Albert Moreno – Page 12

Thermal analysis for low temperature synthesis of oxide thin films from chemical solutions

Written by Albert Moreno on September 6, 2013. Posted in Materials for information science and electronics, Scientific Highlights.

D. Sanchez-Rodriguez, J. Farjas, P Roura, S. Ricart, N. Mestres Andreu, X. Obradors and T. Puig Journal of Physical Chemistry C 117, 20133-20138 (2013) DOI: 10.1021/jp4049742 The possibility of synthesizing functional oxide thin films at low temperature via combustion synthesis is analyzed both experimentally and numerically. To this aim, the decomposition of several oxide precursors [copper and cerium acetates, yttrium trifluoroacetate, and In₂O₃ and La_0.7Sr_0.3MnO₃ (LSMO) nitrate based precursors] has been analyzed by thermal analysis techniques. It is shown that, although these precursors decompose via combustion when they are in the form of powders, their corresponding films show no evidence of combustion. The reason for this different behavior is clearly revealed with numerical simulations. Thin films will hardly experience combustion because the precursor front extinguishes before reaching the precursor–substrate interface leaving a “cool zone” hundreds of micrometers thick. In contrast, it is argued that thin oxide films can be obtained at temperatures lower than powders because of the enhanced gas transport mechanisms that usually limit the decomposition rate.

Soft-Chemistry–Based Routes to Epitaxial α-Quartz Thin Films with Tunable Textures

Written by Albert Moreno on June 22, 2013. Posted in Scientific Highlights.

A. Carretero-Genevrier , M. Gich , L. Picas , J. Gazquez , G. L. Drisko , C. Boissiere , D. Grosso , J. Rodriguez-Carvajal , C. Sanchez ,*

Science 17 May 2013: Vol. 340 no. 6134 pp. 827-831 DOI: 10.1126/science.1232968

Piezoelectric nanostructured quartz films of high resonance frequencies are needed for microelectronic devices; however, synthesis methods have been frustrated by the inhomogeneous crystal growth, crystal twinning, and loss of nanofeatures upon crystallization. We report the epitaxial growth of nanostructured polycrystalline quartz films on silicon [Si(100)] substrates via the solution deposition and gelation of amorphous silica thin films, followed by thermal treatment. Key to the process is the combined use of either a strontium (Sr²⁺) or barium (Ba²⁺) catalyst with an amphiphilic molecular template. The silica nanostructure constructed by cooperative self-assembly permits homogeneous distribution of the cations, which are responsible for the crystallization of quartz. The low mismatch between the silicon and α-quartz cell parameters selects this particular polymorph, inducing epitaxial growth.

Photoemission electron microscopy study of sub-200 nm self-assembled La0.7Sr0.3MnO3 epitaxial islands

Written by Albert Moreno on February 3, 2013. Posted in Materials for information science and electronics, Scientific Highlights.

J. Zabaleta, S. Valencia, F. Kronast, C. Moreno, Patricia Abellan, J. Gazquez Alabart, H. Sepehri-Amin, F. Sandiumenge Ortiz, T. Puig Molina, N. Mestres Andreu and X. Obradors Berenguer Nanoscale 5, 2990-2998 (2013) DOI: 10.1039/C3NR33346A The chemical composition and the magnetic structure of individual La0.7Sr0.3MnO3 (LSMO) ferromagnetic manganite epitaxial nanostructures less than 200 nm in width are explored using Photoemission Electron Microscopy (PEEM). X-ray absorption spectra (XAS) provide separate information on the surface and the bulk composition of the nanoislands and give evidence of Mn2+ present on the surface of otherwise stoichiometric nanostructures. Ferromagnetic domains less than 70 nm are resolved using X-ray magnetic circular dichroism (XMCD), which allows for the detection of magnetic vortex states in both (001)LSMO square and (111)LSMO triangular manganite nanoislands. The evolution of single nanostructures under an in-plane magnetic field is seen to depend on the specific nanoisland size and geometry. In particular, PEEM XMCD imaging allows detecting opposite chiralities as well as a variety of magnetization behaviors for different nanoislands.

Strain-driven broken twin boundary coherence in YBa2Cu3O7−δ nanocomposite thin films

Written by Albert Moreno on January 15, 2013. Posted in Materials for information science and electronics, Scientific Highlights.

