National Institute Of Materials Physics - Romania

We investigated the relaxation of the irreversible magnetization in a series of 200 nm thick YBa2Cu3O7/PrBa2Cu3O7 [(YBCO)(n)/(PrBCO)(m)] superlattices, where the thickness m of the nonsuperconducting PrBCO layer (measured in unit cells) was kept to m = 4 (sufficient to decouple the superconducting YBCO layers), whereas the thickness n of the YBCO layer was varied between 2 and 20 unit cells. The analysis of standard zero-field-cooling dc magnetization relaxation data obtained in the low temperature T region with the applied magnetic field H oriented along the c axis reveals the occurrence of a crossover elastic (collective) vortex creep at low T-plastic vortex creep at high T, generated by the T dependent macroscopic currents induced in the sample during measurements. For thin superlattices (n < 20) the creep crossover temperature T-cr proportional to n, and T-cr decreases linearly with increasing ln(H) for a fixed n. This crossover represents an alternative to the elastic vortex glass behavior reported for superlattices, as well as to 'quantum vortex creep' at unexpectedly high T inferred for thin films. We also discuss the absence of an increase of the magnetically determined critical current density with decreasing YBCO thickness in our superlattices, which apparently contradicts the collective pinning theories.

We report an investigation of the temperature-dependence of the refractive index of potassium acid phthalate (KAP) crystal. Refractive index measurements are based on a refractometer setup operating in a temperature range from 25 degrees C to 200 degrees C and using five different laser wavelengths in the visible and near-infrared. Temperature-dependent dispersion relations are proposed, with an average fitting quality that exceeds experimental accuracy, and compared to previous room-temperature Sellmeier equations. Consequently, the new relations are employed for the calculation of various linear and nonlinear optical properties of KAP. (C) 2011 Elsevier B.V. All rights reserved.

Phase transformation behavior of Ti50Ni30Cu20 shape memory alloys prepared by powder metallurgy is analyzed with respect to the duration of mechanical alloying. The processed blends were studied by differential scanning calorimetry and room temperature X-ray diffraction. The martensitic transformations evidenced by thermal scans are discussed in correlation with the relative phase content obtained from the refinement of the X-ray diffraction patterns. (c) 2011 Elsevier B.V. All rights reserved.

The paper presents the influence of pulsed laser deposition (PLD) parameters on the structural and optical properties of PZT thin films grown on platinum substrate. X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) are used to determine the thin film properties. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to get additional information. By changing the distance between target and substrate, different crystalline orientations of PZT are obtained. The thin film thickness and its roughness, as well as the refractive index are also influenced by the chosen distance. (C) 2011 Elsevier B.V. All rights reserved.

In this paper we present the morphological, structural, optical and electrical properties of aluminium doped zinc oxide films prepared by spin coating technique from a zinc acetate dihydrate and 2-methoxyethanol (0.5M) solution. AlCl3 and Al(NO3)(3) were used as doping agents in different concentrations (1at%, 4at% and 6at% in starting solution). After deposition, films were dried at 100 degrees C and then annealed at temperatures between 400 degrees C and 500 degrees C. The characterization of deposited layer was performed by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and UV-Vis spectroscopy. The results show that the optical and electrical properties of the structures strongly depend on the deposition conditions of ZnO:Al. In addition, the resistivity can be easily varied depending on ZnO:Al annealing temperatures and Al concentration.

This paper proposes to extend the exploration of mouse melanoma B16 cells death by photodynamic therapy (PDT), under irradiation with different light sources and in the presence of 5,10,15,20-tetrap-sulphonato-phenyl-porphyrin (TSPP). The viability studies showed that B16 mouse melanoma is sensitive to photodynamic damage induced by TSPP 1 mM for either one, two, three or four hours. The control had TSPP added immediately prior to timelapse imaging (no incubation). They were then irradiated with red light He-Ne laser (lambda = 632.8 nm, energy 180 J/cm(2) for 20 min). Also, it has been used a laser diode GaInAs 25 mW/cm(2), lambda = 650 nm. The cells demonstrated clear morphological changes associated with apoptosis by mitochondrial pathway. There were changes in texture, as expected. Changes appeared to occur more quickly at lamp irradiation than at HeNe and GaInAs diode laser. Addition of TSPP just prior to exposure and observation, with no incubation, did not result in changes in cell morphology or cell death. Also, the proteins changes have been observed, because those with high molecular weights have been scissored under irradiation and this could be reason of the proteins concentrating in the area of low molecular weights, and the dissapearing of the proteic band of 75 kDa in the electrophoregramm. The immunized animals with B16-TSPP had the highest survival rate (40 days) by comparison with the control (death at 20 days) or with immunized animals with supernatants B16 (death at 25 days).

The electronic properties of two-dimensional toroidal surfaces of nanometer size have been investigated by approximately solving the time-independent Schrodinger equation. The effects of the quantum confinement on the electron population of these structures were shown by studying the average electron density on the surface of the torus. The unique electron spread that resulted from such computations encouraged further study on the field emission properties of this two-dimensional manifold. The Wentzel-Kramers-Brillouin approximate approach was used for a preliminary study of the field emission properties of the nanotori for various geometrical parameters. (c) 2011 American Vacuum Society. [DOI: 10.1116/1.3531935]

Graphene sheets were prepared using electrochemical and chemical steps followed graphite electrochemical oxidation, graphite chemical oxidation, ultrasound expholiation and chemical reduction of carbon material. Films of graphene were electrophoretically deposited from aqueous dispersion on FTO electrode. These films were tested as cathode for a dye-sensitized solar cell. The morphology of the prepared products was imaged by scanning electron microscopy; the intermediate compound, graphene oxide was characterized by IR spectroscopy.

Experimental data show that the normal state resistivity of superconducting Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi-2212) whiskers increases after a 6 h irradiation by a synchrotron mu-beam with 17 keV photons. We analyse this result on the basis of previously reported effects in Bi-2212 whiskers due to ageing or heating processes. A finite element model of the experimental setup clarifies that the heat load induced by the microbeam has to be excluded as a possible cause for the material changes. The knock on the interstitial, loosely bound, O species by secondary electrons is discussed as the most likely mechanism responsible for this effect.

We investigated the anisotropy dependence of the characteristic fields of the second peak magnetization, specifically, the onset field B-on and the peak field B-sp, in Y1-xPrxBa2Cu3O7-delta single crystals. The empirical dependence arising from data analysis suggests a logarithmic dependence of both these fields on the anisotropy factor gamma which disagrees with the universal scaling law gamma(2)(B) = F(t) proposed previously. We attribute the faster decrease of the two fields at high anisotropy to the dramatic changes in the magnetic state of the system which starts to display a noticeable paramagnetic contribution at high Pr-doping, hence high anisotropy. The incipient phase separation could also reduce the elastic properties of the flux line lattice which determines onset of the second peak magnetization. (C) 2010 Elsevier B.V. All rights reserved.