of metastable He2 ∗ tracer molecules. These molecular tracers are created via femtosecond-laser field-ionization of helium atoms and can be imaged using a laser-induced fluorescence technique. By observing the displacement and distortion of the tracer lines in helium, quantitative information about the flow field can be extracted. We present experimental results in the study of thermal counterflow in superfluid helium that validate the concept of this technique. We also discuss anticipated future developments of this powerful visualization technique.

  4. Producing and imaging a thin line of He*₂ molecular tracers in helium-4.

    PubMed

    Gao, J; Marakov, A; Guo, W; Pawlowski, B T; Van Sciver, S W; Ihas, G G; McKinsey, D N; Vinen, W F

    2015-09-01

    Cryogenic helium-4 has long been recognized as a useful material in fluids research. The unique properties of helium-4 in the gaseous phase and the normal liquid phase allow for the generation of turbulent flows with exceptionally high Reynolds and Rayleigh numbers. In the superfluid phase, helium-4 exhibits two-fluid hydrodynamics and possesses fascinating properties due to its quantum nature. However, studying the flows in helium-4 has been very challenging largely due to the lack of effective visualization and velocimetry techniques. In this article, we discuss the development of novel instrumentation for flow-visualization in helium based on the generation and imaging of thin lines of metastable He*₂ tracer molecules. These molecular tracers are created via femtosecond-laser field-ionization of helium atoms and can be imaged using a laser-induced fluorescence technique. By observing the displacement and distortion of the tracer lines in helium, quantitative information about the flow field can be extracted. We present experimental results in the study of thermal counterflow in superfluid helium that validate the concept of this technique. We also discuss anticipated future developments of this powerful visualization technique. PMID:26429454

  5. Molecular Ionization-Desorption Analysis Source (MIDAS) for Mass Spectrometry: Thin-Layer Chromatography

    NASA Astrophysics Data System (ADS)

    Winter, Gregory T.; Wilhide, Joshua A.; LaCourse, William R.

    2016-02-01

    Molecular ionization-desorption analysis source (MIDAS), which is a desorption atmospheric pressure chemical ionization (DAPCI) type source, for mass spectrometry has been developed as a multi-functional platform for the direct sampling of surfaces. In this article, its utility for the analysis of thin-layer chromatography (TLC) plates is highlighted. Amino acids, which are difficult to visualize without staining reagents or charring, were detected and identified directly from a TLC plate. To demonstrate the full potential of MIDAS, all active ingredients from an analgesic tablet, separated on a TLC plate, were successfully detected using both positive and negative ion modes. The identity of each of the compounds was confirmed from their mass spectra and compared against standards. Post separation, the chemical signal (blue permanent marker) as reference marks placed at the origin and solvent front were used to calculate retention factor (Rf) values from the resulting ion chromatogram. The quantitative capabilities of the device were exhibited by scanning caffeine spots on a TLC plate of increasing sample amount. A linear curve based on peak are, R2 = 0.994, was generated for seven spots ranging from 50 to 1000 ng of caffeine per spot.

  6. Frictional Response of Molecularly Thin Liquid Polymer Films Subject to Constant Shear Stress

    NASA Astrophysics Data System (ADS)

    Tschirhart, Charles; Troian, Sandra

    2014-03-01

    Measurements of the frictional response of nanoscale viscous films are typically obtained using the surface force apparatus in which a fluid layer is confined between smooth solid substrates approaching at constant speed or force. The squeezing pressure causes lateral flow from which the shear viscosity can be deduced. Under these conditions however, molecularly thin films tend to solidify wholly or partially and estimates of the shear viscosity can exceed those in macroscale films by many orders of magnitude. This problem can be avoided altogether by examining the response of an initially flat, supported, free surface film subject to comparable values of surface shear stress by application of an external inert gas stream. This method was first conceived by Derjaguin in 1944; more recent studies by Mate et al. at IBM Almaden on complex polymeric systems have uncovered fluid layering and other interesting behaviors. The only drawback is that this alternative technique requires an accurate model for interface distortion. We report on ellipsometric measurements of ultrathin polymeric films in efforts to determine whether the usual interface equations for free surface films based purely on continuum models can be properly extended to nanoscale films. Supported by a Fred and Jean Felberg Fellowship and G. W. Housner Student Discovery Fund.

  7. Small molecular weight organic thin-film photodetectors and solar cells

    NASA Astrophysics Data System (ADS)

    Peumans, Peter; Yakimov, Aharon; Forrest, Stephen R.

    2003-04-01

    In this review, we discuss the physics underlying the operation of single and multiple heterojunction, vacuum-deposited organic solar cells based on small molecular weight thin films. For single heterojunction cells, we find that the need for direct contact between the deposited electrode and the active organics leads to quenching of excitons. An improved device architecture, the double heterojunction, is shown to confine excitons within the active layers, allowing substantially higher internal efficiencies to be achieved. A full optical and electrical analysis of the double heterostructure architecture leads to optimal cell design as a function of the optical properties and exciton diffusion lengths of the photoactive materials. Combining the double heterostructure with novel light trapping schemes, devices with external efficiencies approaching their internal efficiency are obtained. When applied to an organic photovoltaic cell with a power conversion efficiency of 1.0%±0.1% under 1 sun AM1.5 illumination, devices with external power conversion efficiencies of 2.4%±0.3% are reported. In addition, we show that by using materials with extended exciton diffusion lengths LD, highly efficient double heterojunction photovoltaic cells are obtained, even in the absence of a light trapping geometry. Using C60 as an acceptor material, double heterostructure external power conversion efficiencies of 3.6%±0.4% under 1 sun AM1.5 illumination are obtained. Stacking of single heterojunction devices leads to thin film multiple heterojunction photovoltaic and photodetector structures. Thin bilayer photovoltaic cells can be stacked with ultrathin (˜5 Å), discontinuous Ag layers between adjacent cells serving as efficient recombination sites for electrons and holes generated in the neighboring cells. Such stacked cells have open circuit voltages that are n times the open circuit voltage of a single cell, where n is the number of cells in the stack. In optimized structures, the

  8. Structural and Magnetic Phase Transitions in Manganese Arsenide Thin-Films Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Jaeckel, Felix Till

    Phase transitions play an important role in many fields of physics and engineering, and their study in bulk materials has a long tradition. Many of the experimental techniques involve measurements of thermodynamically extensive parameters. With the increasing technological importance of thin-film technology there is a pressing need to find new ways to study phase transitions at smaller length-scales, where the traditional methods are insufficient. In this regard, the phase transitions observed in thin-films of MnAs present interesting challenges. As a ferromagnetic material that can be grown epitaxially on a variety of technologically important substrates, MnAs is an interesting material for spintronics applications. In the bulk, the first order transition from the low temperature ferromagnetic alpha-phase to the beta-phase occurs at 313 K. The magnetic state of the beta-phase has remained controversial. A second order transition to the paramagnetic gamma-phase takes place at 398 K. In thin-films, the anisotropic strain imposed by the substrate leads to the interesting phenomenon of coexistence of alpha- and beta-phases in a regular array of stripes over an extended temperature range. In this dissertation these phase transitions are studied in films grown by molecular beam epitaxy on GaAs (001). The films are confirmed to be of high structural quality and almost purely in the A0 orientation. A diverse set of experimental techniques, germane to thin-film technology, is used to probe the properties of the film: Temperature-dependent X-ray diffraction and atomic-force microscopy (AFM), as well as magnetotransport give insights into the structural properties, while the anomalous Hall effect is used as a probe of magnetization during the phase transition. In addition, reflectance difference spectroscopy (RDS) is used as a sensitive probe of electronic structure. Inductively coupled plasma etching with BCl3 is demonstrated to be effective for patterning MnAs. We show

  9. Defect-free thin InAs nanowires grown using molecular beam epitaxy.

    PubMed

    Zhang, Zhi; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2016-01-21

    In this study, we designed a simple method to achieve the growth of defect-free thin InAs nanowires with a lateral dimension well below their Bohr radius on different substrate orientations. By depositing and annealing a thin layer of Au thin film on a (100) substrate surface, we have achieved the growth of defect-free uniform-sized thin InAs nanowires. This study provides a strategy to achieve the growth of pure defect-free thin nanowires. PMID:26671780

  10. Reprint of "Stable hydrogen and carbon isotopic compositions of long-chain (C21-C33) n-alkanes and n-alkenes in insects"

    NASA Astrophysics Data System (ADS)

    Chikaraishi, Yoshito; Kaneko, Masanori; Ohkouchi, Naohiko

    2013-06-01

    We report the molecular and stable isotopic (δD and δ13C) compositions of long-chain n-alkanes in common insects including the cabbage butterfly, swallowtail, wasp, hornet, grasshopper, and ladybug. Insect n-alkanes are potential candidates of the contamination of soil and sedimentary n-alkanes that are believed to be derived from vascular plant waxes. Long-chain n-alkanes (range C21-33; maximum C23-C29) are found to be abundant in the insects (31-781 μg/dry g), with a carbon preference index (CPI) of 5.1-31.5 and an average chain length (ACL) of 24.9-29.3. The isotopic compositions (mean ± 1σ, n = 33) of the n-alkanes are -195 ± 16‰ for hydrogen and -30.6 ± 2.4‰ for carbon. The insect n-alkanes are depleted in D by approximately 30-40‰ compared with wax n-alkanes from C3 (-155 ± 25‰) and C4 vascular plants (-167 ± 13‰), whereas their δ13C values fall between those of C3 (-36.2 ± 2.4‰) and C4 plants (-20.3 ± 2.4‰). Thus, the contribution of insect-derived n-alkanes to soil and sediment could potentially shift δD records of n-alkanes toward more negative values and potentially muddle the assumed original C3/C4 balance in the δ13C records of the soil and sedimentary n-alkanes. n-Alkenes are also found in three insects (swallowtail, wasp and hornet). They are more depleted in D relative to the same carbon numbered n-alkanes (δDn-alkene - δDn-alkane = -17 ± 16‰), but the δ13C values are almost identical to those of the n-alkanes (δ13Cn-alkene - δ13Cn-alkane = 0.1 ± 0.2‰). These results suggest that these n-alkenes are desaturated products of the same carbon numbered n-alkanes.

  11. Stable hydrogen and carbon isotopic compositions of long-chain (C21-C33) n-alkanes and n-alkenes in insects

    NASA Astrophysics Data System (ADS)

    Chikaraishi, Yoshito; Kaneko, Masanori; Ohkouchi, Naohiko

    2012-10-01

    We report the molecular and stable isotopic (δD and δ13C) compositions of long-chain n-alkanes in common insects including the cabbage butterfly, swallowtail, wasp, hornet, grasshopper, and ladybug. Insect n-alkanes are potential candidates of the contamination of soil and sedimentary n-alkanes that are believed to be derived from vascular plant waxes. Long-chain n-alkanes (range C21-33; maximum C23-C29) are found to be abundant in the insects (31-781 μg/dry g), with a carbon preference index (CPI) of 5.1-31.5 and an average chain length (ACL) of 24.9-29.3. The isotopic compositions (mean ± 1σ, n = 33) of the n-alkanes are -195 ± 16‰ for hydrogen and -30.6 ± 2.4‰ for carbon. The insect n-alkanes are depleted in D by approximately 30-40‰ compared with wax n-alkanes from C3 (-155 ± 25‰) and C4 vascular plants (-167 ± 13‰), whereas their δ13C values fall between those of C3 (-36.2 ± 2.4‰) and C4 plants (-20.3 ± 2.4‰). Thus, the contribution of insect-derived n-alkanes to soil and sediment could potentially shift δD records of n-alkanes toward more negative values and potentially muddle the assumed original C3/C4 balance in the δ13C records of the soil and sedimentary n-alkanes. n-Alkenes are also found in three insects (swallowtail, wasp and hornet). They are more depleted in D relative to the same carbon numbered n-alkanes (δDn-alkene - δDn-alkane = -17 ± 16‰), but the δ13C values are almost identical to those of the n-alkanes (δ13Cn-alkene - δ13Cn-alkane = 0.1 ± 0.2‰). These results suggest that these n-alkenes are desaturated products of the same carbon numbered n-alkanes.

  12. Nitrated metalloporphyrins as catalysts for alkane oxidation

    DOEpatents

    Ellis, Jr., Paul E.; Lyons, James E.

    1992-01-01

    Alkanes are oxidized by contact with oxygen-containing gas in the presence as catalyst of a metalloporphyrin in which hydrogen atoms in the porphyrin ring have been replaced with one or more nitro groups. Hydrogen atoms in the porphyrin ring may also be substituted with halogen atoms.

  13. Nitrated metalloporphyrins as catalysts for alkane oxidation

    DOEpatents

    Ellis, Jr., Paul E.; Lyons, James E.

    1994-01-01

    Compositions of matter comprising nitro-substituted metal complexes of porphyrins are catalysts for the oxidation of alkanes. The metal is iron, chromium, manganese, ruthenium, copper or cobalt. The porphyrin ring has nitro groups attached thereto in meso and/or .beta.-pyrrolic positions.

  14. Nitrated metalloporphyrins as catalysts for alkane oxidation

    DOEpatents

    Ellis, P.E. Jr.; Lyons, J.E.

