Displacive phase transition at the 5/3 monolayer of Pb on Ge(001)

International Nuclear Information System (INIS)

Cvetko, D.; Ratto, F.; Cossaro, A.; Floreano, L.; Bavdek, G.; Morgante, A.

2005-01-01

At a coverage of 5/3 monolayer (ML), Pb adsorbed on Ge(001) forms a ground phase displaying a ((2 1/0 6)) symmetry. This phase undergoes two reversible phase transitions ((2 1/0 6))↔((2 1/0 3))↔(2x1) at the critical temperatures T c 1 ∼178 K and T c 2 ∼375 K, respectively. We investigated the behavior of the relevant order parameters at the critical temperatures by means of He and in-plane x-ray diffraction (HAS and XRD, respectively). Both phase transitions at the critical temperature put in evidence a clear order-disorder behavior, in agreement with the universality class expected for the corresponding symmetry group transformation. The low-temperature transition yields the critical exponent of the two-dimensional (2-D) Ising universality class, whereas the three-state Potts' critical exponents are found for the high-temperature transition. By out-of-plane XRD measurements, the low-temperature phase transition is observed to be accompanied by a static surface distortion at room temperature. A complementary HAS study of the temperature evolution of the surface charge corrugation reveals that the complete ((2 1/0 6))↔((2 1/0 3)) transition is of the displacive type. On the contrary, the high-temperature phase transition does not show any change of the surface corrugation up to its irreversible decomposition, thus pointing to a pure order-disorder character

Quantifying cell behaviors in negative-pressure induced monolayer cell movement

Directory of Open Access Journals (Sweden)

Shu-Er Chow

2016-02-01

Conclusion: A quick membrane ruffling formation, an early cell–substratum separation, and an ensuing decrease in the cellular interaction occur in cells at NP. These specific monolayer cell behaviors at NP have been quantified and possibly accelerate wound healing.

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

Directory of Open Access Journals (Sweden)

Changlong Tan

2016-10-01

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

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

International Nuclear Information System (INIS)

Ouyang, Bin; Lan, Guoqiang; Song, Jun; Guo, Yinsheng; Mi, Zetian

2015-01-01

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

Liquid-Phase Exfoliation into Monolayered BiOBr Nanosheets for Photocatalytic Oxidation and Reduction

Energy Technology Data Exchange (ETDEWEB)

Yu, Hongjian [Beijing; Huang, Hongwei [Beijing; Xu, Kang [Center; Hao, Weichang [Center; Guo, Yuxi [Beijing; Wang, Shuobo [Beijing; Shen, Xiulin [Beijing; Pan, Shaofeng [Beijing; Zhang, Yihe [Beijing

2017-09-26

Monolayered photocatalytic materials have attracted huge research interests in terms of their large specific surface area and ample active sites. Sillén-structured layered BiOX (X = Cl, Br, I) casts great prospects owing to their strong photo-oxidation ability and high stability. Fabrication of monolayered BiOX by a facile, low-cost, and scalable approach is highly challenging and anticipated. Herein, we describe the large-scale preparation of monolayered BiOBr nanosheets with a thickness of ~0.85 nm via a readily achievable liquid-phase exfoliation strategy with assistance of formamide at ambient conditions. The as-obtained monolayered BiOBr nanosheets are allowed diverse superiorities, such as enhanced specific surface area, promoted band structure, and strengthened charge separation. Profiting from these benefits, the advanced BiOBr monolayers not only show excellent adsorption and photodegradation performance for treating contaminants, but also demonstrate a greatly promoted photocatalytic activity for CO2 reduction into CO and CH4. Additionally, monolayered BiOI nanosheets have also been obtained by the same synthetic approach. Our work offers a mild and general approach for preparation of monolayered BiOX, and may have huge potential to be extended to the synthesis of other single-layer two-dimensional materials.

Influence of palmitic acid and hexadecanol on the phase transition temperature and molecular packing of dipalmitoylphosphatidyl-choline monolayers at the air-water interface

Science.gov (United States)

Lee, Ka Yee C.; Gopal, Ajaykumar; von Nahmen, Anja; Zasadzinski, Joseph A.; Majewski, Jaroslaw; Smith, Gregory S.; Howes, Paul B.; Kjaer, Kristian

2002-01-01

Palmitic acid (PA) and 1-hexadecanol (HD) strongly affect the phase transition temperature and molecular packing of dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface. The phase behavior and morphology of mixed DPPC/PA as well as DPPC/HD monolayers were determined by pressure-area-isotherms and fluorescence microscopy. The molecular organization was probed by synchrotron grazing incidence x-ray diffraction using a liquid surface diffractometer. Addition of PA or HD to DPPC monolayers increases the temperature of the liquid-expanded to condensed phase transition. X-ray diffraction shows that DPPC forms mixed crystals both with PA and HD over a wide range of mixing ratios. At a surface pressure (π) of 40 mN/m, increasing the amount of the single chain surfactant leads to a reduction in tilt angle of the aliphatic chains from nearly 30° for pure DPPC to almost 0° in a 1:1 molar ratio of DPPC and PA or HD. At this composition we also find closest packing of the aliphatic chains. Further increase of the amount of PA or HD does not change the lattice or the tilt.

ATR-IR spectroscopy for the detection of induced-phase transition in Langmuir-Blodgett monolayer film

International Nuclear Information System (INIS)

Widayati, Suci

1996-01-01

The rate at which a solid substrate is transferred through the Air/Water interface in the Langmuir-Blodgett process of preparing monomolecular films influences the final structure of the transferred film. This phenomenon has been observed from the attenuated total reflectance infra-red (ATR-IR) spectra of fatty acid monolayer transferred onto germanium substrate. This transfer-induced effect is most evidence when the monolayer is transferred from an expanded region of the surface-pressure-molecular area isotherm, but has limited influence on the hydrocarbon chain conformation of film molecules transferred in the condensed phases at high surface pressure. Such a conformational ordering may due to a kinetically limited phase transition taking place in the meniscus formed between the solid substrate and aqueous sub phase. In addition, these results suggest that the structure of the amphiphilic molecules may modulate the extent and nature of the dipping-speed-induced structural changes taking place in the monomolecular L-B film. In order to use monomolecular L-B films to accurately characterize the structure, orientation and phase properties of monolayers at the Air/Water interface, the L-B transfer must be performed at transfer speeds that minimize this structural phase transition

Cation effects on phosphatidic acid monolayers at various pH conditions.

Science.gov (United States)

Zhang, Ting; Cathcart, Matthew G; Vidalis, Andrew S; Allen, Heather C

2016-10-01

The impact of pH and cations on phase behavior, stability, and surface morphology for dipalmitoylphosphatidic acid (DPPA) monolayers was investigated. At pHCations are found to expand and stabilize the monolayer in the following order of increasing magnitude at pH 5.6: Na + >K + ∼Mg 2+ >Ca 2+ . Additionally, cation complexation is tied to the pH and protonation state of DPPA, which are the primary factors controlling the monolayer surface behavior. The binding affinity of cations to the headgroup and thus deprotonation capability of the cation, ranked in the order of Ca 2+ >Mg 2+ >Na + >K + , is found to be well explained by the law of matching water affinities. Nucleation of surface 3D lipid structures is observed from Ca 2+ , Mg 2+ , and Na + , but not from K + , consistent with the lowest binding affinity of K + . Unraveling cation and pH effects on DPPA monolayers is useful in further understanding the surface properties of complex systems such as organic-coated marine aerosols where organic films are directly influenced by the pH and ionic composition of the underlying aqueous phase. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Bovine insulin-phosphatidylcholine mixed Langmuir monolayers: behavior at the air-water interface.

Science.gov (United States)

Pérez-López, S; Blanco-Vila, N M; Vila-Romeu, N

2011-08-04

The behavior of the binary mixed Langmuir monolayers of bovine insulin (INS) and phosphatidylcholine (PC) spread at the air-water interface was investigated under various subphase conditions. Pure and mixed monolayers were spread on water, on NaOH and phosphate-buffered solutions of pH 7.4, and on Zn(2+)-containing solutions. Miscibility and interactions between the components were studied on the basis of the analysis of the surface pressure (π)-mean molecular area (A) isotherms, surface compression modulus (C(s)(-1))-π curves, and plots of A versus mole fraction of INS (X(INS)). Our results indicate that intermolecular interactions between INS and PC depend on both the monolayer state and the structural characteristics of INS at the interface, which are strongly influenced by the subphase pH and salt content. Brewster angle microscopy (BAM) was applied to investigate the peptide aggregation pattern at the air-water interface in the presence of the studied lipid under any experimental condition investigated. The influence of the lipid on the INS behavior at the interface strongly depends on the subphase conditions.

Domain size polydispersity effects on the structural and dynamical properties in lipid monolayers with phase coexistence

Science.gov (United States)

Rufeil-Fiori, Elena; Banchio, Adolfo J.

Lipid monolayers with phase coexistence are a frequently used model for lipid membranes. In these systems, domains of the liquid-condensed phase always present size polydispersity. However, very few theoretical works consider size distribution effects on the monolayer properties. Because of the difference in surface densities, domains have excess dipolar density with respect to the surrounding liquid expanded phase, originating a dipolar inter-domain interaction. This interaction depends on the domain area, and hence the presence of a domain size distribution is associated with interaction polydispersity. Inter-domain interactions are fundamental to understanding the structure and dynamics of the monolayer. For this reason, it is expected that polydispersity significantly alters monolayer properties. By means of Brownian dynamics simulations, we study the radial distribution function (RDF), the average mean square displacement and the average time-dependent self-diffusion coefficient, D(t), of lipid monolayers with normal distributed size domains. It was found that polydispersity strongly affects the value of the interaction strength obtained, which is greatly underestimated if polydispersity is not considered. However, within a certain range of parameters, the RDF obtained from a polydisperse model can be well approximated by that of a monodisperse model, suitably fitting the interaction strength, even for 40% polydispersities. For small interaction strengths or small polydispersities, the polydisperse systems obtained from fitting the experimental RDF have an average mean square displacement and D(t) in good agreement with that of the monodisperse system.

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

DEFF Research Database (Denmark)

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

2009-01-01

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...... 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...

Synchrotron X-ray diffraction studies of phase transitions in physisorbed monolayers of rare gases on graphite

International Nuclear Information System (INIS)

Bohr, J.

1984-01-01

This study is an investigation of phase transition in monoatomic layers adsorbed on graphite. Such effects can be considered physical realizations of two-dimensional systems. The experimental technique used is synchrotron X-ray diffraction. Systems which have been investigated include the commensurate-incommensurate phase transition in krypton monolayer. By adjusting the spreading pressure in the krypton layer by means of a coadsorbent deuterium gas it has been unambiguously demonstrated that at low temperatures the phase transition is of first order. A melting study of incommensurate argon monolayers demonstrates an experimental verification of the possibility for having a continuous melting transition in two-dimensions. Mixtures of two-components have been investigated for their phases. No (chemical) order-disorder transition is seen. A discussion is given on this lack of a chemical order. This lack is utilized to study the commensurate-incommensurate phase transition driven by average particle size. Finally, a special low-temperature phase is identified in a xenon monlayer which is diluted with freon. (Auth.)

Adsorption behavior of Fe atoms on a naphthalocyanine monolayer on Ag(111) surface

Energy Technology Data Exchange (ETDEWEB)

Yan, Linghao; Wu, Rongting; Bao, Deliang; Ren, Junhai; Zhang, Yanfang; Zhang, Haigang; Huang, Li; Wang, Yeliang; Du, Shixuan; Huan, Qing; Gao, Hong-Jun

2015-05-29

Adsorption behavior of Fe atoms on a metal-free naphthalocyanine (H₂Nc) monolayer on Ag(111) surface at room temperature has been investigated using scanning tunneling microscopy combined with density functional theory (DFT) based calculations. We found that the Fe atoms adsorbed at the centers of H₂Nc molecules and formed Fe-H₂Nc complexes at low coverage. DFT calculations show that the configuration of Fe at the center of a molecule is the most stable site, in good agreement with the experimental observations. After an Fe-H₂Nc complex monolayer was formed, the extra Fe atoms self-assembled to Fe clusters of uniform size and adsorbed dispersively at the interstitial positions of Fe-H₂Nc complex monolayer. Furthermore, the H₂Nc monolayer grown on Ag(111) could be a good template to grow dispersed magnetic metal atoms and clusters at room temperature for further investigation of their magnetism-related properties.

The structure of a lipid-water lamellar phase containing two types of lipid monolayers

International Nuclear Information System (INIS)

Ranck, J.L.; Luzzati, V.; Zaccai, G.

1980-01-01

One lamellar phase, observed in the mitochondrial lipids-water system at low temperature (ca 253 K) and at low water content (ca 15%), contains four lipid monolayers in its unit cell, two of type α and two of type β. Previous X-ray scattering studies of this phase led to an ambiguity: the phase could contain either two homogeneous bilayers, one α and one β, or two mixed bilayers, each formed by an α and a β monolayer. A solution to this problem was sought in a neutron scattering study as a function of the D 2 O/H 2 O ratio. Because of limited resolution, straightforward analysis of the neutron scattering data leads also to ambiguous results. Using a more sophisticated analysis based upon the zeroth- and second-order moments of the Patterson peaks relevant to the exchangeable components, it is shown that the weight of the evidence is in favour of a structure containing mixed bilayers. (Auth.)

Conformal and highly luminescent monolayers of Alq3 prepared by gas-phase molecular layer deposition.

Science.gov (United States)

Räupke, André; Albrecht, Fabian; Maibach, Julia; Behrendt, Andreas; Polywka, Andreas; Heiderhoff, Ralf; Helzel, Jonatan; Rabe, Torsten; Johannes, Hans-Hermann; Kowalsky, Wolfgang; Mankel, Eric; Mayer, Thomas; Görrn, Patrick; Riedl, Thomas

2014-01-22

The gas-phase molecular layer deposition (MLD) of conformal and highly luminescent monolayers of tris(8-hydroxyquinolinato)aluminum (Alq3) is reported. The controlled formation of Alq3 monolayers is achieved for the first time by functionalization of the substrate with amino groups, which serve as initial docking sites for trimethyl aluminum (TMA) molecules binding datively to the amine. Thereby, upon exposure to 8-hydroxyquinoline (8-HQ), the self-limiting formation of highly luminescent Alq3 monolayers is afforded. The growth process and monolayer formation were studied and verified by in situ quartz crystal monitoring, optical emission and absorption spectroscopy, and X-ray photoelectron spectroscopy. The nature of the MLD process provides an avenue to coat arbitrarily shaped 3D surfaces and porous structures with high surface areas, as demonstrated in this work for silica aerogels. The concept presented here paves the way to highly sensitive luminescent sensors and dye-sensitized metal oxides for future applications (e.g., in photocatalysis and solar cells).

Lateral electron transport in monolayers of short chains at interfaces: A Monte Carlo study

International Nuclear Information System (INIS)

George, Christopher B.; Szleifer, Igal; Ratner, Mark A.

2010-01-01

Graphical abstract: Electron hopping between electroactive sites in a monolayer composed of redox-active and redox-passive molecules. - Abstract: Using Monte Carlo simulations, we study lateral electronic diffusion in dense monolayers composed of a mixture of redox-active and redox-passive chains tethered to a surface. Two charge transport mechanisms are considered: the physical diffusion of electroactive chains and electron hopping between redox-active sites. Results indicate that by varying the monolayer density, the mole fraction of electroactive chains, and the electron hopping range, the dominant charge transport mechanism can be changed. For high density monolayers in a semi-crystalline phase, electron diffusion proceeds via electron hopping almost exclusively, leading to static percolation behavior. In fluid monolayers, the diffusion of chains may contribute more to the overall electronic diffusion, reducing the observed static percolation effects.

Solution-processable septithiophene monolayer transistor

NARCIS (Netherlands)

Defaux, M.; Gholamrezaie, F.; Wang, J.; Kreyes, A.; Ziener, U.; Anokhin, D.V.; Ivanov, D.A.; Moser, A.; Neuhold, A.; Salzmann, I.; Resel, R.; Leeuw, de D.M.; Meskers, S.C.J.; Moeller, M.; Mourran, A.

2012-01-01

Septithiophene with endgroups designed to form liquid crystalline phases and allows controlled deposition of an electrically connected monolayer. Field effect mobilies mobilities of charge carriers and spectroscopic properties of the monolayer provide evidence of sustainable transport and

Solution-Processable Septithiophene Monolayer Transistor

NARCIS (Netherlands)

Defaux, Matthieu; Gholamrezaie, Fatemeh; Wang, Jingbo; Kreyes, Andreas; Ziener, Ulrich; Anokhin, Denis V.; Ivanov, Dimitri A.; Moser, Armin; Neuhold, Alfred; Salzmann, Ingo; Resel, Roland; de Leeuw, Dago M.; Meskers, Stefan C. J.; Moeller, Martin; Mourran, Ahmed

2012-01-01

Septithiophene with endgroups designed to form liquid crystalline phases and allows controlled deposition of an electrically connected monolayer. Field effect mobilies mobilities of charge carriers and spectroscopic properties of the monolayer provide evidence of sustainable transport and

Mechanical and electronic properties of Janus monolayer transition metal dichalcogenides

Science.gov (United States)

Shi, Wenwu; Wang, Zhiguo

2018-05-01

The mechanical and electronic properties of Janus monolayer transition metal dichalcogenides MXY (M  =  Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W; X/Y  =  S, Se, Te) were investigated using density functional theory. Results show that breaking the out-of-plane structural symmetry can be used to tune the electronic and mechanical behavior of monolayer transition metal dichalcogenides. The band gaps of monolayer WXY and MoXY are in the ranges of 0.16–1.91 and 0.94–1.69 eV, respectively. A semiconductor to metallic phase transition occurred in Janus monolayer MXY (M  =  Ti, Zr and Hf). The monolayers MXY (M  =  V, Nb, Ta and Cr) show metallic characteristics, which show no dependence on the structural symmetry breaking. The mechanical properties of MXY depended on the composition. Monolayer MXY (M  =  Mo, Ti, Zr, Hf and W) showed brittle characteristic, whereas monolayer CrXY and VXY are with ductile characteristic. The in-plane stiffness of pristine and Janus monolayer MXY are in the range between 22 and 158 N m‑1. The tunable electronic and mechanical properties of these 2D materials would advance the development of ultra-sensitive detectors, nanogenerators, low-power electronics, and energy harvesting and electromechanical systems.

Phase behavior of mixed submonolayer films of krypton and xenon on graphite.

Science.gov (United States)

Patrykiejew, A; Sokołowski, S

2012-04-14

Using the results of extensive Monte Carlo simulations in the canonical and grand canonical ensembles, we discuss the phase behavior of mixed submonolayer films of krypton and xenon adsorbed on the graphite basal plane. The calculations have been performed using two- and three-dimensional models of the systems studied. It has been demonstrated that out-of-plane motion does not affect the properties of the films as long as the total density is well below the monolayer completion and at moderate temperatures. For the total densities close to the monolayer completion, the promotion of particles to the second layer considerably affects the film properties. Our results are in a reasonable agreement with the available experimental data. The melting point of submonolayer films has been shown to exhibit non-monotonous changes with the film composition, and reaches minimum for the xenon concentration of about 50%. At the temperatures below the melting point, the structure of solid phases depends upon the film composition and the temperature; one can also distinguish commensurate and incommensurate phases. Two-dimensional calculations have demonstrated that for the xenon concentration between about 15% and 65% the adsorbed film exhibits the formation of a superstructure, in which each Xe atom is surrounded by six Kr atoms. This superstructure is stable only at very low temperatures and transforms into the mixed commensurate (√3×√3)R30° phase upon the increase of temperature. Such a superstructure does not appear when a three-dimensional model is used. Grand canonical ensemble calculations allowed us to show that for the xenon concentration of about 3% the phase diagram topology of monolayer films changes from the krypton-like (with incipient triple point) to the xenon-like (with ordinary triple point).

Temperature-Dependent Change of Packing Structure of Condensed-Phase in a Micro-Phase Separated Langmuir Monolayer Studied by Grazing-Incidence X-ray Diffraction

Energy Technology Data Exchange (ETDEWEB)

Iimura, Ken-ichi [Department of Applied Chemisty, Faculty of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya 321-8585, Utsunomiya (Japan); Kato, Teiji [Department of Applied Chemisty, Faculty of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya 321-8585, Utsunomiya (Japan); Brezesinski, Gerald [Max-Planck Instutite of Colloids and Interfaces, Research Campus Golm, D-14476 Potsdam (Germany)

2007-10-15

Packing structure of condensed-phase in a binary mixed Langmuir monolayer of behenic acid (C22) and perfluoro-2,5,8-trimethyl-3,6,9-trioxadodecanoic acid (PFPE) on a cadmium acetate aqueous solution was studied by grazing incidence X-ray diffraction (GIXD) as a function of the subphase temperature. The measurements were made during temperature scan at a fixed molecular area to explain the morphological change of the condensed-phase domains due to a thermal treatment reported previously. Analysis of GIXD data implies that the condensed-phase domains are composed of only the C22 molecules perpendicularly oriented and very closely packed in a centered rectangular unit cell with orthorhombic distortion at low temperatures. As the temperature increases the area occupied by molecule increases, and above 25 deg. C the lattice becomes disordered, which would allow morphological transformation of the condensed-phase domains. The process of packing structure change is almost reversible except for non-equilibrium phases observed for the monolayer spread at a low temperature, 5.5 deg. C.

Temperature-Dependent Change of Packing Structure of Condensed-Phase in a Micro-Phase Separated Langmuir Monolayer Studied by Grazing-Incidence X-ray Diffraction

International Nuclear Information System (INIS)

Iimura, Ken-ichi; Kato, Teiji; Brezesinski, Gerald

2007-01-01

Packing structure of condensed-phase in a binary mixed Langmuir monolayer of behenic acid (C22) and perfluoro-2,5,8-trimethyl-3,6,9-trioxadodecanoic acid (PFPE) on a cadmium acetate aqueous solution was studied by grazing incidence X-ray diffraction (GIXD) as a function of the subphase temperature. The measurements were made during temperature scan at a fixed molecular area to explain the morphological change of the condensed-phase domains due to a thermal treatment reported previously. Analysis of GIXD data implies that the condensed-phase domains are composed of only the C22 molecules perpendicularly oriented and very closely packed in a centered rectangular unit cell with orthorhombic distortion at low temperatures. As the temperature increases the area occupied by molecule increases, and above 25 deg. C the lattice becomes disordered, which would allow morphological transformation of the condensed-phase domains. The process of packing structure change is almost reversible except for non-equilibrium phases observed for the monolayer spread at a low temperature, 5.5 deg. C

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

Science.gov (United States)

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

2009-08-01

We present evidence from neutron diffraction measurements and molecular dynamics (MD) simulations of three different monolayer phases of the intermediate-length alkanes tetracosane (n-C24H50 denoted as C24) and dotriacontane (n-C32H66 denoted as C32) adsorbed on a graphite basal-plane surface. Our 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 Å=√3 ag, where ag=2.46 Å 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 ˜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.

Magnetism of Ta dichalcogenide monolayers tuned by strain and hydrogenation

Energy Technology Data Exchange (ETDEWEB)

Manchanda, Priyanka; Sellmyer, D. J.; Skomski, Ralph [Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588 (United States); Sharma, Vinit [Department of Materials Science and Engineering and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269 (United States); Yu, Hongbin [School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, Arizona 85287 (United States)

2015-07-20

The effects of strain and hydrogenation on the electronic, magnetic, and optical properties of monolayers of Ta based dichalcogenides (TaX{sub 2}; X = S, Se, and Te) are investigated using density-functional theory. We predict a complex scenario of strain-dependent magnetic phase transitions involving paramagnetic, ferromagnetic, and modulated antiferromagnetic states. Covering one of the two chalcogenide surfaces with hydrogen switches the antiferromagnetic/nonmagnetic TaX{sub 2} monolayers to a semiconductor, and the optical behavior strongly depends on strain and hydrogenation. Our research opens pathways towards the manipulation of magnetic as well as optical properties for future spintronics and optoelectronics applications.

Interactions of phospholipid monolayer with single-walled carbon nanotube wrapped by lysophospholipid

Energy Technology Data Exchange (ETDEWEB)

Lim, Siwool; Kim, Hyungsu, E-mail: hkim@dku.edu

2012-10-01

In this study, we prepared single-walled carbon nanotubes (SWNTs) wrapped by 1-stearoyl-2-hydroxy-sn-glycero-3-phospho-(1 Prime -rac-glycerol) (LPG), leading to a complex of SWNT-LPG. In an attempt to investigate the interactions of SWNT-LPG with a mimicked cell surface, SWNT-LPG solution was injected into the sub-phase of Langmuir trough to form a mixed monolayer with dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG), respectively. In addition to the measurement of typical surface pressure-area isotherms under compression mode, area changes occurring during insertion of SWNT-LPG into the monolayer were recorded at various surface pressures. Changes in surface potential were also measured for evident tracing of the degree of interactions between sub-phase and monolayer. A systematic comparison of relaxation patterns and insertion behavior along with surface potential data provided a rational basis to distinguish the degree of interactions between SWNT-LPG and the designated monolayer. The observed tendencies were found to be in accordance with the surface topography as revealed by the tapping mode atomic force microscopy. It was consistently observed that SWNT-LPG interacted with DPPC to a greater extent than with DPPG, when the sufficient coverage of nanotube surface by LPG molecules was assured. - Highlights: Black-Right-Pointing-Pointer Complex of single-walled carbon nanotubes and lysophospholipid (SWNT-LPG) is formed. Black-Right-Pointing-Pointer Composite monolayer is formed by inserting SWNT-LPG into the phospholipid monolayer. Black-Right-Pointing-Pointer We measure area-pressure responses and dipole potentials during the insertion process. Black-Right-Pointing-Pointer Properties of composite monolayer depend on the kind of phospholipid and LPG content.

Phase transitions in an Ising model for monolayers of coadsorbed atoms

International Nuclear Information System (INIS)

Lee, H.H.; Landau, D.P.

1979-01-01

A Monte Carlo method is used to study a simple S=1 Ising (lattice-gas) model appropriate for monolayers composed of two kinds of atoms on cubic metal substrates H = K/sub nn/ Σ/sub nn/ S 2 /sub i/zS 2 /sub j/z + J/sub nnn/ Σ/sub nnn/ S/sub i/zS/sub j/z + Δ Σ/sub i/ S 2 /sub i/z (where nn denotes nearest-neighbor and nnn next-nearest-neighbor pairs). The phase diagram is determined over a wide range of Δ and T for K/sub nn//J/sub nnn/=1/4. For small (or negative) Δ we find an antiferromagnetic 2 x 1 ordered phase separated from the disordered state by a line of second-order phase transitions. The 2 x 1 phase is separated by a line of first-order transitions from a c (2 x 2) phase which appears for larger Δ. The 2 x 1 and c (2 x 2) phases become simultaneously critical at a bicritical point and the phase boundary of the c (2 x 2) → disordered transition shows a tricritical point

A trough for improved SFG spectroscopy of lipid monolayers

Science.gov (United States)

Franz, Johannes; van Zadel, Marc-Jan; Weidner, Tobias

2017-05-01

Lipid monolayers are indispensable model systems for biological membranes. The main advantage over bilayer model systems is that the surface pressure within the layer can be directly and reliably controlled. The sensitive interplay between surface pressure and temperature determines the molecular order within a model membrane and consequently determines the membrane phase behavior. The lipid phase is of crucial importance for a range of membrane functions such as protein interactions and membrane permeability. A very reliable method to probe the structure of lipid monolayers is sum frequency generation (SFG) vibrational spectroscopy. Not only is SFG extremely surface sensitive but it can also directly access critical parameters such as lipid order and orientation, and it can provide valuable information about protein interactions along with interfacial hydration. However, recent studies have shown that temperature gradients caused by high power laser beams perturb the lipid layers and potentially obscure the spectroscopic results. Here we demonstrate how the local heating problem can be effectively reduced by spatially distributing the laser pulses on the sample surface using a translating Langmuir trough for SFG experiments at lipid monolayers. The efficiency of the trough is illustrated by the detection of enhanced molecular order due to reduced heat load.

Decoupling of crystalline and conformational degrees of freedom in lipid monolayers

DEFF Research Database (Denmark)

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

1989-01-01

of variables which describe the orientations of crystalline domains in the solid. The phase behavior of the model as a function of temperature and lateral pressure is explored using mean-field theory and computer-simulation techniques. Attention is paid to the particular interplay between the two types......-formation processes observed along the isotherms in the phase diagram spanned by lateral pressure and area. A description is given of the kinetics of the nonequilibrium phase transitions and the concomitant heterogeneous microstructure of the monolayer. This leads to an explanation of the peculiarities...

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

International Nuclear Information System (INIS)

Stanley, Jacob; Boucheron, Leandra; Shpyrko, Oleg; Lin, Binhua; Meron, Mati

2015-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-04-20

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

Phases of phosphatidyl ethanolamine monolayers studied by synchrotron x-ray scattering

DEFF Research Database (Denmark)

Helm, C.A.; Tippmann-Krayer, P.; Möhwald, H.

1991-01-01

For the first time, phospholid monolayers at the air/water interface have been studied by x-ray diffraction and reflection all along the isotherm from the laterally isotropic fluid (the so-called LE phase) to the ordered phases. The model used to analyze the data, and the accuracy of the parameters...... deduced, were tested by comparing the results obtained with two lipids having the same head group but different chain lengths. Compression of the fluid phase leads predominantly to a change of thickness of the hydrophobic moiety, much less of its density, with the head group extension remaining constant....... The main transition involves a considerable increase (approximately 10%) of the electron density in the hydrophobic region, a dehydration of the head group and a positional ordering of the aliphatic tails, albeit with low coherence lengths (approximately 10 spacings). On further compression of the film...

Structure and shear response of lipid monolayers

International Nuclear Information System (INIS)

Dutta, P.; Ketterson, J.B.

1990-02-01

Organic monolayers and multilayers are both scientifically fascinating and technologically promising; they are, however, both complex systems and relatively inaccessible to experimental probes. In this Progress Report, we describe our X-ray diffraction studies, which have given us substantial new information about the structures and phase transitions in monolayers on the surface of water; our use of these monolayers as a unique probe of the dynamics of wetting and spreading; and our studies of monolayer mechanical properties using a simple but effective technique available to anyone using the Wilhelmy method to measure surface tension

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

DEFF Research Database (Denmark)

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

1994-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-01-26

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

Experimental evidence for an original two-dimensional phase structure: An antiparallel semifluorinated monolayer at the air-water interface

International Nuclear Information System (INIS)

El Abed, A.; Faure, M-C.; Pouzet, E.; Abillon, O.

2002-01-01

We show the spontaneous formation of an antiparallel monolayer of diblock semifluorinated n-alkane molecules spread at the air-water interface. We used simultaneous measurements of surface pressure and surface potential versus molecular area and performed grazing x-ray reflectivity experiments to characterize the studied monolayer, which is obtained at almost zero surface pressure and precedes the formation of a bilayer at higher surface pressure. Its thickness, equal to 2.7 nm, was found to be independent of the molecular area. This behavior may be explained by van der Waals and electrostatic interactions

Shear thinning behavior of monolayer liquid lubricant films measured by fiber wobbling method

International Nuclear Information System (INIS)

Hamamoto, Y; Itoh, S; Fukuzawa, K; Zhang, H

2010-01-01

It is essential to clarify mechanical properties of monolayer lubricant films coated on magnetic disks under shearing motion for designing future hard disk drives with ultra-low flying height. Many of previous researchers reported that strong shear rate dependence of viscoelasticity was one of the typical phenomena observed with molecularly thin liquid films. However, it has not been clarified whether or not perfluoropolyether (PFPE) lubricant films, which are used for the head-disk interface (HDI) lubrication, show shear thinning behavior under actual HDI conditions. In this study, we used the fiber wobbling method that can achieve both highly-sensitive shear force measurement and precise gap control and measured shear rate dependence of viscoelastic properties of monolayer PFPE films coated on the magnetic disk. Our experimental results showed that shear thinning does occur at high shear rate ranged from 10 2 to 10 6 s -1 .

Morphology of compressed dipalmitoyl phosphatidylcholine monolayers investigated by atomic force microscopy

International Nuclear Information System (INIS)

Yang, Y.-P.; Tsay, R.-Y.

2007-01-01

The effectiveness of a substitute of natural lung surfactants on replacement therapy strongly depends on the stability of the monolayer of those substitute molecules. An atomic force microscope is utilized to investigate the microstructure of the films of the major components of natural lung surfactants, dipalmitoyl phosphatidylcholine-DPPC, which are transferred to mica substrates by the Langmuir-Blodgett film technique. A concave deformation structure was first observed for DPPC in solid phase. The depth of the concave domain was about 6 nm and was remarkably uniform. For a collapsed DPPC monolayer, the surface film consists of a granular convex multilayer structure and a disc-like concave structure. Dynamic cyclic compression-expansion experiments indicate that the formation of the concave domain is a reversible process while the process for convex multilayer formation is irreversible. This gives direct evidence that convex grain is the collapsed structure of DPPC monolayer and the concave shallow disc corresponds to the elastic deformation of a DPPC solid film. Results of atomic force microscopy indicate that the nucleation and growth model instead of the fracture model can better describe the collapse behavior of a DPPC monolayer

Lipid dip-pen nanolithography on self-assembled monolayers

International Nuclear Information System (INIS)

Gavutis, Martynas; Navikas, Vytautas; Rakickas, Tomas; Vaitekonis, Šarūnas; Valiokas, Ramūnas

2016-01-01

Dip-pen nanolithography (DPN) with lipids as an ink enables functional micro/nanopatterning on different substrates at high process speeds. However, only a few studies have addressed the influence of the physicochemical properties of the surface on the structure and phase behavior of DPN-printed lipid assemblies. Therefore, by combining the scanning probe and optical imaging techniques in this work we have analyzed lipid microdomain formation on the self-assembled monolayers (SAMs) on gold as well-defined model surfaces that displayed hydrophilic (protein-repellent) or hydrophobic (protein-adhesive) characteristics. We have found that on the tri(ethylene glycol)-terminated SAM the lipid ink transfer was fast (∼10 –1 μm 3 s −1 ), quasi-linear and it yielded unstable, sparsely packed lipid microspots. Contrary to this, on the methyl-terminated SAM the lipid transfer was ∼20 times slower, nonlinear, and the obtained stable dots of ∼1 μm in diameter consisted of lipid multilayers. Our comparative analysis indicated that the measured lipid transfer was consistent with the previously reported so-called polymer transfer model (Felts et al 2012, Nanotechnology 23 215301). Further on, by employing the observed distinct contrast in the DPN ink behavior we constructed confined lipid microdomains on pre-patterned SAMs, in which the lipids assembled either into monolayer or multilamellar phases. Such microdomains can be further utilized for lipid membrane mimetics in microarray and lab-on-a-chip device formats. (paper)

Analysis of the induction of the myelin basic protein binding to the plasma membrane phospholipid monolayer

International Nuclear Information System (INIS)

Zhang Lei; Hao Changchun; Feng Ying; Gao Feng; Lu Xiaolong; Li Junhua; Sun Runguang

2016-01-01

Myelin basic protein (MBP) is an essential structure involved in the generation of central nervous system (CNS) myelin. Myelin shape has been described as liquid crystal structure of biological membrane. The interactions of MBP with monolayers of different lipid compositions are responsible for the multi-lamellar structure and stability of myelin. In this paper, we have designed MBP-incorporated model lipid monolayers and studied the phase behavior of MBP adsorbed on the plasma membrane at the air/water interface by thermodynamic method and atomic force microscopy (AFM). By analyzing the pressure–area ( π – A ) and pressure–time ( π – T ) isotherms, univariate linear regression equation was obtained. In addition, the elastic modulus, surface pressure increase, maximal insertion pressure, and synergy factor of monolayers were detected. These parameters can be used to modulate the monolayers binding of protein, and the results show that MBP has the strongest affinity for 1,2-dipalmitoyl-sn-glycero-3- phosphoserine (DPPS) monolayer, followed by DPPC/DPPS mixed and 1,2-dipalmitoyl-sn-glycero-3-phospho-choline (DPPC) monolayers via electrostatic and hydrophobic interactions. AFM images of DPPS and DPPC/DPPS mixed monolayers in the presence of MBP (5 nM) show a phase separation texture at the surface pressure of 20 mN/m and the incorporation of MBP put into the DPPC monolayers has exerted a significant effect on the domain structure. MBP is not an integral membrane protein but, due to its positive charge, interacts with the lipid head groups and stabilizes the membranes. The interaction between MBP and phospholipid membrane to determine the nervous system of the disease has a good biophysical significance and medical value. (special topic)

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

CERN Document Server

Lee, S R; Follstaedt, D M

2001-01-01

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

11-Hydroxyundecyl octadecyl disulfide self-assembled monolayers on Au(1 1 1)

Energy Technology Data Exchange (ETDEWEB)

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

2014-08-30

Highlights: • 11-Hydroxyundecyl octadecyl disulfide self-assembled monolayers on Au(1 1 1) surface were grown by supersonic molecular beam deposition. • Two different lying down monolayer phases were observed depending on the substrate temperature. • High temperature monolayer phase has a diffraction pattern similar to that of mercaptoundecanol SAMs. • Desorption from several different chemisorbed and physisorbed states were observed. - Abstract: Here, we report a helium atom diffraction study of 11-hydroxyundecyl octadecyl disulfide (CH{sub 3}-(CH{sub 2}){sub 17}-S-S-(CH{sub 2}){sub 11}-OH, HOD) self-assembled monolayers (SAMs) produced by supersonic molecular beam deposition (SMBD). Two different lying down monolayer phases were observed depending on the substrate temperature. At low temperatures a poorly ordered phase was observed, while the diffraction patterns of the film grown at high temperatures were similar to that of mercaptoundecanol (MUD) SAMs reported previously in the literature. The transition from the low temperature phase to the high temperature phase is due to S-S bond cleavage at the surface. Desorption from several different chemisorbed and physisorbed states were observed with energies in the same range as observed for MUD and octadecanelthiol (ODT) SAMs.

Self-assembled monolayers and chemical derivatization of Ba0.5Sr0.5TiO3 thin films: Applications in phase shifter devices

International Nuclear Information System (INIS)

Morales-Cruz, Angel L.; Van Keuls, Fred W.; Miranda, Felix A.; Cabrera, Carlos R.

2005-01-01

Thin films of barium strontium titanate (Ba 1-x Sr x TiO 3 (BSTO)) have been used in coupled microstrip phase shifters (CMPS) for possible insertion in satellite and wireless communication platforms primarily because of their high dielectric constant, low loss, large tunability, and good structural stability. In an attempt to improve the figure of merit K (phase shift deg /dB of loss) of phase shifters, modification of the metal/BSTO interface of these devices has been done through surface modification of the BSTO layer using a self-assembled monolayer approach. The impact of this nanotechnology promises to reduce RF losses by improving the quality of the metal/BSTO interface. In this study, compounds such as 3-mercaptopropyltrimethoxysilane (MPS), 16-mercaptohexadecanois acid (MHDA) and 3-mercaptopropionic acid (MPA) were used to form the self-assembled monolayers on the BSTO surface. As a result of the previous modification, chemical derivatization of the self-assembled monolayers was done in order to increase the chain length. Chemical derivatization was done using 3-aminopropyltrimethoxysilane (APS) and 16-mercaptohexadecanoic acid. Surface chemical analysis was done to reveal the composition of the derivatization via X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared (FT-IR). Low and high frequencies measurements of phase shifters were done in order measure the performance of these devices for insertion in antennas. X-ray photoelectron spectroscopy characterization of modified BSTO thin films with MPS showed a binding energy peak at 162.9 eV, indicative of a possible S-O interaction: sulfur of the mercapto compound, MPS, used to modify the surface with the oxygen site of the BSTO thin film. This interaction is at higher binding energies compared with the thiolate interaction. This behavior is observed with the other mercapto compounds such as: MHDA and MPA. An FT-IR analysis present a band at 780 cm -1 , which is characteristic of an O

Sub-THz Characterisation of Monolayer Graphene

Directory of Open Access Journals (Sweden)

Ehsan Dadrasnia

2014-01-01

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

Incorporation of poly-saccharidic derivatives in model biological systems: monolayers, lamellar phases and vesicles

International Nuclear Information System (INIS)

Deme, Bruno

1995-01-01

Our aim is to introduce a soluble polymer in a lyotropic lamellar phase, and to modify the force balance in the case of a collapsed system where no repulsive contribution overcomes the van der Waals attraction, except at very short distances where hydration forces dominate (i.e. a collapsed stack of membranes). Mixed layers of a synthetic lecithin (DMPC) and a hydrophobically modified polysaccharide (cholesteryl-pullulan, CHP) have been investigated at the air-water interface by surface tension experiments and by specular reflection of neutrons. The DMPC/CHP/water ternary phase diagram has been determined by small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS). CHP derivatives are associative polymers bearing lateral cholesterol groups that interact with a polar phases such as phospholipid monolayers and biological membranes. These derivatives are surface active and self-aggregate in solution leading to the formation of soluble micellar type aggregates. The interaction of CHP derivatives with lipidic structures involves the anchoring of the cholesterol groups that yields to the tethering of the poly-saccharidic backbones at lipid/water interfaces. These poly-saccharidic backbones are flexible chains in good solvent in water. Using these derivatives and a new preparation procedure, we show that it is possible to avoid the depletion of the polysaccharide due to its steric exclusion by the collapsed DMPC lamellar phase. We are able to prepare samples at thermodynamic equilibrium with the polysaccharide solubilized in the lamellar phase, a situation opposed to the well known behavior of mixed polysaccharide/lecithin Systems commonly used in osmotic stress experiments. Here, the osmotic pressure of the chains confined in the lamellar lattice acts as a new long range repulsive contribution in the DMPC lyotropic L_α phase and results in the swelling of the lamellar phase at large membrane separations (570 A). Such bilayer separations allow out of

X-Ray Reflectometry of DMPS Monolayers on a Water Substrate

Science.gov (United States)

Tikhonov, A. M.; Asadchikov, V. E.; Volkov, Yu. O.; Roshchin, B. S.; Ermakov, Yu. A.

2017-12-01

The molecular structure of dimyristoyl phosphatidylserine (DMPS) monolayers on a water substrate in different phase states has been investigated by X-ray reflectometry with a photon energy of 8 keV. According to the experimental data, the transition from a two-dimensional expanded liquid state to a solid gel state (liquid crystal) accompanied by the ordering of the hydrocarbon tails C14H27 of the DMPS molecule occurs in the monolayer as the surface pressure rises. The monolayer thickness is 20 ± 3 and 28 ± 2 Å in the liquid and solid phases, respectively, with the deflection angle of the molecular tail axis from the normal to the surface in the gel phase being 26° ± 8°. At least a twofold decrease in the degree of hydration of the polar lipid groups also occurs under two-dimensional monolayer compression. The reflectometry data have been analyzed using two approaches: under the assumption about the presence of two layers with different electron densities in the monolayer and without any assumptions about the transverse surface structure. Both approaches demonstrate satisfactory agreement between themselves in describing the experimental results.

Surface Charge Transfer Doping of Monolayer Phosphorene via Molecular Adsorption.

Science.gov (United States)

He, Yuanyuan; Xia, Feifei; Shao, Zhibin; Zhao, Jianwei; Jie, Jiansheng

2015-12-03

Monolayer phosphorene has attracted much attention owing to its extraordinary electronic, optical, and structural properties. Rationally tuning the electrical transport characteristics of monolayer phosphorene is essential to its applications in electronic and optoelectronic devices. Herein, we study the electronic transport behaviors of monolayer phosphorene with surface charge transfer doping of electrophilic molecules, including 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), NO2, and MoO3, using density functional theory combined with the nonequilibrium Green's function formalism. F4TCNQ shows optimal performance in enhancing the p-type conductance of monolayer phosphorene. Static electronic properties indicate that the enhancement is originated from the charge transfer between adsorbed molecule and phosphorene layer. Dynamic transport behaviors demonstrate that additional channels for hole transport in host monolayer phosphorene were generated upon the adsorption of molecule. Our work unveils the great potential of surface charge transfer doping in tuning the electronic properties of monolayer phosphorene and is of significance to its application in high-performance devices.

Molecular tilt on monolayer-protected nanoparticles

KAUST Repository

Giomi, L.

2012-02-01

The structure of the tilted phase of monolayer-protected nanoparticles is investigated by means of a simple Ginzburg-Landau model. The theory contains two dimensionless parameters representing the preferential tilt angle and the ratio ε between the energy cost due to spatial variations in the tilt of the coating molecules and that of the van der Waals interactions which favors the preferential tilt. We analyze the model for both spherical and octahedral particles. On spherical particles, we find a transition from a tilted phase, at small ε, to a phase where the molecules spontaneously align along the surface normal and tilt disappears. Octahedral particles have an additional phase at small ε characterized by the presence of six topological defects. These defective configurations provide preferred sites for the chemical functionalization of monolayer-protected nanoparticles via place-exchange reactions and their consequent linking to form molecules and bulk materials. Copyright © EPLA, 2012.

Molecular tilt on monolayer-protected nanoparticles

KAUST Repository

Giomi, L.; Bowick, M. J.; Ma, X.; Majumdar, A.

2012-01-01

The structure of the tilted phase of monolayer-protected nanoparticles is investigated by means of a simple Ginzburg-Landau model. The theory contains two dimensionless parameters representing the preferential tilt angle and the ratio ε between the energy cost due to spatial variations in the tilt of the coating molecules and that of the van der Waals interactions which favors the preferential tilt. We analyze the model for both spherical and octahedral particles. On spherical particles, we find a transition from a tilted phase, at small ε, to a phase where the molecules spontaneously align along the surface normal and tilt disappears. Octahedral particles have an additional phase at small ε characterized by the presence of six topological defects. These defective configurations provide preferred sites for the chemical functionalization of monolayer-protected nanoparticles via place-exchange reactions and their consequent linking to form molecules and bulk materials. Copyright © EPLA, 2012.

Numerical study of friction of flake and adsorbed monolayer on atomically clean substrate

International Nuclear Information System (INIS)

Matsukawa, Hiroshi; Haraguchi, Kazuhiro; Ozaki, Shinsuke

2007-01-01

Frictional behaviors of flake and adsorbed monolayer on substrate can be observed by Frictional force microscope and Quartz crystal microbalance experiments and are typical problems in nano-friction. Computer simulations had been played important roles in understanding those behaviors, but in most of them the driving direction coincides with one of the crystal axes of the substrate. Here we report our numerical results of direction dependence of friction of flake and adsorbed monolayer. We found a new kind of dynamical phase transition in which flake and adsorbed monlayer change their structure relative to the substrate and make incommensurae structure to reduce kinetic frictional force after certain transition time. When the driving velocity is decreased the transition time tends to diverge at certain critical velocity for the flake. For the adsorbed monlayer the transition time tends to diverge at certain critical magnitudes of the external force or the interaction strength between adsorbates when they are decreased

Thermodynamic and real-space structural evidence of a 2D critical point in phospholipid monolayers

DEFF Research Database (Denmark)

Nielsen, Lars K.; Bjørnholm, Thomas; Mouritsen, Ole G.

2007-01-01

The two-dimensional phase diagram of phospholipid monolayers at air-water interfaces has been constructed from Langmuir compression isotherms. The coexistence region between the solid and fluid phases of the monolayer ends at the critical temperature of the transition. The small-scale lateral...... structure of the monolayers has been imaged by atomic force microscopy in the nm to mu m range at distinct points in the phase diagram. The lateral structure is immobilized by transferring the monolayer from an air-water interface to a solid mica support using Langmuir-Blodgett techniques. A transfer...

Headgroup effects of template monolayers on the adsorption behavior and conformation of glucose oxidase adsorbed at air/liquid interfaces.

Science.gov (United States)

Wang, Ke-Hsuan; Syu, Mei-Jywan; Chang, Chien-Hsiang; Lee, Yuh-Lang

2011-06-21

Stearic acid (SA) and octadecylamine (ODA) monolayers at the air/liquid interface were used as template layers to adsorb glucose oxidase (GOx) from aqueous solution. The effect of the template monolayers on the adsorption behavior of GOx was studied in terms of the variation of surface pressure, the evolution of surface morphology observed by BAM and AFM, and the conformation of adsorbed GOx. The results show that the presence of a template monolayer can enhance the adsorption rate of GOx; furthermore, ODA has a higher ability, compared to SA, to adsorb GOx, which is attributed to the electrostatic attractive interaction between ODA and GOx. For adsorption performed on a bare surface or on an SA monolayer, the surface pressure approaches an equilibrium value (ca. 8 mN/m) after 2 to 3 h of adsorption and remains nearly constant in the following adsorption process. For the adsorption on an ODA monolayer, the surface pressure will increase further 1 to 2 h after approaching the first equilibrium pressure, which is termed the second adsorption stage. The measurement of circular dichroism (CD) spectroscopy indicates that the Langmuir-Blodgett films of adsorbed GOx transferred at the first equilibrium state (π = 8 mN/m) have mainly a β-sheet conformation, which is independent of the type of template monolayers. However, the ODA/GOx LB film transferred at the second adsorption stage has mainly an α-helix conformation. It is concluded that the specific interaction between ODA and GOx not only leads to a higher adsorption rate and adsorbed amount of GOx but also induces a conformation change in adsorbed GOx from β-sheet to α-helix. The present results indicate that is possible to control the conformation of adsorbed protein by selecting the appropriate template monolayer. © 2011 American Chemical Society

Analysis of the induction of the myelin basic protein binding to the plasma membrane phospholipid monolayer

Science.gov (United States)

Zhang, Lei; Hao, Changchun; Feng, Ying; Gao, Feng; Lu, Xiaolong; Li, Junhua; Sun, Runguang

2016-09-01

Myelin basic protein (MBP) is an essential structure involved in the generation of central nervous system (CNS) myelin. Myelin shape has been described as liquid crystal structure of biological membrane. The interactions of MBP with monolayers of different lipid compositions are responsible for the multi-lamellar structure and stability of myelin. In this paper, we have designed MBP-incorporated model lipid monolayers and studied the phase behavior of MBP adsorbed on the plasma membrane at the air/water interface by thermodynamic method and atomic force microscopy (AFM). By analyzing the pressure-area (π-A) and pressure-time (π-T) isotherms, univariate linear regression equation was obtained. In addition, the elastic modulus, surface pressure increase, maximal insertion pressure, and synergy factor of monolayers were detected. These parameters can be used to modulate the monolayers binding of protein, and the results show that MBP has the strongest affinity for 1,2-dipalmitoyl-sn-glycero-3- phosphoserine (DPPS) monolayer, followed by DPPC/DPPS mixed and 1,2-dipalmitoyl-sn-glycero-3-phospho-choline (DPPC) monolayers via electrostatic and hydrophobic interactions. AFM images of DPPS and DPPC/DPPS mixed monolayers in the presence of MBP (5 nM) show a phase separation texture at the surface pressure of 20 mN/m and the incorporation of MBP put into the DPPC monolayers has exerted a significant effect on the domain structure. MBP is not an integral membrane protein but, due to its positive charge, interacts with the lipid head groups and stabilizes the membranes. The interaction between MBP and phospholipid membrane to determine the nervous system of the disease has a good biophysical significance and medical value. Project supported by the National Natural Science Foundation of China (Grant Nos. 21402114 and 11544009), the Natural Science Basic Research Plan in Shaanxi Province of China (Grant No. 2016JM2010), the Fundamental Research Funds for the Central

Structure of adsorbed monolayers. The surface chemical bond

International Nuclear Information System (INIS)

Somorjai, G.A.; Bent, B.E.

1984-06-01

This paper attempts to provide a summary of what has been learned about the structure of adsorbed monolayers and about the surface chemical bond from molecular surface science. While the surface chemical bond is less well understood than bonding of molecules in the gas phase or in the solid state, our knowledge of its properties is rapidly accumulating. The information obtained also has great impact on many surface science based technologies, including heterogeneous catalysis and electronic devices. It is hoped that much of the information obtained from studies at solid-gas interfaces can be correlated with molecular behavior at solid-liquid interfaces. 31 references, 42 figures, 1 table

Visualizing monolayers with a water-soluble fluorophore to quantify adsorption, desorption, and the double layer.

Science.gov (United States)

Shieh, Ian C; Zasadzinski, Joseph A

2015-02-24

Contrast in confocal microscopy of phase-separated monolayers at the air-water interface can be generated by the selective adsorption of water-soluble fluorescent dyes to disordered monolayer phases. Optical sectioning minimizes the fluorescence signal from the subphase, whereas convolution of the measured point spread function with a simple box model of the interface provides quantitative assessment of the excess dye concentration associated with the monolayer. Coexisting liquid-expanded, liquid-condensed, and gas phases could be visualized due to differential dye adsorption in the liquid-expanded and gas phases. Dye preferentially adsorbed to the liquid-disordered phase during immiscible liquid-liquid phase coexistence, and the contrast persisted through the critical point as shown by characteristic circle-to-stripe shape transitions. The measured dye concentration in the disordered phase depended on the phase composition and surface pressure, and the dye was expelled from the film at the end of coexistence. The excess concentration of a cationic dye within the double layer adjacent to an anionic phospholipid monolayer was quantified as a function of subphase ionic strength, and the changes in measured excess agreed with those predicted by the mean-field Gouy-Chapman equations. This provided a rapid and noninvasive optical method of measuring the fractional dissociation of lipid headgroups and the monolayer surface potential.

Nonlinear dynamics in experimental devices with compressed/expanded surfactant monolayers

International Nuclear Information System (INIS)

Higuera, M; Perales, J M; Vega, J M

2014-01-01

A theory is provided for a common experimental set up that is used to measure surface properties in surfactant monolayers. The set up consists of a surfactant monolayer (over a shallow liquid layer) that is compressed/expanded in a periodic fashion by moving in counter-phase two parallel, slightly immersed solid barriers, which vary the free surface area and thus the surfactant concentration. The simplest theory ignores the fluid dynamics in the bulk fluid, assuming spatially uniform surfactant concentration, which requires quite small forcing frequencies and provides reversible dynamics in the compression/expansion cycles. In this paper, we present a long-wave theory for not so slow oscillations that assumes local equilibrium but takes the fluid dynamics into account. This simple theory uncovers the physical mechanisms involved in the surfactant behavior and allows for extracting more information from each experimental run. The conclusion is that the fluid dynamics cannot be ignored, and that some irreversible dynamics could well have a fluid dynamic origin. (paper)

Langmuir monolayer formation of metal complexes from polymerizable amphiphilic ligands

NARCIS (Netherlands)

Werkman, P.J; Schouten, A.J.

1996-01-01

The monolayer behaviour of 4-(10,12-pentacosadiynoicamidomethyl)-pyridine at the air-water interface was studied by measuring the surface pressure-area isotherms. The amphiphile formed stable monolayers with a clear liquid-expanded (LE) to liquid-condensed phase transition at various temperatures.

Controllable optical bistability and multistability in a graphene monolayer system

Energy Technology Data Exchange (ETDEWEB)

Zhang, Duo, E-mail: zhangduo10@126.com [School of Electrical and Electronic Engineering, Wuhan Polytechnic University, Wuhan 430023 (China); Sun, Zhaoyu [School of Electrical and Electronic Engineering, Wuhan Polytechnic University, Wuhan 430023 (China); Ding, Chunling [School of Physics and Electronics, Henan University, Kaifeng 475004 (China); Yu, Rong [School of Science, Hubei Province Key Laboratory of Intelligent Robot, Wuhan Institute of Technology, Wuhan 430073 (China); Yang, Xiaoxue [Wuhan National Laboratory for Optoelectronics and School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

2016-02-15

We theoretically investigate the behavior of optical bistability (OB) and optical multistability (OM) in a graphene monolayer system driven by an elliptically polarized control field and a right-hand circularly polarized probe field. Our numerical results show that it is easy to realize the transition from OB to OM or vice versa by adjusting the frequency detunings of the probe field and the control field, as well as the polarization-dependent phase difference between the two components of the control laser field. The influences of the intensity of the control field and the cooperation parameter on the OB behavior are also discussed in detail. These results may provide some new possibilities for technological applications in optoelectronics and solid-state quantum information science.

Controlled electrodeposition of Au monolayer film on ionic liquid

Energy Technology Data Exchange (ETDEWEB)

Ma, Qiang; Pang, Liuqing; Li, Man; Zhang, Yunxia; Ren, Xianpei [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710062 (China); Liu, Shengzhong Frank, E-mail: szliu@dicp.ac.cn [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710062 (China); Dalian Institute of Chemical Physics, Dalian National Laboratory for Clean Energy, Chinese Academy of Sciences, Dalian 116023 (China)

2016-05-15

Highlights: • We fabricate Au monolayer film on Ionic liquid substrate using an electrochemical deposition technique. • Au monolayer film was deposited on a “soft substrate” for the first time. • Au monolayer film can contribute extra Raman enhancement. - Abstract: Gold (Au) nanoparticles have been attractive for centuries for their vibrant appearance enhanced by their interaction with sunlight. Nowadays, there have been tremendous research efforts to develop them for high-tech applications including therapeutic agents, sensors, organic photovoltaics, medical applications, electronics and catalysis. However, there remains to be a challenge to fabricate a monolayer Au coating with complete coverage in controlled fashion. Here we present a facile method to deposit a uniform Au monolayer (ML) film on the [BMIM][PF{sub 6}] ionic liquid substrate using an electrochemical deposition process. It demonstrates that it is feasible to prepare a solid phase coating on the liquid-based substrate. Moreover, the thickness of the monolayer coating can be controlled to a layer-by-layer accuracy.

Pressure-area isotherm of a lipid monolayer from molecular dynamics simulations

NARCIS (Netherlands)

Baoukina, Svetlana; Monticelli, Luca; Marrink, Siewert J.; Tieleman, D. Peter

2007-01-01

We calculated the pressure-area isotherm of a dipalmitoyl-phosphatidylcholine (DPPC) lipid monolayer from molecular dynamics simulations using a coarse-grained molecular model. We characterized the monolayer structure, geometry, and phases directly from the simulations and compared the calculated

Collective cell motion in endothelial monolayers

International Nuclear Information System (INIS)

Szabó, A; Ünnep, R; Méhes, E; Czirók, A; Twal, W O; Argraves, W S; Cao, Y

2010-01-01

Collective cell motility is an important aspect of several developmental and pathophysiological processes. Despite its importance, the mechanisms that allow cells to be both motile and adhere to one another are poorly understood. In this study we establish statistical properties of the random streaming behavior of endothelial monolayer cultures. To understand the reported empirical findings, we expand the widely used cellular Potts model to include active cell motility. For spontaneous directed motility we assume a positive feedback between cell displacements and cell polarity. The resulting model is studied with computer simulations and is shown to exhibit behavior compatible with experimental findings. In particular, in monolayer cultures both the speed and persistence of cell motion decreases, transient cell chains move together as groups and velocity correlations extend over several cell diameters. As active cell motility is ubiquitous both in vitro and in vivo, our model is expected to be a generally applicable representation of cellular behavior

Molecular dynamics and energy landscape of decanethiolates in self-assembled monolayers on Au(111) by STM

NARCIS (Netherlands)

Sotthewes, Kai; Wu, Hairong; Kumar, Avijit; Vancso, Gyula J.; Schön, Peter Manfred; Zandvliet, Henricus J.W.

2013-01-01

The energetics and dynamics of the various phases of decanethiolate self-assembled monolayers on Au(111) surfaces were studied with scanning tunneling microscopy. We have observed five different phases of the decanethiolate monolayer on Au(111): four ordered phases (β, δ, χ*, and ) and one

X-ray diffraction and molecular-dynamics studies: Structural analysis of phases in diglyceride monolayers

DEFF Research Database (Denmark)

Peters, Günther H.J.; Larsen, Niels Bent; Bjørnholm, T.

