Advanced Materials

Cover image for Vol. 14 Issue 24

December, 2002

Volume 14, Issue 24

Pages 1789–1899

    1. Fabricating Ordered Voids in a Colloidal Crystal Film–Substrate System by Using Organic Liquid Patterns as Templates (pages 1799–1802)

      G. Lu, X. Chen, J. Yao, W. Li, G. Zhang, D. Zhao, B. Yang and J. Shen

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290002

      A colloidal crystal film–substrate system with ordered voids has been fabricated using a combination of microcontact printing, self-organization of organic liquid on the patterned self-assembled monolayers, and a vertical deposition technique. The Figure shows an SEM image of the bottom surface of a colloidal crystal film that had been peeled off the substrate after the solvent has evaporated.

    2. Incorporation of Proteins into Polymer Materials by a Novel Supercritical Fluid Processing Method (pages 1802–1804)

      M.S. Watson, M.J. Whitaker, S.M. Howdle and K.M. Shakesheff

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290003

      A very clean route to porous materials, utilizing the combination of conventional solution and supercritical fluid processing, is exploited to prepare porous tissue engineering scaffolds that contain biologically active material for controlled release. This allows accurate dosing of the biological agent, whilst retaining the advantages of supercritical fluid technology. The retention of biological activity throughout the processing is also demonstrated. A wide range of alternative morphologies, including microparticles, are possible simply via control of the method of depressurization.

    3. Oriented Free-Standing Three-Dimensional Silicon Inverted Colloidal Photonic Crystal Microfibers (pages 1805–1808)

      H. Míguez, S.M. Yang, N. Tétreault and G.A. Ozin

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290004

      Inverse colloidal photonic crystals (see Figure and cover) can be fashioned in the form of free-standing, oriented rectangular- and V-shaped microfibers via a self-assembly strategy. Microspectroscopy of these microfibers is consistent with the existence of a complete photonic bandgap near 1.5 μm, making these microfiber constructions interesting as optical components of microphotonic crystal circuits.

    4. Polymer Gel Light-Modulation Materials Imitating Pigment Cells (pages 1808–1811)

      R. Akashi, H. Tsutsui and A. Komura

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290005

      Novel light-modulation materials composed of stimuli-responsive gel particles with an added high concentration of colorants, which can modulate light due to an induced volume phase transition, have been obtained (see Figure). The light-modulation mechanism and constitution of this material are similar to those of pigment cells existing in cephalopods, and the light absorption change is based on diffusion and aggregation of the colorants.

    5. Fabrication of Chemically Patterned Surfaces Based on Template-Directed Self-Assembly (pages 1812–1815)

      N. Lu, M. Gleiche, J. Zheng, S. Lenhert, B. Xu, L. Chi and H. Fuchs

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290006

      Patterned surfaces with selective chemical activity are fabricated on Si/SiO2 surfaces using self-assembly techniques and structured Langmuir–Blodgett monolayers as templates (see Figure). Molecules with different functional groups can be arranged to form regular patterns of lines with different surface free energies and chemical activities over macroscopic areas.

    6. Highly Dispersive Micropatterns in Ion-Exchanged Glass Formed by Ion Irradiation Through a Mask of Colloidal Particles (pages 1815–1818)

      C. Strohhöfer, J.P. Hoogenboom, A. van Blaaderen and A. Polman

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290007

      Refractive index gratings with hexagonal symmetry (see Figure) have been fabricated in ion-exchanged borosilicate glass by ion irradiation through a mask of self-organized silica colloidal particles. Light scattering measurements show diffraction rings and peaks belonging to hexagonal symmetry with a lattice constant approximately equal to the diameter of the particles in the colloidal mask.

    7. Modification of Electronic Structures of a Carbon Nanotube by Hydrogen Functionalization (pages 1818–1821)

      K.S. Kim, D.J. Bae, J.R. Kim, K.A. Park, S.C. Lim, J.-J. Kim, W.B. Choi, C.Y. Park and Y.H. Lee

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290008

      A rigorous method to engineer the electronic structure of carbon nanotubes from metallic to semiconducting is reported (see inside front cover). An intramolecular junction in carbon nanotube is fabricated, where half of the nanotube is masked by a silicon oxide thin film. Functionalization of the nanotube by atomic hydrogen leads to the formation of an intramolecular junction, resulting in clear rectifying behavior at room temperature. This represents an important step towards the practical realization of nanotube-based nanotransistors.

