Advanced Materials

Cover image for Advanced Materials

September, 2000

Volume 12, Issue 17

Pages 1237–1302

    1. Organogels and Low Molecular Mass Organic Gelators (pages 1237–1247)

      D. J. Abdallah and R. G. Weiss

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1237::AID-ADMA1237>3.0.CO;2-B

      Organogels from low molecular mass organic gelators (LMOGs) are able to be cycled between the liquid and the gel state, which is important for applications where on-demand flow is desirable. Their structural complexity can vary from simple alkanes to CEP (see Figure), which is known to form molecular wires when gelling chloroform. These authors discuss the relationship between structure and function and give an overview of present and potential applications.

    2. Application of Screen Printing in the Fabrication of Organic Light-Emitting Devices (pages 1249–1252)

      D. A. Pardo, G. E. Jabbour and N. Peyghambarian

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1249::AID-ADMA1249>3.0.CO;2-Y

      Screen printing as a new approach to fabricating and patterning OLEDs is reported here. The method allows the deposition of organic layers with less than 100 nm film thickness, and is reported to be versatile, simple, fast, and cost-effective, making it valuable for producing low information content displays. The Figure shows a photoluminescent image of a conducting-polymer logo printed using this technique.

    3. Fabrication of Nanometer-Scale Patterns by Ion-Milling with Porous Anodic Alumina Masks (pages 1252–1257)

      D. Almawlawi, K. A. Bosnick, A. Osika and M. Moskovits

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1252::AID-ADMA1252>3.0.CO;2-0

      The use of porous anodic alumina as a contact mask for ion-milling is demonstrated here to produce highly regular periodic arrays of nano-holes or bosses in an aluminum surface. The interaction of the molten aluminum with the alumina can be either wetting or non-wetting, according to the temperature of the melt, resulting in the formation of bosses (see Figure) or holes.

    4. Preferential Self-Assembly of Surface-Modified Si/SiOx Nanoparticles on UV/Ozone Micropatterned Poly(dimethylsiloxane) Films (pages 1257–1261)

      T. S. Phely-Bobin, R. J. Muisener, J. T. Koberstein and F. Papadimitrakopoulos

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1257::AID-ADMA1257>3.0.CO;2-7

      The specific self-assembly of Si/SiOxcore–shell nanoparticles onto UV/ozone micropatterned poly(dimethylsiloxane) (PDMS) films is reported here. Auger and Raman spectroscopic mapping document the preferential Si/SiOx nanoparticle adsorption within PDMS domains (see Figure). These nanoparticles display a high refractive index, which renders them potentially important for photonic bandgap applications.

    5. Microfabrication of Ceramics by Filling of Photoresist Molds (pages 1261–1263)

      U. P. Schönholzer, R. Hummel and L. J. Gauckler

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1261::AID-ADMA1261>3.0.CO;2-4

      Filling of photo-resist molds is a new method for the generation of micropatterned ceramic surfaces. A flat substrate is first patterned with a photoresist. The ceramic coating is then applied to the substrates by pouring 50 vol.-% alumina suspension over the mold, excess material being removed with a polymer blade (see Figure). Alumina structures of high quality were produced on silicon wafers and on sapphire single crystals.

    6. Electrodeposited Nanocomposite n–p Heterojunctions for Solid-State Dye-Sensitized Photovoltaics (pages 1263–1267)

      B. O'Regan, D. T. Schwartz, S. M. Zakeeruddin and M. Grätzel

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1263::AID-ADMA1263>3.0.CO;2-T

      A new electrodeposition method for making porous ZnO layers with highly oriented and columnar morphology is reported here. A monolayer of dye is adsorbed onto the ZnO followed by electrodeposition of p-type CuSCN to create a complete inner-surface electrical contact, resulting in a bicontinuous-network heterojunction (see Figure) to give a photovoltaic cell showing record conversion efficiency.

    7. Electrooptic Effects in the Nematic and Isotropic Phases of Aqueous V2O5 Suspensions (pages 1267–1270)

      S. Lamarque-Forget, O. Pelletier, I. Dozov, P. Davidson, P. Martinot-Lagarde and J. Livage

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1267::AID-ADMA1267>3.0.CO;2-5

      In water-based lyotropic liquid crystals (LCs), e.g., aqueous suspensions of V2O5, the electrooptical effects typical of thermotropic mesophases are difficult to observe, owing to the large conductivity and electrochemical reactions of the suspensions. Overcoming these difficulties, the authors demonstrate that V2O5 aqueous nematic suspensions can be aligned and even reoriented in a low AC electric field—in addition to the recently reported slow (30 min) alignment in magnetic fields. The response time of ∼1 s indicates that mineral LCs may be suitable for simple display applications.

    8. Electron Trapping in Dye/Polymer Blend Photovoltaic Cells (pages 1270–1274)

      J. J. Dittmer, E. A. Marseglia and R. H. Friend

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1270::AID-ADMA1270>3.0.CO;2-8

      Charge separation and charge transport have been limiting factors in photovoltaic cells that utilize conjugated polymer blends. These authors have exploited the ability of a soluble perylene dye (see Figure) to form crystals within a polymer matrix to achieve a blend that enables good charge transfer and separation, due largely to the crystals' ability to act as electron traps.

