Advanced Materials

Cover image for Advanced Materials

December, 1998

Volume 10, Issue 17

Pages 1415–1492

    1. Poly(sulfur nitride): The First Polymeric Metal (pages 1415–1429)

      Arthur J. Banister and Ian B. Gorrell

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1415::AID-ADMA1415>3.0.CO;2-L

      Poly(sulfur nitride)—the first polymeric metal—has received much attention since reports of its metallic character and its superconducting properties. In this up-to-date account, poly(sulfur nitride), (SN)x, research is reviewed. Special emphasis is given to the wide range of physical studies that made the rationalization of much of the behavior of (SN)x in terms of an anisotropic model possible. The Figure shows (SN)x coated on glass.

    2. Large-Area, Full-Color Image Sensors Made with Semiconducting Polymers (pages 1431–1434)

      Gang Yu, Jian Wang, Jon McElvain and Alan J. Heeger

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1431::AID-ADMA1431>3.0.CO;2-4

      The photoresponse of semiconducting polymers can be enhanced significantly by photoinduced charge transfer (CT). The discovery of photoinduced CT in composites of conducting polymers and C60 and its derivatives provided a molecular approach to high-efficiency solar cells and high-sensitivity photodetectors. Here the authors demonstrate the first large-area image sensor made with such photosensitve composites. These image sensors have high photosensitivity, low dark current, large dynamic range, and can be fabricated by simple coating processes on flexible or curved substrates at low temperature.

    3. Nanostructuring of Highly Ordered C60 Films by Charge Transfer (pages 1434–1438)

      Pavel Janda, Torsten Krieg and Lothar Dunsch

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1434::AID-ADMA1434>3.0.CO;2-N

      Highly ordered surfaces of C60 films are formed on highly ordered pyrolytic graphite (see Figure for a scanning tunneling microscopy image). Electrochemical reduction of these films leads to the first reported electrochemical nanostructuring of fullerene films, where nanometer-sized clusters of potassium fullerides are formed in fullerene layers at the electrode surface. The resulting stable structures cannot be destroyed by chemical reactions.

    4. Light-Induced Color Change of Cholesteric Copolymers (pages 1438–1441)

      Martin Brehmer, Johan Lub and Peter van de Witte

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1438::AID-ADMA1438>3.0.CO;2-#

      Light-induced color change of cholesteric copolymers containing a menthone derivative is reported here. In addition, solutions of these copolymers in low molecular mass liquid crystal mixtures to allow local changes of the reflection color are investigated. The ability to reflect visible light makes cholesteric liquid crystals of interest for several applications in display technology or smart reflectors. The authors demonstrate an easy method for the color patterning of cholesteric liquid crystals based on photoisomerization of chiral dopants.

    5. Imaging Current Flow Distributions in Polycrystalline Bi2Sr2CaCu2Ox Superconductors by Magnetic Force Microscopy (pages 1442–1448)

      Filip Král, Dainius Perednis, Bryan Huey, Dawn A. Bonnell, Gernot Kostorz and Ludwig J. Gauckler

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1442::AID-ADMA1442>3.0.CO;2-X

      Imaging of current transport at low temperatures; in a Bi-based thick-film superconductor is reported here. The approach is based on magnetic force microscopy (a scheme of the microscope is shown in the Figure) and is supplemented by finite element calculations of magnetic fields induced by current flow. The results (see cover) show that the current flows mainly in thin layers close to the grain boundaries of the superconductor.

    6. A New Inductive Furnace Based on Microwave Irradiation for Growing Long YBa2Cu3O7–δ Single-Domain Bars (pages 1448–1452)

      Sylvain Marinel and Gilbert Desgardin

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1448::AID-ADMA1448>3.0.CO;2-Y

      Growing long YBa2Cu3O7–δ single domain bars requires new designs of inductive furnaces based on microwave irradiation. In this paper the authors present a new susceptor design using inductive heating to obtain a positive radial thermal gradient from the heating source. With this system textured YBa2Cu3O7–δ (Y123) ceramics are produced and compared with the conventional microwave melt textured growth process. No regulation system is needed and thermal radiation from the sample placed inside the tube is totally eliminated, which may normally cause parasitic nucleations at the periphery of the Y123 bars.