    8. Low-Temperature Self-Assembly of Novel Encapsulated Compound Nanowires (pages 1821–1824)

      S. Hofmann, C. Ducati and J. Robertson

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290009

      Nickel sulfide nanowires and compound-filled MoS2 nanotubes have been grown by controlled annealing of patterned fullerene and nickel thin films on molybdenum substrates. The versatile synthesis route gives highly crystalline nanostructures at temperatures below 550 °C with a high degree of positional control. The Figure shows a portion of an as-grown nickel sulfide nanowire 19 nm in diameter (scale bar 2 nm).

    9. Macroporous Silica From Solid-Stabilized Emulsion Templates (pages 1824–1827)

      B.P. Binks

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290010

      Macroemulsions stabilized solely by nanoparticles of modified silica are used to prepare porous silica solid materials (see Figure), following slow evaporation of the two liquids. Both oil-in-water and water-in-oil emulsions can be employed, and the average pore size is close to the original emulsion drop diameter. Spherical or bicontinuous-like pores may form, depending on the properties of the template emulsion.

    10. A Combined Top–Down/Bottom–Up Approach to the Microscopic Localization of Metallic Nanodots (pages 1827–1832)

      J.P. Spatz, V.Z.-H. Chan, S. Mößmer, F.-M. Kamm, A. Plettl, P. Ziemann and M. Möller

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290011

      Periodic and aperiodic two-dimensional nanostructures with hierarchical order have been prepared by a combined top–down/bottom–up approach. This method allows 7 nm nanoparticles to be positioned with a accuracy of 10 nm or less, with a separation distance of several micrometers. The Figure is an optical dark field microscopy image of a square arrangement of Au dots on a Si wafer.

    11. Exchange Coupling and Remanence Enhancement in Nanocomposite Multilayer Magnets (pages 1832–1834)

      W. Liu, Z.-d. Zhang, J.-p. Liu, L.-j. Chen, L.-l. He, Y. Liu, X.-k. Sun and D.J. Sellmyer

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290012

      Nanocomposite thin films (see Figure) that are prepared by sputtering and heat treatment demonstrate exchange coupling and remanence enhancement. A high remanence of Jr = 1.31 T and a maximum energy product of (B H)max = 203 kJ m–3 are achieved. These multilayer films consist of magnetically hard Nd2Fe14B-type phase with a grain size of 40 nm and soft α-Fe phase, existing in the form of continuous layers.

    12. Triplet Formation In Polyfluorene Devices (pages 1834–1837)

      A.S. Dhoot and N.C. Greenham

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290013

      The fraction of excitons formed as singlets governs the efficiency of a polymer light-emitting diode (LED) (see Figure). By measuring absorptions due to triplet excitons in working poly(9,9-dioctylfluorene) devices, the singlet formation probability is calculated. A lower limit of 58 % is found, significantly larger than that predicted statistically. In devices based on the copolymer F8BT, no triplet exciton absorption can be detected.

    13. Conjugated Polymer Inverse Opals for Potentiometric Biosensing (pages 1837–1841)

      T. Cassagneau and F. Caruso

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290014

      Colloidal crystals of poly(styrene) spheres can be used as templates to fabricate a conjugated polymer inverse opal potentiometric biosensor (see Figure) incorporating an enzyme. After core removal, a seven-fold increase in sensitivity relative to conventional films is measured for analyte concentrations varying from 1 to 100 μM. The presence of large pores enables the formation of a Schottky junction, which governs the sensing response.

