Home About us Contact
|
Home About us Contact | ||
|
|
||
Spectroscopy Shows (spectroscopy + shows)
Selected AbstractsMorphological, structural and optical study of quasi-1D SnO2 nanowires and nanobeltsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005D. Calestani Abstract 0.1,0.3 mm thick entanglements of quasi-one-dimensional semiconducting Tin dioxide nanocrystals, in form of nanowires and nanobelts, are successfully grown by low cost Chemical Vapour Deposition directly on large area (100 mm2) Al2O3, SiO2 and Si substrates. Their lateral size ranges from 50 to 700 nm and their length can achieve several hundreds of micrometers. Transmission Electron Microscopy reveals either the nanowires and the nanobelts grow in the tetragonal Rutile structure. Diffraction contrast analyses and selected area diffraction investigations show the nanowires are single crystals without defects while the nanobelts sometimes present twins inside. An almost cylindrical shape and an average diameter of about 30,50 nm for the smallest nanowires is reported. X-ray diffraction investigations exclude the presence of spurious phases. A broad band structured in two emissions peaked at about 450 nm and 560 nm is revealed by large area Cathotoluminescence, while single nanocrystal spectroscopy shows that the reduction of the lateral dimension of the nanobelts from 1000 nm to 50 nm blue-shifts the main emission band at 560 nm of about 40 nm (at room temperature). These preliminary results suggest a possible role of oxygen vacancies and of the surface/volume ratio on the origin and the blue shift of Cathodoluminescence spectra. The near band edge emission, typical of bulk tin dioxide (,320 nm), is not found in nanobelts narrower than 1000 nm. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Tris(dibenzo[a,d]cycloheptenyl)phosphane: A Bulky Monodentate or Tetrapodal LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2007Urs Fischbach Abstract The tetradendate phosphane tris(5H -dibenzo[a,d]cyclohepten-5-yl)phosphane (trop3P, 1) was synthesized from tris(trimethylsilyl)phosphane and 5-chloro-5H -dibenzo[a,d]cycloheptene. Sulfurization of 1 with elemental sulfur led to trop3P=S. Complexes of 1 with AgI, AuI, RhI, IrI, and PdII were prepared. The structures of trop3P (1), trop3P=S (2), [AgCl(trop3P)] (3), [Au(trop3P)(MeCN)]PF6 (5), [RhCl(trop3P)] (6) and [Pd(trop3P)(H2O)](OTf)2 (9) were determined by X-ray diffraction studies. In the coinage metal complexes, 1 serves as monodentate extremely bulky ,1 -phosphane ligand (cone angle ca. 250°). In the RhI, IrI, and PdII complexes, 1 acts as tetradendate ligand. CP MAS NMR spectroscopy shows that the span of the chemical shift tensor increases in 7, 6, and 9 in this order (, = 310 ppm, 410 ppm, 465 ppm) and contains two strongly deshielded components, which are responsible for the unusual high frequency isotropic shift of the 31P resonances. This property correlates inversely with the metal to olefin backbonding (M,C=Ctrop) and ,(31P) decreases with increasing M,C=Ctrop in the order 9 (, = 260 ppm) > 7 (, = 196 ppm) > 6 (, = 135 ppm) > 3 (, = ,30.9 ppm). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Biophysical studies of the development of amyloid fibrils from a peptide fragment of cold shock protein BFEBS JOURNAL, Issue 9 2000Deborah K. Wilkins The peptide CspB-1, which represents residues 1,22 of the cold shock protein CspB from Bacillus subtilis, has been shown to form amyloid fibrils when solutions containing this peptide in aqueous (50%) acetonitrile are diluted in water [M. Großet al. (1999) Protein Science8, 1350,1357] We established conditions in which reproducible kinetic steps associated with the formation of these fibrils can be observed. Studies combining these conditions with a range of biophysical methods reveal that a variety of distinct events occurs during the process that results in amyloid fibrils. A CD spectrum indicative of ,,structure is observed within 1 min of the solvent shift, and its intensity increases on a longer timescale in at least two kinetic phases. The characteristic wavelength shift of the amyloid-binding dye Congo Red is established within 30 min of the initiation of the aggregation process and corresponds to one of the phases observed by CD and to changes in the Fourier transform-infrared spectrum indicative of ,,structure. Short fibrillar structures begin to be visible under the electron microscope after these events, and