Surfaces states manipulation via surface/interface defects and adsorbates

[EN]: Wave-particle duality firmly established for light in the beginning of the twentieth century and, later, for electrons has set a great analogue between the latter and photons and brought together their corresponding physics. A number of physical properties have, since then, shown to hold for both electrons and photons. The band theory, first, fulfilled for electrons in periodic solids, has been successfully applied to photons and a variety of artificial periodic 1D, 2D and 3D photonic crystals have been extensively studied. For nanophotonics applications, structures with periodicity of the order of the light wavelength (300-1000 nm) are required and the lithographic techniques were commonly used for this purpose. Noble metal surfaces, for example, host Shockley type surface states characterized by a Fermi wavelength of the order of 1-3 nm. Clearly, much smaller periodic structure is required to fabricate surface state based devices. Techniques, such as self-assembly, made the fabrication of these nanostructures possible. A case study in the present thesis is a 2D lateral superlattice made by combination of two noble metal surfaces with large lattice mismatch. Such combinations commonly self-assemble into moire superstructures. The 1 ML Ag/Cu(111), in particular, exhibits an irreversible transformation from such moir´e pattern into hexagonal lattice of dislocation network (periodicity ∼ 2.4 nm). In contrast to the ring-like Fermi Surface (FS) characteristics for Ag and Cu apart, the presence of such superstructure has led to a highly featured FS and surface band structure with 25 meV wide gap above the Fermi level. In analogy to photonic crystals, electron guiding and focusing on this system has been theoretically examined and a new technology, namely “Surface State Nanoelectronics”(SSNE), has been proposed. Toward experimental realization and potential applications of SSNE the full gap of this system has to be set at the Fermi level and, for further generaliza
[ES]: La tesis doctoral describe la estructura electrónica de una superred metálica bidimensional, que se induce de manera espontánea por evaporación de Plata sobre una superficie cristalina de Cobre. La estructura a nanoescala es una red hexagonal de dislocaciones triangulares, con un parámetro de red muy parecido a la semi-longitud de onda de los electrones libres de la superficie. Como consecuencia, la banda de electrones libres se modula en la energía de Fermi, donde se abre un gap.El trabajo comienza con la descripción del contexto científico/experimental de los sistemas que se analizan, es decir, la manipulación a nanoescala de las superficies metálicas. A continuación demuestra el grado de perfección con el que consigue producir la red de dislocaciones Ag/Cu, donde se miden propiedades electrónicas, como la vida media de las excitaciones producidas en fotoemisión. Se acaba demostrando la capacidad de sintonización de la estructura de bandas mediante "dopaje" de la interfase con átomos de Au, que posibilitan la novedosa observación de la llamada transición de Lifschitz, propia de semiconductores, en un metal noble.