Advanced Materials

Cover image for Vol. 13 Issue 9

May, 2001

Volume 13, Issue 9

Pages 631–686

    1. Direct Visualization of the Nanoscale Morphology of Conducting Polythiophene Monolayers Studied by Electrostatic Force Microscopy (pages 631–634)

      T. Hassenkam, D. R. Greve and T. Bjørnholm

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<631::AID-ADMA631>3.0.CO;2-F

      The relation between electronic properties and morphology of conducting polymers has been a central issue since the very beginning of the field. The present paper provides the first direct visualization of highly conducting domains extending over hundreds of nanometers (see cover) in a conductive polythiophene thin film fabricated by the Langmuir–Schaefer technique and studied by electrostatic force microscopy (principle shown in Figure).

    2. Combined Visible and Infrared Electrochromism Using Dual Polymer Devices (pages 634–637)

      I. Schwendeman, J. Hwang, D. M. Welsh, D. B. Tanner and J. R. Reynolds

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<634::AID-ADMA634>3.0.CO;2-3

      Electrochromic polymers capable of modulating both visible and infrared light are investigated here. Devices based on these materials can be reversibly switched from the neutral state to the p-doped state with a concomitant color change (see Figure) over a broad range of spectral energies.

    3. A Cross-linked Large Channel Organic Coordination Solid (pages 637–641)

      Z. Xu, S. Lee, Y.-H. Kiang, A. B. Mallik, N. Tsomaia and K. T. Mueller

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<637::AID-ADMA637>3.0.CO;2-S

      A new approach to fully covalent crystalline networks is revealed. It is a template technique in which a metal salt is co-crystallized with a mesoscopic organic molecule. The Figure shows a phenylacetylenenitrile silver triflate molecule, which is reacted with silyl ditriflates to form high molecular weight polymers. Details of the technique and physical properties are discussed.

    4. Photocontrolled Alignment of Chiral Nematic Liquid Crystals (pages 641–644)

      C. Ruslim and K. Ichimura

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<641::AID-ADMA641>3.0.CO;2-B

      The first successful alignment of helix axes of chiral nematic liquid crystals (LCs) by the photoalignment technique is reported here. The helix axis aligns perpendicularly to the propagation direction of the incident non-polarized light. Dark and bright images (see Figure) of the aligned helix axis of a chiral nematic LC are reversed by rotating the crossed polarizers at 45°.

    5. Organic Aerogels with Very High Impact Strength (pages 644–646)

      C. Tan, B. M. Fung, J. K. Newman and C. Vu

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<644::AID-ADMA644>3.0.CO;2-#

      Crosslinked cellulose aerogels with extremely high impact strengths are very promising new materials. Their physical properties, which are described in this communication, may lead to promising applications, such as special coatings, thermal insulation, acoustical barriers, and membranes, for which the materials can be handled and used under rugged conditions. They can also serve as templates for the formation of binary aerogel composites with metal oxides.

    6. Low-Threshold Amplified Spontaneous Emission in a Fluorene-Based Liquid Crystalline Polymer Blend (pages 646–649)

      Y. C. Kim, T.-W. Lee, O. O. Park, C. Y. Kim and H. N. Cho

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<646::AID-ADMA646>3.0.CO;2-S

      Efficient energy transfer in polymer blends, comprising a fluorene-based liquid-crystalline polymer (see Figure) and a non-liquid-crystalline photoluminescent polymer, is demonstrated. Low-threshold amplified spontaneous emission, originating from the efficient Förster-type energy transfer between the host and the guest molecules, is observed, which offers a wide range of lasing applications for these materials.

    7. Nanoscale Materials with Mesostructured Interiors (pages 649–652)

      C. E. Fowler, D. Khushalani, B. Lebeau and S. Mann

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<649::AID-ADMA649>3.0.CO;2-G

      Routine preparation of mesostructured nanoparticles (see Figure) at room temperature is possible using the simple quenching procedure presented here. Silica particles with mesostructured interiors and diameters as small as 15 nm can be synthesized as can organo-silica derivatives with chemically functionalized mesopores. Preliminary insights into the mechanism of growth of these materials are also gained.

    8. Meso-Tetra-Alkynyl Porphyrins for Optical Limiting—A Survey of Group III and IV Metal Complexes (pages 652–656)

      A. Krivokapic, H. L. Anderson, G. Bourhill, R. Ives, S. Clark and K. J. McEwan

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<652::AID-ADMA652>3.0.CO;2-3

      Indium porphyrin 1 is an excellent optical limiterat visible wavelengths (480–620 nm). Absorption of light results in quantitative formation of the triplet excited state, which absorbs light 48 times more strongly than the ground state and has a lifetime of 0.8 ms. This should provide strong nonlinear attenuation of laser pulses on picosecond to microsecond timescales.

