Advanced Materials

Cover image for Vol. 17 Issue 11

June, 2005

Volume 17, Issue 11

Pages 1311–1446

    1. Cover Picture: Microscopic Evidence for Spatially Inhomogeneous Charge Trapping in Pentacene (Adv. Mater. 11/2005)

      E. M. Muller and J. A. Marohn

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200590055

      Charge traps in pentacene thin-film transistors (Figure, left) have been imaged using electric force microscopy. The Figure shows a map of the trap distribution just below (middle) and well above (right) the transistor threshold voltage. It is found that the long-lived charge traps in polycrystalline pentacene are distributed inhomogeneously and do not appear to be associated with grain boundaries, as is generally assumed (see cover).

    2. Inside Front Cover: Polarized-Light-Emitting Quantum-Rod Diodes (Adv. Mater. 11/2005)

      R. A. M. Hikmet, P. T. K. Chin, D. V. Talapin and H. Weller

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200590056

      For the first time, polarized-light-emitting quantum-rod diodes have been successfully produced, using thin layers of quantum rods oriented by a rubbing technique. Diode emission at 620 nm with a luminance efficiency of 0.65 Cd A–1 and an external quantum efficiency of 0.49 % is obtained (see Figure and inside cover).

    3. Precipitation of Selenium from CdSe Nanocrystal Solutions (pages 1321–1324)

      N. Zaitseva, L. Manna, D. Gerion and C. K. Saw

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401597

    4. Reply: Self-Assembly of Monodisperse Nanocrystals Into Faceted Crystal Superlattices (pages 1325–1329)

      D. V. Talapin, E. V. Shevchenko, N. Gaponik, I. L. Radtchenko, A. Kornowski, M. Haase, A. L. Rogach and H. Weller

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200500672

    5. Block Copolymer Nanocomposites: Perspectives for Tailored Functional Materials (pages 1331–1349)

      M. R. Bockstaller, R. A. Mickiewicz and E. L. Thomas

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200500167

      Thumbnail image of graphical abstract

      Incorporation of nanoparticles in a block copolymer (BCP) matrix (see Figure) allows unprecedented levels of control over orientation and spatial distribution of nanoscale filler materials, providing new opportunities for scientific insight into the physics of self-organization, as well as a vast range of potential applications. This review highlights recent research efforts in the field of structure formation in BCP-based nanocomposite materials.

    6. Single-Crystalline Diluted Magnetic Semiconductor GaN:Mn Nanowires (pages 1351–1356)

      H.-J. Choi, H.-K. Seong, J. Chang, K.-I. Lee, Y.-J. Park, J.-J. Kim, S.-K. Lee, R. He, T. Kuykendall and P. Yang

      Version of Record online: 24 MAR 2005 | DOI: 10.1002/adma.200401706

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      Single-crystalline diluted magnetic semiconductor GaN:Mn nanowires with controlled Mn concentrations have been successfully synthesized and incorporated into devices (see Figure). These nanowires exhibit Curie temperatures above room temperature, magnetoresistances near room temperature, and spin-dependent transport. The nanowires are used as building blocks for the fabrication of GaN:Mn/n-SiC based light-emitting diodes.

    7. Registered Deposition of Nanoscale Ferroelectric Grains by Template-Controlled Growth (pages 1357–1361)

      S. Clemens, T. Schneller, A. van der Hart, F. Peter and R. Waser

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401695

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      Regular patterns of ferroelectric PbTiO3 nanostructures (see Figure) with lateral dimensions down to 30–60 nm have been grown onto platinized Si substrates by chemical solution deposition. The high registration of the grains is achieved by “top–down”-generated templates of TiO2 dots as seeds for their deposition. Ferroelectricity was verified by piezoresponse force microscopy.

    8. Cutting into Solids with Micropatterned Gels (pages 1361–1365)

      S. K. Smoukov, K. J. M. Bishop, R. Klajn, C. J. Campbell and B. A. Grzybowski

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200402086

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      Hydrogel stamps can microstructure solid surfaces, i.e., modify the surface topology of metals, glasses, and crystals. It is demonstrated that stamps soaked in an appropriate etchant can remove material with micrometer-scale precision. The Figure shows an array of concentric circles etched in glass using the immersion wet stamping process described (scale bar: 500 μm).

