Advanced Materials

Cover image for Vol. 18 Issue 1

January, 2006

Volume 18, Issue 1

Pages 3–130

    1. Cover Picture: Self-Assembly of Single-Walled Carbon Nanotubes into a Sheet by Drop Drying (Adv. Mater. 1/2006)

      R. Duggal, F. Hussain and M. Pasquali

      Article first published online: 23 DEC 2005 | DOI: 10.1002/adma.200690004

      Drops of a suspension of individual single-walled carbon nanotubes in F68 Pluronic surfactant dry on glass substrates to form a “crust” at the free surface. The crust is extremely thin (∼ 100 nm) and consists of an entangled mesh of nanotubes and Pluronic. The convective flow associated with the drying preferentially assembles the nanotube-Pluronic micelles into a hexagonal arrangement, as revealed by birefringent patterns (see Figure and Cover).

    2. Inside Front Cover: Multicolor Photoluminescence from Porous Silicon Using Focused, High-Energy Helium Ions (Adv. Mater. 1/2006)

      E. J. Teo, M. B. H. Breese, A. A. Bettiol, D. Mangaiyarkarasi, F. Champeaux, F. Watt and D. J. Blackwood

      Article first published online: 23 DEC 2005 | DOI: 10.1002/adma.200690005

      An image of a dragon is replicated in porous silicon by using 2 MeV helium irradiation prior to electrochemical etching. By careful control of the ion dose at each region, the photoluminescence (PL) wavelength can be tuned to produce a PL image matching that of the original. Results have been explained in terms of ion-induced changes in the wafer resistivity.

    3. Contents: Adv. Mater. 1/2006 (pages 3–11)

      Article first published online: 23 DEC 2005 | DOI: 10.1002/adma.200690003

    4. Guide for Authors Adv. Mater. 1/2006 (pages 12–13)

      Article first published online: 23 DEC 2005 | DOI: 10.1002/adma.200690000

    5. You have free access to this content
      The Future of Materials Research (pages 14–16)

      E. Levy

      Article first published online: 23 DEC 2005 | DOI: 10.1002/adma.200502646

      Materials science continues to prove to be a fertile ground for innovative research, as demonstrated by the recent Materials Research Society meeting in Boston, which broke records for attendance, and by the continuing success of Advanced Materials, which broke records for submissions, downloads, and published Communications in 2005.

    6. Polymer Nanofibers and Nanotubes: Charge Transport and Device Applications (pages 17–27)

      A. N. Aleshin

      Article first published online: 5 DEC 2005 | DOI: 10.1002/adma.200500928

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      Conducting polymer nanowires and nanotubes hold promise for their applications in devices such as field- effect transistors (FETs, see Figure), as nanotips in field-emission displays, and as sensors. This review analyzes recent advances in the synthesis and electrical characterization of nanotubes, and discusses their charge-transport properties in light of theories for tunneling in one-dimensional conductors.

    7. Self-Assembly of Single-Walled Carbon Nanotubes into a Sheet by Drop Drying (pages 29–34)

      R. Duggal, F. Hussain and M. Pasquali

      Article first published online: 15 NOV 2005 | DOI: 10.1002/adma.200500625

      Thumbnail image of graphical abstract

      Drops of a suspension of individual single-walled carbon nanotubes in F68 Pluronic surfactant dry on glass substrates to form a “crust” at the free surface. The crust is extremely thin (∼ 100 nm) and consists of an entangled mesh of nanotubes and Pluronic. The convective flow associated with the drying preferentially assembles the nanotube-Pluronic micelles into a hexagonal arrangement, as revealed by birefringent patterns (see Figure and Cover).

    8. Experimental Evidence for Grain-Boundary Sliding in Ultrafine-Grained Aluminum Processed by Severe Plastic Deformation (pages 34–39)

      N. Q. Chinh, P. Szommer, Z. Horita and T. G. Langdon

      Article first published online: 15 NOV 2005 | DOI: 10.1002/adma.200501232

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      Evidence for grain boundary sliding in ultrafine-grained aluminum after processing with equal channel angular pressing (ECAP) is presented (see Figure). Pure aluminum is used as a model material; depth sensing indentation testing and atomic force microscopy are used to measure the nature of the displacements around indentations for samples in an annealed and work-hardened condition, and after processing using ECAP.

