Publications

Thermally induced changes in the structure and composition of the shell of tightly aggregated cubic ZnS/Zn(OH)(2) core shell quantum dots of 1.9 nm average core size were investigated by multifrequency electron paramagnetic resonance of Mn2+ probing ions. The observed three-steps temperature induced transformation of the Mn2+ surface centers in the 80-450 degrees C temperature range Zn(OH)(2) shell into ZnO, with the formation of the Zn2O(OH)(2) and Zn4O3(OH)(2) intermediate nanocompounds. The presence of a 0.3 to 1.9 nm thick surface layer of disordered nanomaterial separating the cubic ZnS cores and its shrinking to a few atomic layers by mass loss after annealing up to 350 degrees C was observed by high resolution transmission electron microscopy. Unlike the single step dehydration around 120 degrees C of the bulk epsilon-Zn(OH)(2), the complex decomposition of the epsilon-Zn(OH)(2) shell is attributed to its nanosized, disordered structure.

The improvement of graphene derivates' fluorescence properties is a challenging topic and very few ways were reported up to now. In this Letter we propose an easy method to enhance the fluorescence of highly reduced graphene oxide (rGO) through non-covalent binding to a molecular fluorophore, namely the riboflavin (Rb). While the fluorescence of Rb is quenched, the Rb - decorated rGO exhibits strong blue fluorescence and significantly increased fluorescence lifetime, as compared to its pristine form. The data reported here represent a promising start towards tailoring the optical properties of rGOs, having utmost importance in optical applications. (C) 2013 Elsevier B.V. All rights reserved.

Cobalt ferrite was obtained by the thermolysis of two new cobalt ferrioxalate coordination compounds, namely [Fe2Co(C2O4)(3)(OH)(2)(OH2)(4)].2H(2)O (I) and [Fe2Co(C2O4)(4)(OH2)(6)] (II). The precursors were characterized by chemical analysis, electronic and vibrational spectra and thermal analysis. The corresponding oxides obtained after a heating treatment of the precursors at 350 degrees C/h were extensively investigated by various methods such as XRD, IR, SEM, TEM coupled with EDX, TPR, Mossbauer spectroscopy, magnetic investigations and N-2 adsorption-desorption isotherms. The mesoporous oxides, consisting of homogeneous particles as shape and size with mean crystallites size values of 111(I) and 86 (II) angstrom, exhibit high surface areas (77.6 (I) and 55.7 (II) m(2) g(-1)). The cobalt ferrites' catalytic performances for methane combustion are close to that of a platinum-based catalyst, the catalytic activity being analyzed and interpreted considering ferrites distinctive properties. (C) 2013 Elsevier B.V. All rights reserved.

Ferrofluid samples consisting of magnetite nanoparticles (NPs) coated with oleic acid and dispersed in a non-polar organic solvent have been synthesized by chemical routes. Different volume fractions, phi, of magnetic NPs were considered. The overall structural characterization of NPs has been performed by x-ray diffractometry, with lattice parameters and average coherence lengths evaluated via Rietveld refinements. The magnetic properties of different samples have been analysed by SQUID magnetometry and temperature-dependent Mossbauer spectroscopy and finally explained by adequate magnetic relaxation mechanisms. Zero field cooling-field cooling protocols provided useful information about specific volume fraction dependent magnetic relaxation and de-freezing processes, the lack of the Verwey transition and stronger dipolar interactions at higher volume fractions. Anisotropy energies as obtained by both temperature dependent Mossbauer spectroscopy and magnetometry data are compared and a new procedure for a quantitative characterization of the dipolar interactions is proposed.

Electroless deposition was successfully applied in developing crystalline particles of zinc oxide onto polyester textile materials; this deposition is here presented in comparison with other materials made from poly(lactic acid), polyamide or hemp. Structural and spectroscopic characterization of the raw and deposited samples has been performed. The structure of zinc oxide particles was that of wurtzite type as indicated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Crystallites were 20-500 nm in diameter and up to 1 mu m in length. The grown particles cover the fibers not only on the fabric surface but in the textile depth. Contact angle measurement by the sessile drop method was used to study the wettability behavior of the investigated composite systems. The hierarchical roughness structure generates superhydrophobic properties onto polyester fabrics, for which water contact angles exceed 150 degrees. The other functionalized samples also become more hydrophobic after deposition. Cassie-Baxter model was found suitable to describe the behavior, though the fraction of surface occupied by the water-solid interface is high enough. The electroless deposition technique applied previously for cotton fabrics was once more proven to be highly reproducible, easy scalable, and cheap, allowing a wide range of applications. (c) 2013 Wiley Periodicals, Inc.

