Advanced Materials

Cover image for Advanced Materials

July/August 1994

Volume 6, Issue 7-8

Pages fmi–fmi, 527–618

  1. Masthead

    1. Top of page
    2. Masthead
    3. Essay
    4. Reviews
    5. Communications
    6. Research News
    7. Book Reviews
    1. Masthead (page fmi)

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060701

  2. Essay

    1. Top of page
    2. Masthead
    3. Essay
    4. Reviews
    5. Communications
    6. Research News
    7. Book Reviews
    1. The Development of Liquid Crystal Research (pages 527–528)

      Dr. Volkmar Vill

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060702

      Statistics and trends in liquid crystal (LC) research are presented, taken from the new “Liqcryst” database. Did you know that more than 50000 mesogenic compounds had been studied by 1990? Or that more than 2000 papers and 1500 patents are published in the field of liquid crystals each year? Some particular breakthroughs are highlighted and the current rate of development of chiral LCs, which exhibit ferroelectric, ferrielectric, and antiferroelectric phases, is compared with that of nematic displays some years ago.

  3. Reviews

    1. Top of page
    2. Masthead
    3. Essay
    4. Reviews
    5. Communications
    6. Research News
    7. Book Reviews
    1. Starburst/Cascade Dendrimers: Fundamental building blocks for a new nanoscopic chemistry set (pages 529–539)

      Prof. Donald A. Tomalia

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060703

      That dendrimer structures act as fundamental chemical building blocks (see Figure), forming a “nanoscopic chemistry set” analogous to the “picoscopic chemistry set” formed by atoms, is discussed in this review. Following the logic used by 19th century chemists while defining the atomic “chemistry set”, it is shown that the ability to preface directionality in dendrimer systems validates this approach.

    2. Tuning Schottky Barriers by atomic layer control at metal—semiconductor interfaces (pages 540–548)

      Prof. Fernando Flores and Prof. Rodolfo Miranda

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060704

      Metal-semiconductor contacts are essentially of two kinds : ohmic contacts and Schottky barriers. The physics governing the formation of metalsemiconductor Schottky barriers–which are the basis of most electronic devices–and ways of tuning their height are reviewed, concentrating on the theory. It is shown that tuning can be achieved by modifying the interface geometry, by modifying the surface dangling bonds, or, in the case of heterojunction interfaces, by the addition of an interlayer. Directions for (experimental) future research are suggested.

    3. Novel Ultrahard Materials (pages 549–560)

      Prof. Ralf Riedel

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060705

      Superhard materials are needed to replace diamond in applications at high temperatures, where diamond is unstable. Novel carbon- and boron-based materials are described whose discovery or postulation has greatly stimulated research in this area. The use of calculations to predict the properties of new materials is illustrated for B-C3N4, which was synthesized only after its structure (see Figure) had been calculated.

  4. Communications

    1. Top of page
    2. Masthead
    3. Essay
    4. Reviews
    5. Communications
    6. Research News
    7. Book Reviews
    1. Conformational chirality of oligothiophenes in the solid state. X-Ray structure of 3,4′,4″-trimethyl-2,2′:5′,2″-terthiophene (pages 561–564)

      Dr. Giovanna Barbarell, Massimo Zambianchi, Prof. Alessandro Bongini and Prof. Luciano Antolini

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060706

      Chiral crystals of organic compounds have many potential applications, particularly in laser technology. The first case among oligothiophenes of chirality in the solid state is reported, the crystal structure being given along with selected NMR data and force field MM2 calculations that provide information about the conformational properties of the compound in solution. Two structural features new for α-conjugated oligothiophenes are exhibited: a chiral space group and a crystal packing that involves short van der Waals contacts.

    2. Magnetic properties of ferrocene-based conjugated polymers (pages 564–568)

      Dr. Mohamed Hmyene, Dr. Abderrahim Yassar, Dr. Marcel Escorne, Dr. Annick Percheron-Guegan and Dr. Francis Garnier

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060707

      A novel route to organic ferromagnetic materials is proposed that is based on the stability of spin-containing organometallic moieties such as ferricenium and the electronic or topological interactions contributed by a polymer. The magnetic properties of the new high-spin polymers (see Figure) are shown to be sensitively dependent on the chemical nature of the bridge linking the ferricenium units.

