Advanced Materials

Cover image for Vol. 17 Issue 19

October, 2005

Volume 17, Issue 19

Pages 2271–2392

    1. Cover Picture: Direct Correlation of Organic Semiconductor Film Structure to Field-Effect Mobility (Adv. Mater. 19/2005)

      D. M. DeLongchamp, S. Sambasivan, D. A. Fischer, E. K. Lin, P. Chang, A. R. Murphy, J. M. J. Fréchet and V. Subramanian

      Article first published online: 23 SEP 2005 | DOI: 10.1002/adma.200590099

      Near-edge X-ray fine structure spectroscopy is used to measure simultaneous chemical conversion, molecular ordering, and defect formation in soluble oligothiophene precursor films. Film structure is correlated to OFET performance. Molecular orientation is determined by evaluating antibonding orbital overlap with the polarized electric field vector of incident soft X-rays (see Figure and cover). Upon conversion, the molecules become vertically oriented, allowing π overlap in the plane of hole transport.

    2. Contents: Adv. Mater. 19/2005 (pages 2271–2278)

      Article first published online: 23 SEP 2005 | DOI: 10.1002/adma.200590095

    3. Light-Emitting Polythiophenes (pages 2281–2305)

      I. F. Perepichka, D. F. Perepichka, H. Meng and F. Wudl

      Article first published online: 30 AUG 2005 | DOI: 10.1002/adma.200500461

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      The unique electronic properties of polythiophenes present a number of opportunities for applications in light-emitting materials. This article reviews achievements to date in the application of thiophene-based polymers and oligomers as electroluminescent materials (see Figure). Special attention is paid to the consequences of structural variations for controlling the optical properties of polythiophenes and the performance of light-emitting diodes fabricated with these materials.

    4. Memory Effect and Negative Differential Resistance by Electrode- Induced Two-Dimensional Single- Electron Tunneling in Molecular and Organic Electronic Devices (pages 2307–2311)

      W. Tang, H. Z. Shi, G. Xu, B. S. Ong, Z. D. Popovic, J. C. Deng, J. Zhao and G. H. Rao

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200500232

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      Mysterious negative differential resistances and memory effects are commonly observed in molecular electronic thin-film devices such as organic light-emitting diodes. The authors describe how this may result from the formation of metallic nanospheres (see Figure) inside crevices resulting from defects, such as dust particles. Single-electron tunneling between the nanospheres, which are formed by nucleation and growth processes at the defect sites, results in the observed anomalous effects.

    5. Large Electro-optic Kerr Effect in Nanostructured Chiral Liquid-Crystal Composites over a Wide Temperature Range (pages 2311–2315)

      Y. Haseba, H. Kikuchi, T. Nagamura and T. Kajiyama

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200500042

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      Optically transparent and isotropic liquid-crystalline composites are successfully prepared by in-situ photopolymerization of crosslinking monomers in the isotropic phase of chiral liquid crystals. An anomalously large electro-optical Kerr constant (K) was observed in the composite over a broad temperature range (see Figure). These composites could provide new flat-panel liquid-crystal displays with high-speed responses and without the need for a rubbing process during fabrication.

    6. High-Performance Ambipolar Pentacene Organic Field-Effect Transistors on Poly(vinyl alcohol) Organic Gate Dielectric (pages 2315–2320)

      Th. B. Singh, F. Meghdadi, S. Günes, N. Marjanovic, G. Horowitz, P. Lang, S. Bauer and N. S. Sariciftci

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200501109

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      Growing organic semiconductors on dielectrics with different surface energies and dielectric constants results in striking changes of the film morphology (Figure, right). Ambipolar transport is reported in pentacene transistors on a PVA gate dielectric (left). The current–voltage characteristics correlate with capacitance–voltage investigations on metal–insulator–semiconductor structures.

