National Institute Of Materials Physics - Romania

Publications

5781 articles found

3381. Resonant Raman scattering and absorption spectroscopy studies on individual carbon nanotubes in surfactant solutions

Authors: Husanu, M; Baibarac, M; Preda, N; Baltog, I

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1726, DOI:

Carbon Nanotubes are exotic low-dimensional systems, and due to their remarkable properties, are promising components for technological applications. The electronic and vibrational signatures raising from their existence as individual entities or associated in bundles, is still a controversed subject. A careful analysis of the G (similar to 1600 cm(-1)) and RBM (100-200 cm(-1)) band features as: profile, peak position and intensity in the Raman spectra may be a valuable indication about their dispersion state. The UV-VIS-NIR absorption spectrum comes to support this assumption. Observing the absorption spectra associated to resonant excitation of semiconducting and metallic nanotubes, may reveal complementary informations concerning the individualization procedure efficiency.

3382. Polaron activation energy as evidenced by EMR in colossal magnetoresistive nanowires

Authors: Popa, A; Toloman, D; Grecu, MN; Mihailescu, G; Darabont, A; Pop, CVL; Raita, O; Fardis, M; Idziak, S; Hoffmann, SK; Giurgiu, LM

Published: JUL 2008, APPLIED MAGNETIC RESONANCE, 34, 26, DOI: 10.1007/s00723-008-0097-5

In the present work an X-band electron magnetic resonance (EMR) investigation in the paramagnetic regime of colossal magnetoresistive manganite La2/3Ca1/3 MnO3 (LCMO) nanowires was carried out. The temperature dependence of the EMR line width has been analyzed in terms of the small polaron hopping scenario. From this analysis, the polaron activation energy E-a in LCMO nanowires was evaluated. A discussion is given concerning the factors which could explain the smaller value of E-a as compared with the corresponding ones for LCMO nanoparticles.

3383. Pressure response of Ce(Ag, Ni)Sb(2) compounds

Authors: Khan, RT; Galos, R; Bauer, E; Popescu, B; Galatanu, A

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1615, DOI:

The pressure response of CeAg(1-x)Ni(x)Sb(2) is Studied by means of electrical resistivity measurements. The ferromagnetic ordering temperatures T(c) of this series decrease as pressure is applied, except CeNiSb(2), showing a pressure driven continuous increase of T(c). This refers to crystalline electric field effects originating distinct different magnetic ground states. Concomitantly, the pressure response of various material dependent parameters also behave in the opposite direction.

3384. The impact of the "memory effect" on the catalytic activity of Mg/Al; Mg,Zn/Al; Mg/Al,Ga hydrotalcite-like compounds used as catalysts for cycloxene epoxidation

Authors: Angelescu, E; Pavel, OD; Birjega, R; Florea, M; Zavoianu, R

Published: JUN 15 2008, , DOI: 10.1016/j.apcata.2007.12.022

3385. Thermally-induced self-assembling nanotechnology of gold nano-dots on CeO2-buffered sapphire for superconducting films

Authors: Crisan, A; Wordenweber, R; Hollmann, E; Kutzner, R; Button, TW; Abell, JS

Published: JUN 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1373, DOI:

A typical facility for fabrication of devices based on high temperature superconducting (HTS) films grown on the less-expensive CeO2-buffered sapphire substrates comprises a transfer chamber, a chamber for CeO2 growth, a chamber for YBa2Cu3Oy (YBCO) growth, and a chamber for Au deposition at room temperature. Here we present the adaptation of our previously-reported method to create artificial pinning centres in HTS films through self-assembled nano-scale islands for this type of facility without making any modifications. We succeeded to grow Au nano-dots from an ultra-thin layer of Au grown at room temperature subsequently annealed in the chamber for YBCO deposition, in the same conditions as for YBCO growth. AFM and RBS were used to investigate the formation of Au nano-dots, while XRD and susceptibility measurements were used to study the properties of nano-structured YBCO films.

3386. Potassium hydrogen phthalate (KAP) micro- and nano-rods prepared by a template approach

Authors: Enculescu, M

Published: JUN 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1504, DOI:

Micro and nanorods of potassium acid phthalate (KAP) with diameters ranging from a hundred nanometers to tens of microns were obtained by solution growth in polycarbonate (PC) ion track templates. The ion track templates were produced by swift heavy ion irradiation of PC foils (e.g. U with 11.4 MeV/nucleon specific energy) and subsequently etching. After the growth the host templates were partially dissolved in dichlormethane and imagined by scanning electron microscopy. The template approach allows the fabrication of arrays of uniform nanostructures with a controlled morphology.

