Advanced Materials

Cover image for Advanced Materials

June, 1999

Volume 11, Issue 8

Pages 605–685

    1. Energy Level Alignment and Interfacial Electronic Structures at Organic/Metal and Organic/Organic Interfaces (pages 605–625)

      Hisao Ishii, Kiyoshi Sugiyama, Eisuke Ito and Kazuhiko Seki

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<605::AID-ADMA605>3.0.CO;2-Q

      The function of electronically functional organic materials often originates at an interface, one example being organic electroluminescent devices (the Figure shows a typical energy diagram). Therefore, elucidation of the electronic structure at interfaces will lead to a better understanding of these devices, enabling their performance to be improved. Basic concepts are reexamined and recent progress in the area is reviewed.

    2. Microcavity Effect from a Novel Terbium Complex Langmuir–Blodgett Film (pages 627–629)

      Yanyi Huang, Anchi Yu, Chun-Hui Huang, Liangbing Gan, Xinsheng Zhao, Yong Lin and Bei Zhang

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<627::AID-ADMA627>3.0.CO;2-A

      Two important microcavity effects—fluorescence intensity enhancement and lifetime shortening—are demonstrated to be exhibited by new microcavities consisting of a pure terbium complex sandwiched between silver mirrors. The advantages of the use of the fluorescent rare-earth complex as the emitting material and the Langmuir–Blodgett technique for the construction of microcavities are discussed. Microcavities acting as optical resonators have potential applications as high-density light sources for optical communications and color displays.

    3. Ceramic Parts Patterned in the Micrometer Range (pages 630–632)

      Urs P. Schönholzer and Ludwig J. Gauckler

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<630::AID-ADMA630>3.0.CO;2-Y

      Micropatterning of ceramics (with feature sizes down to 2 μm in the horizontal and vertical directions) by means of soft, elastomeric molds in order to produce crack-free samples is reported. Particular attention is paid to the influence of the initial powder particle size. The cavities shown in the Figure were replicated using 45 nm boehmite powder (scale bar represents 10 μm).

    4. Doped Mesoporous Silica Fibers: A New Laser Material (pages 632–636)

      Frank Marlow, Michael D. McGehee, Dongyuan Zhao, Bradley F. Chmelka and Galen D. Stucky

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<632::AID-ADMA632>3.0.CO;2-Q

      The fabrication of a laser based on mesoporous fibers is shown to be possible, demonstrating for the first time that mesostructural systems can be applied as advanced optical materials. The amplification of a guided mode in the fiber and the resulting, gain-narrowed emission (illustrated on the cover of this issue) are reported. It is stressed that the system used—a composite containing the dye rhodamine 6G—is a relatively simple type of laser material and better results can be expected in the future with different types of lasing guests in mesoporous fibers.

    5. Radial Patterns in Mesoporous Silica (pages 636–642)

      Igor Sokolov, Hong Yang, Geoffrey A. Ozin and Charles T. Kresge

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<636::AID-ADMA636>3.0.CO;2-A

      The morphogenesis of mesoporous silica shapes is thought to be initiated by topological defects in a hexagonal silica liquid crystal (LC). The authors show that application of the classical theory of elasticity for LCs to a hexagonal silicate mesophase containing a 2π line disclination defect leads to the emergence of radial patterns (see Figure) that bear a striking resemblance to those observed experimentally.

    6. A Simple Colloidal Route to Nanocrystalline ZnO/CuInS2 Bilayers (pages 643–646)

      Constantin Czekelius, Michael Hilgendorff, Lubomir Spanhel, Idriss Bedja, Martin Lerch, Gerd Müller, Ulrike Bloeck, Dang-Sheng Su and Michael Giersig

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<643::AID-ADMA643>3.0.CO;2-I

      CuInS2 (CIS) films for solar energy applications are typically made by rapid thermal sintering of the elements on a molybdenum-coated glass substrate. The photovoltaic cell is then completed by adding a CdS buffer layer and an Al/ZnO transparent electrode, all in all an expensive process. A low-cost colloidal route to nanocrystalline ZnO/CIS bilayers on indium tin oxide (ITO) glass is presented here, together with the optical and electrical characterization of the films. The concentrated coating colloids with size-quantized CIS particles that were developed for the film deposition are described.