    1994-01-18

    Compositions of matter comprising nitro-substituted metal complexes of porphyrins are catalysts for the oxidation of alkanes. The metal is iron, chromium, manganese, ruthenium, copper or cobalt. The porphyrin ring has nitro groups attached thereto in meso and/or [beta]-pyrrolic positions.

  15. Direct hydrodeoxygenation of raw woody biomass into liquid alkanes.

    PubMed

    Xia, Qineng; Chen, Zongjia; Shao, Yi; Gong, Xueqing; Wang, Haifeng; Liu, Xiaohui; Parker, Stewart F; Han, Xue; Yang, Sihai; Wang, Yanqin

    2016-01-01

    Being the only sustainable source of organic carbon, biomass is playing an ever-increasingly important role in our energy landscape. The conversion of renewable lignocellulosic biomass into liquid fuels is particularly attractive but extremely challenging due to the inertness and complexity of lignocellulose. Here we describe the direct hydrodeoxygenation of raw woods into liquid alkanes with mass yields up to 28.1 wt% over a multifunctional Pt/NbOPO4 catalyst in cyclohexane. The superior performance of this catalyst allows simultaneous conversion of cellulose, hemicellulose and, more significantly, lignin fractions in the wood sawdust into hexane, pentane and alkylcyclohexanes, respectively. Investigation on the molecular mechanism reveals that a synergistic effect between Pt, NbOx species and acidic sites promotes this highly efficient hydrodeoxygenation of bulk lignocellulose. No chemical pretreatment of the raw woody biomass or separation is required for this one-pot process, which opens a general and energy-efficient route for converting raw lignocellulose into valuable alkanes. PMID:27025898

  16. Direct hydrodeoxygenation of raw woody biomass into liquid alkanes

    PubMed Central

    Xia, Qineng; Chen, Zongjia; Shao, Yi; Gong, Xueqing; Wang, Haifeng; Liu, Xiaohui; Parker, Stewart F.; Han, Xue; Yang, Sihai; Wang, Yanqin

    2016-01-01

    Being the only sustainable source of organic carbon, biomass is playing an ever-increasingly important role in our energy landscape. The conversion of renewable lignocellulosic biomass into liquid fuels is particularly attractive but extremely challenging due to the inertness and complexity of lignocellulose. Here we describe the direct hydrodeoxygenation of raw woods into liquid alkanes with mass yields up to 28.1 wt% over a multifunctional Pt/NbOPO4 catalyst in cyclohexane. The superior performance of this catalyst allows simultaneous conversion of cellulose, hemicellulose and, more significantly, lignin fractions in the wood sawdust into hexane, pentane and alkylcyclohexanes, respectively. Investigation on the molecular mechanism reveals that a synergistic effect between Pt, NbOx species and acidic sites promotes this highly efficient hydrodeoxygenation of bulk lignocellulose. No chemical pretreatment of the raw woody biomass or separation is required for this one-pot process, which opens a general and energy-efficient route for converting raw lignocellulose into valuable alkanes. PMID:27025898

  17. Structure and Mass Transport Characteristics at the Intrinsic Liquid-Vapor Interfaces of Alkanes.

    PubMed

    Chilukoti, Hari Krishna; Kikugawa, Gota; Ohara, Taku

    2016-07-28

    In this paper, an instantaneous interface definition has been used to study the intrinsic structure and self-diffusion coefficient in the vicinity of the liquid-vapor interfaces of decane and tetracosane at three different temperatures using molecular dynamics simulations, and the results have been compared with those obtained on the basis of the conventional Gibbs dividing surface (time- and space-averaged interface). The alkane molecules were modeled using the united atom NERD force field. Partial layered structures of alkane molecules at the liquid-vapor interface are observed as a pinned structure of alkane liquids based on the intrinsic interface. This kind of characteristic has not been observed in the density profiles obtained based on the Gibbs dividing surface. By examining the orientation order parameter and radius of gyration of the alkane molecules, it was observed that the alkane molecules were preferentially oriented to be more parallel to the intrinsic interface than to the Gibbs dividing surface, and the shape of the alkane molecules is slightly changed in the vicinity of the liquid-vapor interfaces. The self-diffusion coefficient parallel to the intrinsic interface was examined using the Green-Kubo relation, where the projection of the velocity in the parallel direction to the local intrinsic interface is used in the velocity correlation function. It was found that the self-diffusion coefficient in the direction parallel to the intrinsic interface changes as the position approaches the interface in a more obvious manner as compared with the self-diffusion coefficient obtained with respect to the Gibbs dividing surface. These results suggest that the use of an instantaneous interface definition allowed us to capture sharp variations in transport properties which are originating due to steeper structure at the liquid-vapor interfaces. PMID:27387788

  18. Isomerization of alkanes on sulfated zirconia: Promotion by Pt and by adamantyl hydride transfer species

    SciTech Connect

    Iglesia, E.; Soled, S.L.; Kramer, G.M. )

    1993-11-01

    The work shows that hydride transfer species, such as adamantane, increase isomerization rates and inhibit C-C scission reactions. n-Heptane isomerization rates show positive hydrogen kinetic orders, suggesting that the reaction proceeds on Pt/ZrO[sub 2]-SO[sub 4] via chain transfer pathways, in which carbenium ions propagate, after a chain initiation step involvings loss of hydrogen from alkanes, by hydride transfer from neutral species to carbonations. These pathways contrast with those involved in the bifunctional (metal-acid) catalytic sequences usually required for alkane isomerization, in which metal sites catalyze alkane dehydrogenation and acid sites catalyze skeletal rearrangements of alkenes. Rate-limiting hydride transfer steps are consistent with the strong influence of molecular hydride transfer agents such as adamantane, which act as co-catalysts and increase isomerization rate and selectivity. The addition of small amounts of adamantane (0.1-0.8 wt%) to n-heptane increases isomerizations rates by a factor of 3 and inhibits undesirable cracking reactions. Adamantane increases hydride transfer and carbenium ion termination rates, thus reducing the surface residence time required for a catalytic turnover. As a result, desorption occurs before secondary cracking of isomerized carbenium ions. Less effective hydride transfer agents (n-alkanes, isoalkanes) also increase n-alkanes isomerization rate and selectivity, but require much higher concentrations than adamantane. Dihydrogen also acts as a hydride source in alkane isomerization catalysis, but it requires the additional presence of metals or reducible oxides, which catalyze H[sub 2] dissociation and the formation of hydridic and protonic forms of hydrogen. 40 refs., 10 figs., 4 tabs.

  19. Molecular Packing Structure of Mesogenic Octa-Hexyl Substituted Phthalocyanine Thin Film by X-ray Diffraction Analysis.

    PubMed

    Ohmori, Masashi; Higashi, Takuya; Fujii, Akihiko; Ozaki, Masanori

    2016-04-01

    The molecular packing structure in a thin film of the liquid crystalline phthalocyanine, 1,4,8,11,15,18,22,25-octahexylphthalocyanine (C6PcH2), which is a promising small-molecular material for solution-processable organic thin-film solar cells, has been investigated by X-ray diffraction (XRD) measurement. The crystal structure of C6PcH2 in the spin-coated film was determined to be a centered rectangular structure (a = 36.4 Å, b = 20.3 Å). The tilt angle of the phthalocyanine core normal vector was 34-39° from the column axis, and the shortest intermolecular distance was 3.9-4.0 A. The crystal structure determined by XRD analysis was ascertained to be consistent with that calculated by Fourier analvsis. PMID:27451624

  20. Water solubility of selected C9-C18 alkanes using a slow-stir technique: Comparison to structure - property models.

    PubMed

    Letinski, Daniel J; Parkerton, Thomas F; Redman, Aaron D; Connelly, Martin J; Peterson, Brian

    2016-05-01

    Aqueous solubility is a fundamental physical-chemical substance property that strongly influences the distribution, fate and effects of chemicals upon release into the environment. Experimental water solubility was determined for 18 selected C9-C18 normal, branched and cyclic alkanes. A slow-stir technique was applied to obviate emulsion formation, which historically has resulted in significant overestimation of the aqueous solubility of such hydrophobic liquid compounds. Sensitive GC-MS based methods coupled with contemporary sample extraction techniques were employed to enable reproducible analysis of low parts-per billion aqueous concentrations. Water solubility measurements for most of the compounds investigated, are reported for the first time expanding available data for branched and cyclic alkanes. Measured water solubilities spanned four orders of magnitude ranging from 0.3 μg/L to 250 μg/L. Good agreement was observed for selected alkanes tested in this work and reported in earlier literature demonstrating the robustness of the slow-stir water solubility technique. Comparisons of measured alkane water solubilities were also made with those predicted by commonly used quantitative structure-property relationship models (e.g. SPARC, EPIWIN, ACD/Labs). Correlations are also presented between alkane measured water solubilities and molecular size parameters (e.g. molar volume, solvent accessible molar volume) affirming a mechanistic description of empirical aqueous solubility results and prediction previously reported for a more limited set of alkanes. PMID:26924078

  1. RESEARCH ON THE ELECTRONIC AND OPTICAL PROPERTIES OF POLYMER AND OTHER ORGANIC MOLECULAR THIN FILMS

    SciTech Connect

    ALEXEI G. VITUKHNOVSKY; IGOR I. SOBELMAN - RUSSIAN ACADEMY OF SCIENCES

    1995-09-06

    Optical properties of highly ordered films of poly(p-phenylene) (PPP) on different substrates, thin films of mixtures of conjugated polymers, of fullerene and its composition with polymers, molecular J-aggregates of cyanine dyes in frozen matrices have been studied within the framework of the Agreement. Procedures of preparation of high-quality vacuum deposited PPP films on different substrates (ITO, Si, GaAs and etc.) were developed. Using time-correlated single photon counting technique and fluorescence spectroscopy the high quality of PPP films has been confirmed. Dependence of structure and optical properties on the conditions of preparation were investigated. The fluorescence lifetime and spectra of highly oriented vacuum deposited PPP films were studied as a function of the degree of polymerization. It was shown for the first time that the maximum fluorescence quantum yield is achieved for the chain length approximately equal to 35 monomer units. The selective excitation of luminescence of thin films of PPP was performed in the temperature range from 5 to 300 K. The total intensity of luminescence monotonically decreases with decreasing temperature. Conditions of preparation of highly cristallyne fullerene C{sub 60} films by the method of vacuum deposition were found. Composites of C{sub 60} with conjugated polymers PPV and polyacetylene (PA) were prepared. The results on fluorescence quenching, IR and resonant Raman spectroscopy are consistent with earlier reported ultrafast photoinduced electron transfer from PPV to C{sub 60} and show that the electron transfer is absent in the case of the PA-C{sub 60} composition. Strong quenching of PPV fluorescence was observed in the PPV-PA blends. The electron transfer from PPV to PA can be considered as one of the possible mechanisms of this quenching. The dynamics of photoexcitations in different types of J-aggregates of the carbocyanine dye was studied at different temperatures in frozen matrices. The optical

  2. Shear thinning behavior of linear polymer melts under shear flow via nonequilibrium molecular dynamics

    NASA Astrophysics Data System (ADS)

    Xu, Xiaolei; Chen, Jizhong; An, Lijia

    2014-05-01

    The properties of both untangled and entangled linear polymer melts under shear flow are studied by nonequilibrium molecular dynamics simulations. The results reveal that the dependence of shear viscosity η on shear rate dot{γ }, expressed by η ˜ dot{γ }^{-n}, exhibits three distinct regimes. The first is the well-known Newtonian regime, namely, η independent of shear rate at small shear rates dot{γ }<τ 0^{-1} (where τ0 is the longest polymer relaxation time at equilibrium). In the non-Newtonian regime (dot{γ }>τ 0^{-1}), the shear dependence of viscosity exhibits a crossover at a critical shear rate dot{γ }c dividing this regime into two different regimes, shear thinning regime I (ST-I) and II (ST-II), respectively. In the ST-I regime (τ ^{-1}_0dot{γ }c) a universal power law η ˜ dot{γ }^{-0.37} is found for considered chain lengths. Furthermore, the longer the polymer chain is, the smaller the shear viscosity for a given shear rate in the ST-II regime. The simulation also shows that a characteristic chain length, below which dot{γ }c will be equal to τ 0^{-1}, lies in the interval 30 < N < 50. For all considered chain lengths in the ST-II regime, we also find that the first and second normal stress differences N1 and N2 follow power laws of N1 ˜ dot{γ }^{2/3} and N2 ˜ dot{γ }^{0.82}, respectively; the orientation resistance parameter mG follows the relation mG ˜ dot{γ }^{0.75} and the tumbling frequency ftb follows f_{tb} ˜ dot{γ }^{0.75}. These results imply that the effects of entanglement on the shear dependences of these properties may be negligible in the ST-II regime. These findings may shed some light on the nature of shear thinning in flexible linear polymer melts.