3387. Size-broadening anisotropy in whole powder pattern fitting. Application to zinc oxide and interpretation of the apparent crystallites in terms of physical models

Authors: Popa, NC; Balzar, D

Published: JUN 2008, JOURNAL OF APPLIED CRYSTALLOGRAPHY, 41, 627, DOI: 10.1107/S0021889808012223

A new anisotropic size-broadening model based on a spherical-harmonics representation allowing determination of both volume-and area-averaged apparent crystallites and convenient for implementation into Rietveld programs is described. The model effectiveness is demonstrated on a ZnO powder pattern exhibiting strongly anisotropic size broadening and pronounced super-Lorentzian peak shapes. Moreover, it is shown how the apparent crystallites can be interpreted in terms of physical models by using ellipsoidal and cylindrical crystallites with lognormal size distributions. This interpretation is critically assessed and it is argued that both simplified physical models and a priori complementary information (obtained by transmission electron microscopy, for instance) are often needed to avoid unstable and non-unique solutions.

3388. In-band pumping of Nd-vanadate thin-disk lasers

Authors: Pavel, N; Krankel, C; Peters, R; Petermann, K; Huber, G

Published: JUN 2008, APPLIED PHYSICS B-LASERS AND OPTICS, 91, 419, DOI: 10.1007/s00340-008-3013-7

We investigate the output performance of the 1.06 mu m(4)F(3/2)-->I-4(11/2) transition in Nd:GdVO4 and Nd:YVO4 thin-disk lasers under multi-pass pumping with diode lasers at 0.81 mu m and at 0.88 mu m, which corresponds to direct in-band pumping of the F-4(3/2) emitting level. The use of a pump module with 24 passes through the crystal allowed the realization of an in-band pumped Nd:GdVO4 thin-disk laser with 14.9 W of continuous wave (cw) output power at 1.06 mu m; the overall optical-to-optical efficiency was 0.50 and the slope efficiency with respect to the incident pump power was 0.52. Intracavity frequency-doubling of the Nd:GdVO4 thin-disk laser with a LiB3O5 (LBO) nonlinear crystal yielded 9.1 W of cw output power in the green at 0.53 mu m with an overall optical-to-optical efficiency of 0.31.

3389. Electron and hole trapping in irradiated PbBr2 : Tl single crystals

Authors: Stefan, M; Nistor, SV; Darabont, A; Neamtu, C; Goovaerts, E

Published: JUN 2008, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 266, 2761, DOI: 10.1016/j.nimb.2008.03.179

Several hole trapped centres, namely Tl2+, self-trapped hole and A-type centres, were observed by ESR in PbBr2:Tl single crystals after X-ray irradiation at 77 K. The corresponding spectra are visible up to 200 K for all three defect centres. The STH centres are observed at higher temperatures than in the undoped PbBr2 single crystals, probably due to the stabilising effect of the Tl+ impurities. The ESR parameters of the Tl2+ centre point to stronger covalency effects in PbBr2 than in the isostructural PbCl2 crystals. All hole trapped centres started decaying around 160 K, probably due to recombination with nonparamagnetic electron trapped centres. Besides a small concentration of self-trapped electron centres, no other electron trapped centres were observed. (c) 2008 Elsevier B.V. All rights reserved.

3390. Hyperfine interactions and dynamics characteristics of Sn-119 in xSnO(2)-(1-x)alpha-Fe2O3 nanoparticle system

Authors: Constantinescu, S; Diamandescu, L; Bibicu, I; Tarabasanu-Mihaila, D; Feder, M

Published: JUN 2008, HYPERFINE INTERACTIONS, 184, 89, DOI: 10.1007/s10751-008-9770-1

The hyperfine interactions and dynamics aspects in nanoparticles system of the xSnO(2)-(1-x)alpha-Fe2O3 (x = 0.0-1.0) have been investigated by Sn-119-Mossbauer and XRD techniques. The change revealed by the XRD (XRDSs) and Mossbauer spectra (MSs) vs. x was discussed in terms of the phase and lattice-dynamics changes. The evidences of the triple hyperfine magnetic fields' distributions (MHFDs) and their dependencies x (< 0.175) are discussed taking into account the super-transferred hyperfine interactions (STHI), the local disorder Sn4+/Fe3+ around the tin isotope probe and the reduced dimension effect.