R. Guzman, J. Gazquez, V. Rouco, A. Palau, C. Magen, M. Varela, J. Arbiol, X Obradors and T. Puig Appl. Phys. Lett. 102, 081906 (2013) http://dx.doi.org/10.1063/1.4793749 In this letter we use high resolution scanning transmission electron microscopy to study epitaxial YBa₂ Cu ₃O_7−δ (YBCO) nanocomposite thin films. We find that twin boundaries (TB) in YBCOnanocomposite thin films are disturbed by the presence of secondary phase nanoparticles as well as by intergrowths. Secondary phases promote the nucleation of TBs and, at the same time, result in bending, decreasing and changing the TB’s spacing. On the other hand, the local strain ensuing from the partial dislocation associated to Y248 and Y125 intergrowths break the verticalcoherence of TBs. This interaction results in a complex domain structure where twin boundarycoherence is no longer satisfied and twin spacing is reduced down to a few nanometers precluding vortex channeling at low temperatures.

El CSIC lidera el mayor proyecto de superconductores de la UE

Written by Albert Moreno on November 10, 2012. Posted in News.

Eurotapes (acrónimo de European development of Superconducting Tapes), busca impulsar la industria europea de la superconductividad. “Se trata de conseguir que las cintas superconductoras, los cables, los generadores y otros componentes superconductores sean suficientemente competitivos y económicos para que su uso se extienda”, explica el investigador del CSIC Xavier Obradors, director del Instituto de Ciencia de Materiales de Barcelona y líder del consorcio.

Los otros socios participantes de España son la Universidad Autónoma de Barcelona, el centro tecnológico LEITAT y las empresas Lafarga Lacambra y Oxolutia. Esta última es una spin-off del Instituto de Ciencia de Materiales de Barcelona, y será la responsable de convertir en innovación los resultados científicos que se obtengan en este centro.

Mejorar las prestaciones, reducir el coste

“Después de más de 25 años del descubrimiento de los superconductores de alta temperatura, las perspectivas de aplicaciones de estos materiales son diversas y prometedoras. No obstante, la producción a nivel industrial sigue siendo costosa, lo que impide su aplicación generalizada”, añade el investigador del CSIC.

Superar ese escollo es el principal objetivo de Eurotapes. Para ello, los laboratorios participantes, pioneros en Europa en el desarrollo de los materiales superconductores, trabajarán para obtener materiales superconductores con mejores prestaciones eléctricas y a menor coste. Lo harán mediante estrategias diversas, como modificar la estructura de las cintas superconductoras o implementar nuevas metodologías de su producción.

Los materiales conductores que se desarrollarán en Eurotapes se utilizan en diversas aplicaciones: cables para la distribución y transporte eficiente de la energía eléctrica en redes más seguras y menos invasivas; generadores para la energía eléctrica renovable (eólica en particular); imanes de campos magnéticos elevados para la biomedicina (diagnóstico mediante resonancia magnética y diseño molecular) y para instalaciones científicas (aceleradores y generación eléctrica por fusión).

Tal como explica Obradors, “si se sustituyeran los generadores convencionales por superconductores, con un solo molino eólico se conseguiría la energía equivalente a la de dos o tres. O, lo que es lo mismo, frente a un generador convencional de 4 Megavatios de potencia, un generador superconductor similar en peso y tamaño conseguiría de 10 a 12 Megavatios”.

En el campo de la distribución, el proyecto persigue aumentar las prestaciones eléctricas, magnéticas y mecánicas de las cintas superconductoras introduciendo nuevos desarrollos científicos basados en la nanotecnología. El objetivo es conseguir aumentar la corriente eléctrica que se puede transportar, sin pérdidas, incluso bajo campos magnéticos elevados.

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Growth, nanostructure and vortex pinning in superconducting YBa2Cu3O7 thin films based on trifluoroacetate solutions

Written by Albert Moreno on October 26, 2012. Posted in Materials for information science and electronics, Scientific Highlights.

