National Institute Of Materials Physics - Romania

Publications

5781 articles found

2731. Unusual Behavior of a Novel Heterogeneous Chiral Dimer Cr(III)-Salen Complex in the Epoxidation/Epoxide Ring-Opening Reaction of trans-Methylcinnamate Ester

Authors: Protesescu, L; Tudorache, M; Neatu, S; Grecu, MN; Kemnitz, E; Filip, P; Parvulescu, VI; Coman, SM

Published: FEB 3 2011, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 1122, DOI: 10.1021/jp106281z

A dimer chromium(III)-salen complex immobilized on modified silica is an effective catalyst for the epoxidation/epoxide ring-opening reaction of trans-methylcinnamate ester and gave significantly high ee in methyl (2R,3S)-2,3-dihydroxy-3-phenylpropionate. For the first time, it is shown that a donor ligand (e.g., Et3N) can be involved into the enantioselective mechanism of the product configuration. It is suggested that the additive is interacting with the reaction intermediate in a manner that prolongs its lifetime, thus affording a free rotation of the C-C single bond in this species and a selective collapse to the cis-epoxide product. In the presence of water, this epoxide led to methyl (2S,3R)-2,3-dihydroxy-3-phenylpropionate. Alternatively, the donor additives may give rise to a new chromium-based oxidant that effects epoxidation and its consecutive ring opening to diols via an unusual pathway.

2732. Pulsed laser deposition of semiconducting crystalline double-doped barium titanate thin films on nickel substrates

Authors: Apostol, I; Stefan, N; Luculescu, CR; Birjega, R; Socol, M; Miroiu, M; Mihailescu, IN

Published: FEB 1 2011, APPLIED SURFACE SCIENCE, 257, 3576, DOI: 10.1016/j.apsusc.2010.11.078

We synthesized by pulsed laser deposition (Ba,Sr,Y)TiO3 and (Ba,Pb,Y)TiO3 thin films on mechanically polished nickel substrates. The synthesized thin films were analyzed for: crystalline structure by X-ray diffractometry, morphology and surface topography by atomic force microscopy, optical and scanning electron microscopy, and elemental composition by energy dispersive X-ray spectroscopy and electrical properties by electrical measurements. We have shown that film properties were determined by the dopants, target composition, and deposition parameters (oxygen pressure, substrate temperature and incident laser fluence). All films exhibited a semiconducting behavior, as proved by the decrease of electrical resistance with heating temperature. (C) 2010 Elsevier B. V. All rights reserved.

2733. Structural changes during the crystallization of the Bi4Ge3O12 glasses

Authors: Polosan, S; Nastase, F; Secu, M

Published: FEB 1 2011, JOURNAL OF NON-CRYSTALLINE SOLIDS, 357, 1113, DOI: 10.1016/j.jnoncrysol.2010.10.016

Bismuth-germanate glass ceramics with the composition 40% Bi2O3-60% GeO2 (in molar percents) were prepared through controlled crystallization of melt-quenched glass. The Raman and FTIR spectra recorded in the as-made glasses show broad bands at 240, 400, 780 cm(-1) and 400, 745 cm(-1) have been assigned Ge-O bonds which appear right after preparation. X-ray diffraction has shown that the as-made glasses are amorphous, but after annealing above the crystallization temperature at 558 degrees C, BGO nano-crystallites with a size of about 50 nm precipitate in the glass matrix. The Raman and FTIR spectra reveal sharp peaks associated to the "internal" and "external vibrations" of GeO4 tetrahedral groups inside the BGO nano-crystallites. In the glass ceramic sample the transparency region is shifted at longer wavelengths compared to as-made glass, due to the Rayleigh scattering on the BGO nano-crystallites. (C) 2010 Elsevier B.V. All rights reserved.