    7. Thin-Film Light-Emitting Devices Based on Sequentially Adsorbed Multilayers of Water-Soluble Poly(p-phenylene)s (pages 1452–1455)

      Jeff W. Baur, Seungho Kim, Peter B. Balanda, John R. Reynolds and Michael F. Rubner

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1452::AID-ADMA1452>3.0.CO;2-V

      In thin-film electroluminescent devices, conjugated polymers are used as efficient emitters. Here the authors demonstrate that thin films of combined anionic (see Figure for the chemical structure) and cationic water-soluble poly(p-phenylene) polyelectrolytes can be readily processed into multilayer light-emitting devices. Fabrication with solely one type of conjugated backbone—as here—may greatly improve device efficiency.

    8. Strongly Luminescent Poly(ethylene glycol)-2,2′-bipyridine Lanthanide Ion Complexes (pages 1455–1458)

      Vlasoula Bekiari and Panagiotis Lianos

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1455::AID-ADMA1455>3.0.CO;2-D

      A highly efficient luminescent material is produced from a 2,2′-bipyridine-lanthinide-ion coordination complex. The authors describe how this coordination complex can be stabilized by ethylene glycol oligomers. The material, obtained by simple mixing of the components, emits blue, green, and red photoluminescence by single near-UV excitation. Additionally, the complex can be mixed with silica through a sol-gel process, producing transparent soft solids that preserve all photophysical characteristics of the original liquid mixture. These materials may find applications in electroluminescent displays, lasers, or high-density optical storage.

    9. FT-Raman Studies of Charged Defects Created on Methyl End-Capped Oligothiophenes by Doping with NOBF4 (pages 1458–1461)

      Juan Casado, Víctor Hernández, Shu Hotta and Juan T. López Navarrete

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1458::AID-ADMA1458>3.0.CO;2-W

      Oligothiophenes have been investigated extensively as models of polythiophenes with defect-free chemical structures. Here the authors report on the FT-Raman spectra of α-methyl-substituted oligomers of thiophene (see Figure for the chemical structure) doped with NOBF4, a relatively strong acceptor. The Raman spectra of the second oxidized species for longer chain oligomers are found to closely reproduce the spectra of the charge carriers in doped polythiophene.

    10. Structure–Magnetism Relationships in α-Nitronyl Nitroxide Radicals: Pitfalls and Lessons to be Learned (pages 1461–1466)

      Mercè Deumal, Joan Cirujeda, Jaume Veciana and Juan J. Novoa

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1461::AID-ADMA1461>3.0.CO;2-Z

      Rational design of persistent radicals with crystals having ferromagnetic ordering at high critical temperatures is an important challenge in materials science. This can only be achieved through the control of the crystal packaging of the radicals and a well founded structure–magnetism relationship. A statistical analysis is presented that shows that in α-nitronyl nitroxide crystals it is not possible to define the magnetic role of the NO ⃛ON or C—-H ⃛ON contacts just by looking at the local distance and geometry of one type of contacts; magneto-structural correlations in these crystals must be collective.

    11. Fabrication of Silicon MOSFETs Using Soft Lithography (pages 1466–1469)

      Noo Li Jeon, Junmin Hu, GeorgeM. Whitesides, Martin K. Erhardt and Ralph G. Nuzzo

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1466::AID-ADMA1466>3.0.CO;2-5

      Fabrication of metal-oxide semiconductor field-effect transistors (MOSFETs) in silicon using processes in which MIMIC (micromolding in capillaries—a soft lithographic technique) rather than photolithography is used is described. The Figure shows a micrograph of an array of p-MOSFETs obtained from this process. This demonstrates that MIMIC is compatible with Si fabrication processes, and its application is not limited to single-level processes.