  3. Atomically-thin molecular layers for electrode modification of organic transistors

    NASA Astrophysics Data System (ADS)

    Gim, Yuseong; Kang, Boseok; Kim, Bongsoo; Kim, Sun-Guk; Lee, Joong-Hee; Cho, Kilwon; Ku, Bon-Cheol; Cho, Jeong Ho

    2015-08-01

    Atomically-thin molecular layers of aryl-functionalized graphene oxides (GOs) were used to modify the surface characteristics of source-drain electrodes to improve the performances of organic field-effect transistor (OFET) devices. The GOs were functionalized with various aryl diazonium salts, including 4-nitroaniline, 4-fluoroaniline, or 4-methoxyaniline, to produce several types of GOs with different surface functional groups (NO2-Ph-GO, F-Ph-GO, or CH3O-Ph-GO, respectively). The deposition of aryl-functionalized GOs or their reduced derivatives onto metal electrode surfaces dramatically enhanced the electrical performances of both p-type and n-type OFETs relative to the performances of OFETs prepared without the GO modification layer. Among the functionalized rGOs, CH3O-Ph-rGO yielded the highest hole mobility of 0.55 cm2 V-1 s-1 and electron mobility of 0.17 cm2 V-1 s-1 in p-type and n-type FETs, respectively. Two governing factors: (1) the work function of the modified electrodes and (2) the crystalline microstructures of the benchmark semiconductors grown on the modified electrode surface were systematically investigated to reveal the origin of the performance improvements. Our simple, inexpensive, and scalable electrode modification technique provides a significant step toward optimizing the device performance by engineering the semiconductor-electrode interfaces in OFETs.Atomically-thin molecular layers of aryl-functionalized graphene oxides (GOs) were used to modify the surface characteristics of source-drain electrodes to improve the performances of organic field-effect transistor (OFET) devices. The GOs were functionalized with various aryl diazonium salts, including 4-nitroaniline, 4-fluoroaniline, or 4-methoxyaniline, to produce several types of GOs with different surface functional groups (NO2-Ph-GO, F-Ph-GO, or CH3O-Ph-GO, respectively). The deposition of aryl-functionalized GOs or their reduced derivatives onto metal electrode surfaces dramatically

  4. Distribution, activity and function of short-chain alkane degrading phylotypes in hydrothermal vent sediments

    NASA Astrophysics Data System (ADS)

    Adams, M. M.; Joye, S. B.; Hoarfrost, A.; Girguis, P. R.

    2012-12-01

    hydrocarbon species characteristic of these metalliferous sediments. These systems are also characterized by sharp physicochemical gradients that have been shown to have a pronounced effect on microbial ecology and activity. Sediments were collected from a Middle Valley field with relatively high concentrations of short-chain alkanes and incubated in anaerobic batch reactors with each individual alkane (C1, C2, C3 and C4, respectively) at a range of temperatures (25, 55 and 75 °C) to mimic environmental physico-chemical conditions in a closed system. Stable carbon isotope ratios and radiotracer incubations provide clear evidence for C2-C4 alkane oxidation in the sediments over time. Upon identifying sediments with anaerobic alkane oxidation activity, microbial communities were screened via 16S rRNA pyrosequencing, and key phylotypes were then quantified using both molecular and microscopic methods. There were shifts in overall community composition and putative alkane-oxidizing phylotypes after the incubation period with the alkane substrates. These are the first evidence to date indicating that anaerobic C2-C4 alkane oxidation occurs across a broad range of temperatures in metalliferous sediments.

  5. Ultrafast structural dynamics of LaVO3 thin films grown by hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Brahlek, Matthew; Lapano, Jason; Stoica, Vladimir; Zhang, Lei; Zhang, Hai-Tian; Akamatsu, Hirofumi; Eaton, Craig; Gopalan, Venkatraman; Freeland, John; Wen, Haidan; Engel-Herbert, Roman

    LaVO3, with a partially full d-shell is expected to be metallic, but due to electron-electron interactions a gap emerges and the ground state is a Mott insulator. Such effects are a strong function of the bonding geometry, and particularly the V-O-V bond angle. Controlling these structural effects on the ultrafast time scale can lead to control over the underlying electronic ground state. Here we report the ultrafast structural dynamics of 25 and 50 nm thick LaVO3 thin films grown by the hybrid molecular beam epitaxy technique on SrTiO3 when excited across the bandgap by 800 nm light. Using time-resolved x-ray diffraction on the 100 ps time scale at Sector 7 of the Advanced Photon Source, we directly measured the structural changes with atomic accuracy by monitoring integer Bragg diffraction peaks and find a large out-of-plane strain of 0.18% upon optical excitation; the recovery time is ~1 ns for the 25 nm film and ~2 ns for the 50 nm film, consistent with the thermal transport from the film to the substrate. Further, we will discuss the response of the oxygen octahedral rotation patterns indicated by changes of the half-order diffraction peaks. Understanding such ultrafast structural deformation is important for optimizing optical excitations to create new metastable phases starting from a Mott insulator. This work was supported by the Department of Energy under Grant DE-SC0012375, and DE-AC02-06CH11357.

  6. Phase sensitive molecular dynamics of self-assembly glycolipid thin films: A dielectric spectroscopy investigation

    NASA Astrophysics Data System (ADS)

    Velayutham, T. S.; Ng, B. K.; Gan, W. C.; Majid, W. H. Abd.; Hashim, R.; Zahid, N. I.; Chaiprapa, Jitrin

    2014-08-01

    Glycolipid, found commonly in membranes, is also a liquid crystal material which can self-assemble without the presence of a solvent. Here, the dielectric and conductivity properties of three synthetic glycolipid thin films in different thermotropic liquid crystal phases were investigated over a frequency and temperature range of (10-2-106 Hz) and (303-463 K), respectively. The observed relaxation processes distinguish between the different phases (smectic A, columnar/hexagonal, and bicontinuous cubic Q) and the glycolipid molecular structures. Large dielectric responses were observed in the columnar and bicontinuous cubic phases of the longer branched alkyl chain glycolipids. Glycolipids with the shortest branched alkyl chain experience the most restricted self-assembly dynamic process over the broad temperature range studied compared to the longer ones. A high frequency dielectric absorption (Process I) was observed in all samples. This is related to the dynamics of the hydrogen bond network from the sugar group. An additional low-frequency mechanism (Process II) with a large dielectric strength was observed due to the internal dynamics of the self-assembly organization. Phase sensitive domain heterogeneity in the bicontinuous cubic phase was related to the diffusion of charge carriers. The microscopic features of charge hopping were modelled using the random walk scheme, and two charge carrier hopping lengths were estimated for two glycolipid systems. For Process I, the hopping length is comparable to the hydrogen bond and is related to the dynamics of the hydrogen bond network. Additionally, that for Process II is comparable to the bilayer spacing, hence confirming that this low-frequency mechanism is associated with the internal dynamics within the phase.

  7. Fidelity of fossil n-alkanes from leaf to paleosol and applications to the Paleocene-Eocene Thermal Maximum

    NASA Astrophysics Data System (ADS)

    Bush, R. T.; McInerney, F. A.; Baczynski, A. A.; Wing, S. L.

    2011-12-01

    modern plant data. These results suggest that n-alkanes extracted directly from a fossil leaf provide a true signature of an individual leaf fossil rather than a mixture from the entire plant community. Therefore, comparisons between fossil morphotypes and between fossil and related modern taxa should be robust. Furthermore, by placing fossil leaf data within the context of the chemostratigraphy of Bighorn Basin sediments across the P-E boundary, fossil leaf n-alkanes can be used to bridge the gap between our understanding of modern plant lipids and bulk lipid data from sediments across the PETM. It has been hypothesized that changes in the both the molecular distribution and carbon isotope composition of n-alkanes across the PETM were due to changes in the local plant community, which included a large proportion of deciduous gymnosperms before and after-but not during-the PETM. Analysis of fossils such as Ginkgo and angiosperms provides the opportunity to compare and distinguish the molecular and isotopic signatures of gymnosperms and angiosperms. These comparisons shed light on the dynamics of climate and ecosystem changes as they are recorded in the signatures of lipid biomarkers.

  8. Density Functional Steric Analysis of Linear and Branched Alkanes

    SciTech Connect

    Ess, Daniel H.; Liu, Shubin; De Proft, Frank

    2010-11-18

    Branched alkane hydrocarbons are thermodynamically more stable than straight-chain linear alkanes. This thermodynamic stability is also manifest in alkane bond separation energies. To understand the physical differences between branched and linear alkanes, we have utilized a novel density functional theory (DFT) definition of steric energy based on the Weizäcker kinetic energy. Using the M06-2X functional, the total DFT energy was partitioned into a steric energy term (Ee[[ρ]), an electrostatic energy term (Ee[ρ]), and a fermionic quantum energy term (Eq[[ρ]). This analysis revealed that branched alkanes have less (destabilizing) DFT steric energy than linear alkanes. The lower steric energy of branched alkanes is mitigated by an equal and opposite quantum energy term that contains the Pauli component of the kinetic energy and exchange-correlation energy. Because the steric and quantum energy terms cancel, this leaves the electrostatic energy term that favors alkane branching. Electrostatic effects, combined with correlation energy, explains why branched alkanes are more stable than linear alkanes.

  9. Density functional steric analysis of linear and branched alkanes.

    PubMed

    Ess, Daniel H; Liu, Shubin; De Proft, Frank

    2010-12-16

    Branched alkane hydrocarbons are thermodynamically more stable than straight-chain linear alkanes. This thermodynamic stability is also manifest in alkane bond separation energies. To understand the physical differences between branched and linear alkanes, we have utilized a novel density functional theory (DFT) definition of steric energy based on the Weizäcker kinetic energy. Using the M06-2X functional, the total DFT energy was partitioned into a steric energy term (E(s)[ρ]), an electrostatic energy term (E(e)[ρ]), and a fermionic quantum energy term (E(q)[ρ]). This analysis revealed that branched alkanes have less (destabilizing) DFT steric energy than linear alkanes. The lower steric energy of branched alkanes is mitigated by an equal and opposite quantum energy term that contains the Pauli component of the kinetic energy and exchange-correlation energy. Because the steric and quantum energy terms cancel, this leaves the electrostatic energy term that favors alkane branching. Electrostatic effects, combined with correlation energy, explains why branched alkanes are more stable than linear alkanes. PMID:21086970

  10. Oxidative dehydrogenation of alkanes to unsaturated hydrocarbons

    DOEpatents

    Kung, Harold H.; Chaar, Mohamed A.

    1988-01-01

    Oxidative dehydrogenation of alkanes to unsaturated hydrocarbons is carried out over metal vanadate catalysts under oxidizing conditions. The vanadate catalysts are represented by the formulas M.sub.3 (VO.sub.4).sub.2 and MV.sub.2 O.sub.6, M representing Mg, Zn, Ca, Pb, or Cd. The reaction is carried out in the presence of oxygen, but the formation of oxygenate by-products is suppressed.

  11. Oxidative dehydrogenation of alkanes to unsaturated hydrocarbons

    DOEpatents

    Kung, H.H.; Chaar, M.A.

    1988-10-11

    Oxidative dehydrogenation of alkanes to unsaturated hydrocarbons is carried out over metal vanadate catalysts under oxidizing conditions. The vanadate catalysts are represented by the formulas M[sub 3](VO[sub 4])[sub 2] and MV[sub 2]O[sub 6], M representing Mg, Zn, Ca, Pb, or Cd. The reaction is carried out in the presence of oxygen, but the formation of oxygenate by-products is suppressed.

  12. Ordered Self-assembled Alkane Monolayer on Graphite and Graphene Surface

    NASA Astrophysics Data System (ADS)

    Su, Yudan; Han, Huiling; Wang, Feng; Cai, Qun; Tian, Chuanshan; Shen, Y. R.

    2015-03-01

    The 2D self-assembly of long chain alkane molecule on graphite and graphene had been studied with phase-sensitive sum-frequency vibrational spectroscopy (PS-SFVS) and scanning tunneling microscopy (STM). The spectrum of Imχs(2) (ωIR) which directly characterizes the surface resonances, shows 10-cm-1 red-shift of the symmetric-stretch frequency of the CH2 groups pointing towards graphite (or graphene) surface indicating Van der Waals interaction in between. The Gibbs adsorption energy of polyethylene (PE, n ~ 140) on graphite from chloroform solution was determined to be -42kJ/mol per molecule or -0.6 kJ/mol per CH2 unit. This large adsorption energy drives the long alkane chain to form an ordered self-assembled monolayer on graphite (or graphene). The sum frequency spectra suggest the orientation of carbon skeleton plane of alkane is predominately perpendicular to the graphite/graphene surface. Our STM result also provides clear evidence for the proposed molecular adsorption model. These results explain the large amount residual of long chain alkane on polystyrene (PS) or poly(methyl methacrylate) (PMMA) transferred graphene, and facilitate a better way to fabricate cleaner large-size graphene.

  13. The Structure of Ice Nanoclusters and Thin-films of Water Ice: Implications for Icy Grains in Cold Molecular Clouds

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance; Blake, David; Uffindell, Christine; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    The cubic to hexagonal phase transformation in water ice (I(sub c) yields I(sub h)) is used to measure the extent to which surface structure and impurities control bulk properties. In pure crystalline (I(sub c)) water ice nanoclusters and in thin-films of impure water ice, I(sub c) yields I(sub h) occurs at lower temperatures than in thin-films of pure water ice. The disordered surface of the 20 nm diameter nanoclusters promotes transformations or reactions which would otherwise be kinetically hindered. Likewise, impurities such as methanol introduce defects into the ice network, thereby allowing sluggish structural transitions to proceed. Such surface-related phenomena play an important role in promoting chemical reactions on interstellar ice grains within cold molecular clouds, where the first organic compounds are formed.

