Suchergebnisse

Electrical and Hall resistivity studies have been carried out on a new class of melt-spun, Al-T-R, Al-rich (above 75 at. %) ternary amorphous alloys in order to study the possible correlation between their electronic and enhanced mechanical properties. We find for all these alloys (over 26 of them) the room-temperature Hall coefficient has a negative sign and increases significantly in magnitude with the (T-R) content, which indicates a decrease in the effective carrier concentration. This is consistent with the suggestion that the observed remarkable mechanical properties in these alloys are due to the enhanced strength of the additional local Al-T and AL-R bonds. In these alloys the electrical resistivity at room temperature increases from about 65 μΩ cm for the binary Al90(R)10 amorphous alloys to over 250 μΩ cm on further substitution of Al with less than 15 at. % of T elements. From a systematic study the importance of s-d scattering mechanism and a crossover in the electronic properties from s- to d-band amorphous metal with T substitution are discussed. ; It is our pleasure to acknowledge many valuable discussions with Professor Y. Makino during this work. We also acknowledge the keen interest and many comments on this work from Professor J. S. Munoz, Autonoma University of Barcelona. One of us (M.P.) is thankful to the Spanish Government for support. Work in Sweden has been supported through a research grant from the Swedish Board for Technical Development, STU, under a >ram program> on rapid solidification technology. ; Peer Reviewed

10 págs.; 11 figs.; invited paper ; In this work, we report the near infrared and upconversion emissions of Er3+-doped transparent fluorotellurite glass- ceramics obtained by heat treatment of the precursor Er-doped TeO2-ZnO-ZnF2 glass. Structural analysis shows that ErF3 nanocrystals nucleated in the glass-ceramic sample are homogeneously distributed in the glass matrix with a typical size of 45±10 nm. The comparison of the fluorescence properties of Er3+-doped precursor glass and glass-ceramic confirms the successful incorporation of the rare-earth into the nanocrystals. An enhancement of the red upconversion emission due to 4F9/2¿4I15/2 transition together with weak emission bands due to transitions from 2H9/2, 4F3/2,5/2, and 4F7/2 levels to the ground state are observed under excitation at 801 nm in the glass-ceramic sample. The temporal evolution of the red emission together with the excitation upconversion spectrum suggest that energy transfer processes are responsible for the enhancement of the red emission. © 2015 SPIE ; We deeply acknowledge A. Ruiz-Caridad from the Laboratory of Electron Nanoscopies (LENS, University of Barcelona) and A. Tomas from the National Centre for Metallurgical Research (CENIM, CSIC) for HRTEM and EDX analysis, respectively. This work was supported by the Spanish Government MEC under Projects No. TEC2012-38901- C02-01, FIS2011-27968, MAT2013-48246-C2-2-P and Basque Country Government IT-659-13. A. Miguel and R. Morea acknowledge FPI grants from the Spanish Government. ; Peer Reviewed

In this work we present, for the first time to our knowledge, laser emission under wavelength selective laser-pulsed pumping in Nd3+-doped TeO2-ZnO-ZnF2 bulk glass for two different Nd3+ concentrations. The fluorescence properties of Nd3+ ions in this matrix which include, Judd-Ofelt calculation, stimulated emission cross-section of the laser transition and lifetimes are also presented. The site-selective emission and excitation spectra along the 4I9/2-4F3/2 absorption band show the inhomogeneous behaviour of the crystal field felt by Nd3+ ions in this fluorotellurite glass which allows for spectral tuning of the laser output pulse as a function of the pumping wavelength. The emission cross-section obtained from the Judd-Ofelt analysis and spectral data (4.9x10-20 cm2) is in fairly good agreement with the value obtained from the analysis of the laser threshold data (4x10-20 cm2). © 2013 Optical Society of America ; This work was supported by the Spanish Government MEC under Projects No. MAT2009- 14282-C02-02, MAT2009-14282-C02-01, FIS2011-27968, Consolider SAUUL CSD2007- 00013, and Basque Country Government (IT-659-13 and SAIOTEK S-PE12UN016). ; Peer Reviewed

