Advanced Materials

Cover image for Advanced Materials

July, 1999

Volume 11, Issue 10

Pages 793–876

    1. Cracks and Atoms (pages 793–806)

      Dominic Holland and Michael Marder

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<793::AID-ADMA793>3.0.CO;2-B

      Atomic features are essential for understanding some materials properties. The example of brittle fracture is reviewed here, concentrating on molecular dynamics simulations of silicon. The Figure shows a visualization of an unstable crack at 8.97 % strain along (111). The choice of the potential, the implementation of non-zero temperature, and comparison of the results with experiment are particularly emphasized.

    2. Anodic Polymerization of Phenol-Modified Biotin: Patterned Deposition and Layer Characterization (pages 809–814)

      Jürgen Mack, Dietmar Leipert, Antonella Badia, Wolfgang Knoll and Günther Jung

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<809::AID-ADMA809>3.0.CO;2-J

      An approach to the immobilization of compounds on surfaces that should also be applicable to combinatorial libraries is described. The attachment of an electrochemically polymerizable phenol group to molecules, in this case biotin, followed by anodic polymerization is shown to yield thin insulating layers. When the polymerization takes place in several mini-cells simultaneously, the parallel immobilization of substances can be achieved. The characterization of layers of three anodically polymerized biotinylated phenols is also described in detail.

    3. Selective Growth of Poly(p-phenylene vinylene) Prepared by Chemical Vapor Deposition (pages 814–820)

      Kathleen M. Vaeth and Klavs F. Jensen

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<814::AID-ADMA814>3.0.CO;2-Z

      Spontaneous selective deposition of poly(p-phenylene vinylene) (PPV) by chemical vapor deposition is demonstrated for substrates treated with PPV-growth-inhibiting layers of iron. The Figure shows a Nomarski image of selectively grown parylene-N (squares) and PPV (black square spiral) integrated onto the same substrate; the electroluminescent device shows spatially defined regions of luminescence.

    4. A Combinatorial Study of the Dependence of Organic LED Characteristics on Layer Thickness (pages 821–826)

      Christoph Schmitz, Mukundan Thelakkat and Hans-Werner Schmidt

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<821::AID-ADMA821>3.0.CO;2-6

      Optimization of the device structure of organic light-emitting diodes (OLEDs) is required for improved reliability and performance. An apparatus is described that enables a matrix of OLEDs to be fabricated in a single experiment, i.e., under comparable conditions, on a single substrate by combinatorial techniques. It is demonstrated that the influence of layer thickness variation of one or more layers on the device performance can be easily studied—as illustrated on the cover of this issue. The technique is also suitable for the fast screening and optimization of materials.

    5. Low Energy Electron Degradation of Poly(p-phenylenevinylene) (pages 826–832)

      Per Bröms, Nicklas Johansson, Richard W. Gymer, Stephen C. Graham, Richard H. Friend and William R. Salaneck

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<826::AID-ADMA826>3.0.CO;2-N

      Quenching of the electroluminescence of polymer LEDs by the application of an aluminum protective layer by electron-beam evaporation has been investigated. It is shown that the secondary electrons present whenever the electron beam is on are responsible for the degradation. The Figure illustrates how the poly (p-phenylene vinylene) device was masked to rule out the involvement of X-rays.

    6. Ion Transport in Glassy Side-Group Liquid Crystalline Polymer Electrolytes (pages 832–834)

      Corrie T. Imrie, Malcolm D. Ingram and Gillian S. McHattie

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<832::AID-ADMA832>3.0.CO;2-Z

      Enhanced cation transport in polymer electrolytes, with consequent improved performance in batteries and other electrochemical applications, is reported. In general, ionic transport in polymer electrolytes is closely coupled to segmental motion of the backbone, leading to severely restricted cation mobility as the glass transition temperature Tg is approached. In the new side-group liquid-crystalline polymer electrolyte system described here, the ionic conductivity is shown to be insensitive to Tg, with sub-Tg conductivities of ∼10–5 S cm–1. An explanation for this behavior is proposed.

