National Institute Of Materials Physics - Romania

Publications

5714 articles found

2641. Shaping distinct magnetic interactions in molecular compounds

Authors: Filoti, G; Bartolome, J; Palade, P; Prisecaru, I; Valsangiacom, C; Kuncser, V; Mindru, I; Patron, L

Published: APR 2011, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 323, 1053, DOI: 10.1016/j.jmmm.2010.12.002

Oxalates containing various 3d transitional elements and positive NH(4) or negative OH groups were newly synthesized. Each above-mentioned component has directly influenced the structure, the electronic or interaction properties, while some unexpected behaviors were revealed by various magnetic and Mossbauer measurements. The main magnetic parameters, the long-range anti-ferromagnetic couplings observed at very low temperature and, particularly the uncompensated moment are discussed in detail. The induced lower spin states for bivalent ions and especially the anti-parallel arrangement of the spins belonging to trivalent and bivalent iron inside the molecule are also emphasized. (C) 2010 Elsevier B.V. All rights reserved.

2642. Optical spectroscopy of heavily Ho3+-doped BaY2F8 crystals

Authors: Tsuboi, T; Jang, KH; Polosan, S; Shimamura, K; Bettinelli, M; Seo, HJ

Published: APR 2011, JOURNAL OF LUMINESCENCE, 131, 700, DOI: 10.1016/j.jlumin.2010.11.020

The ultraviolet, visible, and near IR (0.8-2.4 mu m) luminescence spectra of BaY2F8 single crystals heavily doped with Ho3+ ions (10 and 30 mol%) have been investigated at room temperature and 12 K, together with the luminescence decay curves (up to 300 mu s) of the visible emission. Excitation in the visible region gives rise to very strong emission bands originating from the first I-5(7) level and located around 2070 nm. However the I-5(7) emission is not observed upon excitation at wavelengths shorter than 300 nm. The inter-ionic processes are found to shorten the decay times of the levels emitting in the visible region with respect to the corresponding radiative lifetimes. (C) 2010 Elsevier B.V. All rights reserved.

2643. Calculation of the quantum efficiency for the absorption on confinement levels in quantum dots

Authors: Iancu, V; Mitroi, MR; Lepadatu, AM; Stavarache, I; Ciurea, ML

Published: APR 2011, JOURNAL OF NANOPARTICLE RESEARCH, 13, 1612, DOI: 10.1007/s11051-010-9913-6

The quantum efficiency of the absorption on quantum confinement levels is investigated. This is achieved by modeling the electron confinement in a spherical quantum dot (QD). The confinement levels are calculated using both infinite and finite rectangular quantum wells. The spectral internal quantum efficiency is evaluated within both the models, by computing Einstein's coefficients for the transitions between confinement levels. The size of QDs (1-3 nm radius) leads to negligible many body effects. The nature of the QD material and of the matrix embedding is taken into account in the finite rectangular quantum well approximation and introduces only a small correction. The temperature dependence of the efficiency is also taken into account. A numerical application is performed for a silicon QD of 2.5 nm radius, embedded in amorphous silica. It is proved that the absorption threshold shifts toward the far infrared limit and that the spectral internal quantum efficiency reaches 4-5% at the threshold.

2644. Vortex creep crossover in YBCO/PrBCO superlattices during standard magnetization relaxation measurements

Authors: El Tahan, A; Jakob, G; Miu, D; Ivan, I; Badica, P; Miu, L

Published: APR 2011, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 24, DOI: 10.1088/0953-2048/24/4/045014

We investigated the relaxation of the irreversible magnetization in a series of 200 nm thick YBa2Cu3O7/PrBa2Cu3O7 [(YBCO)(n)/(PrBCO)(m)] superlattices, where the thickness m of the nonsuperconducting PrBCO layer (measured in unit cells) was kept to m = 4 (sufficient to decouple the superconducting YBCO layers), whereas the thickness n of the YBCO layer was varied between 2 and 20 unit cells. The analysis of standard zero-field-cooling dc magnetization relaxation data obtained in the low temperature T region with the applied magnetic field H oriented along the c axis reveals the occurrence of a crossover elastic (collective) vortex creep at low T-plastic vortex creep at high T, generated by the T dependent macroscopic currents induced in the sample during measurements. For thin superlattices (n < 20) the creep crossover temperature T-cr proportional to n, and T-cr decreases linearly with increasing ln(H) for a fixed n. This crossover represents an alternative to the elastic vortex glass behavior reported for superlattices, as well as to 'quantum vortex creep' at unexpectedly high T inferred for thin films. We also discuss the absence of an increase of the magnetically determined critical current density with decreasing YBCO thickness in our superlattices, which apparently contradicts the collective pinning theories.

2645. Temperature-dependent refractive index of potassium acid phthalate (KAP) in the visible and near-infrared

Authors: Moutzouris, K; Stavrakas, I; Triantis, D; Enculescu, M

Published: APR 2011, OPTICAL MATERIALS, 33, 816, DOI: 10.1016/j.optmat.2010.12.021

We report an investigation of the temperature-dependence of the refractive index of potassium acid phthalate (KAP) crystal. Refractive index measurements are based on a refractometer setup operating in a temperature range from 25 degrees C to 200 degrees C and using five different laser wavelengths in the visible and near-infrared. Temperature-dependent dispersion relations are proposed, with an average fitting quality that exceeds experimental accuracy, and compared to previous room-temperature Sellmeier equations. Consequently, the new relations are employed for the calculation of various linear and nonlinear optical properties of KAP. (C) 2011 Elsevier B.V. All rights reserved.