    9. Independent Optical Control of Microfluidic Valves Formed from Optomechanically Responsive Nanocomposite Hydrogels (pages 1366–1368)

      S. R. Sershen, G. A. Mensing, M. Ng, N. J. Halas, D. J. Beebe and J. L. West

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401239

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      Independent optical control of microfluidic valves (see Figure) formed from optomechanically responsive nanocomposite hydrogels is achieved using strongly absorbing Au nanoparticles or nanoshells embedded within a thermally responsive polymer. Valves formed from composites with different nanoparticles could be independently controlled by changing the illumination wavelength.

    10. A Full-Color Electroluminescent Device and Patterned Photoalignment Using Light-Emitting Liquid Crystals (pages 1368–1372)

      M. P. Aldred, A. E. A. Contoret, S. R. Farrar, S. M. Kelly, D. Mathieson, M. O'Neill, W. C. Tsoi and P. Vlachos

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200500258

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      Blue, green, and red polymerizable light-emitting liquid crystals have been patterned photolithographically in a full-color liquid-crystal electroluminescent display (see Figure). A new hole-transporting photoalignment copolymer is also reported and the spatial patterning of the polarization direction of emission is demonstrated.

    11. Wavelength-Controlled Lasing in ZnxCd1–xS Single-Crystal Nanoribbons (pages 1372–1377)

      Y. Liu, J. A. Zapien, Y. Y. Shan, C.-Y. Geng, C. S. Lee and S.-T. Lee

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401606

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      ZnxCd1xS single-crystal nanoribbons of controlled composition (where 0 ≤ x ≤ 1) can be synthesized by combining laser ablation with thermal evaporation. The nanoribbons (see Figure) exhibit lasing emission that can be continuously tuned within the ranges of 340–390 nm and 485–515 nm. These results suggest that ZnxCd1–xS nanoribbon lasers of pre-selected “tunable” wavelengths between 340 and 515 nm may be achievable by tailoring the value of x.

    12. Extraordinary Strengthening Effect of Carbon Nanotubes in Metal-Matrix Nanocomposites Processed by Molecular-Level Mixing (pages 1377–1381)

      S. I. Cha, K. T. Kim, S. N. Arshad, C. B. Mo and S. H. Hong

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401933

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      Carbon-nanotube-reinforced Cu matrix nanocomposites have been fabricated by molecular-level mixing of functionalized carbon nanotubes (CNTs) with Cu ions, followed by spark plasma sintering. The compressive strengths and Young's moduli of CNT-reinforced nanocomposites are considerably higher than those of the Cu matrix due to the homogeneously dispersed CNTs embedded in the Cu matrix (see Figure).

    13. Fabrication of Polypyrrole– Poly(N-vinylcarbazole) Core–Shell Nanoparticles with Excellent Electrical and Optical Properties (pages 1382–1386)

      J. Jang, Y. Nam and H. Yoon

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401841

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      Polypyrrole–poly(N-vinylcarbazole) (PPy–PVK) core–shell nanoparticles have been fabricated by nanoparticle-seeded dispersion polymerization. The monodisperse PPy nanoseeds are fabricated by micelle templating, and the PVK shell thickness is easily tuned by varying the amount of N-vinylcarbazole monomer. The PPy core and PVK shell produce superior conductivity and fluorescence, respectively (see Figure).

    14. Water-Bridge-Assisted Ionic Conduction in Probe-Induced Conical Polymer Pattern Formation (pages 1386–1390)

      X. N. Xie, H. J. Chung, C. H. Sow, A. A. Bettiol and A. T. S. Wee

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200500204

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      Formation of conical polymer structures by atomic force microscopy (AFM) nanolithography (see Figure) and the electrical-conduction mechanism involved in the AFM- probe-induced patterning process are reported. The current is dominated by water-bridge-assisted ionic conduction. Polymer phase transition and mass redistribution occur without modification or degradation of the poly(methyl methacrylate) (PMMA) material.

