Advanced Materials

Cover image for Advanced Materials

December, 1999

Volume 11, Issue 17

Pages 1409–1480

    1. Wafer Bonding and Layer Splitting for Microsystems (pages 1409–1425)

      Q.-Y. Tong and U. M. Gösele

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1409::AID-ADMA1409>3.0.CO;2-W

      Two fundamental technologies for the fabrication of advanced microsystems are reviewed—wafer bonding and hydrogen-implantation-induced layer splitting. The basic processes of these generic techniques as well as examples of bonding and layer splitting of bare and processed semiconductor and oxide wafers are described. The Figure shows the microcleanroom set-up used for wafer bonding.

    2. Formation of Hollow Helicoids in Mesoporous Silica: Supramolecular Origami (pages 1427–1431)

      S. M. Yang, I. Sokolov, N. Coombs, C. T. Kresge and G. A. Ozin

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1427::AID-ADMA1427>3.0.CO;2-3

      Siliceous hollow helicoids (Archimedian screw shapes) with spiraling mesoscale channels are the result of a new way of controlling the growth and form of hexagonal mesoporous silica. These novel helicoids (see Figure) are produced when a patch of the hexagonal silicate liquid-crystal film contracts on hydrolytic polycondensation, triggering “roll-up”. A supramolecular Origami theoretical model is invoked to rationalize hollow helicoid formation.

    3. Patterning Self-Assembled Monolayers on Oxide Surfaces Using a Lift-off Technique (pages 1431–1433)

      S. Walheim, R. Müller, M. Sprenger, E. Loser, J. Mlynek and U. Steiner

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1431::AID-ADMA1431>3.0.CO;2-0

      A new lift-off technique for microcontact printing of thiol-terminated alkane chains on gold to oxide surfaces is presented here. The technique involves transferring the stamped pattern (the Figure shows a self-assembled monolayer of octadecylsilane) onto a silicon oxide surface, giving greater control over environmental parameters. Specific substrates are not required for the technique, which should thus be available for a wide variety of surfaces.

    4. Fabrication of Ordered Two-Dimensional Arrays of Micro- and Nanoparticles Using Patterned Self-Assembled Monolayers as Templates (pages 1433–1437)

      D. Qin, Y. Xia, B. Xu, H. Yang, C. Zhu and G. M. Whitesides

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1433::AID-ADMA1433>3.0.CO;2-P

      A new method for the fabrication of ordered arrays of small particles is reported here. A combination of microcontact printing of SAMs, surface-templated self-assembly, and confined crystallization has been used to produce 2D arrays of micro- and nanoparticles. The method allows highly accurate control over size distribution and spatial arrangement for a broad range of substrates, such as CdS on Au, as shown in the Figure.

    5. Electrodeposited Quantum Dots: Metastable Rocksalt CdSe Nanocrystals on {111} Gold Alloys (pages 1437–1441)

      Y. Zhang, G. Hodes, I. Rubinstein, E. Grünbaum, R. R. Nayak and J. L. Hutchison

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1437::AID-ADMA1437>3.0.CO;2-1

      Thin layers of epitaxial CdSe nanocrystals with rocksalt structure have been electrodeposited onto gold alloy films. The rocksalt phase does not normally exist for CdSe at ambient pressure, and its (meta)-stability is attributed to the strong interaction between CdSe and Cd–Au (since the phase is virtually absent for deposition onto pure gold films), and to the compressive surface tension forces of the very thin crystals. As the deposition continues, the crystals undergo a solid–solid phase transition to the more stable zincblende and wurtzite phases.

    6. A Novel Route for the Preparation of CuSe and CuInSe2 Nanoparticles (pages 1441–1444)

      M. A. Malik, P. O'Brien and N. Revaprasadu

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1441::AID-ADMA1441>3.0.CO;2-Z

      CuInSe2 quantum dots are reported here for the first time. The highly crystalline nanoparticles of CuInSe2 and also of CuSe were prepared by reaction in tri-n-octylphosphine oxide (TOPO), producing TOPO-capped particles that are close to monodisperse. Transmission electron microscopy shows that the particles are spherical, with clear lattice fringes (see Figure).

    7. Quantum-Confined Gallium Nitride in MCM-41 (pages 1444–1448)

      H. Winkler, A. Birkner, V. Hagen, I. Wolf, R. Schmechel, H. von Seggern and R. A. Fischer

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1444::AID-ADMA1444>3.0.CO;2-H

      Filling the pores of molecular sieves is a way to achieve regular nanoscale arrays of materials at drastically reduced production costs. The loading of zeolite MCM-41with semiconductor GaN is reported here for the first time using the triazidogallium precursor shown in the Figure. The loading process and the subsequent conversion into GaN are thus possible in a non-aqueous medium and can be conveniently followed by IR.

    8. Alignment of Mesostructured Silica on a Langmuir–Blodgett Film (pages 1448–1452)

      H. Miyata and K. Kuroda

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1448::AID-ADMA1448>3.0.CO;2-U

      Biomimetic control over the hierarchical structure of inorganic materialsusing ordered organic surfaces can give rise to elongation and uniaxial alignment, shown here for mesostructured silica particles (see Figure). The alignment direction was normal to the axis of the polymer chains of the Langmuir–Blodgett film, which indicates that an alignment mechanism different from the rubbing method dominates this alignment.

