Advanced Materials

Cover image for Advanced Materials

December, 2004

Volume 16, Issue 23-24

Pages 2075–2249

    1. Multiscale Scanning Tunneling Microscopy Study of Self-Assembly Phenomena in Two-Dimensional Polycrystals of π-Conjugated Polymers: The Case of Regioregular Poly(dioctylbithiophene-alt-fluorenone) (pages 2087–2092)

      M. Brun, R. Demadrille, P. Rannou, A. Pron, J.-P. Travers and B. Grévin

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400088

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      A regioregular π-conjugated alternating copolymer that contains fluorenone and bithiophene subunits forms self-organized polycrystals with meso- and nanoscopic structural features is imaged by low-current scanning tunneling microscopy. Unlike conjugated polymers lacking the fluorenone subunit (Figure, left), the rigidity of the copolymer discourages chain folding and results in “fold-free” monodomains (right).

    2. Incorporation of Luminescent Nanocrystals into Monodisperse Core–Shell Silica Microspheres (pages 2092–2097)

      Y. Chan, J. P. Zimmer, M. Stroh, J. S. Steckel, R. K. Jain and M. G. Bawendi

      Version of Record online: 17 NOV 2004 | DOI: 10.1002/adma.200400237

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      Silica microspheres coated with a silica or titania shell containing fluorescent semiconductor nanocrystals are described. Since the coating process does not affect the monodispersity of the silica microspheres, microspheres of a defined size and emission wavelength, potentially useful for biological applications, can be fabricated. The Figure shows 100 nm diameter blue-light-emitting and 500 nm diameter red-light-emitting microspheres circulating in the brain of a mouse.

    3. High-Performance n- and p-Type Single-Crystal Organic Transistors with Free-Space Gate Dielectrics (pages 2097–2101)

      E. Menard, V. Podzorov, S.-H. Hur, A. Gaur, M. E. Gershenson and J. A. Rogers

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200401017

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      A novel single-crystal organic field-effect transistor (OFET) is described, in which the gate dielectric is replaced by a thin gap that can be occupied by a gas or vacuum. When used in combination with high-quality rubrene or tetracyanoquinodimethane (TCNQ) crystals, n- and p-devices with extremely good mobilities and normalized sub-threshold slopes, representing the ultimate in OFET performance, are realized.

    4. Highly Efficient Multicolour Upconversion Emission in Transparent Colloids of Lanthanide-Doped NaYF4 Nanocrystals (pages 2102–2105)

      S. Heer, K. Kömpe, H.-U. Güdel and M. Haase

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400772

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      Highly efficient photon upconversion in solution is demonstrated for the first time. Transparent colloidal solutions of Yb/Er and Yb/Tm doped NaYF4 nanocrystals show bright upconversion emission in the red, green, and blue spectral region by excitation around 1 μm with a laser of moderate power (see Figure). These new systems show a substantial improvement on the order of 108 compared to previously reported systems.

    5. Flow-Through-Type DNA Array Based on Ideally Ordered Anodic Porous Alumina Substrate (pages 2105–2108)

      F. Matsumoto, K. Nishio and H. Masuda

      Version of Record online: 17 NOV 2004 | DOI: 10.1002/adma.200400360

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      A flow-through-type DNA array fabricated from an ideally ordered anodic porous alumina substrate is reported. Single-stranded probe DNA was affixed to the walls of the sub-micrometer-diameter holes, and fluorescently labelled target DNA was passed through the holes in the substrate. Fluorescence microscopy revealed an ordered array of fluorescent spots after the hybridization (see Figure), demonstrating the applicability of these porous alumina substrates to fabrication of high-density DNA arrays.

    6. Transparent Slanted Phase Gratings in Emissive Waveguides (pages 2108–2111)

      H. J. B. Jagt, H. J. Cornelissen, C. W. M. Bastiaansen and D. J. Broer

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400330

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      A new front-illumination principle is demonstrated for use in energy efficient and bright reflective liquid crystal displays (LCDs). The new emissive waveguide principle presented is based on Bragg diffraction of waveguided light at a tuned holographic grating. The frontlight exhibits negligible image deterioration due to an excellent transparency and a high preference for (linearly polarized) light emission towards the display.

    7. Self-Cleaning Fabrics for Decontamination of Organophosphorous Pesticides and Related Chemical Agents (pages 2112–2115)

      A. Singh, Y. Lee and W. J. Dressick

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400660

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      Cotton threads bearing adsorbed branched polyethylenimine–organophosphorous hydrolase (BPEI/OPH) multilayers are woven into cotton cloth (CC) that actively hydrolyzes methyl parathion (MPT) in solution to p-nitrophenol (PNP) over several weeks. These results form the basis for smart fabrics capable of remediation of environmental toxins.

