National Institute Of Materials Physics - Romania

Publications

5714 articles found

1871. Magnetic and Martensitic Transformations in the bulk and melt spun ribbons of Ni57-xNdxFe18Ga25 Ferromagnetic Shape Memory Alloys

Authors: Tolea, F; Crisan, AD; Sofronie, M; Tolea, M; Valeanu, M

Published: 2015, MATERIALS TODAY-PROCEEDINGS, 2, 878, DOI: 10.1016/j.matpr.2015.07.421

Influence of Nd substitution for Ni on the magnetic properties and the martensitic transformation (MT) characteristics are investigated on Ni57-xNdxFe18Ga25 (x=0 divided by 4) ferromagnetic shape memory alloys (FSMAs) in bulk and also in ribbons prepared by melt spinning method and subjected to different thermal treatments. Increasing the Nd content induces a decrease of both the Curie and the MT temperatures. (C) 2015 The Authors. Published by Elsevier Ltd.

1872. Tuning the properties of Ge and Si nanocrystals based structures by tailoring the preparation conditions Review

Authors: Ciurea, ML; Lepadatu, AM

Published: JAN-MAR 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 87, DOI:

Ge and Si nanocrystals (NCs), quantum dots (QDs), and amorphous nanoparticles (NPs) have a significant role in the developement of micro- and nanoelectronic devices due to capability to tune their electrical and photoconductive properties by tailoring the morphology and structure parameters. Ge and Si NCs/QDs/NPs are zero-dimensional (0D) systems and the SiO2 films containing them are percolative systems. In this review, the role of deposition and annealing conditions in the morphology and structure of Ge and Si NCs/QDs/NPs embedded in amorphous SiO2 matrix is discussed for a wide variety of films and multilayered structures. The electrical and photoconductive properties of nanostructures deposited by different techniques as magnetron sputtering, ion implantation, chemical vapour deposition, sol-gel and molecular beam epitaxy, and subsequently annealed in conventional furnace or by rapid thermal annealing under different conditions are analised. We demonstrate how the electrical and photoconductive properties of nanostructures can be tuned by varying the deposition and annealing parameters. The role of Si-rich oxide and defects in the formation of Ge and Si NCs is shown and the role of defects in improving electrical properties and enhancing the photoconductivity of films and multilayered structures is highlighted. We evidence the contribution of quantum confinement effect and show that the most probable transport mechanisms in these percolative systems are tunnelling and hopping.

1873. Submillimeter-wave properties of Zn2SiO4 ceramics

Authors: Nedelcu, L; Geambasu, CD; Banciu, MG; Iwamae, A; Furuya, T; Tani, M

Published: 2015, 2015 40TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER AND TERAHERTZ WAVES (IRMMW-THZ), DOI: 10.1109/IRMMW-THz.2015.7327946

Zinc silicate ceramics have been prepared by using conventional ceramic technology. Morphological, structural, and dielectric characterizations of the samples were performed using scanning electron microscopy, X-ray diffraction, and terahertz time-domain spectroscopy. The achieved absorption properties of zinc silicates make them very attractive solutions for submillimeter-wave applications.

1874. 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.

1875. 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.

1876. 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.

1877. 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 %.

1878. 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.

1879. 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.

1880. 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.