1998-01-01

We report a detailed structural analysis of the phases of 1,2-sn-dipalmitoylglycerol Langmuir monolayers at room temperature. Pressure-induced transitions have been investigated by combination of molecular-dynamics simulations and grazing-incidence x-ray diffraction (XRD). The diglyceride film...... undergoes two phase transitions occurring at 38.3 and 39.8 Angstrom(2)/molecule. Simulation indicates that the first transition involves a reorientation of the headgroups while simulation and XRD show that in the second transition the order parameter is the tilt angle of the alkyl chains. A methodology......; At the lowest pressure the tilt angle reaches approximate to 14 degrees in a direction close to a nearest neighbor direction. Both arrangements of the alkyl chains are confirmed by XRD. For higher order and fractional order Bragg peaks, simulations predict higher intensities than observed with XRD. This may...

Behavior of lysozyme adsorbed onto biological liquid crystal lipid monolayer at the air/water interface

Science.gov (United States)

Lu, Xiaolong; Shi, Ruixin; Hao, Changchun; Chen, Huan; Zhang, Lei; Li, Junhua; Xu, Guoqing; Sun, Runguang

2016-09-01

The interaction between proteins and lipids is one of the basic problems of modern biochemistry and biophysics. The purpose of this study is to compare the penetration degree of lysozyme into 1,2-diapalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethano-lamine (DPPE) by analyzing the data of surface pressure-area (π-A) isotherms and surface pressure-time (π-T) curves. Lysozyme can penetrate into both DPPC and DPPE monolayers because of the increase of surface pressure at an initial pressure of 15 mN/m. However, the changes of DPPE are larger than DPPC, indicating stronger interaction of lysozyme with DPPE than DPPC. The reason may be due to the different head groups and phase state of DPPC and DPPE monolayers at the surface pressure of 15 mN/m. Atomic force microscopy reveals that lysozyme was absorbed by DPPC and DPPE monolayers, which leads to self-aggregation and self-assembly, forming irregular multimers and conical multimeric. Through analysis, we think that the process of polymer formation is similar to the aggregation mechanism of amyloid fibers. Project supported by the National Natural Science Foundation of China (Grant Nos. 21402114 and 11544009), the Natural Science Basic Research Plan in Shaanxi Province of China (Grant No. 2016JM2010), the Fundamental Research Funds for the Central Universities of China (Grant No. GK201603026), and the National University Science and Technology Innovation Project of China (Grant No. 201610718013).

Neutrophil-endothelial cell interactions on endothelial monolayers grown on micropore filters.

Science.gov (United States)

Taylor, R F; Price, T H; Schwartz, S M; Dale, D C

1981-01-01

We have developed a technique for growing endothelial monolayers on micropore filters. These monolayers demonstrate confluence by phase and electron microscopy and provide a functional barrier to passage of radiolabeled albumin. Neutrophils readily penetrate the monolayer in response to chemotaxin, whereas there is little movement in the absence of chemotaxin. This system offers unique advantages over available chemotaxis assays and may have wider applications in the study of endothelial function. Images PMID:7007441

Chiral hierarchical self-assembly in Langmuir monolayers of diacetylenic lipids

KAUST Repository

Basnet, Prem B.

2013-01-01

When compressed in the intermediate temperature range below the chain-melting transition yet in the low-pressure liquid phase, Langmuir monolayers made of chiral lipid molecules form hierarchical structures. Using Brewster angle microscopy to reveal this structure, we found that as the liquid monolayer is compressed, an optically anisotropic condensed phase nucleates in the form of long, thin claws. These claws pack closely to form stripes. This appears to be a new mechanism for forming stripes in Langmuir monolayers. In the lower temperature range, these stripes arrange into spirals within overall circular domains, while near the chain-melting transition, the stripes arrange into target patterns. We attributed this transition to a change in boundary conditions at the core of the largest-scale circular domains. © 2013 The Royal Society of Chemistry.

Structure and phase behaviour of diblock copolymer monolayers investigated by means of Monte Carlo simulation

International Nuclear Information System (INIS)

Słyk, Edyta; Rżysko, Wojciech; Bryk, Paweł

2015-01-01

We use grand canonical Monte Carlo simulation paired with multiple histogram reweighting, hyperparallel tempering and finite size scaling to investigate the structure and phase behaviour of monolayers of diblock copolymers. The chain molecules are arranged on the square lattice and we consider both fully flexible and rod-coil polymer models. In contrast to the majority of previous studies we assume that the interactions between the segments belonging to one of the two subunits are weaker than the remaining segment–segment interactions. We find that when the diblock copolymer is fully flexible, this choice of the interactions leads to a suppression of the ordered phase, and the phase behaviour is analogous to that of the fully flexible homopolymer model. However, when one of the subunits is rigid, we observe the formation of a novel hairpin chessboard ordered structure with fully stretched chains bent in the middle. The topology of the phase diagram depends on the chain length. For shorter chains the global phase diagram features a critical point and a triple point. For longer chains the gas—disordered liquid phase transition is suppressed and only the order–disorder transition remains stable. The resulting phase diagram is of the swan neck type. (paper)

Wavepacket revivals in monolayer and bilayer graphene rings.

Science.gov (United States)

García, Trinidad; Rodríguez-Bolívar, Salvador; Cordero, Nicolás A; Romera, Elvira

2013-06-12

We have studied the existence of quantum revivals in graphene quantum rings within a simplified model. The time evolution of a Gaussian-populated wavepacket shows revivals in monolayer and bilayer graphene rings. We have also studied this behavior for quantum rings in a perpendicular magnetic field. We have found that revival time is an observable that shows different values for monolayer and bilayer graphene quantum rings. In addition, the revival time shows valley degeneracy breaking.

Liquid Phase Deposition of Silica on the Hexagonally Close-Packed Monolayer of Silica Spheres

Directory of Open Access Journals (Sweden)

Seo Young Yoon

2013-01-01

Full Text Available Liquid phase deposition is a method used for the nonelectrochemical production of polycrystalline ceramic films at low temperatures, most commonly silicon dioxide films. Herein, we report that silica spheres are organized in a hexagonal close-packed array using a patterned substrate. On this monolayer of silica spheres, we could fabricate new nanostructures in which deposition and etching compete through a modified LPD reaction. In the early stage, silica spheres began to undergo etching, and then, silica bridges between the silica spheres appeared by the local deposition reaction. Finally, the silica spheres and bridges disappeared completely. We propose the mechanism for the formation of nanostructure.

Monolayer arrangement of fatty hydroxystearic acids on graphite: Influence of hydroxyl groups

Energy Technology Data Exchange (ETDEWEB)

Medina, S. [Laboratorio de Rayos-X, Centro de Investigación Tecnología e Innovación, de la Universidad de Sevilla (CITIUS), Universidad de Sevilla, Avenida Reina Mercedes, 4B. 41012, Sevilla (Spain); Benítez, J.J.; Castro, M.A. [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain); Cerrillos, C. [Servicio de Microscopía, Centro de Investigación Tecnología e Innovación, de la Universidad de Sevilla (CITIUS), Universidad de Sevilla, Avenida Reina Mercedes, 4B. 41012, Sevilla (Spain); Millán, C. [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain); Alba, M.D., E-mail: alba@icmse.csic.es [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain)

2013-07-31

Previous studies have indicated that long-chain linear carboxylic acids form commensurate packed crystalline monolayers on graphite even at temperatures above their melting point. This study examines the effect on the monolayer formation and structure of adding one or more secondary hydroxyl, functional groups to the stearic acid skeleton (namely, 12-hydroxystearic and 9,10-dihydroxystearic acid). Moreover, a comparative study of the monolayer formation on recompressed and monocrystalline graphite has been performed through X-ray diffraction (XRD) and Scanning Tunneling Microscopy (STM), respectively. The Differential Scanning Calorimetry (DSC) and XRD data were used to confirm the formation of solid monolayers and XRD data have provided a detailed structural analysis of the monolayers in good correspondence with obtained STM images. DSC and XRD have demonstrated that, in stearic acid and 12-hydroxystearic acid adsorbed onto graphite, the monolayer melted at a higher temperature than the bulk form of the carboxylic acid. However, no difference was observed between the melting point of the monolayer and the bulk form for 9,10-dihydroxystearic acid adsorbed onto graphite. STM results indicated that all acids on the surface have a rectangular p2 monolayer structure, whose lattice parameters were uniaxially commensurate on the a-axis. This structure does not correlate with the initial structure of the pure compounds after dissolving, but it is conditioned to favor a) hydrogen bond formation between the carboxylic groups and b) formation of hydrogen bonds between secondary hydroxyl groups, if spatially permissible. Therefore, the presence of hydroxyl functional groups affects the secondary structure and behavior of stearic acid in the monolayer. - Highlights: • Hydroxyl functional groups affect structure and behavior of acids in the monolayer. • Acids on the surface have a rectangular p2 monolayer structure. • Lattice parameters of acids are uniaxially

Study of the interaction of lactoferricin B with phospholipid monolayers and bilayers.

Science.gov (United States)

Arseneault, Marjolaine; Bédard, Sarah; Boulet-Audet, Maxime; Pézolet, Michel

2010-03-02

Bovine lactoferricin (LfcinB) is an antimicrobial peptide obtained from the pepsin cleavage of lactoferrin. The activity of LfcinB has been extensively studied on diverse pathogens, but its mechanism of action still has to be elucidated. Because of its nonspecificity, its mode of action is assumed to be related to interactions with membranes. In this study, the interaction of LfcinB with a negatively charged monolayer of dipalmitoylphosphatidylglycerol has been investigated as a function of the surface pressure of the lipid film using in situ Brewster angle and polarization modulation infrared reflection absorption spectroscopy and on transferred monolayers by atomic force microscopy and polarized attenuated total reflection infrared spectroscopy. The data show clearly that LfcinB forms stable films at the air-water interface. They also reveal that the interaction of LfcinB with the lipid monolayer is modulated by the surface pressure. At low surface pressure, LfcinB inserts within the lipid film with its long molecular axis oriented mainly parallel to the acyl chains, while at high surface pressure, LfcinB is adsorbed under the lipid film, the hairpin being preferentially aligned parallel to the plane of the interface. The threshold for which the behavior changes is 20 mN/m. At this critical surface pressure, LfcinB interacts with the monolayer to form discoidal lipid-peptide assemblies. This structure may actually represent the mechanism of action of this peptide. The results obtained on monolayers are correlated by fluorescent probe release measurements of dye-containing vesicles made of lipids in different phases and support the important role of the lipid fluidity and packing on the activity of LfcinB.

Fullerene monolayer formation by spray coating

NARCIS (Netherlands)

Cervenka, J.; Flipse, C.F.J.

2010-01-01

Many large molecular complexes are limited in thin film applications by their insufficient thermal stability, which excludes deposition via commonly used vapour phase deposition methods. Here we demonstrate an alternative way of monolayer formation of large molecules by a simple spray coating method

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-01-07

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

Wavepacket revivals in monolayer and bilayer graphene rings

International Nuclear Information System (INIS)

García, Trinidad; Rodríguez-Bolívar, Salvador; Cordero, Nicolás A; Romera, Elvira

2013-01-01

We have studied the existence of quantum revivals in graphene quantum rings within a simplified model. The time evolution of a Gaussian-populated wavepacket shows revivals in monolayer and bilayer graphene rings. We have also studied this behavior for quantum rings in a perpendicular magnetic field. We have found that revival time is an observable that shows different values for monolayer and bilayer graphene quantum rings. In addition, the revival time shows valley degeneracy breaking. (paper)

Defects and oxidation of group-III monochalcogenide monolayers

Science.gov (United States)

Guo, Yu; Zhou, Si; Bai, Yizhen; Zhao, Jijun

2017-09-01

Among various two-dimensional (2D) materials, monolayer group-III monochalcogenides (GaS, GaSe, InS, and InSe) stand out owing to their potential applications in microelectronics and optoelectronics. Devices made of these novel 2D materials are sensitive to environmental gases, especially O2 molecules. To address this critical issue, here we systematically investigate the oxidization behaviors of perfect and defective group-III monochalcogenide monolayers by first-principles calculations. The perfect monolayers show superior oxidation resistance with large barriers of 3.02-3.20 eV for the dissociation and chemisorption of O2 molecules. In contrast, the defective monolayers with single chalcogen vacancy are vulnerable to O2, showing small barriers of only 0.26-0.36 eV for the chemisorption of an O2 molecule. Interestingly, filling an O2 molecule to the chalcogen vacancy of group-III monochalcogenide monolayers could preserve the electronic band structure of the perfect system—the bandgaps are almost intact and the carrier effective masses are only moderately disturbed. On the other hand, the defective monolayers with single vacancies of group-III atoms carry local magnetic moments of 1-2 μB. These results help experimental design and synthesis of group-III monochalcogenides based 2D devices with high performance and stability.

Atomic defects and doping of monolayer NbSe2

OpenAIRE

Nguyen, Lan; Komsa, Hannu-Pekka; Khestanova, Ekaterina; Kashtiban, Reza J; Peters, Jonathan J.P.; Lawlor, Sean; Sanchez, Ana M.; Sloan, Jeremy; Gorbachev, Roman; Grigorieva, Irina; Krasheninnikov, Arkady V.; Haigh, Sarah

2017-01-01

We have investigated the structure of atomic defects within monolayer NbSe2 encapsulated in graphene by combining atomic resolution transmission electron microscope imaging, density functional theory (DFT) calculations, and strain mapping using geometric phase analysis. We demonstrate the presence of stable Nb and Se monovacancies in monolayer material and reveal that Se monovacancies are the most frequently observed defects, consistent with DFT calculations of their formation energy. We reve...

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

DEFF Research Database (Denmark)

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

Pulmonary surfactant forms the alveolar monolayer at the air/aqueous interface within the lung. During the breathing process, the surface pressure periodically varies from ~40mN/m up to ~70mN/m. The film is mechanically stable during this rapid and reversible expansion. The monolayer consists...... of the alveolae monolayer and at the same time allows reduction of the interfacial tension to ~0mN/m....

Phase transition and field effect topological quantum transistor made of monolayer MoS2

Science.gov (United States)

Simchi, H.; Simchi, M.; Fardmanesh, M.; Peeters, F. M.

2018-06-01

We study topological phase transitions and topological quantum field effect transistor in monolayer molybdenum disulfide (MoS2) using a two-band Hamiltonian model. Without considering the quadratic (q 2) diagonal term in the Hamiltonian, we show that the phase diagram includes quantum anomalous Hall effect, quantum spin Hall effect, and spin quantum anomalous Hall effect regions such that the topological Kirchhoff law is satisfied in the plane. By considering the q 2 diagonal term and including one valley, it is shown that MoS2 has a non-trivial topology, and the valley Chern number is non-zero for each spin. We show that the wave function is (is not) localized at the edges when the q 2 diagonal term is added (deleted) to (from) the spin-valley Dirac mass equation. We calculate the quantum conductance of zigzag MoS2 nanoribbons by using the nonequilibrium Green function method and show how this device works as a field effect topological quantum transistor.

Studies of the structure and properties of organic monolayers, multilayers and superlattices

International Nuclear Information System (INIS)

Dutta, P.; Ketterson, J.B.

1990-01-01

Organic monolayers and multilayers are both scientifically fascinating and technologically promising; they are, however, both complex systems and relatively inaccessible to experimental probes. In this progress report, we describe our x-ray diffraction studies, which have given us substantial new information about the structures and phase transitions in monolayers on the surface of water; our use of these monolayers as a unique probe of the dynamics of wetting and spreading; and our studies of monolayer mechanical properties using a simple but effective technique available to anyone using the Wilhelmy method to measure surface tension. 20 refs., 11 figs

Conductance fluctuations in high mobility monolayer graphene: Nonergodicity, lack of determinism and chaotic behavior.

Science.gov (United States)

da Cunha, C R; Mineharu, M; Matsunaga, M; Matsumoto, N; Chuang, C; Ochiai, Y; Kim, G-H; Watanabe, K; Taniguchi, T; Ferry, D K; Aoki, N

2016-09-09

We have fabricated a high mobility device, composed of a monolayer graphene flake sandwiched between two sheets of hexagonal boron nitride. Conductance fluctuations as functions of a back gate voltage and magnetic field were obtained to check for ergodicity. Non-linear dynamics concepts were used to study the nature of these fluctuations. The distribution of eigenvalues was estimated from the conductance fluctuations with Gaussian kernels and it indicates that the carrier motion is chaotic at low temperatures. We argue that a two-phase dynamical fluid model best describes the transport in this system and can be used to explain the violation of the so-called ergodic hypothesis found in graphene.

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

DEFF Research Database (Denmark)

Hansen, Flemming Yssing; Taub, H.

1987-01-01

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

Palmitic Acid on Salt Subphases and in Mixed Monolayers of Cerebrosides: Application to Atmospheric Aerosol Chemistry

Directory of Open Access Journals (Sweden)

Ellen M. Adams

2013-10-01

Full Text Available Palmitic acid (PA has been found to be a major constituent in marine aerosols, and is commonly used to investigate organic containing atmospheric aerosols, and is therefore used here as a proxy system. Surface pressure-area isotherms (π-A, Brewster angle microscopy (BAM, and vibrational sum frequency generation (VSFG were used to observe a PA monolayer during film compression on subphases of ultrapure water, CaCl2 and MgCl2 aqueous solutions, and artificial seawater (ASW. π-A isotherms indicate that salt subphases alter the phase behavior of PA, and BAM further reveals that a condensation of the monolayer occurs when compared to pure water. VSFG spectra and BAM images show that Mg2+ and Ca2+ induce ordering of the PA acyl chains, and it was determined that the interaction of Mg2+ with the monolayer is weaker than Ca2+. π-A isotherms and BAM were also used to monitor mixed monolayers of PA and cerebroside, a simple glycolipid. Results reveal that PA also has a condensing effect on the cerebroside monolayer. Thermodynamic analysis indicates that attractive interactions between the two components exist; this may be due to hydrogen bonding of the galactose and carbonyl headgroups. BAM images of the collapse structures show that mixed monolayers of PA and cerebroside are miscible at all surface pressures. These results suggest that the surface morphology of organic-coated aerosols is influenced by the chemical composition of the aqueous core and the organic film itself.

Characterization of mechanical behavior of an epithelial monolayer in response to epidermal growth factor stimulation

International Nuclear Information System (INIS)

Yang, Ruiguo; Chen, Jennifer Y.; Xi, Ning; Lai, King Wai Chiu; Qu, Chengeng; Fung, Carmen Kar Man; Penn, Lynn S.; Xi, Jun

2012-01-01

Cell signaling often causes changes in cellular mechanical properties. Knowledge of such changes can ultimately lead to insight into the complex network of cell signaling. In the current study, we employed a combination of atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D) to characterize the mechanical behavior of A431 cells in response to epidermal growth factor receptor (EGFR) signaling. From AFM, which probes the upper portion of an individual cell in a monolayer of cells, we observed increases in energy dissipation, Young's modulus, and hysteresivity. Increases in hysteresivity imply a shift toward a more fluid-like mechanical ordering state in the bodies of the cells. From QCM-D, which probes the basal area of the monolayer of cells collectively, we observed decreases in energy dissipation factor. This result suggests a shift toward a more solid-like state in the basal areas of the cells. The comparative analysis of these results indicates a regionally specific mechanical behavior of the cell in response to EGFR signaling and suggests a correlation between the time-dependent mechanical responses and the dynamic process of EGFR signaling. This study also demonstrates that a combination of AFM and QCM-D is able to provide a more complete and refined mechanical profile of the cells during cell signaling. -- Highlights: ► The EGF-induced cellular mechanical response is regionally specific. ► The EGF-induced cellular mechanical response is time and dose dependent. ► A combination of AFM and QCM-D provides a more complete mechanical profile of cells.

Phase behavior and phase inversion for dispersant systems

International Nuclear Information System (INIS)

Solheim, A.; Brandvik, P.J.

1991-06-01

This report describes some preliminary phase behavior studies and phase inversion temperature measurements in seawater, bunker oil and dispersant. The objectives have been to find new ways of characterizing dispersants for dispersing oil spill at sea and, perhaps, to throw new lights on the mechanism of dispersion formation (oil-in-water emulsification). The work has been focussed on the relation to phase behavior and the existence of microemulsion in equilibrium with excess oil and water phases. The dispersing process is also compared to the recommended conditions for emulsion formation. When forming an oil-in-water emulsion in an industrial process, it is recommended to choose an emulsifier which gives a phase inversion temperature (PIT) which is 20 - 60 o C higher than the actual temperature for use. The emulsification process must take place close to the PIT which is the temperature at which the emulsion change from oil-in-water emulsion to water-in-oil emulsion when the system is stirred. This condition corresponds to the temperature where the phase behavior change character. The purpose has been to find out if the composition of the dispersants corresponds to the recommendations for oil-in-water emulsification. The amount of experimental work has been limited. Two kinds of experiments have been carried out. Phase behavior studies have been done for seawater, bunker oil and four different dispersants where one had an optimal composition. The phase behavior was hard to interpret and is not recommended for standard dispersants test. The other experimental technique was PIT-measurements by conductivity measurements versus temperature. 4 figs., 1 tab., 4 refs

Phase behaviour in binary mixed Langmuir-Blodgett monolayers of triglycerides

NARCIS (Netherlands)

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

2007-01-01

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

The interaction of trace heavy metal with lipid monolayer in the sea surface microlayer.

Science.gov (United States)

Li, Siyang; Du, Lin; Tsona, Narcisse T; Wang, Wenxing

2018-04-01

Lipid molecules and trace heavy metals are enriched in sea surface microlayer and can be transferred into the sea spray aerosol. To better understand their impact on marine aerosol generation and evolution, we investigated the interaction of trace heavy metals including Fe 3+ , Pb 2+ , Zn 2+ , Cu 2+ , Ni 2+ , Cr 3+ , Cd 2+ , and Co 2+ , with dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface. Phase behavior of the DPPC monolayer on heavy metal solutions was probed with surface pressure-area (π-A) isotherms. The conformation order and orientation of DPPC alkyl chains were characterized by infrared reflection-absorption spectroscopy (IRRAS). The π-A isotherms show that Zn 2+ and Fe 3+ strongly interact with DPPC molecules, and induce condensation of the monolayers in a concentration-dependent manner. IRRAS spectra show that the formation of cation-DPPC complex gives rise to conformational changes and immobilization of the headgroups. The current results suggest that the enrichment of Zn 2+ in sea spray aerosols is due to strong binding to the DPPC film. The interaction of Fe 3+ with DPPC monolayers can significantly influence their surface organizations through the formation of lipid-coated particles. These results suggest that the sea surface microlayer is capable of accumulating much higher amounts of these metals than the subsurface water. The organic and metal pollutants may transfer into the atmosphere by this interaction. Copyright © 2017 Elsevier Ltd. All rights reserved.

Monolayer-directed Assembly and Magnetic Properties of FePt Nanoparticles on Patterned Aluminum Oxide

Directory of Open Access Journals (Sweden)

Guus Rijnders

2010-03-01

Full Text Available FePt nanoparticles (NPs were assembled on aluminum oxide substrates, and their ferromagnetic properties were studied before and after thermal annealing. For the first time, phosph(onates were used as an adsorbate to form self-assembled monolayers (SAMs on alumina to direct the assembly of NPs onto the surface. The Al2O3 substrates were functionalized with aminobutylphosphonic acid (ABP or phosphonoundecanoic acid (PNDA SAMs or with poly(ethyleneimine (PEI as a reference. FePt NPs assembled on all of these monolayers, but much less on unmodified Al2O3, which shows that ligand exchange at the NPs is the most likely mechanism of attachment. Proper modification of the Al2O3 surface and controlling the immersion time of the modified Al2O3 substrates into the FePt NP solution resulted in FePt NPs assembly with controlled NP density. Alumina substrates were patterned by microcontact printing using aminobutylphosphonic acid as the ink, allowing local NP assembly. Thermal annealing under reducing conditions (96%N2/4%H2 led to a phase change of the FePt NPs from the disordered FCC phase to the ordered FCT phase. This resulted in ferromagnetic behavior at room temperature. Such a process can potentially be applied in the fabrication of spintronic devices.

Controlled electrodeposition of Au monolayer film on ionic liquid

Science.gov (United States)

Ma, Qiang; Pang, Liuqing; Li, Man; Zhang, Yunxia; Ren, Xianpei; Liu, Shengzhong Frank

2016-05-01

Gold (Au) nanoparticles have been attractive for centuries for their vibrant appearance enhanced by their interaction with sunlight. Nowadays, there have been tremendous research efforts to develop them for high-tech applications including therapeutic agents, sensors, organic photovoltaics, medical applications, electronics and catalysis. However, there remains to be a challenge to fabricate a monolayer Au coating with complete coverage in controlled fashion. Here we present a facile method to deposit a uniform Au monolayer (ML) film on the [BMIM][PF6] ionic liquid substrate using an electrochemical deposition process. It demonstrates that it is feasible to prepare a solid phase coating on the liquid-based substrate. Moreover, the thickness of the monolayer coating can be controlled to a layer-by-layer accuracy.

Examination of fluorination effect on physical properties of saturated long-chain alcohols by DSC and Langmuir monolayer.

Science.gov (United States)

Nakahara, Hiromichi; Nakamura, Shohei; Okahashi, Yoshinori; Kitaguchi, Daisuke; Kawabata, Noritake; Sakamoto, Seiichi; Shibata, Osamu

2013-02-01

Partially fluorinated long-chain alcohols have been newly synthesized from a radical reaction, which is followed by a reductive reaction. The fluorinated alcohols have been investigated by differential scanning calorimetry (DSC) and compression isotherms in a Langmuir monolayer state. Their melting points increase with an increase in chain length due to elongation of methylene groups. However, the melting points for the alcohols containing shorter fluorinated moieties are lower than those for the typical hydrogenated fatty alcohols. Using the Langmuir monolayer technique, surface pressure (π)-molecular area (A) and surface potential (ΔV)-A isotherms of monolayers of the fluorinated alcohols have been measured in the temperature range from 281.2 to 303.2K. In addition, a compressibility modulus (Cs(-1)) is calculated from the π-A isotherms. Four kinds of the alcohol monolayers show a phase transition (π(eq)) from a disordered to an ordered state upon lateral compression. The π(eq) values increase linearly with increasing temperatures. A slope of π(eq) against temperature for the alcohols with shorter fluorocarbons is unexpectedly larger than that for the corresponding fatty alcohols. Generally, fluorinated amphiphiles have a greater thermal stability (or resistance), which is a characteristic of highly fluorinated or perfluorinated compounds. Herein, however, the alcohols containing perfluorobutylated and perfluorohexylated chains show the irregular thermal behavior in both the solid and monolayer states. Copyright © 2012 Elsevier B.V. All rights reserved.

Chiral Spin Texture in the Charge-Density-Wave Phase of the Correlated Metallic Pb /Si (111 ) Monolayer

Science.gov (United States)

Tresca, C.; Brun, C.; Bilgeri, T.; Menard, G.; Cherkez, V.; Federicci, R.; Longo, D.; Debontridder, F.; D'angelo, M.; Roditchev, D.; Profeta, G.; Calandra, M.; Cren, T.

2018-05-01

We investigate the 1 /3 monolayer α -Pb /Si (111 ) surface by scanning tunneling spectroscopy (STS) and fully relativistic first-principles calculations. We study both the high-temperature √{3 }×√{3 } and low-temperature 3 ×3 reconstructions and show that, in both phases, the spin-orbit interaction leads to an energy splitting as large as 25% of the valence-band bandwidth. Relativistic effects, electronic correlations, and Pb-substrate interaction cooperate to stabilize a correlated low-temperature paramagnetic phase with well-developed lower and upper Hubbard bands coexisting with 3 ×3 periodicity. By comparing the Fourier transform of STS conductance maps at the Fermi level with calculated quasiparticle interference from nonmagnetic impurities, we demonstrate the occurrence of two large hexagonal Fermi sheets with in-plane spin polarizations and opposite helicities.

Monolayer atomic crystal molecular superlattices

Science.gov (United States)

Wang, Chen; He, Qiyuan; Halim, Udayabagya; Liu, Yuanyue; Zhu, Enbo; Lin, Zhaoyang; Xiao, Hai; Duan, Xidong; Feng, Ziying; Cheng, Rui; Weiss, Nathan O.; Ye, Guojun; Huang, Yun-Chiao; Wu, Hao; Cheng, Hung-Chieh; Shakir, Imran; Liao, Lei; Chen, Xianhui; Goddard, William A., III; Huang, Yu; Duan, Xiangfeng

2018-03-01

Artificial superlattices, based on van der Waals heterostructures of two-dimensional atomic crystals such as graphene or molybdenum disulfide, offer technological opportunities beyond the reach of existing materials. Typical strategies for creating such artificial superlattices rely on arduous layer-by-layer exfoliation and restacking, with limited yield and reproducibility. The bottom-up approach of using chemical-vapour deposition produces high-quality heterostructures but becomes increasingly difficult for high-order superlattices. The intercalation of selected two-dimensional atomic crystals with alkali metal ions offers an alternative way to superlattice structures, but these usually have poor stability and seriously altered electronic properties. Here we report an electrochemical molecular intercalation approach to a new class of stable superlattices in which monolayer atomic crystals alternate with molecular layers. Using black phosphorus as a model system, we show that intercalation with cetyl-trimethylammonium bromide produces monolayer phosphorene molecular superlattices in which the interlayer distance is more than double that in black phosphorus, effectively isolating the phosphorene monolayers. Electrical transport studies of transistors fabricated from the monolayer phosphorene molecular superlattice show an on/off current ratio exceeding 107, along with excellent mobility and superior stability. We further show that several different two-dimensional atomic crystals, such as molybdenum disulfide and tungsten diselenide, can be intercalated with quaternary ammonium molecules of varying sizes and symmetries to produce a broad class of superlattices with tailored molecular structures, interlayer distances, phase compositions, electronic and optical properties. These studies define a versatile material platform for fundamental studies and potential technological applications.

Ab initio study of adsorption and diffusion of lithium on transition metal dichalcogenide monolayers

Directory of Open Access Journals (Sweden)

Xiaoli Sun

2017-12-01

Full Text Available Using first principles calculations, we studied the stability and electronic properties of transition metal dichalcogenide monolayers of the type MX2 (M = Ti, Zr, Hf, V, Nb, Ta, Mo, Cr, W; X= S, Se, Te. The adsorption and diffusion of lithium on the stable MX2 phase was also investigated for potential application as an anode for lithium ion batteries. Some of these compounds were found to be stable in the 2H phase and some are in the 1T or 1T' phase, but only a few of them were stable in both 2H/1T or 2H/1T' phases. The results show that lithium is energetically favourable for adsorption on MX2 monolayers, which can be semiconductors with a narrow bandgap and metallic materials. Lithium cannot be adsorbed onto 2H-WS2 and 2H-WSe2, which have large bandgaps of 1.66 and 1.96 eV, respectively. The diffusion energy barrier is in the range between 0.17 and 0.64 eV for lithium on MX2 monolayers, while for most of the materials it was found to be around 0.25 eV. Therefore, this work illustrated that most of the MX2 monolayers explored in this work can be used as promising anode materials for lithium ion batteries.

Ab initio study of adsorption and diffusion of lithium on transition metal dichalcogenide monolayers.

Science.gov (United States)

Sun, Xiaoli; Wang, Zhiguo

2017-01-01

Using first principles calculations, we studied the stability and electronic properties of transition metal dichalcogenide monolayers of the type MX 2 (M = Ti, Zr, Hf, V, Nb, Ta, Mo, Cr, W; X= S, Se, Te). The adsorption and diffusion of lithium on the stable MX 2 phase was also investigated for potential application as an anode for lithium ion batteries. Some of these compounds were found to be stable in the 2H phase and some are in the 1T or 1T' phase, but only a few of them were stable in both 2H/1T or 2H/1T' phases. The results show that lithium is energetically favourable for adsorption on MX 2 monolayers, which can be semiconductors with a narrow bandgap and metallic materials. Lithium cannot be adsorbed onto 2H-WS 2 and 2H-WSe 2 , which have large bandgaps of 1.66 and 1.96 eV, respectively. The diffusion energy barrier is in the range between 0.17 and 0.64 eV for lithium on MX 2 monolayers, while for most of the materials it was found to be around 0.25 eV. Therefore, this work illustrated that most of the MX 2 monolayers explored in this work can be used as promising anode materials for lithium ion batteries.

Monolayer MoSe 2 Grown by Chemical Vapor Deposition for Fast Photodetection

KAUST Repository

Chang, Yung-Huang

2014-08-26

Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe 2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs in 2D material-based optoelectronic devices. © 2014 American Chemical Society.

Well-ordered monolayers of alkali-doped coronene and picene: Molecular arrangements and electronic structures

Energy Technology Data Exchange (ETDEWEB)

Yano, M.; Endo, M.; Hasegawa, Y.; Okada, R.; Yamada, Y., E-mail: yamada@bk.tsukuba.ac.jp; Sasaki, M. [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan)

2014-07-21

Adsorptions of alkali metals (such as K and Li) on monolayers of coronene and picene realize the formation of ordered phases, which serve as well-defined model systems for metal-intercalated aromatic superconductors. Upon alkali-doping of the monolayers of coronene and picene, scanning tunneling microscopy and X-ray absorption spectroscopy revealed the rearrangement of the entire molecular layer. The K-induced reconstruction of both monolayers resulted in the formation of a structure with a herringbone-like arrangement of molecules, suggesting the intercalation of alkali metals between molecular planes. Upon reconstruction, a shift in both the vacuum level and core levels of coronene was observed as a result of a charge transfer from alkali metals to coronene. In addition, a new density of states near the Fermi level was formed in both the doped coronene and the doped picene monolayers. This characteristic electronic feature of the ordered monolayer has been also reported in the multilayer picene films, ensuring that the present monolayer can model the properties of the metal-intercalated aromatic hydrocarbons. It is suggested that the electronic structure near the Fermi level is sensitive to the molecular arrangement, and that both the strict control and determinations of the molecular structure in the doped phase should be important for the determination of the electronic structure of these materials.

Controlled synthesis of high-quality crystals of monolayer MoS2 for nanoelectronic device application

DEFF Research Database (Denmark)

Yang, Xiaonian; Li, Qiang; Hu, Guofeng

2016-01-01

. Monolayer MoS2 so far can be obtained by mechanical exfoliation or chemical vapor deposition (CVD). However, controllable synthesis of large area monolayer MoS2 with high quality needs to be improved and their growth mechanism requires more studies. Here we report a systematical study on controlled...... synthesis of high-quality monolayer MoS2 single crystals using low pressure CVD. Large-size monolayer MoS2 triangles with an edge length up to 405 mu m were successfully synthesized. The Raman and photoluminescence spectroscopy studies indicate high homogenous optical characteristic of the synthesized...... monolayer MoS2 triangles. The transmission electron microscopy results demonstrate that monolayer MoS2 triangles are single crystals. The back-gated field effect transistors (FETs) fabricated using the as-grown monolayer MoS2 show typical n-type semiconductor behaviors with carrier mobility up to 21.8 cm(2...

Vanadium oxide monolayer catalysts : The vapor-phase oxidation of methanol

NARCIS (Netherlands)

Roozeboom, Fred; Cordingley, Peter D.; Gellings, P.J.

1981-01-01

The oxidation of methanol over vanadium oxide, unsupported and applied as a monolayer on γ-Al2O3, CeO2, TiO2, and ZrO2, was studied between 100 and 400 °C in a continuous-flow reactor. At temperatures from 150 to about 250 °C two main reactions take place, (a) dehydration of methanol to dimethyl

Transport properties in monolayer-bilayer-monolayer graphene planar junctions

Institute of Scientific and Technical Information of China (English)

Kai-Long Chu; Zi-Bo Wang; Jiao-Jiao Zhou; Hua Jiang

2017-01-01

The transport study of graphene based junctions has become one of the focuses in graphene research.There are two stacking configurations for monolayer-bilayer-monolayer graphene planar junctions.One is the two monolayer graphene contacting the same side of the bilayer graphene,and the other is the two-monolayer graphene contacting the different layers of the bilayer graphene.In this paper,according to the Landauer-Büttiker formula,we study the transport properties of these two configurations.The influences of the local gate potential in each part,the bias potential in bilayer graphene,the disorder and external magnetic field on conductance are obtained.We find the conductances of the two configurations can be manipulated by all of these effects.Especially,one can distinguish the two stacking configurations by introducing the bias potential into the bilayer graphene.The strong disorder and the external magnetic field will make the two stacking configurations indistinguishable in the transport experiment.

Ultralow lattice thermal conductivity in monolayer C3N as compared to graphene

KAUST Repository

Sarath Kumar, S. R.

2017-09-21

Using density functional theory and the Boltzmann transport equation for phonons, we demonstrate that the thermal conductivity is massively reduced in monolayer CN as compared to isostructural graphene. We show that larger phase space for three-phonon scattering processes is available in monolayer CN, which results in much shorter phonon life-times. Although both materials are characterized by sp hybridisation, anharmonicity effects are found to be enhanced for the C-N and C-C bonds in monolayer CN, reflected by a Grüneisen parameter of -8.5 as compared to -2.2 in graphene. The combination of these properties with the fact that monolayer CN is organic, non-toxic, and built of earth abundant elements gives rise to great potential in thermoelectric applications.

Structure of cholesterol/ceramide monolayer mixtures

DEFF Research Database (Denmark)

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

2005-01-01

The structure of monolayers of cholesterol/ ceramide mixtures was investigated using grazing incidence x-ray diffraction, immunofluorescence, and atomic force microscopy techniques. Grazing incidence x-ray diffraction measurements showed the existence of a crystalline mixed phase of the two....... As ceramide incorporates the lipid backbone common to all sphingolipids, this arrangement may be relevant to the understanding of the molecular organization of lipid rafts....

Spreading dynamics of 2D dipolar Langmuir monolayer phases.

Science.gov (United States)

Heinig, P; Wurlitzer, S; Fischer, Th M

2004-07-01

We study the spreading of a liquid 2D dipolar droplet in a Langmuir monolayer. Interfacial tensions (line tensions) and microscopic contact angles depend on the scale on which they are probed and obey a scaling law. Assuming rapid equilibration of the microscopic contact angle and ideal slippage of the 2D solid/liquid and solid/gas boundary, the driving force of spreading is merely expressed by the shape-dependent long-range interaction integrals. We obtain good agreement between experiment and numerical simulations using this theory.

Diamondoid monolayers as electron emitters

Science.gov (United States)

Yang, Wanli [El Cerrito, CA; Fabbri, Jason D [San Francisco, CA; Melosh, Nicholas A [Menlo Park, CA; Hussain, Zahid [Orinda, CA; Shen, Zhi-Xun [Stanford, CA

2012-04-10

Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

Pattern Formation in Langmuir Monolayers Due to Long-Range Electrostatic Interactions

Science.gov (United States)

Fischer, Thomas M.; Lösche, Mathias

A distinctive characteristic of Langmuir monolayers that bears important consequences for the physics of structure formation within membranes is the uniaxial orientation of the constituent dipolar molecules, brought about by the symmetry break which is induced by the surface of the aqueous substrate. The association of oriented molecular dipoles with the interface leads to the formation of image dipoles within the polarizeable medium - the subphase - such that the effective dipole orientation of every of the individual molecules is strictly normal to the surface, even within molecularly disordered phases. As a result, dipole-dipole repulsions play an eminently important role for the molecular interactions within the system - independent of the state of phase (while the dipole area density does of course depend on the state of phase) - and control the morphogenesis of the phase boundaries in their interplay with the one-dimensional (1D) line tension between coexisting phases. The physics of these phenomena is only now being explored and is particularly exciting for systems within a three-phase coexistence region where complete or partial wetting, as well as dewetting between the coexisting phases may be experimentally observed by applying fluorescence microscopy to the monolayer films. It is revealed that the wetting behavior depends sensitively on the details of the electrostatic interactions, in that the apparent contact angles observed at three-phase contact points depends on the sizes of the coexisting phases. This is in sharp contrast to the physics of wetting in conventional 3D systems where the contact angle is a materials property, independent of the local details. In 3D systems, this leads to Youngs equation - which has been established more than two centuries ago. We report recent progress in the understanding of this unusual and rather unexpected behavior of a quasi-2D system by reviewing recent experimental results from optical microscopy on equilibrium

Chiral hierarchical self-assembly in Langmuir monolayers of diacetylenic lipids

KAUST Repository

Basnet, Prem B.; Mandal, Pritam; Malcolm, Dominic W.; Mann, Elizabeth; Chaieb, Saharoui

2013-01-01

When compressed in the intermediate temperature range below the chain-melting transition yet in the low-pressure liquid phase, Langmuir monolayers made of chiral lipid molecules form hierarchical structures. Using Brewster angle microscopy to reveal

Theory of lithium islands and monolayers: Electronic structure and stability

International Nuclear Information System (INIS)

Quassowski, S.; Hermann, K.

1995-01-01

Systematic calculations on planar clusters and monolayers of lithium are performed to study geometries and stabilities of the clusters as well as their convergence behavior with increasing cluster size. The calculations are based on ab initio methods using density-functional theory within the local-spin-density approximation for exchange and correlation. The optimized nearest-neighbor distances d NN of the Li n clusters, n=1,...,25, of both hexagonal and square geometry increase with cluster size, converging quite rapidly towards the monolayer results. Further, the cluster cohesive energies E c increase with cluster size and converge towards the respective monolayer values that form upper bounds. Clusters of hexagonal geometry are found to be more stable than square clusters of comparable size, consistent with the monolayer results. The size dependence of the cluster cohesive energies can be described approximately by a coordination model based on the concept of pairwise additive nearest-neighbor binding. This indicates that the average binding in the Li n clusters and their relative stabilities can be explained by simple geometric effects which derive from the nearest-neighbor coordination

Spin polarization driven by a charge-density wave in monolayer 1T−TaS2

KAUST Repository

Zhang, Qingyun

2014-08-06

Using first-principles calculations, we investigate the electronic and vibrational properties of monolayer T-phase TaS2. We demonstrate that a charge-density wave is energetically favorable at low temperature, similar to bulk 1T-TaS2. Electron-phonon coupling is found to be essential for the lattice reconstruction. The charge-density wave results in a strong localization of the electronic states near the Fermi level and consequently in spin polarization, transforming the material into a magnetic semiconductor with enhanced electronic correlations. The combination of inherent spin polarization with a semiconducting nature distinguishes the monolayer fundamentally from the bulk compound as well as from other two-dimensional transition metal dichalcogenides. Monolayer T-phase TaS2 therefore has the potential to enable two-dimensional spintronics. © 2014 American Physical Society.

Spin polarization driven by a charge-density wave in monolayer 1T−TaS2

KAUST Repository

Zhang, Qingyun; Gan, Liyong; Cheng, Yingchun; Schwingenschlö gl, Udo

2014-01-01

Using first-principles calculations, we investigate the electronic and vibrational properties of monolayer T-phase TaS2. We demonstrate that a charge-density wave is energetically favorable at low temperature, similar to bulk 1T-TaS2. Electron-phonon coupling is found to be essential for the lattice reconstruction. The charge-density wave results in a strong localization of the electronic states near the Fermi level and consequently in spin polarization, transforming the material into a magnetic semiconductor with enhanced electronic correlations. The combination of inherent spin polarization with a semiconducting nature distinguishes the monolayer fundamentally from the bulk compound as well as from other two-dimensional transition metal dichalcogenides. Monolayer T-phase TaS2 therefore has the potential to enable two-dimensional spintronics. © 2014 American Physical Society.

Ab initio phonon thermal transport in monolayer InSe, GaSe, GaS, and alloys

Energy Technology Data Exchange (ETDEWEB)

Pandey, Tribhuwan; Parker, David S.; Lindsay, Lucas

2017-10-17

We compare vibrational properties and phonon thermal conductivities (κ) of monolayer InSe, GaSe and GaS systems using density functional theory and Peierls-Boltzmann transport methods. In going from InSe to GaSe to GaS, system mass decreases giving both increasing acoustic phonon velocities and decreasing scattering of these heat-carrying modes with optic phonons, ultimately giving κInSe< κGaSe< κGaS. This behavior is demonstrated by correlating the scattering phase space limited by fundamental conservation conditions with mode scattering rates and phonon dispersions for each material. We also show that, unlike flat monolayer systems such as graphene, thermal transport is governed by in-plane vibrations in InSe, GaSe and GaS, similar to buckled monolayer materials such as silicene. Alloying of InSe, GaSe and GaS systems provides an effective method for modulating their κ through intrinsic vibrational modifications and phonon scattering from mass disorder giving reductions ~2-3.5 times. This disorder also suppresses phonon mean free paths in the alloy systems compared to those in their crystalline counterparts. This work provides fundamental insights of lattice thermal transport from basic vibrational properties for an interesting set of two-dimensional materials.

Monolayer II-VI semiconductors: A first-principles prediction

Science.gov (United States)

Zheng, Hui; Chen, Nian-Ke; Zhang, S. B.; Li, Xian-Bin

A systematic study of 32 honeycomb monolayer II-VI semiconductors is carried out by first-principles methods. It appears that BeO, MgO, CaO, ZnO, CdO, CaS, SrS, SrSe, BaTe, and HgTe honeycomb monolayers have a good dynamic stability which is revealed by phonon calculations. In addition, from the molecular dynamic (MD) simulation of other unstable candidates, we also find two extra monolayers dynamically stable, which are tetragonal BaS and orthorhombic HgS. The honeycomb monolayers exist in form of either a planar perfect honeycomb or a low-buckled 2D layer, all of which possess a band gap and most of them are in the ultraviolet region. Interestingly, the dynamically stable SrSe has a gap near visible light, and displays exotic electronic properties with a flat top of the valence band, and hence has a strong spin polarization upon hole doping. The honeycomb HgTe has been reported to achieve a topological nontrivial phase under appropriate in-plane tensile strain and spin-orbital coupling (SOC). Some II-VI partners with less than 5% lattice mismatch may be used to design novel 2D heterojunction devices. If synthesized, potential applications of these 2D II-VI families could include optoelectronics, spintronics, and strong correlated electronics. Distinguished Student (DS) Program of APS FIP travel funds.

Monolayer-by-monolayer growth of platinum films on complex carbon fiber paper structure

Energy Technology Data Exchange (ETDEWEB)

Pang, Liuqing; Zhang, Yunxia [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Key Laboratory for Advanced Energy Devices, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119 (China); Liu, Shengzhong, E-mail: szliu@dicp.ac.cn [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Key Laboratory for Advanced Energy Devices, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119 (China); Dalian National Laboratory for Clean Energy, iChEM, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (China)

2017-06-15

Graphical abstract: A controlled monolayer-by-monolayer deposition process has been developed to fabricate Pt coating on carbon fiber paper with complex network structures using a dual buffer strategy. This development may pave a way to fabricate superior Pt catalysts with the minimal Pt usage. In fact, the present Pt group metal loading is 25 times lower than the U.S. DOE 2017 target value. - Highlights: • Developed a controlled monolayer-by-monolayer Pt deposition using a dual buffer strategy. • The present Pt group metal loading is 25 times lower than the U.S. DOE 2017 target value. • This development may pave a way to fabricate superior Pt catalysts with the minimal Pt usage. - Abstract: A controlled monolayer-by-monolayer deposition process has been developed to fabricate Pt coating on carbon fiber paper with complex network structures using a dual buffer (Au/Ni) strategy. The X-ray diffraction, electrochemical quartz crystal microbalance, current density analyses, and X-ray photoelectron spectroscopy results conclude that the monolayer deposition process accomplishes full coverage on the substrate and that the thickness of the deposition layer can be controlled on a single atom scale. This development may pave a way to fabricate superior Pt catalysts with the minimal Pt usage. In fact, the present Pt group metal loading is 25 times lower than the U.S. DOE 2017 target value.

Chiral and herringbone symmetry breaking in water-surface monolayers

DEFF Research Database (Denmark)

Peterson, I.R.; Kenn, R.M.; Goudot, A.

1996-01-01

We report the observation from monolayers of eicosanoic acid in the L(2)' phase of three distinct out-of-plane first-order diffraction peaks, indicating molecular tilt in a nonsymmetry direction and hence the absence of mirror symmetry. At lower pressures the molecules tilt in the direction of th...

Overcrowding drives the unjamming transition of gap-free monolayers

Science.gov (United States)

Lan, Ganhui; Su, Tao

Collective cell motility plays central roles in various biological phenomena such as wound healing, cancer metastasis and embryogenesis. These are demonstrations of the unjamming transition in biology. However, contradictory to the typical density-driven jamming in particulate assemblies, cellular systems often get unjammed in highly packed, sometimes overcrowding environments. Here, we investigate monolayers' collective behaviors when cell number changes under the gap-free constraint. We report that overcrowding can unjam gap-free monolayers through increasing isotropic compression. We show that the transition boundary is determined by the isotropic compression and the cell-cell adhesion. Furthermore, we construct the free energy landscape for the T1 topological transition during monolayer rearrangement, and discover that the landscape evolves from single-barrier W shape to double-barrier M shape during the unjamming process. We also discover a distributed-to-disordered morphological transition of cells' geometry, coinciding with the unjamming transition. Our analyses reveal that the overcrowding and adhesion induced unjamming reflects the mechanical yielding of the highly deformable monolayer, suggesting an alternative mechanism that cells may robustly gain collective mobility through proliferation in confined environments, which differs from those caused by loosing up a packed particulate assembly. This work is supported by the GWU College Facilitating Funds.

Electrochemical Properties of Alkanethiol Monolayers Adsorbed on Nanoporous Au Surfaces

International Nuclear Information System (INIS)

Chu, Yeon Yi; Seo, Bora; Kim, Jong Won

2010-01-01

We investigated the electrochemical properties of alkanethiol monolayers adsorbed on NPG surfaces by cyclic voltammetry and electrochemical impedance spectroscopy, and the results are compared to those on flat Au surfaces. The reductive desorption of alkanethiols on NPG surfaces is observed in more negative potential regions than that on flat Au surfaces due the stronger S-Au interaction on NPG surfaces. While the electron transfer through alkanethiol monolayers on flat Au surfaces occurs via a tunneling process through the monolayer films, the redox species can permeate through the monolayers on NPG surfaces to transfer the electrons to the Au surfaces. The results presented here will help to elucidate the intrinsic electrochemical properties of alkanethiol monolayers adsorbed on curved Au surfaces, particularly on the surface of AuNPs. Self-assembled monolayers (SAMs) of thiolate molecules on Au surfaces have been the subject of intensive research for the last few decades due to their unique physical and chemical properties. The well-organized surface structures of thiolate SAMs with various end-group functionalities can be further utilized for many applications in biology and nanotechnology. In addition to the practical applications, SAMs of thiolate molecules on Au surfaces also provide unique opportunities to address fundamental issues in surface chemistry such as self-organized surface structures, electron transfer behaviors, and moleculesubstrate interactions. Although there have been numerous reports on the fundamental physical and chemical properties of thiolate SAMs on Au surfaces, most of them were investigated on flat Au surfaces, typically on well-defined Au(111) surfaces

Conformations and orientations of a signal peptide interacting with phospholipid monolayers

International Nuclear Information System (INIS)

Cornell, D.G.; Dluhy, R.A.; Briggs, M.S.; McKnight, C.J.; Gierasch, L.M.

1989-01-01

The interaction of a chemically synthesized 25-residue signal peptide of LamB protein from Escherichia coli with phospholipids has been studied with a film balance technique. The conformation, orientation, and concentration of the peptides in lipid monolayers have been determined from polarized infrared spectroscopy, ultraviolet spectroscopy, and assay of 14 C-labeled peptide in transferred films. When the LamB signal peptide in injected into the subphase under a phosphatidylethanolamine-phosphatidylglycerol monolayer at low initial pressure, insertion of a portion of the peptide into the lipid film is evidenced by a rapid rise in film pressure. Spectroscopic results obtained on films transferred to quartz plates and Ge crystals show that the peptide is a mixture of α-helix and β-conformation where the long axis of the α-helix penetrates the monolayer plane and the β-structure which is coplanar with the film. By contrast, when peptide is injected under lipid at high initial pressure, no pressure rise is observed, and the spectroscopic results show the presence of only β-structure which is coplanar with the monolayer. The spectroscopic and radioassay results are all consistent with the picture of a peptide anchored to the monolayer through electrostatic binding with a helical portion inserted into the lipid region of the monolayer and a β-structure portion resident in the aqueous phase. The negative charges on the lipid molecules are roughly neutralized by the positive charges of the peptide

Structure and morphology of pentacene thin films - from sub-monolayers to application relevant multilayers

International Nuclear Information System (INIS)

Resel, R.; Werzer, O.; Nabok, D.; Puschnig, P.; Ambrosch-Draxl, C.; Smilgies, D.; Haase, A.; Stadlober, B.

2008-01-01

Full text: The conjugated molecule pentacene is one of the most prominent material for application in organic thin film transistors. Charge carrier mobilities of about 1 cm 2 /Vs are realized in different device geometries which are used in integrated circuits. The device performance depends on the detailed structure and morphology of the pentacene thin films. This work presents an combined atomic force microscopy / x-ray scattering study on the formation of pentacene thin films starting from sub-monolayer coverage to the first closed monolayer to finally multilayer structures as they are used in device structures. Thin films of pentacene are prepared on oxidized silicon wafer with nominal thicknesses between 0.2 nm up to 180 nm. The films are investigated ex-situ by x-ray reflectivity and grazing incidence diffraction. In the sub-monolayer regime the formation of separated islands with up-right standing molecules are observed. The islands show typically dendritic shape with a separation of 2 μm from each other. With increasing coverage the dendritic islands coalescent until the first monolayer closes. Fitting of the x-ray reflectivity reveals that an additional layer between the substrate and the up-right standing pentacene molecules is present. During the formation of the second monolayer crystalline islands are formed. The crystallites grow in lateral and vertical size with increasing film thickness. The crystal structure of pentacene within the films is a surface induced phase. The crystal structure of this metastable phase could be solved by a combined experimental and theoretical approach. At a nominal film thickness of about 40 nm the equilibrium bulk structure of pentacene appears; both phases remain existent up the thickest films investigated in this study. (author)

Ordered Fe(II)Ti(IV)O3 Mixed Monolayer Oxide on Rutile TiO2(011).

Science.gov (United States)

Halpegamage, Sandamali; Ding, Pan; Gong, Xue-Qing; Batzill, Matthias

2015-08-25

Oxide monolayers supported or intermixed with an oxide support are potential nanocatalysts whose properties are determined by the interplay with the support. For fundamental studies of monolayer oxides on metal oxide supports, well-defined systems are needed, but so far, the synthesis of monolayer oxides with long-range order on single-crystal oxide surfaces is rare. Here, we show by a combination of scanning tunneling microscopy, photoemission spectroscopy, and density functional theory (DFT)-based computational analysis that the rutile TiO2(011) surface supports the formation of an ordered mixed FeTiO3 monolayer. Deposition of iron in a slightly oxidizing atmosphere (10(-8) Torr O2) and annealing to 300 °C results in a well-ordered surface structure with Fe in a 2+ charge state and Ti in a 4+ charge states. Low-energy ion scattering suggests that the cation surface composition is close to half Fe and half Ti. This surface is stable in ultrahigh vacuum to annealing temperatures of 300 °C before the iron is reduced. DFT simulations confirm that a surface structure with coverage of 50% FeO units is stable and forms an ordered structure. Although distinct from known bulk phases of the iron-titanium oxide systems, the FeTiO3 monolayer exhibits some resemblance to the ilmenite structure, which may suggest that a variety of different mixed oxide phases (of systems that exist in a bulk ilmenite phase) may be synthesized in this way on the rutile TiO2(011) substrate.

Packing of ganglioside-phospholipid monolayers

DEFF Research Database (Denmark)

Majewski, J.; Kuhl, T.L.; Kjær, K.

2001-01-01

Using synchrotron grazing-incidence x-ray diffraction (GIXD) and reflectivity, the in-plane and out-of-plane structure of mixed ganglioside-phospholipid monolayers was investigated at the air-water interface. Mixed monolayers of 0, 5, 10, 20, and 100 mol% ganglioside GM, and the phospholipid...... monolayers did not affect hydrocarbon tail packing (fluidization or condensation of the hydrocarbon region). This is in contrast to previous investigations of lipopolymer-lipid mixtures, where the packing structure of phospholipid monolayers was greatly altered by the inclusion of lipids bearing hydrophilic...

Double-brush Langmuir-Blodgett monolayers of alpha-helical diblock copolypeptides

NARCIS (Netherlands)

Nguyen, Le-Thu T.; Vorenkamp, Eltjo J.; Daumont, Christophe J. M.; ten Brinke, Gerrit; Schouten, Arend J.; Vukovic, Ivana; Loos, Katja

2010-01-01

The synthesis of amphiphilic diblock copolypeptides consisting of poly(alpha-L-glutamic acid) (PLGA) and poly(gamma-methyl-L-glutamate-ran-gamma-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) and their monolayer behavior at the air-water interface have been studied.

Strain-tunable half-metallicity in hybrid graphene-hBN monolayer superlattices

International Nuclear Information System (INIS)

Meng, Fanchao; Zhang, Shiqi; Lee, In-Ho; Jun, Sukky; Ciobanu, Cristian V.

2016-01-01

Highlights: • Armchair superlattices have a bandgap modulated by the deformed domain widths. • Strain and domain width lead to novel spin-dependent behavior for zigzag boundaries. • Limits for spin-dependent bandgap and half-metallic behavior have been charted. - Abstract: As research in 2-D materials evolves toward combinations of different materials, interesting electronic and spintronic properties are revealed and may be exploited in future devices. A way to combine materials is the formation of spatially periodic domain boundaries in an atom-thick monolayer: as shown in recent reports, when these domains are made of graphene and hexagonal boron nitride, the resulting superlattice has half-metallic properties in which one spin component is (semi)metallic and the other is semiconductor. We explore here the range of spin-dependent electronic properties that such superlattices can develop for different type of domain boundaries, domain widths, and values of tensile strain applied to the monolayer. We show evidence of an interplay between strain and domain width in determining the electronic properties: while for armchair boundaries the bandgap is the same for both spin components, superlattices with zigzag boundaries exhibit rich spin-dependent behavior, including different bandgaps for each spin component, half-metallicity, and reversal of half-metallicity. These findings can lead to new ways of controlling the spintronic properties in hybrid-domain monolayers, which may be exploited in devices based on 2-D materials.

Magnetic tunnel junctions with monolayer hexagonal boron nitride tunnel barriers

Energy Technology Data Exchange (ETDEWEB)

Piquemal-Banci, M.; Galceran, R.; Bouzehouane, K.; Anane, A.; Petroff, F.; Fert, A.; Dlubak, B.; Seneor, P. [Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau 91767 (France); Caneva, S.; Martin, M.-B.; Weatherup, R. S.; Kidambi, P. R.; Robertson, J.; Hofmann, S. [Department of Engineering, University of Cambridge, Cambridge CB21PZ (United Kingdom); Xavier, S. [Thales Research and Technology, 1 avenue Augustin Fresnel, Palaiseau 91767 (France)

2016-03-07

We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions (MTJs). The h-BN monolayer is directly grown by chemical vapor deposition on Fe. The Conductive Tip Atomic Force Microscopy (CT-AFM) measurements reveal the homogeneity of the tunnel behavior of our h-BN layers. As expected for tunneling, the resistance depends exponentially on the number of h-BN layers. The h-BN monolayer properties are also characterized through integration into complete MTJ devices. A Tunnel Magnetoresistance of up to 6% is observed for a MTJ based on a single atomically thin h-BN layer.

Dynamics of decanethiol self-assembled monolayers on Au(111) studied by Scanning tunnelling microscopy

NARCIS (Netherlands)

Wu, Hairong; Sotthewes, Kai; Kumar, Avijit; Vancso, Gyula J.; Schön, Peter Manfred; Zandvliet, Henricus J.W.

