National Institute Of Materials Physics - Romania

Publications

5781 articles found

2251. Direct sintering of SiC-W composites with enhanced thermal conductivity

Authors: Galatanu, M; Popescu, B; Enculescu, M; Tiseanu, I; Craciunescu, T; Galatanu, A

Published: OCT 2013, FUSION ENGINEERING AND DESIGN, 88, 2602, DOI: 10.1016/j.fusengdes.2013.05.036

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.

2252. Stoichiometry dependence of the optical properties of amorphous-like Inx-wGawZn1-xO1+0.5x-delta thin films

Authors: Galca, AC; Socol, G; Trinca, LM; Craciun, V

Published: SEP 15 2013, APPLIED SURFACE SCIENCE, 281, 99, DOI: 10.1016/j.apsusc.2013.01.176

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.

2253. Dense Ge nanocrystal layers embedded in oxide obtained by controlling the diffusion-crystallization process

Authors: Lepadatu, AM; Stoica, T; Stavarache, I; Teodorescu, VS; Buca, D; Ciurea, ML

Published: SEP 15 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1981-y

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.

2254. Room and high temperature toughening in directionally solidified B4C-TiB2 eutectic composites by Si doping

Authors: Bogomol, I; Badica, P; Shen, YQ; Nishimura, T; Loboda, P; Vasylkiv, O

Published: SEP 5 2013, JOURNAL OF ALLOYS AND COMPOUNDS, 570, 99, DOI: 10.1016/j.jallcom.2013.03.084

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.

2255. Strong bonding between sputtered bioglass-ceramic films and Ti-substrate implants induced by atomic inter-diffusion post-deposition heat-treatments

Authors: Stan, GE; Popa, AC; Galca, AC; Aldica, G; Ferreira, JMF

Published: SEP 1 2013, APPLIED SURFACE SCIENCE, 280, 538, DOI: 10.1016/j.apsusc.2013.05.022

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.

2256. NO2 sensing mechanism of ZnO-Eu2O3 binary oxide under humid air conditions

Authors: Stanoiu, A; Simion, CE; Somacescu, S

Published: SEP 2013, SENSORS AND ACTUATORS B-CHEMICAL, 186, 694, DOI: 10.1016/j.snb.2013.06.083

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.

2257. Efficient laser emission in diode-pumped Nd:YAG buried waveguides realized by direct femtosecond-laser writing

Authors: Pavel, N; Salamu, G; Voicu, F; Jipa, F; Zamfirescu, M; Dascalu, T

Published: SEP 2013, LASER PHYSICS LETTERS, 10, DOI: 10.1088/1612-2011/10/9/095802

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.

2258. Thermal stability of new biologic active copper(II) complexes with 5,6-dimethylbenzimidazole

Authors: Vlaicu, ID; Constand, M; Olar, R; Marinescu, D; Grecu, MN; Lazar, V; Chifiriuc, MC; Badea, M

Published: SEP 2013, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 113, 1377, DOI: 10.1007/s10973-013-2948-z

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.

2259. Nanosize induced effects in luminescent ZnS:Mn2+ quantum dots

Authors: Nistor, SV; Stefan, M; Ghica, D; Nistor, LC

Published: SEP 2013, RADIATION MEASUREMENTS, 56, 43, DOI: 10.1016/j.radmeas.2013.01.046

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.

2260. Detailed characterization of functionalized magnetite and ascertained effects

Authors: Culita, DC; Patron, L; Oprea, O; Bartha, C; Palade, P; Teodorescu, V; Filoti, G

Published: SEP 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1916-7

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.