    8. Reversible 300 K Ferromagnetic Ordering in a Diluted Magnetic Semiconductor (pages 2115–2119)

      D. A. Schwartz and D. R. Gamelin

      Version of Record online: 3 NOV 2004 | DOI: 10.1002/adma.200400456

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      Reversible 300 K ferromagnetic ordering in a diluted magnetic semiconductor, Co2+:ZnO, is achieved by lattice incorporation and removal of the native n-type defect, interstitial Zn, resulting in “off” and “on” states (Figure, red triangles and blue circles). Spectroscopic and magnetic data implicate a double-exchange mechanism for ferromagnetism. These results suggest new opportunities for integrating magnetism and conductivity in semiconductor sensor or spin-based electronics devices.

    9. Solvent-Induced Ordering in Thin Film Diblock Copolymer/Homopolymer Mixtures (pages 2119–2123)

      S. H. Kim, M. J. Misner and T. P. Russell

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200306577

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      A new way to control the characteristic dimensions of morphologies in polymer systems is demonstrated with a mixture of a block copolymer and a small amount of homopolymer. Controlled solvent annealing and casting produces long-range order over large areas for the blends (see Figure), and through the selective removal of the homopolymer, almost defect-free arrays of nanoscopic holes are produced in the block copolymer film.

    10. Surface Modification of Multiwalled Carbon Nanotubes by Poly(2-vinylpyridine): Dispersion, Selective Deposition, and Decoration of the Nanotubes (pages 2123–2127)

      X. Lou, C. Detrembleur, C. Pagnoulle, R. Jérôme, V. Bocharova, A. Kiriy and M. Stamm

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400298

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      Polymer modification of carbon nanotubes is accomplished using a “grafting-to” approach. Radicals formed by the thermolysis of poly(2-vinylpyridine) terminated with a radical-stabilizing nitroxide can react with the surface of nanotubes (see Figure), resulting in grafting densities up to 12 wt.-%. The modified nanotubes, which are easily dispersed in water, can immobilize metal nanoclusters on their surfaces.

    11. Collective Optical Behavior of Cationic Water-Soluble Dendrimers (pages 2127–2132)

      S. Wang, B. S. Gaylord and G. C. Bazan

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200401036

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      Water-soluble dendrimers containing cationic charges and optically active units on the periphery of the macromolecular structure have been designed. Collective optical behavior of the chromophores on the surface was demonstrated by fluorescence quenching and energy-transfer experiments. These water-soluble dendrimers can be used for optically amplified DNA detection (see Figure) in homogeneous media.

    12. Photopolymerization in Microfluidic Gradient Generators: Microscale Control of Substrate Compliance to Manipulate Cell Response (pages 2133–2137)

      N. Zaari, P. Rajagopalan, S. K. Kim, A. J. Engler and J. Y. Wong

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400883

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      Integration of a microfluidic gradient generator and photopolymerization to fabricate novel hydrogels with tunable mechanical properties on the microscale (see Figure) is reported. This concept introduces a new class of materials that can be used to investigate the role of substrate elastic moduli in controlling cell morphology and cytoskeletal organization, and more generally, cell behavior.

    13. Soft-Lithographically Embossed, Multilayered Distributed-Feedback Nanocrystal Lasers (pages 2137–2141)

      V. C. Sundar, H.-J. Eisler, T. Deng, Y. Chan, E. L. Thomas and M. G. Bawendi

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400033

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      Multiple-wavelength distributed-feedback lasers are made from multilayered composites by utilizing the solution-processing ease of cadmium selenide semiconductor nanocrystals and soft lithography. The Figure shows three types of emission obtained from such structures across a wide range of the visible spectrum: fluorescence (dotted lines), amplified spontaneous emission (dashed lines), and feedback-induced lasing (solid lines).

    14. Surface-Initiated Polymerization on Nanopatterns Fabricated by Electron-Beam Lithography (pages 2141–2145)

      S. J. Ahn, M. Kaholek, W.-K. Lee, B. LaMattina, T. H. LaBean and S. Zauscher

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200401055

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      Micro- and nanopatterns of polymer brushes (see Figure) are fabricated using a “top–down/bottom–up” approach. A silicon surface is patterned with gold using lift-off electron-beam lithography (“top–down”), and the resulting pattern is then amplified by surface-initiated atom-transfer radical polymerization (“bottom–up”) of N-isopropylacrylamide from an immobilized thiol initiator.