[Full-text paper not available yet] ; The dynamics and the reactivity of the plasma produced during pulsed laser ablation of LiNbO3 have been investigated. Optical emission spectroscopy combined with time-gated imaging with high spatial resolution is applied to the study of the factors that influence the plasma expansion process, the dynamics of the ejected species the influence of a background atmosphere (O2 and Ar) and the reactivity of the expanding plasma. Direct evidence for O2 dissociation occurring during expansion is presented and the temporal evolution of the spatial distribution of the dissociated O2 is studied in detail. The influence of dissociation and velocities of the ablated species on the quality of thin films grown by pulsed laser deposition are discussed. ; This work was partially funded by CICYT (Spain), under Project No. TIC 2002-03235 and by European Union under Project No. HPRN-CT-2002-00328. ; Peer reviewed

We report a hybrid imaging technique capable of performing measurements of the spatial, temporal, and spectral emission characteristics of laser-induced plasmas by use of a single detection system. We apply this technique to study the plasma produced by laser ablation of LiNbO3 and observe phenomena not seen in such detail with standard instruments. These include extreme line broadening up to a few nanometers accompanied by self-absorption near the target surface, and expansion dynamics that differ strongly between the different species. Overall, the wealth of quantitative information provided by this novel technique sheds new light on processes occurring during plasma expansion. © 2004 Optical Society of America. ; G. Epurescu acknowledges funding by the European Union (HPRN-CT-2000-00160). ; Peer Reviewed

5 pages, 4 figures, 1 table. ; We demonstrate that optical extinction spectroscopy can be used to determine the effective shape of Cu nanocrystals (NCs) embedded in a transparent amorphous Al2O3 host both produced by pulsed laser deposition. The axial ratio of the NCs was extracted from the positions of the surface plasmon modes of the optical extinction spectra of the nanocomposite film. Comparison to the results obtained by grazing incidence small angle x-ray scattering shows excellent agreement. Thus, optical spectroscopy can be used as a simple, easily accessible, and versatile tool for the characterization of the NCs that form nanocomposite films. ; This work was supported by the European Union (BRITE Project No. 98-0616). ; Peer reviewed

7 pags. ; 7 figs. ; 1 tab. ; Structured nanocomposite films consisting of five Fe layers embedded in an amorphous Al2O3 matrix (Fe:Al₂O₃) have been grown by sequential pulsed laser deposition. The formation of well isolated quasispherical nanocrystals is observed for samples with Fe content per layer close to 6.5×10¹⁵ atoms/cm². Increasing the Fe content leads first to the formation of elongated nanocrystals and then to quasicontinuous layers. The evolution in the shape and size of the nanocrystals is reflected in the magnetic behavior of these systems. A crossover from a low temperature ferromagnetic regime to a high temperature superparamagnetic regime is observed at a temperature of 23 K in the samples containing isolated quasi-spherical nanocrystals. In this case, a reduced moment per Fe atom (1.4 μβ/atom) with respect to the value for α-Fe (2.2 μβ/atom) is estimated. This behavior is attributed to the presence of a Fe-oxide surface shell on the nanocrystals. The large values of the estimated effective magnetic anisotropy (1.4×10⁶ J/m³) and the low temperature coercivity in these samples are attributed to a strong surface contribution to anisotropy, whereas the temperature dependence of coercivity is attributed to thermal activation. ; This work has been partially supported by the European Union (BRITE Project No. 98-0616) and the Spanish CICYT~TIC Project No. 99-0866. One of the authors (N. M. D.) had a Marie Curie fellowship from the European Union. The authors acknowledge the support of the French and Spanish governments (HF1998-0055) and the British Council-Spanish government (HB1998-0182) Integrated Actions scheme for travel. ; Peer reviewed