    7. One-Dimensional Quantum-Confinement Effect in α-Fe2O3 Ultrafine Nanorod Arrays (pages 2320–2323)

      L. Vayssieres, C. Sathe, S. M. Butorin, D. K. Shuh, J. Nordgren and J. Guo

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200500992

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      A 1D quantum confinement effect in hematite thin films consisting of oriented ultrafine nanorod bundles (see Figure) is investigated by resonant inelastic x-ray scattering of synchrotron radiation. The direct observation of a substantial bandgap increase compared to bulk hematite is revealed. This finding shows that these low-dimensional nanomaterials may be used for the generation of hydrogen by solar illumination without applied bias.

    8. The Patterning and Alignment of Muscle Cells Using the Selective Adhesion of Poly(oligoethylene glycol methyl ether methacrylate)-based ABA Block Copolymers (pages 2324–2329)

      D. C. Popescu, R. Lems, N. A. A. Rossi, C.-T. Yeoh, J. Loos, S. J. Holder, C. V. C. Bouten and N. A. J. M. Sommerdijk

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200500039

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      The selective adhesion/delamination behavior of poly(oligoethylene glycol methyl ether methacrylate)-based ABA block copolymers is exploited to generate patterned substrates consisting of alternating lanes of glass and copolymer-coated gold. These patterns have been successfully used for the patterning and alignment of C2C12 muscle cells. The parallel-oriented myotubes (see Figure) contract upon electrical stimulation, forming a promising 2D in-vitro model for muscles.

    9. Spontaneous Formation of Blood-Compatible Surfaces on Hydrophobic Polymers: Surface Enrichment of a Block Copolymer with a Water-Soluble Block (pages 2329–2332)

      A. Oyane, T. Ishizone, M. Uchida, K. Furukawa, T. Ushida and H. Yokoyama

      Article first published online: 22 AUG 2005 | DOI: 10.1002/adma.200500945

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      A polymer surface with excellent blood compatibility has been produced via spontaneous surface segregation of a block copolymer. The water-soluble polymer block (PME3MA) spontaneously segregates into hydrophobic and hydrophilic environments (see Figure), causing the blocks to expel biological substances including proteins, cells and platelets via flexible chain motion.

    10. Large-Area, Selective Transfer of Microstructured Silicon: A Printing- Based Approach to High-Performance Thin-Film Transistors Supported on Flexible Substrates (pages 2332–2336)

      K. J. Lee, M. J. Motala, M. A. Meitl, W. R. Childs, E. Menard, A. K. Shim, J. A. Rogers and R. G. Nuzzo

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200500578

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      The selective transfer and accurate registration of microstructured silicon (μs-Si) across large areas is demonstrated using a printing-based procedure applicable to both rigid (i.e., glass) and flexible plastic substrates (see Figure). The utility of this technique to construct macroelectronic systems that incorporate high-performance μs-Si thin-film transistors on flexible substrates is also demonstrated.

    11. Photogeneration of Fluorescent Silver Nanoclusters in Polymer Microgels (pages 2336–2340)

      J. Zhang, S. Xu and E. Kumacheva

      Article first published online: 22 AUG 2005 | DOI: 10.1002/adma.200501062

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      Photoactivated template-based synthesis of fluorescent Ag nanoclusters in the interior of microgel particles has been demonstrated. Photoluminescence intensity and emission wavelength varies with the time of photoactivated synthesis. Optical properties of the photogenerated Ag nanoclusters strongly depend on the acidity of the medium. The resulting hybrid microgels show stable photoluminescence and strong response to external stimuli.

    12. Direct Correlation of Organic Semiconductor Film Structure to Field-Effect Mobility (pages 2340–2344)

      D. M. DeLongchamp, S. Sambasivan, D. A. Fischer, E. K. Lin, P. Chang, A. R. Murphy, J. M. J. Fréchet and V. Subramanian

      Article first published online: 30 AUG 2005 | DOI: 10.1002/adma.200500263

      Thumbnail image of graphical abstract

      Near-edge X-ray fine structure spectroscopy is used to measure simultaneous chemical conversion, molecular ordering, and defect formation in soluble oligothiophene precursor films. Film structure is correlated to OFET performance. Molecular orientation is determined by evaluating antibonding orbital overlap with the polarized electric field vector of incident soft X-rays (see Figure and cover). Upon conversion, the molecules become vertically oriented, allowing π overlap in the plane of hole transport.