2013-01-01

We investigated the dynamics of decanethiol self-assembled monolayers on Au(111) surfaces using time-resolved scanning tunneling microscopy at room temperature. The expected ordered phases (β, δ, χ*, and ) and a disordered phase (ε) were observed. Current–time traces with the feedback loop disabled

Cholesterol Depletion from a Ceramide/Cholesterol Mixed Monolayer: A Brewster Angle Microscope Study

KAUST Repository

Mandal, Pritam

2016-06-01

Cholesterol is crucial to the mechanical properties of cell membranes that are important to cells’ behavior. Its depletion from the cell membranes could be dramatic. Among cyclodextrins (CDs), methyl beta cyclodextrin (MβCD) is the most efficient to deplete cholesterol (Chol) from biomembranes. Here, we focus on the depletion of cholesterol from a C16 ceramide/cholesterol (C16-Cer/Chol) mixed monolayer using MβCD. While the removal of cholesterol by MβCD depends on the cholesterol concentration in most mixed lipid monolayers, it does not depend very much on the concentration of cholesterol in C16-Cer/Chol monolayers. The surface pressure decay during depletion were described by a stretched exponential that suggested that the cholesterol molecules are unable to diffuse laterally and behave like static traps for the MβCD molecules. Cholesterol depletion causes morphology changes of domains but these disrupted monolayers domains seem to reform even when cholesterol level was low.

Fluctuation effects in bulk polymer phase behavior

International Nuclear Information System (INIS)

Bates, F.S.; Rosedale, J.H.; Stepanek, P.; Lodge, T.P.; Wiltzius, P.; Hjelm R, Jr.; Fredrickson, G.H.

1990-01-01

Bulk polymer-polymer, and block copolymer, phase behaviors have traditionally been interpreted using mean-field theories. Recent small-angle neutron scattering (SANS) studies of critical phenomena in model binary polymer mixtures confirm that non-mean-field behavior is restricted to a narrow range of temperatures near the critical point, in close agreement with the Ginzburg criterion. In contrast, strong derivations from mean-field behavior are evident in SANS and rheological measurements on model block copolymers more than 50C above the order-disorder transition (ODT), which can be attributed to sizeable composition fluctuations. Such fluctuation effects undermine the mean-field assumption, conventionally applied to bulk polymers, and result in qualitative changes in phase behavior, such as the elimination of a thermodynamic stability limit in these materials. The influence of fluctuation effects on block copolymer and binary mixture phase behavior is compared and contrasted in this presentation

Substoichiometric cobalt oxide monolayer on Ir(100)-(1 x 1)

International Nuclear Information System (INIS)

Gubo, M; Ebensperger, C; Meyer, W; Hammer, L; Heinz, K

2009-01-01

A substoichiometric monolayer of cobalt oxide has been prepared by deposition and oxidation of slightly less than one monolayer of cobalt on the unreconstructed surface of Ir(100). The ultrathin film was investigated by scanning tunnelling microscopy (STM) and quantitative low-energy electron diffraction (LEED). The cobalt species of the film reside in or near hollow positions of the substrate with, however, unoccupied sites (vacancies) in a 3 x 3 arrangement. In the so-formed 3 x 3 supercell the oxide's oxygen species are both threefold and fourfold coordinated to cobalt, forming pyramids with a triangular and square cobalt basis, respectively. These pyramids are the building blocks of the oxide. Due to the reduced coordination as compared to the sixfold one in the bulk of rock-salt-type CoO, the Co-O bond lengths are smaller than in the latter. For the threefold coordination they compare very well with the bond length in oxygen terminated CoO(111) films investigated recently. The substoichiometric 3 x 3 oxide monolayer phase transforms to a stoichiometric c(10 x 2)-periodic oxide monolayer under oxygen exposure, in which, however, cobalt and oxygen species are in (111) orientation and so form a CoO(111) layer.

Miscibility of dl-α-tocopherol β-glucoside in DPPC monolayer at air/water and air/solid interfaces

Energy Technology Data Exchange (ETDEWEB)

Neunert, G. [Department of Physics and Biophysics, Poznan University of Life Sciences, 60-637 Poznan (Poland); Makowiecki, J.; Piosik, E.; Hertmanowski, R. [Faculty of Technical Physics, Poznan University of Technology, 60-965 Poznan (Poland); Polewski, K. [Department of Physics and Biophysics, Poznan University of Life Sciences, 60-637 Poznan (Poland); Martynski, T., E-mail: tomasz.martynski@put.poznan.pl [Faculty of Technical Physics, Poznan University of Technology, 60-965 Poznan (Poland)

2016-10-01

The role of newly synthesized tocopherol glycosidic derivative in modifying molecular organization and phase transitions of phospholipid monolayer at the air/water interface has been investigated. Two-component Langmuir films of dl-α-tocopheryl β-D-glucopyranoside (BG) mixed with dipalmitoyl phosphatidylcholine (DPPC) in the whole range of mole fractions were formed at the water surface. An analysis of surface pressure versus mean molecular area (π-A) isotherms and Brewster angle microscope images showed that the presence of BG molecules changes the structure and packing of the DPPC monolayer in a BG concentration dependent manner. BG molecules incorporated into DPPC monolayer inhibit its liquid expanded to liquid condensed phase transition proportionally to the BG concentration. The monolayers were also transferred onto solid substrates and visualized using an atomic force microscope. The results obtained indicate almost complete miscibility of BG and DPPC in the monolayers at surface pressures present in the biological cell membrane (30-35·10{sup -3} N·m{sup -1}) for a BG mole fraction as high as 0.3. This makes the monolayer less packed and more disordered, leading to an increased permeability. The results support our previous molecular dynamics simulation data. - Highlights: • Langmuir films of α-tocopherol derivative with DPPC was studied thermodynamically. • Mixed DPPC/BG films were transferred onto mica substrates for topography imaging by using AFM. • Miscibility of BG/DPPC films at surface pressures present in membranes was observed up to MF = 0.3.

Phosphatidylcholine-fatty Alcohols Equilibria in Monolayers at the Air/Water Interface.

Science.gov (United States)

Serafin, Agnieszka; Figaszewski, Zbigniew Artur; Petelska, Aneta Dorota

2015-08-01

Monolayers of phosphatidylcholine (PC), tetradecanol (TD), hexadecanol (HD), octadecanol (OD) and eicosanol (E) and their binary mixtures were investigated at the air/water interface. The surface tension values of pure and mixed monolayers were used to calculate π-A isotherms. The surface tension measurements were carried out at 22 °C using a Teflon trough and a Nima 9000 tensiometer. The interactions between phosphatidylcholine and fatty alcohols (tetradecanol, hexadecanol, octadecanol, eicosanol) result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air/water interface was developed in order to obtain the stability constants, Gibbs free energy values and areas occupied by one molecules of PC-TD, PC-HD, PC-OD and PC-E complexes. We considered the equilibrium between the individual components and the complex and established that phosphatidylcholine and fatty alcohols formed highly stable 1:1 complexes.

Conduction quantization in monolayer MoS2

Science.gov (United States)

Li, T. S.

2016-10-01

We study the ballistic conduction of a monolayer MoS2 subject to a spatially modulated magnetic field by using the Landauer-Buttiker formalism. The band structure depends sensitively on the field strength, and its change has profound influence on the electron conduction. The conductance is found to demonstrate multi-step behavior due to the discrete number of conduction channels. The sharp peak and rectangular structures of the conductance are stretched out as temperature increases, due to the thermal broadening of the derivative of the Fermi-Dirac distribution function. Finally, quantum behavior in the conductance of MoS2 can be observed at temperatures below 10 K.

Point defect weakened thermal contraction in monolayer graphene.

Science.gov (United States)

Zha, Xian-Hu; Zhang, Rui-Qin; Lin, Zijing

2014-08-14

We investigate the thermal expansion behaviors of monolayer graphene and three configurations of graphene with point defects, namely the replacement of one carbon atom with a boron or nitrogen atom, or of two neighboring carbon atoms by boron-nitrogen atoms, based on calculations using first-principles density functional theory. It is found that the thermal contraction of monolayer graphene is significantly decreased by point defects. Moreover, the corresponding temperature for negative linear thermal expansion coefficient with the maximum absolute value is reduced. The cause is determined to be point defects that enhance the mechanical strength of graphene and then reduce the amplitude and phonon frequency of the out-of-plane acoustic vibration mode. Such defect weakening of graphene thermal contraction will be useful in nanotechnology to diminish the mismatching or strain between the graphene and its substrate.

Morphological changes of monolayers of two polymerizable pyridine amphiphiles upon complexation with Cu(II) ions at the air-water interface

NARCIS (Netherlands)

Werkman, P.J.; Schouten, A.J.; Noordegraaf, M.A.; Kimkes, P.; Sudhölter, E.J.R.

1998-01-01

The monolayer behavior of two amphiphilic, diacetylenic units containing pyridine Ligands at the air-water interface is studied by measuring the surface pressure-area isotherms and by Brewster angle microscopy(BAM). Both amphiphiles form stable monolayers at the air-water interface. The amphiphile

Surface Structures and Thermal Desorption Behaviors of Cyclopentanethiol Self-Assembled Monolayers on Au(111)

International Nuclear Information System (INIS)

Kang, Hun Gu; Kim, You Young; Park, Tae Sun; Noh, Jae Geun; Park, Joon B.; Ito, Eisuke; Hara, Masahiko

2011-01-01

The surface structures, adsorption conditions, and thermal desorption behaviors of cyclopentanethiol (CPT) self-assembled monolayers (SAMs) on Au(111) were investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). STM imaging revealed that although the adsorption of CPT on Au(111) at room temperature generates disordered SAMs, CPT molecules at 50 .deg. C formed well-ordered SAMs with a (2√3 x √5)R41".deg. packing structure. XPS measurements showed that CPT SAMs at room temperature were formed via chemical reactions between the sulfur atoms and gold surfaces. TDS measurements showed two dominant TD peaks for the decomposed fragments (C_5H_9 "+, m/e = 69) generated via C-S bond cleavage and the parent molecular species (C_5H_9SH"+, m/e = 102) derived from a recombination of the chemisorbed thiolates and hydrogen atoms near 440 K. Interestingly, dimerization of sulfur atoms in n-alkanethiol SAMs usually occurs during thermal desorption and the same reaction did not happen for CPT SAMs, which may be due to the steric hindrance of cyclic rings of the CPT molecules. In this study, we demonstrated that the alicyclic ring of organic thiols strongly affected the surface structure and thermal desorption behavior of SAMs, thus providing a good method for controlling chemical and physical properties of organic thiol SAMs

Modeling mechanical inhomogeneities in small populations of proliferating monolayers and spheroids.

Science.gov (United States)

Lejeune, Emma; Linder, Christian

2018-06-01

Understanding the mechanical behavior of multicellular monolayers and spheroids is fundamental to tissue culture, organism development, and the early stages of tumor growth. Proliferating cells in monolayers and spheroids experience mechanical forces as they grow and divide and local inhomogeneities in the mechanical microenvironment can cause individual cells within the multicellular system to grow and divide at different rates. This differential growth, combined with cell division and reorganization, leads to residual stress. Multiple different modeling approaches have been taken to understand and predict the residual stresses that arise in growing multicellular systems, particularly tumor spheroids. Here, we show that by using a mechanically robust agent-based model constructed with the peridynamic framework, we gain a better understanding of residual stresses in multicellular systems as they grow from a single cell. In particular, we focus on small populations of cells (1-100 s) where population behavior is highly stochastic and prior investigation has been limited. We compare the average strain energy density of cells in monolayers and spheroids using different growth and division rules and find that, on average, cells in spheroids have a higher strain energy density than cells in monolayers. We also find that cells in the interior of a growing spheroid are, on average, in compression. Finally, we demonstrate the importance of accounting for stochastic fluctuations in the mechanical environment, particularly when the cellular response to mechanical cues is nonlinear. The results presented here serve as a starting point for both further investigation with agent-based models, and for the incorporation of major findings from agent-based models into continuum scale models when explicit representation of individual cells is not computationally feasible.

Self-assembled monolayers of perfluoroalkylsilane on plasma-hydroxylated silicon substrates

Energy Technology Data Exchange (ETDEWEB)

Wu, Lin; Cai, Lu; Liu, Anqi; Wang, Wei; Yuan, Yanhua [College of Textile, Clothing Engineering, Soochow University, Suzhou 215021 (China); National Engineering Laboratory for Modern Silk, Suzhou 215123 (China); Li, Zhanxiong, E-mail: lizhanxiong@suda.edu.cn [College of Textile, Clothing Engineering, Soochow University, Suzhou 215021 (China); State Key Laboratory of Disaster Prevention & Mitigation of Explosion & Impact, Nanjing 210007 (China)

2015-09-15

Highlights: • A novel kind of fluoroalkylsilane monomers with different fluoroalkyl chain length was synthesized. • The fluoroalkyl-terminated self-assembled monolayers (SAMs) on silanol-terminated silicon substrates were chemically fabricated using the liquid phase deposition method. • Fluoroalkylsilanes were used for the self-assembly rather than the silane coupling agents and fluorochemicals to fabricate controllable, ordered SAMs. • The angle-dependent XPS study was conducted to investigate the changes of surface structures as well as elemental compositions of the SAMs. • The results indicated that fluoroalkyl groups would migrate from the inner part of the monolayers to the outermost interface after heat treatment, resulting into the microphase separation of the SAMs surface. - Abstract: In this study, a novel kind of fluoroalkylsilane monomers with different fluoroalkyl chain lengths was synthesized via three steps method and characterized by Fourier transform infrared (FT-IR) spectroscopy, {sup 1}H and {sup 19}F nuclear magnetic resonance ({sup 1}H NMR and {sup 19}F NMR), and mass spectra (MS). Fluoroalkyl-terminated self-assembled monolayers (SAMs) on silanol-terminated silicon substrates (O{sub 2} plasma treatment) were chemically fabricated via –Si–O– covalent bonds using the liquid phase deposition method (LPD). The wetabilities of the SAMs were characterized by water contact angles (CA), surface free energies and adhesive force (AF) measurements. 3-(1H,1H,2H,2H-perfluorooctyloxycarbonyl) -propionamidepropyl-triethoxysilane (PFOPT) assembled monolayer was chosen for in-depth investigation as its CA was higher than the others. Attenuated total reflection infrared spectroscopy (ATR-IR) and X-ray photoelectron spectroscopy (XPS) were used to validate the attachment of PFOPT on the silicon substrate, together with the chemical composition and structure of the SAMs. The surface morphologies and roughness of the monolayers were obtained and

Electrical resistivity of nanoporous gold modified with thiol self-assembled monolayers

Energy Technology Data Exchange (ETDEWEB)

Hakamada, Masataka, E-mail: hakamada.masataka.3x@kyoto-u.ac.jp; Kato, Naoki, E-mail: katou.naoki.75w@st.kyoto-u.ac.jp; Mabuchi, Mamoru, E-mail: mabuchi@energy.kyoto-u.ac.jp

2016-11-30

Highlights: • Nanoporous gold is modified with thiol-containing self-assembled monolayers. • The electrical resistivity of the thiol-modified nanoporous gold increases. • The electrical resistivity increases with increasing thiol concentration. • Monolayer tail groups enhance the atmosphere dependence of electrical resistivity. - Abstract: The electrical resistivity of nanoporous gold (NPG) modified with thiol self-assembled monolayers (SAMs) has been measured at 298 K using a four-probe method. We found that the adsorption of thiol SAMs increases the electrical resistivity of NPG by up to 22.2%. Dependence of the electrical resistivity on the atmosphere (air or water) was also observed in SAMs-modified NPG, suggesting that the electronic states of the tail groups affect the electrons of the binding sulfur and adjacent surface gold atoms. The present results suggest that adsorption of thiol molecules can influence the behavior of the conducting electrons in NPG and that modification of NPG with SAMs may be useful for environmental sensing.

Atomic Defects and Doping of Monolayer NbSe2.

Science.gov (United States)

Nguyen, Lan; Komsa, Hannu-Pekka; Khestanova, Ekaterina; Kashtiban, Reza J; Peters, Jonathan J P; Lawlor, Sean; Sanchez, Ana M; Sloan, Jeremy; Gorbachev, Roman V; Grigorieva, Irina V; Krasheninnikov, Arkady V; Haigh, Sarah J

2017-03-28

We have investigated the structure of atomic defects within monolayer NbSe 2 encapsulated in graphene by combining atomic resolution transmission electron microscope imaging, density functional theory (DFT) calculations, and strain mapping using geometric phase analysis. We demonstrate the presence of stable Nb and Se monovacancies in monolayer material and reveal that Se monovacancies are the most frequently observed defects, consistent with DFT calculations of their formation energy. We reveal that adventitious impurities of C, N, and O can substitute into the NbSe 2 lattice stabilizing Se divacancies. We further observe evidence of Pt substitution into both Se and Nb vacancy sites. This knowledge of the character and relative frequency of different atomic defects provides the potential to better understand and control the unusual electronic and magnetic properties of this exciting two-dimensional material.

The structure and dynamics of Nano Particles encapsulated by the SDS monolayer collapse at the water/TCE interface

Science.gov (United States)

Shi, Wenxiong

2016-11-01

The super-saturated surfactant monolayer collapses with the nanoparticles (NPs) at the water/trichloroethylene (TCE) interface are investigated using molecular dynamics (MD) simulations. The results show that sodium alkyl sulfate (SDS) monolayer collapse is initiated by buckling and followed primarily by budding and the bud encapsulating the NPs and oil molecules. The developed bud detaches from the monolayer into a water phase and forms the swollen micelle emulsion with NPs and oil molecules. We investigate the wavelength of the initial budding and the theoretical description of the budding process. The wavelength of the monolayer increases with bending modulus. The energy barrier of the budding can be easily overcome by thermal fluctuation energy, which indicates that budding process proceeds rapidly.

Nanoscale Trapping and Squeeze-Out of Confined Alkane Monolayers.

Science.gov (United States)

Gosvami, N N; O'Shea, S J

2015-12-01

We present combined force curve and conduction atomic force microscopy (AFM) data for the linear alkanes CnH2n+2 (n = 10, 12, 14, 16) confined between a gold-coated AFM tip and a graphite surface. Solvation layering is observed in the force curves for all liquids, and conduction AFM is used to study in detail the removal of the confined (mono)layer closest to the graphite surface. The squeeze-out behavior of the monolayer can be very different depending upon the temperature. Below the monolayer melting transition temperatures the molecules are in an ordered state on the graphite surface, and fast and complete removal of the confined molecules is observed. However, above the melting transition temperature the molecules are in a disordered state, and even at large applied pressure a few liquid molecules are trapped within the tip-sample contact zone. These findings are similar to a previous study for branched alkanes [ Gosvami Phys. Rev. Lett. 2008, 100, 076101 ], but the observation for the linear alkane homologue series demonstrates clearly the dependence of the squeeze-out and trapping on the state of the confined material.

An effective approach to synthesize monolayer tungsten disulphide crystals using tungsten halide precursor

International Nuclear Information System (INIS)

Thangaraja, Amutha; Shinde, Sachin M.; Kalita, Golap; Tanemura, Masaki

2016-01-01

The synthesis of large-area monolayer tungsten disulphide (WS 2 ) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS 2 crystals using tungsten hexachloride (WCl 6 ) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl 6 in ethanol was drop-casted on SiO 2 /Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS 2 crystals on the substrate. The crystal geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS 2 single crystalline monolayer can be grown using the WCl 6 precursor. Our finding shows an easier and effective approach to grow WS 2 monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction

Strain Tuning of the Charge Density Wave in Monolayer and Bilayer 1T-TaS2

KAUST Repository

Gan, Liyong

2015-12-07

By first-principles calculations, we investigate the strain effects on the charge density wave states of monolayer and bilayer 1T-TaS2. The modified stability of the charge density wave in the monolayer is understood in terms of the strain dependent electron localization, which determines the distortion amplitude. On the other hand, in the bilayer the effect of strain on the interlayer interaction is also crucial. The rich phase diagram under strain opens new venues for applications of 1T-TaS2. We interpret the experimentally observed insulating state of bulk 1T-TaS2 as inherited from the monolayer by effective interlayer decoupling.

Dynamical phases of attractive particles sliding on a structured surface

International Nuclear Information System (INIS)

Hasnain, J; Jungblut, S; Dellago, C

2015-01-01

Inspired by experiments on quartz crystal microbalance setups, we study the mobility of a monolayer of Lennard-Jones particles driven over a hexagonal external potential. We pay special attention to the changes in the dynamical phases that arise when the lattice constant of the external substrate potential and the Lennard-Jones interaction are mismatched. We find that if the average particle separation is such that the particles repel each other, or interact harmonically, the qualitative behavior of the system is akin to that of a monolayer of purely repulsive Yukawa particles. On the other hand, if the particles typically attract each other, the ensuing dynamical states are determined entirely by the relative strength of the Lennard-Jones interaction with respect to that of the external potential. (paper)

Phase transition behaviors of the supported DPPC bilayer investigated by sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM).

Science.gov (United States)

Wu, Heng-Liang; Tong, Yujin; Peng, Qiling; Li, Na; Ye, Shen

2016-01-21

The phase transition behaviors of a supported bilayer of dipalmitoylphosphatidyl-choline (DPPC) have been systematically evaluated by in situ sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM). By using an asymmetric bilayer composed of per-deuterated and per-protonated monolayers, i.e., DPPC-d75/DPPC and a symmetric bilayer of DPPC/DPPC, we were able to probe the molecular structural changes during the phase transition process of the lipid bilayer by SFG spectroscopy. It was found that the DPPC bilayer is sequentially melted from the top (adjacent to the solution) to bottom leaflet (adjacent to the substrate) over a wide temperature range. The conformational ordering of the supported bilayer does not decrease (even slightly increases) during the phase transition process. The conformational defects in the bilayer can be removed after the complete melting process. The phase transition enthalpy for the bottom leaflet was found to be approximately three times greater than that for the top leaflet, indicating a strong interaction of the lipids with the substrate. The present SFG and AFM observations revealed similar temperature dependent profiles. Based on these results, the temperature-induced structural changes in the supported lipid bilayer during its phase transition process are discussed in comparison with previous studies.

Evaluation of monolayers and mixed monolayers formed from mercaptobenzothiazole and decanethiol as sensing platforms

International Nuclear Information System (INIS)

Mary Vergheese, T.; Berchmans, Sheela

2004-01-01

In this investigation, the characterisation of monolayer and mixed monolayers formed from mercaptobenzothiazole (MBT) and decanethiol (DT) has been carried out with cyclic voltammetry. The SAMs have been tested for their stability and electron transfer blocking properties. The redox probes used in the present study are [Fe(China) 6 ] 4- , [Ru(NH 3 ) 6 ] 2+ and Cu underpotential deposition (upd). The electron transfer kinetics is investigated in acid and neutral pH range. Electron transfer kinetics is altered by the nature of charge on the redox probe and the charge on the monolayer. Electron transfer kinetics of negatively charged redox probes like ferrocyanide ions is blocked when the surface pK a medium and at pK a >pH medium reversible features is observed for negatively charged probes. An exactly reverse effect is observed in the case of positively charged redox species like [Ru(NH 3 ) 6 ] 2+/3+ . Cu under potential deposition studies reflects the structural integrity and compactness of the SAM layer. The utility of these monolayers and mixed monolayer for selective sensing of dopamine is discussed based on their ability to discriminate between positively and negatively charged redox species at different pH

Anisotropic colloids: bulk phase behavior and equilibrium sedimentation

NARCIS (Netherlands)

Marechal, M.A.T.

2009-01-01

This thesis focuses on the phase behavior of anisotropically shaped (i.e. non-spherical) colloids using computer simulations. Only hard-core interactions between the colloids are taken into account to investigate the effects of shape alone. The bulk phase behavior of three different shapes of

Surface Structures and Thermal Desorption Behaviors of Cyclopentanethiol Self-Assembled Monolayers on Au(111)

Energy Technology Data Exchange (ETDEWEB)

Kang, Hun Gu; Kim, You Young; Park, Tae Sun; Noh, Jae Geun [Hanyang University, Seoul (Korea, Republic of); Park, Joon B. [Chonbuk National University, Jeonju (Korea, Republic of); Ito, Eisuke; Hara, Masahiko [RIKEN-HYU Collaboration Center, Saitama (Japan)

2011-04-15

The surface structures, adsorption conditions, and thermal desorption behaviors of cyclopentanethiol (CPT) self-assembled monolayers (SAMs) on Au(111) were investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). STM imaging revealed that although the adsorption of CPT on Au(111) at room temperature generates disordered SAMs, CPT molecules at 50 .deg. C formed well-ordered SAMs with a (2√3 x √5)R41{sup .}deg. packing structure. XPS measurements showed that CPT SAMs at room temperature were formed via chemical reactions between the sulfur atoms and gold surfaces. TDS measurements showed two dominant TD peaks for the decomposed fragments (C{sub 5}H{sub 9} {sup +}, m/e = 69) generated via C-S bond cleavage and the parent molecular species (C{sub 5}H{sub 9}SH{sup +}, m/e = 102) derived from a recombination of the chemisorbed thiolates and hydrogen atoms near 440 K. Interestingly, dimerization of sulfur atoms in n-alkanethiol SAMs usually occurs during thermal desorption and the same reaction did not happen for CPT SAMs, which may be due to the steric hindrance of cyclic rings of the CPT molecules. In this study, we demonstrated that the alicyclic ring of organic thiols strongly affected the surface structure and thermal desorption behavior of SAMs, thus providing a good method for controlling chemical and physical properties of organic thiol SAMs.

Alloying as a Route to Monolayer Transition Metal Dichalcogenides with Improved Optoelectronic Performance: Mo(S1–xSex)2 and Mo1–yWyS2

KAUST Repository

Shi, Zhiming

2018-04-26

On the basis of first-principles and cluster expansion calculations, we propose an effective approach to realize monolayer transition metal dichalcogenides with sizable band gaps and improved optoelectronic performance. We show that monolayer Mo(S1–xSex)2 and Mo1–yWyS2 with x = 1/3, 2/3 and y = 1/3, 1/2, 2/3 are stable according to phonon calculations and realize 1T′ or 1T″ phases. The transition barriers from the 2H phase are lower than for monolayer MoS2, implying that the 1T′ or 1T″ phases can be achieved experimentally. Furthermore, it turns out that the 1T″ monolayer alloys with x = 1/3, 2/3 and y = 1/3, 2/3 are semiconductors with band gaps larger than 1 eV, due to trimerization. The visible light absorption and carrier mobility are strongly improved as compared to 2H monolayer MoS2, MoSe2, and WS2. Thus, the 1T″ monolayer alloys have the potential to expand the applications of transition metal dichalcogenides, for example, in solar cells.

Polymer blend lithography: A versatile method to fabricate nanopatterned self-assembled monolayers

Directory of Open Access Journals (Sweden)

Cheng Huang

2012-09-01

Full Text Available A rapid and cost-effective lithographic method, polymer blend lithography (PBL, is reported to produce patterned self-assembled monolayers (SAM on solid substrates featuring two or three different chemical functionalities. For the pattern generation we use the phase separation of two immiscible polymers in a blend solution during a spin-coating process. By controlling the spin-coating parameters and conditions, including the ambient atmosphere (humidity, the molar mass of the polystyrene (PS and poly(methyl methacrylate (PMMA, and the mass ratio between the two polymers in the blend solution, the formation of a purely lateral morphology (PS islands standing on the substrate while isolated in the PMMA matrix can be reproducibly induced. Either of the formed phases (PS or PMMA can be selectively dissolved afterwards, and the remaining phase can be used as a lift-off mask for the formation of a nanopatterned functional silane monolayer. This “monolayer copy” of the polymer phase morphology has a topographic contrast of about 1.3 nm. A demonstration of tuning of the PS island diameter is given by changing the molar mass of PS. Moreover, polymer blend lithography can provide the possibility of fabricating a surface with three different chemical components: This is demonstrated by inducing breath figures (evaporated condensed entity at higher humidity during the spin-coating process. Here we demonstrate the formation of a lateral pattern consisting of regions covered with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS and (3-aminopropyltriethoxysilane (APTES, and at the same time featuring regions of bare SiOx. The patterning process could be applied even on meter-sized substrates with various functional SAM molecules, making this process suitable for the rapid preparation of quasi two-dimensional nanopatterned functional substrates, e.g., for the template-controlled growth of ZnO nanostructures.

Polymer blend lithography: A versatile method to fabricate nanopatterned self-assembled monolayers.

Science.gov (United States)

Huang, Cheng; Moosmann, Markus; Jin, Jiehong; Heiler, Tobias; Walheim, Stefan; Schimmel, Thomas

2012-01-01

A rapid and cost-effective lithographic method, polymer blend lithography (PBL), is reported to produce patterned self-assembled monolayers (SAM) on solid substrates featuring two or three different chemical functionalities. For the pattern generation we use the phase separation of two immiscible polymers in a blend solution during a spin-coating process. By controlling the spin-coating parameters and conditions, including the ambient atmosphere (humidity), the molar mass of the polystyrene (PS) and poly(methyl methacrylate) (PMMA), and the mass ratio between the two polymers in the blend solution, the formation of a purely lateral morphology (PS islands standing on the substrate while isolated in the PMMA matrix) can be reproducibly induced. Either of the formed phases (PS or PMMA) can be selectively dissolved afterwards, and the remaining phase can be used as a lift-off mask for the formation of a nanopatterned functional silane monolayer. This "monolayer copy" of the polymer phase morphology has a topographic contrast of about 1.3 nm. A demonstration of tuning of the PS island diameter is given by changing the molar mass of PS. Moreover, polymer blend lithography can provide the possibility of fabricating a surface with three different chemical components: This is demonstrated by inducing breath figures (evaporated condensed entity) at higher humidity during the spin-coating process. Here we demonstrate the formation of a lateral pattern consisting of regions covered with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) and (3-aminopropyl)triethoxysilane (APTES), and at the same time featuring regions of bare SiO(x). The patterning process could be applied even on meter-sized substrates with various functional SAM molecules, making this process suitable for the rapid preparation of quasi two-dimensional nanopatterned functional substrates, e.g., for the template-controlled growth of ZnO nanostructures [1].

Light phase testing of social behaviors: not a problem

Directory of Open Access Journals (Sweden)

Mu Yang

2008-12-01

Full Text Available The rich repertoire of mouse social behaviors makes it possible to use mouse models to study neurodevelopmental disorders characterized by social deficits. The fact that mice are naturally nocturnal animals raises a critical question of whether behavioral experiments should be strictly conducted in the dark phase and whether light phase testing is a major methodologically mistake. Although mouse social tasks have been performed in both phases in different laboratories, there seems to be no general consensus on whether testing phase is a critical factor or not. A recent study from our group showed remarkably similar social scores obtained from inbred mice tested in the light and the dark phase, providing evidence that light phase testing could yield reliable results as robust as dark phase testing for the sociability test. Here we offer a comprehensive review on mouse social behaviors measured in light and dark phases and explain why it is reasonable to test laboratory mice in experimental social tasks in the light phase.

Stretching and breaking of monolayer MoS2—an atomistic simulation

International Nuclear Information System (INIS)

Lorenz, Tommy; Joswig, Jan-Ole; Seifert, Gotthard

2014-01-01

We report on the simulation of the nanoindentation process of monolayer MoS 2 using molecular-dynamics simulations and a density-functional based tight-binding method. A circular sheet of MoS 2 with clamped boundaries was indented by a slowly moved tip, which deformed and finally pierced the layer. We found the Young’s modulus of monolayer MoS 2 to be 262 GPa, which is in good agreement with experimental observations. Furthermore, the energetic and structural behavior during the indentation process was analyzed. Elasticity theory supplies the necessary equations to explain the experiment. Thereby, the nature of the linear term in the force-deflection relation is discussed. (letter)

Superconductivity in the graphene monolayer calculated using the Kubo formulalism

Science.gov (United States)

Lima, L. S.

2018-03-01

We have employed the massless Dirac's fermions formalism together with the Kubo's linear response theory to study the transport by electrons in the graphene monolayer. We have calculated the electric conductivity and verified the behavior of the AC and DC electric conductivities of the system that is known to be a relativistic electron plasma. Our results show a superconductor behavior to the electron transport and consequently the spin transport for all values of T > 0 and a behavior of the AC conductivity tending to infinity in the limit ω → 0. In T = 0 our results show an insulator behavior with a transition from a superconductor state at T > 0 to an insulator state at T = 0 .

Evaluation of monolayers and mixed monolayers formed from mercaptobenzothiazole and decanethiol as sensing platforms

Energy Technology Data Exchange (ETDEWEB)

Mary Vergheese, T.; Berchmans, Sheela

2004-02-15

In this investigation, the characterisation of monolayer and mixed monolayers formed from mercaptobenzothiazole (MBT) and decanethiol (DT) has been carried out with cyclic voltammetry. The SAMs have been tested for their stability and electron transfer blocking properties. The redox probes used in the present study are [Fe(China){sub 6}]{sup 4-}, [Ru(NH{sub 3}){sub 6}]{sup 2+} and Cu underpotential deposition (upd). The electron transfer kinetics is investigated in acid and neutral pH range. Electron transfer kinetics is altered by the nature of charge on the redox probe and the charge on the monolayer. Electron transfer kinetics of negatively charged redox probes like ferrocyanide ions is blocked when the surface pK{sub a}pH{sub medium} reversible features is observed for negatively charged probes. An exactly reverse effect is observed in the case of positively charged redox species like [Ru(NH{sub 3}){sub 6}]{sup 2+/3+}. Cu under potential deposition studies reflects the structural integrity and compactness of the SAM layer. The utility of these monolayers and mixed monolayer for selective sensing of dopamine is discussed based on their ability to discriminate between positively and negatively charged redox species at different pH.

Metal-free spin and spin-gapless semiconducting heterobilayers: monolayer boron carbonitrides on hexagonal boron nitride.

Science.gov (United States)

Pan, Hongzhe; Zhang, Hongyu; Sun, Yuanyuan; Ding, Yingchun; Chen, Jie; Du, Youwei; Tang, Nujiang

2017-06-07

The interfaces between monolayer boron carbonitrides and hexagonal boron nitride (h-BN) play an important role in their practical applications. Herein, we respectively investigate the structural and electronic properties of two metal-free heterobilayers constructed by vertically stacking two-dimensional (2D) spintronic materials (B 4 CN 3 and B 3 CN 4 ) on a h-BN monolayer from the viewpoints of lattice match and lattice mismatch models using density functional calculations. It is found that both B 4 CN 3 and B 3 CN 4 monolayers can be stably adsorbed on the h-BN monolayer due to the van der Waals interactions. Intriguingly, we demonstrate that the bipolar magnetic semiconductor (BMS) behavior of the B 4 CN 3 layer and the spin gapless semiconductor (SGS) property of the B 3 CN 4 layer can be well preserved in the B 4 CN 3 /BN and B 3 CN 4 /BN heterobilayers, respectively. The magnetic moments and spintronic properties of the two systems originate mainly from the 2p z electrons of the carbon atoms in the B 4 CN 3 and B 3 CN 4 layers. Furthermore, the BMS behavior of the B 4 CN 3 /BN bilayer is very robust while the electronic property of the B 3 CN 4 /BN bilayer is sensitive to interlayer couplings. These theoretical results are helpful both in understanding the interlayer coupling between B 4 CN 3 or B 3 CN 4 and h-BN monolayers and in providing a possibility of fabricating 2D composite B 4 CN 3 /BN and B 3 CN 4 /BN metal-free spintronic materials theoretically.

Cholesterol-Induced Buckling in Physisorbed Polymer-Tethered Lipid Monolayers

Directory of Open Access Journals (Sweden)

Christoph A. Naumann

2013-04-01

Full Text Available The influence of cholesterol concentration on the formation of buckling structures is studied in a physisorbed polymer-tethered lipid monolayer system using epifluorescence microscopy (EPI and atomic force microscopy (AFM. The monolayer system, built using the Langmuir-Blodgett (LB technique, consists of 3 mol % poly(ethylene glycol (PEG lipopolymers and various concentrations of the phospholipid, 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC, and cholesterol (CHOL. In the absence of CHOL, AFM micrographs show only occasional buckling structures, which is caused by the presence of the lipopolymers in the monolayer. In contrast, a gradual increase of CHOL concentration in the range of 0–40 mol % leads to fascinating film stress relaxation phenomena in the form of enhanced membrane buckling. Buckling structures are moderately deficient in CHOL, but do not cause any notable phospholipid-lipopolymer phase separation. Our experiments demonstrate that membrane buckling in physisorbed polymer-tethered membranes can be controlled through CHOL-mediated adjustment of membrane elastic properties. They further show that CHOL may have a notable impact on molecular confinement in the presence of crowding agents, such as lipopolymers. Our results are significant, because they offer an intriguing prospective on the role of CHOL on the material properties in complex membrane architecture.

First principles study of the electronic properties and band gap modulation of two-dimensional phosphorene monolayer: Effect of strain engineering

Science.gov (United States)

Phuc, Huynh V.; Hieu, Nguyen N.; Ilyasov, Victor V.; Phuong, Le T. T.; Nguyen, Chuong V.

2018-06-01

The effect of strain on the structural and electronic properties of monolayer phosphorene is studied by using first-principle calculations based on the density functional theory. The intra- and inter-bond length and bond angle for monolayer phosphorene is also evaluated. The intra- and inter-bond length and the bond angle for phosphorene show an opposite tendency under different directions of the applied strain. At the equilibrium state, monolayer phosphorene is a semiconductor with a direct band gap at the Γ-point of 0.91 eV. A direct-indirect band gap transition is found in monolayer phosphorene when both the compression and tensile strain are simultaneously applied along both zigzag and armchair directions. Under the applied compression strain, a semiconductor-metal transition for monolayer phosphorene is observed at -13% and -10% along armchair and zigzag direction, respectively. The direct-indirect and phase transition will largely constrain application of monolayer phosphorene to electronic and optical devices.

An effective approach to synthesize monolayer tungsten disulphide crystals using tungsten halide precursor

Energy Technology Data Exchange (ETDEWEB)

Thangaraja, Amutha; Shinde, Sachin M.; Kalita, Golap, E-mail: kalita.golap@nitech.ac.jp; Tanemura, Masaki [Department of Frontier Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)

2016-02-01

The synthesis of large-area monolayer tungsten disulphide (WS{sub 2}) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS{sub 2} crystals using tungsten hexachloride (WCl{sub 6}) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl{sub 6} in ethanol was drop-casted on SiO{sub 2}/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS{sub 2} crystals on the substrate. The crystal geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS{sub 2} single crystalline monolayer can be grown using the WCl{sub 6} precursor. Our finding shows an easier and effective approach to grow WS{sub 2} monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction.

Structure and dynamics of lipid monolayers: Implications for enzyme catalysed lipolysis

DEFF Research Database (Denmark)

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

1995-01-01

We have investigated the role of the substrate on the interfacial activation of Upases by an interdisciplinary study of the structure and dynamics of 1,2-sn dipalmitoylglycerol monolayers at distinct surface pressures. The diglyceride Langmuir film undergoes two phase transitions occurring at 38......, the alkyl chains pack in an hexagonal structure relaxing to a distorted-hexagonal lattice in the lowest pressure phase with the alkyl chains tilted by approx 14° in a direction close to a nearest neighbour direction....

Influence of calcium on ceramide-1-phosphate monolayers

Directory of Open Access Journals (Sweden)

Joana S. L. Oliveira

2016-02-01

Full Text Available Ceramide-1-phosphate (C1P plays an important role in several biological processes, being identified as a key regulator of many protein functions. For instance, it acts as a mediator of inflammatory responses. The mediation of the inflammation process happens due to the interaction of C1P with the C2 domain of cPLA2α, an effector protein that needs the presence of submicromolar concentrations of calcium ions. The aim of this study was to determine the phase behaviour and structural properties of C1P in the presence and absence of millimolar quantities of calcium in a well-defined pH environment. For that purpose, we used monomolecular films of C1P at the soft air/liquid interface with calcium ions in the subphase. The pH was varied to change the protonation degree of the C1P head group. We used surface pressure versus molecular area isotherms coupled with other monolayer techniques as Brewster angle microscopy (BAM, infrared reflection–absorption spectroscopy (IRRAS and grazing incidence X-ray diffraction (GIXD. The isotherms indicate that C1P monolayers are in a condensed state in the presence of calcium ions, regardless of the pH. At higher pH without calcium ions, the monolayer is in a liquid-expanded state due to repulsion between the negatively charged phosphate groups of the C1P molecules. When divalent calcium ions are added, they are able to bridge the highly charged phosphate groups, enhancing the regular arrangement of the head groups. Similar solidification of the monolayer structure can be seen in the presence of a 150 times larger concentration of monovalent sodium ions. Therefore, calcium ions have clearly a strong affinity for the phosphomonoester of C1P.

Janus Monolayer Transition-Metal Dichalcogenides.

Science.gov (United States)

Zhang, Jing; Jia, Shuai; Kholmanov, Iskandar; Dong, Liang; Er, Dequan; Chen, Weibing; Guo, Hua; Jin, Zehua; Shenoy, Vivek B; Shi, Li; Lou, Jun

2017-08-22

The crystal configuration of sandwiched S-Mo-Se structure (Janus SMoSe) at the monolayer limit has been synthesized and carefully characterized in this work. By controlled sulfurization of monolayer MoSe 2 , the top layer of selenium atoms is substituted by sulfur atoms, while the bottom selenium layer remains intact. The structure of this material is systematically investigated by Raman, photoluminescence, transmission electron microscopy, and X-ray photoelectron spectroscopy and confirmed by time-of-flight secondary ion mass spectrometry. Density functional theory (DFT) calculations are performed to better understand the Raman vibration modes and electronic structures of the Janus SMoSe monolayer, which are found to correlate well with corresponding experimental results. Finally, high basal plane hydrogen evolution reaction activity is discovered for the Janus monolayer, and DFT calculation implies that the activity originates from the synergistic effect of the intrinsic defects and structural strain inherent in the Janus structure.

The Rheological Properties of Lipid Monolayers Modulate the Incorporation of l-Ascorbic Acid Alkyl Esters.

Science.gov (United States)

Díaz, Yenisleidy de Las Mercedes Zulueta; Mottola, Milagro; Vico, Raquel V; Wilke, Natalia; Fanani, María Laura

2016-01-19

In this work, we tested the hypothesis that the incorporation of amphiphilic drugs into lipid membranes may be regulated by their rheological properties. For this purpose, two members of the l-ascorbic acid alkyl esters family (ASCn) were selected, ASC16 and ASC14, which have different rheological properties when organized at the air/water interface. They are lipophilic forms of vitamin C used in topical pharmacological preparations. The effect of the phase state of the host lipid membranes on ASCn incorporation was explored using Langmuir monolayers. Films of pure lipids with known phase states have been selected, showing liquid-expanded, liquid-condensed, and solid phases as well as pure cholesterol films in liquid-ordered state. We also tested ternary and quaternary mixed films that mimic the properties of cholesterol containing membranes and of the stratum corneum. The compressibility and shear properties of those monolayers were assessed in order to define its phase character. We found that the length of the acyl chain of the ASCn compounds induces differential changes in the rheological properties of the host membrane and subtly regulates the kinetics and extent of the penetration process. The capacity for ASCn uptake was found to depend on the phase state of the host film. The increase in surface pressure resultant after amphiphile incorporation appears to be a function of the capacity of the host membrane to incorporate such amphiphile as well as the rheological response of the film. Hence, monolayers that show a solid phase state responded with a larger surface pressure increase to the incorporation of a comparable amount of amphiphile than liquid-expanded ones. The cholesterol-containing films, including the mixture that mimics stratum corneum, allowed a very scarce ASCn uptake independently of the membrane diffusional properties. This suggests an important contribution of Cho on the maintenance of the barrier function of stratum corneum.

Cyclic voltammetry and scanning electrochemical microscopy studies of methylene blue immobilized on the self-assembled monolayer of n-dodecanethiol

International Nuclear Information System (INIS)

Salamifar, Seyed Ehsan; Mehrgardi, Masoud Ayatollahi; Kazemi, Sayed Habib; Mousavi, Mir Fazllollah

2010-01-01

Electron transfer (ET) kinetics through n-dodecanethiol (C 12 SH) self-assembled monolayer on gold electrode was studied using cyclic voltammetry (CV), scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). An SECM model for compensating pinhole contribution, was used to measure the ET kinetics of solution-phase probes of ferrocyanide/ferricyanide (Fe(CN) 6 4-/3- ) and ferrocenemethanol/ferrociniummethanol (FMC 0/+ ) through the C 12 SH monolayer yielding standard tunneling rate constant (k ET 0 ) of (4 ± 1) x 10 -11 and (3 ± 1) x 10 -10 cm s -1 for Fe(CN) 6 4-/3- and FMC 0/+ respectively. Decay tunneling constants (β) of 0.97 and 0.96 A -1 for saturated alkane thiol chains were obtained using Fe(CN) 6 4- and FMC respectively. Also, it was found that methylene blue (MB) molecules are effectively immobilized on the C 12 SH monolayer and can mediate the ET between the solution-phase probes and underlying gold substrate. SECM-mediated model was used to simultaneously measure the bimolecular ET between the solution-phase probes and the monolayer-immobilized MB molecules, as well as tunneling ET between the monolayer-immobilized MB molecules and the underlying gold electrode, allowing the measurement of k BI = (5 ± 1) x 10 6 and (4 ± 2) x 10 7 cm 3 mol -1 s -1 for the bimolecular ET and k ET/MB 0 =(1±0.3)x10 -3 and (7 ± 3) x 10 -2 s -1 for the standard tunneling rate constant of ET using Fe(CN) 6 4-/3- and FMC 0/+ probes respectively.

Preparation and Photoluminescence of Tungsten Disulfide Monolayer

Directory of Open Access Journals (Sweden)

Yanfei Lv

2018-05-01

Full Text Available Tungsten disulfide (WS2 monolayer is a direct band gap semiconductor. The growth of WS2 monolayer hinders the progress of its investigation. In this paper, we prepared the WS2 monolayer through chemical vapor transport deposition. This method makes it easier for the growth of WS2 monolayer through the heterogeneous nucleation-and-growth process. The crystal defects introduced by the heterogeneous nucleation could promote the photoluminescence (PL emission. We observed the strong photoluminescence emission in the WS2 monolayer, as well as thermal quenching, and the PL energy redshift as the temperature increases. We attribute the thermal quenching to the energy or charge transfer of the excitons. The redshift is related to the dipole moment of WS2.

Transfer plate radioassay using cell monolayers to detect anti-cell surface antibodies synthesized by lymphocyte hybridomas

International Nuclear Information System (INIS)

Schneider, M.D.; Eisenbarth, G.S.

1979-01-01

A solid phase [ 125 I] Protein A radioassay for anti-cell surface antibodies is described, which employs target cell monolayers cultured on fenestrated polyvinyl chloride 96-well plates ('transfer plates'). The calibrated aperture in the bottom of each well is small enough to retain fluid contents by surface tension during monolayer growth, but also permits fluid to enter the wells when transfer plate are lowered into receptacles containing washing buffer on test sera. To assay for antibodies directed against target cell surface antigens, transfer plates bearing monolayers are inserted into microculture plates with corresponding 96-well geometry, thereby simultaneously sampling 96 wells. This assay allows rapid screening of hundreds of hybrid cell colonies for production of antibodies with desired tissue specificity. (Auth.)

Biomimetic mineralization of CaCO3 on a phospholipid monolayer: from an amorphous calcium carbonate precursor to calcite via vaterite.

Science.gov (United States)

Xiao, Junwu; Wang, Zhining; Tang, Yecang; Yang, Shihe

2010-04-06

A phospholipid monolayer, approximately half the bilayer structure of a biological membrane, can be regarded as an ideal model for investigating biomineralization on biological membranes. In this work on the biomimetic mineralization of CaCO(3) under a phospholipid monolayer, we show the initial heterogeneous nucleation of amorphous calcium carbonate precursor (ACC) nanoparticles at the air-water interface, their subsequent transformation into the metastable vaterite phase instead of the most thermodynamically stable calcite phase, and the ultimate phase transformation to calcite. Furthermore, the spontaneity of the transformation from vaterite to calcite was found to be closely related to the surface tension; high surface pressure could inhibit the process, highlighting the determinant of surface energy. To understand better the mechanisms for ACC formation and the transformation from ACC to vaterite and to calcite, in situ Brewster angle microscopy (BAM), ex situ scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction analysis were employed. This work has clarified the crystallization process of calcium carbonate under phospholipid monolayers and therefore may further our understanding of the biomineralization processes induced by cellular membranes.

Correlation of Effective Dispersive and Polar Surface Energies in Heterogeneous Self-Assembled Monolayer Coatings

DEFF Research Database (Denmark)

Zhuang, Yanxin; Hansen, Ole

2009-01-01

grown oil oxidized (100) silicon Surfaces in a vapor phase process using five different precursors. Experimentally, effective surface energy components of the fluorocarbon self-assembled monolayers were determined from measured contact angles using the Owens-Wendt-Rabel-Kaelble method. We show...

Human disc cells in monolayer vs 3D culture: cell shape, division and matrix formation

Directory of Open Access Journals (Sweden)

Hanley Edward N

2000-10-01

Full Text Available Abstract Background The relationship between cell shape, proliferation, and extracellular matrix (ECM production, important aspects of cell behavior, is examined in a little-studied cell type, the human annulus cell from the intervertebral disc, during monolayer vs three-dimensional (3D culture. Results Three experimental studies showed that cells respond specifically to culture microenvironments by changes in cell shape, mitosis and ECM production: 1 Cell passages showed extensive immunohistochemical evidence of Type I and II collagens only in 3D culture. Chondroitin sulfate and keratan sulfate were abundant in both monolayer and 3D cultures. 2 Cells showed significantly greater proliferation in monolayer in the presence of platelet-derived growth factor compared to cells in 3D. 3 Cells on Matrigel™-coated monolayer substrates became rounded and formed nodular colonies, a finding absent during monolayer growth. Conclusions The cell's in vivo interactions with the ECM can regulate shape, gene expression and other cell functions. The shape of the annulus cell changes markedly during life: the young, healthy disc contains spindle shaped cells and abundant collagen. With aging and degeneration, many cells assume a strikingly different appearance, become rounded and are surrounded by unusual accumulations of ECM products. In vitro manipulation of disc cells provides an experimental window for testing how disc cells from given individuals respond when they are grown in environments which direct cells to have either spindle- or rounded-shapes. In vitro assessment of the response of such cells to platelet-derived growth factor and to Matrigel™ showed a continued influence of cell shape even in the presence of a growth factor stimulus. These findings contribute new information to the important issue of the influence of cell shape on cell behavior.

Computer simulation of monolayer growth kinetics of Fe2B phase during the paste-boriding process: Influence of the paste thickness

International Nuclear Information System (INIS)

Keddam, M.

2006-01-01

This paper deals with the effect of boron paste thickness on the study of the monolayer growth kinetics of Fe 2 B phase forming on AISI 1045 steel by the paste-boriding process. A mathematical diffusion model based on the Fick's phenomenological equations was applied in order to estimate the growth rate constant at (Fe 2 B/γ-Fe) interface, the layer thickness of iron boride as well as the associated mass gain depending on the boriding parameters such as time, temperature and surface boron concentration related to the boron paste thickness. The simulation results are found to be in a fairly good agreement with the experimental data derived from the literature

Monolayer Superconductivity in WS2

NARCIS (Netherlands)

Zheliuk, Oleksandr; Lu, Jianming; Yang, Jie; Ye, Jianting

Superconductivity in monolayer tungsten disulfide (2H-WS2) is achieved by strong electrostatic electron doping of an electric double-layer transistor (EDLT). Single crystals of WS2 are grown by a scalable method - chemical vapor deposition (CVD) on standard Si/SiO2 substrate. The monolayers are

Coupled Interfacial Tension and Phase Behavior Model Based on Micellar Curvatures

KAUST Repository

Torrealba, V. A.

2017-11-08

This article introduces a consistent and robust model that predicts interfacial tensions for all microemulsion Winsor types and overall compositions. The model incorporates film bending arguments and Huh\\'s equation and is coupled to phase behavior so that simultaneous tuning of both interfacial tension (IFT) and phase behavior is possible. The oil-water interfacial tension and characteristic length are shown to be related to each other through the hydrophilic-lipophilic deviation (HLD). The phase behavior is tied to the micelle curvatures, without the need for using the net average curvature (NAC). The interfacial tension model is related to solubilization ratios in order to introduce a coupled interfacial tension-phase behavior model for all phase environments. The approach predicts two- and three-phase interfacial tensions and phase behavior (i.e., tie lines and tie triangles) for changes in composition and HLD input parameters, such as temperature, pressure, surfactant structure, and oil equivalent alkane carbon number. Comparisons to experimental data show excellent fits and predictive capability.

Thermotropic and Barotropic Phase Behavior of Phosphatidylcholine Bilayers

Directory of Open Access Journals (Sweden)

Nobutake Tamai

2013-01-01

Full Text Available Bilayers formed by phospholipids are frequently used as model biological membranes in various life science studies. A characteristic feature of phospholipid bilayers is to undergo a structural change called a phase transition in response to environmental changes of their surroundings. In this review, we focus our attention on phase transitions of some major phospholipids contained in biological membranes, phosphatidylcholines (PCs, depending on temperature and pressure. Bilayers of dipalmitoylphosphatidylcholine (DPPC, which is the most representative lipid in model membrane studies, will first be explained. Then, the bilayer phase behavior of various kinds of PCs with different molecular structures is revealed from the temperature–pressure phase diagrams, and the difference in phase stability among these PC bilayers is discussed in connection with the molecular structure of the PC molecules. Furthermore, the solvent effect on the phase behavior is also described briefly.

Ionic interactions in electroactive self-assembled monolayers of ferrocene species

Science.gov (United States)

Delong, Hugh C.; Donohue, John J.; Buttry, Daniel A.

1991-04-01

The electrochemical and interfacial behavior of two types of electroactive self-assembled monolayer systems is investigated at gold electrodes. The first type is a ferrocene-based surfactant (a redox surfactant) derived from (dimethylamino)methylferrocene via quaternization of the amino group with various n-alkylbromides. These have a long alkyl chain with 16 or 18 carbons in the chain pendent from the cationic ammonium group. These are referred to as C16 and C18. The second type is a ferrocene-based dimeric species with a disulfide functional group capable of providing a permanent anchor to the Au electrode, thus endowing monolayers of this species with exceptional stability towards desorption. The electrochemical quartz crystal microbalance (EQM) is used to monitor the mass changes which occur at the electrode surface during the redox processes of these two species.

Monolayer MoS{sub 2} self-switching diodes

Energy Technology Data Exchange (ETDEWEB)

Al-Dirini, Feras, E-mail: alf@unimelb.edu.au; Hossain, Md Sharafat [Department of Electrical and Electronic Engineering, University of Melbourne, Victoria (Australia); Centre for Neural Engineering, University of Melbourne, Victoria (Australia); Victorian Research Laboratory, National ICT Australia, West Melbourne, Victoria (Australia); Hossain, Faruque M.; Skafidas, Efstratios [Department of Electrical and Electronic Engineering, University of Melbourne, Victoria (Australia); Centre for Neural Engineering, University of Melbourne, Victoria (Australia); Mohammed, Mahmood A. [Princess Sumaya University for Technology, Amman (Jordan); Nirmalathas, Ampalavanapillai [Department of Electrical and Electronic Engineering, University of Melbourne, Victoria (Australia); Melbourne Networked Society Institute (MNSI), University of Melbourne, Victoria (Australia)

2016-01-28

This paper presents a new molybdenum disulphide (MoS{sub 2}) nanodevice that acts as a two-terminal field-effect rectifier. The device is an atomically-thin two-dimensional self-switching diode (SSD) that can be realized within a single MoS{sub 2} monolayer with very minimal process steps. Quantum simulation results are presented confirming the device's operation as a diode and showing strong non-linear I-V characteristics. Interestingly, the device shows p-type behavior, in which conduction is dominated by holes as majority charge carriers and the flow of reverse current is enhanced, while the flow of forward current is suppressed, in contrast to monolayer graphene SSDs, which behave as n-type devices. The presence of a large bandgap in monolayer MoS{sub 2} results in strong control over the channel, showing complete channel pinch-off in forward conduction, which was confirmed with transmission pathways plots. The device exhibited large leakage tunnelling current through the insulating trenches, which may have been due to the lack of passivation; nevertheless, reverse current remained to be 6 times higher than forward current, showing strong rectification. The effect of p-type substitutional channel doping of sulphur with phosphorus was investigated and showed that it greatly enhances the performance of the device, increasing the reverse-to-forward current rectification ratio more than an order of magnitude, up to a value of 70.

Origin of the monolayer Raman signature in hexagonal boron nitride: a first-principles analysis.

Science.gov (United States)

Ontaneda, Jorge; Singh, Anjali; Waghmare, Umesh V; Grau-Crespo, Ricardo

2018-05-10

Monolayers of hexagonal boron nitride (h-BN) can in principle be identified by a Raman signature, consisting of an upshift in the frequency of the E 2g vibrational mode with respect to the bulk value, but the origin of this shift (intrinsic or support-induced) is still debated. Herein we use density functional theory calculations to investigate whether there is an intrinsic Raman shift in the h-BN monolayer in comparison with the bulk. There is universal agreement among all tested functionals in predicting the magnitude of the frequency shift upon a variation in the in-plane cell parameter. It is clear that a small in-plane contraction can explain the Raman peak upshift from bulk to monolayer. However, we show that the larger in-plane parameter in the bulk (compared to the monolayer) results from non-local correlation effects, which cannot be accounted for by local functionals or those with empirical dispersion corrections. Using a non-local-correlation functional, we then investigate the effect of finite temperatures on the Raman signature. We demonstrate that bulk h-BN thermally expands in the direction perpendicular to the layers, while the intralayer distances slightly contract, in agreement with observed experimental behavior. Interestingly, the difference in in-plane cell parameter between bulk and monolayer decreases with temperature, and becomes very small at room temperature. We conclude that the different thermal expansion of bulk and monolayer partially 'erases' the intrinsic Raman signature, accounting for its small magnitude in recent experiments on suspended samples.

Origin of the monolayer Raman signature in hexagonal boron nitride: a first-principles analysis

Science.gov (United States)

Ontaneda, Jorge; Singh, Anjali; Waghmare, Umesh V.; Grau-Crespo, Ricardo

2018-05-01

Monolayers of hexagonal boron nitride (h-BN) can in principle be identified by a Raman signature, consisting of an upshift in the frequency of the E2g vibrational mode with respect to the bulk value, but the origin of this shift (intrinsic or support-induced) is still debated. Herein we use density functional theory calculations to investigate whether there is an intrinsic Raman shift in the h-BN monolayer in comparison with the bulk. There is universal agreement among all tested functionals in predicting the magnitude of the frequency shift upon a variation in the in-plane cell parameter. It is clear that a small in-plane contraction can explain the Raman peak upshift from bulk to monolayer. However, we show that the larger in-plane parameter in the bulk (compared to the monolayer) results from non-local correlation effects, which cannot be accounted for by local functionals or those with empirical dispersion corrections. Using a non-local-correlation functional, we then investigate the effect of finite temperatures on the Raman signature. We demonstrate that bulk h-BN thermally expands in the direction perpendicular to the layers, while the intralayer distances slightly contract, in agreement with observed experimental behavior. Interestingly, the difference in in-plane cell parameter between bulk and monolayer decreases with temperature, and becomes very small at room temperature. We conclude that the different thermal expansion of bulk and monolayer partially ‘erases’ the intrinsic Raman signature, accounting for its small magnitude in recent experiments on suspended samples.

Edge Delamination of Monolayer Transition Metal Dichalcogenides.

