Characteristics of electrochemically grown dendritic metallic zinc

A simple electrochemical process has been implemented to fabricated fractal structured leaf-like metallic zinc. The fabricated material was structurally characterized using X-ray diffraction that reveals the hexagonal unit cell structure. Also the growth of the structure is anisotropic. Field emission scanning electron microscopic images revealed clearly the leaf-like morphology of the fabricated material is fern like and ∼500 μm in length, ∼50-60 μm wide and the platelets thickness is ∼5 μm. The growth of this structure is diffusion controlled and locally accomplished with the oriented attachment. Raman shift measurement revealed the existence of surface optical phonon modes which is very significant for surface defects.     

Performance study of LaBr3:Ce detectors coupled to R2083 PM tube for energy and timing characteristics

Journal of Radioanalytical and Nuclear Chemistry - Performance of 1″?×?1″ LaBr3 (5% Ce) scintillator coupled to Hamamatsu R2083 PM Tube has been investigated for the...     

Studies on CdS nanoparticles dispersed in silica matrix prepared by sol-gel technique

SiO₂/CdS-nanoparticle composite films (SiO₂:CdS=85:15, 80:20, 75:25 and 70:30) were prepared by the sol-gel route. The films were characterized by studying microstructural (XRD and TEM) and optical (transmittance and photoluminescence) properties. Band gaps of these films annealed at different temperatures (373-473 K) for different times (10-120 min) indicated that the signature of nanocrystallinity is retained throughout the range of our experimental conditions. A thermal diffusion process controlled growth in the crystallite size with increasing annealing time and temperature. The average radii of the nanoparticles varied as the cube root of the annealing time but showed exponential dependence on the inverse of annealing temperature. Photoluminescence (PL) studies of the composite films indicated excitonic transitions. Theoretical analysis of the line shapes of the PL peaks recorded at 300 K and 80 K could be accounted for by the combined effects of size distribution and phonon broadening. It was observed that the deformation potential (E _d) effectively controlled the line shapes of the PL measurements. Received 24 May 2002 Published online 27 January 2003 RID="a" ID="a"e-mail: msakp@mahendra.iacs.res.in     

Role of vacancy and metal doping on combustive oxidation of Zr/ZrO2 core-shell particles

We studied self-propagated combustion synthesis of transition-metal-doped tetragonal ZrO₂ (t-ZrO₂) with first principles-based one-dimensional diffusion reaction model. The optimal reaction condition for the combustion process was investigated by calculating energetic stability and surface reactivity of oxygen vacancy defects on (101) surface termination of t-ZrO₂ using first-principles density functional methods. In the first-principles model, the surface was doped with 14 different metal impurities in the 4th and 5th row of the periodic table to examine the role of transition-metal doping on the combustion process. Results indicate that there are clear trends in the defect stability and reactivity depending upon the type of metal impurity and their relative location with respect to the oxygen vacancy. Surface density of states and charge density information also show that there is a trade-off between the vacancy stability and chemical activity of the surface defect states. Based on the thermodynamic information obtained from first principles, we analyze the combustion process of a Zr metal particle by using a one-dimensional diffusion-reaction model. The competition between the vacancy-assisted chemisorption and the vacancy diffusion results in an optimal point for rate of combustion reaction with respect to the vacancy stability. From this, we suggest a plausible screening strategy for metal-doping which can be applied at different temperatures and pressures, as well as with different particle sizes. Our analysis indicates that first-principles calculation provides key information that can be subsequently used for an optimization of the reaction rate for a self-sustained combustion process. An explicit inclusion of rates of defect and ionic transport will be introduced into our model in future work.     

Nearly monodispersed ZnS nanospheres: Synthesis and optical properties

ZnS nanoparticles of diameters of 3–4 nm were self-assembled to form dense nanospheres of sizes 100 nm by a colloidal precipitation method using PVP as the stabilizing agent. Studies indicated that the ZnS nanoparticles maintained their individual properties inside the nanospheres. Optical absorption spectra of the samples demonstrated the effect of quantum confinement in the ZnS nanocrystals. Room temperature photoluminescence measurements showed a sharp UV emission at 370 nm, attributed to sulfur vacancies.     

