National Institute Of Materials Physics - Romania

Publications

5975 articles found

3421. Point and extended defects in irradiated silicon and consequences for detectors

Authors: Lazanu, S; Ciurea, ML; Lazanu, I

Published: 2009, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 6, NO 8, 6, +, DOI: 10.1002/pssc.200881434

The interactions by which ions lose their energy in silicon are investigated at the microscopic level. this theoretical study put in evidence that the ionization could also represent a source of structural defects, and, contrary to the processes initiated by elementary particles, could generate extended primary defects, as, e.g. four-fold coordinated defects, due to the simultaneous breaking of bond for more neighbouring atoms in the lattice in a single interaction, in the ionisation core. The average energy transferred per atom is calculated, and also the energy spent by ionisation. The time dependence of the temperature in the ionisation core is derived in some simplifying assumptions. These contributions not considered yet in the studies of degradation of silicon detectors in radiation fields and could account for the discrepancies observed between models and measurements at microscopic versus device level for hadrons and ions. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

3422. EPR AND X-RAY DIFFRACTION INVESTIGATION OF SOME GREEK MARBLES AND LIMESTONES

Authors: Duliu, OG; Grecu, MN; Cristea, C

Published: 2009, ROMANIAN REPORTS IN PHYSICS, 61, 499, DOI:

12 different marble and limestone samples collected from well-known Greek quarries have been investigated by X-ray diffraction and electron paramagnetic resonance (EPR). Xray diffraction spectra permitted to determine both major (calcite and dolomite) and minor (quartz or magnesite) mineralogical components. EPR has been used to investigate the same samples unirradiated and after 10 kGy gamma-ray irradiation. The unirradiated samples display typical EPR spectra of Mn2+ in calcite and dolomite as well as a superposition of these while some samples displayed EPR free radicals signals of centers (low field signal) and centers (high field signal). From X-ray diffraction and EPR spectra it was possible to extract numerical values of several numerical parameters such as dolomite to calcite ratio, EPR intensity parameter, and low field to high field EPR signals intensity ratio. These values as well as the correlation coefficients between the digital functions that described the low field Mn2+ ions EPR line have been used as entry data for cluster analysis to quantify the resemblance and differences between analyzed samples.

3423. Fabrication and Transport Properties of Manganite-Polyacrylamide-Based Composites

Authors: Sandu, V; Popa, S; Ivan, I; Plapcianu, C; Sandu, E; Mihailescu, C; Doroftei, F

Published: 2009, JOURNAL OF NANOMATERIALS, 2009, DOI: 10.1155/2009/429430

We present the fabrication and transport properties of a series of composites made of La2/3Sr1/3MnO3 and acrylamide-based copolymers. The most important result is the very narrow transition, of only 27 K, displayed by the peak that appears around the metal-insulator transition of the composites made with poly(acrylamide-vinylacetate). Although the amount of polymer is rather low, different copolymers change drastically the electric transport characteristics. Copyright (C) 2009

3424. Characterization of magnetic nano-fluids via Mossbauer spectroscopy

Authors: Filoti, G; Kuncser, V; Schinteie, G; Palade, P; Morjan, I; Alexandrescu, R; Bica, D; Vekas, L

Published: 2009, ISIAME 2008, +, DOI: 10.1007/978-3-642-01369-0_50

The laser pyrolysis became a useful tool, providing various ways, in production of nano materials. The iron Mossbauer spectroscopy is one very accurate method in evidencing the physical properties and related processes in the nano scale compounds. The effect of pressure, laser spot area and induced combustion, of gas mixture and laser power on the phase composition and inside particle distribution, grain size as well as the related phenomena were investigated by temperature dependent Mossbauer spectroscopy. A selection of most relevant properties is presented and discussed in details.