Science.gov (United States)

Ly, Thuc Hue; Yun, Seok Joon; Thi, Quoc Huy; Zhao, Jiong

2017-07-25

Delamination of thin films from the supportive substrates is a critical issue within the thin film industry. The emergent two-dimensional, atomic layered materials, including transition metal dichalcogenides, are highly flexible; thus buckles and wrinkles can be easily generated and play vital roles in the corresponding physical properties. Here we introduce one kind of patterned buckling behavior caused by the delamination from a substrate initiated at the edges of the chemical vapor deposition synthesized monolayer transition metal dichalcogenides, led by thermal expansion mismatch. The atomic force microscopy and optical characterizations clearly showed the puckered structures associated with the strain, whereas the transmission electron microscopy revealed the special sawtooth-shaped edges, which break the geometrical symmetry for the buckling behavior of hexagonal samples. The condition of the edge delamination is in accordance with the fracture behavior of thin film interfaces. This edge delamination and buckling process is universal for most ultrathin two-dimensional materials, which requires more attention in various future applications.

Monolayer collapse regulating process of adsorption-desorption of palladium nanoparticles at fatty acid monolayers at the air-water interface.

Science.gov (United States)

Goto, Thiago E; Lopez, Ricardo F; Iost, Rodrigo M; Crespilho, Frank N; Caseli, Luciano

2011-03-15

In this paper, we investigate the affinity of palladium nanoparticles, stabilized with glucose oxidase, for fatty acid monolayers at the air-water interface, exploiting the interaction between a planar system and spheroids coming from the aqueous subphase. A decrease of the monolayer collapse pressure in the second cycle of interface compression proved that the presence of the nanoparticles causes destabilization of the monolayer in a mechanism driven by the interpenetration of the enzyme into the bilayer/multilayer structure formed during collapse, which is not immediately reversible after monolayer expansion. Surface pressure and surface potential-area isotherms, as well as infrared spectroscopy [polarization modulation infrared reflection adsorption spectroscopy (PM-IRRAS)] and deposition onto solid plates as Langmuir-Blodgett (LB) films, were employed to construct a model in which the nanoparticle has a high affinity for the hydrophobic core of the structure formed after collapse, which provides a slow desorption rate from the interface after monolayer decompression. This may have important consequences on the interaction between the metallic particles and fatty acid monolayers, which implies the regulation of the multifunctional properties of the hybrid material.

Design of a new two-dimensional diluted magnetic semiconductor: Mn-doped GaN monolayer

International Nuclear Information System (INIS)

Zhao, Qian; Xiong, Zhihua; Luo, Lan; Sun, Zhenhui; Qin, Zhenzhen; Chen, Lanli; Wu, Ning

2017-01-01

Highlights: • It is found nonmagnetic GaN ML exhibits half-metallic FM behavior by Mn doping due to double exchange mechanism. • Interestingly, the FM coupling is enhanced with the increasing tensile strain due to stronger interaction between Mn-3d and N-2p state. • While, the FM interaction is weakened with the increasing compressive strain until it transforms into AFM under strain of −9.5%. • These results provide a feasible approach for the fabrication of 2D DMS based GaN ML. - Abstract: To meet the need of low-dimensional spintronic devices, we investigate the electronic structure and magnetic properties of Mn-doped GaN monolayer using first-principles method. We find the nonmagnetic GaN monolayer exhibits half-metallic ferromagnetism by Mn doping due to double-exchange mechanism. Interestingly, the ferromagnetic coupling in Mn-doped GaN monolayer is enhanced with tensile strain and weakened with compressive strain. What is more, the ferromagnetic–antiferromagnetic transformation occurs under compressive strain of −9.5%. These results provide a feasible approach for fabrication of a new GaN monolayer based diluted magnetic semiconductor.

Design of a new two-dimensional diluted magnetic semiconductor: Mn-doped GaN monolayer

Energy Technology Data Exchange (ETDEWEB)

Zhao, Qian [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China); Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Xiong, Zhihua, E-mail: xiong_zhihua@126.com [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China); Luo, Lan [School of Materials Science and Engineering, Nanchang University, Nanchang 330031 (China); Sun, Zhenhui [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China); Qin, Zhenzhen [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China); Chen, Lanli [Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Wu, Ning [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China)

2017-02-28

Highlights: • It is found nonmagnetic GaN ML exhibits half-metallic FM behavior by Mn doping due to double exchange mechanism. • Interestingly, the FM coupling is enhanced with the increasing tensile strain due to stronger interaction between Mn-3d and N-2p state. • While, the FM interaction is weakened with the increasing compressive strain until it transforms into AFM under strain of −9.5%. • These results provide a feasible approach for the fabrication of 2D DMS based GaN ML. - Abstract: To meet the need of low-dimensional spintronic devices, we investigate the electronic structure and magnetic properties of Mn-doped GaN monolayer using first-principles method. We find the nonmagnetic GaN monolayer exhibits half-metallic ferromagnetism by Mn doping due to double-exchange mechanism. Interestingly, the ferromagnetic coupling in Mn-doped GaN monolayer is enhanced with tensile strain and weakened with compressive strain. What is more, the ferromagnetic–antiferromagnetic transformation occurs under compressive strain of −9.5%. These results provide a feasible approach for fabrication of a new GaN monolayer based diluted magnetic semiconductor.

Cyclic voltammetry and scanning electrochemical microscopy studies of methylene blue immobilized on the self-assembled monolayer of n-dodecanethiol

Energy Technology Data Exchange (ETDEWEB)

Salamifar, Seyed Ehsan [Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran (Iran, Islamic Republic of); Mehrgardi, Masoud Ayatollahi [Department of Chemistry, University of Isfahan, Isfahan (Iran, Islamic Republic of); Kazemi, Sayed Habib [Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan (Iran, Islamic Republic of); Mousavi, Mir Fazllollah, E-mail: mousavim@modares.ac.i [Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran (Iran, Islamic Republic of)

2010-12-30

Electron transfer (ET) kinetics through n-dodecanethiol (C{sub 12}SH) self-assembled monolayer on gold electrode was studied using cyclic voltammetry (CV), scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). An SECM model for compensating pinhole contribution, was used to measure the ET kinetics of solution-phase probes of ferrocyanide/ferricyanide (Fe(CN){sub 6}{sup 4-/3-}) and ferrocenemethanol/ferrociniummethanol (FMC{sup 0/+}) through the C{sub 12}SH monolayer yielding standard tunneling rate constant (k{sub ET}{sup 0}) of (4 {+-} 1) x 10{sup -11} and (3 {+-} 1) x 10{sup -10} cm s{sup -1} for Fe(CN){sub 6}{sup 4-/3-} and FMC{sup 0/+} respectively. Decay tunneling constants ({beta}) of 0.97 and 0.96 A{sup -1} for saturated alkane thiol chains were obtained using Fe(CN){sub 6}{sup 4-} and FMC respectively. Also, it was found that methylene blue (MB) molecules are effectively immobilized on the C{sub 12}SH monolayer and can mediate the ET between the solution-phase probes and underlying gold substrate. SECM-mediated model was used to simultaneously measure the bimolecular ET between the solution-phase probes and the monolayer-immobilized MB molecules, as well as tunneling ET between the monolayer-immobilized MB molecules and the underlying gold electrode, allowing the measurement of k{sub BI} = (5 {+-} 1) x 10{sup 6} and (4 {+-} 2) x 10{sup 7} cm{sup 3} mol{sup -1} s{sup -1} for the bimolecular ET and k{sub ET/MB}{sup 0}=(1{+-}0.3)x10{sup -3} and (7 {+-} 3) x 10{sup -2} s{sup -1} for the standard tunneling rate constant of ET using Fe(CN){sub 6}{sup 4-/3-} and FMC{sup 0/+} probes respectively.

Multiple-phase behavior and memory effect of polymer gel

CERN Document Server

Annaka, M; Nakahira, T; Sugiyama, M; Hara, K; Matsuura, T

2002-01-01

A poly(4-acrylamidosalicylic acid) gel (PASA gel) exhibits multiple phases as characterized by distinct degrees of swelling; the gel can take one of four different swelling values, but none of the intermediate values. The gel has remarkable memory: the phase behavior of the gel depends on whether the gel has experienced the most swollen phase or the most collapsed phase in the immediate past. The information is stored and reversibly erased in the form of a macroscopic phase transition behavior. The structure factors corresponding to these four phases were obtained by SANS, which indicated the presence of characteristic structures depending on pH and temperature, particularly in the shrunken state. (orig.)

Fabrication of P3HT/gold nanoparticle LB films by P3HT templating Langmuir monolayer

International Nuclear Information System (INIS)

Chen, Liang-Huei; Hsu, Wen-Ping; Chan, Han-Wen; Lee, Yuh-Lang

2014-01-01

Highlights: • Addition of ODA into the P3HT monolayer can significantly improve the dispersion ability of P3HT molecules. • The adsorption ability of the P3HT monolayer to the dispersed AuNPs can also be enhanced by the presence of ODA. - Abstract: Regioregular poly(3-hexyl thiophene) (rr-P3HT) and mixed P3HT/octadecyl amine (ODA) were used as template monolayers to adsorb the gold nanoparticles (AuNPs) dispersed in subphase. The behaviors of P3HT and P3HT/ODA monolayers were investigated by surface pressure area per molecule (π–A) isotherms, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The experimental results show that P3HT does not form a homogeneous film and tends to aggregate at the air/water interface. Meanwhile, the amount of AuNPs adsorbed by the P3HT monolayers is low, attributable to the weak interaction between AuNPs and P3HT. By introduction of ODA molecules into the P3HT monolayer, the spreading of P3HT molecules at the air/water interface is improved and the aggregation of P3HT is significantly inhibited. A nearly uniform and homogeneously mixed P3HT/ODA monolayer can be obtained when 50% of ODA is introduced. It is also found that the introduction of ODA can significantly increase the adsorption of AuNPs. For the mixed monolayer with low ratio of ODA (P3HT/ODA = 1/0.2), a higher concentration of adsorbed AuNPs was observed on the corresponding monolayer. However, when the ODA/P3HT ratio increases to 1/1, the AuNPs tend to form three-dimensional (3D) aggregates and the AuNPs cannot distribute well as a homogeneous monolayer. This result is ascribed to the increasing hydrophobicity of the adsorbed AuNPs because of capping of more ODA molecules

Study of the helium cross-section of unsymmetric disulfide self-assembled monolayers on Au(111)

Energy Technology Data Exchange (ETDEWEB)

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

2016-12-30

Highlights: • Unsymmetrtic disulfide (HDD and HOD) self assembled monolayers were grown on Au(111) by supersonic molecular beam deposition. • Helium scattering cross sections for these two different unsymmetric disulfides were determined. • A common low temperature film phase was observed for the studied disulfides. - Abstract: We have investigated the formation of self-assembled monolayers (SAMs) of 11-hydroxyundecyl decyl disulfide (CH{sub 3}-(CH{sub 2}){sub 9}-S-S-(CH{sub 2}){sub 11}-OH, HDD) and 11-hydroxyundecyl octadecyl disulfide (CH{sub 3}-(CH{sub 2}){sub 17}-S-S-(CH{sub 2}){sub 11}-OH, HOD) produced by supersonic molecular beam deposition (SMBD). The study has been carried out by means of helium diffraction at very low film coverage. In this regime helium single molecule cross sections have been estimated in a temperature range between 100 K and 450 K. The results show a different behavior above 300 K that has been interpreted as the starting of mobility with the formation of two thiolate moieties either linked by a gold adatom or distant enough to prevent cross section overlapping. Finally, helium diffraction patterns measured at 80 K for the SAMs grown at 200 K are discussed and the results support the proposed hypothesis of molecular dissociation based on the cross section data.

Effect of metal ions on the formation and properties of monolayers and nanosized Langmuir-Blodgett films based on diphilic aminomethylated calix[4]resorcinarenes

International Nuclear Information System (INIS)

Neveshkin, A.A.; Rusanova, T.Yu.; Rumyantseva, S.S.; Serdobintsev, A.A.; Podkosov, K.V.; Shtykov, S.N.; Klimov, B.N.; Gorin, D.A.; Ryzhkina, I.S.

2008-01-01

The behavior of the monolayers of three diphilic aminomethylated calix[4]resorcinarene (CRA) derivatives on the surface of a pure aqueous subphase and subphase containing copper(II), nickel(II), europium(III), terbium(III), and lanthanum(III) ions was investigated. The monolayer transfer to the quartz and single-crystal silicon substrates was accomplished by the Langmuir-Blodgett (LB) technique. The films were studied by ellipsometry and mass-spectrometry. Metal ions were found to exert effect on the limit area per one CRA molecule in the monolayer, on the surface collapse pressure and transfer coefficient of monolayer, and on the thickness and refractive index of the CRA-based LB films [ru

First-principles study of adsorption-induced magnetic properties of InSe monolayers

Science.gov (United States)

Fu, Zhaoming; Yang, Bowen; Zhang, Na; Ma, Dongwei; Yang, Zongxian

2018-04-01

In this work we studied the adsorption-induced magnetic behaviors on the two-dimensional InSe monolayer. Six kinds of adatoms (H, B, C, N, O and F) are taken into account. It is found that the InSe with adsorbing C and F have nonzero magnetic moments and good stability. Importantly, the magnetism of C and F modified InSe monolayers completely comes from p electrons of adatoms and substrates. The strength of magnetic exchange interaction can be controlled by changing the coverage of adsorbates. This p-electron magnetic material is thought to have obvious advantages compared to conventional d- or f-electron magnets. Our research is meaningful for practical applications in spintronic electronics and two dimensional magnetic semiconductors.

Phase Transition Behavior in a Neutral Evolution Model

Science.gov (United States)

King, Dawn; Scott, Adam; Maric, Nevena; Bahar, Sonya

2014-03-01

The complexity of interactions among individuals and between individuals and the environment make agent based modeling ideal for studying emergent speciation. This is a dynamically complex problem that can be characterized via the critical behavior of a continuous phase transition. Concomitant with the main tenets of natural selection, we allow organisms to reproduce, mutate, and die within a neutral phenotype space. Previous work has shown phase transition behavior in an assortative mating model with variable fitness landscapes as the maximum mutation size (μ) was varied (Dees and Bahar, 2010). Similarly, this behavior was recently presented in the work of Scott et al. (2013), even on a completely neutral landscape, for bacterial-like fission as well as for assortative mating. Here we present another neutral model to investigate the `critical' phase transition behavior of three mating types - assortative, bacterial, and random - in a phenotype space as a function of the percentage of random death. Results show two types of phase transitions occurring for the parameters of the population size and the number of clusters (an analogue of species), indicating different evolutionary dynamics for system survival and clustering. This research was supported by funding from: University of Missouri Research Board and James S. McDonnell Foundation.

Monolayer MoS2 heterojunction solar cells

KAUST Repository

Tsai, Menglin

2014-08-26

We realized photovoltaic operation in large-scale MoS2 monolayers by the formation of a type-II heterojunction with p-Si. The MoS 2 monolayer introduces a built-in electric field near the interface between MoS2 and p-Si to help photogenerated carrier separation. Such a heterojunction photovoltaic device achieves a power conversion efficiency of 5.23%, which is the highest efficiency among all monolayer transition-metal dichalcogenide-based solar cells. The demonstrated results of monolayer MoS 2/Si-based solar cells hold the promise for integration of 2D materials with commercially available Si-based electronics in highly efficient devices. © 2014 American Chemical Society.

Quasielastic neutron scattering and molecular dynamics simulation studies of the melting transition in butane and hexane monolayers adsorbed on graphite

DEFF Research Database (Denmark)

Hervig, K.W.; Wu, Z.; Dai, P.

1997-01-01

Quasielastic neutron scattering experiments and molecular dynamics (MD) simulations have been used to investigate molecular diffusive motion near the melting transition of monolayers of flexible rod-shaped molecules. The experiments were conducted on butane and hexane monolayers adsorbed...... comparison with experiment, quasielastic spectra calculated from the MD simulations were analyzed using the same models and fitting algorithms as for the neutron spectra. This combination of techniques gives a microscopic picture of the melting process in these two monolayers which is consistent with earlier...... neutron diffraction experiments. Butane melts abruptly to a liquid phase where the molecules in the trans conformation translationally diffuse while rotating about their center of mass. In the case of the hexane monolayer, the MD simulations show that the appearance of quasielastic scattering below T...

Phase behavior of the 38-atom Lennard-Jones cluster

International Nuclear Information System (INIS)

Sehgal, Ray M.; Maroudas, Dimitrios; Ford, David M.

2014-01-01

We have developed a coarse-grained description of the phase behavior of the isolated 38-atom Lennard-Jones cluster (LJ 38 ). The model captures both the solid-solid polymorphic transitions at low temperatures and the complex cluster breakup and melting transitions at higher temperatures. For this coarse model development, we employ the manifold learning technique of diffusion mapping. The outcome of the diffusion mapping analysis over a broad temperature range indicates that two order parameters are sufficient to describe the cluster's phase behavior; we have chosen two such appropriate order parameters that are metrics of condensation and overall crystallinity. In this well-justified coarse-variable space, we calculate the cluster's free energy landscape (FEL) as a function of temperature, employing Monte Carlo umbrella sampling. These FELs are used to quantify the phase behavior and onsets of phase transitions of the LJ 38 cluster

First-principles studies of Te line-ordered alloys in a MoS2 monolayer

Science.gov (United States)

Andriambelaza, N. F.; Mapasha, R. E.; Chetty, N.

2018-04-01

The thermodynamic stability, structural and electronic properties of Te line-ordered alloys are investigated using density functional theory (DFT) methods. Thirty four possible Te line-ordered alloy configurations are found in a 5×5 supercell of a MoS2 monolayer. The calculated formation energies show that the Te line-ordered alloy configurations are thermodynamically stable at 0 K and agree very well with the random alloys. The lowest energy configurations at each concentration correspond to the configuration where the Te atom rows are far apart from each other (avoiding clustering) within the supercell. The variation of the lattice constant at different concentrations obey Vegard's law. The Te line-ordered alloys fine tune the band gap of a MoS2 monolayer although deviating from linearity behavior. Our results suggest that the Te line-ordered alloys can be an effective way to modulate the band gap of a MoS2 monolayer for nanoelectronic, optoelectronic and nanophotonic applications.

Quantum mechanical rippling of a MoS2 monolayer controlled by interlayer bilayer coupling.

Science.gov (United States)

Zheng, Yi; Chen, Jianyi; Ng, M-F; Xu, Hai; Liu, Yan Peng; Li, Ang; O'Shea, Sean J; Dumitrică, T; Loh, Kian Ping

2015-02-13

Nanoscale corrugations are of great importance in determining the physical properties of two-dimensional crystals. However, the mechanical behavior of atomically thin films under strain is not fully understood. In this Letter, we show a layer-dependent mechanical response of molybdenum disulfide (MoS(2)) subject to atomistic-precision strain induced by 2H-bilayer island epitaxy. Dimensional crossover in the mechanical properties is evidenced by the formation of star-shaped nanoripple arrays in the first monolayer, while rippling instability is completely suppressed in the bilayer. Microscopic-level quantum mechanical simulations reveal that the nanoscale rippling is realized by the twisting of neighboring Mo-S bonds without modifying the chemical bond length, and thus invalidates the classical continuum mechanics. The formation of nanoripple arrays significantly changes the electronic and nanotribological properties of monolayer MoS(2). Our results suggest that quantum mechanical behavior is not unique for sp(2) bonding but general for atomic membranes under strain.

Ag-related alloy formation and magnetic phases for Ag/Co/Ir(111) ultrathin films

International Nuclear Information System (INIS)

Tsay, Jyh-Shen; Tsai, Du-Cheng; Chang, Cheng-Hsun-Tony; Chen, Wei-Hsiang

2013-01-01

The Kerr intensity versus the Ag thickness for Ag grown on the top of Co/Ir(111) exhibits an oscillating behavior with a period around one monolayer which should be due to the morphological change related electronic structure differences of the Ag layer. From systematical investigations of Ag/Co/Ir(111) films with the Co layer thinner than 4 monolayers at temperatures below 900 K, a magnetic phase diagram has been established. As the annealing temperature increases for Ag/Co/Ir(111) films, enhancements of the coercive force occur in both the polar and longitudinal configurations due to the intermixing of Ag and Co at the interface and the formation of Co–Ir alloy. The disappearance of ferromagnetism is mainly attributed to the reduced atomic percent of cobalt in Co–Ir alloy, the lowered Curie temperature by a reduction of the thickness of magnetic layers, and the intermixing of Ag and Co at the Ag/Co interface. - Highlights: • An oscillating behavior occurs due to the morphological change for Ag on Co/Ir(111). • A magnetic phase diagram has been established for Ag/Co/Ir(111). • Some Ag atoms intermix with the underlying Co layer at high temperatures. • Polar coercive force is enhanced due to the compositional change

The Phase Behavior of γ-Oryzanol and β-Sitosterol in Edible Oil

NARCIS (Netherlands)

Sawalha, H.I.M.; Venema, P.; Bot, A.; Flöter, E.; Adel, den R.; Linden, van der E.

2015-01-01

The phase behavior of binary mixtures of ¿-oryzanol and ß-sitosterol and ternary mixtures of ¿-oryzanol and ß-sitosterol in sunflower oil was studied. Binary mixtures of ¿-oryzanol and ß-sitosterol show double-eutectic behavior. Complex phase behavior with two intermediate mixed solid phases was

Lateral pressure profiles in lipid monolayers

NARCIS (Netherlands)

Baoukina, Svetlana; Marrink, Siewert J.; Tieleman, D. Peter

2010-01-01

We have used molecular dynamics simulations with coarse-grained and atomistic models to study the lateral pressure profiles in lipid monolayers. We first consider simple oil/air and oil/water interfaces, and then proceed to lipid monolayers at air/water and oil/water interfaces. The results are

Traders' behavioral coupling and market phase transition

Science.gov (United States)

Ma, Rong; Zhang, Yin; Li, Honggang

2017-11-01

Traditional economic theory is based on the assumption that traders are completely independent and rational; however, trading behavior in the real market is often coupled by various factors. This paper discusses behavioral coupling based on the stock index in the stock market, focusing on the convergence of traders' behavior, its effect on the correlation of stock returns and market volatility. We find that the behavioral consensus in the stock market, the correlation degree of stock returns, and the market volatility all exhibit significant phase transitions with stronger coupling.

Topography-specific isotropic tunneling in nanoparticle monolayer with sub-nm scale crevices.

Science.gov (United States)

Wang, Guisheng; Jiao, Weihong; Yi, Lizhi; Zhang, Yuejiao; Wu, Ke; Zhang, Chao; Lv, Xianglong; Qian, Lihua; Li, Jianfeng; Yuan, Songliu; Chen, Liang

2016-10-07

Material used in flexible devices may experience anisotropic strain with identical magnitude, outputting coherent signals that tend to have a serious impact on device reliability. In this work, the surface topography of the nanoparticles (NPs) is proposed to be a parameter to control the performance of strain gauge based on tunneling behavior. In contrast to anisotropic tunneling in a monolayer of spherical NPs, electron tunneling in a monolayer of urchin-like NPs actually exhibits a nearly isotropic response to strain with different loading orientations. Isotropic tunneling of the urchin-like NPs is caused by the interlocked pikes of these urchin-like NPs in a random manner during external mechanical stimulus. Topography-dependent isotropic tunneling in two dimensions reported here opens a new opportunity to create highly reliable electronics with superior performance.

Ab initio study of adsorption and diffusion of lithium on transition metal dichalcogenide monolayers

OpenAIRE

Sun, Xiaoli; Wang, Zhiguo

2017-01-01

Using first principles calculations, we studied the stability and electronic properties of transition metal dichalcogenide monolayers of the type MX2 (M = Ti, Zr, Hf, V, Nb, Ta, Mo, Cr, W; X= S, Se, Te). The adsorption and diffusion of lithium on the stable MX2 phase was also investigated for potential application as an anode for lithium ion batteries. Some of these compounds were found to be stable in the 2H phase and some are in the 1T or 1T' phase, but only a few of them were stable in bot...

Large Friction Anisotropy of a Polydiacetylene Monolayer

International Nuclear Information System (INIS)

Burns, A.R.; Carpick, R.W.; Sasaki, D.Y.

1999-01-01

Friction force microscopy measurements of a polydiacetylene monolayer film reveal a 300% friction anisotropy that is correlated with the film structure. The film consists of a monolayer of the red form of N-(2-ethanol)- 10,12 pentacosadiynamide, prepared on a Langmuir trough and deposited on a mica substrate. As confirmed by atomic force microscopy and fluorescence microscopy, the monolayer consists of domains of linearly oriented conjugated backbones with pendant hydrocarbon side chains above and below the backbones. Maximum friction occurs when the sliding direction is perpendicular to the backbone. We propose that the backbones impose anisotropic packing of the hydrocarbon side chains which leads to the observed friction anisotropy. Friction anisotropy is therefore a sensitive, optically-independent indicator of polymer backbone direction and monolayer structural properties

Liquid-solid surface phase transformation of fluorinated fullerene on monolayer tungsten diselenide

KAUST Repository

Song, Zhibo

2018-04-04

Hybrid van der Waals heterostructures constructed by the integration of organic molecules and two-dimensional (2D) transition metal dichalcogenide (TMD) materials have useful tunable properties for flexible electronic devices. Due to the chemically inert and atomically smooth nature of the TMD surface, well-defined crystalline organic films form atomically sharp interfaces facilitating optimal device performance. Here, the surface phase transformation of the supramolecular packing structure of fluorinated fullerene (C60F48) on single-layer tungsten diselenide (WSe2) is revealed by low-temperature scanning tunneling microscopy, from thermally stable liquid to solid phases as the coverage increases. Statistical analysis of the intermolecular interaction potential reveals that the repulsive dipole-dipole interaction induced by interfacial charge transfer and substrate-mediated interactions play important roles in stabilizing the liquid C60F48 phases. Theoretical calculations further suggest that the dipole moment per C60F48 molecule varies with the surface molecule density, and the liquid-solid transformation could be understood from the perspective of the thermodynamic free energy for open systems. This study offers insights into the growth behavior at 2D organic/TMD hybrid heterointerfaces.

Liquid-solid surface phase transformation of fluorinated fullerene on monolayer tungsten diselenide

Science.gov (United States)

Song, Zhibo; Wang, Qixing; Li, Ming-Yang; Li, Lain-Jong; Zheng, Yu Jie; Wang, Zhuo; Lin, Tingting; Chi, Dongzhi; Ding, Zijing; Huang, Yu Li; Thye Shen Wee, Andrew

2018-04-01

Hybrid van der Waals heterostructures constructed by the integration of organic molecules and two-dimensional (2D) transition metal dichalcogenide (TMD) materials have useful tunable properties for flexible electronic devices. Due to the chemically inert and atomically smooth nature of the TMD surface, well-defined crystalline organic films form atomically sharp interfaces facilitating optimal device performance. Here, the surface phase transformation of the supramolecular packing structure of fluorinated fullerene (C60F48 ) on single-layer tungsten diselenide (WSe2) is revealed by low-temperature scanning tunneling microscopy, from thermally stable liquid to solid phases as the coverage increases. Statistical analysis of the intermolecular interaction potential reveals that the repulsive dipole-dipole interaction induced by interfacial charge transfer and substrate-mediated interactions play important roles in stabilizing the liquid C60F48 phases. Theoretical calculations further suggest that the dipole moment per C60F48 molecule varies with the surface molecule density, and the liquid-solid transformation could be understood from the perspective of the thermodynamic free energy for open systems. This study offers insights into the growth behavior at 2D organic/TMD hybrid heterointerfaces.

Thermal conductivity of a h-BCN monolayer.

Science.gov (United States)

Zhang, Ying-Yan; Pei, Qing-Xiang; Liu, Hong-Yuan; Wei, Ning

2017-10-18

A hexagonal graphene-like boron-carbon-nitrogen (h-BCN) monolayer, a new two-dimensional (2D) material, has been synthesized recently. Herein we investigate for the first time the thermal conductivity of this novel 2D material. Using molecular dynamics simulations based on the optimized Tersoff potential, we found that the h-BCN monolayers are isotropic in the basal plane with close thermal conductivity magnitudes. Though h-BCN has the same hexagonal lattice as graphene and hexagonal boron nitride (h-BN), it exhibits a much lower thermal conductivity than the latter two materials. In addition, the thermal conductivity of h-BCN monolayers is found to be size-dependent but less temperature-dependent. Modulation of the thermal conductivity of h-BCN monolayers can also be realized by strain engineering. Compressive strain leads to a monotonic decrease in the thermal conductivity while the tensile strain induces an up-then-down trend in the thermal conductivity. Surprisingly, the small tensile strain can facilitate the heat transport of the h-BCN monolayers.

Anomalous lattice vibrations of monolayer MoS 2 probed by ultraviolet Raman scattering

KAUST Repository

Liu, Hsiang Lin; Guo, Huaihong; Yang, Teng; Zhang, Zhidong; Kumamoto, Yasuaki; Shen, Chih Chiang; Hsu, Yu Te; Li, Lain-Jong; Saito, Riichiro; Kawata, Satoshi

2015-01-01

We present a comprehensive Raman scattering study of monolayer MoS2 with increasing laser excitation energies ranging from the near-infrared to the deep-ultraviolet. The Raman scattering intensities from the second-order phonon modes are revealed to be enhanced anomalously by only the ultraviolet excitation wavelength 354 nm. We demonstrate theoretically that such resonant behavior arises from a strong optical absorption that forms near the Γ point and of the band structure and an inter-valley resonant electronic scattering by the M-point phonons. These results advance our understanding of the double resonance Raman scattering process in low-dimensional semiconducting nanomaterials and provide a foundation for the technological development of monolayer MoS2 in the ultraviolet frequency range. © the Owner Societies 2015.

Fractal growth in impurity-controlled solidification in lipid monolayers

DEFF Research Database (Denmark)

Fogedby, Hans C.; Sørensen, Erik Schwartz; Mouritsen, Ole G.

1987-01-01

A simple two-dimensional microscopic model is proposed to describe solidifcation processes in systems with impurities which are miscible only in the fluid phase. Computer simulation of the model shows that the resulting solids are fractal over a wide range of impurity concentrations and impurity...... diffusional constants. A fractal-forming mechanism is suggested for impurity-controlled solidification which is consistent with recent experimental observations of fractal growth of solid phospholipid domains in monolayers. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....

Interaction between lipid monolayers and poloxamer 188: An X-ray reflectivity and diffraction study

DEFF Research Database (Denmark)

Wu, G.H.; Majewski, J.; Ege, C.

2005-01-01

The mechanism by which poloxamer 188 (P188) seals a damaged cell membrane is examined using the lipid monolayer as a model system. X-ray reflectivity and grazing-incidence x-ray diffraction results show that at low nominal lipid density, P188, by physically occupying the available area and phase ...

Strain-engineered band parameters of graphene-like SiC monolayer

International Nuclear Information System (INIS)

Behera, Harihar; Mukhopadhyay, Gautam

2014-01-01

Using full-potential density functional theory (DFT) calculations we show that the band gap and effective masses of charge carriers in SiC monolayer (ML-SiC) in graphene-like two-dimensional honeycomb structure are tunable by strain engineering. ML-SiC was found to preserve its flat 2D graphene-like structure under compressive strain up to 7%. A transition from indirect-to-direct gap-phase is predicted to occur for a strain value lying within the interval (1.11 %, 1.76%). In both gap-phases band gap decreases with increasing strain, although the rate of decrease is different in the two gap-phases. Effective mass of electrons show a non-linearly decreasing trend with increasing tensile strain in the direct gap-phase. The strain-sensitive properties of ML-SiC, may find applications in future strain-sensors, nanoelectromechanical systems (NEMS) and nano-optomechanical systems (NOMS) and other nano-devices

Monolayer-Mediated Growth of Organic Semiconductor Films with Improved Device Performance.

Science.gov (United States)

Huang, Lizhen; Hu, Xiaorong; Chi, Lifeng

2015-09-15

Increased interest in wearable and smart electronics is driving numerous research works on organic electronics. The control of film growth and patterning is of great importance when targeting high-performance organic semiconductor devices. In this Feature Article, we summarize our recent work focusing on the growth, crystallization, and device operation of organic semiconductors intermediated by ultrathin organic films (in most cases, only a monolayer). The site-selective growth, modified crystallization and morphology, and improved device performance of organic semiconductor films are demonstrated with the help of the inducing layers, including patterned and uniform Langmuir-Blodgett monolayers, crystalline ultrathin organic films, and self-assembled polymer brush films. The introduction of the inducing layers could dramatically change the diffusion of the organic semiconductors on the surface and the interactions between the active layer with the inducing layer, leading to improved aggregation/crystallization behavior and device performance.

Non-Darcy behavior of two-phase channel flow.

Science.gov (United States)

Xu, Xianmin; Wang, Xiaoping

2014-08-01

We study the macroscopic behavior of two-phase flow in porous media from a phase-field model. A dissipation law is first derived from the phase-field model by homogenization. For simple channel geometry in pore scale, the scaling relation of the averaged dissipation rate with the velocity of the two-phase flow can be explicitly obtained from the model which then gives the force-velocity relation. It is shown that, for the homogeneous channel surface, Dacry's law is still valid with a significantly modified permeability including the contribution from the contact line slip. For the chemically patterned surfaces, the dissipation rate has a non-Darcy linear scaling with the velocity, which is related to a depinning force for the patterned surface. Our result offers a theoretical understanding on the prior observation of non-Darcy behavior for the multiphase flow in either simulations or experiments.

Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. I. Structure

DEFF Research Database (Denmark)

Enevoldsen, Ann Dorrit; Hansen, Flemming Yssing; Diama, A.

2007-01-01

their backbone and squalane has, in addition, six methyl side groups. Upon adsorption, there are significant differences as well as similarities in the behavior of these molecular films. Both molecules form ordered structures at low temperatures; however, while the melting point of the two-dimensional (2D......The structure of a monolayer film of the branched alkane squalane (C30H62) adsorbed on graphite has been studied by neutron diffraction and molecular dynamics (MD) simulations and compared with a similar study of the n-alkane tetracosane (n-C24H52). Both molecules have 24 carbon atoms along...... temperature. The neutron diffraction data show that the translational order in the squalane monolayer is significantly less than in the tetracosane monolayer. The authors' MD simulations suggest that this is caused by a distortion of the squalane molecules upon adsorption on the graphite surface. When...

Challenges in analysing and visualizing large-scale molecular dynamics simulations: domain and defect formation in lung surfactant monolayers

International Nuclear Information System (INIS)

Mendez-Villuendas, E; Baoukina, S; Tieleman, D P

2012-01-01

Molecular dynamics simulations have rapidly grown in size and complexity, as computers have become more powerful and molecular dynamics software more efficient. Using coarse-grained models like MARTINI system sizes of the order of 50 nm × 50 nm × 50 nm can be simulated on commodity clusters on microsecond time scales. For simulations of biological membranes and monolayers mimicking lung surfactant this enables large-scale transformation and complex mixtures of lipids and proteins. Here we use a simulation of a monolayer with three phospholipid components, cholesterol, lung surfactant proteins, water, and ions on a ten microsecond time scale to illustrate some current challenges in analysis. In the simulation, phase separation occurs followed by formation of a bilayer fold in which lipids and lung surfactant protein form a highly curved structure in the aqueous phase. We use Voronoi analysis to obtain detailed physical properties of the different components and phases, and calculate local mean and Gaussian curvatures of the bilayer fold.

Zitterbewegung in monolayer silicene in a magnetic field

International Nuclear Information System (INIS)

Romera, E.; Roldán, J.B.; Santos, F. de los

2014-01-01

We study the Zitterbewegung in monolayer silicene under a perpendicular magnetic field. Using an effective Hamiltonian, we have investigated the autocorrelation function and the density currents in this material. Moreover, we have analyzed other types of periodicities of the system (classical and revival times). Finally, the above results are compared with their counterparts in two other monolayer materials subject to a magnetic field: graphene and MoS 2 . - Highlights: • We study Zitterbewegung in monolayer silicene in a magnetic field. • We have analyzed other types of periodicities in silicene. • The above results are compared with other monolayer materials (graphene and MoS 2 )

Zitterbewegung in monolayer silicene in a magnetic field

Energy Technology Data Exchange (ETDEWEB)

Romera, E. [Departamento de Física Atómica, Molecular y Nuclear and Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain); Roldán, J.B. [Departamento de Electrónica y Tecnología de Computadores and CITIC, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain); Santos, F. de los [Departamento de Electromagnetismo y Física de la Materia, and Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain)

2014-07-04

We study the Zitterbewegung in monolayer silicene under a perpendicular magnetic field. Using an effective Hamiltonian, we have investigated the autocorrelation function and the density currents in this material. Moreover, we have analyzed other types of periodicities of the system (classical and revival times). Finally, the above results are compared with their counterparts in two other monolayer materials subject to a magnetic field: graphene and MoS{sub 2}. - Highlights: • We study Zitterbewegung in monolayer silicene in a magnetic field. • We have analyzed other types of periodicities in silicene. • The above results are compared with other monolayer materials (graphene and MoS{sub 2})

Structure of a monolayer of molecular rotors on aqueous subphase from grazing-incidence X-ray diffraction.

Science.gov (United States)

Kaleta, Jiří; Wen, Jin; Magnera, Thomas F; Dron, Paul I; Zhu, Chenhui; Michl, Josef

2018-03-23

In situ grazing-incidence X-ray scattering shows that a monolayer of artificial rod-shaped dipolar molecular rotors produced on the surface of an aqueous subphase in a Langmuir trough has a structure conducive to a 2D ferroelectric phase. The axes of the rotors stand an average of 0.83 nm apart in a triangular grid, perpendicular to the surface within experimental error. They carry 2,3-dichlorophenylene rotators near rod centers, between two decks of interlocked triptycenes installed axially on the rotor axle. The analysis is based first on simultaneous fitting of observed Bragg rods and second on fitting the reflectivity curve with only three adjustable parameters and the calculated rotor electron density, which also revealed the presence of about seven molecules of water near each rotator. Dependent on preparation conditions, a minor and variable amount of a different crystal phase may also be present in the monolayer.

Adsorption of alkali, alkaline-earth, simple and 3d transition metal, and nonmetal atoms on monolayer MoS2

Directory of Open Access Journals (Sweden)

X. D. Li

2015-05-01

Full Text Available Single adsorption of different atoms on pristine two-dimensional monolayer MoS2 have been systematically investigated by using density functional calculations with van der Waals correction. The adatoms cover alkali metals, alkaline earth metals, main group metal, 3d-transition metals, coinage metal and nonmetal atoms. Depending on the adatom type, metallic, semimetallic or semiconducting behavior can be found in direct bandgap monolayer MoS2. Additionally, local or long-range magnetic moments of two-dimensional MoS2 sheet can also attained through the adsorption. The detailed atomic-scale knowledge of single adsorption on MoS2 monolayer is important not only for the sake of a theoretical understanding, but also device level deposition technological application.

Characterization of 10,12-pentacosadiynoic acid Langmuir–Blodgett monolayers and their use in metal–insulator–metal tunnel devices

Directory of Open Access Journals (Sweden)

Saumya Sharma

2014-11-01

Full Text Available The characterization of Langmuir–Blodgett thin films of 10,12-pentacosadiynoic acid (PDA and their use in metal–insulator–metal (MIM devices were studied. The Langmuir monolayer behavior of the PDA film was studied at the air/water interface using surface tension–area isotherms of polymeric and monomeric PDA. Langmuir–Blodgett (LB, vertical deposition and Langmuir–Schaefer (LS, horizontal deposition techniques were used to deposit the PDA film on various substrates (glass, quartz, silicon, and nickel-coated film on glass. The electrochemical, electrical and optical properties of the LB and LS PDA films were studied using cyclic voltammetry, current–voltage characteristics (I–V, and UV–vis and FTIR spectroscopies. Atomic force microscopy measurements were performed in order to analyze the surface morphology and roughness of the films. A MIM tunnel diode was fabricated using a PDA monolayer assembly as the insulating barrier, which was sandwiched between two nickel layers. The precise control of the thickness of the insulating monolayers proved critical for electron tunneling to take place in the MIM structure. The current–voltage characteristics of the MIM diode revealed tunneling behavior in the fabricated Ni–PDA LB film–Ni structures.

Testing the effectiveness of monolayers under wind and wave conditions.

Science.gov (United States)

Palada, C; Schouten, P; Lemckert, C

2012-01-01

Monolayers are highly desirable for their evaporation reducing capabilities due to their relatively minimal cost and ease of application. Despite these positive attributes, monolayers have consistently failed to perform effectively due to the harsh wind and wave conditions prevalent across real-world water reserves. An exhaustive and consistent study testing the influence of wind and wave combinations on monolayer performance has yet to be presented in the literature. To remedy this, the effect of simultaneous wind and wave conditions on a benchmark high-performance monolayer (octadecanol suspension, CH(3)(CH(2))(16)CH(2)OH) has been analysed. Subjected only to waves, the monolayer remained intact due to its innate ability to compress and expand. However, the constant simultaneous application of wind and waves caused the monolayer to break up and gather down-wind where it volatilised over time. At wind speeds above 1.3 m s(-1) the monolayer was completely ineffective. For wind speeds below this threshold, the monolayer had an influence on the evaporation rate dependent on wind speed. From these results a series of application protocols can now be developed for the optimised deployment of monolayers in real-world water reserves. This will be of interest to private, commercial and government organisations involved in the storage and management of water resources.

Phase behavior, rheological characteristics and microstructure of sodium caseinate-Persian gum system.

Science.gov (United States)

Sadeghi, Farzad; Kadkhodaee, Rassoul; Emadzadeh, Bahareh; Phillips, Glyn O

2018-01-01

In this study, the phase behavior of sodium caseinate-Persian gum mixtures was investigated. The effect of thermodynamic incompatibility on phase distribution of sodium caseinate fractions as well as the flow behavior and microstructure of the biopolymer mixtures were also studied. The phase diagram clearly demonstrated the dominant effect of Persian gum on the incompatibility of the two biopolymers. SDS-PAGE electrophoresis indicated no selective fractionation of sodium caseinate subunits between equilibrium phases upon de-mixing. The microstructure of mixtures significantly changed depending on their position within the phase diagram. Fitting viscometric data to Cross and Bingham models revealed that the apparent viscosity, relaxation time and shear thinning behavior of the mixtures is greatly influenced by the volume ratio and concentration of the equilibrium phases. There is a strong dependence of the flow behavior of sodium caseinate-Persian gum mixtures on the composition of the equilibrium phases and the corresponding microstructure of the system. Copyright © 2017. Published by Elsevier Ltd.

Controlling block copolymer phase behavior using ionic surfactant

Energy Technology Data Exchange (ETDEWEB)

Ray, D.; Aswal, V. K. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085, India E-mail: debes.phys@gmail.com (India)

2016-05-23

The phase behavior of poly(ethylene oxide)-poly(propylene oxide-poly(ethylene oxide) PEO-PPO-PEO triblock copolymer [P85 (EO{sub 26}PO{sub 39}EO{sub 26})] in presence of anionic surfactant sodium dodecyl sulfate (SDS) in aqueous solution as a function of temperature has been studied using dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The measurements have been carried out for fixed concentrations (1 wt%) of block copolymer and surfactants. Each of the individual components (block copolymer and surfactant) and the nanoparticle–surfactant mixed system have been examined at varying temperature. The block copolymer P85 forms spherical micelles at room temperature whereas shows sphere-to-rod like micelle transition at higher temperatures. On the other hand, SDS surfactant forms ellipsoidal micelles over a wide temperature range. Interestingly, it is found that phase behavior of mixed micellar system (P85 + SDS) as a function of temperature is drastically different from that of P85, giving the control over the temperature-dependent phase behavior of block copolymers.

Interfacial Interactions and Nano structure Changes in DPPG/HD Monolayer at the Air/Water Interface

International Nuclear Information System (INIS)

Zhu, H.; Zhang, P.; Sun, R.; Hao, Ch.; Wang, J.; Zhu, H.; Zhang, T.; Zhang, P.; Li, Sh.

2015-01-01

Lung surfactant (LS) plays a crucial role in regulating surface tension during normal respiration cycles by decreasing the work associated with lung expansion and therefore decreases the metabolic energy consumed. Monolayer surfactant films composed of a mixture of phospholipids and spreading additives are of optional utility for applications in lung surfactant-based therapies. A simple, minimal model of such a lung surfactant system, composed of 1,2-dipalmitoyl-sn-glycero-3-[phosphor-rac-(1-glycerol)] (DPPG) and hexadecanol (HD), was prepared, and the surface pressure-area π-A) isotherms and nano structure characteristics of the binary mixture were investigated at the air/water interface using a combination of Langmuir-Blodgett (LB) and atomic force microscopy (AFM) techniques. Based on the regular solution theory, the miscibility and stability of the two components in the monolayer were analyzed in terms of compression modulusC_s"-1) , excess Gibbs free energy (δG"π_exc) , activity coefficients (γ), and interaction parameterζ. The results of this paper provide valuable insight into basic thermodynamics and nano structure of mixed DPPG/HD monolayers; it is helpful to understand the thermodynamic behavior of HD as spreading additive in LS monolayer with a view toward characterizing potential improvements to LS performance brought about by addition of HD to lung phospholipids

Evidence of indirect gap in monolayer WSe2

KAUST Repository

Hsu, Wei-Ting

2017-10-09

Monolayer transition metal dichalcogenides, such as MoS2 and WSe2, have been known as direct gap semiconductors and emerged as new optically active materials for novel device applications. Here we reexamine their direct gap properties by investigating the strain effects on the photoluminescence of monolayer MoS2 and WSe2. Instead of applying stress, we investigate the strain effects by imaging the direct exciton populations in monolayer WSe2–MoS2 and MoSe2–WSe2 lateral heterojunctions with inherent strain inhomogeneity. We find that unstrained monolayer WSe2 is actually an indirect gap material, as manifested in the observed photoluminescence intensity–energy correlation, from which the difference between the direct and indirect optical gaps can be extracted by analyzing the exciton thermal populations. Our findings combined with the estimated exciton binding energy further indicate that monolayer WSe2 exhibits an indirect quasiparticle gap, which has to be reconsidered in further studies for its fundamental properties and device applications.

Mixed monolayers of dipalmitoyl phosphatidylcholine and ethyl palmitate at the air/water interface

Energy Technology Data Exchange (ETDEWEB)

Gzyl, Barbara [Department of Physical Chemistry and Electrochemistry, Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Cracow (Poland)]. E-mail: gzyl@chemia.uj.edu.pl; Paluch, Maria [Department of Physical Chemistry and Electrochemistry, Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Cracow (Poland)

2005-06-30

The behaviour of monolayers containing dipalmitoyl phosphatidylcholine and ethyl palmitate and their mixtures at different molar fraction, using surface pressure-molecular area results, was investigated. The negative deviation from additivity of the mean molecular areas as a function of the mixture composition indicates the miscibility. The miscibility was confirmed by applying the two-dimensional phase rule, since the collapse pressure values vary with the composition of the mixtures. Also the free energy of mixing {delta}G{sub mix} and the excess free energy of mixing {delta}G{sub mix}{sup E} were determined. The negative values of {delta}G{sub mix} and {delta}G{sub mix}{sup E} indicate that the mixed monolayers are thermodynamically more stable compared to the pure ones and that the compounds in the two dimensional state experience mainly attractive interactions.

Multiphase, multicomponent phase behavior prediction

Science.gov (United States)

Dadmohammadi, Younas

Accurate prediction of phase behavior of fluid mixtures in the chemical industry is essential for designing and operating a multitude of processes. Reliable generalized predictions of phase equilibrium properties, such as pressure, temperature, and phase compositions offer an attractive alternative to costly and time consuming experimental measurements. The main purpose of this work was to assess the efficacy of recently generalized activity coefficient models based on binary experimental data to (a) predict binary and ternary vapor-liquid equilibrium systems, and (b) characterize liquid-liquid equilibrium systems. These studies were completed using a diverse binary VLE database consisting of 916 binary and 86 ternary systems involving 140 compounds belonging to 31 chemical classes. Specifically the following tasks were undertaken: First, a comprehensive assessment of the two common approaches (gamma-phi (gamma-ϕ) and phi-phi (ϕ-ϕ)) used for determining the phase behavior of vapor-liquid equilibrium systems is presented. Both the representation and predictive capabilities of these two approaches were examined, as delineated form internal and external consistency tests of 916 binary systems. For the purpose, the universal quasi-chemical (UNIQUAC) model and the Peng-Robinson (PR) equation of state (EOS) were used in this assessment. Second, the efficacy of recently developed generalized UNIQUAC and the nonrandom two-liquid (NRTL) for predicting multicomponent VLE systems were investigated. Third, the abilities of recently modified NRTL model (mNRTL2 and mNRTL1) to characterize liquid-liquid equilibria (LLE) phase conditions and attributes, including phase stability, miscibility, and consolute point coordinates, were assessed. The results of this work indicate that the ϕ-ϕ approach represents the binary VLE systems considered within three times the error of the gamma-ϕ approach. A similar trend was observed for the for the generalized model predictions using

Large-area and bright pulsed electroluminescence in monolayer semiconductors

KAUST Repository

Lien, Der-Hsien; Amani, Matin; Desai, Sujay B.; Ahn, Geun Ho; Han, Kevin; He, Jr-Hau; Ager, Joel W.; Wu, Ming C.; Javey, Ali

2018-01-01

Transition-metal dichalcogenide monolayers have naturally terminated surfaces and can exhibit a near-unity photoluminescence quantum yield in the presence of suitable defect passivation. To date, steady-state monolayer light-emitting devices suffer from Schottky contacts or require complex heterostructures. We demonstrate a transient-mode electroluminescent device based on transition-metal dichalcogenide monolayers (MoS, WS, MoSe, and WSe) to overcome these problems. Electroluminescence from this dopant-free two-terminal device is obtained by applying an AC voltage between the gate and the semiconductor. Notably, the electroluminescence intensity is weakly dependent on the Schottky barrier height or polarity of the contact. We fabricate a monolayer seven-segment display and achieve the first transparent and bright millimeter-scale light-emitting monolayer semiconductor device.

Large-area and bright pulsed electroluminescence in monolayer semiconductors

KAUST Repository

Lien, Der-Hsien

2018-04-04

Transition-metal dichalcogenide monolayers have naturally terminated surfaces and can exhibit a near-unity photoluminescence quantum yield in the presence of suitable defect passivation. To date, steady-state monolayer light-emitting devices suffer from Schottky contacts or require complex heterostructures. We demonstrate a transient-mode electroluminescent device based on transition-metal dichalcogenide monolayers (MoS, WS, MoSe, and WSe) to overcome these problems. Electroluminescence from this dopant-free two-terminal device is obtained by applying an AC voltage between the gate and the semiconductor. Notably, the electroluminescence intensity is weakly dependent on the Schottky barrier height or polarity of the contact. We fabricate a monolayer seven-segment display and achieve the first transparent and bright millimeter-scale light-emitting monolayer semiconductor device.

Protonation of octadecylamine Langmuir monolayer by adsorption of halide counterions

Science.gov (United States)

Sung, Woongmo; Avazbaeva, Zaure; Lee, Jonggwan; Kim, Doseok

Langmuir monolayer consisting of octadecylamine (C18H37NH2, ODA) was investigated by heterodyne vibrational sum-frequency generation (HD-VSFG) spectroscopy in conjunction with surface pressure-area (π- A) isotherm, and the result was compared with that from cationic-lipid (DPTAP) Langmuir monolayer. In case of ODA monolayer on pure water, both SF intensity of water OH band and the surface pressure were significantly smaller than those of the DPTAP monolayer implying that only small portion of the amine groups (-NH3+ is protonated in the monolayer. In the presence of sodium halides (NaCl and NaI) in the subphase water, it was found that the sign of Imχ (2) of water OH band remained the same as that of the ODA monolayer on pure water, but there was a substantial increase in the SF amplitude. From this, we propose that surface excess of the halide counterions (Cl- and I-) makes the solution condition near the ODA monolayer/water interface more acidic so that ODA molecules in the monolayer are more positively charged, which works to align the water dipoles at the interface.

Growth and time dependent alignment of KCl crystals in Hemoglobin LB monolayer

International Nuclear Information System (INIS)

Mahato, Mrityunjoy; Pal, Prabir; Tah, Bidisha; Kamilya, Tapanendu; Talapatra, G.B.

2012-01-01

Nature and organism often use the biomineralization technique to build up various highly regular structures such as bone, teeth, kidney stone etc., and recently this becomes the strategy to design and synthesis of novel biocomposite materials. We report here the controlled crystallization of KCl in Langmuir and Langmuir Blodgett (LB) monolayer of Hemoglobin (Hb) at ambient condition. The nucleation and growth of KCl crystals in Hb monolayer has temporal and KCl concentration dependency. The growth of KCl crystals in LB film of Hb has distinct behavior in the alignment of crystals from linear to fractal like structures depending on growth time. The crystallographic identity of the biomineralized KCl crystal is confirmed from HR-TEM, XRD, and from powder diffraction simulation. Our results substantiated that the template of Langmuir monolayer of proteins plays a crucial role in biomineralization as well as in designing and synthesizing of novel biocomposite materials. Highlights: ► Biomineralization of KCl crystal has been studied in Hemoglobin LB film. ► KCl crystal growth is time and concentration of KCl dependent. ► The alignment of KCl crystal growth is fractal nature with time. ► The unfolding of Hb and evaporation factor has some role in crystallization and fractal growth.

Self-assembled monolayers with different chemical group substrates for the study of MCF-7 breast cancer cell line behavior

International Nuclear Information System (INIS)

Yan, Hongji; Yin, Yanbin; Li, Yu; Tian, Weiming; Zhang, Song; Nie, Yongzhan; He, Jin; Wang, Xiumei; Cui, Fuzhai; Chen, Xiongbiao

2013-01-01

The interactions between cancer cells and the extracellular matrix (ECM) are important with respect to a number of cell behavoirs, yet remain unclear. In this study, self-assembled monolayers with different terminal chemical groups (hydroxyl (-OH), carboxyl (-COOH), animo (-NH 2 ), mercapto (-SH), and methyl (-CH 3 )) were employed as substrates for the culture of MCF-7 cells to examine effects on cell behavior. Cell spreading was investigated by scanning electron microscopy, tallin expression by immunofluorescence, proliferation rate by counting cell numbers, cell cycle by flow cytometry, metabolism by high-performance liquid chromatography and cell migration by live cell imaging. Annexin V-FITC (fluorescein isothiocyanate) and JC-1 assays were performed to determine cell apoptosis and mitochondrial membrane potential, respectively. Our results demonstrate the varied behaviors of MCF-7 cells in response to different chemical groups. Specifically, NH 2 and COOH terminal functional groups promote proliferation, the production of lactic acid and mobility of MCF-7 cells; SH and OH terminal groups enhance the expression and distribution of tallin but result in weak cell proliferation, metabolism, spreading and mobility. These results are meaningful for uncovering the interactions between the ECM and cancer cells; they are potentially useful for designing novel cancer treatment strategies. (paper)

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

NARCIS (Netherlands)

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

2007-01-01

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

Adsorption of alkali, alkaline-earth, simple and 3d transition metal, and nonmetal atoms on monolayer MoS{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Li, X. D.; Fang, Y. M.; Wu, S. Q., E-mail: zzhu@xmu.edu.cn, E-mail: wsq@xmu.edu.cn [Department of Physics and Institute of Theoretical Physics and Astrophysics, Xiamen University, Xiamen 361005 (China); Zhu, Z. Z., E-mail: zzhu@xmu.edu.cn, E-mail: wsq@xmu.edu.cn [Department of Physics and Institute of Theoretical Physics and Astrophysics, Xiamen University, Xiamen 361005 (China); Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, Xiamen 361005 (China)

2015-05-15

Single adsorption of different atoms on pristine two-dimensional monolayer MoS{sub 2} have been systematically investigated by using density functional calculations with van der Waals correction. The adatoms cover alkali metals, alkaline earth metals, main group metal, 3d-transition metals, coinage metal and nonmetal atoms. Depending on the adatom type, metallic, semimetallic or semiconducting behavior can be found in direct bandgap monolayer MoS{sub 2}. Additionally, local or long-range magnetic moments of two-dimensional MoS{sub 2} sheet can also attained through the adsorption. The detailed atomic-scale knowledge of single adsorption on MoS{sub 2} monolayer is important not only for the sake of a theoretical understanding, but also device level deposition technological application.

Packing stress reduction in polymer-lipid monolayers at the air-water interface: An X-ray grazing-incidence diffraction and reflectivity study

Energy Technology Data Exchange (ETDEWEB)

Kuhl, T.L.; Majewski, J.; Howes, P.B.; Kjaer, K.; Nahmen, A. von; Lee, K.Y.C.; Ocko, B.; Israelachvili, J.N.; Smith, G.S.

1999-08-25

Using synchrotron grazing-incidence X-ray diffraction (GIXD) and reflectivity (XR), the authors have determined the in-plane and out-of-plane structure of phospholipid monolayers at the air-water interface as a function of hydrophilic lipid headgroup size. Di-stearoyl-phosphatidyl-ethanolamine (DSPE) lipid monolayers were systematically modified by chemically grafting hydrophilic poly(ethylene glycol) (PEG) chains of MW = 90 g/mol (2 ethylene oxide, EO, units), MW = 350 g/mol (8 EO units), and MW = 750 g/mol (17 EO units) to the lipid headgroups. The monolayers were studied in the solid phase at a surface pressure of 42 mN/m. At these high lipid packing densities, the PEG chains are submerged in the water subphase. The increased packing stresses from these bulky polymer headgroups distort the unit cell and the in-plane packing modes of the monolayers, leading to large out-of-plane alterations and staggering of the lipid molecules. Surprisingly, a change in the molecular packing of the monolayer toward higher packing densities (lower area per molecule) was observed on increasing the PEG MW to 750 g/mol (17 EO units). This rearrangement of the monolayer structure may be due to a conformational change in the PEG chains.

Integrated circuits based on conjugated polymer monolayer.

Science.gov (United States)

Li, Mengmeng; Mangalore, Deepthi Kamath; Zhao, Jingbo; Carpenter, Joshua H; Yan, Hongping; Ade, Harald; Yan, He; Müllen, Klaus; Blom, Paul W M; Pisula, Wojciech; de Leeuw, Dago M; Asadi, Kamal

2018-01-31

It is still a great challenge to fabricate conjugated polymer monolayer field-effect transistors (PoM-FETs) due to intricate crystallization and film formation of conjugated polymers. Here we demonstrate PoM-FETs based on a single monolayer of a conjugated polymer. The resulting PoM-FETs are highly reproducible and exhibit charge carrier mobilities reaching 3 cm 2  V -1  s -1 . The high performance is attributed to the strong interactions of the polymer chains present already in solution leading to pronounced edge-on packing and well-defined microstructure in the monolayer. The high reproducibility enables the integration of discrete unipolar PoM-FETs into inverters and ring oscillators. Real logic functionality has been demonstrated by constructing a 15-bit code generator in which hundreds of self-assembled PoM-FETs are addressed simultaneously. Our results provide the state-of-the-art example of integrated circuits based on a conjugated polymer monolayer, opening prospective pathways for bottom-up organic electronics.

