Advanced Materials

Cover image for Vol. 15 Issue 11

June, 2003

Volume 15, Issue 11

Pages 847–946

    1. Contents: Adv. Mater. 11/2003 (pages 847–850)

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200390143

    2. Electrochemistry of Poly(3,4-alkylenedioxythiophene) Derivatives (pages 855–879)

      L. Groenendaal, G. Zotti, P.-H. Aubert, S.M. Waybright and J.R. Reynolds

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200300376

      The electrochemistry of one of the most important classes of electrically and optically active polymers, poly(3,4-alkylenedioxythiophene)s, is reviewed. In addition to an extensive overview of the electrochemical synthesis and characterization, the electrical and optical properties of the polymer films attained are described, along with structural and morphological aspects.

    3. Scanning Tunneling Microscopy Investigations of Self-Organized Poly(3-hexylthiophene) Two-Dimensional Polycrystals (pages 881–884)

      B. Grévin, P. Rannou, R. Payerne, A. Pron and J.-P. Travers

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304580

      Scanning tunneling microscopy images of thin films of polythiophene cast on highly oriented pyrolytic graphite gives structural insight on both local (chain-packing and conformational) and mesoscopic (polycrystal structure) scales. It is revealed that 2D polycrystals form mono-domains (20 nm parallel and perpendicular to the polymer backbone) (see Figure), partially interconnected by folded chains.

    4. Highly Efficient Red Electrophosphorescent Devices Based on Iridium Isoquinoline Complexes: Remarkable External Quantum Efficiency Over a Wide Range of Current (pages 884–888)

      Y.-J. Su, H.-L. Huang, C.-L. Li, C.-H. Chien, Y.-T. Tao, P.-T. Chou, S. Datta and R.-S. Liu

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304630

      Outstanding performance as an emissive dopant in organic light-emitting devices is shown by red phosphorescent iridium complexes based on an isoquinoline framework (such as that shown in the Figure). Remarkably high efficiency can be maintained in the devices at high currents with a negligible effect from either triplet–triplet (T–T) annihilation or saturation of the excited states.

    5. Cell-Responsive Synthetic Hydrogels (pages 888–892)

      M.P. Lutolf, G.P. Raeber, A.H. Zisch, N. Tirelli and J.A. Hubbell

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304621

      Synthetic biomaterial matrices have been formed in the presence of cells by a Michael-type addition reaction between a difunctional protease substrate peptide, a monofunctional cell adhesion peptide, and a tetrafunctional poly(ethylene glycol). These materials locally degrade in response to cell-surface proteases, allowing cells to create paths for 3D cell migration (see Figure).

    6. Photonic Papers and Inks: Color Writing with Colorless Materials (pages 892–896)

      H. Fudouzi and Y. Xia

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304795

      A photonic paper/ink system for color writing on and with colorless materials is described. The “paper” is a 3D crystal of polymer beads embedded in an elastomer matrix made of poly(dimethylsiloxane) (PDMS), and the “ink” is a liquid (e.g., a silicone fluid or organic solvent) capable of swelling the matrix, changing the lattice constant and hence wavelength of light diffracted (see Figure and cover).

    7. Highly Anisotropic Opto-electronic Properties of Aligned Films of Self-Assembled Platinum Molecular Wires (pages 896–899)

      M.G. Debije, M.P. de Haas, T.J. Savenije, J.M. Warman, M. Fontana, N. Stutzmann, W.R. Caseri and P. Smith

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304603

      Self-assembled columns of alternating tetrachloro- and tetraalkylaminoplatinum moieties form stable, highly oriented, optically anisotropic films on a friction-deposited polytetrafluoroethylene surface (see Figure). Charge transport in the films is rapid (mobility ≥ ca. 10–2 cm2 V–1 s–1) and highly one-dimensional along the axis of the columns (anisotropy ≥ 20), further substantiating the potential application of these materials in molecular opto-electronic devices.

    8. Strong Optical Limiting of Soluble Axially Substituted Gallium and Indium Phthalocyanines (pages 899–902)

      Y. Chen, M. Fujitsuka, S.M. O'Flaherty, M. Hanack, O. Ito and W.J. Blau

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304487

      Optical limiting in In- and Ga-phthalocyanines exhibits a range of saturation densities and absorption cross-section ratios. Substitution of the p-trifluoromethylphenyl group at the central metal in tBu4PcGaCl and tBu4PcInCl reduces the saturation energy density by a factor of >3. Tailorable optical limiting properties are shown in the Figure, which plots the nonlinear absorption coefficient as a function of intensity for the five compounds studied.

    9. Assemblies of Metal Nanoparticles and Self-Assembled Peptide Fibrils—Formation of Double Helical and Single-Chain Arrays of Metal Nanoparticles (pages 902–906)

      X. Fu, Y. Wang, L. Huang, Y. Sha, L. Gui, L. Lai and Y. Tang

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304624

      Double helical and single-chain arrays of Au and Pd metal nanoclusters have been achieved by assembling the corresponding metal nanoparticles on peptide nanofibril templates at different pH values. The assembled metal nanoparticles are useful for studying the superstructures of the peptide nanofibrils. Pd nanowires of different shapes have also been prepared by varying the amount of metal deposition.

    10. Stimulated Emission from a Needle-like Single Crystal of an End-Capped Fluorene/Phenylene Co-oligomer (pages 906–909)

      X. Zhu, D. Gindre, N. Mercier, P. Frère and J.-M. Nunzi

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304816

      Owing to light confinement, naturally shaped needle-like organic semiconductor single crystals of an end-capped fluorene/phenylene co-oligomer provide low-threshold unidimensional stimulated emission. The Figure shows a photograph of the ∼1.5 mm long crystals, and gain-narrowed normalized emission spectra from a polycrystal (dotted line) and a single crystal at 700 μJ cm–2 (unbroken line).

