National Institute Of Materials Physics - Romania

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5781 articles found

2261. Thermal, spectral, magnetic and antimicrobial behaviour of new Ni(II), Cu(II) and Zn(II) complexes with a hexaazamacrocyclic ligand

Authors: Patrascu, F; Badea, M; Grecu, MN; Stanica, N; Marutescu, L; Marinescu, D; Spinu, C; Tigae, C; Olar, R

Published: SEP 2013, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 113, 1429, DOI: 10.1007/s10973-012-2898-x

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.

2262. Precursor method-A nonconventional route for the synthesis of ZnCr2O4 spinel

Authors: Gingasu, D; Mindru, I; Patron, L; Culita, DC; Calderon-Moreno, JM; Diamandescu, L; Feder, M; Oprea, O

Published: SEP 2013, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 74, 1302, DOI: 10.1016/j.jpcs.2013.04.007

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.

2263. Investigation of thermal stability, spectral, magnetic, and antimicrobial behavior for new complexes of Ni(II), Cu(II), and Zn(II) with a bismacrocyclic ligand

Authors: Bucur, C; Korosec, RC; Badea, M; Calu, L; Chifiriuc, MC; Grecu, N; Stanica, N; Marinescu, D; Olar, R

Published: SEP 2013, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 113, 1295, DOI: 10.1007/s10973-012-2912-3

Novel complexes of type M2LCl4 center dot nH(2)O (M: Ni, n = 4; M: Cu, n = 2.5 and M: Zn, n = 1.5; L: ligand resulted from 1,3-phenylenediamine, 3,6-diazaoctane-1,8-diamine, and formaldehyde one-pot condensation) were synthesized and characterized. The ligand was also isolated and characterized. The complexes features have been assigned from microanalytical, electrospray ionization tandem mass spectrometry, IR, UV-vis, H-1 NMR, and EPR spectra as well as magnetic data at room temperature. Simultaneous thermogravimetric/dynamic scanning calorimetry/evolved gas analysis measurements were performed to evidence the nature of the gaseous products formed in each step. Processes as water elimination, fragmentation, and oxidative degradation of the organic ligand as well as chloride elimination were observed during the thermal decomposition. The final product of decomposition was metal(II) oxide except for copper complex where CuCl remained also in the oxide network. The complexes exhibited an improved antibacterial activity in comparison with the ligand concerning both planktonic as well as biofilm-embedded cells.

2264. Weighting the influence of TiO2 anatase/brookite ratio in TiO2-Ag porous nanocomposites on visible photocatalytic performances

Authors: Iancu, V; Baia, M; Diamandescu, L; Pap, Z; Vlaicu, AM; Danciu, V; Baia, L

Published: AUG 15 2013, MATERIALS CHEMISTRY AND PHYSICS, 141, 239, DOI: 10.1016/j.matchemphys.2013.05.005

Nanocomposites based on TiO2 aerogel and Ag nanoparticles have been successfully obtained through different synthesis methods and their specific surface areas have been determined by N-2 sorption (BET method). The photocatalytic potential for salicylic acid degradation has been evaluated. It was found that under visible light irradiation, all synthesized nanocomposites exhibit higher photocatalytic activity than the commercially available Aeroxide P25. By correlating the structural parameters with the photocatalytic performances, it has been found that the Ag nanoparticles and brookite phase presence alongside the anatase play important roles on the visible photocatalysts behavior. For the Ag containing samples with mixed anatase brookite phases, it has been observed that the visible photocatalytic performance decreases with the increase in brookite crystalline phase content. On the other hand, the addition of Ag nanoparticles results, as expected, in a clear enhancement of the visible photocatalytic activity. (C) 2013 Elsevier B.V. All rights reserved.

2265. Role of Hyperfine Coupling in Magnetic and Quadrupolar Ordering of Pr3Pd20Si6

Authors: Steinke, L; Mitsumoto, K; Miclea, CF; Weickert, F; Donni, A; Akatsu, M; Nemoto, Y; Goto, T; Kitazawa, H; Thalmeier, P; Brando, M

Published: AUG 14 2013, PHYSICAL REVIEW LETTERS, 111, DOI: 10.1103/PhysRevLett.111.077202

We study the ternary clathrate Pr3Pd20Si6 in specific heat and ac susceptibility measurements on a high-quality single crystal, distinguishing antiferromagnetic and antiferroquadrupolar ordering, as well as a hitherto unknown magnetic low-temperature transition. The specific heat shows the direct involvement of nuclear spin degrees of freedom in the antiferromagnetic ordering, which is well supported by our calculation of the hyperfine level scheme without adjustable parameters. Pr3Pd20Si6 is, therefore, one of the rare materials where the nuclear moments are involved in the formation of the magnetic ground state.

2266. Superconductivity and charge density wave formation in TlxV6S8

Authors: Miclea, CF; Hochheimer, HD; Martin, B; Miclea, C; Ohtani, T

Published: AUG 2 2013, NEW JOURNAL OF PHYSICS, 15, DOI: 10.1088/1367-2630/15/8/083008

We report on specific heat and resistivity measurements under hydrostatic pressure on the quasi-one dimensional metal TlxV6S8. We studied the interplay between the low temperature superconducting (SC) ground state and a high temperature charge density wave (CDW) instability. We observed a clear dependency of the physical properties of TlxV6S8 on the Tl concentration x. The CDW anomaly is present in all investigated samples that are strongly enhanced at half Tl filling, x = 0.47. This is also the only composition for which no signature of superconductivity is observed. The specific heat results regarding the SC phase in Tl0.63V6S8 suggest that this compound is a highly anisotropic, weak coupling superconductor. Pressure suppresses both SC and CDW transitions to lower temperatures. Nevertheless, as the CDW gap is closed at a critical pressure p(c), the increase in the density of states leads to a small enhancement of T-c suggesting that SC and CDW compete for parts of the Fermi-surface.