longer, well-defined amyloid fibrils are established on a timescale of hours. NMR spectroscopy shows that there are no significant changes in the concentration of monomeric species in solution during the events leading to fibril formation, but that soluble aggregates too large to be visible in NMR spectra are present throughout the process. A model for amyloid formation by this peptide is presented which is consistent with these kinetic data and with published work on a variety of disease-related systems. These findings support the concept that the ability to form amyloid fibrils is a generic property of polypeptide chains, and that the mechanism of their formation is similar for different peptides and proteins. [source] Electropolymerization of a Bifunctional Ionic Liquid Monomer Yields an Electroactive Liquid-Crystalline PolymerADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Sungwon Lee Abstract The preparation and polymerization of a bifunctional imidazolium-based ionic liquid (IL) monomer that incorporates both a vinyl group and a thiophene moiety is reported. Potentiodynamic electropolymerization of the monomer produces an optically birefringent polymer film that strongly adheres to the electrode surface. Fourier transform IR spectroscopy shows that polymerization occurs through both the vinyl and thienyl groups. Cylic voltammetry (CV) is used to determine the polymer oxidation potential (1.66,V) and electrochemical bandgap, Eg, of 2.45,eV. The polymer exhibits electrochromism, converting from yellow in the neutral form (,max,=,380,nm) to blue in the polaronic state at 0.6,V (,max,=,672,nm) and to blue-grey in the bipolaronic state at 1.2,V (,max,>,800,nm). Topographic atomic force microscopy (AFM) images reveal isolated (separated) fibrils. Grazing-incidence small-angle X-ray scattering (GISAXS) studies indicate a lamellar structure with a lattice spacing of 3.2,nm. Wide-angle X-ray diffraction (WAXD) studies further suggest that the polymerized thiophene sheets are oriented perpendicular to the polymerized vinylimidazolium. The electrical conductivity, as determined by four-probe dc conductivity measurements was found to be 0.53,S cm,1 in the neutral form and 2.36,S cm,1 in the iodine-doped state, values higher than typically observed for polyalkylthiophenes. The structural ordering is believed to contribute to the observed enhancement of the electrical conductivity. [source] Bottom-Up Engineering of Subnanometer Copper Diffusion Barriers Using NH2 -Derived Self-Assembled MonolayersADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Arantxa Maestre Caro Abstract A 3-aminopropyltrimethoxysilane-derived self-assembled monolayer (NH2SAM) is investigated as a barrier against copper diffusion for application in back-end-of-line (BEOL) technology. The essential characteristics studied include thermal stability to BEOL processing, inhibition of copper diffusion, and adhesion to both the underlying SiO2 dielectric substrate and the Cu over-layer. Time-of-flight secondary ion mass spectrometry and X-ray spectroscopy (XPS) analysis reveal that the copper over-layer closes at 1,2-nm thickness, comparable with the 1.3-nm closure of state-of-the-art Ta/TaN Cu diffusion barriers. That the NH2SAM remains intact upon Cu deposition and subsequent annealing is unambiguously revealed by energy-filtered transmission electron microscopy supported by XPS. The SAM forms a well-defined carbon-rich interface with the Cu over-layer and electron energy loss spectroscopy shows no evidence of Cu penetration into the SAM. Interestingly, the adhesion of the Cu/NH2SAM/SiO2 system increases with annealing temperature up to 7.2,J m,2 at 400,°C, comparable to Ta/TaN (7.5,J m,2 at room temperature). The corresponding fracture analysis shows that when failure does occur it is located at the Cu/SAM interface. Overall, these results demonstrate that NH2SAM is a suitable candidate for subnanometer-scale diffusion barrier application in a selective coating for copper advanced interconnects. [source] Pirouetting in chiral [2]catenanes,ISRAEL JOURNAL OF CHEMISTRY, Issue 2 2007Seogshin Kang One of the best known classes of mechanically interlocked molecules is the category of [2]catenanes, which exhibit donor-acceptor interactions between the 1,5-dioxynaphthalene (DNP) units in a crown ether and the bipyridinium units in the tetracationic cyclophane, cyclobis(paraquat- p -phenylene) (CBPQT4+). In order to gain an