Advanced Materials

Cover image for Advanced Materials

August, 2000

Volume 12, Issue 15

Pages 1099–1151

    1. Current/Voltage Characteristics of Monolayers of Redox-Switchable [2]Catenanes on Gold (pages 1099–1102)

      M. Asakawa, M. Higuchi, G. Mattersteig, T. Nakamura, A. R. Pease, F. M. Raymo, T. Shimizu and J. F. Stoddart

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1099::AID-ADMA1099>3.0.CO;2-2

      Redox-controllable molecular switches composed of two interlocking rings are incorporated here into Langmuir films starting from two different redox states. The morphologies of the resulting monolayers and their current–voltage characteristics are then investigated. These switches are considered to be ideal candidates for the fabrication of molecule-based electronic devices.

    2. Full Color Emission from II–VI Semiconductor Quantum Dot–Polymer Composites (pages 1102–1105)

      J. Lee, V. C. Sundar, J. R. Heine, M. G. Bawendi and K. F. Jensen

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1102::AID-ADMA1102>3.0.CO;2-J

      Nearly full color emission has been achieved using quantum dot (QD)–polymer composites. The fluorescence of the resulting composites spans the entire visible range with narrow emission profiles and high photoluminescence (PL) quantum yields. Moreover, mixed colors are easily produced by controlling the mixing ratio of different sized QDs. The Figure shows end-on rods of QD–polymer composites excited from underneath by a UV lamp.

    3. Thermo-Reversible Self-Assembly of Nanoparticles Derived from Elastin-Mimetic Polypeptides (pages 1105–1110)

      T. A. T. Lee, A. Cooper, R. P. Apkarian and V. P. Conticello

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1105::AID-ADMA1105>3.0.CO;2-1

      Large protein-based micellar aggregates (see Figure) are reversibly formed upon self-assembly of the amphiphilic diblock copolymer—based on elastin-mimetic peptide sequences—biosynthesized here. The biocompatibility, high recombinant protein yields, physiological stability, and tunable responsive properties of these polymers make them attractive candidates for controlled delivery and release applications.

    4. Excitation Transfer in Polymer Photodiodes for Enhanced Quantum Efficiency (pages 1110–1114)

      L. Chen, L. S. Roman, D. M. Johansson, M. Svensson, M. R. Andersson, R. A. J. Janssen and O. Inganäs

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1110::AID-ADMA1110>3.0.CO;2-T

      The realization of polymer solar cells is the driving force behind this research. In an idea inspired by photosynthesis, the authors have constructed efficient bilayer photodiodes by a well-chosen combination of conjugated polymers (see Figure) in the donor layer. Förster energy transfer within the donor layer allows the absorbed light to be channeled to the C60 acceptor layer, improving the total photoconversion of the blend device.

    5. Facile Assembly of Zeolite Monolayers on Glass, Silica, Alumina, and Other Zeolites Using 3-Halopropylsilyl Reagents as Covalent Linkers (pages 1114–1117)

      K. Ha, Y.-J. Lee, H. J. Lee and K. B. Yoon

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1114::AID-ADMA1114>3.0.CO;2-5

      Perfect one-dimensional orientation of zeolite microcrystals on glass can be obtained with very high surface coverage (see Figure), as demonstrated here. The approach, which involves covalently linking the zeolite to the glass, is highly efficient and can be extended to the assembly of zeolite crystals on other supports, such as silica, alumina, and other zeolites.

    6. Dendrimers with Thermally Labile End Groups: An Alternative Approach to Chemically Amplified Resist Materials Designed for Sub-100 nm Lithography (pages 1118–1122)

      D. C. Tully, A. R. Trimble and J. M. J. Fréchet

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1118::AID-ADMA1118>3.0.CO;2-I

      Chemically amplified resists based on dendritic polymer resins are investigated by these authors. The synthesis of the dendrimers, which are based on the polyfunctional core shown in the Figure, is described and properties such as Tdecomp and Tg are examined. Resist formulations prepared from these dendrimers are shown to be highly sensitive to both deep UV and e-beam exposure, allowing reproducible patterning well below 100 nm.

    7. Blue Electroluminescence from a Novel Donor/Acceptor Polymer Structure (pages 1122–1125)

      S.-C. Ng, H.-F. Lu, H. S. O. Chan, A. Fujii, T. Laga and K. Yoshino

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1122::AID-ADMA1122>3.0.CO;2-F

      The right balance in the rates of electron and hole injection is critical in order to achieve high-efficiency light-emitting diodes. Here is reported a new series of blue-emitting conjugated polymers (see Figure) comprising alternating π-rich phenylene and π-deficient pyridyl moieties prepared by a Suzuki coupling method. Devices prepared using the polymers showed strong blue emission at room temperature.

