Advanced Materials

Cover image for Vol. 13 Issue 1

January, 2001

Volume 13, Issue 1

Pages 11–79

    1. Nanoengineering of Particle Surfaces (pages 11–22)

      F. Caruso

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<11::AID-ADMA11>3.0.CO;2-N

      The creation of core–shell particles is attracting a great deal of interest because of the diverse applicability of these colloidal particles; e.g., as building blocks for photonic crystals, in multi-enzyme biocatalysis, and in drug delivery. This review presents the state-of-the-art in strategies for engineering particle surfaces, such as the layer-by-layer deposition process (see Figure), which allows fine control over shell thickness and composition.

    2. Rapid Calcination of Nanostructured Silicate Composites by Microwave Irradiation (pages 23–26)

      K. W. Gallis and C. C. Landry

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<23::AID-ADMA23>3.0.CO;2-9

      The use of microwave radiation for the calcination of nanocomposite materials is shown here to provide a rapid and inexpensive method of preparing nanoporous materials. The intense heat produced by microwave radiation gives products of the same quality as those produced by furnace methods in a fraction of the time. The upper image shows MCM-48 after 10 min in the microwave, the lower sample after 135 min in a furnace.

    3. Tuning Solvent-Dependent Color Changes of Three-Dimensionally Ordered Macroporous (3DOM) Materials Through Compositional and Geometric Modifications (pages 26–29)

      C. F. Blanford, R. C. Schroden, M. Al-Daous and A. Stein

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<26::AID-ADMA26>3.0.CO;2-S

      Striking color changes in the visible spectrumare produced when the voids of three-dimensionally ordered macroporous (3DOM) silica, alumina, and zirconia (“inverse opals”) are filled with solvents, it is reported here (see Figure). The wavelength of these colors is linearly related to the refractive index of the fluid filling the pores and can be tuned by modifying the refractive index of the wall material as well as the size and spacing of the pores.

    4. Synthesis and Electronic Properties of Potassium Fulleride Nanowires in a Mesoporous Niobium Oxide Host (pages 29–33)

      B. Ye, M. Trudeau and D. Antonelli

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<29::AID-ADMA29>3.0.CO;2-A

      K3C60 has been quantum-confined inside the pores of mesoporous niobium oxide. Examination of the electronic properties of this new family of 1D potassium (shown in pink in the Figure) fullerides shows that, contrary to previous experimental data on bulk K3C60 (but consistent with theoretical calculations), these nanowires are insulating at room temperature and do not undergo a superconducting transition at liquid-helium temperature.

    5. A Self-Assembly Approach to the Fabrication of Patterned, Two-Dimensional Arrays of Microlenses of Organic Polymers (pages 34–37)

      Y. Lu, Y. Yin and Y. Xia

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<34::AID-ADMA34>3.0.CO;2-1

      Arrayed microlenses are used in a variety of applications that involve miniaturized optical components, such as optical communications systems, facsimile machines, laser printers, and other digitized information storage or processing devices. Here, a self-assembly method is presented which facilitates the production of 2D arrays of monodispersed polystyrene beads (microlenses) with well-controlled lateral dimensions in the range of 1–10 μm (see Figure).

    6. Conformation-Assisted Amplification of Chirality Transfer of Chiral Z-Azobenzenes (pages 37–40)

      C. Ruslim and K. Ichimura

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<37::AID-ADMA37>3.0.CO;2-K

      Photoisomerization of azobenzenes is an active area of researchsince it may play an important role in light-driven molecular systems. Here is described the first example of a chiral azobenzene system where the Z-isomer (see Figure) has greater helical twisting power than the corresponding E-isomer. This is the opposite of what occurs with conventional chiral azobenzenes, which holds significance for the molecular design of optical devices.

    7. Effects of Photo-Controlled Nanophase Segregation in a Re-entrant Nematic Liquid Crystal (pages 40–43)

      S. K. Prasad and G. G. Nair

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<40::AID-ADMA40>3.0.CO;2-N

      Liquid crystals composed of photoactive groups, such as azobenzene, are promising materials for optical switching and image storage applications. On exposure to light LC materials commonly undergo an order-to disorder transition. Here, an unusual disorder-to-order transition is presented (the Figure shows a photo-induced smectic texture surrounded by a nematic phase), and a photo-controlled nanophase segregation mechanism is invoked to explain it.

    8. Transfer Processes in Semiconducting Polymer–Porphyrin Blends (pages 44–47)

      V. Cleave, G. Yahioglu, P. Le Barny, D. H. Hwang, A. B. Holmes, R. H. Friend and N. Tessler

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<44::AID-ADMA44>3.0.CO;2-#

      The role played by triplet excitons in polymer-based LEDs can be analysed by examining the behavior of the excitons in host polymers in a variety of host–guest polymer blend systems (the guest is a porphyrin such as that shown in the Figure) reported here. Charge and energy transfer at heterojunctions in OLEDs depends on these excitons, so an improved understanding of these processes should enable device performance to be improved.