    9. High-Performance Polymer Membranes for Natural-Gas Sweetening (pages 39–44)

      H. Lin, E. Van Wagner, R. Raharjo, B. D. Freeman and I. Roman

      Article first published online: 21 NOV 2005 | DOI: 10.1002/adma.200501409

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      Rubbery membrane materials based on high-solubility selectivity for the removal of CO2 from natural gas are made from highly branched, crosslinked poly(ethylene oxide) (XLPEO) which exhibits high CO2/CH4 selectivity (αmath image) even in the presence of high activities of plasticizing agents (e.g., CO2 and higher hydrocarbons). Decreasing temperature improves the separation performance. Many conventional glassy gas separation materials, including polyimides such as 6FDA-mPD, lose selectivity when strongly plasticized (see Figure).

    10. Charge Mobility in the Room-Temperature Liquid-Crystalline Semiconductor Poly(di-n- butylstannane) (pages 44–47)

      M. P. de Haas, F. Choffat, W. Caseri, P. Smith and J. M. Warman

      Article first published online: 15 NOV 2005 | DOI: 10.1002/adma.200501287

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      The mobility of charge along the σ-bonded backbone of tin atoms in poly(di-n-butylstannane) is ca. 0.1 cm2 V–1 s–1 in the crystalline phase. It decreases by only a factor of three in the liquid-crystalline mesophase, which is stable down to –25 °C on cooling from room temperature (see Figure). The high mobility and the ease with which the polymer chains can be aligned make it a prime candidate for applications in molecular electronic devices.

    11. Laser Emission from a Polymer-Stabilized Liquid-Crystalline Blue Phase (pages 48–51)

      S. Yokoyama, S. Mashiko, H. Kikuchi, K. Uchida and T. Nagamura

      Article first published online: 5 DEC 2005 | DOI: 10.1002/adma.200501355

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      A molecularly assembled three-dimensional photonic crystal was prepared in the liquid-crystalline blue phase for organic solid-state laser applications (see Figure). The polymer network in the blue phase stabilized the laser operation over a temperature range 35 °C wide. Narrow laser emission, low threshold response, and circular polarization were measured due to the photonic-bandgap effect of the blue phase of the photonic crystal.

    12. Multicolor Photoluminescence from Porous Silicon Using Focused, High-Energy Helium Ions (pages 51–55)

      E. J. Teo, M. B. H. Breese, A. A. Bettiol, D. Mangaiyarkarasi, F. Champeaux, F. Watt and D. J. Blackwood

      Article first published online: 21 NOV 2005 | DOI: 10.1002/adma.200501138

      Thumbnail image of graphical abstract

      An image of a dragon is replicated in porous silicon by using 2 MeV helium irradiation prior to electrochemical etching. By careful control of the ion dose at each region, the photoluminescence (PL) wavelength can be tuned to produce a PL image matching that of the original. Results have been explained in terms of ion-induced changes in the wafer resistivity.

    13. Self-Assembly Combined with Photopolymerization for the Fabrication of Fluorescence “Turn-On” Vesicle Sensors with Reversible “On–Off” Switching Properties (pages 55–60)

      G. Ma, A. M. Müller, C. J. Bardeen and Q. Cheng

      Article first published online: 21 NOV 2005 | DOI: 10.1002/adma.200501455

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      A self-amplifying fluorescence sensor has been fabricated by vesicular assembly of polydiacetylene and lipophilic fluorescent dyes. The intensity of vesicles can be reversibly manipulated by adjusting the pH of the solution, demonstrating an “on–off” switching property (see Figure), transforming external stimuli into a fluorescence intensity change. The mechanism may involve static fluorescence quenching by association of dyes with the polymer backbone.