    15. Discontinuous Molecular Films Can Control Metal/Semiconductor Junctions (pages 2145–2151)

      H. Haick, M. Ambrico, T. Ligonzo and D. Cahen

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400923

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      Molecular control over charge transport across a metal/semiconductor interface persists even if there is only a partial monolayer of polar molecules at the interface. This is because the long-range electrostatic effect of the dipole layer also affects the semiconductor regions under the film's pinholes. Thus, all types of polar molecules that show average order at the interface can be used.

    16. Gate-Voltage Control of Optically- Induced Charges and Memory Effects in Polymer Field-Effect Transistors (pages 2151–2155)

      S. Dutta and K. S. Narayan

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400084

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      Memory operations in polymer phototransistors have been demonstrated. A fraction of light-induced drain current in the depletion mode of a polythiophene-based field-effect transistor persists after switching off the photoexcitation, and can be erased by reversing the gate voltage (Vg) (see Figure). Write, store, read, and erase operations can be performed by applying a combination of gate voltages and incident light over a wide temperature range.

    17. Ultrahigh-Density Arrays of Ferromagnetic Nanorings on Macroscopic Areas (pages 2155–2159)

      F. Q. Zhu, D. Fan, X. Zhu, J.-G. Zhu, R. C. Cammarata and C.-L. Chien

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400675

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      Arrays of ten billion Co nanorings, with inner diameters of 100 nm, wall widths of 20 nm, and of an ultrahigh areal density of 45 rings μm–2, are fabricated on a macroscopic area. Magnetometric measurements and micromagnetic simulations reveal two parallel switching processes: a vortex reversal process and a rotating onion process.

    18. Oriented Sexiphenyl Single Crystal Nanoneedles on TiO2 (110) (pages 2159–2162)

      G. Koller, S. Berkebile, J. R. Krenn, G. Tzvetkov, G. Hlawacek, O. Lengyel, F. P. Netzer, C. Teichert, R. Resel and M. G. Ramsey

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400276

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      Para-sexiphenyl is found to assemble into azimuthally oriented crystalline nanoneedles on a TiO2 substrate (see Figure). The needles grow after prolonged exposure until they completely tile the surface with a film of uniform thickness. This novel morphology combined with the unique orientation of the molecules (all parallel to each other and the substrate and all with their molecular planes tilted with respect to the substrate) appears useful for both light-emitting diodes and field-effect transistor applications.

    19. Gold Nano-Antennas for Increasing Luminescence (pages 2163–2166)

      C. Louis, S. Roux, G. Ledoux, L. Lemelle, P. Gillet, O. Tillement and P. Perriat

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400299

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      Energy transfer between nanoscale particles is demonstrated for a gold/rare-earth oxide nanocomposite. The gold nanoparticle acts as an antenna, absorbing light that can then be transferred to the bound rare-earth oxide (see Figure), enhancing the oxide luminescence by a factor of 40. This could provide a route to enhanced fluorescence labels for biological systems based on optimized absorber and emitter nanocomposite tags.

    20. Large-Area Three-Dimensional Structuring by Electrochemical Etching and Lithography (pages 2166–2170)

      S. Matthias, F. Müller, C. Jamois, R. B. Wehrspohn and U. Gösele

      Version of Record online: 26 OCT 2004 | DOI: 10.1002/adma.200400436

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      The fabrication of three-dimensional silicon networks (see Figure) via a self-stabilized electrochemical etching technique onto lithographically pre-structured substrates is demonstrated. The optical characterization confirms a complete three-dimensional photonic bandgap of about 4 % centered at 3 μm.

    21. Sub-Microsecond Molecular Thermometry Using Thermal Spin Flips (pages 2170–2174)

      J. Stehr, J. M. Lupton, M. Reufer, G. Raschke, T. A. Klar and J. Feldmann

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400277

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      The application of platinumporphyrin (an organic semiconductor) as a sensitive molecular thermometer is demonstrated. The instantaneous temperature controls the rate of reverse intersystem crossing after optical population of the triplet, so the ratio of triplet-to-singlet emission provides a measure of temperature (see Figure). Sudden electrical heating of a metallic electrode is monitored with sub-microsecond accuracy, providing input to display design considerations.

    22. Ambipolar Organic Field-Effect Transistors Based on a Solution-Processed Methanofullerene (pages 2174–2179)

      T. D. Anthopoulos, C. Tanase, S. Setayesh, E. J. Meijer, J. C. Hummelen, P. W. M. Blom and D. M. de Leeuw

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400309

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      Organic field-effect transistors (OFETs, see Figure), based on the solution- processible methanofullerene [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), have been fabricated in a bottom-contact device configuration using gold electrodes. The OFET functions either as a p- or n-channel device, depending upon the bias conditions. This is the first example of ambipolar charge transport in FETs based on pristine PCBM.

