Publications

Amorphous Ge/SiO2 multilayer structures deposited by magnetron sputtering have been annealed at different temperatures between 650 and 800 degrees C for obtaining Ge nanocrystals in oxide matrix. The properties of the annealed structures were investigated by transmission electron microscopy, Raman spectroscopy, and low temperature photoluminescence. The Ge crystallization is partially achieved at 650 degrees C and increases with annealing temperature. Insight of the Ge nanocrystal formation was acquired by comparing two annealing procedures, i.e., in a conventional tube furnace and by a rapid thermal annealing. By rapid thermal annealing in comparison to conventional furnace one, the Ge crystallization process is faster than Ge diffusion, resulting in the formation of more compact layers of Ge nanocrystals with 8-9.5-nm size as Raman spectroscopy reveals. These findings are important to improve the annealing efficiency in the nanocrystals formation for a precise control of their sizes and location in oxide matrix and for the possibility to create systems with interacting nanoparticles for charge or excitonic transfer. The infrared photoluminescence of Ge nanocrystals at low temperatures shows strong emission with two sharp peaks at about 1,000 meV.

Directionally solidified B4C-TiB2 eutectics doped with different Si contents were prepared by floating zone method. Silicon doping (up to 3 vol.%) promotes a more coherent interface between B4C matrix and TiB2 inclusions, a decrease of the spacing between TiB2 (when solidification rate is constant), and formation of a more uniform morphology with thinner inclusions. These features lead to simultaneous enhancement of Vickers hardness (HV), fracture toughness (K-1c) and bending strength (sigma) when compared with Si-free B4C-TiB2 eutectics. For our materials, the average HV, K-1c and sigma were 45.2 GPa, 7.04 MPa m(1/2), and 460 MPa at room temperature or 487 MPa at 1600 degrees C, respectively. The values of sigma at indicated temperatures are approximately twice higher than for the Si-free B4C-TiB2 eutectic composites. (C) 2013 Elsevier B.V. All rights reserved.

Bioglasses (BG) are the inorganic materials exhibiting the highest indices of bioactivity. Their appliance as films for bio-functionalization of metallic implant surfaces has been regarded as an optimal solution for surpassing their limited bulk mechanical properties. This study reports on magnetron sputtering of alkali-free BG thin films by varying the target-to-substrate working distance, which proved to play an important role in determining the films' properties. Post deposition heat-treatments at temperatures slightly above the glass transformation temperature were then applied to induce inter-diffusion processes at the BG/titanium substrate interface and strengthening the bonding as determined by pull-out adherence measurements. The morphological and structural features assessed by SEM-EDS, XRD, and FTIR revealed a good correlation between the formations of inter-metallic titanium silicide phases and the films' bonding strength. The highest mean value of pull-out adherence (60.3 +/- 4.6 MPa), which is adequate even for load-bearing biomedical applications, was recorded for films deposited at a working distance of 35 mm followed by a heat-treatment at 750 degrees C for 2 h in air. The experimental findings are explained on the basis of structural, compositional and thermodynamic considerations. (C) 2013 Elsevier B.V. All rights reserved.

In order to understand the role of ambient humidity on NO2 detection, electrical resistance and work function changes were recorded simultaneously on ZnO-Eu2O3 material. Thus, surface band bending and electron affinity could be evaluated, according to the Schottky model. The lack of electron affinity changes during NO2 exposure in dry air conditions, reveals that only the free charge concentration is affected. Exposure to NO2 in humid background leads to an increase in sensor signals and a significant change in the electron affinity as well. This effect suggests an interaction between NO2 and surface hydroxyl species; thereby additional charge carriers are involved in the overall sensing process. High resolution XPS analysis proves the presence of Eu solely in the 3(+) oxidation state before and after NO2 exposure. A gas-sensing interaction mechanism has been proposed. (C) 2013 Elsevier B.V. All rights reserved.

Laser emission at 1.06 and 1.3 mu m under pumping with diode lasers was obtained from buried waveguides that were realized in a 0.7 at.% Nd:YAG single crystal by direct writing with a femtosecond laser. A depressed circular waveguide with a diameter of 110 mu m yielded laser pulses at 1.06 mu m with an energy of 1.4 mJ under the pump with pulses of 9.1 mJ energy at 807 nm; in continuous-wave operation, an output power of 0.54 W with optical to optical efficiency of 0.14 was achieved. Emission at 1.3 mu m is demonstrated for the first time from such waveguides, with an energy of 0.4 mJ per pulse. Results for laser emission in other depressed cladding types and two-line-type waveguides are discussed.