Aerial oxidation of primary alcohols and amines catalyzed by Cu(II) complexes of 2,2'-selenobis(4,6-di-tert-butylphenol) providing [O,Se,O]-donor atoms

Seven copper(II)-complexes 1-7 with the ligand 2,2'-selenobis(4,6-di-tert-butylphenol) providing [O,Se,O]-donor atoms have been isolated and characterized. Three of them 1, 2 and 3 are mononuclear, two 4 and 7 dinuclear and 5, 6 are trinuclear. The crystal structures of the complexes were determined by X-ray diffraction and the electronic structures were established by various physical methods including EPR and variable temperature (2-290 K) susceptibility measurements. The magnetic behaviour of the compounds 4-6 exhibits antiferromagnetic exchange coupling resulting in well-isolated S(t)= 1/2 ground state for 5 and 6 and a diamagnetic spin state for 4. Complexes 5 and 6 belong to the class of asymmetric trinuclear copper(II) complexes modelling the trinuclear copper site in multicopper oxidases. Complex 1 is a catalyst in the presence of a strong base for the aerial oxidation of primary alcohols to the corresponding aldehydes. A dinuclear complex, seemed to be 4, prepared in situ has been found to be a catalyst for the aerial oxidation of primary amines containing alpha-C-H atoms. Primary kinetic isotope effects show that H-abstraction from the alpha-carbon atom of a coordinated substrate (alcoholato or amine) is the rate-determining step in both cases. Two functional models for the metalloenzymes galactose oxidase and amine oxidases are thus described.     

Structural analyses and magnetic properties of 3D coordination polymeric networks of nickel(II) maleate and manganese(II) adipate with the flexible 1,2-bis(4-pyridyl)ethane ligand

Two novel inorganic-organic hybrid 3D extended networks of Ni(II) and Mn(II) having molecular formulas [(maleate)(2)Ni(3)(bpe)(4)(H(2)O)(4)](NO(3))(2).H(2)O (1) and [(adipate)Mn(bpe)] (2) (bpe = 1, 2-bis(4-pyridyl)ethane), respectively, have been synthesized and characterized by single-crystal X-ray diffraction studies and low-temperature (300-2 K) magnetic measurements. Compound 1 crystallizes in the monoclinic system, space group C2/c (No. 15), with chemical formula C(56)H(62)N(10)Ni(3)O(19), a = 30.955(4) A, b = 12.705(3) A, c = 17.058(5) A, beta = 117.26(2) degrees, and Z = 4. Compound 2 crystallizes in the triclinic system, space group Ponemacr; (No. 2), with chemical formula C(18)H(20)MnN(2)O(4), a = 8.492(2) A, b = 9.444(2) A, c = 11.533(3) A, alpha = 97.19(1) degrees, beta = 94.64(1) degrees, gamma = 105.02(1) degrees, and Z = 2. The structure determination reveals for both a 3D network. Compound 1 contains two crystallographically independent Ni(II) ions in different octahedral environments. Ni(1) lies on an inversion center, and its coordination environment comprises two chelating maleate anions and two bpe nitrogen donors, while the Ni(2) ion is surrounded by meridionally disposed three bpe N atoms, two water molecules, and one oxygen donor from the dicarboxylate anion. Of the three crystallographic independent bpe ligand, one presents an anti and the others a gauche conformation. The corresponding N-to-N distances are 9.344, 6.543, and 6.187 A. Variable-temperature magnetic susceptibility measurement of the complex reveals the existence of a dominant ferromagnetic interaction within the molecule. Compound 2 is composed of Mn(2) dimer units linked by adipate anions to form corrugated 2D sheets which, on interconnection through bpe (anti conformation, N-to-N distance of 9.391 A), produces an interpenetrated 3D alpha-polonium-related type net. Complex 2 reveals to be antiferromagnetic fitting data using a dimeric Mn(II) model that considers negligible magnetic transmission through the carbon skeleton of adipate and the bpe pathway.     

Spectrophotometric determination of uranium(VI) with benzoylacetanilide

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Use of complex forming substitution reactions for the selective enthalpiometric determination of cations and anions