Advanced Materials

Cover image for Advanced Materials

January, 1998

Volume 10, Issue 1

Pages 13–75

    1. Structural Analysis of Self-Assembling Nanocrystal Superlattices (pages 13–30)

      Zhong Lin Wang

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<13::AID-ADMA13>3.0.CO;2-W

      Nanocrystal engineered superlattices are a new type of material, differing from either a single particle or the corresponding bulk material, explains Z. L. Wang. He briefly outlines what is meant by a self-assembled nanocrystal lattice—the Figure shows an example consisting of faceted particles—before reviewing their structural analysis, concentrating on transmission electron microscopy and related techniques.

    2. Effects of Sodium on Polycrystalline Cu(In,Ga)Se2 and Its Solar Cell Performance (pages 31–36)

      Leeor. Kronik, David Cahen and Hans Werner Schock

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<31::AID-ADMA31>3.0.CO;2-3

      The promising new generation of solar cells based on CIGS (Cu(I,Ga)Se2) exhibits behavior differing from that of earlier cells because of changes in the method of preparation, leading, among other things, to a difference in sodium content. A simple defect chemical model is presented for the effects of sodium on the surface chemistry and electronic properties of CIGS thin films. The model, based on the well-known catalytic effect that alkali metals have on surface oxidation of semiconductors, is shown to be consistent with the experimental data available in the literature.

    3. Rapid Charge Transport Along Self-Assembling Graphitic Nanowires (pages 36–38)

      Anick M. van de Craats, John M. Warman, Klaus Müllen, Yves Geerts and Johann D. Brand

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<36::AID-ADMA36>3.0.CO;2-A

      The conductive properties of molecular wires constructed by columnar self-assembly of peripherally substituted large aromatic macrocycles are reported. The Figure illustrates how planar, disc-shaped aromatic molecules form a discotic liquid crystal (LC) phase consisting effectively of coaxially insulated wires of “one-dimensional graphite”. The intracolumnar charge mobility is the largest yet for a discotic LC material.

    4. The Origin of Electroluminescence at Porous p-Silicon Layers–Electrolyte Interfaces (pages 38–42)

      J. David Moreno, Ricardo Guerrero-Lemus, José M. Martínez-Duart, M. Luisa Marcos and Jaime González-Velasco

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<38::AID-ADMA38>3.0.CO;2-Z

      The electroluminescent properties of p-type porous silicon layers (p-PSLs) in aqueous solutions can be significantly improved by the presence of hydrogen peroxide, as demonstrated by the electroluminescence (EL) and electrochemical results presented. The possible species responsible for electron injection into the conduction band of porous silicon—necessary for EL—are discussed in the light of these results. Particular attention is paid to the possibilities of formation of HO2 during anodic treatments of p-PSLs or a reaction involving OH radicals and Si–H bonds.

    5. Very Soft Chemistry: Room Temperature Self-Assembly of (DABCOH)2Sn3S7, a Microporous Layered Tin(IV) Sulfide (pages 42–46)

      Tong Jiang, Alan Lough and Geoffre A. Ozin

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<42::AID-ADMA42>3.0.CO;2-W

      Self-assembled metal chalcogenide open-framework materials such as that shown in the Figure—a projection on the [100] plane of the structure of a microporous layered tin(IV) sulfide (DABCOH)2Sn3S71, where DABCOH denotes singly protonated 1,8-diazabicyclooctane—are of interest for chemical sensing applications. A “very soft chemistry”, room temperature synthesis of 1 is reported.

    6. Directed Crystallization of Selected Aluminophosphate Hydrates by pH Control (pages 46–49)

      Jesús García-Carmona, Rafael Rodríguez-Clemente and Jaime Gómez-Morales

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<46::AID-ADMA46>3.0.CO;2-8

      Is a systematization of the synthesis of aluminophosphates possible? A step away from trial and error syntheses is permitted by an investigation of the link between the structure of aluminophosphate hydrates and the structure of the predominant species in the gel precursor. The ratio Al(O)/Al(T), i.e., the ratio of octahedrally to tetrahedrally coordinated aluminum, depends on the pH of the gel precursor. Thus, it is demonstrated that the crystallization reaction can be directed to the desired aluminophosphate phase simply by controlling the gel precursor pH.

    7. Nanosized Hydroxyapatite Precipitation from Homogeneous Calcium/Citrate/Phosphate Solutions Using Microwave and Conventional Heating (pages 49–53)

      Anabel López-Macipe, Jaime Gómez-Morales and Rafael Rodríguez-Clemente

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<49::AID-ADMA49>3.0.CO;2-R

      Materials for bone repair and replacement can be prepared from nanometer-size hydroxyapatite (HA). A method of precipitating nanosize HA at atmospheric pressure, rapidly, using microwave heating is presented, and particles obtained by this and a conventional heating method are compared. The transmission electron micrograph shows particles obtained after microwave heating for 60 min.

