Advanced Materials

Cover image for Advanced Materials

November, 2004

Volume 16, Issue 21

Pages 1871–1970

    1. You have free access to this content
      Materials Science at the Small Scale (pages 1879–1880)

      E. Levy

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200401830

      Science at the nanometer scale is currently receiving great attention from the materials science community and represents a significant proportion of the manuscripts both received and published by Advanced Materials. The Editor of Advanced Materials discusses the impact of this development, and explains how the new journal from Wiley-VCH, Small, will help to meet the challenge of serving this community's needs.

    2. Hall and Field-Effect Mobilities of Electrons Accumulated at a Lattice-Matched ZnO/ScAlMgO4 Heterointerface (pages 1887–1890)

      T. I. Suzuki, A. Ohtomo, A. Tsukazaki, F. Sato, J. Nishii, H. Ohno and M. Kawasaki

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200401018

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      At a lattice-matched ZnO/ScAlMgO4 heterointerface, Hall and field-effect mobilities of grain-boundary-free ZnO channels have been simultaneously characterized under a gate electric field (EG) applied through a ScAlMgO4 dielectric gate. The field-effect mobility increased linearly with increasing EG (see Figure), clearly in contrast to the supralinear (exponential) dependence that has been previously reported for polycrystalline channels.

    3. Synthesis and Fabrication of High-Performance n-Type Silicon Nanowire Transistors (pages 1890–1893)

      G. Zheng, W. Lu, S. Jin and C. M. Lieber

      Version of Record online: 23 SEP 2004 | DOI: 10.1002/adma.200400472

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      Single crystal n-type silicon nanowires (SiNWs) with controlled phosphorus dopant concentrations have been successfully synthesized for the first time (see Figure). Field-effect transistor (FET) devices fabricated from these n-SiNWs exhibit good device properties, with mobilities more than 100 times greater than previous reports, and comparable to high-performance planar silicon FETs.

    4. Growth of High-Quality Precipitate-Free Thin Films Suitable for Electronic Devices: A New Concept for Substrates (pages 1894–1897)

      K. Endo, P. Badica, H. Sato and H. Akoh

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400750

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      Precipitate-free thin films of multicomponent materials (e.g. superconductors) have been successfully grown (see Figure) on substrates onto whose surfaces artificial steps have been generated. The steps had widths that were equal to twice the migration length of the atomic species being deposited on the films. The resulting clean, high-quality films were due to the gathering of precipitates at the step edges, where the free energy is lowest.

    5. Nanoporous Gold Leaf: “Ancient Technology”/Advanced Material (pages 1897–1900)

      Y. Ding, Y.-J. Kim and J. Erlebacher

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400792

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      A free-standing nanoporous gold (NPG) membrane is made by dealloying commercially available white-gold leaf in nitric acid (see Figure). This porous material has an unusual combination of characteristics in that it is metallic with a continuous crystal lattice throughout the porous network, and has a pore size that is adjustable via simple room-temperature post-processing. This ultra-high-surface-area material is potentially very useful for applications such as electrocatalysis and sensing.

    6. A New Superconducting Phase of Sodium Cobalt Oxide (pages 1901–1905)

      K. Takada, H. Sakurai, E. Takayama-Muromachi, F. Izumi, R. A. Dilanian and T. Sasaki

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400756

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      A new superconducting sodium cobalt oxide (see Figure, left) has been synthesized through soft-chemical modification using α-NaCoO2 as a parent compound, in place of the γ-Na0.7CoO2 used to make the first cobalt oxide superconductor (see Figure, right). A three-layer periodicity of the CoO2 stacking sequence exists in the present material, in contrast to a two-layer one in the previous. The new oxide has a superconducting transition at 4.6 K.

    7. Red, Green, and Blue Colors in Polymeric Electrochromics (pages 1905–1908)

      G. Sonmez, H. B. Sonmez, C. K. F. Shen and F. Wudl

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400546

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      Additive primary color-space has been completed by the discovery of the first green polymeric electrochromic. Mixing any two of the three additive primary colors (red, green, and blue (RGB)) produces thousands of colors (see Figure) resulting from the tones of polymers in different oxidation states. It is envisioned that the completion of the three components of color-space and the discovery of the first green polymeric electrochromic will herald a new polymeric electrochromic device era.

