Advanced Functional Materials

Cover image for Vol. 15 Issue 1

January, 2005

Volume 15, Issue 1

Pages 3–174

    1. Cover Picture: Photolithographic Route to the Fabrication of Micro/Nanowires of III–V Semiconductors (Adv. Funct. Mater. 1/2005)

      Y. Sun, D.-Y. Khang, F. Hua, K. Hurley, R. G. Nuzzo and J. A. Rogers

      Version of Record online: 18 JAN 2005 | DOI: 10.1002/adfm.200590003

      Semiconductor nanowires with triangular cross-sections (see Figure) have been fabricated via a “top–down” process. Photoresist stripes are patterned on a surface, followed by anisotropic chemical etching. Then, continuous etching results in the formation of nanowires, which can be as long as the photoresist stripes. The wires can be transfer printed onto plastic substrates for potential use as large-area flexible electronics components.

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      Growing Strong (pages 13–14)

      E. Levy

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400606

      As Advanced Functional Materials enters its fifth year, the Editor describes the rapid growth of the journal in every sense, and how it is changing to adapt to its ever-expanding author- and readership.

    3. Growth Control and Optics of Organic Nanoaggregates (pages 17–24)

      F. Balzer and H.-G. Rubahn

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400367

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      Blue-light-emitting para-hexaphenyl organic microrings and mutually aligned nanofibers have been investigated (see Figure; the left nanofiber is 530 nm wide). The morphology and optical properties of individual aggregates and dense bunches of aggregates can be studied. These aggregates, whose morphology and alignment can be controlled by the appropriate growth conditions and substrate surfaces, form excellent model systems for the study of sub-wavelength optics, and may become key elements of new optoelectronic devices.

    4. Air-Pulse-Drive Fabrication of Photonic Crystal Films of Colloids with High Spectral Quality (pages 25–29)

      T. Kanai, T. Sawada, A. Toyotama and K. Kitamura

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200305160

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      A novel method of fabricating large films of photonic crystals of colloids is reported. A charge-stabilized colloidal suspension is run in a flat capillary driven by a pressure-regulated air pulse. Above a critical pressure, the capillary was filled with a single-domain texture showing angle-dependent diffraction colors and a distinct laser diffraction pattern (see Figure). This method is easily applicable to industrial processes.

    5. Photolithographic Route to the Fabrication of Micro/Nanowires of III–V Semiconductors (pages 30–40)

      Y. Sun, D.-Y. Khang, F. Hua, K. Hurley, R. G. Nuzzo and J. A. Rogers

      Version of Record online: 20 DEC 2004 | DOI: 10.1002/adfm.200400411

      Thumbnail image of graphical abstract

      Semiconductor nanowires with triangular cross-sections (see Figure) have been fabricated via a “top–down” process. Photoresist stripes are patterned on a surface, followed by anisotropic chemical etching. Then, continuous etching results in the formation of nanowires, which can be as long as the photoresist stripes. The wires can be transfer printed onto plastic substrates for potential use as large-area flexible electronics components.

    6. Formation of Oxynitride as the Photocatalytic Enhancing Site in Nitrogen-Doped Titania Nanocatalysts: Comparison to a Commercial Nanopowder (pages 41–49)

      X. Chen, Y.-B. Lou, A. C. S. Samia, C. Burda and J. L. Gole

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400184

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      A comparison between UV-visible reflectance spectra for TiO2 nanocolloid particles Degussa P25 TiO2 nanopowder, and their nitrided analogs (see Figure) is described. The nitridation of the nanocolloid which can be accomplished in seconds at room temperature provides a visible light absorbing photocatalyst.

    7. Plastic Electronic Devices Through Line Patterning of Conducting Polymers (pages 51–56)

      D. Hohnholz, H. Okuzaki and A. G. MacDiarmid

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400241

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      The method of “line patterning” for producing transparent conducting-polymer patterns employs standard office equipment such as a laser printer and commercial overhead transparencies. A seven-segment liquid-crystal display (see Figure) and an 11-key keypad, prepared from a common conducting-polymer blend, are described in detail.

    8. Growth of Aligned Square-Shaped SnO2 Tube Arrays (pages 57–62)

      Y. Liu and M. Liu

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400001

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      Aligned single crystal SnO2 tubes (see Figure) with square-shaped cross sections of tunable size (50 nm to 0.5 μm) are synthesized on quartz substrates using a combustion chemical vapor deposition (CVD) method in an open atmosphere at 850 °C to 1150 °C.

    9. Temperature-Controlled Catalytic Growth of ZnS Nanostructures by the Evaporation of ZnS Nanopowders (pages 63–68)

      X. S. Fang, C. H. Ye, L. D. Zhang, Y. H. Wang and Y. C. Wu

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200305008

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      Several ZnS nanostructures, such as nanorods (see Figure), nanowires, nanobelts, and nanosheets have been synthesized simultaneously in bulk quantities by the evaporation of ZnS nanopowders. Control of the morphology of ZnS nanostructures on substrates is achieved by regulating the substrate temperature and catalyst.

