Advanced Materials

Cover image for Vol. 13 Issue 14

July, 2001

Volume 13, Issue 14

Pages 1053–1119

    1. Interchain Interactions in Organic π-Conjugated Materials: Impact on Electronic Structure, Optical Response, and Charge Transport (pages 1053–1067)

      J. Cornil, D. Beljonne, J.-P. Calbert and J.-L. Brédas

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1053::AID-ADMA1053>3.0.CO;2-7

      The electronic structure characteristicsand interfacial properties as well as transport properties of organic π-conjugated materials that are of fundamental importance in the fields of optoelectronic devices, photovoltaic cells, field-effect transistors, etc. are thoroughly discussed in this article. Furthermore, this review relates these properties to the incorporation and the ultimate performance of a material in a given device (see also cover).

    2. Tunable Mirrorless Lasing in Cholesteric Liquid Crystalline Elastomers (pages 1069–1072)

      H. Finkelmann, S. T. Kim, A. Muñoz, P. Palffy-Muhoray and B. Taheri

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1069::AID-ADMA1069>3.0.CO;2-6

      Tuning the wavelength of a laser emission by mechanical deformation is not as implausible as it may seem. This communication proves that it can be done with cholesteric liquid crystal elastomers. The Figure shows what happens when a beam is focussed on the sample in its relaxed (left) and its stretched form (right).

    3. Polarized Electroluminescence in Double-Layer Light-Emitting Diodes with Perpendicularly Oriented Polymers (pages 1072–1075)

      A. Bolognesi, C. Botta, D. Facchinetti, M. Jandke, K. Kreger, P. Strohriegl, A. Relini, R. Rolandi and S. Blumstengel

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1072::AID-ADMA1072>3.0.CO;2-9

      Polarized light over a large spectral region is provided by the novel procedure described in this work. The active material of these light-emitting diodes (LEDs) is formed by two polymer layers that are oriented perpendicularly to each other. The orientation is obtained using the rubbing technique combined with thermal annealing. The Figure represents the electroluminescence (EL) emission from the two-layer LED and its structure (see also inside front cover).

    4. Fabrication of Highly Ordered Multilayer Films Using a Spin Self-Assembly Method (pages 1076–1078)

      J. Cho, K. Char, J.-D. Hong and K.-B. Lee

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1076::AID-ADMA1076>3.0.CO;2-M

      A very short processing time for making well-organized multilayer films can be achieved employing the novel spin self-assembly method described in this paper. The authors elaborate on the advantages of this method versus conventional self-assembly methods for the fabrication of multilayer polyelectrolyte films. The Figure illustrates that the spinning process (bottom) yields far better organized layers than for instance the direct dipping method (top).

    5. Microscopic Surface Patterns of a Liquid Crystalline Polyacrylate Film (pages 1079–1081)

      D. Sentenac, B. I. Ostrovskii and W. H. de Jeu

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1079::AID-ADMA1079>3.0.CO;2-4

      Lamellae-like surface ripples, as shown in the Figure, can be induced on liquid crystalline polyacrylate films. The film surface shows regular height modulations, which are attributed to coupling between local liquid crystal ordering and surface curvature energy. The properties of these films, including their use for the patterning of otherwise homogeneous surfaces, are discussed in this communication.

    6. Sintering of Nanocrystalline CeO2 Ceramics (pages 1081–1085)

      C. Kleinlogel and L. J. Gauckler

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1081::AID-ADMA1081>3.0.CO;2-D

      Sintering CeO2 to maximum density at low temperatures retaining nanometer-sized grains can be achieved by the addition of transition metal oxides. The densification rate and obtainable density are highly increased due to the size-dependent melting of the dopant. The transient nature of the grain boundary layer allows tailoring of the electrical properties of CeO2, making this material very attractive for many electrochemical applications.

    7. Highly Organized Mesoporous Titania Thin Films Showing Mono-Oriented 2D Hexagonal Channels (pages 1085–1090)

      D. Grosso, G. J. de A. A. Soler-Illia, F. Babonneau, C. Sanchez, P.-A. Albouy, A. Brunet-Bruneau and A. R. Balkenende

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1085::AID-ADMA1085>3.0.CO;2-Q

      Structure-directing agents that aid in the formation of ordered, mesostructured titania have been found in poly(ethylene oxide) surfactants. Thermal treatment of the films results in stiffening of the titania network, thereby providing straight channels with elliptical pore cross sections (see Figure). The preparation, characterization, and properties of these films are thoroughly discussed, as well as the possibility of extending the technique for the preparation of 3D structures.

    8. Multilayer Assemblies of Silica-Encapsulated Gold Nanoparticles on Decomposable Colloid Templates (pages 1090–1094)

      F. Caruso, M. Spasova, V. Salgueiriño-Maceira and L. M. Liz-Marzán

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1090::AID-ADMA1090>3.0.CO;2-H

      Core–shell particles with tailored optical properties are obtained via manipulation of the number of Au@SiO2 nanoparticle layers deposited onto larger polymer spheres. The surface characteristics of silica, which surrounds the gold nanoparticles, are exploited to achieve a dense and uniform nanoparticle coating. The layer-by-layer (LbL) self-assembly technique yet again proves to be a worthy asset for the preparation of these novel metal-based core–shell and hollow colloids (see Figure).

