Advanced Materials

Cover image for Advanced Materials

February, 1999

Volume 11, Issue 2

Pages 91–177

    1. Deposition of Powder Phosphors for Information Displays (pages 91–105)

      Keith Y. Sasaki and Jan B. Talbot

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<91::AID-ADMA91>3.0.CO;2-K

      Information displays, whether cathode ray tubes or field emitter displays, require that a thin layer of phosphor be laid down upon a glass substrate (the screen)—the final result is sketched in the Figure. Recent phosphor deposition methods are reviewed in detail and future improvements in deposition methods that will be made necessary by the demand for higher definition information displays are outlined.

    2. Hybrid Organic–Inorganic Light-Emitting Diodes (pages 107–112)

      Tony Dantes de Morais, Frederic Chaput, Khalid Lahlil and Jean-Pierre Boilot

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<107::AID-ADMA107>3.0.CO;2-J

      High-efficiency light-emitting diodes (LEDs) using air-stable electrodes remain an important goal. Here the authors report the design and synthesis of electroluminescent hybrid organic–inorganic materials using the sol-gel process in order to improve the aging and environmental stability of LEDs. Devices—which emitted in the orange—consisting of a sol-gel layer sandwiched between a transparent indium tin oxide (ITO) electrode and an evaporated aluminum cathode were also prepared, demonstrating the electroluminescent properties of the sol-gel materials.

    3. Interface Morphology in Organic Light-Emitting Diodes (pages 112–115)

      Sylvie Goncalves-Conto, Michel Carrard, Lynda Si-Ahmed and Libero Zuppiroli

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<112::AID-ADMA112>3.0.CO;2-Z

      Heat dissipation can be a problem in organic LEDs, leading to high working temperatures. The SEM study reported here shows that the temperature-variable morphology of an electroactive film—the Figure shows the efficient blue emitter N,N′-diethyl-3,3′-bicarbazyl deposited at 70 °C on a bare ITO substrate—depends essentially on how well the film wets the substrate and on the diffusion of the organic molecules on the substrate.

    4. Exciton Migration and Trapping in Copolymers Based on Dialkylfluorenes (pages 115–119)

      Gerrit Klärner, Jeong-Ik Lee, Mark H. Davey and Robert D. Miller

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<115::AID-ADMA115>3.0.CO;2-N

      Poly(fluorenes) have potential use in light-emitting diodes; however, their application has been hampered by their tendency to form excimers and aggregates. In this paper, the copolymerization of 2,7-dibromo-9,9-dialkylfluorenes with low-bandgap chromophores, such as 3,9(3,10)-dibromoperylene and 4,4′-dibromo-α-cyanostilbene, is described. These readily soluble and processable polymers display longer wavelength emissions than polyfluorene homopolymers in thin films, which indicates rapid exciton migration and trapping in these systems.

    5. Electroluminescent Behavior of a Homologous Series of Phenylenevinylene Oligomers (pages 119–123)

      Volker Gebhardt, Andreas Bacher, Mukundan Thelakkat, Ulf Stalmach, Herbert Meier, Hans-Werner Schmidt and Dietrich Haarer

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<119::AID-ADMA119>3.0.CO;2-7

      Oligomeric LED systems have received little attention compared to that devoted to polymeric LED systems. This paper focuses on the electroluminescent behavior of a homologous series of six phenylenevinylene oligomers—their molecular structure is illustrated in the Figure—in LEDs in combination with a comparative study of related cyclic voltammetry data.

    6. Influence of Glass-Transition Temperature and Chromophore Content on the Steady-State Performance of Poly(N-vinylcarbazole)-Based Photorefractive Polymers (pages 123–127)

      Reinhard Bittner, Thomas K. Däubler, Dieter Neher and Klaus Meerholz

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<123::AID-ADMA123>3.0.CO;2-R

      In optimizing the performance of organic photorefractive (PR) materials, the glass transition temperature Tg is an important factor, according to the investigation reported here. The influence of Tg on the steady-state performance of four series of PR polymer composites at room temperature with chromophore content ρchr ranging from 20 to 50 wt.-% has been studied. The performance optimum found for highly doped materials with Tg approximately equal to room temperature is demonstrated to be a result of several counteracting effects. Organic PR materials are highly promising for holographic applications.

