National Institute Of Materials Physics - Romania

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5781 articles found

4311. Structure and properties of As25Te35Si40 glass

Authors: Lorinczi, A; Sava, F; Iovu, M; Leonovici, M; Halm, T; Popescu, M; Hoyer, W

Published: NOV 2003, PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 240, 36, DOI: 10.1002/pssb.200301850

The glassy composition As25Te35Si40 was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), Raman spectroscopy, and infrared absorption (IR) measurements. X-ray diffraction patterns at room temperature and at temperatures around T-g were recorded and the radial distribution functions have been calculated. A continuous random network model for the ideal homogeneous glass structure has been proposed.

4312. Copper nanowires electrodeposited in etched single-ion track templates

Authors: Enculescu, I; Siwy, Z; Dobrev, D; Trautmann, C; Toimil-Molares, ME; Neumann, R; Hjort, K; Westerberg, L; Spohr, R

Published: NOV 2003, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 77, 755, DOI: 10.1007/s00339-003-2216-3

The replication of single-ion track templates opens up the possibility of accessing electrical properties of nanowires without using lithographic techniques. Polycarbonate foils of 30-mum thickness were irradiated with single swift heavy ions (e.g. An 11.4 or Xe 8.3 MeV/nucleon). By controlled one-sided etching of the damage trail caused by the ion, templates containing a single conical pore were prepared. The narrow pore openings had diameters down to 25 nm and opening angles up to 2degrees. By electrochemical deposition of copper, single conical wires were obtained. The electric current recorded during electrodeposition reflects the geometry of the pore. The wires were provided with electrical contacts. Current-voltage measurements confirmed that their resistance was ohmic. The wires could withstand a maximum current density above 10(8) A/cm(2).

4313. The study on the inhibition of steel-carbon corrosion with ethylenethioureea (ETU) in ammonium chloride using Mossbauer spectrometry

Authors: Samide, A; Bibicu, I; Rogalski, M; Preda, M

Published: NOV 2003, REVISTA DE CHIMIE, 54, 931, DOI:

The inhibiting effect of ETU has been studied regarding the corrosion of carbon-steel in NH4Cl 0.1 M solution at 25degreesC and 50degreesC. The effects of the inhibitor have been demonstrated using weight loss and electrochemical measurements as well as Mossbauer spectrometry. The efficiency of ETU increases with the raise of the concentration, but lowers with the temperature. An activation energy was determined using the Arrhenius equation. The experimental data characterize a Langmuir type adsorption isotherm and the results were correlated to the adsorption of the inhibitor Mossbauer spectrometry shows the formation of a superficial film on the surface of the corroded sample in the presence of ETU. This film provides a good corrosion protection for the sample.

4314. BiOx clusters occluded in a ZSM-5 matrix: preparation, characterization, and catalytic behavior in liquid-phase oxidation of hydrocarbons

Authors: Dumitriu, D; Barjega, R; Frunza, L; Macovei, D; Hu, T; Xie, Y; Parvulescu, VI; Kaliaguine, S

Published: OCT 25 2003, JOURNAL OF CATALYSIS, 219, 351, DOI: 10.1016/S0021-9517(03)00216-1

A series of Bi-ZSM-5 containing 4.26, 5.54, and 6.64 wt% bismuth oxide was prepared by introducing Bi during ZSM-5 synthesis. For comparison. 5 wt% Bi (expressed as bismuth oxide)-impregnated ZSM-5 samples were also prepared. These samples were characterized by N-2 adsorption-desorption isotherms at 77 K, XRD, XPS, IR spectroscopy in the lattice vibration range and in the presence of chemisorbed pyridine and CO2 and EXAFS. The characterization data confirmed the occlusion of bismuth oxide clusters in the zeolite pores. An intrinsic acidity due to bismuth oxide clusters was evidenced. This consisted, on one hand, in weak Lewis acid sites, ascribed to coordinatively unsaturated bismuth cations, and, on the other hand, in strong Bronsted acid sites, attributed to boundary Bi (. . .) O-Si linkages. These catalysts were tested in the liquid-phase oxidation of benzene, toluene, and cyclohexane using hydrogen peroxide as oxidizing agent. The results showed that Bi-ZSM-5 catalysts are more active than the reported titanium silicalites, but the efficiency of H2O2 use was quite small, an important part of this being nonselectively decomposed. A good selectivity was observed in cyclohexane oxidation. (C) 2003 Elsevier Inc. All rights reserved.

4315. Polyaniline and carbon nanotubes based composites containing whole units and fragments of nanotubes

Authors: Baibarac, M; Baltog, I; Lefrant, S; Mevellec, JY; Chauvet, O

Published: OCT 21 2003, CHEMISTRY OF MATERIALS, 15, 4156, DOI: 10.1021/cm021287x

Using surface-enhanced Raman scattering (SERS) and Fourier transform infrared (FTIR) spectroscopy, we show that composites based on polyaniline (PANI) and single-walled carbon nanotubes (SWNTs) are different when they are prepared by two different methods: (1) by adding dispersed SWNTs to the polymer solutions and (2) by chemical polymerization of aniline in the presence of SWNTs. The difference originates from the irreversible chemical transformation of SWNTs in the polymerization medium. The synthesis medium used for the preparation of PANI transforms SWNTs into fragments of shorter length like closed-shell fullerenes. This explains the similarity of SERS and FTIR spectra of the composites PANI/SWNTs and PANI/C-60 chemically prepared. All compounds exhibit an absorption band at 1144 cm(-1) in their FTIR spectra, increasing with the carbon nanoparticules content, as a signature of a charge transfer between the constituents. Besides, the FTIR spectrum of the compounds obtained by adding SWNTs to the polymer solution display an intense absorption band with two components at 773 and 755 cm(-1), which are associated with the vibration of deformation of the benzene and the quinoid ring, respectively. This indicates a strong hindrance effect produced by the binding on the polymer chain of voluminous carbon particles as nanotubes and large fragments of nanotubes.

