National Institute Of Materials Physics - Romania

Publications

5781 articles found

2541. Effect of the morphology on the optical and electrical properties of polycarbonate film doped with aniline derivatives monomers

Authors: Stanculescu, F; Stanculescu, A; Girtan, M; Socol, M; Rasoga, O

Published: JAN 2012, SYNTHETIC METALS, 161, 2597, DOI: 10.1016/j.synthmet.2011.09.012

In this paper we present some comparative studies between the optical and electrical properties of the films prepared by vacuum evaporation from amidic monomeric compounds obtained from maleic anhydride and aniline derivative with different functional groups [CN; NO2], and the composite films prepared by spin-coating from a polycarbonate of bisphenol A matrix embedding clusters of these amidic monomers. We have emphasised the effect of the polymeric matrix on the properties of the synthesised monomers with the purpose to change the physical properties of the films (optical transmission, luminescence, electrical conduction, optical non-linear phenomena). The correlation between the morphology of the films and the optical and electrical properties has also been investigated. (C) 2011 Elsevier B.V. All rights reserved.

2542. Optical and electrical properties of arylenevinylene compounds thin films prepared by vacuum evaporation

Authors: Rasoga, O; Vacareanu, L; Grigoras, M; Enculescu, M; Socol, M; Stanculescu, F; Ionita, I; Stanculescu, A

Published: JAN 2012, SYNTHETIC METALS, 161, 2617, DOI: 10.1016/j.synthmet.2011.10.001

This paper discusses the properties of two arylenevinylene oligomers thin films deposited by vacuum evaporation on different substrates. The morphology of the thin films was investigated by scanning electron microscopy and atomic force microscopy, and the optical properties by UV-Vis and fluorescence spectroscopy. The optical nonlinear phenomenon of two-photon absorption induced fluorescence has been evidenced in the thin films of these compounds. We have also investigated the electrical properties of semiconductor/insulator/semiconductor (ITO/oligomer/Si) heterostructures in correlation with the contact energetic barriers, morphological and structural properties of the layers. (C) 2011 Elsevier B.V. All rights reserved.

2543. Pentylcyanobiphenyl as Test Molecule for the Acid Sites of Powdered Titanium(IV) Oxides: Sensitivity of Core Levels to the Local Structure

Authors: Ungureanu, F; Manea, AS; Frunza, L; Frunza, S; Ganea, CP; Cotorobai, F; Diamandescu, L; Schonhals, A

Published: 2012, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 562, 217, DOI: 10.1080/15421406.2012.697416

Pentylcyanobiphenyl was used successfully as a testmolecule to show the acid sites upon some commercial nanoscaled titanium dioxide materials. The surface interactions were investigated in detail using methods sensitive to the surface or to the bulk material, e. g., X-ray photoelectron spectroscopy (XPS), infrared spectroscopy, and thermal analysis. Different oxidation states of surface Ti ions were revealed. Several species were found: the majority were bonded through the nitrogen lone pair of the cyano group, but bonding to the surface OH groups by benzene pi electrons might also appear. The N 1s lines of adsorbed 5CB were able to distinguish between Lewis acid and relatively weak Bronsted acid sites.

2544. The influence of the chemical treatment on the ferromagnetic behavior of carbon nanotubes synthesized using ferromagnetic catalyst

Authors: Stancu, M; Ruxanda, G; Stanica, N; Dinescu, A; Nistor, L; Ciuparu, D

Published: JUL-AUG 2012, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 6, 726, DOI:

In this contribution we report results of our investigations on the ferromagnetic behavior of pristine and chemically treatedcarbon nanotubes, synthesized by AC arc discharge method using iron powder as catalyst. The magnetic properties of the carbon nanotubes samples before and after chemical treatment were measured at room temperature in a vibrating - sample magnetometer. We observed significant changes of the ferromagnetic behavior of carbon nanotubes after the purification and concluded that the magnetic properties of carbon nanotubes synthesized using ferromagnetic catalyst are governed by the ferromagnetic catalyst nanoparticles attached to their walls during synthesis.

2545. OBTAINING AND CHARACTERIZATION OF HA/Y2O3:alpha Al2O3 SYSTEM FOR BIOAPPLICATIONS

Authors: Mercioniu, I; Stan, GE; Bercia, R; Ciuca, S; Popescu-Pogrion, N

Published: JUL-SEP 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 932, DOI:

A new HA/Y2O3:alpha Al2O3 system was obtained by the deposition of a hydroxyapatite thin layer (similar to 150 nm), by magnetron sputtering, onto sintered substrates of low yttria (150 ppm) doped alumina. The yttria doped alumina was synthesized from very pure nanopowders, by mechanical homogenization, followed of pressing, sintering and different annealing regimes, in order to obtain bodies with various degree of nano-micro-structuration. TEM/HRTEM, SEM and EDS morpho-compositional analysis techniques were used to characterize the yttria doped alumina substrate and the hydroxyapatite superficial layer. The interfacial bonding strength between the sintered substrate and the hydroxyapatite thin film was analyzed by SEM. The evolution of the grains growth of the Y2O3:alpha Al2O3 substrate samples, with and without the hydroxyapatite covering layer is observed and discussed. A strong structural interdependence between the covering layer and the sintered substrate was emphasized. The grains' growth behaviour of the studied samples showed a linear evolution. A mathematical model for the grain growth process description was built, the grain size being interpreted as a random variable having a log-normal or Weibull probability density function.

