Advanced Materials

Cover image for Advanced Materials

October, 2001

Volume 13, Issue 19

Pages 1431–1511

    1. Nanocomposite Materials Formed by Ion Implantation (pages 1431–1444)

      A. Meldrum, R. F., Jr. Haglund, L. A. Boatner and C. W. White

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1431::AID-ADMA1431>3.0.CO;2-Z

      Ion implantation is a versatile and powerful technique for synthesizing nanometer-scale clusters and crystals embedded in the near-surface region of a variety of hosts in order to create nanocomposite materials with often unique properties. Some of the principal features of this nanophase materials synthesis technique (see Figure), as well as the materials properties that are exhibited by nanocomposites created using ion beams, are reviewed.

    2. Rubbed Films of Functionalized Bovine Serum Albumin as Substrates for the Imaging of Protein–Receptor Interactions Using Liquid Crystals (pages 1445–1449)

      S.-R. Kim and N. L. Abbott

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1445::AID-ADMA1445>3.0.CO;2-9

      Rubbing is an essential pre-treatment for covalently immobilized, receptor-functionalized films of bovine serum albumin to function in liquid-crystal (LC) imaged protein chips. Only on the rubbed film will LCs form a nematic phase whose disruption by docking target protein is specific and quantifiable using polarized light. The Figure shows the appearance at two anti-biotin IgG concentrations, the polarizer aligned with the direction of rubbing (left) and shifted by 45° (right).

    3. Fabrication of Polymer Thin Films and Arrays with Spatial and Topographical Controls (pages 1449–1451)

      M. A. Bartlett and M. Yan

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1449::AID-ADMA1449>3.0.CO;2-M

      An easy and versatile photochemical procedure for immobilizing polymer films on silicon wafers has been developed by the authors. An organic azide, covalently linked to the wafer surface, serves as the precursor of a reactive nitrene that inserts into C–H bonds in the polymer. Due to the photochemical nature of the process, patterns of different polymers can be created by use of opaque masks. The Figure shows an AFM image of a polystyrene/poly-(2-ethyl-2-oxazoline) array on silicon wafer.

    4. Self-Waveguided Gain-Narrowing of Blue Light Emission from Epitaxially Oriented p-Sexiphenyl Crystals (pages 1452–1455)

      H. Yanagi, T. Ohara and T. Morikawa

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1452::AID-ADMA1452>3.0.CO;2-P

      The fabrication of microwaveguides from self-organized single crystals of p-phenylene oligomers is proposed here—one step towards the realization of room-temperature organic continuous-wave lasers. p-Sexiphenyl (p-6P, see Figure) is more stable than other common emissive molecules for organic electroluminescence devices and is shown to be a promising candidate for an organic semiconductor blue laser.

    5. Layer-by-Layer Assembly of PEDOT/Polyaniline Electrochromic Devices (pages 1455–1459)

      D. DeLongchamp and P. T. Hammond

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1455::AID-ADMA1455>3.0.CO;2-7

      A fully functional switchable chromic device (see Figure) in which complementary coloration is achieved from electrostatically assembled films containing poly(aniline) (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT) is demonstrated. The color changes accompanying doping and undoping are reversible and present true optical contrast.

    6. Emulsion Templating Using High Internal Phase Supercritical Fluid Emulsions (pages 1459–1463)

      R. Butler, C. M. Davies and A. I. Cooper

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1459::AID-ADMA1459>3.0.CO;2-K

      A new method for producing well-defined porous materials by templating scCO2 emulsions is revealed here. The technique involves forming a high internal phase emulsion (HIPE) and locking in the structure of the “external” phase. By this method it is also possible to produce templated, crosslinked poly-(vinyl alcohol) (PVA) materials (see Figure and also inside front cover).

