Advanced Materials

Cover image for Vol. 13 Issue 7

April, 2001

Volume 13, Issue 7

Pages 467–533

    1. Imprinted Polymers (pages 467–478)

      M. J. Whitcombe and E. N. Vulfson

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<467::AID-ADMA467>3.0.CO;2-T

      Imprinted polymers (see Figure) find applications in chemistry, biotechnology, food technology, and materials science. Here the current trends in imprinted polymers and the methods used in their preparation are reviewed, leading to a discussion of examples of applications, such as separation media, analytical systems, sensors, and catalysts.

    2. Realization of Gated Field Emitters for Electrophotonic Applications Using Carbon Nanotube Line Emitters Directly Grown into Submicrometer Holes (pages 479–482)

      Y.-H. Lee, Y.-T. Jang, D.-H. Kim, J.-H. Ahn and B. Ju

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<479::AID-ADMA479>3.0.CO;2-H

      Carbon nanotube field emission pixels with gate electrodes are reported to have been fabricated for the first time. The interesting electronic application of carbon nanotubes (CNTs) as field electron emitters had not been realized previously because of the difficulty of achieving precisely controlled selective growth of CNTs within a hole of diameter ∼1 μm (see Figure).

    3. Electrochemical Fabrication of 3D Microperiodic Porous Materials (pages 482–485)

      P. V. Braun and P. Wiltzius

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<482::AID-ADMA482>3.0.CO;2-4

      3D periodic microstructures of high-refractive index materials(see Figure), in particular the II–VI semiconductors CdS and CdSe, have been synthesized by electrodeposition through silica- or polystyrene-based colloidal assemblies. The highest refractive index contrast is achieved after removal of the silica or polystyrene templates with HF or toluene, respectively.

    4. The Polyrotaxane Gel: A Topological Gel by Figure-of-Eight Cross-links (pages 485–487)

      Y. Okumura and K. Ito

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<485::AID-ADMA485>3.0.CO;2-T

      Supramolecules with topological characteristicshave attracted great interest both experimentally and theoretically. A new kind of gel has been obtained by chemically cross-linking polyrotaxane molecules in solution. The polymer chains are topologically interlocked by figure-of-eight cross-links (see Figure), which can pass along the polymer chains freely to equalize the “tension” of the threaded polymer chains just like pulleys.

    5. A Ferroelectric Ferromagnet Composed of (PLZT)x(BiFeO3)1–x Solid Solution (pages 487–490)

      T. Kanai, S. Ohkoshi, A. Nakajima, T. Watanabe and K. Hashimoto

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<487::AID-ADMA487>3.0.CO;2-L

      (PLZT)x(BiFeO3)1–xsolid solutions exhibiting both ferromagnetism and ferroelectricity have been prepared by a solid-state reaction. Their structures are cubic in the range 0 < x ≤ 1. For x = 0.10–0.45 the materials simultaneously show magnetic and ferroelectric hysteresis loops at room temperature. The observed spontaneous magnetization is due to the weak ferromagnetism present in the system, which originates from the cant of the antiparallel spins of Fe3+ ions through the structural distortion from rhombic to cubic caused by the incorporation of PLZT.

    6. Novel Magnetic Resonance Signal Enhancing Coating Material (pages 490–493)

      X. Jiang, H. Yu, R. Frayne, O. Unal and C. M. Strother

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<490::AID-ADMA490>3.0.CO;2-8

      Magnetic resonance (MR) guided endovascular intervention is an attractive guiding technique, but until now it has been difficult to visualize the catheter. Here it is revealed that by chemically attaching a Gd complex to the polyethylene surface of the catheter strong MR signals and a clear contrast between the coated materials and the background can be obtained. The Figure shows one uncoated (d) and three coated (a,b, c) samples.

    7. Ion-Imprinted Zeolite: A Surface Functionalization Methodology Based on the “Ship-in-Bottle” Technique (pages 493–496)

      Z. Zhang, S. Dai, R. D. Hunt, Y. Wei and S. L. Qiu

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<493::AID-ADMA493>3.0.CO;2-X

      A new methodology to effectively modify the selectivity of zeolites toward a target metal ion via surface molecular imprinting has been developed. A stepwise methodology in which the template complex is assembled inside the zeolite pore in a piece-by-piece fashion is shown (see Figure). Tailored zeolites with surface functionalization show great promise for the realization of shape-selective catalysis.

    8. Supercapacitors Using Single-Walled Carbon Nanotube Electrodes (pages 497–500)

      K. H. An, W. S. Kim, Y. S. Park, Y. C. Choi, S. M. Lee, D. C. Chung, D. J. Bae, S. C. Lim and Y. H. Lee

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<497::AID-ADMA497>3.0.CO;2-H

      The key factors determining the performance of supercapacitorshave been studied using single-walled carbon nanotube (CNT) electrodes. Heat treatment at high temperatures is found to increase the capacitance and reduce the CNT electrode resistance. A very efficient energy storage device was obtained with a CNT-Ni foam hybrid electrode as the energy density does not change appreciably with increasing power density due to its small equivalent series resistance (ESR). This approach demonstrates the possibility of using CNTs as energy storage devices.

    9. The Generation of “Armored Latexes” and Hollow Inorganic Shells Made of Clay Sheets by Templating Cationic Miniemulsions and Latexes (pages 500–503)

      B. zu Putlitz, K. Landfester, H. Fischer and M. Antonietti

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<500::AID-ADMA500>3.0.CO;2-3

      A single-step synthesis of inorganic microcapsulesfilled with organic liquids or polymers is achieved by complexation of cationic surfactant–stabilized miniemulsion latexes with disc-shaped silica particles. Interlinking the discs by condensation with silicic acid further stabilizes the capsules. The structure survives depolymerization and evaporation of a polymeric organic template. The Figure shows hollow nanocapsules.

