National Institute Of Materials Physics - Romania

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873 articles found

721. Electrical properties of electrodeposited CdS nanowires

Authors: Ghenescu, M; Ion, L; Enculescu, I; Tazlaoanu, C; Antohe, VA; Sima, M; Enculescu, M; Matei, E; Neumann, R; Ghenescu, O; Covlea, V; Antohe, S

Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2488, DOI: 10.1016/j.physe.2007.09.188

A template method was used to obtain cadmium sulfide (CdS) nanowires. Polymer ion tracks foils (30 mu m tick) were used as templates, after etching with solutions containing NaOH and methanol. CdS nanowires were electrochemically grown in the resulting pores. The nanowires were contacted by sputtering a gold layer on top of the membrane, and the electrical properties were recorded in the temperature range 40-300K. An activated electrical resistance was observed, with activation energy of 0.27eV at temperatures larger than 180 K. I-V characteristics show a symmetric, non-linear shape, in the voltage range used in this experiment. (C) 2007 Elsevier B.V. All rights reserved.

722. Luminescence and EPR study of ZnO : Mn : Cu nanowire array

Authors: Sima, M; Enculescu, I; Grecu, MN; Secu, M; Sima, M; Matei, E; Vasile, V

Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2498, DOI: 10.1016/j.physe.2007.08.075

We report on photoluminescence studies on manganese and copper-doped ZnO nanowire array prepared by template method. The ZnO:Mn:Cu semiconductor grown using the electrochemical technique was characterized by electron paramagnetic resonance (EPR) and optical reflection measurements. Morphology and the structure were observed by SEM and X-ray diffraction. The photoluminescence of this system was correlated with manganese and copper concentration in the ZnO matrix. (C) 2007 Elsevier B.V. All rights reserved.

723. Density functional theory analysis of a mixed-ligand iridium compound for multi-color organic light-emitting diodes

Authors: Polosan, S; Chow, TJ; Tsuboi, T

Published: APR 2008, JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, 21, 320, DOI: 10.1002/poc.1329

Electronic states and their energies are calculated for a mixed-ligand Ir(III) compound, (5-chloro-8-hydroxyquinoline) bis(2-phenylpyridyl) iridium (called IrQ(ppy)(2)-5CI) using time-dependent density functional theory (TDDFT) calculations and are compared with the experimental result. A good agreement is obtained between the calculated and measured absorption spectra: The d-pi(Q)* molecular orbital transition gives the lowest-energy triplet state absorption band. Its energy is estimated as 1.84 eV (671 nm), which is close to the absorption band position of 1.86 eV (666 nm) observed for IrQ(ppy)(2)-5CI doped in 4,4'-NN'-dicarbazole-biphenyl (CBP) host and of 1.88 eV (660 nm) observed for IrQ(ppy)(2)-5CI doped in polystyrene (PS). The second triplet state absorption band is caused by d-pi(ppy) transition. Its position is calculated as 2.51 eV (494 nm). The dipole moment is estimated as 3.45 D, which is lower than the dipole moment of fac-Ir(ppy)(3). This is understood by a reduced charge transfer between Ir(III) and quinoline ligand. Copyright (C) 2008 John Wiley & Sons, Ltd.

724. Thermal behaviour study of some sol-gel TiO2 based materials

Authors: Crisan, M; Braileanu, A; Crisan, D; Raileanu, M; Dragan, N; Mardare, D; Teodorescu, V; Ianculescu, A; Birjega, R; Dumitru, M

Published: APR 2008, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 92, 13, DOI: 10.1007/s10973-007-8720-5

Among the great number of sol-gel materials prepared, TiO2 holds one of the most important places due to its photocatalytic properties, both in the case of powders and coatings. Impurity doping is one of the typical approaches to extend the spectral response of a wide band gap semiconductor to visible light. This work has studied some un-doped and Pd-doped sol-gel TiO2 nanopowders, presenting various surface morphologies and structures. The obtained powders have been embedded in vitreous TiO2 matrices and the corresponding coatings have been prepared by dipping procedure, on glass substrates. The relationship between the synthesis conditions and the properties of titania narrosized materials, such as thermal stability, phase composition, crystallinity, morphology and size of particles, and the influence of dopant was investigated. The influence of Pd on TiO2 crystallization both for supported and unsupported materials was studied (lattice parameters, crystallite sizes, internal strains). The hydrophilic properties of the films were also connected with their structure, composition and surface morphology. The methods used for the characterization of the materials have been: simultaneous thermogravimetry and differential thermal analysis, powder X-ray diffraction, electron microscopy (TEM, SAED) and AFM.

