National Institute Of Materials Physics - Romania

Publications

5714 articles found

2391. Persistent oscillatory currents in a 1D ring with Rashba and Dresselhaus spin-orbit interactions excited by a terahertz pulse

Authors: Nita, M; Marinescu, DC; Manolescu, A; Ostahie, B; Gudmundsson, V

Published: SEP 2012, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 46, 20, DOI: 10.1016/j.physe.2012.08.017

Persistent, oscillatory charge and spin currents are shown to be driven by a two-component terahertz laser pulse in a one-dimensional mesoscopic ring with Rashba and Dresselhaus spin-orbit interactions (SOI) linear in the electron momentum. The characteristic interference effects result from the opposite precession directions imposed on the electron spin by the two SOI couplings. The time dependence of the currents is obtained by solving numerically the equation of motion for the density operator, which is later employed in calculating statistical averages of quantum operators on few electron eigenstates. The parameterization of the problem is done in terms of the SOI coupling constants and of the phase difference between the two laser components. Our results indicate that the amplitude of the oscillations is controlled by the relative strength of the two SOI's, while their frequency is determined by the difference between the excitation energies of the electron states. Furthermore, the oscillations of the spin current acquire a beating pattern of higher frequency that we associate with the nutation of the electron spin between the quantization axes of the two SOI couplings. This phenomenon disappears at equal SOI strengths, whereby the opposite precessions occur with the same probability. (c) 2012 Elsevier B.V. All rights reserved.

2392. Sn-Doped Hydroxylated MgF2 Catalysts for the Fast and Selective Saccharification of Cellulose to Glucose

Authors: Wuttke, S; Negoi, A; Gheorghe, N; Kuncser, V; Kemnitz, E; Parvulescu, V; Coman, SM

Published: SEP 2012, CHEMSUSCHEM, 5, 1711, DOI: 10.1002/cssc.201200303

2393. The Meyer-Neldel rule in amorphous TiO2 films with different Fe content

Authors: Mardare, D; Yildiz, A; Apetrei, R; Rambu, P; Florea, D; Gheorghe, NG; Macovei, D; Teodorescu, CM; Luca, D

Published: SEP 2012, JOURNAL OF MATERIALS RESEARCH, 27, 2277, DOI: 10.1557/jmr.2012.193

Amorphous titania thin films with increasing Fe content have been prepared by RF magnetron sputtering. X-ray absorption spectroscopy revealed modifications of both local structures/environment of the Ti and Fe atoms, with formation of phases containing amorphous material and a magnetite-like phase. The temperature dependence of the electrical conductivity of the films was investigated for temperatures higher than half of the Debye temperature (T > 391 K). It was found that the electrical conductivity in the amorphous Fe/TiO2 films obeys the Meyer-Neldel rule. The origin of this behavior is explained on the basis of the multiphonon-assisted hopping model.

2394. Evaluation of antibacterial effect of silver doped hydroxyapatite nanoparticles

Authors: Prodan, AM; Le Coustumer, P; Predoi, D

Published: SEP 2012, FEBS JOURNAL, 279, 98, DOI:

2395. Effect of Nucleators and Intermediates on the Magnetic Properties of Nanosized Magnetite Obtained by Glass Crystallization

Authors: Sandu, V; Nicolescu, MS; Kuncser, V; Popa, S; Pasuk, L; Sandu, E

Published: SEP 2012, JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, 9, 1545, DOI: 10.1166/jctn.2012.2241

We investigate the role of chromium and phosphorous oxides on the growth and magnetic properties of crystallized Fe-containing borosilicate glasses as well as their evolution under different thermal processing. The glasses have the ratio between SiO2 and Fe2O3 in the range 1.49 to 2.68 and Al2O3/MgO as intermediate/modifier oxides. X-ray diffraction and Mossbauer spectroscopy data revealed the presence of magnetite as the major crystalline phase in all as-prepared samples but additional amounts of hematite and of Fe-rich paramagnetic phases are also visible in some samples. The magnetic response is correlated with the disorder observed in the different sites (tetrahedral and octahedral) of the magnetite.

