National Institute Of Materials Physics - Romania

Publications

5714 articles found

1921. Electro-Optic Sampling of Terahertz Pulses Using BaTiO3 in Non-Collinear Cherenkov Phase-Matching Scheme

Authors: Ozawa, S; Hori, T; Azuma, S; Funkner, S; Niehues, G; Yamamoto, K; Furuya, T; Kitahara, H; Banciu, G; Nedelcu, L; Estacio, E; Bakunov, MI; Tani, M

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

In this paper we report electro-optic (EO) sampling of THz pulses using ferroelectric crystal in the non-collinear Cherenkov phase-matching scheme, where an effective velocity matching is achieved in an EO crystal with a large refractive index in the THz frequency region. We demonstrate efficient THz EO sampling using LiNbO3 and BaTiO3 crystals in the Cherenkov-phase-matching scheme. It is shown that the efficiency of EO sampling with BaTiO3 is smaller than that with LiNbO3, even though the EO coefficient (r(33)) of BaTiO3 is three times higher than that of LiNbO3. The reason of the poor performance of BaTiO3 is attributed to the strong absorption in the THz frequency region.

1922. STUDY OF THE LEAKAGE CURRENT IN EPITAXIAL FERROELECTRIC Pb(Zr0.52Ti0.48)O-3 LAYER WITH SrRuO3 BOTTOM ELECTRODE AND DIFFERENT METALS AS TOP CONTACTS

Authors: Boni, AG; Chirila, C; Hrib, L; Pintilie, I; Pintilie, L

Published: OCT-DEC 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 1265, DOI:

The leakage current was studies in epitaxial ferroelectric Pb(Zr0.52Ti0.48)O-3 layer with common SrRuO3 bottom electrode and different metals as top contacts (SrRuO3, Pt, Ir, Ru). It was found that the dominant conduction mechanism in the 200-350 K temperature range and for voltages significantly larger than the coercive value is the thermionic emission governed by the Schottky-Simmons equation. The height of the potential barriers was estimated and was found that this is about the same for negative and positive voltage polarities. No correlation was found between the height of the potential barriers for different top contacts and the work function difference between the bottom and top electrodes. The results suggest that the potential barrier is controlled by the polarization charges in a similar way to the one reported for Pb(Zr0.2Ti0.8)O-3 and BaTiO3 epitaxial films with bottom SrRuO3 electrode and different metals as top contacts. It was also found that above 350 K the conduction mechanism changes to ohmic and/or space charge limited currents.

1923. Optical properties of bioactive europium doped hydroxyapatite (HAp:Eu3+)

Authors: Andronescu, E; Iordache, FM; Ciobanu, CS; Badea, ML; Costescu, A; Prodan, AM

Published: SEP-OCT 2015, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 9, 1159, DOI:

The aim of this study was to investigate the influence of Ca10-x Eu-x(PO4)(6)(OH)(2), ( x(Eu)=0; 0.05) before and after immersion in simulated body fluid (SBF) for 72 hours. The samples have been investigated by X-Ray Diffraction, FT-IR Spectroscopy, Raman Spectroscopy and Steady-State Photoluminescence. Moreover, it was studied the antibacterial activity of the powders against Staphylococcus aureus and Escherichia coli bacterial strains. Our studies revealed that after soaking in SBF solution, the average crystallite size of the samples increased. Moreover, it was noticed that the luminescence of the samples is strongly influenced by the immersion in SBF solution.

1924. ELECTRICAL CONDUCTIVITY STUDIES OF SCANDIA DOPED CERIA CERAMIC COMPOSITES

Authors: Ionascu, AM; Raikova, G; Mladenova, E; Mercioniu, I

Published: OCT-DEC 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 1280, DOI:

In this paper electrical conductivity analysis of a new material, designed to be used as a solid electrolyte for intermediate temperature fuel cells (IT-SOFC) was performed. The material is based on a composite of scandia doped ceria (SDC) and yttria doped alumina (YA) which ensures higher mechanical stability. The initial powders were obtained by sol-gel method. The samples were prepared by cold pressing and sintering at 1500 degrees C. Materials with variation of the composition (SDC/YA = 95/5; 90/10, 85/15 mass %) were studied. The conductivity was determined by Electrochemical Impedance Spectroscopy. According of the electrochemical analysis the composites with 5 and 10 mass % YA exhibit better conductivity. The results are in correlation with morphological investigation, realized by SEM.

1925. Electro-optical properties of As-Se-S-dielectric structure for optical information recording in real time

Authors: Chirita, A; Prlepov, V; Popescu, M; Corsac, O; Chetrus, P; Nasedchina, N

Published: JUL-AUG 2015, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 9, 923, DOI:

The results of electro-optical properties studies of chalcogenide glassy semiconductors thin film structures based on Xat.%As2S3:(100-X)at.%As2Se3 system for holographic information recording on to photo-thermoplastic carriers in stationary and pulsed modes.