    7. Nanostructured Dihexadecyldimethylammonium–Poly(1,4-phenylene-ethinylene-carboxylate): An Ionic Complex with Blue Electroluminescence (pages 127–130)

      Andreas F. Thünemann

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<127::AID-ADMA127>3.0.CO;2-B

      Transferral of the interesting fluorescence properties, seen in solution, of a brittle solid polymer with a conjugated backbone to a material in a more convenient state is shown to be possible. A flexible, mesomorphously structured film is obtained by complexing the brittle polymer with a surfactant, resulting in the title complex. The Figure shows the “herring school texture” of the complex observed by optical polarization microscopy.

    8. Surface-Confined Nanoparticles as Substrates for Photopolymerizable Self-Assembled Monolayers (pages 131–134)

      Henning Menzel, Mark D. Mowery, Mei Cai and Christine E. Evans

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<131::AID-ADMA131>3.0.CO;2-V

      Constraints on substrate size and shape are minimized in the fully solution-based approach to surface fabrication reported here. It is shown that not only is it possible to prepare self-assembled monolayers of a diacetylene compound on colloidal gold nanoparticles that are adsorbed onto supported organic films, but also subsequent polymerization yields highly conjugated poly(diacetylene). The ability to fabricate nanosized gold particles coated with conjugated polymers holds interesting possibilities for applications in nonlinear optics and electronics.

    9. Extended Oligothienylenevinylenes End-Capped with 1,4-Dithiafulvenyl π-Donor Groups: Toward a Supramolecular Control of Effective Conjugation Length (pages 134–138)

      Isabelle Jestin, Pierre Frère, Eric Levillain and Jean Roncali

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<134::AID-ADMA134>3.0.CO;2-J

      Oligothienylenevinylenes (nTVs) have potential as molecular wires because of their long effective conjugation lengths. The synthesis of a series of nTVs end-capped with 1,4-dithiafulvenyl π-donor groups (n = 8 in the Figure)—the longest TTF analogues ever reported — is described. The donor groups are shown to enhance interchain interactions in the solid state, leading to a significant reduction of the bandgap.

    10. Silica Sol-Gel Glasses with Embedded Organic Liquids (pages 138–141)

      Horst Böttcher, Karl-Heinz Kallies, Helfried Haufe and Jürgen Seidel

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<138::AID-ADMA138>3.0.CO;2-3

      Silica powders and films with embedded organic liquids (OLs) that are storage stable can be prepared with high OL concentrations when modern sol-gel techniques are used. The preparation and thermal release behavior of silica sol-gel glasses with different embedded organic liquids are described and the results discussed with particular regard to potential applications. The encapsulation of OLs by the sol-gel technique offers many advantages for controlled-release systems in the food and cosmetics industries compared to the polymeric systems in use today.

    11. Nano-objects with Controlled Shape, Size, and Composition from Block Copolymer Mesophases (pages 141–146)

      Ralph Ulrich, Alexander Du Chesne, Markus Templin and Ulrich Wiesner

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<141::AID-ADMA141>3.0.CO;2-R

      Nano-engineering of ceramic materials is investigated using block copolymers obtained from poly(isoprene- b-ethyleneoxide). The dimensions of these “hairy”, nano-sized products can be tuned by adding varying amounts of two metal alkoxides to give rise to objects of different shapes. The Figure shows a TEM image of cylindrical aluminosilicate coated with a thin layer of block copolymer.

    12. An Effective Synthetic Route for a Novel Electrolyte: Nanocrystalline Solid Solutions of (CeO2)1–x(BiO1.5)x (pages 146–149)

      Guangshe Li, Liping Li, Shouhua Feng, Minqiang Wang, Liangying Zhang and Xi Yao

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<146::AID-ADMA146>3.0.CO;2-7

      The development of mild chemistry routes to novel oxides—instead of the traditional ceramic method—is an active area of research with an additional aim of finding new electrolytes. The authors report the low temperature hydrothermal synthesis and the property characterization of a wide range of nanocrystalline solutions (CeO2)1–x(BiO1.5)x (0.0 ≤ x ≤ 0.50). All of the solutions exhibited the same structure. The ionic transport properties were measured and the bulk and grain boundary resistances determined, together with their temperature dependence.

    13. Micellar Inorganic–Polymer Hybrid Systems—A Tool for Nanolithography (pages 149–153)

      Joachim P. Spatz, Thomas Herzog, Stefan Mößmer, Paul Ziemann and Martin Möller

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<149::AID-ADMA149>3.0.CO;2-W

      A approach to nanolithography based on the self-assembly and formation of mono-micellar films of a diblock-copolymer is reported. The Figure shows the formation of islands using an inorganically modified micellar mask. Au3+ in the micelles leads to islands while the formation of a Au-nanoparticle in each single micelle results in holes, owing to an inversion of the etching rate.

