Defectos superficiales en Au (001) generados mediante bombardeo iónico y nanoindentación

Tesis de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, leída el 21-05-2002Hemos estudiado los defectos superficiales en Au(001) 5x20 generados mediante dos diferentes técnicas experimentales: bombardeo iónico de baja energía y nanoindentación. Hemos analizado estos defectos con microscopía de efecto túnel (STM). Los experimentos de bombardeo de iones Ar+ con energía E=600 eV revelan que los defectos producidos a muy bajas dosis son dipolos de dislocación bidimensionales. Se forman mediante la difusión anisótropa y agregación de las vacantes generadas por cada uno de los impactos iónicos. A dosis media observamos transformaciones estructurales en la reconstrucción, que puede rotar o desaparecer. Finalmente, a altas dosis, observamos una superficie nanoestructurada, con cráteres formando un red que puede llegar a tener un cierto orden a corto alcance. Respecto a los defectos producidos por nanoindentación identificamos los mecanismos incipientes de deformación plástica en una superficie fcc (001). Por un lado, se emiten dislocaciones helicoidales que mediante deslizamiento dan lugar a terrazas alrededor del punto de indentación. Por otro lado, observados y caracterizamos la emisión, hasta distancias del orden de cientos de angstroms, de semilazos de dislocación disociados emergentes, que son fruto del desplazamiento plástico expulsado a lo largo de un sistema de deslizamiento principal del cristalDepto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

Diseño e implementación de un laboratorio virtual para el estudio de "Defectos puntuales en cristales iónicos"

El programa: Diseño e implementación de un laboratorio virtual para el estudio de "Defectos puntuales en cristales iónicos" enseña de forma interactiva las reglas de balance necesarias para escribir las ecuaciones de defectos en los cristales iónicos, usando la notación de Kröger-Vink para los defectos puntuales

Stele of Alionus. Unpublished inscription from Rabanales de Aliste (Zamora)

El municipio de Rabanales de Aliste, localizado al noroeste de la provincia de Zamora, acoge un buen número de inscripciones, principalmente estelas funerarias, que han sido objeto de estudio desde comienzos del siglo XX por diferentes investigadores. Aunque muchas de ellas han sido reutilizadas con posterioridad en paredes de casas o en la iglesia del municipio, las recientes excavaciones arqueológicas apuntan a su posible vinculación con el yacimiento de El Castrico, ocupado durante la segunda mitad del siglo I d. C. y la primera del II d. C. En este trabajo se analiza una estela funeraria inédita descubierta en 2021 empotrada en el interior de la iglesia de El Salvador, concretamente en el acceso a la base del campanario desde la nave central, que servía como sillar del dintel del vano de la puerta. Gracias al uso de técnicas novedosas como la fotogrametría digital y aplicación de análisis con SIG se ha podido leer correctamente la inscripción y descartar de la lectura algunas marcas, provocadas por las sucesivas alteraciones del bloque tras su reutilización. De esta manera, podemos minimizar el riesgo de interpretar erróneamente caracteres inexistentes en la pieza. A pesar de tratarse de una inscripción sencilla de tipo funerario, su análisis ha permitido dar a conocer la primera atestiguación del antropónimo Caraucus en el Imperio, de clara tradición celta, así como una posible relación de parentesco del tipo abuelo-padre-hijo, pudiendo completar la ascendencia familiar de otro personaje mencionado en el corpus epigráfico de Rabanales: Potitus, hijo de Alionus y nieto de Caraucus.The municipality of Rabanales de Aliste, located in the northwest of the province of Zamora, is home to a large number of inscriptions, mainly funerary stelae, which have been the focus of study since the beginning of the 20th century by various researchers. Although all of them have subsequently been reused in the wall structures of houses or in the local church, recent archaeological excavations point to their possible link with the site of El Castrico, occupied during the second half of the 1st century AD and the first half of the 2nd century AD. This paper analyses an unpublished funerary stele discovered in 2021 embedded in the interior of the church of El Salvador, specifically in the access to the base of the bell tower from the central nave, which served as an ashlar for the lintel of the doorway. Thanks to the use of innovative techniques such as digital photogrammetry and the application of GIS analysis, it has been possible to read the inscription correctly and to discard some marks caused by successive alterations to the block after its reuse. In this way, we can minimise the risk of misinterpreting non-existent characters on the part. Despite being a simple funerary inscription, its analysis has revealed the first evidence of the anthroponym Caraucus in the Roman Empire, of clear Celtic tradition, as well as a possible grandfather-father-son relationship, thus completing the family ancestry of another character mentioned in the epigraphic corpus of Rabanales: Potitus, son of Alionus and grandson of Caraucus.El presente trabajo se ha realizado en el marco del proyecto Tituli Zoelarum, galardonado por la International Digital Epigraphy Association (IDEA) en la convocatoria Small Grants 2023

Magnetism in nanometer-thick magnetite

The oldest known magnetic material, magnetite, is of current interest for use in spintronics as a thin film. An open question is how thin can magnetite films be and still retain the robust ferrimagnetism required for many applications. We have grown 1-nm-thick magnetite crystals and characterized them in situ by electron and photoelectron microscopies including selected-area x-ray circular dichroism. Well-defined magnetic patterns are observed in individual nanocrystals up to at least 520 K, establishing the retention of ferrimagnetism in magnetite two unit cells thick

