National Institute Of Materials Physics - Romania

Publications

5781 articles found

2831. PROPERTIES OF RARE EARTH Ga-La-S GLASSES OBTAINED BY RF INDUCTOR HEATING

Authors: Popescu, AA; Savastru, D; Miclos, S; Braic, V; Popescu, M; Manea, A; Kiss, A

Published: APR-JUN 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 348, DOI:

A new synthesis method for 70Ga(2)S(3)30La(2)S(3) (GLS) lanthanum based glass, which uses a RF-heating inductor, has been developed. The method gives the possibility to quench the melt without taking the crucible out of the reaction chamber. Glasses with good optical quality were obtained. The samples characterized by X-ray diffraction prove the amorphous state. The re-heating of GaLaS at temperatures of 620 degrees C leads to the appearance of large 30-80 mu m crystals, Ga3La1.66S7 structure being the main crystal form. High quality GLS thin films have been obtained by RF sputtering. The calculated refractive index was 2.48 for the thin films obtained by RF sputtering and 2.55 for bulk samples. Two kinds of the Urbach-density of state distribution are distinguished from optical transmission measurements corresponding to activation energies of 0.12 eV and 0.66 eV.

2832. Redox behavior of hemin at p-GaAs(1 0 0) electrode

Authors: Toader, AM; Volanschi, E; Lazarescu, MF; Lazarescu, V

Published: DEC 30 2010, ELECTROCHIMICA ACTA, 56, 866, DOI: 10.1016/j.electacta.2010.09.083

Electrochemical behavior of hemin on p-GaAs(1 0 0) electrodes was examined by cyclic voltammetry (CV) and impedance spectroscopy (EIS) in phosphate buffer solutions (PBS) at pH 7.45. CV investigations in 0.6 mM hemin in PBS revealed a pair of reversible peaks at -0.44 and -0.32 V vs. SCE resulting in stable adsorbed species. EIS spectra analysis pointed out that these adsorbed species bring significant changes in the semiconductor surface state population and the potential drop distribution between the semiconductor space charge region and the Helmholtz layer. (C) 2010 Elsevier Ltd. All rights reserved.

2833. Skin Layer Defects in Si by Optimized Treatment in Hydrogen RF Plasma

Authors: Ghica, C; Nistor, LC; Vizireanu, S; Dinescu, G; Moldovan, A; Dinescu, M

Published: DEC 20 2010, PLASMA PROCESSES AND POLYMERS, 7, 991, DOI: 10.1002/ppap.201000066

The first step of the smartcut (TM) process consists in inducing structural defects below the free surface of a silicon wafer, usually by implantation of light elements, such as hydrogen or helium. An alternative way to induce subsurface defects is by plasma treatment. In this work, we present a morphological and structural study on silicon wafers submitted to hydrogen plasma treatment, using two plasma-processing geometries. The parameters of the plasma treatment have been varied in order to limit the surface roughness and to confine the induced defects in a narrow region (50 nm) below the wafer surface. The morphological and structural investigations have been performed by AFM and TEM.

2834. Differentiation of mesenchymal stem cells onto highly adherent radio frequency-sputtered carbonated hydroxylapatite thin films

Authors: Sima, LE; Stan, GE; Morosanu, CO; Melinescu, A; Ianculescu, A; Melinte, R; Neamtu, J; Petrescu, SM

Published: DEC 15 2010, JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 95A, 1214, DOI: 10.1002/jbm.a.32947