Tracing the 4000 year history of organic thin films: From monolayers on liquids to multilayers on solids

Energy Technology Data Exchange (ETDEWEB)

Greene, J. E. [University of Illinois, Urbana, Illinois 61801 (United States); Linköping University, 581 83 Linköping (Sweden); National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China)

2015-03-15

The recorded history of organic monolayer and multilayer thin films spans approximately 4000 years. Fatty-acid-based monolayers were deposited on water by the ancients for applications ranging from fortune telling in King Hammurabi's time (∼1800 BC, Mesopotamia) to stilling choppy waters for sailors and divers as reported by the Roman philosopher Pliny the Elder in ∼78 AD, and then much later (1774) by the peripatetic American statesman and natural philosopher Benjamin Franklin, to Japanese “floating-ink” art (suminagashi) developed ∼1000 years ago. The modern science of organic monolayers began in the late-1800s/early-1900s with experiments by Lord Rayleigh and the important development by Agnes Pockels, followed two decades later by Irving Langmuir, of the tools and technology to measure the surface tension of liquids, the surface pressure of organic monolayers deposited on water, interfacial properties, molecular conformation of the organic layers, and phase transitions which occur upon compressing the monolayers. In 1935, Katherine Blodgett published a landmark paper showing that multilayers can be synthesized on solid substrates, with controlled thickness and composition, using an apparatus now known as the Langmuir-Blodgett (L-B) trough. A disadvantage of LB films for some applications is that they form weak physisorbed bonds to the substrate. In 1946, Bigelow, Pickett, and Zisman demonstrated, in another seminal paper, the growth of organic self-assembled monolayers (SAMs) via spontaneous adsorption from solution, rather than from the water/air interface, onto SiO{sub 2} and metal substrates. SAMs are close-packed two-dimensional organic crystals which exhibit strong covalent bonding to the substrate. The first multicomponent adsorbed monolayers and multilayer SAMs were produced in the early 1980s. Langmuir monolayers, L-B multilayers, and self-assembled mono- and multilayers have found an extraordinarily broad range of applications including

Tracing the 4000 year history of organic thin films: From monolayers on liquids to multilayers on solids

International Nuclear Information System (INIS)

Greene, J. E.

2015-01-01

The recorded history of organic monolayer and multilayer thin films spans approximately 4000 years. Fatty-acid-based monolayers were deposited on water by the ancients for applications ranging from fortune telling in King Hammurabi's time (∼1800 BC, Mesopotamia) to stilling choppy waters for sailors and divers as reported by the Roman philosopher Pliny the Elder in ∼78 AD, and then much later (1774) by the peripatetic American statesman and natural philosopher Benjamin Franklin, to Japanese “floating-ink” art (suminagashi) developed ∼1000 years ago. The modern science of organic monolayers began in the late-1800s/early-1900s with experiments by Lord Rayleigh and the important development by Agnes Pockels, followed two decades later by Irving Langmuir, of the tools and technology to measure the surface tension of liquids, the surface pressure of organic monolayers deposited on water, interfacial properties, molecular conformation of the organic layers, and phase transitions which occur upon compressing the monolayers. In 1935, Katherine Blodgett published a landmark paper showing that multilayers can be synthesized on solid substrates, with controlled thickness and composition, using an apparatus now known as the Langmuir-Blodgett (L-B) trough. A disadvantage of LB films for some applications is that they form weak physisorbed bonds to the substrate. In 1946, Bigelow, Pickett, and Zisman demonstrated, in another seminal paper, the growth of organic self-assembled monolayers (SAMs) via spontaneous adsorption from solution, rather than from the water/air interface, onto SiO 2 and metal substrates. SAMs are close-packed two-dimensional organic crystals which exhibit strong covalent bonding to the substrate. The first multicomponent adsorbed monolayers and multilayer SAMs were produced in the early 1980s. Langmuir monolayers, L-B multilayers, and self-assembled mono- and multilayers have found an extraordinarily broad range of applications including

A MOLECULAR-DYNAMICS STUDY OF LECITHIN MONOLAYERS

NARCIS (Netherlands)

AHLSTROM, P; BERENDSEN, HJC

1993-01-01

Two monolayers of didecanoyllecithin at the air-water interface have been studied using molecular dynamics simulations. The model system consisted of two monolayers of 42 lecithin molecules each separated by a roughly 4 nm thick slab of SPC water. The area per lecithin molecule was 0.78 nm(2)

WSe2 Monolayer

KAUST Repository

Zhang, Shuai; Wang, Chen-Guang; Li, Ming-yang; Huang, Di; Li, Lain-Jong; Ji, Wei; Wu, Shiwei

2017-01-01

dichalcogenide materials, intrinsic defects in WSe2 arise surprisingly from single tungsten vacancies, leading to the hole (p-type) doping. Furthermore, we found these defects to dominate the excitonic emission of the WSe2 monolayer at low temperature. Our work

Orientational epitaxy in adsorbed monolayers

International Nuclear Information System (INIS)

Novaco, A.D.; McTague, J.P.

1977-01-01

The ground state for adsorbed monolayers on crystalline substrates is shown to involve a definite relative orientation of the substrate and adsorbate crystal axes, even when the relative lattice parameters are incommensurate. The rotation angle which defines the structure of the monolayer-substrate system is determined by the competition between adsorbate-substrate and adsorbate-adsorbate energy terms, and is generally not a symmetry angle. Numerical predictions are presented for the rare gas-graphite systems, whose interaction potentials are rather well known. Recent LEED data for some of these systems appear to corroborate these predictions

A low voltage programmable unipolar inverter with a gold nanoparticle monolayer on plastic.

Science.gov (United States)

Zhou, Ye; Han, Su-Ting; Huang, Long-Biao; Huang, Jing; Yan, Yan; Zhou, Li; Roy, V A L

2013-05-24

A programmable low voltage unipolar inverter with saturated-load configuration has been demonstrated on a plastic substrate. A self-assembled monolayer of gold (Au) nanoparticles was inserted into the dielectric layer acting as a charge trapping layer. The inverter operated well with supply voltages of inverter. Furthermore, the programmable behavior was maintained well at various bending states, demonstrating the adequate flexibility of our devices.

Theoretical potential for low energy consumption phase change memory utilizing electrostatically-induced structural phase transitions in 2D materials

Science.gov (United States)

Rehn, Daniel A.; Li, Yao; Pop, Eric; Reed, Evan J.

2018-01-01

Structural phase-change materials are of great importance for applications in information storage devices. Thermally driven structural phase transitions are employed in phase-change memory to achieve lower programming voltages and potentially lower energy consumption than mainstream nonvolatile memory technologies. However, the waste heat generated by such thermal mechanisms is often not optimized, and could present a limiting factor to widespread use. The potential for electrostatically driven structural phase transitions has recently been predicted and subsequently reported in some two-dimensional materials, providing an athermal mechanism to dynamically control properties of these materials in a nonvolatile fashion while achieving potentially lower energy consumption. In this work, we employ DFT-based calculations to make theoretical comparisons of the energy required to drive electrostatically-induced and thermally-induced phase transitions. Determining theoretical limits in monolayer MoTe2 and thin films of Ge2Sb2Te5, we find that the energy consumption per unit volume of the electrostatically driven phase transition in monolayer MoTe2 at room temperature is 9% of the adiabatic lower limit of the thermally driven phase transition in Ge2Sb2Te5. Furthermore, experimentally reported phase change energy consumption of Ge2Sb2Te5 is 100-10,000 times larger than the adiabatic lower limit due to waste heat flow out of the material, leaving the possibility for energy consumption in monolayer MoTe2-based devices to be orders of magnitude smaller than Ge2Sb2Te5-based devices.

Subcellular topological effect of particle monolayers on cell shapes and functions.

Science.gov (United States)

Miura, Manabu; Fujimoto, Keiji

2006-12-01

We studied topological effects of subcellular roughness displayed by a closely packed particle monolayer on adhesion and growth of endothelial cells. Poly(styrene-co-acrylamide) (SA) particles were prepared by soap-free emulsion copolymerization. Particle monolayers were prepared by Langmuir-Blodgett deposition using particles, which were 527 (SA053) and 1270 nm (SA127) in diameter. After 24-h incubation, cells tightly adhered on a tissue culture polystyrene dish and randomly spread. On the other hand, cells attached on particle monolayers were stretched into a narrow stalk-like shape. Lamellipodia spread from the leading edge of cells attached on SA053 monolayer to the top of the particles and gradually gathered to form clusters. This shows that cell-cell adhesion became stronger than cell-substrate interaction. Cells attached to SA127 monolayer extended to the reverse side of a particle monolayer and engulfed particles. They remained immobile without migration 24h after incubation. This shows that the inhibition of extensions on SA127 monolayer could inhibit cell migration and cell proliferation. Cell growth on the particle monolayers was suppressed compared with a flat TCPS dish. The number of cells on SA053 gradually increased, whereas that on SA127 decreased with time. When the cell seeding density was increased to 200,000 cells cm(-2), some adherent cells gradually became into contact with adjacent cells. F-actin condensations were formed at the frame of adherent cells and the thin filaments grew from the edges to connect each other with time. For the cell culture on SA053 monolayer, elongated cells showed a little alignment. Cells showed not arrangement of actin stress fibers but F-actin condensation at the contact regions with neighboring cells. Interestingly, the formed cell monolayer could be readily peeled from the particle monolayer. These results indicate that endothelial cells could recognize the surface roughness displayed by particle monolayers and

Molecular printboards: monolayers of beta-cyclodextrins on silicon oxide surfaces.

Science.gov (United States)

Onclin, Steffen; Mulder, Alart; Huskens, Jurriaan; Ravoo, Bart Jan; Reinhoudt, David N

2004-06-22

Monolayers of beta-cyclodextrin host molecules have been prepared on SiO2 surfaces. An ordered and stable cyano-terminated monolayer was modified in three consecutive surface reactions. First, the cyanide groups were reduced to their corresponding free amines using Red Al as a reducing agent. Second, 1,4-phenylene diisothiocyanate was used to react with the amine monolayer where it acts as a linking molecule, exposing isothiocyanates that can be derivatized further. Finally, per-6-amino beta-cyclodextrin was reacted with these isothiocyanate functions to yield a monolayer exposing beta-cyclodextrin. All monolayers were characterized by contact angle measurements, ellipsometric thickness measurements, Brewster angle Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry, which indicate the formation of a densely packed cyclodextrin surface. It was demonstrated that the beta-cyclodextrin monolayer could bind suitable guest molecules in a reversible manner. A fluorescent molecule (1), equipped with two adamantyl groups for complexation, was adsorbed onto the host monolayer from solution to form a monolayer of guest molecules. Subsequently, the guest molecules were desorbed from the surface by competition with increasing beta-cyclodextrin concentration in solution. The data were fitted using a model. An intrinsic binding constant of 3.3 +/- 1 x 10(5) M(-1) was obtained, which corresponds well to previously obtained results with a divalent guest molecule on beta-cyclodextrin monolayers on gold. In addition, the number of guest molecules bound to the host surface was determined, and a surface coverage of ca. 30% was found.

Metal ion interaction with phosphorylated tyrosine analogue monolayers on gold.

Science.gov (United States)

Petoral, Rodrigo M; Björefors, Fredrik; Uvdal, Kajsa

2006-11-23

Phosphorylated tyrosine analogue molecules (pTyr-PT) were assembled onto gold substrates, and the resulting monolayers were used for metal ion interaction studies. The monolayers were characterized by X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRAS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), both prior to and after exposure to metal ions. XPS verified the elemental composition of the molecular adsorbate and the presence of metal ions coordinated to the phosphate groups. Both the angle-dependent XPS and IRAS results were consistent with the change in the structural orientation of the pTyr-PT monolayer upon exposure to metal ions. The differential capacitance of the monolayers upon coordination of the metal ions was evaluated using EIS. These metal ions were found to significantly change the capacitance of the pTyr-PT monolayers in contrast to the nonphosphorylated tyrosine analogue (TPT). CV results showed reduced electrochemical blocking capabilities of the phosphorylated analogue monolayer when exposed to metal ions, supporting the change in the structure of the monolayer observed by XPS and IRAS. The largest change in the structure and interfacial capacitance was observed for aluminum ions, compared to calcium, magnesium, and chromium ions. This type of monolayer shows an excellent capability to coordinate metal ions and has a high potential for use as sensing layers in biochip applications to monitor the presence of metal ions.

The role of terminations and coordination atoms on the pseudocapacitance of titanium carbonitride monolayers.

Science.gov (United States)

Zhang, Wenqiang; Cheng, Chuan; Fang, Peilin; Tang, Bin; Zhang, Jindou; Huang, Guoming; Cong, Xin; Zhang, Bao; Ji, Xiao; Miao, Ling

2016-02-14

Nowadays, MXenes have received extensive concern as a prominent electrode material of electrochemical capacitors. As two important factors to the capacitance, the influence of the intrinsical terminations (F, O and OH) and coordination atoms (C and N) is investigated using first-principles calculations. According to the density of states aligned with the standard hydrogen electrode, it turns out that a Ti3CNO2 monolayer is proven to show an obvious pseudocapacitive behavior, while the bare, F and OH terminated Ti3CN monolayers may only present electrochemical double layer characters in an aqueous electrolyte. Moreover, the illustration of molecular orbitals over the Fermi level are mainly contributed by the d-orbitals of Ti atoms coordinated with O and N atoms, indicating that the redox pseudocapacitance of the Ti3CNO2 monolayer is promoted by the coordination N atoms. Then the superiority of N bonded Ti atoms in accepting charges can be visualized through the charge population. Further, the larger ratio of C/N in the coordination environment of Ti atoms indicates that more electrons can be stored. Our investigation can give an instructional advice in the MXenes-electrode production.

High-efficiency omnidirectional photoresponses based on monolayer lateral p–n heterojunctions

KAUST Repository

Tsai, Meng-Lin

2016-10-28

Electrical and optical properties of lateral monolayer WSe2–MoS2 p–n heterojunctions were characterized to demonstrate a high responsivity of 0.26 A W−1 with an excellent omnidirectional photodetection capability. The heterojunction functioning as a diode exhibits a prominent gate-tuning behavior with an ideality factor of 1.25. In addition, ultrafast photoresponse, low-light detectability, and high-temperature operation have been achieved. These unique characteristics pave a way for the future development of sub-nano semiconductor devices.

A pentacene monolayer trapped between graphene and a substrate.

Science.gov (United States)

Zhang, Qicheng; Peng, Boyu; Chan, Paddy Kwok Leung; Luo, Zhengtang

2015-09-21

A self-assembled pentacene monolayer can be fabricated between the solid-solid interface of few-layered graphene (FLG) and the mica substrate, through a diffusion-spreading method. By utilizing a transfer method that allows us to sandwich pentacene between graphene and mica, followed by controlled annealing, we enabled the diffused pentacene to be trapped in the interfaces and led to the formation of a stable monolayer. We found that the formation of a monolayer is kinetically favored by using a 2D Ising lattice gas model for pentacene trapped between the graphene-substrate interfaces. This kinetic Monte Carlo simulation results indicate that, due to the graphene substrate enclosure, the spreading of the first layer proceeds faster than the second layer, as the kinetics favors the filling of voids by molecules from the second layer. This graphene assisted monolayer assembly method provides a new avenue for the fabrication of two-dimensional monolayer structures.

Surface-segregated monolayers: a new type of ordered monolayer for surface modification of organic semiconductors.

Science.gov (United States)

Wei, Qingshuo; Tajima, Keisuke; Tong, Yujin; Ye, Shen; Hashimoto, Kazuhito

2009-12-09

We report a new type of ordered monolayer for the surface modification of organic semiconductors. Fullerene derivatives with fluorocarbon chains ([6,6]-phenyl-C(61)-buryric acid 1H,1H-perfluoro-1-alkyl ester or FC(n)) spontaneously segregated as a monolayer on the surface of a [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) film during a spin-coating process from the mixture solutions, as confirmed by X-ray photoelectron spectroscopy (XPS). Ultraviolet photoelectron spectroscopy (UPS) showed the shift of ionization potentials (IPs) depending on the fluorocarbon chain length, indicating the formation of surface dipole moments. Surface-sensitive vibrational spectroscopy, sum frequency generation (SFG) revealed the ordered molecular orientations of the C(60) moiety in the surface FC(n) layers. The intensity of the SFG signals from FC(n) on the surface showed a clear odd-even effect when the length of the fluorocarbon chain was changed. This new concept of the surface-segregated monolayer provides a facile and versatile approach to modifying the surface of organic semiconductors and is applicable to various organic optoelectronic devices.

Density determination of langmuir-blodgett monolayer films using x-ray reflectivity technique

International Nuclear Information System (INIS)

Damar Yoga Kusuma

2015-01-01

Monolayer deposition by Langmuir-Blodgett technique produces monolayer films that are uniform with controllable thickness down to nanometer scale. To evaluate the quality of the monolayer deposition, X-ray reflectivity technique are employed to monitor the monolayers density. Langmuir-Blodgett monolayer with good coverage and uniformity results in film density close to its macroscopic film counterpart whereas films with presence of air gaps shows lower density compared to its macroscopic film counterpart. (author)

Nonlinear optical characteristics of monolayer MoSe{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Le, Chinh Tam; Ullah, Farman; Senthilkumar, Velusamy; Kim, Yong Soo [Department of Physics and Energy Harvest Storage Research Center, University of Ulsan (Korea, Republic of); Clark, Daniel J.; Jang, Joon I. [Department of Physics, Applied Physics and Astronomy, Binghamton University, Binghamton, NY (United States); Sim, Yumin; Seong, Maeng-Je [Department of Physics, Chung-Ang University, Seoul (Korea, Republic of); Chung, Koo-Hyun [School of Mechanical Engineering, University of Ulsan (Korea, Republic of); Park, Hyoyeol [Electronics, Communication and Semiconductor Applications Department, Ulsan College (Korea, Republic of)

2016-08-15

In this study, we utilized picosecond pulses from an Nd:YAG laser to investigate the nonlinear optical characteristics of monolayer MoSe{sub 2}. Two-step growth involving the selenization of pulsed-laser-deposited MoO{sub 3} film was employed to yield the MoSe{sub 2} monolayer on a SiO{sub 2}/Si substrate. Raman scattering, photoluminescence (PL) spectroscopy, and atomic force microscopy verified the high optical quality of the monolayer. The second-order susceptibility χ{sup (2)} was calculated to be ∝50 pm V{sup -1} at the second harmonic wavelength λ{sub SHG} ∝810 nm, which is near the optical gap of the monolayer. Interestingly, our wavelength-dependent second harmonic scan can identify the bound excitonic states including negatively charged excitons much more efficiently, compared with the PL method at room temperature. Additionally, the MoSe{sub 2} monolayer exhibits a strong laser-induced damage threshold ∝16 GW cm{sup -2} under picosecond-pulse excitation{sub .} Our findings suggest that monolayer MoSe{sub 2} can be considered as a promising candidate for high-power, thin-film-based nonlinear optical devices and applications. (copyright 2016 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Reversed-phase thin-layer chromatography behavior of aldopentose derivatives

Directory of Open Access Journals (Sweden)

Malbaša Radomir V.

2012-01-01

Full Text Available Quantitative structure-retention relationships (QSRR have been used to study the chromatographic behavior of some aldopentose. The behavior of aldopentose derivatives was investigated by means of the reversed-phase thin-layer chromatography (RP TLC on the silica gel impregnated with paraffin oil stationary phases. Binary mixtures of methanol-water, acetone-water and dioxane-water were used as mobile phases. Retention factors, RM0, corresponding to zero percent organic modifier in the aqueous mobile phase was determined. Lipophilicity C0 was calculated as the ratio of the intercept and slope values. There was satisfactory correlation between them and log P values calculated using different theoretical procedures. Some of these correlations offer very good predicting models, which are important for a better understanding of the relationships between chemical structure and retention. The study showed that the hydrophobic parameters RM0 and C0 can be used as a measures of lipophilicity of investigated compounds.

Phase Behaviors of Reservoir Fluids with Capillary Eff ect Using Particle Swarm Optimization

KAUST Repository

Ma, Zhiwei

2013-05-06

The study of phase behavior is important for the oil and gas industry. Many approaches have been proposed and developed for phase behavior calculation. In this thesis, an alternative method is introduced to study the phase behavior by means of minimization of Helmholtz free energy. For a system at fixed volume, constant temperature and constant number of moles, the Helmholtz free energy reaches minimum at the equilibrium state. Based on this theory, a stochastic method called Particle Swarm Optimization (PSO) algorithm, is implemented to compute the phase diagrams for several pure component and mixture systems. After comparing with experimental and the classical PT-ash calculation, we found the phase diagrams obtained by minimization of the Helmholtz Free Energy approach match the experimental and theoretical diagrams very well. Capillary effect is also considered in this thesis because it has a significant influence on the phase behavior of reservoir fluids. In this part, we focus on computing the phase envelopes, which consists of bubble and dew point lines. Both fixed and calculated capillary pressure from the Young-Laplace equation cases are introduced to study their effects on phase envelopes. We found that the existence of capillary pressure will change the phase envelopes. Positive capillary pressure reduces the dew point and bubble point temperatures under the same pressure condition, while the negative capillary pressure increases the dew point and bubble point temperatures. In addition, the change of contact angle and pore radius will affect the phase envelope. The effect of the pore radius on the phase envelope is insignificant when the radius is very large. These results may become reference for future research and study. Keywords: Phase Behavior; Particle Swarm Optimization; Capillary Pressure; Reservoir Fluids; Phase Equilibrium; Phase Envelope.

Phase Behaviors of Reservoir Fluids with Capillary Eff ect Using Particle Swarm Optimization

KAUST Repository

Ma, Zhiwei

2013-01-01

The study of phase behavior is important for the oil and gas industry. Many approaches have been proposed and developed for phase behavior calculation. In this thesis, an alternative method is introduced to study the phase behavior by means of minimization of Helmholtz free energy. For a system at fixed volume, constant temperature and constant number of moles, the Helmholtz free energy reaches minimum at the equilibrium state. Based on this theory, a stochastic method called Particle Swarm Optimization (PSO) algorithm, is implemented to compute the phase diagrams for several pure component and mixture systems. After comparing with experimental and the classical PT-ash calculation, we found the phase diagrams obtained by minimization of the Helmholtz Free Energy approach match the experimental and theoretical diagrams very well. Capillary effect is also considered in this thesis because it has a significant influence on the phase behavior of reservoir fluids. In this part, we focus on computing the phase envelopes, which consists of bubble and dew point lines. Both fixed and calculated capillary pressure from the Young-Laplace equation cases are introduced to study their effects on phase envelopes. We found that the existence of capillary pressure will change the phase envelopes. Positive capillary pressure reduces the dew point and bubble point temperatures under the same pressure condition, while the negative capillary pressure increases the dew point and bubble point temperatures. In addition, the change of contact angle and pore radius will affect the phase envelope. The effect of the pore radius on the phase envelope is insignificant when the radius is very large. These results may become reference for future research and study. Keywords: Phase Behavior; Particle Swarm Optimization; Capillary Pressure; Reservoir Fluids; Phase Equilibrium; Phase Envelope.

Chaotic behavior in Casimir oscillators: A case study for phase-change materials.

Science.gov (United States)

Tajik, Fatemeh; Sedighi, Mehdi; Khorrami, Mohammad; Masoudi, Amir Ali; Palasantzas, George

2017-10-01

Casimir forces between material surfaces at close proximity of less than 200 nm can lead to increased chaotic behavior of actuating devices depending on the strength of the Casimir interaction. We investigate these phenomena for phase-change materials in torsional oscillators, where the amorphous to crystalline phase transitions lead to transitions between high and low Casimir force and torque states, respectively, without material compositions. For a conservative system bifurcation curve and Poincare maps analysis show the absence of chaotic behavior but with the crystalline phase (high force-torque state) favoring more unstable behavior and stiction. However, for a nonconservative system chaotic behavior can take place introducing significant risk for stiction, which is again more pronounced for the crystalline phase. The latter illustrates the more general scenario that stronger Casimir forces and torques increase the possibility for chaotic behavior. The latter is making it impossible to predict whether stiction or stable actuation will occur on a long-term basis, and it is setting limitations in the design of micronano devices operating at short-range nanoscale separations.

Unexpectedly normal phase behavior of single homopolymer chains

International Nuclear Information System (INIS)

Paul, W.; Strauch, T.; Rampf, F.; Binder, K.

2007-01-01

Employing Monte Carlo simulations, we show that the topology of the phase diagram of a single flexible homopolymer chain changes in dependence on the range of an attractive square well interaction between the monomers. For a range of attraction larger than a critical value, the equilibrium phase diagram of the single polymer chain and the corresponding polymer solution phase diagram exhibit vapor (swollen coil, dilute solution), liquid (collapsed globule, dense solution), and solid phases. Otherwise, the liquid-vapor transition vanishes from the equilibrium phase diagram for both the single chain and the polymer solution. This change in topology of the phase diagram resembles the behavior known for colloidal dispersions. The interplay of enthalpy and conformational entropy in the polymer case thus can lead to the same topology of phase diagrams as the interplay of enthalpy and translational entropy in simple liquids

Formation of Bimolecular Membranes from Lipid Monolayers and a Study of Their Electrical Properties

Science.gov (United States)

Montal, M.; Mueller, P.

1972-01-01

Bimolecular membranes are formed from two lipid monolayers at an air-water interface by the apposition of their hydrocarbon chains when an aperture in a Teflon partition separating two aqueous phases is lowered through the interface. Formation of the membrane is monitored by an increase of the electrical capacity, as measured with a voltage clamp. Electrical resistance of the unmodified membrane is analogous to that of conventional planar bilayers (black lipid membranes) prepared in the presence of a hydrocarbon solvent, i.e., 106-108 ohm cm2; the resistance can be lowered to values of 103 ohm cm2 by gramicidin, an antibiotic that modifies the conductance only when the membranes are of biomolecular thickness. In contrast to the resistance, there is a significant difference between the capacity of bilayers made from mono-layers and that of hydrocarbon-containing bilayers made by phase transition; the average values are 0.9 and 0.45 μF cm-2, respectively. The value of 0.9 μF cm-2 approximates that of biological membranes. Assuming a dielectric constant of 2.1 for the hydrocarbon region, the dielectric thickness, as calculated from a capacity of 0.9 μF cm-2, is 22 Å. This value is 6-10 Å smaller than the actual thickness of the hydrocarbon region of bilayers and cell membranes, as determined by x-ray diffraction. The difference may be due to a limited penetration of water into the hydrocarbon region near the ester groups that would lower the electrical resistance of this region and reduce the dielectric thickness. Asymmetric membranes have been formed by adjoining two lipid monolayers of different chemical composition. Images PMID:4509315

Reaction of a phospholipid monolayer with gas-phase ozone at the air-water interface: measurement of surface excess and surface pressure in real time.

Science.gov (United States)

Thompson, Katherine C; Rennie, Adrian R; King, Martin D; Hardman, Samantha J O; Lucas, Claire O M; Pfrang, Christian; Hughes, Brian R; Hughes, Arwel V

2010-11-16

The reaction between gas-phase ozone and monolayers of the unsaturated lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, on aqueous solutions has been studied in real time using neutron reflection and surface pressure measurements. The reaction between ozone and lung surfactant, which contains POPC, leads to decreased pulmonary function, but little is known about the changes that occur to the interfacial material as a result of oxidation. The results reveal that the initial reaction of ozone with POPC leads to a rapid increase in surface pressure followed by a slow decrease to very low values. The neutron reflection measurements, performed on an isotopologue of POPC with a selectively deuterated palmitoyl strand, reveal that the reaction leads to loss of this strand from the air-water interface, suggesting either solubilization of the product lipid or degradation of the palmitoyl strand by a reactive species. Reactions of (1)H-POPC on D(2)O reveal that the headgroup region of the lipids in aqueous solution is not dramatically perturbed by the reaction of POPC monolayers with ozone supporting degradation of the palmitoyl strand rather than solubilization. The results are consistent with the reaction of ozone with the oleoyl strand of POPC at the air-water interface leading to the formation of OH radicals. The highly reactive OH radicals produced can then go on to react with the saturated palmitoyl strands leading to the formation of oxidized lipids with shorter alkyl tails.

Advanced chemistry of monolayers at interfaces trends in methodology and technology

CERN Document Server

Imae, Toyoko

2007-01-01

Advanced Chemistry of Monolayers at Interfaces describes the advanced chemistry of monolayers at interfaces. Focusing on the recent trends of methodology and technology, which are indispensable in monolayer science. They are applied to monolayers of surfactants, amphiphiles, polymers, dendrimers, enzymes, and proteins, which serve many uses.Introduces the methodologies of scanning probe microscopy, surface force instrumentation, surface spectroscopy, surface plasmon optics, reflectometry, and near-field scanning optical microscopy. Modern interface reaction method, lithographic tech

Pressure-dependent optical and vibrational properties of monolayer molybdenum disulfide

KAUST Repository

Nayak, Avinash P.; Pandey, Tribhuwan; Voiry, Damien; Liu, Jin; Moran, Samuel T.; Sharma, Ankit; Tan, Cheng; Chen, Changhsiao; Li, Lain-Jong; Chhowalla, Manish U.; Lin, Jungfu; Singh, Abhishek Kumar; Akinwande, Deji

2015-01-01

vibrational dynamics of the distorted monolayer 1T-MoS2 (1T′) and the monolayer 2H-MoS2 via a diamond anvil cell (DAC) and density functional theory (DFT) calculations. The direct optical band gap of the monolayer 2H-MoS2 increases by 11.7% from 1.85 to 2.08 e

Graphene Oxide Monolayer as a Compatibilizer at the Polymer-Polymer Interface for Stabilizing Polymer Bilayer Films against Dewetting.

Science.gov (United States)

Kim, Tae-Ho; Kim, Hyeri; Choi, Ki-In; Yoo, Jeseung; Seo, Young-Soo; Lee, Jeong-Soo; Koo, Jaseung

2016-12-06

We investigate the effect of adding graphene oxide (GO) sheets at the polymer-polymer interface on the dewetting dynamics and compatibility of immiscible polymer bilayer films. GO monolayers are deposited at the poly(methyl methacrylate) (PMMA)-polystyrene (PS) interface by the Langmuir-Schaefer technique. GO monolayers are found to significantly inhibit the dewetting behavior of both PMMA films (on PS substrates) and PS films (on PMMA substrates). This can be interpreted in terms of an interfacial interaction between the GO sheets and these polymers, which is evidenced by the reduced contact angle of the dewet droplets. The favorable interaction of GO with both PS and PMMA facilitates compatibilization of the immiscible polymer bilayer films, thereby stabilizing their bilayer films against dewetting. This compatibilization effect is verified by neutron reflectivity measurements, which reveal that the addition of GO monolayers broadens the interface between PS and the deuterated PMMA films by 2.2 times over that of the bilayer in the absence of GO.

Enhanced piezoelectricity of monolayer phosphorene oxides: a theoretical study.

Science.gov (United States)

Yin, Huabing; Zheng, Guang-Ping; Gao, Jingwei; Wang, Yuanxu; Ma, Yuchen

2017-10-18

Two-dimensional (2D) piezoelectric materials have potential applications in miniaturized sensors and energy conversion devices. In this work, using first-principles simulations at different scales, we systematically study the electronic structures and piezoelectricity of a series of 2D monolayer phosphorene oxides (POs). Our calculations show that the monolayer POs have tunable band gaps along with remarkable piezoelectric properties. The calculated piezoelectric coefficient d 11 of 54 pm V -1 in POs is much larger than those of 2D transition metal dichalcogenide monolayers and the widely used bulk α-quartz and AlN, and almost reaches the level of the piezoelectric effect in recently discovered 2D GeS. Furthermore, two other considerable piezoelectric coefficients, i.e., d 31 and d 26 with values of -10 pm V -1 and 21 pm V -1 , respectively, are predicted in some monolayer POs. We also examine the correlation between the piezoelectric coefficients and energy stability. The enhancement of piezoelectricity for monolayer phosphorene by oxidation will broaden the applications of phosphorene and phosphorene derivatives in nano-sized electronic and piezotronic devices.

Phase-specific Surround suppression in Mouse Primary Visual Cortex Correlates with Figure Detection Behavior Based on Phase Discontinuity.

Science.gov (United States)

Li, Fengling; Jiang, Weiqian; Wang, Tian-Yi; Xie, Taorong; Yao, Haishan

2018-05-21

In the primary visual cortex (V1), neuronal responses to stimuli within the receptive field (RF) are modulated by stimuli in the RF surround. A common effect of surround modulation is surround suppression, which is dependent on the feature difference between stimuli within and surround the RF and is suggested to be involved in the perceptual phenomenon of figure-ground segregation. In this study, we examined the relationship between feature-specific surround suppression of V1 neurons and figure detection behavior based on figure-ground feature difference. We trained freely moving mice to perform a figure detection task using figure and ground gratings that differed in spatial phase. The performance of figure detection increased with the figure-ground phase difference, and was modulated by stimulus contrast. Electrophysiological recordings from V1 in head-fixed mice showed that the increase in phase difference between stimuli within and surround the RF caused a reduction in surround suppression, which was associated with an increase in V1 neural discrimination between stimuli with and without RF-surround phase difference. Consistent with the behavioral performance, the sensitivity of V1 neurons to RF-surround phase difference could be influenced by stimulus contrast. Furthermore, inhibiting V1 by optogenetically activating either parvalbumin (PV)- or somatostatin (SOM)-expressing inhibitory neurons both decreased the behavioral performance of figure detection. Thus, the phase-specific surround suppression in V1 represents a neural correlate of figure detection behavior based on figure-ground phase discontinuity. Copyright © 2018 IBRO. Published by Elsevier Ltd. All rights reserved.

Interaction of toremifene with dipalmitoyl-phosphatidyl-glycerol in monolayers at the air–water interface followed by fluorescence microscopy in Langmuir–Blodgett films

International Nuclear Information System (INIS)

Romão, Rute I.S.; Maçôas, Ermelinda; Martinho, José M.G.; Gonçalves da Silva, Amélia M.P.S.

2013-01-01

Langmuir monolayers of dipalmitoyl-phosphatidyl-glycerol (DPPG) containing toremifene (TOR), an antiestrogen drug derivative of tamoxifen, were prepared in order to study the interaction of the drug with the cell membrane. TOR is not surface active but it remains at the interface in DPPG rich monolayers anchored by electrostatic interaction with the anionic DPPG up to the equimolar composition. The fluidity of mixed monolayers increases up to the TOR mole fraction X TOR = 0.3, remaining practically invariant for higher compositions. Brewster angle microscopy shows that the TOR disturbs the DPPG organization and the liquid condensed (LC) domains of DPPG become undetectable for X TOR ≥ 0.4. Laser scanning confocal fluorescence microscopy images of the LB films doped with rhodamine B-piperazine amide dye confirm the progressive reduction in size of LC domains, from which TOR and rhodamine are excluded. The incorporation of TOR in DPPG monolayers up to the equimolar composition supports the formation of a TOR:DPPG complex (1:1) due to electrostatic interactions between the negatively charged polar groups of DPPG and protonated TOR. - Highlights: • Toremifene (TOR) in dipalmitoyl-phosphatidyl-glycerol (DPPG) monolayers • Electrostatic interactions between DPPG and TOR form a 1:1 complex. • TOR increases the fluidity of DPPG monolayers. • Incorporation of TOR in the fluid phase of DPPG followed by fluorescence imaging

Interaction of toremifene with dipalmitoyl-phosphatidyl-glycerol in monolayers at the air–water interface followed by fluorescence microscopy in Langmuir–Blodgett films

Energy Technology Data Exchange (ETDEWEB)

Romão, Rute I.S. [Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal); Maçôas, Ermelinda [Centro de Química-Física Molecular and IN — Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal); Martinho, José M.G. [Centro de Química-Física Molecular and IN — Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal); Departamento de Engenharia Química, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal); Gonçalves da Silva, Amélia M.P.S., E-mail: ameliags@ist.utl.pt [Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal); Departamento de Engenharia Química, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal)

2013-05-01

Langmuir monolayers of dipalmitoyl-phosphatidyl-glycerol (DPPG) containing toremifene (TOR), an antiestrogen drug derivative of tamoxifen, were prepared in order to study the interaction of the drug with the cell membrane. TOR is not surface active but it remains at the interface in DPPG rich monolayers anchored by electrostatic interaction with the anionic DPPG up to the equimolar composition. The fluidity of mixed monolayers increases up to the TOR mole fraction X{sub TOR} = 0.3, remaining practically invariant for higher compositions. Brewster angle microscopy shows that the TOR disturbs the DPPG organization and the liquid condensed (LC) domains of DPPG become undetectable for X{sub TOR} ≥ 0.4. Laser scanning confocal fluorescence microscopy images of the LB films doped with rhodamine B-piperazine amide dye confirm the progressive reduction in size of LC domains, from which TOR and rhodamine are excluded. The incorporation of TOR in DPPG monolayers up to the equimolar composition supports the formation of a TOR:DPPG complex (1:1) due to electrostatic interactions between the negatively charged polar groups of DPPG and protonated TOR. - Highlights: • Toremifene (TOR) in dipalmitoyl-phosphatidyl-glycerol (DPPG) monolayers • Electrostatic interactions between DPPG and TOR form a 1:1 complex. • TOR increases the fluidity of DPPG monolayers. • Incorporation of TOR in the fluid phase of DPPG followed by fluorescence imaging.

Exciton Binding Energy of Monolayer WS2

Science.gov (United States)

Zhu, Bairen; Chen, Xi; Cui, Xiaodong

2015-03-01

The optical properties of monolayer transition metal dichalcogenides (TMDC) feature prominent excitonic natures. Here we report an experimental approach to measuring the exciton binding energy of monolayer WS2 with linear differential transmission spectroscopy and two-photon photoluminescence excitation spectroscopy (TP-PLE). TP-PLE measurements show the exciton binding energy of 0.71 +/- 0.01 eV around K valley in the Brillouin zone.

An in situ study of the adsorption behavior of functionalized particles on selfassembled monolayers via different chemical interactions

NARCIS (Netherlands)

Ling, X.Y.; Malaquin, Laurent; Reinhoudt, David; Wolf, Heiko; Huskens, Jurriaan

2007-01-01

The formation of particle monolayers by convective assembly was studied in situ with three different kinds of particle-surface interactions: adsorption onto native surfaces, with additional electrostatic interactions, and with supramolecular host-guest interactions. In the first case

Study on Shale Adsorption Equation Based on Monolayer Adsorption, Multilayer Adsorption, and Capillary Condensation

Directory of Open Access Journals (Sweden)

Qing Chen

2017-01-01

Full Text Available Shale gas is an effective gas resource all over the world. The evaluation of pore structure plays a critical role in exploring shale gas efficiently. Nitrogen adsorption experiment is one of the significant approaches to analyze pore size structure of shale. Shale is extremely heterogeneous due to component diversity and structure complexity. Therefore, adsorption isotherms for homogeneous adsorbents and empirical isotherms may not apply to shale. The shape of adsorption-desorption curve indicates that nitrogen adsorption on shale includes monolayer adsorption, multilayer adsorption, and capillary condensation. Usually, Langmuir isotherm is a monolayer adsorption model for ideal interfaces; BET (Brunauer, Emmett, Teller adsorption isotherm is a multilayer adsorption model based on specific assumptions; Freundlich isotherm is an empirical equation widely applied in liquid phase adsorption. In this study, a new nitrogen adsorption isotherm is applied to simultaneously depict monolayer adsorption, multilayer adsorption, and capillary condensation, which provides more real and accurate representation of nitrogen adsorption on shale. In addition, parameters are discussed in relation to heat of adsorption which is relevant to the shape of the adsorption isotherm curve. The curve fitting results indicate that our new nitrogen adsorption isotherm can appropriately describe the whole process of nitrogen adsorption on shale.

Defect-Mediated Lithium Adsorption and Diffusion on Monolayer Molybdenum Disulfide.

Science.gov (United States)

Sun, Xiaoli; Wang, Zhiguo; Fu, Y Q

2015-12-22

Monolayer Molybdenum Disulfide (MoS2) is a promising anode material for lithium ion batteries because of its high capacities. In this work, first principle calculations based on spin density functional theory were performed to investigate adsorption and diffusion of lithium on monolayer MoS2 with defects, such as single- and few-atom vacancies, antisite, and grain boundary. The values of adsorption energies on the monolayer MoS2 with the defects were increased compared to those on the pristine MoS2. The presence of defects causes that the Li is strongly bound to the monolayer MoS2 with adsorption energies in the range between 2.81 and 3.80 eV. The donation of Li 2s electron to the defects causes an enhancement of adsorption of Li on the monolayer MoS2. At the same time, the presence of defects does not apparently affect the diffusion of Li, and the energy barriers are in the range of 0.25-0.42 eV. The presence of the defects can enhance the energy storage capacity, suggesting that the monolayer MoS2 with defects is a suitable anode material for the Li-ion batteries.

The Phase Behavior of γ-Oryzanol and β-Sitosterol in Edible Oil.

Science.gov (United States)

Sawalha, Hassan; Venema, Paul; Bot, Arjen; Flöter, Eckhard; Adel, Ruud den; van der Linden, Erik

The phase behavior of binary mixtures of γ-oryzanol and β-sitosterol and ternary mixtures of γ-oryzanol and β-sitosterol in sunflower oil was studied. Binary mixtures of γ-oryzanol and β-sitosterol show double-eutectic behavior. Complex phase behavior with two intermediate mixed solid phases was derived from differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) data, in which a compound that consists of γ-oryzanol and β-sitosterol molecules at a specific ratio can be formed. SAXS shows that the organization of γ-oryzanol and β-sitosterol in the mixed phases is different from the structure of tubules in ternary systems. Ternary mixtures including sunflower oil do not show a sudden structural transition from the compound to a tubule, but a gradual transition occurs as γ-oryzanol and β-sitosterol are diluted in edible oil. The same behavior is observed when melting binary mixtures of γ-oryzanol and β-sitosterol at higher temperatures. This indicates the feasibility of having an organogelling agent in dynamic exchange between solid and liquid phase, which is an essential feature of triglyceride networks.

Molecular dynamics of contact behavior of self-assembled monolayers on gold using nanoindentation

Energy Technology Data Exchange (ETDEWEB)

Fang, Te-Hua [Institute of Mechanical and Electromechanical Engineering National Formosa University, Yunlin 632, Taiwan (China); Chang, Win-Jin, E-mail: changwj@mail.ksu.edu.tw [Department of Mechanical Engineering Kun Shan University, Tainan 710, Taiwan (China); Fan, Yu-Cheng [Institute of Mechanical and Electromechanical Engineering National Formosa University, Yunlin 632, Taiwan (China); Weng, Cheng-I [Department of Mechanical Engineering National Cheng Kung University, Tainan, 710, Taiwan (China)

2009-08-15

Molecular dynamics simulation is used to study nanoindentation of the self-assembled monolayers (SAMs) on an Au surface. The interaction of SAM atoms is described by a general universal force field (UFF), the tight-binding second-moment approximation (TB-SMA) is used for Au substrate, and the Lennard-Jones potential function is employed to describe interaction among the indenter, the SAMs, and the Au substrate atoms. The model consists of a planar Au substrate with n-hexadecanethiol SAM chemisorbed to the substrate. The simulation results show that the contact pressure increases as the SAMs temperature increases. In addition, the contact pressure also increases as the depth and velocity of indentation increase.

Molecular dynamics of contact behavior of self-assembled monolayers on gold using nanoindentation

International Nuclear Information System (INIS)

Fang, Te-Hua; Chang, Win-Jin; Fan, Yu-Cheng; Weng, Cheng-I

2009-01-01

Molecular dynamics simulation is used to study nanoindentation of the self-assembled monolayers (SAMs) on an Au surface. The interaction of SAM atoms is described by a general universal force field (UFF), the tight-binding second-moment approximation (TB-SMA) is used for Au substrate, and the Lennard-Jones potential function is employed to describe interaction among the indenter, the SAMs, and the Au substrate atoms. The model consists of a planar Au substrate with n-hexadecanethiol SAM chemisorbed to the substrate. The simulation results show that the contact pressure increases as the SAMs temperature increases. In addition, the contact pressure also increases as the depth and velocity of indentation increase.

Characterization of Bitumen Micro-Mechanical Behaviors Using AFM, Phase Dynamics Theory and MD Simulation

Directory of Open Access Journals (Sweden)

Yue Hou

2017-02-01

Full Text Available Fundamental understanding of micro-mechanical behaviors in bitumen, including phase separation, micro-friction, micro-abrasion, etc., can help the pavement engineers better understand the bitumen mechanical performances at macroscale. Recent researches show that the microstructure evolution in bitumen will directly affect its surface structure and micro-mechanical performance. In this study, the bitumen microstructure and micro-mechanical behaviors are studied using Atomic Force Microscopy (AFM experiments, Phase Dynamics Theory and Molecular Dynamics (MD Simulation. The AFM experiment results show that different phase-structure will occur at the surface of the bitumen samples under certain thermodynamic conditions at microscale. The phenomenon can be explained using the phase dynamics theory, where the effects of stability parameter and temperature on bitumen microstructure and micro-mechanical behavior are studied combined with MD Simulation. Simulation results show that the saturates phase, in contrast to the naphthene aromatics phase, plays a major role in bitumen micro-mechanical behavior. A high stress zone occurs at the interface between the saturates phase and the naphthene aromatics phase, which may form discontinuities that further affect the bitumen frictional performance.

Characterization of Bitumen Micro-Mechanical Behaviors Using AFM, Phase Dynamics Theory and MD Simulation.

Science.gov (United States)

Hou, Yue; Wang, Linbing; Wang, Dawei; Guo, Meng; Liu, Pengfei; Yu, Jianxin

2017-02-21

Fundamental understanding of micro-mechanical behaviors in bitumen, including phase separation, micro-friction, micro-abrasion, etc., can help the pavement engineers better understand the bitumen mechanical performances at macroscale. Recent researches show that the microstructure evolution in bitumen will directly affect its surface structure and micro-mechanical performance. In this study, the bitumen microstructure and micro-mechanical behaviors are studied using Atomic Force Microscopy (AFM) experiments, Phase Dynamics Theory and Molecular Dynamics (MD) Simulation. The AFM experiment results show that different phase-structure will occur at the surface of the bitumen samples under certain thermodynamic conditions at microscale. The phenomenon can be explained using the phase dynamics theory, where the effects of stability parameter and temperature on bitumen microstructure and micro-mechanical behavior are studied combined with MD Simulation. Simulation results show that the saturates phase, in contrast to the naphthene aromatics phase, plays a major role in bitumen micro-mechanical behavior. A high stress zone occurs at the interface between the saturates phase and the naphthene aromatics phase, which may form discontinuities that further affect the bitumen frictional performance.

Chain Stretching and Order-Disorder Transitions in Block Copolymer Monolayers and Multilayers

Science.gov (United States)

Kramer, Edward J.; Mishra, Vindhya; Stein, Gila E.; Sohn, Karen E.; Hur, Sumi; Fredrickson, Glenn H.; Cochran, Eric W.

2009-03-01

Both monolayers of block copolymer cylinders and spheres undergo order to disorder transitions (ODT) at temperatures well below those of the bulk. Monolayers of PS-b-P2VP cylinders undergo a ``nematic'' to ``isotropic'' transition at temperatures about 20 K below the bulk ODT while monolayers of PS-b-P2VP with P2VP spheres undergo a 2D crystal to hexatic transition at least 10 K below the bulk ODT. Bilayers of each structure disorder at temperatures well above that of the monolayers. While one is tempted to attribute all of the difference to the fact that ordered monolayers are quasi 2 dimensional while bilayers are not, an alternative explanation exists. In the cylinder monolayer the corona PS chains must stretch to fill a nearly square cross-section domain rather than a hexagonal one in the bulk, while the corona PS chains in a sphere monolayer must stretch to fill a hexagonal prism rather than an octahedron in the bulk. The more non-uniform stretching of the chains in the monolayer should increase its free energy and decrease its order-disorder temperature.

The interaction of insulin, glucose, and insulin-glucose mixtures with a phospholipid monolayer.

Science.gov (United States)

Shigenobu, Hayato; McNamee, Cathy E

2012-12-15

We determined how glucose or insulin interacts with a phospholipid monolayer at the air/water interface and explained these mechanisms from a physico-chemical point of view. The 1,2-dipalmitoyl-2-sn-glycero-3-phosphatidylcholine (DPPC) monolayer at an air/water interface acted as a model membrane, which allowed the effect of the molecular packing density in the monolayer on the interactions to be determined. The interaction of glucose, insulin, and a mixture of glucose and insulin to the DPPC monolayer were investigated via surface pressure-area per molecule Langmuir isotherms and fluorescence microscopy. Glucose adsorbed to the underside of the DPPC monolayer, while insulin was able to penetrate through the monolayer when the phospholipid molecules were not densely packed. The presence of a mixture of insulin and glucose affected the molecular packing in the DPPC monolayer differently than the pure insulin or glucose solutions, and the glucose-insulin mixture was seen to be able to penetrate through the monolayer. These results indicated that glucose and insulin interact with one another, giving a material that may then transported through a pore in the monolayer or through the spaces between the molecules of the monolayer. Copyright © 2012 Elsevier Inc. All rights reserved.

Complex band structures of transition metal dichalcogenide monolayers with spin–orbit coupling effects

International Nuclear Information System (INIS)

Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

2016-01-01

Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2 , where M   =  Mo, W; X   =  S, Se, Te) while including spin–orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed. (paper)

Complex band structures of transition metal dichalcogenide monolayers with spin-orbit coupling effects

Science.gov (United States)

Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

2016-09-01

Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2, where M  =  Mo, W; X  =  S, Se, Te) while including spin-orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed.

Nonlinear optical studies of organic monolayers

International Nuclear Information System (INIS)

Shen, Y.R.

1988-02-01

Second-order nonlinear optical effects are forbidden in a medium with inversion symmetry, but are necessarily allowed at a surface where the inversion summary is broken. They are often sufficiently strong so that a submonolayer perturbation of the surface can be readily detected. They can therefore be used as effective tools to study monolayers adsorbed at various interfaces. We discuss here a number of recent experiments in which optical second harmonic generation (SHG) and sum-frequency generation (SFG) are employed to probe and characterize organic monolayers. 15 refs., 5 figs

Unanticipated C=C bonds in covalent monolayers on silicon revealed by NEXAFS.

Science.gov (United States)

Lee, Michael V; Lee, Jonathan R I; Brehmer, Daniel E; Linford, Matthew R; Willey, Trevor M

2010-02-02

Interfaces are crucial to material properties. In the case of covalent organic monolayers on silicon, molecular structure at the interface controls the self-assembly of the monolayers, which in turn influences the optical properties and electrical transport. These properties intrinsically affect their application in biology, tribology, optics, and electronics. We use near-edge X-ray absorption fine structure spectroscopy to show that the most basic covalent monolayers formed from 1-alkenes on silicon retain a double bond in one-fifth to two-fifths of the resultant molecules. Unsaturation in the predominantly saturated monolayers will perturb the regular order and affect the dependent properties. The presence of unsaturation in monolayers produced by two different methods also prompts the re-evaluation of other radical-based mechanisms for forming covalent monolayers on silicon.

Emergence of complex chemistry on an organic monolayer.

Science.gov (United States)

Prins, Leonard J

2015-07-21

In many origin-of-life scenarios, inorganic materials, such as FeS or mineral clays, play an important role owing to their ability to concentrate and select small organic molecules on their surface and facilitate their chemical transformations into new molecules. However, considering that life is made up of organic matter, at a certain stage during the evolution the role of the inorganic material must have been taken over by organic molecules. How this exactly happened is unclear, and, indeed, a big gap separates the rudimentary level of organization involving inorganic materials and the complex organization of cells, which are the building blocks of life. Over the past years, we have extensively studied the interaction of small molecules with monolayer-protected gold nanoparticles (Au NPs) for the purpose of developing innovative sensing and catalytic systems. During the course of these studies, we realized that the functional role of this system is very similar to that typically attributed to inorganic surfaces in the early stages of life, with the important being difference that the functional properties (molecular recognition, catalysis, signaling, adaptation) originate entirely from the organic monolayer rather than the inorganic support. This led us to the proposition that this system may serve as a model that illustrates how the important role of inorganic surfaces in dictating chemical processes in the early stages of life may have been taken over by organic matter. Here, we reframe our previously obtained results in the context of the origin-of-life question. The following functional roles of Au NPs will be discussed: the ability to concentrate small molecules and create different local populations, the ability to catalyze the chemical transformation of bound molecules, and, finally, the ability to install rudimentary signaling pathways and display primitive adaptive behavior. In particular, we will show that many of the functional properties of the system

Tunable thermoelectricity in monolayers of MoS2 and other group-VI dichalcogenides

KAUST Repository

Tahir, M

2014-10-31

We study the thermoelectric properties of monolayers of MoS2 and other group-VI dichalcogenides under circularly polarized off-resonant light. Analytical expressions are derived for the Berry phase mediated magnetic moment, orbital magnetization, as well as thermal and Nernst conductivities. Tuning of the band gap by off-resonant light enhances the spin splitting in both the valence and conduction bands and, thus, leads to a dramatic improvement of the spin and valley thermoelectric properties.

Tunable thermoelectricity in monolayers of MoS2 and other group-VI dichalcogenides

KAUST Repository

Tahir, M; Schwingenschlö gl, Udo

2014-01-01

We study the thermoelectric properties of monolayers of MoS2 and other group-VI dichalcogenides under circularly polarized off-resonant light. Analytical expressions are derived for the Berry phase mediated magnetic moment, orbital magnetization, as well as thermal and Nernst conductivities. Tuning of the band gap by off-resonant light enhances the spin splitting in both the valence and conduction bands and, thus, leads to a dramatic improvement of the spin and valley thermoelectric properties.

Characterization of self-assembled monolayers on a ruthenium surface

NARCIS (Netherlands)

Shaheen, Amrozia; Sturm, Jacobus Marinus; Ricciardi, R.; Huskens, Jurriaan; Lee, Christopher James; Bijkerk, Frederik

2017-01-01

We have modified and stabilized the ruthenium surface by depositing a self-assembled monolayer (SAM) of 1-hexadecanethiol on a polycrystalline ruthenium thin film. The growth mechanism, dynamics, and stability of these monolayers were studied. SAMs, deposited under ambient conditions, on

Heterointerface Screening Effects between Organic Monolayers and Monolayer Transition Metal Dichalcogenides

KAUST Repository

Zheng, Yu Jie; Huang, Yu Li; Chen, Yifeng; Zhao, Weijie; Eda, Goki; Spataru, Catalin D.; Zhang, Wenjing; Chang, Yung-Huang; Li, Lain-Jong; Chi, Dongzhi; Quek, Su Ying; Wee, Andrew Thye Shen

2016-01-01

© 2016 American Chemical Society. The nature and extent of electronic screening at heterointerfaces and their consequences on energy level alignment are of profound importance in numerous applications, such as solar cells, electronics etc. The increasing availability of two-dimensional (2D) transition metal dichalcogenides (TMDs) brings additional opportunities for them to be used as interlayers in "van der Waals (vdW) heterostructures" and organic/inorganic flexible devices. These innovations raise the question of the extent to which the 2D TMDs participate actively in dielectric screening at the interface. Here we study perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) monolayers adsorbed on single-layer tungsten diselenide (WSe2), bare graphite, and Au(111) surfaces, revealing a strong dependence of the PTCDA HOMO-LUMO gap on the electronic screening effects from the substrate. The monolayer WSe2 interlayer provides substantial, but not complete, screening at the organic/inorganic interface. Our results lay a foundation for the exploitation of the complex interfacial properties of hybrid systems based on TMD materials.

Heterointerface Screening Effects between Organic Monolayers and Monolayer Transition Metal Dichalcogenides

KAUST Repository

Zheng, Yu Jie

2016-01-21

© 2016 American Chemical Society. The nature and extent of electronic screening at heterointerfaces and their consequences on energy level alignment are of profound importance in numerous applications, such as solar cells, electronics etc. The increasing availability of two-dimensional (2D) transition metal dichalcogenides (TMDs) brings additional opportunities for them to be used as interlayers in "van der Waals (vdW) heterostructures" and organic/inorganic flexible devices. These innovations raise the question of the extent to which the 2D TMDs participate actively in dielectric screening at the interface. Here we study perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) monolayers adsorbed on single-layer tungsten diselenide (WSe2), bare graphite, and Au(111) surfaces, revealing a strong dependence of the PTCDA HOMO-LUMO gap on the electronic screening effects from the substrate. The monolayer WSe2 interlayer provides substantial, but not complete, screening at the organic/inorganic interface. Our results lay a foundation for the exploitation of the complex interfacial properties of hybrid systems based on TMD materials.

Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

Directory of Open Access Journals (Sweden)

Peng Xia

2017-11-01

Full Text Available A facile and low-cost process was developed for fabricating write-once-read-many-times (WORM Cu/Ag NPs/Alumina/Al memory devices, where the alumina passivation layer formed naturally in air at room temperature, whereas the Ag nanoparticle monolayer was in situ prepared through thermal annealing of a 4.5 nm Ag film in air at 150°C. The devices exhibit irreversible transition from initial high resistance (OFF state to low resistance (ON state, with ON/OFF ratio of 107, indicating the introduction of Ag nanoparticle monolayer greatly improves ON/OFF ratio by four orders of magnitude. The uniformity of threshold voltages exhibits a polar-dependent behavior, and a narrow range of threshold voltages of 0.40 V among individual devices was achieved upon the forward voltage. The memory device can be regarded as two switching units connected in series. The uniform alumina interfacial layer and the non-uniform distribution of local electric fields originated from Ag nanoparticles might be responsible for excellent switching uniformity. Since silver ions in active layer can act as fast ion conductor, a plausible mechanism relating to the formation of filaments sequentially among the two switching units connected in series is suggested for the polar-dependent switching behavior. Furthermore, we demonstrate both alumina layer and Ag NPs monolayer play essential roles in improving switching parameters based on comparative experiments.

Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

Science.gov (United States)

Xia, Peng; Li, Luman; Wang, Pengfei; Gan, Ying; Xu, Wei

2017-11-01

A facile and low-cost process was developed for fabricating write-once-read-many-times (WORM) Cu/Ag NPs/Alumina/Al memory devices, where the alumina passivation layer formed naturally in air at room temperature, whereas the Ag nanoparticle monolayer was in situ prepared through thermal annealing of a 4.5 nm Ag film in air at 150°C. The devices exhibit irreversible transition from initial high resistance (OFF) state to low resistance (ON) state, with ON/OFF ratio of 107, indicating the introduction of Ag nanoparticle monolayer greatly improves ON/OFF ratio by four orders of magnitude. The uniformity of threshold voltages exhibits a polar-dependent behavior, and a narrow range of threshold voltages of 0.40 V among individual devices was achieved upon the forward voltage. The memory device can be regarded as two switching units connected in series. The uniform alumina interfacial layer and the non-uniform distribution of local electric fields originated from Ag nanoparticles might be responsible for excellent switching uniformity. Since silver ions in active layer can act as fast ion conductor, a plausible mechanism relating to the formation of filaments sequentially among the two switching units connected in series is suggested for the polar-dependent switching behavior. Furthermore, we demonstrate both alumina layer and Ag NPs monolayer play essential roles in improving switching parameters based on comparative experiments.