    14. Improved Charge Transfer at Carbon Nanotube Electrodes (pages 154–157)

      Pichumani J. Britto, Kalathur S. V. Santhanam, Angel Rubio, Julio A. Alonso and Pulickel M. Ajayan

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<154::AID-ADMA154>3.0.CO;2-B

      The potential of using carbon nanotubes in fuel cells and other electrodic applications is confirmed by the investigation described here. Results of the electrocatalytic reduction of dissolved oxygen (an important H2-O2 fuel cell reaction) using microelectrodes constructed from multiwalled nanotubes are presented. Also, ab initio calculations are reported for oxygen deposited on the lattice and defect sites of nanotube surfaces to determine the charge transfer during oxygen reduction; these results are compared with those for similar reactions on planar graphite.

    15. Nanotubes Formed by Detonation of C/N Precursors (pages 158–161)

      Edwin Kroke, Marcus Schwarz, Véronique Buschmann, Gerhard Miehe, Hartmut Fuess and Ralf Riedel

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<158::AID-ADMA158>3.0.CO;2-W

      Individual carbon nanotubes, both unfilled and containing metal nanocrystals in a string-of-beads-like arrangement, as shown in the Figure, can be obtained reproducibly by detonative decomposition of a hydrogen-free C/N precursor, it is reported here. This method may challenge traditional techniques for the synthesis of carbon nanotubes, which are energy and hardware intensive.

    16. Elastic Modulus of Ordered and Disordered Multiwalled Carbon Nanotubes (pages 161–165)

      Jean-Paul Salvetat, Andrzej J. Kulik, Jean-Marc Bonard, G. Andrew D. Briggs, Thomas Stöckli, Karine Méténier, Sylvie Bonnamy, François Béguin, Nancy A. Burnham and Lásló Forró

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<161::AID-ADMA161>3.0.CO;2-J

      Multiwalled carbon nanotubes (MWNTs) have unique mechanical properties and are ideal candidates for high-performance composites. Elastic measurements, performed with an atomic force microscope, are described for MWNTs produced by two methods: the arc-discharge method and the thermal decomposition of hydrocarbons in the presence of catalysts. Extended stacking defects, such as produced in the second production method (which unlike the first can yield almost continuous production of long fibers), are shown to have a much larger effect than point defects on the elastic properties of the nanotubes.

    17. Synthesis of Photonic Crystals for Optical Wavelengths from Semiconductor Quantum Dots (pages 165–169)

      Yurii A. Vlasov, Nan Yao and David J. Norris

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<165::AID-ADMA165>3.0.CO;2-3

      Quantum-dot solids and polycrystalline semiconductors that are patterned in three dimensions can be produced by the new route described here. Both materials have potential as photonic crystals. The method combines colloidal chemistry with two steps of hierarchical selfassembly: first, semiconductor nanocrystals are induced to self-assemble inside a self-organized silica template, then the template is removed, leaving a three-dimensionally patterned material consisting solely of densely packed nanocrystals. This issue's cover shows micrographs of such a material.

    18. Gas Sensor Materials Based on Metallodendrimers (pages 171–174)

      Martin Albrecht and Gerard van Koten

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<171::AID-ADMA171>3.0.CO;2-F

      Functionalized metallodendrimers are a rational synthetic target for gas sensing since a range of transition metal centers can potentially be used and the ligand fragments may serve as anchoring points to an appropriate support. The authors summarize the synthetic approach to compounds such as that shown in the Figure complexed with SO2 and the properties that render them ideal diagnostic materials for SO2.

    19. New Coatings by Nanostructuring (pages 175–177)

      Roland Hauert, Jörg Patscheider, Lukas Knoblauch and Matthieu Diserens

      Article first published online: 25 MAR 1999 | DOI: 10.1002/(SICI)1521-4095(199902)11:2<175::AID-ADMA175>3.0.CO;2-#

      Coatings of nanocomposites or multiphase materials are two approaches to optimizing the wear and corrosion properties of materials. The authors summarize recent research into multiphase coatings, e.g., amorphous nanoscaled multilayer coatings consisting of layers of various types of amorphous hydrogenated carbon (a-C:H), formed by plasma-assisted chemical vapor deposition, and into nanocomposite coatings consisting of immiscible phases, e.g., nanocrystals of TiN embedded in amorphous SiNx, formed by a physical vapor deposition method. Both approaches are seen to produce coatings with outstanding wear resistance.

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