    7. Pure Silica Zeolite Films as Low-k Dielectrics by Spin-On of Nanoparticle Suspensions (pages 1463–1466)

      Z. B. Wang, A. Mitra, H. T. Wang, L. M. Huang and Y. Yan

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1463::AID-ADMA1463>3.0.CO;2-H

      The preparation of ultra low-k zeolite films with high mechanical strength by a simple spin-on process is demonstrated. Continuous, smooth, thin zeolite silicalite films with a dielectric constant of 2.1 and elastic modulus of 16–18 GPa are obtained by this process, which is simple and compatible with the requirements of the semiconductor manufacturers. Polishing experiments showed that the film is potentially compatible with chemical mechanical polishing (CMP). The described pure silica film could be an attractive candidate for ultra-low-k materials for future generation microprocessors.

    8. Electromechanical Writing on Silver Ion Conductors (pages 1466–1468)

      A. Spangenberg, J. Fleig and J. Maier

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1466::AID-ADMA1466>3.0.CO;2-#

      The cathodic deposition of silver on AgCl occurs preferentially in mechanically pre-structured tracks, which is probably related to the higher surface energy in such tracks. This effect can be used to write miniaturized and complex metal structures on solid electrolytes. These experiments also demonstrate that AFM micro-tips are very appropriate to observe the cathodic deposition process in situ (see Figure).

    9. Tin Dioxide Opals and Inverted Opals: Near-Ideal Microstructures for Gas Sensors (pages 1468–1472)

      R. W. J. Scott, S. M. Yang, G. Chabanis, N. Coombs, D. E. Williams and G. A. Ozin

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1468::AID-ADMA1468>3.0.CO;2-O

      Periodic macroporous forms of nc-SnO2 have been synthesized by two methods, giving opals and inverse opals that can be used as structurally well-defined gas sensors, as demonstrated for CO gas, as well as for toluene and ethanol vapors. The inverse opals, in particular, seem to approximate “ideal” behavior. The Figure shows an SEM image of the amorphous SnO2 inverse opal structure after toluene extraction.

    10. Poly(L-lysine) Aggregates as Templates for the Formation of Hollow Silica Spheres (pages 1472–1476)

      K. J. C. van Bommel, J. H. Jung and S. Shinkai

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1472::AID-ADMA1472>3.0.CO;2-L

      A novel and facile method for the fabrication of hollow spherical silica is presented. Mixing poly(L-lysine) together with lipophilic amine additives in water results in the formation of large aggregates, which can be transcribed into their spherical silica analogues by the addition of tetraethylorthosilicate (TEOS). By varying the additives it has been established that the amino moieties of the additive, rather than those of the poly(L-lysine), play a crucial role in the transcription process.

    11. Indium Tin Oxide Alternatives—High Work Function Transparent Conducting Oxides as Anodes for Organic Light-Emitting Diodes (pages 1476–1480)

      J. Cui, A. Wang, N. L. Edleman, J. Ni, P. Lee, N. R. Armstrong and T. J. Marks

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1476::AID-ADMA1476>3.0.CO;2-Y

      High electrical conductivity, outstanding optical transparency, and work functions considerably greater than that of commercial indium tin oxide (ITO) organic light-emitting devices (OLEDs) have been obtained with non-ITO anodes. The Figure shows the crosslinked form of triarylamine (TAA), which is spin-coated on top of the anode to improve cohesion and charge injection efficiency.

    12. Selective Microorganism Detection with Cell Surface Imprinted Polymers (pages 1480–1483)

      O. Hayden and F. L. Dickert

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1480::AID-ADMA1480>3.0.CO;2-V

      Surface imprinting of polyurethane with yeasts allows selective and highly sensitive enrichment of microorganisms in flowing conditions. The selectivity of the highly robust sensor allows yeasts, gram positive, and gram negative bacteria to be distinguished. The surface imprinted polymers are truly an alternative to biological recognition layers, such as antibodies, as they operate with a high sensitivity and label-free detection. The results are encouraging to extend the search for artificial recognition sites to the micrometer scale.

    13. Functionalized Fluorinated Hyperbranched Polymers for Optical Waveguide Applications (pages 1483–1487)

      C. Pitois, D. Wiesmann, M. Lindgren and A. Hult

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1483::AID-ADMA1483>3.0.CO;2-D

      Fluorinated dendritic or hyperbranched polymers are demonstrated for the first time to be potentially useful for optical waveguide applications, for example in telecommunications. The required materials properties include the control of the refractive index over a wide range and UV-crosslinking for ease of processing and stable long-term mechanical properties. The authors report the synthesis of suitable functionalized fluorinated hyperbranched polymers and how the above requirements can be met by functionalization at the periphery of the polymers.