    14. ZnO Nanoneedles Grown Vertically on Si Substrates by Non-Catalytic Vapor-Phase Epitaxy (pages 1841–1843)

      W.I. Park, G.-C. Yi, M. Kim and S.J. Pennycook

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290015

      Catalyst-free metal–organic chemical vapor deposition (MOCVD) is used to prepare ZnO nanoneedles, grown vertically on Si substrates. Electron microscopy reveals that the nanoneedles are sharp, have uniform diameters, lengths, and densities, and high crystallinity. The photoluminescence spectrum displays a strong emission peak at 3.29 eV with a very weak deep-level emission, indicating that the nanoneedles are of high optical quality.

    15. 3,4-Ethylenedioxythiophene–Pyridine-Based Polymers: Redox or n-Type Electronic Conductivity? (pages 1844–1846)

      C.J. DuBois and J.R. Reynolds

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290016

      A family of polymers based on alternating bi-EDOT and pyridine units is reported. Poly(BEDOT-PyrPyr-Ph2), with a bandgap of 1.2 eV, has four electrochemically accessible colors (dark gray, burgundy, lime green, and light gray) each corresponding to a distinct redox state. In-situ conductance measurements illustrate high n-type doping conductances only thirty times less than those of the p-type doping conductances.

    16. Growth and Optical Properties of Self-Organized Au2Si Nanospheres Pea-Podded in a Silicon Oxide Nanowire (pages 1847–1850)

      J.S. Wu, S. Dhara, C.T. Wu, K.H. Chen, Y.F. Chen and L.C. Chen

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290017

      Silicon-based nanowires with embedded self-assembled chains of gold silicide nanospheres (Au2Si@SiONW) have been prepared by annealing Si/Au bilayers. The diameter, number density, and length of the wires can be controlled by adjusting the bilayer thickness. The composite material displayed a new sharp photoluminescence peak thought to result from inter-band transitions in the “pea-podded” (see Figure) gold silicide crystals.

    17. Bicontinuous Cubic Block Copolymer Photonic Crystals (pages 1850–1853)

      A.M. Urbas, M. Maldovan, P. DeRege and E.L. Thomas

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290018

      Three-dimensional photonic crystals are fabricated from block copolymers, forming a double gyroid network structure. Further processing produces three-dimensionally nanoporous, freestanding materials (see Figure), and allows dielectric enhancement and infiltration, which dramatically improve optical and material properties. These etched materials provide a path to highly effective photonic crystals via self-assembly.

    18. Surface-Specific Zeolite-Binding Proteins (pages 1853–1856)

      S. Nygaard, R. Wendelbo and S. Brown

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290019

      Proteins that distinguish the crystallographic planes of zeolites have been identified. On EMT zeolite the proteins obscure only the (001) face and are able to immobilize an enzyme with negligible loss of activity (see dye-exclusion assay, Figure). A general method for isolating proteins able to distinguish spatial orientations of atoms on non-biological surfaces is described.

    19. Super-Hydrophobic Surfaces: From Natural to Artificial (pages 1857–1860)

      L. Feng, S. Li, Y. Li, H. Li, L. Zhang, J. Zhai, Y. Song, B. Liu, L. Jiang and D. Zhu

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290020

      The study of natural lotus leaves reveals that to obtain a super-hydrophobic surface with both a large contact angle (CA) and small sliding angle (α), cooperation of micro- and nanostructures is required. Accordingly, lotus-like aligned carbon nanotube (ACNT) films with a CA of ∼166° (see Figure) and α of ∼3° have been fabricated. Other super-hydrophobic surfaces of polymer nanofibers and different patterned ACNT films are also highlighted.

    20. Light-Emitting Silicon Nanocrystals from Laser Pyrolysis (pages 1861–1865)

      F. Huisken, G. Ledoux, O. Guillois and C. Reynaud

      Version of Record online: 23 DEC 2002 | DOI: 10.1002/adma.200290021

      Crystalline silicon nanoparticles with diameters between 2.5 and 20 nm are prepared by CO2-laser-induced decomposition of silane in a gas flow reactor. The strong visible photoluminescence (PL) (see Figure) of the Si nanocrystals is studied as a function of their size and as a function of the time they are exposed to air. All observations can be explained on the basis of quantum confinement as the only origin of the PL.