    13. Dynamic Tuning of Photoluminescent Dyes in Crystalline Colloidal Arrays (pages 2344–2349)

      J. R. Lawrence, G. H. Shim, P. Jiang, M. G. Han, Y. Ying and S. H. Foulger

      Article first published online: 22 AUG 2005 | DOI: 10.1002/adma.200500617

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      Real-time tuning of the emission characteristics of a dye encapsulated in a colloidal crystal through in-situ modification of the rejection wavelength is demonstrated. Mechanochromic tuning is used to modify the emission spectra of hydrogel-encapsulated crystalline colloidal arrays composed of electrostatically self-assembled monodisperse polystyrene particles coated with the photoluminescent dye Rhodamine-B, as shown in the Figure.

    14. Chemical Sintering of Nanoparticles: A Methodology for Low-Temperature Fabrication of Dye-Sensitized TiO2 Films (pages 2349–2353)

      N.-G. Park, K. M. Kim, M. G. Kang, K. S. Ryu, S. H. Chang and Y.-J. Shin

      Article first published online: 22 AUG 2005 | DOI: 10.1002/adma.200500288

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      A binder-free nanocrystalline TiO2 paste with high viscosity (see Figure) has been developed using non-thermal sintering conditions to deposit a TiO2 film with good interparticle connectivity. A dye-sensitized TiO2 film dried at 150 °C demonstrates an overall conversion efficiency of 3.52 % under AM 1.5 (1000 W m–2) illumination. The binder-free TiO2 paste is expected to be utilizable in flexible dye-sensitized solar cells.

    15. Preparation of Fluorescent SiO2 Particles with Single CdTe Nanocrystal Cores by the Reverse Microemulsion Method (pages 2354–2357)

      Y. Yang and M. Y. Gao

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200500403

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      Highly fluorescent CdTe@SiO2 core–shell-structured spheres (see Figure) are prepared via hydrolysis and condensation of tetraethyl orthosilicate in water-in-oil emulsions. Systematic results reveal that the electrostatic interactions between negatively charged CdTe nanocrystals (NCs) and silica intermediates play a critical role in determining the final structures of the resultant particles. Following this mechanism, the number of CdTe NCs encapsulated in silica spheres is successfully tuned.

    16. Self-Rupturing Microcapsules (pages 2357–2361)

      B. G. De Geest, C. Déjugnat, G. B. Sukhorukov, K. Braeckmans, S. C. De Smedt and J. Demeester

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200401951

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      Self-rupturing microcapsules are prepared by layer-by-layer coating of degradable dextran-hydroxyethyl methacrylate microgels with the polyelectrolytes poly(allylamine hydrochloride) and sodium poly(styrene sulfonate). When the microgel core degrades, the swelling pressure increases and, at a critical value of the swelling pressure, the surrounding membrane suddenly ruptures (see Figure). This type of microcapsule could be very promising for pulsed drug delivery.

    17. Large-Scale “Surface-Programmed Assembly” of Pristine Vanadium Oxide Nanowire-Based Devices (pages 2361–2364)

      S. Myung, M. Lee, G. T. Kim, J. S. Ha and S. Hong

      Article first published online: 22 AUG 2005 | DOI: 10.1002/adma.200500682

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      “Surface-programmed assembly” is presented as a technique (see Figure) to achieve high-precision assembly and alignment of a large number of pristine V2O5 nanowires on solid substrates. Positively charged surface molecular patterns guide the assembly and alignment of negatively charged V2O5 nanowires on solid substrates. Large-scale assembly of V2O5 nanowire-based transistors is demonstrated and their gating effects are confirmed.

