Advanced Materials

Cover image for Advanced Materials

November, 2000

Volume 12, Issue 21

Pages 1563–1632

    1. ICSM 2000 and the Advanced Materials Innovation Prize (page 1563)

      E. G. Levy

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1563::AID-ADMA1563>3.0.CO;2-J

      In order to encourage and reward young scientists carrying out research in the field of synthetic metals, the Advanced Materials Innovation Prize was created and awarded for the first time at The International Conference on the Science and Technology of Synthetic Metals (ICSM) 2000 at Bad Gastein, Austria, this year. To find out who won, turn to page 1563.

    2. ICSM 2000: Over Twenty-Five Years of Synthetic Metals (pages 1565–1570)

      J. R. Reynolds and A. J. Epstein

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1565::AID-ADMA1565>3.0.CO;2-7

      The International Conference on the Science and Technology of Synthetic Metals (ICSM), its impact on the scientific community, and the rapid progress that has occurred throughout this broad field of materials science are reflected upon. These meetings are held in beautiful and stimulating locations around the world as exemplified by the Figure.

    3. GaN Electronics (pages 1571–1580)

      S. J. Pearton and F. Ren

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1571::AID-ADMA1571>3.0.CO;2-T

      Gallium nitride electronic devices for high-power, high-temperature applications are reviewed here. Devices ranging from heterostructure field effect transistors (HFETs) and heterojunction bipolar transistors, to Schottky and p–i–n rectifiers are discussed. The Figure shows a schematic of a planar diode fabricated with p-guard rings, such edge termination methods being shown to significantly increase reverse breakdown voltage in GaN diode rectifiers.

    4. Microporous Honeycomb-Structured Films of Semiconducting Block Copolymers and Their Use as Patterned Templates (pages 1581–1583)

      B. de Boer, U. Stalmach, H. Nijland and G. Hadziioannou

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1581::AID-ADMA1581>3.0.CO;2-R

      Two-dimensional honeycomb-structured films have been prepared using a new light-emitting rod–coil block copolymer. Carbon disulfide was used to drop-cast the films, during the cooling of which water droplets condensed on the still-liquid surface and organized themselves in a highly regular fashion. The resulting porous films were then used as templates for a two-dimensional array of aluminum microdots (see Figure).

    5. Inhomogeneous Photon Emission Properties of Self-Assembled Metallic Nanocrystals (pages 1583–1587)

      A. O. Gusev, A. Taleb, F. Silly, F. Charra and M.-P. Pileni

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1583::AID-ADMA1583>3.0.CO;2-F

      Nanocrystal particle mobility and quenching of photon emission are reported to be correlated. During a study of photon emission from self-organized arrays of nanocrystals induced by interaction with the tip of a scanning tunneling microscope (STM), a comparison of photon maps with STM images revealed large variations in photon emission efficiency depending on how tightly a nanoparticle is embedded in the hexagonal network. This quenching–mobility correlation is explained in terms of electron relaxation processes involving the nanocrystals' surface phonon modes.

    6. Color-Tunable Highly Polarized Emissions from Uniaxially Aligned Thin Films of Thiophene/Phenylene Co-oligomers (pages 1587–1591)

      Y. Yoshida, N. Tanigaki, K. Yase and S. Hotta

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1587::AID-ADMA1587>3.0.CO;2-S

      Epitaxial growth of thiophene/phenylene co-oligomers(e.g., see Figure) on uniaxially oriented poly(p-phenylene) (PPP) is reported. The emission properties of these co-oligomer thin films are investigated and compared to those of films grown on quartz. Color-tunable emission highly polarized along the direction of orientation of the PPP is observed in the former case, while isotropic emission occurs on the quartz substrate.

    7. High-Efficiency Organic Electroluminescent Devices Using an Organoterbium Emitter (pages 1591–1594)

      S. Capecchi, O. Renault, D.-G. Moon, M. Halim, M. Etchells, P. J. Dobson, O. V. Salata and V. Christou

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1591::AID-ADMA1591>3.0.CO;2-P

      A new, highly luminescent terbium complex (see Figure) is investigated here as a material for organic light-emitting diodes (OLEDs). It is demonstrated that device efficiencies of over 2.6 lm/W are possible—the highest yet reported for a lanthanide-based OLED. This indicates that lanthanide-based materials are a viable alternative to Alq- and PPV-based polymers for use in commercial OLED displays.