    11. Carbon-Nanotube-Templated Assembly of Rare-Earth Phthalocyanine Nanowires (pages 909–913)

      L. Cao, H.-Z. Chen, H.-B. Zhou, L. Zhu, J.-Z. Sun, X.-B. Zhang, J.-M. Xu and M. Wang

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304637

      Multi-walled carbon nanotubes are used for the templated assembly of HErPc2 nanowires via the phase-separation method. When the solvent is evaporated gradually, HErPc2 nanoparticles and nanowires are found to self-assemble on the exterior walls of CNTs, as shown in the Figure. The CNT–HErPc2 hybrid materials exhibit improved photoconductivity owing to the contribution from the photoinduced charge transfer from HErPc2 to CNTs.

    12. Charge Density and Film Morphology Dependence of Charge Mobility in Polymer Field-Effect Transistors (pages 913–916)

      S. Shaked, S. Tal, Y. Roichman, A. Razin, S. Xiao, Y. Eichen and N. Tessler

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304653

      A qualitative comparison between the extended disorder model for charge transport and the measured charge density dependence of the field-effect mobility is presented for field-effect transistors (see Figure) using a poly(phenylenevinylene) layer. By varying the film morphology through the use of polymers of different molecular weights, further insight into the role of morphology is gained.

    13. Relationship Between Molecular Structure and Electrical Performance of Oligothiophene Organic Thin Film Transistors (pages 917–922)

      M. Halik, H. Klauk, U. Zschieschang, G. Schmid, S. Ponomarenko, S. Kirchmeyer and W. Weber

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304654

      Organic thin film transistors (TFTs) based on alkyl-substituted oligothiophenes with varying chromophore and alkyl side-chain length have been fabricated. The TFT performance is shown to depend on side-chain length and contact configuration, but is found to be relatively insensitive to chromophore length. Mobilities as large as 1.1 cm2/V s were obtained. TFTs with ultra-thin self-assembled monolayer gate dielectrics have also been prepared and investigated.

    14. Nanoparticle Actuators (pages 922–926)

      B. Raguse, K.-H. Müller and L. Wieczorek

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304698

      The actuator response of a thin porous film of functionalized gold nanoparticles is found to be fast (< 0 .5 s) and require low voltages (< 0.6 V, see Figure), relative to other comparable systems. The mechanism of reaction is based on non-Faradaic double-layer charging of the films in electrolyte solution. Response can be controlled by varying the nature of the molecules coating the nanoparticles, the thickness of the film, and the electrolyte.

    15. Fabrication of the MgCxCo3 Ternary Phase Encapsulated in Carbon Nanoflasks (pages 926–930)

      R.K. Rana, X.N. Xu, Y. Yeshurun and A. Gedanken

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304690

      Carbon nanoflasks encapsulating the MgCxCo3 ternary phase have been synthesized. Structural and compositional analyses of the encapsulated particles (see Figure) revealed that the MgCxCo3 particles are crystalline and well protected by the covering graphene layers. The encapsulated particles exhibit mixed superparamagnetic and ferromagnetic behavior.

    16. Soluble Microcapsules Assembled Stepwise from Weak Polyelectrolytes Using Acid-Decomposable Cores (pages 930–933)

      C.-Y. Gao, H. Möhwald and J.-C. Shen

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304667

      Decomposable microcapsules with tunable permeability, loading, and release properties—with potential applications as chemical reservoirs and for controlled drug release—have been fabricated by assembly of weak polyelectrolytes on melamine formaldehyde templates followed by removal of the cores at low pH by precise control of the time of acid treatment. The Figure shows capsules before (left) and after (right) treatment with 0.1 M HCl.

    17. Templated Nanowire Assembly on the Surface of a Patterned Nanosphere (pages 933–935)

      L. Nagle and D. Fitzmaurice

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304533

      The deposition of a single gold nanoparticle on a silica nanosphere (see Figure, left) is effected using a nanoporous membrane as template. These findings are significant because they offer the prospect of assembling novel asymmetric nanoscale architectures. In support of this assertion, the assembly of a gold nanowire at the surface of the patterned nanosphere (Figure, right) is demonstrated.

    18. Large-Scale Synthesis of Ultralong Bi2S3 Nanoribbons via a Solvothermal Process (pages 936–940)

      Z. Liu, S. Peng, Q. Xie, Z. Hu, Y. Yang, S. Zhang and Y. Qian

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304693

      Ultralong Bi2S3 nanoribbons have been synthesized by a solvothermal process, using a mixture of aqueous NaOH solution and glycerol as the solvent. These nanoribbons (see Figure) are 50–300 nm wide, 20–80 nm thick, and up to several millimeters long, and the initial formation of the precursor polycrystalline NaBiS2 phase is crucial to their formation. The nucleation and growth process was interpreted as a solid–solution–solid transformation.

    19. Tunable and Latchable Liquid Microlens with Photopolymerizable Components (pages 940–943)

      S. Yang, T.N. Krupenkin, P. Mach and E.A. Chandross

      Article first published online: 2 JUN 2003 | DOI: 10.1002/adma.200304745

      A novel liquid microlens with photopolymerizable components is described (see Figure). When the lens is in liquid form, both its position and curvature can be reversibly tuned through electrowetting. After the liquid microlens is precisely aligned on the substrate, it is exposed to UV light to initiate polymerization and thus lock its position and shape.