X. Obradors, T. Puig Molina, S. Ricart, M. Coll Bau, J. Gazquez Alabart, A. Palau Masoliver and X. Granados Superconductor Science and Technology 25, 123001 (2012) DOI: 10.1088/0953-2048/25/12/123001 Chemical solution deposition (CSD) is a very competitive technique to obtain epitaxial films and multilayers of high quality with controlled nanostructures. Based on the strong attractiveness from the cost point of view, the production of long length coated conductors based on the CSD approach is being extensively developed. The trifluoroacetate route (TFA) is the most widely used route to achieve epitaxial YBa₂Cu₃O₇ (YBCO) layers with high critical currents, however a deep understanding of all the individual consecutive processing steps, as well as their mutual influence and relationship, is required to achieve superconducting materials with high performance. In this work, we review advances in the knowledge of all the steps relevant to the preparation of YBCO thin films based on TFA precursors as a CSD methodology: solution preparation and deposition, pyrolysis processes, intermediate phase evolution, nucleation and growth phenomena, microstructural evolution and its influence on percolating supercurrents, as well as vortex pinning by natural existing defects. Finally, we discuss the open issues still existing in the TFA approach, particularly that of film nanostructuration, and we provide a future outlook for this outstanding methodology.

Low Temperature Epitaxial Oxide Ultrathin Films and Nanostructures by Atomic Layer Deposition

Written by Albert Moreno on September 4, 2012. Posted in Materials for information science and electronics, Scientific Highlights.

M. Coll Bau, J. Gazquez Alabart, A. Palau Masoliver, M Varela, X. Obradors and T. Puig Chemistry of Materials, 24, 3723 (2012) DOI: 10.1021/cm301864c Highly epitaxial and pure (001) CeO₂ ultrathin films have been prepared by atomic layer deposition (ALD) at 275 °C on Y-stabilized ZrO₂ cubic fluorite single crystal substrate using cerium β-diketonate (Ce(thd)₄) and ozone (O₃) as precursors. Substrate temperature and precursor pulses have been optimized to set the ALD window obtaining a growth per cycle of ≈0.2 Å/cycle. This extremely low growth rate has been identified as a key parameter to ensure epitaxial growth at these low temperatures. Post-thermal treatments at 900 °C in oxygen further improve ALD-CeO₂ film texture while maintaining film stoichiometry and ultrasmooth surface, rms < 0.4 nm. ALD-CeO₂ thin film growth has also been tested on perovskite single crystal substrates, SrTiO₃ and LaAlO₃, exhibiting CeO₂ epitaxial growth and thus validating ALD as an outstanding method for low temperature epitaxial growth. Furthermore, we demonstrate that by combining e-beam lithography and ALD it is feasible to obtain size-controlled CeO₂ nanostructures.

Facile and efficient one-pot solvothermal and microwave-assisted synthesis of stable colloidal solutions of MFe2O4 spinel magnetic nanoparticles

Written by Albert Moreno on July 25, 2012. Posted in Materials for information science and electronics, Scientific Highlights.

E. Solano, F. Perez-Mirabet, R. Martínez-Julián, R. Guzman, J Arbiol, T. Puig Molina, X. Obradors Berenguer, R. Yanez, A. Pomar Barbeito, S. Ricart and J. Ros Journal of Nanoparticle Research 14, 1034 (2012) DOI: 10.1007/s11051-012-1034-y Well-defined synthesis conditions of high quality MFe₂O₄ (M = Mn, Fe, Co, Ni, Zn, and Cu) spinel ferrite magnetic nanoparticles, with diameters below 10 nm, have been described based on facile and efficient one-pot solvothermal or microwave-assisted heating procedures. Both methods are reproducible and scalable and allow forming concentrated stable colloidal solutions in polar solvents, but microwave-assisted heating allows reducing 15 times the required annealing time and leads to an enhanced monodispersity of the nanoparticles. Non-agglomerated nanoparticles dispersions have been achieved using a simple one-pot approach where a single compound, triethyleneglycol, behaves at the same time as solvent and capping ligand. A narrow nanoparticle size distribution and high quality crystallinity have been achieved through selected nucleation and growth conditions. High resolution transmission electron microscopy images and electron energy loss spectroscopy analysis confirm the expected structure and composition and show that similar crystal faceting has been formed in both synthetic approaches. The spinel nanoparticles behave as ferrimagnets with a high saturation magnetization and are superparamagnetic at room temperature. The influence of synthesis route on phase purity and unconventional magnetic properties is discussed in some particular cases such as CuFe₂O₄, CoFe₂O₄, and ZnFe₂O₄.

2012

Written by Albert Moreno on February 25, 2012. Posted in Outreach.

