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Structural Order (structural + order)
Selected AbstractsStructural order on different length scales in amorphous silicon investigated by Raman spectroscopyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2010S. Muthmann Abstract Parameters for the structural short (SRO) and medium range order (MRO) of hydrogenated amorphous silicon (a-Si:H) films on the edge of the microcrystalline silicon (µc-Si:H) phase transition were studied with Raman spectroscopy. The observed samples were deposited using radio frequency plasma enhanced chemical vapor deposition. The studied films were grown with various constant and non-constant silane concentrations (SCs). A substrate dependent correlation of SC to the intensity ratio (IMRO) of the transversal acoustical (TA) and the transversal optical (TO) phonon bands was found. A strong correlation between width and position of the (TO) phonon band was observed. These two easily accessible parameters show an increase of SRO when IMRO decreases. [source] Thiophene,Benzothiadiazole Co-Oligomers: Synthesis, Optoelectronic Properties, Electrical Characterization, and Thin-Film PatterningADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Manuela Melucci Abstract Newly synthesized thiophene (T) and benzothiadiazole (B) co-oligomers of different size, alternation motifs, and alkyl substitution types are reported. Combined spectroscopic data, electrochemical analysis, and theoretical calculations show that the insertion of a single electron-deficient B unit into the aromatic backbone strongly affects the LUMO energy level. The insertion of additional B units has only a minor effect on the electronic properties. Cast films of oligomers with two alternated B rings (B,T,B inner core) display crystalline order. Bottom-contact FETs based on films cast on bare SiO2 show hole-charge mobilities of 1,×,10,3,5,×,10,3,cm2 V,1s,1 and Ion/Ioff ratios of 105,106. Solution-cast films of cyclohexyl-substituted compounds are amorphous and do not show FET behavior. However, the lack of order observed in these films can be overcome by nanorubbing and unconventional wet lithography, which allow for fine control of structural order in thin deposits. [source] Reduced Surfactant Uptake in Three Dimensional Assemblies of VOx Nanotubes Improves Reversible Li+ Intercalation and Charge CapacityADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Colm O'Dwyer Abstract The relationship between the nanoscale structure of vanadium pentoxide nanotubes and their ability to accommodate Li+ during intercalation/deintercalation is explored. The nanotubes are synthesized using two different precursors through a surfactant-assisted templating method, resulting in standalone VOx (vanadium oxide) nanotubes and also "nano-urchin". Under highly reducing conditions, where the interlaminar uptake of primary alkylamines is maximized, standalone nanotubes exhibit near-perfect scrolled layers and long-range structural order even at the molecular level. Under less reducing conditions, the degree of amine uptake is reduced due to a lower density of V4+ sites and less V2O5 is functionalized with adsorbed alkylammonium cations. This is typical of the nano-urchin structure. High-resolution TEM studies revealed the unique observation of nanometer-scale nanocrystals of pristine unreacted V2O5 throughout the length of the nanotubes in the nano-urchin. Electrochemical intercalation studies revealed that the very well ordered xerogel-based nanotubes exhibit similar specific capacities (235,mA h g,1) to Na+ -exchange nanorolls of VOx (200,mA h g,1). By comparison, the theoretical maximum value is reported to be 240,mA h g,1. The VOTPP-based nanotubes of the nano-urchin 3D assemblies, however, exhibit useful charge capacities exceeding 437,mA h g,1, which is a considerable advance for VOx based nanomaterials and one of the highest known capacities for Li+ intercalated laminar vanadates. [source] Supramolecular Organization of ssDNA-Templated ,-Conjugated Oligomers via Hydrogen BondingADVANCED MATERIALS, Issue 10-11 2009Mathieu Surin The templated self-assembly of water-soluble ,-conjugated molecules bearing a diaminotriazine moiety H-bonding to a single-strand oligothymine template leads to defined structures. We study these assemblies with molecular modeling, circular dichroism spectroscopy, and scanning probe microscopy, to get a better understanding of the factors governing the supramolecular organization and structural order. [source] Functionalized Arylacetylene Oligomers for Organic Thin-Film Transistors (OTFTs),ADVANCED MATERIALS, Issue 10 2005Oligo(arylacetylene)-based organic thin-film transistors (OTFTs) possess good structural order and smooth film morphologies, and exhibit field-effect mobilities of 0.3,cm2,V,1,s,1, one of the highest field-effect mobilities reported for an OTFT device that does not possess a self-assembled-layer configuration. The Figure shows the measured output characteristics (drain,source current, IDS versus drain,source voltage, VDS) at different gate voltages (VG). [source] Probing the Building Blocks of Eumelanins Using Scanning Electron MicroscopyPIGMENT