  14. Influence of molecular structure peculiarities of phthalocyanine derivatives on their supramolecular organization and properties in the bulk and thin films

    NASA Astrophysics Data System (ADS)

    Usol'tseva, Nadezhda V.; Kazak, Alexandr V.; Luk'yanov, Ivan Yu.; Sotsky, Valentin V.; Smirnova, Antonina I.; Yudin, Sergey G.; Shaposhnikov, Gennadiy P.; Galanin, Nikolay E.

    2014-08-01

    In order to study the influence of molecular structure peculiarities on supramolecular organization and properties in the bulk and thin films of discotic mesogens six new mix-substituted phthalocyanine derivatives with 3,6-dioctyloxyphthalonitrile and 3,4,5,6-tetrachlorophthalonitrile fragments were synthesized. Temperatures of phase transitions, types of mesophase and their dependence on molecule structure, chemical nature, position and ratio of different substituents as well as presence of holmium in the metal complexes were analyzed. The behavior of the studied molecules on the boundary between water and air was investigated and the peculiarity of supramolecular organization in floating layers as well as in thin films was determined. Quenching of luminescence in solutions of the studied compounds in the presence of fullerene C60 was determined, thus giving prospects for application of these compounds as sensors for fullerene microquantities.

  15. Self-regulated growth of LaVO{sub 3} thin films by hybrid molecular beam epitaxy

    SciTech Connect

    Zhang, Hai-Tian; Engel-Herbert, Roman; Dedon, Liv R.; Martin, Lane W.

    2015-06-08

    LaVO{sub 3} thin films were grown on SrTiO{sub 3} (001) by hybrid molecular beam epitaxy. A volatile metalorganic precursor, vanadium oxytriisopropoxide (VTIP), and elemental La were co-supplied in the presence of a molecular oxygen flux. By keeping the La flux fixed and varying the VTIP flux, stoichiometric LaVO{sub 3} films were obtained for a range of cation flux ratios, indicating the presence of a self-regulated growth window. Films grown under stoichiometric conditions were found to have the largest lattice parameter, which decreased monotonically with increasing amounts of excess La or V. Energy dispersive X-ray spectroscopy and Rutherford backscattering measurements were carried out to confirm film compositions. Stoichiometric growth of complex vanadate thin films independent of cation flux ratios expands upon the previously reported self-regulated growth of perovskite titanates using hybrid molecular beam epitaxy, thus demonstrating the general applicability of this growth approach to other complex oxide materials, where a precise control over film stoichiometry is demanded by the application.

  16. Effect of native oxide layers on copper thin-film tensile properties: A reactive molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Skarlinski, Michael D.; Quesnel, David J.

    2015-12-01

    Metal-oxide layers are likely to be present on metallic nano-structures due to either environmental exposure during use, or high temperature processing techniques such as annealing. It is well known that nano-structured metals have vastly different mechanical properties from bulk metals; however, difficulties in modeling the transition between metallic and ionic bonding have prevented the computational investigation of the effects of oxide surface layers. Newly developed charge-optimized many body [Liang et al., Mater. Sci. Eng., R 74, 255 (2013)] potentials are used to perform fully reactive molecular dynamics simulations which elucidate the effects that metal-oxide layers have on the mechanical properties of a copper thin-film. Simulated tensile tests are performed on thin-films while using different strain-rates, temperatures, and oxide thicknesses to evaluate changes in yield stress, modulus, and failure mechanisms. Findings indicate that copper-thin film mechanical properties are strongly affected by native oxide layers. The formed oxide layers have an amorphous structure with lower Cu-O bond-densities than bulk CuO, and a mixture of Cu2O and CuO charge character. It is found that oxidation will cause modifications to the strain response of the elastic modulii, producing a stiffened modulii at low temperatures (<75 K) and low strain values (<5%), and a softened modulii at higher temperatures. While under strain, structural reorganization within the oxide layers facilitates brittle yielding through nucleation of defects across the oxide/metal interface. The oxide-free copper thin-film yielding mechanism is found to be a tensile-axis reorientation and grain creation. The oxide layers change the observed yielding mechanism, allowing for the inner copper thin-film to sustain an FCC-to-BCC transition during yielding. The mechanical properties are fit to a thermodynamic model based on classical nucleation theory. The fit implies that the oxidation of the films

  17. Stimulation of Lipase Production During Bacterial Growth on Alkanes

    PubMed Central

    Breuil, Colette; Shindler, D. B.; Sijher, J. S.; Kushner, D. J.

    1978-01-01

    Acinetobacter lwoffi strain O16, a facultative psychrophile, can grow on crude oil, hexadecane, octadecane, and most alkanes when tested at 20 but not at 30°C. Growth occurred on a few alkanes at 30°C but after a longer lag than at 20°C. Cells grown on alkanes as sole carbon sources had high levels of cell-bound lipase. In contrast, previous work has shown that those grown on complex medium produced cell-free lipase and those grown on defined medium without alkanes produced little or no lipase. Low concentrations of the detergent Triton X-100 caused the liberation of most of the lipase activity of alkane-grown cells and increased total lipase activity. When ethanol and hexadecane were both present in a mineral medium, diauxic growth occurred; until the ethanol was completely used up, hexadecane was not utilized, and the lipase activity was very low. When growth on hexadecane began, lipase activity increased, reaching a level 50- to 100-fold higher than that of cells growing on ethanol. A similar pattern of lipase formation and hexadecane utilization was observed with Pseudomonas aeruginosa. Whenever A. lwoffi and other bacteria degraded alkanes they exhibited substantial lipase activity. Not all bacteria that produced lipase, however, could attack alkanes. Bacteria that could not produce lipase did not attack alkanes. The results suggest that a correlation may exist between lipase formation and alkane utilization. PMID:627533

  18. Diverse Bacterial Groups Contribute to the Alkane Degradation Potential of Chronically Polluted Subantarctic Coastal Sediments.

    PubMed

    Guibert, Lilian M; Loviso, Claudia L; Borglin, Sharon; Jansson, Janet K; Dionisi, Hebe M; Lozada, Mariana

    2016-01-01

    We aimed to gain insight into the alkane degradation potential of microbial communities from chronically polluted sediments of a subantarctic coastal environment using a combination of metagenomic approaches. A total of 6178 sequences annotated as alkane-1-monooxygenases (EC 1.14.15.3) were retrieved from a shotgun metagenomic dataset that included two sites analyzed in triplicate. The majority of the sequences binned with AlkB described in Bacteroidetes (32 ± 13 %) or Proteobacteria (29 ± 7 %), although a large proportion remained unclassified at the phylum level. Operational taxonomic unit (OTU)-based analyses showed small differences in AlkB distribution among samples that could be correlated with alkane concentrations, as well as with site-specific variations in pH and salinity. A number of low-abundance OTUs, mostly affiliated with Actinobacterial sequences, were found to be only present in the most contaminated samples. On the other hand, the molecular screening of a large-insert metagenomic library of intertidal sediments from one of the sampling sites identified two genomic fragments containing novel alkB gene sequences, as well as various contiguous genes related to lipid metabolism. Both genomic fragments were affiliated with the phylum Planctomycetes, and one could be further assigned to the genus Rhodopirellula due to the presence of a partial sequence of the 23S ribosomal RNA (rRNA) gene. This work highlights the diversity of bacterial groups contributing to the alkane degradation potential and reveals patterns of functional diversity in relation with environmental stressors in a chronically polluted, high-latitude coastal environment. In addition, alkane biodegradation genes are described for the first time in members of Planctomycetes. PMID:26547568

  19. Molecular fouling resistance of zwitterionic and amphiphilic initiated chemically vapor-deposited (iCVD) thin films

    SciTech Connect

    Yang, R; Goktekin, E; Wang, MH; Gleason, KK

    2014-01-01

    Biofouling is a universal problem in various applications ranging from water purification to implantable biomedical devices. Recent advances in surface modification have created a rich library of antifouling surface chemistries, many of which can be categorized into one of the two groups: hydrophilic surfaces or amphiphilic surfaces. We report the straightforward preparation of antifouling thin film coatings in both categories via initiated chemical vapor deposition. A molecular force spectroscopy-based method is demonstrated as a rapid and quantitative assessment tool for comparing the differences in antifouling characteristics. The fouling propensity of single molecules, as opposed to bulk protein solution or bacterial culture, is assessed. This method allows for the interrogation of molecular interaction without the complication resulted from protein conformational change or micro-organism group interactions. The molecular interaction follows the same trend as bacterial adhesion results obtained previously, demonstrating that molecular force probe is a valid method for the quantification and mechanistic examination of fouling. In addition, the molecular force spectroscopy-based method is able to distinguish differences in antifouling capability that is not resolvable by traditional static protein adsorption tests. To lend further insight into the intrinsic fouling resistance of zwitterionic and amphiphilic surface chemistries, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, advancing and receding water contact angles, and atomic force microscopy are used to elucidate the film properties that are relevant to their antifouling capabilities.

  20. Molecular fouling resistance of zwitterionic and amphiphilic initiated chemically vapor-deposited (iCVD) thin films

    SciTech Connect

    Yang, R; Goktekin, E; Wang, MH; Gleason, KK

    2014-08-08

    Biofouling is a universal problem in various applications ranging from water purification to implantable biomedical devices. Recent advances in surface modification have created a rich library of antifouling surface chemistries, many of which can be categorized into one of the two groups: hydrophilic surfaces or amphiphilic surfaces. We report the straightforward preparation of antifouling thin film coatings in both categories via initiated chemical vapor deposition. A molecular force spectroscopy-based method is demonstrated as a rapid and quantitative assessment tool for comparing the differences in antifouling characteristics. The fouling propensity of single molecules, as opposed to bulk protein solution or bacterial culture, is assessed. This method allows for the interrogation of molecular interaction without the complication resulted from protein conformational change or micro-organism group interactions. The molecular interaction follows the same trend as bacterial adhesion results obtained previously, demonstrating that molecular force probe is a valid method for the quantification and mechanistic examination of fouling. In addition, the molecular force spectroscopy-based method is able to distinguish differences in antifouling capability that is not resolvable by traditional static protein adsorption tests. To lend further insight into the intrinsic fouling resistance of zwitterionic and amphiphilic surface chemistries, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, advancing and receding water contact angles, and atomic force microscopy are used to elucidate the film properties that are relevant to their antifouling capabilities.

  1. Effect of molecular coverage on the electric conductance of a multi-walled carbon nanotube thin film

    NASA Astrophysics Data System (ADS)

    Kokabu, Takuya; Inoue, Shuhei; Matsumura, Yukihiko

    2016-06-01

    We investigated the influence of water adsorption on a CNT thin film. When we assumed that the magnitude of the change in electrical resistance was correlated with the surface coverage of the adsorbed molecules, this phenomenon could be explained by two-layer adsorption. The first layer was expressed by Langmuir adsorption and that on the second layer was expressed by Fowler-Guggenheim adsorption, which was derived by Bragg-Williams approximation and involved a lateral molecular interaction. The adsorption energy estimated by this assumption was on the same order as derived by DFT calculation.

  2. Improving stability of photoluminescence of ZnSe thin films grown by molecular beam epitaxy by incorporating Cl dopant

    NASA Astrophysics Data System (ADS)

    Wang, J. S.; Chen, W. J.; Yang, C. S.; Tsai, Y. H.; Wang, H. H.; Chen, R. H.; Shen, J. L.; Tsai, C. D.

    2011-01-01

    This investigation studies the effect of chlorine (Cl) dopant in ZnSe thin films that were grown by molecular beam epitaxy on their photoluminescence (PL) and the stability thereof. Free excitonic emission was observed at room-temperature in the Cl-doped sample. Photon irradiation with a wavelength of 404 nm and a power density of 9.1 W/cm2 has a much stronger effect on PL degradation than does thermal heating to a temperature of 150 °C. Additionally, this study shows that the generation of nonradiative centers by both photon irradiation and thermal heating can be greatly inhibited by incorporating Cl dopant.

  3. Characterization of the non-uniform reaction in chemically-amplified calix[4]resorcinarene molecular resist thin films

    SciTech Connect

    Prabhu, Vivek M.; Kang, Shuhui; Kline, R. Joseph; DeLongchamp, Dean M.; Fischer, Daniel A.; Wu, Wen-li; Satija, Sushil K.; Bonnesen, Peter V; Sha, Jing; Ober, Christoper K.

    2011-01-01

    The ccc stereoisomer-purified tert-butoxycarbonyloxy (t-Boc) protected calix[4]resorcinarene molecular resists blended with photoacid generator exhibit a non-uniform photoacid catalyzed reaction in thin films. The surface displays a reduced reaction extent, compared to the bulk, with average surface-layer thickness (7.0 1.8) nm determined by neutron reflectivity with deuterium-labeled t-Boc groups. Ambient impurities (amines and organic bases) are known to quench surface reactions and contribute, but grazing incidence X-ray diffraction shows an additional effect that the protected molecular resist are preferentially oriented at the surface, while the bulk of the film displayed diffuse scattering representative of amorphous packing. The surface deprotection reaction and presence of photoacid was quantified by near-edge X-ray absorption fine structure measurements.

  4. Molecular weight effects in the third-harmonic generation spectroscopy of thin films of the conjugated polymer MEH-PPV.

