Advanced Materials

Cover image for Advanced Materials

October, 1998

Volume 10, Issue 14

Pages 1073–1141

    1. Microstructuring of Molecularly Thin Polymer Layers by Photolithography (pages 1073–1077)

      Oswald Prucker, Martin Schimmel, Günter Tovar, Wolfgang Knoll and Jürgen Rühe

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1073::AID-ADMA1073>3.0.CO;2-D

      Laterally structured ultrathin polymer films attached to solid surfaces can be obtained using photolithographic techniques developed for electronic device fabrication. The Figure shows a surface plasmon (SP) microscopy image of a structured polystyrene (PS) film of 21.5 nm thickness prepared by photopolymerization. The authors report a strong adhesion of the polymer films to the substrate due to covalent linking.

    2. Preparation of Self-Standing Transparent Films of Silica–Surfactant Mesostructured Materials and the Conversion to Porous Silica Films (pages 1077–1080)

      Makoto Ogawa and Takaaki Kikuchi

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1077::AID-ADMA1077>3.0.CO;2-Q

      Self-standing films of surfactant mesostructured materials have been prepared with vinyltrimethoxysilane (VTMOS) as a silica source. The transparent films, obtained by the co-condensation of VTMOS and tetramethoxysilane, can easily be converted to porous silica films by calcination. The authors reveal the porous structure of these materials by X-ray diffraction and transmission electron microscopy investigations. Application of the self-standing films and the porous materials is envisaged in the fields of catalyst supports, separation, and hosts for bulky organic species.

    3. Optically Active Diarylethenes for Multimode Photoswitching Between Liquid-Crystalline Phases (pages 1080–1082)

      Chagit Denekamp and Ben L. Feringa

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1080::AID-ADMA1080>3.0.CO;2-T

      Multimode photoswitching between liquid-crystalline phases (nematic and isotropic) by photochromic organic molecules is reported here. The authors use optically active diarylethylenes to induce chirality in nematic liquid-crystalline (LC) phases and to obtain effective photomodulation of LC phases as well as gradual changes in the pitch values. The Figure shows the texture of a nematic LC phase.

    4. A Blue-Emitting CdS/Dendrimer Nanocomposite (pages 1083–1087)

      Kelly Sooklal, Leo H. Hanus, Harry J. Ploehn and Catherine J. Murphy

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1083::AID-ADMA1083>3.0.CO;2-B

      CdS/dendrimer nanocomposites that emit blue light are formed by the arrested precipitation of nanometer-scale CdS quantum dots in the presence of Starburst (poly(aminoamine)) dendrimers as the stabilizing host. The authors report a strong photoluminescence with emission maxima at about 450 nm. The optoelectronic properties of the CdS clusters are shown to be sensitive to synthesis conditions, including dendrimer type, solvent type, and the concentration of dendrimer and other solutes. Thin films of these materials prepared by solution casting retain the optoelectronic properties of the parent solutions.

    5. Ionic Self-Assembly of Ultrahard ZrO2/Polymer Nanocomposite Thin Films (pages 1087–1091)

      Aprillya Rosidian, Yanjing Liu and Richard O. Claus

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1087::AID-ADMA1087>3.0.CO;2-O

      Fabrication of zirconia nanoparticle coatings by the ionic self-assembled monolayer (ISAM) method is reported. This technique allows the preparation of dense and homogeneous thin films of very small ZrO2 particles with improved properties. The structure of the ZrO2/polymer nanocomposite thin film is shown schematically in the Figure. It is demonstrated that the obtained coatings have higher hardness compared to similar zirconia films.

    6. A Composite from Poly(m-phenylenevinylene-co-2,5-dioctoxy-p-phenylenevinylene) and Carbon Nanotubes: A Novel Material for Molecular Optoelectronics (pages 1091–1093)

      Seamus A. Curran, Pulickel M. Ajayan, Werner J. Blau, David L. Carroll, Johnathan N. Coleman, Alan B. Dalton, Andrew P. Davey, Anna Drury, Brendan McCarthy, Stephanie Maier and Adam Strevens

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1091::AID-ADMA1091>3.0.CO;2-L

      A novel material for molecular optoelectronics consisting of a composite of carbon nanotubes and poly(m-phenylenevinylene-co-2,5-dioctoxy-p-phenylenevinylene) (PmPV) is reported. Incorporation of the nanotubes is demonstrated to increase the electrical conductivity of the polymer by up to eight orders of magnitude. The nanotubes appear to act as nanometric heat sinks, preventing the build up of large thermal effects, which degrade these conjugated systems. It is also shown that the composite can be used as the emissive layer in an organic light-emitting diode, which promises future applications in optoelectronics.

