1,721,122 research outputs found
Keep it simple and switch to pure tellurium
No full textResearchers, inspired by neurobiological functions and architecture of the human brain, have been developing neuromorphic computing by using artificial neurons and synapses to perform processing and storage in the same physical place. However, no conceptual technology can become reality without hardware. The class of memory devices known as phase change (PC) memories is expected to enable more efficient learning algorithms in neuromorphic computers, owing to their capability to also work as a processing unit (1). On page 1390 of this issue, Shen et al. (2) use pure elemental tellurium to build an electrical switch with a large drive current and rapid switching speed that can be used to efficiently operate PC cells in the cross-point memory architecture (see the figure). By creating the logic gate out of a single element, the design gets around challenges presented by material stoichiometry and selective elemental migration. The single-element design represents a step toward high-density, fast, and nonvolatile PC memories
GaN Nanowhiskers: structural, electrical and optical characterization.
No full textIl progetto riguarda lo studio di strutture a nanowhiskers in nitruro di gallio (GaN) per applicazioni dispositivistiche. Esso si propone inoltre di ottimizzare la qualita’ dei nanowhiskers identificando i diversi tipi di difetti e di trappole e analizzandone il ruolo nei meccanismi di trasporto di carica. E’ importante sottolineare che le strutture a nanowires mostrano proprieta’ elettriche ed ottiche molto diverse rispetto al materiale bulk. Lo studio di queste nanostrutture rappresenta dunque una sfida scientifica che richiede l’impegno sinergico di gruppi qualificati e in possesso di competenze ed esperienza nel campo
Evolution of strained Ge islands grown on Si(111): a scanning probe microscopy study
No full textWe have followed the evolution of strained Ge/Si(111) Stranski-Krastanov islands by atomic force and scanning tunneling microscopies. Following the morphological evolution during the annealing of the samples we were able to recognize the key features of the relaxation process in these structures. The introduction of edge misfit dislocations after a critical thickness, and the inhomogeneous strain field inside the islands, lead to an intra-island ripening mechanism. We show that this mechanism changes the island shape from truncated tetrahedron to `atoll-like'
Epitaxial growth of GeTe/Sb2Te3 superlattices
No full textIn the quest for superlattices with engineered interfaces for disruptive applications such as neuromorphic computing, we present a dedicated study on the epitaxial growth of nominal GeTe/Sb2Te3 chalcogenide superlattices (CSL) on the Sb passivated Si(111) − (√3 × √3)R30°− Sb surface. Intermixing at the GeTe and Sb2Te3 interface is assessed by X-Ray diffraction and reflectivity. A new growth procedure with element flux interruptions is proposed to engineer the degree of intermixing and the tailoring of the GeSbTe layers into Sb-rich compositions
Crystallization Study of Ge-Rich (GeTe) m (Sb 2 Te 3 ) n Using Two-Step Annealing Process
No full textA combination of X-ray diffraction and Raman scattering is employed to investigate (GeTe) m (Sb 2 Te 3 ) n alloys crystallized by thermal annealing from the amorphous (a-) phase. The films are deposited by molecular beam epitaxy on Si(111) substrates. First, a series of a-GeSbTe (GST) films of different composition is deposited and studied by Raman spectroscopy to identify the Ge-rich features of the alloys. Second, the crystallization properties of Ge 10 Sb 2 Te 13 are studied upon different annealing conditions. The aim of this work is to develop a procedure to avoid segregation of Ge and GeTe at the GST crystallization onset (T x ). This is here achieved by means of an incubation step at temperature lower than T x . The crystallization onset T x increased to 270 °C, which is about 160 °C higher compared to a reference GeTe sample, while the alloy always crystallizes in the stable Ge 1 Sb 2 Te 4 composition. The increase of T x is observed for all annealing conditions, regardless the amount of crystalline Ge segregated. For the optimized annealing treatment, the presence of Ge nanocrystals along with crystalline GeSbTe is unveiled by Raman measurements, paving the way for the control of the microstructure and electrical/thermal properties of Ge-rich alloys
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
Designing epitaxial GeSbTe alloys by tuning the phase, the composition, and the vacancy ordering
No full textIn this study, we present a significant advance in the growth of epitaxial GeTe-Sb2Te3 alloys on Si(111)-(√3 × √3)R30°-Sb reconstructed surface by means of Molecular Beam Epitaxy. By employing X-ray diffraction and Raman spectroscopy, we show how phase, composition, and vacancy ordering can be tailored by tuning the growth parameters such as Ge and Te elemental fluxes as well as the substrate temperature. The effect of each parameter on the GeSbTe composition and phase is also discussed. A very surprising finding is that GeSbTe alloys are more ordered when grown at lower substrate temperatures. In addition, it was possible to fabricate ordered GeSbTe even for substrate temperatures as low as 120 °C. In situ high-energy electron diffraction is employed to monitor the crystallinity and surface roughness of GeSbTe films at different stages of growth. Thus, we identify the deposition parameter ranges whereby high structural quality GeSbTe with flat surfaces can be obtained
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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