    10. Non-dispersive Hole Transport in a Soluble Poly(p-phenylene vinylene) (pages 504–508)

      A. R. Inigo, C. H. Tan, W. Fann, Y.-S. Huang, G.-Y. Perng and S.-A. Chen

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<504::AID-ADMA504>3.0.CO;2-O

      Understanding the relationship between charge transport and morphology is critical for improving the efficiency of conjugated polymer–based devices. Time of flight measurements are used here to examine hole transport in films of poly(2-methoxy-5-(2′-ethylhexoxy)-1,4,-phenylene vinylene) (MEH-PPV). Films cast from three different solvents, toluene, p-xylene, and chlorobenzene, are investigated. It is shown that the MEH-PPV films can exhibit either non-dispersive or dispersive transport, depending on the solvent used.

    11. Fine Tuning of Au/SiO2/Si Diodes by Varying Interfacial Dipoles Using Molecular Monolayers (pages 508–511)

      Y. Selzer and D. Cahen

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<508::AID-ADMA508>3.0.CO;2-8

      The electron affinity of semiconductors and the work function of metalscan be systematically varied by the adsorption of a series of organic molecules with varying dipole moment. This effect can be used to induce molecular control over the electrical characteristics of some metal/semiconductor diodes. The variety of molecules that can be bonded to metals, together with those that are available for bonding to semiconductors, makes the method quite flexible and may enable the build up of more sophisticated interfacial structures.

    12. Enhanced Visible Light Conversion Efficiency Using Nanocrystalline WO3 Films (pages 511–514)

      C. Santato, M. Ulmann and J. Augustynski

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<511::AID-ADMA511>3.0.CO;2-W

      Drastically improved photooxidation efficiencies,when compared to bulk WO3, are obtained with nanocrystalline WO3 films (see Figure) deposited from a colloidal solution of tungstic acid. Saturation of the photocurrent, which occurs even for moderate potential differences, indicates a completely different mechanism of charge separation. The electrodes should be highly effective for photoelectrolysis of water by sunlight.

    13. Dense Nanostructured t-ZrO2 Coatings at Low Temperatures via Modified Emulsion Precipitation (pages 514–516)

      F. C. M. Woudenberg, W. F. C. Sager, N. G. M. Sibelt and H. Verweij

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<514::AID-ADMA514>3.0.CO;2-K

      Nanostructured coatings on metals, plastics, and textiles have numerous applications, for example, as antifogging and self-cleaning coatings as well as protective coatings against corrosion, heat, or wear. Here the preparation at low temperature of dense nanostructured tetragonal ZrO2 coatings via a modified emulsion precipitation method is presented. The method, which involves the controlled preparation, crystallization, and densification of non-agglomerated ZrO2 nanoparticles, opens up the possibility of applying nanocoatings of high-melting oxides to steel or plastic, where low temperatures are required.

    14. Size-Controlled Synthesis of Pd Nanowires Using a Mesoporous Silica Template via Chemical Vapor Infiltration (pages 517–520)

      K.-B. Lee, S.-M. Lee and J. Cheon

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<517::AID-ADMA517>3.0.CO;2-8

      Free-standing Pd nanowires of controlled size are synthesized by these authors via chemical vapor infiltration of an organometallic precursor into mesoporous silicate. The thus generated Pd nanowires can be isolated by addition of HF to remove the silicate matrix. Wires ranging from 3.7–8.8 nm in diameter and up to several hundred nanometers in length can be obtained (see Figure), depending on the silica template used.

    15. Melting and Welding Semiconductor Nanowires in Nanotubes (pages 520–523)

      Y. Wu and P. Yang

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<520::AID-ADMA520>3.0.CO;2-W

      Significant melting point depression and large hysteresis during the melting–recrystallization cycle are observed for semiconductor Ge nanowires encapsulated within carbon nanotubes. The capability of cutting, linking (see cover), and welding (see Figure) nanowires at relatively modest temperatures may provide a new approach to integrating these 1D nanostructures into functional devices and circuitry.

    16. Interpenetrating Lattices—Materials of the Future (pages 525–527)

      J. S. Miller

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<525::AID-ADMA525>3.0.CO;2-C

      The fascination of mankind with art and architecture has extended to the structural topology of molecules and materials and has led to deliberate syntheses of highly symmetric and strained molecules. Materials comprised of interpenetrating lattices (see Figure) have been discovered and there is high expectation that they will be advanced materials of the future with useful optical, electrical, magnetic, catalytic, or separation properties.

    17. Magnetic Core/Shell and Quantum-Confined Semiconductor Nanoparticles via Chimie Douce Organometallic Synthesis (pages 529–533)

      J. J. Schneider

      Article first published online: 6 APR 2001 | DOI: 10.1002/1521-4095(200104)13:7<529::AID-ADMA529>3.0.CO;2-X

      Ligand-stabilized metal atoms provide a unique entry to the synthesis of magnetic nanosized metal/metal oxide particles. When this technique is used in connection with a mesoporous template, formation of superparamagnetic particles in the pores of the template via a “ship-in-the-bottle” technique is possible. The Figure shows a sculpture of a typical core/shell arrangement often found for composite nanoparticles.