Advanced Materials

Cover image for Advanced Materials

January, 2004

Volume 16, Issue 2

Pages 103–190

    1. Contents: Adv. Mater. 2/2004 (pages 103–110)

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200490003

    2. Programmable Assembly of Heterogeneous Colloidal Particle Arrays (pages 111–115)

      B. B. Yellen and G. Friedman

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200305603

      Magnetically driven self-assembly of colloidal particles into highly ordered structures on a substrate is demonstrated. This process allows for programming of specific geometrical patterns of colloidal particles. It also permits assembly of well-defined colloidal patterns of many different particle types, possibly carrying different labels, e.g., fluorescently labeled beads (see Figure), or different molecular species.

    3. Facile Microstructuring of Organic Semiconducting Polymers by the Breath Figure Method: Hexagonally Ordered Bubble Arrays in Rigid Rod-Polymers (pages 115–118)

      L. Song, R. K. Bly, J. N. Wilson, S. Bakbak, J. O. Park, M. Srinivasarao and U. H. F. Bunz

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200306031

      Microstructuring of conjugated polymers is facile utilizing the breath figure approach. Dilute solutions of conjugated polymers in carbon disulfide form highly ordered 2D hexagonal bubble arrays (see Figure and inside cover). The arrays are obtained if moist air is blown over the polymer solutions. Evaporative cooling leads to condensation of water droplets onto the liquid surface. After the solvent is evaporated, the ordered bubble array is observed.

    4. Solution-based Fabrication of High-κ Gate Dielectrics for Next-Generation Metal-Oxide Semiconductor Transistors (pages 118–123)

      Y. Aoki and T. Kunitake

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200305731

      The layer-by-layer adsorption of precursor metal alkoxides in solution and post-annealing at 400 °C affords an alternate technique to the atomic layer chemical vapour deposition method for fabrication of next-generation high-κ gate dielectrics. A void-free TiO2–La2O3 composite film (see Figure) with 18 nm thickness is readily fabricated, and shows a dielectric constant higher than 30.

    5. Ultra-High-Density Photochromic Main-Chain 1,2-Dithienylcyclopentene Polymers Prepared Using Ring-Opening Metathesis Polymerization (pages 123–125)

      T. J. Wigglesworth and N. R. Branda

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200306094

      Ring-opening metathesis polymerization is used to construct the well-known photoresponsive 1,2-dithienylethene backbone for the generation of ultra-high-density photochromic main-chain polymers (see Figure). The photochromic monomer unit can be easily functionalized to create polymers with diverse structural and electronic properties. Both lipophilic and hydrophilic versions of the polymer have been prepared.

    6. Logic Control of the Fluorescence of a New Dyad, Spiropyran-Perylene Diimide-Spiropyran, with Light, Ferric Ion, and Proton: Construction of a New Three-Input “AND” Logic Gate (pages 125–130)

      X. Guo, D. Zhang and D. Zhu

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200306102

      The fluorescence of a novel dyad with spiropyran and perylene diimide units can be significantly enhanced only under the combined actions of UV light, protons, and ferric ions (see Figure). This behavior corresponds to a new “AND” gate with three inputs.

    7. Continuously Color-Tunable Rubber Laser (pages 130–133)

      M. R. Weinberger, G. Langer, A. Pogantsch, A. Haase, E. Zojer and W. Kern

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200305681

      A photopatternable elastomer [poly(butadiene-co-(4-vinylbenzyl thiocyanate)] bearing UV-sensitive thiocyanate (–SCN) groups, which isomerize to isothiocyanate (–NCS) units upon irradiation with UV light, is reported. This isomerization changes the refractive index of the elastomer, enabling the production of refractive index and relief distributed feedback (DFB) gratings using interference lithography. Blending a laser dye into the elastomer creates an optically pumped laser, which, when strained, allows continuous and reversible tuning of the laser emission wavelength.

    8. Multibit Memory Using Self-Assembly of Mixed Ferrocene/Porphyrin Monolayers on Silicon (pages 133–137)

      Q. Li, G. Mathur, S. Gowda, S. Surthi, Q. Zhao, L. Yu, J. S. Lindsey, D. F. Bocian and V. Misra

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200305680

      An alternative strategy for achieving multi-bit functionality, which uses mixed self-assembled monolayers of a benzyl alcohol-tethered ferrocene (Fc-BzOH) and a benzyl alcohol-tethered porphyrin (Por-BzOH) on silicon surfaces to achieve a four-state (2-bit) memory element, is presented. The four states include the neutral state and three distinct cationic states obtained upon oxidation of Fc-BzOH (monopositive) and Por-BzOH (monopositive, dipositive) molecules. Conventional cyclic voltammetry, capacitance, and conductance methods have been used to characterize the mixed monolayer.