    14. Controlled Synthesis of Abundantly Branched, Hierarchical Nanotrees by Electron Irradiation of Polymers (pages 60–65)

      S. O. Cho, E. J. Lee, H. M. Lee, J. G. Kim and Y. J. Kim

      Article first published online: 15 NOV 2005 | DOI: 10.1002/adma.200501600

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      Hierarchical silicon oxycarbide tree-like nanostructures, which consist of trunks and abundant branches, have been fabricated by electron irradiation of organosilicon polymers. The nanotree structures have two different morphologies, cluster-assembled and nanowire-assembled. The morphology of the nanotrees can be controlled by the irradiation parameters. The proposed approach promises a straightforward means to fabricate complex hierarchical organic–inorganic nanostructures.

    15. Low Threshold Voltage Transistors Based on Individual Single-Crystalline Submicrometer-Sized Ribbons of Copper Phthalocyanine (pages 65–68)

      Q. Tang, H. Li, M. He, W. Hu, C. Liu, K. Chen, C. Wang, Y. Liu and D. Zhu

      Article first published online: 21 NOV 2005 | DOI: 10.1002/adma.200501654

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      Single-crystalline submicrometer-sized ribbons of copper phthalocyanine (CuPc) have been synthesized (see Figure). Organic field-effect transistors (OFETs) fabricated using individual ribbons of CuPc exhibit high mobilities and low threshold voltages. These characteristics are highly reproducible and stable, indicating the high quality of the transistors. Moreover, CuPc submicrometer-sized ribbons show excellent flexibility, which may lead to their application in flexible electronics.

    16. A Mesoporous Nanocomposite of TiO2 and Carbon Nanotubes as a High-Rate Li-Intercalation Electrode Material (pages 69–73)

      I. Moriguchi, R. Hidaka, H. Yamada, T. Kudo, H. Murakami and N. Nakashima

      Article first published online: 15 NOV 2005 | DOI: 10.1002/adma.200501366

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      A mesoporous nanocomposite of TiO2 and cut single-walled carbon nanotubes (c-SWNTs) is successfully synthesized by a bicontinuous microemulsion-aided process. The nanocomposite electrode (see Figure) shows a high capacity even at high charging–discharging rates due to the presence of nanochannels for both ion and electron transport.

    17. Growth of Carbon Nanotubes on Clay: Unique Nanostructured Filler for High-Performance Polymer Nanocomposites (pages 73–77)

      W.-D. Zhang, I. Y. Phang and T. X. Liu

      Article first published online: 15 NOV 2005 | DOI: 10.1002/adma.200501217

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      High-performance composites are produced using nanostructured clay–carbon nanotube (CNT) hybrids as a reinforcing filler. The intercalation of iron particles between the clay platelets serves as the catalyst for the growth of CNTs, while the platelets are exfoliated by the CNTs, forming the unique 3D nanostructured hybrid filler: a 2D clay platelet with several attached 1D CNTs (see Figure). The clay–CNTs hybrid can be directly incorporated into nylon-6 by simple melt compounding.

    18. Quantum-Dot/Organic Semiconductor Composites for Radiation Detection (pages 77–79)

      I. H. Campbell and B. K. Crone

      Article first published online: 21 NOV 2005 | DOI: 10.1002/adma.200501434

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      Improved radiation detection using quantum-dot/organic semiconductor composites is demonstrated. Electron scintillation results (see Figure) demonstrate more than a doubling of photon generation efficiency with quantum-dot volume fraction. Simple estimates suggest that an ionization energy of about 3 eV/photon may be achieved. These composites are promising for low cost and high energy resolution gamma-ray, neutron, and charged-particle detection.

    19. Biofunctionalized pH-Responsive Microgels for Cancer Cell Targeting: Rational Design (pages 80–83)

      M. Das, S. Mardyani, W. C. W. Chan and E. Kumacheva

      Article first published online: 5 DEC 2005 | DOI: 10.1002/adma.200501043

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      The design of a drug-delivery system based on bioconjugated, pH-responsive microgels is demonstrated. Microgels loaded with the anticancer drug Doxorubicin are introduced into the HeLa tumor cells by means of receptor- mediated endocytosis. Changes in pH within the intracellular environment induce shrinkage of microgels, triggering the drug release into the cells. The microgel described in this work shows enhanced cytotoxicity to HeLa cells (see Figure).