    7. A Simple Method for the Subdivision of ITO Glass Substrates (pages 646–649)

      Dirk Hohnholz, Karl-Heinz Schweikart and Michael Hanack

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<646::AID-ADMA646>3.0.CO;2-6

      If organic light-emitting diodes (OLEDs) are to be used for displays, e.g., in seven-segment displays such as that in the Figure, either the metal cathode or the anode (usually indium tin oxide, ITO) must be subdivided. A new subdivision technique based on localized destruction of the ITO layer of commercial substrates by scorching with a tungsten needle is described and experimental and theoretical results are presented.

    8. Photo-Induced Nanopatterns on the Surface of C60 Single Crystals (pages 649–652)

      Lei Jiang, Yousoo Kim, Tomokazu Iyoda, Jin Li, Koichi Kitazawa, Akira Fujishima and Kazuhito Hashimoto

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<649::AID-ADMA649>3.0.CO;2-V

      Photo-induced surface reconstruction of molecular materials has been demonstrated for the first time using C60 as a model. The authors explain why C60 single crystals are good candidates to show photo-induced surface reconstruction and give experimental details. Reconstruction effects that depend on both the lattice symmetry and light polarization are shown to suggest that the phenomenon arises from a cooperative interaction between the photo-induced collective molecular displacement and the anisotropic lattice structure of the crystals.

    9. A Novel Low-Temperature Synthetic Route to Crystalline Si3N4 (pages 653–655)

      Kaibin Tang, Junqing Hu, Qingyi Lu, Yi Xie, Jingsheng Zhu and Yitai Qian

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<653::AID-ADMA653>3.0.CO;2-E

      A low-temperature preparation of crystalline Si3N4 is described that avoids the temperatures above 1200 °C necessary in other methods. Si3N4s chemical stability, high-temperature strength, and excellent creep resistance make it a promising material for high-temperature engineering applications. The Figure shows a transmission electron microscopy image of a Si3N4 sample.

    10. Carbon Nitride Nanocomposites: Formation of Aligned CxNy Nanofibers (pages 655–658)

      Mauricio Terrones, Philipp Redlich, Nicole Grobert, Susana Trasobares, Wen-Kuang Hsu, Humberto Terrones, Yan-Qiu Zhu, Jonathan P. Hare, Christopher L. Reeves, Anthony K. Cheetham, Manfred Rühle, Harold W. Kroto and David R. M. Walton

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<655::AID-ADMA655>3.0.CO;2-6

      The preparation of carbon nitride nanotubes has proved extremely difficult—to date only small quantities of nitrogen (≤5%) have been incorporated into carbon nanotubes or filaments and the synthesis of crystalline C3N4 and CN nanotubes with their interesting predicted properties remains a challenge for the future. Now the generation of aligned C13Nx (x ≤ 1) nanofibers in high yield by pyrolyzing melamine over laser-patterned thin films of Fe and Ni catalyst deposited on a silica substrate is reported. The resulting aligned, hollow, thin-walled fibers exhibit unusual graphitic corrugated morphologies. The authors suggest that pyrolysis of organic precursors containing N (e.g., melamine) may provide an additional route to CN nanostructures.

    11. Ultrathin Electroactive Junctions Assembled from Silicon Nanocrystallites and Polypyrrole (pages 659–664)

      Beata Sweryda-Krawiec, Thierry Cassagneau and Janos H. Fendler

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<659::AID-ADMA659>3.0.CO;2-R

      Rectifying junctions prepared from silicon nanocrystals (Si-nc) by a wet colloid chemical approach are reported. The ultrathin junctions consisted of a derivatized p- or n-type silicon wafer, to which colloidal Si-nc—prepared by sonication of porous silicon in toluene—was attached covalently by self-assembly, and a polypyrrole layer (see Figure). The rectification behavior of various junctions is described.

