Formation of epitaxial BaTiO3/SrTiO3 multilayers grown on Nb-doped SrTiO3 (001) substrates

The formation of epitaxial BaTiO3/SrTiO3 multilayers; is studied in terms of the growth mechanism by investigating surface morphologies, crystalline orientations, microstructures, and structures of the interfaces, as well as by determining the dielectric properties. Under specific conditions, the epitaxial BaTiO3 films follow a layer-then-island (Stranski-Krastanov) mechanism on SrTiO3 (001)-oriented substrates. In view of actual efforts made to grow epitaxial superlattices involving very thin individual layers of BaTiO3 and/or SrTiO3, we have determined that the BaTiO3 films Of up to 6,nm thickness do not show any defects and have a sharp BaTiO3-on-SrTiO3 interface. On the contrary, SrTiO3-on-BaTiO3 interfaces within multilayers are rough, probably due to the different growth mechanisms of the two different materials, or due to a difference in the morphological stability of the growth surfaces caused by different surface energies of BaTiO3 and SrTiO3 and by different mobilities of the Ba and Sr atoms reaching the SrTi3 and BaTiO3 layers, respectively.

Initial growth stages of epitaxial BaTiO3 films on vicinal SrTiO3 : Nb (001) substrates

The growth mechanism of epitaxial BaTiO3 films on vicinal Nb-doped SrTiO3 (srTiO(3):Nb) (001) substrate surfaces was studied in terms of surface morphology, crystalline orientation, microstructure, and film/substrate interface. Well-oriented BaTiO3 thin films were grown on SrTiO3 substrates with well-defined terraces by pulsed laser deposition. The regularly terraced TiO2-terminated surfaces of vicinal SrTiO3:Nb (001) substrates were prepared by a definite chemical and thermal treatment. Under our conditions, BaTiO3 seems to grow with a layer-then-island (Stranski-Krastanov) growth mechanism. In order to investigate the orientation and crystallinity of the BaTiO3 films, x-ray diffraction and high-resolution transmission election microscopy were performed. Ferroelectricity of the BaTiO3 films was proved by electrical measurements performed on Pt/BaTiO3/SrTiO3:Nb heterostructures.

2010_2010051611-001.DOC

Doctrina

Coverage effects on the magnetism of Fe/MgO(001) ultrathin films

Different aspects of the structure-magnetism and morphology-magnetism correlation in the ultrathin limit are studied in epitaxial Fe films grown on MgO(001). In the initial stages of growth the presence of substrate steps, intrinsically higher than an Fe atomic layer, prevent the connection between Fe islands and hence the formation of large volume magnetic regions. This is proposed as an explanation to the superparamagnetic nature of ultrathin Fe films grown on MgO in addition to the usually considered islanded, or Vollmer-Weber, growth. Using this model, we explain the observed transition from superparamagnetism to ferromagnetism for Fe coverages above 3 monolayers (ML). However, even though ferromagnetism and magnetocrystalline anisotropy are observed for 4 ML, complete coverage of the MgO substrate by the Fe ultrathin films only occurs around 6 ML as determined by polar Kerr spectra and simulations that consider different coverage situations. In annealed 3.5 ML Fe films, shape or configurational anisotropy dominates the intrinsic magnetocrystalline anisotropy, due to an annealing induced continuous to islanded morphological transition. A small interface anisotropy in thicker films is observed, probably due to dislocations observed at the Fe¿MgO(001) interface.

MgO/Ag(001) interface structure and STM images from first principles

The interface of MgO/Ag(001) has been studied with density functional theory applied to slabs. We have found that regular MgO films show a small adhesion to the silver substrate, the binding can be increased in off-stoichiometric regimes, either by the presence of O vacancies at the oxide film or by a small excess of O atoms at the interface between the ceramic to the metal. By means of theoretical methods, the scanning tunneling microscopy signatures of these films is also analyzed in some detail. For defect free deposits containing 1 or 2 ML and at low voltages, tunnelling takes place from the surface Ag substrate, and at large positive voltages Mg atoms are imaged. If defects, oxygen vacancies, are present on the surface of the oxide they introduce much easier channels for tunnelling resulting in big protrusions and controlling the shape of the image, the extra O stored at the interface can also be detected for very thin films.