    8. Doping in Solution as an Order-Inducing Tool Prior to Film Formation of Regio-Irregular Polyalkylthiophenes (pages 1594–1597)

      J. J. Apperloo, R. A. J. Janssen, M. M. Nielsen and K. Bechgaard

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1594::AID-ADMA1594>3.0.CO;2-7

      Favorable alignment of regio-irregular poly(3-alkylthiophene)s in a film can be attained, despite the fact that these polymers lack an intrinsic tendency to form well-ordered supramolecular aggregates. As reported here, alignment can be achieved simply by oxidizing the polymer in solution prior to film formation. A delicate balance between the degree of order and the level of oxidation in solution is observed. These results point to a way to improve charge transport efficiency, which is influenced by intra- and interchain order in the polymer.

    9. Synthesis and Photochromic Properties of New Bisthienylethene Derivatives and a Copolymer (pages 1597–1600)

      H. Tian and H.-Y. Tu

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1597::AID-ADMA1597>3.0.CO;2-Q

      Bisthienylethene (BTE)–based photochromic switches exhibit high resistivity, rapid response, and thermal and photo-stability. The synthesis of the BTE derivative shown in the Figure, a new kind of structure for photochromic polymers, is reported. The switching properties—including photo-fatigue resistance—of 1 and its copolymer with methyl methacrylate are detailed.

    10. Combinatorial Generation and Analysis of Nanometer- and Micrometer-Scale Silicon Features via “Dip-Pen” Nanolithography and Wet Chemical Etching (pages 1600–1603)

      D. A. Weinberger, S. Hong, C. A. Mirkin, B. W. Wessels and T. B. Higgins

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1600::AID-ADMA1600>3.0.CO;2-6

      In dip-pen nanolithography, molecules are “written” onto substrates using an atomic force microscope tip. It is shown here that nanostructures generated using this technique can be used as resists for generating three-dimensional multilayered solid-state structures such as that shown in the Figure (a Au/Ti/Si trilayer nanoscale pillar) via wet chemical etching (see also cover).

    11. New High-Yield Luminescent Materials Obtained by Combining Terpyridine, Metal Cations (Including Lanthanides), and Poly(Ethylene Glycol) (pages 1603–1605)

      V. Bekiari and P. Lianos

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1603::AID-ADMA1603>3.0.CO;2-P

      Efficient luminescent materials in solution, powder, or thin-film form are made here by combining poly(ethylene glycol) (PEG), terpyridine, and metal cations. Strong green emitters with a luminescence yield as high as 0.63 are reported for terpyridine–metal ion complexes suspended in liquid PEG. Evidence is presented that the structure of the luminescence spectrum is independent of the metal ion used, while luminescent lanthanides completely lose their emission characteristics. In contrast, solid ternary lanthanide–terpyridine–PEG complexes display emission characteristic of the lanthanide ion.

    12. Synthesis of Silicon Nanoclusters by Solid–Gas Reaction (pages 1605–1610)

      J. Acker, K. Bohmhammel, E. Henneberg, G. Irmer, I. Röver and G. Roewer

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1605::AID-ADMA1605>3.0.CO;2-D

      Silicon nanoparticles have been prepared by many methods, depending on whether porous, amorphous, or crystalline silicon is required. The advantages of the novel solid–gas chemical reaction reported here are that large amounts can be produced in a convenient way, the particles have a very narrow size range, and there is enormous potential for modification of the size and surface of the particles. Details of the synthesis via reaction of lanthanum or LaCl3 with a gaseous mixture of silicon tetrachloride and hydrogen, together with the subsequent characterization of the product, are presented.

