Cette thèse rapporte les mesures de transport réalisées sur des jonctions moléculaires à l'état solide large échelle, mettant en évidence des effets d'interférence quantique. Le premier chapitre pose les bases théoriques de ce phénomène et introduit le formalisme des fonctions de green hors équilibre adapté à la description du couplage molécules/interfaces métalliques. Le second chapitre présente l'état de l'art expérimental dans ce domaine et résume les principales expériences ayant permis de mettre en évidence des effets d'interférences à l'échelle moléculaire. Le troisième chapitre décrit les étapes de fabrication mises en place pour construire les dispositifs mesures pendant ce travail de thèse. Les résultats expérimentaux obtenus sur les mesures de conductance des jonctions moléculaires sont décrits dans le quatrième chapitre et compares a plusieurs modèles théoriques qui confirme la présence d'interférences quantiques. Le dernier chapitre aborde les effets de thermoélectricité qui peuvent avoir lieu dans ces jonctions en présence d'interférence / This thesis reports the transport measurement performed on large scale solid state molecular junctions, highlighting quantum interference effect. First chapter set the theoretical basis of such a phenomenon and introduces the out of equilibrium green's functions formalism which is adapted to the description of coupling molecules/metallic interfaces. Second chapter presents the corresponding experimental state of the art and summarizes the experiments that have contributed to highlight interference effect at the molecular scale. Third chapter describes the fabrication steps optimized to build the devices measured during the thesis work. Experimental results obtained on conductance measurements are described and compared to several theoretical models that confirm the presence of quantum interference. Last chapter deals with thermoelectric effect that can occur in presence of interference

Thesis submitted in fulfillment of the requirements for the degree Master of Technology:Electrical Engineering in the Faculty ofEngineering at the Cape Peninsula University of Technology Supervisor:Prof MTE KAHN Bellville December 2013 / The work presented in this thesis consists of the simulation of a cooling plant for a future mobile satellite ground station in order to minimize the effects of the thermal noise and to maintain comfort temperatures onboard the same station. Thermal problems encountered in mobile satellite ground stations are a source of poor quality signals and also of the premature destruction of the front end microwave amplifiers. In addition, they cause extreme discomfort to the mission operators aboard the mobile station especially in hot seasons. The main concerns of effective satellite system are the quality of the received signal and the lifespan of the front end low noise amplifier (LNA). Although the quality of the signal is affected by different sources of noise observed at various stages of a telecommunication system, thermal noise resulting from thermal agitation of electrons generated within the LNA is the predominant type. This thermal noise is the one that affects the sensitivity of the LNA and can lead to its destruction. Research indicated that this thermal noise can be minimized by using a suitable cooling system. A moveable truck was proposed as the equipment vehicle for a mobile ground station. In the process of the cooling system development, a detailed quantitative study on the effects of thermal noise on the LNA was conducted. To cool the LNA and the truck, a 2 kW solar electric vapor compression system was found the best for its compliance to the IEA standards: clean, human and environment friendly. The principal difficulty in the development of the cooling system was to design a photovoltaic topology that would ensure the solar panels were always exposed to the sun, regardless the situation of the truck. Simulation result suggested that a 3.3 kW three sided pyramid photovoltaic topology would be the most effective to supply the power to the cooling system. A battery system rated 48 V, 41.6 Ah was suggested to be charged by the PV system and then supply the power to the vapor compression system. The project was a success as the objective of this project has been met and the research questions were answered.