    10. Ag-Functionalized Carbon Molecular-Sieve Membranes Based on Polyelectrolyte/Polyimide Blend Precursors (pages 69–75)

      J. N. Barsema, N. F. A. van der Vegt, G. H. Koops and M. Wessling

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200305155

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      Ag-functionalized carbon molecular sieve membranes are characterized by high selectivity and high permeability for gas separations. The membranes (see Figure), prepared from a blend of sulfonated poly(ether ether ketone) with Ag+ as a counterion and P84 co-polyimide, possess selective bypasses around Ag-nanoclusters, where separation takes place based on the fast and selective mechanism of selective surface flow.

    11. Enhancement of Field-Effect Mobility Due to Surface-Mediated Molecular Ordering in Regioregular Polythiophene Thin Film Transistors (pages 77–82)

      D. H. Kim, Y. D. Park, Y. Jang, H. Yang, Y. H. Kim, J. I. Han, D. G. Moon, S. Park, T. Chang, C. Chang, M. Joo, C. Y. Ryu and K. Cho

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400054

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      Surface-mediated molecular ordering (see Figure) has a substantial effect on the preferential orientations of the P3HT chains, and this effect is used to enhance the field-effect mobility. Depending on the surface properties, the P3HT nanocrystals can adopt two different orientations – parallel and perpendicular to the insulator substrate – the field-effect mobilities of which differ by more than a factor of 4 and can reach 0.28 cm2 V–1 s–1.

    12. Primary Cell Adhesion on RGD-Functionalized and Covalently Crosslinked Thin Polyelectrolyte Multilayer Films (pages 83–94)

      C. Picart, R. Elkaim, L. Richert, F. Audoin, Y. Arntz, M. Da Silva Cardoso, P. Schaaf, J.-C. Voegel and B. Frisch

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400106

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      Adhesion and proliferation of osteoblasts on polyelectrolyte multilayer (PEM) films (see Figure) is enhanced by crosslinking, even for films functionalized with the RGD cell-binding peptide sequence. Cell attachment after short times was enhanced by the RGD sequence, but long-term proliferation (after 8 days) was greatly improved by crosslinking, demonstrating the influence of both the chemical and the mechanical properties of the films on cell adhesion.

    13. Solar-Energy Conversion in TiO2/CuInS2 Nanocomposites (pages 95–100)

      M. Nanu, J. Schoonman and A. Goossens

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400150

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      The three-dimensional-solar-cell concept is explored using a new approach. A nanocomposite consisting of a wide-bandgap n-type semiconducting oxide (nanocrystalline TiO2) and a p-type visible-light-sensitive semiconductor (CuInS2), mixed on a nanometer scale (see Figure), is used as the active material.

    14. Transparent Poly(methyl methacrylate)/Single-Walled Carbon Nanotube (PMMA/SWNT) Composite Films with Increased Dielectric Constants (pages 101–106)

      L. M. Clayton, A. K. Sikder, A. Kumar, M. Cinke, M. Meyyappan, T. G. Gerasimov and J. P. Harmon

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200305106

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      Poly(methyl methacrylate)/single-walled carbon nanotube (PMMA/SWNT) composites were prepared via in-situ polymerization induced by heat, UV-light irradiation, and ionizing (gamma) radiation. The composites were dissolved in methylene chloride and then cast into films. The composites (Figure, left) exhibit enhanced transparency compared with the melt-blended composite material (right), and are comparable to neat PMMA (center).

    15. Li6ALa2Ta2O12 (A = Sr, Ba): Novel Garnet-Like Oxides for Fast Lithium Ion Conduction (pages 107–112)

      V. Thangadurai and W. Weppner

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400044

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      A novel garnet-like structure Li6ALa2Ta2O12 (A = Sr, Ba) exhibits fast, lithium ion conductivity and is found to be stable against chemical reactions with molten metallic lithium. Li6BaLa2Ta2O12 shows the highest ionic conductivity of 4.0 × 10–5 S cm–1 at 22 °C (see Figure). The direct current electrical measurements using lithium-ion blocking and reversible electrodes reveal that the electronic conductivity is very small and exhibits high electrochemical stability (≥6 V/Li) at room temperature.

    16. Preparation of Hollow Silica Nanospheres by Surface-Initiated Atom Transfer Radical Polymerization on Polymer Latex Templates (pages 113–117)

      Y. Chen, E. T. Kang, K. G. Neoh and A. Greiner

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400179

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      Hollow silica nanospheres are synthesized by surface-initiated atom transfer radical polymerization (ATRP) of 3-(trimethoxysilyl)propyl methacrylate (TMSPM) from templating poly(vinylbenzyl chloride) (PVBC) latex nanoparticles, followed by polycondensation of tetraethoxysilane (TEOS) in ethanolic ammonia and removal of the PVBC cores by thermal decomposition (see Figure).

