1,721,121 research outputs found
In-line correlation and ordering of InAs/GaAs multistacked Quantum Dots structures
No full textSeveral multilayer InAs/GaAs(001) samples were grown in a Molecular Beam Epitaxy chamber under critical growth conditions in order to induce the self-assembling of chains of InAs Quantum Dots over mounded GaAs surfaces. As the number of deposited layers was increased, an increasing in-line ordering was observed. Finite Element Method simulations confirmed this trend which is driven mainly by the propagation of the elastic strain field through the layers. On the other hand, the morphological features of the surface contribute to improving the alignment of the InAs Quantum Dots in every chain
High Tc-superconductor surface and interfaces by XPS and STM spectroscopies
No full textThe electronic structure of real surfaces of high temperature superconductors is examined for the significant cases of superconductor-vacuum and superconductor-metal interfaces and for different surface preparations: vacuum cleaving and chemical etching. In both cases surfaces of comparable quality are obtained. The chemical etching of the Y-Ba-Cu-0 surface produces a thin insulating layer evidenced by scanning tunnelling microscopy measurements This layer controls the surface reactivity for metal overlayers and determines the tunnel barrier profile
Probing the electronic properties of As-rich reconstructed surfaces of GaAs(001) by Electron Energy Loss Spectroscopy
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Scaling behavior of GaAs and GaMnAs quantum rings grown by droplet epitaxy
No full textThe transition from the liquid phase of Ga droplets to the formation of GaAs and GaMnAs
quantum rings has been studied as a function of temperature. We show that different aggregation
processes involve the GaAs (GaMnAs) island and the droplet formation. Furthermore, the aspect
ratio of the islands exhibits an anomalous scaling law related to a tendency to aggregate in the
vertical direction
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Selective growth of InAs quantum dots on GaAs driven by as kinetics
No full textIn this paper we examine experimentally and theoretically how the As flux direction and intensity influences the recently observed selective growth of InAs quantum dots on the rippled surface of GaAs, where the dots line up only against well determined slopes of the mounded GaAs surface facing the impinging Arsenic flux. We have previously shown that the observed phenomenon is exclusively related to the As constituent, challenging the widespread belief that As plays only a minor role in the dot formation. The selective growth is obtained by Molecular Beam Epitaxy at high growth temperature and under a high As/In flux ratio. To interpret the experimental results, we use a newly developed kinetic model incorporating new features: (i) anions are explicitly considered; (ii) cations and anions follow a different kinetics; (iii) the dot surface is distinguished by the dot bulk and atoms are transferred back and forth between the two phases depending on the surface interaction with the environment. We find that even a very small difference in the As flux intensity impinging over two substrate regions produces a cation current flow from one region to the other, so that the dots form only on the region exposed to the largest flux
Anisotropy of the GaAs(001)-β2(2×4) surface from high-resolution electron energy loss spectroscopy
No full textHigh-resolution electron energy loss spectroscopy has been applied to investigate the anisotropy of the GaAs(001)-beta2(2x4) reconstruction. Measurements have been performed on high-quality samples grown in situ by molecular beam epitaxy. The loss intensity is different in the directions parallel and perpendicular to dimers, particularly close to the fundamental gap. We discuss our data in comparison to reflectance anisotropy spectra in the attempt of identifying the source of the anisotropy close to the bulk critical points where surface and bulk like transitions take place. We find direct evidence of transitions involving the dimers of the top atomic layer. The set of data taken on As-decapped surfaces indicates that the intensity of the structures is markedly affected by the As cap removal. The exposure to increasing amounts of molecular oxygen modifies the spectral features in a way consistent with their surface origin.High-resolution electron energy loss spectroscopy has been applied to investigate the anisotropy of the GaAs(001)-beta2(2x4) reconstruction. Measurements have been performed on high-quality samples grown in situ by molecular beam epitaxy. The loss intensity is different in the directions parallel and perpendicular to dimers, particularly close to the fundamental gap. We discuss our data in comparison to reflectance anisotropy spectra in the attempt of identifying the source of the anisotropy close to the bulk critical points where surface and bulk like transitions take place. We find direct evidence of transitions involving the dimers of the top atomic layer. The set of data taken on As-decapped surfaces indicates that the intensity of the structures is markedly affected by the As cap removal. The exposure to increasing amounts of molecular oxygen modifies the spectral features in a way consistent with their surface origin
Variations on the Author
Full text link“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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