    18. Freestanding Polymer–Metal Oxide Nanocomposite Films for Light-Driven Oxygen Scavenging (pages 2365–2368)

      A. M. Peiró, G. Doyle, A. Mills and J. R. Durrant

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200500397

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      Freestanding films containing nanocrystalline TiO2 and a suitable electron donor embedded in a cellulose matrix deoxygenate a closed environment (see Figure) upon UV illumination as a result of the photocatalytic properties of TiO2. This opens up the potential use of semiconductor photocatalysis in active packaging to achieve light-driven deoxygenation of closed environments.

    19. Fluorinated-Surfactant-Templated Synthesis of Hollow Silica Particles with a Single Layer of Mesopores in Their Shells (pages 2368–2371)

      B. Tan, H. J. Lehmler, S. M. Vyas, B. L. Knutson and S. E. Rankin

      Article first published online: 22 AUG 2005 | DOI: 10.1002/adma.200500344

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      Hollow silica particles with mesoporous walls (see Figure) are synthesized from solution by co-assembly of silica with cationic fluorinated surfactants. The particles resemble vesicles, but retain wall patterns, indicating that they do not form from silica-coated bilayers but by the co-assembly of silica with micelles. Stronger shearing during synthesis causes the particles to aggregate into elongated particles with multiple hollow chambers.

    20. Metal–Organic Chemical Vapor Depostion Synthesis of Hollow Inorganic-Fullerene-Type MoS2 and MoSe2 Nanoparticles (pages 2372–2375)

      J. Etzkorn, H. A. Therese, F. Rocker, N. Zink, U. Kolb and W. Tremel

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200500850

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      Hollow, nested inorganic fullerene- type MoQ2 (Q = S, Se) nanoparticles (see Figure) are prepared in high yield and on a large scale from organometallic precursors. The MoQ2 nanoparticles are obtained by a gas-phase synthesis (using metal-organic chemical vapor deposition) from Mo(CO)6 and S/Se, followed by a subsequent annealing step.

    21. Multifunctional Quantum-Dot-Based Magnetic Chitosan Nanobeads (pages 2375–2380)

      W. B. Tan and Y. Zhang

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200401650

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      Chitosan nanobead encapsulation of quantum dots (QDs) produces water-soluble, stable fluorescent markers for biomedical imaging. As shown in the Figure, derivatization of QDs with 3-mercaptopropionic acid (3MPA) produces a negatively charged surface to which positively charged chitosan is electrostatically attracted. MRI contrast agents such as Gd-DTPA can also be incorporated into the nanobeads, which are small enough to be incorporated into individual cells.

    22. A Self-Supporting Electrode for Supercapacitors Prepared by One-Step Pyrolysis of Carbon Nanotube/Polyacrylonitrile Blends (pages 2380–2384)

      F. Béguin, K. Szostak, G. Lota and E. Frackowiak

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200402103

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      A new type of supercapacitor electrode is reported, prepared by pressing a carbon nanotube/polyacrylonitrile blend and then pyrolyzing the pellet (see Figure). Although their specific surface area is very low, e.g., 200 m2 g–1, the C/C composites demonstrate high values of capacitance, up to 100 F g–1. The authors propose two explanations for these remarkable values.

    23. Submicrometer-Sized Vaterite Tubes Formed Through Nanobubble-Templated Crystal Growth (pages 2384–2388)

      Y. W. Fan and R. Z. Wang

      Article first published online: 16 AUG 2005 | DOI: 10.1002/adma.200500755

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      Electrolytic deposition is used to prepare submicrometer-sized vaterite (CaCO3) tubes (see Figure) in the absence of organic molecules, the presence of which was previously thought to be necessary for the growth of calcium carbonate crystals in complex morphologies. The mechanism of formation is shown experimentally to be hydrogen-nanobubble-templated crystal growth.

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