    PubMed

    Bahtiar, Ayi; Koynov, Kaloian; Ahn, Taek; Bubeck, Christoph

    2008-03-27

    Thin spin-cast films of poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) were prepared from samples whose weight-average molecular weight (Mw) was varied in the range of 10-1600 kg/mol. We have characterized the films by means of transmission and reflection ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy to derive the linear optical constants, and third-harmonic generation spectroscopy with variable laser wavelengths to get the modulus and phase angles of the complex third-order nonlinear optical susceptibility chi(3). Increasing molecular weight yields films with significantly larger chi(3) values, absorption coefficients, and refractive indices. The chi(3) values of films from the largest and lowest Mw differ by a factor of 4, which is caused by chain orientation effects, local field effects, and changes of the effective conjugation length. PMID:18311961

  5. Coexistence of spinodal instability and thermal nucleation in thin-film rupture:Insights from molecular levels

    SciTech Connect

    Nguyen, Trung D; Fuentes-Cabrera, Miguel A; Fowlkes, Jason Davidson; Rack, Philip D

    2014-01-01

    Despite extensive investigation using hydrodynamic models and experiments over the past decades, there remain open questions regarding the origin of the initial rupture of thin liquid films. One of the reasons that makes it difficult to identify the rupture origin is the coexistence of two dewettingmechanisms, namely, thermal nucleation and spinodal instability, as observed in many experimental studies. Using a coarse-grained model and large-scale molecular dynamics simulations, we are able to characterize the very early stage of dewetting in nanometer-thick liquid-metal films wetting a solid substrate. We observe the features characteristic of both spinodal instability and thermal nucleation in the spontaneously dewetting films and show that these two macroscopic mechanisms share a common origin at molecular levels.

  6. High mobility n-type organic thin-film transistors deposited at room temperature by supersonic molecular beam deposition

    SciTech Connect

    Chiarella, F. Barra, M.; Ciccullo, F.; Cassinese, A.; Toccoli, T.; Aversa, L.; Tatti, R.; Verucchi, R.

    2014-04-07

    In this paper, we report on the fabrication of N,N′-1H,1H-perfluorobutil dicyanoperylenediimide (PDIF-CN{sub 2}) organic thin-film transistors by Supersonic Molecular Beam Deposition. The devices exhibit mobility up to 0.2 cm{sup 2}/V s even if the substrate is kept at room temperature during the organic film growth, exceeding by three orders of magnitude the electrical performance of those grown at the same temperature by conventional Organic Molecular Beam Deposition. The possibility to get high-mobility n-type transistors avoiding thermal treatments during or after the deposition could significantly extend the number of substrates suitable to the fabrication of flexible high-performance complementary circuits by using this compound.

  7. Anaerobic oxidation of long-chain n-alkanes by the hyperthermophilic sulfate-reducing archaeon, Archaeoglobus fulgidus

    PubMed Central

    Khelifi, Nadia; Amin Ali, Oulfat; Roche, Philippe; Grossi, Vincent; Brochier-Armanet, Céline; Valette, Odile; Ollivier, Bernard; Dolla, Alain; Hirschler-Réa, Agnès

    2014-01-01

    The thermophilic sulfate-reducing archaeon Archaeoglobus fulgidus strain VC-16 (DSM 4304), which is known to oxidize fatty acids and n-alkenes, was shown to oxidize saturated hydrocarbons (n-alkanes in the range C10–C21) with thiosulfate or sulfate as a terminal electron acceptor. The amount of n-hexadecane degradation observed was in stoichiometric agreement with the theoretically expected amount of thiosulfate reduction. One of the pathways used by anaerobic microorganisms to activate alkanes is addition to fumarate that involves alkylsuccinate synthase as a key enzyme. A search for genes encoding homologous enzymes in A. fulgidus identified the pflD gene (locus-tag AF1449) that was previously annotated as a pyruvate formate lyase. A phylogenetic analysis revealed that this gene is of bacterial origin and was likely acquired by A. fulgidus from a bacterial donor through a horizontal gene transfer. Based on three-dimensional modeling of the corresponding protein and molecular dynamic simulations, we hypothesize an alkylsuccinate synthase activity for this gene product. The pflD gene expression was upregulated during the growth of A. fulgidus on an n-alkane (C16) compared with growth on a fatty acid. Our results suggest that anaerobic alkane degradation in A. fulgidus may involve the gene pflD in alkane activation through addition to fumarate. These findings highlight the possible importance of hydrocarbon oxidation at high temperatures by A. fulgidus in hydrothermal vents and the deep biosphere. PMID:24763368

  8. Comprehensive chemical kinetic modeling of the oxidation of C8 and larger n-alkanes and 2-methylalkanes

    SciTech Connect

    Sarathy, S M; Westbrook, C K; Pitz, W J; Mehl, M; Togbe, C; Dagaut, P; Wang, H; Oehlschlaeger, M; NIemann, U; Seshadri, K; Veloo, P S; Ji, C; Egolfopoulos, F; Lu, T

    2011-03-16

    Conventional petroleum jet and diesel fuels, as well as alternative Fischer-Tropsch (FT) fuels and hydrotreated renewable jet (HRJ) fuels, contain high molecular weight lightly branched alkanes (i.e., methylalkanes) and straight chain alkanes (n-alkanes). Improving the combustion of these fuels in practical applications requires a fundamental understanding of large hydrocarbon combustion chemistry. This research project presents a detailed and reduced chemical kinetic mechanism for singly methylated iso-alkanes (i.e., 2-methylalkanes) ranging from C{sub 8} to C{sub 20}. The mechanism also includes an updated version of our previously published C{sub 8} to C{sub 16} n-alkanes model. The complete detailed mechanism contains approximately 7,200 species 31,400 reactions. The proposed model is validated against new experimental data from a variety of fundamental combustion devices including premixed and nonpremixed flames, perfectly stirred reactors and shock tubes. This new model is used to show how the presence of a methyl branch affects important combustion properties such as laminar flame propagation, ignition, and species formation.

  9. The Uptake and Assembly of Alkanes within a Porous Nanocapsule in Water: New Information about Hydrophobic Confinement.

    PubMed

    Kopilevich, Sivil; Gottlieb, Hugo; Keinan-Adamsky, Keren; Müller, Achim; Weinstock, Ira A

    2016-03-24

    In Nature, enzymes provide hydrophobic cavities and channels for sequestering small alkanes or long-chain alkyl groups from water. Similarly, the porous metal oxide capsule [{Mo(VI) 6 O21 (H2 O)6 }12 {(Mo(V) 2 O4 )30 (L)29 (H2 O)2 }](41-) (L=propionate ligand) features distinct domains for sequestering differently sized alkanes (as in Nature) as well as internal dimensions suitable for multi-alkane clustering. The ethyl tails of the 29 endohedrally coordinated ligands, L, form a spherical, hydrophobic "shell", while their methyl end groups generate a hydrophobic cavity with a diameter of 11 Å at the center of the capsule. As such, C7 to C3 straight-chain alkanes are tightly intercalated between the ethyl tails, giving assemblies containing 90 to 110 methyl and methylene units, whereas two or three ethane molecules reside in the central cavity of the capsule, where they are free to rotate rapidly, a phenomenon never before observed for the uptake of alkanes from water by molecular cages or containers. PMID:26880403

  10. Growth characteristics of Ti-based fumaric acid hybrid thin films by molecular layer deposition.

    PubMed

    Cao, Yan-Qiang; Zhu, Lin; Li, Xin; Cao, Zheng-Yi; Wu, Di; Li, Ai-Dong

    2015-09-01

    Ti-based fumaric acid hybrid thin films were successfully prepared using inorganic TiCl4 and organic fumaric acid as precursors by molecular layer deposition (MLD). The effect of deposition temperature from 180 °C to 350 °C on the growth rate, composition, chemical state, and topology of hybrid films has been investigated systematically by means of a series of analytical tools such as spectroscopic ellipsometry, atomic force microscopy (AFM), high resolution X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The MLD process of the Ti-fumaric acid shows self-limiting surface reaction with a reasonable growth rate of ∼0.93 Å per cycle and small surface roughness of ∼0.59 nm in root-mean-square value at 200 °C. A temperature-dependent growth characteristic has been observed in the hybrid films. On increasing the temperature from 180 °C to 300 °C, the growth rate decreases from 1.10 to 0.49 Å per cycle and the XPS composition of the film's C : O : Ti ratio changes from 8.35 : 7.49 : 1.00 to 4.66 : 4.80 : 1.00. FTIR spectra indicate that the hybrid films show bridging bonding mode at a low deposition temperature of 200 °C and bridging/bidentate mixed bonding mode at elevated deposition temperatures of 250 and 300 °C. The higher C and O amounts deviating from the ideal composition may be ascribed to increased organic incorporation into the hybrid films at lower deposition temperature and temperature-dependent density of reactive sites (-OH). The composition of hybrid films grown at 350 °C shows a dramatic decrease in C and O elemental composition (C : O : Ti = 1.97 : 2.76 : 1.00) due to the thermal decomposition of the fumaric acid precursor. The produced by-product H2O changes the structure of the hybrid films, resulting in the formation of more Ti-O bonds at high temperatures. The stability of the hybrid films against chemical and thermal treatment, and long-term storage by

  11. Conformation of liquid N-alkanes.

    PubMed Central

    Goodsaid-Zalduondo, F; Engelman, D M

    1981-01-01

    The conformations of liquid n-alkanes have been studied using neutron scattering techniques to better understand the conformational forces present in membrane lipid interiors. We have studied hydrocarbon chains having lengths comparable to those found for esterified membrane lipid fatty acids, and find that the steric constraints of packing in the liquid state do not change the conformational distributions of hydrocarbon chains from those imposed by the intrachain forces present in the gas phase. It follows that the central region of membranes containing lipids in the disordered state should contain hydrocarbon chain conformations determined primarily by intrachain forces. PMID:7272453

  12. Molecular dynamics simulations of irradiation of α-Fe thin films with energetic Fe ions under channeling conditions

    NASA Astrophysics Data System (ADS)

    Aliaga, M. J.; Prokhodtseva, A.; Schaeublin, R.; Caturla, M. J.

    2014-09-01

    Using molecular dynamics simulations with recent interatomic potentials developed for Fe, we have studied the defects in thin films of pure bcc Fe induced by the displacement cascade produced by Fe atoms of 50, 100, and 150 keV impinging under a channeling incident angle of 6° to a [0 0 1] direction. The thin films have a thickness between 40 and 100 nm, to reproduce the thickness of the samples used in transmission electron microscope in situ measurements during irradiation. In the simulations we focus mostly on the effect of channeling and free surfaces on damage production. The results are compared to bulk cascades. The comparison shows that the primary damage in thin films of pure Fe is quite different from that originated in the volume of the material. The presence of near surfaces can lead to a variety of events that do not occur in bulk collisional cascades, such as the production of craters and the glide of self-interstitial defects to the surface. Additionally, in the range of energies and the incident angle used, channeling is a predominant effect that significantly reduces damage compared to bulk cascades.

  13. Atomic/Molecular Layer Deposition of Lithium Terephthalate Thin Films as High Rate Capability Li-Ion Battery Anodes.

    PubMed

    Nisula, Mikko; Karppinen, Maarit

    2016-02-10

    We demonstrate the fabrication of high-quality electrochemically active organic lithium electrode thin films by the currently strongly emerging combined atomic/molecular layer deposition (ALD/MLD) technique using lithium terephthalate, a recently found anode material for lithium-ion battery (LIB), as a proof-of-the-concept material. Our deposition process for Li-terephthalate is shown to well comply with the basic principles of ALD-type growth including the sequential self-saturated surface reactions, a necessity when aiming at micro-LIB devices with three-dimensional architectures. The as-deposited films are found crystalline across the deposition temperature range of 200-280 °C, which is a trait highly desired for an electrode material but rather unusual for hybrid inorganic-organic thin films. Excellent rate capability is ascertained for the Li-terephthalate films with no conductive additives required. The electrode performance can be further enhanced by depositing a thin protective LiPON solid-state electrolyte layer on top of Li-terephthalate; this yields highly stable structures with capacity retention of over 97% after 200 charge/discharge cycles at 3.2 C. PMID:26812433

  14. O thin films with different Mg contents on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chen, W.; Pan, X. H.; Ding, P.; Zhang, H. H.; Chen, S. S.; Dai, W.; Huang, J. Y.; Lu, B.; Ye, Z. Z.

    2014-09-01

    We report the growth and characterization of a series of non-polar Zn1- x Mg x O thin films with different Mg contents, which have been prepared on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy. Structural properties are anisotropic and surfaces of films show stripes running along the c-axis direction. The films exhibit atomically smooth surface with the minimal root mean square surface roughness of 0.36 nm. Non-polar Zn1- x Mg x O thin film is much easier to obtain pure a-plane single crystal orientation when Mg content is high. The quality of the non-polar Zn1- x Mg x O thin films is evidenced by X-ray diffraction (XRD) rocking curves full-width at half-maximum of 1,350 arcsec for the () reflection and 1,760 arcsec for the () reflection, respectively. Room temperature photoluminescence peak shifts monotonously from 3.29 to 3.56 eV as Mg content increases from 0 to 0.13. Alloying with Mg is found to widen the bandgap energy of the ZnO.

