National Institute Of Materials Physics - Romania

Publications

5781 articles found

1941. Anti-Stokes Raman spectroscopy as a method to identify metallic and mixed metallic/semiconducting configurations of multi-walled carbon nanotubes

Authors: Baibarac, M; Matea, A; Ilie, M; Baltog, I; Magrez, A

Published: 2015, ANALYTICAL METHODS, 7, 6230, DOI: 10.1039/c5ay01281c

SERS studies were performed on films of two families of multi-wall carbon nanotubes (MWCNTs) under an excitation light of 514.5 nm and 647.1 nm. These included Aldrich-MWCNTs, which alternate semiconducting and metallic tubes and M-MWCNTs that contain only metallic tubes obtained by water assisted catalytic chemical vapour deposition (CCVD). The two families of MWCNTs reveal similar spectra in the Stokes branch, which feature an increasing Raman intensity when the glass substrate is replaced with an Au or Ag substrate, indicating a (surface enhanced Raman scattering) SERS mechanism. In the anti-Stokes branch, despite an enhancement of approximately 100 times compared to the predictions of the Boltzmann law, only Aldrich-MWCNTs exhibit a Raman spectrum with an intensity that increases as a result of the change in the glass substrate to Au or Ag, a fact that is revealed by the signature of the SERS process. The invariance of the Raman intensity in the anti-Stokes branch as a result of the change of the substrate is characteristic of M-MWCNTs and results from a Raman light scattering process that takes place only within the skin depth of the metallic structure.

1942. Model-free Kinetic Analysis of Sr2FeMoO6 Re-crystallization Process Used for Double-Perovskite Monocrystals Grown by Bridgman Method

Authors: Bartha, C; Plapcianu, C; Palade, P; Vizman, D

Published: 2015, TIM14 PHYSICS CONFERENCE: PHYSICS WITHOUT FRONTIERS, 1694, DOI: 10.1063/1.4937258

The synthesis routes for polycrystalline bulk Sr2FeMoO6 (SFMO), offer various possibilities, but in all the cases it is difficult to obtain a single phase of this compound. A new challenge in the field is to achieve mono-crystals using different growing routes and the Bridgman method represents one of them. In order to establish the optimal conditions of mono-crystals growing process, a complex thermal investigation of bulk double perovskite has been performed. Differential thermal analysis investigation in argon inert atmosphere, starting from room temperature up to 1650 degrees C provided information about melting and re-crystallization temperature range. Both, the activation energy of Sr2FeMoO6 re-crystallization process and the re-crystallization mechanism were comparatively analyzed by two free-model estimations (Friedman and Ozawa-Flynn-Wall analysis). The resulted data are very important in order to set up the heating program of Bridgman furnace.

1943. Dielectric Properties of LDH-Type Layered Materials Containing Zn or Mg Ions : On the Non Monotonous Temperature Dependence of Relaxation Times

Authors: Frunza, L; Frunza, S; Ganea, CP; Zgura, I; Neatu, F; Parvulescu, VI

Published: 2015, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 18, 328, DOI:

The electrical behavior of layered double hydroxides containing Al or Ga as the trivalent ions and Mg or Zn as bivalent ions was evaluated using broadband dielectric spectroscopy in a wide temperature range. Besides conduction effects a relaxation peak is observable at high frequencies which is assigned to the reorientational fluctuations of water molecules adsorbed on the oxide surface or in the interlayer voids. The Maxwell-Wagner-Sillars peak, superimposed to the conductivity phenomenon is observable at low frequencies. A non-monotonous temperature dependence of the relaxation rates of the relaxation process has been found. A quantitative description of this dependence was possible based on a model assuming two competing processes: rotational fluctuation of water molecules and formation of additional defects. Reasonable values for the characteristic parameters were obtained. Thus the water behavior in the studied layered oxides is similar to that observed for water in other porous materials. However, the activation energy of the rotational fluctuation, the pre exponential factor and the number of defects are higher whereas the value of the energy of defect formation is lower in the layered oxide materials than for water confined to nanoporous molecular sieves, porous glasses or in bulk ice.