    8. Dichroism Induced by Photoisomerization of Aniline Tetramers in Polymeric Films (pages 1126–1129)

      C. R. Mendonça, D. S. dos Santos Jr., L. De Boni, D. T. Balogh, O. N. Oliveira Jr. and S. C. Zilio

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1126::AID-ADMA1126>3.0.CO;2-S

      Optically induced dichroism is observed here for aniline tetramers dispersed in polycarbonate films. This effect is attributed to molecular reorientation of the tetramers upon photoisomerization. It is shown that the reorientation process saturates with light intensity and its time evolution is biexponential. However, the optical data storage capability of this system is limited by the small amount of anisotropy conserved after relaxation. Improvement is believed to be possible by attaching the aniline tetramer as a side chain to the polymer backbone.

    9. Formation of a Buried Lateral Density Grating in Azobenzene Polymer Films (pages 1129–1132)

      U. Pietsch, P. Rochon and A. Natansohn

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1129::AID-ADMA1129>3.0.CO;2-A

      A density grating buried under a smooth surface is reported for an azobenzene-containing polymer film. The grating is formed by annealing a polymer sample pre-inscribed with a surface grating for several hours above Tg, creating a lateral density difference on the order of 10 %. It is shown that the rate of the process can be influenced by the intensity and polarization of the probe laser. Growth of photoinduced liquid–crystalline aggregates is proposed as the most probable explanation for the observed behavior.

    10. A Novel Intermediate-Temperature Oxygen-Permeable Membrane Based on the High Tc Superconductor Bi2Sr2CaCu2O8 (pages 1132–1134)

      C.-S. Chen, W. Liu, S. Xie, G.-G. Zhang, H. Liu, G.-Y. Meng and D.-K. Peng

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1132::AID-ADMA1132>3.0.CO;2-D

      Dense oxygen permeable membranes are expected to have a great impact on oxygen production and oxygen-involved industrial processes. This work demonstrates that Bi2Sr2-CaCu2O8, a well-known superconductor, is very permeable to oxygen at intermediate temperatures while remaining impervious to nitrogen and other gases. The Figure shows a possible mechanism for the process.

    11. Organic Light-emitting Devices Based on Phosphorescent Hosts and Dyes (pages 1134–1138)

      R. C. Kwong, S. Lamansky and M. E. Thompson

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1134::AID-ADMA1134>3.0.CO;2-1

      Phosphorescent dyes may lead to more efficient electroluminescent devices, since triplets should be formed in a 3-fold excess compared to singlets. Efficient devices are presented here that have been constructed using phosphorescent dye–doped layers as both the electron transporting and emitting layer. Triplet energy transfer from the host Ir(ppy)3 to the red phosphorescent dopant PtOX (see Figure) was observed directly.

    12. Improved Probes for Scanning Near-Field Optical Microscopy (pages 1139–1142)

      Y. D. Suh and R. Zenobi

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1139::AID-ADMA1139>3.0.CO;2-8

      Vastly improved fiber probes for SNOM microscopyare the result of a new chemical etching method. The optical fiber's protective polymer coating is left on during the etching process, which gives rise to greatly improved tip surfaces (see Figure, right). The tips have a much higher damage threshold, allowing brighter transmission and opening the door to Raman imaging (e.g. of DNA) and laser ablation.

    13. Polynitrocubanes: Advanced High-Density, High-Energy Materials (pages 1143–1148)

      P. E. Eaton, R. L. Gilardi and M.-X. Zhang

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1143::AID-ADMA1143>3.0.CO;2-5

      More powerful and less shock-sensitive explosives are continually being sought after for both military and commercial use. Here the qualities a potential candidate must possess to make a good explosive are detailed and the synthesis of octanitrocubane (see Figure)—a very promising candidate—is described. The physical properties of the nitrocubanes synthesized are also summarized and a proposal for the future is made.

    14. Bioskeletons as Templates for Ordered, Macroporous Structures (pages 1149–1151)

      R. Seshadri and F. C. Meldrum

      Version of Record online: 28 JUL 2000 | DOI: 10.1002/1521-4095(200008)12:15<1149::AID-ADMA1149>3.0.CO;2-6

      Ordered macroporous structures have been produced by templating echinoid (sea urchin) skeletal plates. Results are summarized that describe how the CaCO3 plates that form the test of the sea urchin provide excellent templates for producing porous structures. This extremely general method has been used in this case to create gold with 15 μm pores (see Figure).