    7. From Simple Acid–Base Hydrolytic Chemistry to Soluble High Tg Inorganic–Organic Hybrid Materials with Large and Stable Second-Order Nonlinear Optical Susceptibilities (pages 1093–1097)

      Hongwei Jiang and Ashok K. Kakkar

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1093::AID-ADMA1093>3.0.CO;2-9

      Hybrid materials with second-order nonlinear optical (NLO) susceptibilities can be obtained by a new approach based on simple hydrolytic chemistry. As reported by the authors milder reaction conditions than for the similar sol-gel technique are required. The synthesis of the hybrid material (see Figure for a representation of the chemical structure) is based on the hydrolysis of Si(NEt2)4 with a bifunctional NLO chromophore.

    8. Supramolecular Self-Assembly for Enhanced Conductivity in Conjugated Polymer Blends: Ionic Crosslinking in Blends of Poly(3,4-ethylenedioxythiophene)-Poly(styrenesulfonate) and Poly(vinylpyrrolidone) (pages 1097–1099)

      Soumyadeb Ghosh, Johan Rasmusson and Olle Inganäs

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1097::AID-ADMA1097>3.0.CO;2-M

      Enhanced conductivity in conjugated polymer blends can be achieved by supramolecular self-assembly. The authors demonstrate that the morphology of the conducting polymer blend can be modified by crosslinking of one of its components. Ionic crosslinking of the conducting component—poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT-PSS)—is shown to result in a three-dimensional network and an increase in the electrical conductivity by a few orders of magnitude. For the ionic crosslinking a bivalent cation, such as Mg2+, is used.

    9. Electroactivity Enhancement by Redox Matching in Cobalt Salen–Based Conducting Polymers (pages 1100–1104)

      Richard P. Kingsborough and Timothy M. Swager

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1100::AID-ADMA1100>3.0.CO;2-2

      New sensory materials based on polymer–transition metal hybrids are reported. It is demonstrated that by tuning the redox potential of the organic backbone—which is based on cobalt-containing N,N′-ethylenebis(salicylidenimide) (salen) complexes such as those shown in the Figure—high conductivity and high sensitivity to coordinating ligands can be achieved.

    10. Superlattice Structures in Poly(phenylenevinylene)-Based Self-Assembled Films (pages 1104–1108)

      Haiping Hong, Roland Steitz, Stefan Kirstein and Dan Davidov

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1104::AID-ADMA1104>3.0.CO;2-F

      The structure and stability of self-assembled 1D superlattices based on deuterated poly(p-phenylenevinylene) (PPV) and non-deuterated spacer layers is investigated by neutron reflectivity. This allows, in particular, the interlayer penetration to be accurately determined—an important parameter to be able to control and minimize for the fabrication of multilayer devices. It is demonstrated that the successful preparation of superlattices largely depends on drying and removal of excess polyelectrolyte after each deposition cycle by spinning the sample.

    11. Hole Transporting Materials with High Glass Transition Temperatures for Use in Organic Light-Emitting Devices (pages 1108–1112)

      Diarmuid F. O'Brien, Paul E. Burrows, Stephen R. Forrest, Bryan E. Koene, Douglas E. Loy and Mark E. Thompson

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1108::AID-ADMA1108>3.0.CO;2-S

      Efficient and stable organic light-emitting devices (OLEDs) can be fabricated using hole transporting materials with a high glass transition temperature (Tg), as reported here. A series of devices utilizing high Tg hole transporting layers, consisting of compounds with a biphenyl backbone such as the one shown in the Figure, are investigated with respect to their IV characteristics, external quantum efficiencies, ionization potentials, and electron affinities.

    12. Highly Efficient Light-Emitting Diodes Based on an Organic-Soluble Poly(p-phenylenevinylene) Derivative Carrying the Electron-Transporting PBD Moiety (pages 1112–1116)

      Sung-Jae Chung, Ki-Young Kwon, Seung-Wuk Lee, Jung-Il Jin, Chang Hoon Lee, Cheol Eui Lee and Yongsup Park

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1112::AID-ADMA1112>3.0.CO;2-P

      Balanced charge injection and mobility are required for efficient electroluminescence (EL) in light-emitting diodes (LEDs). Here a novel approach towards this end is described—the direct attachment of the electron transporting material 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) to the backbone of poly(p-phenylenevinylene) (PPV). The fabrication and performance efficiency of devices based on this polymer are reported. It is found that the EL efficiency is improved to a remarkable extent, which is ascribed to a more facile electron injection and an enhancement of the electron transporting properties of the polymer.