    7. Dissolution of Single-Walled Carbon Nanotubes (pages 834–840)

      Mark A. Hamon, Jian Chen, Hui Hu, Yongsheng Chen, Misha E. Itkis, Apparao M. Rao, Peter C. Eklund and Robert C. Haddon

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<834::AID-ADMA834>3.0.CO;2-R

      The solubility properties of single-walled carbon nanotubes (SWNTs) and the factors that control the dissolution of these materials have been investigated in detail. The authors report a number of strategies that lead to soluble SWNTs, in particular the covalent attachment of long alkyl chains to the carboxylic acid–terminated SWNTs shown in the Figure (produced by the purification process) via formation of amides and by formation of zwitterions by an acid–base reaction.

    8. Wet-Chemical Synthesis of Doped Colloidal Nanomaterials: Particles and Fibers of LaPO4:Eu, LaPO4:Ce, and LaPO4:Ce,Tb (pages 840–844)

      Heike Meyssamy, Karsten Riwotzki, Andreas Kornowski, Sabine Naused and Markus Haase

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<840::AID-ADMA840>3.0.CO;2-2

      Oxide materials doped with lanthanide ions are technologically important, for example as laser materials and in lighting applications. Here the wet-chemical synthesis of lanthanide-doped nanomaterials, which may eventually find applications in new optoelectronic devices, is reported. It is shown that lanthanide-doped LaPO4 nanomaterials can be prepared in the high-temperature monazite phase in two morphologies—particles and fibers—via a low-temperature synthesis. The symmetry of the main dopant site was determined from the Eu3+ emission to be the same as in bulk LaPO4.

    9. A Simple Route to Silicon-Based Nanostructures (pages 844–847)

      Yan Qiu Zhu, Wei Bing Hu, Wen Kuang Hsu, Mauricio Terrones, Nicole Grobert, Turgay Karali, Humberto Terrones, Jonathan P. Hare, Peter D. Townsend, Harold W. Kroto and David R. M. Walton

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<844::AID-ADMA844>3.0.CO;2-N

      High-quality Si or SiC nanowires sheathed with SiOx (shown in the Figure; the SiOx sheath is lighter in the transmission electron micrograph) are reported to be produced by direct heating of SiC under CO atmosphere in the presence of iron powder or ferrocene. This simple route is also shown to lead to three-dimensional SiO2 nanoflowers if fine Co power is used as the catalyst instead of iron. Quasi-one-dimensional nanostructures have potential in applied nanotechnology.

    10. A Novel Chemical Route to ZnTe Semiconductor Nanorods (pages 847–850)

      Yadong Li, Yi Ding and Zhaoyu Wang

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<847::AID-ADMA847>3.0.CO;2-B

      ZnTe is an attractive material for various opto-electronic devices; however, conventional methods of preparation of nanocrystalline metal tellurides have the limitation of requiring noxious compounds, such as H2Te, or organometallic compounds. Here is reported a solvothermal synthesis for ZnTe, using Zn and Te, with hydrazine hydrate as the solvent. The method was found to produce well-crystallized nanorods in 80–90% yield and to be strongly solvent dependent, in that the hydrazine acts not only as an electron transfer medium, but also as a strong electron donor.

    11. A Novel Ultraviolet Irradiation Photoreduction Technique for the Preparation of Single-Crystal Ag Nanorods and Ag Dendrites (pages 850–852)

      Yong Zhou, Shu H. Yu, Cui Y. Wang, Xiao G. Li, Yu R. Zhu and Zu Y. Chen

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<850::AID-ADMA850>3.0.CO;2-Z

      Single crystal Ag nanorods and elegant highly ordered dendriticsupramolecular nanostructures (see Figure) of Ag nanoparticles have been prepared via a novel ultraviolet photoreduction technique at room temperature using poly(vinylalcohol) (PVA) as protection agent. The concentration of both the PVA and AgNO3 play a significant role in the growth of the nanorods and dendrites.

    12. High Luminescence Gold(I) and Copper(I) Complexes with a Triplet Excited State for Use in Light-Emitting Diodes (pages 852–857)

      Yuguang Ma, Chi-Ming Che, Hsiu-Yi Chao, Xuemei Zhou, Wing-Han Chan and Jiaocong Shen

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<852::AID-ADMA852>3.0.CO;2-R

      Electroluminescence (EL) from the triplet excited statewould extend the range of EL materials able to be used as the emitting layer of organic EL devices from traditional singlet materials to triplet materials such as transition metal complexes. In the EL spectra reported here for highly luminescent gold(I) and copper(I) complexes, the triplet emission intensity is enhanced, while the singlet emission becomes a weak shoulder. This suggests that EL from the triplet state has a larger quantum efficiency than that from the singlet excited state. The bimolecular reaction between triplet excitons is discussed.