    3. Synthesis of functionalized poly(dithienylpyrrole) derivatives and their application in amperometric biosensors (pages 568–571)

      Harald Röckel, Johanna Huber, Prof. Rolf Gleiter and Dr. Wolfgang Schuhmann

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060708

      Biosensors require a method of fixing the sensor components to the transducer surface. For amperometric enzyme electrodes, this means that functionahzed electrode surfaces have to be developed in order to covalently bond enzymes to the electrode surface. The synthesis and electrochemical polymerization of new dithienyl-pyrrole derivatives are described and the biosensor characteristics of the resulting electrodes are demonstrated using immobilized glucose oxidase as a model enzyme.

    4. “Open” analogues of azacycloalkane mesogens: Liquid-crystalline diethylenetriamides (pages 572–574)

      Uwe Stebani, Dr. Günter Lattermann, Michael Wittenberg, Reinhard Festag and Joachim Heinz Wendorff

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060709

      Liquid crystals containing “open” analogues of the mesomorphic amide 1,4,7-triazacyclononane, i.e., 3,4-bis(alkoxy)- benzoyl substituted diethylenetriamine, are reported, showing that the closed-ring structure of the central core is not essential for mesomorphism in these compounds. The Figure shows the pronounced pseudo-focalconic texture observed under the polarizing microscope for the decy1 derivative.

    5. The role of absorbing nonlinear optical chromophores in photorefractive polymers (pages 574–577)

      Henk J. Bolink, Dr. Victor V. Krasnikov, George G. Malliaras and Prof. Georges Hadziioannou

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060710

      Organic photorefractive materials have only recently been considered as alternatives to inorganic crystals such as lithium niobate, despite the fact that they offer possible advantages, such as mechanical flexibility, low fabrication costs, and the ability to chemically tune the properties of the material. The influence of the nonlinear optical chromophore on various phenomena observed in a photorefractive polymer is reported on the basis of a study of samples derived from poly(N-vinylcarbazole) sensitized with 2,4,7-trinitro-9- fluorenone.

    6. Electrochemical formation of a self-doped conductive polymer in the absence of a supporting electrolyte. The copolymerization of o-aminobenzenesulfonic acid and aniline (pages 577–580)

      Dr. Cesar Barbero and Dr. Rüdiger Kötz

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060711

      Electrochemical polymerization without a supporting electrolyte would most probably yield a material with more reproducible and better difined propertis, and is therefore a technique to be encouraged. The formation of an electroactive, self-doped polymer (see Figure) by electropolymerization is described and the analysis of the resulting films presented.

    7. Highly polarizable biaryl salts for liquid crystals and nonlinear optics: Synthesis and properties of a phenol/pyridinium triflate (pages 580–583)

      Dr. Philippe Boy, Dr. Catherine Combellas, Grágoire Mathey, Dr. Serge Palacin, Dr. André Persoons, Dr. André Thiébault and Dr. Thierry Verbiest

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060712

      A nonlinear waveguide material with a good transparency/efficiency trade-off is presented. The synthesis of the biaryl-based salt and its mesomorphic and nonlinear optical properties, including second harmonic generation from floating Langmuir-Blodgett layers, are described. The advantages of this new phenol/pyridinium triflate, which exhibits mesomorphic properties over a 50°C range, compared to the uncharged and zwitterionic analogues are discussed.

    8. The formation of silicon carbide films from disilane derivatives (pages 584–587)

      Prof. Edwin Hengge, Dr. Arno Zechmann, Dr. Ferdinand Hofer, Dr. Peter Pölt, Dr. Benno Lux, Dr. Michael Danzinger and Dr. Roland Haubner

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060713

      The formation of silicon carbide films presents problems arising from the fact that the precursors employed are usually a mixture of compounds. It is demonstrated that high-quality silicon carbide films (see Figure) can be produced by chemical vapor deposition using easily available disilane derivatives as the precursor.