    9. Mechano- and Electroluminescence of a Dissymmetric Hafnium Carborane Complex (pages 1094–1096)

      E. Hong, H. Jang, Y. Kim, S. C. Jeoung and Y. Do

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1094::AID-ADMA1094>3.0.CO;2-U

      The first example of a mechanoluminescent organometallic compound, the hafnium carborane complex depicted in the Figure, has been synthesized and investigated for its luminescence properties by the authors. The compound is also electroluminescent, as verified in experiments with the hafnium carborane complex embedded in a hole-transporting polymer.

    10. Poly-2,8-(indenofluorene-co-anthracene)—A Colorfast Blue-Light-Emitting Random Copolymer (pages 1096–1099)

      D. Marsitzky, J. C. Scott, J.-P. Chen, V. Y. Lee, R. D. Miller, S. Setayesh and K. Müllen

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1096::AID-ADMA1096>3.0.CO;2-I

      The incorporation of anthracene monomers in fluorene polymers (see Figure) suppresses the formation of aggregates severely thereby increasing the electroluminescence quantum efficiency. The spectral properties of these new polymers, their preparation, and applications are discussed.

    11. Spin-on Mesoporous Silica Films with Ultralow Dielectric Constants, Ordered Pore Structures, and Hydrophobic Surfaces (pages 1099–1102)

      C. M. Yang, A. T. Cho, F. M. Pan, T. G. Tsai and K. J. Chao

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1099::AID-ADMA1099>3.0.CO;2-0

      Smooth mesoporous silica films (see Figure) can now be obtained with very low dielectric constants by spin coating, whereby the thickness and hydrophobicity of the films can also be controlled. This is thanks to a functionalized precursor as is unveiled in this communication. These films are sure to be on the wanted list for semiconductor applications as they combine dielectric stability with a low processing temperature, an excellent thermal stability, and reliable mechanical properties.

    12. Recording at the Nanometer Scale on p-Nitrobenzonitrile Thin Films by Scanning Tunneling Microscopy (pages 1103–1105)

      D. X. Shi, Y. L. Song, D. B. Zhu, H. X. Zhang, S. S. Xie, S. J. Pang and H.-J. Gao

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1103::AID-ADMA1103>3.0.CO;2-B

      A data storage density of at least 1014 bits/cm2 is possible using p-nitrobenzonitrile as the data storage medium and scanning tunneling microscopy (STM) as the recording method. This represents the smallest mark size among all the organic thin films studied by these authors. The Figure shows a typical STM image of a recorded pattern.

    13. Polygon Building Block Route to sp2-Carbon-Based Materials (pages 1105–1107)

      C.-Y. Lee, H.-T. Chiu, C.-W. Peng, M.-Y. Yen, Y.-H. Chang and C.-S. Liu

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1105::AID-ADMA1105>3.0.CO;2-#

      Pentagonal- and hexagonal-shaped building block precursors provide a novel, high-yield method for the preparation of carbon onions and nanosized graphite particles. A reaction of hexachlorocyclopentadiene (C5Cl6) with sodium (see Figure) offers carbon onions with 8–50 spherical and elliptical shells. The same reaction with hexachlorobenzene (C6Cl6) results in a mixture of graphite crystallites.

    14. Photocontrol of the Basal Spacing of Azobenzene–Magadiite Intercalation Compound (pages 1107–1109)

      M. Ogawa, T. Ishii, N. Miyamoto and K. Kuroda

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1107::AID-ADMA1107>3.0.CO;2-O

      The intercalation of a cationic azobenzene derivative into the interlayer space of magadiite has been achieved. The spectral properties as well as the X-ray diffraction results reveal that the adsorbed azo cations form head-to-head aggregates in the interlayer space. The basal spacing of the intercalation compound changes reversibly upon photoisomerization of the intercalated azobenzene (see Figure).

    15. Recent Developments in Materials Synthesis and Processing Using Supercritical CO2 (pages 1111–1114)

      A. I. Cooper

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1111::AID-ADMA1111>3.0.CO;2-L

      Supercritical carbon dioxide attracts a lot of attention as an alternative solvent for materials processing and engineering thanks to “green” properties, such as low toxicity, non-flammability, and natural abundance. As highlighted here, some limitations associated with conventional techniques can be overcome by employing carbon dioxide as a solvent, especially for the processing of biomaterials and porous organic materials (see Figure).

    16. Materials Based on Glycoluril (pages 1115–1119)

      M. Kölbel and F. M. Menger

      Article first published online: 12 JUL 2001 | DOI: 10.1002/1521-4095(200107)13:14<1115::AID-ADMA1115>3.0.CO;2-Y

      Self-assembled capsules, molecular switches, nanoporous materials, and supramolecular gels are only a few of the applications that can be achieved by employing glycoluril. This compound has been known for 125 years and has not aged at all thanks to its unique geometry. The Figure shows a self-assembled container with phthalocyanine units that can serve as catalytic sites acting like nanoscopic reaction chambers.