Advanced Materials

Cover image for Advanced Materials

May, 2000

Volume 12, Issue 10

Pages 693–770

    1. Monodispersed Colloidal Spheres: Old Materials with New Applications (pages 693–713)

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

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<693::AID-ADMA693>3.0.CO;2-J

      Monodispersed colloidal spheres in the range 10 nm to 1 μ m are reviewed here. Useful methods for the production of such colloids with tightly controlled sizes and well-defined properties are discussed as are techniques for organizing them into 2D and 3D (see Figure) ordered lattices. In addition, a number of unique applications of these crystalline assemblies are highlighted.

    2. A Scattering Electro-Optical Switch Based on Dendrimers Dispersed in Liquid Crystals (pages 715–719)

      M. W. P. L. Baars, M. C. W. van Boxtel, C. W. M. Bastiaansen, D. J. Broer, S. H. M. Söntjens and E. W. Meijer

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<715::AID-ADMA715>3.0.CO;2-2

      The dispersion of dendrimers in a liquid crystal (LC) is reported as a new approach to LC displays based on light scattering. It is shown that the performance of a fifth-generation palmitoyl-functionalized poly(propylene imine) dendrimer—with 64 “legs”, as shown in the Figure—as an electro-optical switch is superior to that of polymer-filled nematics and polymer-dispersed LC systems (see also cover).

    3. Overlayer-Mediated Superconductivity of Bechgaard-Salt Single Crystals (pages 719–721)

      A. Moradpour, M. Ribault and P. Auban-Senzier

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<719::AID-ADMA719>3.0.CO;2-N

      Thin films of superconducting (TMTSF)2ClO4 (where TMTSF=tetramethyltetraselenafulvalene) have been prepared by simply immersing crystals of (TMTSF)2PF6 in dichloromethane solutions of nBu4N+- ClO4. The mechanism of this unprecedented, highly efficient, ion-exchange process is examined in this communication, while the resistance and magnetoresistance of these layers are studied as a function of temperature. The morphologies of the films are studied by energy dispersive spectrometry.

    4. “Bite-and-Switch” Approach to Creatine Recognition by Use of Molecularly Imprinted Polymers (pages 722–724)

      S. Subrahmanyam, S. A. Piletsky, E. V. Piletska, B. Chen, R. Day and A. P. F. Turner

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<722::AID-ADMA722>3.0.CO;2-A

      The detection of creatine is important in the analysis of athletes and body builders. Here is reported the preparation of a synthetic polymer using imprinting polymerization, which leaves the polymer with receptor-mimicking recognition sites that are specific for creatine. Molecular recognition results in a fluorescent complex (see Figure) and thus represents a “bite-and-switch” mechanism.

    5. “Constructive Nanolithography”: Inert Monolayers as Patternable Templates for In-Situ Nanofabrication of Metal–Semiconductor–Organic Surface Structures—A Generic Approach (pages 725–731)

      R. Maoz, E. Frydman, S. R. Cohen and J. Sagiv

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<725::AID-ADMA725>3.0.CO;2-Z

      Tip-induced nanoelectrochemical oxidation is used to pattern methyl-terminated silane monolayers on silicon via oxidation of their top CH3 groups in the process known as constructive nanolithography. These authors report the utility of such “inert” monolayers as extremely versatile templates for constructing a rich variety of patterns such as the particulate cadmium sulfide features shown in the Figure.

    6. Printing via Photolithography on Micropartitioned Fluid Lipid Membranes (pages 731–734)

      L. A. Kung, J. T. Groves, N. Ulman and S. G. Boxer

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<731::AID-ADMA731>3.0.CO;2-A

      A four-level grayscale image of Abraham Lincoln on a lipid bilayer membrane(see Figure) is used to demonstrate this novel single-exposure photolithographic procedure for printing images on fluid surfaces containing partitioned corrals, the very nature of the fluid membrane allowing true grayscale to be achieved. The potential scope and applications—particularly in biotechnology—of the concept are also discussed.

    7. Chemical Control over Ceramic Porosity Using Carboxylate–Alumoxane Nanoparticles (pages 734–738)

      R. L. Callender and A. R. Barron

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<734::AID-ADMA734>3.0.CO;2-Z

      Control over porosity in ceramics is demonstrated here. Varying the size of the organic substituents in the precursor carboxylate–alumoxane [Al(O)x- (OH)y(O2CR)z]n nanoparticles allows the pores to be contained within the grains of the resulting α-Al2O3. The Figure shows a single crystal of α-Al2O3 in which 20–50 nm pores (white areas) run throughout the crystal.

