Advanced Materials

Cover image for Vol. 13 Issue 18

September, 2001

Volume 13, Issue 18

Pages 1351–1413

    1. Controlling Ion-Transport Selectivity in Gold Nanotubule Membranes (pages 1351–1362)

      C. R. Martin, M. Nishizawa, K. Jirage, M. Kang and S. B. Lee

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1351::AID-ADMA1351>3.0.CO;2-W

      Gold nanotubules supported on a microporous polycarbonate filter are used as a new class of synthetic membranes. The ion transport of these membranes can be reversibly switched between the cation- and anion-permselective states. Size-selectivity can also be obtained thanks to the molecular sieving capability of the membranes. The Figure shows Ru(bpy)32+, which is one of the ions used to investigate the ion-transport properties.

    2. Nanoscale Organization of Conjugated Rods in Rod–Coil Molecules (pages 1363–1368)

      M. Lee, J.-W. Kim, I.-W. Hwang, Y.-R. Kim, N.-K. Oh and W.-C. Zin

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1363::AID-ADMA1363>3.0.CO;2-I

      Conjugated rod molecules bearing flexible coil polymer moieties on both ends self-organize into 1D or 2D structures, and eventually into a 3D tetragonal superlattice (see Figure), depending on the number of monomeric units in the coils. The 3D ordered rods exhibit a highly extended fluorescence lifetime over the 1D or 2D arrays, making synthetic control of the rod-to-coil volume fraction a viable strategy to regulate photophysical properties.

    3. Confined Surface Plasmons in Gold Photonic Nanocavities (pages 1368–1370)

      M. C. Netti, S. Coyle, J. J. Baumberg, M. A. Ghanem, P. R. Birkin, P. N. Bartlett and D. M. Whittaker

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1368::AID-ADMA1368>3.0.CO;2-P

      A simple scheme to produce large-area colored metal surfaces by completely confining surface plasmons inside gold spherical nanocavities has been discovered. The negative nanocavity curvature localizes the electromagnetic fields into small volumes, which can be arranged non-periodically. The Figure shows an image of a graded thickness sample composed of 700 nm diameter nanocavities.

    4. Direct Nanowiring of Carbon Nanotubes for Highly Integrated Electronic and Spintronic Devices (pages 1371–1373)

      Y.-H. Lee, Y.-T. Jang, C.-H. Choi, D.-H. Kim, C.-W. Lee, J.-E. Lee, Y.-S. Han, S.-S. Yoon, J.-K. Shin, S.-T. Kim, E.-K. Kim and B.-K. Ju

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1371::AID-ADMA1371>3.0.CO;2-S

      A feasible fabrication technique for nanomachines that are based on carbon nanotubes (CNTs) is demonstrated. Direct nanowiring of CNTs between micrometer islands is reported to have been achieved by a growth barrier technique, which prevents vertical growth of the CNTs, i.e., towards the substrate. The result is “straight” or “Y-shaped” CNT bridges between predefined electrodes (see Figure).

    5. Visualization of Mesostructures and Organic Guest Inclusion in Molecular Sieves with Confocal Microscopy (pages 1374–1377)

      C. Seebacher, J. Rau, F.-W. Deeg, C. Bräuchle, S. Altmaier, R. Jäger and P. Behrens

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1374::AID-ADMA1374>3.0.CO;2-A

      The visualization of mesopores and defects in porous molecular sieves, as well as of the incorporation dynamics and spatial distribution of guest molecules, is achieved by optical confocal microscopy of single crystals immersed in solutions of fluorescent dyes. The Figure shows a fluorescence image of a silicalite crystal treated with the dye oxazine-1, revealing a defect. The technique permits easy characterization of molecular sieves.

    6. Synthesis of Mesoporous Thin TiO2 Films with Hexagonal Pore Structures Using Triblock Copolymer Templates (pages 1377–1380)

      H.-S. Yun, K. Miyazawa, H. S. Zhou, I. Honma and M. Kuwabara

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1377::AID-ADMA1377>3.0.CO;2-T

      TiO2thin films with a hexagonal mesoporous structure and an anatase-type crystalline framework are easily synthesized by a sol–gel method at low pH, using an EO–PO–EO block copolymer as template. While the TiO2/polymer superstructure originally has a primitive cubic structure, annealing at 150 °C affords a phase transition to hexagonal (see Figure), which persists upon template removal by calcination.

    7. Large-Scale Synthesis of Monodisperse Nanorods of Se/Te Alloys Through a Homogeneous Nucleation and Solution Growth Process (pages 1380–1384)

      B. Mayers, B. Gates, Y. Yin and Y. Xia

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1380::AID-ADMA1380>3.0.CO;2-W

      Uniform single-crystalline nanorods of Se/Te alloys—for example, the Se0.5Te0.5 crystals (934±48 nm × 223±10 nm) shown in the Figure—are reported to have been directly grown from aqueous solutions through a homogeneous nucleation process that involves no physical template, thus facilitating large-scale synthesis.

