National Institute Of Materials Physics - Romania

Conducting polypyrrole:IrQ(ppy)(2) thin films were obtained by electrochemical method which ensure uniform dispersion of the organometallic in the polymer matrix. A thin layer of about 50 nm polypyrrole: IrQ(pPY)(2) thin films were deposited on the ITO/glass substrate and used for spectroscopic, structural, and electric characterization. The photoluminescence spectrum of polypyrrole:IrQ.(ppy)2 have shown the two main emissions of IrQ(ppy)(2) at 2.44 eV (508 nm) and 2 eV (620 nm) besides of the polypyrrole weak emission centered at 2.55 eV (485 nm). The electric conductivity of the doped polypyrrole thin layer has almost the same conductivity with the undoped polypyrrole thin film suggesting an homogenous polypyrrole:IrQ(ppy)(2) composite which can be used as emissive layer in the OLED's structures. (C) 2014 Elsevier B.V. All rights reserved.

We report results regarding the in vitro toxicology of gamma-Bi2O3 represented by its isomorphous phase Bi12TiO20 (gamma-BTO). The gamma-BTO microparticles were synthesized by two methods: coprecipitation from a bismuth nitrate tetrabutyl titanate solution and solid state reaction of Bi2O3 and TiO2 oxides. The structural and morphological characteristics of the obtained materials were determined using X-ray diffraction (XRD), selected area electron diffraction (SAED), transmission (TEM) and scanning (SEM) electron microscopy. The elemental composition was investigated using energy dispersive spectrometry (EDS). The cytotoxicity and oxidative/nitrosative stress (intracellular reactive oxygen species (ROS) and nitric oxide (NO) release) induced by the studied microparticles in HepG2, SH-SY5Y and 3T3-L1 cell cultures were determined using the MIT, DCF-DA (2 ',7 '-dichlorfluorescein-diacetate) and Griess methods respectively. Depending on the cell type and gamma-BTO concentration, results showed only weak cytotoxic effects after 24 h of gamma-BTO exposure and cell proliferation effects for longer treatment times. Only reduced NO release increases (corresponding to high gamma-BTO concentrations) were detected in case of SH-SY5Y and 3T3-L1 cells. The intracellular ROS production (higher for HepG2 cells) appeared inversely proportional to the gamma-BTO concentration. The obtained results indicated a promising in vitro biocompatibility of gamma-BTO and encourage further studies regarding its potential for biomedical applications. (C) 2014 Elsevier Ltd. All rights reserved.

Dye-doped polymer micro- and nanofibers with tailored light emission properties have great potential for applications in optical, optoelectronic, or photonic devices. In this study, these types of structures were obtained by electrospinning rhodamine 6 G-doped polyvinylpyrrolidone (PVP) using a polymer solution of 10% (mass) concentration in ethanol. Polymer nanofibers with different morphologies (smooth and beaded) and diameters of about 500 nm were obtained using different electrospinning conditions with the same solutions. Fluorescence optical microscopy observations showed that the dye was distributed uniformly in the doped PVP nanofibers. Different shifts were observed when we compared the wavelength of the dye emission band peak of the smooth nanofibers (566 nm) and the wavelength of the dye emission band peak of the beaded fibers (561.5 nm) produced by electrospinning in different conditions with the wavelength of the emission band peak for transparent thin films produced by spin coating (558 nm) using the same polymer solution. This demonstrates that it is possible to tune the optical properties of electrospun dye-doped polymer nanofibers simply by modifying the morphology of the material, i.e., the parameters of the electrospinning process. (C) 2014 Elsevier Ltd. All rights reserved.

In this work we have systematically investigated the evolution of structure and stoichiometry in SrCuO2 films grown on TiO2-terminated SrTiO3 substrates as a function of the substrate temperature. Depending on the growth temperature SrCuO2/SrTiO3 films can exhibit either a pure tetragonal high-pressure phase, or a pure orthorhombic low-pressure phase, or a mixed phase. Our results indicate that at low substrate temperatures the non-equilibrium state of the growth process is responsible for the stabilization of the metastable tetragonal high-pressure structure in SrCuO2 thin films grown on ( 0 01) SrTiO3 substrates, whose lattice matches the metastable structure. In addition, at higher substrate temperatures thermodynamics become dominant over other factors and the SrCuO2 thin films are stabilized in the thermodynamically stable orthorhombic phase. (C) 2014 Elsevier B.V. All rights reserved.