    9. Synthesis of Long Silver Nanowires from AgBr Nanocrystals (pages 656–658)

      S. Liu, J. Yue and A. Gedanken

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<656::AID-ADMA656>3.0.CO;2-O

      A novel method for preparing long silver nanowires (see Figure) at room temperature using AgBr nanocrystallites as a precursor is revealed. These nanowires are on average 80 nm in diameter are tens of micrometers long, and in some cases grow as single crystals. Important factors for the growth of these silver nanowires are discussed.

    10. Highly Ordered Structures of a Shape-Persistent Macromolecule: From Side Groups to Entire Molecules (pages 659–662)

      W. Wang, H. X. He, K. C. Toh and G. Wegner

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<659::AID-ADMA659>3.0.CO;2-C

      Experimental evidence of highly ordered structures, self-assembled from polydiacetylene-based molecules, is unveiled. The polydiacetylene structure in the Figure is a typical example of a shape persistent macromolecule—a class of stiff macromolecules featuring a persistent chain trajectory and usually containing a conjugated backbone. X-ray diffraction data and atomic force microscopy images reveal the skeleton and side chains of these structures.

    11. Insulating Ultrathin Silica Films Formed by a Room-Temperature Sol–Gel Process (pages 662–667)

      J. W. Robertson, M. Cai and J. E. Pemberton

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<662::AID-ADMA662>3.0.CO;2-#

      A novel sol–gel approach for the deposition of ultrathin dielectric silica films on metals using a simple, atmospheric-pressure, room-temperature method is reported. High resistivities and intrinsically low capacitances are found. An electric equivalent circuit model (see Figure) is proposed, comprising parallel sub-pF capacitors, to rationalize the low capacitances observed.

    12. Controlled Growth of Mesostructured Organic–Inorganic Composite Films on Oxide Substrates Defined with Micrometer-Scale Dimensions (pages 667–670)

      H. Sugimura, A. Hozumi, T. Kameyama and O. Takai

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<667::AID-ADMA667>3.0.CO;2-G

      Clear evidence that both electrostatic and hydrophobic interactions play a key role in the growth of organic–inorganic composite mesostructures is given in this communication. The use of micropatterned self-assembled monolayers covered with an organic–inorganic film (see Figure) unveils that the film coverage depends on the substrate used.

    13. Novel Positive-Tone Chemically Amplified Resists with Photoacid Generator in the Polymer Chains (pages 670–672)

      H. Wu and K. E. Gonsalves

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<670::AID-ADMA670>3.0.CO;2-3

      The successful synthesis of a series of positive-tone chemically amplified (CA) resists, with photoacid generating units incorporated in the resist matrix, is reported. The resists are found to exhibit excellent film formation behavior and an extremely high sensitivity, which makes them potential candidates for low-voltage electron beam (EB) lithography (a typical pattern is shown in the Figure).

    14. Oxygen-Induced Blinking of Single CdSe Nanocrystals (pages 672–676)

      F. Koberling, A. Mews and T. Basché

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<672::AID-ADMA672>3.0.CO;2-W

      Single-dot microscopy has been employed to unravel the electronic interactions between nanoscopic surfaces and adsorbed molecules. It is illustrated that the blinking effect of single nanocrystals changes in the presence of oxygen. The influence of the surrounding atmosphere as well as illumination on the fluorescence of particle ensembles is clearly visible in the Figure.

    15. Ordered Mesoporous Carbons (pages 677–681)

      R. Ryoo, S. H. Joo, M. Kruk and M. Jaroniec

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<677::AID-ADMA677>3.0.CO;2-C

      Mesoporous silica templates can be used to synthesize ordered mesoporous carbons (see Figure). As highlighted here, carbons with cubic or hexagonal frameworks, narrow mesopore size distributions, high specific surface areas, and large pore volumes have been obtained using templates such as MCM-48, SBA-1, and SBA-15, which exhibit 3D pore structures.

    16. Gd5(SixGe1–x)4: An Extremum Material (pages 683–686)

      V. K. Pecharsky and K. A. Gschneidner Jr.

      Article first published online: 2 MAY 2001 | DOI: 10.1002/1521-4095(200105)13:9<683::AID-ADMA683>3.0.CO;2-O

      A rich variety of unusually powerful magneto-responsive properties, such as the giant magnetocaloric effect, colossal magnetostriction, and giant magnetoresistance, have been discovered for Gd5(SixGe1–x)4 (see Figure). The remarkable flexibility offered by this family of materials, coupled with the possibility of introducing additional changes in the electronic structure, makes these systems uniquely suitable for modeling studies.