2396. Non-monotonous temperature variation of the magnetization relaxation rate in YBCO films with BZO nanorods below the matching field

Authors: Miu, L

Published: SEP 2012, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 479, 182, DOI: 10.1016/j.physc.2011.12.032

Standard zero-field cooling (zfc) magnetization relaxation measurements over a large temperature T interval were performed for YB2Cu3O7 films with BaZrO3 nanorods parallel to the c axis having the matching field B-Phi similar to 2.3 T. A rich non-monotonous T dependence of the normalized magnetization relaxation rate S at low external magnetic fields H (oriented along the nanorods) was observed. For H = 2 kOe, for example, S(T) clearly exhibits two maxima, located around T = 30 K and T = 62 K, as well as a pronounced S(T) deep at T similar to 77 K. It is shown that the first S(T) maximum may have an extrinsic origin, related to the occurrence of thermo-magnetic instabilities in the low-T domain, the second one is due to a crossover between the non-glassy vortex creep regime involving double vortex kink formation and variable range vortex hopping, whereas the S(T) deep at high T is generated by the accommodation of nearly isolated vortices to the nanorods in the presence of the T dependent macroscopic current induced in the specimen. (C) 2012 Elsevier B.V. All rights reserved.

2397. Controllable chirality-induced geometrical Hall effect in a frustrated highly correlated metal

Authors: Ueland, BG; Miclea, CF; Kato, Y; Ayala-Valenzuela, O; McDonald, RD; Okazaki, R; Tobash, PH; Torrez, MA; Ronning, F; Movshovich, R; Fisk, Z; Bauer, ED; Martin, I; Thompson, JD

Published: SEP 2012, NATURE COMMUNICATIONS, 3, DOI: 10.1038/ncomms2075

A current of electrons traversing a landscape of localized spins possessing non-coplanar magnetic order gains a geometrical (Berry) phase, which can lead to a Hall voltage independent of the spin-orbit coupling within the material-a geometrical Hall effect. Here we show that the highly correlated metal UCu5 possesses an unusually large controllable geometrical Hall effect at T < 1.2 K due to its frustration-induced magnetic order. The magnitude of the Hall response exceeds 20% of the nu = 1 quantum Hall effect per atomic layer, which translates into an effective magnetic field of several hundred Tesla acting on the electrons. The existence of such a large geometric Hall response in UCu5 opens a new field of enquiry into the importance of the role of frustration in highly correlated electron materials.

2398. Interaction of NaYF4:Er:Yb Nanoparticles with Phospholipid Monolayers as Models of Biological Membranes

Authors: Petrescu, L; Cinteza, O; Voiculescu, AM; Rosu, T; Enculescu, I; Matei, E; Georgescu, S; Birjega, R; Avram, S; Mihailescu, D

Published: SEP 2012, REVISTA DE CHIMIE, 63, 961, DOI:

Given the evolution of imaging techniques in the biomedical field is becoming more necessary to develop sensitive markers, less toxic and not least more economical. Upconverting luminescent nanocrystals doped with rare earth ions, excited in infrared and emitting in visible, are considered real concurrent to classical fluorescent markers, featuring a number of advantages in rapport with them. The aim of this study is to prepare NaYF4 nanoparticles doped with erbium and ytterbium for biological applications in bioimaging techniques. After synthesis, upconverting nano particles were coated with SiO2 for surface sealing and passivation. The nano particles were characterized by X-ray diffraction, luminescence spectroscopy, electronic microscopy and dynamic light scattering. The interaction of the nanoparticles with mimicking cell membrane models was studied. NaYF4 nanoparticles showed a good size distribution and good emission efficiency. The uncoated nanoparticles increase the fluidity of the lipid monolayer, while the effect of the silica coated nanoparticles is substantially reduced.

2399. Assessing toxicity of two types of magnetite nanoparticles in human hepatocarcinoma cells

Authors: Radu, M; Iconaru, SL; Predoi, D; Costache, M; Dinischiotu, A

Published: SEP 2012, FEBS JOURNAL, 279, 205, DOI:

2400. Synthesis of CdS nanostructures using template-assisted ammonia-free chemical bath deposition

Authors: Preda, N; Enculescu, M; Gherendi, F; Matei, E; Toimil-Molares, ME; Enculescu, I

Published: SEP 2012, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 73, 1089, DOI: 10.1016/j.jpcs.2012.05.003

CdS micro- and nano-structures (micro/nanotubes and nanostructured films) were obtained by ammonia-free chemical bath deposition using polymer templates (ion track-etched polycarbonate membranes and poly(styrene-hydroxyethyl methacrylate) nanosphere arrays). The semiconductor structures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoluminescence and electrical measurements. The diameters of CdS tubes are between 300 nm and few microns and the lengths are up to tens of micrometers. The SEM images prove that the CdS films are nanostructured due to the deposition on the polymer nanosphere arrays. For both CdS structures (tubes and films) the XRD patterns show a hexagonal phase. The optical studies reveal a band gap value of about 2.5 - 2.6 eV and a red luminescence at similar to 1.77 eV. A higher increase of conductivity is observed for illuminating the CdS nanostructured film when compared to the simple semiconductor film. This is a consequence of the periodic patterning induced by the polymer nanosphere array. (C) 2012 Elsevier Ltd. All rights reserved.