National Institute Of Materials Physics - Romania

Publications

839 articles found

511. Study of electrodeposition of (Bi,Sb)(2)Te-3 nanowires by voltammetric methods and electrochemical impedance spectroscopy

Authors: Sima, M; Vasile, E; Sima, M

Published: NOV-DEC 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 1602, DOI:

Nanostructured thermoelectric semiconductors are a promising material to convert waste heat to electricity for energy regeneration due to improvement of Seebeck coefficient and thermal conductivity reducing. Among various thermoelectric materials, bismuth telluride based alloys are the most used in the fabrication of TE devices. The processes associated with the electrodeposition of (Bi,Sb)(2)Te-3 nanowires and films are reported along with an analysis of the composition, morphology and structure of resulting materials. Electrochemical behavior was examined using cyclic and linear voltammetry and electrochemical impedance spectroscopy techniques.

512. OPTICALLY INDUCED BIREFRINGENCE OF A p-AMINOAZOBENZENE-EPDXY RESIN DERIVATIVE

Authors: Beica, T; Zgura, I; Frunza, L; Ganea, P; Frunza, S; Dumitrache, L; Raditoiu, V; Wagner, L

Published: 2011, ROMANIAN REPORTS IN PHYSICS, 63, 752, DOI:

A derivative of p-aminoazobenzene-epoxy resin was studied. Visually examination between crossed polarizers does not show birefringence but it can be optically induced. Changing the polarization direction of the irradiating light leads to the changing of the privileged direction of the induced birefringence. The birefringence value was evaluated and compared with liquid crystals as anisotropic compounds.

513. LIQUID CRYSTAL/COPOLYMER-CLAY NANOSTRUCTURED SYSTEMS: CONTRIBUTION TO THE CONDUCTIVITY OF THE ELECTRODE POLARIZATION

Authors: Ganea, CP; Manaila-Maximean, D

Published: 2011, UNIVERSITY POLITEHNICA OF BUCHAREST SCIENTIFIC BULLETIN-SERIES A-APPLIED MATHEMATICS AND PHYSICS, 73, 216, DOI:

The electrical conductivity of new nanocomposite systems liquid-ctystal/montmorillonite clay is performed using impedance spectroscopy. The dependence of the electrical conductivity on the frequency, temperature and bias voltage is obtained. The results referring to the alternative voltage influence allow getting more information on the conduction mechanism than the previous ones obtained under frequency and temperature influence. An important role has the polarization at the electrode-sample interface, both in continuous and alternative current. The electrode polarization effect on the electrical conductivity in dependence on the above mentioned parameters is also examined.

514. ELECTRICAL PROPERTIES OF (Zn,Cu)O:Mn SUBMICRON WIRES

Authors: Ion, L; Antohe, S; Sima, A; Sima, M

Published: OCT-DEC 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 1700, DOI:

Arrays of multisegment Pd/(Zn,Cu)O:Mn/Pd submicron wires have been grown electrochemically into the pores of nuclear track polycarbonate membranes. Their transport properties were investigated, by measuring current-voltage (I-V) characteristics in a temperature range from 300 K down to 40 K. I-V characteristics of Pd/(Zn,Cu)O:Mn/Pd wires exhibited a symmetric, non-linear shape on applied bias voltage ranging from -20 V to +20V. The ohmic region corresponds to polarization voltage under 3.5V. Comparatively, I-V characteristics of Pd/ZnO/Pd array of wires with diameter about 500 nm are linear in the entire range of applied voltages (-20 V to +20V).

515. Photoluminescence of poly (N vinylcarbazole)/carbon nanotubes composites

Authors: Gontia, II; Baibarac, M; Baltog, I

Published: MAY-JUN 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 582, DOI:

The photoluminescence (PL) of two types of poly (N-vinyl-carbazole)(PVK)/carbon nanotubes (CN) composites, prepared by chemical and electrochemical method, has been investigated. In comparison with the pure PVK, the chemically prepared PVK/NC sample shows a significant PL quenching and a shorter decay time. For the samples prepared electrochemically, PL increases in intensity, red shifts and gets longer decay time with the increase of voltammetric cycles number. In addition, the latter shows a change in emission from high-energy excimer to low-energy excimer after a treatment with NH(4)OH.