    14. Superconducting MgB2 Nanowires (pages 1487–1489)

      Y. Wu, B. Messer and P. Yang

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1487::AID-ADMA1487>3.0.CO;2-Q

      The novel superconductor MgB2 (TC = 39 K) is available as nanowires! Their synthesis has been achieved by a two-step protocol: Slightly Si-doped boron nanowires were generated by transport reaction, and treated with Mg vapor to form polycrystalline nanowires of MgB2 with diameters of 50–400 nm and lengths of several tens of micrometers (see Figure). Superconductivity was proven by a strong Meissner effect at 33 K.

    15. Bicrystalline Silicon Nanowires (pages 1489–1491)

      A. H. Carim, K.-K. Lew and J. M. Redwing

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1489::AID-ADMA1489>3.0.CO;2-E

      The synthesis of bicrystalline silicon nanowires containing a single (111) twin boundary along the entire length of the growth axis (see Figure and also cover) is revealed here. The wires are generally straight and contain no other defects. These unusual structures offer model systems for the study of charge and mass transport along single defects and could serve as templates for novel device structures.

    16. Preparation of Flexible Zeolite-Tethering Vegetable Fibers (pages 1491–1495)

      G. S. Lee, Y.-J. Lee, K. Ha and K. B. Yoon

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1491::AID-ADMA1491>3.0.CO;2-N

      A novel approach to assembling monolayers of zeolite-Y crystals on the surfaces of vegetable fibers, such as cotton, hemp, and linen, via covalent linkages is introduced. By polymer linkage the binding strength can be increased to such a degree that well over 90 % of the surface-lining zeolite crystal can endure sonication in toluene for 1 h. The Figure shows an SEM image of zeolite-Y crystals attached to the surface of cotton fibers.

    17. Stabilizing CdTe/CdS Solar Cells with Cu-Containing Contacts to p-CdTe (pages 1495–1499)

      K. D. Dobson, I. Visoly-Fisher, G. Hodes and D. Cahen

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1495::AID-ADMA1495>3.0.CO;2-#

      High efficiency CdTe/CdS thin-film solar cells require low resistance contacts to p-CdTe, which is frequently achieved by addition of Cu. Decreases in cell efficiency over time, however, have been associated with Cu from the contact. The question that is considered here is if Cu is really detrimental to cell performance? By performing a series of thermal stress tests the authors reach a far more optimistic conclusion than what has hitherto been assumed. The Figure shows the proposed model for action of Cu (and Cl) in the CdTe/CdS cell.

    18. Plasmonics—A Route to Nanoscale Optical Devices (pages 1501–1505)

      S. A. Maier, M. L. Brongersma, P. G. Kik, S. Meltzer, A. A. G. Requicha and H. A. Atwater

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1501::AID-ADMA1501>3.0.CO;2-Z

      Plasmon waveguides, which are based on resonance between collective motions in noble-metal nanoparticles and visible light, should be useful in building novel nanoscale optical devices; calculations predict that corner, switch, and splitter elements are feasible. Experiments with microwaves on macroscopic analogues confirm the guiding and splitting effects. The Figure shows a corner element made of 50 nm ∅, 75 nm spaced gold dots.

    19. Core–Shell Assembled Nanoparticles as Catalysts (pages 1507–1511)

      C. J. Zhong and M. M. Maye

      Version of Record online: 27 SEP 2001 | DOI: 10.1002/1521-4095(200110)13:19<1507::AID-ADMA1507>3.0.CO;2-#

      Recent insights into nanostructured core–shell reactivities and surprising findings of catalytic activities of oxide-supported gold nanoparticles suggest that the deliberate tailoring of nanoparticles supported on oxides, dispersed in dendrimers, and encapsulated in monolayers could generally lead to novel catalytic applications. The Figure shows an AFM image of a core–shell assembled gold nanoparticle sample.