Three new coordinative compounds that contain mixed ligands (5,6-dimethylbenzimidazole and acrylato anion) were synthesized and characterized. The features of complexes have been assigned from microanalytical, IR, UV-Vis and EPR spectra as well as thermal analysis. IR data are in accordance with unidentate nature of 5,6-dimethylbenzimidazole while the acrilato ion acts as uni- or bidentate ligand. The electronic spectra display the characteristic pattern of square pyramidal or octahedral stereochemistry, which were confirmed by the EPR spectra. Antibacterial and antifungal activities of the complexes have been determined in vitro, against various Gram-negative and Gram-positive bacteria and fungi. The tested complexes exhibited different spectra of antimicrobial activity and inhibited the microbial ability to colonize the inert surfaces, acting as potential anti-adherence and biofilm-controlling agents. Thermal decomposition evidenced several well-defined steps as dehydration (complex 2), 5,6-dimethylbenzimidazole molecule release (all complexes) and the acrylate decomposition in carbonate (complex 3). The final residue is in all cases copper (II) oxide.

Nanocrystals (NCs) of II-VI semiconductors of few nanometers average size, called quantum dots (QDs), are now intensely investigated as radiation detectors. Besides the expected quantum confinement and influence of surface states, our electron paramagnetic resonance investigations of cZnS QDs doped with Mn2+ ions, correlated with structural data, underline that other properties should be also taken into consideration in developing the II VI semiconductor QDs as radiation detectors. Thus, the preferential localization of Mn2+ in the core of the cubic ZnS QDs at substitutional Zn2+ cation sites next to a stacking lattice defect is expected to lead, besides changes in the impurity energy levels, to specific aggregation properties. An outer shell of different composition can also influence the structural properties of the QDs core with effects on the optical properties as well. (C) 2013 Elsevier Ltd. All rights reserved.

The paper reports on magnetite successfully functionalized with two new molecules. The investigations, involving chemical and physical methods, provided relevant features involving cell parameters and grain sizes, or the intermingling ratio between magnetite and functionalizing molecules, as deduced from magnetic measurements. A large amount of interesting data concerning various surface and local interaction mechanisms was supplied by detailed Mossbauer measurements. The new outputs are explained in terms of material processing and intimate mixing of the involved molecules.

New species of type MLCl2 center dot nH(2)O (M:Ni, n = 6; M:Cu, n = 1.5 and M:Zn, n = 1; L: 1,8-bis(3'-ketopyridil)-1,3,6,8,10,13-hexaazacyclotetradecane, ligand resulted by 1,2-diaminoethane, nicotinamide and formaldehyde template condensation) were synthesised. The compounds were characterised by chemical analysis, ESI-MS, IR, NMR, UV-Vis-NIR and EPR spectroscopy as well as magnetic data at room temperature. The modifications in the IR and NMR spectra are in accordance with the condensation process. Electronic spectra indicate that Ni(II) adopts an octahedral stereochemistry while the surrounding of Cu(II) is square-pyramidal. The proposed stereochemistry was furthermore confirmed by magnetic moments and EPR spectrum at room temperature. The water is eliminated in one or two steps, respectively, while the oxidative degradation of the ligand and chloride decomposition occur in two steps. The final residues consist of the most stable metallic oxides as X-ray powder diffraction indicates. The newly synthesised compounds were evaluated for their antimicrobial effect against different bacterial and fungal strains.

Zinc chromites (ZnCr2O4) have been synthesized via thermal decomposition of (NH4)(2)[ZnCr2(C4O6OH)(2)]center dot 9H(2)O and (NH4)(3)[ZnCr2(C6O7H11)(4)(OH)(7)]center dot H2O precursors. The complex precursors have been characterized by infrared spectroscopy (IR), ultraviolet-visible spectroscopy (UV-vis), thermal analysis and scanning electron microscopy (SEM). ZnCr2O4 samples have been investigated and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible (UV-vis) and photolumininescence (PL) spectroscopy and Brunauer-Emmett-Teller (BET) N-2 adsorption-desorption analyses. Nanoscaled (similar to 60 nm) single-phase zinc chromites were obtained by heating the precursors at 900 degrees C for 1 h. The influence of thermal treatment of tartarate precursor on structural, morphological and textural properties of ZnCr2O4 is discussed. (C) 2013 Elsevier Ltd. All rights reserved.