    8. Effect of Aging on Luminescence from Isolated Mn2+ Confined in Cd0.95Mn0.05S Clusters (pages 53–57)

      Laurent Levy, Dorothee Ingert, Nicolas Feltin and Marie-Paule Pileni

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<53::AID-ADMA53>3.0.CO;2-O

      Luminescence from dilute magnetic semiconductors (DMSs) such as Cd0.95Mn0.05S, in which the magnetic ion Mn2+ randomly replaces the host cation, has been studied. The spectroscopic behavior of Cd0.95Mn0.05S is reported to change markedly when the particles are aged in micellar solution. It is concluded that the high luminescence efficiency observed for Mn2+-doped nanocrystals cannot be attributed to a particle-size effect, as expected within the framework of an electron–hole localization theory. Instead, the luminescence is attributed to the aging and/or passivation of the particles.

    9. The Influence of Thermal Annealing on the Morphology of Sexithienyl Thin Films (pages 57–60)

      Pascal Viville, Roberto Lazzaroni, Jean Luc Brédas, Paolo Moretti, Paolo Samorí and Fabio Biscarini

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<57::AID-ADMA57>3.0.CO;2-0

      α-Sexithiophene (T6) thin films become smooth and featureless when annealed at temperatures above 160°C. (The Figure shows a typical film before (left) and after (right) being annealed for 20 min at 170°C.) This change in morphology is characterized in terms of the roughness exponent and it is suggested that the threshold temperature represents the onset of fast diffusion of T6 molecules on the surface

    10. A Solid-State Electrochromic Device Based on Two Optically Complementary Conducting Polymers (pages 60–64)

      Wilson A. Gazotti Jr., Giuseppe Casalbore-Miceli, Alessandro Geri and Marco-A. de Paoli

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<60::AID-ADMA60>3.0.CO;2-3

      Materials for high-performance electrochromic windows must fulfill various requirements, e.g., high optical contrast, fast response time, and stability. The construction and characterization of a device with technologically interesting properties are described. The device uses two active polymer electrode materials with complementary electrochromic behavior and a complex between a commercial elastomer and LiClO4 as the solid electrolyte. The cell can be assembled under atmospheric conditions and exhibits good contrast between the colored and bleached forms.

    11. High Peak Brightness Polymer Light-Emitting Diodes (pages 64–68)

      Nir Tessler, Nick T. Harrison and Richard H. Friend

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<64::AID-ADMA64>3.0.CO;2-G

      Laser action is currently limited by device efficiency, rather than peak current density, is one conclusion drawn from this investigation of optically pumped light-emitting diodes (LEDs) made of conjugated polymers. The structure of the LEDs has been optimized to allow high current operation using short drive pulses. Unexpectedly high current densities and high luminous efficiencies at these current densities allow a high peak brightness of 5 × 106 cd/m2; see also the cover of this issue. The implications of these results for the fabrication of injection lasers are discussed.

    12. Diblock Thin Films with Densely Hexagonally Packed Nanochannels (pages 69–71)

      Guojun Liu and Jianfu Ding

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<69::AID-ADMA69>3.0.CO;2-N

      Membranes with “chemical valves” such as described here could be used for controlled drug release or chemical sensing. The membranes contain hexagonally packed and uniformly sized nanochannels that are partially filled with poly(acrylic acid) (PAA), as shown in the Figure. A mode of operation is discussed for the large change in water permeability caused by variations in pH, ionic strength, and ion type.

    13. Fabrication of Microscopic Biosensor Arrays Without Microscopic Alignment (pages 73–75)

      Leonard M. Tender, Kimberl A. Opperman, Philip D. Hampton and Gabriel P. Lopez

      Article first published online: 26 JAN 1999 | DOI: 10.1002/(SICI)1521-4095(199801)10:1<73::AID-ADMA73>3.0.CO;2-K

      Microscopic arrays of biosensors can be formed by patterning chemically or biochemically functional groups onto surfaces, e.g., by photolithography or microprinting. A method of fabrication of microscopic biosensor arrays is described that has the advantage, compared to the above-mentioned methods, of not requiring microscopic alignment: first, selfassembled monolayers (SAMs) are spatially selectively removed from gold arrays by electrochemical desorption, then the exposed elements are re-modified with SAMs formed of different alkanethiolates.