SURFACES

Author: BLANCO REY MARÍA.
Year: 2005.
University: AUTÓNOMA DE MADRID [www.uam.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: INSTITUTO DE CIENCIA DE MATERIALES DE MADRID (CSIC).

Summary: A detailed knowledge of the geometry of the surface of a crystal is crucial for understanding the physical and chemical processes on the surface, and determine their properties, which are generally different from the properties of the solid. The diffraction of low-energy electrons (LEED are his initials in Spanish) is one of the more experimental techniques employed in the structural characterization of surfaces. This thesis consists of several innovative contributions to the theory of LEED in three sections: (i) description rigorous adsorbatos molecular through using a formalism of matriz-t molecular, (ii) development of a comprehensive search algorithm directed structures called "Optimization simultaneous, "and (iii) recovery phase in LEED and developing methods direct alternative to holography and the role of Patterson. Simultaneously, it has been determined the structure of the surface TiO2 (110) -1x2, very interesting technology, from experimental data.

Author: CARRASCO BURGOS ESTHER.
Year: 2005.
University: COMPLUTENSE DE MADRID [www.ucm.es].
Place of defense: FACULTAD DE CIENCIAS FÍSICAS.
Place of preparation: FACULTAD DE CIENCIAS FÍSICAS.

Summary: A procedure reproducible nanoindentación in ultra-alto vacuum, which makes use of the tip of the scanning tunneling microscope (STM), has allowed us to explore the upstream of plastic deformation on the surface of Au (001). Note that are generated around the nanoindentaciones two types of configurations dislocation, we call tables and semilazos helical. In combination with calculations based on the theory of dislocations in the continuum, we characterize in detail the effects created as both spatial distribution or its interaction with the surface steps. We demonstrate that the production of both kinds of dislocation configurations can be held by an individual, independent and controlled. Through new nanoidentaciones in the vicinity of these defects are capable of provoking his movement. The trajectories described for these defects in its sliding reaffirm their character and dislocation are also explained using the theory of dislocations. We present experimental evidence of a new system of sliding in addition to the usual metal fcc. In conjunction with experiments nanoindentación in AFM, we can relate these configurations with dislocation phenomena recorded in the plastic curves force versus displacement (pop-ins). Using the model of Hertzian contact, we make a quantitative estimate of the elastic limit and get a value similar to theoretical for a perfect crystal, which we showed that the mechanical properties of the surface are different from those of the volume. We note that these phenomena plastics generate permanent footprints on the surface and dislocation configurations stable at room temperature. Unlike this kind of defects generated by nanoindentación, we show that the defects caused by ion bombardment at room temperature and the dose range studied have a significant temporal evolution, where sweeping the tip under certain conditions, introduced by the anisotropy reconstruction and surface diffusion influence so relevant.

Author: GÓMEZ LABRADOR ANTONIO.
Year: 2005.
University: SEVILLA [www.us.es].
Place of defense: FACULTAD DE FÍSICA.
Place of preparation: FACULTAD DE FÍSICA.

Summary: The Monte Carlo method is carried out a simulation of catalytic reactions of oxidation of CO, and CO oxidation catalytic reduction of NO and catalytic oxidation of hydrogen. Discusses schemes poisoned and reagents that originate and kinetic phase transitions between them and are characterized fractal structures and multifractales that originate.

Author: SARASOLA IÑIGUEZ ANE.
Year: 2005.
University: PAÍS VASCO [www.ehu.es].
Place of defense: FACULTAD DE QUÍMICA.
Place of preparation: FACULTAD DE QUÍMICA.

Summary: The electronic processes taking place to launch neutral or charged particles on solid or gaseous targets are studied in order to characterize the materials. Depending on the range of time and energy exchanges between the projectile and the target vary the probability of the occurrence of the process, such as excitation and ionization of electrons in the target, creating pairs electrón-hueco or plasmones (both volume and surface), capture or loss of an electron shell of two electrons or processes, such as Auger processes. Thus, Abriremos or close various channels for the loss of energy from the projectile that interacts with the target. In this thesis has been studied three systems in which the process is quite different: 1-Study applicability of the local density approximation (LDA, English, local density approximation), the answer to both electronic white gaseous H, I and Ne, as a white solid metallic Al, and insulation, LiF. There have also been studied magnitudes as power brakes, power loss, section effective braking energy and the width of the distribution of energy loss. 2, - study the probability and energy loss due to the capture of an electron in an atom of hydrogen to launch in grazing incidence on a surface of LiF, whose remarkable feature is having a bandwidth forbidden very large. 3-Study of the difference between different orientations cristalográficas of silver ions with the influence I have, due to the presence of a state surface occupied only for the orientation (111). Calculating the probability of Auger neutralization per unit of time and ion fractions survivors scattered on the surface.