Band-gap tunability and dynamical instability in strained monolayer and bilayer phosphorenes

International Nuclear Information System (INIS)

Huang, G Q; Xing, Z W

2015-01-01

Very recently, field-effect transistors based on few-layer phosphorene crystals with a thickness of down to a few nanometres were successfully fabricated, triggering interest in this new functional two-dimensional material. In this work, we apply first-principles calculations to studying the evolution of electronic and phononic structures with out-of-plane strain for monolayer and bilayer phosphorenes. It is found that the vertical stress can be used to tune the band gap of a semiconducting phosphorene in a wide range. On the other hand, the vertical stress can make the phosphorene lattice become dynamically unstable and surface reconstruction or structural phase transition may occur. Due to the interlayer van der Waals coupling, the dynamically stable range of bilayer phosphorene under vertical stress is wider than that of monolayer phosphorene. It is proposed whether or not a semiconductor-semimetal transition occurring in a strained phosphorene is determined not only by its band gap closing, but also by its lattice stability against strain. This information is essential for the strain engineering of phosphorene and future device fabrication. (paper)

Synthesis and characterization of rod-like ZnO decorated with γ-Fe{sub 2}O{sub 3} nanoparticles monolayer

Energy Technology Data Exchange (ETDEWEB)

Balti, Imen, E-mail: imenbalti12@yahoo.fr [Unité de Recherche 99/UR12-30, Faculté des Sciences de Bizerte, Université de Carthage, 7021 Jarzouna (Tunisia); Laboratoire des Sciences des Procédés et Matériaux, LSPM, CNRS, UPR 3407, Université Paris XIII, 99 Avenue J.B. Clément, 93430 Villetaneuse (France); Smiri, Laila Samia [Unité de Recherche 99/UR12-30, Faculté des Sciences de Bizerte, Université de Carthage, 7021 Jarzouna (Tunisia); Rabu, Pierre [Département de Chimie des Matériaux Inorganiques, IPCMS, UMR 7504, CNRS–UDS, 23, rue du Loess, BP 43, Strasbourg Cedex 2 (France); Gautron, Eric [Institut des Matériaux Jean Rouxel (IMN)-UMR 6502, Université de Nantes, CNRS, 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3 (France); Viana, Bruno [LCMCP, Chimie-Paristech, UPMC, Collège de France, UMR CNRS 7574, 11 rue Pierre et Marie Curie, 75005 Paris (France); Jouini, Noureddine [Laboratoire des Sciences des Procédés et Matériaux, LSPM, CNRS, UPR 3407, Université Paris XIII, 99 Avenue J.B. Clément, 93430 Villetaneuse (France)

2014-02-15

Highlights: ► Rod-like ZnO decorated with γ-Fe{sub 2}O{sub 3} nanoparticles have been prepared using forced hydrolysis in polyol medium. ► The system presents excellent UV photoluminescence properties along with superparamagnetic behavior. -- Abstract: Decorated rod-like ZnO particles with γ-Fe{sub 2}O{sub 3} nanoparticles monolayer (ZnO@γ-Fe{sub 2}O{sub 3}) were prepared via a simple route using forced hydrolysis of metal acetates in a polyol medium. The phases and purity of the as-prepared particles were established by powder X-ray diffraction (PXRD) and X-ray photo-electron spectroscopy (XPS) analyses. Transmission electron microscopy (TEM) showed that the ZnO particles present a typical rod-like morphology with ∼80 nm diameter and ∼200–400 nm length. These nanorods are decorated with well-organized γ-Fe{sub 2}O{sub 3} spherical nanoparticles showing a narrow size distribution around 5 nm. The photoluminescence (PL) spectra of the bare ZnO particles show predominant UV-excitonic and weak visible emission. The latter vanishes after covering the surface with the γ-Fe{sub 2}O{sub 3} nanoparticles suggesting an effect on the oxygen stoichiometry at the surface of the ZnO nanorods. The decorated nanoparticles exhibit magnetic response to an external magnetic field at room temperature and a superparamagnetic character with very low blocking temperature likely related to the organisation of γ-Fe{sub 2}O{sub 3} nanoparticles as monolayer.

Template-Directed Self-Assembly of Alkanethiol Monolayers: Selective Growth on Preexisting Monolayer Edges

NARCIS (Netherlands)

Sharpe, R.B.A.; Burdinski, Dirk; Huskens, Jurriaan; Zandvliet, Henricus J.W.; Reinhoudt, David; Poelsema, Bene

2007-01-01

Self-assembled monolayers were investigated for their suitability as two-dimensional scaffolds for the selective growth of alkanethiol edge structures. Heterostructures with chemical contrast could be grown, whose dimensions were governed by both the initial pattern sizes and the process time.

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys.

Science.gov (United States)

Holder, Aaron M; Siol, Sebastian; Ndione, Paul F; Peng, Haowei; Deml, Ann M; Matthews, Bethany E; Schelhas, Laura T; Toney, Michael F; Gordon, Roy G; Tumas, William; Perkins, John D; Ginley, David S; Gorman, Brian P; Tate, Janet; Zakutayev, Andriy; Lany, Stephan

2017-06-01

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.

Formation and electrochemical investigation of ordered cobalt coordinated peptide monolayers on gold substrates

International Nuclear Information System (INIS)

Wang Xinxin; Nagata, Kenji; Higuchi, Masahiro

2012-01-01

The monolayers composed of cobalt coordinated peptides were prepared on gold substrates by two different approaches. One was the self-assembly method, which was used to prepare a peptide monolayer on the gold substrate via the spontaneous attachment of peptides owing to the interaction between gold and sulfur at the N-terminal of the peptide. The other one was the stepwise polymerization method that was utilized to fabricate the unidirectionally arranged peptide monolayer by the stepwise condensation of amino acids from the initiator fixed on the gold substrate. Leu 2 Ala(4-Pyri)Leu 6 Ala(4-Pyri)Leu 6 sequence was chosen as the cobalt coordinated peptide. The 4-pyridyl alanines, Ala(4-Pyri)s, were introduced as ligands for cobalt to the leucine-rich sequential peptide. The complexation between cobalt and pyridyl groups of the peptide induced the formation of a stable α-helical bundle, which oriented perpendicularly to the substrate surface. In the case of the monolayer fabricated by the stepwise polymerization method, the direction of the peptide macro-dipole moment aligned unidirectionally, and the cobalt complexes were fixed in the monolayer to form the ordered arrangement. On the other hand, the peptides prepared by the self-assembly method formed the mixture of parallel and antiparallel packing owing to the dipole-dipole interaction. The spatial location of the cobalt complexes in the monolayer prepared by the self-assembly method was distorted, compared with that in the monolayer fabricated by the stepwise polymerization method. The vectorial electron flow through the peptide monolayer was achieved by the regular alignment of the peptide macro-dipole moment and the cobalt complexes in the monolayer fabricated by the stepwise polymerization method. - Highlights: ► We fabricated ordered Co coordinated peptide monolayers on the gold substrates. ► The Co complexes in peptide monolayer formed an ordered arrangement of the peptide. ► The peptide macro

X-ray studies of the liquid/vapor interface: Water and polymer and fatty acid monolayers on water

International Nuclear Information System (INIS)

Schlossman, M.L.; Schwartz, D.K.; Kawamoto, E.H.; Kellogg, G.J.; Pershan, P.S.; Ocko, B.M.; Kim, M.W.; Chung, T.C.

1989-01-01

X-ray specular reflectivity is used to study the liquid-vapor interface of pure water and of fatty acid and polymer monolayers at that interface. For the pure water surface the reflectivity was measured for three different spectrometer resolutions and simultaneous fits with only one free parameter to all of the data are in excellent agreement with the prediction of capillary wave theory for the RMS surface roughness. Diffuse scattering away from the specular condition, at wavevectors corresponding to those of the capillary waves, yields intensities and line shapes in agreement with theory with no significant adjustable parameters. Reflectivity from separate monolayers of co-poly 1, 2-butadiene/butyl alcohol (50% random substitution) and lignoceric acid (CH 3 (CH 2 ) 22 COOH) at the water/vapor interface are interpreted to obtain profiles of the average electron density ρ(z) as a function of distance z along the surface normal. For the polymer monolayer we find the following: (1) a local maximum in the electron density approximately 10% larger than that of the bulk polymer and (2) the RMS roughness of the vapor/polymer interface agrees with capillary wave theory predictions for the lower surface pressures. For the highest surface pressure the RMS roughness exceeds the value predicted by the capillary wave model. Measurements of reflectivity from a lignoceric acid monolayer, as a function of surface pressure throughout an isotherm (near room temperature), reveal the following behavior: (1) the overall thickness of the monolayer increases with increasing pressure and (2) the head groups occupy a progressively larger region along the surface normal as the pressure increases, indicating that they rearrange normal to the interface. 15 refs., 5 figs., 2 tabs

Structural, electronic and magnetic properties of Au-based monolayer derivatives in honeycomb structure

Energy Technology Data Exchange (ETDEWEB)

Kapoor, Pooja, E-mail: pupooja16@gmail.com; Sharma, Munish; Ahluwalia, P. K. [Physics Department, Himachal Pradesh University, Shimla, Himachal Pradesh, India 171005 (India); Kumar, Ashok [Centre for Physical Sciences, School of Basic and Applied Sciences, Central University of Punjab, Bathinda, India, 151001 (India)

2016-05-23

We present electronic properties of atomic layer of Au, Au{sub 2}-N, Au{sub 2}-O and Au{sub 2}-F in graphene-like structure within the framework of density functional theory (DFT). The lattice constant of derived monolayers are found to be higher than the pristine Au monolayer. Au monolayer is metallic in nature with quantum ballistic conductance calculated as 4G{sub 0}. Similarly, Au{sub 2}-N and Au{sub 2}-F monolayers show 4G{sub 0} and 2G{sub 0} quantum conductance respectively while semiconducting nature with calculated band gap of 0.28 eV has been observed for Au{sub 2}-O monolayer. Most interestingly, half metalicity has been predicted for Au{sub 2}-N and Au{sub 2}-F monolayers. Our findings may have importance for the application of these monolayers in nanoelectronic and spintronics.

Phase behavior of charged colloids on spherical surfaces

Science.gov (United States)

Kelleher, Colm; Guerra, Rodrigo; Chaikin, Paul

For a broad class of 2D materials, the transition from isotropic fluid to crystalline solid is described by the theory of melting due to Kosterlitz, Thouless, Halperin, Nelson and Young. According to this theory, long-range order is achieved via elimination of the topological defects which proliferate in the fluid phase. However, many natural and man-made 2D systems posses spatial curvature and/or non-trivial topology, which require the presence of defects, even at T = 0 . In principle, the presence of these defects could profoundly affect the phase behavior of such a system. In this presentation, we describe experiments and simulations we have performed on repulsive particles which are bound to the surface of a sphere. We observe spatial structures and inhomogeneous dynamics that cannot be captured by the measures traditionally used to describe flat-space phase behavior. We show that ordering is achieved by a novel mechanism: sequestration of topological defects into freely-terminating grain boundaries (``scars''), and simultaneous spatial organization of the scars themselves on the vertices of an icosahedron. The emergence of icosahedral order coincides with the localization of mobility into isolated ``lakes'' of fluid or glassy particles, situated at the icosahedron vertices.

Mixed carboranethiol self-assembled monolayers on gold surfaces

Science.gov (United States)

Yavuz, Adem; Sohrabnia, Nima; Yilmaz, Ayşen; Danışman, M. Fatih

2017-08-01

Carboranethiol self-assembled monolayers on metal surfaces have been shown to be very convenient systems for surface engineering. Here we have studied pure and mixed self-assembled monolayers (SAMs) of three different carboranethiol (CT) isomers on gold surfaces. The isomers were chosen with dipole moments pointing parallel to (m-1-carboranethiol, M1), out of (m-9-carboranethiol, M9) and into (o-1-carboranethiol, O1) the surface plane, in order to investigate the effect of dipole moment orientation on the film properties. In addition, influence of the substrate surface morphology on the film properties was also studied by using flame annealed (FA) and template stripped (TS) gold surfaces. Contact angle measurements indicate that in M1/M9 and M1/O1 mixed SAMs, M1 is the dominant species on the surface even for low M1 ratio in the growth solution. Whereas for O1/M9 mixed SAMs no clear evidence could be observed indicating dominance of one of the species over the other one. Though contact angle values were lower and hysteresis values were higher for SAMs grown on TS gold surfaces, the trends in the behavior of the contact angles with changing mixing ratio were identical for SAMs grown on both substrates. Atomic force microscopy images of the SAMs on TS gold surfaces indicate that the films have similar morphological properties regardless of mixing ratio.

Piezoelectric effect on the thermal conductivity of monolayer gallium nitride

Science.gov (United States)

Zhang, Jin

2018-01-01

Using molecular dynamics and density functional theory simulations, in this work, we find that the heat transport property of the monolayer gallium nitride (GaN) can be efficiently tailored by external electric field due to its unique piezoelectric characteristic. As the monolayer GaN possesses different piezoelectric properties in armchair and zigzag directions, different effects of the external electric field on thermal conductivity are observed when it is applied in the armchair and zigzag directions. Our further study reveals that due to the elastoelectric effect in the monolayer GaN, the external electric field changes the Young's modulus and therefore changes the phonon group velocity. Also, due to the inverse piezoelectric effect, the applied electric field induces in-plane stress in the monolayer GaN subject to a length constraint, which results in the change in the lattice anharmonicity and therefore affects the phonon mean free path. Furthermore, for relatively long GaN monolayers, the in-plane stress may trigger the buckling instability, which can significantly reduce the phonon mean free path.

Thermodynamics of interaction of ionic liquids with lipid monolayer.

Science.gov (United States)

Bhattacharya, G; Mitra, S; Mandal, P; Dutta, S; Giri, R P; Ghosh, S K

2018-06-01

Understanding the interaction of ionic liquids with cellular membrane becomes utterly important to comprehend the activities of these liquids in living organisms. Lipid monolayer formed at the air-water interface is employed as a model system to follow this interaction by investigating important thermodynamic parameters. The penetration kinetics of the imidazolium-based ionic liquid 1-decyl-3-methylimidazolium tetrafluoroborate ([DMIM][BF4]) into the zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid layer is found to follow the Boltzmann-like equation that reveals the characteristic time constant which is observed to be the function of initial surface pressure. The enthalpy and entropy calculated from temperature-dependent pressure-area isotherms of the monolayer show that the added ionic liquids bring about a disordering effect in the lipid film. The change in Gibbs free energy indicates that an ionic liquid with longer chain has a far greater disordering effect compared to an ionic liquid with shorter chain. The differential scanning calorimetric measurement on a multilamellar vesicle system shows the main phase transition temperature to shift to a lower value, which, again, indicates the disordering effect of the ionic liquid on lipid membrane. All these studies fundamentally point out that, when ionic liquids interact with lipid molecules, the self-assembled structure of a cellular membrane gets perturbed, which may be the mechanism of these molecules having adverse effects on living organisms.

Biotransformation of hydralazine (HDZ) in monolayer cultures of rabbit hepatocytes

International Nuclear Information System (INIS)

McQueen, C.A.; Rosado, R.R.

1990-01-01

Adverse reactions to HDZ have been associated with the acetylator polymorphism; slow acetylators are more likely to develop HDZ-induced lupus erythematosus. In studying the role of this polymorphism in susceptibility to HDZ toxicity, the biotransformation of HDZ was investigated in rabbit hepatocytes. New Zealand white rabbits, like humans, are classified as rapid or slow acetylators. Heptocytes were isolated from rapid acetylator rabbits by collagenase perfusion. Monolayer cultures were initiated and exposed to 14 C-HDZ. Since HDZ is unstable at neutral pH, parallel incubations were done in the absence of cells. Metabolites in the media were determined by reverse phase HPLC. Phthalazine (P), phthalazinone (PZ), triazoloph-thalazine (TP), methyl TP (MTP) and 3-hydroxy MTP were identified. In the absence of cells, more TP was formed than MTP, probably resulting from reaction of HDZ with components in the medium. In the presence of cells, there was a three-fold increase in MTP, while the amount of TP was relatively constant. Only trace amounts of P, PZ 3-hydroxy MTP were detected. These data indicate that monolayer cultures of rapid acetylator rabbit hepatocytes were capable of metabolizing HDZ with acetylation playing a major role. These studies are being extended to cells from slow acetylator rabbits

Thermal behavior for a nanoscale two ferromagnetic phase system based on random anisotropy model

International Nuclear Information System (INIS)

Muraca, D.; Sanchez, F.H.; Pampillo, L.G.; Saccone, F.D.

2010-01-01

Advances in theory that explain the magnetic behavior as function of temperature for two phase nanocrystalline soft magnetic materials are presented. The theory developed is based on the well known random anisotropy model, which includes the crystalline exchange stiffness and anisotropy energies in both amorphous and crystalline phases. The phenomenological behavior of the coercivity was obtained in the temperature range between the amorphous phase Curie temperature and the crystalline phase one.

Comparison of electronic structure between monolayer silicenes on Ag (111)

Science.gov (United States)

Chun-Liang, Lin; Ryuichi, Arafune; Maki, Kawai; Noriaki, Takagi

2015-08-01

The electronic structures of monolayer silicenes (4 × 4 and ) grown on Ag (111) surface are studied by scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations. While both phases have similar electronic structures around the Fermi level, significant differences are observed in the higher energy unoccupied states. The DFT calculations show that the contributions of Si 3pz orbitals to the unoccupied states are different because of their different buckled configurations. Project supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) through Grants-in-Aid for Scientific Research (Grant Nos. 24241040 and 25110008) and the World Premier International Research Center Initiative (WPI), MEXT, Japan.

Gas sensing with self-assembled monolayer field-effect transistors

NARCIS (Netherlands)

Andringa, Anne-Marije; Spijkman, Mark-Jan; Smits, Edsger C. P.; Mathijssen, Simon G. J.; van Hal, Paul A.; Setayesh, Sepas; Willard, Nico P.; Borshchev, Oleg V.; Ponomarenko, Sergei A.; Blom, Paul W. M.; de Leeuw, Dago M.

A new sensitive gas sensor based on a self-assembled monolayer field-effect transistor (SAMFET) was used to detect the biomarker nitric oxide. A SAMFET based sensor is highly sensitive because the analyte and the active channel are separated by only one monolayer. SAMFETs were functionalised for

Orientation of pentacene molecules on SiO2: From a monolayer to the bulk

International Nuclear Information System (INIS)

Zheng, Fan; Park, Byoung-Nam; Seo, Soonjoo; Evans, Paul G.; Himpsel, F. J.

2007-01-01

Near edge x-ray absorption fine structure (NEXAFS) spectroscopy is used to study the orientation of pentacene molecules within thin films on SiO 2 for thicknesses ranging from monolayers to the bulk (150 nm). The spectra exhibit a strong polarization dependence of the π * orbitals for all films, which indicates that the pentacene molecules are highly oriented. At all film thicknesses the orientation varies with the rate at which pentacene molecules are deposited, with faster rates favoring a thin film phase with different tilt angles and slower rates leading to a more bulklike orientation. Our NEXAFS results extend previous structural observations to the monolayer regime and to lower deposition rates. The NEXAFS results match crystallographic data if a finite distribution of the molecular orientations is included. Damage to the molecules by hot electrons from soft x-ray irradiation eliminates the splitting between nonequivalent π * orbitals, indicating a breakup of the pentacene molecule

Defect-Mediated Lithium Adsorption and Diffusion on Monolayer Molybdenum Disulfide

OpenAIRE

Sun, Xiaoli; Wang, Zhiguo; Fu, Yong Qing

2015-01-01

Monolayer Molybdenum Disulfide (MoS2) is a promising anode material for lithium ion batteries because of its high capacities. In this work, first principle calculations based on spin density functional theory were performed to investigate adsorption and diffusion of lithium on monolayer MoS2 with defects, such as single- and few-atom vacancies, antisite, and grain boundary. The values of adsorption energies on the monolayer MoS2 with the defects were increased compared to those on the pristin...

Method for selective immobilization of macromolecules on self assembled monolayer surfaces

Science.gov (United States)

Laskin, Julia [Richland, WA; Wang, Peng [Billerica, MA

2011-11-29

Disclosed is a method for selective chemical binding and immobilization of macromolecules on solid supports in conjunction with self-assembled monolayer (SAM) surfaces. Immobilization involves selective binding of peptides and other macromolecules to SAM surfaces using reactive landing (RL) of mass-selected, gas phase ions. SAM surfaces provide a simple and convenient platform for tailoring chemical properties of a variety of substrates. The invention finds applications in biochemistry ranging from characterization of molecular recognition events at the amino acid level and identification of biologically active motifs in proteins, to development of novel biosensors and substrates for stimulated protein and cell adhesion.

Experimental data showing the thermal behavior of a flat roof with phase change material.

Science.gov (United States)

Tokuç, Ayça; Başaran, Tahsin; Yesügey, S Cengiz

2015-12-01

The selection and configuration of building materials for optimal energy efficiency in a building require some assumptions and models for the thermal behavior of the utilized materials. Although the models for many materials can be considered acceptable for simulation and calculation purposes, the work for modeling the real time behavior of phase change materials is still under development. The data given in this article shows the thermal behavior of a flat roof element with a phase change material (PCM) layer. The temperature and energy given to and taken from the building element are reported. In addition the solid-liquid behavior of the PCM is tracked through images. The resulting thermal behavior of the phase change material is discussed and simulated in [1] A. Tokuç, T. Başaran, S.C. Yesügey, An experimental and numerical investigation on the use of phase change materials in building elements: the case of a flat roof in Istanbul, Build. Energy, vol. 102, 2015, pp. 91-104.

Investigating Alkylsilane Monolayer Tribology at a Single-Asperity Contact with Molecular Dynamics Simulation.

Science.gov (United States)

Summers, Andrew Z; Iacovella, Christopher R; Cummings, Peter T; McCabe, Clare

2017-10-24

Chemisorbed monolayer films are known to possess favorable characteristics for nanoscale lubrication of micro- and nanoelectromechanical systems (MEMS/NEMS). Prior studies have shown that the friction observed for monolayer-coated surfaces features a strong dependence on the geometry of contact. Specifically, tip-like geometries have been shown to penetrate into monolayer films, inducing defects in the monolayer chains and leading to plowing mechanisms during shear, which result in higher coefficients of friction (COF) than those observed for planar geometries. In this work, we use molecular dynamics simulations to examine the tribology of model silica single-asperity contacts under shear with monolayer-coated substrates featuring various film densities. It is observed that lower monolayer densities lead to reduced COFs, in contrast to results for planar systems where COF is found to be nearly independent of monolayer density. This is attributed to a liquid-like response to shear, whereby fewer defects are imparted in monolayer chains from the asperity, and chains are easily displaced by the tip as a result of the higher free volume. This transition in the mechanism of molecular plowing suggests that liquid-like films should provide favorable lubrication at single-asperity contacts.

Collapse of Langmuir monolayer at lower surface pressure: Effect of hydrophobic chain length

Energy Technology Data Exchange (ETDEWEB)

Das, Kaushik, E-mail: kaushikdas2089@gmail.com; Kundu, Sarathi [Physical Sciences Division, Institute of Advanced Study in Science and Technology, Vigyan Path, Paschim Boragaon, Garchuk, Guwahati, Assam 781035 (India)

2016-05-23

Long chain fatty acid molecules (e.g., stearic and behenic acids) form a monolayer on water surface in the presence of Ba{sup 2+} ions at low subphase pH (≈ 5.5) and remain as a monolayer before collapse generally occurs at higher surface pressure (π{sub c} > 50 mN/m). Monolayer formation is verified from the surface pressure vs. area per molecule (π-A) isotherms and also from the atomic force microscopy (AFM) analysis of the films deposited by single upstroke of hydrophilic Si (001) substrate through the monolayer covered water surface. At high subphase pH (≈ 9.5), barium stearate molecules form multilayer structure at lower surface pressure which is verified from the π-A isotherms and AFM analysis of the film deposited at 25 mN/m. Such monolayer to multilayer structure formation or monolayer collapse at lower surface pressure is unusual as at this surface pressure generally fatty acid salt molecules form a monolayer on the water surface. Formation of bidentate chelate coordination in the metal containing headgroups is the reason for such monolayer to multilayer transition. However, for longer chain barium behenate molecules only monolayer structure is maintained at that high subphase pH (≈ 9.5) due to the presence of relatively more tail-tail hydrophobic interaction.

Transfer matrix theory of monolayer graphene/bilayer graphene heterostructure superlattice

International Nuclear Information System (INIS)

Wang, Yu

2014-01-01

We have formulated a transfer matrix method to investigate electronic properties of graphene heterostructure consisting of monolayer graphene and bilayer counterpart. By evaluating transmission, conductance, and band dispersion, we show that, irrespective of the different carrier chiralities in monolayer graphene and bilayer graphene, superlattice consisting of biased bilayer graphene barrier and monolayer graphene well can mimic the electronic properties of conventional semiconductor superlattice, displaying the extended subbands in the quantum tunneling regime and producing anisotropic minigaps for the classically allowed transport. Due to the lateral confinement, the lowest mode has shifted away from the charge neutral point of monolayer graphene component, opening a sizeable gap in concerned structure. Following the gate-field and geometry modulation, all electronic states and gaps between them can be externally engineered in an electric-controllable strategy.

Phase behavior of charged hydrophobic colloids on flat and spherical surfaces

Science.gov (United States)

Kelleher, Colm P.

For a broad class of two-dimensional (2D) materials, the transition from isotropic fluid to crystalline solid is described by the theory of melting due to Kosterlitz, Thouless, Halperin, Nelson and Young (KTHNY). According to this theory, long-range order is achieved via elimination of the topological defects which proliferate in the fluid phase. However, many natural and man-made 2D systems posses spatial curvature and/or non-trivial topology, which require the presence of topological defects, even at T=0. In principle, the presence of these defects could profoundly affect the phase behavior of such a system. In this thesis, we develop and characterize an experimental system of charged colloidal particles that bind electrostatically to the interface between an oil and an aqueous phase. Depending on how we prepare the sample, this fluid interface may be flat, spherical, or have a more complicated geometry. Focusing on the cases where the interface is flat or spherical, we measure the interactions between the particles, and probe various aspects of their phase behavior. On flat interfaces, this phase behavior is well-described by KTHNY theory. In spherical geometries, however, we observe spatial structures and inhomogeneous dynamics that cannot be captured by the measures traditionally used to describe flat-space phase behavior. We show that, in the spherical system, ordering is achieved by a novel mechanism: sequestration of topological defects into freely-terminating grain boundaries ("scars"), and simultaneous spatial organization of the scars themselves on the vertices of an icosahedron. The emergence of icosahedral order coincides with the localization of mobility into isolated "lakes" of fluid or glassy particles, situated at the icosahedron vertices. These lakes are embedded in a rigid, connected "continent" of locally crystalline particles.

Valley- and spin-polarized oscillatory magneto-optical absorption in monolayer MoS2 quantum rings

Science.gov (United States)

Oliveira, D.; Villegas-Lelovsky, L.; Soler, M. A. G.; Qu, Fanyao

2018-03-01

Besides optical valley selectivity, strong spin-orbit interaction along with Berry curvature effects also leads to unconventional valley- and spin-polarized Landau levels in monolayer transition metal dichalcogenides (TMDCs) under a perpendicular magnetic field. We find that these unique properties are inherited to the magneto-optical absorption spectrum of the TMDC quantum rings (QRs). In addition, it is robust against variation of the magnetic flux and of the QR geometry. In stark contrast to the monolayer bulk material, the MoS2 QRs manifest themselves in both the optical valley selectivity and unprecedented size tunability of the frequency of the light absorbed. We also find that when the magnetic field setup is changed, the phase transition from Aharonov-Bohm (AB) quantum interference to aperiodic oscillation of magneto-optical absorption spectrum takes place. The exciton spectrum in a realistic finite thickness MoS2 QR is also discussed.

Liquid crystalline phase behavior of protein fibers in water: experiments versus theory.

Science.gov (United States)

Jung, Jin-Mi; Mezzenga, Raffaele

2010-01-05

We have developed a new method allowing the study of the thermodynamic phase behavior of mesoscopic colloidal systems consisting of amyloid protein fibers in water, obtained by heat denaturation and aggregation of beta-lactoglobulin, a dairy protein. The fibers have a cross section of about 5.2 nm and two groups of polydisperse contour lengths: (i) long fibers of 1-20 microm, showing semiflexible behavior, and (ii) short rods of 100-200 nm long, obtained by cutting the long fibers via high-pressure homogenization. At pH 2 without salt, these fibers are highly charged and stable in water. We have studied the isotropic-nematic phase transition for both systems and compared our results with the theoretical values predicted by Onsager's theory. The experimentally measured isotropic-nematic phase transition was found to occur at 0.4% and at 3% for the long and short fibers, respectively. For both systems, this phase transition occurs at concentrations more than 1 order of magnitude lower than what is expected based on Onsager's theory. Moreover, at low enough pH, no intermediate biphasic region was observed between the isotropic phase and the nematic phase. The phase diagrams of both systems (pH vs concentration) showed similar, yet complex and rich, phase behavior. We discuss the possible physical fundamentals ruling the phase diagram as well as the discrepancy we observe for the isotropic-nematic phase transition between our experimental results and the predicted theoretical results. Our work highlights that systems formed by water-amyloid protein fibers are way too complex to be understood based solely on Onsager's theories. Experimental results are revisited in terms of the Flory's theory (1956) for suspensions of rods, which allows accounting for rod-solvent hydrophobic interactions. This theoretical approach allows explaining, on a semiquantitative basis, most of the discrepancies observed between the experimental results and Onsager's predictions. The sources of

Phase Behavior of Three PBX Elastomers in High-Pressure Chlorodifluoromethane

Science.gov (United States)

Lee, Byung-Chul

2017-10-01

The phase equilibrium behavior data are presented for three kinds of commercial polymer-bonded explosive (PBX) elastomers in chlorodifluoromethane (HCFC22). Levapren^{{registered }} ethylene- co-vinyl acetate (LP-EVA), HyTemp^{{registered }} alkyl acrylate copolymer (HT-ACM), and Viton^{{registered }} fluoroelastomer (VT-FE) were used as the PBX elastomers. For each elastomer + HCFC22 system, the cloud point (CP) and/or bubble point (BP) pressures were measured while varying the temperature and elastomer composition using a phase equilibrium apparatus fitted with a variable-volume view cell. The elastomers examined in this study indicated a lower critical solution temperature phase behavior in the HCFC22 solvent. LP-EVA showed the CPs at temperatures of 323 K to 343 K and at pressures of 3 MPa to 10 MPa, whereas HT-ACM showed the CPs at conditions between 338 K and 363 K and between 4 MPa and 12 MPa. For the LP-EVA and HT-ACM elastomers, the BP behavior was observed at temperatures below about 323 K. For the VT-FE + HCFC22 system, only the CP behavior was observed at temperatures between 323 K and 353 K and at pressures between 6 MPa and 21 MPa. As the elastomer composition increased, the CP pressure increased, reached a maximum value at a specific elastomer composition, and then remained almost constant.

Exploring atomic defects in molybdenum disulphide monolayers

KAUST Repository

Hong, Jinhua; Hu, Zhixin; Probert, Matt; Li, Kun; Lv, Danhui; Yang, Xinan; Gu, Lin; Mao, Nannan; Feng, Qingliang; Xie, Liming; Zhang, Jin; Wu, Dianzhong; Zhang, Zhiyong; Jin, Chuanhong; Ji, Wei; Zhang, Xixiang; Yuan, Jun; Zhang, Ze

2015-01-01

Defects usually play an important role in tailoring various properties of two-dimensional materials. Defects in two-dimensional monolayer molybdenum disulphide may be responsible for large variation of electric and optical properties. Here we present a comprehensive joint experiment-theory investigation of point defects in monolayer molybdenum disulphide prepared by mechanical exfoliation, physical and chemical vapour deposition. Defect species are systematically identified and their concentrations determined by aberration-corrected scanning transmission electron microscopy, and also studied by ab-initio calculation. Defect density up to 3.5 × 10 13 cm '2 is found and the dominant category of defects changes from sulphur vacancy in mechanical exfoliation and chemical vapour deposition samples to molybdenum antisite in physical vapour deposition samples. Influence of defects on electronic structure and charge-carrier mobility are predicted by calculation and observed by electric transport measurement. In light of these results, the growth of ultra-high-quality monolayer molybdenum disulphide appears a primary task for the community pursuing high-performance electronic devices.

Exploring atomic defects in molybdenum disulphide monolayers

KAUST Repository

Hong, Jinhua

2015-02-19

Defects usually play an important role in tailoring various properties of two-dimensional materials. Defects in two-dimensional monolayer molybdenum disulphide may be responsible for large variation of electric and optical properties. Here we present a comprehensive joint experiment-theory investigation of point defects in monolayer molybdenum disulphide prepared by mechanical exfoliation, physical and chemical vapour deposition. Defect species are systematically identified and their concentrations determined by aberration-corrected scanning transmission electron microscopy, and also studied by ab-initio calculation. Defect density up to 3.5 × 10 13 cm \\'2 is found and the dominant category of defects changes from sulphur vacancy in mechanical exfoliation and chemical vapour deposition samples to molybdenum antisite in physical vapour deposition samples. Influence of defects on electronic structure and charge-carrier mobility are predicted by calculation and observed by electric transport measurement. In light of these results, the growth of ultra-high-quality monolayer molybdenum disulphide appears a primary task for the community pursuing high-performance electronic devices.

Affinity of serum apolipoproteins for lipid monolayers

International Nuclear Information System (INIS)

Ibdah, J.A.

1987-01-01

The effects of lipid composition and packing as well as the structure of the protein on the affinities of apolipoproteins for lipid monolayers have been investigated. The adsorption of 14 C-reductively methylated human apolipoproteins A-I and A-II at saturating subphase concentrations to monolayers prepared with synthetic lipids or lipoprotein surface lipids spread at various initial surface pressures has been studied. The adsorption of apolipoproteins is monitored by following the surface radioactivity using a gas flow counter and Wilhelmy plate, respectively. The physical states of the lipid monolayers are evaluated by measurement of the surface pressure-molecular area isotherms using a Langmuir-Adam surface balance. The probable helical regions in various apolipoproteins have been predicted using a secondary structure analysis computer program. The mean residue hydrophobicity and mean residue hydrophobic moment for the predicted helical segments have been calculated. The surface properties of synthetic peptides which are amphipathic helix analogs have been investigated at the air-water and lipid-water interfaces

Janus monolayers of transition metal dichalcogenides

KAUST Repository

Lu, Ang-Yu

2017-05-15

Structural symmetry-breaking plays a crucial role in determining the electronic band structures of two-dimensional materials. Tremendous efforts have been devoted to breaking the in-plane symmetry of graphene with electric fields on AB-stacked bilayers or stacked van der Waals heterostructures. In contrast, transition metal dichalcogenide monolayers are semiconductors with intrinsic in-plane asymmetry, leading to direct electronic bandgaps, distinctive optical properties and great potential in optoelectronics. Apart from their in-plane inversion asymmetry, an additional degree of freedom allowing spin manipulation can be induced by breaking the out-of-plane mirror symmetry with external electric fields or, as theoretically proposed, with an asymmetric out-of-plane structural configuration. Here, we report a synthetic strategy to grow Janus monolayers of transition metal dichalcogenides breaking the out-of-plane structural symmetry. In particular, based on a MoS2 monolayer, we fully replace the top-layer S with Se atoms. We confirm the Janus structure of MoSSe directly by means of scanning transmission electron microscopy and energy-dependent X-ray photoelectron spectroscopy, and prove the existence of vertical dipoles by second harmonic generation and piezoresponse force microscopy measurements.

Mixed DPPC/POPC Monolayers: All-atom Molecular Dynamics Simulations and Langmuir Monolayer Experiments

Czech Academy of Sciences Publication Activity Database

Olžyńska, Agnieszka; Zubek, M.; Roeselová, Martina; Korchowiec, J.; Cwiklik, Lukasz

2016-01-01

Roč. 1858, č. 12 (2016), s. 3120-3130 ISSN 0005-2736 R&D Projects: GA ČR GA15-14292S Institutional support: RVO:61388955 ; RVO:61388963 Keywords : phospholipid monolayers * Lung surfactant * molecular dynamics Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.498, year: 2016

Self assembled monolayers of octadecyltrichlorosilane for dielectric materials

Energy Technology Data Exchange (ETDEWEB)

Kumar, Vijay, E-mail: cirivijaypilani@gmail.com [Centre for Nanoscience and Engineering, Indian Institute of Science-Bangalore (India); Mechanical Engineering Department, Birla Institute of Technology and Science-Pilani (India); Puri, Paridhi; Nain, Shivani [Mechanical Engineering Department, Birla Institute of Technology and Science-Pilani (India); Bhat, K. N. [Centre for Nanoscience and Engineering, Indian Institute of Science-Bangalore (India); Sharma, N. N. [Mechanical Engineering Department, Birla Institute of Technology and Science-Pilani (India); School of Automobile, Mechanical & Mechatronics, Manipal University-Jaipur (India)

2016-04-13

Treatment of surfaces to change the interaction of fluids with them is a critical step in constructing useful microfluidics devices, especially those used in biological applications. Selective modification of inorganic materials such as Si, SiO{sub 2} and Si{sub 3}N{sub 4} is of great interest in research and technology. We evaluated the chemical formation of OTS self-assembled monolayers on silicon substrates with different dielectric materials. Our investigations were focused on surface modification of formerly used common dielectric materials SiO{sub 2}, Si{sub 3}N{sub 4} and a-poly. The improvement of wetting behaviour and quality of monolayer films were characterized using Atomic force microscope, Scanning electron microscope, Contact angle goniometer, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) monolayer deposited oxide surface.

Luminescent monolayer MoS{sub 2} quantum dots produced by multi-exfoliation based on lithium intercalation

Energy Technology Data Exchange (ETDEWEB)

Qiao, Wen [Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures and Jiangsu Provincial Laboratory for NanoTechnology, Nanjing University, Nanjing 210093 (China); Yan, Shiming [Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures and Jiangsu Provincial Laboratory for NanoTechnology, Nanjing University, Nanjing 210093 (China); College of Science, Henan University of Technology, Zhengzhou 450001 (China); Song, Xueyin; Zhang, Xing; He, Xueming [Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures and Jiangsu Provincial Laboratory for NanoTechnology, Nanjing University, Nanjing 210093 (China); Zhong, Wei, E-mail: wzhong@nju.edu.cn [Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures and Jiangsu Provincial Laboratory for NanoTechnology, Nanjing University, Nanjing 210093 (China); Du, Youwei [Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures and Jiangsu Provincial Laboratory for NanoTechnology, Nanjing University, Nanjing 210093 (China)

2015-12-30

Graphical abstract: - Highlights: • A new preparation, multi-exfoliation method based on lithium (Li) intercalation, has been demonstrated for preparing monolayer molybdenum disulfide (MoS{sub 2}) quantum dots (QDs). • The advantage of this approach is that it is capable of producing monolayer MoS{sub 2} QDs in a large number, regardless of whether the raw material is bulk or nanoparticles. • The PL intensity excited at 300 nm can be enhanced by five times after ultrasonicated heating treatment. - Abstract: An effective multi-exfoliation method based on lithium (Li) intercalation has been demonstrated for preparing monolayer molybdenum disulfide (MoS{sub 2}) quantum dots (QDs). The cutting mechanism of MoS{sub 2} QDs may involve the complete breakup around the defects and edges during the reaction of Li{sub x}MoS{sub 2} with water and its following ultrasonication process. The multiply exfoliation make the MoS{sub 2} fragile and easier to break up. After the third exfoliation, a large number of monolayer MoS{sub 2} QDs is formed. The as-prepared MoS{sub 2} QDs show photoluminescence (PL) inactive due to the existence of 1T phase. After heating treatment, the PL intensity excited at 300 nm is enhanced by five times. The MoS{sub 2} QDs solution has an excitation-dependent luminescence emission which shifts to longer wavelengths when the excitation wavelength changes from 280 nm to 370 nm. The optical properties are explored based on the quantum confinement and edge effect.

Phase behavior of model ABC triblock copolymers

Science.gov (United States)

Chatterjee, Joon

The phase behavior of poly(isoprene-b-styrene- b-ethylene oxide) (ISO), a model ABC triblock copolymer has been studied. This class of materials exhibit self-assembly, forming a large array of ordered morphologies at length scales of 5-100 nm. The formation of stable three-dimensionally continuous network morphologies is of special interest in this study. Since these nanostructures considerably impact the material properties, fundamental knowledge for designing ABC systems have high technological importance for realizing applications in the areas of nanofabrication, nanoporous media, separation membranes, drug delivery and high surface area catalysts. A comprehensive framework was developed to describe the phase behavior of the ISO triblock copolymers at weak to intermediate segregation strengths spanning a wide range of composition. Phases were characterized through a combination of characterization techniques, including small angle x-ray scattering, dynamic mechanical spectroscopy, transmission electron microscopy, and birefringence measurements. Combined with previous investigations on ISO, six different stable ordered state symmetries have been identified: lamellae (LAM), Fddd orthorhombic network (O70), double gyroid (Q230), alternating gyroid (Q214), hexagonal (HEX), and body-centered cubic (BCC). The phase map was found to be somewhat asymmetric around the fI = fO isopleth. This work provides a guide for theoretical studies and gives insight into the intricate effects of various parameters on the self-assembly of ABC triblock copolymers. Experimental SAXS data evaluated with a simple scattering intensity model show that local mixing varies continuously across the phase map between states of two- and three-domain segregation. Strategies of blending homopolymers with ISO triblock copolymer were employed for studying the swelling properties of a lamellar state. Results demonstrate that lamellar domains swell or shrink depending upon the type of homopolymer that

Adsorption of GST-PI3Kγ at the Air-Buffer Interface and at Substrate and Nonsubstrate Phospholipid Monolayers

Science.gov (United States)

Hermelink, Antje; Kirsch, Cornelia; Klinger, Reinhard; Reiter, Gerald; Brezesinski, Gerald

2009-01-01

The recruitment of phosphoinositide 3-kinase γ (PI3Kγ) to the cell membrane is a crucial requirement for the initiation of inflammation cascades by second-messenger production. In addition to identifying other regulation pathways, it has been found that PI3Kγ is able to bind phospholipids directly. In this study, the adsorption behavior of glutathione S-transferase (GST)-PI3Kγ to nonsubstrate model phospholipids, as well as to commercially available substrate inositol phospholipids (phosphoinositides), was investigated by use of infrared reflection-absorption spectroscopy (IRRAS). The nonsubstrate phospholipid monolayers also yielded important information about structural requirements for protein adsorption. The enzyme did not interact with condensed zwitterionic or anionic monolayers; however, it could penetrate into uncompressed fluid monolayers. Compression to values above its equilibrium pressure led to a squeezing out and desorption of the protein. Protein affinity for the monolayer surface increased considerably when the lipid had an anionic headgroup and contained an arachidonoyl fatty acyl chain in sn-2 position. Similar results on a much higher level were observed with substrate phosphoinositides. No structural response of GST-PI3Kγ to lipid interaction was detected by IRRAS. On the other hand, protein adsorption caused a condensing effect in phosphoinositide monolayers. In addition, the protein reduced the charge density at the interface probably by shifting the pK values of the phosphate groups attached to the inositol headgroups. Because of their strongly polar headgroups, an interaction of the inositides with the water molecules of the subphase can be expected. This interaction is disturbed by protein adsorption, causing the ionization state of the phosphates to change. PMID:19186139

Adsorption of GST-PI3Kgamma at the air-buffer interface and at substrate and nonsubstrate phospholipid monolayers.

Science.gov (United States)

Hermelink, Antje; Kirsch, Cornelia; Klinger, Reinhard; Reiter, Gerald; Brezesinski, Gerald

2009-02-01

The recruitment of phosphoinositide 3-kinase gamma (PI3Kgamma) to the cell membrane is a crucial requirement for the initiation of inflammation cascades by second-messenger production. In addition to identifying other regulation pathways, it has been found that PI3Kgamma is able to bind phospholipids directly. In this study, the adsorption behavior of glutathione S-transferase (GST)-PI3Kgamma to nonsubstrate model phospholipids, as well as to commercially available substrate inositol phospholipids (phosphoinositides), was investigated by use of infrared reflection-absorption spectroscopy (IRRAS). The nonsubstrate phospholipid monolayers also yielded important information about structural requirements for protein adsorption. The enzyme did not interact with condensed zwitterionic or anionic monolayers; however, it could penetrate into uncompressed fluid monolayers. Compression to values above its equilibrium pressure led to a squeezing out and desorption of the protein. Protein affinity for the monolayer surface increased considerably when the lipid had an anionic headgroup and contained an arachidonoyl fatty acyl chain in sn-2 position. Similar results on a much higher level were observed with substrate phosphoinositides. No structural response of GST-PI3Kgamma to lipid interaction was detected by IRRAS. On the other hand, protein adsorption caused a condensing effect in phosphoinositide monolayers. In addition, the protein reduced the charge density at the interface probably by shifting the pK values of the phosphate groups attached to the inositol headgroups. Because of their strongly polar headgroups, an interaction of the inositides with the water molecules of the subphase can be expected. This interaction is disturbed by protein adsorption, causing the ionization state of the phosphates to change.

Electronic characteristics of p-type transparent SnO monolayer with high carrier mobility

International Nuclear Information System (INIS)

Du, Juan; Xia, Congxin; Liu, Yaming; Li, Xueping; Peng, Yuting; Wei, Shuyi

2017-01-01

Graphical abstract: SnO monolayer is a p-type transparent semiconducting oxide with high hole mobility (∼641 cm 2 V −1 s −1 ), which is much higher than that of MoS 2 monolayer, which indicate that it can be a promising candidate for high-performance nanoelectronic devices. Display Omitted - Highlights: • SnO monolayer is a p-type transparent semiconducting oxide. • The transparent properties can be still maintained under the strain 8%. • It has a high hole mobility (∼641 cm 2 V −1 s −1 ), which is higher than that of MoS 2 monolayer. - Abstract: More recently, two-dimensional (2D) SnO nanosheets are attaching great attention due to its excellent carrier mobility and transparent characteristics. Here, the stability, electronic structures and carrier mobility of SnO monolayer are investigated by using first-principles calculations. The calculations of the phonon dispersion spectra indicate that SnO monolayer is dynamically stable. Moreover, the band gap values are decreased from 3.93 eV to 2.75 eV when the tensile strain is applied from 0% to 12%. Interestingly, SnO monolayer is a p-type transparent semiconducting oxide with hole mobility of 641 cm 2 V −1 s −1 , which is much higher than that of MoS 2 monolayer. These findings make SnO monolayer becomes a promising 2D material for applications in nanoelectronic devices.

Strain-mediated electronic properties of pristine and Mn-doped GaN monolayers

Science.gov (United States)

Sharma, Venus; Srivastava, Sunita

2018-04-01

Graphene-like two-dimensional (2D) monolayer structures GaN has gained enormous amount of interest due to high thermal stability and inherent energy band gap for practical applications. First principles calculations are performed to investigate the electronic structure and strain-mediated electronic properties of pristine and Mn-doped GaN monolayer. Binding energy of Mn dopant at various adsorption site is found to be nearly same indicating these sites to be equally favorable for adsorption of foreign atom. Depending on the adsorption site, GaN monolayer can act as p-type or n-type magnetic semiconductor. The tensile strength of both pristine and doped GaN monolayer (∼24 GPa) at ultimate tensile strain of 34% is comparable with the tensile strength of graphene. The in-plane biaxial strain modulate the energy band gap of both pristine and doped-monolayer from direct to indirect gap semiconductor and finally retendered theme into metal at critical value of applied strain. These characteristics make GaN monolayer to be potential candidate for the future applications in tunable optoelectronics.

Critical behavior at the deconfinement phase phase transition of SU(2) lattice gauge theory in (2+1) dimensions

International Nuclear Information System (INIS)

Christensen, J.; Damgaard, P.H.

1991-01-01

The finite-temperature deconfinement phase transition of SU(2) lattice gauge theory in (2+1) dimensions is studied by Monte Carlo methods. Comparison is made with the expected form of correlation functions on both sides of the critical point. The critical behavior is compared with expectations based on universality arguments. Attempts are made to extract unbiased values of critical exponents on several lattices sizes. The behavior of Polyakov loops in higher representations of the gauge group is studied close to the phase transition. (orig.)

Bioavailability of Echinacea Constituents: Caco-2 Monolayers and Pharmacokinetics of the Alkylamides and Caffeic Acid Conjugates

Directory of Open Access Journals (Sweden)

R. Lehmann

2005-10-01

Full Text Available Many studies have been done over the years to assess the effectiveness of Echinacea as an immunomodulator. We have assessed the potential bioavailability of alkyl- amides and caffeic acid conjugates using Caco-2 monolayers and compared it to their actual bioavailability in a Phase I clinical trial. The caffeic acid conjugates permeated poorly through the Caco-2 monolayers. Alkylamides were found to diffuse rapidly through Caco-2 monolayers. Differences in diffusion rates for each alkylamide correlated to structural variations, with saturation and N-terminal methylation contributing to decreases in diffusion rates. Alkylamide diffusion is not affected by the presence of other constituents and the results for a synthetic alkylamide were in line with those for alkylamides found in an ethanolic Echinacea preparation. We examined plasma from healthy volunteers for 12 hours after ingestion of Echinacea tablets manufactured from an ethanolic liquid extract. Caffeic acid conjugates could not be identified in any plasma sample at any time after tablet ingestion. Alkylamides were detected in plasma 20 minutes after tablet ingestion and for each alkylamide, pharmacokinetic profiles were devised. The data are consistent with the dosing regimen of one tablet three times daily and supports their usage as the primary markers for quality Echinacea preparations.

Influence of the solution pH in the 6-mercaptopurine self-assembled monolayer (6MP-SAM) on a Au(111) single-crystal electrode.

Science.gov (United States)

Madueño, Rafael; García-Raya, Daniel; Viudez, Alfonso J; Sevilla, José M; Pineda, Teresa; Blázquez, Manuel

2007-10-23

Self-assembled monolayers (SAMs) of 6-mercaptopurine (6MP) have been prepared on a Au(111) single-crystal electrode by immersion of the metal surface in a 100 microM 6MP and 0.01 M HClO4 solution. The 6MP-SAM Au(111) single-crystal electrodes were transferred to the cell and allowed to equilibrate with the different aqueous working solutions before the electrochemical experiments. The influence of the solution pH was studied by cyclic voltammetry, double layer capacitance curves, and electrochemical impedance spectroscopy. The electrochemical behavior of the 6MP-SAM in acetic acid at pH 4 presents important differences in comparison to that obtained in 0.1 M KOH solutions. Cyclic voltammograms for the reductive desorption process in acid medium are broad and show some features that can be explained by a phase transition between a chemisorbed and a physisorbed state of the 6MP molecules. The low solubility of these molecules in acid medium could explain this phenomenon and the readsorption of the complete monolayer when the potential is scanned in the positive direction. The variation of the double-layer capacitance values in the potential range of monolayer stability with the pH suggests that the acid-base chemistry of the 6MP molecules is playing a role. This fact has been studied by following the variations of the electron-transfer rate constant of the highly charged redox probes as are Fe(CN)(6)-3/-4 and Ru(NH3)(6)+3/+2 as a function of solution pH. The apparent surface pKa value for the 6MP-SAM (pKa approximately 8) is explained by the total conversion of the different 6MP tautomers that exist in solution to the thiol species in the adsorbed state.

Proton and hydrogen transport through two-dimensional monolayers

International Nuclear Information System (INIS)

Seel, Max; Pandey, Ravindra

2016-01-01

Diffusion of protons and hydrogen atoms in representative two-dimensional materials is investigated. Specifically, density functional calculations were performed on graphene, hexagonal boron nitride (h-BN), phosphorene, silicene, and molybdenum disulfide (MoS 2 ) monolayers to study the surface interaction and penetration barriers for protons and hydrogen atoms employing finite cluster models. The calculated barrier heights correlate approximately with the size of the opening formed by the three-fold open sites in the monolayers considered. They range from 1.56 eV (proton) and 4.61 eV (H) for graphene to 0.12 eV (proton) and 0.20 eV (H) for silicene. The results indicate that only graphene and h-BN monolayers have the potential for membranes with high selective permeability. The MoS 2 monolayer behaves differently: protons and H atoms become trapped between the outer S layers in the Mo plane in a well with a depth of 1.56 eV (proton) and 1.5 eV (H atom), possibly explaining why no proton transport was detected, suggesting MoS 2 as a hydrogen storage material instead. For graphene and h-BN, off-center proton penetration reduces the barrier to 1.38 eV for graphene and 0.11 eV for h-BN. Furthermore, Pt acting as a substrate was found to have a negligible effect on the barrier height. In defective graphene, the smallest barrier for proton diffusion (1.05 eV) is found for an oxygen-terminated defect. Therefore, it seems more likely that thermal protons can penetrate a monolayer of h-BN but not graphene and defects are necessary to facilitate the proton transport in graphene. (paper)

Proton and hydrogen transport through two-dimensional monolayers

Science.gov (United States)

Seel, Max; Pandey, Ravindra

2016-06-01

Diffusion of protons and hydrogen atoms in representative two-dimensional materials is investigated. Specifically, density functional calculations were performed on graphene, hexagonal boron nitride (h-BN), phosphorene, silicene, and molybdenum disulfide (MoS2) monolayers to study the surface interaction and penetration barriers for protons and hydrogen atoms employing finite cluster models. The calculated barrier heights correlate approximately with the size of the opening formed by the three-fold open sites in the monolayers considered. They range from 1.56 eV (proton) and 4.61 eV (H) for graphene to 0.12 eV (proton) and 0.20 eV (H) for silicene. The results indicate that only graphene and h-BN monolayers have the potential for membranes with high selective permeability. The MoS2 monolayer behaves differently: protons and H atoms become trapped between the outer S layers in the Mo plane in a well with a depth of 1.56 eV (proton) and 1.5 eV (H atom), possibly explaining why no proton transport was detected, suggesting MoS2 as a hydrogen storage material instead. For graphene and h-BN, off-center proton penetration reduces the barrier to 1.38 eV for graphene and 0.11 eV for h-BN. Furthermore, Pt acting as a substrate was found to have a negligible effect on the barrier height. In defective graphene, the smallest barrier for proton diffusion (1.05 eV) is found for an oxygen-terminated defect. Therefore, it seems more likely that thermal protons can penetrate a monolayer of h-BN but not graphene and defects are necessary to facilitate the proton transport in graphene.

Experimental data showing the thermal behavior of a flat roof with phase change material

Directory of Open Access Journals (Sweden)

Ayça Tokuç

2015-12-01

Full Text Available The selection and configuration of building materials for optimal energy efficiency in a building require some assumptions and models for the thermal behavior of the utilized materials. Although the models for many materials can be considered acceptable for simulation and calculation purposes, the work for modeling the real time behavior of phase change materials is still under development. The data given in this article shows the thermal behavior of a flat roof element with a phase change material (PCM layer. The temperature and energy given to and taken from the building element are reported. In addition the solid–liquid behavior of the PCM is tracked through images. The resulting thermal behavior of the phase change material is discussed and simulated in [1] A. Tokuç, T. Başaran, S.C. Yesügey, An experimental and numerical investigation on the use of phase change materials in building elements: the case of a flat roof in Istanbul, Build. Energy, vol. 102, 2015, pp. 91–104.

PHASE BEHAVIOR OF LIGHT GASES IN HYDROCARBON AND AQUEOUS SOLVENTS

Energy Technology Data Exchange (ETDEWEB)

KHALED A.M. GASEM; ROBERT L. ROBINSON, JR.

1998-08-31

Under previous support from the Department of Energy, an experimental facility has been established and operated to measure valuable vapor-liquid equilibrium data for systems of interest in the production and processing of coal fluids. To facilitate the development and testing of models for prediction of the phase behavior for such systems, we have acquired substantial amounts of data on the equilibrium phase compositions for binary mixtures of heavy hydrocarbon solvents with a variety of supercritical solutes, including hydrogen, methane, ethane, carbon monoxide, and carbon dioxide. The present project focuses on measuring the phase behavior of light gases and water in Fischer-Tropsch (F-T) type solvents at conditions encountered in indirect liquefaction processes and evaluating and developing theoretically-based correlating frameworks to predict the phase behavior of such systems. Specific goals of the proposed work include (a) developing a state-of-the-art experimental facility to permit highly accurate measurements of equilibrium phase compositions (solubilities) of challenging F-T systems, (b) measuring these properties for systematically-selected binary, ternary and molten F-T wax mixtures to provide critically needed input data for correlation development, (c) developing and testing models suitable for describing the phase behavior of such mixtures, and (d) presenting the modeling results in generalized, practical formats suitable for use in process engineering calculations. During the present period, the Park-Gasem-Robinson (PGR) equation of state (EOS) has been modified to improve its volumetric and equilibrium predictions. Specifically, the attractive term of the PGR equation was modified to enhance the flexibility of the model, and a new expression was developed for the temperature dependence of the attractive term in this segment-segment interaction model. The predictive capability of the modified PGR EOS for vapor pressure, and saturated liquid and

Kohn-Luttinger superconductivity in monolayer and bilayer semimetals with the Dirac spectrum

International Nuclear Information System (INIS)

Kagan, M. Yu.; Mitskan, V. A.; Korovushkin, M. M.

2014-01-01

The effect of Coulomb interaction in an ensemble of Dirac fermions on the formation of superconducting pairing in monolayer and bilayer doped graphene is studied using the Kohn-Luttinger mechanism disregarding the Van der Waals potential of the substrate and impurities. The electronic structure of graphene is described using the Shubin-Vonsovsky model taking into account the intratomic, interatomic, and interlayer (in the case of bilayer graphene) Coulomb interactions between electrons. The Cooper instability is determined by solving the Bethe-Saltpeter integral equation. The renormalized scattering amplitude is obtained with allowance for the Kohn-Luttinger polarization contributions up to the second order of perturbation theory in the Coulomb interaction. It plays the role of effective interaction in the Bethe-Salpeter integral equation. It is shown that the allowance for the Kohn-Luttinger renormalizations as well as intersite Coulomb interaction noticeably affects the competition between the superconducting phases with the f-wave and d + id-wave symmetries of the order parameter. It is demonstrated that the superconducting transition temperature for an idealized graphene bilayer with significant interlayer Coulomb interaction between electrons is noticeably higher than in the monolayer case

Electronic characteristics of p-type transparent SnO monolayer with high carrier mobility

Energy Technology Data Exchange (ETDEWEB)

Du, Juan [College of Physics and Materials Science, Henan Normal University, Xinxiang, Henan 453007 (China); Xia, Congxin, E-mail: xiacongxin@htu.edu.cn [College of Physics and Materials Science, Henan Normal University, Xinxiang, Henan 453007 (China); Liu, Yaming [Henan Institute of Science and Technology, Xinxiang 453003 (China); Li, Xueping [College of Physics and Materials Science, Henan Normal University, Xinxiang, Henan 453007 (China); Peng, Yuting [Department of Physics, University of Texas at Arlington, TX 76019 (United States); Wei, Shuyi [College of Physics and Materials Science, Henan Normal University, Xinxiang, Henan 453007 (China)

2017-04-15

Graphical abstract: SnO monolayer is a p-type transparent semiconducting oxide with high hole mobility (∼641 cm{sup 2} V{sup −1} s{sup −1}), which is much higher than that of MoS{sub 2} monolayer, which indicate that it can be a promising candidate for high-performance nanoelectronic devices. Display Omitted - Highlights: • SnO monolayer is a p-type transparent semiconducting oxide. • The transparent properties can be still maintained under the strain 8%. • It has a high hole mobility (∼641 cm{sup 2} V{sup −1} s{sup −1}), which is higher than that of MoS{sub 2} monolayer. - Abstract: More recently, two-dimensional (2D) SnO nanosheets are attaching great attention due to its excellent carrier mobility and transparent characteristics. Here, the stability, electronic structures and carrier mobility of SnO monolayer are investigated by using first-principles calculations. The calculations of the phonon dispersion spectra indicate that SnO monolayer is dynamically stable. Moreover, the band gap values are decreased from 3.93 eV to 2.75 eV when the tensile strain is applied from 0% to 12%. Interestingly, SnO monolayer is a p-type transparent semiconducting oxide with hole mobility of 641 cm{sup 2} V{sup −1} s{sup −1}, which is much higher than that of MoS{sub 2} monolayer. These findings make SnO monolayer becomes a promising 2D material for applications in nanoelectronic devices.

Lower lattice thermal conductivity in SbAs than As or Sb monolayers: a first-principles study.