    9. Micropatterns of Poly(4,4′-dimethoxy-2,2′-bithiophene) Generated by the Scanning Electrochemical Microscope (pages 47–51)

      C. Marck, K. Borgwarth and J. Heinze

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<47::AID-ADMA47>3.0.CO;2-I

      Micropatterning of a conducting polymer using the scanning electrochemical microscope (SECM) in the feedback mode is described, in which the local polymerization is performed on a monomer-covered surface with an ultramicroelectrode. The effects of scan speed and tip–substrate distance on the micropatterns are reported, along with a newly developed reading procedure—based on the reduction of iodine—that enables characterization of the synthesized polymer. The SECM and its local polymerization possibilities extend the microtechnological applications of conducting polymers.

    10. Anti-Reflection Surface with Particle Coating Deposited by Electrostatic Attraction (pages 51–54)

      H. Hattori

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<51::AID-ADMA51>3.0.CO;2-F

      Single-layer particulate coatings with special anti-reflection (AR) properties were deposited by an electrostatic attraction between the negatively charged colloidal particles and the positively charged surface of polyelectrolyte multilayers (see Figure). It is shown that the AR properties of the coating depend on the number of sequential depositions as well as on the treatment of the particles after deposition.

    11. Fabrication of High Performance Ceramic Microstructures from a Polymeric Precursor Using Soft Lithography (pages 54–58)

      H. Yang, P. Deschatelets, S. T. Brittain and G. M. Whitesides

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<54::AID-ADMA54>3.0.CO;2-Y

      Ceramic components for microelectromechanical (MEMS) systems, for example the micrometer-sized gear made from SiBNC shown in the Figure, offer the opportunity to extend MEMS technology towards high-temperature and oxidizing-environment applications, such as microturbines and high-temperature sensors and actuators. Preceramic polymers are used in conjunction with soft lithography and subsequent pyrolysis to produce the high aspect ratio structures.

    12. Domain Shapes and Superlattices Made of Cobalt Nanocrystals (pages 58–62)

      J. Legrand, A. T. Ngo, C. Petit and M.-P. Pileni

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<58::AID-ADMA58>3.0.CO;2-A

      3D organization of magnetic nanoparticles has until now only been observed on a small scale. In this communication, the formation of large-scale 3D superlattices of cobalt nanocrystals (see Figure) is reported, in which the degree of organization is shown to be highly dependent on the strength of magnetic field applied during deposition.

    13. Single-Crystalline Copper Nanowires Produced by Electrochemical Deposition in Polymeric Ion Track Membranes (pages 62–65)

      M. E. Toimil Molares, V. Buschmann, D. Dobrev, R. Neumann, R. Scholz, I. U. Schuchert and J. Vetter

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<62::AID-ADMA62>3.0.CO;2-7

      The fabrication of copper nanowires by electrodeposition in ion track membranes is reported. The large-grain copper needle deposited at 40 °C shown in the Figure is a transition between the polycrystalline needles formed at room temperature and the single-crystalline morphology at 60 °C. A systematic study of the DC deposition parameters required for single-crystalline growth is presented.

    14. Phosphorescence in Conjugated Poly(para-phenylene)-Derivatives (pages 65–70)

      D. Hertel, S. Setayesh, H. G. Nothofer, U. Scherf, K. Müllen and H. Bässler

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<65::AID-ADMA65>3.0.CO;2-Q

      The quantum efficiency of fluorescent light emitting diodes is limited by the occurrence of non-radiative decay of triplet states. It is therefore important to improve the understanding of the first excited triplet state, its lifetime, and its population and depopulation mechanisms. The variation of the characteristics of this triplet state with chemical structure are examined for a series of conjugated polymers with the aim of improving the performance of organic LEDs.

    15. Nanostructured Fibers via Electrospinning (pages 70–72)

      M. Bognitzki, W. Czado, T. Frese, A. Schaper, M. Hellwig, M. Steinhart, A. Greiner and J. H. Wendorff

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<70::AID-ADMA70>3.0.CO;2-H

      Structured polymer fibers with diameters down to tens of nanometers are of interest for applications in filters, in composite reinforcement, or as templates for the preparation of functional nanotubes. The Figure shows fibers of poly-L-lactide produced by electrospinning from a dichloromethane solution exhibiting regular pores or pits in the 100 nm range.

    16. Self-Organized Oligosilanes; a New Class of Organic Hole-Transport Materials (pages 72–76)

      H. Okumoto, T. Yatabe, M. Shimomura, A. Kaito, N. Minami and Y. Tanabe

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<72::AID-ADMA72>3.0.CO;2-5

      Oligosilanes are reported here to be excellent candidates as hole transport materials, since they possess mobile σ-conjugated electrons, like the related polysilanes. Oligosilanes, however, display the important property of self-organization (see Figure). The high hole mobilities observed by these authors for polycrystalline permethyldecasilane thin films are discussed here in terms of local and global structure.

    17. Perpendicular Actuation with Individually Controlled Polymer Microactuators (pages 76–79)

      E. W. H. Jager, O. Inganäs and I. Lundström

      Version of Record online: 16 JAN 2001 | DOI: 10.1002/1521-4095(200101)13:1<76::AID-ADMA76>3.0.CO;2-I

      Actuator systems based on conducting polymers, such as polypyrole, with which three-dimensional movement can be controlled, are described. The Figure shows a combination of two such microactuators which are used to “kick” a glass bead across the surface of a silicon wafer. The microfabrication methods used to produce the systems are described and the potential uses, for example microrobotic arms, discussed.