    8. Functionalized Carbon Nanotubes for Molecular Hydrogen Sensors (pages 1384–1386)

      J. Kong, M. G. Chapline and H. Dai

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1384::AID-ADMA1384>3.0.CO;2-8

      Excellent sensors for molecular hydrogen,to be used, e.g., for leakage control in H2-based energy sources, are fabricated by functionalization of single-walled carbon nanotubes (SWNTs) with a non-continuous coating of palladium. These sensors, with large electrical conductivity modulation in the presence of small H2 concentrations in air, show fast response and high sensitivity even at room temperature. The Figure presents an AFM image of a Pd-coated SWNT.

    9. Capillary Force Lithography (pages 1386–1389)

      K. Y. Suh, Y. S. Kim and H. H. Lee

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1386::AID-ADMA1386>3.0.CO;2-X

      A simple yet robust method for large-area patterning of polymer films—capillary force lithography—is presented here. This method, which combines the essential features of imprint lithography and microcontact printing, allows the replication of features down to 100 nm. The Figure shows a typical pattern.

    10. Seed-Mediated Growth Approach for Shape-Controlled Synthesis of Spheroidal and Rod-like Gold Nanoparticles Using a Surfactant Template (pages 1389–1393)

      N. R. Jana, L. Gearheart and C. J. Murphy

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1389::AID-ADMA1389>3.0.CO;2-F

      A seed-mediated growth approach to improved monodispersity of nanoparticles that involves controlling nucleation and growth in solution is presented. Using this approach, spheroidal and rod-like gold particles (see Figure) could be prepared in the presence of a rod-like micellar template. The aspect ratio of the particles could be varied from 1 to 10 by varying the ratio of preformed seed to metal salt.

    11. Sol–Gel Template Synthesis of an Array of Single Crystal CdS Nanowires on a Porous Alumina Template (pages 1393–1394)

      H. Q. Cao, Y. Xu, J. M. Hong, H. B. Liu, G. Yin, B. L. Li, C. Y. Tie and Z. Xu

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1393::AID-ADMA1393>3.0.CO;2-C

      An array of single crystal CdS nanowires has been fabricated in the pores of an alumina membrane by sol–gel synthesis. The CdS crystals have a hexagonal structure, which is verified by electron diffraction. As CdS is an important semiconducting material this synthesis may prove very useful for the fabrication of nanosized semiconducting structures. The Figure shows a scanning electron microscopy image of the nanowires.

    12. Attaching Silica Nanoparticles from Suspension onto Surface Charge Patterns Generated by a Conductive Atomic Force Microscope Tip (pages 1395–1398)

      P. Mesquida and A. Stemmer

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1395::AID-ADMA1395>3.0.CO;2-0

      A conductive atomic force microscope (AFM) tip acts as a nanopencilto write positive or negative charge patterns into a fluorocarbon film. Silica nanobeads (with a positive surface charge) can be attached to negative patterns by Coulombic interaction. While the resolution of the writing process is up to 100 nm, coagulation of the silica beads makes 1 μm a realistic minimum width for structures thus formed (see Figure and also cover).

    13. Fluorescent Trimeric Liquid Crystals: Modular Design of Emissive Mesogens (pages 1398–1401)

      A. C. Sentman and D. L. Gin

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1398::AID-ADMA1398>3.0.CO;2-J

      Integration of luminescent and mesogenic properties—instead of a compromise between the two—in light-emissive thermotropic liquid crystals is achieved by a modular approach: a weakly mesogenic, but highly fluorescent core is joined, through flexible linkages, to two strongly mesogenic moieties (see Figure).

    14. Luminescent Erbium-Doped Porous Silicon Bilayer Structures (pages 1402–1405)

      L. Gu, Z. Xiong, G. Chen, Z. Xiao, D. Gong, X. Hou and X. Wang

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1402::AID-ADMA1402>3.0.CO;2-U

      A novel method for preparing luminescent erbium-doped porous silicon(PSi) is presented. By anodic etching of an Er and O co-doped Si single crystalline film grown by molecular beam epitaxy, an Er-doped PSi/PSi bilayer structure is formed. The advantages of such a bilayer structure are efficient excitation of Er ions and suppression of energy back transfer for the de-excitation process. The Figure is an SEM image of a PSi:Er sample.

    15. Nanoporous Catalytic Materials with Organic Frameworks (pages 1407–1410)

      D. L. Gin and W. Gu

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1407::AID-ADMA1407>3.0.CO;2-0

      Organic frameworks have tempting propertiesfor nanostructured heterogeneous catalysts with active sites that are size- and pH-tunable, yet working examples are sparse. The authors present a promising structure type, i.e., cross-linked assemblies of lyotropic liquid crystals (LLCs), whose polar termini form ordered channels with enhanced basic or acidic catalytic activity (see Figure for a Lewis-acidic system).

    16. Photochromic Magnetic Materials (pages 1411–1413)

      K. Nakatani and P. Yu

      Version of Record online: 5 SEP 2001 | DOI: 10.1002/1521-4095(200109)13:18<1411::AID-ADMA1411>3.0.CO;2-Y

      Incorporation of organic photochromes into magnetic systems not only provides new ways to photo-control magnetic behavior but may also lead to interesting photochromics. Cationic spiropyrans exhibit this type of behavior depending on whether the structure is open or closed (see Figure). These structures can also be incorporated into rigid layered MnPS3 materials where a reversible photo-switching of magnetic coercivity is observed.