Science.gov (United States)

Guo, San-Dong; Liu, Jiang-Tao

2017-12-06

Phonon transport in group-VA element (As, Sb and Bi) monolayer semiconductors has been widely investigated in theory, and, of them, monolayer Sb (antimonene) has recently been synthesized. In this work, phonon transport in monolayer SbAs is investigated with a combination of first-principles calculations and the linearized phonon Boltzmann equation. It is found that the lattice thermal conductivity of monolayer SbAs is lower than those of both monolayer As and Sb, and the corresponding sheet thermal conductance is 28.8 W K -1 at room temperature. To understand the lower lattice thermal conductivity in monolayer SbAs than those in monolayer As and Sb, the group velocities and phonon lifetimes of monolayer As, SbAs and Sb are calculated. The calculated results show that the group velocities of monolayer SbAs are between those of monolayer As and Sb, but that the phonon lifetimes of SbAs are smaller than those of both monolayer As and Sb. Hence, the low lattice thermal conductivity in monolayer SbAs is attributed to very small phonon lifetimes. Unexpectedly, the ZA branch has very little contribution to the total thermal conductivity, only 2.4%, which is obviously different from those of monolayer As and Sb with very large contributions. This can be explained by very small phonon lifetimes for the ZA branch of monolayer SbAs. The lower lattice thermal conductivity of monolayer SbAs compared to that of monolayer As or Sb can be understood by the alloying of As (Sb) with Sb (As), which should introduce phonon point defect scattering. We also consider the isotope and size effects on the lattice thermal conductivity. It is found that isotope scattering produces a neglectful effect, and the lattice thermal conductivity with a characteristic length smaller than 30 nm can reach a decrease of about 47%. These results may offer perspectives on tuning the lattice thermal conductivity by the mixture of multiple elements for applications of thermal management and

Emergence of Dirac and quantum spin Hall states in fluorinated monolayer As and AsSb

KAUST Repository

Zhang, Qingyun

2016-01-21

Using first-principles calculations, we investigate the electronic and vibrational properties of monolayer As and AsSb. While the pristine monolayers are semiconductors (direct band gap at the Γ point), fluorination results in Dirac cones at the K points. Fluorinated monolayer As shows a band gap of 0.16 eV due to spin-orbit coupling, and fluorinated monolayer AsSb a larger band gap of 0.37 eV due to inversion symmetry breaking. Spin-orbit coupling induces spin splitting similar to monolayer MoS2. Phonon calculations confirm that both materials are dynamically stable. Calculations of the edge states of nanoribbons by the tight-binding method demonstrate that fluorinated monolayer As is topologically nontrivial in contrast to fluorinated monolayer AsSb.

Detailed behavioral modeling of bang-bang phase detectors

DEFF Research Database (Denmark)

Jiang, Chenhui; Andreani, Pietro; Keil, U. D.

2006-01-01

In this paper, the metastability of current-mode logic (CML) latches and flip-flops is studied in detail. Based on the results of this analysis, a behavioral model of bang-bang phase detectors (BBPDs) is proposed, which is able to reliably capture the critical deadzone effect. The impact of jitter...

Surface chemistry of lipid raft and amyloid Aβ (1-40) Langmuir monolayer.

Science.gov (United States)

Thakur, Garima; Pao, Christine; Micic, Miodrag; Johnson, Sheba; Leblanc, Roger M

2011-10-15

Lipid rafts being rich in cholesterol and sphingolipids are considered to provide ordered lipid environment in the neuronal membranes, where it is hypothesized that the cleavage of amyloid precursor protein (APP) to Aβ (1-40) and Aβ (1-42) takes place. It is highly likely that the interaction of lipid raft components like cholesterol, sphingomylein or GM1 leads to nucleation of Aβ and results in aggregation or accumulation of amyloid plaques. One has investigated surface pressure-area isotherms of the lipid raft and Aβ (1-40) Langmuir monolayer. The compression-decompression cycles and the stability of the lipid raft Langmuir monolayer are crucial parameters for the investigation of interaction of Aβ (1-40) with the lipid raft Langmuir monolayer. It was revealed that GM1 provides instability to the lipid raft Langmuir monolayer. Adsorption of Aβ (1-40) onto the lipid raft Langmuir monolayer containing neutral (POPC) or negatively charged phospholipid (DPPG) was examined. The adsorption isotherms revealed that the concentration of cholesterol was important for adsorption of Aβ (1-40) onto the lipid raft Langmuir monolayer containing POPC whereas for the lipid raft Langmuir monolayer containing DPPG:cholesterol or GM1 did not play any role. In situ UV-vis absorption spectroscopy supported the interpretation of results for the adsorption isotherms. Copyright © 2011 Elsevier B.V. All rights reserved.

Disorder-derived, strong tunneling attenuation in bis-phosphonate monolayers

Science.gov (United States)

Pathak, Anshuma; Bora, Achyut; Liao, Kung-Ching; Schmolke, Hannah; Jung, Antje; Klages, Claus-Peter; Schwartz, Jeffrey; Tornow, Marc

2016-03-01

Monolayers of alkyl bisphosphonic acids (bisPAs) of various carbon chain lengths (C4, C8, C10, C12) were grown on aluminum oxide (AlO x ) surfaces from solution. The structural and electrical properties of these self-assembled monolayers (SAMs) were compared with those of alkyl monophosphonic acids (monoPAs). Through contact angle (CA) and Kelvin-probe (KP) measurements, ellipsometry, and infrared (IR) and x-ray photoelectron (XPS) spectroscopies, it was found that bisPAs form monolayers that are relatively disordered compared to their monoPA analogs. Current-voltage (J-V) measurements made with a hanging Hg drop top contact show tunneling to be the prevailing transport mechanism. However, while the monoPAs have an observed decay constant within the typical range for dense monolayers, β mono  =  0.85  ±  0.03 per carbon atom, a surprisingly high value, β bis  =  1.40  ±  0.05 per carbon atom, was measured for the bisPAs. We attribute this to a strong contribution of ‘through-space’ tunneling, which derives from conformational disorder in the monolayer due to strong interactions of the distal phosphonic acid groups; they likely form a hydrogen-bonding network that largely determines the molecular layer structure. Since bisPA SAMs attenuate tunnel currents more effectively than do the corresponding monoPA SAMs, they may find future application as gate dielectric modification in organic thin film devices.

Anisotropic transport of normal metal-barrier-normal metal junctions in monolayer phosphorene.

Science.gov (United States)

De Sarkar, Sangita; Agarwal, Amit; Sengupta, K

2017-07-19

We study transport properties of a phosphorene monolayer in the presence of single and multiple potential barriers of height U 0 and width d, using both continuum and microscopic lattice models, and show that the nature of electron transport along its armchair edge (x direction) is qualitatively different from its counterpart in both conventional two-dimensional electron gas with Schrödinger-like quasiparticles and graphene or surfaces of topological insulators hosting massless Dirac quasiparticles. We show that the transport, mediated by massive Dirac electrons, allows one to achieve collimated quasiparticle motion along x and thus makes monolayer phosphorene an ideal experimental platform for studying Klein paradox in the context of gapped Dirac materials. We study the dependence of the tunneling conductance [Formula: see text] as a function of d and U 0 , and demonstrate that for a given applied voltage V its behavior changes from oscillatory to decaying function of d for a range of U 0 with finite non-zero upper and lower bounds, and provide analytical expression for these bounds within which G decays with d. We contrast such behavior of G with that of massless Dirac electrons in graphene and also with that along the zigzag edge (y direction) in phosphorene where the quasiparticles obey an effective Schrödinger equation at low energy. We also study transport through multiple barriers along x and demonstrate that these properties hold for transport through multiple barriers as well. Finally, we suggest concrete experiments which may verify our theoretical predictions.

Anisotropic transport of normal metal-barrier-normal metal junctions in monolayer phosphorene

Science.gov (United States)

De Sarkar, Sangita; Agarwal, Amit; Sengupta, K.

2017-07-01

We study transport properties of a phosphorene monolayer in the presence of single and multiple potential barriers of height U 0 and width d, using both continuum and microscopic lattice models, and show that the nature of electron transport along its armchair edge (x direction) is qualitatively different from its counterpart in both conventional two-dimensional electron gas with Schrödinger-like quasiparticles and graphene or surfaces of topological insulators hosting massless Dirac quasiparticles. We show that the transport, mediated by massive Dirac electrons, allows one to achieve collimated quasiparticle motion along x and thus makes monolayer phosphorene an ideal experimental platform for studying Klein paradox in the context of gapped Dirac materials. We study the dependence of the tunneling conductance G\\equiv {{G}xx} as a function of d and U 0, and demonstrate that for a given applied voltage V its behavior changes from oscillatory to decaying function of d for a range of U 0 with finite non-zero upper and lower bounds, and provide analytical expression for these bounds within which G decays with d. We contrast such behavior of G with that of massless Dirac electrons in graphene and also with that along the zigzag edge (y direction) in phosphorene where the quasiparticles obey an effective Schrödinger equation at low energy. We also study transport through multiple barriers along x and demonstrate that these properties hold for transport through multiple barriers as well. Finally, we suggest concrete experiments which may verify our theoretical predictions.

Landau levels in biased graphene structures with monolayer-bilayer interfaces

Science.gov (United States)

Mirzakhani, M.; Zarenia, M.; Vasilopoulos, P.; Ketabi, S. A.; Peeters, F. M.

2017-09-01

The electron energy spectrum in monolayer-bilayer-monolayer and in bilayer-monolayer-bilayer graphene structures is investigated and the effects of a perpendicular magnetic field and electric bias are studied. Different types of monolayer-bilayer interfaces are considered as zigzag (ZZ) or armchair (AC) junctions which modify considerably the bulk Landau levels (LLs) when the spectra are plotted as a function of the center coordinate of the cyclotron orbit. Far away from the two interfaces, one obtains the well-known LLs for extended monolayer or bilayer graphene. The LL structure changes significantly at the two interfaces or junctions where the valley degeneracy is lifted for both types of junctions, especially when the distance between them is approximately equal to the magnetic length. Varying the nonuniform bias and the width of this junction-to-junction region in either structure strongly influence the resulting spectra. Significant differences exist between ZZ and AC junctions in both structures. The densities of states (DOSs) for unbiased structures are symmetric in energy whereas those for biased structures are asymmetric. An external bias creates interface LLs in the gaps between the LLs of the unbiased system in which the DOS can be quite small. Such a pattern of LLs can be probed by scanning tunneling microscopy.

Highly Surface-Active Ca(OH)2 Monolayer as a CO2 Capture Material.

Science.gov (United States)

Özçelik, V Ongun; Gong, Kai; White, Claire E

2018-03-14

Greenhouse gas emissions originating from fossil fuel combustion contribute significantly to global warming, and therefore the design of novel materials that efficiently capture CO 2 can play a crucial role in solving this challenge. Here, we show that reducing the dimensionality of bulk crystalline portlandite results in a stable monolayer material, named portlandene, that is highly effective at capturing CO 2 . On the basis of theoretical analysis comprised of ab initio quantum mechanical calculations and force-field molecular dynamics simulations, we show that this single-layer phase is robust and maintains its stability even at high temperatures. The chemical activity of portlandene is seen to further increase upon defect engineering of its surface using vacancy sites. Defect-containing portlandene is capable of separating CO and CO 2 from a syngas (CO/CO 2 /H 2 ) stream, yet is inert to water vapor. This selective behavior and the associated mechanisms have been elucidated by examining the electronic structure, local charge distribution, and bonding orbitals of portlandene. Additionally, unlike conventional CO 2 capturing technologies, the regeneration process of portlandene does not require high temperature heat treatment because it can release the captured CO 2 by application of a mild external electric field, making portlandene an ideal CO 2 capturing material for both pre- and postcombustion processes.

Plasma resistance behavior during the linear decay phase of RFPs in ETA BETA II

International Nuclear Information System (INIS)

Nalesso, G.F.

1982-01-01

In the aided-reversal mode RFP discharges produced in ETA BETA II, the plasma current is characterized by a linear decay phase, which follows an approximately exponential phase. During the same period the measured toroidal voltage is negative and initially increasing in absolute value (exponential phase) and then decreasing to almost zero during the linear phase before the current termination. The same behavior of the current has been observed in the quiescent phase in Zeta where a negative toroidal electric field was also observed. In this note we present a model that can explain the linear decay phase and fits with the experimental parameters and allows us to estimate the plasma resistance behavior during the linear phase of slow reversed field pinch discharges

Solid-Phase and Oscillating Solution Crystallization Behavior of (+)- and (-)-N-Methylephedrine.

Science.gov (United States)

Tulashie, Samuel Kofi; Polenske, Daniel; Seidel-Morgenstern, Andreas; Lorenz, Heike

2016-11-01

This work involves the study of the solid-phase and solution crystallization behavior of the N-methylephedrine enantiomers. A systematic investigation of the melt phase diagram of the enantiomeric N-methylephedrine system was performed considering polymorphism. Two monotropically related modifications of the enantiomer were found. Solubilities and the ternary solubility phase diagrams of N-methylephedrine enantiomers in 2 solvents [isopropanol:water, 1:3 (Vol) and (2R, 3R)-diethyl tartrate] were determined in the temperature ranges between 15°C and 25°C, and 25°C and 40°C, respectively. Preferential nucleation and crystallization experiments at higher supersaturation leading to an unusual oscillatory crystallization behavior as well as a successful preferential crystallization experiment at lower supersaturation are presented and discussed. Copyright © 2016. Published by Elsevier Inc.

Molecular printboards: monolayers of beta-cyclodextrins on silicon oxide surfaces

NARCIS (Netherlands)

Onclin, S.; Mulder, A.; Huskens, Jurriaan; Ravoo, B.J.; Reinhoudt, David

2004-01-01

Monolayers of β-cyclodextrin host molecules have been prepared on SiO2 surfaces. An ordered and stable cyano-terminated monolayer was modified in three consecutive surface reactions. First, the cyanide groups were reduced to their corresponding free amines using Red Al as a reducing agent. Second,

A self-assembled monolayer-assisted surface microfabrication and release technique

NARCIS (Netherlands)

Kim, B.J.; Liebau, M.; Huskens, Jurriaan; Reinhoudt, David; Brugger, J.P.

2001-01-01

This paper describes a method of thin film and MEMS processing which uses self-assembled monolayers as ultra-thin organic surface coating to enable a simple removal of microfabricated devices off the surface without wet chemical etching. A 1.5-nm thick self-assembled monolayer of

Infrared spectroscopy of self-assembled monolayer films on silicon

Science.gov (United States)

Rowell, N. L.; Tay, Lilin; Boukherroub, R.; Lockwood, D. J.

2007-07-01

Infrared vibrational spectroscopy in an attenuated total reflection (ATR) geometry has been employed to investigate the presence of organic thin layers on Si-wafer surfaces. The phenomena have been simulated to show there can be a field enhancement with the presented single-reflection ATR (SR-ATR) approach which is substantially larger than for conventional ATR or specular reflection. In SR-ATR, a discontinuity of the field normal to the film contributes a field enhancement in the lower index thin film causing a two order of magnitude increase in sensitivity. SR-ATR was employed to characterize a single monolayer of undecylenic acid self-assembled on Si(1 1 1) and to investigate a two monolayer system obtained by adding a monolayer of bovine serum albumin protein.

Triptycene-terminated thiolate and selenolate monolayers on Au(111

Directory of Open Access Journals (Sweden)

Jinxuan Liu

2017-04-01

Full Text Available To study the implications of highly space-demanding organic moieties on the properties of self-assembled monolayers (SAMs, triptycyl thiolates and selenolates with and without methylene spacers on Au(111 surfaces were comprehensively studied using ultra-high vacuum infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy and thermal desorption spectroscopy. Due to packing effects, the molecules in all monolayers are substantially tilted. In the presence of a methylene spacer the tilt is slightly less pronounced. The selenolate monolayers exhibit smaller defect densities and therefore are more densely packed than their thiolate analogues. The Se–Au binding energy in the investigated SAMs was found to be higher than the S–Au binding energy.

Active cell-matrix coupling regulates cellular force landscapes of cohesive epithelial monolayers

Science.gov (United States)

Zhao, Tiankai; Zhang, Yao; Wei, Qiong; Shi, Xuechen; Zhao, Peng; Chen, Long-Qing; Zhang, Sulin

2018-03-01

Epithelial cells can assemble into cohesive monolayers with rich morphologies on substrates due to competition between elastic, edge, and interfacial effects. Here we present a molecularly based thermodynamic model, integrating monolayer and substrate elasticity, and force-mediated focal adhesion formation, to elucidate the active biochemical regulation over the cellular force landscapes in cohesive epithelial monolayers, corroborated by microscopy and immunofluorescence studies. The predicted extracellular traction and intercellular tension are both monolayer size and substrate stiffness dependent, suggestive of cross-talks between intercellular and extracellular activities. Our model sets a firm ground toward a versatile computational framework to uncover the molecular origins of morphogenesis and disease in multicellular epithelia.

Producing air-stable monolayers of phosphorene and their defect engineering.

Science.gov (United States)

Pei, Jiajie; Gai, Xin; Yang, Jiong; Wang, Xibin; Yu, Zongfu; Choi, Duk-Yong; Luther-Davies, Barry; Lu, Yuerui

2016-01-22

It has been a long-standing challenge to produce air-stable few- or monolayer samples of phosphorene because thin phosphorene films degrade rapidly in ambient conditions. Here we demonstrate a new highly controllable method for fabricating high quality, air-stable phosphorene films with a designated number of layers ranging from a few down to monolayer. Our approach involves the use of oxygen plasma dry etching to thin down thick-exfoliated phosphorene flakes, layer by layer with atomic precision. Moreover, in a stabilized phosphorene monolayer, we were able to precisely engineer defects for the first time, which led to efficient emission of photons at new frequencies in the near infrared at room temperature. In addition, we demonstrate the use of an electrostatic gate to tune the photon emission from the defects in a monolayer phosphorene. This could lead to new electronic and optoelectronic devices, such as electrically tunable, broadband near infrared lighting devices operating at room temperature.

Universality in the phase behavior of soft matter: a law of corresponding states.

Science.gov (United States)

Malescio, G

2006-10-01

We show that the phase diagram of substances whose molecular structure changes upon varying the thermodynamic parameters can be mapped, through state-dependent scaling, onto the phase diagram of systems of molecules having fixed structure. This makes it possible to identify broad universality classes in the complex phase scenario exhibited by soft matter, and enlightens a surprisingly close connection between puzzling phase phenomena and familiar behaviors. The analysis presented provides a straightforward way for deriving the phase diagram of soft substances from that of simpler reference systems. This method is applied here to study the phase behavior exhibited by two significative examples of soft matter with temperature-dependent molecular structure: thermally responsive colloids and polymeric systems. A region of inverse melting, i.e., melting upon isobaric cooling, is predicted at relatively low pressure and temperature in polymeric systems.

Magnetism in the p-type Monolayer II-VI semiconductors SrS and SrSe

Science.gov (United States)

Lin, Heng-Fu; Lau, Woon-Ming; Zhao, Jijun

2017-01-01

Using density functional theory calculations, we study the electronic and magnetic properties of the p-type monolayer II-VI semiconductors SrX (X = S,Se). The pristine SrS and SrSe monolayers are large band gap semiconductor with a very flat band in the top valence band. Upon injecting hole uniformly, ferromagnetism emerges in those system in a large range of hole density. By varying hole density, the systems also show complicated phases transition among nonmagnetic semiconductor, half metal, magnetic semiconductor, and nonmagnetic metal. Furthermore, after introducing p-type dopants in SrS and SrSe via substitutionary inserting P (or As) dopants at the S (or Se) sites, local magnetic moments are formed around the substitutional sites. The local magnetic moments are stable with the ferromagnetic order with appreciable Curie temperature. The ferromagnetism originates from the instability of the electronic states in SrS and SrSe with the large density of states at the valence band edge, which demonstrates a useful strategy for realizing the ferromagnetism in the two dimensional semiconductors. PMID:28378761

Characterization of the Lateral Distribution of Fluorescent Lipid in Binary-Constituent Lipid Monolayers by Principal Component Analysis

Directory of Open Access Journals (Sweden)

István P. Sugár

2010-01-01

Full Text Available Lipid lateral organization in binary-constituent monolayers consisting of fluorescent and nonfluorescent lipids has been investigated by acquiring multiple emission spectra during measurement of each force-area isotherm. The emission spectra reflect BODIPY-labeled lipid surface concentration and lateral mixing with different nonfluorescent lipid species. Using principal component analysis (PCA each spectrum could be approximated as the linear combination of only two principal vectors. One point on a plane could be associated with each spectrum, where the coordinates of the point are the coefficients of the linear combination. Points belonging to the same lipid constituents and experimental conditions form a curve on the plane, where each point belongs to a different mole fraction. The location and shape of the curve reflects the lateral organization of the fluorescent lipid mixed with a specific nonfluorescent lipid. The method provides massive data compression that preserves and emphasizes key information pertaining to lipid distribution in different lipid monolayer phases. Collectively, the capacity of PCA for handling large spectral data sets, the nanoscale resolution afforded by the fluorescence signal, and the inherent versatility of monolayers for characterization of lipid lateral interactions enable significantly enhanced resolution of lipid lateral organizational changes induced by different lipid compositions.

Strongly bound excitons in monolayer PtS2 and PtSe2

KAUST Repository

Sajjad, M.

2018-01-22

Based on first-principles calculations, the structural, electronic, and optical properties of monolayers PtS2 and PtSe2 are investigated. The bond stiffnesses and elastic moduli are determined by means of the spring constants and strain-energy relations, respectively. Dynamic stability is confirmed by calculating the phonon spectra, which shows excellent agreement with experimental reports for the frequencies of the Raman-active modes. The Heyd-Scuseria-Ernzerhof functional results in electronic bandgaps of 2.66 eV for monolayer PtS2 and 1.74 eV for monolayer PtSe2. G0W0 calculations combined with the Bethe-Salpeter equation are used to predict the optical spectra and exciton binding energies (0.78 eV for monolayer PtS2 and 0.60 eV for monolayer PtSe2). It turns out that the excitons are strongly bound and therefore very stable against external perturbations.

Disorder-derived, strong tunneling attenuation in bis-phosphonate monolayers

International Nuclear Information System (INIS)

Pathak, Anshuma; Bora, Achyut; Tornow, Marc; Liao, Kung-Ching; Schwartz, Jeffrey; Schmolke, Hannah; Jung, Antje; Klages, Claus-Peter

2016-01-01

Monolayers of alkyl bisphosphonic acids (bisPAs) of various carbon chain lengths (C4, C8, C10, C12) were grown on aluminum oxide (AlO x ) surfaces from solution. The structural and electrical properties of these self-assembled monolayers (SAMs) were compared with those of alkyl monophosphonic acids (monoPAs). Through contact angle (CA) and Kelvin-probe (KP) measurements, ellipsometry, and infrared (IR) and x-ray photoelectron (XPS) spectroscopies, it was found that bisPAs form monolayers that are relatively disordered compared to their monoPA analogs. Current–voltage (J–V) measurements made with a hanging Hg drop top contact show tunneling to be the prevailing transport mechanism. However, while the monoPAs have an observed decay constant within the typical range for dense monolayers, β mono   =  0.85  ±  0.03 per carbon atom, a surprisingly high value, β bis   =  1.40  ±  0.05 per carbon atom, was measured for the bisPAs. We attribute this to a strong contribution of ‘through-space’ tunneling, which derives from conformational disorder in the monolayer due to strong interactions of the distal phosphonic acid groups; they likely form a hydrogen-bonding network that largely determines the molecular layer structure. Since bisPA SAMs attenuate tunnel currents more effectively than do the corresponding monoPA SAMs, they may find future application as gate dielectric modification in organic thin film devices. (paper)

Correlations between phase behaviors and ionic conductivities of (ionic liquid + alcohol) systems

International Nuclear Information System (INIS)

Park, Nam Ku; Bae, Young Chan

2010-01-01

To understand the basic properties of ionic liquids (ILs), we examined the phase behavior and ionic conductivity characteristics using various compositions of different ionic liquids (1-ethyl-3-methylimidazolium hexafluorophosphate [emim] [PF6] and 1-benzyl-3-methylimidazolium hexafluorophosphate [bzmim] [PF6]) in several different alcohols (ethanol, propanol, 1-butanol, 2-butanol, and hexanol). We conducted a systematic study of the impact of different factors on the phase behavior of imidazolium-based ionic liquids in alcohols. Using a new experimental method with a liquid electrolyte system, we observed that the ionic conductivity of the ionic liquid/alcohol was sensitive to the surrounding temperature. We employed Chang et al.'s thermodynamic model [Chang et al. (1997, 1998) ] based on the lattice model. The obtained co-ordinated unit parameter from this model was used to describe the phase behavior and ionic conductivities of the given system. Good agreement with experimental data of various alcohol and ILs systems was obtained in the range of interest.

Defect Structure of Localized Excitons in a WSe2 Monolayer

KAUST Repository

Zhang, Shuai

2017-07-26

The atomic and electronic structure of intrinsic defects in a WSe2 monolayer grown on graphite was revealed by low temperature scanning tunneling microscopy and spectroscopy. Instead of chalcogen vacancies that prevail in other transition metal dichalcogenide materials, intrinsic defects in WSe2 arise surprisingly from single tungsten vacancies, leading to the hole (p-type) doping. Furthermore, we found these defects to dominate the excitonic emission of the WSe2 monolayer at low temperature. Our work provided the first atomic-scale understanding of defect excitons and paved the way toward deciphering the defect structure of single quantum emitters previously discovered in the WSe2 monolayer.

Methods for top-down fabrication of wafer scale TMDC monolayers

Science.gov (United States)

Das, Saptarshi; Bera, Mrinal K.; Roelofs, Andreas K; Antonio, Mark

2017-11-07

A method of forming a TMDC monolayer comprises providing a multi-layer transition metal dichalcogenide (TMDC) film. The multi-layer TMDC film comprises a plurality of layers of the TMDC. The multi-layer TMDC film is positioned on a conducting substrate. The conducting substrate is contacted with an electrolyte solution. A predetermined electrode potential is applied on the conducting substrate and the TMDC monolayer for a predetermined time. A portion of the plurality of layers of the TMDC included in the multi-layer TMDC film is removed by application of the predetermined electrode potential, thereby leaving a TMDC monolayer film positioned on the conducting substrate.

Current Transport Properties of Monolayer Graphene/n-Si Schottky Diodes

Science.gov (United States)

Pathak, C. S.; Garg, Manjari; Singh, J. P.; Singh, R.

2018-05-01

The present work reports on the fabrication and the detailed macroscopic and nanoscale electrical characteristics of monolayer graphene/n-Si Schottky diodes. The temperature dependent electrical transport properties of monolayer graphene/n-Si Schottky diodes were investigated. Nanoscale electrical characterizations were carried out using Kelvin probe force microscopy and conducting atomic force microscopy. Most the values of ideality factor and barrier height are found to be in the range of 2.0–4.4 and 0.50–0.70 eV for monolayer graphene/n-Si nanoscale Schottky contacts. The tunneling of electrons is found to be responsible for the high value of ideality factor for nanoscale Schottky contacts.

SYNCHROTRON X-RAY OBSERVATIONS OF A MONOLAYER TEMPLATE FOR MINERALIZATION

International Nuclear Information System (INIS)

Dimasi, E.; Gower, L.B.

2000-01-01

Mineral nucleation at a Langmuir film interface has been studied by synchrotron x-ray scattering. Diluted calcium bicarbonate solutions were used as subphases for arachidic and stearic acid monolayers, compressed in a Langmuir trough. Self-assembly of the monolayer template is observed directly, and subsequent crystal growth monitored in-situ

Self-renewing Monolayer of Primary Colonic or Rectal Epithelial CellsSummary

Directory of Open Access Journals (Sweden)

Yuli Wang

2017-07-01

Full Text Available Background & Aims: Three-dimensional organoid culture has fundamentally changed the in vitro study of intestinal biology enabling novel assays; however, its use is limited because of an inaccessible luminal compartment and challenges to data gathering in a three-dimensional hydrogel matrix. Long-lived, self-renewing 2-dimensional (2-D tissue cultured from primary colon cells has not been accomplished. Methods: The surface matrix and chemical factors that sustain 2-D mouse colonic and human rectal epithelial cell monolayers with cell repertoires comparable to that in vivo were identified. Results: The monolayers formed organoids or colonoids when placed in standard Matrigel culture. As with the colonoids, the monolayers exhibited compartmentalization of proliferative and differentiated cells, with proliferative cells located near the peripheral edges of growing monolayers and differentiated cells predominated in the central regions. Screening of 77 dietary compounds and metabolites revealed altered proliferation or differentiation of the murine colonic epithelium. When exposed to a subset of the compound library, murine organoids exhibited similar responses to that of the monolayer but with differences that were likely attributable to the inaccessible organoid lumen. The response of the human primary epithelium to a compound subset was distinct from that of both the murine primary epithelium and human tumor cells. Conclusions: This study demonstrates that a self-renewing 2-D murine and human monolayer derived from primary cells can serve as a physiologically relevant assay system for study of stem cell renewal and differentiation and for compound screening. The platform holds transformative potential for personalized and precision medicine and can be applied to emerging areas of disease modeling and microbiome studies. Keywords: Colonic Epithelial Cells, Monolayer, Organoids, Compound Screening

InSe monolayer: synthesis, structure and ultra-high second-harmonic generation

Science.gov (United States)

Zhou, Jiadong; Shi, Jia; Zeng, Qingsheng; Chen, Yu; Niu, Lin; Liu, Fucai; Yu, Ting; Suenaga, Kazu; Liu, Xinfeng; Lin, Junhao; Liu, Zheng

2018-04-01

III–IV layered materials such as indium selenide have excellent photoelectronic properties. However, synthesis of materials in such group, especially with a controlled thickness down to monolayer, still remains challenging. Herein, we demonstrate the successful synthesis of monolayer InSe by physical vapor deposition (PVD) method. The high quality of the sample was confirmed by complementary characterization techniques such as Raman spectroscopy, atomic force microscopy (AFM) and high resolution annular dark field scanning transmission electron microscopy (ADF-STEM). We found the co-existence of different stacking sequence (β- and γ-InSe) in the same flake with a sharp grain boundary in few-layered InSe. Edge reconstruction is also observed in monolayer InSe, which has a distinct atomic structure from the bulk lattice. Moreover, we discovered that the second-harmonic generation (SHG) signal from monolayer InSe shows large optical second-order susceptibility that is 1–2 orders of magnitude higher than MoS2, and even 3 times of the largest value reported in monolayer GaSe. These results make atom-thin InSe a promising candidate for optoelectronic and photosensitive device applications.

Tuning of electrostatic vs. depletion interaction in deciding the phase behavior of nanoparticle-polymer system

Energy Technology Data Exchange (ETDEWEB)

Kumar, Sugam, E-mail: sugam@barc.gov.in; Aswal, V. K. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Kohlbrecher, J. [Laboratory for Neutron Scattering, Paul Scherrer Institut, H-5232 PSI Villigen (Switzerland)

2015-06-24

Nanoparticle-polymer system interestingly show a re-entrant phase behavior where charge stabilized silica nanoparticles (phase I) undergo particle clustering (phase II) and then back to individual particles (phase I) as a function of polymer concentration. Such phase behavior arises as a result of dominance of various interactions (i) nanoparticle-nanoparticle electrostatic repulsion (ii) polymer induced attractive depletion between nanoparticles and (iii) polymer-polymer repulsion, at different concentration regimes. Small-angle neutron scattering (SANS) has been used to study the evolution of interaction during this re-entrant phase behavior of nanoparticles by contrast-marching the polymer. The SANS data have been modeled using a two-Yukawa potential accounting for both attractive and repulsive parts of the interaction between nanoparticles. The degree of both of these parts has been separately tuned by varying the polymer concentration and ionic strength of the solution. Both of these parts are found to have long-range nature. At low polymer concentrations, the electrostatic repulsion dominates over the depletion attraction. The magnitude and the range of the depletion interaction increase with the polymer concentration leading to nanoparticle clustering. At higher polymer concentrations, the increased polymer-polymer repulsion reduces the strength of depletion leading to re-entrant phase behavior. The clusters formed under depletion attraction are found to have surface fractal morphology.

Tuning of electrostatic vs. depletion interaction in deciding the phase behavior of nanoparticle-polymer system

International Nuclear Information System (INIS)

Kumar, Sugam; Aswal, V. K.; Kohlbrecher, J.

2015-01-01

Nanoparticle-polymer system interestingly show a re-entrant phase behavior where charge stabilized silica nanoparticles (phase I) undergo particle clustering (phase II) and then back to individual particles (phase I) as a function of polymer concentration. Such phase behavior arises as a result of dominance of various interactions (i) nanoparticle-nanoparticle electrostatic repulsion (ii) polymer induced attractive depletion between nanoparticles and (iii) polymer-polymer repulsion, at different concentration regimes. Small-angle neutron scattering (SANS) has been used to study the evolution of interaction during this re-entrant phase behavior of nanoparticles by contrast-marching the polymer. The SANS data have been modeled using a two-Yukawa potential accounting for both attractive and repulsive parts of the interaction between nanoparticles. The degree of both of these parts has been separately tuned by varying the polymer concentration and ionic strength of the solution. Both of these parts are found to have long-range nature. At low polymer concentrations, the electrostatic repulsion dominates over the depletion attraction. The magnitude and the range of the depletion interaction increase with the polymer concentration leading to nanoparticle clustering. At higher polymer concentrations, the increased polymer-polymer repulsion reduces the strength of depletion leading to re-entrant phase behavior. The clusters formed under depletion attraction are found to have surface fractal morphology

Platinum Monolayer Electrocatalysts for Anodic Oxidation of Alcohols.

Science.gov (United States)

Li, Meng; Liu, Ping; Adzic, Radoslav R

2012-12-06

The slow, incomplete oxidation of methanol and ethanol on platinum-based anodes as well as the high price and limited reserves of Pt has hampered the practical application of direct alcohol fuel cells. We describe the electrocatalysts consisting of one Pt monolayer (one atom thick layer) placed on extended or nanoparticle surfaces having the activity and selectivity for the oxidation of alcohol molecules that can be controlled with platinum-support interaction. The suitably expanded Pt monolayer (i.e., Pt/Au(111)) exhibits a factor of 7 activity increase in catalyzing methanol electrooxidation relative to Pt(111). Sizable enhancement is also observed for ethanol electrooxidation. Furthermore, a correlation between substrate-induced lateral strain in a Pt monolayer and its activity/selectivity is established and rationalized by experimental and theoretical studies. The knowledge we gained with single-crystal model catalysts was successfully applied in designing real nanocatalysts. These findings for alcohols are likely to be applicable for the oxidation of other classes of organic molecules.

Measuring the Edge Recombination Velocity of Monolayer Semiconductors.

Science.gov (United States)

Zhao, Peida; Amani, Matin; Lien, Der-Hsien; Ahn, Geun Ho; Kiriya, Daisuke; Mastandrea, James P; Ager, Joel W; Yablonovitch, Eli; Chrzan, Daryl C; Javey, Ali

2017-09-13

Understanding edge effects and quantifying their impact on the carrier properties of two-dimensional (2D) semiconductors is an essential step toward utilizing this material for high performance electronic and optoelectronic devices. WS 2 monolayers patterned into disks of varying diameters are used to experimentally explore the influence of edges on the material's optical properties. Carrier lifetime measurements show a decrease in the effective lifetime, τ effective , as a function of decreasing diameter, suggesting that the edges are active sites for carrier recombination. Accordingly, we introduce a metric called edge recombination velocity (ERV) to characterize the impact of 2D material edges on nonradiative carrier recombination. The unpassivated WS 2 monolayer disks yield an ERV ∼ 4 × 10 4 cm/s. This work quantifies the nonradiative recombination edge effects in monolayer semiconductors, while simultaneously establishing a practical characterization approach that can be used to experimentally explore edge passivation methods for 2D materials.

Photo-induced travelling waves in condensed Langmuir monolayers

Energy Technology Data Exchange (ETDEWEB)

Tabe, Y [Yokoyama Nano-Structured Liquid Crystal Project, ERATO, Japan Science and Technology Corporation, 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan (Japan); Yamamoto, T [Yokoyama Nano-Structured Liquid Crystal Project, ERATO, Japan Science and Technology Corporation, 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan (Japan); Yokoyama, H [Yokoyama Nano-Structured Liquid Crystal Project, ERATO, Japan Science and Technology Corporation, 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan (Japan)

2003-06-01

We report the detailed properties of photo-induced travelling waves in liquid crystalline Langmuir monolayers composed of azobenzene derivatives. When the monolayer, in which the constituent rodlike molecules are coherently tilted from the layer normal, is weakly illuminated to undergo the trans-cis photo-isomerization, spatio-temporal periodic oscillations of the molecular azimuth begin over the entire excited area and propagate as a two-dimensional orientational wave. The wave formation takes place only when the film is formed at an asymmetric interface with broken up-down symmetry and when the chromophores are continuously excited near the long-wavelength edge of absorption to induce repeated photo-isomerizations between the trans and cis forms. Under proper illumination conditions, Langmuir monolayers composed of a wide variety of azobenzene derivatives have been confirmed to exhibit similar travelling waves with velocity proportional to the excitation power irrespective of the degree of amphiphilicity. The dynamics can be qualitatively explained by the modified reaction-diffusion model proposed by Reigada, Sagues and Mikhailov.

Pressure-dependent optical and vibrational properties of monolayer molybdenum disulfide

KAUST Repository

Nayak, Avinash P.

2015-01-14

Controlling the band gap by tuning the lattice structure through pressure engineering is a relatively new route for tailoring the optoelectronic properties of two-dimensional (2D) materials. Here, we investigate the electronic structure and lattice vibrational dynamics of the distorted monolayer 1T-MoS2 (1T′) and the monolayer 2H-MoS2 via a diamond anvil cell (DAC) and density functional theory (DFT) calculations. The direct optical band gap of the monolayer 2H-MoS2 increases by 11.7% from 1.85 to 2.08 eV, which is the highest reported for a 2D transition metal dichalcogenide (TMD) material. DFT calculations reveal a subsequent decrease in the band gap with eventual metallization of the monolayer 2H-MoS2, an overall complex structure-property relation due to the rich band structure of MoS2. Remarkably, the metastable 1T′-MoS2 metallic state remains invariant with pressure, with the J2, A1g, and E2g modes becoming dominant at high pressures. This substantial reversible tunability of the electronic and vibrational properties of the MoS2 family can be extended to other 2D TMDs. These results present an important advance toward controlling the band structure and optoelectronic properties of monolayer MoS2 via pressure, which has vital implications for enhanced device applications.

Growth of cells superinoculated onto irradiated and nonirradiated confluent monolayers

International Nuclear Information System (INIS)

Matsuoka, H.; Ueo, H.; Sugimachi, K.

1990-01-01

We prepared confluent monolayers of normal BALB/c 3T3 cells and compared differences in the growth of four types of cells superinoculated onto these nonirradiated and irradiated monolayers. The test cells were normal BALB/c 3T3 A31 cells, a squamous cell carcinoma from a human esophageal cancer (KSE-1), human fetal fibroblasts, and V-79 cells from Chinese hamster lung fibroblasts. Cell growth was checked by counting the cell number, determining [3H]thymidine incorporation and assessing colony formation. We found that on nonirradiated monolayers, colony formation of human fetal fibroblasts and normal BALB/c 3T3 cells was completely inhibited. On irradiated cells, test cells did exhibit some growth. KSE-1 cells, which had a low clonogenic efficiency on plastic surfaces, formed colonies on both irradiated and nonirradiated cells. On these monolayers, the clonogenic efficiency of V-79 cells was also higher than that on plastic surfaces. We conclude that the nonirradiated monolayer of BALB/c 3T3 cells completely inhibits the growth of superinoculated normal BALB/c 3T3 and human fetal fibroblasts, while on the other hand, they facilitate the growth of neoplastic KSE-1 and V-79 cells by providing a surface for cell adherence and growth, without affecting the presence of normal cells in co-cultures

A simple method to tune graphene growth between monolayer and bilayer

Directory of Open Access Journals (Sweden)

Xiaozhi Xu

2016-02-01

Full Text Available Selective growth of either monolayer or bilayer graphene is of great importance. We developed a method to readily tune large area graphene growth from complete monolayer to complete bilayer. In an ambient pressure chemical vapor deposition process, we used the sample temperature at which to start the H2 flow as the control parameter and realized the change from monolayer to bilayer growth of graphene on Cu foil. When the H2 starting temperature was above 700°C, continuous monolayer graphene films were obtained. When the H2 starting temperature was below 350°C, continuous bilayer films were obtained. Detailed characterization of the samples treated under various conditions revealed that heating without the H2 flow caused Cu oxidation. The more the Cu substrate oxidized, the less graphene bilayer could form.

Penetration of Milk-Derived Antimicrobial Peptides into Phospholipid Monolayers as Model Biomembranes

Directory of Open Access Journals (Sweden)

Wanda Barzyk

2013-01-01

Full Text Available Three antimicrobial peptides derived from bovine milk proteins were examined with regard to penetration into insoluble monolayers formed with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC or 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol sodium salt (DPPG. Effects on surface pressure (Π and electric surface potential (ΔV were measured, Π with a platinum Wilhelmy plate and ΔV with a vibrating plate. The penetration measurements were performed under stationary diffusion conditions and upon the compression of the monolayers. The two type measurements showed greatly different effects of the peptide-lipid interactions. Results of the stationary penetration show that the peptide interactions with DPPC monolayer are weak, repulsive, and nonspecific while the interactions with DPPG monolayer are significant, attractive, and specific. These results are in accord with the fact that antimicrobial peptides disrupt bacteria membranes (negative while no significant effect on the host membranes (neutral is observed. No such discrimination was revealed from the compression isotherms. The latter indicate that squeezing the penetrant out of the monolayer upon compression does not allow for establishing the penetration equilibrium, so the monolayer remains supersaturated with the penetrant and shows an under-equilibrium orientation within the entire compression range, practically.

Better Organic Ternary Memory Performance through Self-Assembled Alkyltrichlorosilane Monolayers on Indium Tin Oxide (ITO) Surfaces.

Science.gov (United States)

Hou, Xiang; Cheng, Xue-Feng; Zhou, Jin; He, Jing-Hui; Xu, Qing-Feng; Li, Hua; Li, Na-Jun; Chen, Dong-Yun; Lu, Jian-Mei

2017-11-16

Recently, surface engineering of the indium tin oxide (ITO) electrode of sandwich-like organic electric memory devices was found to effectively improve their memory performances. However, there are few methods to modify the ITO substrates. In this paper, we have successfully prepared alkyltrichlorosilane self-assembled monolayers (SAMs) on ITO substrates, and resistive random access memory devices are fabricated on these surfaces. Compared to the unmodified ITO substrates, organic molecules (i.e., 2-((4-butylphenyl)amino)-4-((4-butylphenyl)iminio)-3-oxocyclobut-1-en-1-olate, SA-Bu) grown on these SAM-modified ITO substrates have rougher surface morphologies but a smaller mosaicity. The organic layer on the SAM-modified ITO further aged to eliminate the crystalline phase diversity. In consequence, the ternary memory yields are effectively improved to approximately 40-47 %. Our results suggest that the insertion of alkyltrichlorosilane self-assembled monolayers could be an efficient method to improve the performance of organic memory devices. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Behavior of pumps conveying two-phase liquid flow

International Nuclear Information System (INIS)

Grison, Pierre; Lauro, J.-F.

1979-01-01

Determination of the two-phase flow (critical or otherwise) through a pump is an essential requirement for complete description of a loss of primary coolant accident in a PWR plant. Theoretical and experimental research at Electricite de France on this subject is described and problems associated with the introduction of a two-phase fluid (with mass transfer) are discussed, with an attempt to single out new phenomena involved and establish their effect on pump behavior. A complementary experimental investigation is described and the results of tests at pressures and temperatures up to 120 bars and 320 0 C respectively are compared with the theoretical model data [fr

Behavior of pumps conveying two-phase liquid flow

Energy Technology Data Exchange (ETDEWEB)

Grison, P; Lauro, J F [Electricite de France, 78 - Chatou. Direction des Etudes et Recherches

1979-01-01

Determination of the two-phase flow (critical or otherwise) through a pump is an essential requirement for complete description of a loss of primary coolant accident in a PWR plant. Theoretical and experimental research at Electricite de France on this subject is described and problems associated with the introduction of a two-phase fluid (with mass transfer) are discussed, with an attempt to single out new phenomena involved and establish their effect on pump behavior. A complementary experimental investigation is described and the results of tests at pressures and temperatures up to 120 bars and 320/sup 0/C respectively are compared with the theoretical model data.

Epitaxially Grown Ultra-Flat Self-Assembling Monolayers with Dendrimers

Directory of Open Access Journals (Sweden)

Takane Imaoka

2018-02-01

Full Text Available Mono-molecular films formed by physical adsorption and dendrimer self-assembly were prepared on various substrate surfaces. It was demonstrated that a uniform dendrimer-based monolayer on the subnanometer scale can be easily constructed via simple dip coating. Furthermore, it was shown that an epitaxially grown monolayer film reflecting the crystal structure of the substrate (highly ordered pyrolytic graphite (HOPG can also be formed by aligning specific conditions.

The interplay between excitons and trions in a monolayer of MoSe2

Science.gov (United States)

Lundt, N.; Cherotchenko, E.; Iff, O.; Fan, X.; Shen, Y.; Bigenwald, P.; Kavokin, A. V.; Höfling, S.; Schneider, C.

2018-01-01

The luminescence and absorption properties of transition metal dichalcogenide monolayers are widely determined by neutral and charged excitonic complexes. Here, we focus on the impact of a free carrier reservoir on the optical properties of excitonic and trionic complexes in a MoSe2 monolayer at cryogenic temperatures. By applying photodoping via a non-resonant pump laser, the electron density can be controlled in our sample, which is directly reflected in the contribution of excitons and trions to the luminescence signal. We find significant shifts of both the exciton and trion energies in the presence of an induced electron gas both in power- and in time evolution (on the second to minute scale) in our photoluminescence spectra. In particular, in the presence of the photo-doped carrier reservoir, we observe that the splitting between excitons and trions can be enhanced by up to 4 meV. This behaviour is phenomenologically explained by an interplay between an increased screening of excitons via electrons in our system and a modification of the Fermi level. We introduce a simple but still quantitative treatment of these effects within a variational approach that takes into account both screening and phase space filling effects.

Effect of lipid composition and packing on the adsorption of apolipoproteins to lipid monolayers

International Nuclear Information System (INIS)

Ibdah, J.A.; Lund-Katz, S.; Phillips, M.C.

1987-01-01

The monolayer system has been used to study the effects of lipoprotein surface lipid composition and packing on the affinities of apolipoproteins for the surfaces of lipoprotein particles. The adsorption of apolipoproteins injected beneath lipid monolayers prepared with pure lipids or lipoprotein surface lipids is evaluated by monitoring the surface pressure of the film and the surface concentration (Gamma) of 14 C-labelled apolipoprotein. At a given initial film pressure (π/sub i/) there is a higher adsorption of human apo A-I to unsaturated phosphatidylcholine (PC) monolayers compared to saturated PC monolayers (e.g., at π/sub i/ = 10 mN/m, Gamma = 0.35 and 0.06 mg/m 2 for egg PC and distearoyl PC, respectively, with 3 x 10 -4 mg/ml apo A-I in the subphase). In addition, adsorption of apo A-I is less to an egg sphingomyelin monolayer than to an egg PC monolayer. The adsorption of apo A-I to PC monolayers is decreased by addition of cholesterol. Generally, apo A-I adsorption diminishes as the lipid molecular area decreases. Apo A-I adsorbs more to monolayers prepared with HDL 3 surface lipids than with LDL surface lipids. These studies suggest that lipoprotein surface lipid composition and packing are crucial factors influencing the transfer and exchange of apolipoproteins among various lipoprotein classes during metabolism of lipoprotein particles

Alloying as a Route to Monolayer Transition Metal Dichalcogenides with Improved Optoelectronic Performance: Mo(S1–xSex)2 and Mo1–yWyS2

KAUST Repository

Shi, Zhiming; Zhang, Qingyun; Schwingenschlö gl, Udo

2018-01-01

–xSex)2 and Mo1–yWyS2 with x = 1/3, 2/3 and y = 1/3, 1/2, 2/3 are stable according to phonon calculations and realize 1T′ or 1T″ phases. The transition barriers from the 2H phase are lower than for monolayer MoS2, implying that the 1T′ or 1T″ phases

Low temperature photoresponse of monolayer tungsten disulphide

Directory of Open Access Journals (Sweden)

Bingchen Cao

2014-11-01

Full Text Available High photoresponse can be achieved in monolayers of transition metal dichalcogenides. However, the response times are inconveniently limited by defects. Here, we report low temperature photoresponse of monolayer tungsten disulphide prepared by exfoliation and chemical vapour deposition (CVD method. The exfoliated device exhibits n-type behaviour; while the CVD device exhibits intrinsic behaviour. In off state, the CVD device has four times larger ratio of photoresponse for laser on/off and photoresponse decay–rise times are 0.1 s (limited by our setup, while the exfoliated device has few seconds. These findings are discussed in terms of charge trapping and localization.

Electrically tunable magnetic configuration on vacancy-doped GaSe monolayer

Science.gov (United States)

Tang, Weiqing; Ke, Congming; Fu, Mingming; Wu, Yaping; Zhang, Chunmiao; Lin, Wei; Lu, Shiqiang; Wu, Zhiming; Yang, Weihuang; Kang, Junyong

2018-03-01

Group-IIIA metal-monochalcogenides with the enticing properties have attracted tremendous attention across various scientific disciplines. With the aim to satisfy the multiple demands of device applications, here we report a design framework on GaSe monolayer in an effort to tune the electronic and magnetic properties through a dual modulation of vacancy doping and electric field. A half-metallicity with a 100% spin polarization is generated in a Ga vacancy doped GaSe monolayer due to the nonbonding 4p electronic orbital of the surrounding Se atoms. The stability of magnetic moment is found to be determined by the direction of applied electric field. A switchable magnetic configuration in Ga vacancy doped GaSe monolayer is achieved under a critical electric field of 0.6 V/Å. Electric field induces redistribution of the electronic states. Finally, charge transfers are found to be responsible for the controllable magnetic structure in this system. The magnetic modulation on GaSe monolayer in this work offers some references for the design and fabrication of tunable two-dimensional spintronic device.

Phase behavior of random copolymers in quenched random media

International Nuclear Information System (INIS)

Chakraborty, A.K.; Shakhnovich, E.I.

1995-01-01

In this paper, we consider the behavior of random heteropolymers in a quenched disordered medium. We develop a field theory and obtain a mean-field solution that allows for replica symmetry breaking. The presence of an external disorder leads to the formation of compact states; a homopolymeric effect. We compute the phase diagram for two classes of problems. First, we consider the situation wherein the bare heteropolymer prefers like segments to segregate, and second, we examine cases where the bare heteropolymer prefers unlike segments to mix. For the first class of systems, we find a phase diagram characterized by a replica symmetry broken phase that exists below a particular temperature. This temperature grows with the strength of the external disorder. In the second class of situations, the phase diagram is much richer. Here we find two replica symmetry broken phases with different patterns separated by a reentrant phase. The reentrant phase and one of the two replica symmetry broken phases are induced by interactions with the external disorder. The dependence of the location of the phase boundaries on the strength of the external disorder are elucidated. We discuss our results from a physical standpoint, and note the testable experimental consequences of our findings. copyright 1995 American Institute of Physics

Nanotubes based on monolayer blue phosphorus

KAUST Repository

Montes Muñ oz, Enrique; Schwingenschlö gl, Udo

2016-01-01

We demonstrate structural stability of monolayer zigzag and armchair blue phosphorus nanotubes by means of molecular dynamics simulations. The vibrational spectrum and electronic band structure are determined and analyzed as functions of the tube

Collective cell streams in epithelial monolayers depend on cell adhesion

International Nuclear Information System (INIS)

Czirók, András; Varga, Katalin; Méhes, Előd; Szabó, András

2013-01-01

We report spontaneously emerging, randomly oriented, collective streaming behavior within a monolayer culture of a human keratinocyte cell line, and explore the effect of modulating cell adhesions by perturbing the function of calcium-dependent cell adhesion molecules. We demonstrate that decreasing cell adhesion induces narrower and more anisotropic cell streams, reminiscent of decreasing the Taylor scale of turbulent liquids. To explain our empirical findings, we propose a cell-based model that represents the dual nature of cell–cell adhesions. Spring-like connections provide mechanical stability, while a cellular Potts model formalism represents surface-tension driven attachment. By changing the relevance and persistence of mechanical links between cells, we are able to explain the experimentally observed changes in emergent flow patterns. (paper)

Observation of Wigner crystal phase and ripplon-limited mobility behavior in monolayer CVD MoS₂ with grain boundary

KAUST Repository

Chen, Jyun-Hong; Zhong, Yuan-Liang; Li, Lain-Jong; Chen, Chii-Dong

2018-01-01

-limited mobility behavior at lower temperatures. Although these mobility behaviors have been studied on the surface of liquid helium through theories and experiments, they have not previously analyzed in 2D materials and semiconductors. We are the first research

Supramolecular domains in mixed peptide self-assembled monolayers on gold nanoparticles.

Science.gov (United States)

Duchesne, Laurence; Wells, Geoff; Fernig, David G; Harris, Sarah A; Lévy, Raphaël

2008-09-01

Self-organization in mixed self-assembled monolayers of small molecules provides a route towards nanoparticles with complex molecular structures. Inspired by structural biology, a strategy based on chemical cross-linking is introduced to probe proximity between functional peptides embedded in a mixed self-assembled monolayer at the surface of a nanoparticle. The physical basis of the proximity measurement is a transition from intramolecular to intermolecular cross-linking as the functional peptides get closer. Experimental investigations of a binary peptide self-assembled monolayer show that this transition happens at an extremely low molar ratio of the functional versus matrix peptide. Molecular dynamics simulations of the peptide self-assembled monolayer are used to calculate the volume explored by the reactive groups. Comparison of the experimental results with a probabilistic model demonstrates that the peptides are not randomly distributed at the surface of the nanoparticle, but rather self-organize into supramolecular domains.

Vertical uniformity of cells and nuclei in epithelial monolayers.

Science.gov (United States)

Neelam, Srujana; Hayes, Peter Robert; Zhang, Qiao; Dickinson, Richard B; Lele, Tanmay P

2016-01-22

Morphological variability in cytoskeletal organization, organelle position and cell boundaries is a common feature of cultured cells. Remarkable uniformity and reproducibility in structure can be accomplished by providing cells with defined geometric cues. Cells in tissues can also self-organize in the absence of directing extracellular cues; however the mechanical principles for such self-organization are not understood. We report that unlike horizontal shapes, the vertical shapes of the cell and nucleus in the z-dimension are uniform in cells in cultured monolayers compared to isolated cells. Apical surfaces of cells and their nuclei in monolayers were flat and heights were uniform. In contrast, isolated cells, or cells with disrupted cell-cell adhesions had nuclei with curved apical surfaces and variable heights. Isolated cells cultured within micron-sized square wells displayed flat cell and nuclear shapes similar to cells in monolayers. Local disruption of nuclear-cytoskeletal linkages resulted in spatial variation in vertical uniformity. These results suggest that competition between cell-cell pulling forces that expand and shorten the vertical cell cross-section, thereby widening and flattening the nucleus, and the resistance of the nucleus to further flattening results in uniform cell and nuclear cross-sections. Our results reveal the mechanical principles of self-organized vertical uniformity in cell monolayers.

Photocarrier dynamics in monolayer phosphorene and bulk black phosphorus.

Science.gov (United States)

Zereshki, Peymon; Wei, Yaqing; Ceballos, Frank; Bellus, Matthew Z; Lane, Samuel D; Pan, Shudi; Long, Run; Zhao, Hui

2018-06-13

We report a combined theoretical and experimental study on photocarrier dynamics in monolayer phosphorene and bulk black phosphorus. Samples of monolayer phosphorene and bulk black phosphorus were fabricated by mechanical exfoliation, identified according to their reflective contrasts, and protected by covering them with hexagonal boron nitride layers. Photocarrier dynamics in these samples was studied by an ultrafast pump-probe technique. The photocarrier lifetime of monolayer phosphorene was found to be about 700 ps, which is about 9 times longer than that of bulk black phosphorus. This trend was reproduced in our calculations based on ab initio nonadiabatic molecular dynamics combined with time-domain density functional theory in the Kohn-Sham representation, and can be attributed to the smaller bandgap and stronger nonadiabatic coupling in bulk. The transient absorption response was also found to be dependent on the sample orientation with respect to the pump polarization, which is consistent with the previously reported anisotropic absorption of phosphorene. In addition, an oscillating component of the differential reflection signal at early probe delays was observed in the bulk sample and was attributed to the layer-breathing phonon mode with an energy of about 1 meV and a decay time of about 1.35 ps. These results provide valuable information for application of monolayer phosphorene in optoelectronics.

A comparative study of post-irradiation growth kinetics of spheroids and monolayers

International Nuclear Information System (INIS)

Dertinger, J.; Luecke-Huhle, C.

1975-01-01

Post-irradiation growth kinetics of γ-irradiated spheroid and monolayer cells in exponential growth phase was investigated by means of dose-response curves based on cell counts after specified time intervals following irradiation. A mathematical model of cell-growth after irradiation was fitted to these curves. The model parameters (related to division delay and growth of non-surviving cells) obtained from this analysis consistently indicated increasing resistance to sub-lethal damage of cells cultured as multicellular spheroids under conditions of increasing three-dimensional contact. In contrast, no indication of an increased radiation-resistance was found with cells cultured on a substratum under a variety of conditions. (author)

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

Energy Technology Data Exchange (ETDEWEB)

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

2016-01-01

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

Adsorption behavior of magnetite nanoparticles into the DPPC model membranes

International Nuclear Information System (INIS)

Hao, Changchun; Li, Junhua; Mu, Wenning; Zhu, Lingqing; Yang, Jiaxiang; Liu, Hongwei; Li, Bin; Chen, Shi; Sun, Runguang

2016-01-01

Graphical abstract: A represents the state when DPPC was spread on air/water interface at 5 mN/m surface pressures. DPPC is in the liquid expanded state at the interface. B represents 15 mN/m surface pressures and DPPC monolayer is in the liquid condensed state at the interface. - Highlights: • The adsorption of Fe 3 O 4 nanoparticles on DPPC monolayer has been investigated. • The lifting area/molecule of DPPC monolayers increased with Fe 3 O 4 increasing. • The π–t curves were well fitted by single exponential association equation. • AFM images depended on surface pressure and concentration in subphase. - Abstract: In this report, we have studied the adsorption behavior of Fe 3 O 4 nanoparticles into dipalmitoylphosphatidylcholine (DPPC) monolayer. Adsorption kinetics (π–t) process as well as the surface pressure (π–A) isotherms were monitored by Langmuir Wilhelmy plate. The measurement data indicated the Fe 3 O 4 nanoparticles incorporated into the monolayer at the air–water interface. The lifting area/molecule isotherms of DPPC monolayers increased with the increasing concentration of Fe 3 O 4 in the subphase, however, the values of elasticity reduced. The curves of π–t were well fitted by single exponential association equation. Observation by atomic force microscopy (AFM) on monolayers extracted at 5 mN/m and 15 mN/m suggested that the different interaction of Fe 3 O 4 with DPPC monolayer depended on surface pressure of monolayers and concentration in the subphase. The results of observations were in agreement with the fitted results.

The langmuir monolayer: an efficient model for studying interfacial properties of biomembranes

International Nuclear Information System (INIS)

Cirak, J.; Sokolsky, M.; Dobrocka, E.; Weis, M.