2646. Martensitic transformation of Ti50Ni30Cu20 alloy prepared by powder metallurgy

Authors: Valeanu, M; Lucaci, M; Crisan, AD; Sofronie, M; Leonat, L; Kuncser, V

Published: MAR 31 2011, JOURNAL OF ALLOYS AND COMPOUNDS, 509, 4498, DOI: 10.1016/j.jallcom.2011.01.154

Phase transformation behavior of Ti50Ni30Cu20 shape memory alloys prepared by powder metallurgy is analyzed with respect to the duration of mechanical alloying. The processed blends were studied by differential scanning calorimetry and room temperature X-ray diffraction. The martensitic transformations evidenced by thermal scans are discussed in correlation with the relative phase content obtained from the refinement of the X-ray diffraction patterns. (c) 2011 Elsevier B.V. All rights reserved.

2647. Substrate-target distance dependence of structural and optical properties in case of Pb(Zr,Ti)O-3 films obtained by pulsed laser deposition

Authors: Galca, AC; Stancu, V; Husanu, MA; Dragoi, C; Gheorghe, NG; Trupina, L; Enculescu, M; Vasile, E

Published: MAR 1 2011, APPLIED SURFACE SCIENCE, 257, 5943, DOI: 10.1016/j.apsusc.2011.01.056

The paper presents the influence of pulsed laser deposition (PLD) parameters on the structural and optical properties of PZT thin films grown on platinum substrate. X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) are used to determine the thin film properties. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to get additional information. By changing the distance between target and substrate, different crystalline orientations of PZT are obtained. The thin film thickness and its roughness, as well as the refractive index are also influenced by the chosen distance. (C) 2011 Elsevier B.V. All rights reserved.

2648. Influence of Al doping agents nature on the physical properties of Al:ZnO films deposited by spin-coating technique

Authors: Ghomrani, FZ; Iftimie, S; Gabouze, N; Serier, A; Socol, M; Stanculescu, A; Sanchez, F; Antohe, S; Girtan, M

Published: MAR 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 251, DOI:

In this paper we present the morphological, structural, optical and electrical properties of aluminium doped zinc oxide films prepared by spin coating technique from a zinc acetate dihydrate and 2-methoxyethanol (0.5M) solution. AlCl3 and Al(NO3)(3) were used as doping agents in different concentrations (1at%, 4at% and 6at% in starting solution). After deposition, films were dried at 100 degrees C and then annealed at temperatures between 400 degrees C and 500 degrees C. The characterization of deposited layer was performed by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and UV-Vis spectroscopy. The results show that the optical and electrical properties of the structures strongly depend on the deposition conditions of ZnO:Al. In addition, the resistivity can be easily varied depending on ZnO:Al annealing temperatures and Al concentration.

2649. Sensitizer localization and immune response in photodynamic therapy of B16 cells

Authors: Pop, SF; Ion, RM; Neagu, M; Constantin, C

Published: MAR 2011, LASER PHYSICS, 21, 581, DOI: 10.1134/S1054660X11050239

This paper proposes to extend the exploration of mouse melanoma B16 cells death by photodynamic therapy (PDT), under irradiation with different light sources and in the presence of 5,10,15,20-tetrap-sulphonato-phenyl-porphyrin (TSPP). The viability studies showed that B16 mouse melanoma is sensitive to photodynamic damage induced by TSPP 1 mM for either one, two, three or four hours. The control had TSPP added immediately prior to timelapse imaging (no incubation). They were then irradiated with red light He-Ne laser (lambda = 632.8 nm, energy 180 J/cm(2) for 20 min). Also, it has been used a laser diode GaInAs 25 mW/cm(2), lambda = 650 nm. The cells demonstrated clear morphological changes associated with apoptosis by mitochondrial pathway. There were changes in texture, as expected. Changes appeared to occur more quickly at lamp irradiation than at HeNe and GaInAs diode laser. Addition of TSPP just prior to exposure and observation, with no incubation, did not result in changes in cell morphology or cell death. Also, the proteins changes have been observed, because those with high molecular weights have been scissored under irradiation and this could be reason of the proteins concentrating in the area of low molecular weights, and the dissapearing of the proteic band of 75 kDa in the electrophoregramm. The immunized animals with B16-TSPP had the highest survival rate (40 days) by comparison with the control (death at 20 days) or with immunized animals with supernatants B16 (death at 25 days).

2650. Electronic and field emission properties of two-dimensional nanotori

Authors: Filip, MR; Filip, LD

Published: MAR 2011, JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B, 29, DOI: 10.1116/1.3531935

The electronic properties of two-dimensional toroidal surfaces of nanometer size have been investigated by approximately solving the time-independent Schrodinger equation. The effects of the quantum confinement on the electron population of these structures were shown by studying the average electron density on the surface of the torus. The unique electron spread that resulted from such computations encouraged further study on the field emission properties of this two-dimensional manifold. The Wentzel-Kramers-Brillouin approximate approach was used for a preliminary study of the field emission properties of the nanotori for various geometrical parameters. (c) 2011 American Vacuum Society. [DOI: 10.1116/1.3531935]