    9. Oriented growth of quinquethiophene on SiO2—An atomic force microscopy study (pages 587–589)

      Oliver Böhme, Dr. Christiane Ziegler and Prof. Wolfgang Göpel

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060714

      Highly ordered organic films must be prepared and characterized if the electrical properties of future organic-based electronic devices are to be improved, because it is only then that our understanding of intermolecular transport in polymer films can increase. An atomic force microscopy study is presented that shows that quinquethiophene can be physisorbed on Si02 to form highly ordered layers. A change from layer-by-layer to multilayer growth is reported to occur upon completion of the second monolayer.

    10. Localized incorporation of lanthanum carbide crystals in carbon nanotubes (pages 590–592)

      Dr. Masafumi Ata, Dr. Yasunori Kijima, Dr. Andrew J. Hudson, Dr. Hiroshi Imoto, Dr. Nobuyuki Matsuzawa and Dr. Noboru Takahashi

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060715

      Carbon nanotubes containing lanthanum carbide suggest that lanthanum may show catalytic activity for the formation of nanotubes. Images of the graphitic structures growing on the surface of silver-colored deposits such as the SEM image of a straight carbon nanotube shown in the Figure, are presented.

  5. Research News

    1. Top of page
    2. Masthead
    3. Essay
    4. Reviews
    5. Communications
    6. Research News
    7. Book Reviews
    1. Processing of high-temperature superconducting tapes (pages 593–594)

      Dr. Peter Majewski

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060716

      Long high-temperature superconductor tapes have progressed immensely recently. For example, the past two years have seen a factor of five improvement in the effective critical current of (Bi,Pb)2 + xSr2Ca2Cu3O10 + d cables. The various synthesis and processing techniques are briefly reviewed and areas pointed out where much work still remains to be done, for example, on improving the mechanical properties of the silver sheath by alloying.

    2. Molecular recognition and chemoresistive materials (pages 595–597)

      Prof. Timothy M. Swager and Michael J. Marsella

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060717

      Conducting-polymer-based sensory materials systems are designed to exhibit ionochromic, electrochemical, and/or resistive responses to specific chemical signals. The integration of molecular recognition elements into them is described. Poly(bithiophene) undergoes a twisting of the polymer backbone upon ion complexation, producing a reduction in conductivity.

    3. Ferroelectric liquid-crystalline elastomers (pages 598–599)

      Prof. Rudolf Zentel and Martin Brehmer

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060718

      Liquid-crystalline (LC) elastomers, which combine the properties of LC phases and the rubber-like elasticity of polymer networks, are of particular interest when the LC phases exhibit ferroelectric properties. Recent work is described on monodomains of chiral smectic C elastomers produced by photo-crosslinking. These materials are being investigated for potential applications as self-poling piezoelements and pyrodetectors.

    4. Microfabrication by microcontact printing of self-assembled monolayers (pages 600–604)

      Dr. James L. Wilbur, Dr. Amit Kumar, Enoch Kim and Prof. George M. Whitesides

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060719

      Microcontact printing, is described. It offers extreme experimental simplicity and flexibility, relying on the ability of self-assembled monolayers (SAMs) of longchain alkanethiolates on gold and other metals to act as nanometer resists. The Figure is an electron micrograph of a silicon microstructure resulting from chemical etching of a patterned SAM.

    5. Toward organic synthesis of a nanometer-size magnetic particle (pages 605–607)

      Prof. Andrzej Rajca

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060720

      Magnetic phenomena in small magnetic particles include giant magnetoresistance and mesoscopic tunneling of quantum magnetization. Further progress in this area requires the availability of particles of uniform size and shape. Recent developments in the synthesis of monodisperse organic particles are discussed, in particular in the area of dendritic molecules, which could lead to an extension of the applications of such particles, which presently range from magnetic memories to permanent magnets.

    6. Charged guest recognition by redox responsive ligand systems (pages 607–609)

      Dr. Paul D. Beer

      Article first published online: 15 SEP 2004 | DOI: 10.1002/adma.19940060721

      Redox responsive macrocyclic ligands can be used for the recognition of charged guest molecules and so are of importance for potential new molecular sensory devices. Systems are reported that enable the electrochemical recognition of various cations and anions. Tripodal cobalticinium and ferrocene ionophores electrochemically recognize H2PO4 in the presence of excess HSO4 and Cl anions.

  6. Book Reviews

    1. Top of page
    2. Masthead
    3. Essay
    4. Reviews
    5. Communications
    6. Research News
    7. Book Reviews

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