National Institute Of Materials Physics - Romania

Publications

5714 articles found

2761. Influence of defects on the switching speed of Ge2Sb2Te5

Authors: Velea, A; Popescu, M; Lorinczi, A; Sava, F; Simandan, ID; Mihai, C

Published: NOV-DEC 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 1596, DOI:

Chalcogenide phase change materials are one of the major contenders for the new non-volatile memory applications. Here is reported that the switching speed of Ge2Sb2Te5 is strongly dependent on the percent of defects in the material. Using cellular automata simulations it was shown that the size of the percolation cluster is minimum, thus the switching speed is maximum, for a percent of around 25% defects in the material. This is a property of the Ge2Sb2Te5 that can be useful for new phase change materials and devices design with better switching properties.

2762. Current enhancement and negative differential conductance in parallel quantum dot systems

Authors: Tanatar, B; Moldoveanu, V

Published: 2011, PHYSICS OF SEMICONDUCTORS: 30TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, 1399, DOI: 10.1063/1.3666366

We present calculations on the transport properties of a double quantum dot (DQD) capacitively coupled to another individually biased dot. The effects of the intradot and interdot Coulomb interaction are included within the random-phase approximation (RPA) implemented in the Keldysh formalism. We show that by increasing the bias on the nearby dot the inelastic Coulomb scattering modifies the current in the double dot. The sign of the current depends on the detuning of the double dot levels and intradot transitions lead to negative differential conductance. The enhancement of the current due to the energy quanta transferred from the strongly biased dot suggests a quantum ratchet or Coulomb drag mechanism.

2763. Sn-119- AND Fe-57- MOSSBAUER INVESTIGATION OF xSnO(2)-[(1-X)[alpha-Fe2O3] NANOPARTICLE SYSTEM. (I) MAGNETIC HYPERFINE FIELD DISTRIBUTION IN Sn-LOW DILUTE SYSTEM

Authors: Constantinescu, S; Diamandescu, L; Bibicu, I; Tarabasanu-Mihaila, D; Feder, M

Published: 2011, ROMANIAN JOURNAL OF PHYSICS, 56, 707, DOI:

A series of xSnO(2)-(1-x)alpha-Fe2O3 (x=0.0-1.0) was prepared by a hydrothermal route starting with an aqueous mixture of iron (III) chloride hexahydrate, FeCl3 center dot 6H(2)O, and tin (IV) chloride pentahydrate, SnCl4 center dot 5H(2)O. The as resulted nanoscaled powders have been investigated by X-ray diffraction (XRD) and Sn-119 Mossbauer spectroscopy in transmission geometry and conversion electron. Under x = 0.300, the spectra reveal the appearance of magnetic hyperfine induced structure. At x = 0.300, the spectrum shows a magnetic phase (M) with the percentage of about 17%. The appearance of hyperfine magnetic fields suggests the location of the nonmagnetic Sn4+ ions, surrounded by the Fe3+ ions, in the interstitial and substitutional sites of alpha-Fe2O3 phase. On the other hand, the dependence of the total spectrum areas, vs. molar concentration x, displays a jump around x similar to 0.45, suggesting a change of the characteristic Debye temperature in the Mossbauer factor. The reported spectra have been fitted and the obtained hyperfine parameters are discussed in terms of reduced dimensional effects, super-transferred hyperfine interactions (STHI) and magnetic hyperfine field distribution (MHFD).

2764. 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.

2765. 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.

2766. 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.

2767. 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.

2768. 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

2769. 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]

2770. 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.