    9. The Use of Mesoporous Silica in Liquid Chromatography (pages 1452–1455)

      K. W. Gallis, J. T. Araujo, K. J. Duff, J. G. Moore and C. C. Landry

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1452::AID-ADMA1452>3.0.CO;2-R

      Preparative chromatography is a potential application for mesoporous silica due to its high surface area. Mesoporous spheres (MSs) have been prepared quickly from acid solution (see Figure), and their properties with regard to liquid chromatography and high-performance liquid chromatography (HPLC) explored. A new chromatographic technique, reverse-phase flash HPLC, is presented that relies on the use of these acid-prepared MSs.

    10. Synthesis by a Solvothermal Route and Characterization of CuInSe2 Nanowhiskers and Nanoparticles (pages 1456–1459)

      B. Li, Y. Xie, J. Huang and Y. Qian

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1456::AID-ADMA1456>3.0.CO;2-3

      CuInSe2 is a leading material for high-efficiency and radiation-hard solar cell applications. The device properties of CuInSe2-based solar cells are known to be critically influenced by their stoichiometric compositions, defect chemistry, and structure; however, with the current methods of synthesis high temperature and pressure are needed to maintain satisfactory stoichiometry. Reported here is a solvothermal route to chalcopyrite CuInSe2 nanocrystals using alkylamines as a solvent. High-quality CuInSe2 nanowhiskers and spherical nanoparticles with stoichiometric composition were produced at a greatly reduced temperature.

    11. A New Class of Blue-Emitting Materials Based on 1,3,5-Oxadiazole Metal Chelate Compounds for Electroluminescent Devices (pages 1460–1463)

      N.-X. Hu, M. Esteghamatian, S. Xie, Z. Popovic, A.-M. Hor, B. Ong and S. Wang

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1460::AID-ADMA1460>3.0.CO;2-0

      A new class of beryllium-oxadiazole compounds (see Figure) for electroluminescent (EL) devices has been synthesized. These materials have high thermal stability, and EL devices with these beryllium chelate compounds as the light-emitting layers exhibit excellent current–voltage characteristics and provide highly saturated blue emission with high luminance.

    12. Blue Light-Emitting Device Based on a Unidentate Organometallic Complex Containing Lithium as an Emission Layer (pages 1463–1466)

      Y. Kim, J.-G. Lee and S. Kim

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1463::AID-ADMA1463>3.0.CO;2-J

      Pure and bright blue emission is very important for the realization of full-color organic electroluminescent devices. Here is reported the synthesis of the novel unidentate organometallic complex shown in the Figure. Analysis of its luminescence and thermal stability properties reveal that the complex is highly stable, and its electronic transition characteristics show that it could be modified for balanced charge injection and transport.

    13. New Separation Science Using Shape-Selective Ion Exchange Intercalation Chemistry (pages 1466–1469)

      A. M. Fogg, V. M. Green, H. G. Harvey and D. O'Hare

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1466::AID-ADMA1466>3.0.CO;2-1

      The ability to tailor the intercalation preferences of porous solids would have important applications in sensing, separations, and catalysis. Shape-selective intercalation is reported here for a crystalline-ordered, layered double hydroxide, whose preference for the intercalation of 1,5- or 2,6-naphthalenedicarboxylate (shown in the Figure) can be controlled and even reversed by altering the temperature and the solvent of the intercalation reaction.

    14. Record Charge Carrier Mobility in a Room-Temperature Discotic Liquid-Crystalline Derivative of Hexabenzocoronene (pages 1469–1472)

      A. M. van de Craats, J. M. Warman, A. Fechtenkötter, J. D. Brand, M. A. Harbison and K. Müllen

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1469::AID-ADMA1469>3.0.CO;2-K

      The largest charge mobility yet for discotic materials has been achieved with a series of hexaalkyl-substituted hexabenzocoronene derivatives (see Figure). When the mesogenic alkyl groups are coupled to the aromatic core via paraphenylene moieties both the high mobility and liquid-crystallinity are retained even at room temperature, making the materials particularly attractive candidates for the conducting layer in electronic devices.

    15. Plowing on the Sub-50nm Scale: Nanolithography Using Scanning Force Microscopy (pages 1473–1475)

      U. Kunze and B. Klehn

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1473::AID-ADMA1473>3.0.CO;2-H

      A new nanolithography technique based on mechanical surface deformation with the tip of a scanning force microscope is reported here. In the lithographic step, the furrow is dynamically plowed into the substrate (see Figure). The pattern transfer is then carried out in a separate wet chemical etching step, thus preserving the tip. The technique can provide linewidths as narrow as 20 nm.

    16. A Mechanism for Strong SHG by Centrosymmetric Anilinosquaraine Dyes (pages 1477–1480)

      C. L. Honeybourne

      Article first published online: 26 NOV 1999 | DOI: 10.1002/(SICI)1521-4095(199912)11:17<1477::AID-ADMA1477>3.0.CO;2-U

      Aggregation of centrosymmetric squaraines into acentric dimers, followed by intermolecular charge transfer (CT) between the centric monomers of the dimer, has been proposed in the past as the mechanism by which these molecules exhibit surprisingly high SHG when deposited as Langmuir–Blodgett monolayer films. Here an alternative mechanism is considered, in which the center of symmetry is destroyed by distortion of the charge distribution in one molecule by the highly polar molecular environment of its nearest neighbors, so that the large potential contributions from intramolecular CT to SHG become symmetry allowed.