    15. Electrochemical Switching of Chromogenic Monolayers Self-Assembled on Transparent Platinum Electrodes (pages 1390–1393)

      S. Sortino, S. Di Bella, S. Conoci, S. Petralia, M. Tomasulo, E. J. Pacsial and F. M. Raymo

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200500200

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      Transparent, ultrathin Pt electrodes permit the simultaneous electrochemical and spectroscopic investigation of self-assembled monolayers of electrochromic compounds. Voltage stimulations applied to the Pt substrate reversibly alter the redox state of the chemisorbed molecules and, hence, modulate the intensity of the light transmitted through the Pt/monolayer assembly (see Figure).

    16. ZnO Nanorod Logic Circuits (pages 1393–1397)

      W. I. Park, J. S. Kim, G.-C. Yi and H.-J. Lee

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401732

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      Logic devices, including OR, AND, NOT, and NOR gates, based on single-crystalline ZnO nanorods are demonstrated (see Figure). In these devices, ZnO nanorods are employed as semiconducting channels. They control metal/oxide semiconductor junction characteristics, to yield either good ohmic or Schottky contacts, ensuring fabrication of high-performance Schottky diodes and metal-semiconductor field-effect transistors.

    17. Chemical Nanopatterns via Nanoimprint Lithography for Simultaneous Control over Azimuthal and Polar Alignment of Liquid Crystals (pages 1398–1401)

      S. Park, C. Padeste, H. Schift, J. Gobrecht and T. Scharf

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200400989

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      Chemical nanopatterns down to 50 nm in feature size have been fabricated via nanoimprint lithography and used to simultaneously control azimuthal and polar orientation of liquid crystals (LCs). The polar orientation depends on the ratio of the homeotropic/planar surface potential areas, while the LC azimuthally orients along the direction of the silane patterns (see Figure).

    18. Single-Crystalline α-Al2O3 Nanotubes Converted from Al4O4C Nanowires (pages 1401–1405)

      Y. B. Li, Y. Bando and D. Golberg

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401384

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      Single-crystalline Al4O4C nanowires can be synthesized at a high yield via a simple high-temperature solid reaction. A two-step method has been developed to convert the prepared nanowires into single-crystalline α-Al2O3 nanotubes (see Figure). These nanotubes may find high-temperature applications due to their unmatched refractory properties.

    19. Routes to Grow Well-Aligned Arrays of ZnSe Nanowires and Nanorods (pages 1405–1410)

      X. Zhang, Z. Liu, Q. Li, Y. Leung, K. Ip and S. Hark

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401891

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      Well-aligned ZnSe nanowires and nanorods can be grown on ZnSe epilayers on different GaAs substrates, with and without catalyst, by metal–organic chemical vapor deposition. Gold particles affect the number density, growth direction, and the morphology of the resulting nanostructures. In the absence of the gold catalyst, hexagonal nanorods grow along the <111> directions (see Figure). Growth defects on the epilayers may be the nucleation sites of the nanorods.

    20. Microscopic Evidence for Spatially Inhomogeneous Charge Trapping in Pentacene (pages 1410–1414)

      E. M. Muller and J. A. Marohn

      Version of Record online: 24 MAR 2005 | DOI: 10.1002/adma.200401174

      Thumbnail image of graphical abstract

      Charge traps in pentacene thin-film transistors (Figure, left) have been imaged using electric force microscopy. The Figure shows a map of the trap distribution just below (middle) and well above (right) the transistor threshold voltage. It is found that the long-lived charge traps in polycrystalline pentacene are distributed inhomogeneously and do not appear to be associated with grain boundaries, as is generally assumed (see cover).

