Electronic trasport and mechanical properties in nanostructures.

Abstract

"El trabajo de investigacion doctoral se ha desarrollado sobre transporte electronico en moleculas organicas e inorganicas y sobre el estudio de propiedades mecanicas en nanoestructuras bajo presion. Para la primera parte se ha considerado un modelo Huckel extendido (EHT) y c alculos de primeros principios (LSDA) para describir agregados de silicio (Si29H24) y moleculas organicas (styrene, biphenyl). Fenomenos de transporte son estudiados usando EHT y el formalismo de funciones de Green fuera de equilibrio. La importancia de la interacci on agregado-super cie es estudiadas como el control de la conductancia a trav es de, por ejemplo, dopamiento de superficies, distorsi on estructural de la mol ecula, efecto de punta STM, etc. Fen omenos asociados a dispositivos electr onicos, como diodos o el efecto de resistencia negativa, han sido encontrados en estas moleculas y metodos de control son ademas presentados. Estos resultados refuerzan la idea de poder utilizar moleculas organicas e inorganicas como dispositivos electronicos a escala at omica. Ademas se ha utilizado un modelo clasico para estudiar la respuesta mecanica de nanoestructuras como nanotubos de carbono bajo una presi on externa encontrando transiciones estructurales a fases estables y metaestables."

"The doctoral research has been developed considering the electronic transport in organic and inorganic molecules and the study of mechanical properties in nanostructures under pressure. The rst part considers the extended Huckel model (EHT) and rst principle calculations (LSDA) to describe silicon clusters (Si29H24) and organic molecules (styrene, biphenyl). The electronic transport regime is modeled with the EHT apporach and the formalism of non equilibrium Green functions. The importance of the cluster-surface interaction is studied as well as the control of the conductance by doping eect on surfaces, structural distortions of molecules, STM tip effect, etc. Several phenomena associated to electronic devices such as diode effect or negative dierential resistance have been found in these molecules and control methods are also presented in this work. The obtained results reinforce the idea of using organic and inorganice molecules as electronic components at atomic scale. Besides this, we have used a classical model to study the mechanical response of nanostructures such as carbon nanotubes under an external pressure nding structural transitions to stable and metastable congurations."