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  • 1
    Electronic Resource
    Electronic Resource
    The chemical and electronic structure of the interface between aluminum and polythiophene semiconductors (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 664-672 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have investigated the chemical nature and the electronic structure of the interface between a low work function metal, aluminum, and a conjugated polymer semiconductor, polythiophene. We have studied the initial stages of the interface formation by depositing the metal onto the surface of a polymer film. Charge transfer processes between the metal and the polymer are analyzed using core-level x-ray photoelectron spectroscopy (XPS); the evolution upon metallization of the valence electronic levels directly related to the polymer electronic structure is followed with ultraviolet photoelectron spectroscopy (UPS). With these techniques, we investigate the deposition of aluminum on two polythiophene systems (i) the alkyl-substituted poly-3-octylthiophene and (ii) the α-sexithiophene oligomer. The experimental data are compared to the results of a recent quantum chemical study on model systems consisting of thiophene oligomers (up to sexithiophene) interacting with a few Al atoms. The interaction of polythiophene with Al atoms is found to modify dramatically the structure of the conjugated backbone, as strong carbon–aluminum bonds are formed in the α positions of the thiophene rings. A large charge transfer takes place from the Al atoms to the polymer chain, and the upper π levels of the polymer are strongly affected. The metallization is contrasted to the doping of conjugated polymers with alkali metals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466217
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  • 2
    Electronic Resource
    Electronic Resource
    Metal/conjugated polymer interfaces: A theoretical investigation of the interaction between aluminum and trans-polyacetylene oligomers (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4253-4262 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular model systems are used to quantum chemically investigate the interface between aluminum and trans-polyacetylene. Modifications to the chemical and electronic structure of trans-polyacetylene oligomers upon interaction with a submonolayer of aluminum are studied at the semiempirical and ab initio Hartree–Fock levels. An aluminum atom is found to react strongly with a carbon atom of the trans-polyacetylene chain to form a heteropolar covalent bond. In this process, the binding carbon evolves from an sp2- to an sp3-hybridized electronic structure. Significant contributions from Al 3s and 3p atomic orbitals are found in the frontier molecular orbitals in aluminum/polyene complexes. This results in the fact that despite the presence of sp3 sites due to Al–C bonds, which reduces π conjugation along the chain, a large degree of delocalization in π levels is maintained. Our calculations are discussed in relation to experimental ultraviolet photoelectron spectra (UPS) taken during initial stages of aluminum deposition on oxygen-free films of trans-polyacetylene oligomers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465032
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  • 3
    Electronic Resource
    Electronic Resource
    Reactions of low work function metals Na, Al, and Ca on α,ω-diphenyltetradecaheptaene. Implications for metal/polymer interfaces (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 6765-6771 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interactions between different low work function metals aluminium, calcium and sodium, and α,ω-diphenyltetradecaheptaene, a model molecule for certain conjugated polymers, have been investigated using both x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The spectra are interpreted with the help of the results of quantum chemical calculations performed within the local spin density (LSD) approximation methodology. The metals are found to interact with the conjugated system in very different ways. Aluminium forms a covalent bond, which strongly modifies the π-electronic structure of the conjugated molecule, while both the sodium and the calcium atoms act as doping agents, inducing new states in the otherwise forbidden bandgap. These new gap states can be viewed as a soliton–antisoliton pair for the Na/DP7 and a bipolaronic-like defect for Ca/DP7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467035
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  • 4
    Electronic Resource
    Electronic Resource
    Metal/conjugated polymer interfaces: Sodium, magnesium, aluminum, and calcium on trans-polyacetylene (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9137-9142 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum chemical calculations are performed to theoretically study the interaction between low work function metal atoms and trans-tetradecaheptaene, an extended model molecule for π-conjugated polymers. We present characterizations of metal/polyene complexes obtained by the local spin density method. The results show that charge transfer reactions occur for Na and Ca and the formation of a covalent bond for Al. Mg atoms, however, are found not to react significantly with π-conjugated systems. Differences in the bonding mechanism between the metals are discussed and the theoretical density of valence states are compared to experimental photoelectron spectroscopy (UPS) data. The results demonstrate that the local spin density method can be successfully used to interpret valence UPS spectra from early stages of metal/π-conjugated interface formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468043
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  • 5
    Electronic Resource
    Electronic Resource
    A theoretical investigation of the interactions between thiophene and vanadium, chromium, copper, and gold (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 6153-6158 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have employed quantum chemical methods, at the local spin density approximation level, to study the interaction between an organic semiconductor, polythiophene, and potential metals for hole injecting contacts in devices: vanadium, chromium, copper, and gold. The results show that there is a strong interaction between vanadium and the thiophene ring, mainly due to covalent bond formation between the metal and the S and Cα atoms of the thiophene. Vanadium is therefore predicted to provide good conditions for chemisorption and mechanical stability at the polymer/contact interface. A similar, but considerably weaker, covalent interaction is found between chromium and all the conjugated atoms of the thiophene molecule. For both these metals, the interactions cause the thiophene ring to lose its aromaticity and planarity which, as a consequence, would interrupt the π-electron system in a polymer and impair charge transport along the chains. In the case of copper, the metal is found to react only with the sulfur atom of the thiophene and to a very small extent. For gold, the results indicate that there are no significant chemical interactions. Our results are in good qualitative agreement with XPS measurements performed during metallization of thin films of poly(3-hexylthiophene). The calculations confirm the general trend of reactivities for this series of metals: V(approximately-greater-than)Cr(approximately-greater-than)Cu(approximately-greater-than)Au=0. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469349