    12. Host–Guest Complexation: A Strategy to Form Sexithiophene Exhibiting Self-Assembly Properties (pages 664–667)

      Corinne Lagrost, Jean-Christophe Lacroix, Kathleen I. Chane-Ching, Mohamed Jouini, Salah Aeiyach and Pierre-Camille Lacaze

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<664::AID-ADMA664>3.0.CO;2-6

      A new route for the electrosynthesis of sexithiophene (6T) films with well-ordered structure is described. Applications of oligothiophenes in organic electronic devices—to which 6T is well suited owing to its attractive charge-transport properties—necessitate a well-defined structural order. The formation of an inclusion complex of terthiophene (3T) in the host hydroxypropyl-β-cyclodextrin in an aqueous medium is demonstrated and also that the subsequent electropolymerization leads essentially to 6T. It is shown that use of the β-cyclodextrin induces an ordering effect.

    13. Functionalized Liquid-Crystalline Donor–Acceptor Triple Compounds Containing Azobenzene for Optical Storage (pages 667–670)

      Andreas Stracke, Joachim H. Wendorff, Dietmar Janietz and Sven Mahlstedt

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<667::AID-ADMA667>3.0.CO;2-V

      A non-symmetric, three-component, charge-transfer molecule is introduced and experimental results on structure formation and optical storage are presented. The storage process takes place via the isomerization of the functional azo group in a transparent film. The Figure shows the molecule, consisting of a disc-like pentaalkynylbenzene donor group linked to a flat nitrofluorenone acceptor by a rod-like chromophoric azo moiety.

    14. Blue Polarized Electroluminescence from a Liquid Crystalline Polyfluorene (pages 671–675)

      Martin Grell, Wolfgang Knoll, Donald Lupo, Andreas Meisel, Tzenka Miteva, Dieter Neher, Heinz-Georg Nothofer, Ullrich Scherf and Akio Yasuda

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<671::AID-ADMA671>3.0.CO;2-E

      Highly polarized electroluminescence from a liquid-crystal polymer device, based on a branched polyfluorene with a branched side chain, is demonstrated here as a further step towards the use of organic electroluminescent (EL) devices as backlights in conventional liquid-crystal displays. The modification of a polyimide (PI) for hole conduction by addition of a suitable filler at moderate concentration is reported and the performance of a device containing such a rubbed, hole-conductor-filled PI layer as the alignment layer is compared with that of a device with a PI-only alignment layer.

    15. A Dynamic Grating Using a Photochemical Phase Transition of Polymer Liquid Crystals Containing Azobenzene Derivatives (pages 675–677)

      Makoto Hasegawa, Takahiro Yamamoto, Akihiko Kanazawa, Takeshi Shiono and Tomiki Ikeda

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<675::AID-ADMA675>3.0.CO;2-Z

      The rapid formation (and erasure) of a dynamic phase grating is one condition required of materials for dynamic holography. The photochemical nematic–isotropic transition of the side-chain polymer liquid crystal (PLC) shown in the Figure, caused by the transcis photoisomerization of the azobenzene moiety, is reported to cause a dynamic grating with fringe spacing of 1.4 μm to form in ∼150 ms.

    16. Virus Particles as Templates for Materials Synthesis (pages 679–681)

      Trevor Douglas and Mark Young

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<679::AID-ADMA679>3.0.CO;2-J

      Virus protein cages, capsids, which display a wide range of sizes and shapes, can be used for constrained materials synthesis. The authors briefly review recent work involving capsids, including the use of spherical viruses for inorganic mineralization and organic polymer encapsulation and the mineralization of anisotropic structures such as the tobacco mosaic virus, which can lead to mineralized fibers of iron oxide or silica with very high aspect ratios. The topic of gating—which enables the selective entrapment and release of materials from within the central cavity—is briefly touched upon.

    17. Dye-Doped Photosensitive Mesostructure Materials (pages 683–685)

      Hao Shen Zhou and Itaru Honma

      Version of Record online: 16 JUN 1999 | DOI: 10.1002/(SICI)1521-4095(199906)11:8<683::AID-ADMA683>3.0.CO;2-2

      The incorporation of dyes into mesoporous materials can be accomplished by the new approach reviewed here. The Figure shows schematically the resulting mesostructured material. The dye, e.g., phthalocyanine or chlorophyll, is embedded between the hydrophobic tails of the surfactant molecules in micelles. The micelles then self-organize into a periodic array. Examples of systems are given.