CELL & MELANOMA RESEARCH, Issue 3 2000J. BRIAN NOFSINGER Scanning electron microscopy (SEM) is used to examine the structure of natural and synthetic melanins. Eumelanin from Sepia officinalis and synthetic eumelanin are found to be structurally dissimilar. The natural sample has a significant structural order with subunits that have a lateral dimension of ,15 nm. The synthetic samples, on the other hand, appear to be amorphous solids. These results lend support for the existence of fundamental structural units proposed from the analyses of wide-angle X-ray diffraction measurements and previous mass-spectrometry results. These findings also provide insight into the disparate photophysical behavior of Sepia and synthetic eumelanin. [source] Stably folded de novo proteins from a designed combinatorial libraryPROTEIN SCIENCE, Issue 1 2003Yinan Wei Abstract Binary patterning of polar and nonpolar amino acids has been used as the key design feature for constructing large combinatorial libraries of de novo proteins. Each position in a binary patterned sequence is designed explicitly to be either polar or nonpolar; however, the precise identities of these amino acids are varied extensively. The combinatorial underpinnings of the "binary code" strategy preclude explicit design of particular side chains at specified positions. Therefore, packing interactions cannot be specified a priori. To assess whether the binary code strategy can nonetheless produce well-folded de novo proteins, we constructed a second-generation library based upon a new structural scaffold designed to fold into 102-residue four-helix bundles. Characterization of five proteins chosen arbitrarily from this new library revealed that (1) all are ,-helical and quite stable; (2) four of the five contain an abundance of tertiary interactions indicative of well-ordered structures; and (3) one protein forms a well-folded structure with native-like features. The proteins from this new 102-residue library are substantially more stable and dramatically more native-like than those from an earlier binary patterned library of 74-residue sequences. These findings demonstrate that chain length is a crucial determinant of structural order in libraries of de novo four-helix bundles. Moreover, these results show that the binary code strategy,if applied to an appropriately designed structural scaffold,can generate large collections of stably folded and/or native-like proteins. [source] Structures of mannose-6-phosphate isomerase from Salmonella typhimurium bound to metal atoms and substrate: implications for catalytic mechanismACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2009S. R. Sagurthi Mannose-6-phosphate isomerase (MPI) catalyzes the interconversion of mannose 6-phosphate and fructose 6-phosphate. X-ray crystal structures of MPI from Salmonella typhimurium in the apo form (with no metal bound) and in the holo form (with bound Zn2+) and two other structures with yttrium bound at an inhibitory site and complexed with Zn2+ and fructose 6-phosphate (F6P) were determined in order to gain insights into the structure and the isomerization mechanism. Isomerization involves acid/base catalysis with proton transfer between the C1 and C2 atoms of the substrate. His99, Lys132, His131 and Asp270 are close to the substrate and are likely to be the residues involved in proton transfer. The interactions observed at the active site suggest that the ring-opening step is probably catalyzed by His99 and Asp270. An active-site loop consisting of residues 130,133 undergoes conformational changes upon substrate binding. Zn2+ binding induces structural order in the loop consisting of residues 50,54. The metal atom appears to play a role in substrate binding and is probably also important for maintaining the architecture of the active site. Isomerization probably follows the previously suggested cis -enediol mechanism. [source] Geminal Ionic Liquids: A Combined Approach to Investigate Their Three-Dimensional OrganisationCHEMISTRY - A EUROPEAN JOURNAL, Issue 47 2009Francesca D'Anna Dr. Abstract Different investigations, such as 1D and 2D NMR spectroscopy, resonance light scattering spectroscopy and molecular dynamics simulations, have been jointly used to achieve a deeper understanding of the degree of structural order in two geminal ionic liquids. In particular, 3,3,-di- n -butyl-1,1,-(1,3-phenylenedimethylene)diimidazolium and 3,3,-di- n -butyl-1,1,-(1,4-phenylenedimethylene)diimidazolium bis[bis(trifluoromethanesulfonyl)imide] have been studied. These geminal ionic liquids were chosen because of the presence of both a rigid phenylenedimethylene link between two imidazolium rings, which should give a high degree of order to the solvent system, and the different shapes of the two cations of the isomers, which could induce different properties and packing in the liquid state. Data collected here show that the two geminal ionic liquids are characterised by a different degree of structural order that induces, for example, a different sensitivity of the two solvent systems to temperature changes or to the presence of a co-solvent such as methanol. [source] | |||||||||||||