    21. Morphologically Templated Growth of Aligned Spinel CoFe2O4 Nanorods (pages 1415–1419)

      Z. Zhang, A. J. Rondinone, J. X. Ma, J. Shen and S. Dai

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200500009

      Thumbnail image of graphical abstract

      Uniaxially aligned CoFe2O4 nanorods (see Figure) are obtained by coprecipitation of Co2+, Fe2+, and C2O42– ions in a microemulsion solution, and subsequent high-temperature decomposition of CoFe2(C2O4)3. Each nanorod is made up of a “tectonic” assembly of CoFe2O4 nanocrystals. Magnetization of such CoFe2O4 materials may lead to their use in high-density magnetic recording media and high-performance electromagnetic and spintronic devices.

    22. Room-Temperature, Low-Pressure Nanoimprinting Based on Cationic Photopolymerization of Novel Epoxysilicone Monomers (pages 1419–1424)

      X. Cheng, L. J. Guo and P.-F. Fu

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401192

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      A new UV-curable liquid resist based on cationic polymerization of silicone epoxies has been developed for UV-assisted nanoimprint lithography. Uniform films with thicknesses ranging from below 50 nm to over 1 μm can be easily spin-coated using a suitable undercoating layer on a substrate. Patterns with feature sizes ranging from tens of micrometers to 20 nm (see Figure) are imprinted at room temperature with a pressure of less than 0.1 MPa.

    23. Size Distribution of Cobalt Nanocrystals: A Key Parameter in Formation of Columns and Labyrinths in Mesoscopic Structures (pages 1424–1429)

      V. Germain and M.-P. Pileni

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401559

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      Columnar or labyrinthine mesostructures of magnetic nanocrystals (see Figure) are obtained by applying a perpendicular magnetic field during evaporation of the nanocrystal solution. The effect of the polydispersity of the nanocrystals is investigated, and the size distribution of the nanocrystals appears to be a key factor in the formation of one particular structure.

    24. Super-Stable, High-Quality Fe3O4 Dendron–Nanocrystals Dispersible in Both Organic and Aqueous Solutions (pages 1429–1432)

      M. Kim, Y. Chen, Y. Liu and X. Peng

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401991

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      High-quality Fe3O4 nanocrystals coated with stearate groups are successfully converted to dendron-coated nanocrystals (dendron–nanocrystals). Poly(ethylene glycol) oligomers are used as major terminal groups for the dendron ligands, which afford excellent dispersibility of the dendron–nanocrystals in a broad spectrum of solvents, ranging from dichloromethane to water (see Figure).

    25. Aligning Single-Layer Cylinders of Block Copolymer Nanodomains using Soft Molding (pages 1432–1436)

      L. Li and H. Yokoyama

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401591

      Thumbnail image of graphical abstract

      By a novel “soft molding” method, a single layer of cylindrical nanodomains in a copolymer thin film is aligned on the macroscopic scale. The domains orient parallel to the surface and perpendicular to the grating pattern of the mold with a density of 3 × 105 lines cm–2. The arrow in the Figure shows the direction of the grating (parallel to the contour line) of the mold. The fast Fourier transform in the inset indicates the well-oriented cylinders obtained.

    26. Polarized-Light-Emitting Quantum-Rod Diodes (pages 1436–1439)

      R. A. M. Hikmet, P. T. K. Chin, D. V. Talapin and H. Weller

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200401763

      Thumbnail image of graphical abstract

      For the first time, polarized-light-emitting quantum-rod diodes have been successfully produced, using thin layers of quantum rods oriented by a rubbing technique. Diode emission at 620 nm with a luminance efficiency of 0.65 Cd A–1 and an external quantum efficiency of 0.49 % is obtained (see Figure and inside cover).

    27. Organic Donor–Acceptor System Exhibiting Electrical Bistability for Use in Memory Devices (pages 1440–1443)

      C. W. Chu, J. Ouyang, J.-H. Tseng and Y. Yang

      Version of Record online: 24 MAY 2005 | DOI: 10.1002/adma.200500225

      Thumbnail image of graphical abstract

      An all-organic electrically bistable device and its application in non-volatile memory is reported (see Figure). The switching mechanism is attributed to electric-field-induced charge transfer from an organic electron donor to an acceptor, so that the device switches from a low- to a high-conductivity state. This device provides a new direction for data-storage technology based on organic composites.

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