1944. Effect of optical coating in the thin-film system of chalcogenide glassy semiconductor-dielectric when recording the holographic optical information

Authors: Chirita, A; Prilepov, V; Popescu, M; Andries, I; Caraman, M; Jidcov, IU

Published: JUL-AUG 2015, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17, 929, DOI:

In this paper we show that the possibility of obtaining the high values of efficiency of relief-phase holographic gratings formed in the photo-thermoplastic recording process holds not only due to the non-sinusoidal profile form, but also due to the effect of optical coating that appears in the two-layer system of photo-semiconductor deformed thermoplastic. Analyzed are the conditions, under which takes place the antireflection optical coating, reducing unwanted reflections from surfaces and thereby enhancing efficiency. It is shown that by careful choice of the thicknesses and refractive indices of the layers materials the efficiency of holographic gratings can be improved by 2-5 %.

1945. COMPOSITES OF MgB2 - RARE-EARTH-OXIDES: FABRICATION BY SPARK PLASMA SINTERING AND FUNCTIONAL PROPERTIES

Authors: Batalu, D; Aldica, G; Badica, P

Published: 2015, 20TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS, DOI:

Dense MgB2 samples with La2O3 addition were obtained by spark plasma sintering. We used two different La2O3 raw powders showing different particle sizes and shapes. The as-obtained composite samples have significant differences in microstructure and Vickers hardness. A deposited phosphate layer was obtained by immersing the samples in PBS, and drying. Formation of phosphate needles, gathered in bouquets, show a possible bioactive behavior of MgB2.

1946. SYNTHESIS, CHARACTERIZATION AND CYTOTOXICITY EVALUATION ON ZINC DOPED HYDROXYAPATITE IN COLLAGEN MATRIX

Authors: Popa, CL; Bartha, CM; Albu, M; Guegan, R; Motelica-Heino, M; Chifiriuc, MC; Bleotu, C; Badea, ML; Antohe, S

Published: APR-JUN 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 691, DOI:

The goal of this study was to obtain at low temperature a functional nano-composite with characteristics similar to the natural bone by using a cost effective method. The structure and morphology of collagen coated zinc doped hydroxyapatite bio-composites (Zn:HAp-CBc) were examined by X-Ray diffraction (XRD) and Scanning Electron Microscopy (SEM). XRD analysis revealed that the unique hexagonal Ca-10(PO4)(6)(OH)(2) in P-63m space group was observed in the obtained nanocomposites Zn: HAp-CBc. The cytotoxicity of the Zn: HAp-CBc was studied on HeLa cell lines. Cell cycle distribution after treatment was examined by flow cytometry analysis. Our preliminary in vitro studies revealed that the obtained composites based on Zn doped HAp embedded in collagen matrix have excellent biocompatibility and support their further characterization by in vivo approaches and development as a biomaterial used in bone regeneration.

1947. IN-SITU IODINE DOPED POLYTHIOPHENE-LIKE THIN FILMS OBTAINED BY POST-DISCHARGE RF PLASMA

Authors: Satulu, V; Ion, V; Aldica, G; Mitu, B; Dinescu, G

Published: 2015, ROMANIAN JOURNAL OF PHYSICS, 60, 1560, DOI:

This work reports on the synthesis of polythiophene-like thin films by using a post-discharge RF plasma configuration in which thiophene vapors are introduced in the substrate proximity. The deposition process is assisted by a controlled iodine flow for in-situ doping leading to a material with improved conductivity. The influence of iodine mass flow rate on the deposition rate, optical parameters, composition, chemical structure and electrical properties of the material obtained in various discharge conditions is reported.