    13. Direct Observation of Mesoporous Silica by High Resolution Scanning Electron Microscopy (pages 857–860)

      Hirokatsu Miyata and Kazuyuki Kuroda

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<857::AID-ADMA857>3.0.CO;2-7

      The direct observation of 2D mesoporous silica by HRSEM(high resolution scanning electron microscopy) is reported here for the first time. The HRSEM images reveal that the structure consists of hexagonally packed short silicate rods (shown schematically in the Figure), which helps to explain the observed properties of mesoporous silica.

    14. Beyond the Bethe Limit: Tunable Enhanced Light Transmission Through a Single Sub-Wavelength Aperture (pages 860–862)

      Daniel E. Grupp, Henri J. Lezec, Tineke Thio and Thomas W. Ebbesen

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<860::AID-ADMA860>3.0.CO;2-V

      The possibility of controlling structures at the light-wavelength scalewould be of great consequence for near-field optical applications, such as microscopy and photolithography. These authors have created an artificial 2D crystal structure in a surrounding silver-metal film with which they demonstrate control and enhancement of the light from a single subwavelength aperture, showing a way around the Bethe limit for the transmission through a single hole. In addition the transmission can be tuned to a given wavelength through the proper design of the 2D lattice.

    15. Conclusive Demonstration of the Ferromagnetic Nature of the Interaction Between Holmium(III) and Aminoxyl Radicals (pages 863–865)

      Jean-Pascal Sutter, Myrtil L. Kahn and Olivier Kahn

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<863::AID-ADMA863>3.0.CO;2-J

      Metal–organo magnetic interactions involving lanthanideshave become important in the search for molecular magnetic materials. Here is reported the synthesis of a holmium(III)–nitronyl oxide compound (see Figure). The temperature dependence of its magnetic susceptibility reveals that it has a ferromagnetic ground state, which verifies theoretical predictions.

    16. A Polyaniline with Near-Infrared Optical Response to Saccharides (pages 865–868)

      Erika Pringsheim, Ewald Terpetschnig, Sergey A. Piletsky and Otto S. Wolfbeis

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<865::AID-ADMA865>3.0.CO;2-B

      A sugar-binding polymer film capable of continuous sensingarises from the copolymerization of aniline and 3-aminophenylboronic acid. Its absorption spectrum between 500 and 800 nm undergoes large changes on addition of various saccharides at neutral pH, changes which are dependent on the saccharide concentration and are fully reversible. These films represent an interesting alternative to enzyme-based glucose sensors because of their ease of preparation, compatibility with LED and diode laser light sources, and their thermal and temporal stability.

    17. Hybrid Organic/Inorganic Langmuir–Blodgett Films. A Supramolecular Approach to Ultrathin Magnetic Films (pages 869–872)

      Eugenio Coronado and Christophe Mingotaud

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<869::AID-ADMA869>3.0.CO;2-W

      Thin organic films with interesting magnetic propertiessuch as the magnetic memory effect have been achieved using the Langmuir–Blodgett technique. Results are summarized in this report whereby polyoxometalate anions containing magnetically active transition metals have been incorporated as layers of discrete clusters (see Figure) between monolayers of behenic acid.

    18. Lost Silicon Mold Process for PZT Microstructures (pages 873–876)

      Shinan Wang, Jing-Feng Li, Katsuhiro Wakabayashi, Masayoshi Esashi and Ryuzo Watanabe

      Version of Record online: 22 JUL 1999 | DOI: 10.1002/(SICI)1521-4095(199907)11:10<873::AID-ADMA873>3.0.CO;2-F

      Lead zirconate titanate (PZT) is an excellent piezoelectric actuator,however, its usefulness has been limited by its requirement for a high driving voltage. Here is described a novel silicon mold process that uses a combination of Si micromachining and ceramic sintering. The process yields many-layer PZT structures (giving larger actuator forces) with very thin plates (allowing the actuator to be driven with a lower voltage), intercalated by Si electrodes. These ceramic microstructures possess finer feature sizes and higher aspect ratios.