2546. On the scaling of pinning force in ceramic MgB2

Authors: Sandu, V; Ivan, I

Published: 2012, 26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5, 400, DOI: 10.1088/1742-6596/400/2/022102

We present an investigation of the field dependence of the pinning force of dense MgB2-based superconducting composites as obtained by spark plasma sintering with different ingredients which are designated to enhance the pinning force F. Generally, the latter quantity, scaled to the maximum pinning force F-max, obeys a scaling law as a function of the scaled field h when the irreversibility field B-irr is considered as scaling field. The scaled function is described in terms of a generalized scaled function h(p)(1-h)(q). However, in our samples the scaling is absent. In addition, the peak of the scaled function shifts to higher reduced fields h when the temperature increases. Depending on the level of doping and the nature of the nanosized particles used to built the superconducting composites, we found that the scaled force can be depicted either with a combination of generalized scaled functions with different exponents or with a single function but multiplied with an envelope, usually an exponential factor. The former dependence is present in the samples with a high amount of nanoparticles and mirrors two types of pinning of close weights. The presence of the exponential factor in the latter dependence is attributed to the combined effect of the intrinsic anisotropy of MgB2 and the random orientation of the grains relative to the magnetic field.

2547. THEORETICAL STUDY OF THE REACTION OF LiBH4 WITH MgH2 IN PRESENCE OF CARBON SUBSTRATE

Authors: Chihaia, V; Munteanu, C; Scurtu, R; Palade, P

Published: APR-MAY 2012, REVUE ROUMAINE DE CHIMIE, 57, 442, DOI:

In this work we design some atomic scale simulation methods as investigative tools in the study of the formation of compounds for the reversible storage of hydrogen in bulk materials. It was verified that the reaction between the LiBH4 and MgH2 is energetically favored for temperatures above 280 K and that this system can be used in the hydrogen storage and the fuel cell application. To identify the reaction mechanism at the interface of LiBH4, MgH2 and carbon layers we performed some Molecular Dynamics simulations and QM/MM calculations. The results show that the layers of ions formed at the interface with the graphite may assure the right arrangement of the atoms to start the formation of the crystals. Moreover, the presence of the hexagonal layers of graphite may play a role as a pattern template for the layers of boron atoms in the MgB2 lattice.

2548. Modeling single quantum dots in microcavities

Authors: Gies, C; Florian, M; Jahnke, F; Gartner, P

Published: 2012, QUANTUM OPTICS WITH SEMICONDUCTOR NANOSTRUCTURES, 114, DOI:

This chapter presents a theoretical framework for the description of the light-matter interaction of a single semiconductor quantum dot in a microcavity. A particular focus is the semiconductor properties of the device, the contributions of various electronic configurations, and the embedded nature of the quantum dot due to its coupling to delocalized states. Stimulated emission from the excitonic ground state and from higher excited states is discussed together with the photon statistics and cavity emission spectra. The role of dephasing for transitions between different configurations is explained. We exploit a direct solution of the von Neumann equation for the statistical operator including the full light-matter interaction in terms of the Jaynes-Cummings interaction Hamiltonian, as well as the Coulomb interaction of the quantum-dot carriers. Various dissipative processes are systematically considered using Lindblad terms.

2549. TILT c AXIS CRYSTALLITE GROWTH OF ALUMINIUM NITRIDE FILMS BY REACTIVE RF-MAGNETRON SPUTTERING

Authors: Stan, GE; Pasuk, I; Trinca, LM; Galca, AC; Enculescu, M; Miculescu, F

Published: JAN-MAR 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 50, DOI:

The article reports on the tilted growth of textured aluminium nitride thin films obtained by radio-frequency magnetron sputtering onto 50 mm diameter Si (111) wafers, in reactive atmosphere, in a planar sputtering system without tilting the substrate and with no additional sputtering geometry alterations. The films were investigated using, X-ray diffraction, spectroscopic ellipsometry and scanning electronic microscopy, done by local measurements on the wafer surface, at different distances from the centre. A progressive increase of the tilt angle when moving away from the sample centre has been found. The maximum tilt angle of the columnar AlN crystallites, obtained near the edges of the wafer, is about 7 degrees. The results showed also that tilting is associated with smaller thickness and larger dispersion of the c axis orientation. Synthesizing inclined c axis AlN films should allow the fabrication of surface acoustic wave devices based on shear waves for liquid sensor applications.

2550. A HIGH PERFORMANCE PIEZOCERAMIC MATERIAL FOR A VIBRATION TRANSDUCER FOR BALANCING OF ROTATING PARTS

Authors: Miclea, CT; Cioangher, M; Miclea, CF; Trupina, L; Miclea, C; Amarande, L; Spanulescu, S; Faibis, R

Published: 2012, 2012 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 2, 294, DOI:

A high performance piezoceramic material of PZT type, doped with 6 atomic % W, was prepared in order to be used as sensing element for a vibration transducer used to equilibrate the motor-fan group of auto vehicles. The piezoelectric parameters of material showed high values which recommended it for the vibration transducer. The transducer consists of a ring shaped active element sandwiched between two steel blocks. The transducer works in quasistatic regime, at frequencies much lower than the resonance frequency, being tightly screwed in the measurement system by a metallic cover attached at the back end.