National Institute Of Materials Physics - Romania

Glass-ceramics containing RE3+-doped BaF2 nanocrystals (RE = Eu, Sm, Dy, Ho and Pr) with the size below 10 nm size have been made by using the controlled crystallization at higher temperatures of the RE3+-doped SiO2-BaF2 xerogels. Photoluminescence measurements have indicated the incorporation of the RE3+ ions in both silica network and in the BaF2 nanocrystals. Thermoluminescence measurements have shown a peak whose position depends on the nature of RE3+-dopant as it follows: 140 degrees C (for Ho3+, Dy3+), 340 degrees C (for Sm3+) and 370 degrees C (for Eu3+); in Eu3+-doped SiO2 glass the TL peak is shifted to 383 degrees C. The peaks in glass-ceramics were assigned to the recombination of the electrons thermal released from the RE3+-electron traps located in both glass-matrix and BaF2 nanocrystals. Within the series the trivalent lanthanide ions act as increasingly deeper electron trapping centres. (C) 2011 Elsevier B.V. All rights reserved.

New polymeric chelate structures derived from maleic anhydride-dicyclopentadiene copolymer (MA-DCPD) were synthesized by chemical modifications with triethylenetetramine ( TETA), from Riedel De HaSn AG Seelze, Hannover. Germany. Both amide and imide forms of these new polymers have been tested in the retention process of Cr (III) ions. Experimental results referring mainly to the retention capacity and retention efficiency, for different values of the working parameters: contact procedure, batch time, concentration of chelators, and pH, are presented. The polymer structures and their metal complexes were characterized by IR spectroscopy. IR spectra proved that the metal was coordinated by nitrogen from TETA. The thermal properties of modified polymers and polychelates were also examined. Based on these experimental results and literature data, we discuss a possible binding mechanism and suggest the polychelate structures. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121:1867-1874, 2011

It is shown that the short-circuit photocurrent measured under illumination in Pb(Zr,Ti)O-3 epitaxial films is strongly dependent on the metal used as the top electrode. The magnitude of the photocurrent varies by more than 2 orders of magnitude from Pt (largest signal) to Al (smallest signal). The differences are for both directions of polarization. The imprint is also dependent on the top metal electrode, with a direct effect on the shape of the spectral distribution. The results support the hypothesis that the origin of the photovoltaic effect in ferroelectric thin films is different from that of the anomalous photovoltaic effect observed in bulk ceramics and single crystals. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624738]

Under certain conditions, we prove the existence of a steady-state transport regime for interacting mesoscopic systems coupled to reservoirs (leads). The partitioning and partition-free scenarios are treated on an equal footing. Our time-dependent scattering approach is exact and proves, among other things, the independence of the steady-state quantities from the initial state of the sample. Closed formulas for the steady-state current amenable for perturbative calculations with regard to the interaction strength are also derived. In the partitioning case, we calculate the first-order correction and recover the mean-field (Hartree-Fock) results.

The aim of this study is to investigate the micrometer and submicrometer scale structuring of silicon by liquid chlorine and fluorine precursors with 200 fs laser pulses working at both fundamental (775 nm) and frequency doubled (387 nm) wavelengths. The silicon surface was irradiated at normal incidence by immersing the Si (111) substrates in a glass container filled with liquid chlorine (CCl(4)) and fluorine (C(2)Cl(3)F(3)) precursors. We report that silicon surfaces develop an array of spikes with single step irradiation processes at 775 nm and equally at 387 nm. When irradiating the Si surface with 400 pulses at 330 mJ/cm(2) laser fluence and a 775 nm wavelength, the average height of the formed Si spikes in the case of fluorine precursors is 4.2 mu m, with a full width at half maximum of 890 nm. At the same irradiation wavelength chlorine precursors develop Si spikes 4 mu m in height and with a full width at half maximum of 2.3 mu m with irradiation of 700 pulses at 560 mJ/cm(2) laser fluence. Well ordered areas of submicrometer spikes with an average height of about 500 nm and a width of 300 nm have been created by irradiation at 387 nm by chlorine precursors, whereas the fluorine precursors fabricate spikes with an average height of 700 nm and a width of about 200 nm. Atomic force microscopy and scanning electron microscopy of the surface show that the formation of the micrometer and sub-micrometer spikes involves a combination of capillary waves on the molten silicon surface and laser-induced etching of silicon, at both 775 nm and 387 nm wavelength irradiation. The energy-dispersive x-ray measurements indicate the presence of chlorine and fluorine precursors on the structured surface. The fluorine precursors create a more ordered area of Si spikes at both micrometer and sub-micrometer scales. The potential use of patterned Si substrates with gradient topography as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell adhesion and growth is envisaged. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3619856]

Rare-earth doped xerogels (Eu3+, Sm3+, Ho3+, Pr3+) were prepared by using the sal-gel method and their magneto-optical and optical properties have been studied. The Magnetic Circular Dichroism (MCD) spectra are quite similar to those recorded in the RE-doped fluorozirconate glasses; the fine structures shown by the MCD spectra are better resolved compared to the optical absorption spectra. The MCD technique has been correlated with optical measurements in order to investigate the site symmetry in the particular case of Eu3+-doped xerogel and oxyfluoride glasses. In the xerogel, coordination symmetry around the Eu3+ ions is close to (D) under bar (3h) and is lower in the oxyfluoride glass. (C) 2011 Elsevier B.V. All rights reserved.

Nanocrystalline Ho-doped BaTiO3, with average nanocrystals size of 20 nm, have been prepared using a sol-gel combustion technique. The structural and morphological properties of the powders have been investigated by X-ray powder diffraction and high resolution transmission electron microscopy. Chemical states of the holmium on the Ba0.97Ho0.03TiO3 ceramic surface were analyzed using X-ray photoelectron spectroscopy. Furthermore, their photoluminescence properties were analyzed.

In the so-called 'step-shape' angular spin distribution model for layered systems, the non-collinear directions of the atomic magnetic moments are confined to the film plane and form a homogeneous fan spanning inside an (in-plane) angular interval Delta phi centered at an angle phi(0). A general approach for deriving the two parameters phi(0) and Delta phi via Fe-57 Mossbauer spectroscopy measurements is discussed. The analysis extends our previously reported treatment, which assumed that the angular aperture Delta phi develops symmetrically versus a fixed direction phi(0) (e.g., the in-plane easy axis of magnetization) oriented either along or perpendicular to the in-plane projection of the Mossbauer gamma-ray direction. The proposed approach is also applicable for those cases when not only the spin aperture Delta phi is changing but also the aperture center phi(0) is rotating under the influence of different external parameters, such as applied field, temperature, stress, etc. The method is suitable for applications to nanoscale layered heterostructures with in-plane uniaxial or unidirectional magnetic anisotropy. The method is applied to experimental data obtained on a 2-nm thick defected Fe layer with in-plane magnetic texture. (C) 2011 Elsevier B.V. All rights reserved.

Clean Si(001) single crystal surfaces provided different surface reconstructions: p(1 x 2) and c(n x 2) (n = 4, 6) at room temperature. The in situ oxidation of these surfaces was followed by Auger electron spectroscopy and by X-ray photoelectron spectroscopy. It is found that, in similar ultrahigh vacuum conditions, much faster contamination (about 500 times) occurs when the samples are investigated by AES than by XPS, owing to the interaction of the electron beam with the sample surface. With the sample subject to the AES investigation, the contamination occurs by forming >Si2C=O complexes based on the Si dimers. During XPS, reaction with water molecules from the residual gas should also be taken into account.