    23. Linear Assemblies of Silica-Coated Gold Nanoparticles Using Carbon Nanotubes as Templates (pages 2179–2184)

      M. A. Correa-Duarte, N. Sobal, L. M. Liz-Marzán and M. Giersig

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400626

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      Silica-coated gold nanoparticles were assembled on carbon nanotubes by polymer wrapping and layer-by-layer assembly (see Figure). The procedure was applied to ordered arrays of vertically aligned nanotubes, resulting in parallel nanotubes of compact nanoparticle monolayers for potential use in photonics.

    24. Optically Addressable Nanostructured Capsules (pages 2184–2189)

      B. Radt, T. A. Smith and F. Caruso

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400920

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      Optically addressable nanostructured capsules of polyelectrolyte multilayers containing gold nanoparticles are prepared via layer-by-layer colloid templating. The nanocomposite capsule shell, due to the presence of the metal nanoparticles, can be addressed with laser light in the near-infrared (NIR) to induce morphological changes in the capsules (see Figure). Enzyme encapsulated within these capsules is released remotely and on demand with nanosecond laser pulses in the NIR, while retaining its activity.

    25. A New Fe-based Bulk Glassy Alloy with Outstanding Mechanical Properties (pages 2189–2192)

      A. Inoue and B. L. Shen

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400301

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      A new Fe-based bulk glassy alloy with high glass-forming ability, super-high fracture strength, and plasticity is described. The [(Fe0.8Co0.1Ni0.1)0.75B0.2Si0.05]96Nb4 alloy has a super-high strength of over 4000 MPa, the highest yet reported for Fe-based bulk alloys. In compressive failure, a shear band with an angle of 43° relative to the compression direction can be observed by scanning electron microscopy (see Figure).

    26. Highly Ordered Nanosphere Imprinted Nanochannel Alumina (NINA) (pages 2193–2196)

      S. Fournier-Bidoz, V. Kitaev, D. Routkevitch, I. Manners and G. A. Ozin

      Version of Record online: 29 OCT 2004 | DOI: 10.1002/adma.200400484

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      A nanoimprinting technique (not requiring nanoscale lithography) that is applied to the synthesis of highly ordered nanosphere imprinted nanochannel alumina (NINA) films (see Figure) is reported. The synthesis is effected by the anodic oxidation of nanoimprinted aluminum in phosphoric acid. Films with inter-pore distances ranging between 80 nm and 500 nm are produced using this approach.

    27. Non-Aqueous Synthesis of High-Purity Metal Oxide Nanopowders Using an Ether Elimination Process (pages 2196–2200)

      N. Pinna, G. Garnweitner, M. Antonietti and M. Niederberger

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400460

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      A soft-chemistry route to (impurity free) Ta2O5 and HfO2 nanopowders (see Figure) based upon a synthesis protocol that involves the reaction of metal alkoxides with benzyl alcohol is presented. The formation of HfO2 proceeds via an unprecedented ether-elimination process and extends the available non-aqueous reaction methodologies in addition to the well-known ester and alkyl halide eliminations.

    28. Elastomeric Molds with Tunable Microtopography (pages 2201–2206)

      J. M. Hoffman, J. Shao, C.-H. Hsu and A. Folch

      Version of Record online: 17 NOV 2004 | DOI: 10.1002/adma.200400441

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      Elastomeric “microtunable” molds (μTMs) whose microtopography can be tuned post-fabrication at certain pre-defined locations have been devised. Their features make them very attractive for the molding of complex microstructures. The Figure shows a scanning electron microscopy image of poly(dimethylsiloxane) double- replicas of a μTM whose membrane contains a 1.18 mm spiral.

    29. Supramolecular Multiscale Fibers through One-Dimensional Assembly of Dendritic Molecules (pages 2206–2212)

      M. Ornatska, S. Peleshanko, B. Rybak, J. Holzmueller and V. V. Tsukruk

      Version of Record online: 16 DEC 2004 | DOI: 10.1002/adma.200400334

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      One-dimensional supramolecular structures self-assemble from irregular, highly branched, flexible amphiphiles containing a polyester core and an alkyl- or anthracene-functionalized shell. A combination of intermolecular interactions and steric limitations cause the structures to form nearly perfectly organized microfibers that form bundles from tens of micrometers to centimeters in length (see Figure). The fibers from anthracene-modified molecules possess strong fluorescence properties.