Surface sensitive probe of the morphological and structural aspects of CdSe core-shell nanoparticles

The promising technological applications of colloids of CdSe nanoparticles in solid state devices is hampered due to issues related to their stoichiometry, agglomeration effects and core-shell relationship. Due to the short inelastic mean free path of core-level electrons, X-ray photoelectron spectroscopy is the most reliable method for analysis at the nanometer depth scale, and in conjunction with layer by layer ion beam erosion it can provide valuable information regarding distribution of elements along the depth of the sample. In this work, we address the issue of synthesis of CdSe nanoparticles and probing them by XPS and conventional techniques such as like transmission electron microscopy (TEM) and X-ray diffraction (XRD). Cd/Se input precursor ratio is varied to form colloidal TOP/TOPO capped CdSe nanoparticles. An optimum input precursor ratio is determined where stoichiometric yield, efficiently capped smallest sized (∼5 nm) CdSe nanoparticles with superior optical, structural and morphological properties are obtained. Electron diffraction and deconvolution of XPS-core-levels enables the identification of the different compositional regimes of CdSe nanocrystallites. For non-optimal precursor ratios, the presence of Cd- and Se-related oxides are observed. This multi-technique approach has enabled us to pictorially model the compositional, structural and morphological aspects of TOP/TOPO capped CdSe nanoparticles.     

Computation of linear and nonlinear stationary states of photonic structures using modern iterative solvers

In this paper we describe efficient methods to obtain the stationary states of linear and nonlinear photonic systems, which have gained particular interest in the field of integrated and nonlinear optics. While the methods presented are directly applicable to optical physics, they are also general and should be of interest in a broad range of phenomena presently under study in other areas of physics and engineering. The strategy consists in combining the use of classical methods, such as inverse iteration or the Newton method, together with modern, nonstationary linear solvers, such as SYMMLQ or GMRES, in order to obtain efficient numerical computations to problems involving large matrices. We have selected several example problems in order to discuss the practical implementation details, not normally described in the present literature. Moreover, the problems we have selected provide a backdrop to contrast and motivate the use of different methods for systems which are symmetric and non-symmetric, single and multi-component, and also real and complex. Information relative to numerical performance of the different algorithms, including a survey for a nonsymmetric problem, which requires the adjustment of a restarting parameter for the GMRES algorithm, is also presented.     

Entanglement and the Kondo effect in serially coupled double quantum dots

We investigate entanglement between electrons in serially coupled double quantum dots attached to noninteracting leads. In addition to local repulsion we consider the influence of capacitive inter-dot interaction. We show how the competition between extended Kondo and local singlet phases determines the ground state and thereby the entanglement. The results are additionally discussed in connection with the linear conductance through the system.     

Regioselective ring opening of amino epoxides with nitriles: an easy synthesis of (2R,3S)- and (2S,3S)-1,3-diaminoalkan-2-ols with differently protected amine functions

[reaction: see text] Transformation of enantiopure (2R,1'S)- or (2S,1'S)-2-(1-aminoalkyl)epoxides 1 or 2 into the corresponding (2R,3S)- and (2S,3S)-1,3-diaminoalkan-2-ols 3 or 4 is described. The opening of the epoxide ring with different nitriles (Ritter reaction) takes place with total selectivity and in high yields in the presence of BF3.Et2O. Interestingly, the two amine groups are differently protected. A mechanism to explain this transformation is proposed.     

Reactivity of Grubbs' catalysts with urea- and amide-substituted olefins. Metathesis and isomerization

[Chemical reaction: see text] The reactions of a series of urea- and amide-substituted olefins with Grubbs' catalysts are presented. Depending on the substrate's nature, the formation of either cross-metathesis or isomerization products is observed. To favor the cross-metathesis products, the reactions have been carried out using a wide range of experimental conditions. Upon addition of monophenyl phosphoester to these reactions, the isomerization of the olefins is completely suppressed and the cross-metathesis products are obtained in up to 60% yield.     

Structural Evolution and Fluorescence Properties of Dy<Superscript>3+</Superscript>: Silica Matrix

Silica glasses doped with Dy³⁺ were prepared by sol–gel method. The FTIR and thermo gravimetric analysis (TGA) clearly show complete densification (density = 2.2 gm/cm³) of the gels around 1000C. The fluorescence properties of Dy³⁺ ion are utilized to study the structural changes during the gel to glass transition of the silica xerogels. The fluorescence intensity and full width at half maximum (FWHM) of the emission bands show an increasing tendency with heat treatment. This is attributed to a glassy silica network with an asymmetric environment. The (Y/B) ratio for the Dy³⁺ ion is found to be less sensitive to site symmetry effects.     

Subphthalocyanines as fluoro-chromogenic probes for anions and their application to the highly selective and sensitive cyanide detection

The use of a subphthalocyanine derivative as a selective chromo-fluorogenic reporter for the anion cyanide in mixed aqueous solutions is reported.     

Unexpected conversion of a hexacyanometallate to a homoleptic nitrile complex with triphenylborane substituents

The homoleptic, triphenylborane adduct of the hexacyanochromate anion was structurally characterized and found to be a product in which all six cyanide ligands have undergone isomerization to nitrile groups.     

Evaluation of the acidity constants of the 4-hidroxy-5-[salicylideneamino]-2-7-naphthalenedisulfonic acid (Azomethine-H) using UV-vis spectrophotometry

The time stability of the azomethine-H species was determined not to be better than 10 min in the absence of oxygen and light, however under phosphate buffered conditions the azomethine-H species remained stable for longer periods, as indicated by the spectrophotometric behaviour. Nevertheless, the analysis time still exceeded the stability allowance. Therefore, the determination of the acidity constants of the Azomethine-H species was studied by means of UV-vis spectrophotometry in buffered media by means of the point-by-point analysis and data processing with SQUAD to refine the resulting constants, which were: pK(a1) = 3.39, pK(a2) 7.36 and pK(a3) 8.73. The latter were associated to the corresponding acid-base equilibria of the amine and hydroxy groups constituting the molecule.