2734. Eu3+-doped CaF2 nanocrystals in sol-gel derived glass-ceramics

Authors: Secu, M; Secu, CE; Ghica, C

Published: FEB 2011, OPTICAL MATERIALS, 33, 617, DOI: 10.1016/j.optmat.2010.11.016

Glass-ceramics containing Eu3+-doped CaF2 nanocrystals of about 16 nm size have been made using the controlled crystallization at higher temperatures of the Eu3+-doped CaF2-SiO2 xerogels. In the glass-ceramic material the Eu3+ ions are embedded in both silica network and in the non-centrosymmetric sites of the CaF2 nanocrystals structure. Lower phonon energy of CaF2 and the dehydratation processes reduce the probability of non-radiative de-excitations and as a result a luminescence enhancement and an increase of the PL lifetime is observed. Eu-doping modifies the traps distribution within the glass-ceramics and as a result an additional broad thermoluminescence peak at about 380 degrees C was observed. The peak was assigned to the recombination of the electrons thermal released from the Eu3+-related traps in the glass matrix and in the CaF2 nanocrystals. (C) 2010 Elsevier B.V. All rights reserved.

2735. 1-BUTANOL DEHYDRATION AND DEHYDROGENATION OVER VANADIUM ALUMINIUM OXYNITRIDE CATALYSTS

Authors: Florea, M; Delsarte, S; van Keulen, E; Grange, P

Published: FEB 2011, , DOI:

2736. Tailoring immobilization of immunoglobulin by excimer laser for biosensor applications

Authors: Sima, F; Axente, E; Ristoscu, C; Mihailescu, IN; Kononenko, TV; Nagovitsin, IA; Chudinova, G; Konov, VI; Socol, M; Enculescu, I; Sima, LE; Petrescu, SM

Published: FEB 2011, JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 96A, 394, DOI: 10.1002/jbm.a.32991

The sheltered transfer and immobilization of rabbit anti-human antiserum immunoglobulin G (IgG) by matrix-assisted pulsed laser evaporation (MAPLE) are reported. The iced targets submitted to laser irradiation consisted of 0.2-2 mg/mL IgG blended or not with lipid (L-a-phosphatidylcholine dipalmitoyl) dissolved in distilled water-based saline buffer. Thin IgG coatings were obtained at room temperature onto glass, fused silica, or silicon substrates. Ten thousand subsequent laser pulses of 0.33, 0.5, or 0.67 J/cm(2) fluence were applied for the synthesis of each sample. Morphology and composition of the thin films were studied by optical, scanning, and atomic force microscopy and Fourier transformed infrared spectrometry. Optical labeling methods such as spectrofluorimetry and fluorescence microscopy were selected to verify the biosensor transduction principle because of their high sensitivity for detecting low amounts of antigen (IgG). Protein immobilization to the substrate surface was demonstrated for all obtained structures after immersion in the donkey anti-rabbit secondary antibody solution. The IgG transfer and immobilization onto substrates were improved by addition of lipid to MAPLE solutions. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 96A: 384-394, 2011.

2737. 'Beautiful' unconventional synthesis and processing technologies of superconductors and some other materials

Authors: Badica, P; Crisan, A; Aldica, G; Endo, K; Borodianska, H; Togano, K; Awaji, S; Watanabe, K; Sakka, Y; Vasylkiv, O

Published: FEB 2011, SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 12, DOI: 10.1088/1468-6996/12/1/013001

Superconducting materials have contributed significantly to the development of modern materials science and engineering. Specific technological solutions for their synthesis and processing helped in understanding the principles and approaches to the design, fabrication and application of many other materials. In this review, we explore the bidirectional relationship between the general and particular synthesis concepts. The analysis is mostly based on our studies where some unconventional technologies were applied to different superconductors and some other materials. These technologies include spray-frozen freeze-drying, fast pyrolysis, field-assisted sintering (or spark plasma sintering), nanoblasting, processing in high magnetic fields, methods of control of supersaturation and migration during film growth, and mechanical treatments of composite wires. The analysis provides future research directions and some key elements to define the concept of 'beautiful' technology in materials science. It also reconfirms the key position and importance of superconductors in the development of new materials and unconventional synthesis approaches.