1948. Preliminary histological studies on the influence of glycerol-iron-oxide nanoparticles

Authors: Popa, CL; Andronescu, E; Turculet, C; Beuran, M; Le Coustomer, P; Badea, ML; Surugiu, A; Prodan, AM

Published: SEP-OCT 2015, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17, 1576, DOI:

This paper reports structural and morphological studies as well as in vivo evaluation of glycerol-iron-oxide nanoparticles (GIO-NPs) in order to investigate their influence on different organic tissues. Transmission electron microscopy (TEM) studies confirm the structure characteristic to iron oxide nanoparticles and their ellipsoidal shape. The histopathological examinations indicated that the studied nanoparticles induce many morphological alterations to the liver, kidneys and spleen tissues 24h, 48h and 72h exposure.

1949. Analysis of bimodal thermally-induced denaturation of type I collagen extracted from calfskin

Authors: Staicu, T; Circu, V; Ionita, G; Ghica, C; Popa, VT; Micutz, M

Published: 2015, RSC ADVANCES, 5, 38406, DOI: 10.1039/c5ra02708j

The most widely occurring collagen in the extracellular matrix of the mammalian tissues - type I collagen has attracted huge interest from both theoretical and practical points of view. The results presented herein are mainly confined to a study of the thermal stability of type I collagen (CI) extracted from calfskin in acidic solutions (10(-2) M HCl). A two-step process associated with the heat-induced denaturation of CI was revealed by using ultra sensitive differential scanning calorimetry. The minor endothermic transition (peak temperatures of about 30.5-30.8 degrees C) has been assigned to the defibrillation of small supramolecular CI assemblies (occurring in solution) while the major endothermic transition (about 34.8-35.0 degrees C) has been ascribed to denaturation of CI, consisting of a complete unfolding of the native triple-helical conformation of the collagen molecule. The calorimetric data were supported by information obtained from capillary viscometry performed on the same solutions. The native state of CI (molecular integrity and triple-helical conformation) for all the systems studied in this paper was confirmed by transmission electron microscopy, ultraviolet circular dichroism and capillary viscometry. At the same time, based on the sodium dodecyl sulphate-polyacrylamide gel electrophoresis and an appropriate image processing of the corresponding electropherogram, a certain degree of intramolecular crosslinking of CI was detected, mainly between alpha 1 and alpha 2 chains of the collagen triple-helix. Such a feature seems to be caused by both the nature of the extraction procedure and the storage conditions.

1950. Spectro-microscopic photoemission evidence of charge uncompensated areas in Pb(Zr,Ti)O-3(001) layers

Authors: Popescu, DG; Husanu, MA; Trupina, L; Hrib, L; Pintilie, L; Barinov, A; Lizzit, S; Lacovig, P; Teodorescu, CM

Published: 2015, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 520, DOI: 10.1039/c4cp04546g

Photoelectron spectroscopy studies of (001) oriented PbTi0.8Zr0.2O3 (PZT) single crystal layers with submicron resolution revealed areas with different Pb 5d binding energies, attributed to the different charge and polarization states of the film surface. Two novel effects are evidenced by using intense synchrotron radiation beam experiments: (i) the progressive increase of a low binding energy component for the Pb core levels (evidenced for both 5d and 4f, on two different measurement setups), which can be attributed to a partial decomposition of the PZT film at its surface and promoting the growth of metallic Pb during the photoemission process, with the eventuality of the progressive formation of areas with downwards ferroelectric polarization; (ii) for films annealed in oxygen under clean conditions (in an ultrahigh vacuum installation) a huge shift of the Pb 5d core levels (by 8-9 eV) towards higher binding energies is attributed to the formation of areas with depleted mobile charge carriers, whose surface density is insufficient to screen the depolarization field. This shift is attenuated progressively with time, as the sample is irradiated with high flux soft X-rays. The formation of these areas with strong internal electric field promotes these films as good candidates for photocatalysis and solar cells, since in the operation of these devices the ability to perform charge separation and to avoid electron-hole recombination is crucial.