1,721,080 research outputs found
Nanociencia y Nanotechnología: un viaje fascinante al Nanocosmos
No full text4 páginas. 3 figuras.Peer reviewe
Tailoring quantum confinement using extended organic nanoporous networks
No full textResumen del trabajo presentado a la Trends in Nanotechnology (TNT) International Conference, celebrada en San Sebastian (España) del 30 de septiembre al 4 de octubre de 2019.Organic nanoporous networks grown on (111) noble metal surfaces are highly successful model systems to study scattering electron phenomena. On such surfaces, the 2D molecular scaffolds are able to confine the surface state electrons and are commonly named “quantum dot arrays”. The resulting confined states result in sizable energy shifts of the Shockley states and the formation of shallow bands, as a results from the repulsive scattering at the molecular walls and partial quantum confinement within each pore. We have studied 6 extended 2D nanoporous networks grown on noble metal surfaces which yield single domain structures. Our findings show that depending on the geometry and building units it is possible to tune the energy shifts in opposite directions (towards and away from the Fermi energy), independently of the substrate. The nature of this effect is related to metal-organic overlayer-substrate interactions in the form of adatom-surface state hybridizations. The electronic structure in all cases is determined by two state-of-theart, highly complementary techniques (STM and ARPES), and supported by first principles and model calculations
Estructura electrónica y vibracional de sistemas de baja dimensionalidad
No full textTesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura : 30-01-200
Characterizing surface states of noble metals using angle resolved photoemission (ARPES): from cross-section modulations to scattering phenomena
No full textEvery solid-state material has electrons at its surface with spatial and energetic distributions that depend both on the atomic elements that conform it and its crystalline structure. These surface electrons can give rise to surface states that have been experimentally investigated ever since both vacuum conditions and surface sensitive techniques were accessible. A lot of effort has been devoted into understanding the nature of surface states of noble metals not only on ideal (flat and clean) surfaces but also when they are nanostructured. These surface states wavefunctions are defined as two-dimensional Bloch waves decoupled from the bulk that feature exponentially decaying oscillations toward the interior of the crystal. In this seminar I will review the photoemission cross-section of Shockley states of Cu(111), Ag(111) and Au(111) which show rich structures and marked differences to one another that do not follow the generally accepted nearly free electron (NFE) model for the final state. Angle resolved photoemission data are interpreted within a one-step ab initio theory, revealing a multiple Bloch wave structure of photoemission final states. The role of the surface reconstruction is key to understand the cross-section lineshape in the case of Au(111). On a second part of the talk I will discuss the lateral scattering of surface electrons on a curved crystal of Ag(111) [3]. The beauty of these surfaces is that they present a smooth variation of the vicinal angle from the flat case to terraces of the order of 10nm, i.e., a tunable step lattice constant, and allow for a straightforward and rational investigation of all physical-chemical phenomena related to the presence of atomic steps. Our STM and ARPES data show that the Shockley state scatters at both step an dislocation arrays. The formation of laterally confined quantum well states in vicinal surfaces as opposed to propagating superlattice states depends on the loss of coherence driven by imperfection in the superlattice order.Peer Reviewe
Synthesis and control of atomically precise polymeric chains by on-surface chemistry
No full textResumen del trabajo presentado al 2nd ELECMI International Workshop, celebrado en Zaragoza (España) del 11 al 13 de junio de 2018.Peer Reviewe
Curved crystal surfaces: A playground for general surface concepts and dimensionality transitions
No full textResumen del trabajo presentado a la 13th European Conference on Surface Crystallography and Dynamics, celebrada en Donostia-San Sebastián (España) del 19 al 21 de junio de 2017.Crystal surfaces with a small deviation from a high symmetry plane have enormous potential for surface science research and applications. Such "vicinal" planes, characterized by arrays of atomic steps, exhibit distinct chemical and electronic properties, and are useful templates to achieve uniaxial symmetry and single azimuthal domains in epitaxial layers, or to drive self-organized nanostructure growth. A way of systematically studying step-related phenomena is to use curved crystals. The beauty of these special substrates is that they integrate all vicinal directions, which are accessible by scanning the source beam or tip along the curvature of the crystal. In this way, the sample provides a smooth variation of the step density that is directly related to a terrace width variation from sub-micron to the nanometer range. These samples has allowed us to revisit old and to explore new surface science problems. I will discuss step-lattice interactions, scattering of surface states and growth. Our experiments demonstrate the immense power of the curved surface approach, which allows one to directly image fine physical-chemical properties of surface systems, such as to settle controversial issues and to unveil new phenomena.Peer reviewe
Effect of photoelectron mean free path on the photoemission cross section of noble metal Shockley states
No full textTrabajo presentado a: "24th Conference of the EPS Condensed Matter Division, 29th European Conference on Surface Science, 11th European Conference on Surface Crystallography and Dynamics and UK Condensed Matter and Materials Physics Conference" celebradas en Edimburgo (UK) del 3 al 7 de Septiembre de 2012.Every solid-state material has electrons at its surface with spatial and energetic distributions that depend on both the atomic elements that conforms it and its crystalline structure. These surface electrons can give rise to well defined surface states, such as Shockley states in the case of noble metals. The intensity of these vary with the photon energy as illustrated by its photoemission cross-section. By combining angle resolved photoemission (ARPES) experimental data with ab initio calculations we are able to understand the complex photoemission cross-section of the Shockley states of (111) terminated noble metals. The generally accepted final-state free-electron band picture based on the nearly-free-electron (NFE) model fails to reproduce the unprecedented fine details observed. Furthermore, the width of the photoemission cross-section curve has no straight relation to the wave function penetration depth, as often believed. Importantly, the differences observed in the photoemission cross-section at the L resonance between the two noble metals can be rationalized with the outgoing electrons mean free path, as calculated from the crystal band structure and the optical potential. The present results are particularly relevant for nanostructured systems, for example vicinal surfaces, where the resonant character of their surface states might be investigated through such kind of photoemission cross-section curves in particular, the question of whether the surface state changes into a surface resonance when increasing the density of steps at the surface, which is still controversial.Peer Reviewe
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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