    9. Magnetic-Field-Induced Growth of Single-Crystalline Fe3O4 Nanowires (pages 137–140)

      J. Wang, Q. Chen, C. Zeng and B. Hou

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200306136

      Single-crystalline nanowires of Fe3O4 hydrothermally synthesized under a magnetic field are reported. The square and hexagonal crystals formed in zero applied field are shown to give way to nanowires as the magnetic field is increased. The Figure shows the situation for a 0.25 T field. The structure and magnetic properties are characterized by transmission electron microscopy, X-ray and electron diffraction, and magnetometry.

    10. Rational Design of Macrocellular Silica Scaffolds Obtained by a Tunable Sol–Gel Foaming Process (pages 140–144)

      F. Carn, A. Colin, M.-F. Achard, H. Deleuze, Z. Saadi and R. Backov

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200306067

      A technique that uses a non-static patterning method has been employed for rational design toward macrocellular silica scaffolds (see Figure). The technique allows complete control over the width, length, and curvature of the plateau borders of the silica foam. Furthermore, this macroscale void space structuration is associated with secondary micro- and mesoscale porosity thus reaching hierarchically organized monolith-type materials.

    11. Carbon-Encapsulated Radioactive 99mTc Nanoparticles (pages 144–149)

      H. B. S. Chan, B. L. Ellis, H. L. Sharma, W. Frost, V. Caps, R. A. Shields and S. C. Tsang

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200305407

      A macroscopic quantity of quasi-spherical fullerene-like shells (see Figure) that encapsulate iron nanoparticles containing radioisotope 99mTc are prepared for the first time. The nanocomposite is acid-non-leachable, retaining radioactivity at an extremely high level. This method will enable rigorous studies of what are currently theoretical descriptions of nanometer-scale medicinal delivery vehicles for diagnostic and therapeutic purposes.

    12. Water-Based Single-Walled-Nanotube-Filled Polymer Composite with an Exceptionally Low Percolation Threshold (pages 150–153)

      J. C. Grunlan, A. R. Mehrabi, M. V. Bannon and J. L. Bahr

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200305409

      An emulsion polymer (i.e., latex) has been used as the polymer matrix starting material in order to lower the percolation threshold of single-walled-carbon-nanotube (SWNT)-filled polymer composites (e.g., see Figure). A percolation threshold below 0.04 wt.-% SWNT is achieved. This composite system offers the potential for conductive polymers that are relatively inexpensive, mechanically robust, environmentally stable, and easy to process.

    13. Growth and Field-Emission Properties of Crystalline, Thin-Walled Carbon Microtubes (pages 153–156)

      J. Q. Hu, Y. Bando, F. F. Xu, Y. B. Li, J. H. Zhan, J. Y. Xu and D. Golberg

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200306193

      A crystalline graphitic structure—uniform diameter, thin-walled carbon microtubes (see Figure)—has been prepared via a thermal reaction between ZnS and activated carbon. The microtubes have outer diameters of ∼ 1–2 μm, wall thicknesses of 10–20 nm, and lengths from several hundreds of micrometers to millimeters. The field-emission turn-on of the carbon microtubes is as low as ∼ 1.0–1.3 V μm–1.

    14. Compliant, Robust, and Truly Nanoscale Free-Standing Multilayer Films Fabricated Using Spin-Assisted Layer-by-Layer Assembly (pages 157–161)

      C. Jiang, S. Markutsya and V. V. Tsukruk

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200306010

      Free-standing multilayer gold-nanoparticle containing films with an overall thickness ranging from 20–70 nm have been fabricated. These films are compliant, robust, and long-living, and can be manufactured very time-efficiently with spin-assisted layer-by-layer assembly with an exceptionally high level of uniformity and integrity, which facilitate their ability to sustain multiple elastic deformations (see Figure).