  15. GC-{sup 13}C IRMS characterisation of extractable and covalently bound alkanes in petroleum source rocks to reveal compositional fractionation effects

    SciTech Connect

    Love, G.D.; Fallick, A.E.; Taylor, C.

    1995-12-31

    The application of a sequential extraction/degradation scheme to differentiate between molecular alkanes (both easily extractable and physically-trapped) and covalently-bound alkyl moieties to a number of vitrinite concentrates and petroleum source rocks has been reported previously. Gas chromatography-isotope ratio mass spectrometry GC-s{sup 13}C IRMS has now been applied to the different awe fractions to probe compositional fractionation effects that might occur from the different initial biological inputs. For a Turkish oil shale (Goynuk - Type I kerogen), inputs from diverse sources, including phytoplanktron, higher plants and bacteria were implied from analysis of solvent-extractable alkanes. However, the much larger quantities of covalently-bound alkanes had an isotopic signature typical of eukarytoic (freshwater) algae. The isotopic uniformity of alkanes/alkenes released from sequential hydropyrolysis of a torbanite (Duunet shale) confirmed that this sample was largely derived from the selective preservation of resistant aliphatic biopolymers found in Botryococcus cell walls.

  16. Selective Adsorption of n-Alkanes from n-Octane on Metal-Organic Frameworks: Length Selectivity.

    PubMed

    Bhadra, Biswa Nath; Jhung, Sung Hwa

    2016-03-16

    The liquid-phase adsorption of n-alkanes (from n-octane (C8) solvent) with different chain lengths was carried out over three metal-organic frameworks (MOFs), viz., metal-azolate framework-6 (MAF-6), copper-benzenetricarboxylate (Cu-BTC), and iron-benzenetricarboxylate (MIL-100(Fe)), and a conventional adsorbent activated carbon (AC). MAF-6 and Cu-BTC were found to have significant selectivity for the adsorption of n-dodecane (C12) and n-heptane (C7), respectively, from C8. Selectivity for C12 on MAF-6 was also observed in competitive adsorption from binary adsorbate systems. To understand the selective adsorption of C12 on MAF-6 more, the adsorption of C12 from C8 over MAF-6 was investigated in detail and compared with that over AC. The obtained selectivities over MAF-6 and Cu-BTC for C12 and C7, respectively, might be explained by the similarity between cavity size of adsorbents and molecular length of n-alkanes. In the case of AC and MIL-100(Fe), no specific adsorption selectivity was observed because the cavity sizes of the two adsorbents are larger than the size of the n-alkanes used in this study. The adsorption capacities (qt) of n-alkanes over AC and MIL-100(Fe) decreased and increased, respectively, as the polarity (or length) of the adsorbates increased, probably because of nonpolar and polar interactions between the adsorbents and n-alkanes. On the basis of the results obtained, it can be concluded that matching the cavity size (of adsorbents) with the molecular length (of n-alknaes) is more important parameter than the MOF's hydrophilicity/hydrophobicity for the selective adsorption/separation of alkanes. PMID:26905721

  17. Prediction of static contact angles on the basis of molecular forces and adsorption data

    NASA Astrophysics Data System (ADS)

    Diaz, M. Elena; Savage, Michael D.; Cerro, Ramon L.

    2016-08-01

    At a three-phase contact line, a liquid bulk phase is in contact with and coexists with a very thin layer of adsorbed molecules. This adsorbed film in the immediate vicinity of a liquid wedge modifies the balance of forces between the liquid and solid phases such that, when included in the balance of forces, a quantitative relationship emerges between the adsorbed film thickness and the static contact angle. This relationship permits the prediction of static contact angles from molecular forces and equilibrium adsorption data by means of quantities that are physically meaningful and measurable. For n-alkanes on polytetrafluoroethylene, for which there are experimental data available on adsorption and contact angles, our computations show remarkable agreement with the data. The results obtained are an improvement on previously published calculations—particularly for alkanes with a low number of carbon atoms, for which adsorption is significant.

  18. Maximizing the dielectric response of molecular thin films via quantum chemical design.

    PubMed

    Heitzer, Henry M; Marks, Tobin J; Ratner, Mark A

    2014-12-23

    Developing high-capacitance organic gate dielectrics is critical for advances in electronic circuitry based on unconventional semiconductors. While high-dielectric constant molecular substances are known, the mechanism of dielectric response and the fundamental chemical design principles are not well understood. Using a plane-wave density functional theory formalism, we show that it is possible to map the atomic-scale dielectric profiles of molecule-based materials while capturing important bulk characteristics. For molecular films, this approach reveals how basic materials properties such as surface coverage density, molecular tilt angle, and π-system planarity can dramatically influence dielectric response. Additionally, relatively modest molecular backbone and substituent variations can be employed to substantially enhance film dielectric response. For dense surface coverages and proper molecular alignment, conjugated hydrocarbon chains can achieve dielectric constants of >8.0, more than 3 times that of analogous saturated chains, ∼2.5. However, this conjugation-related dielectric enhancement depends on proper molecular orientation and planarization, with enhancements up to 60% for proper molecular alignment with the applied field and an additional 30% for conformations such as coplanarity in extended π-systems. Conjugation length is not the only determinant of dielectric response, and appended polarizable high-Z substituents can increase molecular film response more than 2-fold, affording estimated capacitances of >9.0 μF/cm2. However, in large π-systems, polar substituent effects are substantially attenuated. PMID:25415650

  19. Catalytic conversion of light alkanes. Quarterly progress report, April 1--June 30, 1992

    SciTech Connect

    Lyons, J.E.

    1992-06-30

    The second Quarterly Report of 1992 on the Catalytic Conversion of Light Alkanes reviews the work done between April 1, 1992 and June 31, 1992 on the Cooperative Agreement. The mission of this work is to devise a new catalyst which can be used in a simple economic process to convert the light alkanes in natural gas to oxygenate products that can either be used as clean-burning, high octane liquid fuels, as fuel components or as precursors to liquid hydrocarbon uwspomdon fuel. During the past quarter we have continued to design, prepare, characterize and test novel catalysts for the mild selective reaction of light hydrocarbons with air or oxygen to produce alcohols directly. These catalysts are designed to form active metal oxo (MO) species and to be uniquely active for the homolytic cleavage of the carbon-hydrogen bonds in light alkanes producing intermediates which can form alcohols. We continue to investigate three molecular environments for the active catalytic species that we are trying to generate: electron-deficient macrocycles (PHASE I), polyoxometallates (PHASE II), and regular oxidic lattices including zeolites and related structures as well as other molecular surface structures having metal oxo groups (PHASE I).

  20. Catalytic conversion of light alkanes: Quarterly report, January 1-March 31, 1992

    SciTech Connect

    Biscardi, J.; Bowden, P.T.; Durante, V.A.; Ellis, P.E. Jr.; Gray, H.B.; Gorbey, R.G.; Hayes, R.C.; Hodge, J.; Hughes, M.; Langdale, W.A.; Lyons, J.E.; Marcus, B.; Messick, D.; Merrill, R.A.; Moore, F.A.; Myers, H.K. Jr.; Seitzer, W.H.; Shaikh, S.N.; Tsao, W.H.; Wagner, R.W.; Warren, R.W.; Wijesekera, T.P.

    1997-05-01

    The first Quarterly Report of 1992 on the Catalytic Conversion of Light Alkanes reviews the work done between January 1. 1992 and March 31, 1992 on the Cooperative Agreement. The mission of this work is to devise a new catalyst which can be used in a simple economic process to convert the light alkanes in natural gas to oxygenate products which can either be used as clean-burning, high octane liquid fuels, as fuel components or as precursors to liquid hydrocarbon transportation fuel. During the past quarter we have continued to design, prepare, characterize and test novel catalysts for the mild selective reaction of light hydrocarbons with air or oxygen to produce alcohols directly. These catalysts are designed to form active metal oxo (MO) species and to be uniquely active for the homolytic cleavage of the carbon-hydrogen bonds in light alkanes producing intermediates which can form alcohols. We continue to investigate three molecular environments for the active catalytic species that we are trying to generate: electron-deficient porphryinic macrocycles (PHASE I), polyoxometallates (PHASE II), and regular oxidic lattices including zeolites and related structures as well as other molecular surface structures having metal oxo groups (PHASE III).

  1. 40 CFR 721.535 - Halogenated alkane (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.535 Halogenated alkane (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halogenated alkane (PMN P-01-433) is...

  2. 40 CFR 721.536 - Halogenated phenyl alkane.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.536 Halogenated phenyl alkane. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halogenated phenyl alkane (PMN P-89-867)...

  3. 40 CFR 721.535 - Halogenated alkane (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721.535 Halogenated alkane (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halogenated alkane (PMN P-01-433) is...

  4. Thomas Reiche Kuhn populations in alkanes

    NASA Astrophysics Data System (ADS)

    Lazzeretti, P.; Caputo, M. C.; Ferraro, M. B.

    1999-07-01

    Atomic populations in a molecule have been defined via the Thomas-Reiche-Kuhn sum rule for oscillator strengths written within the acceleration gauge. These atomic populations are related to nuclear electric shieldings, i.e., to geometrical derivatives of electric dipole moment, and can therefore be connected with observable infrared intensities. A number of relationships can be considered to test a priori the quality of calculated electronic charges and to assess their physical meaning. It is shown via extended numerical tests on the first members of the alkane series that the Thomas-Reiche-Kuhn populations are consistent with a (small) polarity C +-H - of carbon-hydrogen bond in methane, for which a bond dipole moment can be exactly defined. Although the idea of bond dipole cannot be extended to the C-H fragments belonging to other alkane molecules in the absence of local C3 v symmetry, the calculations prove that the same electron charge polarization should characterize the whole homologous series.

  5. Alkanes in benthic organisms from the Buccaneer oil field

    SciTech Connect

    Middleditch, B.S.; Basile, B.

    1980-06-01

    About 200 g per day of alkanes are present in brine discharged from each of two production platforms in the Buccaneer oil field in the NW Gulf of Mexico. These alkanes disperse rapidly in the water column, so that seawater concentrations of petroleum alkanes in this region are generally very low. They can be taken up to some extent by plankton, fish, and barnacles, but the petroleum alkane concentrations in these organisms are also relatively low. The largest pool of petroleum alkanes is in the surficial sediments, where concentrations of up to 25 ppM are observed, with concentration gradients extending more than 20 m from the production platforms. Organisms are examined which are exposed to these sediments and, for comparison, other specimens from control sites around structures from which there are no discharges.

  6. Utilization of n-Alkanes by Cladosporium resinae

    PubMed Central

    Teh, J. S.; Lee, K. H.

    1973-01-01

    Four different isolates of Cladosporium resinae from Australian soils were tested for their ability to utilize liquid n-alkanes ranging from n-hexane to n-octadecane under standard conditions. The isolates were unable to make use of n-hexane, n-heptane, and n-octane for growth. In fact, these hydrocarbons, particularly n-hexane, exerted an inhibitory effect on spore germination and mycelial growth. All higher n-alkanes from n-nonane to n-octadecane were assimilated by the fungus, although only limited growth occurred on n-nonane and n-decane. The long chain n-alkanes (C14 to C18) supported good growth of all isolates, but there was no obvious correlation between cell yields and chain lengths of these n-alkanes. Variation in growth responses to individual n-alkane among the different isolates was also observed. The cause of this variation is unknown. PMID:4735447

  7. Sophorolipids from Torulopsis bombicola: possible relation to alkane uptake.

    PubMed Central

    Ito, S; Inoue, S

    1982-01-01

    Torulopsis bombicola produces extracellular sophorolipids when it is grown on water-insoluble alkanes. Sophorolipids and related model compounds, which were not themselves used for growth, were found to stimulate markedly the growth of T. bombicola on alkanes. This stimulatory effect was restricted to growth on C10 to C20 alkanes, whereas no significantly influence was observed for growth on fatty alcohols, fatty acids, glucose, or glycerol. The nonionic methyl ester of the glycolipid supported the greatest cell yield. However, a number of synthetic nonionic surfactants were unable to replace the glycolipid. When organisms were grown on hexadecane, stimulation of growth by sophorolipids was observed almost exclusively with strains of Torulopsis yeasts. In contrast, the growth of other typical alkane-utilizing yeasts, such as candida and Pichia strains, was inhibited or not affected. It appears that sophorolipids are involved in alkane dissimilation by T. bombicola through an undetermined mechanism. PMID:7201782

  8. Synthesis, conformational and theoretical studies of 1,n-di(2-formyl-4-phenylazophenoxy)alkanes

    NASA Astrophysics Data System (ADS)

    Balachander, R.; Manimekalai, A.

    2016-01-01

    1,n-di(2-Formyl-4-phenylazophenoxy)alkanes 1 and 2 and 1,3-di(2-formyl-4-phenylazophenoxymethyl)benzene 3 were synthesis and characterized by FT-IR, UV-Vis, 1H, 13C NMR and mass spectral studies. The stable conformations of 1-3 were predicted theoretically and selected geometrical parameters were derived from optimized structures. The molecular parameters of HOMO-LUMO energies, polarizability, hyperpolarizability, natural bond orbital (NBO), atom in molecule (AIM) analysis and molecular electrostatic potential (MEP) surfaces were determined by the density functional theory (DFT) method and analysed.