725. Optical spectroscopy of Yb2+ ions in YbF3-doped CaF2 crystals

Authors: Nicoara, I; Lighezan, L; Enculescu, M; Enculescu, I

Published: APR 2008, JOURNAL OF CRYSTAL GROWTH, 310, 2032, DOI: 10.1016/j.jcrysgro.2007.11.183

Transparent colorless Ca1-xYbxF2+x (X = 0-0007-0.016) crystals were grown using the vertical Bridgman technique. In order to obtain efficient Yb3+-Yb2+ conversion in the as-grown crystals, a special procedure has been developed. Room temperature optical absorption spectra reveal the characteristic UV absorption bands of the Yb2+ ions in the as-grown crystals, with intensities more than 10 times higher than those reported by other authors using various conversion procedures. The influence of YbF3 content and of codoping with Pb2+ ions on the absorption and emission spectra has been studied. Room temperature emission bands in the near UV (not reported before) and in the visible spectral domain have been observed. The emission intensity depends on the dopant concentration. A comparison of our results with those obtained by other authors is also given. (c) 2007 Elsevier B.V. All rights reserved.

726. Effect of additives on nickel nanowires electrochemical deposition

Authors: Matei, E; Enculescu, I; Enculescu, M; Neumann, R

Published: MAR 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 511, DOI:

The paper presents the effect of additives on nickel nanowires preparation by employing a template approach. The nanostructures were obtained by electrochemical deposition in ion track nanoporous membranes. The main goal was to find a wetting agent which increases the pores filling efficiency. Due to the fact that the polycarbonate nanoporous membranes used as templates are strongly hydrophobic problems appear when filling the nanopores with the aqueous electrochemical baths. We found that polyvinylpyrrolidone (PVP) added in the bath improves membrane wetting, thus increasing the deposition efficiency up to 80%. Electrochemical polarization and chronoamperometry were employed for identifying and studying the processes which take place in the case of cathodic deposition of nickel nanowires. Scanning electron microscopy was employed for nanostructure morphology characterization.

727. Study of iron oxide nanoparticles coated with dextrin obtained by coprecipitation

Authors: Vatasescu-Balcan, RA; Predoi, D; Ungureanu, F; Costache, M

Published: MAR 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 696, DOI:

In this paper we present the preparation and biological tests of iron oxide nanoparticles coated with dextrin. Iron oxide was also prepared by co-precipitation. The samples were characterized by transmission electron microscopy (TEM) and 14 scanning electron microscopy (SEM). Biocompatibility test of the iron oxide nanoparticles coated with dextrin substrate has been done using primary osteoblast cell line. After osteoblast culture achievement, the cells were treated with trypsin 0.05% and splitted in 35/35 mm Petri dish. The influence in vitro was assessed using primary osteoblast cell line and various techniques to observe cell-particles interactions. The results of these analyses are presented in this work.

728. Nickel nanotubes prepared by electroless deposition in ion track templates

Authors: Enculescu, I; Sima, M; Enculescu, M; Matei, E; Molares, MET; Cornelius, T

Published: MAR 2008, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 2, 136, DOI:

Nickel nano- and micro- tubes were prepared by electroless deposition in ion track template membranes. By choosing the appropriate etching conditions membranes with cylindrical or conical pores were obtained allowing the preparation of cylindrical or conical tubules. The activation of the membranes was a two step process. The bath used for deposition was an acidic one. Typically for acidic bath deposition, by energy dispersive X ray analysis, a phosphorous content of up to 10 % was found in the deposit.

729. Creatinine biomaterial thin films grown by laser techniques

Authors: Gyorgy, E; Axente, E; Mihailescu, IN; Predoi, D; Ciuca, S; Neamtu, J

Published: MAR 2008, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 19, 1339, DOI: 10.1007/s10856-007-3254-8

Creatinine thin films were synthesised by matrix assisted pulsed laser deposition (PLD) techniques for enzyme-based biosensor applications. An UV KrF* (lambda = 248 nm, tau similar to 10 ns) excimer laser source was used for the irradiation of the targets at incident fluence values in the 0.3-0.5 J/cm(2) range. For the matrix assisted PLD the targets consisted on a frozen composite obtained by dissolving the biomaterials in distilled water. The surface morphology, chemical composition and structure of the obtained biomaterial thin films were investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, and electron dispersive X-ray spectroscopy as a function of the target preparation procedure and incident laser fluence.

730. Photoluminescence processes in Er3+-doped calcium niobium gallium garnet (CNGG) crystals

Authors: Polosan, S; Shimamura, K; Tsuboi, T

Published: MAR 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 532, DOI:

Photoluminescence properties of Er3+-doped calcium niobium gallium garnet (CNGG) disordered crystals have been studied in the range of 200-2000 nm at 10-290 K. In addition to emission bands due to Er3+, a broad emission band is observed at 470 nm. From the emission spectra that were obtained by various excitations, level assignment has been established for the emission bands. Different temperature dependences are observed between the emission bands at 522 and 543 nm. This is explained using non-radiative phonon relaxation between the H-2(11/2) and S-4(3/2) states. Besides the 1535 nm Er3+ emission band, near infrared emission bands are observed at 860 and 1240 nm, which are attributed to the transitions from the S-4(3/2) state to the (4)vertical bar(13/2) and vertical bar 4(11/2) states, respectively.