Home > Seminars
Inicio > Seminarios |
|
Seminars of the Research Lines
Nanostructures, Surfaces and Coatings
|
22 May 2012, 12:00 h. Salón de Actos
EL ULTRA ALTO VACÍO Y LOS GRANDES ACELERADORES DE PARTÍCULAS
José L. de Segovia
Instituto de Ciencia de Materiales de Madrid CSIC |
| Se presenta el descubrimiento del ultra alto vacío y su impacto en el desarrollo de los grandes sistemas de vacío, especialmente los aceleradores de partículas, anillos de almacenamiento de partículas (radiación sincrotrón), y sistemas de fusión termonuclear. Entre los primeros se presentan las características y los medios de lograr presiones tan bajas como 10-12 mbar del “Large Hadron Collider” (Gran Colisionador de Partículas”) del CERN en un sistema de vacío circular de 56 km de longitud, que permite obtener partículas con una energía de 14 TeV ! (109eV). Se describe su revolucionario sistema de vacío y el desarrollo de tecnologías muy específicas para lograr esa presión tan baja. A continuación se describen las particularidades de los “anillos de almacenamiento de partículas”, conocidos como “Sincrotrón”, como trabajan y en qué condiciones se puede obtener el ultra alto vacío necesario. Por último, se presenta la “máquina” llamada “TOKAMAK” donde se pretende crear un “plasma” de tal temperatura que permita la “fusión termonuclear”, pero con problemas físico-químicos que impiden, de momento, llegar a esa temperatura. |
 |
28 February 2012, 12:00 h. Sala de Seminarios, 182
Morphology analysis of nanoscale island arrays grown by MBE on flat and patterned Si(001) surfaces
Alejandro González-González
Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC) |
| Building up patterns at the nanoscale in a controlled manner attracts scientific and technological interest as an appropriate route for tailoring relevant functional properties of surfaces. Nano-engineering processes are often focused on a combination of top-down/bottom-up strategies, in which any self assembling phenomena of the synthesis procedure is promoted by substrate pre-patterning. Here we report on the formation of Si island arrays on planar and pit-patterned areas of Si(001) substrates. Patterns are prepared by electron beam lithography and reactive ion etching. Thin Si layers are grown by molecular beam epitaxy (MBE) on these surfaces, using conditions that promote the formation of nanoscale pyramid-like islands. The effect of the pre-pattern and Si growth parameters on the morphology of the resulting island ensembles is studied by atomic force and scanning electron microscopies (AFM, SEM). AFM measurements are combined with an improved topographic image processing procedure. Examples of surface orientation maps, statistical analysis of the exposed surface facets and total island volume calculations obtained with this image tessellation method are presented. This quantitative study is used, e.g. to discuss the formation of deep trenches around some pyramids on planar substrates. |
|
16 February 2012, 16:00 h. Sala de Seminarios, 182
Resonant Inelastic Soft X-ray Scattering with Vibrational Resolution - On the road to in-situ soft x-ray RIXS
Annette Pietzsch
Directora de la línea de sincrotrón I511 en MAX-LAB |
| The function of complex molecular systems is to a great deal governed by the local electronic and dynamic properties of different molecular building blocks. With Resonant Inelastic X-ray Scattering (RIXS) it is possible to access the site-specific electronic structure information on the atomic length scale. As a photon-in/photon-out technique, it is also ideally suited for the investigation of liquids. However, the lack of adequate sources has up to now limited the direct access to information about local coordination and dynamics leaving a major part of the inherent potential unused.
We present RIXS spectra of liquids (acetone, water) and gases (O2, CO2) excited at the oxygen K-edge with a resolution o of E/dE~10000. For the first time, we are able to resolve single vibrational modes, opening a wealth of new possibilities such as mapping local potential energy surfaces of the electronic ground state which no other technique can access. Highly energy resolved spectra obtained at the ADRESS beamline at the SLS are presented along with ab-initio multimode scattering calculations that resemble the data in very high detail. |
|
03 February 2012, 12:00 h. Sala de Seminarios, 182
Ionoluminescence as a powerful tool to study the damage produced by swift heavy ions
Ovidio Y. Peña Rodríguez
Centro de Micro-Análisis de Materiales CMAM - UAM |
| Luminescence is a very sensitive technique, often applied for characterization of dielectric and semiconductor materials. It provides information on the electronic structure of the solid, particularly on intra-gap levels associated to impurity and defect centers, such as those introduced by irradiation. Specifically, the luminescence induced by ion-beam irradiation, commonly named ionoluminescence (IL), is an appropriate technique to investigate the microscopic processes accompanying the generation of damage, its kinetic evolution with the irradiation fluence, and the formation of color centers. It can be considered as an Ion Beam Analysis (IBA) technique that is complementary to Rutherford backscattering spectrometry (RBS), particle-induced X-ray emission (PIXE), and nuclear reaction analysis (NRA) methods. However, IL is far less used that the other IBA techniques because the analysis of the IL data is more complex and requires theoretical methods not yet sufficiently developed. The capabilities and limitations of IL for tracking the damage induced by swift heavy ions will be discussed in this talk. Its usage is exemplified mainly for silica and α-quartz; however, there is no reason limiting its application for other materials. The experiments were performed in the 5 MV tandetron accelerator installed at CMAM. Various elements (B, O, F, Cl and Br) were used for the irradiations, with energies ranging from 3 to 25 MeV. |
|
23 January 2012, 12:00 h. Sala de Seminarios, 182
Caracterización de materiales a escala nanométrica mediante Atom Probe Tomography
María Angustias Auger Martínez
Departamento de Física. Universidad Carlos III de Madrid |
Actualmente, la técnica Atom Probe Tomography es la única que permite identificar la especie atómica de átomos individuales y reconstruir la estructura tridimensional del volumen analizado. Esta técnica de caracterización microestructural de ultra-alta resolución proporciona valiosa información acerca de la composición, tamaño, morfología y densidad de precipitados ultrafinos en un material, distribución de impurezas, segregación de elementos en fronteras de grano u otras interfases, etc. Inicialmente sólo metales, semiconductores y algunas cerámicas podían ser caracterizados mediante Atom Probe Tomography, pero la introducción de nuevas técnicas de preparación de muestras como el FIB (Focused Ion Beam) y las continuas mejoras en los equipos de análisis han supuesto un importante aumento en su rango de aplicación.
En este seminario se intentará dar una visión general de la técnica Atom Probe Tomography desde sus inicios hasta el estado actual, mostrando los fundamentos de la misma, aspectos importantes de la preparación de muestras y ejemplos de sorprendentes resultados obtenidos en diferentes materiales. |
|
|
|
