Impurity states on the honeycomb lattice using the Green's function method

Using the Green's function method, we study the effect of an impurity potential on the electronic structure of the honeycomb lattice in the one-band tight-binding model that contains both the nearest neighbor ($t$) and the second neighbor ($t'$) interactions. The model is relevant to the case of the substitutional vacancy in graphene. If the second neighbor interaction is large enough ($t' > t /3$), then the linear Dirac bands no longer occur at the Fermi energy and the electronic structure is therefore fundamentally changed. With only the nearest neighbor interactions present, there is particle-hole symmetry, as a result of which the vacancy induces a "zero-mode" state at the band center with its wave function entirely on the majority sublattice, i. e., on the sublattice not containing the vacancy. With the introduction of the second neighbor interaction, the zero-mode state broadens into a resonance peak and its wave function spreads into both sublattices, as may be argued from the Lippmann-Schwinger equation. The zero-mode state disappears entirely for the triangular lattice and if $t'$ is large for the honeycomb lattice as well. In case of graphene, $t'$ is relatively small, so that a well-defined zero-mode state occurs in the vicinity of the band center.Comment: 8 pages, 9 figure

Geodireito e a Geografia de Estado no Brasil

Tese (doutorado)—Universidade de Brasília, Pós Graduação em Geografia, 2014.A Geografia e o Direito são ciências representantes de tradições milenares, mas caminham de forma paralela desde a Modernidade, com raros pontos de diálogo, por força de suas opções científicas. O objetivo deste trabalho é aproximar estes ramos para o enfrentamento científico do século XXI, de forma a articulá-las epistemologicamente, identificar formas de interação, propor o Geodireito enquanto método interdisciplinar de mediação e analisar a Geografia de Estado do Brasil enquanto estudo de caso. Com método fenomenológico, e estudo de caso realizado de forma historiográfica, será adotado o critério social como ponto de partida para a identificação do critério espacial e do critério coercitivo, que pressupõem relações fenomenológicas, axiológicas e instrumentais. Este método possibilitou uma interação com o território, o lugar e a região em diversas escalas, produzindo governanças distintas. Foi empregada a simetria como mecanismo de aproximação, de dimensionamento e de interação entre a Geografia e o Direito, de maneira a promover uma releitura da Teoria dos Sistemas de Milton Santos e da Teoria Tridimensional do Direito de Miguel Reale que, mediante propostas de convergência, comporão duas faces de um sistema único. Para tanto foi realizada uma contextualização filosófica e sociológica, com base no pensamento geográfico na qualidade de grande sistema historicizado. O Geodireito, enquanto resultante deste entrelaçamento interdisciplinar, passa a edificar ramo de estudo com princípios autônomos que possibilita analisar a Geografia de Estado do Brasil desde a Proclamação da Independência. Desta maneira, viabilizou-se uma releitura do critério espacial do Estado e do critério coercitivo do espaço, com base em 700 normas e em seis frentes de estudo interdisciplinar, situação que renova a forma como a Geografia se relaciona com o Estado e como o Direito se relaciona com o espaço. Os principais resultados serão identificar mecanismos para se cumprir a Constituição Federal de 1988, destacar a importância de uma Geografia oficial, identificar a infraestrutura geográfica enquanto bem de domínio público, identificar meios de reestruturar a profissão geográfica, sugerir o aprimoramento do ensino da Geografia e propor uma renovada política pública geográfica no Brasil.Geography and Law are sciences representing millennial traditions, however they have trailed parallel paths since the Modern Age, with rare converging points for their scientific options. The objective of this paper is to bring these paths closer for a scientific approach of the XXI Century, so as to articulate them epistemologically, to identify forms of interaction, to propose Law and Geography as an interdisciplinary method for mediation and to analyze the State Geography of Brazil as case study. Adopting a phenomenological method and a historiographical study, social criterion shall be adopted as the starting point for identifying spatial and coercive criteria, which assume phenomenological, axiological and instrumental relationships. Such method allowed an interaction with territory, location and region in various scales, producing distinct governances. The mechanism adopted for approaching, dimensioning and interaction between Geography and Law was symmetry, so as to promote a new reading of Milton Santos’s Theory of Systems and of Miguel Reale’s Three-Dimensional Theory of Law which, within convergence proposals, will comprise two sides of a single system. In this regard, a philosophical and sociological contextualization was made, based on geographical thinking in the form of great historicized system. Law and Geography, as a resultant of such interdisciplinary entanglement, comes to edify a study branch with its own principles, which allows analyzing the State Geography of Brazil since the Proclamation of the Independence. A new approach has thus been enabled for the spatial criterion of the State and for the coercive criterion of Space, based on 700 norms and six interdisciplinary study fronts, a situation that renovates the way Geography relates to the State and the way the Law relates to the Space. The main result will be the identification of mechanisms to comply with the 1988 Federal Constitution, regarding the creation of an official Geography, restructuring the geographic profession, improving the way Geography is taught, and proposing a renovated public policy for Geography in Brazil

