Por favor, use este identificador para citar o enlazar a este item: http://hdl.handle.net/10261/246801
COMPARTIR / EXPORTAR:
logo share SHARE BASE
Visualizar otros formatos: MARC | Dublin Core | RDF | ORE | MODS | METS | DIDL | DATACITE

Invitar a revisión por pares abierta
Título

Surfaces states manipulation via surface/interface defects and adsorbates

AutorAbd El-Fattah, Z. M. CSIC ORCID
DirectorOrtega, J. Enrique CSIC ORCID; Schiller, Frederik CSIC ORCID
Fecha de publicación2012
EditorUniversidad del País Vasco
Resumen[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 generalization, tunable and locally controlled nano-periodicities are required. Using Angle Resolved Photoemission Spectroscopy (ARPES), we will show that interfacial doping of the 1 ML Ag/Cu with Au atoms allowed us to tune the energetic position of the surface state without significant broadening of its electronic features, hence without affecting its lifetime. For certain combination of Au doping and annealing temperature, we observed a complete “Lifshitz transition”at such noble metal surfaces. The tunable periodicity required for SSNE generalization has been experimentally examined on the 1 ML Ag grown on vicinal Cu(111) crystal with tunable 1D periodicity. Highly shaped and tunable constant energy surfaces were obtained by tuning the step-step periodicity. Particularly, the situation where the step-step periodicity is the same or twice the dislocation periodicity was examined, and both the dislocation and step induced gaps were coexisting. Fundamentally, we also noticed that the Ag steps are highly transparent to surface defects. In more qualitative view, we will also show that the 1 ML Ag/Cu system, when grown on “magnetic”Ni(111) substrate, exhibits significantly different surface electronic structure. In particular, transition from the gapped surface state to an apparent spin-orbit split state was observed for Cu thicknesses less than 4 ML. Scattering of surface states by periodic array of scatterers is what allows us to engineer their full dispersions, in the first place. Recently a new class of materials, namely “topological insulators”, was found to host topological surface states that are robust against scattering by surface defects/impurities. We investigate the near surface electronic structure of such a topological insulator crystal, namely Bi2Se3. In particular, we noticed that a Rashba-split 2D electron gas and M-shaped surface states coexist with the topological state after exposure to few Rb atoms. Interestingly, we found that -by slight annealing of the sample- Rb atoms initially at the surface, incorporate into the bulk and enhance the stability of the near surface electronic states even under intentional exposure to oxygen, the finding of which clearly points towards environmental applications.
[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.
DescripciónA thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy by Zakaria M. Abd El-Fattah.
URIhttp://hdl.handle.net/10261/246801
Aparece en las colecciones: (CFM) Tesis




Ficheros en este ítem:
Fichero Descripción Tamaño Formato
surfaadsorba.pdf38,56 MBAdobe PDFVista previa
Visualizar/Abrir
Mostrar el registro completo

CORE Recommender

Page view(s)

76
checked on 28-mar-2024

Download(s)

70
checked on 28-mar-2024

Google ScholarTM

Check


NOTA: Los ítems de Digital.CSIC están protegidos por copyright, con todos los derechos reservados, a menos que se indique lo contrario.