2012-01-01

In this communication, we describe aspects of monolayer technology by focusing on effects of calcium ions on physical properties of phospholipid monolayers using results of measurements of surface pressure, x-ray reflectivity and AFM. These experiments are motivated by the search for lipid-DNA complexes with high transfection efficiency but without toxicity which might be a promising tool in gene therapy. In each part methodological importance is stressed and its specificity for studying molecular interactions at a lipid monolayer. (authors)

Quantification of stromal vascular cell mechanics with a linear cell monolayer rheometer

Energy Technology Data Exchange (ETDEWEB)

Elkins, Claire M., E-mail: cma9@stanford.edu; Fuller, Gerald G. [Department of Chemical Engineering, Stanford University, Stanford, California 94305 (United States); Shen, Wen-Jun; Khor, Victor K.; Kraemer, Fredric B. [Division of Endocrinology, Gerontology and Metabolism, Stanford University, Stanford, California 94305 and Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304 (United States)

2015-01-15

Over the past few decades researchers have developed a variety of methods for measuring the mechanical properties of whole cells, including traction force microscopy, atomic force microscopy (AFM), and single-cell tensile testing. Though each of these techniques provides insight into cell mechanics, most also involve some nonideal conditions for acquiring live cell data, such as probing only one portion of a cell at a time, or placing the cell in a nonrepresentative geometry during testing. In the present work, we describe the development of a linear cell monolayer rheometer (LCMR) and its application to measure the mechanics of a live, confluent monolayer of stromal vascular cells. In the LCMR, a monolayer of cells is contacted on both top and bottom by two collagen-coated plates and allowed to adhere. The top plate then shears the monolayer by stepping forward to induce a predetermined step strain, while a force transducer attached to the top plate collects stress information. The stress and strain data are then used to determine the maximum relaxation modulus recorded after step-strain, G{sub r}{sup 0}, referred to as the zero-time relaxation modulus of the cell monolayer. The present study validates the ability of the LCMR to quantify cell mechanics by measuring the change in G{sub r}{sup 0} of a confluent cell monolayer upon the selective inhibition of three major cytoskeletal components (actin microfilaments, vimentin intermediate filaments, and microtubules). The LCMR results indicate that both actin- and vimentin-deficient cells had ∼50% lower G{sub r}{sup 0} values than wild-type, whereas tubulin deficiency resulted in ∼100% higher G{sub r}{sup 0} values. These findings constitute the first use of a cell monolayer rheometer to quantitatively distinguish the roles of different cytoskeletal elements in maintaining cell stiffness and structure. Significantly, they are consistent with results obtained using single-cell mechanical testing methods

Conformation, orientation and interaction in molecular monolayers

International Nuclear Information System (INIS)

Superfine, R.; Huang, J.Y.; Shen, Y.R.

1989-01-01

Knowledge of the conformation and ordering of molecular monolayers is essential for a detailed understanding of a wide variety of surface and interfacial phenomena. Over the past several years, surface second harmonic generation (SHG) has proven to be a valuable and versatile probe of monolayer systems. Our group has recently extended the technique to infrared-visible sum frequency generation (SFG) which has unique capabilities for surface vibrational spectroscopy. Like second harmonic generation, SFG is highly surface specific with submonolayer sensitivity at all interfaces accessible by light. The orientation of individual groups within an adsorbate molecule can be deduced by a polarization analysis of the SFG signal from the vibrational modes of the groups. The authors have used SHG and SFG to study orientations and conformations of surfactant and liquid crystal (LC) monolayers and their interaction on a substrate. The interfacial properties of LC are of great interest to many researchers for both basic science understanding and practical application to LC devices. It is well known that the bulk alignment of a liquid crystal in a cell is strongly affected by the surface treatment of the cell walls. The reason behind it is not yet clear. The theoretical background and experimental arrangement of SHG and SFG have been described elsewhere. In the setup, a 30 psec. Nd:YAG mode-locked laser system together with nonlinear accessories generates a visible beam at .532μm and an infrared beam tunable about 3.4μm. Both beams are focused to a common spot of 300μm dia. The typical signal off the surface from a compact ordered alkyl chain monolayer is ∼500 photons per pulse, easily detected with a photomultiplier tube

Spheroidization behavior of dendritic b.c.c. phase in Zr-based モ-phase composite

Directory of Open Access Journals (Sweden)

Sun Guoyuan

2013-03-01

Full Text Available The spheroidization behavior of the dendritic b.c.c. phase dispersed in a bulk metallic glass (BMG matrix was investigated through applying semi-solid isothermal processing and a subsequent rapid quenching procedure to a Zr-based モ-phase composite. The Zr-based composite with the composition of Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 was prefabricated by a water-cooled copper mold-casting method and characterized by X-ray diffraction (XRD and scanning electron microscope (SEM. The results show that the composite consists of a glassy matrix and uniformly distributed fine dendrites of the モ-Zr solid solution with the body-centered-cubic (b.c.c. structure. Based on the differential scanning calorimeter (DSC examination results, and in view of the b.c.c. モ-Zr to h.c.p. メ-Zr phase transition temperature, a semi-solid holding temperature of 900 ìC was determined. After reheating the prefabricated composite to the semi-solid temperature, followed by an isothermal holding process at this temperature for 5 min, and then quenching the semi-solid mixture into iced-water; the two-phase microstructure composed of a BMG matrix and uniformly dispersed spherical b.c.c. モ-Zr particles with a high degree of sphericity was achieved. The present spheroidization transition is a thermodynamically autonomic behavior, and essentially a diffusion process controlled by kinetic factors; and the formation of the BMG matrix should be attributed to the rapid quenching of the semi-solid mixture as well as the large glass-forming ability of the remaining melt in the semi-solid mixture.

Electronic and magnetic properties of SnS2 monolayer doped with 4d transition metals

Science.gov (United States)

Xiao, Wen-Zhi; Xiao, Gang; Rong, Qing-Yan; Chen, Qiao; Wang, Ling-Ling

2017-09-01

We investigate the electronic structures and magnetic properties of SnS2 monolayers substitutionally doped with 4-d transition-metal through systematic first principles calculations. The doped complexes exhibit interesting electronic and magnetic behaviors, depending on the interplay between crystal field splitting, Hund's rule, and 4d levels. The system doped with Y is nonmagnetic metal. Both the Zr- and Pd-doped systems remain nonmagnetic semiconductors. Doping results in half-metallic states for Nb-, Ru-, Rh-, Ag, and Cd doped cases, and magnetic semiconductors for systems with Mo and Tc dopants. In particular, the Nb- and Mo-doped systems display long-ranged ferromagnetic ordering with Curie temperature above room temperature, which are primarily attributable to the double-exchange mechanism, and the p-d/p-p hybridizations, respectively. Moreover, The Mo-doped system has excellent energetic stability and flexible mechanical stability, and also possesses remarkable dynamic and thermal (500 K) stability. Our studies demonstrate that Nb- and Mo-doped SnS2 monolayers are promising candidates for preparing 2D diluted magnetic semiconductors, and hence will be a helpful clue for experimentalists.

Surface cleaning and adsorbate layer formation: Dual role of alkylamines in the formation of self-assembled monolayers on cuprate superconductors

International Nuclear Information System (INIS)

Ritchie, J.E.; Murray, W.R.; Kershan, K.; Diaz, V.; Tran, L.; McDevitt, J.T.

1999-01-01

The development of monolayer adsorption chemistry for superconductor surfaces is particularly important for a number of practical and fundamental reasons. As high-T c superconductors begin to approach the marketplace in areas of communications, power industries, medical applications, and scientific instrumentation, the development of new soft chemistry approaches for the surface modification of these technologically relevant electronic materials becomes increasingly important. Monolayer adsorption chemistry has been developed extensively for electronic materials such as metals, semiconductors, and insulators. These methodologies have been expanded recently to include a variety of high-temperature superconductors (HTSCs). The authors describe a series of new X-ray photoelectron spectroscopy (XPS), four-point conductivity, critical current, atomic absorption spectroscopy (AAS), grazing angle infrared spectroscopy, and GE--MS experiments, which lead the suggestion that an entirely different mechanism is involved in the formation of HTSC-localized monolayers. According to the new model, the amine reagents serve two chemically distinct roles. In the initial phase, the degraded superconductor exteriors is etched away with the help of the amine compounds. The etching process proceeds to the point where fresh YBa 2 Cu 3 O 7 is exposed, and only at this point do the amines adsorb and remain at the YBa 2 Cu 3 O 7 surface. As the adsorption process continues, there is an accumulation of an organized monolayer at the surface, which prevents further etching of the YBa 2 Cu 3 O 7 material

Electrostatic Effects in Phase Transitions of Biomembranes between Cubic Phases and Lamellar Liquid-Crystalline (Lα) phase

Science.gov (United States)

Masum, Shah Md.; Li, Shu Jie; Tamba, Yukihiro; Yamashita, Yuko; Yamazaki, Masahito

2004-04-01

Elucidation of the mechanisms of transitions between cubic phase and liquid-crystalline (Lα) phase, and between different IPMS cubic phases, are essential for understanding of dynamics of biomembranes and topological transformation of lipid membranes. Recently, we found that electrostatic interactions due to surface charges of lipid membranes induce transition between cubic phase and Lα phase, and between different IPMS cubic phases. As electrostatic interactions increase, the most stable phase of a monoolein (MO) membrane changes: Q224 ⇒ Q229 ⇒ Lα. We also found that a de novo designed peptide partitioning into electrically neutral lipid membrane changed the phase stability of the MO membranes. As peptide-1 concentration increased, the most stable phase of a MO membrane changes: Q224 ⇒ Q229 ⇒Lα. In both cases, the increase in the electrostatic repulsive interaction greatly reduced the absolute value of spontaneous curvature of the MO monolayer membrane. We also investigated factors such as poly (L-lysine) and osmotic stress to control structure and phase stability of DOPA/MO membranes. Based on these results, we discuss the mechanism of the effect of electrostatic interactions on the stability of cubic phase.

The strength evaluation and σ-phase aging behavior of cast stainless steel

International Nuclear Information System (INIS)

Kwon, Jae Do; Park, Joong Cheul; Lee, Woo Ho; Jang, Sun Sik

1999-01-01

σ-phase of cast stainless steel(CF8M) was artificially precipitated by means of thermal aging at 700 deg C with various holding time (0.33, 5, 15, 50 and 150 hrs) to evaluate the behavior of thermal aging status of strength change. The structure observation, hardness test, tensile test, impact test and fatigue crack growth rates test for as-received and degraded material were also performed to evaluate static strength, toughness and fatigue crack growth behavior corresponding to the aging condition of CF8M. The results showed that the area fraction of σ-phase and hardness value increased with thermal aging time. But, for the impact values, upper shelf energy decreased and fatigue crack growth rates increased with σ-phase aging progressed than that of virgin material

Microchannel-flowed-plasma modification of octadecyltrichlorosilane self-assembled-monolayers for liquid crystal alignment

International Nuclear Information System (INIS)

Zheng, W.; Chiang, C.-Y.; Underwood, I.

2013-01-01

We report that a chemical patterning technique based on local plasma modification of self-assembled monolayers has been utilized to fabricate surfaces for domain liquid crystal alignment. Highly hydrophobic octadecyltrichlorosilane monolayers deposited on glass substrates coated with Indium-Tin-Oxide were brought into contact with elastomeric stamps comprising trenches on a micro scale, and then exposed to an oxygen plasma. In the regions exposed to the plasma the monolayer was etched away leaving a patterned surface that exhibited surface energy differences between surface domains. The surfaces that bear the micropatterns have been shown to be capable of producing patterned alignment of nematic liquid crystal. - Highlights: • Chemical surface-patterning is used to fabricate liquid crystal alignment surface. • Highly hydrophobic octadecyltrichlorosilane monolayer is deposited on substrate. • O 2 plasma flow is used to etch the monolayer to form patterned surface. • The patterned surface exhibits surface energy differences between surface domains. • The surface borne the micropatterns is capable of domain liquid crystal alignment

Interferon induction in bovine and feline monolayer cultures by four bluetongue virus serotypes.

OpenAIRE

Fulton, R W; Pearson, N J

1982-01-01

The interferon inducing ability of bluetongue viruses was studied in bovine and feline monolayer cultures inoculated with each of four bluetongue virus serotypes. Interferon was assayed by a plaque reduction method in monolayer cultures with vesicular stomatitis virus as challenge virus. Interferon was produced by bovine turbinate, Georgia bovine kidney, and Crandell feline kidney monolayer cultures in response to bluetongue virus serotypes 10, 11, 13 and 17. The antiviral substances produced...

17th International Conference on Petroleum Phase Behavior and Fouling

DEFF Research Database (Denmark)

von Solms, Nicolas; Yan, Wei; Andersen, Simon

2017-01-01

This special section of Energy & Fuels contains contributedpapers from the 17th International Conference on PetroleumPhase Behavior and Fouling (Petrophase 2016). Petrophase 2016 was organized by the Technical University of Denmark and Schlumberger and took place in Elsinore (Helsingør) Denmark...... from June 19th to 23rd at the Beach Hotel Marienlyst. Petrophase is an international conference aimed at researchers in industry and academia dedicated to the study of the properties and chemistry of petroleum fluids and their effect on producing, processing, and refining in the upstream, midstream......, and downstream industries. The conference started in 1999 as “The International Conference on Petroleum Phase Behavior & Fouling” and has since evolved into an annual event taking place in countries all around the world. Petrophase has been fortunate to have enjoyed financial and organizational support from many...

Coulomb Blockade in a Two-Dimensional Conductive Polymer Monolayer.

Science.gov (United States)

Akai-Kasaya, M; Okuaki, Y; Nagano, S; Mitani, T; Kuwahara, Y

2015-11-06

Electronic transport was investigated in poly(3-hexylthiophene-2,5-diyl) monolayers. At low temperatures, nonlinear behavior was observed in the current-voltage characteristics, and a nonzero threshold voltage appeared that increased with decreasing temperature. The current-voltage characteristics could be best fitted using a power law. These results suggest that the nonlinear conductivity can be explained using a Coulomb blockade (CB) mechanism. A model is proposed in which an isotropic extended charge state exists, as predicted by quantum calculations, and percolative charge transport occurs within an array of small conductive islands. Using quantitatively evaluated capacitance values for the islands, this model was found to be capable of explaining the observed experimental data. It is, therefore, suggested that percolative charge transport based on the CB effect is a significant factor giving rise to nonlinear conductivity in organic materials.

Investigation on gallium ions impacting monolayer graphene

Energy Technology Data Exchange (ETDEWEB)

Wu, Xin; Zhao, Haiyan, E-mail: hyzhao@tsinghua.edu.cn; Yan, Dong; Pei, Jiayun [State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, P. R. Chinaand Department of Mechanical Engineering, Tsinghua University, Beijing 100084 (China)

2015-06-15

In this paper, the physical phenomena of gallium (Ga{sup +}) ion impacting monolayer graphene in the nanosculpting process are investigated experimentally, and the mechanisms are explained by using Monte Carlo (MC) and molecular dynamics (MD) simulations. Firstly, the MC method is employed to clarify the phenomena happened to the monolayer graphene target under Ga{sup +} ion irradiation. It is found that substrate has strong influence on the damage mode of graphene. The mean sputtering yield of graphene under 30 keV Ga{sup +} ion irradiation is 1.77 and the least ion dose to completely remove carbon atoms in graphene is 21.6 ion/nm{sup 2}. Afterwards, the focused ion beam over 21.6 ion/nm{sup 2} is used for the irradiation on a monolayer graphene supported by SiO2 experimentally, resulting in the nanostructures, i.e., nanodot and nanowire array on the graphene. The performances of the nanostructures are characterized by atomic force microscopy and Raman spectrum. A plasma plume shielding model is put forward to explain the nanosculpting results of graphene under different irradiation parameters. In addition, two damage mechanisms are found existing in the fabrication process of the nanostructures by using empirical MD simulations. The results can help us open the possibilities for better control of nanocarbon devices.

Electric field effect of GaAs monolayer from first principles

Directory of Open Access Journals (Sweden)

Jiongyao Wu

2017-03-01

Full Text Available Using first-principle calculations, we investigate two-dimensional (2D honeycomb monolayer structures composed of group III-V binary elements. It is found that such compound like GaAs should have a buckled structure which is more stable than graphene-like flat structure. This results a polar system with out-of-plane dipoles arising from the non-planar structure. Here, we optimized GaAs monolayer structure, then calculated the electronic band structure and the change of buckling height under external electric field within density functional theory using generalized gradient approximation method. We found that the band gap would change proportionally with the electric field magnitude. When the spin-orbit coupling (SOC is considered, we revealed fine spin-splitting at different points in the reciprocal space. Furthermore, the valence and conduction bands spin-splitting energies due to SOC at the K point of buckled GaAs monolayers are found to be weakly dependent on the electric field strength. Finally electric field effects on the spin texture and second harmonic generation are discussed. The present work sheds light on the control of physical properties of GaAs monolayer by the applied electric field.

Association of menstrual phase with smoking behavior, mood and menstrual phase-associated symptoms among young Japanese women smokers.

Science.gov (United States)

Sakai, Hiroko; Ohashi, Kazutomo

2013-03-02

Previous studies of the relationship between the menstrual phases and smoking behavior have been problematic, so the association of menstrual phases with smoking behavior and correlations among smoking, psychological and physical conditions in each phase of the menstrual cycle are unclear. To accurately examine the association between menstrual phases and the amount of smoking (number of cigarettes smoked and breath CO concentration), craving of smoking on visual analogue scale (VAS), depression in the Center for Epidemiologic Studies Depression (CES-D) Scale, and menstrual phase-associated symptoms in the Menstrual Distress Questionnaire (MDQ), we improved various methodological issues, specifically, 1) Ovulation was confirmed by measuring the basal body temperature and identifying a urinary luteinizing hormone (LH) surge in two cycles; 2) The menstrual, follicular, and luteal phases were clearly defined for subjects with different menstrual cycles; 3) The breath CO concentration was measured every day. A notice was posted on public bulletin boards to recruit research subjects and twenty-nine young Japanese women smokers aged 19 to 25 years old were analyzed. The number of cigarettes smoked was greater and the CO concentration was higher in the luteal phase than in the follicular phase. The levels of craving for smoking (VAS), depressiveness (CES-D), and menstrual phase-associated symptoms (MDQ) in the menstrual and luteal phases were higher than those in the follicular phase. The mean score for CES-D was 16 points (the cut-off value in screening for depression) or higher in the menstrual (16.9 ± 8.2) and luteal phases (17.2 ± 8.4).The number of cigarettes smoked and CO concentration were significantly correlated with the levels of craving for smoking, depressiveness, and menstrual phase-associated symptoms in all phases except for MDQ scores in follicular phase. The amount of smoking in the luteal phase was most strongly correlated with these symptoms

Network structure control of binary mixed langmuir monolayers of homo-PS and PS-b-P2VP.

Science.gov (United States)

Wen, Gangyao

2010-03-25

Our recent work showed there existed a composition window for mixed Langmuir monolayers of homopolystyrene (h-PS) and a symmetric diblock copolymer polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) to form necklace-network structures at the air/water interface. In order to study further the possible mechanism and control the network structure (i.e., surface coverage and nanoaggregate diameter), effects of spreading solution concentration and volume, subphase temperature, and transfer pressure on the network structure were studied by the Langmuir monolayer technique and tapping mode atomic force microscopy. With the increase of transfer pressure, there existed a novel nonlinear behavior for the nanoaggregate diameter first to increase, then to decrease, and finally to increase again, while the surface coverage tended to increase step by step. Moreover, with the elevation of temperature, chain motion between the adjoining nanoaggregates tended to be improved and thus the nanoaggregate diameter tended to be more uniform.

Interfacial and thermal energy driven growth and evolution of Langmuir-Schaefer monolayers of Au-nanoparticles.

Science.gov (United States)

Mukhopadhyay, Mala; Hazra, S

2018-01-03

Structures of Langmuir-Schaefer (LS) monolayers of thiol-coated Au-nanoparticles (DT-AuNPs) deposited on H-terminated and OTS self-assembled Si substrates (of different hydrophobic strength and stability) and their evolution with time under ambient conditions, which plays an important role for their practical use as 2D-nanostructures over large areas, were investigated using the X-ray reflectivity technique. The strong effect of substrate surface energy (γ) on the initial structures and the competitive role of room temperature thermal energy (kT) and the change in interfacial energy (Δγ) at ambient conditions on the evolution and final structures of the DT-AuNP LS monolayers are evident. The strong-hydrophobic OTS-Si substrate, during transfer, seems to induce strong attraction towards hydrophobic DT-AuNPs on hydrophilic (repulsive) water to form vertically compact partially covered (with voids) monolayer structures (of perfect monolayer thickness) at low pressure and nearly covered buckled monolayer structures (of enhanced monolayer thickness) at high pressure. After transfer, the small kT-energy (in absence of repulsive water) probably fluctuates the DT-AuNPs to form vertically expanded monolayer structures, through systematic exponential growth with time. The effect is prominent for the film deposited at low pressure, where the initial film-coverage and film-thickness are low. On the other hand, the weak-hydrophobic H-Si substrate, during transfer, appears to induce optimum attraction towards DT-AuNPs to better mimic the Langmuir monolayer structures on it. After transfer, the change in the substrate surface nature, from weak-hydrophobic to weak-hydrophilic with time (i.e. Δγ-energy, apart from the kT-energy), enhances the size of the voids and weakens the monolayer/bilayer structure to form a similar expanded monolayer structure, the thickness of which is probably optimized by the available thermal energy.

Regulation of endothelial cell shape and monolayer permeability by atrial natriuretic peptide

International Nuclear Information System (INIS)

Lofton-Day, C.E.

1989-01-01

Atrial natriuretic peptide (ANP), considered to be an important regulator of intravascular fluid volume, binds specifically to receptors on endothelial cells. In this study, the role of ANP-specific binding was investigated by examining the effect of ANP on the morphology and macromolecular permeability of monolayer cultures of bovine aortic endothelial cells. ANP alone had no observable effect on the monolayers. However, incubation of monolayers with ANP antagonized thrombin- or glucose oxidase-induced cell shape changes and intercellular gap formation. ANP pretreatment also opposed the effect of thrombin and glucose oxidase on actin filament distribution as observed by rhodamine-phalloidin staining and digital image analysis of F0actin staining. In addition, ANP reversed cell shape changes and cytoskeletal alterations induced by thrombin treatment but did not reverse alternations induced by glucose oxidase treatment. ANP significantly reduced increases in monolayer permeability to albumin resulting from thrombin or glucose oxidases treatment. Thrombin caused a 2-fold increase in monolayer permeability to 125 I-labeled albumin, which was abolished by 10 -8 -10 -6 M ANP pretreatment. Glucose oxidase caused similar increases in permeability and was inhibited by ANP at slightly shorter time periods

The titration of carboxyl-terminated monolayers revisited: in situ calibrated fourier transform infrared study of well-defined monolayers on silicon.

Science.gov (United States)

Aureau, D; Ozanam, F; Allongue, P; Chazalviel, J-N

2008-09-02

The acid-base equilibrium at the surface of well-defined mixed carboxyl-terminated/methyl-terminated monolayers grafted on silicon (111) has been investigated using in situ calibrated infrared spectroscopy (attenuated total reflectance (ATR)) in the range of 900-4000 cm (-1). Spectra of surfaces in contact with electrolytes of various pH provide a direct observation of the COOH COO (-) conversion process. Quantitative analysis of the spectra shows that ionization of the carboxyl groups starts around pH 6 and extends over more than 6 pH units: approximately 85% ionization is measured at pH 11 (at higher pH, the layers become damaged). Observations are consistently accounted for by a single acid-base equilibrium and discussed in terms of change in ion solvation at the surface and electrostatic interactions between surface charges. The latter effect, which appears to be the main limitation, is qualitatively accounted for by a simple model taking into account the change in the Helmholtz potential associated with the surface charge. Furthermore, comparison of calculated curves with experimental titration curves of mixed monolayers suggests that acid and alkyl chains are segregated in the monolayer.

Molecular dynamics simulations of melting behavior of alkane as phase change materials slurry

International Nuclear Information System (INIS)

Rao Zhonghao; Wang Shuangfeng; Wu Maochun; Zhang Yanlai; Li Fuhuo

2012-01-01

Highlights: ► The melting behavior of phase change materials slurry was investigated by molecular dynamics simulation method. ► Four different PCM slurry systems including pure water and water/n-nonadecane composite were constructed. ► Amorphous structure and periodic boundary conditions were used in the molecular dynamics simulations. ► The simulated melting temperatures are very close to the published experimental values. - Abstract: The alkane based phase change materials slurry, with high latent heat storage capacity, is effective to enhance the heat transfer rate of traditional fluid. In this paper, the melting behavior of composite phase change materials slurry which consists of n-nonadecane and water was investigated by using molecular dynamics simulation. Four different systems including pure water and water/n-nonadecane composite were constructed with amorphous structure and periodic boundary conditions. The results showed that the simulated density and melting temperature were very close to the published experimental values. Mixing the n-nonadecane into water decreased the mobility but increased the energy storage capacity of composite systems. To describe the melting behavior of alkane based phase change materials slurry on molecular or atomic scale, molecular dynamics simulation is an effective method.

Continuous phase transition and critical behaviors of 3D black hole with torsion

International Nuclear Information System (INIS)

Ma, Meng-Sen; Liu, Fang; Zhao, Ren

2014-01-01

We study the phase transition and the critical behavior of the BTZ black hole with torsion obtained in (1 + 2)-dimensional Poincaré gauge theory. According to Ehrenfest’s classification, when the parameters in the theory are arranged properly, the BTZ black hole with torsion may possess the second-order phase transition which is also a smaller mass/larger mass black hole phase transition. Nevertheless, the critical behavior is different from the one in the van der Waals liquid/gas system. We also calculated the critical exponents of the relevant thermodynamic quantities, which are the same as the ones obtained in the Hořava-Lifshitz black hole and the Born–Infeld black hole. (paper)

GaAs monolayer: Excellent SHG responses and semi metallic to metallic transition modulated by vacancy effect

Science.gov (United States)

Rozahun, Ilmira; Bahti, Tohtiaji; He, Guijie; Ghupur, Yasenjan; Ablat, Abduleziz; Mamat, Mamatrishat

2018-05-01

Monolayer materials are considered as a promising candidate for novel applications due to their attractive magnetic, electronic and optical properties. Investigation on nonlinear optical (NLO) properties and effect of vacancy on monolayer materials are vital to property modulations of monolayers and extending their applications. In this work, with the aid of first-principles calculations, the crystal structure, electronic, magnetic, and optical properties of GaAs monolayers with the vacancy were investigated. The result shows gallium arsenic (GaAs) monolayer produces a strong second harmonic generation (SHG) response. Meanwhile, the vacancy strongly affects structural, electronic, magnetic and optical properties of GaAs monolayers. Furthermore, arsenic vacancy (VAs) brings semi metallic to metallic transition, while gallium vacancy (VGa) causes nonmagnetic to magnetic conversion. Our result reveals that GaAs monolayer possesses application potentials in Nano-amplifying modulator and Nano-optoelectronic devices, and may provide useful guidance in designing new generation of Nano-electronic devices.

Strain and electric field induced metallization in the GaX (X = N, P, As & Sb) monolayer

Science.gov (United States)

Bahuguna, Bhagwati Prasad; Saini, L. K.; Sharma, Rajesh O.; Tiwari, Brajesh

2018-05-01

We investigate the strain and electric field dependent electronic properties of two dimensional Ga-based group III-V monolayer from the first-principles approach within density functional theory. The energy bandgap of GaX monolayer increases upto the certain value of compressive strain and then decreases. On the other hand, the energy bandgap of GaX monolayer is monotonically decreased with increasing tensile strain and become metallic at the higher value. Furthermore, the perpendicular electric field decreases the energy band gap of unstrained GaX monolayer and shows semiconductor to metal transition. These results suggest that the nature of energy bands and value of energy bandgap in GaX monolayer can be tuned by the biaxial mechanical strain or perpendicular electrical field. Additionally, we have also studied the optical response of unstrained GaX monolayer in term of optical conductivity. These findings may provide valuable information to develop the Ga-based optoelectronic devices and further the understanding of the GaX monolayer.

Preparation of porous monolayer film by immersing the stearic acid Langmuir-Blodgett monolayer on mica in salt solution

Energy Technology Data Exchange (ETDEWEB)

Wang, S. [Institute of Near-Field Optics and Nano Technology, School of Physics and Optoelectronic Technology, Dalian University of Technology, Street No. 2 Linggong Road, Dalian 116024 (China); Li, Y.L.; Zhao, H.L.; Liang, H. [Institute of Photo-Biophysics, School of Physics and Electronic, Henan University, Jinming, Kaifeng 475004, Henan (China); Liu, B., E-mail: boliu@henu.edu.cn [Institute of Photo-Biophysics, School of Physics and Electronic, Henan University, Jinming, Kaifeng 475004, Henan (China); Pan, S., E-mail: span@dlut.edu.cn [Institute of Near-Field Optics and Nano Technology, School of Physics and Optoelectronic Technology, Dalian University of Technology, Street No. 2 Linggong Road, Dalian 116024 (China)

2012-11-15

Highlights: Black-Right-Pointing-Pointer Porous film has been prepared by immersing the stearic acid Langmuir-Blodgett monolayer on mica in salt solution. Black-Right-Pointing-Pointer The mechanism relies on the electrostatic screening effect of the cations in salt solution. Black-Right-Pointing-Pointer The factors influencing the size and area of the pores were investigated. - Abstract: Porous materials have drawn attention from scientists in many fields such as life sciences, catalysis and photonics since they can be used to induce some materials growth as expected. Especially, porous Langmuir-Blodgett (LB) film is an ideal material with controlled thickness and flat surface. In this paper, stearic acid (SA), which has been extensively explored in LB film technique, is chosen as the template material with known parameters to prepare the LB film, and then the porous SA monolayer film is obtained by means of etching in salt solution. The main etching mechanism is suggested that the cations in the solution block the electrostatic interaction between the polar carboxyl group of SA and the electronegative mica surface. The influencing factors (such as concentration of salt solution, valence of cation and surface pressure) of the porous SA film are systematically studied in this work. The novel method proposed in this paper makes it convenient to prepare porous monolayer film for designed material growth or cell culture.

Scalability and process transfer of mesenchymal stromal cell production from monolayer to microcarrier culture using human platelet lysate.

Science.gov (United States)

Heathman, Thomas R J; Stolzing, Alexandra; Fabian, Claire; Rafiq, Qasim A; Coopman, Karen; Nienow, Alvin W; Kara, Bo; Hewitt, Christopher J

2016-04-01

The selection of medium and associated reagents for human mesenchymal stromal cell (hMSC) culture forms an integral part of manufacturing process development and must be suitable for multiple process scales and expansion technologies. In this work, we have expanded BM-hMSCs in fetal bovine serum (FBS)- and human platelet lysate (HPL)-containing media in both a monolayer and a suspension-based microcarrier process. The introduction of HPL into the monolayer process increased the BM-hMSC growth rate at the first experimental passage by 0.049 day and 0.127/day for the two BM-hMSC donors compared with the FBS-based monolayer process. This increase in growth rate in HPL-containing medium was associated with an increase in the inter-donor consistency, with an inter-donor range of 0.406 cumulative population doublings after 18 days compared with 2.013 in FBS-containing medium. Identity and quality characteristics of the BM-hMSCs are also comparable between conditions in terms of colony-forming potential, osteogenic potential and expression of key genes during monolayer and post-harvest from microcarrier expansion. BM-hMSCs cultured on microcarriers in HPL-containing medium demonstrated a reduction in the initial lag phase for both BM-hMSC donors and an increased BM-hMSC yield after 6 days of culture to 1.20 ± 0.17 × 10(5) and 1.02 ± 0.005 × 10(5) cells/mL compared with 0.79 ± 0.05 × 10(5) and 0.36 ± 0.04 × 10(5) cells/mL in FBS-containing medium. This study has demonstrated that HPL, compared with FBS-containing medium, delivers increased growth and comparability across two BM-hMSC donors between monolayer and microcarrier culture, which will have key implications for process transfer during scale-up. Copyright © 2016 International Society for Cellular Therapy. Published by Elsevier Inc. All rights reserved.

A quaternary lead based perovskite structured materials with diffuse phase transition behavior

International Nuclear Information System (INIS)

Puli, Venkata Sreenivas; Martínez, R.; Kumar, Ashok; Scott, J.F.; Katiyar, Ram S.

2011-01-01

Graphical abstract: (a) Curie–Weiss plot for the inverse of the relative dielectric permittivity and (b) log (1/ε − 1/ε m ) as function of log (T − T m ) for ceramics at 1 kHz. Highlights: ► Retaining phase pure structure with quaternary complex stoichiometric compositions. ► P–E loops with good saturation polarization (P s ∼ 30.7 μC/cm 2 ). ► Diffused relaxor phase transition behavior with γ estimated is ∼1.65. -- Abstract: A lead based quaternary compound composed of 0.25(PbZr 0.52 Ti 0.48 O 3 ) + 0.25(PbFe 0.5 Ta 0.5 O 3 ) + 0.25 (PbF 0.67 W 0.33 O 3 ) + 0.25(PbFe 0.5 Nb 0.5 O 3 ) – (PZT–PFT–PFW–PFN) was synthesized by conventional solid-state reaction techniques. It showed moderate high dielectric constant, low dielectric loss, and two diffuse phase transitions, one below the room temperature ∼261 K and other above ∼410 K. X-ray diffraction (XRD) patterns revealed a tetragonal crystal structure at room temperature where as scanning electron micrograph (SEM) indicates inhomogeneous surface with an average grain size of 500 nm–3 μm. Well saturated ferroelectric hysteresis loops with good saturation polarization (spontaneous polarization, P s ∼ 30.68 μC/cm 2 ) were observed. Temperature-dependent ac conductivity displayed low conductivity with kink in spectra near the phase transition. In continuing search for developing new ferroelectric materials, in the present study we report stoichiometric compositions of complex perovskite ceramic materials: (PZT–PFT–PFW–PFN) with diffuse phase transition behavior. The crystal structure, dielectric properties, and ferroelectric properties were characterized by XRD, SEM, dielectric spectroscopy, and polarization. 1/ε versus (T) plots revealed diffuse relaxor phase transition (DPT) behavior. The compositional variation on the phase transition temperature, dielectric constant, and ferroelectric to paraelectric phase transitions are discussed.

A quaternary lead based perovskite structured materials with diffuse phase transition behavior

Energy Technology Data Exchange (ETDEWEB)

Puli, Venkata Sreenivas, E-mail: pvsri123@gmail.com [Department of Physics and Institute for Functional Nano Materials, University of Puerto Rico, San Juan, PR 00936 (United States); Martinez, R.; Kumar, Ashok [Department of Physics and Institute for Functional Nano Materials, University of Puerto Rico, San Juan, PR 00936 (United States); Scott, J.F. [Department of Physics and Institute for Functional Nano Materials, University of Puerto Rico, San Juan, PR 00936 (United States); Cavendish Laboratory, Dept. Physics, University of Cambridge, Cambridge CB0 3HE (United Kingdom); Katiyar, Ram S., E-mail: rkatiyar@uprrp.edu [Department of Physics and Institute for Functional Nano Materials, University of Puerto Rico, San Juan, PR 00936 (United States)

2011-12-15

Graphical abstract: (a) Curie-Weiss plot for the inverse of the relative dielectric permittivity and (b) log (1/{epsilon} - 1/{epsilon}{sub m}) as function of log (T - T{sub m}) for ceramics at 1 kHz. Highlights: Black-Right-Pointing-Pointer Retaining phase pure structure with quaternary complex stoichiometric compositions. Black-Right-Pointing-Pointer P-E loops with good saturation polarization (P{sub s} {approx} 30.7 {mu}C/cm{sup 2}). Black-Right-Pointing-Pointer Diffused relaxor phase transition behavior with {gamma} estimated is {approx}1.65. -- Abstract: A lead based quaternary compound composed of 0.25(PbZr{sub 0.52}Ti{sub 0.48}O{sub 3}) + 0.25(PbFe{sub 0.5}Ta{sub 0.5}O{sub 3}) + 0.25 (PbF{sub 0.67}W{sub 0.33}O{sub 3}) + 0.25(PbFe{sub 0.5}Nb{sub 0.5}O{sub 3}) - (PZT-PFT-PFW-PFN) was synthesized by conventional solid-state reaction techniques. It showed moderate high dielectric constant, low dielectric loss, and two diffuse phase transitions, one below the room temperature {approx}261 K and other above {approx}410 K. X-ray diffraction (XRD) patterns revealed a tetragonal crystal structure at room temperature where as scanning electron micrograph (SEM) indicates inhomogeneous surface with an average grain size of 500 nm-3 {mu}m. Well saturated ferroelectric hysteresis loops with good saturation polarization (spontaneous polarization, P{sub s} {approx} 30.68 {mu}C/cm{sup 2}) were observed. Temperature-dependent ac conductivity displayed low conductivity with kink in spectra near the phase transition. In continuing search for developing new ferroelectric materials, in the present study we report stoichiometric compositions of complex perovskite ceramic materials: (PZT-PFT-PFW-PFN) with diffuse phase transition behavior. The crystal structure, dielectric properties, and ferroelectric properties were characterized by XRD, SEM, dielectric spectroscopy, and polarization. 1/{epsilon} versus (T) plots revealed diffuse relaxor phase transition (DPT) behavior. The

Anomalously temperature-dependent thermal conductivity of monolayer GaN with large deviations from the traditional 1 /T law

Science.gov (United States)

Qin, Guangzhao; Qin, Zhenzhen; Wang, Huimin; Hu, Ming

2017-05-01

Efficient heat dissipation, which is featured by high thermal conductivity, is one of the crucial issues for the reliability and stability of nanodevices. However, due to the generally fast 1 /T decrease of thermal conductivity with temperature increase, the efficiency of heat dissipation quickly drops down at an elevated temperature caused by the increase of work load in electronic devices. To this end, pursuing semiconductor materials that possess large thermal conductivity at high temperature, i.e., slower decrease of thermal conductivity with temperature increase than the traditional κ ˜1 /T relation, is extremely important to the development of disruptive nanoelectronics. Recently, monolayer gallium nitride (GaN) with a planar honeycomb structure emerges as a promising new two-dimensional material with great potential for applications in nano- and optoelectronics. Here, we report that, despite the commonly established 1 /T relation of thermal conductivity in plenty of materials, monolayer GaN exhibits anomalous behavior that the thermal conductivity almost decreases linearly over a wide temperature range above 300 K, deviating largely from the traditional κ ˜1 /T law. The thermal conductivity at high temperature is much larger than the expected thermal conductivity that follows the general κ ˜1 /T trend, which would be beneficial for applications of monolayer GaN in nano- and optoelectronics in terms of efficient heat dissipation. We perform detailed analysis on the mechanisms underlying the anomalously temperature-dependent thermal conductivity of monolayer GaN in the framework of Boltzmann transport theory and further get insight from the view of electronic structure. Beyond that, we also propose two required conditions for materials that would exhibit similar anomalous temperature dependence of thermal conductivity: large difference in atom mass (huge phonon band gap) and electronegativity (LO-TO splitting due to strong polarization of bond). Our

Chirality-dependent anisotropic elastic properties of a monolayer graphene nanosheet.

Science.gov (United States)

Guo, Jian-Gang; Zhou, Li-Jun; Kang, Yi-Lan

2012-04-01

An analytical approach is presented to predict the elastic properties of a monolayer graphene nanosheet based on interatomic potential energy and continuum mechanics. The elastic extension and torsional springs are utilized to simulate the stretching and angle variation of carbon-carbon bond, respectively. The constitutive equation of the graphene nanosheet is derived by using the strain energy density, and the analytical formulations for nonzero elastic constants are obtained. The in-plane elastic properties of the monolayer graphene nanosheet are proved to be anisotropic. In addition, Young's moduli, Poisson's ratios and shear modulus of the monolayer graphene nanosheet are calculated according to the force constants derived from Morse potential and AMBER force field, respectively, and they were proved to be chirality-dependent. The comparison with experimental results shows a very agreement.

Photoluminescence inhomogeneity and excitons in CVD-grown monolayer WS2

Science.gov (United States)

Ren, Dan-Dan; Qin, Jing-Kai; Li, Yang; Miao, Peng; Sun, Zhao-Yuan; Xu, Ping; Zhen, Liang; Xu, Cheng-Yan

2018-06-01

Transition metal dichalcogenides two-dimensional materials are of great importance for future electronic and optoelectronic applications. In this work, triangular WS2 monolayers with size up to 130 μm were prepared via chemical vapor deposition method. WS2 monolayers presented uniform Raman intensity, while quenched photoluminescence (PL) was observed in the center. The PL quenching in the central part of WS2 monolayer flakes was attributed to the gradually increasing sulfur vacancies toward the center. The proportion of negative trion (X-) in PL spectrum increases with increasing sulfur vacancies in WS2. The enhanced binding energy of X- suggests higher Fermi level and n-doping level with larger sulfur vacancy concentration. Our findings may be beneficial to the development of integrated devices, and also explore the defect-induced optical and electrical properties for nanophotonics.

Phase Behavior and Equations of State of the Actinide Oxides

Science.gov (United States)

Chidester, B.; Pardo, O. S.; Panero, W. R.; Fischer, R. A.; Thompson, E. C.; Heinz, D. L.; Prescher, C.; Prakapenka, V. B.; Campbell, A.

2017-12-01

The distribution of the long-lived heat-producing actinide elements U and Th in the deep Earth has important implications for the dynamics of the mantle and possibly the energy budget of Earth's core. The low shear velocities of the Large Low-Shear Velocity Provinces (LLSVPs) on the core-mantle boundary suggests that these regions are at least partially molten and may contain concentrated amounts of the radioactive elements, as well as other large cations such as the rare Earth elements. As such, by exploring the phase behavior of actinide-bearing minerals at extreme conditions, some insight into the mineralogy, formation, and geochemical and geodynamical effects of these regions can be gained. We have performed in situ high-pressure, high-temperature synchrotron X-ray diffraction experiments and calculations on two actinide oxide materials, UO2 and ThO2, to determine their phase behavior at the extreme conditions of the lower mantle. Experiments on ThO2 reached 60 GPa and 2500 K, and experiments on UO2 reached 95 GPa and 2500 K. We find that ThO2 exists in the fluorite-type structure to 20 GPa at high temperatures, at which point it transforms to the high-pressure cotunnite-type structure and remains thus up to 60 GPa. At room temperature, an anomalous expansion of the fluorite structure is observed prior to the transition, and may signal anion sub-lattice disorder. Similarly, UO2 exists in the fluorite-type structure at ambient conditions and up to 28 GPa at high temperatures. Above these pressures, we have observed a previously unidentified phase of UO2 with a tetragonal structure as the lower-temperature phase and the cotunnite-type phase at higher temperatures. Above 78 GPa, UO2 undergoes another transition or possible dissociation into two separate oxide phases. These phase diagrams suggest that the actinides could exist as oxides in solid solution with other analogous phases (e.g. ZrO2) in the cotunnite-type structure throughout much of Earth's lower mantle.

Mixed carboranethiol self-assembled monolayers on gold surfaces

Energy Technology Data Exchange (ETDEWEB)

Yavuz, Adem [Micro and Nanotechnology Department, Graduate School of Natural and Applied Science, Middle East Technical University, Ankara 06800 (Turkey); Sohrabnia, Nima [Department of Chemistry, Middle East Technical University, Ankara 06800 (Turkey); Yilmaz, Ayşen [Micro and Nanotechnology Department, Graduate School of Natural and Applied Science, Middle East Technical University, Ankara 06800 (Turkey); Department of Chemistry, Middle East Technical University, Ankara 06800 (Turkey); Danışman, M. Fatih, E-mail: danisman@metu.edu.tr [Micro and Nanotechnology Department, Graduate School of Natural and Applied Science, Middle East Technical University, Ankara 06800 (Turkey); Department of Chemistry, Middle East Technical University, Ankara 06800 (Turkey)

2017-08-15

Highlights: • M1 binds to the gold surface preferentially when co-deposited with M9 or O1. • Contact angles show similar trends regardless of the gold substrate roughness. • Contact angles were lower, with higher hysteresis, on template stripped gold. • Mixed carboranethiol SAMs have similar morphological properties regardless of mixing ratio. - Abstract: Carboranethiol self-assembled monolayers on metal surfaces have been shown to be very convenient systems for surface engineering. Here we have studied pure and mixed self-assembled monolayers (SAMs) of three different carboranethiol (CT) isomers on gold surfaces. The isomers were chosen with dipole moments pointing parallel to (m-1-carboranethiol, M1), out of (m-9-carboranethiol, M9) and into (o-1-carboranethiol, O1) the surface plane, in order to investigate the effect of dipole moment orientation on the film properties. In addition, influence of the substrate surface morphology on the film properties was also studied by using flame annealed (FA) and template stripped (TS) gold surfaces. Contact angle measurements indicate that in M1/M9 and M1/O1 mixed SAMs, M1 is the dominant species on the surface even for low M1 ratio in the growth solution. Whereas for O1/M9 mixed SAMs no clear evidence could be observed indicating dominance of one of the species over the other one. Though contact angle values were lower and hysteresis values were higher for SAMs grown on TS gold surfaces, the trends in the behavior of the contact angles with changing mixing ratio were identical for SAMs grown on both substrates. Atomic force microscopy images of the SAMs on TS gold surfaces indicate that the films have similar morphological properties regardless of mixing ratio.

Pressure-temperature phase behavior of mixtures of natural sphingomyelin and ceramide extracts.

Science.gov (United States)

Barriga, Hanna M G; Parsons, Edward S; McCarthy, Nicola L C; Ces, Oscar; Seddon, John M; Law, Robert V; Brooks, Nicholas J

2015-03-31

Ceramides are a group of sphingolipids that act as highly important signaling molecules in a variety of cellular processes including differentiation and apoptosis. The predominant in vivo synthetic pathway for ceramide formation is via sphingomyelinase catalyzed hydrolysis of sphingomyelin. The biochemistry of this essential pathway has been studied in detail; however, there is currently a lack of information on the structural behavior of sphingomyelin- and ceramide-rich model membrane systems, which is essential for developing a bottom-up understanding of ceramide signaling and platform formation. We have studied the lyotropic phase behavior of sphingomyelin-ceramide mixtures in excess water as a function of temperature (30-70 °C) and pressure (1-200 MPa) by small- and wide-angle X-ray scattering. At low ceramide concentrations the mixtures form the ripple gel phase (P(β)') below the gel transition temperature for sphingomyelin, and this observation has been confirmed by atomic force microscopy. Formation of the ripple gel phase can also be induced at higher temperatures via the application of hydrostatic pressure. At high ceramide concentration an inverse hexagonal phase (HII) is formed coexisting with a cubic phase.

A Simplified Micromechanical Modeling Approach to Predict the Tensile Flow Curve Behavior of Dual-Phase Steels

Science.gov (United States)

Nanda, Tarun; Kumar, B. Ravi; Singh, Vishal

2017-11-01

Micromechanical modeling is used to predict material's tensile flow curve behavior based on microstructural characteristics. This research develops a simplified micromechanical modeling approach for predicting flow curve behavior of dual-phase steels. The existing literature reports on two broad approaches for determining tensile flow curve of these steels. The modeling approach developed in this work attempts to overcome specific limitations of the existing two approaches. This approach combines dislocation-based strain-hardening method with rule of mixtures. In the first step of modeling, `dislocation-based strain-hardening method' was employed to predict tensile behavior of individual phases of ferrite and martensite. In the second step, the individual flow curves were combined using `rule of mixtures,' to obtain the composite dual-phase flow behavior. To check accuracy of proposed model, four distinct dual-phase microstructures comprising of different ferrite grain size, martensite fraction, and carbon content in martensite were processed by annealing experiments. The true stress-strain curves for various microstructures were predicted with the newly developed micromechanical model. The results of micromechanical model matched closely with those of actual tensile tests. Thus, this micromechanical modeling approach can be used to predict and optimize the tensile flow behavior of dual-phase steels.

Chemically Transformable Configurations of Mercaptohexadecanoic Acid Self-Assembled Monolayers Adsorbed on Au(111)

International Nuclear Information System (INIS)

van Buuren, T; Bostedt, C; Nelson, A J; Terminello, L J; Vance, A L; Fadley, C S; Willey, T M

2003-01-01

Carboxyl terminated Self-Assembled Monolayers (SAMs) are commonly used in a variety of applications, with the assumption that the molecules form well ordered monolayers. In this work, NEXAFS verifies well ordered monolayers can be formed using acetic acid in the solvent. Disordered monolayers with unbound molecules present in the result using only ethanol. A stark reorientation occurs upon deprotonation of the endgroup by rinsing in a KOH solution. This reorientation of the endgroup is reversible with tilted over, hydrogen bound carboxyl groups while carboxylate-ion endgroups are upright. C1s photoemission shows that SAMs formed and rinsed with acetic acid in ethanol, the endgroups are protonated, while without, a large fraction of the molecules on the surface are carboxylate terminated

Enhanced photoresponse of monolayer molybdenum disulfide (MoS2) based on microcavity structure

Science.gov (United States)

Lu, Yanan; Yang, Guofeng; Wang, Fuxue; Lu, Naiyan

2018-05-01

There is an increasing interest in using monolayer molybdenum disulfide (MoS2) for optoelectronic devices because of its inherent direct band gap characteristics. However, the weak absorption of monolayer MoS2 restricts its applications, novel concepts need to be developed to address the weakness. In this work, monolayer MoS2 monolithically integrates with plane microcavity structure, which is formed by the top and bottom chirped distributed Bragg reflector (DBR), is demonstrated to improve the absorption of MoS2. The optical absorption is 17-fold enhanced, reaching values over 70% at work wavelength. Moreover, the monolayer MoS2-based photodetector device with microcavity presents a significantly increased photoresponse, demonstrating its promising prospects in MoS2-based optoelectronic devices.

Physicochemical properties of phosphatidylcholine (PC) monolayers with different alkyl chains, at the air/water interface

International Nuclear Information System (INIS)

Yun, Hee Jung; Choi, Young Wook; Kim, Nam Jeong; Sohn, Dae Won

2003-01-01

Physicochemical properties of a series of PC monolayers with different alkyl chains (C24, C20, C16, and C8), at the air/water interface were investigated. The surface pressure is influenced mainly by the hydrophobicity of the PCs, which is confirmed by the curve shape and the on-set value of π-A isotherms at the air/water interface by increasing the number of alkyl chain. The on-set values of surface pressure were 125 A 2 /molecule for DOPC(C8), 87 A 2 /molecule for DPPC(C16), 75 A 2 /molecule for DAPC(C20), and 55 A 2 /molecule for DLPC(C24), respectively. The orientations of alkyl chains at the air/water interface are closely connected with the rigidity of the monolayers, and it was confirmed by the tendency of monolayer thickness in ellipsometry data. The temperature dependence of a series of PCs shows that the surface pressure decreases by increasing temperature, because the longer the alkyl chain length, the larger the hydrophobic interaction in surface pressure. The temperature effects and the conformational changes of unsaturated and saturated PCs were confirmed by the computer simulation study of the cis-trans transition with POPC and DPPC(C16). The cis-trans conformational energy difference of POPC is 62.06 kcal/mol and that of DPPC(C16) is 6.75 kcal/mol. Due to the high conformational energy barrier of POPC, phase transition of POPC is limited in comparison with DPPC(C16)

Physicochemical properties of phosphatidylcholine (PC) monolayers with different alkyl chains, at the air/water interface

Energy Technology Data Exchange (ETDEWEB)

Yun, Hee Jung; Choi, Young Wook [Hanyang Univ., Seoul (Korea, Republic of); Kim, Nam Jeong; Sohn, Dae Won [Sahmyook Univ., Seoul (Korea, Republic of)

2003-03-01

Physicochemical properties of a series of PC monolayers with different alkyl chains (C24, C20, C16, and C8), at the air/water interface were investigated. The surface pressure is influenced mainly by the hydrophobicity of the PCs, which is confirmed by the curve shape and the on-set value of {pi}-A isotherms at the air/water interface by increasing the number of alkyl chain. The on-set values of surface pressure were 125 A{sup 2}/molecule for DOPC(C8), 87 A{sup 2}/molecule for DPPC(C16), 75 A{sup 2}/molecule for DAPC(C20), and 55 A{sup 2}/molecule for DLPC(C24), respectively. The orientations of alkyl chains at the air/water interface are closely connected with the rigidity of the monolayers, and it was confirmed by the tendency of monolayer thickness in ellipsometry data. The temperature dependence of a series of PCs shows that the surface pressure decreases by increasing temperature, because the longer the alkyl chain length, the larger the hydrophobic interaction in surface pressure. The temperature effects and the conformational changes of unsaturated and saturated PCs were confirmed by the computer simulation study of the cis-trans transition with POPC and DPPC(C16). The cis-trans conformational energy difference of POPC is 62.06 kcal/mol and that of DPPC(C16) is 6.75 kcal/mol. Due to the high conformational energy barrier of POPC, phase transition of POPC is limited in comparison with DPPC(C16)

Surface mechanical attrition treatment induced phase transformation behavior in NiTi shape memory alloy

International Nuclear Information System (INIS)

Hu, T.; Wen, C.S.; Lu, J.; Wu, S.L.; Xin, Y.C.; Zhang, W.J.; Chu, C.L.; Chung, J.C.Y.; Yeung, K.W.K.; Kwok, D.T.K.; Chu, Paul K.

2009-01-01

The phase constituents and transformation behavior of the martensite B19' NiTi shape memory alloy after undergoing surface mechanical attrition treatment (SMAT) are investigated. SMAT is found to induce the formation of a parent B2 phase from the martensite B19' in the top surface layer. By removing the surface layer-by-layer, X-ray diffraction reveals that the amount of the B2 phase decreases with depth. Differential scanning calorimetry (DSC) further indicates that the deformed martensite in the sub-surface layer up to 300 μm deep exhibits the martensite stabilization effect. The graded phase structure and transformation behavior in the SMATed NiTi specimen can be attributed to the gradient change in strain with depth.

Morphology, defect evolutions and nano-mechanical anisotropy of behenic acid monolayer

International Nuclear Information System (INIS)

Yang Guanghong; Jiang Xiaohong; Dai Shuxi; Cheng Gang; Zhang Xingtang; Du Zuliang

2010-01-01

Langmuir-Blodgett monolayers of behenic acid (BA) were prepared by the vertical deposition method and their morphological evolutions and nano-mechanical anisotropy were studied by atomic force microscopy (AFM) and lateral force microscopy. Results show that there are platforms in the differential surface pressure-area (π-A) isotherm presenting linear relations between the chain tilting angles and surface pressures. The reorganization, appearance and disappearance of defects such as pinholes and holes can strongly affect the profile of π-A isotherm; AFM images reflect evolution rules from pinholes to holes, and from monolayer to bilayers along with compression and relaxation of structures in BA monolayer. Due to higher molecule density and larger real contact area, the tip-monolayer contacts at 15 and 25 mN/m correspond to the Derjaguin-Muller-Toporov (DMT) model showing long-ranged interaction forces. But owing to more easily-deformed conformations, contacts at 5 and 35 mN/m accord with the Johnson-Kendall-Robert and DMT transition cases exhibiting short-ranged interface interactions. A little higher friction is proved in the direction perpendicular to the deposition.

Al-Doped ZnO Monolayer as a Promising Transparent Electrode Material: A First-Principles Study

Directory of Open Access Journals (Sweden)

Mingyang Wu

2017-03-01

Full Text Available Al-doped ZnO has attracted much attention as a transparent electrode. The graphene-like ZnO monolayer as a two-dimensional nanostructure material shows exceptional properties compared to bulk ZnO. Here, through first-principle calculations, we found that the transparency in the visible light region of Al-doped ZnO monolayer is significantly enhanced compared to the bulk counterpart. In particular, the 12.5 at% Al-doped ZnO monolayer exhibits the highest visible transmittance of above 99%. Further, the electrical conductivity of the ZnO monolayer is enhanced as a result of Al doping, which also occurred in the bulk system. Our results suggest that Al-doped ZnO monolayer is a promising transparent conducting electrode for nanoscale optoelectronic device applications.

Substrate effect on the growth of monolayer dendritic MoS2 on LaAlO3 (100) and its electrocatalytic applications

Science.gov (United States)

Li, Cong; Zhang, Yu; Ji, Qingqing; Shi, Jianping; Chen, Zhaolong; Zhou, Xiebo; Fang, Qiyi; Zhang, Yanfeng

2016-09-01

In accommodating the rapid development of two-dimensional (2D) nanomaterials, chemical vapor deposition (CVD) has become a powerful tool for their batch production with desirable characteristics, such as high crystal quality, large domain size, and tunable domain shape. The crystallinity and morphology of the growth substrates usually play a crucial role in the CVD synthesis of high-quality monolayer MoS2, a kind of 2D layered material which has ignited huge interest in nanoelectronics, optoelectronics and energy harvesting, etc. Herein, by utilizing a low-pressure chemical vapor deposition (LPCVD) system, we demonstrate a regioselective synthesis of monolayer MoS2 on the corrugated single-crystal LaAlO3 (100) with twin crystal domains induced by the second-order phase transition. Unique dendritic morphologies with tunable nucleation densities were obtained in different regions of the undulated substrate, presenting a strong substrate modulation effect. Interestingly, the exposure of abundant active edge sites along with the rather high nucleation density makes the monolayer dendritic MoS2 a good electrocatalyst for hydrogen evolution reaction (HER), particularly featured by a rather high exchange current density (70.4 μA cm-2). Furthermore, uniform monolayer MoS2 films can also be obtained and transferred to arbitrary substrates. We believe that this work provides a new growth system for the controllable synthesis of 2D layered materials with unique dendritic morphologies, as well as its great application potential in energy conversion and harvesting.

Synthesis of Novel Amphiphilic Azobenzenes and X-ray Scattering Studies of Their Langmuir Monolayers

DEFF Research Database (Denmark)

Sørensen, Thomas Just; Kjær, Kristian; Breiby, Dag Werner

2008-01-01

. At the air-water interface, the amphiphilic azobenzenes form noncrystalline but stable Langmuir films that display an unusual reversible monolayer collapse close to 35 mN/m. The structures and phase transitions were studied by X-ray reflectivity (XR) and grazing-incidence X-ray diffraction, both utilizing...... synchrotron radiation. Compression beyond the collapse point does not change the XR data, showing that the film is unchanged at the molecular level, even at areas less than half of that of the collapse. This leads to the conclusion that few macroscopic collapse sites are responsible for reversibly removing...

NO2 decreases paracellular resistance to ion and solute flow in alveolar epithelial monolayers

International Nuclear Information System (INIS)

Cheek, J.M.; Kim, K.J.; Crandall, E.D.

1990-01-01

Primary cultured monolayers of rat alveolar epithelial cells grown on tissue culture-treated Nuclepore filters were exposed to 2.5 ppm nitrogen dioxide NO 2 for 2-20 min. Changes in monolayer bioelectric properties and solute permeabilities were subsequently measured. Exposure to NO 2 produced a dose-dependent decrease in monolayer transepithelial electrical resistance (Rt), whereas monolayer short-circuit current was unaffected. Post-exposure monolayer permeability to 14 C-sucrose (which primarily crosses alveolar epithelium via the paracellular pathway) increased markedly. That for 3 H-glycerol (which permeates through both paracellular and transcellular pathways) increased to a lesser extent. Partial recovery of Rt and solute permeabilities was noted by 48-h post-exposure. The time courses of the decrease in Rt and increase in solute permeabilities were similar. These results suggest that NO 2 primarily impairs passive alveolar epithelial barrier functions in vitro, probably by altering intercellular junctions, and does not appear to directly affect cell membrane active ion transport processes. When correlated with results obtained from experimental approaches, studies of in vitro alveolar epithelial monolayers may facilitate investigations of dosimetry, sites, and mechanisms of oxidant injury in the lung

Functionalizable self-assembled trichlorosilyl-based monolayer for application in biosensor technology

Energy Technology Data Exchange (ETDEWEB)

De La Franier, Brian; Jankowski, Alexander; Thompson, Michael, E-mail: mikethom@chem.utoronto.ca

2017-08-31

This paper describes the design and synthesis of 3-(3-(trichlorosilyl)propoxy)propanoyl chloride (MEG-Cl), a compound capable of forming functionalizable monolayers on hydroxylated surfaces. The compound was synthesized in high purity, as suggested by nuclear magnetic resonance analysis, and in moderate overall yield. Contact angle measurement and X-ray photoelectron spectroscopy confirm the binding of MEG-Cl to an amorphous glass substrate and the further modification of the monolayer with a nickel (II)-binding ligand for the purpose of binding polyhistidine-tagged proteins. The compound will be useful in biosensing applications due to its ability to be easily modified with any number of nucleophilic functional groups subsequent to substrate monolayer formation.