    8. Self-Organized Photonic Structures in Polymer Light-Emitting Diodes (pages 1908–1912)

      G. Fichet, N. Corcoran, P. K. H. Ho, A. C. Arias, J. D. MacKenzie, W. T. S. Huck and R. H. Friend

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400316

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      The creation of photonic structures in thin polymer films is reported. This involves replicating a micrometer-sized pattern onto a (poly(ethylenedioxythiophene) doped with polystyrene sulfonic acid) PEDOT:PSS surface (see Figure) with conjugated polymers without compromising the efficiencies of the devices. The technique can be extended to flexible substrates, and in principle to conjugated polymer blends.

    9. Color Micro- and Nanopatterning with Counter-Propagating Reaction–Diffusion Fronts (pages 1912–1917)

      C. J. Campbell, M. Fialkowski, R. Klajn, I. T. Bensemann and B. A. Grzybowski

      Version of Record online: 14 OCT 2004 | DOI: 10.1002/adma.200400383

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      Thin films of ionically doped gelatin have been color-patterned with submicrometer precision using the wet-stamping technique. Inorganic salts are delivered onto the gelatin surface from an agarose stamp, and diffuse into the gelatine layer, producting deeply colored precipitates. Reaction fronts originating from different features of the stamp cease within < 1 μm of each other, leaving sharp, transparent regions in between.

    10. Controlling Degradation of Hydrogels via the Size of Crosslinked Junctions (pages 1917–1921)

      H. J. Kong, E. Alsberg, D. Kaigler, K. Y. Lee and D. J. Mooney

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400014

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      The degradation rates of hydrogels are shown to be regulated by the modulation of the dissociation rates of the polymer chains via a size mismatch in the crosslinking zones. This method (used to control degradation) can be exploited in order to engineer cartilage tissue in vivo (see Figure).

    11. An Artificial Muscle with Lamellar Structure Based on a Nematic Triblock Copolymer (pages 1922–1925)

      M.-H. Li, P. Keller, J. Yang and P.-A. Albouy

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400658

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      A muscle-like material with a lamellar structure has been prepared for the first time from a liquid-crystalline triblock copolymer. The material consists of a repeated series of nematic-polymer blocks and conventional rubber blocks. The motor for the contraction is the reversible macromolecular-chain shape change, from stretched to spherical, of the nematic polymer that occurs at the nematic-to-isotropic phase transition.

    12. All-Polymer-Gel Light Modulator Consisting of a “Gel-in-Gel” System (pages 1925–1929)

      H. Tsutsui, M. Mikami and R. Akashi

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400395

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      A highly flexible and durable light modulator consisting entirely of polymer-gel materials was fabricated. In this light modulator, colored gel particles responsive to stimuli are dispersed and fixed in a second stimuli-non-responsive gel matrix (“gel-in-gel” system), analogous to the skin of a cephalopod. The flexible light modulator exhibits a dramatic change in color as the colored gel particles change volume in response to temperature changes (see Figure).

    13. Dual-Scale Roughness Produces Unusually Water-Repellent Surfaces (pages 1929–1932)

      N. J. Shirtcliffe, G. McHale, M. I. Newton, G. Chabrol and C. C. Perry

      Version of Record online: 11 OCT 2004 | DOI: 10.1002/adma.200400315

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      Super-hydrophobicity can be achieved on relatively smooth surfaces. Short, wide pillars on slightly rough surfaces are shown to produce super-hydrophobic surfaces (see Figure) where neither the pillars nor the slight roughness suffice alone. This use of two length scales to create super-hydrophobic surfaces directly mimics the mechanism used by some plants including the lotus.

    14. Reverse Saturable Absorption in the Near-Infrared by Fused Porphyrin Dimers (pages 1933–1935)

      K. J. McEwan, P. A. Fleitz, J. E. Rogers, J. E. Slagle, D. G. McLean, H. Akdas, M. Katterle, I. M. Blake and H. L. Anderson

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400492

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      Bromine and iodine substituents increase the yield of triplet excited states in a triply linked fused porphyrin dimer (see Figure), resulting in efficient reverse saturable absorption in the near-infrared range at 600–970 nm on the nanosecond timescale.