    8. Large-Scale Catalytic Synthesis of Crystalline Gallium Nitride Nanowires (pages 738–741)

      C.-C. Chen and C.-C. Yeh

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<738::AID-ADMA738>3.0.CO;2-J

      GaN nanowires for high-efficiency optoelectronic devices? The simple method for the large-scale production of GaN nanowires presented here may bring us one step closer. Gallium and ammonia are reacted, using polycrystalline indium powder as a catalyst, to produce wire-like structures (see Figure) that show strong photoluminescence of the nanowires in the UV region.

    9. Photoresponsive Dendritic Monolayers (pages 741–746)

      J.-W. Weener and E. W. Meijer

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<741::AID-ADMA741>3.0.CO;2-6

      Azobenzene derivatives are excellent candidates for optical switching systems, due to their facile and reversible photoisomerization. However, the chromophores are usually aggregated in Langmuir–Blodgett films, which suppresses this cis–trans isomerization. Here is reported the anchoring of palmitoyl and azobenzene functions to a fifth-generation dendrimer (see Figure) to yield very stable monolayers that show reversible photoinduced switching.

    10. Catalytic Growth of β-Ga2O3 Nanowires by Arc Discharge (pages 746–750)

      Y. C. Choi, W. S. Kim, Y. S. Park, S. M. Lee, D. J. Bae, Y. H. Lee, G.-S. Park, W. B. Choi, N. S. Lee and J. M. Kim

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<746::AID-ADMA746>3.0.CO;2-N

      Monoclinic gallium oxide nanowires are prepared here by arc discharge of GaN powder in the presence of a small amount of transition metal catalyst. The nanowires are characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, and Raman spectroscopy, and evidence as to the mechanism of their formation (shown in the Figure) is obtained by high-resolution transmission electron microscopy.

    11. Single-Walled Carbon Nanotube–Polymer Composites: Strength and Weakness (pages 750–753)

      P. M. Ajayan, L. S. Schadler, C. Giannaris and A. Rubio

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<750::AID-ADMA750>3.0.CO;2-6

      Can carbon nanotubes be efficient structural reinforcements for high-strength polymer composites? Here it is shown that, during loading, individual single-walled nanotubes pull out of their bundles (see Figure), making load transfer difficult. It is thus concluded that the effectiveness of reinforcement is determined by the stability and collective behavior of the bundles rather than the strength of individual nanotube components.

    12. Polymer-Filled Nematics: A New Class of Light-Scattering Materials for Electro-Optical Switches (pages 753–757)

      M. C. W. van Boxtel, R. H. C. Janssen, D. J. Broer, H. T. A. Wilderbeek and C. W. M. Bastiaansen

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<753::AID-ADMA753>3.0.CO;2-V

      A new class of mixtures of liquid-crystalline (LC) materials and polymersis presented, consisting of sub-micrometer sized, internally crosslinked polymeric particles (see Figure) dispersed in a continuous (completely phase-separate) LC phase. Initial electro-optical experiments with these “polymer-filled nematics” indicate that their light-scattering properties can be controlled with the application of an electrical field.

    13. Preparation and Optical Properties of Oligophenylenevinylene/Perhydrotriphenylene Inclusion Compounds (pages 757–761)

      J. Gierschner, L. Lüer, D. Oelkrug, E. Musluoğlu, B. Behnisch and M. Hanack

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<757::AID-ADMA757>3.0.CO;2-F

      The channel inclusion compounds (ICs) formed by perhydrotriphenylene (PHTP) with linear or rod-shaped molecules can be used for investigations of guest–guest interactions and in optoelectronics applications, for which high dichroic ratios and high fluorescence quantum yields are desirable. The preparation and characterization of some novel PHTP ICs formed with oligophenylenevinylenes and substituted derivatives are described and the investigation of their optical properties is reported. Results of polarized fluorescence spectroscopy are shown to confirm the expected high optical dichroism.

    14. Fluorescent Indicators for Nitric Oxide (pages 763–765)

      H. Kojima and T. Nagano

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<763::AID-ADMA763>3.0.CO;2-R

      Nitric oxide (NO) is thought to play an important role in the central nervous system; however, its precise role is unclear, due to the lack of a method for the direct, real-time detection of NO. These authors have developed a series of novel diamine fluorescent indicators that allow, via the mechanism shown in the Figure, real-time visualization of the production and diffusion of NO in living cells.

    15. Persistent Honeycomb Structures in Porous and Other Two-Component Solids (pages 767–770)

      Y.-H. Kiang, S. Lee, Z. Xu, W. Choe and G. B. Gardner

      Version of Record online: 22 MAY 2000 | DOI: 10.1002/(SICI)1521-4095(200005)12:10<767::AID-ADMA767>3.0.CO;2-B

      Predicting three-dimensional structure based on the individual components of hybrid structures remains one of the greatest challenges of crystal engineering; however, progress is reported here: For 21 different systems the crystallization of phenylacetylene nitriles with silver triflate salts leads to the same basic hexagonal honeycomb structures (see Figure). A rationalization based on interface minimization is proposed.