Search results for "METAL"
showing 10 items of 7908 documents
Electronic structure of p-type ultraviolet-transparent conducting CuScO2 films
2008
Abstract We investigate the electronic structure of CuScO 2 thin films grown on sapphire and mica substrates by pulsed laser deposition. X-ray diffraction and microanalysis confirm that the films have the expected delafossite crystal structure and stoichiometric proportions. The electronic structure is investigated by means of X-ray and ultraviolet photoelectron spectroscopy. Electronic states in the range 0–1350 eV are identified, making reference to theoretical density-of-states calculations up to 80 eV. Photoelectron spectra near the Fermi energy confirm the p-character of the films. Optical absorption spectroscopy shows that the films are transparent up to 3.7 eV and exhibit an intense …
On nature of the transient IR-absorption STE-like bands at 0.15–0.36eV in alkali halides
2001
New evidence is given that two classes (A and B) of the transient IR-absorption bands: (A) with max. at 0.15-0.36 eV (in NaCl : I, NaBr, NaI, KCl : I, KBr : I, RbCl : I, RbBr : I), due to on-centre self-trapped exciton and (B) with max. at 0.27-0.36 eV (in NaCI, KCl, KBr, RbCl), due to shallow trapped electrons or bound polarons, are caused by the same defect-shallow trapped electron (e-) at the substitutional (cation: c-site) alkali impurity cation (M + ): [M - ] 0 c e - . The A- and B-class IR bands have the same location, similar shape, half-width (exactly coincide for KCl : I and KCl at 80 or 10 K with the same vibration structure). It is established that the same Mollwo-Ivey plot curve…
Pd–M/C (M = Pd, Cu, Pt) Electrocatalysts for Oxygen Reduction Reaction in Alkaline Medium: Correlating the Electronic Structure with Activity
2017
The increasing global needs for clean and renewable energy have fostered the design of new and highly efficient materials for fuel cells applications. In this work, Pd-M (M = Pd, Cu, Pt) and Pt nanoparticles were prepared by a green synthesis method. The carbon-supported nanoparticles were evaluated as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium. A comprehensive electronic and structural characterization of these materials was achieved using X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Their electrochemical properties were investigated by cyclic voltammetry, while the…
Acidochromism of the luminescence of bis(4-pyridylethenyl)arenes
2004
Abstract A series of C 2 -symmetrical bis[( E )-2-(4-pyridyl)ethenyl]arenes has been synthesised via two-fold PO-activated olefinations. 1,4-Benzene, 1,4-naphthalene, 9,10-anthracene and 2,2′-diphenyl were used as central units. These fluorescent compounds were freely soluble in common solvents. The absorption and the emission were sensitive towards solvent polarity and acid, in solution as well as in the solid state. Depending on the concentration of acid, protonation of the ground state and/or the excited state caused reductions of the fluorescence efficiencies, accompanied by bathochromic shifts of the absorption and the emission spectra of some chromophores. The title compounds, except …
Structural, magnetic and electronic characterization of an isostructural series of dinuclear complexes of 3d metal ions bridged by tpbd
2013
Abstract Dinuclear complexes of the type [{M(H2O)(phen)}2(μ-tpbd)](ClO4)4 with N,N,N′,N′-Tetrakis-(2-pyridylmethyl)-benzene-1,4-diamine (tpbd) as bridging ligand and M = Mn(II) (1), Fe(II) (2), Co(II) (3), Ni(II) (4), Cu(II) (5), Zn(II) (6) were synthesized, structurally analyzed and their magnetic as well as their electrochemical properties are determined. A ligand-centered one-electron oxidation leads to radical complexes for which the lifetimes are strongly dependent on the coordinated metal ion as followed from time-resolved UV–Vis absorption spectroscopy. In addition to the six homometallic dinuclear complexes, one analog heterometallic Mn(II)/Ni(II) compound (7) of the same constituti…
Miscibility of cyanine dyes in two-dimensional aggregates
1995
Mixed aggregates of cyanine dyes at a charged lipid monolayer surface are studied by absorption spectroscopy, fluorescence microscopy and electron diffraction. We show that slight variations of the molecular structure can convert a system from being fully miscible to being immiscible, and also that the concentrations of dyes in the solution and in the crystal may deviate considerably. The different concentration in the solution and crystal was observed for a molecule where force field calculations indicated the existence of two isomers in solution and where probably only one fits into the lattice.
Low-temperature optical spectroscopy of cobalt in Cu,Co superoxide dismutase: a structural dynamics study of the solvent-unaccessible metal site.
1995
The temperature dependence (300 to 10 K) of the electronic absorption spectra of the cobalt chromophore in bovine superoxide dismutase (SOD) having the native Zn(II) ion selectivity replaced by Co(II) has been investigated in four different derivatives: Cu(II),Co(II) SOD, N3(-)-Cu(II), Co(II) SOD, Cu(I),Co(II) SOD, and E,Co(II) SOD in which the copper ion has been selectively removed. In the Cu(II),Co(II) SOD, the cobalt spectrum is characterized at room temperature by three bands centered at 18,472, 17,670, and 16,793 cm-1; the low-frequency band is split, at low temperatures, into two components, indicating a lower symmetry contribution to a predominantly tetrahedral crystal field. Additi…
EXAFS and XRD study of Pd–Ag bimetallic catalysts supported on pumice from organometallic precursors
2001
Abstract Silver–palladium bimetallic catalysts were supported on pumice following different procedures, based on mild treatments of organometallic precursors. The experiments for the structural characterization of the synthesized samples, wide angle X-ray diffraction (XRD) and X-ray absorption spectroscopy, were carried out at the beamline GILDA of the European Synchrotron Radiation Facility. The analysis of the data demonstrated that alloying took place with a degree of homogeneity depending on the different preparation routes.
Interaction of Cd(II) and Ni(II) terpyridine complexes with model polynucleotides: A multidisciplinary approach
2016
Two metal complexes of 2,2′:6′,2′′-terpyridine (terpy), i.e. Cd(terpy)Cl2 and Ni(terpy)Cl2·3H2O, have been prepared and extensively characterized. The interaction of Cd(terpy)Cl2 with synthetic DNA models, poly(dA-dT)·poly(dA-dT) (polyAT) and poly(dG-dC)·poly(dG-dC) (polyGC), has been studied by CD, fluorescence and UV-vis electronic absorption spectroscopy at several metal/polynucleotide–phosphate ratios and for different NaCl concentrations. All the experimental results indicate an intercalative mechanism of interaction. The optimized geometry of the cadmium complex intercalated between the sixth and seventh base pairs of (AT) and (GC) dodecanucleotide duplexes, obtained by quantum mechan…
Photochemical generation of E′ centres from Si–H in amorphous SiO2under pulsed ultraviolet laser radiation
2006
In situ optical absorption spectroscopy was used to study the generation of E' centres () in amorphous SiO2 occurring by photo-induced breaking of Si–H groups under 4.7 eV pulsed laser radiation. The dependence on laser intensity of the defect generation rate is consistent with a two-photon mechanism for Si–H rupture, while the growth and saturation of the defects are conditioned by their concurrent annealing due to a reaction with mobile hydrogen arising from the same precursor. A rate equation is proposed to model the kinetics of the defects and is tested on experimental data.