Advanced Materials

Cover image for Advanced Materials

August, 1998

Volume 10, Issue 12

Pages 901–964

    1. Atom Transfer Radical Polymerization and the Synthesis of Polymeric Materials (pages 901–915)

      Timothy E. Patten and Krzysztof Matyjaszewski

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<901::AID-ADMA901>3.0.CO;2-B

      The development of new controlled radical polymerization methods has progressed rapidly over the last five years. One of the most useful of these methods, atom transfer radical polymerization (ATRP), a powerful technique for the design and synthesis of new polymeric materials with novel structures, is reviewed. The Figure represents a hyperbranched polymer resulting from ATRP of p-chloromethylstyrene.

    2. Efficient, Low Operating Voltage Polymer Light-Emitting Diodes with Aluminum as the Cathode Material (pages 917–920)

      Yong Cao, Gang Yu and Alan J. Heeger

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<917::AID-ADMA917>3.0.CO;2-K

      The architecture of polymer light-emitting diodes (LEDs) consists of a thin film of luminescent conjugated polymer sandwiched between two contacts. The difficulty of working with low-workfunction, electron-injecting metals such as calcium, which are generally considered necessary for high luminescence efficiency, has led to relatively high-workfunction metals such as aluminum being examined for their potential as cathode materials. The performance enhancement produced by blending the electroluminescent polymer with a specific class of surfactant molecules is reported.

    3. A Flexible Conjugated Polymer Laser (pages 920–923)

      Christian Kallinger, Martin Hilmer, Andreas Haugeneder, Martin Perner, Wolfgang Spirkl, Uli Lemmer, Jochen Feldmann, Ullrich Scherf, Klaus Müllen, Andreas Gombert and Volker Wittwer

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<920::AID-ADMA920>3.0.CO;2-7

      Collective stimulated emission processes in conjugated polymers makes these materials potential candidates for laser applications. The fabrication of a low-cost flexible distributed feedback laser (see Figure and also the cover) by spin-coating a conjugated polymer onto a specially structured, flexible plastic substrate is reported. Single-mode laser emission in the blue-green spectral region has been achieved.

    4. The Concept of “Threshold Voltage” in Organic Field-Effect Transistors (pages 923–927)

      Gilles Horowitz, Riadh Hajlaoui, Habib Bouchriha, Ramzi Bourguiga and Mohcen Hajlaoui

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<923::AID-ADMA923>3.0.CO;2-W

      The performance of organic field-effect transistors (OFETs) has improved substantially in recent years. Their field-effect mobilities are now comparable to that of hydrogenated amorphous silicon thin-film transistors (TFTs). Both TFTs and OFETs operate in the accumulation regime and the authors here develop a comprehensive model for OFETs in this regime. They show that, in the case of a constant mobility, a threshold voltage cannot be defined. The threshold voltage observed in practice is attributed to a gate-voltage-dependent mobility.

    5. A Multifunctional Photorefractive Material Showing High Optical Gain and Diffraction Efficiency (pages 927–931)

      Wenjie Li, Alireza Gharavi, Qing Wang and Luping Yu

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<927::AID-ADMA927>3.0.CO;2-G

      The design and synthesis of a new photorefractive material by incorporation of an oligo(3-alkylthiophene) segment with a nonlinear optical chromophore is reported by the authors. They demonstrate the potential use of this material as an optical data storage and image processing medium. Studies of the formation dynamics of holographic gratings (the Figure shows a holographic image) reveal the fast response time of the material to optical signals.

    6. Organic Molecular Beam Deposition of Highly Oriented β-Tetrahexylsexithiophene Films (pages 931–934)

      Alessandro Borghesi, Adele Sassella, Riccardo Tubino, Silvia Destri and William Porzio

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<931::AID-ADMA931>3.0.CO;2-#

      Organic molecular beam deposition (OMBD) enables the fabrication of organic materials with controlled and reproducible electronic and optical properties. For electronic and photonic applications of organic materials, poly- and oligothiophenes are among the most interesting. Here the growth of highly oriented films of β-tetrahexylsexithiophene by OMBD onto an organic ionic crystal substrate is reported. Analysis of UV-vis absorption spectra demonstrates a clear relationship between the ordered structure of the film and the crystal lattice of the substrate.

    7. Linear Polarizers Based on Oriented Polymer Blends (pages 934–938)

      Henri Jagt, Yvo Dirix, Rifat Hikmet and Cees Bastiaansen

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<934::AID-ADMA934>3.0.CO;2-O

      Linear sheet polarizers based on the anisotropic scattering of light by drawn polymer blends are introduced here. The proper selection of materials and processing conditions for the production of large-area, flexible films of phase-segregated polymer blends suitable for polarization applications are discussed. The Figure shows an SEM micrograph of a fracture surface of such a polymer blend.