1926. MORPHOLOGICAL AND OPTICAL INVESTIGATION OF CuO FIBERS PREPARED VIA ELECTROSPINNING

Authors: Busuioc, C; Surdu, VA; Andronescu, E

Published: 2015, UNIVERSITY POLITEHNICA OF BUCHAREST SCIENTIFIC BULLETIN SERIES B-CHEMISTRY AND MATERIALS SCIENCE, 77, DOI:

The objective of the paper was the synthesis and characterization of CuO nanofibers. These were obtained by electrospinning a solution of copper (II) acetate monohydrate and polyvinylpyrrolidone in N,N-dimethylformamide, followed by calcination at 400, 450, 500 or 600 degrees C for 2 or 8 h. The compositional, structural, morphological and optical properties of the resulting fibers were investigated by Xray diffraction, scanning electron microscopy and reflectance spectroscopy. The thermally treated samples exhibit CuO unique phase with polycrystalline monoclinic structure. SEM analysis revealed a five times decrease of fiber diameter after calcination, as well as a fiber porosity reduction with calcination temperature increasing. The optical studies led to band gap values of 1.36 +/- 0.01 eV.

1927. CHARACTERISATION OF TUNGSTEN NITRIDE LAYERS AND THEIR EROSION UNDER PLASMA EXPOSURE IN NANO-PSI

Authors: Alegre, D; Acsente, T; Martin-Rojo, AB; Oyarzabal, E; Tabares, FL; Dinescu, G; De Temmerman, G; Birjega, R; Logofatu, C; Kovac, J; Mozetic, M

Published: 2015, ROMANIAN REPORTS IN PHYSICS, 67, 546, DOI:

The properties of tungsten nitride thin films deposited by both reactive RF-magnetron sputtering from tungsten targets in Argon/N-2, and RF generated nitrogen ions bombardment of previously sequentially deposited tungsten layers have been investigated. Films exhibited smaller erosion than pure tungsten in Argon plasmas at NANO-PSI expanding thermal plasma device.

1928. Magnetocaloric effect in Ni-Fe-Ga Heusler alloys with Co and Al substitutions

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

Published: 2015, ESOMAT 2015 - 10TH EUROPEAN SYMPOSIUM ON MARTENSITIC TRANSFORMATIONS, 33, DOI: 10.1051/matecconf/20153305008

The functionality of the ferromagnetic shape memory alloys is related to the martensitic and magnetic order-disorder transformations, both of which may be tailored by doping with other elements or by suitable thermal treatments, so that alloys with concomitant (or sequential but close) structural and magnetic phase transitions may be obtained. Concerning the magnetocaloric applications, it is assumed that the thin melt-spun ribbons assure a more efficient heat transfer. In the present work we investigate the influence of Co and Al substitutions on magnetocaloric effect characteristics of NiFeGa in bulk and also in ribbons prepared by melt spinning method and subjected to different thermal treatments. X-ray diffraction, differential scanning calorimetry, magnetocaloric and magnetoresistive characterizations have been performed. The results highlight the differences between the bulk and the ribbons (both as prepared and annealed) and the role of substitutions.

1929. Band alignment and charge transfer in rutile-TiO2/CH3NH3PbI3-xClx interfaces

Authors: Nemnes, GA; Goehry, C; Mitran, TL; Nicolaev, A; Ion, L; Antohe, S; Plugaru, N; Manolescu, A

Published: 2015, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17, 30423, DOI: 10.1039/c5cp05466d

Rutile-TiO2/hybrid halide perovskite CH3NH3PbI3-xClx interfaces are investigated by ab initio density functional theory calculations. The role of chlorine in achieving enhanced solar cell power conversion efficiencies is in the focus of recent studies, which point to increased carrier mobilities, reduced recombination rates, a driven morphology evolution of the perovskite layer and improved carrier transport across the interface. As it was recently established that chlorine is preferentially localized in the vicinity of the interface and not in the bulk of the perovskite layer, we analyze the changes introduced in the electronic properties by varying the chlorine concentration near the interface. In particular, we discuss the effects introduced in the electronic band structure and show the role of chlorine in the enhanced electron injection into the rutile-TiO2 layer. Taking into account these implications, we discuss the conditions for optimizing the solar cell efficiency in terms of interfacial chlorine concentration.

1930. Cu codoping control over magnetic precipitate formation in ZnCoO nanowires

Authors: Granville, S; Matei, E; Enculescu, I; Toimil-Molares, ME

Published: DEC 22 2014, APPLIED PHYSICS LETTERS, 105, DOI: 10.1063/1.4904987

Using electrodeposition, we have grown nanowires of ZnCoO with Cu codoping concentrations varying from 4-10 at. %, controlled only by the deposition potential. We demonstrate control over magnetic Co oxide nano-precipitate formation in the nanowires via the Cu concentration. The different magnetic behavior of the Co oxide nano-precipitates indicates the potential of ZnCoO for magnetic sensor applications. (C) 2014 AIP Publishing LLC.