El Acto Legislativo 001 de 2003 y el comportamiento electoral de partidos y movimientos políticos, en las elecciones a la Cámara de Representantes 2002 y 2006. Estudio de caso : Antioquia

El presente trabajo tiene como objetivo mostrar los efectos del acto legislativo 01 de 2003, en las elecciones a la Cámara de Representantes de 2006 en el Departamento de Antioquia. Esto con el fin de mostrar el comportamiento de los partidos y movimientos políticos antes y después de entrar en vigencia la reforma. El objetivo principal de la investigación es identificar y entender la cotidianidad y las prácticas políticas a las que los partidos tradicionales y las nuevas organizaciones estaban acostumbradas después de la constitución de 1991. Estas reglas de juego planteadas por las Constitución Política, cambiaron el panorama político tanto para los partidos tradicionalistas, como para las nuevas organizaciones que querían y reclamaban reconocimiento, participación y poder. Reglas que se transformaron con la reforma política, y específicamente con el Acto legislativo 01 de 2003, cambiando el escenario político y por ende el comportamiento electoral.

EdShare workshop 001

Materials and links related to staff workshop on using EdShare.

Implantación de un sistema de gestión ambiental de acuerdo con la Norma UNE-EN ISO 14 001: 2004 en institutos de secundaria : una experiencia en IES Ramón y Cajal, de Valladolid.

Se presentan las principales fases del proyecto de implantación de un sistema de gestión ambiental de acuerdo con al normativa española, en el IES Ramón y Cajal de Valladolid. En una primera fase se procede al diagnóstico ambiental inicial y a la formación por objetivos y áreas de trabajo de los grupos establecidos. A continuación, se procede a la elaboración de la documentación necesaria, entre ella, la política ambiental del IES, y la implantación del sistema. La fase de seguimiento del sistema se realiza a través de auditorías internas y revisiones por parte de la dirección. Finalmente, se obtiene la certificación de la norma por parte de SGS.

Inconstitucionalidad por omisión en la jurisprudencia de la Corte Constitucional ecuatoriana. Sentencia No. 001-1L-SIO-CC (caso No. 0005-10-IO) [Jurisprudencia]

El presente trabajo pretende mostrar de manera objetiva y técnica, las motivaciones, contenidos y demás elementos de sustento utilizados por la Corte Constitucional ecuatoriana en el control abstracto de inconstitucionalidad por omisión normativa. Previo el análisis de la sentencia se presentan conceptos relativos al control de constitucionalidad por omisión en el derecho comparado y en la doctrina, además se hace un breve recorrido histórico del aparecimiento de la mencionada institución jurídica. Finalmente, se revisa la sentencia en cada una de sus partes y se van describiendo los aspectos más relevantes y conflictivos.

Análisis de la sentencia n.º 001-10-SIN-CC. Casos n.º 0008-09-IN y 0011-09-IN sobre acción de inconstitucionalidad en contra de la Ley de Minería y efectos posteriores (Jurisprudencia)

This paper aims to analyze the decision issued by the Constitutional Court for Transition within the unconstitutionality presented against the Mining Act. Proponents, in the main, formal allege unconstitutional by the Mining Law have been issued by the Committee on Legislation and Oversight (National Assembly during the Transitional Period after the adoption of the 2008 Constitution) without the prior execution of a legislative pre query, this query being a collective right of national, indigenous peoples and communities recognized in Article 57 paragraph 17 of the Constitution of the Republic. The Constitutional Court ruled Transition to reject the unconstitutionality confirming the constitutionality of the regulatory body and the substantial and non-formal pre-legislative consultation.

Scanning tunneling microscopy and molecular dynamics study of the Li2TiO3(001) surface

We have investigated the (001) surface structure of lithium titanate (Li2TiO3) using auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). Li2TiO3 is a potential fusion reactor blanket material. After annealing at 1200 K, LEED demonstrated that the Li2TiO3(001) surface was well ordered and not reconstructed. STM imaging showed that terraces are separated in height by about 0.3 nm suggesting a single termination layer. Moreover, hexagonal patterns with a periodicity of ∼0.4 nm are observed. On the basis of molecular dynamics (MD) simulations, these are interpreted as a dynamic arrangement of Li atoms.