The missing atom as a source of carbon magnetism

Atomic vacancies have a strong impact in the mechanical, electronic and magnetic properties of graphene-like materials. By artificially generating isolated vacancies on a graphite surface and measuring their local density of states on the atomic scale, we have shown how single vacancies modify the electronic properties of this graphene-like system. Our scanning tunneling microscopy experiments, complemented by tight binding calculations, reveal the presence of a sharp electronic resonance at the Fermi energy around each single graphite vacancy, which can be associated with the formation of local magnetic moments and implies a dramatic reduction of the charge carriers' mobility. While vacancies in single layer graphene naturally lead to magnetic couplings of arbitrary sign, our results show the possibility of inducing a macroscopic ferrimagnetic state in multilayered graphene samples just by randomly removing single C atoms.Comment: Accepted for publication in Physical Review Letter

Geometry and electronic structure of iridium adsorbed on graphene

We report investigation of the geometry and electronic structure of iridium atoms adsorbed onto graphene through a combined experimental and theoretical study. Ir atoms were deposited onto a flake of graphene on a Pt(111) surface and found to form clusters even at low temperatures. The areal density of the observed clusters on the graphene flake suggests the clusters are most likely pairs of Ir atoms. Theoretical ab initio density functional (DFT) calculations indicate that these Ir dimers are oriented horizontally, near neighboring "bridge" sites of the graphene lattice, as this configuration has the strongest adsorption energy of all high-symmetry configurations for the Ir dimer. A large peak in the local density of states (LDOS) at the Dirac point energy was measured via scanning tunneling spectroscopy, and this result is reproduced by a DFT calculation of the LDOS. The peak at the Dirac point energy is found to be from the Ir s and p states. The LDOS in the monomer case was also calculated, and is found to significantly differ from the experimentally determined data, further supporting the hypothesis of low-temperature clustering

Role of pseudospin in quasiparticle interferences in epitaxial graphene probed by high-resolution scanning tunneling microscopy

Pseudospin, an additional degree of freedom related to the honeycomb structure of graphene, is responsible of many of the outstanding electronic properties found in this material. This article provides a clear understanding of how such pseudospin impacts the quasiparticle interferences of monolayer (ML) and bilayer (BL) graphene measured by low temperature scanning tunneling microscopy and spectroscopy. We have used this technique to map, with very high energy and space resolution, the spatial modulations of the local density of states of ML and BL graphene epitaxialy grown on SiC(0001), in presence of native disorder. We perform a Fourier transform analysis of such modulations including wavevectors up to unit-vectors of the reciprocal lattice. Our data demonstrate that the quasiparticle interferences associated to some particular scattering processes are suppressed in ML graphene, but not in BL graphene. Most importantly, interferences with 2qF wavevector associated to intravalley backscattering are not measured in ML graphene, even on the images with highest resolution. In order to clarify the role of the pseudospin on the quasiparticle interferences, we use a simple model which nicely captures the main features observed on our data. The model unambiguously shows that graphene's pseudospin is responsible for such suppression of quasiparticle interferences features in ML graphene, in particular for those with 2qF wavevector. It also confirms scanning tunneling microscopy as a unique technique to probe the pseudospin in graphene samples in real space with nanometer precision. Finally, we show that such observations are robust with energy and obtain with great accuracy the dispersion of the \pi-bands for both ML and BL graphene in the vicinity of the Fermi level, extracting their main tight binding parameters

A GEOGRAFIA, ANTES DE MAIS NADA, SERVE PARA MEDIAR A PAZ PELA INFRAESTRUTURA DE DADOS ESPACIAIS DA GEOPOLÍTICA AO GEODIREITO

O uso de fatos, valores e técnicas geográficas foram implementadas, em menor ou maior grau, por todas as civilizações ao longo da história. No século XXI, a conversão destas dimensões geográficas enquanto políticas públicas têm possibilitado que a Geografia, por meio da interdisciplinaridade com o Direito, seja cada vez mais importante para a mediação de interesses espaciais

Electronic states of disordered grain boundaries in graphene prepared by chemical vapor deposition