    15. Ferroelectricity in Achiral Liquid-Crystal Systems (pages 1936–1940)

      S. V. Yablonskii, E. A. Soto-Bustamante, R. O. Vergara-Toloza and W. Haase

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200306622

      Ferroelectricity can be detected in systems consisting of liquid-crystalline monomer–polymer mixtures possessing no chiral centers The ferroelectric behavior in mixtures of achiral liquid-crystalline side-chain polymers and achiral liquid-crystalline monomers is reported for the first time. The mixtures manifested high pyroelectric activity, with values of spontaneous polarization close to the theoretical limit and a “figure of merit” comparable to the value of classic organic ferroelectric materials.

    16. Selective Adsorption of Microcapsules on Patterned Polyelectrolyte Multilayers (pages 1940–1944)

      J. Feng, B. Wang, C. Gao and J. Shen

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400573

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      Selective adsorption of microcapsules was achieved by utilizing electrostatic interactions between the capsule surfaces and chemically and physically patterned substrates. Pressing a poly(dimethylsiloxane) stamp consisting of periodic strips and inked with a poly(diallyldimethylammonium chloride) solution onto polyelectrolyte multilayers with an outermost poly(styrene sulfonic acid) layer creates patterns that can guide the linear alignment of the microcapsules.

    17. Electric-Field-Driven Assembly of Oriented Molecular-Sieve Films (pages 1944–1948)

      J.-C. Lin, M. Z. Yates, A. Trajkovska Petkoska and S. Jacobs

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400424

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      Thin films of rod-shaped molecular-sieve crystals have been deposited by sedimentation with preferred orientation under an applied electric field. When the pores of the crystal were filled with dye, the film exhibited polarization-angle-dependent light absorption due to the preferred pore direction.

    18. Enhanced Polymer Light-Emitting Diode Performance Using a Crosslinked-Network Electron-Blocking Interlayer (pages 1948–1953)

      H. Yan, B. J. Scott, Q. Huang and T. J. Marks

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400627

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      Effective electron-blocking layers (EBLs) for multilayer polymer light-emitting diodes (PLEDs) have been made by placing a crosslinked network of siloxane and hole-transporting polymers onto PLED anodes. These EBLs resulted in dramatic performance enhancement of conventional, lectron-dominated PLED devices: the maximum current efficiency increased tenfold to over 17 cd/A, clearly a result of the effectiveness of the EBL.

    19. Synthesis of a Dendritic Core–Shell Nanostructure with a Temperature-Sensitive Shell (pages 1953–1957)

      Y.-Z. You, C.-Y. Hong, C.-Y. Pan and P.-H. Wang

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400362

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      Temperature-sensitive core–shell nanostructures are synthesized by functionalizing a hydroxyl-terminated dendrimer with a reversible addition-fragmentation chain transfer (RAFT) polymerization chain-transfer agent. RAFT polymerization of N-isopropylacrylamide produces a shell around the dendrimer (see Figure). In aqueous solution, changing the temperature by 10 °C can reversibly open and close the poly(N-isopropylacrylamide) shell. Entrapment and temperature-induced liberation of pyrene from the nanostructures is demonstrated.

    20. Silica Particles: A Novel Drug-Delivery System (pages 1959–1966)

      C. Barbé, J. Bartlett, L. Kong, K. Finnie, H. Q. Lin, M. Larkin, S. Calleja, A. Bush and G. Calleja

      Version of Record online: 30 NOV 2004 | DOI: 10.1002/adma.200400771

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      Silica particles present an interesting alternative to organic systems for drug delivery. Combining sol–gel synthesis with emulsion technology can produce particles (see Figure) with independently controlled size and release rates. The particle size is controlled by the emulsion chemistry, while the release rate is controlled by the particle microstructure. Preliminary in-vivo experiments reveal enhanced blood stability of the nanoparticles, which, coupled with sustained release of anti-tumor agents, show good potential for cancer treatment.