  9. Intermolecular electronic coupling in organic molecular thin films measured by temperature modulation spectroscopy

    SciTech Connect

    Yadav, Abhishek; Jin, Y; Chan, P. K. L.; Shtein, Max; Pipe, Kevin P.

    2010-01-01

    Temperature modulation spectroscopy is used to obtain the temperature dependences of oscillator strength, exciton transition energy, and line width for a copper phthalocyanine thin film. With increasing temperature, the oscillator strength exhibits a pronounced decrease for charge transfer (CT) excitons, making this technique suitable for differentiating exciton types. From the measured magnitude and temperature dependence of the CT oscillator strength, we obtain estimates for the intermolecular electronic coupling and its exponential decay coefficient.

  10. Spectroscopy of the tilde A state of NO-alkane complexes (alkane = methane, ethane, propane, and n-butane)

    NASA Astrophysics Data System (ADS)

    Tamé-Reyes, Victor M.; Gardner, Adrian M.; Harris, Joe P.; McDaniel, Jodie; Wright, Timothy G.

    2012-12-01

    We have recorded (1+1) resonance-enhanced multiphoton ionization spectra of complexes formed between NO and the alkanes: CH4, C2H6, C3H8, and n-C4H10. The spectra correspond to the tilde A ← tilde X transition, which is a NO-localized 3s ← 2pπ* transition. In line with previous work, the spectrum for NO-CH4 has well-defined structure, but this is only partially resolved for the other complexes. The spectra recorded in the NO+-alkane mass channels all show a slowly rising onset, followed by a sharp offset, which is associated with dissociation of NO-alkane, from which binding energies in the tilde X and tilde A states are deduced. Beyond this sharp offset, there is a further rise in signal, which is attributed to fragmentation of higher complexes, NO-(alkane)n. Analysis of these features allows binding energies for (NO-alkane) ... alkane to be estimated, and these suggest that in the NO-(alkane)2 complexes, the second alkane molecule is bound to the first, rather than to NO. Calculated structures for the 1:1 complexes are reported, as well as binding energies.

  11. Molecular solution approach to synthesize electronic quality Cu2ZnSnS4 thin films.

    PubMed

    Yang, Wenbing; Duan, Hsin-Sheng; Cha, Kitty C; Hsu, Chia-Jung; Hsu, Wan-Ching; Zhou, Huanping; Bob, Brion; Yang, Yang

    2013-05-01

    Successful implementation of molecular solution processing from a homogeneous and stable precursor would provide an alternative, robust approach to process multinary compounds compared with physical vapor deposition. Targeting deposition of chemically clear, high quality crystalline films requires specific molecular structure design and solvent selection. Hydrazine (N2H4) serves as a unique and powerful medium, particularly to incorporate selected metallic elements and chalcogens into a stable solution as metal chalcogenide complexes (MCC). However, not all the elements and compounds can be easily dissolved. In this manuscript, we demonstrate a paradigm to incorporate previously insoluble transitional-metal elements into molecular solution as metal-atom hydrazine/hydrazine derivative complexes (MHHD), as exemplified by dissolving of the zinc constituent as Zn(NH2NHCOO)2(N2H4)2. Investigation into the evolution of molecular structure reveals the hidden roadmap to significantly enrich the variety of building blocks for soluble molecule design. The new category of molecular structures not only set up a prototype to incorporate other elements of interest but also points the direction for other compatible solvent selection. As demonstrated from the molecular precursor combining Sn-/Cu-MCC and Zn-MHHD, an ultrathin film of copper zinc tin sulfide (CZTS) was deposited. Characterization of a transistor based on the CZTS channel layer shows electronic properties comparable to CuInSe2, confirming the robustness of this molecular solution processing and the prospect of earth abundant CZTS for next generation photovoltaic materials. This paradigm potentially outlines a universal pathway, from individual molecular design using selected chelated ligands and combination of building blocks in a simple and stable solution to fundamentally change the way multinary compounds are processed. PMID:23581974

  12. Path Integral Monte Carlo Simulations of Solid Molecular Hydrogen Surfaces and Thin HELIUM-4 Films on Molecular Hydrogen Substrates

    NASA Astrophysics Data System (ADS)

    Wagner, Marcus

    Based on Richard P. Feynman's formulation of quantum mechanics, Path Integral Monte Carlo is a computational ab-initio method to calculate finite temperature equilibrium properties of quantum many-body systems. As input, only fundamental physical constants and pair-potentials are required. We carry out the first ab-initio particle simulations of three related physical systems. First, the bare H _2 substrate is simulated between 0.5 and 1.3K, because a liquid H_2 film is a candidate for a new superfluid. We find evidence of quantum exchange in surface terraces for up to 1K. Second, the melting of the H_2 surface between 3 and 15K is examined since this is the cleanest example of quantum surface melting. Third, atomically thin superfluid ^4He films on H_2 surfaces are simulated, calculating binding energies per ^4He atom and third sound, an important experimental probe for superfuid ^4 He films. For all systems we compute density profiles perpendicular and parallel to the surface and compare to experiment. We treat both H_2 molecules and ^4He atoms on the same footing, as spherical particles. For simulations of bulk/vapor interfaces and surface adsorption, a realistic representation of the macroscopic surface is crucial. Therefore, we introduce an external potential to account for arbitrarily layered substrates and long-range corrections. Two algorithms for parallel computers with independent processors are introduced, one to manage concurrent simulations of entire phase-diagrams, and one to improve input/output speed for files shared by all processors.

  13. Effect of native oxide layers on copper thin-film tensile properties: A reactive molecular dynamics study

    SciTech Connect

    Skarlinski, Michael D.; Quesnel, David J.

    2015-12-21

    Metal-oxide layers are likely to be present on metallic nano-structures due to either environmental exposure during use, or high temperature processing techniques such as annealing. It is well known that nano-structured metals have vastly different mechanical properties from bulk metals; however, difficulties in modeling the transition between metallic and ionic bonding have prevented the computational investigation of the effects of oxide surface layers. Newly developed charge-optimized many body [Liang et al., Mater. Sci. Eng., R 74, 255 (2013)] potentials are used to perform fully reactive molecular dynamics simulations which elucidate the effects that metal-oxide layers have on the mechanical properties of a copper thin-film. Simulated tensile tests are performed on thin-films while using different strain-rates, temperatures, and oxide thicknesses to evaluate changes in yield stress, modulus, and failure mechanisms. Findings indicate that copper-thin film mechanical properties are strongly affected by native oxide layers. The formed oxide layers have an amorphous structure with lower Cu-O bond-densities than bulk CuO, and a mixture of Cu{sub 2}O and CuO charge character. It is found that oxidation will cause modifications to the strain response of the elastic modulii, producing a stiffened modulii at low temperatures (<75 K) and low strain values (<5%), and a softened modulii at higher temperatures. While under strain, structural reorganization within the oxide layers facilitates brittle yielding through nucleation of defects across the oxide/metal interface. The oxide-free copper thin-film yielding mechanism is found to be a tensile-axis reorientation and grain creation. The oxide layers change the observed yielding mechanism, allowing for the inner copper thin-film to sustain an FCC-to-BCC transition during yielding. The mechanical properties are fit to a thermodynamic model based on classical nucleation theory. The fit implies that the oxidation of the

  14. The role of surface electronic structure in thin film molecular ordering.

    SciTech Connect

    Sakurai, T.; Tromp, R. M.; Meyer zu Heringdorf, F.; Sadowski, J.; Thayer, Gayle Echo

    2005-05-01

    We show that the orientation of pentacene molecules is controlled by the electronic structure of the surface on which they are deposited. We suggest that the near-Fermi level density of states above the surface controls the interaction of the substrate with the pentacene {pi} orbitals. A reduction of this density as compared to noble metals, realized in semimetallic Bi(001) and Si(111)(5 x 2)Au surfaces, results in pentacene standing up. Interestingly, pentacene grown on Bi(001) is highly ordered, yielding the first vertically oriented epitaxial pentacene thin films observed to date.

  15. Molecular Beam Epitaxial (MBE) Growth and Characterization of Thin Films of Semiconductor Tin

    NASA Astrophysics Data System (ADS)

    Folkes, P.; Taylor, P.; Rong, C.; Nichols, B.; Hier, H.; Burke, R.; Neupane, M.

    Recent theoretical predictions that a two-dimensional monolayer of semiconductor tin is a two-dimensional topological insulator and experimental evidence of three-dimensional topological insulator behavior in strained ultrathin films of semiconductor tin grown by MBE on InSb has generated intense research interest. This research is primarily focused on the MBE growth and topological characteristics of ultrathin films of semiconductor tin. In this talk we present results of a study on the MBE growth and the transport, structural and optical characterization of thin films of semiconductor tin on several different substrates.

  16. Kinetic study of asphaltene dissolution in amphiphile/alkane solutions

    SciTech Connect

    Permsukarome, P.; Chang, C.; Fogler, H.S.

    1997-09-01

    The kinetics of dissolution of pentane-insoluble solid asphaltene precipitates by amphiphile/alkane solutions were investigated using a differential reactor flow system. Two amphiphiles, dodecylbenzenesulfonic acid and nonylphenol, and five alkane solvents, ranging from hexane to hexadecane, were used. Results showed that the rate of asphaltene dissolution in amphiphile/alkane fluids could be approximated with a first-order kinetics with respect to the undissolved asphaltene mass in solution. The specific dissolution rate constant, k, varied with the concentration of amphiphiles, the type of alkane solvents, the temperature, and the fluid flow rate. The rate of asphaltene dissolution displayed a Langmuir-Hinshelwood kinetics with respect to the concentration of amphiphiles. Increasing the temperature of amphiphile/alkane fluids also enhanced the rate of asphaltene dissolution. The apparent activation energy for asphaltene dissolution was approximated to be 4--7 kcal/mol. The rate of asphaltene dissolution was also greater in amphiphile solutions containing lighter alkanes, such as hexane, with lower viscosities. These trends suggest that both surface reaction and mass transfer processes are important to the rate of asphaltene dissolution in amphiphile/alkane fluids.

  17. Long-chain alkane production by the yeast Saccharomyces cerevisiae.

    PubMed

    Buijs, Nicolaas A; Zhou, Yongjin J; Siewers, Verena; Nielsen, Jens

    2015-06-01

    In the past decade industrial-scale production of renewable transportation biofuels has been developed as an alternative to fossil fuels, with ethanol as the most prominent biofuel and yeast as the production organism of choice. However, ethanol is a less efficient substitute fuel for heavy-duty and maritime transportation as well as aviation due to its low energy density. Therefore, new types of biofuels, such as alkanes, are being developed that can be used as drop-in fuels and can substitute gasoline, diesel, and kerosene. Here, we describe for the first time the heterologous biosynthesis of long-chain alkanes by the yeast Saccharomyces cerevisiae. We show that elimination of the hexadecenal dehydrogenase Hfd1 and expression of a redox system are essential for alkane biosynthesis in yeast. Deletion of HFD1 together with expression of an alkane biosynthesis pathway resulted in the production of the alkanes tridecane, pentadecane, and heptadecane. Our study provides a proof of principle for producing long-chain alkanes in the industrial workhorse S. cerevisiae, which was so far limited to bacteria. We anticipate that these findings will be a key factor for further yeast engineering to enable industrial production of alkane based drop-in biofuels, which can allow the biofuel industry to diversify beyond bioethanol. PMID:25545362

  18. Epitaxial growth of SrTiO{sub 3} thin film on Si by laser molecular beam epitaxy

    SciTech Connect

    Zhou, X. Y.; Miao, J.; Dai, J. Y.; Chan, H. L. W.; Choy, C. L.; Wang, Y.; Li, Q.

    2007-01-01

    SrTiO{sub 3} thin films have been deposited on Si (001) wafers by laser molecular beam epitaxy using an ultrathin Sr layer as the template. X-ray diffraction measurements indicated that SrTiO{sub 3} was well crystallized and epitaxially aligned with Si. Cross-sectional observations in a transmission electron microscope revealed that the SrTiO{sub 3}/Si interface was sharp, smooth, and fully crystallized. The thickness of the Sr template was found to be a critical factor that influenced the quality of SrTiO{sub 3} and the interfacial structure. Electrical measurements revealed that the SrTiO{sub 3} film was highly resistive.

  19. Nucleation and stochiometry dependence of rutile-TiO2 thin films grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Constantin, Costel; Sun, Kai; Feenstra, R. M.

    2008-03-01

    Considerable interest has been shown of late in transition-metal oxides. One case is the titanium dioxide system, which can have applications as a high-k dielectric gate insulator for Si-based devicesootnotetextZ. J. Luo et al., Appl. Phys. Lett. 79, 2803. In this study, rutile-TiO2 thin films were grown on GaN(0001) substrates by oxygen plasma-assisted molecular beam epitaxy. Two sets of films were grown, one in which the initial GaN surface is prepared WITH the pseudo 1x1 Ga-rich surface reconstruction, and the other set, WITHOUT the pseudo 1x1. On top of these two type of surfaces, the rutile-TiO2 thin films were grown at Ts˜ 600 ^oC, and with a thickness ˜ 40 - 50 nm. During growth, reflection high-energy electron diffraction indicated a reversible stoichiometry transition from O-rich to Ti-rich growth. Post-growth x-ray diffraction measurements performed on the samples WITHOUT the GaN pseudo 1x1, show the presence of additional peaks at 2θ = 52.9^o, which implies the existence of additional phases. In addition, the high-resolution transmission electron microscopy performed on these samples show a high degree of disorder, as compared to the samples prepared WITH the pseudo 1x1. Work supported by ONR.