in-depth understanding and appreciation of the stereochemistry and dynamic behavior of these [2]catenanes, chiral analogues,having both the DNP ring, which is capable of displaying planar chirality, and the axially chiral binaphthol (BINAP) moiety (as both enantiomers and as the racemic modification), in a crown ether, in addition to the CBPQT4+ cyclophane,have been synthesized using a template-directed protocol. Dynamic 1H NMR spectroscopy shows that (i) the presence of immutable axial chirality, arising from the BINAP moiety in the crown ether component, leads to no induction of diastereoselectivity,the chiral catenanes exist as a mixture of diastereoisomers in solution at low temperatures in the approximate ratio of 1:1, (ii) the barrier (,GcD,) to the interconversion between these two diastereoisomers is 7.9 ± 0.1 kcal mol,1 at 171 K, and (iii) no induction of diastereoselectivity is observed upon the addition of a chiral solvating agent to the chrial catenanes. The pattern of behavior in the variable temperature 1H NMR spectra and the low ,TGcD, value indicates that the dynamic process involving the interconversion between these two diastereoisomers is one of a pirouetting nature. Of the four possible diastereoisomers, only two, (R)-(pR/pS) or (S)-(pR/pS), are shown to exist in solution. [source] A ,-amino acid modified heptapeptide containing a designed recognition element disrupts fibrillization of the amyloid ,-peptideJOURNAL OF PEPTIDE SCIENCE, Issue 9 2010Valeria Castelletto Abstract We study the complex formation of a peptide ,A,AKLVFF, previously developed by our group, with A,(1,42) in aqueous solution. Circular dichroism spectroscopy is used to probe the interactions between ,A,AKLVFF and A,(1,42), and to study the secondary structure of the species in solution. Thioflavin T fluorescence spectroscopy shows that the population of fibers is higher in ,A,AKLVFF/A,(1,42) mixtures compared to pure A,(1,42) solutions. TEM and cryo-TEM demonstrate that co-incubation of ,A,AKLVFF with A,(1,42) causes the formation of extended dense networks of branched fibrils, very different from the straight fibrils observed for A,(1,42) alone. Neurotoxicity assays show that although ,A,AKLVFF alters the fibrillization of A,(1,42), it does not decrease the neurotoxicity, which suggests that toxic oligomeric A,(1,42) species are still present in the ,A,AKLVFF/A,(1,42) mixtures. Our results show that our designed peptide binds to A,(1,42) and changes the amyloid fibril morphology. This is shown to not necessarily translate into reduced toxicity. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd. [source] Thermo-Raman spectroscopy of synthetic nesquehonite , implication for the geosequestration of greenhouse gasesJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2008Matthew C. Hales Abstract Pure nesquehonite (MgCO3·3H2O)/Mg(HCO3)(OH)·2H2O was synthesised and characterised by a combination of thermo-Raman spectroscopy and thermogravimetry with evolved gas analysis. Thermo-Raman spectroscopy shows an intense band at 1098 cm,1, which shifts to 1105 cm,1 at 450 °C, assigned to the ,1CO32, symmetric stretching mode. Two bands at 1419 and 1509 cm,1 assigned to the ,3 antisymmetric stretching mode shift to 1434 and 1504 cm,1 at 175 °C. Two new peaks at 1385 and 1405 cm,1 observed at temperatures higher than 175 °C are assigned to the antisymmetric stretching modes of the (HCO3), units. Throughout all the thermo-Raman spectra, a band at 3550 cm,1 is attributed to the stretching vibration of OH units. Raman bands at 3124, 3295 and 3423 cm,1 are assigned to water stretching vibrations. The intensity of these bands is lost by 175 °C. The Raman spectra were in harmony with the thermal analysis data. This research has defined the thermal stability of one of the hydrous carbonates, namely nesquehonite. Thermo-Raman spectroscopy enables the thermal stability of the mineral nesquehonite to be defined, and, further, the changes in the formula of nesquehonite with temperature change can be defined. Indeed, Raman spectroscopy enables the formula of nesquehonite to be better defined as Mg(OH)(HCO3)·2H2O. Copyright © 2008 John Wiley & Sons, Ltd. [source] Raman spectroscopy of hydrotalcites with phosphate in the interlayer: implications for the removal of phosphate from waterJOURNAL OF RAMAN SPECTROSCOPY, Issue 7 2006Ray L. Frost Abstract Hydrotalcites with phosphate in the interlayer were prepared at different pH