Advanced Materials

Cover image for Vol. 14 Issue 18

September, 2002

Volume 14, Issue 18

Pages 1251–1326

    1. Contents: Adv. Mater. 18/2002 (pages 1251–1255)

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1251::AID-ADMA1251>3.0.CO;2-P

    2. Contents: Adv. Funct. Mater. 9/2002 (pages 1257–1259)

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1257::AID-ADMA1257>3.0.CO;2-Q

    3. Materials for Bio-inspired Optics (pages 1261–1264)

      G. Zuccarello, D. Scribner, R. Sands and L.J. Buckley

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1261::AID-ADMA1261>3.0.CO;2-N

      Biological vision systems and the unique material behaviors that give rise to these characteristics are current topics of interest highlighted in this essay. From the graded index of the fish-eye to the hyper-acuity of the compound eye, nature has provided function with amazing simplicity (see Figure). Bio-inspired optical systems have the potential to transform the process of image collection and analysis.

    4. Liquid Crystalline Nature of K4Nb6O17 Nanosheet Sols and Their Macroscopic Alignment (pages 1267–1270)

      N. Miyamoto and T. Nakato

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1267::AID-ADMA1267>3.0.CO;2-O

      Liquid crystallinity of layered niobate K4Nb6O17 colloidally dispersed via exfoliation has been achieved as evidenced by birefringence of the colloid (see Figure). Due to the large lateral size of the nanosheets, the liquid-crystalline state is stable down to low concentrations and macroscopic alignment is easily induced by gravitational force. Potential applications of these nanosheets as anisotropic soft nanohybrids can be foreseen.

    5. Standoff Detection of Chemicals Using Porous Silicon “Smart Dust” Particles (pages 1270–1272)

      T.A. Schmedake, F. Cunin, J.R. Link and M.J. Sailor

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1270::AID-ADMA1270>3.0.CO;2-R

      “Smart dust”—small particles of optically encoded microporous Si—can detect organic vapors by measurement of the intensity of reflected light using a laser probe and a detector stationed 20 m away (see Figure and inside front cover). The porous particles absorb condensable vapors, producing a change in refractive index and consequently a quantitative change in optical reflectivity at the wavelength of the laser.

    6. Organic Field-Effect Transistors Made of Epitaxially Grown Crystals of a Thiophene/Phenylene Co-oligomer (pages 1272–1275)

      M. Ichikawa, H. Yanagi, Y. Shimizu, S. Hotta, N. Suganuma, T. Koyama and Y. Taniguchi

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1272::AID-ADMA1272>3.0.CO;2-F

      Organic field-effect transistors (FETs) based on epitaxially grown crystals of a thiophene/phenylene co-oligomer (see Figure and cover) are described. The FETs exhibit good operation characteristics, and the epitaxial needle-like crystals display good charge transport properties along the needle axis. The maximum hole mobility of 0.66 cm2 V–1 s–1 is close to that of vapor phase grown oligothiophene single crystals.

    7. Flexible Organic Electroluminescent Devices Based on Fluorine-Containing Colorless Polyimide Substrates (pages 1275–1279)

      H. Lim, W.-J. Cho, C.-S. Ha, S. Ando, Y.-K. Kim, C.-H. Park and K. Lee

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1275::AID-ADMA1275>3.0.CO;2-Y

      A fluorine-containing polyimide (PI) has been used as a substrate for a flexible organic electroluminescent device. An indium tin oxide (ITO) thin film on the PI substrate is shown to yield a high performance for the device, comparable to that of devices with conventional ITO-coated glass substrates. The Figure shows a photograph of the working device under a flexing load.

    8. Directed Colloidal Assembly of 3D Periodic Structures (pages 1279–1283)

      J.E. Smay, G.M. Gratson, R.F. Shepherd, J. Cesarano III and J.A. Lewis

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1279::AID-ADMA1279>3.0.CO;2-A

      Colloidal inks, comprised of silica microspheres with tailored attractive interactions between them, have been directly assembled via a robotically controlled deposition technique. 3D periodic lattices, whose periodicity far exceeds the dimensions of the colloidal building blocks (see Figure for a cross-sectional image), were created through layer- by-layer patterning of parallel rods.