516. DEPENDENCE OF OPTICAL RESPONSE ON pH OF A WATER-SOLUBLE Zn(II)-METALLOPORPHYRIN

Authors: Fagadar-Cosma, E; Creanga, I; Maranescu, B; Palade, A; Lorinczi, A; Fagadar-Cosma, G; Popescu, M

Published: JAN-MAR 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 80, DOI:

Nowadays, porphyrin derivatives are extensively used as analytical reagents. This work put the basis for a rapid, simple and inexpensive method developed for pH determination. It was demonstrated the potential for a water soluble metalloporphyrin, 5,10,15,20-tetrakis(N-methyl-4-pyridyl) porphyrin-Zn(II) tetrachloride (Zn-TNMPyP) to be a potential optical pH sensor in the 5.5-10.5 domain. Monitoring of the variations in the absorption spectra of the Zn-TNMPyP, both regarding the Soret and the Q(0,1) band, generated by the exposure to different base concentrations allowed us to notice the linearity of the response at different pH values.

517. Influence of defects on the switching speed of Ge2Sb2Te5

Authors: Velea, A; Popescu, M; Lorinczi, A; Sava, F; Simandan, ID; Mihai, C

Published: NOV-DEC 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 1596, DOI:

Chalcogenide phase change materials are one of the major contenders for the new non-volatile memory applications. Here is reported that the switching speed of Ge2Sb2Te5 is strongly dependent on the percent of defects in the material. Using cellular automata simulations it was shown that the size of the percolation cluster is minimum, thus the switching speed is maximum, for a percent of around 25% defects in the material. This is a property of the Ge2Sb2Te5 that can be useful for new phase change materials and devices design with better switching properties.

518. Skin Layer Defects in Si by Optimized Treatment in Hydrogen RF Plasma

Authors: Ghica, C; Nistor, LC; Vizireanu, S; Dinescu, G; Moldovan, A; Dinescu, M

Published: DEC 20 2010, PLASMA PROCESSES AND POLYMERS, 7, 991, DOI: 10.1002/ppap.201000066

The first step of the smartcut (TM) process consists in inducing structural defects below the free surface of a silicon wafer, usually by implantation of light elements, such as hydrogen or helium. An alternative way to induce subsurface defects is by plasma treatment. In this work, we present a morphological and structural study on silicon wafers submitted to hydrogen plasma treatment, using two plasma-processing geometries. The parameters of the plasma treatment have been varied in order to limit the surface roughness and to confine the induced defects in a narrow region (50 nm) below the wafer surface. The morphological and structural investigations have been performed by AFM and TEM.

519. Effect of the morphology on the optical and electrical properties of TPyP thin films deposited by vacuum evaporation

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

Published: DEC 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 2038, DOI:

We have studied the effect of the morphology on the optical and electrical properties of the TPyP thin films deposited by vacuum evaporation on different substrates (Si with different characteristics, ITO, quartz and glass). The presence of some well-defined B and Q absorption bands has been evidenced. FTIR and photoluminescence measurements have been used to confirm the preservation of the chemical structure of the compound during the evaporation process. The contact Au/TPyP/Si(n) is rectifier, while a blocking behavior has been shown by Si(n)/TPyP/Si(n) and ITO/TPyP/Si(n) and an injector dominated behavior by Si(p)/TPyP/Si(p) and ITO/TPyP/Si(p) heterostructures. The best transmission was obtained on TPyP film deposited on ITO and the highest value of the current in heterostructures Si(n) electrode characterised by a large grain morphology and in consequence by a weak optical and charge carrier scattering at the grain boundaries.

520. On the structural, morphological, optical and electrical properties of sol-gel deposited ZnO In films

Authors: Girtan, M; Socol, M; Pattier, B; Sylla, M; Stanculescu, A

Published: NOV 1 2010, THIN SOLID FILMS, 519, 577, DOI: 10.1016/j.tsf.2010.07.006

Indium-doped zinc oxide thin films deposition was performed by the sol-gel technique using homogeneous and stable solutions of zinc acetate 2-hydrate and indium chloride in ethanol Films were spin coated onto glass substrates After drying and after a heat treatment at 450 degrees C highly transparent (80%-90%) films were obtained The effect on the structural morphological optical and electrical thin films properties of the dopant concentration was investigated The temperature dependencies of the electrical conductivity under vacuum and in open atmosphere were analysed and discussed (C) 2010 Elsevier B V All rights reserved