Title: Cent anys de superconductivitat: acaronant un somni Authors: X. Obradors Conference Name: Real Academia de Ciències i Arts de Barcelona (RACAB) Place: Barcelona Date: January 2012 Title: Nanotecnologia i Nous Materials Authors: S. Ricart Conference Name: Programa El CSIC a l’aula Place: Institut Celesti Bellera Date: 14 April 2012 Title: “Nous Materials: La superconductivitat” Authors: M. Coll Conference Name: Programa El CSIC a l’aula Place: Escola Garbí Pere Vergés, Badalona Date: 03 May 2012 Title: Local lattice strain as a source of a novel vortex pinning mechanism in superconducting YBa2Cu3O7 nanocomposites Authors: T. Puig Conference Name: Regensburg University, Physics Department Colloquium Place: Germany Date: July 2012 Title: S/TEM of Nanomaterials Authors: J. Arbiol Conference Name: “Transmission Electron Microscopy of Nanomaterials” 12th TEM-UCA European Summer Workshop Place: Puerto Real (Cadiz, Spain) Date: 9 July 2012 Title: Polarity assignment in ZnTe, GaAs, ZnO and GaN-AlN nanowires from direct dumbbell analysis Authors: J. Arbiol Conference Name: Massachussets Institute of Technology (MIT) Place: Cambridge (USA) Date: 26 July 2012 Title: “Veure els àtoms de prop: un viatge al nanomon” Authors: J. Arbiol Conference Name: ICMAB a l’Escola Place: Escola Manyanet Molins – Sant Miquel Arcàngel, Molins de Rei Date: 04 October 2012 Title: “Veure els àtoms de prop: un viatge al nanomon” Authors: J. Arbiol Conference Name: ICMAB a l’Escola (Jornades Professors Institut) Place: Bellaterra Date: 21 November 2012 Title: 2011, 2012, 2013: Tres anys de celebracions en superconductivitat Authors: X. Granados Conference Name: Seminari Formatiu per a professors de Física i Química, Organitza: Museu Nacional de la Ciència i de la Tècnica de Catalunya Place: Terrassa (Spain) Date: 30 November 2012 Title: Materials superconductors i algunes aplicacions Authors: X. Granados Conference Name: Seminari d’introducció a la ciència de Materials Place: Cerdanyola del Valles, Spain Date: 21 November 2012 Title: Seminari formatiu per a professors de física i química Authors: X. Granados Conference Name: Museu Nacional de la Ciència i de la Tècnica de Catalunya Place: Terrassa (Spain) Date: 30 November 2012 Title: La Tecnologia superconductora dins la distribució i el transport elèctric Authors: X. Granados Conference Name: Col•legi oficial d’Enginyers Tècnics Industrials de Madrid Place: Madrid (Spain) Date: 29 November 2012 Title: Synchrotron radiation: An eye within the nanomaterials world Authors: X. Obradors Conference Name: Sincrotró ALBA Place: Cerdanyola, Spain Date: November 2012 Title: Technology transfer opportunities at ICMAB based on nanomaterials Authors: X. Obradors Conference Name: Esade Creápolis Place: Sant Cugat del Vallés, Spain Date: November 2012 Title: Synchrotron radiation: An eye within the nanomaterials world Authors: X. Obradors Conference Name: Sincrotró ALBA Place: Barcelona Date: November 2012

Guided vortex motion in YBa2Cu3O7 thin films with collective ratchet pinning potentials

Written by Albert Moreno on January 13, 2012. Posted in Materials for information science and electronics, Scientific Highlights.

A. Palau, C. Montón, V. Rouco, X. Obradors and T. Puig Phys. Rev. B 85, 012502 (2012) DOI: http://dx.doi.org/10.1103/PhysRevB.85.012502 We investigate guided vortex motion in high-temperature YBa2Cu3O7 thin films patterned with an array of asymmetric blind antidots. A preferential vortex motion along spatial asymmetric pinning potentials has been directly observed by changing the driving current direction. Transport measurements reveal that effective ratchet potentials are created by fixed vortices strongly pinned within the antidots while the spatial asymmetry is transferred to interstitial vortices. We study a novel ratchet system that requires vortex-vortex interactions to work, in contrast with the individual vortex effects studied in conventional ratchet systems. By tuning the magnetic field and temperature, we are able to control the transition from a single vortex pinning regime to a region where collective effects become important and determine the range where the rectification effect is activated.

Author: Albert Moreno