    9. Tuning the Optical Properties of Inverse Opal Photonic Crystals by Deformation (pages 1284–1286)

      K. Sumioka, H. Kayashima and T. Tsutsui

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1284::AID-ADMA1284>3.0.CO;2-1

      Simple uniaxial elongation of the air spheres in polymer inverse opal is used to tune the material’s stop band. Stretching causes the distance between the (111) planes parallel to the film surface to decrease, resulting in a shift of the stop band to shorter wavelength. This is coupled with a shift to longer wavelength of the stop band associated with periodicity in the stretching direction. The Figure shows the resulting elongated air voids.

    10. Electrodeposition of Epitaxial ZnSe Films on InP and GaAs from an Aqueous Zinc Sulfate–Selenosulfate Solution (pages 1286–1290)

      G. Riveros, J.F. Guillemoles, D. Lincot, H. Gomez Meier, M. Froment, M.C. Bernard and R. Cortes

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1286::AID-ADMA1286>3.0.CO;2-Q

      Epitaxial growth of ZnSe thin films on InP(111) and GaAs(100) substrates has been achieved by electrodeposition from a zinc sulfate/selenosulfate solution. The deposition was observed over a wide range of applied potentials (–1.6–1.9 V vs. mercury/mercury sulfate). The epitaxy was characterized by reflective high energy electron diffraction (see Figure for a ZnSe epitaxial layer) and grazing angle X-ray diffraction.

    11. Optimization of Diblock Copolymer Thin Film Self Assembly (pages 1290–1294)

      K.W. Guarini, C.T. Black and S.H.I. Yeung

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1290::AID-ADMA1290>3.0.CO;2-N

      How can optimum long-range order be achieved by self-assembly of polystyrene/polymethylmethacrylate (PS/PMMA) block copolymers? Here the film thickness, annealing temperature, annealing time, and molecular weight are varied to derive optimum values for these parameters. The Figure shows SEM images of the microstructures obtained from M = 67 000 and M = 134 000 copolymers after solvolytic PMMA removal.

    12. Featherlike Boron Nanowires Arranged in Large-Scale Arrays with Multiple Nanojunctions (pages 1294–1297)

      L.M. Cao, K. Hahn, Y.Q. Wang, C. Scheu, Z. Zhang, C.X. Gao, Y.C. Li, X.Y. Zhang, L.L. Sun, W.K. Wang and M. Rühle

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1294::AID-ADMA1294>3.0.CO;2-#

      Highly ordered boron nanowire multiple nanojunctions (see Figure) with unilateral feather-like morphology have been created via a simple magnetron sputtering method. These T- and Y-type nanojunctions stand freely in line to form uniform and well-oriented arrays on the substrate surface over areas of up to several tens of square centimeters.

    13. Oligo(phenylethynylene) as a High Photoluminescence Quantum Yield Material and Its Distributed Feedback Laser Emission in Thin Films (pages 1297–1301)

      T. Maillou, J. Le Moigne, V. Dumarcher, L. Rocha, B. Geffroy and J.-M. Nunzi

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1297::AID-ADMA1297>3.0.CO;2-I

      The high photoluminescence quantum yield of phenylethynylene oligomers (see Figure for chemical formula) capped by different terminal groups, such as naphthyl or benzyl benzoates, coupled with their good solubility has led to their introduction as chromophores in a polymer matrix of poly(vinylcarbazole) for laser emission studies.

    14. Monodisperse Mesoporous Silica Microspheres Formed by Evaporation-Induced Self Assembly of Surfactant Templates in Aerosols (pages 1301–1304)

      G.V. Rama Rao, G.P. López, J. Bravo, H. Pham, A.K. Datye, H.F. Xu and T.L. Ward

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1301::AID-ADMA1301>3.0.CO;2-T

      Evaporation-driven surface templating by means of a vibrating orifice aerosol generator (VOAG), a device that produces microdroplets, has been used for the synthesis of non-hollow monodisperse mesoporous silica particles (see Figure for a TEM image). Particle and pore size as well as mesoscopic order are controllable by varying the experimental conditions, precursor chemistry, and VOAG parameters.