    20. Fracture Transitions at a Carbon-Nanotube/Polymer Interface (pages 83–87)

      A. H. Barber, S. R. Cohen, A. Eitan, L. S. Schadler and H. D. Wagner

      Article first published online: 5 DEC 2005 | DOI: 10.1002/adma.200501033

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      The interfacial strength between carbon nanotubes and a polymer matrix increases dramatically when the carbon-nanotube surface is chemically modified. As individual nanotubes are pulled from a polymer matrix, a transition from pullout to fracture occurs (see Figure) at a critical nanotube embedded length, with chemically modified nanotubes showing a smaller critical length than unmodified ones.

    21. Field Emission of Electrons from Single LaB6 Nanowires (pages 87–91)

      H. Zhang, J. Tang, Q. Zhang, G. Zhao, G. Yang, J. Zhang, O. Zhou and L.-C. Qin

      Article first published online: 5 DEC 2005 | DOI: 10.1002/adma.200500508

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      Single-crystalline lanthanum hexaboride (LaB6) nanowires show excellent electric-field-induced electron emission following the Fowler–Nordheim scheme. The LaB6 nanowires grow in the <001> crystallographic direction (see Figure) with diameters of about 20 nm. An emission current of 30 nA from a single nanowire, corresponding to a emission current density of 5 × 105 A cm–2, has been obtained.

    22. Fluorescence Enhancement by Metal-Core/Silica-Shell Nanoparticles (pages 91–95)

      O. G. Tovmachenko, C. Graf, D. J. van den Heuvel, A. van Blaaderen and H. C. Gerritsen

      Article first published online: 15 NOV 2005 | DOI: 10.1002/adma.200500451

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      Fluorescent nanoparticles have been synthesized with a metal core, silica-spacer shell, and a dye-labeled silica shell. Cascade-yellow-labeled, silver-core and carboxyfluorescein-labeled, gold-core nanoparticles with dye–metal distances of 24–25 nm exhibit fluorescence enhancement factors as high as 12.5 and 6.8, respectively. Cascade-yellow-labeled, gold-core particles with a dye–metal distance of ∼15 nm show significant fluorescence quenching.

    23. Bending of a Carbon Nanotube in Vacuum Using a Focused Ion Beam (pages 95–98)

      B. C. Park, K. Y. Jung, W. Y. Song, B.-h. O and S. J. Ahn

      Article first published online: 21 NOV 2005 | DOI: 10.1002/adma.200501223

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      A focused ion beam is used to plastically bend and straighten freestanding multiwalled carbon nanotubes held at the apex of a scanning force microscopy tip (see Figure). The nanotube aligns itself parallel to the beam direction so that its free end is directed toward the ion source. In this orientation, the nanotube is not subject to any external electric or magnetic field. This method may be useful for precisely aligning carbon nanotubes for their testing and application.

    24. Photocurrent Amplification at Carbon Nanotube–Metal Contacts (pages 98–103)

      D.-H. Lien, W.-K. Hsu, H.-W. Zan, N.-H. Tai and C.-H. Tsai

      Article first published online: 15 NOV 2005 | DOI: 10.1002/adma.200500912

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      The photocurrent produced at single-walled carbon nanotube–Zn contacts with zero bias is amplified by a factor of 4–7 upon application of a bias (see Figure). Between ± 0.5 mV biases, the ideality factor only deviates slightly, but at biases of larger magnitude, current amplification becomes nonlinear owing to charge accumulation at the interfacial O2 layer.

    25. High, Purely Electrostrictive Strain in Lead-Free Dielectrics (pages 103–106)

      C. Ang and Z. Yu

      Article first published online: 15 NOV 2005 | DOI: 10.1002/adma.200500951

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      A high electrostrictive strain (∼0.1%) with hysteresis-free behavior is observed in (Sr,Na,Bi)TiO3 solid solutions. Its strain versus polarization (P) completely follows the quadratic relation (see Figure), indicating a purely electrostrictive effect with an electrostrictive coefficient Q11 of 0.02 m4 C–2. These properties of this environmentally friendly lead-free material are comparable with those of the currently used lead-containing materials.

