BaCuO2/SrCuO2 superlattices by pulsed-laser deposition: growth and structural characterization

Summary We have shown that the pulsed-laser deposition (PLD) technique can be successfully used to grow artificial superlattices based on the infinite-layer compounds BaCuO₂ and SrCuO₂. We have demonstrated, by a kinematic analysis of the X-ray diffraction spectra, that the random discrete thickness fluctuations affect both the BaCuO₂ and the SrCuO₂ layers approximately in the same way. Furthermore, such kind of interfacial disorder resulted to be surprisingly low for this system. Such feature is confirmed by the appearance of sharp superstructure peaks even for the (BaCuO₂)₂/(SrCuO₂)₁ superlattice, where only one SrCuO₂ unit cell is deposited in the stacking sequence. These results show that truly new structures can be obtained by a layer-by-layer deposition technique with a low interfacial disorder and give strong support to the idea of synthesizing new artificial high-T _c structures by the PLD technique.     

Growth and optical, magnetic and transport properties of (C4H9NH3)2MCl4 organic-inorganic hybrid films (M = Cu, Sn)

Films of (C₄H₉NH₃)₂MCl₄ (M=Cu and Sn) organic-inorganic hybrid perovskites have been deposited in-situ by a single-source thermal ablation technique on glassy, crystalline and polymeric substrates. Independently of the substrate, the films were well crystallized, c-axis oriented and with a narrow rocking curve of the (0010) reflection (full width at half maximum <1°). The (0 0 ℓ) reflections were consistent with those of the bulk orthorhombic phases and the “c” lattice parameters were 30.85±0.05 and 32.35±0.05 Å, for the Cu- and the Sn-compound, respectively. (C₄H₉NH₃)₂CuCl₄ films had an optical absorption peak at 375 nm at room temperature. From the magnetic point of view they act as layered nanocomposites with a dominant ferromagnetic component localized in planes (2D magnetism). T_c was 7.3±0.1 K and a moderate easy-plane anisotropy was observed. The photoluminescence spectra of typical (C₄H₉NH₃)₂SnCl₄ films at 12 K had a broad yellow band, which did not correspond to any significant peak in the absorption spectrum. The films were semiconducting down to 250 K or, in the case of the best samples, down to 200 K and became insulating at lower temperature. The resistivity of the best films was (5±1) 10⁴ Ω cm at 300 K, and the energy gap was 1.11 eV. PACS 81.07.Pr; 81.15.Kk; 81.16.Dn     

Colorimetric chemosensor for Fe<Superscript>2+</Superscript> and Fe<Superscript>3+</Superscript> based on a ternary mixture of an anionic dye,a cationic polyelectrolyte,and a metal chelator in aqueous solution

A new colorimetric chemosensor based on a simple ternary mixture of an anionic dye, pyrogallol red (PR), a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC), and a metal chelator, N-(2-hydroxyethyl) ethylenediaminetriacetic acid (HEDTA) for the colorimetric detection of Fe²⁺ and Fe³⁺ has been developed in an aqueous solution buffered at pH 5. Upon addition of Fe²⁺ or Fe³⁺ to the mixture, the absorption spectra showed a bathochromic shift; correspondingly, the solution color changed from red to blue, whereas other metal ions basically resulted in insignificant spectral and color changes. From the competitive experiments, no obvious interferences for the colorimetric detection of Fe²⁺ and Fe³⁺ were observed in the presence other metal ions. The results indicated that the mixture could be used as a potential Fe²⁺ and Fe³⁺ colorimetric and naked eye chemosensor in aqueous media. This research demonstrates that the ternary ensemble consisted of an organic dye, an oppositely charged polyelectrolyte, and a metal chelator is a versatile and convenient tool for the facile preparation of a novel chemosensor system.     

Effect of the substrate ferroelastic transition on epitaxial La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> films grown on LaAlO<Subscript>3</Subscript>

Thin films of La_0.7Sr_0.3MnO₃ were grown by molecular beam epitaxy on (001)LaAlO₃ crystals. High resolution X-ray diffraction analysis proves the presence of twins in the films at room temperature, showing that the twin structure of the substrate which forms at the ferroelastic transition at T_F = 813 K served as a template for the film microstructure. Magnetic measurements indicate a thermomagnetic irreversibility which is ascribed to the quenched disorder related to twinning and discussed in terms of coexisting ferromagnetic and spin disordered regions connected with the undeformed domain cores and strained domain walls respectively.     

Tetrathiafulvalene-Inserted Diphenoquinone: Synthesis,Structure, and Dynamic Redox Property

A new tetrathiafulvalene (TTF) derivative is synthesized, which is substituted with two phenoxy radicals on one 1,3-dithiole ring, and may have either open-shell diradical or closed-shell extended-quinoidal ground states. X-ray single crystal analysis and NMR measurements prove that this molecule has a closed-shell extended quinoidal structure both in the solid state and in solution. DFT calculations show the donor–acceptor electronic properties of this molecule with a well-separated HOMO–LUMO distribution and a small HOMO–LUMO energy gap. Because of this donor–acceptor character, this molecule gives both the dication and the dianion species by electrochemical oxidation and reduction. Furthermore, during the redox process between the neutral and dication states, this molecule exhibits unique changes in the cyclic voltammogram upon repeating the cycles or varying the scan rate. The observed electrochemical behavior is explained by the conformational changes in the electrochemically generated species, thus indicating that this molecule is classified as a dynamic redox system.     