    12. Influence of Oxygen on Single Molecule Blinking (pages 1469–1472)

      Oliver Panzer, Wolfgang Göhde, Ulrich C. Fischer, Harald Fuchs and Klaus Müllen

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1469::AID-ADMA1469>3.0.CO;2-O

      The influence of ambient oxygen on blinking (on–off transitions) of individual terrylenediimide (TDI) molecules is investigated by confocal microscopy. The authors show that the “on-times”—during which the fluorescence intensity is above a certain threshold—are shortened significantly in ambient air compared to in nitrogen. The “off-times” are virtually unaffected. In addition, it is shown that single TDI molecules embedded in a polymer film show much longer “on-times” and fewer “blinks” than those adsorbed on a glass surface.

    13. Wetting of Single Shell Carbon Nanotubes (pages 1472–1475)

      Erik Dujardin, Thomas W. Ebbesen, Ajit Krishnan and Michael M. J. Treacy

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1472::AID-ADMA1472>3.0.CO;2-R

      Carbon nanotubes have two major assets for potential technological applications: their electronic properties and their extremely high mechanical strength, which make them excellent components of composites. Essential for such composites is the existence of favorable surface interactions between the nanotubes and the host matrix. The wetting properties of single shell nanotubes (see micrograph in Figure) are presented.

    14. Low-Temperature Solution Route to Molybdenum Nitride (pages 1475–1479)

      Hsin-Tien Chiu, Shiow-Huey Chuang, Gene-Hsiang Lee and Shie-Ming Peng

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1475::AID-ADMA1475>3.0.CO;2-9

      Transition metal nitrides are technologically important materials. An alternative route to high-temperature preparation by direct nitridation or chemical vapor deposition is rapid solid-state synthesis, a highly exothermic self-propagating reaction. The synthesis of molybdenum nitride powder, an effective catalyst for hydro-desulfurization and hydro-denitrogenation of hydrocarbons, via a solution process of the sol-gel type is reported. This first preparation of a transition metal hydride at low temperatures from solution extends the versatile chemistry of interconversions among various metal–nitrogen containing complexes.

    15. A Novel Pathway to PbSe Nanowires at Room Temperature (pages 1479–1481)

      Wenzhong Wang, Yan Geng, Yitai Qian, Mingrong Ji and Xianming Liu

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1479::AID-ADMA1479>3.0.CO;2-M

      One-dimensional (1D) structures with nanometer diameter are expected to have remarkable properties that are in principle tunable by varying the diameter and chirality. Most previous research on 1D materials concentrated on carbon-based nanomaterials and require extreme preparation conditions. Here the authors report a novel route to PbSe nanowires (see Figure) under mild conditions at room temperature.

    16. Nanocrystalline and Nanoporous Ceramics (pages 1483–1486)

      Henk Verweij

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1483::AID-ADMA1483>3.0.CO;2-J

      Nanocrystalline and nanoporous ceramics, renowned for their special transport properties, have typical applications in the fields of energy, the environment, and separation technology. One example is a solid oxide fuel cell, where an anode with improved characteristics was obtained by an optimized nanoscale porous composite architecture. In this article the author also emphasizes the requirements for nanoscale compaction processing and outlines new results of nanoparticle synthesis by emulsion techniques, such as the preparation of aggregate-free oxide particles of 5–10 nm diameter.

    17. Charge Transport in Nanoparticle Arrangements (pages 1487–1492)

      Ulrich Simon

      Article first published online: 8 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199812)10:17<1487::AID-ADMA1487>3.0.CO;2-W

      Single electron tunneling may occur in nanoparticle arrays when metal or semiconductor clusters are separated by distances of ca. 1 nm. The author shows that the electrical properties of these nanoparticles, mainly studied by complex impedance spectroscopy and scanning tunneling spectroscopy, make them candidates for future electronic devices with nanoscale architecture; a possible electrode pattern is sketched in the Figure.