  20. 7-Octenyltrichrolosilane/trimethyaluminum hybrid dielectrics fabricated by molecular-atomic layer deposition on ZnO thin film transistors

    NASA Astrophysics Data System (ADS)

    Huang, Jie; Lee, Mingun; Lucero, Antonio T.; Cheng, Lanxia; Ha, Min-Woo; Kim, Jiyoung

    2016-06-01

    We demonstrate the fabrication of 7-octenytrichlorosilane (7-OTS)/trimethylaluminum (TMA) organic–inorganic hybrid films using molecular-atomic layer deposition (MALD). The properties of 7-OTS/TMA hybrid films are extensively investigated using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and electrical measurements. Our results suggest that uniform and smooth amorphous hybrid thin films with excellent insulating properties are obtained using the MALD process. Films have a relatively high dielectric constant of approximately 5.0 and low leakage current density. We fabricate zinc oxide (ZnO) based thin film transistors (TFTs) using 7-OTS/TMA hybrid material as a back gate dielectric with the top ZnO channel layer deposited in-situ via MALD. The ZnO TFTs exhibit a field effect mobility of approximately 0.43 cm2 V‑1 s‑1, a threshold voltage of approximately 1 V, and an on/off ratio of approximately 103 under low voltage operation (from ‑3 to 9 V). This work demonstrates an organic–inorganic hybrid gate dielectric material potentially useful in flexible electronics application.

  1. Effect of twin boundary on nanoimprint process of bicrystal Al thin film studied by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Xie, Yue-Hong; Xu, Jian-Gang; Song, Hai-Yang; Zhang, Yun-Guang

    2015-02-01

    The effects of a twin boundary (TB) on the mechanical properties of two types of bicrystal Al thin films during the nanoimprint process are investigated by using molecular dynamics simulations. The results indicate that for the TB direction parallel to the imprinting direction, the yield stress reaches the maximum for the initial dislocation nucleation when the mould directly imprints to the TB, and the yield stress first decreases with the increase of the marker interval and then increases. However, for the TB direction perpendicular to the imprinting direction, the effect of the TB location to the imprinting forces is very small, and the yield stress is greater than that with the TB direction parallel to the imprinting direction. The results also demonstrate that the direction of the slip dislocations and the deformation of the thin film caused by spring-back are different due to various positions and directions of the TB. Project supported by the National Natural Science Foundation of China (Grant No. 10902083), the Program for New Century Excellent Talent in University of Ministry of Education of China (Grant No. NCET-12-1046), the Program for New Scientific and Technological Star of Shaanxi Province, China (Grant No. 2012KJXX-39), and the Program for Natural Science Basic Research Plan in Shaanxi Province, China (Grant No. 2014JQ1036).

  2. Research on the electronic and optical properties of polymer and other organic molecular thin films

    SciTech Connect

    1997-02-01

    The main goal of the work is to find materials and methods of optimization of organic layered electroluminescent cells and to study such properties of polymers and other organic materials that can be used in various opto-electronic devices. The summary of results obtained during the first year of work is presented. They are: (1) the possibility to produce electroluminescent cells using a vacuum deposition photoresist technology for commercial photoresists has been demonstrated; (2) the idea to replace the polyaryl polymers by other polymers with weaker hole conductivity for optimization of electroluminescent cells with ITO-Al electrodes has been suggested. The goal is to obtain amorphous processable thin films of radiative recombination layers in electroluminescent devices; (3) procedures of preparation of high-quality vacuum-deposited poly (p-phenylene) (PPP) films on various substrates have been developed; (4) it was found for the first time that the fluorescence intensity of PPP films depends on the degree of polymerization; (5) the role of interfaces between organic compounds, on one side, and metals or semiconductors, on the other side, has been studied and quenching of the fluorescence caused by semiconductor layer in thin sandwiches has been observed; (6) studies of the dynamics of photoexcitations revealed the exciton self-trapping in quasi-one-dimensional aggregates; and (7) conditions for preparation of highly crystalline fullerene C{sub 60} films by vacuum deposition have been found. Composites of C{sub 60} with conjugated polymers have been prepared.

  3. Charge Transfer-Induced Molecular Hole Doping into Thin Film of Metal-Organic Frameworks.

    PubMed

    Lee, Deok Yeon; Kim, Eun-Kyung; Shrestha, Nabeen K; Boukhvalov, Danil W; Lee, Joong Kee; Han, Sung-Hwan

    2015-08-26

    Despite the highly porous nature with significantly large surface area, metal-organic frameworks (MOFs) can be hardly used in electronic and optoelectronic devices due to their extremely poor electrical conductivity. Therefore, the study of MOF thin films that require electron transport or conductivity in combination with the everlasting porosity is highly desirable. In the present work, thin films of Co3(NDC)3DMF4 MOFs with improved electronic conductivity are synthesized using layer-by-layer and doctor blade coating techniques followed by iodine doping. The as-prepared and doped films are characterized using FE-SEM, EDX, UV/visible spectroscopy, XPS, current-voltage measurement, photoluminescence spectroscopy, cyclic voltammetry, and incident photon to current efficiency measurements. In addition, the electronic and semiconductor properties of the MOF films are characterized using Hall Effect measurement, which reveals that, in contrast to the insulator behavior of the as-prepared MOFs, the iodine doped MOFs behave as a p-type semiconductor. This is caused by charge transfer-induced hole doping into the frameworks. The observed charge transfer-induced hole doping phenomenon is also confirmed by calculating the densities of states of the as-prepared and iodine doped MOFs based on density functional theory. Photoluminescence spectroscopy demonstrates an efficient interfacial charge transfer between TiO2 and iodine doped MOFs, which can be applied to harvest solar radiations. PMID:26226050

  4. Engineering of an ultra-thin molecular superconductor by charge transfer

    DOEpatents

    Hla, Saw Wai; Hassanien, Abdelrahim; Kendal, Clark

    2016-06-07

    A method of forming a superconductive device of a single layer of (BETS).sub.2GaCl.sub.4 molecules on a substrate surface which displays a superconducting gap that increases exponentially with the length of the molecular chain is provided.

  5. Formation of Organic Thin Films of Nonlinear Optical Materials by Molecular Layer Epitaxy

    NASA Astrophysics Data System (ADS)

    Burtman, V.; Kopylova, T. N.; Van Der Boom, M.; Gadirov, R. M.; Tel'minov, E. N.; Nikonov, S. Yu.; Nikonova, E. N.

    2016-03-01

    Conditions are described under which films of [(aminophenyl)azo]pyridine are formed by molecular layer epitaxy, and their optical absorption and x-ray photoelectron spectra are investigated. The nonlinear properties of such structures are described with the help of measurements of the intensity of second harmonic generation as a function of the angle of incidence.

  6. Adsorption Behaviors of Mixed Monolayers of n-Alkanes at the Liquid-Solid Interface.

    PubMed

    Hibino, Masahiro

    2016-05-17

    To understand the self-assembly of monolayers at the liquid-solid interface, a thermodynamic model, which describes the contributions of the molecular interactions, is essential. We present an adapted Zimm-Bragg model of the cooperativity transitions for determining the Gibbs free energy for self-assembly at the liquid-solid interface. Scanning tunneling microscopy was used to observe the monolayers formed on graphite from phenyloctane solutions of binary mixtures of n-hexacosane (C26H54) and n-tetratriacontane (C34H70). This revealed that the sharp transition in the monolayers from the full surface coverage of the long-chain alkane, which is adsorbed preferentially, to the full coverage of the short-chain alkane is a function of the mixture composition. The model allows for the estimation of the free-energy changes associated with the difference in the alkyl chain length and the interface between the two different alkane regions in the monolayers. It is also suitable for understanding more complex systems that exhibit intermolecular interactions. PMID:27124544

  7. Diffusion of methane and other alkanes in metal-organic frameworks for natural gas storage

    SciTech Connect

    Borah, B; Zhang, HD; Snurr, RQ

    2015-03-03

    Diffusion of methane, ethane, propane and n-butane was studied within the micropores of several metal organic frameworks (MOFs) of varying topologies, including the MOFs PCN-14, NU-125, NU-1100 and DUT-49. Diffusion coefficients of the pure components, as well as methane/ethane, methane/ propane and methane/butane binary mixtures, were calculated using molecular dynamics simulations to understand the effect of the longer alkanes on uptake of natural gas in MOB. The calculated self diffusion coefficients of all four components are on the order of 10(-8) m(2)/s. The diffusion coefficients of the pure components decrease as a function of chain length in all of the MOFs studied and show different behaviour as a function of loading in different MOB. The self-diffusivities follow the trend DPCN-14 < DNU-125 approximate to DNU-1100 < DDUT-49, which is exactly the reverse order of the densities of the MOFs: PCN-14 > NU-125 approximate to NU-1100 > DUT-49. By comparing the diffusion of pure methane and methane mixtures vvith the higher alkancs, it is observed that the diffusivity of methane is unaffected by the presence of the higher alkanes in the MOFs considered, indicating that the diffusion path of methane is not blocked by the higher alkanes present in natural gas. (C) 2014 Elsevier Ltd. All rights reserved.

  8. Catalytic conversion of light alkanes phase II. Topical report, January 1990--January 1993

    SciTech Connect

    1998-12-31

    The Topical Report on Phase II of the project entitled, Catalytic Conversion of Light Alkanes reviews work done between January 1, 1990 and September 30, 1992 on the Cooperative Agreement. The mission of this work is to devise a new catalyst which can be used in a simple economic process to convert the light alkanes in natural gas to oxygenate products which can either be used as clean-burning, high octane liquid fuels, as fuel components or as precursors to liquid hydrocarbon transportation fuel. This Topical Report documents our efforts to design, prepare, characterize and test novel catalysts for the mild selective reaction of light hydrocarbons with air or oxygen to produce alcohols directly. These catalysts are designed to form active metal oxo (MO) species and to be uniquely active for the homolytic cleavage of the carbon-hydrogen bonds in light alkanes producing intermediates which can form alcohols. Research on the Cooperative Agreement is divided into three Phases relating to three molecular environments for the active catalytic species that we are trying to generate. In this report we present our work on catalysts which have oxidation-active metals in polyoxoanions (PHASE II).

  9. The taxonomic status of the endangered thin-spined porcupine, Chaetomys subspinosus (Olfers, 1818), based on molecular and karyologic data

    PubMed Central

    Vilela, Roberto V; Machado, Taís; Ventura, Karen; Fagundes, Valéria; de J Silva, Maria José; Yonenaga-Yassuda, Yatiyo

    2009-01-01

    Background The thin-spined porcupine, also known as the bristle-spined rat, Chaetomys subspinosus (Olfers, 1818), the only member of its genus, figures among Brazilian endangered species. In addition to being threatened, it is poorly known, and even its taxonomic status at the family level has long been controversial. The genus Chaetomys was originally regarded as a porcupine in the family Erethizontidae, but some authors classified it as a spiny-rat in the family Echimyidae. Although the dispute seems to be settled in favor of the erethizontid advocates, further discussion of its affinities should be based on a phylogenetic framework. In the present study, we used nucleotide-sequence data from the complete mitochondrial cytochrome b gene and karyotypic information to address this issue. Our molecular analyses included one individual of Chaetomys subspinosus from the state of Bahia in northeastern Brazil, and other hystricognaths. Results All topologies recovered in our molecular phylogenetic analyses strongly supported Chaetomys subspinosus as a sister clade of the erethizontids. Cytogenetically, Chaetomys subspinosus showed 2n = 52 and FN = 76. Although the sexual pair could not be identified, we assumed that the X chromosome is biarmed. The karyotype included 13 large to medium metacentric and submetacentric chromosome pairs, one small subtelocentric pair, and 12 small acrocentric pairs. The subtelocentric pair 14 had a terminal secondary constriction in the short arm, corresponding to the nucleolar organizer region (Ag-NOR), similar to the erethizontid Sphiggurus villosus, 2n = 42 and FN = 76, and different from the echimyids, in which the secondary constriction is interstitial. Conclusion Both molecular phylogenies and karyotypical evidence indicated that Chaetomys is closely related to the Erethizontidae rather than to the Echimyidae, although in a basal position relative to the rest of the Erethizontidae. The high levels of molecular and morphological

  10. Alkanes-filled photonic crystal fibers as sensor transducers

    NASA Astrophysics Data System (ADS)

    Marć, P.; Przybysz, N.; Stasiewicz, K.; Jaroszewicz, L. R.

    2015-09-01

    In this paper we propose alkanes-filled PCFs as the new class of transducers for optical fiber sensors. We investigated experimentally thermo-optic properties of a commercially available LMA8 partially filled with different alkanes with a higher number of carbon atoms. A partially filled PCF spliced with standard SMFs constitutes one of the newest type transducer. We have selected a group of eight alkanes which have melting points in different temperatures. An analysis of temperature spectral characteristics of these samples will allow to design an optical fiber sensor with different temperature thresholds at specific wavelengths.