    17. Scaffolds Based on Biopolymeric Foams (pages 118–124)

      A. Barbetta, M. Dentini, M. S. De Vecchis, P. Filippini, G. Formisano and S. Caiazza

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400072

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      Biocompatible and biodegradable porous scaffolds can be synthesized by polymerization of a high-internal-phase emulsion (HIPE). The structure of an oil-in-water emulsion of a vinyl- functionalized biopolymer, such as a polysaccharide or a gelatin, is locked-in by radical-initiated polymerization, forming a highly interconnected, mechanically stable porous structure (see Figure). The size of the pores can be varied, permitting growth of murine retinal cells on and throughout the matrix.

    18. Influence of Side-Chain Structure and Irradiation Condition on Photoalignment of Ladder-Like Polysiloxane Films (pages 125–130)

      H.-W. Gu, P. Xie, P.-F. Fu, T.-Y. Zhang and R.-B. Zhang

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400158

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      Photoalignment films are an alternative to the rubbing technique currently used in the production of liquid-crystal displays. The photo-induced aligning capability (see Figure) of various ladder-like polysiloxane-based photo-alignment films bearing different photo reactive side chains is reported, particular attention being paid to the influence of the side-chain structure and irradiation conditions.

    19. Stability and Hydrogenation of “Bare” Gadolinium Nanoparticles (pages 131–137)

      I. Aruna, B. R. Mehta, L. K. Malhotra and S. M. Shivaprasad

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400097

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      Gadolinium nanoparticles deposited via an inert gas evaporation method show improved stability towards oxidation. No Pd catalytic layer is required for the hydrogenation of the nanoparticles at room temperature and atmospheric pressure. The confirming resistivity measurements are shown in the Figure.

    20. Improving the Brightness and Daylight Contrast of Organic Light-Emitting Diodes (pages 138–142)

      V. Vaenkatesan, R. T. Wegh, J.-P. Teunissen, J. Lub, C. W. M. Bastiaansen and D. J. Broer

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400122

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      Chiral-nematic films in combination with classical circular polarizers are used as additional layers in organic light-emitting diodes (see Figure) to improve the daylight contrast while preserving the emitted light. Increased light efficiency at the expense of some daylight contrast is achieved within the reflection band of the films. Outside the band, the daylight contrast achieved is infinite.

    21. From Blue to Red: Syntheses, Structures, Electronic and Electroluminescent Properties of Tunable Luminescent N,N Chelate Boron Complexes (pages 143–154)

      Q. D. Liu, M. S. Mudadu, R. Thummel, Y. Tao and S. Wang

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200400081

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      Four-coordinate boron compounds with the general formula of BPh2(L) (L is the N,N′-chelate ligand) and emission colors that cover the entire visible spectra are achieved and their uses in electroluminescent devices are demonstrated. The Figure shows the photoluminescence spectra of representative boron compounds.

    22. Limitations of the Förster Description of Singlet Exciton Migration: The Illustrative Example of Energy Transfer to Ketonic Defects in Ladder-type Poly(para-phenylenes) (pages 155–160)

      H. Wiesenhofer, D. Beljonne, G. D. Scholes, E. Hennebicq, J.-L. Brédas and E. Zojer

      Version of Record online: 20 DEC 2004 | DOI: 10.1002/adfm.200400108

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      Energy-transfer processes in optoelectronic devices consisting of conjugated organic materials are usually described in the framework of the Förster model, which relies on a point-dipole approximation. The failure of this model for densely packed films is illustrated by comparing the transfer rates to excited states characterized by various degrees of localization (see Figure).

    23. Defect-Related Optical Behavior in Surface Modified TiO2 Nanostructures (pages 161–167)

      S. M. Prokes, J. L. Gole, X. Chen, C. Burda and W. E. Carlos

      Version of Record online: 13 JAN 2005 | DOI: 10.1002/adfm.200305109

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      The surface modification of TiO2 nanostructures to incorporate nitrogen and form visible light absorbing titanium oxynitride centers is studied. Freshly prepared samples exhibited a strong emission near 560 nm (see Figure) (2.21 eV), which red shifts to 660 nm (1.88 eV) and drops in intensity after atmospheric exposure. Electron spin resonance studies identified a resonance at g = 2.0035, which increased significantly with nitridation.

    24. Cd1–xMnxS Diluted Magnetic Semiconductors as Nanostructured Guest Species in Mesoporous Thin-Film Silica Host Media (pages 168–172)

      A. V. Kouzema, M. Fröba, L. Chen, P. J. Klar and W. Heimbrodt

      Version of Record online: 20 DEC 2004 | DOI: 10.1002/adfm.200400115

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      Diluted magnetic semiconductor materials of type Cd1–xMnxS have been incorporated into the pores of mesoporous thin-film (MTF) host structures. The guest species were prepared by a wet-impregnation technique using an aqueous solution of metal acetates. Photoluminescence excitation measurements were used to show the quantum size effect exhibited by the incorporated nanostructured guest species.

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