Advanced Materials

Cover image for Advanced Materials

September, 2003

Volume 15, Issue 18

Pages 1489–1567

    1. Materials Forum Adv. Mater. 18/2003 (page 1495)

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200390169

    2. New Developments in Transmission Electron Microscopy for Nanotechnology (pages 1497–1514)

      Z.L. Wang

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200300384

      Some of the most recent progresses in transmission electron microscopy (TEM) techniques, including in-situ microscopy, environmental microscopy, angstrom-resolution imaging, and electron holography, and their unique applications for characterizing nanomaterials are reviewed. These techniques are demonstrated to be the future directions of electron microscopy for nanotechnology. The Figure shows a TEM image of a ZnO nanobelt.

    3. Electrical Transport and Confocal Raman Studies of Electrochemically Modified Individual Carbon Nanotubes (pages 1515–1518)

      K. Balasubramanian, M. Friedrich, C. Jiang, Y. Fan, A. Mews, M. Burghard and K. Kern

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200305129

      Electrochemical coating of individual single-walled carbon nanotubes (SWCNTs) with thin films obtained via oxidative coupling of an amine or reductive coupling of an aromatic diazonium salt is reported. The same SWCNTs have been characterized before and after modification by electrical transport measurements and confocal Raman spectroscopy (see Figure, electrode structure white, background dark blue, and SWCNTs light blue to red).

    4. Controlling the Field-Effect Mobility of Regioregular Polythiophene by Changing the Molecular Weight (pages 1519–1522)

      R.J. Kline, M.D. McGehee, E.N. Kadnikova, J. Liu and J.M.J. Fréchet

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200305275

      A clear dependence of the hole mobility on molecular weight of poly(3-hexylthiophene) in films is demonstrated. The charge carrier mobility of regioregular polythiophene is shown to increase by four orders of magnitude as the molecular weight is increased from ∼3 200 g mol–1 to 36 000 g mol–1. These observations could explain why the mobility values obtained in different labs vary so widely and suggest that optimizing the molecular weight of conjugated polymers could lead to significant improvements in device performance.

    5. Luminescent Nanoring Structures on Silicon (pages 1522–1526)

      K. Prabhakaran, F. Meneau, G. Sankar, K. Sumitomo, T. Murashita, Y. Homma, G.N. Greaves and T. Ogino

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200305013

      A unique self-organization of optically active nanoparticles of CdS on a silicon surface forming nanoring structures (see Figure and inside cover) is presented. Tunneling luminescence mapping on these structures show that there is direct correspondence between the morphology and the light emission, suggesting that this novel nanomaterial system could make a significant impact in a wide variety of fields including quantum optics.

    6. Large-Area Two-Dimensional Mesoscale Quasi-Crystals (pages 1526–1528)

      X. Wang, C.Y. Ng, W.Y. Tam, C.T. Chan and P. Sheng

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200305263

      A holographic lithography technique is used to fabricate large 2D Penrose quasi-crystals (see Figure, scale bar: 5 μm). The method combines holography and photo-induced polymerization techniques and is applied for the first time to fabricate quasi-crystals. This method is very versatile and relatively inexpensive in fabricating various mesoscale to nanostructures.

    7. Ultra-Low-k Pure-Silica Zeolite MFI Films Using Cyclodextrin as Porogen (pages 1528–1531)

      S. Li, Z. Li and Y. Yan

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200305173

      Reduction of the dielectric constant k to the ultra low-k range is important for the continuing miniaturization of semiconductor devices. It is demonstrated that γ-cyclodextrin can act as an effective porogen (see Figure) to reduce k while maintaining good film strength. A continuous thin pure-silica zeolite MFI film with k = 1.8 and elastic modulus of 14 GPa is reported, prepared by spin-on from a zeolite nanoparticle suspension.

    8. Moiré Pattern Formation on Porous Alumina Arrays Using Nanoimprint Lithography (pages 1531–1534)

      J. Choi, R.B. Wehrspohn and U. Gösele

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200305251

      Porous alumina arrays with various Moiré patterns (see Figure) are prepared by two-step nanoindentation with different rotation angles and subsequent anodization. The patterns on the porous alumina array are in good agreement with the theory of Moiré patterns in terms of the rotation angles. In addition, replicas of photoresist polymer with the Moiré pattern are successfully prepared.

    9. A New Method to Fabricate Single-Molecule Nanoarrays Using Dendrimer-Based Templates (pages 1534–1538)

      H. Tokuhisa, T. Kubo, E. Koyama, K. Hiratani and M. Kanesato

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200304946

      Dendrimer architectures are used as spacing-templates to fabricate single molecule nanoarrays. It is shown that this new method (see Figure for illustration) fabricates a nanoarray of single thioctic acids separated by a distance related to the dendron size on Au. This approach could be used for assembling single functional molecules for nanotechnology in areas such as molecular electronics.