values. At pH > 11.0 (PO4)3, was the intercalated ionic species, whereas at pH < 11.0 a mixture of (PO4)3, and (HPO4)2, ions was intercalated. Powder X-ray diffraction shows that the hydrotalcite formed at pH 9.5 is poorly diffracting with a d-spacing of 11.9 Å; whereas the d(003) spacing for the phosphate interlayered hydrotalcite formed at pH 11.9 and 12.5 was 8.0 and 7.9 Å respectively. The addition of a thermally activated ZnAl-HT to a phosphate solution resulted in the uptake of the phosphate and the reformation of the hydrotalcite. Raman spectroscopy of the phosphate interlayered hydrotalcites shows that the interlayered anion is pH dependent and only above pH 11.9 is the orthophosphate anion intercalated. At lower pH, the monohydrogen phosphate anion is intercalated. Raman spectroscopy shows that upon addition of the thermally activated hydrotalcite to an aqueous phosphate solution, results in the uptake of phosphate anion from the solution. Copyright © 2006 John Wiley & Sons, Ltd. [source] Efficient Homogeneous Chemical Modification of Bacterial Cellulose in the Ionic Liquid 1- N -Butyl-3-methylimidazolium ChlorideMACROMOLECULAR RAPID COMMUNICATIONS, Issue 19 2006Kerstin Schlufter Abstract Summary: Bacterial cellulose (BC), a unique type of cellulose, with high degree of polymerization of 6,500 could be dissolved easily in the ionic liquid 1- N -butyl-3-methylimidazolium chloride. For the first time, well-soluble BC acetates and carbanilates of high degree of substitution (up to a complete modification of all hydroxyl groups) were accessible under homogeneous and mild reaction conditions. Characterization of the new BC derivatives by NMR and FTIR spectroscopy shows an unexpected distribution of the acetyl moieties in the order O-6,>,O-3,>,O-2. 13C NMR spectrum (DMSO- d6) of a cellulose acetate with a DS of 2.25 synthesized in 1- N -butyl-3-methylimidazolium chloride. [source] High-output-power AlGaN/GaN ultraviolet-light-emitting diodes by activation of Mg-doped p-type AlGaN in oxygen ambientPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2010Kengo Nagata Abstract We demonstrated activation annealing of Mg-doped p-type Al0.17Ga0.83N in different gases. The hole concentration of Al0.17Ga0.83N annealed in oxygen is higher than that annealed in nitrogen or air. A hole concentration of 1.3,×,1016,cm,3 at room temperature was achieved by annealing in oxygen flow at 900,°C. Secondary ion mass spectroscopy shows that hydrogen dissociation from Mg-doped Al0.17Ga0.83N is found to be enhanced by annealing in a flow of oxygen, compared with annealing in a flow of nitrogen. We confirmed the effect of activation annealing in oxygen flow on the performance of UV light-emitting diode (LED). At a DC current of 100,mA, the output power of the LED annealed in oxygen flow at 900,°C is four times higher than that of the LED annealed in nitrogen flow at 800,°C. [source] MOCVD as a dry deposition method of ZnSe buffers for Cu(In,Ga)(S,Se)2 solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2004Susanne Siebentritt Abstract ZnSe prepared by metal organic chemical vapor deposition is used as a buffer layer in Cu(In,Ga)(S,Se)2 solar cells without any utilization of wet chemistry. Cell efficiencies are as good as cells with the conventional CdS buffer. Stability of unencapsulated cells under damp heat conditions is somewhat lower for the alternative buffer. The first stages of photoassisted growth are studied. X-ray photoemission spectroscopy shows that a continuous layer is formed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Raman spectroscopy of silver pertechnetateACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2003Mark J. Sarsfield The title compound, AgTcO4, contains close Ag,O contacts, and Raman spectroscopy shows a reduction in the Tc,O stretching frequencies on changing the pertechnetate counter-cation from K+ to Ag+. [source] Numerous Isomers of Serine Octamer Ions Characterized by Infrared Photodissociation SpectroscopyCHEMPHYSCHEM, Issue 15 2009Xianglei Kong Dr. Building block of life? Infrared photodissociation spectroscopy shows at least six stable (Ser8+H)+ isomers. While retaining the chiral selectivity of the zwitterionic core, these vary mainly in H-bonding of their peripheral OH groups (see picture). This could allow incorporation of any other amino acid to make these isomers unique for prebiotic selectivity of L -amino acids for proteins. [source] | ||||||||||||||||