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  • 6
    Electronic Resource
    Electronic Resource
    Metal/conjugated polymer interfaces: A local density functional study of aluminum/polyene interactions (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 9258-9264 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interactions between aluminum atoms and model molecules representing trans-polyacetylene are studied quantum chemically by a local density functional method. We focus on the chemical and electronic structure of the organoaluminum complexes. Special emphasis is put on a comparison between results at the local spin density approximation and ab initio Hartree–Fock levels. In unmetallized polyenes, the density functional method provides a very good description of the carbon–carbon bond lengths of conjugated systems; in the case of hexatriene, it reproduces the bond dimerization in very good agreement with experimental measurements. Upon metallization, a strong covalent interaction between aluminum and carbon is found. The Al–C bond formation induces an interruption of the bond alternation pattern and reduces the π-conjugation in the oligomer, in qualitative agreement with photoelectron spectroscopy data and previous theoretical results at the Hartree–Fock level. Notably, the π-electron levels in the organoaluminum complexes maintain delocalization. In contrast to Hartree–Fock results where an aluminum atom binds to a single carbon, the interactions calculated with the local spin density approximation lead to (i) formation of multicenter aluminum–carbon bonding; (ii) near planarity of the polyene molecule; and (iii) a lower degree of charge transfer from the metal atom to the polymer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466678
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  • 7
    Electronic Resource
    Electronic Resource
    The chemical and electronic structure of the interface between aluminum and conjugated polymers
    Amsterdam : Elsevier
    Electrochimica Acta 39 (1994), S. 235-244 
    Details
    ISSN: 0013-4686
    Keywords: electronic structure ; interface chemistry ; polymer-based devices
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0013-4686(94)80059-6
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  • 8
    Electronic Resource
    Electronic Resource
    Ab initio Hartree-Fock studies of the binding energy of a soliton to a sodium counterion in doped trans-polyacetylene
    Amsterdam : Elsevier
    Chemical Physics Letters 190 (1992), S. 407-412 
    Details
    ISSN: 0009-2614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0009-2614(92)85164-6
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  • 9
    Electronic Resource
    Electronic Resource
    In vitro real-time characterization of cell attachment and spreading (1998)
    Springer
    Journal of materials science 9 (1998), S. 785-788 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A method based on the piezoelectric quartz crystal microbalance (QCM) technique for in vitro real-time characterization of cell attachment and spreading on surfaces has been developed. The method simultaneously measures the resonant frequency, f, and the dissipation energy, D, of the oscillating system. The QCM responses are sensitive to very small amounts (a few hundreds) of cells and highly specific to surface chemical properties. The first results from deposition of cells on two polystyrene surfaces of different wettability in serum-containing medium are reported. It has previously been shown that a decrease in f is related to the degree of cell spreading. In our data it appears that the extent or quality of cell attachment is reflected in an increase in D caused by adhering cells. The combined information from f and D measured by this technique might therefore be useful to probe cell–surface interactions for biomaterials. © 1998 Kluwer Academic Publishers
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008927624337
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  • 10
    Electronic Resource
    Electronic Resource
    Ultrastructural characterisation of cells specialised for nitrogen fixation in a non-heterocystous cyanobacterium,Trichodesmium spp. (1997)
    Springer
    Protoplasma 197 (1997), S. 76-85 
    Details
    ISSN: 1615-6102
    Keywords: Cell differentiation ; Immunolocalisation ; Nitrogenase ; Non-heterocystous cyanobacteria ; Trichodesmium ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Trichodesmium is the first described example of a filamentous cyanobacterium without heterocysts that contains cells specialised for nitrogen fixation. The ultrastructure of cells with and without nitrogenase were compared using primarilyTrichodesmium tenue Wille, but alsoT. thiebautii Gomont andT. erythraeum Ehrenberg et Gomont. Immunohistochemistry demonstrated that the cytoplasm of certain cells was densely labelled with antibodies against Fe-protein (dinitrogenase reductase). Comparative TEM-image analysis revealed that these cells were also distinguished by a denser thylakoid network, dividing the vacuole-like space into smaller units. The nitrogenase-containing cells also exhibited less extensive gas vacuoles as well as fewer and smaller cyanophycin granules compared to cells which lacked nitrogenase. Carboxysomes were present in both cell types in equal proportion. Longitudinal sections showed that cells with nitrogenase were arranged adjacent to each other, and that groups of cells with and without nitrogenase may coexist in the same trichome. The correlation between modifications in ultrastructure and the presence of nitrogenase suggests a new type of cyanobacterial cell specialisation related to nitrogen fixation. The results obtained also question the systematic affiliation of the genusTrichodesmium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279886
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