National Institute Of Materials Physics - Romania

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5781 articles found

3671. Structural and magnetic properties of FexOy nanoparticles dispersed in silica matrix

Authors: Predoi, D; Clerac, R; Raileanu, M; Crisan, M; Zaharescu, M

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1498, DOI:

Some FexOy-SiO2 composites were prepared by the colloidal and alkoxidic route of the sol-gel method. The dried gels were thermally treated and the samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared absorption (IR) spectroscopy, magnetic susceptibility measurements and Mossbauer spectroscopy. Nanoparticles of gamma and /or alpha iron oxide phase of different size were obtained in the silica matrix depending on the gelation conditions and on the thermal treatment. It was observed that the particle sizes and the thermal stability of the iron oxide phases strongly depend on the preparation method. At temperatures above 400 degrees C, the gamma-phase begins to transform to the alpha-phase.

3672. Preparation of metallic nanowires with magnetic properties using the template method

Authors: Enculescu, I; Sima, M; Enculescu, M; Ghica, C; Enache, M; Neumann, R

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1470, DOI:

Metallic nanowires with magnetic properties were prepared by electrochemical deposition in nanoporous ion track membranes. Thus, we prepared Co-Cu alloy and Co/Cu multilayered nanowires. The technique allows the preparation of uniform arrays of parallel nanowires with desired properties. The process of electrochemical deposition of metals in nanoporous membranes was studied by means of cyclic voltammetry and impedance spectroscopy. The influences of deposition conditions such as bath composition, temperature and deposition potential on the morphological, structural and compositional properties of the nanowires were systematically studied.

3673. Effect of the metallic contact on the electrical properties of organic semiconductor film

Authors: Stanculescu, F; Stanculescu, A; Socol, M

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1357, DOI:

Sandwich type (MIS) heterostructures based on layers of organic semiconductors as meta-dinitrobenzene (m-DNB) and perylene or perylene derivative 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) have been prepared using alternative methods (rapid thermal directional solidification or two-steps, vacuum evaporation and deposition process) on different substrates (single crystal silicon wafer and textolite covered with copper film). Subsequently indium, gallium, aluminium of high purity (5N) and silver have been used for the preparations of the metallic contacts. This paper presents some investigations of the contact between different organic semiconductors and several metals: meta-dinitrobenzene/Cu, perylene/In, peryiene/Al, perylene/Ga, perylene/Ag, PTCDA/AI, PTCDA/Ga, and PTCDA/Ag. The comparative study of the electrical conduction properties of these organic semi conductor/metal contacts has emphasised significant differences depending on the metal type, metal/organic semiconductor interface properties and quality of the contact, which is determined by the preparation method (pressing, melting, vacuum evaporation, painting) and selected contact cinfiguration. The experimental data obtained using the 2 points contact geometry have evidenced linear or power IN dependences of the investigated metallic contacts emphasising the importance of the space-charge phenomenon and defects on the charge carriers' transport in these structures.

3674. Micro and nanorods of alkali halides grown in polymer templates

Authors: Enculescu, M; Enculescu, I; Sima, M; Neumann, R; Trautmann, C

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1563, DOI:

Porous membranes containing cylindrical pores with diameters ranging from a few tens of nanometers to a few tens of micrometers were prepared by using the ion track technique. Swift heavy ions (e.g. Au with 11.4 MeV/nucleon specific energy) were used for creating the ion tracks in polycarbonate foils. Etching was performed using an aqueous solution of NaOH containing methanol. The growth of the alkali-halides micro- and nanorods was performed by evaporation from a saturated solution. The rods were imaged using scanning electron microscopy. The method opens up the possibility of growing nanostructures with applications as nanolaser media or nanoscintillators.

3675. Deposition and properties of CdTe nanowires prepared by template replication

Authors: Enculescu, I; Sima, M; Enculescu, M; Enache, M; Ion, L; Antohe, S; Neumann, R

Published: MAY 2007, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 244, 1611, DOI: 10.1002/pssb.200675109

We used the template method to prepare CdTe wires with diameters ranging from 80 nm to 1 mu m. As templates we used polycarbonate and polyethilene tereplitalate ion track membranes and as the method of filling the pores of such membranes we employed electrochemical deposition. The conditions (i.e. bath composition and deposition potential) necessary to obtain the stoichiometric composition of the semiconductor were found. Scanning and transmission electron microscopy were employed for morphological characterization of the nano and microwires. Energy dispersive X-ray analysis was employed for determining the Cd/Te ratio. Selected area electron diffraction was employed for structural measurements. Reflection spectroscopy measurements were performed on nanowire arrays for determining the band gap of the deposited nanostructures. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

3676. A PZT type piezoceramic material with high planar coupling factor used for a miniature bimorph ventilator

Authors: Miclea, C; Iuga, A; Tanasoiu, C; Amarande, L; Cioangher, M; Miclea, CT

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1515, DOI:

New PZT type ceramic materials, doped with Ni, were prepared by the usual solid state reaction. The best composition proved to be the one containing 6% atomic Ni and having the following chemical formula: Pb0.95Bi0.03Nb0.02Zr0.51 Ti0.43Ni0.06O3. Rectangular samples of this powder were pressed and sintered at 1200 OC for 4 hours and then it was cut in thin slices used to construct an efficient bimorph type ventilator to be used in miniaturized devices for cooling. Miniature ventilators made of PZT ceramics are preferred due to their smallness, high electromechanical efficiency and lack of rotating parts and last but not least of contiguous electrical contacts. We made such a device by using two thin ceramic PZT plates of the material with the best piezoelectric properties, assembled in a flexural oscillator through a proper bimorph association. The emerging doublet behaves itself very much like a bimetal system and possesses a good developed flexural mode. Attaching a metallic elastic plate to the bimorph produces a highly efficient miniature ventilator. A theoretical quantitative study of this flexural bimorph system with elastic plate attached was proposed.

3677. Properties of TiO2 thin films prepared by different techniques

Authors: Ungureanu, F; Medianu, R; Ghita, RV; Negrila, CC; Ghita, P; Manea, AS; Lazarescu, MF

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1461, DOI:

TiO2 thin films prepared by sol-gel method and by RF magnetron sputtering deposited on p-Si(111), n-GaAs(100), and glass have been investigated by XRD, XPS and AFM techniques. The characteristics of the film: colour, adherence and composition are presented in the case of thermal treatments (500 degrees C and 800 degrees C) for sol-gel deposited films as well as for RF sputtering. The TiO2 plasma deposited film is uniform, homogeneous and stoichiometric.

3678. ZnO : Mn : Cu nanowires prepared by template method

Authors: Sima, M; Enculescu, I; Sima, M; Enache, M; Vasile, E; Ansermet, JP

Published: MAY 2007, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 244, 1527, DOI: 10.1002/pssb.200675126

Manganese and copper doped ZnO films and nanowire arrays were prepared by cathodic electrodeposition from aqueous solution. The electrochemical process was examined by linear voltammetry and the morphology and the composition of obtained semiconductor were observed by SEM and EDX measurements. Optical absorption spectra indicated the presence of copper in ZnO: Mn: Cu nanowire arrays as Cu2+ ions. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

3679. Microwave properties of Ba1-xPbxNd2Ti5O14 dielectric resonators

Authors: Ioachim, A; Toacsan, MI; Banciu, MG; Nedelcu, L; Dutu, CA; Stoica, G

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1575, DOI:

The Ba1-xPbxNd2Ti5O14 (BNT: Pb) ceramics are appropriate for microwave devices due to their high dielectric constant and low loss in the microwave domain. Samples with x Pb content in the range 0 + 0.5 were prepared by solid-state reaction and sintered at temperatures T-s = 1230 + 1260 degrees C. XRD and SEM analysis indicate very good crystalline structure and polyhedral well formed grains. Controlled temperature coefficient of resonant frequency alpha is essential for dielectric resonators. The temperature coefficient of the resonant frequency alpha takes values from - 15 ppm/degrees C to + 70 ppm/degrees C. Highdensity values and adequate microwave parameters were obtained for x = 0.5 Pb content. The BNT: Pb ceramics sintered at 1250 degrees C and 1260 degrees C for 2 hours are suitable for dielectric resonators for frequencies up to 5 GHz. epsilon r = 76 + 87 and Q x f similar to 5000 GHz).

3680. Influence of the phosphorous precursors on the structure and properties of the SiO2-P(2)O(5)sol-gel films

Authors: Vasiliu, C; Grigorescu, C; Pavelescu, G; Predoana, L; Todan, L; Gartner, M; Anastasescu, M; Negrila, C; Logofatu, C; Moldovan, A; Zaharescu, M

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1410, DOI:

Thin films in the SiO2-P2O5 system are intensely studied due to their applications in microelectronics, sensing, nanophotonics, optoelectronics and as ionic conductors. Sol-gel is the most used method for preparation of such films. Previous studies established the very low reactivity of the phosphorous alkoxides and the high tendency of the phosphorous oxide to volatilise at thermal treatment. In order to identify the most appropriate precursor for obtaining layers with desired composition and properties a systematic study of the sol-gel film preparation using different phosphorous precursors was carried out. The films were deposited on ITO/SiO2 coated glass substrates at room temperature. To check the influence of the type of precursors on the layers thermal stability and properties a post deposition annealing was performed at temperatures of 150 and 200 degrees C. The film characterization was carried out using various techniques as Spectroscopic Ellipsometry (SE), X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR).