Advanced Materials

Cover image for Vol. 15 Issue 1

January, 2003

Volume 15, Issue 1

Pages 3–86

    1. Contents: Adv. Mater. 1/2003 (pages 3–6)

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390005

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      15 Years of Advanced Materials: Past and Future (pages 13–18)

      E. Levy

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390001

      2003 marks 15 years of publication of Advanced Materials. The events and innovations that have contributed to the present success of Advanced Materials—from its features and services to the science it reports—are highlighted in this Editorial and a glimpse is given of what this year holds in store (see also cover).

    3. Molecular Engineering of Peripherally And Axially Modified Phthalocyanines for Optical Limiting and Nonlinear Optics (pages 19–32)

      S.M. O’Flaherty, S.V. Hold, M.J. Cook, T. Torres, Y. Chen, M. Hanack and W.J. Blau

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390002

      A tremendous degree of design flexibility is offered by phthalocyanines, with which they may be employed to fabricate practical organic passive optical limiters. In this review, the nonlinear optical absorption of a comprehensive representative series of modified phthalocyanines is experimentally determined, modeled, and discussed. Using the simple z-scan technique, the effect of substitution with various central metals and peripheral functional groups is experimentally explored. General trends relating the optical limiting performance of these compounds to their structural characteristics are also discussed.

    4. n-Type Building Blocks for Organic Electronics: A Homologous Family of Fluorocarbon-Substituted Thiophene Oligomers with High Carrier Mobility (pages 33–38)

      A. Facchetti, M. Mushrush, H.E. Katz and T.J. Marks

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390003

      A substantial enhancement of thermal stability, volatility, and electron affinity, switching the semiconducting behavior from p- to n-type, is achieved by fluoroalkyl substitution of thiophene oligomers (see Figure). When this novel series is compared with the fluorine-free analogues, trends in molecular packing, optical absorption, HOMO–LUMO gap, and π–π interactions are found to be strikingly similar.

    5. Characterization of an Organic Hydrogel: A Cryo-Transmission Electron Microscopy and X-ray Diffraction Study (pages 38–42)

      L.A. Estroff, L. Leiserowitz, L. Addadi, S. Weiner and A.D. Hamilton

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390004

      An insight into the molecular assembly processes that lead ultimately to the gelation of water by small organic molecules can be gained by the combination of two powerful techniques. Vitrified ice cryo-transmission electron microscopy (TEM) (see Figure) and X-ray diffraction, have been applied to evaluate the nanoscale structure and molecular organization of an organic hydrogel in its native (hydrated) state.

    6. Isolated Single-Molecule Magnets on the Surface of a Polymeric Thin Film (pages 42–45)

      D. Ruiz-Molina, M. Mas-Torrent, J. Gómez, A.I. Balana, N. Domingo, J. Tejada, M.T. Martínez, C. Rovira and J. Veciana

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390006

      Individual Mn12 single-molecule magnets are arranged onto a polymeric film surface using a new, soft, reliable and simple chemical methodology. Polymeric thin films, prepared from a polycarbonate matrix and Mn12 molecules, are subsequently treated with an organic solvent vapor, resulting in nanocomposite thin films that are flexible and optically transparent and could be used for information storage or in quantum computing.

    7. Electrophosphorescence from a Conjugated Copolymer Doped with an Iridium Complex: High Brightness and Improved Operational Stability (pages 45–49)

      X. Gong, J.C. Ostrowski, G.C. Bazan, D. Moses, A.J. Heeger, M.S. Liu and A.K.-Y. Jen

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390007

      High efficiency electrophosphorescent light-emitting diodes (LEDs), with an emission peak at 600 nm, a luminance of 2200 cd m–2, and good operational stability were fabricated from a conjugated copolymer doped with an iridium complex. The devices exhibited an external quantum efficiency of 1.5 % and a luminous efficiency of 3 cd A–1. These results demonstrate that electrophosphorescent devices with high brightness and operational stability can be produced in the form of polymer LEDs fabricated by processing the active materials from solution.

    8. Fabrication of Two-Dimensional Arrays of CdSe Pillars Using E-Beam Lithography and Electrochemical Deposition (pages 49–51)

      Y.-W. Su, C.-S. Wu, C.-C. Chen and C.-D. Chen

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390008

      Two-dimensional arrays of high refractive index structures can be fabricated using a combination of e-beam lithography for pattern definition and electrochemical deposition for structure formation. The potential of this method is demonstrated for CdSe, where nanopillars, mushrooms (see Figure), walls, and crosses are prepared. Such arrays have potential in optical device applications such as photonic crystals and waveguides.

    9. Ceramics Containing Magnetic Co–Fe Alloy Nanoparticles from the Pyrolysis of a Highly Metallized Organometallic Polymer Precursor (pages 51–55)

      A. Berenbaum, M. Ginzburg-Margau, N. Coombs, A.J. Lough, A. Safa-Sefat, J.E. Greedan, G.A. Ozin and I. Manners

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390009

      Lightweight magnetic ceramics containing bimetallic (Co–Fe) nanoparticles in an essentially amorphous C/SiC matrix have been prepared from the pyrolysis of a polyferrocenylsilane with pendant cobalt clusters. The Figure shows a TEM image of the ceramic material formed at 600 °C under N2. Superparamagnetic or ferromagnetic particles may be made, depending on the pyrolysis temperature.