    8. High Surface Area Silicon Imidonitrides: A New Class of Microporous Solid Base (pages 938–942)

      John S. Bradley, Oliver Vollmer, Riccardo Rovai, Ullrich Specht and Frédéric Lefebvre

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<938::AID-ADMA938>3.0.CO;2-8

      Shape- or size-selective micro- and mesoporous solids find applications as catalysts, catalyst supports, and membrane materials. Here the synthesis of a high surface area microporous base is reported. This material, prepared by ammonolysis of oligomeric methylsilazanes, is a nitride analogue of amorphous silica-based mixed metal oxides. The sharply defined microporosity of silicon imidonitride materials and their observed activity in the base-catalyzed Knoevenagel reaction, together with their large number of N–H groups, raises the possibility that these materials will function as size-selective solid base catalysts.

    9. Tin Sulfide Mesh: AFM Imaging of Lamellae and Mesopores (pages 942–946)

      Igor Sokolov, Tong Jiang and Geoffrey A. Ozin

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<942::AID-ADMA942>3.0.CO;2-S

      A novel tin sulfide composite mesostructure is important because of its unique combination of electrical, optical, and liquid-crystalline properties. The atomic force microscopy (AFM) studies of the material reported here suggest that its structure is a tin sulfide mimic of a mesh phase—a two-periodic square mesh surface is illustrated in the Figure—with rhombohedral or monoclinic space symmetry.

    10. Nanosized Zinc Sulfide Obtained in the Presence of Cationic Surfactants (pages 946–949)

      Jianquan Li, Henri Kessler, Michel Soulard, Lahcen Khouchaf and Marie-Hélène Tuilier

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<946::AID-ADMA946>3.0.CO;2-C

      The synthesis of nanosized zinc blende using organic surfactants as an organic template results in a narrow textural mesopore size distribution after surfactant removal. The findings from X-ray diffraction measurements indicate randomly ordered pores, which is in good agreement with the reported results of transmission electron microscopy investigations. The complete removal of surfactants—much more difficult for microporous sulfides than for microporous oxides—is confirmed by Fourier transform infrared spectroscopy.

    11. Enzyme-Assisted Nanoscale Lithography in Lipid Membranes (pages 949–952)

      Hauke Clausen-Schaumann, Michel Grandbois and Hermann E. Gaub

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<949::AID-ADMA949>3.0.CO;2-0

      Combining biological tools with nanotechnology: The use of a lipolytic enzyme together with an atomic force microscope to locally hydrolyze supported phospholipid membranes is reported. The Figure illustrates how the enzyme cleaves one fatty acid off the glycerol backbone by pulling the lipid out of the membrane. This enzyme-assisted lithography method can be used to structure artificial as well as natural cell membranes.

    12. Nanograined Titanium Nitride Thin Films (pages 952–955)

      Igor Konyashin and German Fox-Rabinovich

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<952::AID-ADMA952>3.0.CO;2-O

      Thin films of titanium nitride are widely used as hard protective coatings and as corrosion-resistant coatings. By filtered arc-evaporation physical vapor deposition (PVD), high-quality nanostructured films of titanium nitride (TiN) can be obtained. These nanograined films are reported to have an excellent surface roughness and higher hardness and fracture toughness than conventionally deposited coarse-grained TiN films. These improved properties result in the high performance of nanograined TiN films as wear-resistant coatings for high-speed steel and cemented carbide cutting tools.

    13. Polymerizable Amidines—Adhesion Mediators and Binding Sites for Molecular Imprinting (pages 957–959)

      Günter Wulff and Rainer Schönfeld

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<957::AID-ADMA957>3.0.CO;2-4

      New styryl amidines have been found to be the first easily polymerizable amidine monomers. The effect of incorporation of these amidines in copolymers and the use of amidinium groups as binding sites in molecularly imprinted polymers are briefly reviewed. The Figure represents a microcavity imprinted by the polymerization of one of the new bisamidinium styryl salts with a transition-state-analogous template.

    14. Detonation Chemistry: A New Access to Nanocrystalline Gallium Nitride (pages 961–964)

      Alissa C. Frank and Roland A. Fischer

      Version of Record online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199808)10:12<961::AID-ADMA961>3.0.CO;2-O

      One of the most promising materials for advanced optoelectronics and high power devices is gallium nitride (GaN). This potential, due to a unique combination of properties, makes a rational synthesis of nanosized GaN highly desirable. It has been found that gallium azides might offer a solution to this problem, since GaN nanocrystallites in a size range from 2 nm to 3000 nm can be prepared by detonations of gallium azides, the detonation energy determining the size of the nanocrystallites. Thus, explosivity, a commonly unwanted property, opens up opportunities for nanochemistry.