3425. High-Temperature Operation of a Diode-Pumped Nd:YAG Laser Passively Q-switched by Cr(4+):YAG Saturable Absorber

Authors: Dascalu, T; Pavel, N; Vasile, N

Published: 2009, 2009 CONFERENCE ON LASERS AND ELECTRO-OPTICS AND QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (CLEO/QELS 2009), VOLS 1-5, 2606, DOI:

The output performances of a Nd:YAG laser passively Q-switched by Cr(4+):YAG saturable absorber are investigated function of temperature. Small variations in pulse energy and duration were observed over the 25 degrees C to 150 degrees C range. (C) 2009 Optical Society of America

3426. MOSSBAUER BACKSCATTERING MEASUREMENTS ON EU-151

Authors: Bibicu, I; Cretu, C

Published: 2009, ROMANIAN JOURNAL OF PHYSICS, 54, 519, DOI:

The possibility to make surface measurements in the nano or micro range by Mossbauer spectroscopy using (151)Eu Mossbauer isotope is demonstrated. Measurements were made with a new flow detector in a backscattering geometry. With this detector it is possible to detect conversion electrons or low energy X-rays. An Eu(2)O(3) sample has been used. These measurements have been performed for the first time in Romania.

3427. ASPECTS OF TEMPERATURE DEPENDENCE ON Au-Ti/GaAs(SI) SCHOTTKY BARRIER

Authors: Negrila, CC; Ungureanu, F; Ghita, RV

Published: 2009, CAS: 2009 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, 458, DOI:

Fabrication of Au-Ti Schottky structure on GaAs semi-insulating wafer was related to an ultra-high vacuum deposition condition and low vacuum annealing in low vacuum and temperature range T=320-360 degrees C. There are presented representative I-V characteristics in dark and in different light (power levels). The spectral response has a maximum in Delta lambda = (850-950) nm corresponding to a band-to-band transition. The complex dependence of optical generated non-equilibrium carriers is related to the equivalent state density at the conduction band edge (in T(3/2) factor) and in exponential distribution factor exp (-(E-F)/kT).

3428. Preparation and Characterization of Polar Aniline Functionalized Copolymers Thin Films for Optical Non-Linear Applications

Authors: Stanculescu, A; Rasoga, O; Preda, N; Socol, M; Stanculescu, F; Ionita, I; Albu, AM; Socol, G

Published: 2009, FERROELECTRICS, 389, 173, DOI: 10.1080/00150190902993291

This paper presents a study of two monomeric structures containing functional groups with different electronegativities [NH/NH-NH and NO2] and two different polymeric structures prepared by the copolymerisation of maleic anhydride and methylmethacrylate/maleic anhydride and vinyl benzyl chloride, and subsequent functionalization with 2,4 dinitroaniline. Thin films have been prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE) and UV-VIS, FTIR, Raman and Photoluminescence Spectroscopy have been used to comparatively investigate the properties of the synthesised compounds. We have evidenced the second harmonic emission (SHG), process sustained by the asymmetry of the chemical structure, which is correlated with the crystallization in non-centrosymmeric structures.

3429. CATALYTIC AND ELECTRICAL PROPERTIES OF IRON OXIDE IN DEEP PROPANE OXIDATION

Authors: Munteanu, C; Ionescu, NI; Feder, M; Diamandescu, L; Caldararu, M

Published: NOV-DEC 2009, REVUE ROUMAINE DE CHIMIE, 54, +, DOI:

The catalytic activity of hematite (alpha-Fe(2)o(3)) was studied in deep propane oxidation. Propane conversion to CO(2) was more than 90% at 400 degrees C in excess of oxygen. The AC electrical conductivity measurements performed in situ showed that at low temperature the surface conductivity is influenced by the presence of moisture in the feed which is adsorbed on the surface. Based on the conductivity data obtained in absence of oxygen coupled with information provided by Mossbauer spectroscopy, the results are discussed in terms of the redox-type mechanism.

3430. Cobalt doped ZnO prepared by electrochemistry: chemistry, morphology, and magnetism

Authors: Enculescu, I; Matei, E; Vasilache, V; Teodorescu, CM

Published: 2009, NANOTECH CONFERENCE & EXPO 2009, VOL 3, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: BIOFUELS, RENEWABLE ENERGY, COATINGS FLUIDICS AND COMPACT MODELING, +, DOI:

ZnO:Co thin Films are prepared by electrochemical deposition at different overpotentials and investigated by scanning electron microscopy, X-ray photoelectron spectroscopy and Kerr magnetometry (MOKE). Increse of structural disorder and crystallite re-orientation are observed for cobalt doped samples (especially for those obtained at - 750 and at - 800 mV overpotentials). MOKE magnetometry revealed room temperature ferromagnetic behaviour only for ZnO:Co deposited at - 850 mV. These are the samples with the less cobalt content and lowest structural perturbation of the ZnO matrix by cobalt.