In this work, an improved version of the radio frequency magnetron sputtering (RF-MS) technique was used to prepare highly adherent B-type carbonated hydroxylapatite (B-CHA) thin films. Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction studies proved that the coatings maintained the composition and revealed the polycrystalline structure of HA. Scanning electron microscopy analysis showed that the CHA films are rough and exhibit a homogeneous microstructure. Energy-dispersive Xray spectroscopy (EDX) mapping demonstrated a uniform distribution of the Ca and P cations while a Ca/P ratio of 1.8 was found. In addition, the FTIR experiments showed a remarkable reproducibility of the nanostructures. Human mesenchymal stem cells (hMSCs), in vitro differentiated osteoblasts, and explanted bone cells were grown over the surface of CHA coatings for periods between a few hours and 21 days. Osteoprogenitor cells maintained viability and characteristic morphology after adhesion on CHA coatings. Ki67-positive osteoblasts were the evidence of cell proliferation events. Cells showed positive staining for markers of osteoblast phenotype such as collagen type I, bone sialoprotein and osteonectin. Our data showed the formation of mineralized foci by differentiation of hMSCs to human primary osteoblasts after cultivation in osteogenic media on RF-sputtered films. The results demonstrate the capacity of B-type CHA coating to support MSCs adhesion and osteogenic differentiation ability. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 95A: 1203-1214,2010.

2835. Study of magnetic nanovectors by Wet-STEM, a new ESEM mode in transmission

Authors: Maraloiu, VA; Hamoudeh, M; Fessi, H; Blanchin, MG

Published: DEC 15 2010, JOURNAL OF COLLOID AND INTERFACE SCIENCE, 352, 392, DOI: 10.1016/j.jcis.2010.08.066

Many nanovectors used for therapy (drug targeting radiation therapy) or diagnostic such as Magnetic Resonance Imaging (MRI) have a composite structure consisting of an organic core or organic coverage encapsulating magnetic nanoparticles and they are commonly dispersed in liquid suspensions for intravenous injection Here is presented the application of a new Environmental Scanning Electron Microscopy (ESEM) mode in transmission so called Wet-STEM for transmission imaging of droplets of such suspensions This is illustrated by Wet-STEM images from PLLA/Re nanospheres (about 100-300 nm in diameter) loaded with magnetite nanoparticles (about 10 nm in diameter) and from iron oxide core (about 5 nm in size) MRI contrast agents both examples in aqueous suspensions It is shown that the Wet STEM mode allows both the collective behavior of such nanovectors in suspension to be characterized and the inner composite structure of individual vectors to be revealed Such experimental results are discussed by comparison with Monte Carlo computer simulations of the distribution of the electrons scattered through the samples in rather large solid angles (between 20 degrees and 47 degrees) corresponding to the detection conditions (C) 2010 Elsevier Inc All rights reserved

2836. Microstructure and ferroic properties of epitaxial [gamma-Fe2O3-BiFeO3]-Bi3.25La0.75Ti3O12 composite bilayers

Authors: Gautreau, O; Harnagea, C; Gunawan, L; Botton, GA; Pintilie, L; Singh, MP; Pignolet, A

Published: DEC 1 2010, JOURNAL OF APPLIED PHYSICS, 108, DOI: 10.1063/1.3514591

Epitaxial [gamma-Fe2O3-BiFeO3]/Bi3.25La0.75Ti3O12 and Bi3.25La0.75Ti3O12/[gamma-Fe2O3-BiFeO3] composite bilayers were grown on SrRuO3 coated (111) SrTiO3 substrates in order to investigate the influence of the morphology of the gamma-Fe2O3-BiFeO3 self assembled nanocomposite layer on the multiferroic properties of the bilayer. Both types of bilayers exhibit high resistivity and simultaneously ferroelectricity and ferrimagnetism at room temperature. When the gamma-Fe2O3-BiFeO3 composite layer is sandwiched between the Bi3.25La0.75Ti3O12 film and the substrate, the BiFeO3 component is not only subjected to epitaxial strain induced by the surface on top of which it grows but also to elastic interactions with the Bi3.25La0.75Ti3O12 capping layer. The latter indeed reduce the amount of gamma-Fe2O3 inclusions, affects the morphology of the grains in the gamma-Fe2O3-BiFeO3 layer, and increases the shape anisotropy of the gamma-Fe2O3 inclusions. Additionally, this modification in the microstructure of the gamma-Fe2O3-BiFeO3 layer induces an imprint in the ferroelectric hysteresis loop as well as a decrease in the saturation magnetization, and its magnetic easy axis direction changes from in-plane to out-of plane. (c) 2010 American Institute of Physics. [doi:10.1063/1.3514591]