    13. New Organic Semiconductor Based on Tetrathiafulvalene and Squarate Radical Ions: Electrochemical Synthesis and Characterization (pages 1610–1614)

      G. Farnia, F. Marcuzzi, M. Meneghetti and G. Sandonà

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1610::AID-ADMA1610>3.0.CO;2-4

      A new organic semiconductor has been synthesized by combination of squaric acid radical anions, tetrathiafulvalene radical cations, and tetrathiafulvalene neutral molecules. Electrochemistry was utilized to oxidize the two reagents and to crystallize the material, which grew in rosettes of needles (see Figure). The semiconducting behavior is concluded to arise from interactions along the tetrathiafulvalene stacks.

    14. Micropatterning of Oriented Zeolite Monolayers on Glass by Covalent Linkage (pages 1614–1617)

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

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1614::AID-ADMA1614>3.0.CO;2-H

      The organization of micrometer-sized zeolite (ZSM-5) crystals into micropatterned, uniformly oriented monolayers on glass (see SEM image) is reported. The simple yet highly versatile process, which has many advantages over conventional molding and heating methods, is based on the formation of covalent links by microcontact printing.

    15. Ambient Monocomponent Ferroelectric Liquid Crystals with a Wide Smectic-C* Range (< –20 to ≤ 65 °C) (pages 1617–1619)

      P. A. Kumar and V. G. K. M. Pisipati

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1617::AID-ADMA1617>3.0.CO;2-#

      Monocomponent ferroelectric liquid crystals based on L-tyrosine (see Figure) are investigated here. It is shown that the series synthesized exhibits a wide ferroelectric thermal range between –20 °C and 65 °C as well as a high magnitude of spontaneous polarization. Hence these materials are a promising alternative to multi-component systems for optical display applications.

    16. Extending the Lifetime of Ceramic Orthopaedic Implants (pages 1619–1621)

      J. Chevalier, A. H. De Aza, G. Fantozzi, M. Schehl and R. Torrecillas

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1619::AID-ADMA1619>3.0.CO;2-O

      A new generation of alumina–zirconia nanocomposites (see Figure: brighter phase, ZrO2; darker phase, Al2O3) for orthopaedic implants is described. These materials, prepared via a new colloidal synthesis route, are shown to have a high resistance to crack propagation. Thus it may be possible to improve the lifetime and reliability of ceramic joint prostheses.

    17. Microwave Synthesis and Consolidation of Gadolinium Aluminum Perovskite, a Ceramic Extraordinaire (pages 1621–1624)

      M. Panneer Selvam and K. J. Rao

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1621::AID-ADMA1621>3.0.CO;2-X

      The synthesis of gadolinium aluminum perovskite (GAP) in under 1 min via microwave irradiation is presented here. Pellets of the thus-formed GAP transform into a translucent ceramic of very high fracture toughness upon sintering in the microwave oven. In contrast, conventional heating yields an opaque material. The Figure shows the microstructure of microwave-sintered, polished, and etched GAP.

    18. Structure and Physical Properties of Tailor-Made Ce,Zr-Doped Carbon Aerogels (pages 1625–1628)

      E. Bekyarova and K. Kaneko

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1625::AID-ADMA1625>3.0.CO;2-9

      Carbon aerogels with controlled porositycan be obtained by doping Ce and/or Zr into the resorcinol–formaldehyde reaction mixture. As highlighted here, the concentration of metal dopant and the pH of the initial reaction mixture can have a profound effect on the structure, porosity, and physical properties of the resulting aerogel. The Figure shows the morphology of a Ce,Zr-doped carbon aerogel synthesized at pH 7.

    19. Crystallization of Mesoscopic Colloids into 3D Opaline Lattices in Packing Cells Fabricated by Replica Molding (pages 1629–1632)

      B. T. Mayers, B. Gates and Y. Xia

      Article first published online: 3 NOV 2000 | DOI: 10.1002/1521-4095(200011)12:21<1629::AID-ADMA1629>3.0.CO;2-M

      For the self-assembly of mesoscopic colloids into 3D opaline lattices via the hydrodynamic flow/physical confinement method, the packing cells had to be patterned and fabricated in a clean room. Here an alternative fabrication method is described that uses replica molding against an elastomeric mold to generate packing cells under normal laboratory conditions. The bottom part of a packing cell is shown schematically in the Figure.