A sandwich structure of four double layers of Ag (5 nm)/As2S3 (82.7 nm) has been prepared by Pulsed Laser Deposition (PLD) method. The effect of broadband light on the multilayer structure has been investigated. The X-ray reflectivity (XRR) patterns after different irradiation times have been measured. Although the fully intermixing of Ag and As2S3 layers should be expected during irradiation with visible light, however even after 5 h of irradiation the intermixing is not completed. The characteristic features of XRR diagrams for long irradiation times have been interpreted by scattering of X-ray radiation on clusters of Ag or Ag-As2S3. (c) 2013 Elsevier B.V. All rights reserved.

Due to their mechanical strength and ability to withstand the large electromagnetic force applied to the superconductors in large magnets during excitation, the Cable-in-Conduit-Conductor (CICC) type superconductors will be employed in the next stage of fusion magnets. Here, we discuss the recent results on the application of a non-invasive method for the characterization of CCIC by X-ray microtomography (mu XCT). The experiments have been carried out on a high,resolution X-ray tomograph in INFLPR (http://tomography.inflpr.ro). An open type nanofocus X-ray source with maximum high voltage of 225 kVp at 15-30W maximum power and multiple targets of W on different windows materials (Be, Al, Cu or diamond) is the main component. X-rays are detected by means of amorphous silicon flat panel sensor in the cone-beam configuration and high-energy efficient line sensor based on individual scintillators in the fan-beam scanning configuration. The quality of tomographic images pm space resolution) allowed the majority of strands of analyzed CICC samples to be fully reconstructed along the investigated segment (up to 300 mm long). Our method provides: (i) local and global void fractions (over a 300 mm length of the sample), (ii) void homogeneity factor as the ratio between void space surface and perimeter and (iii) twist pitch angle of individual strands and its distribution in 3D. It can be used to investigate superconducting CICC during their manufacture, installation or after service inspection, for purposes of QA, characterization or development. (C) 2013 Elsevier B.V. All rights reserved.

Sol-gel route using metal alkoxides and trifluoroacetic acid as precursors has been used to prepare oxyfluoride glass-ceramic containing Eu3+-doped LiYF4 nanocrystals of about tens of nm size embedded in a silica matrix through controlled crystallization at higher temperatures of the xerogel. Photoluminescence spectra and decay curves recorded in the Eu3+-doped LiYF4 polycrystalline pellet and glass ceramic have been discussed using group-theoretical arguments. In the glass-ceramic Eu3+ ions are embedded dominantly inside the LiYF4 nanocrystals most probably as Eu-O center and/or dimer centers in low symmetry (C-2v) sites; oxygen ions were incorporated in their neighborhood during the glass ceramization. (C) 2013 Elsevier B.V. All rights reserved.

Different types of SiC-W composites have been realized by spark plasma sintering in a single step process starting with beta SiC nanometric powder, W nanometric and micrometric sized powders, and W foils. SEM, EDX, XRD and X-ray tomography have been used to analyze the sample morphology while the thermal properties of the resulting materials have been investigated up to 1000 degrees C using a LFA thermal analyzer. The results show the possibility to produce dense W-SiC composites, with enhanced thermal conductivity using a relatively simple route. (C) 2013 Elsevier B.V. All rights reserved.

The paper investigates the dependence of the optical properties on cation concentration of amorphous-like indium gallium zinc oxide thin films (Inx-wGawZn1-xO1+0.5x-delta) with various (In + Ga)/(In + Ga + Zn) and Ga/(In + Ga) ratios obtained by pulsed laser deposition. X-ray reflectivity and spectroscopic ellipsometry thickness results were in good agreement. The proportionality between density and the refractive index in the transparency range is evidenced. The extracted physical parameters are clearly influenced by the variation of cation concentration. (C) 2013 Elsevier B. V. All rights reserved.