Epsilon iron oxide: Origin of the high coercivity stable low Curie temperature magnetic phase found in heated archeological materials

The identification of epsilon iron oxide (-Fe2O3) as the low Curie temperature high coercivity stable phase (HCSLT) carrying the remanence in heated archeological samples has been achieved in samples from two archeological sites that exhibited the clearest evidence of the presence of the HCSLT. This uncommon iron oxide has been detected by Confocal Raman Spectroscopy (CRS) and characterized by rock magnetic measurements. Large numbers of -Fe2O3 microaggregates (in CO) or isolated clusters (in HEL) could be recognized, distributed over the whole sample, and embedded within the ceramic matrix, along with hematite and pseudobrookite and with minor amounts of anatase, rutile, and maghemite. Curie temperature estimates of around 170 degrees C for CO and 190 degrees C for HEL are lower than for pure, synthetic -Fe2O3 (227 degrees C). This, together with structural differences between the Raman spectra of the archeologically derived and synthetic samples, is likely due to Ti substitution in the -Fe2O3 crystal lattice. The -Fe2O3--Fe2O3--Fe2O3 transformation series has been recognized in heated archeological samples, which may have implications in terms of their thermal history and in the factors that govern the formation of -Fe2O3

Formation of a magnetite/hematite epitaxial bilayer generated with low energy ion bombardment

We have used a low-energy ion bombardment to fabricate an epitaxial single-crystalline magnetite/hematite bilayer grown on Au(111). This non-conventional fabrication method involves the transformation of the upper layers of a single-crystalline hematite thin film to single-crystalline magnetite, a process driven by the preferential sputtering of oxygen atoms and favoured by the good structural matching of both phases. We show the reversibility of the transformation between hematite and magnetite, always keeping the epitaxial and single- crystalline character of the films. The magnetic characterization of the bilayer grown using this method shows that the magnetic response is mainly determined by the magnetite thin film, exhibiting a high coercivity. Published by AIP Publishing

Ag-AgO nanostructures on glass substrates by solid-state dewetting: From extended to localized surface plasmons

We present here a study on the modification of morphological and plasmonic properties of Ag thin films deposited on glass substrates upon annealing in air at different temperatures. Initially, Ag films are continuous and exhibit extended surface plasmons with a resonant absorbance that depends on the film thickness. The dewetting process promotes the formation of nanoparticles with different sizes, shapes, and agglomerations states, besides a partial oxidation from Ag to AgO at surface level. The final Ag-AgO nanostructures are dependent on the annealing temperature and initial film thickness. The optical properties evolve from those typical of metallic films with high reflectivity and extended surface plasmon resonance toward localized surface plasmons characteristic of nanoparticles. The optical evolution and the final plasmonic response are evaluated according to the morphological and structural features of nanostructures. Published by AIP Publishing

A Physical optics simulator for multireflector THz imaging systems

This article presents a physical optics-based simulator for the analysis of terahertz (THz) imaging systems. The simulation starts by calculating the electromagnetic interactions inside the multireflector system and the incident field that the focusing system creates on the target under inspection. In a second step, the electric field that the modeled target scatters back to the system receiver, is also calculated. This allows to predict the imaging behavior of the system for different targets before manufacturing. The simulator results are validated by using measurements from an existing 300-GHz standoff imaging system. This contribution aims to help in the development of better imaging systems for security applications in the near future.Atlantic Research Center for Information and Communication TechnologiesMinisterio de Economía y Competitividad | Ref. TEC2015-65353-RMinisterio de Economía y Competitividad | Ref. TEC2015-73908-JINAgencia Estatal de Investigación | Ref. TEC2017-87061-C3-1-RXunta de Galicia | Ref. GRC2015/01

A combined micro-Raman, X-ray absorption and magnetic study to follow the glycerol-assisted growth of epsilon-iron oxide sol-gel coatings

[EN] Epsilon iron oxide (ε-FeO) coatings on Si(100) substrates are obtained by an easy one-pot sol-gel recipe assisted by glycerol in an acid medium. Glycerol, given its small dimensions, enables the formation of ε-FeO nanoparticles with a size of a few nanometers and the highest purity is reached in coatings after a densification treatment at 960 °C. The structural and compositional evolution up to 1200 °C is studied by confocal Raman microscopy and X-ray absorption spectroscopy techniques, correlating the existing magnetic properties. We report a novel characterization method, which allows monitoring the evolution of the precursor micelles as well as the intermediate and final phases formed. Furthermore, the inherent industrial technology transfer of the sol-gel process is also demonstrated with the ε-FeO polymorph, impelling its application in the coatings form.This work has been supported by the Ministerio de Ciencia e Innovación (MCINN, Spain) through the projects PIE: 2021-60-E-030, PIE: 2010-6-OE-013, PID2019-104717RB-I00 (2020–2022), MAT2017-86540-C4-1-R, RTI2018-095856-B-C21 (2019–2021), RTI2018-097895-B-C43 and RTI2018-095303-A-C52. The authors are grateful to The ESRF (France), MCINN and Consejo Superior de Investigaciones Científicas (CSIC, Spain) for the provision of synchrotron radiation facilities and to the BM25-SpLine Staff for their valuable help. A.S.and A.M.-N acknowledge financial support from Comunidad de Madrid (Spain) for an “Atracción de Talento Investigador” Contract 2017-t2/IND5395 and 2018-T1/IND-10360, respectivel