    15. Highly Efficient Single-Layer Polymer Electrophosphorescent Devices (pages 161–166)

      X. Yang, D. Neher, D. Hertel and T. K. Däubler

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200305621

      A commercially available Ir complex has been employed for the preparation of highly efficient (see Figure) single-layer phosphorescent polymer light-emitting diodes by use of appropriate thermal treatment and proper adjustment of the layer composition. These devices exhibit essentially no dependence of the driving field on the concentration of the Ir complex, suggesting that the build-up of space-charge in the layer is insignificant.

    16. Use of Coaxial Gas Jackets to Stabilize Taylor Cones of Volatile Solutions and to Induce Particle-to-Fiber Transitions (pages 166–169)

      G. Larsen, R. Spretz and R. Velarde-Ortiz

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200306021

      A novel method to control the stability of Taylor cones during electrospinning/electrospray of solutions with highly volatile solvents is presented. An additional advantage is that fiber-to-particle transitions are also controlled without changing the chemistry or the voltage/current characteristics. The Figure shows the transition from particles to fibers effected by simply changing the gas flow rate through an outer capillary.

    17. A Color-Neutral, Gd Nanoparticle Switchable Mirror with Improved Optical Contrast and Response Time (pages 169–173)

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

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200305810

      An all-round improvement of the switchable mirror characteristics of any rare earth metal system can be achieved by utilizing two characteristics of nanoparticles: the size-dependent blue shift in the absorption edge and large surface area. Gd nanoparticles show better color neutrality in comparison with polycrystalline, alloy, and multilayer films, and also exhibit increased optical contrast and faster response time than polycrystalline films.

    18. Development of Organic-Dye-Doped Silica Nanoparticles in a Reverse Microemulsion (pages 173–176)

      X. Zhao, R. P. Bagwe and W. Tan

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200305622

      A new synthesis method to produce various organic-dye-doped silica nanoparticles using a reverse microemulsion has been developed. These nanoparticles show extremely high fluorescent signals (see Figure), excellent photostability, and size uniformity and tenability. These dye-doped silica nanoparticles can be used for various applications, especially in ultra-sensitive bioanalysis and in biomedical monitoring.

    19. Pressure-Assisted Capillary Force Lithography (pages 176–179)

      D.-Y. Khang and H. H. Lee

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200305673

      Pressure-assisted capillary force lithography is introduced using a permeable fluoropolymer material as a mold. Slight pressing (∼ 2–3 bar), when combined with a newly developed experimental set-up, ensures conformal contact between the stiff fluoropolymer mold and the substrate. The stiff nature of the mold material makes it possible to pattern sub-100 nm features (see Figure and cover).

    20. Tuning the Electronic Structure and Solubility of Conjugated Polymers with Perfluoroalkyl Substituents: Poly(3-perfluorooctylthiophene), the First Supercritical CO2-soluble Conjugated Polymer (pages 180–183)

      L. Li, K. E. Counts, S. Kurosawa, A. S. Teja and D. M. Collard

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200305333

      Poly(3-perfluorooctylthiophene) is the first reported conjugated polymer that is soluble in supercritical carbon dioxide (see Figure). The electron-withdrawing nature of the perfluoroalkyl groups affords a material that undergoes reversible reduction (n-doping), and the polymer displays a large Stokes shift because of a large difference in the conformation of the ground state and a more planar excited state.

    21. Colloidal Hydrogel Microlenses (pages 184–187)

      M. J. Serpe, J. Kim and L. A. Lyon

      Article first published online: 24 NOV 2003 | DOI: 10.1002/adma.200305675

      The creation of microlenses from hydrogel microparticles is demonstrated. The fabrication of substrate-supported microgels is performed using electrostatic interactions between aminopropyltrimethoxysilane-functionalized glass substrates and acrylic acid groups present on the microgel surface. The lensing ability is illustrated by imaging a photomask through each of the microgels present on the surface (see Figure).

    22. Probing of Funtionalized Mesoporous Silica Nanoparticles Using Transition Metal Clusters (Advanced Materials 2003, 15, 1853.) (page 189)

      S. Hermans, S. Sadasivan, C.M.G. Judkins, B.F.G. Johnson, S. Mann and D. Khushalani

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200490004

    23. Author Index and Subject Index Adv. Mater. 2/2004 (page 190)

      Article first published online: 29 JAN 2004 | DOI: 10.1002/adma.200490005