    15. Nanotube Coated Metals: New Reinforcement Materials for Polymer Matrix Composites (pages 1304–1308)

      R.L. Vander Wal and L.J. Hall

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1304::AID-ADMA1304>3.0.CO;2-B

      Multi-walled carbon nanotubes, synthesized directly upon a stainless steel mesh, remain integrally attached while extending into the surrounding polymer matrix. The bonding between the mesh and polymer matrix is greatly enhanced by a volumetrically distributed interface. The Figure presents evidence of a fractured interface, which demonstrates that the steel mesh wires shear before delamination from the surrounding polymer matrix occurs.

    16. Fabrication and Field Emission of High-Density Silicon Cone Arrays (pages 1308–1311)

      G. Shang, F.Y. Meng, F.C.K. Au, Q. Li, C.S. Lee, I. Bello and S.T. Lee

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1308::AID-ADMA1308>3.0.CO;2-O

      High-density Si cone arrays with a defined orientation and covering a large area (see Figure) have been fabricated by ion beam sputtering. The density of the Si cones is as high as 6 × 108 cm–2. A silicide tip was found on top of each Si cone. The Si cone arrays have a relatively low turn-on field, which may be useful for applications in electronic vacuum devices.

    17. Incorporation of CdS Nanoparticles Inside Ordered Mesoporous Silica SBA-15 via Ion Exchange (pages 1311–1314)

      S. Wang, D.-G. Choi and S.-M. Yang

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1311::AID-ADMA1311>3.0.CO;2-R

      An effective method for incorporating cadmium ions into mesoporous silica SBA-15 is demonstrated. One of the novel features is the assembly of CdS nanoparticles inside the mesopores by selectively functionalizing the external surface of SBA-15 in order to avoid the possible adsorption of the cadmium ions onto this surface. The Figure shows a TEM image with the beam direction parallel to the pore.

    18. Hollow Microspheres of Polyaniline Synthesized with an Aniline Emulsion Template (pages 1314–1317)

      Z. Wei and M. Wan

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1314::AID-ADMA1314>3.0.CO;2-9

      Hollow polyaniline microspheres have been synthesized from a monomeric aniline-based template, which makes template removal unnecessary. The template for the microstructures is an aniline emulsion with β-naphthalenesulfonic acid (NSA) as dopant, and ammonium persulfate (APS) as oxidizer. The Figure is a TEM image of polyaniline/NSA spheres obtained from 0.2 M aniline at an NSA/aniline/APS ratio of 1:4:4.

    19. An Efficient Pure Blue Organic Light-Emitting Device with Low Driving Voltages (pages 1317–1321)

      Y.Q. Li, M.K. Fung, Z. Xie, S.-T. Lee, L.-S. Hung and J. Shi

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1317::AID-ADMA1317>3.0.CO;2-S

      A pure blue OLED device with reduced driving voltage has been constructed from an emissive layer of doped 9,10-bis-(β-naphthyl)-anthrene (see Figure for formula), a hole-blocking/electron transport layer for carrier and exciton confinement, and a MgAg cathode with a thin LiF film on top to further decrease the driving voltage.

    20. Giant Barrier Layer Capacitance Effects in CaCu3Ti4O12 Ceramics (pages 1321–1323)

      T.B. Adams, D.C. Sinclair and A.R. West

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1321::AID-ADMA1321>3.0.CO;2-P

      The grain size dependence of the “giant dielectric effect” in CaCu3Ti4O12 ceramics (arising from a semiconducting grain/insulating grain boundary microstructure) has been revealed by impedance spectroscopy of ceramics sintered for 3 h (see Figure, left) and 24 h (see Figure, right); a rise in permittivity from 9000 to 280 000 was found. The easy-to-prepare CaCu3Ti4O12 is a hot candidate for ceramic capacitor applications.

    21. CdS-Nanoparticle Architectures on Electrodes for Enhanced Photocurrent Generation (pages 1323–1326)

      L. Sheeney-Haj-Ichia, J. Wasserman and I. Willner

      Version of Record online: 16 SEP 2002 | DOI: 10.1002/1521-4095(20020916)14:18<1323::AID-ADMA1323>3.0.CO;2-D

      Enhanced photocurrents are detected in the presence of bipyridinium-modified CdS nanoparticles associated with electrodes. The enhanced photocurrents originate from vectorial electron transfer that retards recombination processes. The Figure shows different architectures for CdS nanoparticles on Au electrodes.