Novel sol–gel synthesis of transparent and electrically bistable LiNbO<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> nanocomposites thin films

The morphological and electrical characterization of transparent nanostructured LiNbO₃–SiO₂ thin films synthesized by a novel sol–gel route is reported. Films annealed at different temperatures exhibit different size of the nanocrystals, as demonstrated by Atomic Force Microscopy and Glancing Incidence X-ray diffraction. The dc electrical measurements performed on planar devices reveal electrical bistability. A clear relationship between the electrical bistability and the size of LiNbO₃ nanocrystals embedded in the matrix is observed.     

Observation of intermolecular N–I interaction during the growth of a 4-cyano-4′-iodobiphenyl molecular crystal on GeS(001)

The electronic and atomic structures of 4-cyano-4′-iodobiphenyl (CIB) during the growth of a molecular crystal on a GeS(001) substrate were studied by ultraviolet photoemission spectroscopy (UPS), atomic force microscopy (AFM), and extended X-ray absorption fine structure (EXAFS) spectroscopy. AFM images suggest that the CIB molecule grows as a microcrystal at a nominal thickness of 80 Å. The microcrystal grows with the crystal plane parallel to the surface and isotropic crystal axis orientation. EXAFS analysis suggests that a CIB crystal forms by strong N···I interaction, called halogen bonding. The formation of the intermolecular N···I bond was demonstrated by EXAFS analyses in which the N–I distance was determined to be 3.29 Å. An upward shift of the highest occupied molecular orbital level was observed by UPS and can be attributed to the aggregation of CIB molecules caused by halogen bonding.     

Validation of a hydrophilic interaction ultra‐performance liquid chromatography–tandem mass spectrometry method for the determination of gemcitabine in human plasma with tetrahydrouridine

A simple and reproducible bioanalytical method for the determination of gemcitabine in human plasma treated with tetrahydrouridine (THU) was developed and validated using a hydrophilic interaction ultra‐performance liquid chromatography with tandem mass spectrometry (UPLC‐MS/MS). To prevent deamination of gemcitabine, blood was treated with THU, and the plasma samples obtained after centrifugation were used in this study. Gemcitabine and gemcitabine‐¹³C, ¹⁵N₂ used as an internal standard, were extracted from human plasma treated with THU using a 96‐well Hybrid SPE‐Precipitation plate. Extracts were chromatographed on a hydrophilic interaction chromatography column with isocratic elution. Detection was performed using Quattro Premier with positive electrospray ionization multiple reaction monitoring mode. The standard curve ranged from 10 to 10,000 ng/mL without carryover. No significant interferences were detected in blank plasma and no interferences by 2′‐2′‐difluoro‐2′‐deoxyuridine, a metabolite of gemcitabine. Accuracy and precision in the intra‐batch reproducibility study using quality control samples with three THU levels did not exceed ±5.4 and 7.3%, respectively, and the inter‐batch reproducibility results also met the criteria. Stability of gemcitabine was ensured in whole blood and plasma as well as stability of THU in solutions. The UPLC‐MS/MS method developed was successfully validated and can be applied for gemcitabine bioanalysis in clinical studies. Copyright © 2015 John Wiley & Sons, Ltd.     

Reaction of olefins using cerium(IV) sulfate tetrahydrate in carbonyl compounds–H2O

The reaction of olefins with cerium(IV) sulfate tetrahydrate [Ce(SO₄)₂·4H₂O, CS] in acetone–H₂O under reflux for 5 h gave 2‐oxo‐ and 2‐oxo‐5‐hydroxy derivatives. In this reaction, the yields of 2‐oxo‐5‐hydroxy derivatives were dependent on the quantity of H₂O. Moreover, the reaction of α, β‐unsaturated ketones with CS in acetone–H₂O yielded 2,7‐dioxo‐3‐hydroxy or 3,8‐dioxo‐4‐hydroxy derivatives. The reaction mechanism is also discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Evidence of local structural transition during oxidation process of RBCO epitaxial films using time resolved reflexafs measurements

We report results of a time resolved X-ray Absorption Spectroscopy (XAS) experiment on the oxidation process of epitaxial Y₁(Nd_0.05Ba_1.95)Cu₃O_x superconducting thin films. For the first time Cu K-edge XAS technique has been used to explore local structural changes around the Cu ions during the oxidation process of a high critical temperature superconducting film. The results show that during the oxygenation of a tetragonal Y₁(Nd_0.05Ba_1.95)Cu₃O_x additional local transitions appear in the orthorhombic I phase, which are not linked to long range order transformations as shown by in situ X-ray diffraction experiment. New questions concerning the dynamic microscopic process leading to the oxygenation and eventually to superconductivity of the complex R_1+xBa_2-xCu₃O_x (R = Y or rare earth) compounds arose from these results. Received 21 December 2001 Published online 25 June 2002