Electropolymerization of diphenylamine (DPA) onto a reduced graphene oxide (RGO) film was carried out to obtain a corresponding RGO/polydiphenylamie (PDPA) composite doped with phosphotungstic acid (H3PW12O40) heteropolyanions (PT). The synthesis was performed in the absence of light, since UVvis spectroscopy and photoluminescence (PL) studies on RGO/DPA blends irradiated by UV light revealed a partial transformation of the DPA monomer into oligomers of PDPA. Raman scattering demonstrates that the electropolymerization of DPA in the presence of H3PW12O40 (PTA) and RGO leads to the formation of PDPA covalently bonded to the RGO sheets (RGO/PDPA:PT). The presence of heteropolyanions in the PDPA matrix (PDPA:PT) is detected by FTIR spectroscopy. Comparing the PL excitation spectra of PDPA:PT and the RGO/PDPA:PT composite highlights an upshift of the band gap that is accompanied by a change in the composition of the PL spectrum in the spectral range of 2.253.54 eV. These changes originate in a charge transfer that takes place at the interface of nongrafted RGO and PDPA:PT. The gradual increase of the PL intensity of RGO covalently grafted with PDPA:PT reveals photochemical reactions under UV irradiation. These involve the CC stretching vibrational mode in the benzene ring of PDPA and indicate the transformation of an RGO/PDPA:PT composite containing HPW12O402 anions into an RGO/PDPA:PT composite stabilized by PW12O403 anions. These results not only provide important insights on the interactions between RGO, conjugated polymers, and stabilizing dopant ions but also impact on the synthesis conditions.

We investigate the equilibrium and nonequilibrium transport through a quantum dot in the Kondo regime, embedded between a normal metal and a topological superconductor supportingMajorana bound states at its end points. We find that the Kondo physics is significantly modified by the presence of theMajorana modes. When the Majorana modes are coupled, aside from the Kondo scale T-K, a new energy scale T* << T-K emerges, that controls the low-energy physics of the system. At lowtemperatures, the ac conductance is suppressed for frequencies below T*, while the noise spectrum acquires a similar to omega(3) dependence. At high temperatures, T >> T-K, the regular logarithmic dependence in the differential conductance is also affected. Under nonequilibrium conditions, and in particular in the {T, B}-> 0 limit, the differential conductance becomes negative. These findings indicate that the changes in transport may serve as clues for detecting the Majorana bound states in such systems. In terms of methods used, we characterize the transport by using a combination of perturbative and renormalization-group approaches.

Four coordination compounds of copper(II) were synthesised and characterised in solid state by elemental analysis, infrared, electronic and EPR spectroscopy, as well as by thermal analysis (TG/DTA). The complexes were formulated on the basis of experimental data as: [Cu(BzIm)(2)(H2O)]center dot H2O (1), [Cu-2(Acr)(4)(HBzIm)(2)] (2), [Cu(Acr)(2)(HBzIm)(2)] (3) and [Cu(Acr)(2)(HBzIm)(2)(H2O)]center dot H2O (4). IR data are in accordance with the unidentate nature of benzimidazole, in complexes (2), (3) and (4), and bridge bidentate nature of benzimidazole, in complex (1), while acrylato acts as uni- or bridge/chelate ligand. The electronic spectra display the characteristic pattern of square planar, square pyramidal, or octahedral stereochemistry, also confirmed by EPR spectra. Thermal decomposition evidenced several well-defined steps as dehydration of complexes (1) and (4), benzimidazole molecule releases for all complexes and acrylate decomposition in carbonate for complexes (3) and (4). In all four cases, the final residue after thermal treatment in air flow is copper(II) oxide, formed during the decomposition steps for complexes (3) and (4), and, respectively, after the oxidation of the metallic copper for complexes (1) and (2). Antimicrobial activities of the complexes have been determined by in vitro assays, against various Gram-negative and Gram-positive bacterial and fungal strains. Copper(II) complexes were also evaluated for their cytotoxicity on eukaryotic cells.

Using forward current injection with densities in the range 15-30A/cm(2) we can effectively eliminate the radiation-induced boron-oxygen complex, which is the main compensating center in irradiated Si solar cells. It was found that for a given forward current density the elimination rate is decreasing with increasing irradiation dose. Additionally, some evidences have been obtained on the negative-U properties of the radiation-induced boron-oxygen complex.

Three new coordinative compounds of the type [Co(en)(2)CO3]center dot 0.75H(2)O (1) and [M(en)(2)(H2O)(2)]CO3 ((2) M:Ni, (3) M:Cu; en: ethylenediamine) were synthesized and characterized. The IR and UV-Vis spectral data indicate that ethylenediamine acts as chelate, while carbonate ions act as bidentate chelate ligand for (1)/counter ion for (2) and (3) generating complexes with octahedral stereochemistry. The thermal behavior provided confirmation of the complexes composition, as well as the number and the nature of water molecules and the intervals of thermal stability. The biological assays revealed a good activity against Enterococcus faecium for copper complex.