2837. Spin splitter regime of a mesoscopic Rashba ring

Authors: Moldoveanu, V; Tanatar, B

Published: DEC 1 2010, PHYSICS LETTERS A, 375, 191, DOI: 10.1016/j.physleta.2010.10.047

Using the non-equilibrium Greens' function formalism we calculate the spin currents in a one-dimensional ring coupled to three leads and in the presence of perpendicular magnetic flux (1) and Rashba spin-orbit coupling. A finite bias is applied between the input lead and the other two output leads. We show that the spin-orbit coupling allows one to operate this system as a spin splitter, i.e. the output leads deliver spin-polarized currents with different orientations. We find that the spin splitter operation can be tuned at integer multiples of phi/phi(0). Its efficiency depends not only on the value of the Rashba coupling but also on the bias applied between the input and output leads. The selected spin orientation of the output leads can be reversed by a slight change of their contact position. We discuss as well the connection between the spin splitter operation and the spectral properties of the ring. (C) 2010 Elsevier B.V. All rights reserved.

2838. Metal oxide nanoparticles synthesized by pulsed laser ablation for proton exchange membrane fuel cells

Authors: Dorcioman, G; Ebrasu, D; Enculescu, I; Serban, N; Axente, E; Sima, F; Ristoscu, C; Mihailescu, IN

Published: DEC 1 2010, JOURNAL OF POWER SOURCES, 195, 7780, DOI: 10.1016/j.jpowsour.2009.09.060

We report on the development of a modified gas diffusion layer for fuel cells consisting of a simple or teflonized carbon cloth pulsed laser deposited with metal oxide nanostructures designed to operate both as co-catalyst, and oxidic support for other electrochemically active catalysts. We selected TiO2, ZnO and Al2O3 doped (2 wt.%) ZnO which were uniformly distributed over the surface of gas diffusion layers in order to improve the catalytic activity, stability and lifetime, and reduce the production costs of proton exchange membrane fuel cells. We evidenced by scanning electron microscopy and energy dispersive spectroscopy that our depositions consisted of TiO2 nanoparticles while in the case of ZnO and Al2O3 doped (2 wt.%) ZnO transparent quasi-continuous films were synthesized. (C) 2009 Elsevier BM. All rights reserved.

2839. Growth and characterization of Y0.7Sc0.3Ca4O(BO3)(3) single crystal for nonlinear optical applications

Authors: Achim, A; Gheorghe, L; Georgescu, S; Voicu, F

Published: DEC 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1980, DOI:

The nonlinear optical (NLO) crystal Y0.7Sc0.3Ca4O(BO3)(3) (starting composition) of good quality has been grown from the melt by the Czochralski pulling method. X-ray diffraction experiments show that the structure of grown crystal belongs to the monoclinic system with space group Cm and its unit cell parameters have been determined to be a = 0.80601(5) nm, b = 1.59946(8) nm, c = 0.35210(7) nm and beta = 101.165(1)degrees. The crystal possesses a wide transmission range from UV to IR, which is advantageous for applications as new NLO material for frequency doubling of solid state lasers operating in the near infrared range.

2840. Topology of two-band superconductors

Authors: Tanaka, Y; Iyo, A; Tokiwa, K; Watanabe, T; Crisan, A; Sundaresan, A; Terada, N

Published: DEC 2010, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 470, S967, DOI: 10.1016/j.physc.2009.10.036

Two-band superconductivity has a topology different from that in single-band superconductivity. The topology is not always stabilized in an infinitely homogeneous sample. The morphology, grain shape, and pattern of the device (topology of the superconducting materials) is effective in stabilizing the topology. In this report, we discuss a vortex having a small magnetic flux but a large winding number as one plausible topology in a two-band superconductor. (C) 2009 Elsevier B.V. All rights reserved.