4316. Hybridization effects in some UTSi (2 : 1 : 3;1 : 1 : 1;2 : 3 : 1) compounds

Authors: Lupsa, I; Valeanu, M

Published: OCT 20 2003, MODERN PHYSICS LETTERS B, 17, 1282, DOI: 10.1142/S0217984903006311

The presence of magnetic moments in uranium atoms in some of U2TSi3, UTSi and U2T3Si (T is a 3d, 4d or 5d transition element) compounds is discussed in terms of the hybridization of s, p, d and f atomic orbitals. The hybridization strength in these ternary series of isostructural compounds was calculated using the semiquantitative band structure approach of Straub and Harrison. The prediction criterion for the presence of magnetic ordering, comparing the band width with a critical energy, seems to hold. The dominant influence of fd hybridization effects in the change of magnetic properties inside an isostructural group is in evidence.

4317. Second-order generation of point defects in gamma-irradiated float-zone silicon, an explanation for 'type inversion' (vol 82, pg 2169, 2003)

Authors: Pintilie, I; Fretwurst, E; Lindstrom, G; Stahl, J

Published: OCT 13 2003, APPLIED PHYSICS LETTERS, 83, 3216, DOI: 10.1063/1.1619226

4318. Deep defect levels in standard and oxygen enriched silicon detectors before and after Co-60-gamma-irradiation

Authors: Stahl, J; Fretwurst, E; Lindstrom, G; Pintilie, I

Published: OCT 11 2003, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 512, 116, DOI: 10.1016/S0168-9002(03)01884-9

Capacitance Deep Level Transient Spectroscopy (C-DLTS) measurements have been performed on standard and oxygen-doped silicon detectors manufactured from high-resistivity n-type float zone material with <111> and < 100> orientation. Three different oxygen concentrations were achieved by the so-called diffusion oxygenated float zone (DOFZ) process initiated by the CERN-RD48 (ROSE) collaboration. Before the irradiation a material characterization has been performed. In contrast to radiation damage by neutrons or high-energy charged hadrons, were the bulk damage is dominated by a mixture of clusters and point defects, the bulk damage caused by Co-60-gamma-radiation is only due to the introduction of point defects. The dominant electrically active defects which have been detected after Co-60-gamma-irradiation by C-DLTS are the electron traps VOi, CiCs, V-2(=/-), V-2(-/0) and the hole trap CiOi. The main difference between standard and oxygenated silicon at low dose values can be seen in the introduction rate of CiCs compared to CiOi. For highly oxygenated silicon the introduction of CiCs is fully suppressed, while the sum of the introduction rates g(CiCs)+g(CiOi) is independent on the oxygen concentration. (C) 2003 Elsevier B.V. All rights reserved.

4319. Study of interactions in carbon nanotubes systems by using Raman and SERS spectroscopy

Authors: Lefrant, S; Buisson, JP; Schreiber, J; Chauvet, O; Baibarac, M; Baltog, I

Published: OCT 9 2003, SYNTHETIC METALS, 139, 785, DOI: 10.1016/S0379-6779(03)00264-9

We present results obtained on carbon nanotube systems by means of Raman scattering and surface enhanced Raman scattering (SERS). Such systems consist of single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs), or polymer/nanotubes composites. In particular, we have focused our studies on the interactions taking place in these compounds which lead to an upshift of the radial breathing mode (RBM) in the case of SWNTs, either when they are arranged in bundles or embedded in polymers. Similar calculations has allowed us to interpret the low frequency Raman modes observed in purified MWNTs. We show that they come from the RBM of individual tubes. From intensity calculations performed to simulate Raman spectra, we demonstrate the importance of two experimental parameters, namely the diameter of internal tubes and the number of shells which constitute the MWNTs, such parameters being extracted experimentally from high resolution transmission electron microscopy images. (C) 2003 Elsevier Science B.V. All rights reserved.

4320. Structure and properties of As25Te35Si40 glass

Authors: Popescu, M; Lorinczi, A; Sava, F; Stegarescu, M; Iovu, M; Leonovici, M; Halm, T; Hoyer, W

Published: OCT 1 2003, JOURNAL OF NON-CRYSTALLINE SOLIDS, 326, 393, DOI: 10.1016/S0022-3093(03)00444-7

The glassy composition As25Te35Si40 was investigated by microhardness, differential scanning calorimetry, X-ray diffraction, electrical conductivity and Raman spectroscopy measurements. A continuous random network model of the glass structure has been developed. (C) 2003 Elsevier B.V. All rights reserved.