    10. Room Temperature Electrochemical Opening of Carbon Nanotubes Followed by Hydrogen Storage (pages 55–57)

      J.M. Skowroński, P. Scharff, N. Pfänder and S. Cui

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390010

      An electrochemical method is used to open multi-walled carbon nanotubes at a room temperature. HRTEM analysis (see Figure, arrows indicate openings) and cyclic voltammetry were undertaken and showed that, owing to the oxidation reactions occurring preferably at the end regions of nanotubes, an enhanced amount of hydrogen is stored in the nanotubes, which, during the cathodic reduction, is reversibly recovered.

    11. Electroactive Surfactant Designed to Mediate Electron Transfer Between CdSe Nanocrystals and Organic Semiconductors (pages 58–61)

      D.J. Milliron, A.P. Alivisatos, C. Pitois, C. Edder and J.M.J. Fréchet

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390011

      An electroactive pentathiophene surfactant containing a phosphonic acid head group was designed and shown to provide strong binding to the surface of a CdSe nanocrystal and facilitate charge transfer between the nanocrystal and an organic semiconducting matrix (see Figure). Incorporation into organic–inorganic heterojunction solar cells could improve the efficiency of these promising devices.

    12. Customization of Poly(dimethylsiloxane) Stamps by Micromachining Using a Femtosecond-Pulsed Laser (pages 62–65)

      D.B. Wolfe, J.B. Ashcom, J.C. Hwang, C.B. Schaffer, E. Mazur and G.M. Whitesides

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390012

      A femtosecond-pulsed Ti:sapphire laser is used to generate surface features in slabs of poly(dimethylsiloxane) with minimum dimensions of 1 μm—smaller than those available by rapid-prototyping techniques using transparency masks. The fabrication of magnetic field concentrators and the addition of custom features to a generic microfluidic channel (see Figure) demonstrate the utility of the technique.

    13. Facile Hydrophilic Surface Modification of Poly(tetrafluoroethylene) Using Fluoroalkyl-Terminated Poly(ethylene glycol)s (pages 66–69)

      G. Tae, R.G.H. Lammertink, J.A. Kornfield and J.A. Hubbell

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390013

      Hydrophilic surface modification of poly(tetrafluoroethylene) (PTFE) has been carried out by coating with a thin layer of fluoroalkyl- terminated poly(ethylene gylcol) (PEG). The coating layer adheres by hydrophobic interactions and is stable, in accord with the sol–gel behavior of the bulk polymer. Stable hydrogel arrays have been prepared by e.g., solvent- assisted micromolding on a perfluorosilanized substrate (see Figure).

    14. Fabrication of Germanium-Filled Silica Nanotubes and Aligned Silica Nanofibers (pages 70–73)

      J.-Q. Hu, X.-M. Meng, Y. Jiang, C.-S. Lee and S.-T. Lee

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390014

      Germanium-filled SiO2 nanotubes and aligned SiO2 nanofibers are synthesized via a two-stage process: thermal evaporation of SiO powder, followed by laser ablation of a Ge target. The nanotubes are either partially filled with Ge nanoparticles/nanorods or completely filled with Ge nanowires, forming Ge/SiO2 nanocables (see Figure). The products were characterized using a variety of spectroscopic techniques.

    15. Preparation of Large-Area 3D Ordered Macroporous Titania Films by Silica Colloidal Crystal Templating (pages 73–75)

      S. Kuai, S. Badilescu, G. Bader, R. Brüning, X. Hu and V.-V. Truong

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390015

      Highly ordered macroporous titania films (see Figure) can be prepared over large areas using colloidal silica spheres as a template. This template material has a number of advantages over the more commonly used polystyrene spheres, such as easy removal of the template by immersion in a warm NaOH solution and shrinkage of the macroporous framework by less than 3 %.

    16. Self-Assembled Surface Patterns of Binary Colloidal Crystals (pages 75–78)

      V. Kitaev and G.A. Ozin

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390016

      Co-assembly of binary dispersions of monodisperse microspheres with large size ratios has been used to produce well-ordered hexagonally close-packed monolayers of large spheres with a superimposed pattern of small spheres (see Figure). The architectures obtained are determined by the size and concentration ratios of the microspheres in the dispersions, are very diverse, and can be obtained reproducibly over millimeter length scales.

    17. Uniform Emulsion-Templated Silica Beads with High Pore Volume and Hierarchical Porosity (pages 78–81)

      H. Zhang, G.C. Hardy, M.J. Rosseinsky and A.I. Cooper

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390017

      A new type of porous silica bead (see Figure) with a narrow size distribution, useful for applications such as catalysis, biomolecule immobilization, and chromatographic separation, can be synthesized via a novel emulsion templating/sedimentation polymerization route. This method might be scaled up for the synthesis of significant quantities of beads, or extended to make, e.g., metal and metal oxide beads with high surface area and macropore volume.

    18. π-Stacked Conjugated Polymers: The Influence of Paracyclophane π-Stacks on the Redox and Optical Properties of a New Class of Broken Conjugated Polythiophenes (pages 81–85)

      F. Salhi and D.M. Collard

      Version of Record online: 10 JAN 2003 | DOI: 10.1002/adma.200390018

      Bis(3-octyl-2-thienyl)-[2.2]paracyclophane is subjected to oxidative polymerization to afford a soluble redox-active polymer (see Figure) consisting of conjugated tetraarenes held in permanent cofacial stacks by cyclophane linkages. The influence of p-stacking of the conjugated units along the polymer chain and the effect of stacking on the extended delocalization and conjugation of excitons and charge carrier is investigated.