2738. Hybrid organic-inorganic materials based on poly(o-phenylenediamine) and polyoxometallate functionalized carbon nanotubes

Authors: Baibarac, M; Baltog, I; Smaranda, I; Scocioreanu, M; Lefrant, S

Published: JAN 31 2011, JOURNAL OF MOLECULAR STRUCTURE, 985, 218, DOI: 10.1016/j.molstruc.2010.10.044

The chemical polymerization of o-phenylenediamine (OPD) on single-walled carbon nanotubes (SWCNTs) in the presence of phosphomolybdic acid (H3PMo12O40 xH(2)O) has been studied by surface enhanced resonant Raman scattering (SERRS) spectroscopy. One demonstrates that an organic-inorganic hybrid composite of the type poly(o-phenylenediamine)/polyoxometallate-functionalized SWCNTs is produced by the chemical interaction between polyoxometallate-functionalized SWCNTs and poly(o-phenylenediamine) (POPD) doped with [H2PMo12O40](-) ions. According to TEM investigations, a result of the chemical interaction of SWCNT with H3PMo12O40 xH(2)O is the formation into the composite mass of tube fragments of shorter length, which behave like closed shell fullerenes since Raman fingerprint is given by lines situated at 240-275 and 1450-1472 cm(-1). The chemical polymerization of OPD on SWCNTs achieved in the absence of H3PMo12O40 xH(2)O leads to a covalent functionalization of the wall side of the tubes, which is revealed in Raman spectra, recorded at the excitation wavelength of 514 nm, by an enhancement of the lines associated with the tangential vibrational modes of SWCNTs. Using FTIR spectroscopy, significant hindrance steric effects are evidenced in the POPD/polyoxometallate-functionalized SWCNT composite. (c) 2010 Elsevier B.V. All rights reserved.

2739. Substitutional and surface Mn2+ centers in cubic ZnS:Mn nanocrystals. A correlated EPR and photoluminescence study

Authors: Stefan, M; Nistor, SV; Ghica, D; Mateescu, CD; Nikl, M; Kucerkova, R

Published: JAN 20 2011, PHYSICAL REVIEW B, 83, DOI: 10.1103/PhysRevB.83.045301

The EPR, radioluminescence, and photoluminescence of cubic ZnS (cZnS) nanocrystals (NCs) with a narrow size distribution centered at 2 nm, doped with 0.1, 0.2, and 0.5 at.% Mn2+ ions were investigated. Besides the main lines from substitutional Mn2+ ions localized in the core of the NCs next to a stacking defect, the EPR spectra exhibited two broader hyperfine sextets, attributed to the so-called Mn(II)and Mn(III) surface centers, which could be separated by adequate thermal treatments. The contribution to the photoluminescence from the Mn2+ ions at various sites was further determined from the analysis of the steady-state and time-resolved photoluminescence data from cZnS: Mn NCs subjected to thermal treatments and from cZnS: Mn single crystals. Thus, the main emission consisting of two intense overlapping bands peaking at 596 and 630 nm was attributed to the T-4(1)-(6)A(1) transition of the substitutional Mn2+ ions in the core of the cZnS nanocrystals and to residual aggregated Mn2+ ions, respectively, the last ones being responsible for a broad EPR line observed in the X-band spectrum. The Mn(II) and Mn(III) centers, consisting of Mn2+ ions in the oxidized and hydrolyzed surface layer of the NCs, respectively, are only indirectly involved in the energy transfer to the substitutional Mn2+ centers, very likely through pairs interaction.

2740. Microwave properties of Ba(Zn1/3Ta2/3)O-3 dielectric resonators

Authors: Nedelcu, L; Toacsan, MI; Banciu, MG; Ioachim, A

Published: JAN 12 2011, JOURNAL OF ALLOYS AND COMPOUNDS, 509, 481, DOI: 10.1016/j.jallcom.2010.09.069

Ba(Zn1/3Ta2/3)O-3 (BZT) dielectric resonators were prepared by solid-state reaction. The starting materials were BaCO3, ZnO, and Ta2O5 powders with high purity. The double calcined BZT pellets were sintered in air at temperatures of 1575, 1600, 1625, and 1650 degrees C for 4 h. The X-ray diffraction data allowed the study of the unit cell distortion degree and the presence of the secondary phases. A long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was observed with the increase of the sintering temperature. The dielectric constant of BZT resonators measured around 6 GHz was between 26 and 28. High values of Q x f product (120 THz) were obtained for BZT resonators sintered at 1650 degrees C/4 h. The temperature coefficient of the resonance frequency exhibits positive values less than 6 ppm/degrees C. The achieved dielectric parameters recommend BZT dielectric resonators for microwave and millimeter wave applications. (C) 2010 Elsevier B.V. All rights reserved.