2267. Novel Fe@C-TiO2 and Fe@C-SiO2 water-dispersible magnetic nanocomposites

Authors: Fleaca, CT; Dumitrache, F; Morjan, I; Alexandrescu, R; Luculescu, C; Niculescu, A; Vasile, E; Kuncser, V

Published: AUG 1 2013, APPLIED SURFACE SCIENCE, 278, 288, DOI: 10.1016/j.apsusc.2013.01.172

We report the synthesis of novel nanocomposites based on Fe@C nanoparticles obtained from Fe(CO)(5) and C2H4/H-2 by laser pyrolysis technique using a three nozzles injector. The alpha Fe-FexCy@C particles (below 24 nm diameter) were first functionalized with hydrophilic groups using Na carboxymethylcellulose. Oxidic precursors (Si(OC2H5)(4) or Ti(OC2H5)(4)) dissolved in ethanol were mixed with ethanolic suspensions of hydrophilized Fe@C nanoparticles using strong ultrasonication, then with water (at different pH values) and finally the Fe-containing composites were recovered by magnetic separation. The SiO2 and TiO2-coated powders were characterized by XRD, FT-IR and TEM techniques and their magnetic hysteresis curves were recorded at different temperatures. Both composites contain submicron aggregates of Fe@C nanoparticles embedded in/surrounded by a disordered porous oxidic matrix/shell. Near superparamagnetic behavior and room temperature and 26 Am-2/kg (for Fe@C/SiO2) or 57Am(2)/kg (for Fe@C/TiO2) saturation magnetization values were recorded and a blocking temperature around 500K was extrapolated. (C) 2013 Elsevier B.V. All rights reserved.

2268. Morphological and structural characterization of SiC based composite nanostructures

Authors: Filipescu, M; Stokker-Cheregi, F; Colceag, D; Nedelcea, A; Birjega, R; Nistor, LC; Dinescu, M

Published: AUG 1 2013, APPLIED SURFACE SCIENCE, 278, 100, DOI: 10.1016/j.apsusc.2013.03.166

This paper reports on producing SiC based nanostructures (SiC, W-SiC, CNS-SiC) by pulsed laser deposition (PLD) and radio-frequency plasma assisted PLD. Simple and composite targets (SiC, 3/4 SiC + 1/4 tungsten and 3/4 SiC + 1/4 graphite) were irradiated by a 266 nm pulsed laser beam having a pulse duration of 7 ns. The silicon substrates were kept either at room temperature or heated up to 600 degrees C. The depositions were performed in argon at various pressures, ranging from 0.05 mbar up to 2 mbar. The influence of deposition parameters on the structure, surface morphology and composition of different SiC based structures was studied by atomic force microscopy, scanning electron microscopy, secondary ion mass spectrometry, transmission electron microscopy and selected area electron diffraction. Fibers, tubes, nanoparticles and rolled sheets structures were obtained by varying laser fluence, substrate temperature, gas pressure and radio-frequency power. (C) 2013 Elsevier B. V. All rights reserved.

2269. Antimicrobial activity of biopolymer-antibiotic thin films fabricated by advanced pulsed laser methods

Authors: Cristescu, R; Popescu, C; Dorcioman, G; Miroiu, FM; Socol, G; Mihailescu, IN; Gittard, SD; Miller, PR; Narayan, RJ; Enculescu, M; Chrisey, DB

Published: AUG 1 2013, APPLIED SURFACE SCIENCE, 278, 213, DOI: 10.1016/j.apsusc.2013.01.062

We report on thin film deposition by matrix assisted pulsed laser evaporation (MAPLE) of two polymer-drug composite thin film systems. A pulsed KrF* excimer laser source (lambda = 248 nm, tau = 25ns, nu = 10 Hz) was used to deposit composite thin films of poly(D,L-lactide) (PDLLA) containing several gentamicin concentrations. FTIR spectroscopy was used to demonstrate that MAPLE-transferred materials exhibited chemical structures similar to those of drop cast materials. Scanning electron microscopy data indicated that MAPLE may be used to fabricate thin films of good morphological quality. The activity of PDLLA-gentamicin composite thin films against Staphylococcus aureus bacteria was demonstrated using drop testing. The influence of drug concentration on microbial viability was also assessed. Our studies indicate that polymer-drug composite thin films prepared by MAPLE may be used to impart antimicrobial activity to implants, medical devices, and other contact surfaces. (C) 2013 Elsevier B.V. All rights reserved.

2270. Ga and As competition for thiolate formation at p-GaAs(111) surfaces

Authors: Preda, L; Negrila, C; Lazarescu, MF; Enache, M; Anastasescu, M; Toader, AM; Ionescu, S; Lazarescu, V

Published: AUG 1 2013, ELECTROCHIMICA ACTA, 104, 11, DOI: 10.1016/j.electacta.2013.04.077

Self-assembled layers of 4,4'-thio-bis-benzene-thiolate spontaneously adsorbed on p-doped GaAs(1 1 1)A and GaAs(1 1 1)B electrodes were examined by EIS, XPS, and AFM investigations. XPS data provide evidence that (i) both As and Ga atoms are involved in the thiolate formation no matter which one is prevailing on the semiconducting surface and (ii) only one of the two thiol groups participates in the chemisorption bond. EIS and AFM results point to a more stable thiolate layer formed on the As-terminated surface than that formed on the Ga-terminated surface due to stronger self-assembling effects developed between the adsorbed species. (C) 2013 Elsevier Ltd. All rights reserved.