    13. Alignment of a Laser Dye in the Channels of the AlPO4-5 Molecular Sieve (pages 1117–1119)

      Guido Ihlein, Ferdi Schüth, Oliver Krauß, Uwe Vietze and Franco Laeri

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1117::AID-ADMA1117>3.0.CO;2-W

      Solid-state laser systems based on molecular sieves may not be far away. Here, the incorporation and linear alignment of a pyridine-based laser dye in the channels of AlPO4-5 is reported and the spectroscopic properties of the composite are investigated. A first indication that AlPO4-5–laser dye composite crystals show laser action is demonstrated for microcrystals with a highly intergrown shape (see Figure).

    14. Charge Carrier Mobility in a Ladder-Type Conjugated Polymer (pages 1119–1122)

      Dirk Hertel, Ullrich Scherf and Heinz Bässler

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1119::AID-ADMA1119>3.0.CO;2-K

      Non-dispersive charge carrier transport and unusually large hole mobilities are reported for the ladder-type methyl-substituted poly(p-phenylene) MeLPPP, as investigated using the time of flight technique. Charge carrier transport in polymers generally occurs much more slowly than in molecular crystals owing to disorder. But, as demonstrated here, ladder-type polymers are promising candidates for conjugated polymers with greatly reduced disorder and hence improved charge carrier transport.

    15. In-Situ Formation of Silver Nanoparticles on Poly(N-isopropylacrylamide)-Coated Polystyrene Microspheres (pages 1122–1126)

      Chun-Wei Chen, Ming-Qing Chen, Takeshi Serizawa and Mitsuru Akashi

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1122::AID-ADMA1122>3.0.CO;2-N

      The formation of Ag nanoparticles on polystyrene microspheres coated with poly(N-isopropylacrylamide) (PNIPAAm) is reported. It is shown that well-dispersed Ag nanoparticles are formed in situ on the surface of the microspheres (see Figure). The surface-grafted PNIPAAm chains are concluded to not only serve as steric stabilizers but also promote adsorption of the Ag nanoparticles.

    16. Pressure-Controlled Synthesis of the Hg0.82Re0.18Ba2Ca2Cu3O8+δ Superconductor (pages 1126–1129)

      Agusti Sin, Alfredo G. Cunha, Albert Calleja, Marcos T. D. Orlando, Francisco G. Emmerich, Elisa Baggio-Saitovitch, Mercé Segarra, Salvador Piñol and Xavier Obradors

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1126::AID-ADMA1127>3.0.CO;2-X

      Obtaining single-phase Hg1–xMxBa2Ca2Cu3O8+δ materials has proved difficult using the sealed quartz tube technique, mainly because of the poor knowledge of the synthesis mechanisms. A technique is described for the measurement of the system pressure in situ, allowing both the thermodynamic and kinetic aspects of the reaction to be investigated. The power of this technique is demonstrated by studying the stability of the Hg0.82Re0.18Ba2Ca2Cu3O8+δ compound, but should also be applicable to in-situ pressure determination in gas–solid reactions.

    17. Etching of ZnO Films with Hexafluoroacetylacetone (pages 1129–1133)

      Steven R. Droes, Toivo T. Kodas and Mark J. Hampden-Smith

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1129::AID-ADMA1129>3.0.CO;2-I

      A dry route to etching metal oxides at low temperatures (<200°C) using gaseous β-diketones is described. The Figure is an SEM micrograph of a ZnO film after etching. This method is a promising alternative to current wet-etching and cleaning methods as easily desorbed, volatile, low-molecular-weight metal–organic products are produced.

    18. Photoinscription of Surface Relief Gratings on Azo-Hybrid Gels (pages 1133–1136)

      Bruno Darracq, Frédéric Chaput, Kalid Lahlil, Yves Lévy and Jean-Pierre Boilot

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1133::AID-ADMA1133>3.0.CO;2-F

      Very stable surface gratings can be inscribed in azo-hybrid thin films prepared by the sol-gel method, as described here. It is shown that in order to obtain high modulation depths a weakly crosslinked network in the gel with a degree of condensation that can be easily controlled by heat treatment and the functionality of the sol-gel precursor is required. In addition, the simultaneous presence of an intensity gradient and a non-zero component of the resultant optical field along this gradient is required. Explanations for the mass transport mechanism are also proposed.

    19. Solid-State Amplified Spontaneous Emission in Some Spiro-Type Molecules: A New Concept for the Design of Solid-State Lasing Molecules (pages 1136–1141)

      Nicklas Johansson, Josef Salbeck, Jacqueline Bauer, Frank Weissörtel, Per Bröms, Annica Andersson and William R. Salaneck

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199810)10:14<1137::AID-ADMA1136>3.0.CO;2-V

      Spectral narrowing in amorphous molecular solid films of spiro-type molecules such as spiro-quarterphenyl (see Figure) is reported. It is demonstrated that introduction of the spiro linkage not only improves the processability and morphological properties but, for the molecules studied here, also suppresses concentration quenching, making these molecular solids attractive candidates for molecular solid-state lasers.