    26. WS2 Closed Nanoboxes Synthesized by Spray Pyrolysis (pages 106–109)

      S. Bastide, D. Duphil, J.-P. Borra and C. Lévy-Clément

      Article first published online: 21 NOV 2005 | DOI: 10.1002/adma.200501735

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      A novel type of inorganic fullerene-like nanoparticle has been synthesized, presenting the unique structure of a closed, nested nanobox. These nanoparticles consist of WS2, and are obtained by spray pyrolysis of (NH4)2WS4 solutions at high temperature. The nanoparticles exhibit the shoebox shape of a rectangular parallelepiped and possess a hollow core surrounded by walls made up of stacked WS2 layers.

    27. The Size-Dependent Growth Direction of ZnSe Nanowires (pages 109–114)

      Y. Cai, S. K. Chan, I. K. Sou, Y. F. Chan, D. S. Su and N. Wang

      Article first published online: 15 NOV 2005 | DOI: 10.1002/adma.200500822

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      Single-crystalline ZnSe nanowires (NWs, see Figure) are fabricated on GaAs substrates using a Au-catalyzed vapor–liquid–solid mechanism. The as-grown ZnSe NWs display size- dependent growth direction properties that are interpreted based on the estimation of the surface and interface energies of the ZnSe NW. The solid/ liquid interface structure at the tip of the NW is the most critical factor influencing the NW growth direction.

    28. Achieving High-Efficiency Polymer White-Light-Emitting Devices (pages 114–117)

      J. Huang, G. Li, E. Wu, Q. Xu and Y. Yang

      Article first published online: 5 DEC 2005 | DOI: 10.1002/adma.200501105

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      The efficiency of polymer light-emitting devices can be significantly increased by introducing an electron-injection and a hole-blocking layer and by using a polymer blend system as the active material. Blending high-bandgap and low-bandgap polymers introduces charge traps into a light-emitting polymer layer. Depending on the blend ratio, a peak efficiency of 16 lm W–1 is observed (see Figure), the highest yet reported for a white-light-emitting polymer device.

    29. Synthesis of [(VSe2)n]1.06[(TaSe2)n] Superlattices Using a Hybrid Approach: Self-Assembly of Amorphous Nanostructured Reactants (pages 118–122)

      N. T. Nguyen, B. Howe, J. R. Hash, N. Liebrecht and D. C. Johnson

      Article first published online: 15 NOV 2005 | DOI: 10.1002/adma.200501400

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      Nanolaminates are produced by a combination of epitaxial growth and self-assembly techniques. The compounds [(VSe2)n]1.06[(TaSe2)n] (n = 1–4) are prepared using self-assembly of designed, nanostructured reactants that provide unit-cell control (see Figure). Many compounds exist that are the only representative of a family of structurally related compounds, and this synthesis approach should enable the preparation of the missing family members.

    30. Polypyrrole Nanowire Actuators (pages 122–125)

      Y. Berdichevsky and Y.-H. Lo

      Article first published online: 5 DEC 2005 | DOI: 10.1002/adma.200501621

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      Polypyrrole nanowires can be template synthesized, and have been tested and characterized as to their ability to function as nanoactuators in an aqueous environment. This is the first report of conducting-polymer nanowires functioning as electrically controlled nanoactuators (see Figure). Bundles of parallel nanowires displayed two modes of actuation: a reversible increase in length of up to 3% and large-scale bimorph-like bending behavior when coupled to a freestanding gold film.

    31. Conference Calendar Adv. Mater. 1/2006 (pages 126–128)

      Article first published online: 23 DEC 2005 | DOI: 10.1002/adma.200690001

    32. Author Index and Subject Index Adv. Mater. 1/2006 (pages 129–130)

      Article first published online: 23 DEC 2005 | DOI: 10.1002/adma.200690002

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