Perturbations of the two dimensional carbon lattice of graphene, such as grain boundaries, have significant influence on the charge transport and mechanical properties of this material. Scanning tunneling microscopy measurements presented here show that localized states near the Dirac point dominate the local density of states of grain boundaries in graphene grown by chemical vapor deposition. Such low energy states are not reproduced by theoretical models which treat the grain boundaries as periodic dislocation-cores composed of pentagonal-heptagonal carbon rings. Using ab initio calculations, we have extended this model to include disorder, by introducing vacancies into a grain boundary consisting of periodic dislocation-cores. Within the framework of this model we were able to reproduce the measured density of states features. We present evidence that grain boundaries in graphene grown on copper incorporate a significant amount of disorder in the form of two-coordinated carbon atoms. © 2013 Elsevier Ltd. All rights reserved

Proyecto de la instalación de alumbrado público del municipio de Villena (Alicante)

[ES] El objetivo del Trabajo Final de Máster consiste en el diseño de la instalación de alumbrado público de la ciudad de Villena. Determinaremos las características de los diferentes tipos de vías y realizaremos el estudio de luminotécnico. Instalando la tecnología de última generación en el campo de la iluminación, mejoraremos la calidad del alumbrado, minimizando la contaminación lumínica y mejorando la eficiencia. Para el diseño del alumbrado público verificaremos Reglamento de Eficiencia Energética en Instalaciones de Alumbrado y se realizan los cálculos luminotécnicos mediante el software DIALux. En relación al diseño de la instalación eléctrica seguiremos las pautas del Reglamento Electrotécnico de Baja Tensión mediante el complemento CYPELEC del software CYPE Ingenieros, con el cual realizaremos el estudio económico.[EN] The objective of the Final Masters Project is the design of the installation of public lighting in the city of Villena. At first we define the characteristics of the different types of roads and we will carry out the public lighting design. Installing the latest generation technology in the field of lighting, get better the quality of the lighting, minimizing light pollution and improving efficiency. For the design of the public lighting we will accor the Regulation of Energy Efficiency in Lighting Installations and the lighting calculations are carried out using software. In relation to the design of the electrical installation will be done according to the guidelines of Reglamento Electrotécnico de Baja Tensión and we will carry out the economic study.Sánchez Ugeda, P. (2021). Proyecto de la instalación de alumbrado público del municipio de Villena (Alicante). Universitat Politècnica de València. http://hdl.handle.net/10251/172624TFG

Point defects on graphene on metals

Understanding the coupling of graphene with its local environment is critical to be able to integrate it in tomorrow's electronic devices. Here we show how the presence of a metallic substrate affects the properties of an atomically tailored graphene layer. We have deliberately introduced single carbon vacancies on a graphene monolayer grown on a Pt(111) surface and investigated its impact in the electronic, structural and magnetic properties of the graphene layer. Our low temperature scanning tunneling microscopy studies, complemented by density functional theory, show the existence of a broad electronic resonance above the Fermi energy associated with the vacancies. Vacancy sites become reactive leading to an increase of the coupling between the graphene layer and the metal substrate at these points; this gives rise to a rapid decay of the localized state and the quenching of the magnetic moment associated with carbon vacancies in free-standing graphene layers

Diseño de identidad visual de una empresa de movilidad sostenible.

[ES] En este proyecto se ha recogido todo el diseño de la identidad corporativa de una nueva marca llamada Miivo, situada en el sector de la movilidad sostenible. El proceso de creación de esta marca se divide en dos ramas de desarrollo. En la primera parte describimos la ideación del naming, logotipo e identidad visual. En la segunda parte construimos y explicamos el diseño junto con el prototipado de la landing-page y de la aplicación. Este proyecto nace de un concurso de emprendimiento de ámbito universitario, de tal modo que se convive con otros integrantes de otros estudios, que aportan otros puntos de vista. En este caso, toda mi aportación gráfica, viene influenciada por las opiniones de todo el equipo. Por último, la aplicación es el producto de mayor valor y de distinción de la marca por su innovación. Por eso todo su desarrollo ha sido el más extenso, dedicando una explicación teórico-práctica detallada. En esta muestro todas las fases creativas desde el flujo de la aplicación al diseño de la iconografía.[EN] This project has included the entire design of the corporate identity of a new brand called Miivo, located in the sustainable mobility sector. The process of creating this brand is divided into two branches of development. In the first part we describe the ideation of the naming, logo, and visual identity. In the second part we build and explain the design together with the prototyping of the landing-page and the application. This project was born out of a university entrepreneurship competition, so that we live together with other members of other studios, who contribute other points of view. In this case, all my graphic contribution is influenced by the opinions of the whole team. Finally, the application is the most valuable and distinctive product of the brand due to its innovation. That is why all its development has been the most extensive, dedicating a detailed theoretical-practical explanation. In it I show all the creative phases from the flow of the application to the design of the iconography.Ugeda Mas, P. (2022). Diseño de identidad visual de una empresa de movilidad sostenible. Universitat Politècnica de València. http://hdl.handle.net/10251/181705TFG