    9. Highly Photoconductive Nanocomposites of Metallophthalocyanines and Conjugated Polymers (pages 1274–1278)

      S. A. Jenekhe and S. Yi

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1274::AID-ADMA1274>3.0.CO;2-L

      Highly photoconductive devices with very broad absorbance spectra are presented here. These double-layer devices consist of nanocrystals of titanyl phthalocyanine (see Figure, M=TiO) dispersed in thin films of a conjugated ladder polymer (BBL). The presence of the BBL increases the spectral range for commercial TiOPc by several hundred nanometers, opening a new spectral range for photosensitive devices.

    10. Polygermyne—A Prototype System for Layered Germanium Polymers (pages 1278–1281)

      G. Vogg, M. S. Brandt and M. Stutzmann

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1278::AID-ADMA1278>3.0.CO;2-Y

      Crystalline polygermyne—a new compound consisting of H-terminated germanium double layers (see Figure) stacked to form a three-dimensional crystal—is reported to have been produced by the topochemical transformation of epitaxial thin CaGe2 films at –30 °C. Polygermyne is found to exhibit strong near-infrared photoluminescence with an intensity comparable to that of siloxene, its silicon homologue.

    11. Amplified Spontaneous Emission from Fluorescent-Dye-Doped DNA–Surfactant Complex Films (pages 1281–1283)

      Y. Kawabe, L. Wang, S. Horinouchi and N. Ogata

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1281::AID-ADMA1281>3.0.CO;2-0

      Laser action in a DNA host is presented here for thin films composed of rhodamine 6G dye intercalated in salmon DNA (shown schematically in the Figure). Recent reports of the semiconducting properties of DNA inspired these authors to investigate its effects in solid-state dye lasing. Amplified spontaneous emission with spectral line narrowing was observed under nanosecond optical pumping.

    12. Glassy Liquid-Crystal Films with Opposite Chirality as High-Performance Optical Notch Filters and Reflectors (pages 1283–1286)

      H. P. Chen, D. Katsis, J. C. Mastrangelo, S. H. Chen, S. D. Jacobs and P. J. Hood

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1283::AID-ADMA1283>3.0.CO;2-P

      Glass-forming liquid crystals combine the ability of liquid crystals to self-organize and that of polymers to undergo glass transition (instead of crystallization) upon cooling. Here is reported the synthesis and implementation of novel right- and left-handed chiral-nematic glass-forming liquid crystals in optical notch filters and reflectors, which have various applications in liquid-crystal displays. The observed attenuation of incident unpolarized light in 3.7 optical density units is the highest ever accomplished with organic and polymeric materials.

    13. Vesicle-Directed Growth of Silica (pages 1286–1290)

      D. H. W. Hubert, M. Jung, P. M. Frederik, P. H. H. Bomans, J. Meuldijk and A. L. German

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1286::AID-ADMA1286>3.0.CO;2-7

      Silica-coated vesicles have been produced by the deposition of silica onto unilamellar vesicles from aqueous solution for the first time. The quaternary ammonium surface of the surfactant vesicles is receptive to silica and facilitates deposition of up to 5–10 nm of it. The “petrified” vesicles are stable to dehydration and can be visualized by conventional TEM (see Figure) without additional staining agents.

    14. Vesicle Templating (pages 1291–1294)

      D. H. W. Hubert, M. Jung and A. L. German

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1291::AID-ADMA1291>3.0.CO;2-Z

      Vesicle templating presents a unique opportunity to construct submicrometer hollow particles. These authors give an overview of recent developments, discussing both polymerization inside the vesicle membrane, and growth on the outer surface of the vesicle (see Figure). Successful vesicle templating requires an understanding of the interactions between the vesicle bilayer, the polymer precursor, and the growing material.

    15. Characterizing the Structure and Properties of Individual Wire-Like Nanoentities (pages 1295–1298)

      Z. L. Wang

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1295::AID-ADMA1295>3.0.CO;2-B

      A new approach to measuring the properties of individual nanowires and nanotubes—in-situ transmission electron microscopy (TEM)—is presented here. The technique allows the determination of both the structure and properties (mechanical, electrical, field-emission) of individual nanowires. Recent developments, including determination of the Young's modulus (the Figure shows a resonating Si nanowire), are summarized here.

    16. Manipulation and Imaging of Individual Single-Walled Carbon Nanotubes with an Atomic Force Microscope (pages 1299–1302)

      H. W. C. Postma, A. Sellmeijer and C. Dekker

      Version of Record online: 13 SEP 2000 | DOI: 10.1002/1521-4095(200009)12:17<1299::AID-ADMA1299>3.0.CO;2-O

      Carbon nanotube junctions have been created using the tip of an atomic force microscope. Individual single-walled nanotubes have been manipulated on a SiO2 surface to produce buckles, bends, and crossings, and also to unravel a nanotube “crop circle” (see Figure), the arrows indicating the path the AFM tip has traveled in each manipulation step. The creation of such artificial junctions and bends opens a route to nanotube transport studies.