    10. Novel Silica Nanotubes with a High Aspect Ratio—Synthesis and Structural Characterization (pages 1538–1541)

      J. Zygmunt, F. Krumeich and R. Nesper

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200305134

      Vanadium oxide hydrate has been used in a new, robust, and inexpensive shape-templating synthesis leading to silica nanotubes (SiO2-NTs, see Figure) with good chemical purity, a well-defined morphology, and high aspect ratio. Unidimensional nanosized cavities or channels are made accessible through the open ends of the SiO2-NTs, which can be functionalized, thus generating particles with magnetic, catalytic, or uptake/release behavior.

    11. Functional Molecularly Imprinted Polymer Microstructures Fabricated Using Microstereolithography (pages 1541–1544)

      P.G. Conrad II, P.T. Nishimura, D. Aherne, B.J. Schwartz, D. Wu, N. Fang, X. Zhang, M.J. Roberts and K.J. Shea

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200304602

      Microstereolithography has been used to fabricate functional, three-dimensional, molecularly imprinted microstructures (e.g., see Figure) with recognition for adenine and its derivatives. The range of target analytes that are responsive to this molecular imprinting technique is large. This and related lithographic techniques will allow for the direct integration of functional polymers with molecular recognition into the microfabrication process.

    12. Fabricating Two-Dimensional Molecular Gradients via Asymmetric Deformation of Uniformly-Coated Elastomer Sheets (pages 1545–1547)

      J. Genzer, D.A. Fischer and K. Efimenko

      Version of Record online: 14 AUG 2003 | DOI: 10.1002/adma.200305151

      Molecular gradients comprising two-dimensional in-plane variation of density of substrate-grafted molecules (see Figure, darker regions in the plot denote regions with higher substrate density) have been fabricated. This is achieved by utilizing the technology of “mechanically assembled monolayers” in conjunction with in-plane asymmetric stretching of elastomeric substrates uniformly-coated with organosilane precursors.

    13. Reduced Operating Voltages in Polymer Light-Emitting Diodes Doped with Rare-Earth Complexes (pages 1547–1551)

      M.R. Robinson, J.C. Ostrowski, G.C. Bazan and M.D. McGehee

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200304651

      Light-emitting diodes (LEDs) were fabricated using two europium complexes, differing only by the addition of tert-butyl groups around the β-diketonate ligands (see Figure), blended into poly(2-(6′-cyano-6′-methyl-heptyloxy)-1,4-phenylene) (CN-PPP). The addition of tert-butyl groups results in CN-PPP–Eu LEDs with increased operational lifetime and decreased operating voltage.

    14. Microgel-Stabilized Metal Nanoclusters: Size Control by Microgel Nanomorphology (pages 1551–1555)

      A. Biffis, N. Orlandi and B. Corain

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200304977

      Soluble crosslinked macromolecules (microgels) used as stabilizers of catalytically active metal nanoclusters allow control of the nanocluster size by simply changing the crosslinking degree of the microgel. Microgel-stabilized metal nanoclusters are easily prepared and stored in the solid state, and those of Pd (see Figure) exhibit high catalytic activity in the Heck reaction of activated aryl bromides.

    15. Highly Circularly Polarized Photoluminescence over a Broad Spectral Range from a Calamitic, Hole-Transporting, Chiral Nematic Glass and from an Indirectly Excited Dye (pages 1555–1558)

      K.L. Woon, M. O'Neill, G.J. Richards, M.P. Aldred, S.M. Kelly and A.M. Fox

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200304960

      A highly birefringent, luminescent chiral nematic liquid crystal is shown to have an extremely broad photonic stop band (see dashed line in Figure) overlapping its emission spectrum. Highly circularly polarized photoluminescence is observed from the liquid crystal itself and from an indirectly excited dye dopant. The liquid crystal is hole-transporting with a room-temperature mobility of 4 × 10–4 cm2 V–1 s–1.

    16. Surface Polymerization of Hydrophilic Methacrylates from Ultrafine Silica Sols in Protic Media at Ambient Temperature: A Novel Approach to Surface Functionalization Using a Polyelectrolytic Macroinitiator (pages 1558–1562)

      X. Chen and S.P. Armes

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200305067

      A convenient one-pot synthesis of polymer-grafted nano-sized silica particles using atom transfer radical polymerization (see Figure) is described. Physical adsorption of a cationic macroinitiator allows polymerization of a range of hydrophilic methacrylates. A high degree of coverage of the silica sol particles by the grafted polymer chains was indicated.

    17. Synthesis and Magnetic Behavior of Periodic Nickel Sphere Arrays (pages 1562–1564)

      L. Xu, L.D. Tung, L. Spinu, A.A. Zakhidov, R.H. Baughman and J.B. Wiley

      Version of Record online: 11 SEP 2003 | DOI: 10.1002/adma.200305030

      Inverse opal polymer replicas serve as excellent templates for the formation of metal sphere arrays (see Figure). Here nickel sphere arrays have been prepared by electrodeposition into poly(methyl methacrylate) templates. Angle-dependent magnetic measurements indicate that these properties are dominated by shape anisotropy.